High-pressure EXAFS measurements of crystalline Ge using nanocrystalline diamond anvils

High-pressure extended x-ray absorption fine structure (EXAFS) measurements on crystalline Ge demonstrate that the use of nanocrystalline diamond anvils can solve the glitch problem from single crystal diamond anvils and improve the quality of the data. Our results indicate that using nanocrystalline diamond anvils for high-pressure EXAFS research can provide a large enough energy range for structural study up to four coordination shell distances. In particular, we obtained the pressure evolution of mean square relative displacement for the first neighbor shells of crystalline Ge and observed different correlation effects for different coordination shells. The use of nanocrystalline diamond anvils will provide a breakthrough for high-pressure EXAFS study, especially for amorphous compounds in which only limited structural information can be obtained by diffraction techniques.

Figure 1

EXAFS signal of Ge obtained with ND anvils (black line) and single-crystal anvils (grey line). EXAFS function of standard amorphous Ge foil obtained without DAC (dotted line). An offset was added to the EXAFS signals.

Figure 2

Normalized XANES absorption spectra at selected pressures (a). Evolution of the edge position with pressure (b). Extracted EXAFS signals k$\chi$(k) ${\AA }^{-1}$ at selected pressure (c). Moduli of the Fourier transform of the experimental EXAFS spectra (d).

Figure 3

EXAFS signal $\chi \left(k\right)$ and the Hanning window used for the Fourier transformation. Results of the quantitative analysis performed on Ge EXAFS data collected using single-crystal diamond anvils. Best fit result at 8.7 GPa (b). Pressure dependence of the Ge-Ge bond lengths up to 60 GPa (c).

Figure 4

Comparison between the experimental EXAFS spectrum collected with ND anvils at 1 GPa (dots) and the best-fit calculation (solid curve) using three Ge-Ge paths. Comparison is reported for the moduli of the Fourier transform (a), the extracted k$\chi$(k)${\AA }^{-1}$ signal (b), and for the real part of the back-transformed signal (c).

Figure 5

Results of the quantitative analysis performed on Ge EXAFS data collected using ND anvils. Pressure dependence of the Ge-Ge bond distances (a). Pressure dependence of the Debye Waller factor (b). Pressure dependence of ${\chi }_{\nu }^2$ obtained analyzing the data collected with ND and single-crystal diamond anvils (c).