Pressure-induced structural and electronic transitions, metallization, and enhanced visible-light responsiveness in layered rhenium disulphide

Triclinic rhenium disulphide ($\mathrm{Re}{\mathrm{S}}_2$) is a promising candidate for postsilicon electronics because of its unique optic-electronic properties. The electrical and optical properties of $\mathrm{Re}{\mathrm{S}}_2$ under high pressure, however, remain unclear. Here we present a joint experimental and theoretical study on the structure, electronic, and vibrational properties, and visible-light responses of $\mathrm{Re}{\mathrm{S}}_2$ up to 50 GPa. There is a direct-to-indirect band-gap transition in $1T\text{−}\mathrm{Re}{\mathrm{S}}_2$ under low-pressure regime up to 5 GPa. Upon further compression, $1T\text{−}\mathrm{Re}{\mathrm{S}}_2$ undergoes a structural transition to distorted-$1T^{\prime }$ phase at 7.7 GPa, followed by the isostructural metallization at 38.5 GPa. Both in situ Raman spectrum and electronic structure analysis reveal that interlayer sulfur–sulfur interaction is greatly enhanced during compression, leading to the remarkable modifications on the electronic properties observed in our subsequent experimental measurements, such as band-gap closure and enhanced photoresponsiveness. This study demonstrates the critical role of pressure in tuning materials properties and the potential usage of layered $\mathrm{Re}{\mathrm{S}}_2$ for pressure-responsive optoelectronic applications.

Figure 1

Structure details, synchrotron XRD patterns, and pressure dependence of the unit-cell volume of $\mathrm{Re}{\mathrm{S}}_2$. (a) The cross-section illustration of layered distorted-$1T$ $\mathrm{Re}{\mathrm{S}}_2$. (b) Schematic diagram of the high-pressure diamond-anvil cell setup. (c) The cross-section illustration of layered distorted-$1T^{\prime }$ $\mathrm{Re}{\mathrm{S}}_2$. (d) Selected XRD patterns of $\mathrm{Re}{\mathrm{S}}_2$ under high pressure. Red stars marking the diffraction peak from distorted $1T^{\prime }$. (e) The volume data of both phases of $\mathrm{Re}{\mathrm{S}}_2$ as function of pressure fitted by third-order Birch-Murnaghan equation of state.

Figure 2

Normalized pressure $F$ vs Eulerian strain $f$. (a) $F$ and $f$ derived with reference volumes at ambient pressure ($V_0$) from BM-EoS for both phases. (b) $F$ and $f$ calculated using the reference pressure of 8.9 GPa for $1T^{\prime }$ phase. Solid lines in both plots are linear fits using Eq. (4).

Figure 3

Raman spectra results of $\mathrm{Re}{\mathrm{S}}_2$ under high pressure. (a) At room temperature and various pressures up to 50 GPa. The prominent modes $E_g$, $E_g$-like, $C_p$, and $A_g$-like are indicated by arrows. (b) The evolution of the most prominent Raman peaks of $\mathrm{Re}{\mathrm{S}}_2$ as a function of pressure. (c) The calculated bond lengths in $1T$ phase and $1T^{\prime }$ phase $\mathrm{Re}{\mathrm{S}}_2$ as a function of pressure. Inset shows the shortest S–S bond between layers. (d)–(f) The key out-of-plane phonon mode $A_g$-like is shown in ELF profiles.

Figure 4

Electric property measurements and the evolution of band gaps of $\mathrm{Re}{\mathrm{S}}_2$ under high pressure. (a) Electrical resistance of $\mathrm{Re}{\mathrm{S}}_2$ as a function of pressure at room temperature. (b)–(d) The temperature dependence of the resistance of $\mathrm{Re}{\mathrm{S}}_2$ at 12.3, 17.6, and 38.5 GPa, respectively. (e) The calculated pressure-dependent band gap of layered $\mathrm{Re}{\mathrm{S}}_2$. The first two data points calculated from distorted $1T$ phase, others from distorted $1T^{\prime }$ phase. The band-gap closure is observed at 40 GPa. The band-gap dependence on pressure was fitted using a quadratic function, $E_g=E_0+aP+b{P}^2$, where $a=-51\mathrm{meV}\mathrm{GP}{\mathrm{a}}^{-1}$ and $b=0.47\mathrm{meV}\mathrm{GP}{\mathrm{a}}^{-2}$.

Figure 5

The calculated valence band and conduction band for various models of $1T\text{−}\mathrm{Re}{\mathrm{S}}_2$. (a) ($k_x,k_y,0$) at 0 GPa; (b) ($k_x,k_y,0.5$) at 0 GPa; (c) ($k_x,k_y,0$) at 5 GPa; (d) ($k_x,k_y,0.5$) at 5 GPa.

Figure 6

The calculated density of states for (a), (b) distorted-$1T\text{−}\mathrm{Re}{\mathrm{S}}_2$ at 0 GPa; (c), (d) distorted-$1T^{\prime }\text{−}\mathrm{Re}{\mathrm{S}}_2$ at 65 GPa.

Figure 7

Photocurrent of (a) bulk $\mathrm{Re}{\mathrm{S}}_2$ sample and (b) single-crystal $\mathrm{Re}{\mathrm{S}}_2$ sample as a function of pressure. The sign of “on” and “off” represent visible-light source switch on and switch off, respectively. (c) Photocurrent–pressure dependence of bulk and single-crystal $\mathrm{Re}{\mathrm{S}}_2$ samples.