Scraping, single crystals

P6 9-10 2p(ris subband) non-observed surface observed for non composition cleaved or Ar-effect sputtered single crystals nonobserved for in situ scraped single crystals 2p(6d) very weak resonance character behaviour, i.e. no 5 f ofv.b, character... 

Schneider and Laubschat attribute to a two-hole satellite the 10 eV structure which has been observed (see Table 3) by some authors. This structure is at 7 eV higher binding energy than the main 5 f peak, in the spectrum of UO2. It disappears, however, for in situ scraped single crystals. A similar satellite structure appears in PUO2 at 9... 

Recent UPS/XPS measurements have been performed in our laboratory on UO2.0 single crystals the surface of which had been prepared in different ways (Ar -sputtering in situ scraping). These results are shown in Fig. 22 and illustrate the 5f character of... 

Inasmuch as single-crystal data, as we will see, are more out of line with bulk properties than polycrystal data, it is occasionally suggested that this could be due to a surface effect. Unfortunately this runs counter to conventional wisdom which states that best coupling to the bulk is obtained in single crystals at normal emission. Indeed, polycrystals, especially scraped polycrystals, are far more likely to exhibit strong surface effects. 

To sum up this section, then, it is apparently crucial for a correct measurement of the near- F intensities in heavy fermions that the surface is a single crystal. Scraping of the surface should be particularly avoided since it was found that in YbAgCu4, a material having a Tk of about 35 K, the scraping of a coarse-grained surface totally eliminated all divalent 4f features (Arko et al., impubhshed), much more consistent with thermodynamic... 

It appears, then, that in Ce compounds there is no temperature dependence of the DOS over and above conventional effects. The same appears to be true in Yb compounds at least where single-crystal data are concerned. Data from scraped polycrystalline surfaces clearly display stronger temperature effects and it remains to be determined whether disruption of the narrow bands by scraping changes the 4f electronic structure sufficiently that the single-impurity case is actually reali2 d. 

Fig. 48. Comparison of an angle-resolved spectrum at resonance (110 eV) with a spectrum at Av = 30eV in single-crystal USb2. Note the improved momentum and energy resolution. The sharp near-E p spike at /iV = 30eV is no more than 30 meV FWHM, thus making it the sharpest f-electron feature ever observed. A difference spectrum of scraped polycrystal UPt, is included to illustrate previous measurements of 5f-DOS width.

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