Effects of Hydrogen on the Electronic State and Electric Conductivity of the Rutile TiO₂(110) Surface

Abstract

The adsorption of atomic hydrogen on a rutile TiO 2 (110) surface was investigated by nuclear reaction analysis (NRA), ultraviolet photoelectron spectroscopy (UPS), and conductivity measurements. The TiO 2 (110) surface was annealed in O 2 of 1 × 10 −4 Pa, which is regarded as a quasi-stoichiometric surface. After exposure to atomic hydrogen, UPS showed a localized in-gap state (IGS) at about 0.8 eV below the Fermi level and downward band bending with a decrease in the work function. Along with these changes, the conductivity was increased by 2.9 µS=□. Our results indicate that hydrogen donates electrons to the substrate. The amount of charge transfer and electric conductivity are discussed on the basis of the experimental data.

Contributions of oxygen vacancies and titanium interstitials to band-gap states of reduced titania

“…Since the monolayer (ML(O b )) of bridging oxygen row is 5 10 14 cm −2 , the creation of 0.1 ML(O b ) would require an exposure of 1.1 10 6 s which is already ∼ 500 times the longest exposure performed in our experiments. Indeed, literature shows that to obtain significant effect of atomic hydrogen on TiO 2 by dissociation on heated tungsten, exposures that are orders of magnitude above ours are required 25,26 .…”

Nuclear Dynamics and Electronic Effects of Hydrogen on Solid Surfaces

“…The UPS spectrum for the clean quasi‐stoichiometric surface of rutile TiO 2 (110) is shown by the black dotted line in Figure (a) . A large intensity ranging from 3 to 9 eV binding energy corresponds to the valence band mainly originating from the O 2p state, and there exists little intensity extending from E F to 3 eV, which represents the band gap.…”

“…It is noted that OH species are also produced by dissociative adsorption of water at an oxygen vacancy site . The presence of hydrogen and its coverage on the surface are unambiguously determined by NRA, which reveals a surface peak corresponding to a saturation coverage of 0.62 ML . A saturation coverage of lower than 1ML is due to the effective repulsion between the partially positively charged adsorbates at a high coverage .…”

“…The charge transfer is evaluated as 0.32 ± 0.08 e/ H from the dipole moment and the hydrogen coverage. This electron transfer from hydrogen to the substrate is consistent with the enhancement of the surface conductivity …”

Blackening of titanium dioxide nanoparticles by atomic hydrogen and the effect of coexistence of water on the blackening

“…2 The reduction of TiO 2 and the production of oxygen vacancies or Ti 3+ , which modify the electronic structure, can be easily caused by vacuum annealing, hydrogen adsorption, electron irradiation, ultraviolet light irradiation, or exposure to molecular or atomic hydrogen. [13][14][15][16] Among these procedures, the exposure to atomic hydrogen is expected to reduce the TiO 2 surface effectively. In this paper, the blackening of the TiO 2 nanoparticles by exposing to atomic hydrogen was studied at various sample temperatures and ambient H 2 pressures.…”