Oxidation of Zn in UHV environment at low temperature

Thermal oxidation of polycrystalline Zn foils at 5 × 10⁻⁷ Torr oxygen pressure and at room temperature, 50 °C, 70 °C, 90 °C and 110 °C was studied. In situ photoemission spectroscopy using synchrotron light with photon energy of 57 eV was used to monitor the formation of ZnO and to determine the thickness of the oxide overlayer. At the initial oxidation, the oxidation rate follows a two-stage logarithmic equation and later trends to saturate at a certain thickness depending on the oxidation temperature. The saturated thickness was found to increase with the oxidation temperature. The two-stage oxidation process may be governed by two kinds of space charge presumably formed in the thin oxide overlayer.     

Sixth AOFSRR in Bangkok

The Sixth Asia Oceania Forum on Synchrotron Radiation Research (6^th AOFSRR) was successfully held in Bangkok, Thailand, from August 8 to 10, 2012. The workshop was hosted by the Synchrotron Light Research Institute (SLRI). Prayoon Songsiriritthigul, former acting director of SLRI, and Sarawut Sujitjorn, the director of SLRI, served as the conference co-chairs. The success of the five previous workshops (Tsukuba in 2006, Hsinchu in 2007, Melbourne in 2008, Shanghai in 2009, and Pohang in 2010) brought 202 engineering and scientific participants from Asia-Oceania to the workshop, and six from other regions (Canada, France, Germany, and the US). In addition to three plenary and 19 invited talks, there were 25 oral and 60 poster presentations contributed by the participants.     

In situ monitoring of ZnO formation by photoemission spectroscopy

Exposure of a clean Zn metal to oxygen in ultra high vacuum provides a mean to gradually form ZnO. With in situ synchrotron photoelectron measurement, the progressive change in the spectra with the oxygen exposure time is observed. The analysis of the spectra allows the determination of ZnO formation. It was found that the oxidation process takes place until reaching the critical thickness, at which the oxidation rate reduces greatly to nearly zero. The critical thickness was determined to be about 2 monolayers.     

Electron affinity study of adamantane on Si(1 1 1)

Recently, tetramantane, a member of diamondoid series (C_4n+6H_4n+12), has shown to exhibit negative-electron-affinity effect which has a potential use for efficient electron emitting devices. Here, we explore the electronic property of adamantane (C₁₀H₁₆), the smallest member of the series. We prepare adamantane films on Si(1 1 1) substrates and then study their electronic structure with photoemission spectroscopy. Photoelectron spectra of adamantane on Si(1 1 1) have shown a peak at low-kinetic energy which could be a generic property of diamondoids. The possibility of the negative-electron-affinity effect in adamantane is further discussed.     

Structural characterizations of sol–gel synthesized TiO2 and Ce/TiO2 nanostructures

Mixed phase TiO₂ and Ce/TiO₂ samples were synthesized by a sol–gel method using different hydrolysis conditions. In pure TiO₂ samples, traditional X-ray diffraction (XRD) and Ti K-edge synchrotron X-ray absorption near edge structures (XANES) independently revealed their anatase/rutile phase ratios. XANES results further revealed a substantial amount of Ti atoms existed in other forms beside anatase and rutile TiO₂ in the sample synthesized by the low hydrolysis condition. An increase in the extent of the hydrolysis during the synthesis leads to an increased rutile ratio and a reduction in other forms. In Ce/TiO₂ samples, the crystal sizes were too small for XRD characterization. Only XANES could be used to characterize their phase ratios. It is found that adding Ce impedes rutile formation; leading to increased anatase ratio. The difference in the fundamental aspects of XRD and XANES techniques in providing the phase ratios is discussed.     

A Water‐Based Chitosan–Maleimide Precursor for Bioconjugation: An Example of a Rapid Pathway for an In Situ Injectable Adhesive Gel

Chitosan conjugated with maleimide (CS–Mal) as a potential precursor for bioconjugation and the example of the application in in situ injectable adhesive gel is proposed. The homogeneous reaction in water/dimethyl sulfoxide (DMSO) (1:1) followed by dialysis in HCl (10 × 10⁻³m ) is a good condition to obtain CS–Mal. When SH–PEG–SH is applied as the crosslinker, the gel can be obtained in a few seconds without any by‐products at room temperature. The gel formation and properties are controllable by simply varying the concentration and the molecular weight of CS, the Mal substitution degree, and the temperature. The gel is injectable and shows adhesive property for soft tissue. Moreover, the gel shows not only biocompatibility to SAOS2 cells but also antimicrobial activity against both gram‐negative and gram‐positive bacteria. CS–Mal is useful not only for bioconjugation of CS but also for development of biomaterials.