Professional Education

  • BS, Bogazici University, Physics (2012)
  • BS, Bogazici University, Electrical Engineering (2012)
  • Doctor of Philosophy, Columbia University (2017)

All Publications

  • Probing the Optical Properties and Strain-Tuning of Ultrathin Mo1-&ITx&ITW&ITx&ITTe2 NANO LETTERS Aslan, O., Datye, I. M., Mleczko, M. J., Cheung, K., Krylyuk, S., Bruma, A., Kalish, I., Davydov, A. V., Pop, E., Heinz, T. F. 2018; 18 (4): 2485–91


    Ultrathin transition metal dichalcogenides (TMDCs) have recently been extensively investigated to understand their electronic and optical properties. Here we study ultrathin Mo0.91W0.09Te2, a semiconducting alloy of MoTe2, using Raman, photoluminescence (PL), and optical absorption spectroscopy. Mo0.91W0.09Te2 transitions from an indirect to a direct optical band gap in the limit of monolayer thickness, exhibiting an optical gap of 1.10 eV, very close to its MoTe2 counterpart. We apply tensile strain, for the first time, to monolayer MoTe2 and Mo0.91W0.09Te2 to tune the band structure of these materials; we observe that their optical band gaps decrease by 70 meV at 2.3% uniaxial strain. The spectral widths of the PL peaks decrease with increasing strain, which we attribute to weaker exciton-phonon intervalley scattering. Strained MoTe2 and Mo0.91W0.09Te2 extend the range of band gaps of TMDC monolayers further into the near-infrared, an important attribute for potential applications in optoelectronics.

    View details for DOI 10.1021/acs.nanolett.8b00049

    View details for Web of Science ID 000430155900040

    View details for PubMedID 29561623

  • Ultrafast Graphene Light Emitters NANO LETTERS Kim, Y., Gao, Y., Shiue, R., Wang, L., Aslan, O., Bae, M., Kim, H., Seo, D., Choi, H., Kim, S., Nemilentsau, A., Low, T., Tan, C., Efetov, D. K., Taniguchi, T., Watanabe, K., Shepard, K. L., Heinz, T. F., Englund, D., Hone, J. 2018; 18 (2): 934–40


    Ultrafast electrically driven nanoscale light sources are critical components in nanophotonics. Compound semiconductor-based light sources for the nanophotonic platforms have been extensively investigated over the past decades. However, monolithic ultrafast light sources with a small footprint remain a challenge. Here, we demonstrate electrically driven ultrafast graphene light emitters that achieve light pulse generation with up to 10 GHz bandwidth across a broad spectral range from the visible to the near-infrared. The fast response results from ultrafast charge-carrier dynamics in graphene and weak electron-acoustic phonon-mediated coupling between the electronic and lattice degrees of freedom. We also find that encapsulating graphene with hexagonal boron nitride (hBN) layers strongly modifies the emission spectrum by changing the local optical density of states, thus providing up to 460% enhancement compared to the gray-body thermal radiation for a broad peak centered at 720 nm. Furthermore, the hBN encapsulation layers permit stable and bright visible thermal radiation with electronic temperatures up to 2000 K under ambient conditions as well as efficient ultrafast electronic cooling via near-field coupling to hybrid polaritonic modes under electrical excitation. These high-speed graphene light emitters provide a promising path for on-chip light sources for optical communications and other optoelectronic applications.

    View details for DOI 10.1021/acs.nanolett.7b04324

    View details for Web of Science ID 000425559700040

    View details for PubMedID 29337567

  • Temperature-Dependent Thermal Boundary Conductance of Monolayer MoS2 by Raman Thermometry ACS APPLIED MATERIALS & INTERFACES Yalon, E., Aslan, O., Smithe, K. H., McClellan, C. J., Suryavanshi, S. V., Xiong, F., Sood, A., Neumann, C. M., Xu, X., Goodson, K. E., Heinz, T. F., Pop, E. 2017; 9 (49): 43013–20
  • Dynamic Optical Tuning of Interlayer Interactions in the Transition Metal Dichalcogenides. Nano letters Mannebach, E. M., Nyby, C., Ernst, F., Zhou, Y., Tolsma, J., Li, Y., Sher, M. J., Tung, I. C., Zhou, H., Zhang, Q., Seyler, K. L., Clark, G., Lin, Y., Zhu, D., Glownia, J. M., Kozina, M. E., Song, S., Nelson, S., Mehta, A., Yu, Y., Pant, A., Aslan, O. B., Raja, A., Guo, Y., DiChiara, A., Mao, W., Cao, L., Tongay, S., Sun, J., Singh, D. J., Heinz, T. F., Xu, X., MacDonald, A. H., Reed, E., Wen, H., Lindenberg, A. M. 2017; 17 (12): 7761–66


    Modulation of weak interlayer interactions between quasi-two-dimensional atomic planes in the transition metal dichalcogenides (TMDCs) provides avenues for tuning their functional properties. Here we show that above-gap optical excitation in the TMDCs leads to an unexpected large-amplitude, ultrafast compressive force between the two-dimensional layers, as probed by in situ measurements of the atomic layer spacing at femtosecond time resolution. We show that this compressive response arises from a dynamic modulation of the interlayer van der Waals interaction and that this represents the dominant light-induced stress at low excitation densities. A simple analytic model predicts the magnitude and carrier density dependence of the measured strains. This work establishes a new method for dynamic, nonequilibrium tuning of correlation-driven dispersive interactions and of the optomechanical functionality of TMDC quasi-two-dimensional materials.

    View details for DOI 10.1021/acs.nanolett.7b03955

    View details for PubMedID 29119791

  • Electrically-driven GHz range ultrafast graphene light emitter Kim, Y., Gao, Y., Shiue, R., Wang, L., Aslan, O., Kim, H., Nemilentsau, A. M., Low, T., Taniguchi, T., Watanabe, K., Bae, M., Heinz, T. F., Englund, D. R., Hone, J., Betz, M., Elezzabi, A. Y. SPIE-INT SOC OPTICAL ENGINEERING. 2017

    View details for DOI 10.1117/12.2252592

    View details for Web of Science ID 000407040100044

  • Linearly Polarized Excitons in Single- and Few-Layer ReS2 Crystals ACS PHOTONICS Aslan, O. B., Chenet, D. A., van der Zande, A. M., Hone, J. C., Heinz, T. F. 2016; 3 (1): 96-101
  • In-Plane Anisotropy in Mono- and Few-Layer ReS2 Probed by Raman Spectroscopy and Scanning Transmission Electron Microscopy NANO LETTERS Chenet, D. A., Aslan, O. B., Huang, P. Y., Fan, C., van der Zande, A. M., Heinz, T. F., Hone, J. C. 2015; 15 (9): 5667-5672


    Rhenium disulfide (ReS2) is a semiconducting layered transition metal dichalcogenide that exhibits a stable distorted 1T phase. The reduced symmetry of this system leads to in-plane anisotropy in various material properties. Here, we demonstrate the strong anisotropy in the Raman scattering response for linearly polarized excitation. Polarized Raman scattering is shown to permit a determination of the crystallographic orientation of ReS2 through comparison with direct structural analysis by scanning transmission electron microscopy (STEM). Analysis of the frequency difference of appropriate Raman modes is also shown to provide a means of precisely determining layer thickness up to four layers.

    View details for DOI 10.1021/acs.nanolett.5b00910

    View details for Web of Science ID 000361252700001

    View details for PubMedID 26280493

  • Optical Properties and Band Gap of Single- and Few-Layer MoTe2 Crystals NANO LETTERS Ruppert, C., Aslan, O. B., Heinz, T. F. 2014; 14 (11): 6231-6236


    Single- and few-layer crystals of exfoliated MoTe2 have been characterized spectroscopically by photoluminescence, Raman scattering, and optical absorption measurements. We find that MoTe2 in the monolayer limit displays strong photoluminescence. On the basis of complementary optical absorption results, we conclude that monolayer MoTe2 is a direct-gap semiconductor with an optical band gap of 1.10 eV. This new monolayer material extends the spectral range of atomically thin direct-gap materials from the visible to the near-infrared.

    View details for DOI 10.1021/nl502557g

    View details for Web of Science ID 000345723800032

    View details for PubMedID 25302768

  • Exciton Binding Energy and Nonhydrogenic Rydberg Series in Monolayer WS2 PHYSICAL REVIEW LETTERS Chernikov, A., Berkelbach, T. C., Hill, H. M., Rigosi, A., Li, Y., Aslan, O. B., Reichman, D. R., Hybertsen, M. S., Heinz, T. F. 2014; 113 (7)


    We have experimentally determined the energies of the ground and first four excited excitonic states of the fundamental optical transition in monolayer WS_{2}, a model system for the growing class of atomically thin two-dimensional semiconductor crystals. From the spectra, we establish a large exciton binding energy of 0.32 eV and a pronounced deviation from the usual hydrogenic Rydberg series of energy levels of the excitonic states. We explain both of these results using a microscopic theory in which the nonlocal nature of the effective dielectric screening modifies the functional form of the Coulomb interaction. These strong but unconventional electron-hole interactions are expected to be ubiquitous in atomically thin materials.

    View details for DOI 10.1103/PhysRevLett.113.076802

    View details for Web of Science ID 000341115700020

    View details for PubMedID 25170725