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Nakao H Ohwada K Takesue N Fujii Y Isobe M Ueda Y Zimmermann M Hill JP Gibbs D Woicik JC Koyama I Murakami Y 《Physical review letters》2000,85(20):4349-4352
Charge ordering of V4+ and V5+ in NaV2O5 has been studied by an x-ray diffraction technique using anomalous scattering near a vanadium K-absorption edge to critically enhance a contrast between the two ions. A dramatic energy dependence of the superlattice intensities is observed below T(C) = 35 K. The charge ordering pattern is the fully charged zigzag-type ladder with the unit cell 2ax2bx4c, but not the chain-type originally proposed for the spin-Peierls state. Charge disproportionation suggested in our model as the average valence V(4.5+/-delta(c)/2) is observed below T(C), showing continuous variation of delta(c) as a function of temperature. 相似文献
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Patrick S. Lysaght Joseph C. Woicik M. Alper Sahiner Byoung-Hun Lee Raj Jammy 《Journal of Non》2008,354(2-9):399-403
A series of 1.4, 1.8, and 4.0 nm thick HfO2 films deposited on Si(1 0 0) substrates have been measured by extended X-ray absorption fine-structure prior to anneal processing, following a standard post deposition anneal of 700 °C for 60 s in NH3 ambient, and following an additional rapid thermal anneal cycle of 1000 °C for 10 s in N2 ambient. Analysis of the second coordination shell gives clear evidence of increased ordering with increasing film thickness at each temperature. Similarly, increased ordering with increasing anneal temperature is evident for each film thickness. Although X-ray diffraction and high resolution transmission electron microscopy indicated the 1.4 nm HfO2 samples to be amorphous, EXAFS has distinguished nanocrystalline from amorphous states for these films. 相似文献