Photoelectron spectroscopy

Ultra-violet photoemission spectroscopy has been used in this project to investigate the changes in photoemission spectra across the order/disorder transition in Cu-Au alloys. Many obvious changes are observed in the valence band spectra of the different phases, particularly in the area of Au-related states. In Cu3Au, the binding energy of Au-4f core levels in the ordered phase are shifted from the pure metal value by an average of 0.46 +- 0.05eV to increased binding energy. In CuAu, the corresponding shift value in the ordered phase is 0.33 +- 0.05eV, also to increased binding energy. In both disordered Cu3Au and CuAu the value of the Au4f core level shift is reduced by 0.12eV from that of their ordered states. Some of the results are new, and others are in good agreement with previous studies.

Several Zn single crystals were grown by the Bridgman method and their orientations were determined by the Laue X-ray back-reflection method. Zn(0001) surfaces were prepared by vacuum cleaving and by Ar+ bombardment with annealing. LEED patterns and UPS spectra were taken on both the cleaved and bombarded Zn(0001) surfaces. The LEED patterns from cleaved surfaces showed 6-fold symmetry whereas those from bombarded surfaces showed a hexagonal array but with some differences: the spots with the same distances from the center of LEED pattern had different intensities and they were dimmer and more blurry compared to those from the cleaved surface. A value of 2.64+-0.07 A for the nearest neighbor spacing was determined from the LEED patterns. The UPS spectra showed that for both types of surfaces the 3d peak is at 9.8 eV with a spin splitting of 0.7 eV, which are in agreement with previous experimental and theoretical results. Differences in spectra between the two types of surfaces were found in the ratios of signal/background and in the ratios of the 3d doublet.

Angle-resolved UV photoelectron spectroscopy has been used to investigate some of the properties of the occupied Shockley-type surface states that exist on the (111) surfaces of Cu, Au, ordered Cu3Au and ordered CuAuI. These states appear in normal and off-normal spectra near the Fermi level and their binding energies are independent of photon energy; however, the intensity of their emission relative to that of the d-bands is photon energy dependent, decreasing monotonically from ArI to NeI to HeI. As the emission angle is increased from the normal, the states move towards and eventually cross the Fermi level, and we have measured this dispersion in k space. We show that the occupied extents of the dispersion relations, delta k, are related to features of the bulk band structures. For example, in Cu and Au the surface state follows the dispersion of the uppermost occupied band edge in the vicinity of the L-point and so the delta k extent is related to the (111) neck radius on the Fermi surface. Because the changes in the delta k extents are of the same order as the experimental uncertainty, we are unable to determine precisely how they vary with composition. We have fitted the dispersion data to 'free-electron' parabolas and calculated an effective electron mass in each case; we find that the effective masses in the alloys are somewhat larger than in the pure metals. The photoemission measurements described here on CuAuI(111) are the first ever to be taken on an alloy of that composition.

The techniques of x-ray and ultra-violet photoemission spectroscopies have been used to investigate the electronic structures in Fe-30%Ni and Fe-27.5%Ni alloys in both the bcc and fcc phases. The similarities between the Fe 3s core level spectra, and between the XPS and UPS EDC's of the valence band, from the bcc and fcc phases of the Fe-Ni alloys, provide evidence that the Fe local magnetic moment persists in the fcc phase, and is about the same magnitude as in the bcc phase. The binding-energies of the Fe-2p1/2 and Fe-2p3/2 core levels of Fe-30%Ni and Fe-27.5%Ni are shifted from the values in pure Fe by + 0.40eV +- 0.05eV. The binding-energy of the Fe-3p core level of Fe-30%Ni is shifted from the value in pure Fe by + 0.40eV +- 0.05eV. The intensity of the Ni-3p core level in XPS spectra is considerably decreased when Fe-30%Ni has undergone the martensitic phase transition. The EDC's of the valence bands of Fe-30%Ni, Fe-27.5%Ni (in both the bcc and fcc phases) and pure Fe agree with published data.

A series of measurements of the various core level binding energies were carried out from pure Fe and V metals and three Fe-V alloys using x-ray photoemission spectroscopy. We observed a shift of the Fe and V core levels on alloying; we find that the binding energy shifts of the Fe core levels are small and those for V appear to increase with the number of Fe neighbors. We have also examined the relationship between the lineshape of the Fe 3s spectra and the Fe local moment in the Fe-V alloys. We find that a shoulder on the higher binding energy side of each spectrum becomes less apparent with increasing V concentration, i.e., as the local moment decreases. This implies that the spin-splitting of the Fe 3s core level may be used as a probe of the local moment in Fe-V alloys.