A theoretical study of light emission from nanoscale silicon

In comparing our calculated exciton energies with those obtained from pseudopotential calculations (Ref. 27) and from a previous tight binding calculation (Ref. 30), we stated that the differences between the three semi-empirical calculations arise because of different treatment of the nanocrystal surfaces. This appears not to be correct. Subsequent calculations with variable Si-H parameters have shown that the band gap is actually rather insensitive to the actual value of these. Instead, the important feature appears to be the overall quality of the bulk band structure parameterization. References 27 and 30 use more extensive and higher quality empirical parameterizations for bulk Si than the sp³s∗ model used by us. Repeating our time dependent calculations with an improved sp³d⁵ parameterization results in similar values to those of Refs. 27 and 30 for the exciton energies.¹ The agreement of the sp³s∗ values with experimental photoluminescence energies (Fig. 7) cannot, therefore, be regarded as well understood at this time.^1,2     

Low-pressure pyrolysis studies of a new phosphorus precursor: Tertiarybutylbis(dimethylamino)phosphine

The low pressure decomposition of tertiarybutylbis(dimethylamino) phosphine, (t-Bu)P(NMe₂)₂, (TBBDMAP), has been studied on quartz and deposited GaP and InP surfaces. This new phosphorus precursor has been found to pyrolyze on quartz surfaces at much lower temperatures than the related compounds tertiarybutylphosphine, (t-Bu)PH₂, (TBP) and tris(dimethylamino)phosphorus, P(NMe₂)₃, (TDMAP). In contrast to the results obtained for TDMAP, GaP and InP surfaces decrease the decomposition temperature of TBBDMAP only slightly. The TBBDMAP reaction products were dimethylamine, methylmethyleneimine, and isobutylene, consistent with previous pyrolysis studies of TBP and TDMAP.     

Design and evaluation of an Ethernet-based residential network

When the information superhighway arrives at the neighborhood, a residential network will connect home appliances to the community access network. These appliances include personal computers, printers, and video clients. Among all local-area network (LAN) protocols, Ethernet is the most economic and the most popular. The unique characteristics of residential networks call for new performance studies. A residential network typically has few nodes and runs different applications than business and academic LANs. Consequently, residential networks have traffic characteristics different from the subject of existing studies. We constructed a residential network testbed to collect typical application traffic statistics. Additional live traffic characterization was obtained from campus networks. Also, we investigated the suitability of Ethernet for video distribution through simulation. This paper discusses the design issues for residential networks and presents a network design that is based on Ethernet technology. Traffic models are established from the actual traffic traces and used for the performance evaluation of residential networks. Furthermore, several future data traffic scenarios are considered with bandwidth up to 6 Mb/s by scaling up current data traffic. The simulation results of the performance suggest that Ethernet can be used as a cost-effective residential network for video and data communications     

Electrical and optical properties of self-assembled quantum dots

One of the main directions of contemporary semiconductor physics is the production and study of structures with a dimension less than two, i.e. quantum wires (QWi) and quantum dots (QDs), in order to realise novel devices that make use of low-dimensional confinement effects.One of the promising fabrication methods is to use self-organised three-dimensional (3D) structures, such as 3D coherent islands, which are often formed during the initial stage of heteroepitaxial growth in lattice-mismatched systems. Quantum dots, for example, are believed to provide a promising way for a new generation of optical light sources such as injection lasers. While quantum well structures are already widely used in optoelectronic devices, QWi and QDs appear to be much more difficult to fabricate for this purpose. Some of the electrical and optical properties of self-assembled QDs will be reported in this paper.     

Beam-cavity interaction circuit at W-band

In this paper, we describe the design, fabrication, and bench study of a millimeter-wave cavity employed as a relativistic klystron output structure. The oxygen-free electronic-grade copper cavity was prepared by electro-discharge machining and diffusion bonding, and cleaned and tuned to 91.4 GHz. Measured cavity characteristics are presented and compared with theory, including quality factor Q, coupling parameter β, scattering matrix S₁₁, and axial electric field profile E_z. This paper provides the basis for an understanding of the cavity as a transfer structure     

Changes in the opto-electronic properties of CuInSe2 following ion implantation

The development of efficient thin-film solar cells based on CuInSe₂ absorber layers has encouraged fundamental research on both thin films and single crystals of this chalcopyrite semiconducting compound. The resistance to radiation and ion bombardment is of technical importance particularly for a material which could find future applications in space photovoltaic power systems. In this paper results are described for an ion implantation study using CuInSe₂ single crystal substrates. Oxygen, helium and neon implantations have produced significant changes in surface resistivity and photoconductivity. Also the near-surface regions ofn-type crystals have been type-converted top-type following ion implantation. It is apparent that the ion implantation process creates defects which affect surface state densities and recombination probabilities. In the case of oxygen there is an additional doping effect caused either by the introduction of acceptor states or by the reduction of the existing donor state population. Following implantation there appears to be an overall decrease in carrier recombination at the surface which leads to an enhanced photoconductive response.     

Atmospheric emission and attenuation in the range 100 to 600 GHz measures from a mountain site

Further measurements of atmospheric emission from a site in the Canary Islands (Izana, âltitude 2.4 km) have been made during the month of August 1980. The measurements were made with a polarising Interferometer and a composite Ge bolometer. An independent measurement of the precipitable water vapour was made using Infrared Hygrometers. The experimental details are described and the spectra obtained are compared with model spectra using the measured precipitable water vapour.     

The polymerase chain reaction: Applications for the detection of foodborne pathogens

Faster methods for the detection of foodborne microbial pathogens are needed. The polymerase chain reaction (PCR) can amplify specific segments of DNA and is used to detect and identify bacterial genes responsible for causing diseases in humans. The major features and requirements for the PCR are described along with a number of important variations. A considerable number of PCR‐based assays have been developed, but they have been applied most often to clinical and environmental samples and more rarely for the detection of foodborne microorganisms. Much of the difficulty in implementing PCR for the analysis of food samples lies in the problems encountered during the preparation of template DNAs from food matrices; a variety of approaches and considerations are examined. PCR methods developed for the detection and identification of particular bacteria, viruses, and parasites found in foods are described and discussed, and the major features of these reactions are summarized.     

A note on the lactation performance of twin-bearing cows

Seven pairs of cows were chosen at parturition. In each pair, 1 member had had a twin pregnancy (T) and the other was a comparable cow with a single calf pregnancy (S). All cows were offered the same amount of feed over the first 28 weeks of lactation. In early lactation, intakes were equal; in mid-lactation the T group ate more. The T cows had a lower peak yield of milk than the S cows, but rates of decline in yield in mid-lactation were equal for the 2 groups. Lactose concentrations in the milk were equal throughout lactation, but the fat and protein concentrations were greater for the T group in early lactation. The T group yielded smaller amounts of milk solids. The T group lost less weight in early lactation and gained more weight subsequently. Three of the T group, but only 1 of the S group, did not conceive during the test lactation.     

Avalanche multiplication characteristics ofAl0.8Ga0.2As diodes

The avalanche multiplication characteristics of Al_0.8Ga _0.2As have been investigated in a series of p-i-n and n-i-p diodes with i-region widths, w, varying from 1 μm to 0.025 μm. The electron ionization coefficient, α, is found to be consistently higher than the hole ionization coefficient, β, over the entire range of electric fields investigated. By contrast with Al_xGa _1-xAs (x⩽0.6) a significant difference between the electron and hole initiated multiplication characteristics of very thin Al_0.8Ga_0.2As diodes (w=0.025 μm) was observed. Dead space effects in the diodes with w⩽0.1 μm were found to reduce the multiplication at low bias below the values predicted from bulk ionization coefficients. Effective α and β that are independent of w have been deduced from measurements and are able to reproduce accurately the multiplication characteristics of diodes with w⩾0.1 μm and breakdown voltages of all diodes with good accuracy. By performing a simple correction for the dead space, the multiplication characteristics of even thinner diodes were also predicted with reasonable accuracy