Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session B53: Device engineering of 2D materials |
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Sponsoring Units: DCMP Room: Mile High Ballroom 1F |
Monday, March 2, 2020 11:15AM - 11:27AM |
B53.00001: Optical Phase Transitions in 1T’-MoTe2 from Thin Film Strain Engineering Ahmad Azizimanesh, Tara Pena, Arfan Sewaket, Stephen M Wu MoTe2 has been shown to have the ability to undergo a semimetallic to semiconducting phase transition induced by strain. In this work, we explore this phase change in 1T’-MoTe2 through static strain induced by thin film stress capping layers, analogous to the ones used in industrial strained silicon processes. The optically transparent stressor film is chosen to be e-beam evaporated Al2O3/MgF2/Al2O3. This film carries a controlled amount of tensile thin film stress depending on MgF2 film thickness. Al2O3 is used as both an adhesion layer to MoTe2, and as a protective capping layer for the MgF2 from the environment. Significant optical contrast change in the few layered MoTe2 flakes is observed after stressor film deposition, which is confirmed to be a phase change with Raman spectroscopy. Al2O3 capped control samples eliminate the possibility that this effect originates from defect formation during device fabrication process. Increasing thin film stress, changes the phase of a larger number of layers from the top of each MoTe2 flake, resulting in thinner flakes to show larger proportional contrast change. Stress is a well-known technique to induce a phase change in MoTe2 and potentially other 2D materials, which may lead to interesting applications in 2D electronics and optics. |
Monday, March 2, 2020 11:27AM - 11:39AM |
B53.00002: Versatile multiscale envelope function formalism to study electron transport in lateral transition-metal dichalcogenide heterostructures Sathwik Bharadwaj, Ashwin Ramasubramaniam, L Ramdas Ram-Mohan Accurate determination of carrier transport properties is critical to design high-performance optoelectronic devices and quantum information platforms. Although, first-principles calculations effectively determine the atomistic potentials associated with heterointerfaces, defects, and impurities, they are ineffective for direct modeling of carrier transport properties at length scales relevant to device applications. Here, we develop a multiscale formalism to investigate electron transport in two-dimensional (2D) materials. We integrate k.p perturbation theory, informed from ab-initio electronic structure calculations, with a novel non-asymptotic quantum scattering theory using the method of sources and absorbers [1]. Our approach fully accounts for the crucial contributions of evanescent solutions that arise in multi-band scattering across heterointerfaces. We apply this method to study electron transport in lateral transition-metal dichalcogenide heterostructures, and discuss the implication of interface patterns on enhancing the thermoelectric power factor of the system. This new formalism provides a versatile variational description, first-principles-informed modeling of electron transport in 2D materials. |
Monday, March 2, 2020 11:39AM - 11:51AM |
B53.00003: Characteristics of the localization of massless pseudospin-1 Dirac particles in 2D in a short-range correlated random one-dimensional potential Seulong Kim, Kihong Kim We study theoretically the characteristics of Anderson localization of two-dimensional massless pseudospin-1 Dirac particles in a correlated random one-dimensional potential. These potentials include both scalar and vector potentials. Using the invariant imbedding method, we calculate the localization length in a numerically precise manner and derive the analytical expressions for the localization length in strong and weak disorder limits. We investigate the dependencies of the localization length on incident angle, disorder correlation length, disorder strength, energy and average potential for the cases with random scalar and/or vector potentials. Disorder correlations affect the scaling dependencies of the localization length on the disorder strength and the particle energy. We explain these dependencies and the crossovers between different scaling regimes using the analytical formulas. |
Monday, March 2, 2020 11:51AM - 12:03PM |
B53.00004: Strong two-body correlations in WS2 – MoSe2 Heterojunction Tunnel Diodes Jedediah Kistner-Morris, Trevor Arp, Nathaniel Gabor Owing to the strong Coulomb interaction between electrons and holes, electron tunneling between individual layers of a van der Waals heterostructure may give rise to highly unusual phenomena not observed in conventional materials. Here we report on optoelectronic transport of encapsulated WS2 – MoSe2 tunneling heterojunctions, in which we observe anomalous photoconductance and strong rectification. Using Multi-Parameter Dynamic Photoresponse Microscopy, we generate ~10X photocurrent images of the heterostructure photoresponse as a function of source-drain voltage, gate voltage, and temperature. Alongside strong rectifying behavior, we observe an anomalous reduction in the interlayer conductance that is tunable with gate voltage and temperature. This behavior becomes significantly enhanced with optical illumination, allowing us to assess the interactions of electrons and holes at the heterostructure interface. Our measurements indicate that strong two-body correlations arise precisely at the onset to a reduction in tunneling conductance, which we speculate is a signature of the crossover from free electron to bound interlayer exciton state. |
Monday, March 2, 2020 12:03PM - 12:15PM |
B53.00005: Transfer-print of graphene, boron nitride and gold patterns onto polymeric materials Evgeniya Lock, Gabriella Gonzalez-Pascual, Daniel Choi, Sandra Villanueva Rodriguez, Ray Auyeung, Heungsoo Kim, Karthik Sridhara, Boris Feylgelson Two dimensional (2-D) materials such as graphene, hexagonal boron nitride (h-BN), black phosphorene (BP), molybdenum disulfide (MoS2) have intriguing electrical, optical and chemical properties, which may enable next generation flexible sensors and photodetectors fabrication. However, placement of 2D materials on polymers to produce large scale 2D material/polymer heterostructures and the following metal deposition remains challenging. In this work, we show a multistep approach towards realization of 2D heterostructures on flexible substrates using a dry transfer-print approach based on differential adhesion. First, plasma treatment of the polymeric materials was performed. Then, organic molecular linker layer was attached for increased polymer adhesion. Then, the polymers and the 2D materials were placed in a nanoimprinter at specified conditions (pressure, temperature and time) and mechanically separated after print. Similarly, gold patterns were transferred to polymers. Optical, chemical, electrical and structural characterization of the samples before and after print was performed. Based on our results, we believe that our 2D material transfer-print approach will allow for large scale fabrication of the next generation 2D/flexible hybrid electronics devices. |
Monday, March 2, 2020 12:15PM - 12:27PM |
B53.00006: A Novel Type of Water Desalination Technology Using MoS2-Based Thin Films for Selective Ion Transport. Gabriel Marcus Molybdenum disulfide (MoS2) is a widely studied transition metal dichalcogenide with a range of potential applications including next-generation electronics, hydrogen evolution, and catalysis. It can also be used as a thermoelectric, exploiting the Seebeck effect to generate an electric voltage in response to a temperature gradient. Additionally, lithium intercalated MoS2 is known to undergo a transition from the 1T to 2H phase. Together, these two properties make this material suitable as a novel desalination technology that relies on selective ion transport. To assess MoS2’s capabilities for ion transport, two types of experiments were conducted. The first set of experiments investigated changes in electric potential resulting from dropwise contact of various salt solutions with an MoS2 membrane. Droplet test data displayed abrupt changes in electric potential followed by an exponential decay representing ion movement over time. A second set of experiments measured ion concentration changes over time using an MoS2 film in contact with separated DI water and salt solutions. Significant changes in solution ion osmolarities were recorded after a duration of one week . Results are promising for future development of a thermoelectric desalination device. |
Monday, March 2, 2020 12:27PM - 12:39PM |
B53.00007: Substrate-Induced Dynamical Anti-Screening of Excitons in Quasi-2D Materials: Renormalization of Quasiparticle and Optical Excitations Chin Shen Ong, Felipe H. da Jornada, Diana Qiu, Steven Louie It is now well established that screening from substrates can strongly reduce the many-electron interactions in quasi-2D insulating materials, and renormalize both the quasiparticle bandgap and exciton binding energy in such systems. However, for metallic substrates, the frequency dependence of screening plays a paramount role that is often ignored. Here, we show that the frequency dependence of metallic substrate screening can induce a strong anti-screening effect in the quasi-2D insulator and lead to anomalously non-hydrogenic exciton energy levels, i.e., there are dramatic additional changes that go beyond the q-dependent static screening of quasi-2D materials. A systematic first-principles study of renormalizations by a wide range of experimentally motivated substrates is carried out, and our calculated results provide conceptual and quantitative explanation of experiments. |
Monday, March 2, 2020 12:39PM - 12:51PM |
B53.00008: Hydrodynamic Anomalous Transport in Interacting Noncentrosymmetric Metals Riki Toshio, Kazuaki Takasan, Norio Kawakami In high-conductive metals with sufficiently strong momentum-conserving scattering, the electron momentum is regarded as a long-lived quantity, whose dynamics can be described by an emergent hydrodynamic theory. In this work, we propose a hydrodynamic theory for noncentrosymmetric metals, where a novel class of electron fluids is realized by lowering crystal symmetries and the resulting geometrical effects. Starting from the Boltzmann equation, we introduce the effects of the Berry curvature to electron hydrodynamics and formulate a generalized Euler equation for noncentrosymmetric metals. We show that this equation reveals a variety of novel anomalous nonlocal/nonlinear transport phenomena; chiral vortical effect, quantum nonlinear Hall effect, thermal-gradient induced anomalous Hall effect, etc., whose transport coefficients are described by geometrical quantities such as Berry curvature dipole [1]. Furthermore, we give a symmetry classification of these coefficients and compare the results with existing hydrodynamic materials. In the presentation, we would like to discuss what phenomena are predicted to be observed in experiments in noncentrosymmetric materials, including bilayer-graphene and transition metal dichalcogenides. |
Monday, March 2, 2020 12:51PM - 1:03PM |
B53.00009: Engineering the electronic, thermoelectric, and excitonic properties of 2D group-III nitrides through alloying (Al1-xGaxN, Ga1-xInxN, B1-xAlxN) Daniel Wines, Fatih Ersan, Can Ataca Recently, two-dimensional (2D) group-III nitride semiconductors such as h-AlN, h-BN, h-GaN, and h-InN have attracted attention due to their exceptional electronic, optical and thermoelectric properties. It has also been demonstrated, theoretically and experimentally, that properties of 2D materials can be controlled by alloying. In this study we performed density functional theory (DFT) calculations to investigate 2D Al1-xGaxN, Ga1-xInxN, and B1-xAlxN alloyed structures. We also calculated the thermoelectric properties of these structures using Boltzmann transport theory based on DFT and the optical properties using the GW method and the Bethe Salpeter equation (BSE). Fundamental band gaps were also calculated with quantum Monte Carlo (QMC) methods for benchmarking purposes. We find that by changing the alloying concentration, the band gap and exciton binding energies of each structure can be tuned accordingly, and for certain concentrations, a high thermoelectric performance is reported with strong dependence on the effective mass of the given alloyed monolayer. With the ability to control such properties by alloying 2D group-III nitrides, this work presents new novel possibilities to engineer the electronic, optical and thermoelectric properties of 2D materials. |
Monday, March 2, 2020 1:03PM - 1:15PM |
B53.00010: Intrinsic gap and temperature collapse of the electric conductivity in bilayer graphene Mohammad Zarenia, Giovanni Vignale
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Monday, March 2, 2020 1:15PM - 1:27PM |
B53.00011: Negative Differential Resistance in MoS2 Esaki Diodes Adam Bruce, Yun-Peng Wang, Shuanglong Liu, Hai-ping Cheng Two dimensional MoS2 is a semiconducting system valued for its potential application as a programmable material. In addition to its direct bandgap in a single layer, an external electric field allows for interlayer band-to-band tunneling in bilayer configuration, which raises the prospect of applications in nanocircuitry. Using a first principles approach via DFT+NEGF, we probe the electronic properties of MoS2 p-i-n junctions. We show both the IV characteristics of our junctions as well as the corresponding partial density of states at biases of interest. By comparing the band alignment of the electrodes and the transmission of our junction, we establish a criterion for band to band tunneling. Finally, we discuss mitigating edge effects on electronic structure and the possible applications of our p-i-n junctions. |
Monday, March 2, 2020 1:27PM - 1:39PM |
B53.00012: Electrochemical intercalation of organometallic molecules in HfS2-based van der Waals material Chinedu Ekuma, Sina Najmaei, Adam A Wilson, Asher Leff, Madan Dubey van der Waals (vdW) materials designed with atomic layers of 2D-based materials exhibit a broad set of novel properties that are highly desirable for enabling heterogeneous device concepts such as neuromorphic and quantum computing. Because of their flexible electronic structure, both carrier dynamics and charge injection are easily tunable with chemical or electrical doping. Using a combined computation and experiment, we demonstrate the feasibility of intercalating electronically active organometallic molecules of two of the family of metallocene: cobaltocene and chromocene into the vdW gap of HfS2-based prototype vdW materials. We achieve high tunability of the electronic and vibrational properties of the hybrid material. Our findings demonstrate a unique approach, leveraging the flexible structural properties of layered materials to create an organic/inorganic interface that tunes and tailor the properties of host materials for distinctive device applications. |
Monday, March 2, 2020 1:39PM - 1:51PM |
B53.00013: Electronic States at Lateral Interfaces in Transition Metal Dichalcogenides Kaelyn Ferris, Sergio E Ulloa Lateral heterostructures of two-dimensional crystals have received attention as defect free interfaces are increasingly grown in experiments. These interfaces show excitations unlike those at the original materials, suggesting the robustness of the interface. Tight binding and first principles calculations show that electronic states along the interface lie within the band gap of the bulk structure and provide a platform for possible use as high performance thermoelectric materials, spin-valley filters without the need for external gating, excitonic solar cells, and photocatalysis [1]. In this work, we explore the appearance of interfacial states in continuum models of such massive Dirac systems at low energy. We use k*p models to characterize lateral interfaces of various 2D materials and analyze the results of appropriate boundary conditions on various types of interfaces. This approach is able to describe midgap interface states that appear under mass or band inversion, as well as sign changes in effective curvature across the two materials. The states exhibit complex dispersion curves with strong spin-orbit effects, while being localized along the interface with different features in different materials. |
Monday, March 2, 2020 1:51PM - 2:03PM |
B53.00014: Advanced atomistic models to accurately simulate graphitic nanostructures, bio-interfaces, and aromatic molecules Krishan Kanhaiya, jordan winetrout, Micheal Nathanson, Hendrik Heinz Graphene and carbon nanomaterials are used in biosensors, batteries, renewable composites, and functional materials. We introduce new atomistic models for the simulation of graphitic nanostructures, bio-interfaces, and aromatic molecules using common energy expressions (CHARMM, AMBER, CVFF, OPLS-AA, PCFF). The model contain virtual π-electrons in graphene/benzene ring that significantly increase the reliability of computed properties. Benchmarking of the new model shows improvements in the reproduction of cation-pi interactions, pi-pi stacking, and electrolyte interfacial properties by ~10 fold. Two dummy electrons are attached to carbon atom to add the multipoles due to π-electrons in the aromatic rings. This leads to columbic interaction in accordance with experiment, which is missing in the old models. The models can accurately predict binding free energies, adsorption sites and biomolecular recognition, binding orientations, surface diffusion, and competitive adsorption of molecules. Details of the validation include agreement with experimental lattice parameters (<0.5% deviation), surface energy (<5% deviation), elastic constants (<15% deviation), hydration energy (10% deviation), water contact angles (<10% deviation) and cation-pi interaction (<15% deviation). |
Monday, March 2, 2020 2:03PM - 2:15PM |
B53.00015: Effects of hydrogen, oxygen, and hydroxyl adsorption on the electronic properties of transition metal dichalcogenides Georgios Kopidakis, Daphne Davelou, Aristea E Maniadaki, Ioannis N Remediakis The unique properties of 2D transition metal dichalgogenides (TMDs) attract a lot of interest for optoelectronics, catalysis and energy related applications. Strain, environment, nanostructuring, affect TMD electronic properties and intensive efforts focus on their controlled modification. We present DFT calculations for the stability and electronic structure of semiconducting MX2 (M=Mo, W and X=S, Se) monolayers and nanostructures with several concentrations of adsorbed hydrogen, oxygen, and hydroxyl and compare our results with pristine systems. The metallic character of the edge states [1] is preserved for all TMD nanoribbons examined, albeit Fermi level shifts that depend on the adsorbed atoms. Tuning electronic properties with strain [2] for improved TMD catalysts [3] is briefly discussed. |
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