Acoustic & Electromagnetic Waves, by D. S. Jones, Oxford tne propagation of waves. The topics range from Maxwell's University Press, Oxford, 1986. $145.00 equations, special relativity, waveguides, to scattering processes. The treatment is almost wholly concerned with the REVIEWED BY J. M. GALLIGAN 1 macroscopic aspects of these topics. The more mathematical aspects of the book are collected in a number of appendices, This highly mathematical treatment of acoustic and elec-including special function such as Mathieu, Legendre, Bessel tromagnetic waves by D. S. Jones considers rather extensively functions and the like. The book is written with the specialist in mind and those who need a coherent treatment of wave propagation. The price, as with most highly specialized books, is out of sight.
Atomic force microscope and scanning tunneling microscope images of photoluminescent anodically etched porous silicon are presented and the development of the porous structure due to different etching stages is investigated. These measurements show that the vertical surface roughness increases with etching while the lateral dimensions remain almost constant, in agreement with known etching models. In addition, the results give strong evidence for an amorphous surface layer that partially covers the porous structure. Tunneling spectroscopy of porous silicon and unetched silicon are also presented. The surface density of states (DOS) measurements of porous silicon are compared with its photoluminescence spectrum. The DOS measurements do not show a peak corresponding to the 1.8 eV photoluminescent peak energy nor do they show an increase in the band gap energy of porous silicon compared with crystalline silicon. However, these measurements do show that while the unetched silicon surface remains p type, the porous silicon surface behaves like an n-type material.
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