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 M42: 2D Materials: Advanced Characterization II |
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Sponsoring Units: DMP Chair: Abigail Derrico, Temple University Room: Room 318 |
Wednesday, March 8, 2023 8:00AM - 8:12AM |
M42.00001: Characterizing Strain in Graphene on Cu(100) Substrate with Raman Spectroscopy Tehseen Adel, Jacob Amontree, Xingzhou Yan, Zizwe A Chase, Renee Harton, Charlezetta E Stokes, Thomas A Searles, Katayun Barmak, James C Hone, Angela R Hight Walker Chemical vapor deposition (CVD) grown graphene offers superior carrier mobility and minimal defects compared to mechanically transferred graphene onto Si/SiO2 substrates. Yet the performance of CVD-derived graphene films can vary across an array of wrinkles, folds, and transfer-related contaminations. Raman spectroscopy is a highly useful non-contact and non-destructive means of characterizing graphene owing to the nature of its band structure which provides strong and unique features stemming from physical effects such as resonant processes and strong electron-phonon coupling. Here, we present a detailed Raman analysis of uniquely grown defect-free graphene on Cu(100) substrate via low-pressure CVD. We observe the blue-shift and narrowing lineshapes of the 2D and G bands, as well as their intensity ratio indicating the graphene monolayer. Furthermore, a compressive strain and significant coupling of the graphene to the Cu substrate are observed with multiple laser excitations. Additionally, Raman is also used to monitor copper oxide at defect sites. We perform a combined electro-optical measurements in aqueous solutions to estimate the electrical material properties of graphene on Cu(100). The outcomes of this study will be used to establish quantitative Raman-based metrics on strain-doping for documentary standards on Gr/Cu compared to epitaxial Gr and other large-scale growth methods. |
Wednesday, March 8, 2023 8:12AM - 8:24AM |
M42.00002: Resonant Raman signatures of two-dimensional layered materials from first-principles calculations Natalya Sheremetyeva, Michael Lamparski, Vincent Meunier Two-dimensional layered materials (2DMs) continue to attract increased research interest as promising building blocks for novel electronic devices. Their electronic properties can be tuned via varying parameters like the number of layers, the layer-stacking order, or applying tensile strain. With such great tunability, exact property control is a key challenge. Raman spectroscopy is a nondestructive tool that is sensitive to subtle structural and electronic changes. Resonant Raman spectroscopy with varying wavelengths of the excitation laser allows for additional insights into the electronic transitions of the studied system. While straightforward experimentally, theoretical modeling of resonant Raman spectra requires the application and efficient implementation of the third-order time-dependent perturbation theory. Here, we present a Density Functional Theory based study of the resonant Raman spectra of various systems including graphene nanoribbons and transition metal dichalcogenides. We discuss the agreement with experimentally available data and provide pathways to property identification from resonant Raman fingerprints. |
Wednesday, March 8, 2023 8:24AM - 8:36AM |
M42.00003: Investigations of Graphene on SrTiO3 Single-Crystal using Confocal Raman Spectroscopy Sujan Shrestha, Celesta S Chang, Sangho Lee, Matteo Minola, Jeehwan Kim, Ambrose Seo We will present the characterizations of graphene layers placed on SrTiO3 single-crystal substrates using temperature-dependent confocal Raman spectroscopy. This approach successfully resolved distinct Raman modes of graphene that are often untraceable in conventional measurements due to the strong Raman scattering background of SrTiO3. Information on defects and strain states was obtained for a few graphene/SrTiO3 samples that were synthesized by different techniques. This confocal Raman spectroscopic approach can shed light on the investigation of not only this graphene/SrTiO3 system but also various two-dimensional layered materials whose Raman modes interfere with their substrates. |
Wednesday, March 8, 2023 8:36AM - 8:48AM |
M42.00004: Capturing Reaction Kinetics of Atomically Thin Device Materials by High-throughput in-operando SEM Ye Fan, Ryo Mizuta, Jinfeng Yang, Maryam Kazemzadeh-Atoufi, Peter W Voorhees, Stephan Hofmann For the ever increasing family of layered 2D materials many exciting properties and device concepts have been reported, yet the understanding of fundamental mechanisms that can underpin scalable process technology for these materials is lagging far behind. We developed cross-correlative operando probing capability to “unblind” the underlying mechanisms, including open and closed cell approaches for XPS, optical spectroscopy, and scanning and transmission electron microscopy.[1-4]. While the previous focus has been to sample select process conditions, this talk will focus on our efforts to access and fast screen the entirety of the vast, interconnected parameter space. We adapted a SEM to allow operando reaction monitoring for the formation and etch reactions of atomically thin WS2 layers. This allows us to unlock a data-driven approach to understanding the underlying complex kinetics across scales. As a model system we focus on the thermal oxidation of WS2 monolayer crystals. Understanding material oxidation is fundamental to corrosion, heterogeneous material interfacing and integrated processing across a horizon of applications. We discuss statistical approaches and analysis of spatial and time dependent behaviour, connecting to previous literature and highlighting the many opportunities our approach can open. |
Wednesday, March 8, 2023 8:48AM - 9:00AM |
M42.00005: Acoustic Phonons of Chemically Tunable 2D Hexagonal Boron Nitride from Brillouin Spectroscopy Kristie J Koski, Bryan W Reed We use Brillouin light scattering spectroscopy to measure the acoustic phonons of 2D layered hexagonal boron nitride at GHz frequencies. Measurements provide longitudinal and transverse sound velocities, nearly complete elastic stiffnesses, refractive indices, and acoustic attenuations. Further, we chemically intercalate noble metals of Au, Ag, and Cu into the van der Waals gap of layered hBN to achieve chemical tunability of the acoustic phonon properties. This work establishes unique chemical control of acoustic phonons in hBN. |
Wednesday, March 8, 2023 9:00AM - 9:12AM |
M42.00006: Comparing the magnetotransport and Raman response of various intercalants in epitaxial graphene on 6H-SiC(0001) Jimmy C Kotsakidis, Gregory Stephen, Rachael L Myers-Ward, Matthew DeJarld, D. Kurt Gaskill, Aubrey T Hanbicki, Adam L Friedman Intercalation is a common way to modify the electronic properties of graphene. For instance, hydrogen intercalation results in p-type graphene, whereas magnesium intercalated graphene results in highly n-type doped graphene (≈1E14 cm-2) with large bandgap (≈0.36 eV) [1][2]. Epitaxial graphene on 6H-SiC(0001) ('Gr/SiC') consists of the SiC substrate, the carbon rich ‘buffer layer’ which is partially bonded to the SiC surface, and the graphene on top. Over the past decade, Gr/SiC has been intercalated with numerous elements. Typically, the intercalant is confined to the region between the buffer layer and the SiC surface, and is able to release the buffer layer from the SiC to form another layer of graphene. |
Wednesday, March 8, 2023 9:12AM - 9:24AM |
M42.00007: Direct observation of motion of interstitial atoms at van der Waals bonded interfaces Joachim Dahl Thomsen, Yaxian Wang, Frances M Ross, Prineha Narang Diffusion processes in two-dimensional materials govern phenomena such as phase transformations, growth by chemical vapor depositions and doping by substitutional and interstitial atoms. Furthermore, intercalation of foreign atomic species into van der Waals (vdW) bonded materials has been studied for tuning of physical properties (electronic, optoelectronic, magnetic), and for uses in energy and battery applications. Here, we directly image the diffusion of W atoms using high-angle annular scanning transmission electron microscopy inside hexagonal boron nitride (BN)/WSe2/BN vdW heterostructures and BN/WSe2 heterostructures. Using thin (~2 nm thick) BN crystals consisting of light B and N atoms allows us to image the heavier W atoms in these heterostructures and allows us to study the electron beam-induced motion of W atoms at three interfaces: BN/vacuum, BN/BN, and WSe2/BN. In combination with density functional theory calculations, we find that the motion is governed by interfacial defect formation. This leads to similar diffusion coefficients at the BN/vacuum and BN/BN interface. Furthermore, we find that the diffusion coefficient is twice as large at the WSe2/BN interface compared to the BN/BN and BN/vacuum interfaces, and we attribute this to differences in defect formation rates or different interlayer spacings. This work highlights the importance of interfacial defects for diffusion properties of atoms at van der Waals interfaces. |
Wednesday, March 8, 2023 9:24AM - 9:36AM |
M42.00008: Density Functional Theory Examination of Electronic and Optical properties of Two-Dimensional Transition Metal Dichalcogenides Functionalized with Forever Chemicals Nathaniel R Bunker, Manuel Smeu Polyfluoroalkyl substances (PFAS), also known as “forever chemicals,” are a class of manufactured chemicals that pose long-term health risks to those exposed. In processes such as battery recycling, where PFAS are commonly released, detection of PFAS is crucial and made possible through portable surface-enhanced Raman spectroscopy (SERS), so long as a proper substrate is chosen. Functionalized two-dimensional (2D) transition metal dichalcogenides (TMDs) are a fast-emerging SERS substrate candidate. We use density functional theory (DFT) to evaluate substrate fitness via the electronic, and adsorptive properties of 2D TMDs functionalized with single Au atoms when laden with PFAS. From calculations of finite difference method phonon dispersions, Born-effective charge tensors, and time-dependent DFT, we simulate both off-resonance and resonance Raman spectra to compare optical properties of MoS2 and WS2 monolayer substrates to the more typical substrate choices of graphene and Au-functionalized silicon. |
Wednesday, March 8, 2023 9:36AM - 9:48AM |
M42.00009: Spectroscopy and Molecular Dynamics Simulation of Graphene Nanoplatelets for Sensitive Gas Sensing Prabhakar Misra, Olasunbo Farinre, Reiley Dorrian, Hawazin Alghamdi, Albert F Rigosi Graphene Nanoplatelets (GnPs) hold promise of being effective gas sensors because of their high surface-to-volume ratio, lightweight and superior conductivity. Pristine and GnPs specifically functionalized with carboxyl, ammonia, nitrogen, oxygen, fluorocarbon and oxygen have been characterized using a variety of spectroscopic techniques, including Raman, FT-IR and X-ray diffraction (XRD), along with Molecular Dynamics simulation and COMSOL Multiphysics modeling. XRD measurements show smaller crystallite sizes for carboxyl-functionalized GnPs as compared to pristine, which has been confirmed using Scanning Electron Microscopy. Modeling and simulations showed that the resistance of a GnP-based gas sensor decreased on exposure to nitrogen dioxide, whereas an opposite trend and enhanced sensitivity was observed for carbon monoxide exposure. |
Wednesday, March 8, 2023 9:48AM - 10:00AM Author not Attending |
M42.00010: In situ Raman spectroscopy provides insights into the crystallization kinetics of 2D covalent organic frameworks Richard G Nile Covalent organic frameworks (COFs) are porous, crystalline materials built from organic aromatic subunits covalently bonded by reticular chemistry into two or three-dimensional networks. Like zeolites and metal organic frameworks (MOFs), COFs possess ordered structures with high surface areas and tunable pore sizes. These properties can be leveraged to design high-performance materials with applications including nanofiltration, gas separation, drug delivery, and catalysis. The implementation of 2D COF films as molecular sieves for nanofiltration, as an example, requires a keen understanding of the material’s crystallinity and subsequent pore structure. Raman spectroscopy has shown great sensitivity to the crystallinity of 2D COFs and has been established herein as a tool to probe the kinetics of crystallization during solvothermal synthesis. Raman spectroscopy allows for in situ monitoring of crystallinity with enhanced sensitivity and spatial resolution compared to methods based on diffraction. This technique can be extended to study the crystallization kinetics for other useful COF morphologies including thin films, mixed-matrix membranes, and nanoparticles. The insights gained from Raman spectroscopy may fill gaps in the understanding of fundamental phenomena including diffusion, reaction kinetics, and solvent interactions which govern the formation and crystallization of COFs. |
Wednesday, March 8, 2023 10:00AM - 10:12AM |
M42.00011: X-ray absorption spectra of first-row transition metal metalloporphenes Hope Whitelock, Bryan S Berggren, Jared Bozzone, Thomas F Magnera, Josef Michl, Daniel S Dessau Two-dimensional organic materials are an exciting avenue for atomically precise optoelectronics and energy efficient nanoelectronics. Most are not easily patterned or tuned; however, Porphene, C20N4H2 is easily polymerized from porphyrin [(C20N4H2)4] on aqueous surfaces and is convertible into M-porphene [(C20N4H2M)4] ,by insertion of M+ ions (M is a metal), making it a promising, highly tunable analog of graphene. We show the first electronic structure characterization studies of this family of 2D materials using polarization-dependent XAS. |
Wednesday, March 8, 2023 10:12AM - 10:24AM |
M42.00012: Electronic Decoupling of Monolayer MoSe2 from Au(111) Substrate by Selenium Intercalation Guan-Hao Chen, Li-Syuan Lu, Pei-Yu Chuang, Cheng-Rong Hsing, Yu-Shiuan Su, Juhn-Jong Lin, Cheng-Maw Cheng, Ching-Ming Wei, Chun-Liang Lin, Wen-Hao Chang Monolayer two-dimensional (2D) materials grown on metal surfaces form a particular set of van der Waals heterostructures with strong interlayer interactions. Unveiling the interaction mechanism may shed light on the issues associated with metal contacts on 2D materials. By using scanning tunneling microscopy/spectroscopy (STM/STS) and angle-resolved photoemission spectroscopy (ARPES), we investigated the electronic structures of MoSe2 epitaxially grown on Au(111) with and without Se intercalation. For MoSe2/Au(111), the STM can visualize the moiré pattern with a periodicity of ~2.3 nm. STS measurements reveal a remnant metallic characteristic with significant conductance in the gap region, indicating a strong 2D-metal interaction. By intercalating Se, a significantly increased gap at the interface, absence of moiré pattern, and recovery of a well-defined semiconducting gap, indicating that the 2D-metal interaction was blocked. Our STS and ARPES results show a significantly increased work function (~0.3 eV) and a remarkably reduced K-Γ energy difference (~0.4 eV) after intercalation. Intriguing, the STS resolved Γ point in the valence band only shows a ~0.1 eV energy modulation within the moiré supercell. Calculations based on density functional theory for the full moiré supercell show reasonable agreements with experimental results. The modification in different electronic bands can be understood from the interactions of different orbital characters of Mo and Se with the Au surface atoms. |
Wednesday, March 8, 2023 10:24AM - 10:36AM |
M42.00013: Graphene transfer over an array of tip-well structures on SiO2/Si substrate for harvesting energy from graphene vibrations Ferdinand Harerimana, Paul M Thibado Due to graphene’s ultimate thinness, its flexibility is 1000 times that of the best silicon nitride cantilevers causing it to move under the influence of even pico-Newton size forces. Due to this property, graphene shows great promise in vibration energy harvesting. In our effort to make a device for harvesting energy from graphene vibrations, a cone-shaped tip has been etched in SiO2/Si substrate. The tip resides inside a 7-microns wide well, which is connected to a trench. Gold is deposited over the tip-well-trench structure to make a two-contact device, where the trench-end forms the tip contact, and the top of the well forms the second contact. In this study we present the procedure for transferring graphene above the tip region in preparation for making a graphene variable capacitor for vibration energy harvesting. Our graphene samples are grown on a nickel film on the top of a silicon wafer. Our first step is to peel off the graphene-nickel layer with a scotch-tape. Next, we etch nickel in iron III chloride solution. Avoiding airdrying which shorts graphene to the tip, we transfer the isolated graphene membrane in deionized water, and then place it above the tip structure region. Finally, we use critical point drying to remove the fluid between graphene and the well. After graphene transfer, we do optical and electrical characterization to confirm graphene suspension. |
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