Papers by Author: Benjamin Valdez

Abstract: Metal-Oxide-Semiconductor structures with silicon nanocrystals in the oxide layer are prepared and characterized by Transmission Electron Microscopy and electrical measurements. High temperature annealing of SiO_1.15 films at 1000 °C for 30 or 60 min leads to formation of silicon nanocrystals with diameters of 2-3 or 4-6 nm. The processes used to obtain the multilayer gate dielectric and to grow nanocrystals do not deteriorate the properties of the cSi wafer/thermal SiO₂ interface. For the interface defect density and the fixed oxide charge values 10¹⁰ cm^-2 eV^-1 and ~ 10¹⁰ cm^-2 were obtained.

Abstract: MOS structures containing silicon nanocrystals in the gate dielectric have been tested as dosimeters for ionizing radiation. Before irradiation the nanocrystals have been charged with electrons by applying a pulse to the gate electrode. The γ-irradiation with doses in the range 0-100 Gy causes approximately linear variation of the flatband voltage, resulting in sensitivities of ~ 2.5 mV/Gy. At higher doses the sensitivity decreases because of decrease of the oxide electric field.

Abstract: X-ray Diffraction and Reflectivity, Transmission Electron Microscopy and Atomic Force Microscopy were applied to study the effect of thermal annealing on the properties of thin SiOx films (~ 15 nm) prepared by thermal evaporation of SiO in vacuum. It has been shown that furnace annealing at 1000 oC causes phase separation and formation of uniformly distributed Si nanocrystals into a SiO2 matrix. Clockwise hysteresis has been observed in the C-V curves measured and explained by assuming charging and discharging of the NCs with carriers, which tunnel from the Si substrate.

Abstract: Thin SiOx films deposited by reactive r.f. magnetron sputtering of Si at partial pressure ratios R between oxygen and argon in the range 15%-0.03% are studied. X-ray photoelectron spectroscopy and Variable angle spectroscopic ellipsometry prove enrichment with Si of the layers deposited at R < 0.5 %. Ellipsometric data give information about the refractive index and extinction coefficient of the films. Atomic Force Microscopy results show that for all samples high temperature annealing at 1000oC leads to a decrease of the surface roughness.

Abstract: A method for real time determination of microbiologically influenced corrosion (MIC) rate provoked by bacteria Thiobacillus Ferrooxidans was developed and applied on carbon steel samples. It is based on biological oxygen demand (BOD) determination of solutions contained Thiobacillus Ferrooxidans performed by the application of a Clark type oxygen probe in especially designed measuring cell.

Abstract: There is a deep universal concern today about the influence of pollutants on the environment including soil, air and in particular water, and about their effects on the durability of engineering materials and the deterioration of structures and the infrastructure. Water pollutants affect the terrestrial, atmospheric and aquatic environments, and even when present at very low levels of a few ppm may impair human health, aquatic life and water quality. The avoidance of water pollution is, therefore, an important part of water resource management. The present work provides an overview of the effects of hydrogen sulfide (H2S) on corrosion in polluted waters, including sea, river, brackish, geothermal and sewage waters.

Abstract: Desalination is a viable solution to the 21th century´s shortage of freshwater. The most widely used desalination processes are thermal and membrane. Other modern techniques apply solar and electrical energy for evaporation and electrodialysis. Many desalination plants (DP) are located in desertic/arid regions with a harsh climate and limited rainfall. About one-fifth of the DPs operate in the Middle East, with Saudi Arabia producing half of the world desalted water. The final selection of materials of construction for plant equipment must be a compromise between technological and economic factors. Corrosion problems and their solutions in several DPs in the Middle East, USA and Mexico are presented.