Electronic structures of $1T\text{−}\mathrm{Ti}{\mathrm{S}}_2$ and the intercalation compound ${\mathrm{Ni}}_{1∕3}\mathrm{Ti}{\mathrm{S}}_2$ from x-ray spectroscopies: Electron correlation and hybridization effects

Electronic structures of a layered semiconductor $1T\text{−}\mathrm{Ti}{\mathrm{S}}_2$ and a Ni intercalation compound ${\mathrm{Ni}}_{1∕3}\mathrm{Ti}{\mathrm{S}}_2$ are studied by means of $\mathrm{Ti}2p$ and $\mathrm{Ni}2p$ x-ray photoemission (XPS), $2p$ x-ray absorption (XAS), and $2p$ core excited resonance x-ray photoemission spectroscopies. It is found that the charge transfer from the guest Ni atom as well as from the S atom to the Ti atom is playing dominant roles in various spectra of ${\mathrm{Ni}}_{1∕3}\mathrm{Ti}{\mathrm{S}}_2$. The origin of photoemission structures just below the Fermi level is interpreted. The importance of the electron correlation and hybridization effects is confirmed through the satellite features of the XPS and XAS spectra.

Figure 1

$\mathrm{Ti}2p$ XPS spectra (dots) of (a) $\mathrm{Ti}{\mathrm{S}}_2$ and (b) ${\mathrm{Ni}}_{1∕3}\mathrm{Ti}{\mathrm{S}}_2$. The $\mathrm{S}2p$ XPS spectrum (solid line) of $\mathrm{Ti}{\mathrm{S}}_2$ is also shown for comparison. $S_1$, $S_2$, and $S_3$ denote the satellite structures accompanying the $\mathrm{Ti}2p$ XPS main peak of $\mathrm{Ti}{\mathrm{S}}_2$.

Figure 2

$\mathrm{Ti}2p$ XAS spectra of (a) $\mathrm{Ti}{\mathrm{S}}_2$ and (b) ${\mathrm{Ni}}_{1∕3}\mathrm{Ti}{\mathrm{S}}_2$. The numerals (1–4) indicate the excitation energies for the spectra in Figs. 3a, 3b, respectively.

Figure 3

Valence band photoemission spectra in the $\mathrm{Ti}2p$ core excitation region of (a) $\mathrm{Ti}{\mathrm{S}}_2$ and (b) ${\mathrm{Ni}}_{1∕3}\mathrm{Ti}{\mathrm{S}}_2$. The numerals (1–4) indicate the excitation energies for the spectra in Figs. 2a, 2b, respectively. The solid spectra show the difference spectra obtained by subtracting the spectrum 1. The base lines for zero intensity are placed in each spectrum at $E_F$.

Figure 4

Constant initial state spectra measured at various $E_B$ in the valence band of ${\mathrm{Ni}}_{1∕3}\mathrm{Ti}{\mathrm{S}}_2$.

Figure 5

(a) $\mathrm{Ni}2p$ XAS spectrum and (b) valence band photoemission spectra in the $\mathrm{Ni}2p$ core excitation region of ${\mathrm{Ni}}_{1∕3}\mathrm{Ti}{\mathrm{S}}_2$. The numerals (1–4) in (a) and (b) correspond to each other.