The electron-induced dissociation of CO(2) adsorbed at the oxygen vacancy defect on the TiO(2)(110) surface has been investigated at the single-molecular level using scanning tunneling microscopy (STM). Electron injection from the STM tip into the adsorbed CO(2) induces the dissociation of CO(2). The oxygen vacancy defect is found to be healed by the oxygen atom released during the dissociation process. Statistical analysis shows that the dissociation of CO(2) is one-electron process. The bias-dependent dissociation yield reveals that the threshold energy for electron-induced dissociation of CO(2) is 1.4 eV above the conduction-band minimum of TiO(2). The formation of a transient negative ion by the injected electron is considered to be the key process in CO(2) dissociation.

The adsorption of methanethiol and n-propanethiol on the Au(111) surface has been studied by temperature-programmed desorption (TPD), Auger electron spectroscopy (AES), and low-temperature scanning tunneling microscopy (LT-STM). Methanethiol desorbs molecularly from the chemisorbed monolayer at temperatures below 220 K in three overlapping desorption processes. No evidence for S-H or C-S bond cleavage has been found on the basis of three types of observations: (1) A mixture of chemisorbed CH3SD and CD3SH does not yield CD3SD, (2) no sulfur remains after desorption, and (3) no residual surface species remain when the adsorbed layer is heated to 300 K as measured by STM. On the other hand, when defects are introduced on the surface by ion bombardment, the desorption temperature of CH3SH is extended to 300 K and a small amount of dimethyl disulfide is observed to desorb at 410 K, indicating that S-H bond scission occurs on defect sites on Au(111) followed by dimerization of CH3S(a) species. Propanethiol also adsorbs nondissociatively on the Au(111) surface and desorbs from the surface below 250 K.

in rutile TiO 2 (110) from the bulk to the surface has been studied utilizing two experimental techniques. Electron-stimulated desorption of O + ions was employed to kinetically monitor the reaction between oxygen adatoms with Ti i 3+ species at temperatures between 360 and 400 K. Scanning tunneling microscopy was also used to measure the Ti i 3+ diffusion rate. Both methods yield a rate constant k Ti i 3+ ) 5 × 10 -4 s -1 at 393 K. The activation energy as measured by the rate dependence on temperature is ∼1.0 eV. Titania (TiO 2 ) has wide applications in the fields of heterogeneous catalysis, photocatalysis, photovoltaic cells, and gas sensors. 1-4 To better understand the relationship between atomic and electronic structure and reactivity, the rutile TiO 2 (110)-(1 × 1) surface ( Figure 1a) has been extensively studied as a model oxide surface. 1-3,5,6 Surface as well as bulk defects have been postulated as active sites for the chemical and photochemical reactivity of the TiO 2 surface. 1,2,7,8 Since reduced TiO 2 crystals contain interstitial Ti i 3+ ions, 8-15 the diffusion of these ions to the TiO 2 surface may well be involved in a variety of surface processes. Noteworthy is the SMSI (strong metal-support interaction) effect, where TiO x layers, produced by Ti i 3+ diffusion to the surface, cover the surface of metal particles deposited on the TiO 2 surface, strongly affecting the rates of surface reaction on the particles. [16][17][18][19] Therefore, accurate measurements of the rate and activation energy for Ti i 3+ bulk diffusion are crucial for an improved understanding of surface processes driven by Ti i 3+ interstitial ions in the TiO 2 bulk. Because of a lack of sensitivity to buried species the study of interstitial species in the bulk and near surface region is a challenge to conventional surface science methods. Recently, however, it has been found from electron-stimulated desorption (ESD) studies that oxygen adatoms (O t ) on the TiO 2 (110)-(1 × 1) surface (Figure 1a), produced by dissociation of O 2 and chemisorption on the 5-fold-coordinated Ti (Ti 5c ) sites, 6,20-22 have a very high ionic cross section for O + production. 23 The high sensitivity of ESD to the O t adatoms therefore provides an excellent tool to measure the kinetics of the reaction between O t adatoms and out-diffusing Ti i 3+ interstitial species. In this letter we study the kinetics of interstitial Ti i 3+ species diffusion through rutile TiO 2 (110) crystals using both ESD and high-resolution scanning tunneling microscopy (STM). Monitoring the reaction between chemisorbed oxygen atoms with Ti i 3+ species at temperatures between 360 and 400 K by means of ESD allows us to deduce the rate and activation energy for the diffusion process. Excellent agreement is found for the Ti i 3+ diffusion rate constant at 393 K, which is ∼5 × 10 -4 s -1 as extracted independently from ESD and STM studies. In addition, an energy barrier of ∼1 eV was estimated for the diffusion of Ti i 3+ interstitials toward the surface.The ESD and STM expe...

Nitric oxide (NO), a radical gas molecule produced by nitric oxide synthase, plays a key role in the human body. However, when endogenous NO is overproduced by physiological disorders, severe inflammatory diseases such as rheumatoid arthritis (RA) can occur. Therefore, scavenging NO may be an alternative strategy for treating inflammatory disorders. In our previous study, we developed a NO-responsive macrosized hydrogel by incorporating a NO-cleavable cross-linker (NOCCL); here, we further evaluate the effectiveness of the NO-scavenging nanosized hydrogel (NO-Scv gel) for treating RA. NO-Scv gel is simply prepared by solution polymerization between acrylamide and NOCCL. When the NO-Scv gel is exposed to NO, NOCCL is readily cleaved by consuming the NO molecule, as demonstrated in a Griess assay. As expected, the NO-Scv gel reduces inflammation levels by scavenging NO in vitro and shows excellent biocompatibility. Furthermore, the more promising therapeutic effect of the NO-Scv gel in suppressing the onset of RA is observed in vivo in a mouse RA model when compared to the effects of dexamethasone, a commercial drug. Therefore, our findings suggest the potential of the NO-Scv gel for biomedical applications and further clinical translation.

The adsorption of water on a reduced rutile TiO2(110)-(1×1) surface has been investigated using scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. The STM measurements show that at a temperature of 50 K, an isolated water monomer adsorbs on top of a Ti(5f) atom on the Ti row in agreement with earlier studies. As the coverage increases, water molecules start to form one-dimensional chain structures along the Ti row direction. Supporting DFT calculations show that the formation of an H-bonded one-dimensional water chain is energetically favorable compared to monomer adsorption. In the chain, there are H-bonds between adjacent water molecules, and the water molecules also form H-bonds to neighboring bridging oxygens of TiO2(110). Thermal annealing at T = 190 K leads to the formation of longer chains facilitated by the diffusion of water on the surface. The results provide insight into the nature of the hydrogen bonding in the initial stage of wetting of TiO2.