Adsorption and desorption kinetics of gallium atoms on 6H-SiC(0001) surfaces

Gallium (Ga) surface adsorption and desorption kinetics on 6H-SiC(0001) are investigated using reflection high-energy electron diffraction. It is found that for Ga adsorption, a wetting layer bonds strongly to the SiC(0001) surface. Additional Ga atoms form droplets on top of the wetting layer. The Ga droplets behave like a metallic liquid. The activation energies for desorption are determined to be 3.5 eV for Ga in the wetting layer and 2.5 eV for Ga in the droplets. It is further found that the desorption of Ga atoms from the wetting layer follows a zero-order kinetics, i.e., the desorption rate is independent of the number of adsorbed atoms. ©2000 The American Physical Society.published_or_final_versio

Synthesis and properties of ZnO nano-ribbon and comb structures

ZnO is of great interest for photonic applications due to its wide band gap (3.37 eV) and large exciton binding energy (60 meV). A large variety of fabrication methods and nanostructure morphologies was reported up to date for this material. Obtained morphologies include nanobelts or nanoribbons, nanowires, nanorods, tetrapod nanostructures, etc. Novel nanostructures like hierarchical nanostructures, nanobridges and nanonails have also been fabricated. In this work, we report a simple method for fabrication of nanoribbon and nanocomb structures. The structures are fabricated by evaporation of a mixture of ZnO and carbon nanotubes (CNT) at 1050°C, and the deposition products have been collected on Si substrates in the temperature range 750-800°C. The growth mechanism of obtained structures is discussed. © 2005 American Institute of Physics.published_or_final_versio

Growth of SiO x nanowire bunches cocatalyzed with Ga and Ni

Si Ox nanowire bunches were fabricated on Ni (N O3) 2* 6 H2 O solution-coated Si(111) substrates in a chemical vapor deposition system in the presence of Ga and under the flow of Ar and N H3 gases. The roles of nickel nitrate hydrate, gallium, and ammonia in the formation of Si Ox nanowire bunches were investigated. It was found that Ni and Ga act as catalysts for the growth, while nickel nitrate hydrate also serves as a source of oxygen. The growth mechanisms of different nanowire structures obtained by varying the fabrication conditions are discussed. © 2005 American Institute of Physics.published_or_final_versio

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

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Reactive interface formation and Co-induced (√7×√7 ) superstructure on a GaN(0001) pseudo- (1×1 ) substrate surface

Deposition of Co on GaN(0001) pseudo- (1×1) surface at room temperature by molecular-beam epitaxy is studied by low-energy electron diffraction, scanning-tunneling microscopy and first-principles total energy calculations. Reactive interface formation where the deposited Co reacts with Ga on GaN substrate forming CoGax (x∼2) compound or alloy can be inferred from surface morphology evolution and mass consideration. At an intermediate coverage about 0.4 monolayers, a specific (√7×√7) surface structural phase develops, as observed by both low-energy electron diffraction and scanning tunneling microscopy studies. First-principles total energy calculations suggest that the (√7×√7) structure is induced by Co-trimers located slightly below the topmost Ga adlayer of the substrate. © 2010 The American Physical Society.published_or_final_versio

A novel high frequency current-driven synchronous rectifier applicable to most switching topologies

A novel current-driven synchronous rectifier is presented in this paper. With the help of current sensing energy recovery circuit, the proposed current-driven synchronous rectifier can operate at high switching frequency with high efficiency. Compared with those voltage-driven synchronous rectification solutions, this current-driven synchronous rectifier has several outstanding characteristics. It can be easily applied to most switching topologies like an ideal diode. Constant gate drive voltage can be obtained regardless of line and load fluctuation. This makes it desirable in high input range application. Converters designed with this synchronous rectifier are also capable of being connected in parallel without taking the risk of reverse power sinking. Principle of operation is given in the paper. A series of experiments verify the analysis and demonstrate the merits.published_or_final_versio

A study of Al1-xInxN growth by reflection high-energy electron diffraction-incorporation of cation atoms during molecular-beam epitaxy

Molecular-beam epitaxy of Al1-x Inx N alloys with different indium (In) contents, x, were studied by in situ reflection high-energy electron diffraction (RHEED). Growth rates of the alloys were measured by the RHEED intensity oscillations for different source flux conditions, while the lattice parameters were derived from the diffraction patterns. It was found that under the excess nitrogen growth regime, incorporation of aluminum was complete whereas incorporation of In atoms was incomplete even at temperatures below 400 °C. © 2008 American Institute of Physics.published_or_final_versio

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

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Current-driven synchronous rectification technique for flyback topology

For low voltage, high current application, synchronous rectification technique can help improve efficiency in a flyback converter. This paper investigates some technical challenges within a synchronous rectification flyback converter. One of the major problems is that the discontinuous current mode (DCM) operation is not achievable with a control-driven or self-driven synchronous rectifier. Continuous current mode operation may introduce excessive RMS current and circulation energy at light load or high line condition. To solve this problem, we propose to use an energy recovery current-driven synchronous rectifier for flyback topology. Analysis and experiments demonstrate the performance of this approach.published_or_final_versio

A study of Inx Ga1-x N growth by reflection high-energy electron diffraction

Epitaxial growth of Inx Ga1-x N alloys on GaN (0001) by plasma-assisted molecular-beam epitaxy is investigated using the in situ reflection high-energy electron-diffraction (RHEED) technique. Based on RHEED pattern changes over time, the transition of growth mode from two-dimensional (2D) nucleation to three-dimensional islanding is studied for various indium compositions. RHEED specular-beam intensity oscillations are recorded during the 2D wetting-layer growth, and the dependences of the oscillation period/frequency on the substrate temperature and source flux are established. By measuring the spacing between diffraction spots in RHEED, we also estimated indium composition, x, in alloys grown under different flux combinations. Incorporation coefficients of both gallium and indium are derived. Possible surface segregation of indium atoms is finally examined. © 2005 American Institute of Physics.published_or_final_versio