A chemistry home page on the World Wide Web

In this article a brief overview of the World Wide Web (WWW) is given, with some examples of the kind of information and services pertaining to analytical chemistry that can be found there. An existing WWW site that has been set up for analytical chemists is used as a case in point. The article concludes with a brief look at some of the issues raised by publishing on the Internet. Received:15 January 1996 / Accepted: 28 January 1996     

Multiple quantum well mixing and index-guided quantum well heterostructure lasers by MeV ion implantation

In recent years considerable interest has been shown in impurity-induced compositional disordering of III–V compound semiconductor devices, especially in efforts directed towards fabricating index-guided buried heterostructure lasers and other unique photonic and electronic devices. In this work we describe the study of compositional disordering induced by MeV implantation of oxygen and krypton into AlAs-GaAs superlattices and the fabrication of index-guided quantum well heterostructure lasers by MeV oxygen ion implantation.     

High pressure experiments on AlxGa1−xAs-GaAs quantum-well heterostructure lasers

Hydrostatic pressure experiments on Al_xGa_1?xAsGaAs quantum-well heterostructure (QWH) laser diodes are described. Data are presented giving ～11.5meV/kbar for the bandgap vs. pressure coefficient at lower pressures, with a change to 8.5–9meV/kbar at higher pressures. We suggest that this behavior is caused by biaxial and shear stresses in the active region induced by doping or composition mismatch relative to the confining layers, or between the n and p confining layers themselves. A model consistent with the experimental data is presented.     

The emission of slow positrons from magnesium oxide powder

From Monte Carlo analyses of measured time-of-flight spectra for slow positrons traveling down a tube which is first evacuated and then filled with low-density helium gas, it is shown that the positrons leave the MgO-coated source grid at angles close to the normal direction. This result is important for low-energy positron collision studies. An interpretation of the result based on the surface charge held by the oxide is proposed.