Band gap states in nanocrystalline WO3 thin films studied by soft x-ray spectroscopy and optical spectrophotometry.

Nanocrystalline tungsten trioxide (WO3) thin films prepared by DC magnetron sputtering have been studied using soft x-ray spectroscopy and optical spectrophotometry. Resonant inelastic x-ray scattering (RIXS) measurements reveal band gap states in sub-stoichiometric γ-WO3-x with x = 0.001-0.005. The energy positions of these states are in good agreement with recently reported density functional calculations. The results were compared with optical absorption measurements in the near infrared spectral region. An optical absorption peak at 0.74 eV is assigned to intervalence transfer of polarons between W sites. A less prominent peak at energies between 0.96 and 1.16 eV is assigned to electron excitation of oxygen vacancies. The latter results are supported by RIXS measurements, where an energy loss in this energy range was observed, and this suggests that electron transfer processes involving transitions from oxygen vacancy states can be observed in RIXS. Our results have implications for the interpretation of optical properties of WO3, and the optical transitions close to the band gap, which are important in photocatalytic and photoelectrochemical applications.

Adsorption of formic acid on rutile TiO2 (110) revisited: an infrared reflection-absorption spectroscopy and density functional theory study.

Formic acid (HCOOH) adsorption on rutile TiO2 (110) has been studied by s- and p-polarized infrared reflection-absorption spectroscopy (IRRAS) and spin-polarized density functional theory together with Hubbard U contributions (DFT+U) calculations. To compare with IRRAS spectra, the results from the DFT+U calculations were used to simulate IR spectra by employing a three-layer model, where the adsorbate layer was modelled using Lorentz oscillators with calculated dielectric constants. To account for the experimental observations, four possible formate adsorption geometries were calculated, describing both the perfect (110) surface, and surfaces with defects; either O vacancies or hydroxyls. The majority species seen in IRRAS was confirmed to be the bridging bidentate formate species with associated symmetric and asymmetric frequencies of the ν(OCO) modes measured to be at 1359 cm(-1) and 1534 cm(-1), respectively. The in-plane δ(C-H) wagging mode of this species couples to both the tangential and the normal component of the incident p-polarized light, which results in absorption and emission bands at 1374 cm(-1) and 1388 cm(-1). IRRAS spectra measured on surfaces prepared to be either reduced, stoichiometric, or to contain surplus O adatoms, were found to be very similar. By comparisons with computed spectra, it is proposed that in our experiments, formate binds as a minority species to an in-plane Ti5c atom and a hydroxyl, rather than to O vacancy sites, the latter to a large extent being healed even at our UHV conditions. Excellent agreement between calculated and experimental IRRAS spectra is obtained. The results emphasize the importance of protonation and reactive surface hydroxyls - even under UHV conditions - as reactive sites in e.g., catalytic applications.

Spectroscopic study of the photofixation of SO2 on anatase TiO2 thin films and their oleophobic properties.

Photoinduced SO(2) fixation on anatase TiO(2) films was studied by in situ Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS). The TiO(2) films were prepared by reactive DC magnetron sputtering and were subsequently exposed to 50 ppm SO(2) gas mixed in synthetic air and irradiated with UV light at substrate temperatures between 298 and 673 K. Simultaneous UV irradiation and SO(2) exposure between 373 and 523 K resulted in significant sulfur (S) deposits on crystalline TiO(2) films as determined by XPS, whereas amorphous films contained negligible amounts of S. At substrate temperatures above 523 K, the S deposits readily desorbed from TiO(2). The oxidation state of sulfur successively changed from S(4+) for SO(2) adsorbed on crystalline TiO(2) films at room temperature without irradiation to S(6+) for films exposed to SO(2) at elevated temperatures with simultaneous irradiation. In situ FTIR was used to monitor the temporal evolution of the photoinduced surface reaction products formed on the TiO(2) surfaces. It is shown that band gap excitation of TiO(2) results in photoinduced oxidation of SO(2), which at elevated temperatures become coordinated to the TiO(2) lattice through interactions with O vacancies and form sulfite and sulfate surface species. These species makes the surface acidic, which is manifested in nondetectable adherence of stearic acid to the modified surface. The modified films show good chemical stability as evidenced by sonication and repeated recycling of the films. The results suggest a new method to functionalize wide band gap oxide surfaces by means of photoinduced reactions in reactive gases at elevated substrate temperatures. In the case of anatase TiO(2) in reactive SO(2) gas, we here show that such functionalization yields surfaces with excellent oleophobic properties, as probed by adhesion of stearic acid.

Oxidation of Pt(110).

Using scanning tunneling microscopy and temperature programmed desorption we investigate the Pt(110) surface under strongly oxidizing conditions involving either high-pressure O2 or atomic oxygen exposure. At low temperatures, only disordered Pt oxide structures are observed. After annealing ordered surface oxide islands are observed to coexist with a highly stable reconstructed (12x2)-O chemisorption structure. From density functional theory calculations a model for the surface oxide phase is revealed. The phase is found to be metastable, and its presence is explained in terms of stabilizing defects in the chemisorption layer and reduced Pt mobility.

Insulin resistance, dietary cholesterol, and cholesterol concentration in postmenopausal women.

Questions remain concerning the effect of variations in cholesterol intake on plasma cholesterol concentration, as well as on the role of factors modulating the metabolic impact of this dietary intervention. To define the impact of wide variations in dietary cholesterol intake on plasma total and low-density lipoprotein (LDL) cholesterol concentrations, as well as testing the hypothesis that resistance to insulin-mediated glucose disposal would accentuate the increase in plasma total and LDL cholesterol concentrations in response to a given increment in dietary cholesterol intake, we performed a prospective, randomized study comparing diets varying in cholesterol content in 65 healthy, postmenopausal women, 31 defined as insulin-resistant and 34 as insulin-sensitive. The changes in total and LDL cholesterol in response to increments in dietary cholesterol of up to approximately 800 mg/day were modest in magnitude, without evidence of a statistically significant diet-induced increase in cholesterol concentration, or of any difference in the responses of insulin-resistant as compared with insulin-sensitive women. These results indicate that relatively large increments in dietary cholesterol intake had little effect on total or LDL cholesterol concentrations in healthy, postmenopausal women, irrespective of whether they were insulin-resistant or insulin-sensitive.

Bridging the pressure gap in surface science at the atomic level: H/Cu(110).

The structural response of the Cu(110) surface to H2 gas pressures ranging from 10(-13) to 1 bar is studied using a novel high-pressure scanning tunneling microscope (HP-STM). We find that at H2 pressures larger than 2 mbar the Cu(110) surface reconstructs into the ( 1x2) "missing-row" structure. From a quantitative analysis of the pressure dependence of the surface reconstruction, we conclude that Cu(110) responds identically to hydrogen at ultrahigh vacuum conditions and at atmospheric pressures. From the HP-STM data, we extract refined values for the adsorption and desorption rate constants.

Diffusion of N adatoms on the Fe(100) surface

The diffusion of individual N adatoms on Fe(100) has been studied using scanning tunneling microscopy and ab initio density functional theory (DFT) calculations. The measured diffusion barrier for isolated N adatoms is E(d) = (0.92+/-0.04) eV, with a prefactor of nu(0) = 4.3x10(12) s(-1), which is in quantitative agreement with the DFT calculations. The diffusion is strongly coupled to lattice distortions, and, as a consequence, the presence of other N adatoms introduces an anisotropy in the diffusion. Based on experimentally determined values of the diffusion barriers and adsorbate-adsorbate interactions, the potential energy surface experienced by a N adatom is determined.

A prospective, randomized trial of phenytoin in nonepileptic subjects with reduced HDL cholesterol.

Observational studies have demonstrated a positive association between phenytoin use and HDL cholesterol (HDL-C). Our goal was to determine whether phenytoin raises HDL-C in nonepileptic subjects at risk for coronary artery disease. We performed a double-blind, placebo-controlled, parallel-group study in 41 subjects with reduced levels of HDL-C. Subjects were placed on an American Heart Association Step I diet and were randomized to receive either phenytoin or placebo for 3 months. Serum levels of phenytoin were monitored and adjusted to between 7.5 and 15 micrograms/mL. Fasting levels of lipids and lipoproteins were determined twice at baseline (weeks -2 and -1) and during the treatment phase of the study (weeks 11 and 12). Compared with dietary baseline, phenytoin-treated subjects experienced significant paired percent increases in total HDL-C (12.4%; P < .01), an effect confined to the HDL2 subfraction (137%; P < .01). The paired percent increases in HDL-C and HDL2 levels remained significant after adjustment for placebo (P < .05, P < .025, respectively). There were no significant differences in the paired percent changes from dietary baseline in total cholesterol, triglyceride, or LDL cholesterol levels between placebo and phenytoin-treated groups. The significant paired percent increases in total HDL-C and HDL2 from dietary baseline suggest a potential role for phenytoin in subjects with reduced levels of HDL-C.

Thyroid function and other clinical chemistry parameters in subjects eating iodine-enriched eggs.

Iodine-enriched (IE) eggs are produced by chickens fed a diet containing kelp. These eggs, which contain an average of 711 micrograms iodine/egg, have been reported to reduce plasma cholesterol in humans and laboratory animals. A modified form of these eggs is under consideration for marketing in the United States. 104 hyperlipidaemic subjects were placed on a low-fat diet for 12 wk. Between wk 4 and 12, approximately half of the subjects were randomized to a dietary control group (n = 53) or a group who ingested one IE egg/day in addition to this diet (n = 51). Some subjects in both groups continued in the study for an additional 4-8 wk. No significant adverse clinical effects were observed or reported, with the exception of one subject who reported an allergic-like reaction soon after beginning egg ingestion. All clinical chemistry values remained within normal limits, and comparisons between the egg group and controls were not significant. Three subjects (two in the egg group and one in the control group) had elevated thyroid stimulating hormone levels during the experimental period. All thyroid function tests remained within normal limits in the remaining subjects. Thus, ingestion of one IE egg of the type used in our study appears to be relatively safe and devoid of clinically significant, short-term adverse effects in healthy individuals.

Plasma lipoproteins in hyperlipidemic subjects eating iodine-enriched eggs.

Iodine-enriched (IE) eggs are produced by chickens fed a diet containing kelp. These eggs have been reported to reduce plasma cholesterol in humans and experimental animals. The purpose of this study was to determine the effect of the ingestion of one IE egg/day on the plasma lipoprotein cholesterol in borderline and hyperlipidemic individuals ingesting a low-fat diet. One hundred three subjects with entry cholesterol levels greater than 5.17 mmol/L were placed on a low-fat, low-cholesterol diet for 12 weeks. Between weeks 4 and 12, approximately half of the subjects were randomly assigned to either a diet control group (n = 53), or a group who ingested one IE egg/day in addition to this diet (n = 50). Subjects in both the egg group and the diet control group had a significant reduction in total plasma cholesterol (TC) at the end of the study compared with study entry; addition of the egg in the diet did not abolish the TC reduction in the egg group. However, paired comparisons of total and lipoprotein cholesterol levels at the end of the egg intervention period with the end of the initial dietary period demonstrated that the egg group had a significantly greater increase than the diet control group in TC (egg group: 7.2 +/- 1.5% increase; diet controls: 1.5 +/- 0.9% increase; p less than 0.01) and low-density lipoprotein cholesterol (egg group: 9.2 +/- 1.7% increase; diet controls: 3.9 +/- 1.5% increase; p less than 0.01). This effect was most pronounced in subjects with higher initial cholesterol levels and subjects with mixed hyperlipidemia (elevated cholesterol and triglyceride). Results suggest that these particular groups of subjects are most susceptible to cholesterol changes associated with ingestion of IE eggs.

Saturated fats, cholesterol, and dietary compliance.

BACKGROUND: Lack of response to a cholesterol-lowering diet can be caused by physiological nonresponsiveness, inadequate knowledge, or inability to change dietary habits (poor compliance). The purpose of this study was to evaluate the dietary compliance of hyperlipidemic individuals who received intensive initial dietary education and followup, and who showed an initial reduction of their plasma cholesterol levels. METHODS: One hundred five individuals with fasting cholesterol levels of 5.17 mmol/L (200 mg/dL) or greater received intensive education and follow-up on the American Heart Association Step I diet during an initial 12-week period. The participants provided 3-day dietary records every week, and fasting lipoprotein analysis was performed biweekly. Six months after termination of this period, the subjects were requested to return for a follow-up evaluation of their lipoprotein profile and dietary adherence. RESULTS: Seventy-three (70%) of the subjects returned for a follow-up evaluation of lipoprotein cholesterol levels. Of these, 42 (58%) had a 10% or greater average initial decrease in total cholesterol levels at weeks 3 and 4 ("baseline"), and they were considered to be "high responders." At the 6-month follow up, the average plasma cholesterol level in these responders remained 6.4% below that at entry level, but it had increased by 19% compared with baseline values (6.30 mmol/L [244 mg/dL] vs 5.43 mmol/L [210 mg/dL], respectively). Corresponding significant increases at 6 months were found in high-density lipoprotein cholesterol (8%), low-density lipoprotein cholesterol (16%), and very-low-density lipoprotein cholesterol (66%) levels. Analysis of dietary histories revealed that dietary cholesterol and percent calories from fat increased significantly, but remained within the recommended guidelines. However, the increase in percent calories from saturated fat (from 10.0% +/- 0.5% to 14.4% +/- 1.0% [mean +/- SEM]) deviated markedly from these guidelines. CONCLUSIONS: The results suggest the long-term compliance to the reduction of dietary saturated fat remains a problem, even in individuals who receive intensive initial training and show an early favorable response. Follow-up evaluation of hyperlipidemic patients who are receiving dietary therapy should take into account this behavioral pattern. It remains to be determined whether continuing supervision and better nutritional labeling will facilitate dietary compliance.