ABSTRACT
The critical terrace width λ for 2D island nucleation and growth (2DNG) on large-scale atomically flat terraces of a step-bunched Si(111)-(7×7) surface has been studied by in situ ultrahigh vacuum reflection electron microscopy as a function of the substrate temperature T and Si deposition rate R. The dependence of λ(2)(R) is characterized by a power law with scaling exponent χ=1.36-1.46, validating an attachment limited (AL) growth kinetics up to 720 °C. At this temperature, the Arrhenius dependencies lnλ(2)(1/T) change their slope, so that the effective 2DNG activation energy E(2D) drops from 2.4 eV down to 0.5 eV at T>720 °C. We first show that the E(2D) change is caused by a transition between AL and DL (diffusion limited) growth kinetics accompanied by a step shape transformation. The AL growth mode is characterized by kinetic length d(-)~10(5)a and the preferential step-down attachment of atoms to steps limited by an energy barrier E(ES)(-)≈0.9 eV.
ABSTRACT
The SiO(x) films of various stoichiometries deposited on Si substrates with the use of the co-sputtering from two separate Si and SiO2 targets were annealed by femtosecond laser pulses. Femtosecond laser treatments were applied for crystallization of amorphous silicon nanoclusters in the silicon-rich oxide films. The treatments were carried out with the use of Ti-Sapphire laser with wavelength 800 nm and pulse duration about 30 fs. Regimes of crystallization of amorphous Si nanoclusters in the initial films were found. Ablation thresholds for SiO(x) films of various stoichiometries were discovered. The effect of laser assisted formation of a-Si nanoclusters in the non-stoichiometric dielectric films with relatively low concentration of additional Si atoms was also observed. This approach is applicable for the creation of dielectric films with semiconductor nanoclusters on non-refractory substrates.
Subject(s)
Crystallization/methods , Lasers , Membranes, Artificial , Nanostructures/chemistry , Nanostructures/ultrastructure , Silicon Dioxide/chemistry , Silicon/chemistry , Hardness , Hot Temperature , Materials Testing , Molecular Conformation/radiation effects , Nanostructures/radiation effects , Particle Size , Silicon/radiation effects , Silicon Dioxide/radiation effects , Surface Properties/radiation effectsABSTRACT
The aim of the present study was to formulate stabilized suspension-type metered-dose inhalation aerosols, and to examine the connection between the stabilizing additives and the optimal particle size. For the stabilization of the suspended particles, hydrophilic- and hydrophobic-type additives were applied. Oleil oleate was selected as a hydrophilic anionic surfactant, and the hydrophobizing agent was dimethyl siloxane polymer. The effect of the amount of the applied hydrophilic and hydrophobic additives on the optimal particle size was modeled by a second-order polynomial equation fitted to the data gathered by a face-centered central composite statistical design. We found that if the proper type and amount of additives are selected, it is possible to acquire the therapeutically best composition.
Subject(s)
Nebulizers and Vaporizers , Surface-Active Agents/analysis , Water/chemistry , Dose-Response Relationship, Drug , Evaluation Studies as Topic , Nonlinear Dynamics , Particle Size , SolubilityABSTRACT
The aim of this study was to examine the influence of the concentrations of surfactant and suspending agent on the quantity of effective particles (size < 10 microm) delivered by metered-dose inhalers. A 2-factor, 3-level, face-centred central composite design was used to construct a second-order polynomial model which describes the effect of formulation factors (suspending agent, surface-active ingredient) on the therapeutically important characteristic (effective particle size) delivered by metered-dose inhalers. Oleic acid was selected as the surface-active ingredient, and the suspending agent was anhydrous alcohol. A non-linear model demonstrated with good correlation the effect of the amounts of surfactant and suspending agent on the quantity of particles of effective size. The results obtained enable determination of the correct amount of surface-active ingredient and the optimum quantity of the suspending agent, thus enabling formulation of a therapeutically effective formulation.
