Anh Tuan Hoang

All Publications

• Nonconventional Strain Engineering for Uniform Biaxial Tensile Strain in MoS2 Thin Film Transistors. ACS nano Shin, H., Katiyar, A. K., Hoang, A. T., Yun, S. M., Kim, B. J., Lee, G., Kim, Y., Lee, J., Kim, H., Ahn, J. H. 2024

  Abstract

  Strain engineering has been employed as a crucial technique to enhance the electrical properties of semiconductors, especially in Si transistor technologies. Recent theoretical investigations have suggested that strain engineering can also markedly enhance the carrier mobility of two-dimensional (2D) transition-metal dichalcogenides (TMDs). The conventional methods used in strain engineering for Si and other bulk semiconductors are difficult to adapt to ultrathin 2D TMDs. Here, we report a strain engineering approach to apply the biaxial tensile strain to MoS2. Metal-organic chemical vapour deposition (MOCVD)-grown large-area MoS2 films were transferred onto SiO2/Si substrate, followed by the selective removal of the underneath Si. The release of compressive residual stress in the oxide layer induces strain in MoS2 on top of the SiO2 layer. The amount of strain can be precisely controlled by the thickness of oxide stressors. After the transistors were fabricated with strained MoS2 films, the array of strained transistors was transferred onto plastic substrates. This process ensured that the MoS2 channels maintained a consistent tensile strain value across a large area.

  View details for DOI 10.1021/acsnano.3c10495

  View details for PubMedID 38277430

• 2D Materials in Flexible Electronics: Recent Advances and Future Prospectives. Chemical reviews Katiyar, A. K., Hoang, A. T., Xu, D., Hong, J., Kim, B. J., Ji, S., Ahn, J. 2023

  Abstract

  Flexible electronics have recently gained considerable attention due to their potential to provide new and innovative solutions to a wide range of challenges in various electronic fields. These electronics require specific material properties and performance because they need to be integrated into a variety of surfaces or folded and rolled for newly formatted electronics. Two-dimensional (2D) materials have emerged as promising candidates for flexible electronics due to their unique mechanical, electrical, and optical properties, as well as their compatibility with other materials, enabling the creation of various flexible electronic devices. This article provides a comprehensive review of the progress made in developing flexible electronic devices using 2D materials. In addition, it highlights the key aspects of materials, scalable material production, and device fabrication processes for flexible applications, along with important examples of demonstrations that achieved breakthroughs in various flexible and wearable electronic applications. Finally, we discuss the opportunities, current challenges, potential solutions, and future investigative directions about this field.

  View details for DOI 10.1021/acs.chemrev.3c00302

  View details for PubMedID 38055207

• Monolithic 3D integration of 2D materials-based electronics towards ultimate edge computing solutions. Nature materials Kang, J. H., Shin, H., Kim, K. S., Song, M. K., Lee, D., Meng, Y., Choi, C., Suh, J. M., Kim, B. J., Kim, H., Hoang, A. T., Park, B. I., Zhou, G., Sundaram, S., Vuong, P., Shin, J., Choe, J., Xu, Z., Younas, R., Kim, J. S., Han, S., Lee, S., Kim, S. O., Kang, B., Seo, S., Ahn, H., Seo, S., Reidy, K., Park, E., Mun, S., Park, M. C., Lee, S., Kim, H. J., Kum, H. S., Lin, P., Hinkle, C., Ougazzaden, A., Ahn, J. H., Kim, J., Bae, S. H. 2023

  Abstract

  Three-dimensional (3D) hetero-integration technology is poised to revolutionize the field of electronics by stacking functional layers vertically, thereby creating novel 3D circuity architectures with high integration density and unparalleled multifunctionality. However, the conventional 3D integration technique involves complex wafer processing and intricate interlayer wiring. Here we demonstrate monolithic 3D integration of two-dimensional, material-based artificial intelligence (AI)-processing hardware with ultimate integrability and multifunctionality. A total of six layers of transistor and memristor arrays were vertically integrated into a 3D nanosystem to perform AI tasks, by peeling and stacking of AI processing layers made from bottom-up synthesized two-dimensional materials. This fully monolithic-3D-integrated AI system substantially reduces processing time, voltage drops, latency and footprint due to its densely packed AI processing layers with dense interlayer connectivity. The successful demonstration of this monolithic-3D-integrated AI system will not only provide a material-level solution for hetero-integration of electronics, but also pave the way for unprecedented multifunctional computing hardware with ultimate parallelism.

  View details for DOI 10.1038/s41563-023-01704-z

  View details for PubMedID 38012388

• Perovskite Light-Emitting Diode Display Based on MoS2 Backplane Thin-Film Transistors. Advanced materials (Deerfield Beach, Fla.) Ji, S., Bae, S. R., Hu, L., Hoang, A. T., Seol, M. J., Hong, J., Katiyar, A. K., Kim, B. J., Xu, D., Kim, S. Y., Ahn, J. H. 2023: e2309531

  Abstract

  The uniform deposition of perovskite light-emitting diodes (PeLEDs) and their integration with backplane thin-film transistors (TFTs) remain challenging for large-area display applications. Herein, an active-matrix PeLED display fabricated via the heterogeneous integration of cesium lead bromide (CsPbBr3 ) LEDs and molybdenum disulfide (MoS2 )-based TFTs is presented. The single-source evaporation method enables the deposition of highly uniform perovskite thin films over large areas. PeLEDs are integrated with MoS2 TFTs to fabricate an active-matrix PeLED display with an 8 × 8 array, which exhibits excellent brightness control capability and high switching speeds. This study demonstrates the potential of PeLEDs as candidates for next generation displays and presents a novel approach for fabricating optoelectronic devices via the heterogeneous integration of 2D materials and perovskites, thereby paving the way toward the fabrication of practical future optoelectronic systems. This article is protected by copyright. All rights reserved.

  View details for DOI 10.1002/adma.202309531

  View details for PubMedID 37985162

• Reduced Defect Density in MOCVD-Grown MoS2 by Manipulating the Precursor Phase. ACS applied materials & interfaces Mawlong, L. P., Hoang, A. T., Chintalapalli, J., Ji, S., Lee, K., Kim, K., Ahn, J. H. 2023

  Abstract

  Advancements in the synthesis of large-area, high-quality two-dimensional transition metal dichalcogenides such as MoS2 play a crucial role in the development of future electronic and optoelectronic devices. The presence of defects formed by sulfur vacancies in MoS2 results in low photoluminescence emission and imparts high n-type doping behavior, thus substantially affecting material quality. Herein, we report a new method in which single-phase (liquid) precursors are used for the metal-organic chemical vapor deposition (MOCVD) growth of a MoS2 film. Furthermore, we fabricated a high-performance photodetector (PD) and achieved improved photoresponsivity and faster photoresponse in the spectral range 405-637 nm compared to those of PDs fabricated by the conventional MOCVD method. In addition, the fabricated MoS2 thin film showed a threshold voltage shift in the positive gate bias direction owing to the reduced number of S vacancy defects in the MoS2 lattice. Thus, our method significantly improved the synthesis of monolayer MoS2 and can expand the application scope of high-quality, atomically thin materials in large-scale electronic and optoelectronic devices.

  View details for DOI 10.1021/acsami.3c09027

  View details for PubMedID 37756669

• Low-temperature growth of MoS2 on polymer and thin glass substrates for flexible electronics. Nature nanotechnology Hoang, A. T., Hu, L., Kim, B. J., Van, T. T., Park, K. D., Jeong, Y., Lee, K., Ji, S., Hong, J., Katiyar, A. K., Shong, B., Kim, K., Im, S., Chung, W. J., Ahn, J. 2023

  Abstract

  Recent advances in two-dimensional semiconductors, particularly molybdenum disulfide (MoS2), have enabled the fabrication of flexible electronic devices with outstanding mechanical flexibility. Previous approaches typically involved the synthesis of MoS2 on a rigid substrate at a high temperature followed by the transfer to a flexible substrate onto which the device is fabricated. A recurring drawback with this methodology is the fact that flexible substrates have a lower melting temperature than the MoS2 growth process, and that the transfer process degrades the electronic properties of MoS2. Here we report a strategy for directly synthesizing high-quality and high-crystallinity MoS2 monolayers on polymers and ultrathin glass substrates (thickness ~30m) at ~150°C using metal-organic chemical vapour deposition. By avoiding the transfer process, the MoS2 quality is preserved. On flexible field-effect transistors, we achieve a mobility of 9.1cm2V-1s-1 and a positive threshold voltage of +5V, which is essential for reducing device power consumption. Moreover, under bending conditions, our logic circuits exhibit stable operation while phototransistors can detect light over a wide range of wavelengths from 405nm to 904nm.

  View details for DOI 10.1038/s41565-023-01460-w

  View details for PubMedID 37500777

• Two-dimensional layered materials and heterostructures for flexible electronics MATTER Hoang, A., Hu, L., Katiyar, A., Ahn, J. 2022; 5 (12): 4116-4132

  View details for DOI 10.1016/j.matt.2022.10.016

  View details for Web of Science ID 000967842900007

• In-plane optical and electrical anisotropy in low-symmetry layered GeS microribbons NPG ASIA MATERIALS Chen, Z., Hwang, W., Cho, M., Hoang, A., Kim, M., Kim, D., Kim, D., Kim, Y., Kim, H., Ahn, J., Soon, A., Choi, H. 2022; 14 (1)

  View details for DOI 10.1038/s41427-022-00390-8

  View details for Web of Science ID 000794880200002

• Topography dependence of conductivity in electrostrictive germanium sulfide nanoribbons 2D MATERIALS Chen, Z., Anh Tuan Hoang, Seo, D., Cho, M., Kim, Y., Yang, L., Ahn, J., Choi, H. 2022; 9 (4)

  View details for DOI 10.1088/2053-1583/ac7c22

  View details for Web of Science ID 000825717600001

• Vertical Conductivity and Topography in Electrostrictive Germanium Sulfide Microribbon via Conductive Atomic Force Microscopy. Nano letters Chen, Z., Hoang, A. T., Hwang, W., Seo, D., Cho, M., Kim, Y. D., Yang, L., Soon, A., Ahn, J. H., Choi, H. J. 2022; 22 (18): 7636-7643

  Abstract

  Layered group IV monochalcogenides are two-dimensional (2D) semiconducting materials with unique crystal structures and novel physical properties. Here, we report the growth of single crystalline GeS microribbons using the chemical vapor transport process. By using conductive atomic force microscopy, we demonstrated that the conductive behavior in the vertical direction was mainly affected by the Schottky barriers between GeS and both electrodes. Furthermore, we found that the topographic and current heterogeneities were significantly different with and without illumination. The topographic deformation and current enhancement were also predicted by our density functional theory (DFT)-based calculations. Their local spatial correlation between the topographic height and current was established. By virtue of 2D fast Fourier transform power spectra, we constructed the holistic spatial correlation between the topographic and current heterogeneity that indicated the diminished correlation with illumination. These findings on layered GeS microribbons provide insights into the conductive and topographic behaviors in 2D materials.

  View details for DOI 10.1021/acs.nanolett.2c02763

  View details for PubMedID 36106948

• Wafer-scale monolithic integration of full-colour micro-LED display using MoS2 transistor. Nature nanotechnology Hwangbo, S., Hu, L., Hoang, A. T., Choi, J. Y., Ahn, J. H. 2022; 17 (5): 500-506

  Abstract

  Large-scale growth of transition metal dichalcogenides and their subsequent integration with compound semiconductors is one of the major obstacles for two-dimensional materials implementation in optoelectronics applications such as active matrix displays or optical sensors. Here we present a novel transition metal dichalcogenide-on-compound-semiconductor fabrication method that is compatible with a batch microfabrication process. We show how a thin film of molybdenum disulfide (MoS2) can be directly synthesized on a gallium-nitride-based epitaxial wafer to form a thin film transistor array. Subsequently, the MoS2 thin film transistor was monolithically integrated with micro-light-emitting-diode (micro-LED) devices to produce an active matrix micro-LED display. In addition, we demonstrate a simple approach to obtain red and green colours through the printing of quantum dots on a blue micro-LED, which allows for the scalable fabrication of full-colour micro-LED displays. This strategy represents a promising route to attain heterogeneous integration, which is essential for high-performance optoelectronic systems that can incorporate the established semiconductor technology and emerging two-dimensional materials.

  View details for DOI 10.1038/s41565-022-01102-7

  View details for PubMedID 35379943

• Bioinspired in-sensor visual adaptation for accurate perception NATURE ELECTRONICS Liao, F., Zhou, Z., Kim, B., Chen, J., Wang, J., Wan, T., Zhou, Y., Hoang, A., Wang, C., Kang, J., Ahn, J., Chai, Y. 2022; 5 (2): 84-91

  View details for DOI 10.1038/s41928-022-00713-1

  View details for Web of Science ID 000750775200001

• Residue-free photolithographic patterning of graphene CHEMICAL ENGINEERING JOURNAL Choi, A., Hoang, A., Van, T., Shong, B., Hu, L., Thai, K., Ahn, J. 2022; 429

  View details for DOI 10.1016/j.cej.2021.132504

  View details for Web of Science ID 000724594200005

• MoS2/Graphene Photodetector Array with Strain-Modulated Photoresponse up to the Near-Infrared Regime. ACS nano Thai, K. Y., Park, I., Kim, B. J., Hoang, A. T., Na, Y., Park, C. U., Chae, Y., Ahn, J. H. 2021; 15 (8): 12836-12846

  Abstract

  MoS2, an emerging material in the field of optoelectronics, has attracted the attention of researchers owing to its high light absorption efficiency, even as an atomically thin layer. However, the covered spectra of the reported MoS2-based photodetectors are restricted to the visible range owing to their electronic bandgap (∼1.9 eV). Strain engineering, which modulates the bandgap of a semiconductor, can extend the application coverage of MoS2 to the infrared spectral range. The shrinkage of the bandgap because of the tensile strain on MoS2 enhances the photoresponsivity in the visible range and extends its sensing capability beyond its fundamental absorption limit. Herein, we report a graphene/MoS2/graphene metal-semiconductor-metal photodetector (PD) array with a strain-modulated photoresponse up to the spectral range of the near-infrared (NIR). The MoS2 PD array on a flexible substrate was stretched in the biaxial direction to a tensile strain level of 1.19% using a pneumatic bulging process. The MoS2-based line-scanning system was implemented by digitizing the output photocurrent of the strained MoS2 linear array with a low-noise complementary metal-oxide-semiconductor (CMOS) readout integrated circuit (IC) and successfully captured vis-NIR images in foggy conditions. Therefore, we extended the application of the MoS2 PD array to the NIR regime and demonstrated its use in real-life imaging systems.

  View details for DOI 10.1021/acsnano.1c04678

  View details for PubMedID 34291913

• Damage-free transfer mechanics of 2-dimensional materials: competition between adhesion instability and tensile strain NPG ASIA MATERIALS Kim, C., Yoon, M., Jang, B., Kim, H., Kim, J., Hoang, A., Ahn, J., Jung, H., Lee, H., Kim, K. 2021; 13 (1)

  View details for DOI 10.1038/s41427-021-00311-1

  View details for Web of Science ID 000650104000001

• Large-area synthesis of transition metal dichalcogenides via CVD and solution-based approaches and their device applications. Nanoscale Hoang, A. T., Qu, K., Chen, X., Ahn, J. H. 2021; 13 (2): 615-633

  Abstract

  For the last decade, two-dimensional transition metal dichalcogenides (TMDCs) have attracted considerable attention due to their unique physical and chemical properties. Novel devices based on these materials are commonly fabricated using the exfoliated samples, which lacks control of the thickness and cannot be scaled. Therefore, the synthesis of large-area TMDC thin films with a high uniformity to advance the field is required. This article reviews the latest advances in the synthesis of wafer-scale thin films using chemical vapor deposition methods. The key factors that determine the electrical performance of TMDCs are introduced, including the interfacial properties and defects. The latest solution-based techniques which suggest the opportunity to obtain large-area TMDC thin films with a low-cost process and the potential applications in electronics and optoelectronics are also discussed. The outlook for future research directions, challenges, and possible development of 2D materials are further discussed.

  View details for DOI 10.1039/d0nr08071c

  View details for PubMedID 33410829

• Epitaxial Growth of Wafer-Scale Molybdenum Disulfide/Graphene Heterostructures by Metal-Organic Vapor-Phase Epitaxy and Their Application in Photodetectors. ACS applied materials & interfaces Hoang, A. T., Katiyar, A. K., Shin, H., Mishra, N., Forti, S., Coletti, C., Ahn, J. H. 2020; 12 (39): 44335-44344

  Abstract

  Van der Waals heterostructures have attracted increasing interest, owing to the combined benefits of their constituents. These hybrid nanostructures can be realized via epitaxial growth, which offers a promising approach for the controlled synthesis of the desired crystal phase and the interface between van der Waals layers. Here, the epitaxial growth of a continuous molybdenum disulfide (MoS2) film on large-area graphene, which was directly grown on a sapphire substrate, is reported. Interestingly, the grain size of MoS2 grown on graphene increases, whereas that of MoS2 grown on SiO2 decreases with an increasing amount of hydrogen in the chemical vapor deposition reactor. In addition, to achieve the same quality, MoS2 grown on graphene requires a much lower growth temperature (400 °C) than that grown on SiO2 (580 °C). The MoS2/graphene heterostructure that was epitaxially grown on a transparent platform was investigated to explore its photosensing properties and was found to exhibit inverse photoresponse with highly uniform photoresponsivity in the photodetector pixels fabricated across a full wafer. The MoS2/graphene heterostructure exhibited ultrahigh photoresponsivity (4.3 × 104 A W-1) upon exposure to visible light of a wide range of wavelengths, confirming the growth of a high-quality MoS2/graphene heterostructure with a clean interface.

  View details for DOI 10.1021/acsami.0c12894

  View details for PubMedID 32877158

  View details for PubMedCentralID PMC7735665

• Full-color active-matrix organic light-emitting diode display on human skin based on a large-area MoS2 backplane. Science advances Choi, M., Bae, S. R., Hu, L., Hoang, A. T., Kim, S. Y., Ahn, J. H. 2020; 6 (28): eabb5898

  Abstract

  Electronic applications are continuously developing and taking new forms. Foldable, rollable, and wearable displays are applicable for human health care monitoring or robotics, and their operation relies on organic light-emitting diodes (OLEDs). Yet, the development of semiconducting materials with high mechanical flexibility has remained a challenge and restricted their use in unusual format electronics. This study presents a wearable full-color OLED display using a two-dimensional (2D) material-based backplane transistor. The 18-by-18 thin-film transistor array was fabricated on a thin MoS2 film that was transferred to Al2O3 (30 nm)/polyethylene terephthalate (6 μm). Red, green, and blue OLED pixels were deposited on the device surface. This 2D material offered excellent mechanical and electrical properties and proved to be capable of driving circuits for the control of OLED pixels. The ultrathin device substrate allowed for integration of the display on an unusual substrate, namely, a human hand.

  View details for DOI 10.1126/sciadv.abb5898

  View details for PubMedID 32923597

  View details for PubMedCentralID PMC7455500

• Controllable P- and N-Type Conversion of MoTe2 via Oxide Interfacial Layer for Logic Circuits. Small (Weinheim an der Bergstrasse, Germany) Park, Y. J., Katiyar, A. K., Hoang, A. T., Ahn, J. H. 2019; 15 (28): e1901772

  Abstract

  To realize basic electronic units such as complementary metal-oxide-semiconductor (CMOS) inverters and other logic circuits, the selective and controllable fabrication of p- and n-type transistors with a low Schottky barrier height is highly desirable. Herein, an efficient and nondestructive technique of electron-charge transfer doping by depositing a thin Al2 O3 layer on chemical vapor deposition (CVD)-grown 2H-MoTe2 is utilized to tune the doping from p- to n-type. Moreover, a type-controllable MoTe2 transistor with a low Schottky barrier height is prepared. The selectively converted n-type MoTe2 transistor from the p-channel exhibits a maximum on-state current of 10 µA, with a higher electron mobility of 8.9 cm2 V-1 s-1 at a drain voltage (Vds ) of 1 V with a low Schottky barrier height of 28.4 meV. To validate the aforementioned approach, a prototype homogeneous CMOS inverter is fabricated on a CVD-grown 2H-MoTe2 single crystal. The proposed inverter exhibits a high DC voltage gain of 9.2 with good dynamic behavior up to a modulation frequency of 1 kHz. The proposed approach may have potential for realizing future 2D transition metal dichalcogenide-based efficient and ultrafast electronic units with high-density circuit components under a low-dimensional regime.

  View details for DOI 10.1002/smll.201901772

  View details for PubMedID 31099978

• Orientation-dependent optical characterization of atomically thin transition metal ditellurides. Nanoscale Hoang, A. T., Shinde, S. M., Katiyar, A. K., Dhakal, K. P., Chen, X., Kim, H., Lee, S. W., Lee, Z., Ahn, J. H. 2018; 10 (46): 21978-21984

  Abstract

  Molybdenum ditellurides (MoTe2) have recently attracted attention owing to their excellent structurally tunable nature between 1T'(metallic)- and 2H(semiconducting)-phases; thus, the controllable fabrication and critical identification of MoTe2 are highly desired. Here, we semi-controllably synthesized 1T'- and 2H-MoTe2 crystals using the atmospheric pressure chemical vapor deposition (APCVD) technique and studied their grain-orientation dependency using polarization-sensitive optical microscopy, Raman scattering, and second-harmonic generation (SHG) microspectroscopy. The polycrystalline 1T'-MoTe2 phase with quasi-1D "Mo-Mo" zigzag chains showed anisotropic optical absorption, leading to a clear visualization of the lattice domains. On the other hand, 2H-MoTe2 lattice grains did not exhibit any discernible difference under polarized light illumination. The combined aforementioned microscopy techniques could be used as an easy-to-access and non-destructive tool for a quick and solid identification of intended lattice orientation development in industry-scale MoTe2 crystal manufacturing.

  View details for DOI 10.1039/c8nr07592a

  View details for PubMedID 30451270

• Surface-Functionalization-Mediated Direct Transfer of Molybdenum Disulfide for Large-Area Flexible Devices ADVANCED FUNCTIONAL MATERIALS Shinde, S. M., Das, T., Anh Tuan Hoang, Sharma, B. K., Chen, X., Ahn, J. 2018; 28 (13)

  View details for DOI 10.1002/adfm.201706231

  View details for Web of Science ID 000428792200016

• A strip array of colorimetric sensors for visualizing a concentration level of gaseous analytes with basicity SENSORS AND ACTUATORS B-CHEMICAL Hoang, A., Cho, Y., Kim, Y. 2017; 251: 1089-1095

  View details for DOI 10.1016/j.snb.2017.06.142

  View details for Web of Science ID 000406184600131

• Sensitive naked-eye detection of gaseous ammonia based on dye-impregnated nanoporous polyacrylonitrile mats SENSORS AND ACTUATORS B-CHEMICAL Hoang, A., Cho, Y., Park, J., Yang, Y., Kim, Y. 2016; 230: 250-259

  View details for DOI 10.1016/j.snb.2016.02.058

  View details for Web of Science ID 000374329300032

• Hollow Pt Nanostructure-decorated MWNT Electrode for Amperometric Hydrogen Detection BULLETIN OF THE KOREAN CHEMICAL SOCIETY Rashid, M., Bui, T., Anh Tuan Hoang, Seong, G., Lim, D., Kim, Y. 2015; 36 (12): 2940-2943

  View details for DOI 10.1002/bkcs.10585

  View details for Web of Science ID 000368125200031