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Roughening procedures including the early stage of the O,+-induced ripple formation of GaAs were studied quantitatively by scanning tunnelling microscopy (STM). Detailed examinations of the beginning of topography develop ment using fast Fourier transform of the STM images revealed that the ripple formation was not caused by any accidental defects, particles or original irregularity on the substrate, but solely by the conditions of the ion b e a m A systematic investigation of the rippled GaAs surface produced under various 0,' bombardment conditioas was conducted. The ripple wavelength and the transition depth were almost exactly proportional to E,.cos 0, where Ep and 8 are the energy of the ion beam and the incident angle, respectively. For GaAs, the secondary ion yield transition occurs when the slope of ripples facing the incident'0,' beam reaches a saturation angle of 20-30" from the macroscopic surface plane. Topography change on other 111-V semiconductors was also examined for comparison. There was no ripple generation observed for Gap; InP gave a ripple-like structure without secondary ion yield change. A relatively rough surface resulted on GaSb and InAs at a much shallower depth than for GaAs. Rippling and ion yield changes during depth profiling have been suppressed successfully by sample rotation even in a magnetic sector-based instrument.

Polyacetylene, which consists entirely of conjugated double bonds, exhibits a number of interesting features with regard to optical, electronic, or magnetic properties such as a nonlinear optical effect,1 electrical conductivity,2 or ferromagnetism.3 Especially, synthesis of polyacetylene films with few sp2 defects has been the subject of many efforts to prepare organic polymer films of high electrical conductivity.4This paper reports that a monolayer of polyacetylene type can be prepared from (19-(trimethylsilyl)-18nonadecynyl)trichlorosilane ((CH3)3SiC=C(CH2)i7Si-CI3: SA-NTS) adsorbed monomolecularly on a silicon substrate by a chemical adsorption (CA) technique developed by Sagiv5-9 followed by polymerization initiated either by (1) catalysts or by (2) high-energy electron beam (EB) irradiation.SA-NTS was selected as film substance in this study, because the polymerization process of (silylmethyl)acetylene derivatives was studied in detail.10-13Synthesized SA-NTS was characterized by NMR, IR, and mass spectrometry. The purity of the compound was determined to be 94.4% by gas chromatography. The method of synthesis will be published elsewhere. The substrate on which the SA-NTS monolayer was deposited was a Si wafer covered with SI02/A1 prior to use for the measurement of IR spectra or a quartz plate for the UV spectra. Other chemicals used, unless otherwise noted, were obtained from Aldrich Chemicals Co., in pure grade, and used without further purification.

Systems Analysis for the Control of Toxics. S. K. Friedlander wishes to express his appreciation for a senior Humboldt award from the German government during the course of this research. Nomenclature A0 preexponential factor, gg/(s-m1 2'Torr) dp diameter of elementary soot spheroids, nm dp0 initial diameter of soot spheroids, 20 nm £a activation energy, kcal/mol k surface reaction rate constant, #ig/(s-m2) kB Boltzmann constant, 1.38 X 10"18 erg/mol m mass of an oxygen molecule, 5.31 X 10"23 g M soot loading per cross sectional area of the filter, jitg/cm2 Mcat catalyst loading per filter cross sectional area, mg/cm2 MWc molecular weight of carbon, 12 g/mol N number of soot spheroids in filter/cm2 iVAv Avogadro number, 6.023 X 1023 mol"1 Pq2 partial pressure of oxygen, Torr t time, s if total reaction time, s T temperature, K p density of the elementary soot spheroid, 2 g/cm3

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