The Radial Flow Planetary Reactor - Low-pressure Versus Atmospheric-pressure Movpe

A comparison between MOVPE of III-V compounds with the radial flow planetary reactor at atmospheric pressure and at reduced pressure has been carried out by numerical simulation and experimentally. The behavior of the reactor at low pressure was found to be very similar to that at atmospheric pressure. The obtained layer thickness uniformity was also +/- 1% at pressures of 100 mbar and 200 mbar. Moreover, the uniformity was found to be almost independent of total mass flow, over the range of 10 to 43 SLM. The first growth on five 3 inch diameter wafers at atmospheric pressure is reported. Optimization of the inlet section led to simultaneous uniformities of approximately 1% in layer thickness and sheet resistance. The first GaAs-(Ga,Al)As lasers grown with this reactor at 200 mbar are reported, with a threshold current density of 400 A/cm2. The first GaAs-(Ga,In)As-(Ga,Al)As pseudomorphic HEMT material grown with this reactor at atmospheric pressure with 22% indium in the channel layer yielded devices with an average maximum transconductance of 383 mS/mm and unity current gain cut-off frequency of 64.5 GHz for a gate length of 0.25-mu-m

Drug Content Effects on the Dispersion Performance of Adhesive Mixtures for Inhalation

<p>The drug content in adhesive mixtures for inhalation is known to influence their dispersion performance, but the direction and magnitude of this influence depends on other variables. In the past decades several mechanisms have been postulated to explain this finding and a number of possible interacting variables have been identified. Still, the role of drug content in the formulation of adhesive mixtures for inhalation, which includes its significance as an interacting variable to other parameters, is poorly understood. Therefore, the results from a series of drug detachment experiments are presented in which the effect of drug content and its dependence on flow rate, the mixing time and the type of drug is studied. Furthermore, it is investigated whether the effect depends on the range within which the drug content is changed. Quantitative and qualitative multiple order interactions are observed between these variables, which may be explained by a shifting balance between three different mechanisms. The results therefore demonstrate that accounting for (multiple order) interactions between variables has to be part of quality by design activities and the rational design of future experiments.</p>

Metal Organic Vapour Phase Epitaxy for the Growth of Semiconductor Structures and Strained Layers

The technological development of semiconductor materials started in the period following the second world war. In the electronics industry, the first transistors were fabricated from germanium, later from silicon. It was soon realized that also the AIII–BV or AII – BVI materials (most often simply termed III–V or II–VI materials) exhibited semiconductive behaviour. The energy difference between the valence band and the conduction band made them candidates for electronic devices which can absorb or emit phonons over a range of frequencies (wavelengths). Direct bandgap materials such as gallium arsenide (GaAs) were suitable for devices in which efficient electron-hole recombinations could take place and high efficiency light emitting devices were a possibility. Stimulated emission was first demonstrated in 1970 with the preparation of the single heterojunction and the double heterojunction laser diodes. These devices are multiple layer structures with a thin waveguide region contained between layers of larger bandgap and different refractive index (for confinement of carriers and radiation, respectively, in the active region). A basic laser diode chip consists of two parallel facets, (110) planes, which are prepared by cleavage and act as mirrors. The Fabry-Perot cavity is defined by these two parallel facets and the passive (cladding) layers. In the longitudinal direction current definition is by mesa etching and/or stripe-contact metallization

Activity of chemolithotrophic nitrifying bacteria under stress in natural soils

Nitrification is an important process in the biogeochemical cycle of nitrogen, linking its reduced and oxidized parts. Since the conversion of ammonium to nitrate has a great impact on the environment, such as weathering of soils, production of greenhouse gases, and eutrophication of surface and ground waters, it is important to know the characteristics of the responsible organisms. Although many organotrophic microorganisms are able to produce oxidized nitrogenous compounds such as nitrite and nitrate, chemolithotrophic nitrifying bacteria are considered to be the most important group producing these compounds from ammonia. A contribution to nitrate production by organotrophic microorganisms has only been observed in some acid coniferous forest soils