Zhengquan Tan

Accurate X-ray absorption spectra obtained from concentrated bulk samples by fluorescence detection

Abstract We have obtained accurate X-ray absorption spectra from concentrated bulk samples by using a normal incidence low angle fluorescence detection method. Our calculated sampling depth with negligible spectrum distortion in copper samples is ≲8000 A. Our method is a truly bulk probe and is therefore complementary to more surface sensitive methods such as the electron yield technique or the technique utilizing the evanescent wave effect used in a recent study by Suzuki.

Silicide formation in high-dose Fe-implanted silicon

We have studied the silicide formation in Fe-implanted Si(100), with 1{times}10{sup 17}--1{times}10{sup 18} Fe/cm{sup 2}, using extended x-ray absorption fine structure (EXAFS), x-ray diffraction and Rutherford backscattering spectrometry (RBS) methods. In the samples as-implanted at 350{degree}C, no silicide was observed at doses below 3{times}10{sup 17} Fe/cm{sup 2}. At 5{times}10{sup 17}, both {alpha}-FeSi{sub 2} and {beta}-FeSi{sub 2} form but {alpha}-FeSi{sub 2} appears to be the majority phase. As the dose increases to 7{times}10{sup 17} and above, ordered FeSi forms, but implantation damage is severe and a large number of Fe atoms are in very disordered environments. In addition to FeSi, Fe{sub 5}Si{sub 3} was also observed in the 1{times}10{sup 18} Fe/cm{sup 2} sample. Upon post-implantation annealing at 700{degree}C or 900{degree}C, single phase {beta}-FeSi{sub 2} was obtained independent of the dosage. 17 refs., 4 figs.

X-Ray Absorption Studies of Vanadium-Containing Yba 2 Cu 3 O 7

Attempted V substitution leads to small but observable lattice expansions of the YBa 2 Cu 3 O 7 main phase but has little effect on the superconducting transition temperature. X‐ray absorption spectra at the AT‐edges of V, Cu and Y and L3‐edge of Ba have been measured on vanadium‐containing YBa 2 Cu 3 O 7 to address the question of V substitution in this material. We found that only a small amount of V can substitute into the YBa 2 Cu 3 O 7 structure. The excess V forms an impurity phase in which V is tetrahedrally coordinated with oxygens.