A5060909779- Graphene research and applications
- Metal and Thin Film Mechanics
- Diamond and Carbon-based Materials Research
- Surface and Thin Film Phenomena
- Catalytic Processes in Materials Science
- Boron and Carbon Nanomaterials Research
- Physics of Superconductivity and Magnetism
- Electronic and Structural Properties of Oxides
- Advanced Chemical Physics Studies
- Magnetic properties of thin films
- Semiconductor materials and devices
- Quantum and electron transport phenomena
- Advanced Condensed Matter Physics
- Advancements in Solid Oxide Fuel Cells
- nanoparticles nucleation surface interactions
- Electron and X-Ray Spectroscopy Techniques
- Iron oxide chemistry and applications
- Chemical and Physical Properties of Materials
- 2D Materials and Applications
- Advancements in Battery Materials
- Magnetic Properties and Synthesis of Ferrites
- Magnetic and transport properties of perovskites and related materials
- Ion-surface interactions and analysis
- Copper Interconnects and Reliability
- X-ray Diffraction in Crystallography
Sandia National Laboratories California
2008-2018
Sandia National Laboratories
1998-2014
Office of Scientific and Technical Information
1999-2012
National Technical Information Service
2005-2011
Interface (United States)
2011
Surface (Brazil)
2011
Nanomaterials Research (United States)
2011
Lawrence Berkeley National Laboratory
2002-2010
University of Maryland, College Park
2010
Waste Management (United States)
2006
Oxygen Control of Graphene Growth The growth graphene on copper surfaces through the decomposition hydrocarbons such as methane can result in a wide variety crystal domain sizes and morphologies. Hao et al. (p. 720 , published online 24 October; see cover) found that presence surface oxygen could limit number nucleation sites allowed centimeter-scale domains to grow diffusion-limited mechanism. electrical conductivity was comparable exfoliated graphene.
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.
We have observed the growth of monolayer graphene on Cu foils using low-energy electron microscopy. On (100)-textured surface foils, four-lobed, 4-fold-symmetric islands nucleate and grow. The in each four lobes has a different crystallographic alignment with respect to underlying substrate. These "polycrystalline" arise from complex heterogeneous nucleation events at imperfections. shape evolution is well explained by an angularly dependent velocity. Well-ordered forms only above ∼790 °C....
Using low-energy electron microscopy (LEEM), we have measured the local concentration of mobile carbon adatoms from which graphene sheets form on a Ru(0001) surface, and simultaneously, growth rates individual islands. Graphene crystal Ru differs strikingly that two-dimensional metal islands metals: (i) C experience large energy barrier to attaching step edges, so adatom diffusion does not limit growth. (ii) The supersaturations needed for appreciable are comparable those required nucleate...
Graphene forms from a relatively dense, tightly bound C-adatom gas when elemental C is deposited on or segregates to the Ru(0001) surface. Nonlinearity of graphene growth rate with density suggests that proceeds by addition atom clusters edge. The generality this picture has now been studied use low-energy electron microscopy (LEEM) observe formation and Ir(111) surfaces are exposed ethylene. finding velocities nucleation rates Ru have precisely same dependence adatom concentration as for...
The intercalation pathway of lithium iron phosphate (LFP) in the positive electrode a lithium-ion battery was probed at ∼40 nm length scale using oxidation-state-sensitive X-ray microscopy. Combined with morphological observations same exact locations transmission electron microscopy, we quantified local state-of-charge approximately 450 individual LFP particles over nearly entire thickness porous electrode. With charged to 50% 0.5 h, observed that overwhelming majority were either almost...
Ion-assisted pulsed laser deposition has been used to produce films containing ≳85% sp3-bonded cubic boron nitride (c-BN). By ablating from a target of hexagonal (h-BN), BN have deposited on heated (50–800 °C) Si(100) surfaces. The growing are irradiated with ions broad beam ion source operated Ar and N2 gasses. Successful c-BN synthesis confirmed by Fourier transform infrared (FTIR) spectroscopy, high-resolution transmission electron microscopy (TEM), selected-area diffraction, energy-loss...
We use low-energy electron microscopy to investigate how graphene grows on Cu(111). Graphene islands first nucleate at substrate defects such as step bunches and impurities. A considerable fraction of these can be rotationally misaligned with the substrate, generating grain boundaries upon interisland impingement. New rotational are also generated across bunches. Thus, rougher substrates lead higher degrees mosaicity than do flatter substrates. Increasing growth temperature improves...
We use low-energy electron microscopy (LEEM), diffraction (LEED), and scanning tunneling (STM) to study different orientations of single-layer graphene sheets on Ir(111). The most-abundant orientation has previously been characterized in the literature. Using selective-area LEED we find three other variants, which are rotated $14\ifmmode^\circ\else\textdegree\fi{}$, $18.5\ifmmode^\circ\else\textdegree\fi{}$, $30\ifmmode^\circ\else\textdegree\fi{}$ with respect most common variant....
Trivalent cerium ions in CeO2 are the key active species a wide range of catalytic and electro-catalytic reactions. We employed ambient pressure X-ray photoelectron spectroscopy electrochemical impedance to quantify simultaneously concentration reactive Ce3+ on surface bulk Sm-doped CeO2(100) hundreds millitorr H2–H2O gas mixtures. Under relatively oxidizing conditions, when is almost entirely 4+ oxidation state, reduced can be over 180 times concentration. Furthermore, stark contrast bulk,...
The electronic structure of graphene on Cu(111) and Cu(100) single crystals is investigated using low energy electron microscopy, diffraction angle resolved photoemission spectroscopy. On both substrates the rotationally disordered interactions between substrate lead to a shift in Dirac crossing $\sim$ -0.3 eV opening 250 meV gap. Exposure samples air resulted intercalation oxygen under Cu(100), which formed ($\sqrt{2} \times 2\sqrt{2}$)R45$^{\rm o}$ superstructure. effect this $\pi$ bands...
We employ angle-resolved photoemission spectroscopy (ARPES) to investigate the electronic structures of two rotational variants epitaxial, single-layer graphene on Ir(111). As grown, more-abundant R0 variant is nearly charge-neutral, with strong hybridization between and Ir bands near Fermi level. The surface its replicas exactly coincide Van Hove singularities in surface. Sublattice symmetry breaking introduces a small gap-inducing potential at Dirac crossing, which revealed by n-doping...
We evaluate how a second graphene layer forms and grows on Cu foils during chemical vapor deposition (CVD). Low-energy electron diffraction microscopy is used to reveal that the nucleates next substrate, i.e., under layer. This underlayer mechanism can facilitate synthesis of uniform single-layer films but presents challenges for growing bilayer by CVD. also show buried overlying layers have same edge termination.
Selected-area diffraction establishes that at least six different in-plane orientations of monolayer graphene on Pd(111) can form during growth. From the intensities low-energy electron microscopy images as a function incident energy, we find work functions rotational domains vary by up to 0.15 eV. Density functional theory calculations show these significant variations result from orientation-dependent charge transfer Pd graphene. These findings suggest electronics will require precise...
Spatially resolved electron field emission measurements from a nanocrystalline diamond film grown by plasma-enhanced chemical transport deposition have been obtained using scanning probe apparatus with micrometer resolution. Macroscopic regions high site density, and turn-on fields below 3 V/μm, comprised approximately 1/2 of the total sample area. The emitting nonemitting specimen are differentiated distinctly Raman spectra subtly morphologies. Both areas largely sp3-bonded, but only...
A complete Raman analysis has been performed on a high-quality ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ crystal made free of twins by mechanical detwinning process. Marked a-b anisotropy is observed in the intensity ${\mathit{A}}_{\mathit{g}}$ phonons at 116, 335, and 495 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. At room temperature, ${\mathrm{\ensuremath{\alpha}}}_{\mathit{y}\mathit{y}}$ component polarizability tensor 116-${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ phonon...
We use low-energy electron microscopy to investigate how graphene is removed from Ru(0001) and Ir(111) by reaction with oxygen. find two mechanisms on Ru(0001). At short times, oxygen reacts carbon monomers the surrounding Ru surface, decreasing their concentration below equilibrium value. This undersaturation causes a flux of monomer gas. In this initial mechanism, etched at rate that given precisely same nonlinear dependence governs growth. Thus, during both growth etching, attaches...
We elucidate how graphene bilayers form on Ir(111). Low-energy electron diffraction (LEED) reveals that the two layers are not always rotationally aligned. Monitoring this misalignment during growth shows second-layer islands nucleate between existing layer and substrate. This mechanism occurs both when C segregates from Ir elemental is deposited above. microscopy (LEEM) angle-resolved photoemission spectroscopy (ARPES) show nucleation preferentially under first-layer rotational variants...