Si-nanostructures formation in amorphous silicon nitride SiNx:H deposited by remote PECVD

The formation of silicon nanoclusters embedded in amorphous silicon nitride (SiN_x:H) can be of great interest for optoelectronic devices such as solar cells. Here amorphous SiN_x:H layers have been deposited by remote microwave-assisted chemical vapor deposition at 300 °C substrate temperature and with different ammonia [NH₃]/silane [SiH₄] gas flow ratios (R=0.5−5). Post-thermal annealing was carried out at 700 °C during 30 min to form the silicon nanoclusters. The composition of the layers was determined by Rutherford back scattering (RBS) and elastic recoil detection analysis (ERDA). Fourier transform infrared spectroscopy (FTIR) showed that the densities of SiH (2160 cm⁻¹) and NH (3330 cm⁻¹) molecules are reduced after thermal annealing for SiN:H films deposited at flow gas ratio R>1.5. Breaking the SiH bonding provide Si atoms in excess in the bulk of the layer, which can nucleate and form Si nanostructures. The analysis of the photoluminescence (PL) spectra for different stoichiometric layers showed a strong dependence of the peak characteristics (position, intensity, etc.) on the gas flow ratio. On the other hand, transmission electron microscopy (TEM) analysis proves the presence of silicon nanoclusters embedded in the films deposited at a gas flow ratio of R=2 and annealed at 700 °C (30 min).     

Activated nitriles in heterocyclic synthesis. Part III. Synthesis of N-amino-2-pyridone,pyranopyrazole and thiazolopyridine derivatives

The reaction of 2-cyanoethanoic acid hydrazide and arylidenemalononitrile was studied as a new route for the synthesis of N-amino-2-pyridones. Pyrano[2,3-c]pyrazole and thiazolo[2,3-a]pyridine could be prepared from the reaction of arylideneazolones with the same reagent.     

Distorted cylindrical shell response to internal acoustic excitation below the cut-off frequency

The mechanism of coupling between a plane wave acoustic mode and a non-axisymmetric structural mode of a thin walled, circular, cylindrical shell, via the geometrical distortion of the shell, is considered. A theoretical model of response below the acoustic cut-off frequency is used to estimate the vibration level induced in a tube having small circumferential variations of wall thickness, radius and modulus of elasticity. The results have been confirmed experimentally.     

Analysis of UV-Laser induced oxidation of implanted silicon by optical reflectivity measurements

The oxidation of ion implanted silicon induced by a repetitive excimer laser working in liquid phase regime has been monitored by a simple in situ technique. It consists to follow the optical reflectivity at the wavelength 633 nm of the silicon samples under irradiation. The influence of implantation and laser irradiation conditions on the oxidation process has been investigated by this technique. The results obtained have been compared using infrared absorption data. The role of the Si/SiO₂ interface roughness on the oxide film quality has been studied.     

Boron doping of silicon by excimer laser irradiation in a reactive atmosphere

UV excimer lasers have been used to dope semiconductors by a one-step process in which the laser serves both to melt a controlled thickness of a sample placed in dopant ambient and to photodissociate the dopant molecules themselves. Here we report the boron doping of silicon by means of an ArF (193 nm) excimer laser. Dopant atoms are obtained by photolysis of BCl₃ or pyrolysis of BF₃ molecules. The doping is performed both in gas ambient and using only an adsorbed layer. We have investigated the dependence of doping parameters such as laser pulse repetition and gas pressure on the subsequent boron impurity profiles and the dopant incorporation rate. These results indicate that the laser doping process is dopant-flux limited for BF₃ and externally rate limited for BCl₃.     

Polyethylene Oxides as Organic Reactions Activators II.1 An Easy Generation of Dihalocarbenes

Polyethylene oxides are shown to promote an efficient dihalocarbene formation from bromo — and chloroform and solid potassium hydroxide — Adducts with olefins are obtained in High yields.     

Silicon nanoparticles formation in annealed SiO/SiO2 multilayers

We present a study on amorphous SiO/SiO₂ superlattice performed by grazing-incidence small-angle X-ray scattering (GISAXS). Amorphous SiO/SiO₂ superlattices were prepared by high-vacuum evaporation of 3 nm thin films of SiO and SiO₂ (10 layers each) onto Si(1 0 0) substrate. After the deposition, samples were annealed at 1100 °C for 1 h in vacuum, yielding to Si nanocrystals formation. Using a Guinier approximation, the shape and the size of the crystals were obtained. The size of the growing nanoparticles in the direction perpendicular to the film surface is well controlled by the bilayer thickness. However, their size varies more significantly in the direction parallel to the film surface.     

Studies of silicon nanocrystals in phosphorus rich SiO2 matrices

In this contribution we present a new type of optoelectronic silicon nanocrystal (Si-nc) based material, namely, Si-nc embedded into solidified pure or doped spin-on-glasses. The resulting self-supporting samples contain thin layers with high Si-nc concentrations. The visible photoluminescence (PL) maximum at room temperature is blue-shifted when the concentration of phosphorus in the spin-on-glass is increased.     

Some Biochemical Aspects of the Protective Effect of Strontium Chloride on Gamma-Irradiated Rats

The effect of treatment with SrCl₂ (10 mg/100 g rat) on rats 15 minutes prior to whole body γ-irradiation (7,5 Gy) was studied. The hazardeous effect of irradiation were greatly corrected in the treated group. The hyperglycemic effect and liver glycogen accumulation in the untreated group decreased to normal level. The enzymatic activities of serum alkaline phosphatase, alanine aminotransferase, aspartate aminotransferase and lactate dehydrogencase were greatly affected showing insignificant changes in the treated group of animals. Life span calculated on 50% survival was also significantly elongated by 36.3%. These results show the potentiality of SrCl₂ as a radioprotective agent which was not used before.     

Characterization of thin silicon oxide obtained by lamp heating

Ultrathin gate oxides (90–300 Å) have been grown on silicon under dry oxygen using a lamp light heater. The oxidation kinetics is quite different from that expected in conventional furnace oxidation since the process is shown to be diffusion limited.Infrared absorption analysis shows neither shift nor broadening of the Si-O stretching mode, indicating that the rapid oxide is stoichiometric with a good structural order. The electrical characteristics of Al-gate capacitors assessed byC-V andG-V measurements with thickness as parameter shows a good quality for oxide films thinner than 100 Å. For thicknesses higher than this value, cleaning techniques and post-oxidation annealing must be used.