A5039999587- 2D Materials and Applications
- Carbon Nanotubes in Composites
- Diamond and Carbon-based Materials Research
- Graphene research and applications
- Perovskite Materials and Applications
- Laser-induced spectroscopy and plasma
- Chalcogenide Semiconductor Thin Films
- MXene and MAX Phase Materials
- Laser-Ablation Synthesis of Nanoparticles
- Fullerene Chemistry and Applications
- Quantum Dots Synthesis And Properties
- Laser Design and Applications
- Nanowire Synthesis and Applications
- Spectroscopy and Laser Applications
- Laser Material Processing Techniques
- Electronic and Structural Properties of Oxides
- Ion-surface interactions and analysis
- Mechanical and Optical Resonators
- Advanced Photocatalysis Techniques
- Thermal properties of materials
- Magnetic and transport properties of perovskites and related materials
- Ferroelectric and Piezoelectric Materials
- Advanced Chemical Physics Studies
- Chemical and Physical Properties of Materials
- Gas Dynamics and Kinetic Theory
Oak Ridge National Laboratory
2016-2025
Center for Nanophase Materials Sciences
2010-2019
Oak Ridge Associated Universities
2015-2017
University of Tennessee at Knoxville
1999-2012
Knoxville College
2010-2011
Georgia Institute of Technology
2010
Fritz Haber Institute of the Max Planck Society
2009
Michigan Technological University
2005
Florida Agricultural and Mechanical University
2004
Materials Science & Engineering
2001
Most studied two-dimensional (2D) materials exhibit isotropic behavior due to high lattice symmetry; however, lower-symmetry 2D such as phosphorene and other elemental very interesting anisotropic properties. In this work, we report the atomic structure, electronic properties, vibrational modes of few-layered PdSe2 exfoliated from bulk crystals, a pentagonal layered noble transition metal dichalcogenide with puckered morphology that is air-stable. Micro-absorption optical spectroscopy...
Pulsed laser deposition (PLD) is a conceptually and experimentally simple yet highly versatile tool for thin-film multilayer research. Its advantages the film growth of oxides other chemically complex materials include stoichiometric transfer, from an energetic beam, reactive deposition, inherent simplicity multilayered structures. With use PLD, artificially layered metastable phases have been created their properties varied by control layer thicknesses. In situ monitoring techniques...
Strong nonlinear light-matter interaction is highly sought-after for a variety of applications including lasing and all-optical light modulation. Recently, resonant plasmonic structures have been considered promising candidates enhancing optical processes due to their ability greatly enhance the near-field; however, small mode volumes prevent inherently large susceptibility metal from being efficiently exploited. Here, we present an alternative approach that utilizes Fano-resonant silicon...
Orthorhombic black phosphorus (BP) and other layered materials, such as gallium telluride (GaTe) tin selenide (SnSe), stand out among two-dimensional (2D) materials owing to their anisotropic in-plane structure. This anisotropy adds a new dimension the properties of 2D stimulates development angle-resolved photonics electronics. However, understanding effect has remained unsatisfactory date, shown by number inconsistencies in recent literature. We use absorption Raman spectroscopies...
van der Waals (vdW) heterostructures are promising building blocks for future ultrathin electronics. Fabricating vdW by stamping monolayers at arbitrary angles provides an additional range of flexibility to tailor the resulting properties than could be expected direct growth. Here, we report fabrication and comprehensive characterizations WSe2/WS2 bilayer heterojunctions with various twist that were synthesized artificially stacking WS2 WSe2 grown chemical vapor deposition. After annealing...
Synthesized two-dimensional GaSe/MoSe 2 misfit heterostructures form p - n junctions with a gate-tunable photovoltaic response.
Solids with ultralow thermal conductivity are of great interest as barrier coatings for insulation or thermoelectrics energy conversion. However, the theoretical limits lattice (κ) unclear. In typical crystals a phonon picture is valid, whereas lowest κ values occur in highly disordered materials where this fails and heat supposedly carried by random walk among uncorrelated oscillators. Here we identify simple crystal, Tl3VSe4, calculated [0.16 Watts per meter-Kelvin (W/m-K)] one-half that...
Abstract Compared with their bulk counterparts, atomically thin two-dimensional (2D) crystals exhibit new physical properties and have the potential to enable next-generation electronic optoelectronic devices. However, controlled synthesis of large uniform monolayer multi-layer 2D is still challenging. Here, we report GaSe on SiO 2 /Si substrates using a vapor phase deposition method. For first time, uniform, (up ~60 μm in lateral size), single-crystalline, triangular were obtained structure...
Two-dimensional ferromagnetic monolayer and few-layer CrSiTe<sub>3</sub>crystals are prepared for the first time from bulk crystals by a simple mechanical exfoliation method.
Imperfections in organometal halide perovskite films such as grain boundaries (GBs), defects, and traps detrimentally cause significant nonradiative recombination energy loss decreased power conversion efficiency (PCE) solar cells. Here, a simple layer-by-layer fabrication process based on air exposure followed by thermal annealing is reported to grow with large, single-crystal grains vertically oriented GBs. The hole-transport medium Spiro-OMeTAD then infiltrated into the GBs form aligned...
Abstract The formation of semiconductor heterojunctions and their high-density integration are foundations modern electronics optoelectronics. To enable two-dimensional crystalline semiconductors as building blocks in next-generation electronics, developing methods to deterministically form lateral is crucial. Here we demonstrate an approach for the lithographically patterned arrays semiconducting within a single crystal. Electron beam lithography used pattern MoSe 2 monolayer crystals with...
Layered gallium telluride (GaTe) has attracted much attention recently, due to its extremely high photoresponsivity, short response time, and promising thermoelectric performance. Different from most commonly studied two-dimensional (2D) materials, GaTe in-plane anisotropy a low symmetry with the C2h3 space group. Investigating optical anisotropy, including electron–photon electron–phonon interactions of is essential in realizing applications optoelectronics thermoelectrics. In this work,...
van der Waals homo- and heterostructures assembled by stamping monolayers together present optoelectronic properties suitable for diverse applications. Understanding the details of interlayer stacking resulting coupling is crucial tuning these properties. We investigated low-frequency shear breathing Raman modes (<50 cm(-1)) in twisted bilayer MoS2 spectroscopy first-principles modeling. Twisting significantly alters coupling, leading to notable frequency intensity changes modes. The...
Atomically thin two-dimensional (2D) materials face significant energy barriers for synthesis and processing into functional metastable phases such as Janus structures. Here, the controllable implantation of hyperthermal species from pulsed laser deposition (PLD) plasmas is introduced a top-down method to compositionally engineer 2D monolayers. The kinetic energies Se clusters impinging on suspended monolayer WS2 crystals were controlled in <10 eV/atom range with situ plasma diagnostics...
As a new two-dimensional layered material, black phosphorus (BP) is very promising material for nanoelectronics and optoelectronics. We use Raman spectroscopy first-principles theory to characterize understand the low-frequency (LF) interlayer breathing modes (<100 cm(-1)) in few-layer BP first time. Using laser polarization dependence study group analysis, are assigned Ag symmetry. Compared high-frequency (HF) modes, LF considerably more sensitive coupling and, thus, their frequencies show...
The remarkable properties of black TiO2 are due to its disordered surface shell surrounding a crystalline core. However, the chemical composition and atomic electronic structure relationship core remain poorly understood. Using advanced transmission electron microscopy methods, we show that outermost layer nanoparticles consists Ti2O3 shell. measurements transition region connects perfect rutile consisting first four five monolayers defective rutile, containing clearly visible Ti...
We report here details of steady-state and time-resolved spectroscopy excitonic dynamics for Janus transition metal dichalcogenide monolayers, including MoSSe WSSe, which were synthesized by low-energy implantation Se into disulfides. Absorbance photoluminescence spectroscopic measurements determined the room-temperature exciton resonances WSSe monolayers. Transient absorption revealed that excitons in structures form faster than those pristine dichalcogenides about 30% due to their enhanced...
The dynamics of nanoparticle formation, transport, and deposition by pulsed laser ablation c-Si into 1–10 Torr He Ar gases are revealed imaging laser-induced photoluminescence Rayleigh-scattered light from gas-suspended nm SiOx particles. Two sets dynamic phenomena presented for times up to 15 s after KrF-laser ablation. Ablation Si heavier results in a uniform, stationary plume nanoparticles, while lighter turbulent ring particles which propagates forward at 10 m/s. Nanoparticles...
Co3O4 exhibits intriguing physical, chemical and catalytic properties has demonstrated great potential for next-generation renewable energy applications. These interesting promising applications are underpinned by its electronic structure optical properties, which unfortunately poorly understood the subject of considerable debate over many years. Here, we unveil a consistent structural description synergetic infrared in situ photoemission spectroscopy as well standard density functional...
The dynamics of laser-ablated yttrium plume propagation through background argon have been investigated with fast time- and spatially-resolved plasma diagnostics in order to characterize a general phenomenon believed be important film growth by pulsed laser deposition (PLD). During expansion into low-pressure gases, the ion flux ablation is observed split slow components over limited range distances including those typically utilized for PLD. Optical absorption emission spectroscopy are...
High growth temperatures (>1100 °C), low production yield, and impurities have prevented research progress applications of boron nitride nanotubes (BNNTs) in the past 10 years. Here, we show that BNNTs can be grown on substrates at 600 °C. These are constructed high-order tubular structures used without purification. Tunneling spectroscopy indicates their band gap ranges from 4.4 to 4.9 eV.
This letter reports on fast and highly anisotropic thermal transport through millimeter-tall, vertically aligned carbon nanotube arrays (VANTAs) synthesized by chemical vapor deposition Si substrates. Thermal diffusivity measurements were performed for both longitudinal transverse to the alignment direction, with values as large 2.1±0.2cm2∕s anisotropy ratios 72. Longitudinal conductivities of 15.3±1.8W∕(mK) porous 8±1vol% VANTAs in air 5.5±0.7W∕(mK) epoxy-infiltrated already exceed those...