Observed Energy Loss Research Articles

Mechanism of Ultrasonic Loss in Silicon and Aluminum

Attenuation in single crystals of silicon was measured as a function of frequency with a previously described technique. It was confirmed that, as in the case of aluminum, this dependence, in the range of frequencies from 20 to 110 Mc/sec, is of the form α=α0 exp (Cf), where α is attenuation, f is frequency, and α0 and C are constants. Heat-treating experiments indicate that the form in which oxygen is present in the material has a pronounced effect on the energy loss. Multiple scattering is proposed as a mechanism of loss in silicon and aluminum single crystals. An empirical model of multiple scattering is discussed. It is confirmed that dislocations in silicon, at room temperature, do not contribute to the observed energy loss. Also it is proposed that the accepted relation for the evaluation of thermoelastic losses should be modified.

Excitation of π Electrons in Polystyrene and Similar Polymers by 20‐keV Electrons

Excitation of the π electrons in thin films of polystyrene and some similar polymers has been observed in the characteristic energy loss spectra of 20‐keV electrons scattered at zero angle. The observed energy loss of approximately 7 eV corresponds to the strong uv absorption near 1800 Å in benzene and its derivatives. An energy loss of 6.97±0.10 eV was measured in films of atactic and isotactic polystyrene, styrene ethylene copolymer, and poly 2,3,4,5,6‐pentadeuterostyrene, and an energy loss of 7.25±0.15 eV was measured in poly 2,3,4,5,6‐pentafluorostyrene. These energy losses appeared as sharp peaks superimposed on a very broad and more intense loss peak with a maximum at 21.3±0.3 eV in all the electron energy loss spectra obtained. The results for the energy loss attributed to the π electrons are correlated with relevant uv absorption data. A discernible decrease in the measured ∼7‐eV loss occurred during electron bombardment of the specimens, and is attributed to film contamination and breakdown. The angular distribution of the intensity of each loss in isotactic polystyrene about zero scattering angle was also measured.