No abstract

The band structure of the quasi-one-dimensional transition metal trichalcogenide ZrS 3 (001) was investigated using nanospot angle resolved photoemission spectroscopy (nanoARPES) and shown to have many similarities with the band structure of TiS 3 (001). We find that ZrS 3 , like TiS 3 , is strongly n-type with the top of the valence band ∼1.9 eV below the Fermi level, at the center of the surface Brillouin zone. The nanoARPES spectra indicate that the top of the valence band of the ZrS 3 ( 001) is located at Γ. The band structure of both TiS 3 and ZrS 3 exhibit strong in-plane anisotropy, which results in a larger hole effective mass along the quasi-one-dimensional chains than perpendicular to them.

Photocurrent production in quasi-one-dimensional (1D) transition-metal trichalcogenides, TiS3(001) and ZrS3(001), was examined using polarization-dependent scanning photocurrent microscopy. The photocurrent intensity was the strongest when the excitation source was polarized along the 1D chains with dichroic ratios of 4:1 and 1.2:1 for ZrS3 and TiS3, respectively. This behavior is explained by symmetry selection rules applicable to both valence and conduction band states. Symmetry selection rules are seen to be applicable to the experimental band structure, as is observed in polarization-dependent nanospot angle-resolved photoemission spectroscopy. Based on these band symmetry assignments, it is expected that the dichroic ratios for both materials will be maximized using excitation energies within 1 eV of their band gaps, providing versatile polarization sensitive photodetection across the visible spectrum and into the near-infrared.

N-type HfS3in vacuo (left) versus p-type HfS3 in air (right); O2 chemisorption changes the n-type EF to p-type EF.

Theoretical and experimental investigations of various exfoliated samples taken from layered In4Se3 crystals are performed. In spite of the ionic character of interlayer interactions in In4Se3 and hence much higher calculated cleavage energies compared to graphite, it is possible to produce few‐nanometer‐thick flakes of In4Se3 by mechanical exfoliation of its bulk crystals. The In4Se3 flakes exfoliated on Si/SiO2 have anisotropic electronic properties and exhibit field‐effect electron mobilities of about 50 cm2 V−1 s−1 at room temperature, which are comparable with other popular transition metal chalcogenide (TMC) electronic materials, such as MoS2 and TiS3. In4Se3 devices exhibit a visible range photoresponse on a timescale of less than 30 ms. The photoresponse depends on the polarization of the excitation light consistent with symmetry‐dependent band structure calculations for the most expected ac cleavage plane. These results demonstrate that mechanical exfoliation of layered ionic In4Se3 crystals is possible, while the fast anisotropic photoresponse makes In4Se3 a competitive electronic material, in the TMC family, for emerging optoelectronic device applications.