Bio


The research in the Bent laboratory is focused on understanding and controlling surface and interfacial chemistry and applying this knowledge to a range of problems in semiconductor processing, micro- and nano-electronics, nanotechnology, and sustainable and renewable energy. Much of the research aims to develop a molecular-level understanding in these systems, and hence the group uses of a variety of molecular probes. Systems currently under study in the group include functionalization of semiconductor surfaces, mechanisms and control of atomic layer deposition, molecular layer deposition, nanoscale materials for light absorption, interface engineering in photovoltaics, catalyst and electrocatalyst deposition.

Academic Appointments


Honors & Awards


  • Bert and Candace Forbes University Fellow in Undergraduate Education, Stanford University (2013)
  • Allan V. Cox Medal for Faculty Excellence Fostering Undergraduate Research, Stanford University (2013)
  • Fellow, American Chemical Society (2013)
  • Jagdeep and Roshni Singh Chair, School of Engineering (2012)
  • Fellow, World Technology Network (2011)
  • Fellow, AVS (2006)
  • Award for Excellence in Undergraduate Teaching, Tau Beta Pi (2006)
  • Coblentz Award, The Coblentz Society (2001)
  • Peter Mark Memorial Award, American Vacuum Society (2000)
  • Terman Faculty Fellow, Stanford University (1998)
  • Camille Dreyfus Teacher-Scholar, The Camille Dreyfus Teacher-Scholar Awards Program (1998)
  • Research Corporation Cottrell Scholar, Research Corporation (1998)
  • Beckman Young Investigator, Arnold and Mabel Beckman Foundation (1997)
  • CAREER Award, National Science Foundation (1995)

Professional Education


  • PhD, Stanford University, Chemistry (1992)
  • BS, U.C. Berkeley, Chemical Engineering (1987)

2013-14 Courses


Journal Articles


  • Ultrathin light absorbers based on plasmonic nanocomposites SPIE Newsroom Hägglund, C., Bent, S., F.

    View details for DOI 10.1117/2.1201309.005135

  • Interface engineering in inorganic-absorber nanostructured solar cells J. Phys. Chem. Lett., Invited Perspective article Roelofs, K., E., Brennan, T., P., Bent, S., F. 2014; 5: 348−360
  • Competing geometric and electronic effects in adsorption of phenylenediamine structural isomers on the Ge(100)-2 x 1 surface SURFACE SCIENCE Kachian, J. S., Squires, K. H., Bent, S. F. 2013; 615: 72-79
  • Semiconductor surface functionalization for advances in electronics, energy conversion, and dynamic systems JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A Teplyakov, A. V., Bent, S. F. 2013; 31 (5)

    View details for DOI 10.1116/1.4810784

    View details for Web of Science ID 000324388800011

  • Vapor transport deposition and epitaxy of orthorhombic SnS on glass and NaCl substrates APPLIED PHYSICS LETTERS Wangperawong, A., Herron, S. M., Runser, R. R., Haegglund, C., Tanskanen, J. T., Lee, H., Clemens, B. M., Bent, S. F. 2013; 103 (5)

    View details for DOI 10.1063/1.4816746

    View details for Web of Science ID 000322723000041

  • Atomic layer deposition of CdO and CdxZn1-xO films MATERIALS CHEMISTRY AND PHYSICS Bakke, J. R., Haegglund, C., Jung, H. J., Sinclair, R., Bent, S. F. 2013; 140 (2-3): 465-471
  • Self-Assembly Based Plasmonic Arrays Tuned by Atomic Layer Deposition for Extreme Visible Light Absorption NANO LETTERS Haegglund, C., Zeltzer, G., Ruiz, R., Thomann, I., Lee, H., Brongersma, M. L., Bent, S. F. 2013; 13 (7): 3352-3357

    View details for DOI 10.1021/nl401641v

    View details for Web of Science ID 000321884300057

  • Highly sensitive, patternable organic films at the nanoscale made by bottom-up assembly. ACS applied materials & interfaces Zhou, H., Blackwell, J. M., Lee, H., Bent, S. F. 2013; 5 (9): 3691-3696

    Abstract

    Nanoscale patterning of organic thin films is of great interest for next-generation technologies. To keep pace with the demands of state-of-the-art lithography, both the sensitivity and resolution of the patternable thin films need to be improved. Here we report a highly sensitive polyurea film grown by bottom-up assembly via the molecular layer deposition (MLD) technique, which allows for high-resolution patterning at the nanoscale. The MLD process used in this work provides an exceptionally high degree of control over the film thickness and composition and also offers high coating conformality. The polyurea film was formed by urea coupling reactions between 1,4-diisocyanatobutane and 2,2'-(propane-2,2-diyldioxy)diethanamine precursors and deposited in a layer-by-layer fashion. Acid-labile ketal groups were incorporated into the backbone of the polymer chains to ensure chemically amplified cleaving reactions when combined with photoacid, which was generated by electron-beam activation of triphenylsulfonium triflate soaked into the polyurea film. With electron-beam lithography, sub-100 ?C/cm(2) sensitivity and sub-100 nm resolution were demonstrated using this new bottom-up assembly approach to resist fabrication.

    View details for DOI 10.1021/am4002887

    View details for PubMedID 23594160

  • Effect of Al2O3 Recombination Barrier Layers Deposited by Atomic Layer Deposition in Solid-State CdS Quantum Dot-Sensitized Solar Cells JOURNAL OF PHYSICAL CHEMISTRY C Roelofs, K. E., Brennan, T. P., Dominguez, J. C., Bailie, C. D., Margulis, G. Y., Hoke, E. T., McGehee, M. D., Bent, S. F. 2013; 117 (11): 5584-5592

    View details for DOI 10.1021/jp311846r

    View details for Web of Science ID 000316773000009

  • Growth of Pt Nanowires by Atomic Layer Deposition on Highly Ordered Pyrolytic Graphite NANO LETTERS Lee, H., Baeck, S. H., Jaramillo, T. F., Bent, S. F. 2013; 13 (2): 457-463

    Abstract

    The formation of Pt nanowires (NWs) by atomic layer deposition on highly ordered pyrolytic graphite (HOPG) is investigated. Pt is deposited only at the step edges of HOPG and not on the basal planes, leading to the formation of laterally aligned Pt NWs. A growth model involving a morphological transition from 0-D to 1-D structures via coalescence is presented. The width of the NWs grows at a rate greater than twice the vertical growth rate. This asymmetry is ascribed to the wetting properties of Pt on HOPG as influenced by the formation of graphene oxide. A difference in Pt growth kinetics based on crystallographic orientation may also contribute.

    View details for DOI 10.1021/nl303803p

    View details for Web of Science ID 000315079500021

    View details for PubMedID 23317031

  • One-Dimensional Pattern Formation of Adsorbed Molecules on the Ge(100)-2 X 1 Surface Driven by Nearest-Neighbor Effects JOURNAL OF PHYSICAL CHEMISTRY C Shong, B., Bent, S. F. 2013; 117 (2): 949-955

    View details for DOI 10.1021/jp3078503

    View details for Web of Science ID 000313932800024

  • In Vacuo Photoemission Studies of Platinum Atomic Layer Deposition Using Synchrotron Radiation JOURNAL OF PHYSICAL CHEMISTRY LETTERS Geyer, S. M., Methaapanon, R., Shong, B., Pianetta, P. A., Bent, S. F. 2013; 4 (1): 176-179

    View details for DOI 10.1021/jz301475z

    View details for Web of Science ID 000313142000029

  • Portable atomic layer deposition reactor for in situ synchrotron photoemission studies REVIEW OF SCIENTIFIC INSTRUMENTS Methaapanon, R., Geyer, S. M., Hagglund, C., Pianetta, P. A., Bent, S. F. 2013; 84 (1)

    Abstract

    We report the design of a portable atomic layer deposition (ALD) reactor that can be integrated into synchrotron facilities for in situ synchrotron photoemission studies. The design allows for universal installation of the system onto different beam line end stations. The ALD reactor operates as a fully functional, low vacuum deposition system under the conditions of a typical ALD reactor while allowing the samples to be analyzed in an ultrahigh vacuum (UHV) chamber through a quick transfer without vacuum break. This system not only minimizes the exposure of the UHV chamber to the ALD reactants, but it also eliminates the necessity of a beam alignment step after installation. The system has been successfully installed at the synchrotron and tested in the mechanistic studies of platinum ALD following individual half reaction cycles.

    View details for DOI 10.1063/1.4773230

    View details for Web of Science ID 000314729100063

    View details for PubMedID 23387692

  • Self-Assembly Based Plasmonic Arrays Tuned by Atomic Layer Deposition for Extreme Visible Light Absorption. Nano letters Hägglund, C., Zeltzer, G., Ruiz, R., Thomann, I., Lee, H. B., Brongersma, M. L., Bent, S. F. 2013

    Abstract

    Achieving complete absorption of visible light with a minimal amount of material is highly desirable for many applications, including solar energy conversion to fuel and electricity, where benefits in conversion efficiency and economy can be obtained. On a fundamental level, it is of great interest to explore whether the ultimate limits in light absorption per unit volume can be achieved by capitalizing on the advances in metamaterial science and nanosynthesis. Here, we combine block copolymer lithography and atomic layer deposition to tune the effective optical properties of a plasmonic array at the atomic scale. Critical coupling to the resulting nanocomposite layer is accomplished through guidance by a simple analytical model and measurements by spectroscopic ellipsometry. Thereby, a maximized absorption of light exceeding 99% is accomplished, of which up to about 93% occurs in a volume-equivalent thickness of gold of only 1.6 nm. This corresponds to a record effective absorption coefficient of 1.7 × 10(7) cm(-1) in the visible region, far exceeding those of solid metals, graphene, dye monolayers, and thin film solar cell materials. It is more than a factor of 2 higher than that previously obtained using a critically coupled dye J-aggregate, with a peak width exceeding the latter by 1 order of magnitude. These results thereby substantially push the limits for light harvesting in ultrathin, nanoengineered systems.

    View details for PubMedID 23805835

  • Formation of stable nitrene surface species by reaction of adsorbed phenyl isocyanate at the Ge(100)-2×1 surface Langmuir Wong, K., T., Tanskanen, J., T., Bent, S., F. 2013; 29: 15842−15850
  • Cross-linked ultrathin polyurea films via molecular layer deposition Macromolecules Zhou, H., Toney, M., F., Bent, S., F. 2013; 46: 5638−5643
  • Fabrication of organic interfacial layers by molecular layer deposition: present status and future opportunities J. Vac. Sci. Technol., invited review Zhou, H., Bent, S., F. 2013; 31: 040801

    View details for DOI 10.1116/1.4804609

  • Insights into the surface chemistry of tin oxide atomic layer deposition from quantum chemical calculations J. Phys. Chem. C Tanskanen, J., T., Bent, S., F. 2013; 117: 19056−19062
  • Highly stable ultrathin carbosiloxane films by molecular layer deposition J. Phys. Chem.C Zhou, H., Bent, S., F. 2013; 117: 19967−19973
  • Efficiency enhancement of solid-state PbS quantum dot-sensitized solar cells with Al2O3 barrier layer JOURNAL OF MATERIALS CHEMISTRY A Brennan, T. P., Trejo, O., Roelofs, K. E., Xu, J., Prinz, F. B., Bent, S. F. 2013; 1 (26): 7566-7571

    View details for DOI 10.1039/c3ta10903h

    View details for Web of Science ID 000320245400004

  • Size dependent effects in nucleation of Ru and Ru oxide thin films by atomic layer deposition measured by synchrotron radiation x-ray diffraction Chem. Mat Methaapanon, R., Geyer, S., M., Brennan, S., Bent, S., F. 2013; 25: 58−3463
  • The dynamical orientation of large molecules on oxide surfaces and its implications for dye-sensitized solar cells Chem. Mat. Brennan, T., P., Tanskanen, J., T., Bakke, J., R., Nguyen, W., H., Nordlund, D., Toney, M., F., Bent, S. F. 2013; 25: 4354−4363
  • Tin oxide atomic layer deposition from tetrakis(dimethylamino)tin and water J. Vac. Sci. Technol. A Mullings, M., N., Hagglund, C., Bent, S., F. 2013; 31: 061503
  • 1D pattern formation of adsorbed molecules on the Ge(100)-2 × 1 surface driven by nearest neighbor effects J. Phys. Chem. C Shong, B., Bent, S., F. 2013; 2 (117): 949-955
  • Vapor transport deposition and epitaxy of orthorhombic SnS on glass and NaCl substrates Appl. Phys. Lett Wangperawong, A., Herron, S., M., Runser, R., R., Hägglund, C., Tanskanen, J., Lee, H., B. R., Bent, S. F. 2013; 103: 052105
  • Adsorption of trimethyl phosphite at the Ge(100)-2×1 surface by nucleophilic reaction J. Phys. Chem. C Wong, K., T., Shong, B., S., Sun, W., Bent, S., F. 2013; 117: 26628−26635
  • Adsorption of structural and stereoisomers of cyclohexanediamineat the Ge(100)-2 × 1 surface: geometric effects in adsorption on a semiconductor surface J. Phys. Chem. C Wong, K., T., Bent, S., F. 2013; 117: 19063−19073
  • Dissociative Adsorption of Dimethyl Sulfoxide at the Ge(100)-2 x 1 Surface JOURNAL OF PHYSICAL CHEMISTRY C Wong, K. T., Chopra, S. N., Bent, S. F. 2012; 116 (50): 26422-26430

    View details for DOI 10.1021/jp309418e

    View details for Web of Science ID 000312519600035

  • Power losses in bilayer inverted small molecule organic solar cells APPLIED PHYSICS LETTERS Trinh, C., Bakke, J. R., Brennan, T. P., Bent, S. F., Navarro, F., Bartynski, A., Thompson, M. E. 2012; 101 (23)

    View details for DOI 10.1063/1.4769440

    View details for Web of Science ID 000312243900099

  • Nucleation-Controlled Growth of Nanoparticles by Atomic Layer Deposition CHEMISTRY OF MATERIALS Lee, H., Mullings, M. N., Jiang, X., Clemens, B. M., Bent, S. F. 2012; 24 (21): 4051-4059

    View details for DOI 10.1021/cm3014978

    View details for Web of Science ID 000311239300008

  • Active MnOx Electrocatalysts Prepared by Atomic Layer Deposition for Oxygen Evolution and Oxygen Reduction Reactions ADVANCED ENERGY MATERIALS Pickrahn, K. L., Park, S. W., Gorlin, Y., Lee, H., Jaramillo, T. F., Bent, S. F. 2012; 2 (10): 1269-1277
  • Single versus Dual Attachment in the Adsorption of Diisocyanates at the Ge(100)-2 x 1 Surface JOURNAL OF PHYSICAL CHEMISTRY C Wong, K. T., Chopra, S. N., Bent, S. F. 2012; 116 (23): 12670-12679

    View details for DOI 10.1021/jp302930g

    View details for Web of Science ID 000305356200038

  • Transition in the Molecular Orientation of Phenol Adsorbates on the Ge(100)-2 x 1 Surface JOURNAL OF PHYSICAL CHEMISTRY C Shong, B., Bent, S. F. 2012; 116 (14): 7925-7930

    View details for DOI 10.1021/jp3009767

    View details for Web of Science ID 000302591300039

  • TiO2-SnO2:F interfacial electronic structure investigated by soft x-ray absorption spectroscopy PHYSICAL REVIEW B Kronawitter, C. X., Kapilashrami, M., Bakke, J. R., Bent, S. F., Chuang, C., Pong, W., Guo, J., Vayssieres, L., Mao, S. S. 2012; 85 (12)
  • Reaction of Hydroquinone and p-Benzoquinone with the Ge(100)-2 x 1 Surface JOURNAL OF PHYSICAL CHEMISTRY C Shong, B., Wong, K. T., Bent, S. F. 2012; 116 (7): 4705-4713

    View details for DOI 10.1021/jp210804v

    View details for Web of Science ID 000301156500044

  • Microstructure-Dependent Nucleation in Atomic Layer Deposition of Pt on TiO2 CHEMISTRY OF MATERIALS Lee, H., Bent, S. F. 2012; 24 (2): 279-286

    View details for DOI 10.1021/cm202764b

    View details for Web of Science ID 000299367500006

  • The importance of dye chemistry and TiCl4 surface treatment in the behavior of Al2O3 recombination barrier layers deposited by atomic layer deposition in solid-state dye-sensitized solar cells PHYSICAL CHEMISTRY CHEMICAL PHYSICS Brennan, T. P., Bakke, J. R., Ding, I., Hardin, B. E., Nguyen, W. H., Mondal, R., Bailie, C. D., Margulis, G. Y., Hoke, E. T., Sellinger, A., McGehee, M. D., Bent, S. F. 2012; 14 (35): 12130-12140

    Abstract

    Atomic layer deposition (ALD) was used to fabricate Al(2)O(3) recombination barriers in solid-state dye-sensitized solar cells (ss-DSSCs) employing an organic hole transport material (HTM) for the first time. Al(2)O(3) recombination barriers of varying thickness were incorporated into efficient ss-DSSCs utilizing the Z907 dye adsorbed onto a 2 ?m-thick nanoporous TiO(2) active layer and the HTM spiro-OMeTAD. The impact of Al(2)O(3) barriers was also studied in devices employing different dyes, with increased active layer thicknesses, and with substrates that did not undergo the TiCl(4) surface treatment. In all instances, electron lifetimes (as determined by transient photovoltage measurements) increased and dark current was suppressed after Al(2)O(3) deposition. However, only when the TiCl(4) treatment was eliminated did device efficiency increase; in all other instances efficiency decreased due to a drop in short-circuit current. These results are attributed in the former case to the similar effects of Al(2)O(3) ALD and the TiCl(4) surface treatment whereas the insulating properties of Al(2)O(3) hinder charge injection and lead to current loss in TiCl(4)-treated devices. The impact of Al(2)O(3) barrier layers was unaffected by doubling the active layer thickness or using an alternative ruthenium dye, but a metal-free donor-?-acceptor dye exhibited a much smaller decrease in current due to its higher excited state energy. We develop a model employing prior research on Al(2)O(3) growth and dye kinetics that successfully predicts the reduction in device current as a function of ALD cycles and is extendable to different dye-barrier systems.

    View details for DOI 10.1039/c2cp42388j

    View details for Web of Science ID 000307648700014

    View details for PubMedID 22850593

  • The low temperature atomic layer deposition of ruthenium and the effect of oxygen exposure JOURNAL OF MATERIALS CHEMISTRY Methaapanon, R., Geyer, S. M., Lee, H., Bent, S. F. 2012; 22 (48): 25154-25160

    View details for DOI 10.1039/c2jm35332f

    View details for Web of Science ID 000311970800023

  • Growth characteristics, material properties, and optical properties of zinc oxysulfide films deposited by atomic layer deposition JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A Bakke, J. R., Tanskanen, J. T., Haegglund, C., Pakkanen, T. A., Bent, S. F. 2012; 30 (1)

    View details for DOI 10.1116/1.3664758

    View details for Web of Science ID 000298992800035

  • Atomic Layer Deposition of CdS Quantum Dots for Solid-State Quantum Dot Sensitized Solar Cells ADVANCED ENERGY MATERIALS Brennan, T. P., Ardalan, P., Lee, H., Bakke, J. R., Ding, I., McGehee, M. D., Bent, S. F. 2011; 1 (6): 1169-1175
  • Electron Enrichment in 3d Transition Metal Oxide Hetero-Nanostructures NANO LETTERS Kronawitter, C. X., Bakke, J. R., Wheeler, D. A., Wang, W., Chang, C., Antoun, B. R., Zhang, J. Z., Guo, J., Bent, S. F., Mao, S. S., Vayssieres, L. 2011; 11 (9): 3855-3861

    Abstract

    Direct experimental observation of spontaneous electron enrichment of metal d orbitals in a new transition metal oxide heterostructure with nanoscale dimensionality is reported. Aqueous chemical synthesis and vapor phase deposition are combined to fabricate oriented arrays of high-interfacial-area hetero-nanostructures comprised of titanium oxide and iron oxide nanomaterials. Synchrotron-based soft X-ray spectroscopy techniques with high spectral resolution are utilized to directly probe the titanium and oxygen orbital character of the interfacial region's occupied and unoccupied densities of states. These data demonstrate the interface to possess electrons in Ti 3d bands and an emergent degree of orbital hybridization that is absent in parent oxide reference crystals. The carrier dynamics of the hetero-nanostructures are studied by ultrafast transient absorption spectroscopy, which reveals the presence of a dense manifold of states, the relaxations from which exhibit multiple exponential decays whose magnitudes depend on their energetic positions within the electronic structure.

    View details for DOI 10.1021/nl201944h

    View details for Web of Science ID 000294790200060

    View details for PubMedID 21834542

  • Three-dimensional nanojunction device models for photovoltaics APPLIED PHYSICS LETTERS Wangperawong, A., Bent, S. F. 2011; 98 (23)

    View details for DOI 10.1063/1.3595411

    View details for Web of Science ID 000291658900066

  • Influence of organozinc ligand design on growth and material properties of ZnS and ZnO deposited by atomic layer deposition JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A Tanskanen, J. T., Bakke, J. R., Pakkanen, T. A., Bent, S. F. 2011; 29 (3)

    View details for DOI 10.1116/1.3572232

    View details for Web of Science ID 000289689000019

  • Coverage dependence of glycine adsorption on the Ge(100)-2 x 1 surface SURFACE SCIENCE Kachian, J. S., Jung, S. J., Kim, S., Bent, S. F. 2011; 605 (7-8): 760-769
  • Molecular Layer Deposition of Functional Thin Films for Advanced Lithographic Patterning ACS APPLIED MATERIALS & INTERFACES Zhou, H., Bent, S. F. 2011; 3 (2): 505-511

    Abstract

    Photoresist materials comprise one of the main challenges faced by lithography to meet the requirements of electronic device size scaling. Here we report for the first time the use of molecular layer deposition (MLD) to produce photoresist materials with controllable placement of functional moieties. Polyurea resists films are deposited by MLD using urea coupling reactions between 1,4-phenylene diisocyanate (PDIC) and ethylenediamine (ED) or 2,2'-(propane-2,2-diylbis(oxy))diethanamine (PDDE) monomers in a layer-by-layer fashion with a linear growth rate, allowing acid-labile groups to be incorporated into the film at well-controlled positions. The films are deposited with stoichiometric compositions and have highly uniform surface morphology as investigated using atomic force microscopy. We show that acid treatment can cleave the backbone of the polyurea film at positions where the acid-labile groups are embedded. We further show that after soaking the polyurea film with photoacid generator (PAG), it acts as a photoresist material and we present several UV patterning demonstrations. This approach presents a new way to make molecularly designed resist films for lithography.

    View details for DOI 10.1021/am1010805

    View details for Web of Science ID 000287639400055

    View details for PubMedID 21302918

  • Effects of Self-Assembled Monolayers on Solid-State CdS Quantum Dot Sensitized Solar Cells ACS NANO Ardalan, P., Brennan, T. P., Lee, H., Bakke, J. R., Ding, I., McGehee, M. D., Bent, S. F. 2011; 5 (2): 1495-1504

    Abstract

    Quantum dot sensitized solar cells (QDSSCs) are of interest for solar energy conversion because of their tunable band gap and promise of stable, low-cost performance. We have investigated the effects of self-assembled monolayers (SAMs) with phosphonic acid headgroups on the bonding and performance of cadmium sulfide (CdS) solid-state QDSSCs. CdS quantum dots ?2 to ?6 nm in diameter were grown on SAM-passivated planar or nanostructured TiO(2) surfaces by successive ionic layer adsorption and reaction (SILAR), and photovoltaic devices were fabricated with spiro-OMeTAD as the solid-state hole conductor. X-ray photoelectron spectroscopy, Auger electron spectroscopy, ultraviolet-visible spectroscopy, scanning electron microscopy, transmission electron microscopy, water contact angle measurements, ellipsometry, and electrical measurements were employed to characterize the materials and the resulting device performance. The data indicate that the nature of the SAM tailgroup does not significantly affect the uptake of CdS quantum dots on TiO(2) nor their optical properties, but the presence of the SAM does have a significant effect on the photovoltaic device performance. Interestingly, we observe up to ?3 times higher power conversion efficiencies in devices with a SAM compared to those without the SAM.

    View details for DOI 10.1021/nn103371v

    View details for Web of Science ID 000287553800093

    View details for PubMedID 21299223

  • Aqueous bath process for deposition of Cu2ZnSnS4 photovoltaic absorbers THIN SOLID FILMS Wangperawong, A., King, J. S., Herron, S. M., Tran, B. P., Pangan-Okimoto, K., Bent, S. F. 2011; 519 (8): 2488-2492
  • Tuning the reactivity of semiconductor surfaces by functionalization with amines of different basicity PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Bent, S. F., Kachian, J. S., Rodriguez-Reyes, J. C., Teplyakov, A. V. 2011; 108 (3): 956-960

    Abstract

    Surface functionalization of semiconductors has been the backbone of the newest developments in microelectronics, energy conversion, sensing device design, and many other fields of science and technology. Over a decade ago, the notion of viewing the surface itself as a chemical reagent in surface reactions was introduced, and adding a variety of new functionalities to the semiconductor surface has become a target of research for many groups. The electronic effects on the substrate have been considered as an important consequence of chemical modification. In this work, we shift the focus to the electronic properties of the functional groups attached to the surface and their role on subsequent reactivity. We investigate surface functionalization of clean Si(100)-2 × 1 and Ge(100)-2 × 1 surfaces with amines as a way to modify their reactivity and to fine tune this reactivity by considering the basicity of the attached functionality. The reactivity of silicon and germanium surfaces modified with ethylamine (CH(3)CH(2)NH(2)) and aniline (C(6)H(5)NH(2)) is predicted using density functional theory calculations of proton attachment to the nitrogen of the adsorbed amine to differ with respect to a nucleophilic attack of the surface species. These predictions are then tested using a model metalorganic reagent, tetrakis(dimethylamido)titanium (((CH(3))(2)N)(4)Ti, TDMAT), which undergoes a transamination reaction with sufficiently nucleophilic amines, and the reactivity tests confirm trends consistent with predicted basicities. The identity of the underlying semiconductor surface has a profound effect on the outcome of this reaction, and results comparing silicon and germanium are discussed.

    View details for DOI 10.1073/pnas.1006656107

    View details for Web of Science ID 000286310300016

    View details for PubMedID 21068370

  • Disulfide Passivation of the Ge(100)-2 x 1 Surface LANGMUIR Kachian, J. S., Tannaci, J., Wright, R. J., Tilley, T. D., Bent, S. F. 2011; 27 (1): 179-186

    Abstract

    Understanding the bonding of sulfur at the germanium surface is important to developing good passivation routes for germanium-based electronic devices. The adsorption behavior of ethyl disulfide (EDS) and 1,8-naphthalene disulfide (NDS) at the Ge(100)-2 × 1 surface has been studied under ultrahigh vacuum conditions to investigate both their fundamental reactivity and their effectiveness as passivants of this surface. X-ray photoelectron spectroscopy, multiple internal reflection-infrared spectroscopy, and density functional theory results indicate that both molecules adsorb via S-S dissociation at room temperature. Upon exposure to ambient air, the thiolate adlayer remains intact for both EDS- and NDS-functionalized surfaces, indicating the stability of this surface attachment. Although both systems resist oxidation compared to the bare Ge(100)-2 × 1 surface, the Ge substrate is significantly oxidized in all cases (17-57% relative to the control), with the NDS-passivated surface undergoing up to two times more oxidation than the EDS-passivated surface at the longest air exposure times studied. The difference in passivation capability is attributed to the difference in surface coverage on Ge(100)-2 × 1, where EDS adsorption leads to a saturation coverage 17% higher than that for NDS/Ge(100)-2 × 1.

    View details for DOI 10.1021/la103614f

    View details for Web of Science ID 000285560400025

    View details for PubMedID 21141841

  • Optical Response of 3D Nano-Architecture Solar Cells and Integration with 3D Device Physics NEXT GENERATION (NANO) PHOTONIC AND CELL TECHNOLOGIES FOR SOLAR ENERGY CONVERSION II Wangperawong, A., Haegglund, C., Bent, S. F. 2011; 8111

    View details for DOI 10.1117/12.893168

    View details for Web of Science ID 000303797800013

  • Atomic layer deposition of CdxZn1-xS films JOURNAL OF MATERIALS CHEMISTRY Bakke, J. R., Tanskanen, J. T., Jung, H. J., Sinclair, R., Bent, S. F. 2011; 21 (3): 743-751

    View details for DOI 10.1039/c0jm02786c

    View details for Web of Science ID 000285749900021

  • Nanoengineering and interfacial engineering of photovoltaics by atomic layer deposition NANOSCALE Bakke, J. R., Pickrahn, K. L., Brennan, T. P., Bent, S. F. 2011; 3 (9): 3482-3508

    Abstract

    Investment into photovoltaic (PV) research has accelerated over the past decade as concerns over energy security and carbon emissions have increased. The types of PV technology in which the research community is actively engaged are expanding as well. This review focuses on the burgeoning field of atomic layer deposition (ALD) for photovoltaics. ALD is a self-limiting thin film deposition technique that has demonstrated usefulness in virtually every sector of PV technology including silicon, thin film, tandem, organic, dye-sensitized, and next generation solar cells. Further, the specific applications are not limited. ALD films have been deposited on planar and nanostructured substrates and on inorganic and organic devices, and vary in thickness from a couple of angstroms to over 100 nm. The uses encompass absorber materials, buffer layers, passivating films, anti-recombination shells, and electrode modifiers. Within the last few years, the interest in ALD as a PV manufacturing technique has increased and the functions of ALD have expanded. ALD applications have yielded fundamental understanding of how devices operate and have led to increased efficiencies or to unique architectures for some technologies. This review also highlights new developments in high throughput ALD, which is necessary for commercialization. As the demands placed on materials for the next generation of PV become increasingly stringent, ALD will evolve into an even more important method for research and fabrication of solar cell devices.

    View details for DOI 10.1039/c1nr10349k

    View details for Web of Science ID 000294472600004

    View details for PubMedID 21799978

  • Adsorption Behavior of Bifunctional Molecules on Ge(100)-2 x 1: Comparison of Mercaptoethanol and Mercaptamine JOURNAL OF PHYSICAL CHEMISTRY C Kachian, J. S., Bent, S. F. 2010; 114 (50): 22230-22236

    View details for DOI 10.1021/jp1085894

    View details for Web of Science ID 000285236800047

  • Deposition of Ultrathin Polythiourea Films by Molecular Layer Deposition CHEMISTRY OF MATERIALS Loscutoff, P. W., Lee, H., Bent, S. F. 2010; 22 (19): 5563-5569

    View details for DOI 10.1021/cm1016239

    View details for Web of Science ID 000282471000019

  • Molecular Level Insights into Atomic Layer Deposition of CdS by Quantum Chemical Calculations JOURNAL OF PHYSICAL CHEMISTRY C Tanskanen, J. T., Bakke, J. R., Bent, S. F., Pakkanen, T. A. 2010; 114 (39): 16618-16624

    View details for DOI 10.1021/jp105911p

    View details for Web of Science ID 000282209800070

  • Reaction of tert-butyl isocyanate and tert-butyl isothiocyanate at the Ge(100)-2 x 1 Surface SURFACE SCIENCE Loscutoff, P. W., Wong, K. T., Bent, S. F. 2010; 604 (19-20): 1791-1799
  • Reaction of Phenyl Isocyanate and Phenyl Isothiocyanate with the Ge(100)-2 x 1 Surface JOURNAL OF PHYSICAL CHEMISTRY C Loscutoff, P. W., Wong, K. T., Bent, S. F. 2010; 114 (33): 14193-14201

    View details for DOI 10.1021/jp104388a

    View details for Web of Science ID 000280961800032

  • Atomic Layer Deposition of CdS Films CHEMISTRY OF MATERIALS Bakke, J. R., Jung, H. J., Tanskanen, J. T., Sinclair, R., Bent, S. F. 2010; 22 (16): 4669-4678

    View details for DOI 10.1021/cm100874f

    View details for Web of Science ID 000280855100021

  • Atomic layer deposition of ZnS via in situ production of H2S THIN SOLID FILMS BAKKE, J. R., King, J. S., Jung, H. J., Sinclair, R., Bent, S. F. 2010; 518 (19): 5400-5408
  • ALD Growth Characteristics of ZnS Films Deposited from Organozinc and Hydrogen Sulfide Precursors LANGMUIR Tanskanen, J. T., Bakke, J. R., Bent, S. F., Pakkanen, T. A. 2010; 26 (14): 11899-11906

    Abstract

    Growth characteristics of zinc sulfide thin films deposited from dialkylzinc and H(2)S reactants by the atomic layer deposition technique have been investigated by quantum chemical methods. The steady-state growth of the films was simulated by studying the reaction of the Zn precursor with the hydrogenated sulfur-terminated (111) surface of zincblende ZnS and then by investigating the chemisorption of hydrogen sulfide on the surface formed by the metal exposure. The behavior of the dissociatively chemisorbed Zn precursors on the growth surface is of particular significance for the film deposition process, since the film growth is limited by the Zn deposition step. Hydrogen sulfide exposure results in the replacement of the surface alkyl groups by SH surface species, whose vibrational features are useful in the experimental verification of the developed growth mechanisms.

    View details for DOI 10.1021/la101128w

    View details for Web of Science ID 000279756700043

    View details for PubMedID 20553010

  • Comparative Study of Titanium Dioxide Atomic Layer Deposition on Silicon Dioxide and Hydrogen-Terminated Silicon JOURNAL OF PHYSICAL CHEMISTRY C Methaapanon, R., Bent, S. F. 2010; 114 (23): 10498-10504

    View details for DOI 10.1021/jp1013303

    View details for Web of Science ID 000278479700025

  • Reaction Mechanism, Bonding, and Thermal Stability of 1-Alkanethiols Self-Assembled on Halogenated Ge Surfaces LANGMUIR Ardalan, P., Sun, Y., Pianetta, P., Musgrave, C. B., Bent, S. F. 2010; 26 (11): 8419-8429

    Abstract

    We have employed synchrotron radiation photoemission spectroscopy to study the reaction mechanism, surface bonding, and thermal stability of 1-octadecanethiolate (ODT) self-assembled monolayers (SAMs) at Cl- and Br-terminated Ge(100) surfaces. Density functional theory (DFT) calculations were also carried out for the same reactions. From DFT calculations, we have found that adsorption of 1-octadecanethiol on the halide-terminated surface via hydrohalogenic acid elimination is kinetically favorable on both Cl- and Br-terminated Ge surfaces at room temperature, but the reactions are more thermodynamically favorable at Cl-terminated Ge surfaces. After ODT SAM formation at room temperature, photoemission spectroscopy experiments show that Ge(100) and (111) surfaces contain monothiolates and possibly dithiolates together with unbound thiol and atomic sulfur. Small coverages of residual halide are also observed, consistent with predictions by DFT. Annealing studies in ultrahigh vacuum show that the Ge thiolates are thermally stable up to 150 degrees C. The majority of the surface thiolates are converted to sulfide and carbide upon annealing to 350 degrees C. By 430 degrees C, no sulfur remains on the surface, whereas Ge carbide is stable to above 470 degrees C.

    View details for DOI 10.1021/la904864c

    View details for Web of Science ID 000277928100104

    View details for PubMedID 20433151

  • Atomic Layer Deposition (ALD) Co-Deposited Pt-Ru Binary and Pt Skin Catalysts for Concentrated Methanol Oxidation CHEMISTRY OF MATERIALS Jiang, X., Guer, T. N., Prinz, F. B., Bent, S. F. 2010; 22 (10): 3024-3032

    View details for DOI 10.1021/cm902904u

    View details for Web of Science ID 000277635000002

  • Periodic Trends in Organic Functionalization of Group IV Semiconductor Surfaces ACCOUNTS OF CHEMICAL RESEARCH Kachian, J. S., Wong, K. T., Bent, S. F. 2010; 43 (2): 346-355

    Abstract

    Organic functionalization of group IV semiconductor surfaces provides a means to precisely control the interfacial properties of some of the most technologically important electronic materials in use today. The 2 x 1 reconstructed group IV (100) surfaces in ultrahigh vacuum, in particular, have a well-defined surface that allows adsorbate-surface interactions to be studied in detail. Surface dimers containing a strong sigma- and weak pi-bond form upon reconstruction of the group IV (100) surfaces, imparting a rich surface reactivity, which allows useful analogies to be made between reactions at the surface and those in classic organic chemistry. To date, most studies have focused on single substrates and a limited number of adsorbate functional groups. In this Account, we bring together experimental and theoretical results from several studies to investigate broader trends in thermodynamics and kinetics of organic molecules reacted with group IV (100)-2 x 1 surfaces. By rationalizing these trends in terms of simple periodic properties, we aim to provide guidelines by which to understand the chemical origin of the observed trends and predict how related molecules or functionalities will react. Results of experimental and theoretical studies are used to show that relative electronegativities and orbital overlap correlate well with surface-adsorbate covalent bond strength, while orbital overlap together with donor electronegativity and acceptor electron affinity correlate with surface-adsorbate dative bond strength. Using such simple properties as predictive tools is limited, of course, but theoretical calculations fill in some of the gaps. The predictive power inherent in periodic trends may be put to use in designing molecules for applications where controlled attachment of organic molecules to semiconductor surfaces is needed. Organic functionalization may facilitate the semiconductor industry's transition from traditional silicon-based architectures to other materials, such as germanium, that offer better electrical properties. Potential applications also exist in other fields ranging from organic and molecular electronics, where control of interfacial properties may allow coupling of traditional semiconductor technology with such developing technologies, to biosensors and nanoscale lithography, where the functionality imparted to the surface may be used directly. Knowledge of thermodynamic and kinetic trends and the fundamental basis of these trends may enable effective development of new functionalization strategies for such applications.

    View details for DOI 10.1021/ar900251s

    View details for Web of Science ID 000274765400018

    View details for PubMedID 20041705

  • Sputtered Pt-Ru Alloys as Catalysts for Highly Concentrated Methanol Oxidation JOURNAL OF THE ELECTROCHEMICAL SOCIETY Jiang, X., Guer, T. M., Prinz, F. B., Bent, S. F. 2010; 157 (3): B314-B319

    View details for DOI 10.1149/1.3273081

    View details for Web of Science ID 000274321900021

  • Catalysts with Pt Surface Coating by Atomic Layer Deposition for Solid Oxide Fuel Cells JOURNAL OF THE ELECTROCHEMICAL SOCIETY Shim, J. H., Jiang, X., Bent, S. F., Prinz, F. B. 2010; 157 (6): B793-B797

    View details for DOI 10.1149/1.3368787

    View details for Web of Science ID 000277260200023

  • Formation of Organic Nanoscale Laminates and Blends by Molecular Layer Deposition ACS NANO Loscutoff, P. W., Zhou, H., Clendenning, S. B., Bent, S. F. 2010; 4 (1): 331-341

    Abstract

    Nanoscale organic films are important for many applications. We report on a system of molecular layer deposition that allows for the deposition of conformal organic films with thickness and composition control at the subnanometer length scale. Nanoscale polyurea films are grown on silica substrates in a layer-by-layer fashion by dosing 1,4-phenylene diisocyanate (PDIC) and ethylenediamine (ED) in the gas phase. Ellipsometry measurements indicate that the film growth occurs at a constant growth rate, with film thicknesses consistent with molecular distances calculated using density functional theory. Characterization of the films by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy reveals formation of stable polyurea films with nearly stoichiometric composition, and transmission electron microscopy indicates that the films uniformly coat the substrate surface. Subnanometer control over the film composition was demonstrated using 2,2'-thiobis(ethylamine) (TBEA) as an alternate diamine to vary the composition of the films. By substituting TBEA for ED, blended films, with homogeneous composition through the film, and nanolaminates, with discrete layers of differing film chemistry, were created.

    View details for DOI 10.1021/nn901013r

    View details for Web of Science ID 000273863400043

    View details for PubMedID 20000603

  • Area Selective Atomic Layer Deposition by Microcontact Printing with a Water-Soluble Polymer JOURNAL OF THE ELECTROCHEMICAL SOCIETY Mullings, M. N., Lee, H., Marchack, N., Jiang, X., Chen, Z., Gorlin, Y., Lin, K., Bent, S. F. 2010; 157 (12): D600-D604

    View details for DOI 10.1149/1.3491376

    View details for Web of Science ID 000283938300050

  • A CHEMICAL BATH PROCESS FOR DEPOSITING Cu2ZnSnS4 PHOTOVOLTAIC ABSORBERS 35TH IEEE PHOTOVOLTAIC SPECIALISTS CONFERENCE Wangperawong, A., King, J. S., Herron, S. M., Tran, B. P., Pangan-Okimoto, K., Bent, S. F. 2010: 1986-1989
  • ALD co-deposited and core-shell Ru-Pt catalysts for concentrated methanol oxidation Chem. Mat Jiang, X., Gür, T., M., Prinz, F., B., Bent, S., F. 2010; 22: 3024-3032
  • Area-Selective ALD with Soft Lithographic Methods: Using Self-Assembled Monolayers to Direct Film Deposition JOURNAL OF PHYSICAL CHEMISTRY C Jiang, X., Bent, S. F. 2009; 113 (41): 17613-17625

    View details for DOI 10.1021/jp905317n

    View details for Web of Science ID 000270459900007

  • Photochemical Covalent Attachment of Alkene-Derived Monolayers onto Hydroxyl-Terminated Silica LANGMUIR ter Maat, J., Regeling, R., Yang, M., Mullings, M. N., Bent, S. F., Zuilhof, H. 2009; 25 (19): 11592-11597

    Abstract

    The functionalization of optically transparent substrates is of importance, for example, in the field of biosensing. In this article, a new method for modification of silica surfaces is presented that is based on a photochemical reaction of terminal alkenes with the surface. This yields highly hydrophobic surfaces, which are thermally stable up to at least 400 degrees C. The formed monolayer provides chemical passivation of the underlying surface, according to studies showing successful blocking of platinum atomic layer deposition (ALD). The reaction is photochemically initiated, requiring light with a wavelength below 275 nm. X-ray photoelectron spectroscopy and infrared spectroscopy studies show that the alkenes initially bind to the surface hydroxyl groups in Markovnikov fashion. At prolonged reaction times (>5 h), however, oligomerization occurs, resulting in layer growth normal to the surface. The photochemical nature of the reaction enables the use of photolithography as a tool to constructively pattern silica surfaces. Atomic force microscopy shows that the features of the photomask are well transferred. The newly developed method can complement existing patterning methods on silica that are based on soft lithography.

    View details for DOI 10.1021/la901551t

    View details for Web of Science ID 000270136900061

    View details for PubMedID 19583192

  • Growth Process of Polyaniline Thin Films Formed by Hot Wire CVD CHEMICAL VAPOR DEPOSITION Zaharias, G. A., Bent, S. F. 2009; 15 (4-6): 133-141
  • Sulfur versus Oxygen Reactivity of Organic Molecules at the Ge(100)-2x1 Surface JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Kachian, J. S., Bent, S. F. 2009; 131 (20): 7005-7015

    Abstract

    The adsorption behavior of sulfur- versus oxygen-containing organic molecules, including ethanol, ethanethiol, diethyl ether, and diethyl sulfide, at the Ge(100)-2 x 1 surface was investigated using a combination of multiple internal reflection infrared (MIR-IR) spectroscopy and density functional theory (DFT). The results show that ethanol and ethanethiol both adsorb via Ch-H dissociation at 310 K, where Ch (chalcogen) is either S or O. DFT calculations indicate that S-H dissociation is both kinetically and thermodynamically favored over O-H dissociation. IR spectra of diethyl ether and diethyl sulfide reveal that both molecules adsorb via dative bonding through the heteroatom for temperatures up to approximately 255 and 335 K, respectively, and reversibly desorb at higher temperatures. From these desorption temperatures, the S-Ge dative bond of a sulfide is calculated to be 5.9 kcal/mol stronger than the O-Ge dative bond of an ether, a trend consistent with results from DFT calculations. Moreover, for all of the molecules studied, SGe dative bonds are found to be stronger than O-Ge dative bonds, with the magnitude of the difference increasing with substitution of bulkier groups on the Ch atom of the adsorbate. Calculations on diethyl selenide show that the Se-Ge dative bond is slightly stronger than the S-Ge dative bond.

    View details for DOI 10.1021/ja808066t

    View details for Web of Science ID 000266484700043

    View details for PubMedID 19413324

  • Controlling Atomic Layer Deposition of TiO2 in Aerogels through Surface Functionalization CHEMISTRY OF MATERIALS Ghosal, S., Baumann, T. F., King, J. S., Kucheyev, S. O., Wang, Y., Worsley, M. A., Biener, J., Bent, S. F., Hamza, A. V. 2009; 21 (9): 1989-1992

    View details for DOI 10.1021/cm900636s

    View details for Web of Science ID 000265781000034

  • Formation of Alkanethiolate Self-Assembled Monolayers at Halide-Terminated Ge Surfaces LANGMUIR Ardalan, P., Musgrave, C. B., Bent, S. F. 2009; 25 (4): 2013-2025

    Abstract

    We have studied Ge halide passivation and formation of 1-octadecanethiolate self-assembled monolayers (SAMs) at Cl- and Br-terminated Ge(100) and Ge(111) surfaces. The results of water contact angle measurements, ellipsometry, transmission infrared spectroscopy, X-ray photoelectron spectroscopy, and Auger electron spectroscopy show that good quality 1-alkanethiolate SAMs can be achieved at both Cl- and Br-terminated surfaces via direct Ge-S bonds. The quality of the SAMs depends on the concentration and the solvent of the 1-alkanethiol solution. Moreover, SAMs formed at Ge(100) surfaces have higher water contact angles, thicknesses, and ambient stability than those formed at Ge(111) surfaces. Surface passivation and light are found to play an important role in the packing and stability of the SAMs. Furthermore, well-packed SAMs can be retrieved by repassivation after degradation due to ambient exposure. This work presents novel routes for Ge surface passivation.

    View details for DOI 10.1021/la803468e

    View details for Web of Science ID 000263373600023

    View details for PubMedID 19152272

  • Ultralow loading Pt nanocatalysts prepared by atomic layer deposition on carbon aerogels NANO LETTERS King, J. S., Wittstock, A., Biener, J., Kucheyev, S. O., Wang, Y. M., Baumann, T. F., Giri, S. K., Hamza, A. V., Baeumer, M., Bent, S. F. 2008; 8 (8): 2405-2409

    Abstract

    Using atomic layer deposition (ALD), we show that Pt nanoparticles can be deposited on the inner surfaces of carbon aerogels (CA). The resultant Pt-loaded materials exhibit high catalytic activity for the oxidation of CO even at loading levels as low as approximately 0.05 mg Pt/cm2. We observe a conversion efficiency of nearly 100% in the 150-250 degrees C temperatures range, and the total conversion rate seems to be limited only by the thermal stability of the CA support in ambient oxygen. The ALD approach described here is universal in nature, and can be applied to the design of new catalytic materials for a variety of applications, including fuel cells, hydrogen storage, pollution control, green chemistry, and liquid fuel production.

    View details for DOI 10.1021/nl801299z

    View details for Web of Science ID 000258440700051

    View details for PubMedID 18636780

  • Application of atomic layer deposition of platinum to solid oxide fuel cells CHEMISTRY OF MATERIALS Jiang, X., Huang, H., Prinz, F. B., Bent, S. F. 2008; 20 (12): 3897-3905

    View details for DOI 10.1021/cm7033189

    View details for Web of Science ID 000256854800020

  • Formation of an oxide-free Ge/TiO2 interface by atomic layer deposition on brominated Ge APPLIED PHYSICS LETTERS Ardalan, P., Pickett, E. R., Harris, J. S., Marshall, A. F., Bent, S. F. 2008; 92 (25)

    View details for DOI 10.1063/1.2951608

    View details for Web of Science ID 000257231200043

  • Surface patterning: Silicon falls into line NATURE NANOTECHNOLOGY Bent, S. F. 2008; 3 (4): 185-186

    View details for DOI 10.1038/nnano.2008.79

    View details for Web of Science ID 000254744300003

    View details for PubMedID 18654496

  • Silicon falls into line Nature Nanotechnology Bent, S., F. 2008; 3: 185-186
  • A model neural interface based on functional chemical stimulation BIOMEDICAL MICRODEVICES Mehenti, N. Z., Fishman, H. A., Bent, S. F. 2007; 9 (4): 579-586

    Abstract

    While functional electrical stimulation has been applied to treat a variety of neurological disorders, it cannot mimic function that is primarily achieved using neurochemical means. In this work, we present a neurotransmitter-based prosthetic interface in the form of a flexible microdevice that selectively releases chemical pulses through an aperture in a polymer membrane. The release profiles through the aperture are controlled by microfluidic switching in an underlying channel network. The profiles have been characterized using fluorescence microscopy as a function of pulse duration and frequency. Hippocampal neurons were cultured on the microdevices and cell stimulation via glutamate delivery was detected using calcium imaging. The release properties could be tuned to repeatedly elicit discrete action potentials in cells seeded proximate to the aperture, including single cell stimulation at 2 Hz. This model neural interface based on functional chemical stimulation may provide the biomimetic platform necessary to restore physiological pathways and function that electrical stimulation cannot fundamentally address.

    View details for DOI 10.1007/s10544-007-9069-z

    View details for Web of Science ID 000248007500016

    View details for PubMedID 17520371

  • Heads or tails: Which is more important in molecular self-assembly? ACS NANO Bent, S. F. 2007; 1 (1): 10-12

    Abstract

    Self-assembled monolayers can modify the functionality of the surfaces on which they assemble. Because they alter the surface properties, self-assembled monolayers can be used for a multitude of applications. Understanding the forces that drive the formation of a self-assembled monolayer on a given surface remains an important area of investigation. A new paper discusses some of the considerations for self-assembly on semiconductors. The results highlight the tradeoffs between achieving crystalline packing of the tail groups and forming commensurate bonding between the head groups and the underlying surface. Where the emphasis should be placed depends on the application, but obtaining both interfacial and intermolecular ordering may be possible.

    View details for DOI 10.1021/nn700118k

    View details for Web of Science ID 000252012200007

    View details for PubMedID 19203125

  • Spatial cues for the enhancement of retinal pigment epithelial cell function in potential transplants BIOMATERIALS Lee, C. J., Fishman, H. A., Bent, S. F. 2007; 28 (13): 2192-2201

    Abstract

    Retinal pigment epithelial (RPE) cellular morphology and function are vital to the health of the retina. In age-related macular degeneration, RPE dysfunction and changes in Bruch's membrane occur. Thus, a potential cure is a dual-layer biomimetic transplant consisting of a layer of healthy RPE cells cultured on a support membrane. In this study, we investigated human anterior lens capsule as a replacement for Bruch's membrane and also explored different seeding methods as ways of inducing the desired cellular morphology and function. Using in vitro assays, we demonstrated that RPE cells cultured on lens capsule exhibited epithelial characteristics, such as the presence of actin belts and the formation of tight junctions in the monolayer. Bovine photoreceptor outer segments were also incubated with the RPE cells in order to quantify the binding and ingestion activity of the RPE cells. With these assays, we determined that cells seeded by centrifugation appeared to possess the most epithelial-like morphology, with the shortest overall length and the smallest elongation. They also exhibited enhanced metabolic activity, with a 1.5-fold increase over conventional gravity seeding. Thus, the spatial cues provided by centrifugation may assist cells in assuming native RPE function. Therefore, a dual-layer transplant, with RPE cells organized by centrifugation onto lens capsule, appears promising in achieving native retinal function.

    View details for DOI 10.1016/j.biomaterials.2007.01.018

    View details for Web of Science ID 000244947100004

    View details for PubMedID 17267030

  • Thin collagen film scaffolds for retinal epithelial cell culture BIOMATERIALS Lu, J. T., Lee, C. J., Bent, S. F., Fishman, H. A., Sabelman, E. E. 2007; 28 (8): 1486-1494

    Abstract

    Collagen films have been used in biological implantation and surgical grafts. The development of thin collagen films on the order of 10 microm thick that ensure a planar distribution of implanted cells is a necessary step towards surgical grafts for treatment of age-related macular degeneration (AMD). Here, collagen films were manufactured on a Teflon support to a thickness of 2.4+/-0.2 microm, comparable to that of native Bruch's membrane. Because one important function of Bruch's membrane is allowing the flow of nutrients and waste to and from the retinal pigment epithelium the diffusion properties of the collagen films were studied using blind-well chambers. The diffusion coefficient of the collagen film was determined to be 4.1 x 10(-10)cm(2)/s for 71,200 Da dextran molecules. Viability studies utilizing the blind-well chambers also confirmed that nutrient transport through the films was sufficient to sustain retinal pigment epithelial (RPE) cells. The films were bioassayed in a RPE cell culture model to confirm cell attachment and viability. RPE cells were shown to form an epithelial phenotype and were able to phagocytize photoreceptor outer segments.

    View details for DOI 10.1016/j.biomaterials.2006.11.023

    View details for Web of Science ID 000244130000004

    View details for PubMedID 17161864

  • Carbon-oxygen coupling in the reaction of formaldehyde on Ge(100)-2x1 JOURNAL OF PHYSICAL CHEMISTRY C Filler, M. A., Musgrave, C. B., Bent, S. F. 2007; 111 (4): 1739-1746

    View details for DOI 10.1021/jp064820v

    View details for Web of Science ID 000245005500029

  • ALD resist formed by vapor-deposited self-assembled monolayers LANGMUIR Hong, J., Porter, D. W., Sreenivasan, R., McIntyre, P. C., Bent, S. F. 2007; 23 (3): 1160-1165

    Abstract

    A new process of applying molecular resists to block HfO2 and Pt atomic layer deposition has been investigated. Monolayer films are formed from octadecyltrichlorosilane (ODTS) or tridecafluoro-1,1,2,2-tetrahydrooctyltrichlorosilane (FOTS) and water vapor on native silicon oxide surfaces and from 1-octadecene on hydrogen-passivated silicon surfaces through a low-pressure chemical vapor deposition process. X-ray photoelectron spectroscopy data indicates that surfaces blocked by these monolayer resists can prevent atomic layer deposition of both HfO2 and Pt successfully. Time-dependent studies show that the ODTS monolayers continue to improve in blocking ability for as long as 48 h of formation time, and infrared spectroscopy measurements confirm an evolution of packing order over these time scales.

    View details for DOI 10.1021/la0606401

    View details for Web of Science ID 000243684100033

    View details for PubMedID 17241027

  • Thermal control of amide product distributions at the Ge(100)-2x1 surface JOURNAL OF PHYSICAL CHEMISTRY C Keung, A. J., Filler, M. A., Bent, S. F. 2007; 111 (1): 411-419

    View details for DOI 10.1021/jp065278d

    View details for Web of Science ID 000244993800060

  • Spatial clues for the enhancement of retinal pigment epithelial cell function in potential implants Biomaterials Lee, C., J., Fishman, H., A., Bent, S., F. 2007; 28: 2192-2201
  • Effect of radical species density and ion bombardment during ashing of extreme ultralow-kappa interlevel dielectric materials JOURNAL OF APPLIED PHYSICS Worsley, M. A., Bent, S. F., Fuller, N. C., Tai, T. L., Doyle, J., Rothwell, M., Dalton, T. 2007; 101 (1)

    View details for DOI 10.1063/1.2405123

    View details for Web of Science ID 000243585200017

  • Area-selective atomic layer deposition of platinum on YSZ substrates using microcontact printed SAMs JOURNAL OF THE ELECTROCHEMICAL SOCIETY Jiang, X., Bent, S. F. 2007; 154 (12): D648-D656

    View details for DOI 10.1149/1.2789301

    View details for Web of Science ID 000250504600043

  • Characterization of neutral species densities in dual frequency capacitively coupled photoresist ash plasmas by optical emission actinometry JOURNAL OF APPLIED PHYSICS Worsley, M. A., Bent, S. F., Fuller, N. C., Dalton, T. 2006; 100 (8)

    View details for DOI 10.1063/1.2358303

    View details for Web of Science ID 000241721900013

  • Highly stable monolayer resists for atomic layer deposition on germanium and silicon CHEMISTRY OF MATERIALS Chen, R., Bent, S. F. 2006; 18 (16): 3733-3741

    View details for DOI 10.1021/cm0607785

    View details for Web of Science ID 000239396900021

  • A model retinal interface based on directed neuronal growth for single cell stimulation BIOMEDICAL MICRODEVICES Mehenti, N. Z., Tsien, G. S., Leng, T., Fishman, H. A., Bent, S. F. 2006; 8 (2): 141-150

    Abstract

    In this work, we use cell micropatterning technologies to direct neuronal growth to individual electrodes, and demonstrate that such an approach can achieve selective stimulation and lower stimulation thresholds than current field-effect based retinal prostheses. Rat retinal ganglion cells (RGCs) were purified through immunopanning techniques, and microcontact printing (microCP) was applied to align and pattern laminin on a microelectrode array, on which the RGCs were seeded and extended neurites along the pattern to individual electrodes. The stimulation threshold currents of RGCs micropatterned to electrodes were found to be significantly less than those of non-patterned RGCs over a wide range of electrode-soma distances, as determined with calcium imaging techniques. Moreover, the stimulation threshold for micropatterned cells was found to be independent of electrode-soma distance, and there was no significant effect of microCP on cell excitability. The effects of additional stimulation parameters, such as electrode size and pulse duration, on threshold currents were determined. The stimulation results quantitatively demonstrate the potential benefits of a retinal prosthetic interface based on directed neuronal growth.

    View details for DOI 10.1007/s10544-006-7709-3

    View details for Web of Science ID 000237486500006

    View details for PubMedID 16688573

  • Detecting free radicals during the hot wire chemical vapor deposition of amorphous silicon carbide films using single-source precursors JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A Zaharias, G. A., Duan, H. L., Bent, S. F. 2006; 24 (3): 542-549

    View details for DOI 10.1116/1.2194023

    View details for Web of Science ID 000238091300023

  • Chemistry for positive pattern transfer using area-selective atomic layer deposition ADVANCED MATERIALS Chen, R., Bent, S. F. 2006; 18 (8): 1086-?
  • Formation of surface-bound acyl groups by reaction of acyl halides on Ge(100)-2x1 JOURNAL OF PHYSICAL CHEMISTRY B Filler, M. A., Keung, A. J., Porter, D. W., Bent, S. F. 2006; 110 (9): 4115-4124

    Abstract

    We have investigated the reaction of a series of acyl halides, including acetyl chloride, acetyl bromide, acetyl-d3 chloride, benzoyl chloride, and pivaloyl chloride, on Ge(100)-2x1 with multiple internal reflection infrared (MIR-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT). Infrared spectra following saturation exposures of acetyl chloride and acetyl bromide to Ge(100)-2x1 at 310 K are nearly identical, both exhibiting strong nu(C=O) stretching peaks near 1685 cm-1 and no vibrational modes in the nu(Ge-H) region. These data provide strong evidence for the presence of a surface-bound acetyl group on Ge(100)-2x1, which results from a C-X dissociation reaction (where X=Cl, Br). For acetyl chloride, DFT calculations predict that the barrier to C-Cl dissociation is only 1 kcal/mol above a chlorine-bound precursor state and is considerably smaller than barriers leading to the [2+2] C=O cycloaddition and alpha-CH dissociation products. In addition to the C-X dissociation product, both infrared and photoelectron results point to the presence of a second structure for acetyl halides where the oxygen of the surface-bound acetyl group donates charge to a nearby surface atom. This interaction is not observed for benzoyl chloride and pivaloyl chloride.

    View details for DOI 10.1021/jp055685+

    View details for Web of Science ID 000235944500045

    View details for PubMedID 16509705

  • Determination of human lens capsule permeability and its feasibility as a replacement for Bruch's membrane BIOMATERIALS Lee, C. J., Vroom, J. A., Fishman, H. A., Bent, S. F. 2006; 27 (8): 1670-1678

    Abstract

    We have investigated human anterior lens capsule as a potential replacement for Bruch's membrane as a treatment for age-related macular degeneration. Any substrate to replace Bruch's membrane should possess certain characteristics to maintain proper function of the overlying retina. One of the important properties of Bruch's membrane is allowing the flow of nutrients and waste between the retinal pigment epithelium and the choriocapillaris. Here, we measured the permeability of the lens capsule by studying the diffusion of various molecular weight FITC-dextran molecules. Expressions for extraction of diffusion coefficients from concentration vs. time data from a blind-well chamber apparatus were derived for both a single and double membrane experiments. The diffusion coefficients in the lens capsule were found to be in the range of 10(-6) to 10(-10)cm2/s. We demonstrated a power law relationship, with the diffusion coefficient possessing a -0.6 order dependence on molecular weight. The molecular weight exclusion limit was determined to be 150+/-40 kDa. We have compared this value with reported values of Bruch's membrane molecular weight exclusion limit and find that the lens capsule has the potential to act as a substitute Bruch's membrane.

    View details for DOI 10.1016/j.biomaterials.2005.09.008

    View details for Web of Science ID 000234731900055

    View details for PubMedID 16199085

  • Carboxylic acid chemistry at the Ge(100)-2 x 1 interface: Bidentate bridging structure formation on a semiconductor surface JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Filler, M. A., Van Deventer, J. A., Keung, A. J., Bent, S. F. 2006; 128 (3): 770-779

    Abstract

    The reactions of acetic acid, acetic-d3 acid-d, and formic acid with the Ge(100)-2 x 1 surface have been investigated using multiple internal reflection Fourier transform infrared (MIR-FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations. The infrared and photoelectron data provide experimental evidence for an O-H dissociation product at 310 K. DFT calculations indicate that the O-H dissociation pathway is significantly favored, both kinetically and thermodynamically, over other potential reaction pathways. All of the carboxylic acids studied exhibit unexpected vibrational modes between 1400 and 1525 cm(-1), which are attributed to the presence of a bidentate bridging structure where both oxygen atoms interact directly with the surface.

    View details for DOI 10.1021/ja0549502

    View details for Web of Science ID 000234815000040

    View details for PubMedID 16417366

  • Reactivity of the germanium surface: Chemical passivation and functionalization ANNUAL REVIEW OF PHYSICAL CHEMISTRY Loscutoff, P. W., Bent, S. F. 2006; 57: 467-495

    Abstract

    With the rapidly changing materials needs of modern microelectronics, germanium provides an opportunity for future-generation devices. Controlling germanium interfaces will be essential for this purpose. We review germanium surface reactivity, beginning with a description of the most commonly used surfaces, Ge(100) and Ge(111). An analysis of oxide formation shows why the poor oxide properties have hindered practical use of germanium to date. This is followed by an examination of alternate means of surface passivation, with particular attention given to sulfide, chloride, and hydride termination. Specific tailoring of the interface properties is possible through organic functionalization. The few solution functionalization methods that have been studied are reviewed. Vacuum functionalization has been studied to a much greater extent, with dative bonding and cycloaddition reactions emerging as principle reaction mechanisms. These are reviewed through molecular reaction studies that demonstrate the versatility of the germanium surface.

    View details for DOI 10.1146/annurev.physchem.56.092503.141307

    View details for Web of Science ID 000237668700016

    View details for PubMedID 16599818

  • Tertiary amide chemistry at the Ge(100)-2 x 1 surface SURFACE SCIENCE Keung, A. J., Filler, M. A., Porter, D. W., Bent, S. F. 2005; 599 (1-3): 41-54
  • Ethylenediamine on Ge(100)-2 x 1: The role of interdimer interactions JOURNAL OF PHYSICAL CHEMISTRY B Kim, A., Filler, M. A., Kim, S., Bent, S. F. 2005; 109 (42): 19817-19822

    Abstract

    We have investigated the reaction of the bifunctional molecule ethylenediamine on Ge(100)-2 x 1 using multiple internal reflection Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and density functional theory calculations. Ethylenediamine exhibits different adsorption behavior than simple methylamines on the Ge(100)-2 x 1 surface. At low coverages, ethylenediamine undergoes dissociative chemisorption via an interdimer dual N-H dissociation reaction. As coverage increases, the N-H dissociation reaction is inhibited and formation of a Ge-N dative-bonded structure dominates.

    View details for DOI 10.1021/jp054340o

    View details for Web of Science ID 000232857900037

    View details for PubMedID 16853562

  • Detection of open or closed porosity in low-kappa dielectrics by solvent diffusion MICROELECTRONIC ENGINEERING Worsley, M. A., Roberts, M., Bent, S. F., GATES, S. M., Shaw, T., Volksen, W., Miller, R. 2005; 82 (2): 113-118
  • The influence of filament material on radical production in hot wire chemical vapor deposition of a-Si : H THIN SOLID FILMS Duan, H. L., Bent, S. F. 2005; 485 (1-2): 126-134
  • Achieving area-selective atomic layer deposition on patterned substrates by selective surface modification APPLIED PHYSICS LETTERS Chen, R., Kim, H., McIntyre, P. C., Porter, D. W., Bent, S. F. 2005; 86 (19)

    View details for DOI 10.1063/1.1922076

    View details for Web of Science ID 000229397900026

  • Layer-by-layer growth on Ge(100) via spontaneous urea coupling reactions JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Kim, A., Filler, M. A., Kim, S., Bent, S. F. 2005; 127 (16): 6123-6132

    Abstract

    We have demonstrated the layer-by-layer growth, via a urea coupling reaction between two bifunctional molecules, ethylenediamine and 1,4-phenylene diisocyanate, to form an ultrathin film on Ge(100)-2 x 1 at room temperature under vacuum conditions. The initial adsorption and subsequent growth of each layer was studied with multiple internal reflection Fourier transform infrared (MIR-FTIR) spectroscopy. Ethylenediamine reacts with Ge(100)-2 x 1 to produce a surface-bound amine group which is available for additional reaction. Subsequent exposure of 1,4-phenylene diisocyanate leads to a spontaneous urea coupling reaction between the surface-bound amine and the highly reactive isocyanate functional group. Three bands at 1665, 1512, and 1306 cm(-)(1) are characteristic of a urea linkage and provide evidence of the coupling reaction. The coupling procedure can be repeated in a binary fashion to create covalently bound ultrathin films at room temperature, and in the present work, we demonstrate the successful growth of four layers. In addition, we have found that an initial exposure of 1,4-phenylene diisocyanate to Ge(100)-2 x 1 produces an isocyanate-functionalized surface which, upon exposure to ethylenediamine, also forms urea linkages. This layer-by-layer deposition method provides a strategy with which to design and produce precisely tailored organic materials at semiconductor interfaces.

    View details for DOI 10.1021/ja042751x

    View details for Web of Science ID 000228602600077

    View details for PubMedID 15839714

  • Effect of plasma interactions with low-kappa films as a function of porosity, plasma, chemistry, and temperature JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B Worsley, M. A., Bent, S. F., GATES, S. M., Fuller, N. C., Volksen, W., Steen, M., Dalton, T. 2005; 23 (2): 395-405

    View details for DOI 10.1116/1.1861038

    View details for Web of Science ID 000228788600011

  • Investigation of self-assembled monolayer resists for hafnium dioxide atomic layer deposition CHEMISTRY OF MATERIALS Chen, R., Kim, H., McIntyre, P. C., Bent, S. F. 2005; 17 (3): 536-544

    View details for DOI 10.1021/cm0486666

    View details for Web of Science ID 000226804000011

  • Quantum chemistry based statistical mechanical model of hydrogen desorption from Si(100)-2 x 1, Ge(100)-2 x 1, and SiGe alloy surfaces JOURNAL OF PHYSICAL CHEMISTRY B Mui, C., Bent, S. F., Musgrave, C. B. 2004; 108 (47): 18243-18253

    View details for DOI 10.1021/jp0379493

    View details for Web of Science ID 000225227700021

  • Directed retinal nerve cell growth for use in a retinal prosthesis interface INVESTIGATIVE OPHTHALMOLOGY & VISUAL SCIENCE Leng, T., Wu, P., Mehenti, N. Z., Bent, S. F., Marmor, M. F., Blumenkranz, M. S., Fishman, H. A. 2004; 45 (11): 4132-4137

    Abstract

    Retinal prosthetic devices that use microelectrode arrays to stimulate retinal nerve cells may provide a viable treatment for degenerative retinal diseases. Current devices are based on electrical field-effect stimulation of remaining functional neural elements. However, the distance between target neurons and electrodes limits the potential density of electrodes and the ability to stimulate specific types of retinal neurons that contribute to visual perceptions. This study was conducted to investigate the use of microcontact printing (muCP) to direct cultured or explant retinal ganglion cell (RGC) neurites to precise and close stimulation positions and to evaluate the cell types that grow from a retinal explant.RGCs and whole retinal explants were isolated from postnatal day-7 Sprague-Dawley rats using immunopanning purification and microdissection, respectively. Aligned muCP was used to direct the growth of RGC neurites from pure cultures (n=105) and retinal explants (n=64) along laminin patterns and to individual microelectrodes. Immunofluorescence stains (n=39) were used to determine the cell types that grew out from the retinal explants.RGC neurite growth was directed reproducibly along aligned laminin micropatterns to individual microelectrodes in pure RGC cultures and from full-thickness explanted rat retinas in 92% of experiments, neurites from pure RGC cultures extended along the laminin lines with an average length of 263 +/- 118 microm (SD; n=27) after 24 hours. Neurites from retinal explants extended in more than 80% of experiments and were observed to grow to an average length of 279 +/- 78 microm (n=64) after 2 days in culture. These neurites grew up to 3 mm after 1 month of culture on the laminin micropatterns. Immunohistochemical stains demonstrated that extended processes from both RGCs and glial cells grew out of retinal explants onto stamped laminin lines.Using muCP to pattern surfaces with growth factors, individual neuronal processes from pure RGC culture and whole retinal explants can be directed to discrete sites on a microelectronic chip surface. By directing RGC neurite processes to specific sites, single cell stimulation becomes possible. This may allow discrete populations of retinal neurons to be addressed so that physiologic retinal processing of visual information can be achieved.

    View details for DOI 10.1167/iovs.03-1335

    View details for Web of Science ID 000224678200039

    View details for PubMedID 15505066

  • A density functional theory study on the effect of Ge alloying on hydrogen desorption from SiGe alloy surfaces JOURNAL OF PHYSICAL CHEMISTRY B Mui, C., Bent, S. F., Musgrave, C. B. 2004; 108 (20): 6336-6350

    Abstract

    We have used density functional theory to investigate hydrogen desorption from SiGe alloy surfaces, and the effect of Ge alloying on the kinetics of hydrogen desorption via the prepairing and interdimer mechanisms. We find that the calculated activation barriers of the prepairing mechanism are affected by the surface atom bonded to the desorbing hydrogen atoms. On the other hand, our calculations show that the activation barrier for hydrogen desorption via the 2H interdimer mechanism is affected by all four surface atoms of the two neighboring dimers. For the 4H interdimer mechanism, we have shown that the activation barrier for hydrogen desorption is not significantly higher than the endothermicity of hydrogen desorption. We also find that the calculated activation barriers of the interdimer mechanisms are generally lower than those of the prepairing mechanism. In addition, our calculations show that surface Ge atoms on neighboring dimers on SiGe alloy surfaces have a minor effect on the calculated activation barriers of both the prepairing and interdimer mechanisms, which indicates that the effect of Ge alloying on hydrogen desorption is local in nature. We also discuss the effects of cluster size and constraints on the calculated reaction energies and activation barriers of hydrogen desorption via the two mechanisms.

    View details for DOI 10.1021/jp037948a

    View details for Web of Science ID 000221455000031

    View details for PubMedID 18950120

  • Self-assembled monolayer resist for atomic layer deposition of HfO2 and ZrO2 high-kappa gate dielectrics APPLIED PHYSICS LETTERS Chen, R., Kim, H., McIntyre, P. C., Bent, S. F. 2004; 84 (20): 4017-4019

    View details for DOI 10.1063/1.1751211

    View details for Web of Science ID 000221269800021

  • Controlling cell adhesion on human tissue by soft lithography LANGMUIR Lee, C. J., Blumenkranz, M. S., Fishman, H. A., Bent, S. F. 2004; 20 (10): 4155-4161

    Abstract

    Soft lithographic techniques are widely used for fundamental biological applications. This study investigates the extension of soft lithography for use on human tissue to create a biological implant by systematically studying the effect of pattern size on cellular morphology. We focus on mimicking a key layer of the physiological retina with an organized monolayer of epithelial cells to act as a new treatment for age-related macular degeneration. We show that epithelial cells can be confined to cytophilic islands defined on lens capsule by the inhibitory polymer poly(vinyl alcohol). In addition, as the size of the cytophilic islands grows, both the fraction of islands with cells attached and the number of cells adhered to each island increase. High densities of cell adhesion and single cell attachment per island were achieved with a 25 microm pattern size. Over time, the cells spread over the 5 microm wide barriers to form a confluent monolayer that may eventually serve as a functional retinal implant. With the ability to apply soft lithography to tissue samples, human tissue may become a universal membrane substrate for other ocular diseases or in tissue engineering applications elsewhere in the body.

    View details for DOI 10.1021/la035467c

    View details for Web of Science ID 000221319400049

    View details for PubMedID 15969410

  • A quantum chemistry based statistical mechanical model of hydrogen desorption from Si(100)‑2x1, Ge(100)‑2x1, and SiGe alloy surfaces J. Phys. Chem. B Mui, C., Bent, S., F., Musgrave, C., B. 2004; 108: 12559-12565
  • Pushing the limits of artificial vision IEEE Potentials Mehenti, N., Z., Fishman, H., A., Bent, S., F. 2004; 23: 21-23
  • Reactions of nitriles at semiconductor surfaces JOURNAL OF PHYSICAL CHEMISTRY B Mui, C., Filler, M. A., Bent, S. F., Musgrave, C. B. 2003; 107 (44): 12256-12267

    View details for DOI 10.1021/jp034864t

    View details for Web of Science ID 000186282200030

  • The artificial synapse chip: A flexible retinal interface based on directed retinal cell growth and neurotransmitter stimulation ARTIFICIAL ORGANS Peterman, M. C., Mehenti, N. Z., Bilbao, K. V., Lee, C. J., Leng, T., Noolandi, J., Bent, S. F., Blumenkranz, M. S., Fishman, H. A. 2003; 27 (11): 975-985

    Abstract

    The Artificial Synapse Chip is an evolving design for a flexible retinal interface that aims to improve visual resolution of an electronic retinal prosthesis by addressing cells individually and mimicking the physiological stimulation achieved in synaptic transmission. We describe three novel approaches employed in the development of the Artificial Synapse Chip: (i) micropatterned substrates to direct retinal cell neurite growth to individual stimulation sites; (ii) a prototype retinal interface based on localized neurotransmitter delivery; and (iii) the use of soft materials to fabricate these devices. By patterning the growth of cells to individual stimulation sites, we can improve the selectivity of stimulation and decrease the associated power requirements. Moreover, we have microfabricated a neurotransmitter delivery system based on a 5- micro m aperture in a 500-nm-thick silicon nitride membrane overlying a microfluidic channel. This device can release neurotransmitter volumes as small as 2 pL, demonstrating the possibility of chemical-based prostheses. Finally, we have fabricated and implanted an equivalent device using soft flexible materials that conform to the retinal tissue more effectively. As many of the current retinal prosthesis devices use hard materials and electrical excitation at a lower resolution, our approach may provide more physiologic retinal stimulation.

    View details for Web of Science ID 000186491900003

    View details for PubMedID 14616516

  • The surface as molecular reagent: organic chemistry at the semiconductor interface PROGRESS IN SURFACE SCIENCE Filler, M. A., Bent, S. F. 2003; 73 (1-3): 1-56
  • Localized neurotransmitter release for use in a prototype retinal interface INVESTIGATIVE OPHTHALMOLOGY & VISUAL SCIENCE Peterman, M. C., Bloom, D. M., Lee, C., Bent, S. F., Marmor, M. E., Blumenkranz, M. S., Fishman, H. A. 2003; 44 (7): 3144-3149

    Abstract

    Current neural prostheses use electricity as the mode of stimulation, yet information transfer in neural circuitry is primarily through chemical transmitters. To address this disparity, this study was conducted to devise a prototype interface for a retinal prosthetic based on localized chemical delivery. The goal was to determine whether fluidic delivery through microfabricated apertures could be used to stimulate at single-cell dimensions.A drug delivery system was microfabricated based on a 5- or 10- microm aperture in a 500-nm thick silicon nitride membrane to localize and limit transmitter release. The aperture overlies a microfluidic delivery channel in a silicone elastomer. To demonstrate the effectiveness of this transmitter-based prosthesis, rat pheochromocytoma cells (PC12 cell line) were grown on the surface of the device to test the precision of stimulation, using bradykinin as a stimulant and measuring fluorescence from the calcium indicator, fluo-4.The extent of stimulation could be controlled accurately by varying the concentration of stimulant, from a single cell adjacent to the aperture to a broad area of cells. The stimulation radius was as small as 10 microm, corresponding to stimulation volumes as small as 2 pL. The relationship between the extent of stimulation and concentration was linear.The demonstration of localized chemical stimulation of excitable cells illustrates the potential of this technology for retinal prostheses. Although this is only a proof of concept of neurotransmitter stimulation for a retinal prosthesis, it is a significant first step toward mimicking neurotransmitter release during synaptic transmission.

    View details for DOI 10.1167/iovs.02-1097

    View details for Web of Science ID 000183795800048

    View details for PubMedID 12824264

  • Reactions of cyclic aliphatic and aromatic amines on Ge(100)-2x1 and Si(100)-2x1 JOURNAL OF PHYSICAL CHEMISTRY B Wang, G. T., Mui, C., Tannaci, J. F., Filler, M. A., Musgrave, C. B., Bent, S. F. 2003; 107 (21): 4982-4996

    View details for DOI 10.1021/jp026864j

    View details for Web of Science ID 000183066000014

  • Competition and selectivity in the reaction of nitriles on Ge(100)-2x1 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Filler, M. A., Mui, C., Musgrave, C. B., Bent, S. F. 2003; 125 (16): 4928-4936

    Abstract

    We have experimentally investigated bonding of the nitrile functional group (R-Ctbd1;N:) on the Ge(100)-2x1 surface with multiple internal reflection infrared spectroscopy. Density functional theory calculations are used to help explain trends in the data. Several probe molecules, including acetonitrile, 2-propenenitrile, 3-butenenitrile, and 4-pentenenitrile, were studied to elucidate the factors controlling selectivity and competition on this surface. It is found that acetonitrile does not react on the Ge(100)-2x1 surface at room temperature, a result that can be understood with thermodynamic and kinetic arguments. A [4+2] cycloaddition product through the conjugated pi system and a [2+2] C=C cycloaddition product through the alkene are found to be the dominant surface adducts for the multifunctional molecule 2-propenenitrile. These two surface products are evidenced, respectively, by an extremely intense nu(C=C=N), or ketenimine stretch, at 1954 cm(-)(1) and the nu(Ctbd1;N) stretch near 2210 cm(-)(1). While the non-conjugated molecules 3-butenenitrile and 4-pentenenitrile are not expected to form a [4+2] cycloaddition product, both show vibrational modes near 1954 cm(-)(1). Additional investigation suggests that 3-butenenitrile can isomerize to 2-butenenitrile, a conjugated nitrile, before introduction into the vacuum chamber, explaining the presence of the vibrational modes near 1954 cm(-)(1). Pathways directly involving only the nitrile functional group are thermodynamically unfavorable at room temperature on Ge(100)-2x1, demonstrating that this functional group may prove useful as a vacuum-compatible protecting group.

    View details for DOI 10.1021/ja027887e

    View details for Web of Science ID 000182331800052

    View details for PubMedID 12696912

  • Reaction of cyclic aliphatic and aromatic amines on Ge(100)-2x1 and Si(100)-2x1 J. Phys. Chem. B Wang, G., T., Mui, C., Tannaci, J., F., Filler, M., A., Musgrave, C., B., Bent, S., F. 2003; 107: 4982
  • Microcontact printing on human tissue for retinal cell transplantation ARCHIVES OF OPHTHALMOLOGY Lee, C. J., Huie, P., Leng, T., Peterman, M. C., Marmor, M. F., Blumenkranz, M. S., Bent, S. F., Fishman, H. A. 2002; 120 (12): 1714-1718

    Abstract

    To demonstrate that microcontact printing, a modern materials fabrication technique, can be used to engineer the surface of human tissue and to show that inhibitory molecules can be used to pattern the growth of retinal pigment epithelial cells or iris pigment epithelial cells on human lens capsule for transplantation.Photolithographic techniques were used to fabricate photoresist-coated silicon substrates into molds. Poly(dimethylsiloxane)stamps for microcontact printing were made from these molds. The poly(dimethylsiloxane) stamps were then used to "wet-transfer" growth inhibitory molecules to the surface of prepared human lens capsules that were obtained during cataract surgery. Human retinal pigment epithelial and rabbit iris pigment epithelial cells were grown on a lens capsule substrate in the presence and absence of a patterned array of inhibitory factors.We found that human lens capsule could be microprinted with a precision similar to that obtained on glass or synthetic polymers. Retinal pigment epithelial cells and iris pigment epithelial cells cultured onto an untreated lens capsule showed spreading and formed into fusiform-appearing cells. In contrast, cells cultured on a lens capsule with a hexagonal micropattern of growth inhibitory molecules retained an epithelioid form within the inhibitory hexagons.Inhibitory growth molecules can be micropatterned onto human lens capsule, and these micropatterns can control the organization of retinal pigment epithelial cells or iris pigment epithelial cells cultured onto the lens capsule surface.Microprinting on autologous human tissue may facilitate efforts to effectively organize cell cultures and transplantations for the replacement of vital ocular tissues such as the retinal pigment epithelium in age-related macular degeneration.

    View details for Web of Science ID 000179737900014

    View details for PubMedID 12470147

  • Detecting reactive species in hot wire chemical vapor deposition CURRENT OPINION IN SOLID STATE & MATERIALS SCIENCE Duan, H. L., Zaharias, G. A., Bent, S. F. 2002; 6 (5): 471-477
  • Competition and selectivity of organic reactions on semiconductor surfaces: Reaction of unsaturated ketones on Si(100)-2x1 and Ge(100)-2x1 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Wang, G. T., Mui, C., Musgrave, C. B., Bent, S. F. 2002; 124 (30): 8990-9004

    Abstract

    A combined experimental and theoretical study of a model system of multifunctional unsaturated ketones, including ethyl vinyl ketone (EVK), 2-cyclohexen-1-one, and 5-hexen-2-one, on the Si(100)-2 x 1 and Ge(100)-2 x 1 surfaces was performed in order to probe the factors controlling the competition and selectivity of organic reactions on clean semiconductor surfaces. Multiple internal reflection infrared spectroscopy data and density functional theory calculations indicate that EVK and 2-cyclohexen-1-one undergo selective [4 + 2] hetero-Diels-Alder and [4 + 2] trans cycloaddition reactions on the Ge(100)-2 x 1 surface at room temperature. In contrast, on the Si(100)-2 x 1 surface, evidence is seen for significant ene and possibly [2 + 2] C=O cycloaddition side products. The greater selectivity of these compounds on Ge(100) versus Si(100) is explained by differences between the two surfaces in both thermodynamic factors and kinetic factors. With 5-hexen-2-one, for which [4 + 2] cycloaddition is not possible, a small [2 + 2] C=C cycloaddition product is observed on Ge(100) and possibly Si(100), even though the [2 + 2] C=C transition state is calculated to be the highest barrier reaction by several kilocalories per mole. The results suggest that, due to the high reactivity of clean semiconductor surfaces, thermodynamic selectivity and control will play important roles in their selective functionalization, favoring the use of Ge for selective attachment of multifunctional organics.

    View details for DOI 10.1021/ja026330w

    View details for Web of Science ID 000177074400049

    View details for PubMedID 12137555

  • Proton transfer reactions on semiconductor surfaces JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Mui, C., Han, J. H., Wang, G. T., Musgrave, C. B., Bent, S. F. 2002; 124 (15): 4027-4038

    Abstract

    The concept of proton affinity on semiconductor surfaces has been explored through an investigation of the chemistry of amines on the Ge(100)-2 x 1, Si(100)-2 x 1, and C(100)-2 x 1 surfaces. Multiple internal reflection Fourier transform infrared (MIR-FTIR) spectroscopy, temperature programmed desorption (TPD), and density functional theory (DFT) calculations were used in the studies. We find that methylamine, dimethylamine, and trimethylamine undergo molecular chemisorption on the Ge(100)-2 x 1 surface through the formation of Ge-N dative bonds. In contrast, primary and secondary amines react on the Si(100)-2 x 1 surface via N-H dissociation. Since N-H dissociation of amines at semiconductor surfaces mimics a proton-transfer reaction, the difference in chemical reactivities of the Ge(100)-2 x 1 and Si(100)-2 x 1 surfaces toward N-H dissociation can be interpreted as a decrease of proton affinity down a group in the periodic table. The trend in proton affinities of the two surfaces is explained in terms of thermodynamics and kinetics. Solid-state effects on the C(100)-2 x 1 surface and the surface proton affinity concept are discussed based on our theoretical predictions.

    View details for DOI 10.1021/ja0171512

    View details for Web of Science ID 000175014000046

    View details for PubMedID 11942841

  • Attaching organic layers to semiconductor surfaces JOURNAL OF PHYSICAL CHEMISTRY B Bent, S. F. 2002; 106 (11): 2830-2842

    View details for DOI 10.1021/jp012995t

    View details for Web of Science ID 000174551500005

  • Organic functionalization of group IV semiconductor surfaces: principles, examples, applications, and prospects SURFACE SCIENCE Bent, S. F. 2002; 500 (1-3): 879-903
  • Example of a thermodynamically controlled reaction on a semiconductor surface: Acetone on Ge(100)-2 x 1 JOURNAL OF PHYSICAL CHEMISTRY B Wang, G. T., Mui, C., Musgrave, C. B., Bent, S. F. 2001; 105 (50): 12559-12565

    View details for DOI 10.1021/jp013058o

    View details for Web of Science ID 000172945700019

  • Reactions of methylamines at the Si(100)-2x1 surface JOURNAL OF CHEMICAL PHYSICS Mui, C., Wang, G. T., Bent, S. F., Musgrave, C. B. 2001; 114 (22): 10170-10180
  • Effect of a methyl-protecting group on the adsorption of pyrrolidine on Si(100)-2 x 1 JOURNAL OF PHYSICAL CHEMISTRY B Wang, G. T., Mui, C., Musgrave, C. B., Bent, S. F. 2001; 105 (16): 3295-3299
  • Chemical engineering: Poised for progress CHEMICAL & ENGINEERING NEWS Bent, S. F. 2001; 79 (13): 58-58
  • Probing radicals in hot wire decomposition of silane using single photon ionization APPLIED PHYSICS LETTERS Duan, H. L., Zaharias, G. A., Bent, S. F. 2001; 78 (12): 1784-1786
  • The effect of a methyl protecting group on the adsorption of pyrrolidine on Si(100)-2x1 J. Phys. Chem. B Wang, G., T., Mui, C., Musgrave, C., B., Bent, S., F. 2001; 105: 3295
  • Temperature effects in the hot wire chemical vapor deposition of amorphous hydrogenated silicon carbon alloy JOURNAL OF APPLIED PHYSICS Lee, M. S., Bent, S. F. 2000; 87 (9): 4600-4610
  • Interaction of C-6 cyclic hydrocarbons with a Si(100)-2x1 surface: Adsorption and hydrogenation reactions JOURNAL OF PHYSICAL CHEMISTRY B Kong, M. J., Teplyakov, A. V., Jagmohan, J., Lyubovitsky, J. G., Mui, C., Bent, S. F. 2000; 104 (14): 3000-3007
  • A theoretical study of the structure and thermochemistry of 1,3-butadiene on the Ge/Si(100)-2 x 1 surface JOURNAL OF PHYSICAL CHEMISTRY A Mui, C., Bent, S. F., Musgrave, C. B. 2000; 104 (11): 2457-2462
  • Functionalization of diamond(100) by Diels-Alder chemistry JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Wang, G. T., Bent, S. F., RUSSELL, J. N., Butler, J. E., D'Evelyn, M. P. 2000; 122 (4): 744-745
  • Cycloaddition of cyclopentadiene and dicyclopentadiene on Si(100)-2x1: Comparison of monomer and dimer adsorption JOURNAL OF PHYSICAL CHEMISTRY B Wang, G. T., Mui, C., Musgrave, C. B., Bent, S. F. 1999; 103 (32): 6803-6808
  • Adsorption of ethylene on the Ge(100)-2 x 1 surface: Coverage and time-dependent behavior JOURNAL OF CHEMICAL PHYSICS Lal, P., Teplyakov, A. V., Noah, Y., Kong, M. J., Wang, G. T., Bent, S. F. 1999; 110 (21): 10545-10553
  • NEXAFS studies of adsorption of benzene on Si(100)-2 x 1 SURFACE SCIENCE Kong, M. J., Teplyakov, A. V., Lyubovitsky, J. G., Bent, S. F. 1998; 411 (3): 286-293
  • Evidence for a retro-Diels-Alder reaction on a single crystalline surface: Butadienes on Ge(100) JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Teplyakov, A. V., Lal, P., Noah, Y. A., Bent, S. F. 1998; 120 (29): 7377-7378
  • Diels-Alder reactions of butadienes with the Si(100)-2x1 surface as a dienophile: Vibrational spectroscopy, thermal desorption and near edge x-ray absorption fine structure studies JOURNAL OF CHEMICAL PHYSICS Teplyakov, A. V., Kong, M. J., Bent, S. F. 1998; 108 (11): 4599-4606
  • Spectroscopic and thermal studies of a-SiC:H film growth: comparison of mono-, tri-, and tetramethylsilane J. Vac. Sci. Technol. A Lee, M., S., Bent, S., F. 1998; 16: 1658
  • Etching, insertion, and abstraction reactions of atomic deuterium with amorphous silicon hydride films JOURNAL OF PHYSICAL CHEMISTRY B Chiang, C. M., GATES, S. M., Lee, S. S., Kong, M., Bent, S. F. 1997; 101 (46): 9537-9547
  • Vibrational spectroscopic studies of Diels-Alder reactions with the Si(100)-2x1 surface as a dienophile JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Teplyakov, A. V., Kong, M. J., Bent, S. F. 1997; 119 (45): 11100-11101
  • Bonding and thermal reactivity in thin a-SiC:H films grown by methylsilane CVD J. Phys. Chem. B Lee, M., S., Bent, S., F. 1997; B101: 9195
  • Infrared study of the reactions of atomic deuterium with amorphous silicon monohydride JOURNAL OF PHYSICAL CHEMISTRY Lee, S. S., Kong, M. J., Bent, S. F., Chiang, C. M., GATES, S. M. 1996; 100 (51): 20015-20020
  • Infrared spectroscopy of methyl groups on silicon CHEMICAL PHYSICS LETTERS Kong, M. J., Lee, K. S., Lyubovitsky, J., Bent, S. F. 1996; 263 (1-2): 1-7
  • Synthesis, layer assembly, and fluorescence dynamics of poly(phenylene vinylene) oligomer phosphonates J. Am. Chem. Soc. Katz, H., E., Bent, S., F., Wilson, W., L., Schilling, M., L., Ungashe, S. 1994; 116: 6631
  • Structural characterization of self-assembled multilayers by FTIR Chem. Mater. Bent, S., F., Schilling, M., L., Wilson, W., L., Katz, H., E., Harris, A., L. 1994; 6: 122
  • Photoluminescence studies of self-assembled phenylene vinylene oligomer films Polym. Prepr. (Am. Chem. Soc., Div. Polym. Chem.) Shane (Bent), S., F., Wilson, W., L., Katz, H., E., Schilling, M., L., Ungashe, S. 1994; 35: 315
  • Structural studies of zirconium alkylphosphonate monolayers and multilayer assemblies Langmuir. Schilling, M., L., Katz, H., E., Stein, S., M., Shane (Bent), S., F., Wilson, W., L., Ungashe, S., B. 1993; 9: 2156
  • Control of polarity and supramolecular optical effects in rigid surface assemblies Polym. Prepr. (Am. Chem. Soc., Div. Polym. Chem.) Katz, H., E., Schilling, M., L., Ungashe, S., B., Shane (Bent), S., Scheller, G., Wilson, W., L. 1993; 34: 793
  • Recombinative desorption of H2 on Si(100)-(2x1) and Si(111)-(7x7): comparison of internal state distributions J. Chem. Phys Shane (Bent), S., F., Kolasinski, K., W., Zare, R., N. 1992; 97: 1520
  • Internal-state distributions of recombinative hydrogen desorption from Si(100) J. Chem. Phys Kolasinski, K., W., Shane (Bent), S., F., Zare, R., N. 1992; 96: 3995
  • Internal-state distributions of H2 desorbed from mono- and dihydride species on Si(100) J. Chem. Phys Shane (Bent), S., F., Kolasinski, K., W., Zare, R., N. 1992; 97: 3704
  • A state-specific study of hydrogen desorption from Si(100)-(2x1): comparison of disilane and hydrogen adsorption J. Vac. Sci. Technol Shane (Bent), S., F., Kolasinski, K., W., Zare, R., N. 1992; A10: 2287
  • Probing the dynamics of hydrogen recombination on Si(100) J. Chem. Phys Kolasinski, K., W., Shane, S., F., Zare, R., N. 1991; 95: 5482
  • Vibrational energy transfer to metal surfaces probed by sum generation: CO/Cu(100) and CH3S/Ag(111) J. Electron Spectrosc. Related Phenom Harris, A., L., Levinos, N., J., Rothberg, L., Dhar, L., H., Shane (Bent), S., F., Morin, M. 1990; 54/55: 5
  • Rotational population and alignment distributions for inelastic scattering and trapping/desorption of NO on Pt(111) J. Chem. Phys Jacobs, D., C., Kolasinski, K., W., Shane (Bent), S., F., Zare, R., N. 1989; 91: 3182
  • The electronic state-selective photodissociation of CH2BrI at 248, 210, and 193 nm J. Chem. Phys Butler, L., J., Hintsa, E., J., Shane (Bent), S., F., Lee, Y., T. 1987; 86: 2051

Books and Book Chapters


  • Hydrogen recombinative desorption dynamics Laser Spectroscopy and Photochemistry on Metal Surfaces Bent, S., F., Michelsen, H., A., Zare, R., N. edited by Dai, H.-L., Ho, W. World Scientific, New Jersey. 1995

Conference Proceedings


  • Fabrication of organic thin films for copper diffusion barrier layers using molecular layer deposition Loscutoff, P., W., Clendenning, S., B., Bent, S., F. 2010
  • Plasma ash processing solutions for advanced interconnect technology Fuller, N. C., Worsley, M. A., Tai, L., Bent, S., Labelle, C., Arnold, J., Dalton, T. ELSEVIER SCIENCE SA. 2008: 3558-3563
  • Spatial control over atomic layer deposition using microcontact-printed resists Jiang, X., Chen, R., Bent, S. F. ELSEVIER SCIENCE SA. 2007: 8799-8807
  • Characterization of polyconjugated thin films synthesized by hot-wire chemical vapor deposition of aniline Zaharias, G. A., Shi, H. H., Bent, S. F. ELSEVIER SCIENCE SA. 2006: 341-345
  • Area selective atomic layer deposition by soft lithography Chen, R., Kim, H., Porter, D., W., McIntyre, P., C., Bent, S., F. 2006
  • Hot wire chemical vapor deposition as a novel synthetic method for electroactive organic thin films Zaharias, G., A., Shi, H., H., Bent, S., F. 2004
  • Controlling area-selective atomic layer deposition of HfO2 dielectric by self-assembled monolayers Chen, R., Kim, H., McIntyre, P., C., Bent, S., F. 2004
  • The study of modified layers in SiCOH dielectrics using spectroscopic ellipsometry Worsley, M., A., Bent, S., F., Gates, S., M., Kumar, K., Dalton, T., Hedrick, J., C. 2003
  • Effect of filament material on the decomposition of SiH4 in hot wire CVD of Si-based films Duan, H., L., Zaharias, G., A., Bent, S., F. 2002
  • pi bond versus radical character of the diamond (100)-2 x 1 surface RUSSELL, J. N., Butler, J. E., Wang, G. T., Bent, S. F., Hovis, J. S., Hamers, R. J., D'Evelyn, M. P. ELSEVIER SCIENCE SA. 2001: 147-151
  • The effect of filament temperature on the gaseous radicals in the hot wire decomposition of silane Duan, H. L., Zaharias, G. A., Bent, S. F. ELSEVIER SCIENCE SA. 2001: 36-41
  • Identification of growth precursors in hot wire CVD of amorphous silicon films Duan, H., L., Zaharias, G., A., Bent, S., F. 2001
  • In situ diagnostics of methane/hydrogen plasma interactions with Si(100) Duan, H., L., Bent, S., F. 1999
  • Temperature-dependent studies of a-SiC:H growth by remote plasma CVD using methylsilanes Lee, M., S., Lal, P., Bent, S., F. 1998
  • Synthesis, layer assembly, and fluorescence dynamics of poly(phenylene vinylene) oligomer phosphonates Katz, H., E., Shane (Bent), S., F., Wilson, W., L., Schilling, M., L., Ungashe, S., B. 1994
  • Surface vibrational energy relaxation by coupling to electron-hole pairs: c(2x2)-CO/Cu(100) Shane (Bent), S., F., Rothberg, L., Dubois, L., H., Levinos, N., J., Morin, M., Harris, A., L 1990