Honors & Awards


  • SPIE Optics and Photonics Education Scholarship, Society of Photo-optical Instrumentation Engineers (SPIE) (May 2020)
  • The ECE Graduate Research Assistant Excellence Award (Gatech), Georgia Institute of Technology (Mar 2020)
  • The Best Poster Award in the IEEE Photonics Conference, Institute of Electrical and Electronics Engineers (IEEE) (Oct 2017)

Professional Education


  • Ph.D., Georgia Institute of Technology, Electrical & Computer Engineering (2020)
  • M.Sc., Georgia Institute of Technology, Materials Science & Engineering (2016)
  • M.Sc., University of Tehran, Solid State Physics & Electronics (2014)

Stanford Advisors


All Publications


  • Synthetic Engineering of Morphology and Electronic Band Gap in Lateral Heterostructures of Monolayer Transition Metal Dichalcogenides ACS NANO Taghinejad, H., Taghinejad, M., Eftekhar, A. A., Li, Z., West, M. P., Javani, M. H., Abdollahramezani, S., Zhang, X., Tian, M., Johnson-Averette, T., Ajayan, P. M., Vogel, E. M., Shi, S., Cai, W., Adibi, A. 2020; 14 (5): 6323–30

    Abstract

    Heterostructures of two-dimensional transition metal dichalcogenides (TMDs) can offer a plethora of opportunities in condensed matter physics, materials science, and device engineering. However, despite state-of-the-art demonstrations, most current methods lack enough degrees of freedom for the synthesis of heterostructures with engineerable properties. Here, we demonstrate that combining a postgrowth chalcogen-swapping procedure with the standard lithography enables the realization of lateral TMD heterostructures with controllable dimensions and spatial profiles in predefined locations on a substrate. Indeed, our protocol receives a monolithic TMD monolayer (e.g., MoSe2) as the input and delivers lateral heterostructures (e.g., MoSe2-MoS2) with fully engineerable morphologies. In addition, through establishing MoS2xSe2(1-x)-MoS2ySe2(1-y) lateral junctions, our synthesis protocol offers an extra degree of freedom for engineering the band gap energies up to ∼320 meV on each side of the heterostructure junction via changing x and y independently. Our electron microscopy analysis reveals that such continuous tuning stems from the random intermixing of sulfur and selenium atoms following the chalcogen swapping. We believe that, by adding an engineering flavor to the synthesis of TMD heterostructures, our study lowers the barrier for the integration of two-dimensional materials into practical optoelectronic platforms.

    View details for DOI 10.1021/acsnano.0c02885

    View details for Web of Science ID 000537682300114

    View details for PubMedID 32364693

  • Photocarrier-Induced Active Control of Second-Order Optical Nonlinearity in Monolayer MoS2 SMALL Taghinejad, M., Xu, Z., Wang, H., Taghinejad, H., Lee, K., Rodrigues, S. P., Adibi, A., Qian, X., Lian, T., Cai, W. 2020; 16 (5): e1906347

    Abstract

    Atomically thin transition metal dichalcogenides (TMDs) in their excited states can serve as exceptionally small building blocks for active optical platforms. In this scheme, optical excitation provides a practical approach to control light-TMD interactions via the photocarrier generation, in an ultrafast manner. Here, it is demonstrated that via a controlled generation of photocarriers the second-harmonic generation (SHG) from a monolayer MoS2 crystal can be substantially modulated up to ≈55% within a timeframe of ≈250 fs, a set of performance characteristics that showcases the promise of low-dimensional materials for all-optical nonlinear data processing. The combined experimental and theoretical study suggests that the large SHG modulation stems from the correlation between the second-order dielectric susceptibility χ(2) and the density of photoexcited carriers in MoS2 . Indeed, the depopulation of the conduction band electrons, at the vicinity of the high-symmetry K/K' points of MoS2 , suppresses the contribution of interband electronic transitions in the effective χ(2) of the monolayer crystal, enabling the all-optical modulation of the SHG signal. The strong dependence of the second-order optical response on the density of photocarriers reveals the promise of time-resolved nonlinear characterization as an alternative route to monitoring carrier dynamics in excited states of TMDs.

    View details for DOI 10.1002/smll.201906347

    View details for Web of Science ID 000506918800001

    View details for PubMedID 31943782

  • Transient Second-Order Nonlinear Media: Breaking the Spatial Symmetry in the Time Domain via Hot-Electron Transfer PHYSICAL REVIEW LETTERS Taghinejad, M., Xu, Z., Lee, K., Lian, T., Cai, W. 2020; 124 (1): 013901

    Abstract

    Second-order optical effects are essential to the active control of light and the generation of new spectral components. The inversion symmetry, however, prevents achieving a bulk χ^{(2)} response, limiting the portfolio of the second-order nonlinear materials. Here, we demonstrate subpicosecond conversion of a statically passive dielectric to a transient second-order nonlinear medium upon the ultrafast transfer of hot electrons. Induced by an optical switching signal, the amorphous dielectric with vanishing intrinsic χ^{(2)} develops dynamically tunable second-order nonlinear responses. By taking the second-harmonic generation as an example, we show that breaking the inversion symmetry through hot-electron dynamics can be leveraged to address the critical need for all-optical control of second-order nonlinearities in nanophotonics. Our approach can be generically adopted in a variety of material and device platforms, offering a new class of complex nonlinear media with promising potentials for all-optical information processing.

    View details for DOI 10.1103/PhysRevLett.124.013901

    View details for Web of Science ID 000505495300012

    View details for PubMedID 31976680

  • Electrically Biased Silicon Metasurfaces with Magnetic Mie Resonance for Tunable Harmonic Generation of Light ACS PHOTONICS Lee, K., Taghinejad, M., Yan, J., Kim, A. S., Raju, L., Brown, D. K., Cai, W. 2019; 6 (11): 2663–70
  • All-Optical Control of Light in Micro- and Nanophotonics ACS PHOTONICS Taghinejad, M., Cai, W. 2019; 6 (5): 1082–93
  • Metasurfaces for Near-Eye Augmented Reality ACS PHOTONICS Lan, S., Zhang, X., Taghinejad, M., Rodrigues, S., Lee, K., Liu, Z., Cai, W. 2019; 6 (4): 864–70
  • Sharp and Tunable Crystal/Fano-Type Resonances Enabled by Out-of-Plane Dipolar Coupling in Plasmonic Nanopatch Arrays ANNALEN DER PHYSIK Taghinejad, M., Taghinejad, H., Malak, S. T., Moradinejad, H., Woods, E. V., Xu, Z., Liu, Y., Eftekhar, A. A., Lian, T., Tsukruk, V. V., Adibi, A. 2018; 530 (10)
  • Ultrafast Control of Phase and Polarization of Light Expedited by Hot-Electron Transfer NANO LETTERS Taghinejad, M., Taghinejad, H., Xu, Z., Lee, K., Rodrigues, S. P., Yan, J., Adibi, A., Lian, T., Cai, W. 2018; 18 (9): 5544–51

    Abstract

    All-optical modulation is an entangled part of ultrafast nonlinear optics with promising impacts on tunable optical devices in the future. Current advancements in all-optical control predominantly offer modulation by means of altering light intensity, while the ultrafast manipulation of other attributes of light have yet to be further explored. Here, we demonstrate the active modulation of the phase, polarization, and amplitude of light through the nonlinear modification of the optical response of a plasmonic crystal that supports subradiant, high Q, and polarization-selective resonance modes. The designed mode is exclusively accessible via TM-polarized light, which enables significant phase modulation and polarization conversion within the visible spectrum. To tailor the device performance in the time domain, we exploit the ultrafast transport dynamics of hot electrons at the interface of plasmonic metals and charge acceptor materials to facilitate an ultrafast switching speed. In addition, the operating wavelength of the proposed device can be tuned through the control of the in-plane momentum of light. Our work reveals the viability of dynamic phase and polarization control in plasmonic systems for all-optical switching and data processing.

    View details for DOI 10.1021/acs.nanolett.8b01946

    View details for Web of Science ID 000444793500028

    View details for PubMedID 30071164

  • Strain relaxation via formation of cracks in compositionally modulated two-dimensional semiconductor alloys NPJ 2D MATERIALS AND APPLICATIONS Taghinejad, H., Eftekhar, A. A., Campbell, P. M., Beatty, B., Taghinejad, M., Zhou, Y., Perini, C. J., Moradinejad, H., Henderson, W. E., Woods, E. V., Zhang, X., Ajayan, P., Reed, E. J., Vogel, E. M., Adibi, A. 2018; 2: 1–8
  • Hot-Electron-Assisted Femtosecond All-Optical Modulation in Plasmonics ADVANCED MATERIALS Taghinejad, M., Taghinejad, H., Xu, Z., Liu, Y., Rodrigues, S. P., Lee, K., Lian, T., Adibi, A., Cai, W. 2018; 30 (9)

    Abstract

    The optical Kerr nonlinearity of plasmonic metals provides enticing prospects for developing reconfigurable and ultracompact all-optical modulators. In nanostructured metals, the coherent coupling of light energy to plasmon resonances creates a nonequilibrium electron distribution at an elevated electron temperature that gives rise to significant Kerr optical nonlinearities. Although enhanced nonlinear responses of metals facilitate the realization of efficient modulation devices, the intrinsically slow relaxation dynamics of the photoexcited carriers, primarily governed by electron-phonon interactions, impedes ultrafast all-optical modulation. Here, femtosecond (≈190 fs) all-optical modulation in plasmonic systems via the activation of relaxation pathways for hot electrons at the interface of metals and electron acceptor materials, following an on-resonance excitation of subradiant lattice plasmon modes, is demonstrated. Both the relaxation kinetics and the optical nonlinearity can be actively tuned by leveraging the spectral response of the plasmonic design in the linear regime. The findings offer an opportunity to exploit hot-electron-induced nonlinearities for design of self-contained, ultrafast, and low-power all-optical modulators based on plasmonic platforms.

    View details for DOI 10.1002/adma.201704915

    View details for Web of Science ID 000426491600007

    View details for PubMedID 29333735

  • Preserving Spin States upon Reflection: Linear and Nonlinear Responses of a Chiral Meta-Mirror NANO LETTERS Kang, L., Rodrigues, S. P., Taghinejad, M., Lan, S., Lee, K., Liu, Y., Werner, D. H., Urbas, A., Cai, W. 2017; 17 (11): 7102–9

    Abstract

    Conventional metallic mirrors flip the spin of a circularly polarized wave upon normal incidence by inverting the direction of the propagation vector. Altering or maintaining the spin state of light waves carrying data is a critical need to be met at the brink of photonic information processing. In this work, we report a chiral metamaterial mirror that strongly absorbs a circularly polarized wave of one spin state and reflects that of the opposite spin in a manner conserving the circular polarization. A circular dichroic response in reflection as large as ∼0.5 is experimentally observed in a near-infrared wavelength band. By imaging a fabricated pattern composed of the enantiomeric unit cells, we directly visualize the two key features of our engineered meta-mirrors, namely the chiral-selective absorption and the polarization preservation upon reflection. Beyond the linear regime, the chiral resonances enhance light-matter interaction under circularly polarized excitation, greatly boosting the ability of the metamaterial to perform chiral-selective signal generation and optical imaging in the nonlinear regime. Chiral meta-mirrors, exhibiting giant chiroptical responses and spin-selective near-field enhancement, hold great promise for applications in polarization sensitive electro-optical information processing and biosensing.

    View details for DOI 10.1021/acs.nanolett.7b03882

    View details for Web of Science ID 000415029000089

    View details for PubMedID 29072915

  • Dark plasmonic modes in diatomic gratings for plasmoelectronics LASER & PHOTONICS REVIEWS Lan, S., Rodrigues, S. P., Taghinejad, M., Cai, W. 2017; 11 (2)
  • Resonant Light-Induced Heating in Hybrid Cavity-Coupled 2D Transition-Metal Dichalcogenides ACS PHOTONICS Taghinejad, H., Taghinejad, M., Tarasov, A., Tsai, M., Hosseinnia, A. H., Moradinejad, H., Campbell, P. M., Eftekhar, A. A., Vogel, E. M., Adibi, A. 2016; 3 (4): 700–707
  • The conformal silicon deposition on carbon nanotubes as enabled by hydrogenated carbon coatings for synthesis of carbon/silicon core/shell heterostructure photodiodes CARBON Taghinejad, H., Taghinejad, M., Abdolahad, M., Rajabali, S., Rostamian, A., Mohajerzadeh, S., Hosseinian, E. 2015; 87: 299–308
  • Integration of Ni2Si/Si Nanograss Heterojunction on n-MOSFET to Realize High-Sensitivity Phototransistors IEEE TRANSACTIONS ON ELECTRON DEVICES Taghinejad, M., Taghinejad, H., Ganji, M., Rostamian, A., Mohajerzadeh, S., Abdolahad, M., Kolahdouz, M. 2014; 61 (9): 3239–44
  • A Nickel-Gold Bilayer Catalyst Engineering Technique for Self-Assembled Growth of Highly Ordered Silicon Nanotubes (SiNT) NANO LETTERS Taghinejad, M., Taghinejad, H., Abdolahad, M., Mohajerzadeh, S. 2013; 13 (3): 889–97

    Abstract

    We report the growth of vertically aligned high-crystallinity silicon nanotube (SiNT) arrays on silicon substrate by means of a Ni-Au bilayer catalyst engineering technique. Nanotubes were synthesized through solid-liquid-solid method as well as vapor-liquid-solid. A precise evaluation utilizing atomic force microscopy and lateral force microscopy describes that the gold profile in Ni regions leads to the construction of multiwall SiNTs. The agreement of the structural geometry and stiffness of the obtained SiNTs with previous theoretical predictions suggest sp(3) hybridization as the mechanism of tube formation. Apart from scanning electron and transmission electron microscopy techniques, photoluminescence spectroscopy (PL) has been conducted to investigate the formation of nanostructures. PL spectroscopy confirms the evolution of ultrafine walls of the silicon nanotubes, responsible for the observed photoemission properties.

    View details for DOI 10.1021/nl303558f

    View details for Web of Science ID 000316243800006

    View details for PubMedID 23394626

  • Fabrication and modeling of high sensitivity humidity sensors based on doped silicon nanowires SENSORS AND ACTUATORS B-CHEMICAL Taghinejad, H., Taghinejad, M., Abdolahad, M., Saeidi, A., Mohajerzadeh, S. 2013; 176: 413–19