Band-gap measurements of bulk and nanoscale hematite by soft x-ray spectroscopy

Abstract

Chemical and photochemical processes at semiconductor surfaces are highly influenced by the size of the band gap, and ability to control the band gap by particle size in nanomaterials is part of their promise. The combination of soft x-ray absorption and emission spectroscopies provides band-gap determination in bulk and nanoscale itinerant electron semiconductors such as CdS and ZnO, but this approach has not been established for materials such as iron oxides that possess band-edge electronic structure dominated by electron correlations. We performed soft x-ray spectroscopy at the oxygen K-edge to reveal band-edge electronic structure of bulk and nanoscale hematite. Good agreement is found between the hematite band gap derived from optical spectroscopy and the energy separation of the first inflection points in the x-ray absorption and emission onset regions. By applying this method to two sizes of phase-pure hematite nanoparticles, we find that there is no evidence for size-driven change in the band gap of hematite nanoparticles down to around 8 nm.

Magnetic, dielectric and photo-absorption study of a ferromagnetic semiconductor α-Fe1.4Ga0.6O3

“…The intercept of the (αhν) 2 vs. hν straight line on the hν axis provides E g of the sample. 46,47 The band gap energy of α-Ga 2 O 3 and α-Fe 2 O 3 are 4.61 eV and 2.08 eV, respectively are well compared with reported values. 47 The calculated band gap energy of the Ga doped samples is in between the band gap of α-Ga 2 O 3 (4.61 eV) and α-Fe 2 O 3 (2.08 eV), in other words more close to the band gap value of α-Fe 2 O 3 .…”

“…46,47 The band gap energy of α-Ga 2 O 3 and α-Fe 2 O 3 are 4.61 eV and 2.08 eV, respectively are well compared with reported values. 47 The calculated band gap energy of the Ga doped samples is in between the band gap of α-Ga 2 O 3 (4.61 eV) and α-Fe 2 O 3 (2.08 eV), in other words more close to the band gap value of α-Fe 2 O 3 . We noted that band gap energy (∼ 2.08 eV) of α-Fe 2 O 3 has been widened by Ga doping (∼ 2.48, 2.46, 2.41, 2.39 eV for MA20V8, MA60V8, MA100V8 and V8M200 samples, respectively).…”

Electrical transport properties of Ti-doped Fe2O3(0001) epitaxial films

“…6 Pure synthetic hematite is insulating with an experimental bandgap of ~2.2 eV. 7 With generally low conductivity limiting the usefulness of pure hematite, understanding and improving its transport properties has been of considerable interest. 8 Early experimental studies suggested that hematite exhibits an unusually low electron mobility.…”

X-ray spectroscopies studies of the 3d transition metal oxides and applications of photocatalysis

“…Through the RIXS investigations, the aforementioned blue-shift of the X-ray emission, which corresponds to the occurrence of the indirect bandgap, has been seen in diamond, Be chalcogenides, metal doped and pristine BiVO 4 , and Fe 2 O 3 . [37][38][39][40][41] To further demonstrate the correlation between size and band gap we refer to previous studies on the electronic properties of Fe 2 O 3 by Vayssieres et al 40,42 Previously, observed at the high emission energy region. The blue-shift of the emission spectra is a strong indication that Fe 2 O 3 is an indirect bandgap semiconductor.…”