Inelastic Electron Scattering at Low Temperatures

We have recently installed a low-temperature sample mount on the Virginia Inelastic electron scattering spectrometer that will allow us to broaden our capabilities. We start by discussing the experimental and theoretical background necessary to understand the work included here. Then the sample mount is described. The high Voltage (300 kV) involved in the electron spectrometer presents numerous problems which must be overcome. The solutions to these problems are discussed. Then we discuss a project accomplished using the new sample mount. We have measured the electron energy loss spectrum of cubic solid nitrogen from 2 to 60 eV energy loss and out to 1.1 A^{ -1} momentum transfer. We have performed a Kramers-Kronig analysis and evaluated the oscillator strength of a quadrupole molecular transition and compared our results with the analogous results obtained on molecular nitrogen. We find that the results are markedly different as a function of momentum transfer, and conclude that the difference is due to local field effects. We have computed the local field factor as a function of momentum transfer and find good agreement with theoretical predictions. This is the first direct measurement of this effect.