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 N32: Novel Semiconductors Thin Film Growth and Characterization |
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Sponsoring Units: DCMP Chair: Mariana Fazio, University of Strathclyde Room: Room 224 |
Wednesday, March 8, 2023 11:30AM - 11:42AM |
N32.00001: Molecular beam epitaxy of MoSe2 and WSe2 monolayers in large-scale on on-axis Au Yipu XIA, Degong Ding, Ke Xiao, Junqiu Zhang, Shaogang Xu, Daliang He, Xingyu Yue, Xiong Wang, Sujuan Ding, Mengfei Yuan, Wingkin Ho, Hu Xu, Xiaodong Cui, Chuanhong Jin, Maohai Xie Ultrathin two-dimensional transition-metal dichalcogenides (TMDs) with sizeable bandgaps have been pursued in recent years for their potentials in electronics, optoelectronics, spin- and valley-electronics. To this end, it is needed to synthesize crystalline TMD monolayers at large-scale. Lately, remarkable progresses have been made, where wafer-size metal disulfides (MoS2 and WS2) have been realized by chemical vapor deposition (CVD) on various vicinal substrates and explained by a step-guide mechanism. [1-5] Here, we report growth of large-scale single crystalline MoSe2 and WSe2 monolayer by molecular-beam epitaxy (MBE) at low temperature on on-axis Au substrates. Electron diffraction measurements reveal consistent three-fold symmetry across the whole sample, signifying single crystalline MSe2 (M = Mo, W). Optical measurements reveal high spatial uniformity of the epifilms. Defect density is estimated to be in the range of low 1012 cm-2. Mirror twin domain boundaries (MTBs), which are commonly seen in MBE-grown MoSe2 on graphene or HOPG, is rarely observed in films on Au. Moreover, we show that MSe2 grows on Au via the van der Waals (vdW) epitaxy mechanism, where a continuous film extends across the whole surface, hangs over atomic-layer steps on substrate. By following the initial stage nucleation, we identify that the highly crystalline MSe2 is not by the guidance of Au steps but rooted from a moderate Au-MSe2 interaction. |
Wednesday, March 8, 2023 11:42AM - 11:54AM |
N32.00002: Photoconductivity of WSe2 layers deposited on mica and (0001) Sapphire with pulsed laser ablation Marcus A Rose, Prabesh Bajracharya, Serene Kamal, Arlene Chiu, Jesse Liebman, Rajeswari M Kolagani, Natalia Drichko, Susanna M Thon, Ramesh C Budhani Refractory metal dichalcogenides of the van der Waals family have attracted much attention in recent years due to their novel electro-photonic properties that emanate from a direct bandgap and large exciton energy. Here we describe preparation of WSe2 thin films on mica and c-plane sapphire substrates with pulsed laser ablation of a meltcast target of WSe2.2. By precisely controlling the deposition rate per laser pulse and growth temperature we have successfully deposited WSe2 films of thickness ranging from a few monolayers to several tens of monolayer. Raman spectroscopy of these films reveals characteristic vibrational modes corresponding to the 2H structure of WSe2. We have also measured the photoconductivity response (PCR) of our films with laser excitations of wavelength 405, 532 and 915 nm. A robust PCR is seen in thicker films whereas the photo response of the thinner films is dominated by thermal effects. We have successfully modelled these data to separate out the contributions of thermal effects and the change in conductivity due to photoexcitation of carriers across the bandgap. Details of this analysis will be presented at the meeting. |
Wednesday, March 8, 2023 11:54AM - 12:06PM |
N32.00003: Scalable Growth of 2D WSe2 with tungsten and tungsten trioxide films as precursors Rohit R Srivastava, Rajeev Nepal, Pranish Shrestha, Ravinder Kumar, vinay Sharma, Alexander Samokhvalov, Birol Ozturk, Ramesh C Budhani Atomically thin 2D tungsten diselenide (WSe2) layers have drawn much interest due to their remarkable optical properties and potential applications in next-generation optoelectronics and energy harvesting devices [1]. High-quality wafer-scale synthesis of 2D materials is necessary for their practical applications [2]. Herein, we demonstrate a scalable synthesis of WSe2 layers of controlled thickness using the Chemical vapor deposition (CVD) technique. We have deposited WO3 and W films on thermally oxidized silicon and sapphire wafers by thermal evaporation and magnetron sputtering respectively. The WO3 deposited substrates were selenized in an atmospheric pressure CVD reactor at high temperature in the presence of Ar/H2 mixture. The WSe2 films synthesized by this process show the characteristic Raman mode at ≈ 250 cm-1, which is indicative of the out-plane vibration of Se atoms. The WSe2 films show robust photoconductivity response (PCR). On the other hand, the WSe2 synthesized from pure tungsten films shows superior surface morphology, PCR and optical response. Further details of the structure, bonding and PCR of these films will be presented at the meeting with a clear objective to establish the advantages and drawbacks of the two selenization processes discussed here. |
Wednesday, March 8, 2023 12:06PM - 12:18PM Author not Attending |
N32.00004: Laser assisted formation of locally defined Cu(In,Ga)Se2 microstructures Setareh Zahedi Azad, Owen.C. Ernst, Torsten Boeck In this work, the local nucleation of Cu(In,Ga)Se2 absorbers at micrometer scale is investigated. The aim is to reduce the consumption of indium and gallium for micro-concentrator Cu(In,Ga)Se2 solar cells. |
Wednesday, March 8, 2023 12:18PM - 12:30PM |
N32.00005: A comprehensive study of valence band structure and work function in DLC and Q-carbon films using Photoelectron Spectroscopies Saif Al Arafin Taqy, Pallab Kumar Sarkar, Subrata Karmakar, Ariful Haque Diamond-like carbon (DLC) and quenched carbon (Q-carbon) are two types of amorphous carbon whose properties depend on the sp2-sp3 carbon content. Due to the suitability and potential of these materials in electronic applications and device fabrication, it is important to analyze the effects of the composition on the work function and valence band structure of these thin films. In this study, DLC films having different sp2-sp3 ratios are deposited using pulsed laser deposition (PLD), and Q-carbon is fabricated through subsequent pulsed laser annealing (PLA) of the DLC films. X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS) are utilized to investigate the chemical composition, valence band, and work function of nitrogen-doped and undoped DLC and Q-carbon films. The results indicate that the valence band structure strongly depends on both the nitrogen partial pressure and the ratio of sp2-sp3 carbon. The C 1s peak study indicates a significant shift to higher binding energy with doping while the D-parameter of the C KLL peak provides an extensive understanding of the newly discovered Q-carbon structure. The results obtained from this study will provide a roadmap to develop a comprehensive understanding of the electronic band structures and workfunctions of amorphous carbon films, especially Q-carbon, which holds great promise for different electronic applications, i.e. electron field emission devices, superconductivity, sensing devices, etc. |
Wednesday, March 8, 2023 12:30PM - 12:42PM |
N32.00006: Nb and Re substitutional doping in MoSe2 monolayer: shallow dopants, defect creation and heterointerfaces Junqiu Zhang, Yipu XIA, Zhoubin Yu, Mengfei Yuan, Xingyu Yue, Yuanjun Jin, Yue Feng, Bin Li, Bo Wang, Wingkin Ho, Chang Liu, Hu Xu, Chuanhong Jin, Maohai Xie Intentional doping offers an effective way to manipulate the physical properties and functionalities of two-dimensional materials. Charge transfer by gating, surface modifications and substitutional doping are three primary doping strategies. Among them, the substitutional doping directly modifies the sample structure and thus produces stable doping effect. |
Wednesday, March 8, 2023 12:42PM - 12:54PM |
N32.00007: Two-Dimensional Silica Bilayers on Ru(0001): Structure and Substrate Registry Kristen Burson, Edmar A Soares, Joachim Paier, Leonard Gura, Catherine N Ryczek, Zechao Yang, Fernando Stavale, Markus Heyde, H J Freund Early studies on the growth and structure of silica bilayers introduced a new two-dimensional material to the toolbox. Building on those studies, substrate supported silica bilayers were recently used as a model system for confined space reactions.[1] The observed reactions were best explained by assuming lateral and vertical movement of the bilayer relative to the substrate due to changes in the interfacial oxygen concentration during the reaction. Motivated by these observations, we sought to experimentally determine the structure of the silica bilayer, and, in particular, the distance between the film and the substrate, as well as its registry with respect to the substrate. Here present a low energy electron diffraction (I/V-LEED) study, supported by a detailed set of density functional theory (DFT) calculations. We conclude that a high-quality structure determination is only possible if several structural motives are taken into account by superimposing bilayer structures with varying registry to the oxygen covered substrate. |
Wednesday, March 8, 2023 12:54PM - 1:06PM |
N32.00008: Determining the Atomic Structure of Sub-Micron Amorphous Thin Films Kiran Prasai, Riccardo Bassiri, Hai-Ping Cheng, Martin M Fejer Amorphous thin films, with thickness in the range of 0.1 to 1 μm, are of interest for use in optical, electronic or sensing devices. The design and optimization choices of such devices are often guided from the knowledge of atomic structure of the amorphous films. Determining the atomic structure of sub-micron thick amorphous films can be difficult. We discuss some of the challenges associated with determining the atomic structure and recommend some methods for building atomic structure models under availability of x-ray or electron scattering data. A focus of the discussion will be on how low-z atomic correlations can be correctly captured in computer models when the scattering data are heavily weighted towards high-z correlations. |
Wednesday, March 8, 2023 1:06PM - 1:18PM |
N32.00009: Patterning of metal traces and contact pads over an array of tip-well-trench structures for graphene vibration-based applications. Tamzeed Bani Amin, Ferdinand Harerimana, Paul M Thibado Freestanding graphene is a promising candidate for harvesting energy from vibration forces as small as a pico-newton. Our research consists of 4 steps, which are, putting crosshairs on silicon wafers, patterning of the tip, well and trench structures, patterning of metal traces and contact pads, and the transfer of graphene over the wafer to act as a variable capacitor. This study will focus on step 3, following the patterning of the well & trenches and the formation of tips from the use of buffered oxide etchant (BOE). We spin coat the wafer with polymethyl methacrylate (PMMA) and bake it at 180o for 5 minutes. Afterward, an electron beam lithography (EBL) device is used to pattern the position and size of metal traces and contact pads. These are precisely set up in the trenches using the crosshair marks. The metal contact pad connects to the tip, while the other to graphene and ends in a horseshoe-like design. This horseshoe has a length of 14um on the sides and 20um at the back with a width of 4um and at a distance of 3.5um from each part of the tip. The pattern is designed to ensure that the transferred graphene only makes electrical contact with the metal contact pad and not with the tip. It is then developed using methyl isobutyl ketone (MIBK) and 5nm of chromium and 100nm of gold are deposited on the chip. The tip deposited with gold acts as one-half of the variable capacitor. Then we use remover PG for liftoff, clean the chip, and blow dry it with nitrogen. We use an optical microscope to obtain the outlook of the patterning over the whole wafer. Then an atomic force microscope (AFM) is used to determine the thickness of the metal layer and the distance between the tip and top of the wafer. |
Wednesday, March 8, 2023 1:18PM - 1:30PM |
N32.00010: Raman Characterization of SiC(0001) with Hydrogen Passivated Surface Lance He Silicon carbide (SiC) is a widely used substrate for thin film deposition and semiconductor applications. For many such uses, the SiC surface must be atomically flat and cleaned by high-temperature annealing, then passivated with hydrogen atoms. To achieve hydrogen passivation, we constructed a custom hydrogen chamber capable of ultra-high vacuum (UHV) and 1600°C heating concurrent with high-purity hydrogen flow. We used atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) to confirm the topography and chemical composition of the substrate surface. Because hydrogen is too small to be imaged by AFM, and too light to be seen by XPS, we demonstrated that Raman spectroscopy can identify the Si-H bonds of the SiC(0001) surface. We report on the optimization of hydrogen annealing conditions to achieve atomically flat SiC with hydrogen passivation. |
Wednesday, March 8, 2023 1:30PM - 1:42PM |
N32.00011: De-wrinkling the 2D black phosphorus using electron beam irradiation MANPREET KAUR Large area 2D nanomaterials are susceptible to formation of surface corrugations during synthesis, transfer and handling of samples and their physicochemical properties are extraordinarily affected by the formation of surface corrugations. Even though several strategies have been devised by researchers for smoothing the 2D flakes, the issue is far from resolved. Here, we report the straightening of Black Phosphorus (BP) flakes using electron beam irradiation that enables the removal of ripples, disclination and line defects from lattice. The crystallinity and buckling of flake is controlled by varying the electron fluence rate and irradiation time in a high resolution transmission electron microscopy set-up. Experimental results show that the optimal electron beam exposure (20 to 30 minutes of exposure at fluence rate = 1.02 ×1029 m-2 s-1) de-stresses/ relaxes the lattice and the maximum ordering of lattice planes is achieved; beyond which, the stress in lattice rises again and lattice planes start buckling. Thus, straightening the 2D flakes using electron beam ensures removal of surface corrugations with nanoscale precision and allows for real-time monitoring of the process. |
Wednesday, March 8, 2023 1:42PM - 1:54PM |
N32.00012: Vapor Phase η6 Surface Functionalization of Hexagonal Boron Nitride nanosheets Kartikey Sharma, Vikas Berry, Songwei Che Hexagonal boron nitride (h-BN) exhibits high tensile strength (~100 GPa), wide bandgap (~6 eV), high thermal conductivity (227-280 W.m-1.K-1), excellent insulation and chemical stability. Functionalizing these nanostructures for expanding their application in electronics (such as depositing conductive film atop hBN flakes can provide a unique metal/single-atom-layer junctions), catalysis, and biomedical sensors require further investigation. Here, we show a novel organometallic covalent functionalization of h-BN with chromium carbonyl without distorting its lattice planarity or cleaving the B-N bonds. A chemical vapor deposition technique was employed for the vapor phase η6 functionalization of h-BN for a clean and efficient process. Spectroscopic evidence shows that this unique functionalization route retains the lattice connectivity between the B- and N- centers, while the metal binds to each member of the hBN ring. The computational analysis demonstrates that the surface reaction occurs spontaneously with ?G = -35.50 kcal/mol. Further, we also show that the carbonyl group on the metal center can be employed to attach silver nanoparticles forming a conductive layer atop hBN. This non-destructive and chemically active functionalization of hBN can enable the incorporation of hBN's structural and thermal properties into several applications. |
Wednesday, March 8, 2023 1:54PM - 2:06PM Author not Attending |
N32.00013: Controlled Switching of Stationary Surface Silicon Dimers Furkan M Altincicek, Christopher Leon, Taras Chutora, Max Yuan, Jeremiah Croshaw, Roshan Achal, Lucian Livadaru, Jason Pitters, Robert A Wolkow Dimer pairs of the unterminated Si(100)-2x1 surface undergo an energy lowering lattice distortion. In this ground state, the Si dimer buckles, causing one atom to lower while the other is raised. This buckling phenomenon disappears when the surface is terminated with a hydrogen monolayer. Selectively removing pairs of H atoms that belong to Si dimers causes the dimer buckling to return. STM imaging of dimer structures at high biases allow us to observe them in a dynamic regime where dimers rapidly switch between buckled configurations. At very low biases, however, we enter the static regime where the buckling of dimers remains fixed. Furthermore, STM pulses on dimer structures enables for the controlled flipping of the buckled dimer orientation. We explore the underlying physics behind this and their possible applications. |
Wednesday, March 8, 2023 2:06PM - 2:18PM |
N32.00014: Interfacial engineering ferroelectricity in two-dimensional CuInP2S6 Du Li, Kun Wang, Jia Wang, Yifei Hao, Hailey Anderson, Xia Hong, Li Yang CuInP2S6 (CIPS), a layered van der Waals material, has been regarded as a promising candidate for realizing two-dimensional (2D) ferroelectrics. However, its high mobility of Cu ions makes it challenging to achieve precise domain control and obtain high Curie temperature (TC). In this collaborative work, we find that placing CIPS on PbTiO3 (PTO) substrate is helpful to overcome these challenges. Employing first-principles density functional theory calculation of monolayer CIPS on PTO substrate, we find that accumulated charges on the PTO surface provide an intrinsic field that tilts the free energy well of CIPS and help promote the polar alignment in CIPS. Meanwhile, the PTO substrate modulates the atomic structure of CIPS and increases the energy barrier for switching polarization. As a result, the Monte Carlo (MC) simulation shows that the Curie temperature is significantly increased from 400 K to 650 K. These theoretical calculations agree with experimental measurements. This study points to a new strategy to engineer the nanoscale domain structure and piezoelectricity of the 2D ferroelectrics for technological implementation, such as nonvolatile memories, nanoelectronics and optoelectronics. |
Wednesday, March 8, 2023 2:18PM - 2:30PM |
N32.00015: Influences of native defect on bulk and surface electronic properties of SnS: an experimental and first-principles study Rohit Dahule, Chetan C Singh, Emila Panda, Kenta Hongo, Ryo Maezono The semiconductor SnS is a promising candidate for a low-cost, earth-abundant, photovoltaic absorbing layer for thin film solar cells. An understanding of bulk and surface electrical properties would aid in comprehending transport behavior and, therefore, would be extremely useful for the fabrication of high-performance devices. In this context, anomalies in bulk and surface electrical properties of SnS were investigated using a combination of experiment and theory. In experiments, RF magnetron sputtering was used to fabricate single-phase polycrystalline SnS films, which were investigated for their detailed microstructure, optical properties, and electrical properties of bulk and surface SnS. First-principles density functional theory (DFT) computations of the bulk and surface SnS were employed to evaluate the electronic structures and analyze the observed anomalies in their bulk and surface electrical properties. The experimentally observed semi-metallic behavior utilizing scanning tunnelling spectroscopy was further addressed by DFT calculations on various native surface defects including vacancy, interstitials, and antisites. |
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