Strain in epitaxial Bi2Se3 grown on GaN and graphene substrates: A reflection high-energy electron diffraction study

published_or_final_versio

Molecular-beam epitaxy of topological insulator Bi2Se3 (111) and (221) thin films

postprin

Doping of GaN by Mg diffusion

published_or_final_versio

Growth of N, N′-di(naphthalene-1-yl)-N, N′-diphenyl-benzidine dome structures

N,N′-di(naphthalene-1-yl)-N,N′-diphenyl-benzidine samples exhibiting interesting nano/microstructure were fabricated by thermal evaporation in a tube furnace under Ar gas flow. We investigated the influence of the substrate type, substrate temperature, source temperature, and the gas flow rate on the obtained morphology. The deposited material was investigated using scanning electron microscopy, x-ray diffraction, and photoluminescence. We found that the substrate temperature was the factor which significantly affected the obtained morphology, while other factors such as substrate type, source temperature, and gas flow mainly affected the size distribution of the features but not the type of morphology observed. © 2005 American Institute of Physics.published_or_final_versio

ZnO nanostructures prepared from ZnO:CNT mixtures

Due to its wide band gap (3.37 eV) and large exciton binding energy (60 meV), ZnO is of great interest for photonic applications. A number of different morphologies, such as nanobelts, nanowires, tetrapod nanostructures, tubular nanostructures, hierarchical nanostructures, nanobridges, nanonails, oriented nanorod arrays, nanoneedles, nanowalls, and nanosheets, were reported. A range of synthesis methods for fabrication of ZnO nanostructures was reported as well. A common method is evaporation from mixture of ZnO and carbon, which is usually in the form of graphite. In this work, we studied the morphology of the ZnO nanostructures fabricated from the mixture of ZnO (micron-sized and nanoparticles) and carbon (graphite, single-wall carbon nanotubes). When graphite and ZnO powders were used, tetrapod structures were obtained. If one of the reactants was nanosized, the diameter of the tetrapod arms was no longer constant. Finally, when both reactants were nanosized, novel morphologies were obtained. We studied the dependence of the morphology on the amount of starting material and the type of carbon used. The ZnO nanostructures were studied using field emission scanning electron microscopy, transmission electron microscopy, selected area electron diffraction, and X-ray diffraction. Growth mechanism and factors affecting the morphologies are discussed.published_or_final_versio

An innovative approach for testing bioinformatics programs using metamorphic testing

Background: Recent advances in experimental and computational technologies have fueled the development of many sophisticated bioinformatics programs. The correctness of such programs is crucial as incorrectly computed results may lead to wrong biological conclusion or misguide downstream experimentation. Common software testing procedures involve executing the target program with a set of test inputs and then verifying the correctness of the test outputs. However, due to the complexity of many bioinformatics programs, it is often difficult to verify the correctness of the test outputs. Therefore our ability to perform systematic software testing is greatly hindered

Anisotropic step-flow growth and island growth of GaN(0001) by molecular beam epitaxy

GaN(0001) thin films are grown using radio frequency plasma assisted molecular beam epitaxy. By changing the growth temperature, anisotropic growth rate behavior is observed in both the step-flow growth mode and the 2D island growth mode. Tunneling scanning microscopy reveals, in the step-flow growth mode, strong influences from the growth anisotropy on the shape of the terrace edges, resulting in striking differences between hexagonal and cubic films. In the 2D nucleation growth mode, triangularly shaped islands are formed. The significance of growth anisotropy to growing high quality GaN films is discussed.published_or_final_versio

Molecular-beam epitaxy of monolayer and bilayer WSe2: a scanning tunneling microscopy/spectroscopy study and deduction of exciton binding energy

Interest in two-dimensional (2D) transition-metal dichalcogenides (TMDs) has prompted some recent efforts to grow ultrathin layers of these materials epitaxially using molecular-beam epitaxy (MBE). However, growths of monolayer (ML) and bilayer (BL) WSe2—an important member of the TMD family—by the MBE method remain uncharted, probably because of the difficulty in generating tungsten fluxes from the elemental source. In this work, we present a scanning tunneling microscopy and spectroscopy (STM/S) study of MBE-grown WSe2 ML and BL, showing atomically flat epifilm with no domain boundary (DB) defect. This contrasts epitaxial MoSe2 films grown by the same method, where a dense network of the DB defects is present. The STS measurements of ML and BL WSe2 domains of the same sample reveal not only the bandgap narrowing upon increasing the film thickness from ML to BL, but also a band-bending effect across the boundary (step) between ML and BL domains. This band-bending appears to be dictated by the edge states at steps of the BL islands. Finally, comparison is made between the STS-measured electronic bandgaps with the exciton emission energies measured by photoluminescence, and the exciton binding energies in ML and BL WSe2 (and MoSe2) are thus estimated.postprin

Different origins of visible luminescence in ZnO nanostructures fabricated by the chemical and evaporation methods

Zinc oxide nanostructures were fabricated using chemical and thermal evaporation methods. Scanning electron microscopy (SEM), x-ray diffraction, photoluminescence, and electron paramagnetic resonance (EPR) spectroscopy were used to study the properties of fabricated nanostructures. The nanostructures fabricated by evaporationg methods exhibited green PL from surface centers. The results show that the luminescence in the visible region has different peak positions in samples prepared by chemical and evaporation methods.published_or_final_versio

Hábitos de higiene bucal e a utilização dos serviços odontológicos em escolares

xx