Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session S37: Devices from 2D Materials V - OptoelectronicsFocus
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Sponsoring Units: DMP Chair: Xiaoxiao Zhang, Stanford University Room: LACC 411 |
Thursday, March 8, 2018 11:15AM - 11:27AM |
S37.00001: Engineering and optical characterization of large area, aligned single-wall carbon nanotubes Luis Royo Romero, Angela Hight Walker, Jeffrey Fagan Single-wall carbon nanotubes (SWCNTs) possess unique optical and electronic properties due to their strictly one-dimensional nature, that can be enhanced at the macroscopic scale when the SWCNTs are well-aligned. Engineering of a large-scale (mm2) architecture of aligned SWCNTs has challenged the community for years and presents a major drawback in their use in many applications. The reproduction of the first demonstration of high-quality aligned films of SWCNTs was reported by X. He et al. remains a challenge due to insufficient methodical details and a lack of understanding of the role of certain experimental parameters. The goal of our work is to refine their reported method and establish the robust capability to produce aligned macroscopic films at NIST using tubes of varying chiralities and surfactants. Creating monodomain, aligned films utilizing a slow vacuum filtration technique and a rigid protocol varying several parameters, including SWCNT concentration, surfactant concentration, and filtration flow rate. Once films are produced, they need to be transferred from the polycarbonate nanopore membrane used during filtration onto other substrates for device fabrication and characterization, including polarized optical microscopy, Raman spectroscopy, and absorption. |
Thursday, March 8, 2018 11:27AM - 11:39AM |
S37.00002: Graphene Capped Silicon Nanocrystals for Optoelectronic Devices Anupam Nandi, Sudipta Chakrabarty, susmita Biswas, Syed Hossain Quantum confinement effect combined with surface states at the SiNCs/SiOx interface has revealed efficient light emission under UV illumination. It’s a challenge when charged carriers are needed to be injected into the core for getting efficient luminescence for LED applications or photogenerated e-h pairs form the core of SiNCs are to be extracted for photovoltaic applications. This is because the SiNCs are embedded in insulating silicon oxide matrix that restricts injection or extraction of charge carriers from the core. We have encapsulated SiNCs by graphene layer, so that the optoelectronic property of the SiNCs is not suppressed and obtain additional electrical path through which electronic interaction can be possible. SiNCs and GO were procured and subjected for in-situ wet chemical technique, where RGO encapsulate each single SiNC through which charged carriers can be injected and extracted. Encapsulation of SiNCs by RGO also minimizes the thickness of the SiOx shell without any significant change in optical properties. Respective signature characterizations viz. Raman, UV-Vis spectroscopy, TEM and PL have been carried out and the optoelctronic properties have been studied to confirm the potential application of the composite for optoelectronic devices. |
Thursday, March 8, 2018 11:39AM - 11:51AM |
S37.00003: Shape Enhancement of the Photothermal Interaction with Graphene Nanomechanical Resonators Andrew Blaikie, David Miller, Max Kant, Benjamin Aleman The motion of suspended graphene can couple to light through photothermal interactions which shift the mechanical resonant frequency by tightening the graphene upon absorbing light. The applications of photothermal interactions are vast and include laser cooling, induced self-oscillations, and strain tuning. These photothermal interactions and many related applications depend strongly on the photothermal frequency shift and the characteristic thermal relaxation time. The effect of graphene device geometry on the photothermal interaction is expected to play a large role, but the study of this effect has been limited to simple drumhead geometries. Here, we show that a trampoline geometry consisting of a central suspended graphene structure supported by tethers exhibits an enhancement in the photothermal resonant frequency shift by two orders of magnitude. Furthermore, we find the photothermal relaxation time can be modified by the support tether width. We also present finite element simulations that suggest that these tethers act as thermal resistors to tune both the relaxation time and the frequency response. |
Thursday, March 8, 2018 11:51AM - 12:03PM |
S37.00004: Automated searching and assembly of atomic layers: a robotic building system of van der Waals superlattices Satoru Masubuchi, Masataka Morimoto, Momoko Onodera, Sei Morikawa, Kenji Watanabe, Takashi Taniguchi, Tomoki Machida Ever since the advent of mechanical exfoliation of atomically thin two-dimensional (2D) crystals and van der Waals (vdW) heterostructures, random nature in the shape, thickness, and positions of exfoliated 2D crystals have insisted researchers for repetitive manual tasks of optical microscopy-based searching and subsequent mechanical transfer. In this work, we developed a robotic system that automatically searches exfoliated 2D crystals and assembles them into vdW superlattices. The system was built in an enclosure with inert gas, and fully remotely operated by a computer software. Its enduring capacity was shown to be the analyzing of 12,000 optical microscope images per hour, detecting of 400 monolayer graphene flakes per hour with a small error rate (< 7%), and stacking of four cycles of the designated 2D crystals per hour. The system enabled fabrication of the vdW superlattice structures consisting of 29 alternating layers of the graphene and the hexagonal boron nitride (hBN) flakes. The system's enduring capacity provides a scalable approach for prototyping a variety of vdW superlattices. |
Thursday, March 8, 2018 12:03PM - 12:15PM |
S37.00005: Polarization sensitive phototransistors based on layered germanium selenide Enze Zhang, Peng Wang, Chang Niu, Ce Huang, Linfeng Ai, Shanshan Liu, Weida Hu, Faxian Xiu Atomically-thin 2D layered materials are attracting increasing attention owning to its promising potential device applications and the hosting of so many emerging electronic, spintronic and photonic properties. Among them, germanium selenide is a material exhibits strong in-plane anisotropy due to the lacking of crystal symmetry. Here, the anisotropic nature of germanium selenide is revealed by electrical transport measurement and polarization resolved Raman scattering, in which its electrical conductance and Raman intensity changes regularly when electrical contact and polarization direction of incident light changes along different crystal directions. Utilized its linear dichroism, we have successfully built phototransistors based on layered germanium selenide which shows highly responsivity photodetection of linear polarized light. The newly functionality in germanium selenide based phototransistors and exotic physical properties of it demonstrated in this study identify germanium selenide as an emerging candidate for future applications in electronic and optoelectronic devices. |
Thursday, March 8, 2018 12:15PM - 12:27PM |
S37.00006: Tri-layer black phosphorus as a light source in Telecom optical wavelength bands Ya-Qing Bie, Jiabao Zheng, Ren-Jye Shiue, Gabriele Grosso, Melis Tekant, Dirk Englund, Pablo Jarillo-Herrero Light sources in telecom bands are crucial for many types of optical communications, such as on-chip, chip-to-chip, rack to rack and fiber communications. However, the common light sources based on III-V group materials have been suffering from integration difficulties. Recently, layered material black phosphorus (BP) has been proved as a direct band gap semiconductor for all different thickness. The emission from BP is not only anisotropic but also thickness dependent. Especially for tri-layer black phosphorus, the emission energy is peaked near 0.86 eV and the broad emission extends to both Telecom E-band and S-band. Limited by the air-sensitive nature, the study related to light emitting devices based on thin layer black phosphorus is still challenging. Here we focus on developing h-BN encapsulated black phosphorus inside glovebox for silicon photonics compatible light sources. The rich electronic and optical properties of BP allow for multiple functionalities and provides new opportunities for integrated optoelectronic systems. |
Thursday, March 8, 2018 12:27PM - 1:03PM |
S37.00007: 2D Materials in 3D Architectures with Photodetector Applications Invited Speaker: Jong-Hyun Ahn Two dimensional (2D) materials such as graphene and MoS2 are of considerable current interest in the nanoscience/nanotechnology community, due to their exceptional electronic, mechanical and optical properties. Past reports focus on the use of such 2D materials in devices with traditional, planar architectures. In this talk, I will report scalable means to exploit 2D materials in complex, three dimensional (3D) formats, with examples in unique nanosystems with levels of function in photoimaging/detection that cannot be easily reproduced with conventional materials and/or conventional device layouts. |
Thursday, March 8, 2018 1:03PM - 1:15PM |
S37.00008: Broadband Photoresponse from Asymmetric Hot-Carrier Thermalizations in Atomically Thin Lateral Heterojunctions Yuxuan Lin, Qiong Ma, Pin-Chun Shen, Mildred Dresselhaus, Pablo Jarillo-Herrero, Xi Ling, Jing Kong, Tomas Palacios The massless Dirac electron transport in graphene makes electron-electron scatterings much faster than the electron-phonon scatterings that dominate conventional semiconducting materials. This leads to an ultrafast (~ps) hot-carrier induced photothermoelectric (PTE) photoresponse, which is very promising for optical communications. However, it becomes more challenging to further optimized the devices, mainly because the spectral range, thermoelectric power factor, and the electron-phonon coupling strength are all coupled to the Fermi level of graphene. Here we proposed an asymmetric lateral heterojunction PTE photodetector that decouples the optimization of the spectral range and the responsivity. As a proof of concept, we synthesized graphene-MoS2 lateral heterojunctions through seed molecule selective “sowing” method and the as-fabricated devices showed broadband (400 nm to 1.6 µm) response, and good electrostatic gating tunability. The device behaviors can be explained through large discrepancies of the gate-tunable thermal relaxation pathways on the two sides of the asymmetric junction. Our proposed structure provided a new platform for the study of hot electron transport in strong electron-correlated systems and paved a way for high-performance, broadband photodetectors. |
Thursday, March 8, 2018 1:15PM - 1:27PM |
S37.00009: Real-Space Mapping of Polaritons in 2D Materials Max Eisele, Adrian Cernescu, Sergiu Amarie The performance of the next-generation electronic devices based on graphene and other 2D materials is strongly influenced by the structure-function relationship. Scattering-type scanning near-field optical microscopy (s-SNOM) is the ideal technology to investigate such material systems at the nanoscale. s-SNOM combines the best of two worlds: (i) the high spatial resolution of Atomic Force Microscopy (AFM) and (ii) the analytical power of optical microscopy and spectroscopy. Achieving an unmatched spatial resolution below 10nanometer this technology opens a new era for modern nano-analytical applications such as chemical identification, free-carrier profiling and plasmonic near-field mapping. Recent research highlights on graphene and other 2D materials include contact-free access to the local conductivity, the electron mobility, and the intrinsic electron doping by resolving propagating phonon-, plasmon-, and exciton-polariton directly in space and time. In this presentation we will introduce the basic principles of near-field microscopy for imaging and spectroscopy with 10 nanometer spatial resolution and address their impact and key applications in the field of 2D materials. |
Thursday, March 8, 2018 1:27PM - 1:39PM |
S37.00010: A chiral waveguide directional coupler using transition metal dichalcogenide monolayers Zhili Yang, Edo Waks Recent discoveries and advances in transition metal dichalcogenide monolayer materials have brought new possibilities and research interests. When the materials come to atomically thin monolayers, their indirect energy bandgaps in bulk become direct band. The most unique feature of these TMD monolayers is the valley dependent property based on inversion symmetry breaking and spin-orbit coupling. That is, circular polarized light with opposite angular momentum can only excite excitons in a certain valley. This spin-valley coupling gives rise to a new degree of freedom of the material, enabling new applications and the emergence of spin-valleytronics. In this work, we demonstrate an on-chip broadband polarization-dependent directional coupler based on coupling between a glide-plane photonic crystal waveguide and WSe2 monolayers. The direction of propagation and output in the device depends on the helicity of the input signal with a high directionality close to 0.5. This demonstrated coupling of spin-valley degree of freedom to photonic devices could serve as building blocks in integrated optical networks, and enlighten future works on utilizing this new degree of freedom in fundamental photonic elements such as diodes and transistors. |
Thursday, March 8, 2018 1:39PM - 1:51PM |
S37.00011: Scalable fabrication of high performance monolayer MoS2 photodetectors Alexander Yore, Kirby Smithe, sauraj jha, Kyle Ray, Noah Scandrette, V. Costa, Eric Pop, Akm Newaz Scalable fabrication of high quality photodetectors derived from synthetically grown monolayer transition metal dichalcogenides is highly desired and important for a wide range of nanophotonic applications. We present here scalable fabrication of monolayer MoS2 photodetectors on sapphire substrates through an efficient process, which includes growing large scale monolayer MoS2 via chemical vapor deposition (CVD) and multi-step optical lithography for device patterning and high quality metal electrode fabrication. In every measured device, we observed the following universal features: (i) negligible dark current (Idark≤10 fA), (ii) sharp peaks in photocurrent at ∼1.9 eV and ∼2.1 eV attributable to the optical transitions due to band edge excitons, and (iii) a rapid onset of photocurrent above ∼2.5 eV peaked at ∼2.9 eV due to an excitonic absorption originating from the van Hove singularity of MoS2. We observe a low (≤300%) device-to-device variation of photoresponsivity. Furthermore, we observe a fast DC time response of ∼0.5 ms, which is two orders of magnitude faster than other reported CVD grown 1L-MoS2 based photodetectors. The combination of scalable device fabrication, high sensitivity, and high speed offers great potential for applications in photonics. |
Thursday, March 8, 2018 1:51PM - 2:03PM |
S37.00012: Photonic-Crystal Exciton-Polaritons in Monolayer Semiconductors Long Zhang, Rahul Gogna, Gregory Burg, Emanuel Tutuc, Hui Deng Semiconductor microcavity polaritons, formed via strong exciton-photon coupling, provide a quantum many-body system on a chip, featuring rich physics phenomena for better photonic technology. However, conventional polariton cavities are bulky, difficult to integrate, and inflexible for mode control, especially for room temperature materials. Here we demonstrate sub-wavelength thick one-dimensional photonic crystals (PCs) as a designable, compact and practical platform for strong coupling with atomically thin van der Waals Crystals (vdWCs). Polariton dispersions and mode anti-crossings are measured up to room temperature. Non-radiative decay to dark excitons was suppressed due to polariton enhancement of the radiative decay. Unusual features, including highly anisotropic dispersions and adjustable Fano resonances in reflectance, may facilitate high temperature polariton condensation in variable dimensions. Combining slab PCs and vdWCs in the strong coupling regime allows for exploring novel polariton phenomena and device concepts. |
Thursday, March 8, 2018 2:03PM - 2:15PM |
S37.00013: Excitonic emission of monolayer semiconductors near-field coupled to high-Q microresonators Clement Javerzac-Galy, Anshuman Kumar, Jacob Khurgin, Andrea Ferrari, Tobias Kippenberg We present quantum yield measurements of single layer WSe2 (1L-WSe2) integrated with high-Q (Q>106) optical microdisk cavities, using an efficient (>90%) near-field coupling scheme based on a tapered optical fiber. Coupling of the excitonic emission is achieved by placing 1L-WSe2 to the evanescent cavity field. This preserves the microresonator high intrinsic quality factor (Q>106) below the bandgap of 1L-WSe2. The nonlinear excitation power dependence of the cavity quantum yield is in agreement with an exciton-exciton annihilation model. The cavity quantum yield is QYc∼10−3, consistent with operation in the broad emitter regime (i.e. the emission lifetime of 1L-WSe2 is significantly shorter than the bare cavity decay time). We discuss criteria for rigorous identification of lasing with layered materials. |
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