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We have studied electron transport in two closely spaced, but electrically isolated, two-dimensional electron gases (2DEGs) formed in GaAs/AIGaAs double quantum wells. A frictional drag voltage is found to be induced in one layer when a current is passed through the other. This voltage represents a direct measure of the interlayer electron-electron interactions, since it is determined by the momentum transfer due to scattering events between electrons in the different layers. We present new experimental data, based on a detailed carrier density dependence of these electron-electron interactions. Our results stronglysupporta recent theory proposing an interaction via virtual acoustic phonons. We have shown, in particular, that the 'phonon part' of t h e interlayer scattering rate is a function of the relative electron densities in the layers, with a maximum scattering rate when the densities are matched.

Amorphous hydrogenated silicon carbide (a-Sic : H) films are prepared by magnetron sputtering of crystalline silicon in an argon-hydrogen-methane atmosphere. The specific absorption modes (wagging, rocking, deformation, stretching) of the Sic-, (CH,),C/Si-(n = 1, 2, 3; m = 2, 3), and SiH,-(m = 1,2) groups are assigned and analyzed. The composition of the films is determined by nuclear reaction techniques. Structural, electrical, and optical properties of the films show characteristic changes near an alloy composition of a-Sil-&,: H, x = 0.5 which indicate the transition t o a structure with threefold coordinated carbon. For x 2 0.75 in the infrared absorption spectra an absorption band is identified which arises from graphitic constituents. Amorphe hydrogenierte Siliziumkarbidfilme (a-Sic: H) werden durch Magnetronsputtern von kristallinem Silizium in einer Argon-Wasserstoff-Methan-Atmosphkre hergestellt. Die Zusammensetzung der Filme wird durch Kernreaktionstechniken bestimmt. Die spezifischen Absorptionsmoden (wagging, rocking, deformation, stretching) der Sic-, (CH,),C/Si-(n = 1 , 2 , 3; m = 2, 3) und SiH,-(m = 1, 2)-Gruppen werden analysiert und zugeordnet. Strukturelle, elektrische und optische Eigenschaften der Filme zeigen ab einer Filmzusammensetzung a-Sil -zC,: H, x = 0,5, charakteristische Anderungen, die einen ubergang zu einer Struktur mit dreifach koordiniertem Kohlenstoff anzeigen. Fur x 2 0,75 wird im Infrarotabsorptionsspektrum eine Absorptionsbande identifiziert, die von graphitischen Anteilen herruhrt.

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