A5030666876- Carbon Nanotubes in Composites
- Graphene research and applications
- Electronic and Structural Properties of Oxides
- Semiconductor materials and devices
- Diamond and Carbon-based Materials Research
- Magnetic and transport properties of perovskites and related materials
- 2D Materials and Applications
- Thermal properties of materials
- ZnO doping and properties
- Advanced Condensed Matter Physics
- Silicon Nanostructures and Photoluminescence
- Thin-Film Transistor Technologies
- Topological Materials and Phenomena
- Fullerene Chemistry and Applications
- Electron and X-Ray Spectroscopy Techniques
- Chemical and Physical Properties of Materials
- Copper-based nanomaterials and applications
- Ion-surface interactions and analysis
- Nanowire Synthesis and Applications
- Chalcogenide Semiconductor Thin Films
- Quantum Dots Synthesis And Properties
- Advanced Photocatalysis Techniques
- Advanced Electron Microscopy Techniques and Applications
- Transition Metal Oxide Nanomaterials
- Catalytic Processes in Materials Science
Oak Ridge National Laboratory
2016-2025
Center for Nanophase Materials Sciences
2008-2020
Oak Ridge Associated Universities
2020
Argonne National Laboratory
2019
Naval Research Laboratory Materials Science and Technology Division
2010-2014
University of Tennessee at Knoxville
1991-2012
Materials Science & Engineering
2010
Knoxville College
1994-2010
Fritz Haber Institute of the Max Planck Society
2009
Rice University
2008
We show that graphene chemical vapor deposition growth on copper foil using methane as a carbon source is strongly affected by hydrogen, which appears to serve dual role: an activator of the surface bound necessary for monolayer and etching reagent controls size morphology domains. The resulting rate fixed partial pressure has maximum at hydrogen pressures 200-400 times methane. domains, well number layers, change with from irregularly shaped incomplete bilayers well-defined perfect single...
We describe plasmonic interactions in suspended gold bowtie nanoantenna leading to strong electromagnetic field (E) enhancements. Surface-enhanced Raman scattering (SERS) was used demonstrate the performance of nanoantenna. In addition well-known gap size dependence, up 2 orders magnitude additional enhancement is observed with elevated bowties. The overall behavior described by a SERS factor exceeding 10(11) along an anomalously weak power law dependence E on range from 8 50 nm that...
The results of studies patterned growth vertically aligned carbon nanofibers (VACNFs) prepared by plasma-enhanced chemical vapor deposition are reported. Nickel (Ni) dots various diameters and Ni lines with variable widths shapes were fabricated using electron beam lithography evaporation, served for catalytic VACNFs whose structure was determined high resolution transmission microscopy. It is found that upon plasma pre-etching heating up to 600–700 °C, thin films break into droplets which...
``Noncompensated $n\mathrm{\text{\ensuremath{-}}}p$ codoping'' is established as an enabling concept for enhancing the visible-light photoactivity of ${\mathrm{TiO}}_{2}$ by narrowing its band gap. The embodies two crucial ingredients: electrostatic attraction within dopant pair enhances both thermodynamic and kinetic solubilities, noncompensated nature ensures creation tunable intermediate bands that effectively narrow demonstrated using first-principles calculations, validated direct...
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...
The correlation between prepatterned catalyst film thickness and carbon nanotube (CNT) growth by selective area chemical vapor deposition (CVD) was studied using Fe Ni as catalyst. To eliminate sample-to-sample variations create a environment in which the is sole variable, samples with continuously changing from 0 to 60 nm were fabricated electron-gun evaporation. Using thermal CVD CNTs preferentially grow dense mat on thin regions of film. Moreover, beyond certain critical no tubes...
Pulsed-laser deposition (PLD) is one of the most promising techniques for formation complex-oxide heterostructures, superlattices, and well controlled interfaces. The first part this paper presents a review several useful modifications process, including methods inspired by combinatorial approaches. We then discuss detailed growth kinetics results, which illustrate that 'true' layer-by-layer (LBL) can only be approached, not fully met, even though many characterization reveal interfaces with...
In this paper we discuss the effect of background pressure and synthesis temperature on graphene crystal sizes in chemical vapor deposition (CVD) copper catalyst. For first time, quantitatively demonstrate a fundamental role provide activation energy for nucleation atmospheric CVD (9 eV), which is substantially higher than low (4 eV). We attribute difference to greater importance sublimation CVD, where severe evaporation likely dictates desorption rate active carbon from surface. At...
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...
The ability to manipulate oxygen anion defects rather than metal cations in complex oxides can facilitate creating new functionalities critical for emerging energy and device technologies. However, the difficulty activating at reduced temperatures hinders deliberate control of important defects, vacancies. Here, strontium cobaltite (SrCoOx) is used demonstrate that epitaxial strain a powerful tool manipulating vacancy concentration even under highly oxidizing environments annealing as low...
Defect engineering has been a critical step in controlling the transport characteristics of electronic devices, and ability to create, tune, annihilate defects is essential enable range next-generation devices. Whereas defect formation well-demonstrated three-dimensional semiconductors, similar exploration heterogeneity atomically thin two-dimensional semiconductors link between their atomic structures, defects, properties not yet extensively studied. Here, we demonstrate growth MoSe2-x...
Abstract Strong Coulomb repulsion and spin–orbit coupling are known to give rise exotic physical phenomena in transition metal oxides. Initial attempts investigate systems, where both of these fundamental interactions comparably strong, such as 3 d 5 complex oxide superlattices, have revealed properties that only slightly differ from the bulk ones constituent materials. Here we observe interfacial between antiferromagnetic insulator SrMnO paramagnetic SrIrO is enormously yielding an...
Synthesis of functional metal chalcogenide (GaSe) nanosheet networks by stoichiometric transfer laser‐vaporized material from bulk GaSe targets is presented. Uniform coverage interconnected, crystalline, and photoresponsive nanosheets in both in‐plane out‐of‐plane orientations are achieved under different ablation conditions. The propagation the characterized situ ICCD‐imaging. High (1 Torr) Ar background gas pressure found to be crucial for growth networks. Individual 1–3 layer triangular...
Abstract In the transition from graphene to graphite, addition of each individual layer modifies electronic structure and produces a different material with unique properties. Controlled growth few-layer is therefore fundamental interest will provide access materials engineered structure. Here we combine isothermal etching experiments in situ scanning electron microscopy reveal stacking sequence interlayer coupling strength graphene. The observed layer-dependent rates relative...
In this work we explore the kinetics of single-crystal graphene growth as a function nucleation density. addition to standard methods for suppressing by pretreatment Cu foils using oxidation, annealing, and reduction prior growth, introduce new method that further reduces density interacting directly with process at onset nucleation. The successive application these two results in roughly 3 orders magnitude We use kinetic model show vanishingly low densities carbon incorporation occurs...
Energetic processing methods such as hyperthermal implantation hold special promise to achieve the precision synthesis of metastable two-dimensional (2D) materials Janus monolayers; however, they require precise control. Here, we report a feedback approach reveal and control transformation pathways in by pulsed laser deposition (PLD) apply it investigate kinetics monolayer WS2 crystals into WSSe WSe2 Se clusters with different maximum kinetic energies (<42 eV/Se-atom) generated ablation...
Abstract We have demonstrated near‐edge X‐ray absorption fine structure (NEXAFS) spectroscopy as a particularly useful and effective technique for simultaneously probing the surface chemistry, molecular orientation, degree of order, electronic carbon nanotubes related nanomaterials. Specifically, we employ NEXAFS in study single‐walled nanotube multi‐walled powders, films, arrays, well boron nitride nanotubes. focused on advantages an exciting, complementary tool to conventional microscopy...
The main obstacle to widespread application of single-wall carbon nanotubes is the lack reproducible synthesis methods pure material. We describe a new growth method for that uses molecular beams precursor gases impinge on heated substrate coated with catalyst thin film. In this environment gas and temperature are decoupled nanotube occurs by surface reactions without contribution from homogeneous gas-phase reactions. This controlled reaction revealed SWCNT complex multicomponent in which...
Highly ordered gold nanopillar arrays were fabricated using anodized aluminum oxide (AAO) templates. Nanopillars with a dimension of 110 ± 15 nm in vertical height and 75 10 base diameter formed density 150 μm-2. The give reproducible surface-enhanced Raman scattering (SERS) at detection limit 10-8 M thionine as probing molecules. enhancement by the Au was comparable or better than that dispersed nanoparticle SERS substrates. This work demonstrates new technique for producing highly...
2D crystals of WS 2 stretch as they grow over curved surfaces, allowing strain engineering their optoelectronic properties.
The field of spintronics has seen a surge interest in altermagnetism due to novel predictions and many possible applications. MnTe is leading altermagnetic candidate that significant across its layered antiferromagnetic structure, high Neel temperature (TN ~ 310 K) semiconducting properties. We present results on molecular beam epitaxy (MBE) grown MnTe/InP(111) films. Here, it found the electronic magnetic properties are driven by natural stoichiometry MnTe. Electronic transport situ...