Influence of experimental parameters on physical properties of porous silicon and oxidized porous silicon layers

This paper reports physical properties of porous silicon and oxidized porous silicon, manufactured by anodisation from heavily p-type doped silicon wafers as a function of experimental parameters. The growth rate and refractive index of the layers were studied at different applied current densities and glycerol concentrations in electrolyte. When the current density varied from 5 to 100 mA/cm², the refractive index was between 1.2 and 2.4 which corresponded to a porosity range from 42 to 85%. After oxidation, the porosity decreased and was between 2 and 45% for a refractive index range from 1.22 to 1.46. The thermal processing also induced an increase in thickness which was dependent on the initial porosity. This increase in thickness was more important for the lowest porosities. Lastly, the roughness of the porous layer/silicon substrate interface was studied at different applied current densities and glycerol concentrations in solution. Roughness decreased when the current density or glycerol concentration increased. Moreover, roughness was also reduced by thermal oxidation.     

Scaling of submonolayer island growth with reversible adatom exchange in surfactant-mediated epitaxy

Surfactant-mediated epitaxial growth is studied with a realistic model, which includes three main kinetic processes: diffusion of adatoms on the surfactant terrace, exchange of adatoms with their underneath surfactant atoms, and reexchange in which an exchanged adatom resurfaces to the top of the surfactant layer. The scaling behavior of nucleus density and island size distributions in the initial stage of growth is investigated by using kinetic Monte Carlo simulations. The results show that the temperature dependence of nucleus density and island size distributions governed by the reexchanging-controlled nucleation at high temperatures exhibits similar scaling behavior to that obtained by the standard diffusion-mediated nucleation at low temperatures. However, at intermediate temperatures, the exchanging-controlled nucleation leads to an increase of nucleus density with temperature, while the island size distribution scales to a monotonically decreasing function, showing nonstandard scaling behavior.     

Kinetic stabilization of Fe film on GaAs(1 0 0): An in situ X-ray reflectivity study

We study the growth of Fe films on GaAs(1 0 0) at a low temperature, 140 K, by in situ X-ray reflectivity (XRR) using synchrotron radiation. The XRR curves are well modeled by a single Fe layer on GaAs both at the growth temperature and after annealed at the room temperature. We found that the surface became progressively rougher during the growth with the growth exponent, β_S = 0.43 ± 0.14. The observed β_S is attributed to the restricted interlayer diffusion at the low growth temperature. The change of the interface width during growth was minimal. When the Fe film was annealed to room temperature, the surface smoothed, keeping the interface width almost unchanged. The confinement of the interface derives from that the diffusion of Ga and As proceeds via the inefficient bulk diffusion, and the overlying Fe film is kinetically stabilized.     

Growth and surface characterization of sputter-deposited molybdenum oxide thin films

Molybdenum oxide thin films were produced by magnetron sputtering using a molybdenum (Mo) target. The sputtering was performed in a reactive atmosphere of an argon-oxygen gas mixture under varying conditions of substrate temperature (T_s) and oxygen partial pressure (pO₂). The effect of T_s and pO₂ on the growth and microstructure of molybdenum oxide films was examined in detail using reflection high-energy electron diffraction (RHEED), Rutherford backscattering spectrometry (RBS), energy-dispersive X-ray spectrometry (EDS), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) measurements. The analyses indicate that the effect of T_s and pO₂ on the microstructure and phase of the grown molybdenum oxide thin films is remarkable. RHEED and RBS results indicate that the films grown at 445 °C under 62.3% O₂ pressure were stoichiometric and polycrystalline MoO₃. Films grown at lower pO₂ were non-stoichiometric MoO_x films with the presence of secondary phase. The microstructure of the grown Mo oxide films is discussed and conditions were optimized to produce phase pure, stoichiometric, and highly textured polycrystalline MoO₃ films.     

Growth kinetics of metastable (3 3 1) nanofacet on Au and Pt(1 1 0) surfaces

A theoretical epitaxial growth model with realistic barriers for surface diffusion is investigated by means of kinetic Monte Carlo simulations to study the growth modes of metastable (3 3 1) nanofacets on Au and Pt(1 1 0) surfaces. The results show that under experimental atomic fluxes, the (3 3 1) nanofacets grow by 2D nucleation at low temperature in the submonolayer regime. A metastable growth phase diagram that can be useful to experimentalists is presented and looks similar to the one found for the stationary growth of the bcc(0 0 1) surface in the kinetic 6-vertex model.     

Initial oxidation of Ni(1 1 1) observed by electron emission microscopy: PEEM and MEEM

The initial oxidation of Ni(1 1 1) in the temperature range of 550-700 K has been monitored by photoelectron emission microscopy (PEEM) and metastable-atom electron emission microscopy (MEEM). The PEEM and MEEM images show uniform patterns for the chemisorbed overlayer, reflecting the electronic homogeneity as seen at the μm scale. During the nucleation and lateral growth of oxide, however, the μm-scale pattern due to the formation of oxide domains appears and its evolution depends strongly on the substrate temperature and dose pressure of gaseous O₂. Our data indicate that the high-temperature oxidation is regarded as a successive multi-nucleation process in a reaction-diffusion field.     

Flexible software reliability growth model with testing effort dependent learning process

A lot of importance has been attached to the testing phase of the Software Development Life Cycle (SDLC). It is during this phase it is checked whether the software product meets user requirements or not. Any discrepancies that are identified are removed. But testing needs to be monitored to increase its effectiveness. Software Reliability Growth Models (SRGMs) that specify mathematical relationships between the failure phenomenon and time have proved useful. SRGMs that include factors that affect failure process are more realistic and useful. Software fault detection and removal during the testing phase of SDLC depend on how testing resources (test cases, manpower and time) are used and also on previously identified faults. With this motivation a Non-Homogeneous Poisson Process (NHPP) based SRGM is proposed in this paper which is flexible enough to describe various software failure/reliability curves. Both testing efforts and time dependent fault detection rate (FDR) are considered for software reliability modeling. The time lag between fault identification and removal has also been depicted. The applicability of our model is shown by validating it on software failure data sets obtained from different real software development projects. The comparisons with established models in terms of goodness of fit, the Akaike Information Criterion (AIC), Mean of Squared Errors (MSE), etc. have been presented.     

The effect of adsorbed atomic hydrogen on the growth of ultrathin silicon films on Ge(100) studied by positron-annihilation-induced Auger electron spectroscopy (PAES)

The effects of adsorbed atomic hydrogen on the stability of silicon films grown on a Ge(100) substrate were studied by using positron-annihilation-induced Auger electron spectroscopy (PAES) and electron-induced Auger electron spectroscopy (EAES). PAES is almost exclusively sensitive to the topmost atomic layer due to the trapping of positrons in an image potential well just outside the surface before annihilation. This surface specificity was exploited in the study of film stability and interfacial mixing during the growth of silicon on Ge(100). The PAES results show that the prior adsorption of hydrogen prevented the segregation of germanium on top of the deposited silicon, and that the hydrogen adsorption was useful in growing a thermally stable structure.     

微量元素硼对小麦生长发育及碳水化合物代谢的影响

春小麦赛洛斯用适宜浓度的认浸种和各期根外追肥的方法处理后，皆可促进小麦幼苗根系的生长发育；促进生长锥的分化和器官的形成过程；可提高主茎旗叶面积和花粉生活力；可促进小麦叶部和生殖器官糖类的合成和叶内由光合作用制造出的糖类向生殖器官的运转；春小麦赛洛斯用硼进行根外追肥的时期，从孕穗－开花期喷射效果最显；用硼进行播种前处理和根外喷射，皆能提高小麦产量。     

On finite unions of ideals and cosets

Abstract

Although it is well known that the growth of Thompson's group F is exponential, the exact growth function is still unknown. Elements of its submonoid of positive words can be described using a binary rooted tree, whose norm can be computed assigning weights to each caret. Combining this fact with a combinatorial argument, the growth function of the submonoid is computed and thus providing a first step in the computation of the growth function of the group, as well as a lower bound for the growth rate for the group.