Mingguang Kong

Influence of phosphine flow rate on Si growth rate in gas source molecular beam epitaxy

As reported by other authors, we have also observed that the Si growth rate decreases with increasing phosphine (PH3) flow rate in gas source-Si molecular beam epitaxy using phosphorous (P) as a n-type dopant. Why small quantity PH3 can affect Si growth rate? Up to now, the quantitative characterization of PH3 flow influence on Si growth rate is little known. In this letter, the PH, influence will be analyzed in detail and a model considering strong P surface segregation and its absorption of hydrogen will be proposed to characterize the effect

Changing the size and shape of Ge island by chemical etching

Self-assembled Ge islands were grown on Si (1 0 0) substrate by Si2H6-Ge molecular beam epitaxy. Subjected to a chemical etching, it is found that the size and shape (i.e. ratio of height to base width) of Ge islands change with etching time. In addition, the photoluminescence from the etched Ge islands shifted to the higher energy side compared to that of the as-deposited Ge islands. Our results demonstrated that chemical etching can be a way to change the size and shape of the as-deposited islands as well as their luminescence property

Influence of rapid thermal annealing on the optical properties of gallium nitride grown by gas-source molecular-beam epitaxy

Raman scattering, photoluminescence (PL), and nuclear reaction analysis (NRA) have been employed to investigate the effects of rapid thermal annealing (RTA) on GaN films grown on sapphire (0001) substrates by gas-source molecular-beam epitaxy. The Raman spectra showed the presence of the E2 (high) mode of GaN and shift of this mode from 572 to 568u2009cm−1 caused by annealing. The results showed that RTA has a significant effect on the strain relaxation caused by the lattice and thermal expansion misfit between the GaN epilayer and the substrate. The PL peak exhibited a blueshift in its energy position and a decrease in the full width at half maximum after annealing, indicating an improvement in the optical quality of the film. Furthermore, a green luminescence appeared after annealing and increased in intensity with increasing annealing time. This effect was attributed to H concentration variation in the GaN film, which was measured by NRA. A high H concentration exists in as-grown GaN, which can neutralize ...

Morella-rubra-like metal–organic-framework-derived multilayered Co3O4/NiO/C hybrids as high-performance anodes for lithium storage

Co3O4/NiO/C microspheres with a multilayered ball-in-ball hollow nanoarchitecture were synthesized via carbonization and oxidation treatments of Morella-rubra-like CoNi-based metal–organic frameworks (CoNi-MOFs). The shell walls of each ball were entirely composed of uniform nanorods. This unique multilayered hollow structure can strongly mitigate the change in the volume of the electrodes, which maintains the structural integrity of the Co3O4/NiO/C hybrids during the lithiation–delithiation process. In addition, the C scaffolds improve the conductivity of the electrode and function as a buffer material to mitigate the pulverization of Co3O4 and NiO nanoparticles. Therefore, in Li-ion cells, the multilayered Co3O4/NiO/C hybrids exhibit a high reversible capacity (864 mA h g−1 at 1 A g−1), an excellent rate capacity (421 mA h g−1 at 4 A g−1), and a long-lifetime cycling performance (776 mA h g−1, even after 1000 cycles at 1 A g−1) for Li storage.

Effect of Microstructure on the Thermal Conductivity of Plasma-Sprayed Al2O3-YSZ Coatings

The microstructures of three atmospheric plasma-sprayed (APS) Al2O3-ZrO2 coatings were investigated using x-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The differences in the microstructures of the three Al2O3-ZrO2 coatings, including their phase compositions, cracks, pores, grain sizes, and solid solutions, were analyzed in detail. A close relationship was observed between the thermal conductivities of the coatings and the microstructures, and the Al2O3-YSZ coatings with more spherical pores, fewer vertical cracks, and finer grains exhibited the lowest thermal conductivity of 0.91xa0W/m·K. Compared with YSZ coatings, Al2O3-YSZ coatings can exhibit lower thermal conductivity, which may be attributed to the formation of an amorphous phase, smaller grains, and Al2O3-YSZ solid solution.

Effect of Si overgrowth on the structural and luminescence properties of Ge islands on Si(100)

The effect of Si overgrowth on the structural and luminescence properties of strained Ge layer grown on Si(1 0 0) is studied. Capping Si leads to the dissolution of Ge island apex and reduced island height. The structural changes in island shape, especially in chemical composition during Si overgrowth have a large effect on the PL properties. The integrated PL intensity of Ge layer increases and there are large blue shifts in peak energies after capping Si. The PL spectra from buried Ge layer are consistent with type-II band alignment in SiGe/Si. We show that the PL properties from buried Ge layer may be tailored by modifying the cap layer growth conditions as well as post-growth annealing

Evolution of height distribution of Ge islands on Si(1 0 0)

Evolution of the height distribution of Ge islands during in situ annealing of Ge films on Si(1 0 0) has been studied. Island height is found to have a bimodal distribution. The standard deviation of the island height divided by the mean island height, for the mode of larger island size is more than that for the other mode. We suggest that the presence of Ehrlich-Schwoebel barriers, combined with the misfit strain, can lead to the bimodal distribution of island size, the mode of larger island size having narrower base size distribution, but wider height distribution for Ge islands on Si(1 0 0). The bimodal distribution of island size could be stable due to kinetics without necessarily regarding it as minimum-energy configuration

Structural identification of a cubic phase in hexagonal GaN films grown on sapphire by gas-source molecular beam epitaxy

The structural characteristics of gallium nitride (GaN) films grown on sapphire(0001) substrates by gas source molecular beam epitaxy (GSMBE) have been investigated using high-resolution synchrotron irradiation X-ray diffraction and cathodoluminescence with a variable energy electron beam. Besides the well-known GaN hexagonal structure, a small portion of cubic phase GaN was observed. The X-ray measurements provide an essential means for the structural identification of the GaN layers. Arising from the variable penetration depth of the electron beam in the cathodoluminescence measurements, it was found that the fraction of the GaN cubic-phase typically increased as the probing depth was increased. The results suggest that the GaN cubic phase is mostly located near the interface between the substrate and GaN layer due to the initial nucleation.

Low-temperature growth properties of Si1−xGex by disilane and solid-Ge molecular beam epitaxy

Low temperature (similar to 500 degrees C) growth properties of Si1-xGex by disilane and solid-Ge molecular beam epitaxy have been studied with an emphasis on surface morphology and growth kinetics. It is found that low-temperature growth( 0.5). Ge composition dependence on substrate temperature, Ge cell temperature and disilane flow rate have been investigated. It is found that in low-temperature growth (less than or equal to 500 degrees C) and under large disilane flux, Ge composition increases with the increase of Ge flux and further increase of Ge flux leads to the saturation of Ge composition. Similar compositional dependence has been found at different growth temperatures. The saturated composition increases with the decrease of substrate temperature. The results can be explained if H desorption is assumed to occur from both Si and Ge monohydrides without diffusional exchange and the presence of Ge enhances H desorption on a Si site

Ge composition saturation behavior during low-temperature Si1 − xGex growth by disilane and solid Ge molecular beam epitaxy

Ge composition dependence on the Ge cell temperature has been studied during the growth of Si1-xGex by disilane and solid Ge molecular beam epitaxy at a substrate temperature of 500 degrees C. It is found that the composition x increases and then saturates when the Ge cell temperature increases, which is different from the composition-dependent behavior in growth at high temperature as well as in growth by molecular beam epitaxy using disilane and germane. The enhanced hydrogen desorption from a Ge site alone cannot account for this abnormal composition-variation behavior. We attribute this behavior to the increase of rate constant of H desorption on a Si site when the Ge cell temperature increases.