WA 8 t O dt 4. PEMORMIWA ORGAWIATION REPORT NUMIER(S) S. MONITORING ORGANIZATION REPORT h4UMIER(SiP go MAWE OF PERFOR1miNG ORGANIZATION 60 OFFICE SYMIOL 7& IIINE OF MONITORING ORGANIZATION 2we htgert of the Of appicable) 1) OttPsdn dnsttv Wwivrsit of California 2) OMR AlexandriA' Technical G. ADDRESS "O~. &iM. W4d t co*) 7b. A5010*Csft; Strv. u'W 10 Coe)

Thin films that are grown by the process of sputtering are, by and large, quite unlike the smooth, featureless structures that one might expect. In general, these films have a complicated surface morphology and an extended network of grooves and voids in their interiors. Such features can have a profound effect on the physical properties of a thin film. The surface irregularities and the bulk defects are the result of a growth instability due to competitive shadowing, an effect that also plays a role in geological processes such as erosion. For amorphous thin films, the shadow instability can be described by a remarkably simple model, which can be shown to reproduce many important observed characteristics of thin film morphology.

The electron dynamics for electron energies up to 5 eV has been studied by soft x-ray photoemission spectroscopy. Monte Carlo simulations have been performed to derive the energy dependence of the pair-production rate using these results in combination with published data on the ionization coefficient and on the quantum yield for pair production. The obtained ionization rate shows a very soft threshold at 1.2 eV, approaching the results by Kane [Phys. Rev. 159, 624 (1967)] at higher energies. Several published models have been found to be inconsistent with the full set of experimental data we have considered.

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It is shown that LiF(100) films with the electronic properties of cleaved bulk LiF crystals can be grown epitaxially on Ge(100). These include an exceptionally large, negative electron affinity of −2.7 eV, which leads to intense photoemission at zero kinetic energy. The valence band offset ranges from 7.3–7.6 eV.

The band dispersion of the localized, F 2p-like valence band of LiF is mapped using an imaging technique to obtain k(E). The bandwidth is 3.5 eV (from T\s to X'A). This is 17% wider than predicted by first-principles band calculations, implying an expansion of the bandwidth by self-energy effects in qualitative agreement with quasiparticle calculations. The self-energy effect is opposite to that seen in delocalized systems, such as alkali metals.PACS numbers: 71.25.Tn, 79.60.Eq The electronic structure of highly correlated, localized systems is experiencing a renaissance with the advent of high-temperature superconductivity and powerful computational techniques to handle electronic states that are neither completely delocalized (bandlike) nor completely localized (such as core levels). The most basic characteristic of these states is their bandwidth. Its value relative to the Coulomb-exchange energy determines the degree of correlation. The bandwidth has been taken [1-3] as a crucial measure of self-energy effects in testing quasiparticle calculations, which represent the state of the art in band theory. The 3d and 4/, 5/systems typically associated with highly correlated states are rather complex, even in simple crystal structures [4], let alone in the multilayered perovskite structures of high-temperature superconductors. Therefore, it is useful to search for simpler prototype materials containing p or s electrons, preferably with low atomic number. We have chosen the F 2p valence band of LiF as a model system. It may be considered the deepest valence band of any solid because LiF has the largest band gap [5] of ordinary materials (with the exception of exotic solids, such as rare gases). Recently we have found a way to grow LiF(lOO) epitaxially on Ge(100) with bulklike crystal quality [6]. This avoids many broadening effects, such as charging, small crystallite size, and inhomogeneous Fermi-level pinning, which have hampered previous attempts to obtain bandwidths of alkali halides [7-11]. Using angle-resolved photoemission we are able to accurately determine the dispersion and width of the F 2p band in LiF. Our width of 3.5 eV is 17% larger than predicted by first-principles, ground-state band calculations, which shows that selfenergy effects play a role in determining the bandwidth. This agrees qualitatively with the 10% bandwidth increase calculated for LiCl in state-of-the-art quasiparticle calculations. Interestingly, the sign of the self-energy effect is opposite to that for free-electron-like materials, again in agreement with quasiparticle calculations.The band mapping method used here differs from the usual approach of taking angle-resolved photoelectron spectra. Instead of determining the energy distribution of photoelectrons at fixed momentum we obtain the momentum distribution at fixed energy using a display spectrometer [12,13]. Reversing the two variables helps for nar-

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