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The behaviour of the surface potential of ethanol layers deposited on a cooled substrate was studied. A spontaneous surface potential increase was detected for samples deposited at temperatures close to the well known phase transition (crystallization to crystal I phase) temperature. The activation energy for crystallization was estimated to be 20.7 f 0.4 kl/mol. In addition, thermally stimulated current (TSC) spectra were measured. It was suggested that the amorphous ethanol condensed below 125 K might exist in a glassy state and that the crystallization to crystal I phase runs from a glassy state via a crystal I1 phase.

It is known that the electron bombardment of alkali halide causes radiation damages and considerable decomposition in the surface region [1,2]. In the electron stimulated desorption (ESD) process the halogen is more effectively desorbed leaving the alkali metal enriched target surface. In some cases, the alkali atoms agglomerate to form clusters [3]. Such clusters can serve as a convenient tool for studying the properties of finite alkali and alkali halide grains. In this note, we present results of the electron energy loss spectroscopy (EELS) in the reflectance mode of the LiF/Si(100) system. LiF does not grow epitaxially on Si(100) [4], therefore the sizes of clusters of alkali-halide in this system are expected to be coverage dependent. Our low energy electron diffraction (LEED) data indicate that layer structure substantially depends on the deposition temperature. In particular, at 100 K the substrate two-domain (2 Â 1) pattern vanishes for the coverage of about one ML 1 ) and no other pattern appears. At room temperature, the substrate LEED pattern transforms into (1 Â 1) reconstruction for about one ML and becomes more diffuse during the subsequent deposition of a few ML of LiF. This suggests that LiF islands are much smaller for the lowtemperature deposition than in the case of the room-temperature layer formation.The experiments were performed in a UHV system (5 Â 10 ± ±10 mPa) equipped with several surface analyses instruments, but only the four-grid LEED optics and hemispherical spectrometer were used in this experiment. Primary electron beam of 120 eV and 100 nA/mm 2 (normal to the sample surface) was applied for the loss spectra measurement. LiF films were vapour-deposited from 99.9 % purity LiF crystal pieces onto the Si (100) wafers. The layer deposition rate was about 1.2 ML/min. Hemispherical analyser, used for EELS measurements, was fixed for the measuring of the secondary beam under an angle of 15 to the surface normal. Fig. 1 shows the evolution of EELS spectra with increasing film thickness and, hence, with increasing grain sizes. As it is seen, the LiF features emerge at energies of 10.8 eV, 14 to 18 eV, and about 24.5 eV. The intensities of these characteristic losses grow with LiF coverage while their energy positions are stable. Moreover, all these peaks coincide (within the limit of experimental error) with peaks measured for LiF single crystals [5,6]. Such behaviour may be attributed to the strong localization of the electronic states to which the observed characteristic losses correspond. This suggests that not only excitons but also valence electron plasmons (25 eV peak) are localized excitations. Measurements of EELS for LiF layers deposited at 100 K lead to a similar conclusion. An additional confirmation of this conclusion comes from the experiment in which the 6 ML LiF layer was continually bombarded by an electron beam and the loss spectra were measured after variable irradiation doses. In the course of irradiation, all LiF peaks vanish with rates similar one to the other and with...

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