A5021106127- Physics of Superconductivity and Magnetism
- Surface and Thin Film Phenomena
- Magnetic properties of thin films
- Magnetic and transport properties of perovskites and related materials
- nanoparticles nucleation surface interactions
- Graphene research and applications
- Copper Interconnects and Reliability
- Electron and X-Ray Spectroscopy Techniques
- Advanced Condensed Matter Physics
- Theoretical and Computational Physics
- Semiconductor materials and devices
- 2D Materials and Applications
- Advanced Materials Characterization Techniques
- Electronic and Structural Properties of Oxides
- Semiconductor Quantum Structures and Devices
- Semiconductor materials and interfaces
- Surface Roughness and Optical Measurements
- Quantum and electron transport phenomena
- Chemical and Physical Properties of Materials
- Advancements in Battery Materials
- Quantum Dots Synthesis And Properties
- Boron and Carbon Nanomaterials Research
- ZnO doping and properties
- Diamond and Carbon-based Materials Research
- Iron-based superconductors research
University of Missouri
2012-2023
University of the Western Cape
2017-2023
Oak Ridge National Laboratory
2019
Georgia Institute of Technology
2019
University of Central Missouri
2017
University of Illinois Urbana-Champaign
1987-2002
University of Toronto
1996
Core Competence
1987-1991
Northeastern University
1990
TD Bank
1987
The mixed ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{M}}_{\mathrm{x}}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{y}}$ (M=Ni, Zn, Fe, Co, and Al) phases have been characterized for their structural, magnetic, superconducting properties. oxygen content in these is dependent on the nature amount of doping, especially Co Fe. material remains orthorhombic when Cu replaced by Ni or Zn whereas it evolves to tetragonal symmetry Fe-, Co-, Al-doped compounds...
Abstract While the discovery of two-dimensional (2D) magnets opens door for fundamental physics and next-generation spintronics, it is technically challenging to achieve room-temperature ferromagnetic (FM) order in a way compatible with potential device applications. Here, we report growth properties single- few-layer CrTe 2 , van der Waals (vdW) material, on bilayer graphene by molecular beam epitaxy (MBE). Intrinsic ferromagnetism Curie temperature ( T C ) up 300 K, an atomic magnetic...
2000 Å as-deposited high Tc superconducting Y1Ba2Cu3O7−x films with zero-resistance temperatures of ∼89 K and critical current densities about 0.7×106 A/cm2 at 77 have been reproducibly fabricated a substrate holder temperature 650 °C, using pulsed laser deposition, no post-annealing. One key to these results is the injection gaseous oxygen into laser-produced plume just in front target. In this way, correct amount incorporated as-grown film so that post-deposition treatment becomes...
We present the results of a neutron powder-diffraction study on ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Co}}_{\mathrm{x}}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{y}}$. find that Co preferentially occupies Cu(1) site, simultaneously attracting extra oxygen into these layers in an amount consistent with Co(III) replacing Cu(II). This compound displays transition from orthorhombic-to-tetragonal structure for x between 0.05 and 0.1, while...
ZnO films were synthesized on GaAs substrates at different growth conditions by pulse laser deposition. High-purity (99.999%) oxygen was used as the ambient gas. The pressure of gas for film varied from 20 to 50 mTorr, and temperature 300 450 °C. showed very strong bound exciton peaks located between 3.37 3.35 eV. full width half maximum peak is less than 5 meV. These results indicate can be optical devices such light-emitting diodes. other significant properties textured are described.
Thin films of Y-Ba-Cu-O superconductors on (100) SrTiO3 were prepared using the pulsed excimer laser evaporation technique. After an annealing treatment in oxygen exhibited superconductivity with zero resistance at 85 K transition widths (90%–10%) as narrow a 2 K. A considerable amount orientation respect to substrates was observed by x-ray diffraction and ion channeling techniques. Interface reaction revealed Rutherford backscattering Auger electron spectrometry resulted thickness...
Single crystals of the n-type Nd-Ce-Cu-O superconducting materials have been grown via a flux technique, and their structural physical properties characterized. Optimum crystal growth conditions were arrived at from survey various compositions temperatures. We determine that charge composition (50 mol % ${\mathrm{Nd}}_{2}$${\mathrm{O}}_{3}$--${\mathrm{CeO}}_{2}$, 50 CuO) held temperature 1300 \ifmmode^\circ\else\textdegree\fi{}C followed by slow cooling to 1000 produces plateletlike phase...
Superconducting thin films of Y1Ba2Cu3Ox with superconducting transition temperature (Tc) near 90 K have been prepared by a laser deposition technique. We show that on sapphire, lithium niobate, and strontium titanate under identical processing conditions exhibit different electrical characteristics. The film surfaces, interfaces, crystallinity studied number analytical techniques. conclude the substrate influences properties primarily in three ways: thermal expansion mismatch introduces...
The structure and magnetic properties of the ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{Cu}}_{1\ensuremath{-}x}{M}_{x}{\mathrm{O}}_{y}$ ($M=\mathrm{Co}\mathrm{and}\mathrm{Fe}$) materials were studied. limits solid solution formation are at $x=0.5$ for Fe system $x=1$ Co system. Crystals new ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}\mathrm{Co}{\mathrm{O}}_{y}$ phase grown established by x-ray crystallography. subcell is same as that 10-K superconductor,...
Configurational disorder can have a dominating role in the formation of macroscopic functional responses strongly correlated materials. Here, we use entropy-stabilization synthesis to create single-crystal epitaxial $\mathrm{AB}{\mathrm{O}}_{3}$ perovskite thin films with equal atomic concentration 3d transition-metal cations on B-site sublattice. X-ray diffraction, force microscopy, and scanning transmission electron microscopy...
Motivated by x-ray-scattering measurements performed on ErAs(001)/GaAs(001) and ${\mathrm{In}}_{0.7}$${\mathrm{Ga}}_{0.3}$P(001)/GaAs(001), we present a model that explains the origin of narrow peak diffuse scattering, which are frequently observed at Bragg reflections in epitaxial systems. Central to is correlation length for mosaiclike rotational disorder arises lattice-mismatched films. The adhesive force between film substrate found play crucial role leads striking anisotropy line shapes.
Abstract One of the most promising avenues in 2D materials research is synthesis antiferromagnets employing van der Waals (vdW) magnets. However, it has proven challenging, due part to complicated fabrication process and undesired adsorbates as well significantly deteriorated ferromagnetism at atomic layers. Here, engineering antiferromagnetic (AFM) interlayer exchange coupling between atomically thin yet ferromagnetic CrTe 2 layers an ultra‐high vacuum‐free magnetic crystal, Cr 5 Te 8...
Kinetic roughening during homoepitaxial growth was studied for Ag(111) and Ag(001). For Ag(111), from 150 to 500 K, the rms roughness exhibits a power law, $\ensuremath{\sigma}\ensuremath{\propto}{t}^{\ensuremath{\beta}}$ over nearly three decades in thickness. $\ensuremath{\beta}\ensuremath{\approx}\frac{1}{2}$ at low temperatures, there is an abrupt transition smaller values above 300 K. In contrast, Ag(001) layer-by-layer with significantly $\ensuremath{\beta}$. These results are first...
We demonstrate a facile two-step low-pressure vapor deposition of methylammonium lead iodide (MAPbI3) perovskite films in single reactor. Continuous, polycrystalline (PbI2) were deposited the first step and successfully converted to high quality second during exposure PbI2 (MAI) vapor. A complete conversion was realized after 90 min with an average grain size 3.70 ± 1.80 μm. The starts at surface through intercalation reaction MAI molecules progresses toward PbI2/substrate interface....
Tunneling cyclotron resonance is used to measure the tunneling rate deep in band gap of a pure AlAs barrier thin GaAs/AlAs superlattice. The experimental results are analyzed terms four-band k\ensuremath{\cdot}P model which leads renormalized effective mass barrier. Excellent agreement with experiment achieved and we able conclude that strongly down 0.09${m}_{e}$ from bulk-conduction-band value 0.15${m}_{e}$. .AE
We present a neutron scattering study of oxygen-deficient $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3\ensuremath{-}x}{\mathrm{Co}}_{x}{\mathrm{O}}_{6+y}$ where, with increasing Co concentration, long-range antiferromagnetic order develops on the chain sites. For $x=0.2$, two magnetic transitions are found: Below ${T}_{{N}_{2}}=211$ K, there is an ordered moment both Cu sites, while for ${T}_{{N}_{2}}<T<{T}_{{N}_{1}}=415$ K only "plane" present. $x=0.8$, appears sites single transition at...
Surface x-ray scattering and scanning-tunneling microscopy experiments reveal novel coarsening behavior of Pb nanocrystals grown on Si(111)-(7 x 7). It is found that quantum size effects lead to the breakdown classical Gibbs-Thomson analysis. This manifested by lack scaling island densities. In addition, decay times tau are orders magnitude faster than expected from analysis have an unusual dependence growth flux F (i.e., approximately 1/F). As a result, highly monodispersed 7-layer height...
Using highly controlled coverages of graphene on SiC(0001), we have studied the structure first layer that grows SiC interface. This layer, known as buffer is semiconducting. x-ray reflectivity and standing wave analysis, performed a comparative study with without an additional monolayer above it. We show no more than 26% carbon covalently bonded to Si in also top bilayer depleted likely cause incommensuration previously observed this system. When forms buffer, becomes less corrugated signs...
Tuning interactions between Dirac states in graphene has attracted enormous interest because it can modify the electronic spectrum of 2D material, enhance electron correlations, and give rise to novel condensed-matter phases such as superconductors, Mott insulators, Wigner crystals, quantum anomalous Hall insulators. Previous works predominantly focus on flat band dispersion coupled from different twisted layers. In this work, a new route realizing physics monolayer under periodic modulation...
We present the results of a high-resolution x-ray scattering study lattice relaxation in [001]ErAs epitaxial layers grown on [001]GaAs. Three thickness regimes are found. ErAs is pseudomorphic GaAs for thicknesses below 70 Å and between 300 observed concomitant with an increase in-plane mosaic due to formation misfit dislocations. Above Å, out-of-plane transverse from planes no longer specular further appears be related mosaic. The ratio elastic constants, C12/C11, measured 0.126. Thin-film...
Controlling polarization in ferroelectric oxides has enabled fast switching and low-power operation metal-oxide-semiconductor field-effect transistors (MOSFETs). Parallel studies on the performance of ferroelectric-polymer-based organic FETs (OFETs), where direction is rotated by 90\ifmmode^\circ\else\textdegree\fi{}, are lacking. This article examines effects external electrical poling small-molecule OFETs. The overall transistor properties enhanced when layer vertically poled, easily...
Chemical vapor deposition (CVD) offers a large-area, scalable, and conformal growth of perovskite thin films without the use solvents. Low-dimensional organic–inorganic halide perovskites, with alternating layers organic spacer groups inorganic layers, are promising for enhancing stability optoelectronic devices. Moreover, their multiple quantum-well structures provide powerful platform tuning excitonic physics. In this work, we show that CVD process is conducive to 2D hybrid films. Using...