Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session Z41: Defects in Low-dimensional Materials |
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Sponsoring Units: DMP Chair: Shuang Tang, SUNY Polytechnic Institute Room: Room 319 |
Friday, March 10, 2023 11:30AM - 11:42AM Author not Attending |
Z41.00001: Spin-valley coupling in defect-bound electrons in a MoS2 transistor Sangram Biswas, Radha Krishnan, Yu-ling Hsueh, Rajib Rahman, Bent Weber Atomically thin two-dimensional transition metal dichalcogenides, such as MoS2, are actively being explored for applications in next-generation electronics and quantum information processing. Electronic ground states in the conduction band of MoS2 are predicted spin-valley locked, promising robust quantum bits (qubits) with potentially enhanced spin lifetime. However, the difficulty in achieving high mobility devices with transparent contact at low temperatures has made it challenging to achieve confinement of single or few-electron spins to quantum dots, and hence to probe spin-valley locked states experimentally. We report resonant tunneling through well-resolved spin states in MoS2, whose spin-valley coupling we demonstrate by ground-state magneto-spectroscopy. We measure an effective out-of-plane g-factor as large as ≈ 8 and spin-orbit coupling of ΔSO ∼ 100 eV. We believe that our results are a significant step towards harnessing electron spins in these materials to realize spin-valley qubits. |
Friday, March 10, 2023 11:42AM - 11:54AM |
Z41.00002: In-plane InAs nanowires with buffer and capping layers by molecular beam epitaxy selective area growth Pradip Adhikari, Anjali Rathore, Bernadeta R Srijanto, Joon Sue Lee Complex branched geometries of in-plane InAs nanowires prepared by selective area growth can be used as a scalable platform to realize and study quantum devices. Defects and disorder at the interface between InAs and the substrate as well as at the bare top surface are limiting factors that degrade the electrical properties of the nanowires. We studied selective area growth of InAs, GaAs, InGaAs, GaSb nanowires on InP(100) and InP(111) B substrates using molecular beam epitaxy. Highly insulating InGaAs and GaSb with lattice constant closely matched to InAs can be used as a buffer layer or a capping layer, which can reduce defects in InAs. The use of atomic hydrogen during growth enabled clean native oxide desorption and improved selectivity as well as quality of InGaAs nanowires. The improved selectivity and the change in the major facet planes as per the substrate orientation were observed by scanning electron micrograph. Further characterizations were carried out by using x-ray diffraction and atomic force microscopy. Electrical properties of InAs nanowires with and without buffer and capping layers will also be discussed. |
Friday, March 10, 2023 11:54AM - 12:06PM |
Z41.00003: Examining the Relationship between Dislocations and Nanoparticle Morphology Zachary J Barringer, Edwin Fohtung, Nimish P Nazirkar, Xiaowen Shi, Skye Williams Defects play an important role in the growth and properties of materials at all length scales. At the nanoscale in particular, dislocations can relieve epitaxial strain, enable growth mechanisms such as spiral growth, and form small angle grain boundaries affecting both particle morphology and material properties. The study of dislocations is often performed with transmission electron microscopy techniques (TEM). However, TEM requires destructive sample preparation and only provides information on the sample in 2 dimensions. Coherent Diffractive Imaging is a technique that uses coherent x-rays to non-destructively probe the lattice of a crystal in 3 dimensions, allowing us to characterize single dislocations throughout the volume of the crystal. While the identification of dislocations using this technique is established in the literature [1], its insight into the relationship between the identifies defects and the crystal shape is underexplored. This work will present a numerical analysis of one such imaging of a semiconducting nanocrystal, showing how the 3-dimensional information provided using coherent imaging can be directly linked to particle morphology. |
Friday, March 10, 2023 12:06PM - 12:18PM |
Z41.00004: Bandgap engineering in III-V nanowires by post-growth hydrogen implantation Nadine Denis, Elena Blundo, Ada Krasnovsky, Ilaria Zardo, Mitsuki Yukimune, Fumitaro Ishikawa, Antonio Polimeni, Marta De Luca Quantum dots and rings in semiconductor nanowires are valuable assets in the toolbox for quantum optics applications. To create these structures, the electronic bandgap has to be engineered on the nanoscale, which is typically done by varying the material composition or crystal phase during growth. Even though this approach is very powerful, it gives limited control over the size and emission energy of the quantum structure. Here, we report bandgap engineering of GaAs/GaAsN nanowires by hydrogen implantation post-growth. The low concentration of N-atoms (0.7-3%) creates a perturbation potential leading to a downshift of the GaAs bandgap energy [1]. By forming stable N-H complexes, we can shift the bandgap by up to 400meV back to the value of GaAs in the regions subjected to low energy H irradiation. Simultaneously, we show that this H-implantation is accompanied by a giant optical signal increase of one order of magnitude due to a passivation of surface and interface states. With μ-Raman and μ-photoluminescence measurements we study the peculiarities of the material, while the preliminary g2-measurement demonstrates the potential of our nanowire material to act as single photon emitter. |
Friday, March 10, 2023 12:18PM - 12:30PM |
Z41.00005: Scanning Tunneling Microscopy Study of Vibronic Coupling due to Charged Impurity in Monolayer WS2 on Graphite Lisa Frammolino, Madisen A Holbrook, Hyunsue Kim, Andrew Murphy, Chih-Kang Shih Electron-phonon coupling of localized atomic systems in 2D crystals act as a decoherence conduit which substantially affect transport properties of the crystal. Here, we report a novel impurity on chemical vapor deposition (CVD)-grown monolayer tungsten disulfide (WS2) on graphite. From scanning tunneling microscopy (STM) images, we have found that these impurities are negatively charged, exhibiting upward band bending with respect to the neighboring WS2 band. The defect exhibits a two-fold lobal structure observed at small positive sample bias, indicating the existence of unoccupied mid-gap states. Utilizing scanning tunneling spectroscopy (STS) to probe the impurity electronic structure, we discover that there are a series of nearly equidistant oscillatory resonant peaks in the band gap at both positive and negative bias. We observe as many as 8-10 of these peaks in the dI/dV spectrum suggesting that they do not originate from a single particle electron state. We therefore attribute them to coupling of the impurity to vibronic modes with the surrounding lattice. We hypothesize that the chemical species of this impurity to be a hydrogen atom attached at a vacant sulfur lattice site originating from the CVD growth process. By introducing excess hydrogen to deterministically dope the sulfur vacancies, we intend to uncover the origin of these impurities. |
Friday, March 10, 2023 12:30PM - 12:42PM |
Z41.00006: Printing homogeneous single-layer oxidized graphene (SOG) via excimer UV for engineering graphene FETs MOHD MUSAIB HAIDARI, Jin Hong Kim, Jin Sik Choi UV treatment is a feasible method to produce homogeneous graphene oxide (GO), which is not only crucial to unlocking its enormous potential applications but also allows us to adjust graphene FET characteristics. However, the oxidation rate of graphene under a UV environment is highly sensitive to UV bandwidth and irradiation time. In this work, we utilize an excimer UV in an ambient environment to synthesize single-layer oxidized graphene (SOG). First, we discuss multiple oxidation phases and defect types by analyzing correlations between XPS and Raman spectra. The main three stages are namely, polymer residual cleaning, oxidation, and defective lattice. Nonetheless, the optimal condition lies within 60 s of UV irradiation with ~20% oxygen content as epoxide (C-O-C) groups on the graphene plane. AFM and TEM images confirm the preservation of graphene lattice at optimized oxidation conditions with an average thickness of 0.79 nm. Additionally, we exploited this technique to modify the performance of CVD-graphene FETs. Since SOG exhibits insulating electrical properties compared to monolayer graphene, we employed e-beam lithography and PMMA mask to isolate and pattern graphene channels in FETs. As result, UV patterned devices show well-defined edges with homogeneous epoxide groups at their boundaries compared to plasma etching which typically shows highly defective edges inhibiting random functionalities. This opens up the possibility of printing numerous graphene-SOG interfaces for a wide range of applications where the graphene boundary sharpness is only limited by lithography precision. |
Friday, March 10, 2023 12:42PM - 12:54PM |
Z41.00007: Spin, orbital, and valley structure of chalcogen vacancies in monolayer MoS2 Hongyang Ma, Aliyar Thasneem, Bent Weber, Rajib Rahman Vacancies in 2D materials have attracted much attention recently as single photon emitters and potential spin qubits. However, an atomic-level understanding of their bound states and wave functions remains elusive. In this work, we combine low-temperature scanning tunneling microscopy (STM) and ab-initio density functional theory (DFT) calculations to unambiguously identify and characterize the single and double chalcogen vacancies in monolayer MoS2. The real space STM images of the electronic energy levels introduced by chalcogen vacancies are explored, showing lobe-like shapes, corresponding to the unpaired electrons bound to the defects. The spin quantization axis and spin-orbit coupling are found to play key roles in the determination of direction and shape of the lobes observed in the STM images. Additionally, STM images in reciprocal space, dI/dV analysis, and density of states (DOS) are comprehensively investigated, providing a detailed understanding of the MoS2 electronic device properties. This atomic-level analysis can also be extended to other transition-metal dichalcogenides (TMDs), which will offer useful insights for quantum computing and sensing applications. |
Friday, March 10, 2023 12:54PM - 1:06PM |
Z41.00008: Ultrafast Dynamics of Electron Injection from Cu Embedded Nanoparticles in CeO2 Aerogels Tara Michael Wide bandgap semiconductors, such as TiO2 and CeO2, have photocatalytic properties activated in the UV that can be used to drive electrical currents and enhance electrochemical reactions. The activity range of wide bandgap semiconductors can be extended into the visible by coupling the semiconductor to a metal nanostructure in close contact. A localized surface plasmon resonance is excited in the metal nanostructure with visible light, and excited electrons with enough momentum can be injected into the semiconductor before relaxation and recombination with the metal nanostructure. The injection time and subsequent relaxation of free electrons from Cu nanoparticles photodeposited onto a CeO2 aerogel is investigated using ultrafast transient absorption spectroscopy. The Cu nanoparticles are excited with pulsed visible light and the appearance of free electrons in the CeO2 aerogel are detected with mid-infrared light. The transient signals appear within 300 fs, providing a timeframe for electron transfer from Cu to CeO2. Transient signals are measured over a range of mid-infrared probe wavelengths, attributed to free or trapped electrons in CeO2. Unlike other transition metal oxides, CeO2 has an additional empty 4f state between its conduction and valence bands that can store electrons and form small polarons. The role of the 4f state in electron-phonon decay is explored by probing the 4f state directly with 266 nm light and 350 nm probe. The results presented here examine the utility of using Cu nanoparticles to enhance the properties of CeO2 as a photocatalyst. |
Friday, March 10, 2023 1:06PM - 1:18PM |
Z41.00009: Dislocations as natural quantum wires in Diamond Sevim Polat Genlik, Roberto C Myers, Maryam Ghazisaeidi Different bonding environment of dislocations leads to locally unique, anisotropic properties across one dimensional defect line. For this reason, dislocations and low dimensional materials are similar to each other, except for the fact that dislocations are naturally occurring and environmentally protected by their host material. Here, we systematically investigate electronic properties of the glide set of partial dislocations in diamond with first principles calculations using hybrid exchange correlation functionals. The electronic band structure of dislocations and the anisotropic carrier mobilities are calculated and compared with the host crystals band structure and carrier mobilities. The results reveal that dislocations create one-dimensional (1D) metallic and semiconducting wires based on the character and position of defect states which heavily depend on the local core structures. 1D metallic bands appeared within the core of unreconstructed 30 partial dislocations, with a characteristic 1D density of states (1/√E). Map of charge density distribution along the cross-plane of dislocation line reveal that spatially localized 1D chain of overlapping pz orbitals creates conduction pathway for 1D Fermi gas. On the other hand, unreconstructed pure edge dislocation in diamond is found to be semiconducting with a band gap of 3.21 eV. These results open the door for exploitation of dislocations as 1D active components in functional devices. |
Friday, March 10, 2023 1:18PM - 1:30PM |
Z41.00010: p-type degenerate doping of 2H-MoTe2 Anjaly Rajendran, Hae Yeon Lee, Luke N Holtzman, Song Liu, Katayun Barmak, James C Hone On-chip fiber optic communication systems require photodiodes and light emitting diodes which operate in the infrared (IR) / Near-infrared (NIR) regions. Among the different direct bandgap van der Waals semiconductors, monolayer Molybdenum Telluride (2H-phase) is an excellent candidate. 2H-MoTe2 has a bandgap of 1.1 eV in the monolayer limit. However, this material is very air-sensitive and requires a passivation layer to operate in ambient conditions. |
Friday, March 10, 2023 1:30PM - 1:42PM Author not Attending |
Z41.00011: Spin-defect characteristics of single sulfur vacancies in monolayer MoS2 Andreas Stier, Alexander Hötger, Tomer Amit, Julian Klein, Katja Barthelmi, Thomas Pelini, Alex Delhomme, Marek Potemski, Clement Faugeras, Galit Cohen, Daniel Hernangomez-Perez, Takashi Taniguchi, Kenji Watanabe, Christoph Kastl, Jonathan J Finley, Alexander Holleitner Single spin defects in 2D transition-metal dichalcogenides are natural spin-photon interfaces for quantum applications. Here we report high-field magneto-spectroscopy to B=27T from three emission lines of deterministically induced sulfur vacancies in monolayer MoS2 [1]. The distinct valley-Zeeman splitting and the brightening of dark states necessitates spin-valley selectivity of the defect states and lifted spin-degeneracy at zero field. Comparing our results to ab-initio calculations identifies the nature of the defect luminescence. Analysis of the optical degree of circular polarization as a function of magnetic field and gate voltage reveals that the Fermi level is a parameter that enables the tunability of the emitter. These combined results show that defects in 2D semiconductors may be utilized for quantum technologies. |
Friday, March 10, 2023 1:42PM - 1:54PM |
Z41.00012: Symmetry-enabled discovery of quantum defects in two-dimensional materials Jeng-Yuan Tsai, Arun Bansil, Qimin Yan Point defects in solid-state materials such as NV center in diamond have been demonstrated to be promising qubit candidates for quantum information science and technologies. Being atomically thin, two-dimensional (2D) materials renders a new paradigm for the realization of quantum defect fabrication and controllable manipulation. In these 2D materials, searching for defects with triplet ground states is one of the most crucial steps to identify more NV-like quantum defects that support multiple quantum functionalities. We design a comprehensive workflow for identifying promising quantum defects in a large group of 2D materials based on a site-symmetry-based hypothesis, which significantly increases the probability of finding triplet spin defects. To identify multiple functionalities for these quantum defect candidates, their magneto-optical properties are comprehensively estimated from high-throughput computations. We demonstrate that antisite defects in various hosts, including post-transition metal monochalcogenides (PTMCs) and transition metal dichalcogenides (TMDs) are promising quantum defects. Most importantly, we propose that 16 antisites in PTMCs serve as the most promising 2D-material-based quantum defect platform, due to their well-defined defect levels, optimal magneto-optical properties, and the availability of host materials. |
Friday, March 10, 2023 1:54PM - 2:06PM |
Z41.00013: Quantum Oscillations in High Mobility Few-Layer PdSe2 Yuxin Zhang
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Friday, March 10, 2023 2:06PM - 2:18PM Author not Attending |
Z41.00014: Vanadium-vacancy defect complexes in monolayer tungsten diselenide Jingda Zhang, Leyi Loh, Michel Bosman, Goki Eda, Su Ying Quek We present a comprehensive study of the formation of defect complexes of vanadium substitutional dopants and selenium vacancies in monolayer tungsten diselenide. Different defect complexes were identified and analyzed by the statistical treatment of scanning transmission electron microscope (STEM) datasets. Using density functional theory (DFT) calculations, we studied the thermodynamic stability of these defect complexes under experimental growth conditions. Both theory and experiment reveal that vanadium substitutional defects lower the formation energy of surrounding selenium vacancies. Increasing the vanadium concentration results in a larger density and average size of the vanadium-vacancy complexes. Nevertheless, the formation of larger complexes requires higher energy costs, and the most commonly observed defect complex configuration consists of a single vacancy adjacent to a vanadium defect. Our results pave the way for exploration of engineering impurity-vacancy complexes by substitutional doping in 2D TMDs. |
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