Structure of glassy lithium sulfate films sputtered in nitrogen: Insight from Raman spectroscopy and ab initio calculations

Raman spectra of thin solid electrolyte films obtained by sputtering a ${\mathrm{Li}}_2\mathrm{S}{\mathrm{O}}_4$ target in nitrogen plasma are measured and compared to ab initio electronic structure calculations for clusters composed of 28 atoms. Agreement between measured and calculated spectra is obtained only when some oxygen atoms are replaced by nitrogen atoms and when these nitrogen atoms form bonds with each other. This suggests that the incorporation of nitrogen during the sputtering process leads to structures in the film, which prevent crystallization of these thin film salt glasses.

Figure 1

(a) Polarized and (b) depolarized difference Raman spectra of LISON films on a silicon substrate. The difference signal is obtained by subtracting the spectrum of a bare silicon substrate from the spectrum of the sample. The insets show the raw data from the sample and the substrate (dashed lines, silicon; solid lines, LISON film sample). The spectra have been offset for clarity.

Figure 2

(a) Polarized and (b) depolarized difference Raman spectra of films on a silicon substrate, which were sputtered from a $0.7{\mathrm{Li}}_2\mathrm{S}{\mathrm{O}}_4\text{−}0.3\mathrm{Li}\mathrm{B}{\mathrm{O}}_2$ target in an argon atmosphere. As in Fig. 1, the difference signal is obtained by subtracting the spectrum of a bare silicon substrate from the spectrum of the sample. The insets show the raw data from the sample and the substrate (dashed lines, silicon; solid lines, film sample). The spectra have been offset for clarity.

Figure 3

Comparison of two calculated Raman spectra for ${\mathrm{Li}}_2\mathrm{S}{\mathrm{O}}_4$ clusters with the experimental Raman data.

Figure 4

Comparison of four calculated Raman spectra (dotted lines) for LISON clusters with the experimental Raman data (solid lines).

Figure 5

(Color online) Atomic configuration of the optimal LISON cluster (corresponding to spectrum 1 in Fig. 4). Oxygen atoms are marked in red (dark gray, large spheres), sulfur atoms in yellow (light gray, midsize spheres), nitrogen atoms in blue (dark gray, midsize spheres), and lithium atoms in silver (gray, small spheres).