A5044886416- Surface and Thin Film Phenomena
- 2D Materials and Applications
- Graphene research and applications
- Magnetic properties of thin films
- Electron and X-Ray Spectroscopy Techniques
- X-ray Diffraction in Crystallography
- Crystallization and Solubility Studies
- Crystallography and molecular interactions
- Perovskite Materials and Applications
- Physics of Superconductivity and Magnetism
- Advanced Materials Characterization Techniques
- Chalcogenide Semiconductor Thin Films
- Hydrogen Storage and Materials
- Complex Systems and Time Series Analysis
- MXene and MAX Phase Materials
- Chemical and Physical Properties of Materials
- Topological Materials and Phenomena
- Boron and Carbon Nanomaterials Research
- Advanced Chemical Physics Studies
- Quantum and electron transport phenomena
- Climate variability and models
- Quantum Dots Synthesis And Properties
- Diamond and Carbon-based Materials Research
- Organoboron and organosilicon chemistry
- Advanced Electron Microscopy Techniques and Applications
National Polytechnic School
1969-2023
Oak Ridge National Laboratory
2013-2016
University of Illinois Urbana-Champaign
2003-2005
By adapting the concept of epitaxy to two-dimensional space, we show growth a single-atomic-layer, in-plane heterostructure prototypical material system--graphene and hexagonal boron nitride (h-BN). Monolayer crystalline h-BN grew from fresh edges monolayer graphene with atomic lattice coherence, forming an abrupt one-dimensional interface, or boundary. More important, orientation is solely determined by graphene, forgoing configurations favored supporting copper substrate.
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...
Thickness dependent photon adsorption and phototransistors of multilayer InSe nanosheets have been demonstrated. Phototransistors based on show a broad spectral response ultrahigh photoresponsivity detectiviy.
The tunable optoelectronic properties of stacked two-dimensional (2D) crystal monolayers are determined by their stacking orientation, order, and atomic registry. Atomic-resolution Z-contrast scanning transmission electron microscopy (AR-Z-STEM) energy loss spectroscopy (EELS) can be used to determine the exact registration between different layers, in few-layer 2D stacks; however, fast optical characterization techniques essential for rapid development field. Here, using two- three-layer...
Two-dimensional (2D) van der Waals (vdW) heterostructures are a family of artificially structured materials that promise tunable optoelectronic properties for devices with enhanced functionalities. Compared to transferring, direct epitaxy vdW is ideal clean interlayer interfaces and scalable device fabrication. Here we report the synthesis preferred orientations 2D GaSe atomic layers on graphene (Gr) by epitaxy. crystals found nucleate predominantly random wrinkles or grain boundaries...
Carrier-type modulation is demonstrated in 2D transition metal dichalcogenides as n-type monolayer MoSe2 converted to nondegenerate p-type Mo1−xWxSe2 through isoelectronic doping. Although the alloys are mesoscopically uniform, conduction appears originate from upshift of valenceband maximum toward Fermi level at highly localized "W-rich" regions lattice. As a service our authors and readers, this journal provides supporting information supplied by authors. Such materials peer reviewed may...
Atomic engineering is envisioned to involve selectively inducing the desired dynamics of single atoms and combining these steps for larger-scale assemblies. Here, we focus on first part by surveying single-step graphene dopants, primarily phosphorus, caused electron irradiation both in experiment simulation, develop a theory describing probabilities competing configurational outcomes depending postcollision momentum vector primary knock-on atom. The predicted branching ratio transformations...
Abstract Characterizing and controlling the interlayer orientations stacking orders of two‐dimensional (2D) bilayer crystals van der Waals (vdW) heterostructures is crucial to optimize their electrical optoelectronic properties. The four polymorphs layered gallium selenide (GaSe) that result from different layer stackings provide an ideal platform study configurations in 2D crystals. Through a controllable vapor‐phase deposition method, GaSe were selectively grown two preferred 0° or 60°...
Real-time in situ x-ray studies of continuous Pb deposition on Si(111)-(7x7) at 180 K reveal an unusual growth behavior. A wetting layer forms first to cover the entire surface. Then islands a fairly uniform height about five monolayers form top and grow fill The then switches layer-by-layer mode upon further deposition. This behavior alternating island can be attributed spontaneous quantum phase separation based first-principles calculation system energy.
We have studied the nanoscale structural evolution of Pb films grown at 110 K on a Si(111) substrate as they are annealed to increasingly higher temperatures. Surface x-ray diffraction from synchrotron source is used observe morphology evolve an initial smooth film through various metastable states before reaching state local equilibrium, which point coverage different height structures analyzed and related thickness-dependent surface energy. Rich patterns seen in resulting energy landscape...
Understanding the underlying physical principles that determine internal structure of objects at atomic scale is critical for advancement nanoscale science. We have performed synchrotron x-ray diffraction studies to structural properties smooth Pb films with varying thicknesses 6 18 monolayers deposited on a Si(111) substrate 110 K. observe quasibilayer variations in interlayer spacings consistent charge density oscillations due quantum confinement conduction electrons and surface-interface...
We have used surface x-ray diffraction from a synchrotron source, along with models based upon free-electron gas confined to quantum well, study size effects in the energy of ultrathin Pb films grown on pretreated Si(111) substrates. Films at $110\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ are smooth, but as they annealed near room temperature, their morphology is observed evolving through various metastable states and eventually roughened state local equilibrium. Strong variations stability...
Quantum well states in thin films are commonly described terms of a quasiparticle confined quantum box, but this single-particle picture can fail dramatically near substrate band edge, as shown by angle-resolved photoemission study. Atomically uniform Ag prepared on Ge(111) to facilitate accurate line shape and dispersion relation measurements. A peak is observed split into two peaks the Ge valence edge. The unusual shapes be due many-body interactions quantitatively explained Green's...
Abstract Acetonitrile (CH 3 CN) is the simplest and one of most stable nitriles. Reactions usually occur on C≡N triple bond, while C−H bond very inert can only be activated by a strong base or metal catalyst. It demonstrated that bonds cyano group under high pressure, but at room temperature. The hydrogen atom transfers from CH to CN along CH⋅⋅⋅N which produces an amino initiates polymerization form dimer, 1D chain, 2D nanoribbon with mixed sp 2 bonded carbon. Finally, it transforms into...
We present surface x-ray-diffraction results from Pb films grown on pretreated Si(111) substrates at $110\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. Time-resolved data show that the follow a metastable layer-by-layer growth mode. The resulting film roughness is small, allowing for thickness-dependent study of layer structure and its distortion (strain) relative to bulk. strain arises as result quantum confinement electrons in film, which leads charge distortions similar Friedel oscillations....
We have performed in situ reflectivity measurements using synchrotron radiation of Ag films deposited on Ge(111) over the thickness range 3–12 atomic layers. The at a substrate temperature 110 K are not well ordered, but become ordered upon annealing, as evidenced by substantial changes x-ray data. distribution for each annealed film, deduced from fit to data, is remarkably narrow, with just two or three adjacent discrete thicknesses present, despite large lattice mismatch between and Ge. In...
Growth of metallic Pb islands on Si(111) by vacuum deposition was studied in real time using synchrotron x-ray diffraction. The coarsen and order, maintaining a nearly uniform interisland distance but without angular correlation. resulting structure is akin to two-dimensional liquid. Over wide temperature range, the ordering well correlated with development “magic” island heights caused energy minimization electrons. results demonstrate quantum confinement effects as driving force for...
Abstract Characterizing and controlling the interlayer orientations stacking orders of two‐dimensional (2D) bilayer crystals van der Waals (vdW) heterostructures is crucial to optimize their electrical optoelectronic properties. The four polymorphs layered gallium selenide (GaSe) that result from different layer stackings provide an ideal platform study configurations in 2D crystals. Through a controllable vapor‐phase deposition method, GaSe were selectively grown two preferred 0° or 60°...
Abstract Acetonitrile (CH 3 CN) is the simplest and one of most stable nitriles. Reactions usually occur on C≡N triple bond, while C−H bond very inert can only be activated by a strong base or metal catalyst. It demonstrated that bonds cyano group under high pressure, but at room temperature. The hydrogen atom transfers from CH to CN along CH⋅⋅⋅N which produces an amino initiates polymerization form dimer, 1D chain, 2D nanoribbon with mixed sp 2 bonded carbon. Finally, it transforms into...
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Airborne Wind Energy (AWE) is an emerging technology designed to harness the power of high-altitude winds, offering a solution several limitations conventional wind turbines. AWE based on flying devices (usually gliders or kites) that, tethered ground station and driven by wind, convert its mechanical energy into electrical means generator. Such systems are usually controlled manoeuvering kite so as follow predefined path prescribed optimal control techniques, such model-predictive control....
Extended abstract of a paper presented at Microscopy and Microanalysis 2013 in Indianapolis, Indiana, USA, August 4 – 8, 2013.