Total Angular Momentum Conservation During Tunnelling through Semiconductor Barriers

We have investigated the electrical transport through strained p-Si/Si_{1-x}Ge_x double-barrier resonant tunnelling diodes. The confinement shift for diodes with different well width, the shift due to a central potential spike in a well, and magnetotunnelling spectroscopy demonstrate that the first two resonances are due to tunnelling through heavy hole levels, whereas there is no sign of tunnelling through the first light hole state. This demonstrates for the first time the conservation of the total angular momentum in valence band resonant tunnelling. It is also shown that conduction through light hole states is possible in many structures due to tunnelling of carriers from bulk emitter states.Comment: 4 pages, 4 figure

The clubfoot assessment protocol (CAP); description and reliability of a structured multi-level instrument for follow-up

BACKGROUND: In most clubfoot studies, the outcome instruments used are designed to evaluate classification or long-term cross-sectional results. Variables deal mainly with factors on body function/structure level. Wide scorings intervals and total sum scores increase the risk that important changes and information are not detected. Studies of the reliability, validity and responsiveness of these instruments are sparse. The lack of an instrument for longitudinal follow-up led the investigators to develop the Clubfoot Assessment Protocol (CAP). The aim of this article is to introduce and describe the CAP and evaluate the items inter- and intra reliability in relation to patient age. METHODS: The CAP was created from 22 items divided between body function/structure (three subgroups) and activity (one subgroup) levels according to the International Classification of Function, Disability and Health (ICF). The focus is on item and subgroup development. Two experienced examiners assessed 69 clubfeet in 48 children who had a median age of 2.1 years (range, 0 to 6.7 years). Both treated and untreated feet with different grades of severity were included. Three age groups were constructed for studying the influence of age on reliability. The intra- rater study included 32 feet in 20 children who had a median age of 2.5 years (range, 4 months to 6.8 years). The Unweighted Kappa statistics, percentage observer agreement, and amount of categories defined how reliability was to be interpreted. RESULTS: The inter-rater reliability was assessed as moderate to good for all but one item. Eighteen items had kappa values > 0.40. Three items varied from 0.35 to 0.38. The mean percentage observed agreement was 82% (range, 62 to 95%). Different age groups showed sufficient agreement. Intra- rater; all items had kappa values > 0.40 [range, 0.54 to 1.00] and a mean percentage agreement of 89.5%. Categories varied from 3 to 5. CONCLUSION: The CAP contains more detailed information than previous protocols. It is a multi-dimensional observer administered standardized measurement instrument with the focus on item and subgroup level. It can be used with sufficient reliability, independent of age, during the first seven years of childhood by examiners with good clinical experience. A few items showed low reliability, partly dependent on the child's age and /or varying professional backgrounds between the examiners. These items should be interpreted with caution, until further studies have confirmed the validity and sensitivity of the instrument

Transatlantic intelligence and security cooperation

Despite recent advances in transatlantic intelligence and security cooperation, significant problems remain. The bombings in Madrid in March 2004 have demonstrated how terrorists and criminals can continue to exploit the limits of hesitant or partial exchange to dangerous effect. Intelligence and security cooperation remain problematic because of the fundamental tension between an increasingly networked world, which is ideal terrain for the new religious terrorism, and highly compartmentalized national intelligence gathering. If cooperation is to improve, we require a better mutual understanding about the relationship between privacy and security to help us decide what sort of intelligence should be shared. This is a higher priority than building elaborate new structures. While most practical problems of intelligence exchange are ultimately resolvable, the challenge of agreeing what the intelligence means in broad terms is even more problematic. The last section of this article argues that shared NATO intelligence estimates would be difficult to achieve and of doubtful value

Effects of zinc anneals in the (400-550 °C) range on the acceptor concentration in ZnTe

Annealing ZnTe in Zinc vapour at 400-550 °C gives two effects : within the bulk of the samples, impurities (copper and lithium) are released from the Te excess and act as CuZn and LiZn. On the surface, an electrically compensated zone is created. The result of these effects is the appearance of an acceptor bump located below the surface exposed to a short time anneal under zinc pressure.Les recuits thermiques à (400-550 °C) sous vapeur de zinc dans le ZnTe ont deux effets : dans le coeur des échantillons, on libère les impuretés cuivre et lithium qui passent en site accepteur Cuzn et Li zn. La surface des échantillons exposée aux vapeurs de zinc devient compensée. Le raccord entre les deux effets est traduit dans des recuits de courte durée par l'existence d'une bosse d'accepteurs située sous la surface exposée aux vapeurs de zinc

RECRISTALLISATION DE Si POLY PAR FAISCEAUX D'ENERGIE

Cet article passe en revue différents résultats obtenus lors de la recristallisation de Si poly avec des faisceaux d'énergie : laser, électron, ou plus récemment barreau de graphite, lampes. Suivant la puissance transférée dans les couches, la recristallisation peut se passer en phase solide, ou en phase liquide. Le recuit phase solide a surtout été utilisé pour améliorer les performances de dispositifs déjà existants alors qu'avec le passage par la phase liquide, on pourra disposer de substrats utilisables en VLSI. Dans ce dernier cas, la stabilité de l'interface liquide-solide, les encapsulants et la croissance volontairement orientée sont discutés.Recently developped methods for fast and localized annealing such as laser and e-beam crystallization have spurred interest in this field. We review the results obtained in material research, more particularly growth kinetics of poly-Si in the solid phase. In the liquid phase case, results open up to possibility of monocrystalline layers with crystallographic orientation. According to the different methods, we can obtain crystallized islands with lasers or large sheets with graphite strip heaters

TRANSISTORS MADE IN SINGLE-CRYSTAL SOI FILMS

Des transistors ont été réalisés dans des films de silicium déposés sur isolant et recristallisés par laser. L'utilisation de bandes anti-reflets de nitrure de silicium a permis de contrôler l'interface liquide-solide à l'arrière du spot laser, lors de la recristallisation. Cette technique permet de contrôler la position des joints de grains avec une bonne précision. Les joints de grains ont été ensuite dissous dans une étape d'oxydation localisée classique, laissant des bandes de silicium monocristallin complètement entourées d'oxyde. Des transistors MOS à canal N, ainsi que des oscillateurs en anneau ont été fabriqués dans ce matériau. La mobilité de surface des électrons y atteint 650 cm2/V.sec., et le délais par étage est de 1 nsec. dans les oscillateurs (L = 5 µm).Transistors have been realized in laser-recrysallized silicon-on-insulator films. Antireflecting stripes of silicon nitride were used to shape the trailing edge of the silicon as it quenches under laser scan, which allows accurate control of the grain boundary location. The grain boundaries were oxidized in a standard LOCOS process which left single-crystal silicon stripes completely embedded in the oxide. N-channel transistors as well as ring oscillators were made in the recrystallized material. A surface mobility of 650 cm2/V.sec. was observed in the transistors, and a 1 nsec. delay per stage was measured in the ring oscillators (L = 5 µm)

A comparison between furnace and cw laser annealing of a-Si : evidence of different crystallization states

Two states of crystallization of silicon can be obtained by cw laser annealing of amorphous material before melting temperature. Comparison between furnace and cw laser annealing of amorphous films give insights about the nucleation and growth process at high temperatures

Optical Properties of Low Dimensional Silicon Nanostructures

NATO ASI Series E: Applied Science This book describes the state of the art on the luminescent properties of porous silicon. The dramatic results of the major international laboratories and groups working in this subject are presented. The majority of the participants agree that a quantum confinement effect and a good passivation of the surface crystallites are responsible for the observed luminescence properties. New characterisation techniques are for the first time presented as a comprehensive survey of the theoretical models. Both efficient and wavelength tunable electroluminescence are demonstrated using liquid contacts and a cathodic injection system. Localised cathodoluminescence in a scanning electron miscroscope and a scanning tunneling microscope is also presented. This book demonstrates that a consensus is emerging on the origin of the visible luminescence of highly porous Si. This novel nanostructure is extending our knowledge into a new area of solid state physics