Anisotropy of the electron spectra of the cleavage surface (100) of layered In4Se3 crystals
Chem. Met. Alloys 4 (2011) 63-66
Pavlo V. GALIY, Taras M. NENCHUK, Ostap R. DVERIY, Yaroslav B. LOSOVYJ
It is shown from angle resolved ultraviolet photoemission spectroscopy that the ordered surfaces of the In4Se3 (100) system exhibit anisotropy of the electron spectra (i.e. discernable and significant valence band dispersion), both parallel and perpendicular to the cleavage plane. Parallel to the cleavage plane, the electron spectra differ along the crystallographic axes b and c. Band widths (extent of dispersion) of @ 1 eV are observed along the surface chain rows and about 0.5 eV perpendicular to the surface “furrows”. The downward dispersion (towards greater binding energy) of the band at the valence band maximum, away from the G point, can be understood since this band is dominated by In-s and Se-py bonds. The band widths of 0.3 to 0.4 eV perpendicular to the chain direction (G-Y) and 1.25 eV along the chain direction (G-X), for bands within the valence region, are in line with the expectations from the calculated band structure.
(a) Schematic crystal structure of In4Se3. The lattice constants of the crystal structure are: a = 15.296(1) Å, b = 12.308(1) Å, c = 4.0806(5) Å; space group Pnnm; the structure is dominated by (In3)5+ multivalent clusters bonded to selenium through ionic covalent bonds. The cleavage direction is indicated by the triangle in the upper left; (b) STM image of a 30×30 nm2 crystal fragment of the interlayer cleavage (100) surface of In4Se3, corresponding to the crystal structure (a) and 2D/3D In chain along the x direction (lattice spacing c) is indicated.
Layered crystals / Angle resolved ultraviolet photoemission spectroscopy / Electron spectra / In4Se3