Isotope exchange studies of the oxidation and reduction of SrTiO3 single crystal surfaces by water and hydrogen (original) (raw)
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Surface Science, 1980
,4bout one monolayer of Ti3+ species is detectable at the surface of reduced SrTiOa(111) single crystals by XPS and UPS. 02, Ha and Ha0 have been adsorbed in the dark and the decrease on the concentration of the Ti3+ species has been monitored as a function of the gas exposures. Subsequent band gap illumination partially restores the Ti3+ initial concentration in the cases of Oa and Ha exposures but not in the case of HaO. The Ti3+ photogeneration on the oxygen covered surface is associated with oxygen photodesorption as indicated by XPS and UPS. UPS measurements give evidence for surface hydroxylation resulting from water and hydrogen adsorption. The activity of the stoichiometric SrTiOa(111) crystal face for 02 and Ha adsorption is very low when compared with the reduced SrTiOa samples.
Surface Science, 2004
Strontium titanate (SrTiO 3) is a promising material for resistive high temperature oxygen sensors. Unfortunately, thermal treatment results in undesirable surface reconstruction and the formation of secondary phases. Each of the three stable surface orientations ((1 0 0), (1 1 0) and (1 1 1)) shows a characteristic reconstruction of the topmost layers. To investigate these changes in more detail, SrTiO 3 (1 1 0) single crystals were heated up to 1000°C in ultrahigh vacuum and synthetic air, respectively. Atomic force microscopy (AFM) was applied to characterize the surface topography. Metastable impact electron spectroscopy (MIES) and Auger electron spectroscopy (AES) yielded information on the electronic structure and the chemical composition of the surface and the near surface region. Under all investigated conditions microfaceting of the (1 1 0) surface could be observed resulting in TiO 2-terminated ridges.
Ultraviolet-light-induced desorption of oxygen from SrTiO3 surfaces
We have previously reported that SrTiO 3 -based thin films can be used to detect trace amounts of oxygen (e.g., down to 0.001 ppt). However, the SrTiO 3 surfaces are highly active against oxygen adsorption. Therefore, the slow desorption response can affect the response speed of the sensors against the sudden change in oxygen concentration. We have reported that UV light irradiation is effective for accelerating oxygen desorption, and in this paper, we will show that the increase in the irradiation intensity of UV light can be an efficient way of improving the response speed. As an example, an apparent hysteresis in the sensor resistance versus oxygen concentration curve, which is shown after the UV irradiation at a low intensity, diminishes after the UV irradiation at a high intensity, even after short-lasting treatments.
Na adsorption on SrTiO3 (001) surface and its interaction with water: A DFT calculation
Applied Surface Science, 2013
Na adsorption on SrTiO 3 (0 0 1) surface and its interaction with water were studied by using density functional theory approach. Our results showed that, owing to the stronger screening effect of SrO termination, TiO 2 termination was more favorable for Na adsorption than the SrO termination. Doping with N at the site of oxygen in SrTiO 3 was used to enhance Na adsorption. The adsorption energy of Na adsorption on the N doped SrTiO 3 (0 0 1) surface was enhanced remarkably, which attributed to charge compensation between Na and N. However, the Na adsorbed SrTiO 3 (0 0 1) surface did not facilitate water dissociation, which was consistent with the experimental results.
Journal of Physical Chemistry, 1987
The chemisorption and surface reactions of thiophene, D2 and the hydrodesulfurization products (1,3-butadiene and butenes) have been studied on Re(OOOl) at low ambient pressure (10-9 Torr) using thermal desorption spectroscopy (TDS), low energy electron diffraction (LEED), and Auger electron spectroscopy (AES). D2 adsorption was found to be blocked by sulfur or carbon overlayers. Sulfur pre-adsorption induced small changes in the D2 desorption energy and adsorption was completely blocked above 0.4 monolayers of sulfur (8 =0.4). s Carbon pre-adsorption lowered the temperature of the desorption maxima (380K to 290K), and blocked D" adsorption nonlinearly. Sequential dehydrogenation of "" the adsorbed unsaturated hydrocarbons leading to complete decomposition at high temperatures (> 700K) was observed on the clean Re(OOOl) surface.
MRS Proceedings, 2005
Ab initio calculations based on density functional theory (DFT) were used to study the energetics, geometry of fully relaxed structure, and electronic charge redistribution for adsorbed atomic and molecular oxygen on defectless unreconstructed SrTiO 3 (001) surfaces, both SrO-and TiO 2 -terminated. B3PW functional used in our calculations contains a ''hybrid'' of the DFT exchange and correlation functionals with exact non-local Hartree-Fock (HF) exchange. We performed calculations of two-dimensional slabs with unit cells large enough for the adsorbed species to be treated as isolated. We found substantial binding energies for atomic O adsorption at bridge positions between the two adjacent metal and oxygen surface ions (much closer to the latter) on both SrO-and TiO 2 -terminated surface (over 2.0 eV with respect to free atom). In both cases strong bonding is rather caused by formation of surface molecular peroxide ion in singlet state. For molecular adsorption, different adsorption sites and orientations of O 2 molecule were studied, however, adsorption energy never exceeded 0.1 eV. However, energy gain obtained from adsorption of atomic oxygen is not sufficient for molecule dissociation.
Adsorption and desorption ofSO2on theTiO2(110)−(1×1)surface: A photoemission study
Physical Review B, 2001
By means of synchrotron radiation photoemission spectroscopy, we have investigated the adsorption and desorption processes of the SO 2 molecule on a rutile TiO 2 (110)-(1ϫ1) surface. We have recorded the S 2p core-level photoemission peaks for different SO 2 exposures at a substrate temperature of 120 K in order to get information about the divers species formed on the surface. We have also recorded real-time photoemission spectra to study the adsorption from the early stages to large exposures and to follow the chemical transformations occurring with the adsorbed species as the temperature increases. We have seen that the first arriving molecules react with the oxygen atoms of the surface forming SO x species, both at low and room temperature. Doses higher than the saturation dose ͑6 L͒ lead to the dissociation of the molecule generating adsorbed S. SO 2 multilayer has been found for exposures higher than around 250 L. We have found a progressive reduction of the SO x species with the temperature and the formation of sulphide as the most stable phase. We have not found any signature of molecular ordered species at the interface.
MRS Online Proceeding Library
Ab initio calculations based on density functional theory (DFT) were used to study the energetics, geometry of fully relaxed structure, and electronic charge redistribution for adsorbed atomic and molecular oxygen on defectless unreconstructed SrTiO3(001) surfaces, both SrO- and TiO2-terminated. B3PW functional used in our calculations contains a ‘‘hybrid’’ of the DFT exchange and correlation functionals with exact non-local Hartree–Fock (HF) exchange. We performed calculations of two-dimensional slabs with unit cells large enough for the adsorbed species to be treated as isolated. We found substantial binding energies for atomic O adsorption at bridge positions between the two adjacent metal and oxygen surface ions (much closer to the latter) on both SrO- and TiO2-terminated surface (over 2.0 eV with respect to free atom). In both cases strong bonding is rather caused by formation of surface molecular peroxide ion in singlet state. For molecular adsorption, different adsorption sit...
Reactivity of TiO 2 with hydrogen and deuterium
Applied Surface Science, 2004
The reactivity of rutile phase TiO2 (1 1 0) and polycrystalline anatase surfaces with molecular and ionized deuterium and hydrogen was investigated. Thermal Desorption Spectroscopy (TDS), following exposure to more than 100 kL of molecular deuterium, showed a D2 desorption peak at ∼440 K on both single crystal rutile and polycrystalline anatase surfaces. The desorption peak was observed following exposure only at surface temperatures between 140–270 K. Ionized D2 is significantly more reactive with the titania surface and two desorption peaks at 380 K and ∼550 K were observed together with a small D2O peak observed at ∼440 K. Dosing the surfaces with hydrogen and deuterium either in succession or as a mixture showed HD desorption with no change in the desorption peaks, consistent with dissociative adsorption of both ionized and molecular species. The experimental data was compared to Density Functional Theory calculations and modeled as a two-step process of hydrogen dissociation at oxygen vacancy sites on TiO2.