Power-dependent Raman analysis of highly strained Si nanobridges.

Strain analysis of complex three-dimensional nanobridges conducted via Raman spectroscopy requires careful experimentation and data analysis supported by simulations. A method combining micro-Raman spectroscopy with finite element analysis is presented, enabling a detailed understanding of strain-sensitive Raman data measured on Si nanobridges. Power-dependent measurements are required to account for the a priori unknown scattering efficiency related to size and geometry. The experimental data is used to assess the validity of previously published phonon deformation potentials.

Strain distribution in Si capping layers on SiGe islands: influence of cap thickness and footprint in reciprocal space.

We present investigations on the strain properties of silicon capping layers on top of regular SiGe island arrays, in dependence on the Si-layer thickness. Such island arrays are used as stressors for the active channel in field-effect transistors where the desired tensile strain in the Si channel is a crucial parameter for the performance of the device. The thickness of the Si cap was varied from 0 to 30 nm. The results of high resolution x-ray diffraction experiments served as input to perform detailed strain calculations via finite element method models. Thus, detailed information on the Ge distribution within the buried islands and the strain interaction between the SiGe island and Si cap was obtained. It was found that the tensile strain within the Si capping layer strongly depends on its thickness, even if the Ge concentration of the buried dot remains unchanged, with tensile strains degrading if thicker Si layers are used.

Top-down fabricated silicon nanowires under tensile elastic strain up to 4.5%.

Strained Si nanowires are among the most promising transistor structures for implementation in very large-scale integration due to of their superior electrostatic control and enhanced transport properties. Realizing even higher strain levels within such nanowires are thus one of the current challenges in microelectronics. Here we achieve 4.5% of elastic strain (7.6 GPa uniaxial tensile stress) in 30 nm wide Si nanowires, which considerably exceeds the limit that can be obtained using SiGe-based virtual substrates. Our approach is based on strain accumulation mechanisms in suspended dumbbell-shaped bridges patterned on strained Si-on-insulator, and is compatible with complementary metal oxide semiconductor fabrication. Potentially, this method can be applied to any tensile prestrained layer, provided the layer can be released from the substrate, enabling the fabrication of a variety of strained semiconductors with unique properties for applications in nanoelectronics, photonics and photovoltaics. This method also opens up opportunities for research on strained materials.

Minimization of amorphous layer in Ar+ ion milling for UHR-EM.

We present a comprehensive study on the influence of Ar(+) ion milling parameters in the range of low acceleration voltages (0.5-6 kV) and etching angles (3-10(°)) on the quality of standard high resolution Si TEM samples. The quality was assessed by the evaluation of HR-TEM images acquired from real TEM samples considering the thickness of the amorphous layer and the interlocking between crystalline and amorphous parts of the sample created by ion-beam induced amorphization, as well as topographical BSE-SEM investigation of the surface of those TEM samples. Increasing voltage clearly results in increased amorphous layer thickness as well as interlocking. The impact of the etching angle is less significant but still influences the amorphous layer thickness. It has, however, a strong effect on the preparation time, which is inversely correlated to the etching angle. Finally the experimental data were compared to model estimations by TRIM and the Schuhrke-Winterbon approximation, which fitted well to the experimental data for low voltage and angle, but were less accurate for higher voltage and angle. Despite their limitations, the models could reproduce trend and order of magnitude of the data, thus making them a useful tool for estimating the amorphous layer thickness after TEM sample preparation.

Manual de calidad del aire en el medio urbano / Manual on urban air quality management

La presente publicacion, cubre en forma practica los aspectos mas importantes de los sistemas de vigilancia de la calidad del aire y de la lucha contra la contaminacion. Contiene resenas de todo el problema de la reduccion y lucha contra la contaminacion atmosferica, pautas y criterios sobre ciertos contaminantes del aire urbano, sistemas automaticos de vigilancia de la calidad del aire. El proposito es orientar acerca de los metodos y medios para combatir la contaminacion atmosferica mediante la aplicacion de tecnicas y disposiciones legales.

Polynuclear aromatic hydrocarbons in the water environment.

Many polynuclear aromatic hydrocarbons (PAH) are known to be carcinogenic to animals and probably to man. This review is concerned with carcinogenic and non-carcinogenic PAH in the water environment, with emphasis on 3,4-benzpyrene (BP) because it is ubiquitous, is one of the most potent of the carcinogenic PAH and has been widely studied. Although PAH are formed in combustion and other high-temperature processes, there is also evidence for their endogenous formation in plants, which may explain their ubiquity therein. Although the solubility of these compounds in pure water is very low, they may be solubilized by such materials as detergents, or they may otherwise occur in aqueous solution associated with or adsorbed on to a variety of colloidal materials or biota, and thereby be transported through the water environment. A notable characteristic of PAH is their sensitivity to light.PAH have been found in industrial and municipal waste effluents, and occur in soils, ground waters and surface waters, and their sediments and biota. With the exception of filtration or sorption by activated carbon, conventional water treatment processes do not efficiently remove them, and they have been found in domestic water supplies. Because of the ubiquity of PAH in the environment, it is impossible to prevent completely man's exposure to them; nevertheless their surveillance should be continued and their concentrations in the environment should be reduced where practicable.