No abstract

No abstract

The possibility of obtaining a detailed picture of the electronic structure makes surface photovoltage spectroscopy (SPS) eminently suitable for bridging the gap between the chemical, physical, optical and electrical properties of semiconductors. In SPS, changes in band bending (both at the free semiconductor surface and at buried interfaces) are monitored as a function of external illumination. Surface photovoltage spectroscopy can provide detailed, quantitative information on bulk properties (e.g. bandgap and type, carrier diffusion length and lifetime) and can be used for complete construction of surface and interface band diagrams, including the measurement of energy levels in quantum structures. A particular strength is that a comprehensive analysis of surface and bulk defect state distributions and properties is made possible. Measurements using SPS are contactless and non-destructive. In addition, they can be performed both in situ and ex situ, at any reasonable temperature, on any semiconducting material, at any ambient and at any lateral resolution down to the atomic scale. This review starts with an overview of SPS-related surface and interface theory, describes the SPS experimental set-up and presents applications for surface and interface characterization of a wide variety of materials and structures, cross-correlating them with other methodologies.

Objective: Obese patients demonstrate a variety of biochemical, metabolic, and pulmonary abnormalities. Inflammatory mediators such as tumor necrosis factor-␣ and interleukin-6 (IL-6) may have a direct effect on glucose and lipid metabolism. Hypoxemia in itself induces release of IL-6. The aim of this study was to examine the relationship between IL-6 levels in healthy volunteers (control group) and three different groups of obese patients: patients without obstructive sleep apnea syndrome (OSAS), patients with OSAS, and patients with obesity hypoventilation syndrome (OHS) (daytime baseline oxygen saturation of Ͻ93%). Research Methods and Procedures:We measured serum IL-6 levels in 25 obese patients (body mass index of Ͼ35 kg/m 2 ) and 12 healthy women. Results:The results demonstrate statistically significant differences in serum IL-6 levels between the control group (1.28 Ϯ 0.85 pg/mL) and obese patients without OSAS (7.69 Ϯ 5.06 pg/mL, p Ͻ 0.05) and with OSAS (5.58 Ϯ 0.37 pg/mL, p Ͻ 0.0005). In the patients with OHS, IL-6 concentrations were highest (43.13 Ϯ 24.27 pg/mL). Discussion: We conclude that serum IL-6 is increased in obese patients. The highest IL-6 levels were found in the patients with OHS.

No abstract

Dipole formation processes at self-assembled monolayers of benzene derivatives chemisorbed on the Si͑111͒ surface are investigated from first principles. The surface dipole is shown to be sensitive to the molecular coverage and dominated by intramolecular charge rearrangement due to long-range, cooperative behavior. This cooperative behavior suppresses substrate contributions to dipole formation.

The properties of Si(111) surfaces grafted with benzene derivatives were investigated using ultraviolet photoemission spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS). The investigated materials were nitro-, bromo-, and methoxybenzene layers (-C 6 H 4 -X, with X ) NO 2 , Br, O-CH 3 ) deposited from diazonium salt solutions in a potentiostatic electrochemical process. The UPS spectra of the valence band region are governed by the molecular orbital density of states of the adsorbates, which is modified from the isolated state in the gas phase due to molecule-molecule and molecule-substrate interaction. Depending on the adsorbate, clearly different emission features are observed. The analysis of XPS intensities clearly proves multilayer formation for bromo-and nitrobenzene in agreement with the amount of charge transferred during the grafting process. Methoxybenzene forms only a sub-monolayer coverage. The detailed analysis of binding energy shifts of the XPS emissions for determining the band bending and the secondary electron onset in UPS spectra for determining the work function allow one to discriminate between surface dipole layerss changing the electron affinitysand band bending, affecting only the work function. Thus, complete energy band diagrams of the grafted Si(111) surfaces can be constructed. It was found that silicon surface engineering can be accomplished by the electrochemical grafting process using nitrobenzene and bromobenzene: siliconderived interface gap states are chemically passivated, and the adsorbate-related surface dipole effects an increase of the electron affinity.

The deep level energy distribution associated with the well-known ''yellow luminescence'' in GaN is studied by means of two complementary deep level techniques: photoluminescence and surface photovoltage spectroscopy. The combined experimental results show that the yellow luminescence is due to capture of conduction band electrons, or electrons from shallow donors ͑with a maximum depth on the order of the thermal energy͒ by a deep acceptor level with a broad energy distribution, centered at ϳ2.2 eV below the conduction band edge. In addition, the results show that the density of yellow luminescence related states possesses a significant surface component. ͓S0163-1829͑99͒16215-5͔