An InP(001)-͑2 3 1͒ reconstruction was prepared by metal-organic vapor-phase epitaxy. Scanning tunneling micrographs and infrared spectra of adsorbed hydrogen revealed that the ͑2 3 1͒ is terminated with a complete layer of buckled phosphorous dimers, giving rise to p͑2 3 2͒ and c͑4 3 2͒ domains. A surface band gap of 1.2 6 0.2 eV was measured by scanning tunneling spectroscopy. The buckling can be explained by electron correlation among the dangling bonds of pairs of phosphorous dimers. This allows the surface to achieve a lower energy, semiconducting state. This reconstruction mimics the Si(100)-͑2 3 1͒, which is terminated with buckled silicon dimers. [S0031-9007(99)08534-8]

Elevated proportions of Candida albicans in biofilms formed on dentures are associated with stomatitis whereas Streptococcus mutans accumulation on restorative materials can cause secondary caries. Candida albicans, S. mutans, saliva-derived and C. albicans/saliva-derived mixed biofilms were grown on different materials including acrylic denture, porcelain, hydroxyapatite (HA), and polystyrene. The resulting biomass was analysed by three-dimensional image quantification and assessment of colony-forming units. The efficacy of biofilm treatment with a dissolved denture cleansing tablet (Polident(®)) was also evaluated by colony counting. Biofilms formed on HA exhibited the most striking differences in biomass accumulation: biofilms comprising salivary bacteria accrued the highest total biomass whereas C. albicans biofilm formation was greatly reduced on the HA surface compared with other materials, including the acrylic denture surface. These results substantiate clinical findings that acrylic dentures can comprise a reservoir for C. albicans, which renders patients more susceptible to C. albicans infections and stomatitis. Additionally, treatment efficacy of the same type of biofilms varied significantly depending on the surface. Although single-species biofilms formed on polystyrene surfaces exhibited the highest susceptibility to the treatment, the most surviving cells were recovered from HA surfaces for all types of biofilms tested. This study demonstrates that the nature of a surface influences biofilm characteristics including biomass accumulation and susceptibility to antimicrobial treatments. Such treatments should therefore be evaluated on the surfaces colonized by the target pathogen(s).

Using a representative sample of 478 doctors, nurses, and lab technicians working with people living with HIV/AIDS (PLWHA), a cross-sectional study was conducted to assess the impact of the AIDS epidemic on medical care systems and service providers in China. Correlation analyses showed significant association between internalized shame reported by service providers and their perception of being stigmatized due to working with PLWHA. Multivariate analyses revealed that the perceived level of institutional support for AIDS care was significantly related to the stigmatization and shame reported by the service providers. The study findings suggest that improved institutional support for AIDS care at the facility level and HIV-related stigma reduction intervention are crucial to maintain a high quality performance by the workforce in the health care system.

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The site-specific chemistry of carbon tetrachloride decomposition on GaAs(001) (2 × 4) and (4 × 2) surfaces was studied by scanning tunneling microscopy and multiple internal reflection infrared spectroscopy of adsorbed hydrogen. By monitoring the changes in the vibrational spectra of the As and Ga hydrides upon the coadsorption of CCl 4 , it was discovered that this molecule dissociatively adsorbs onto Ga dimers and second-layer Ga atoms at 473 K. Upon heating to 673 K, the chlorine desorbs from these sites as GaCl, thereby reducing the Ga coverage. Scanning tunneling micrographs reveal that GaCl desorption produces a highly disordered (2 × 4) surface, and transforms the (4 × 2) into a new (3 × 2) reconstruction. The (3 × 2) surface appears to be stabilized by carbon incorporation.The incorporation of dopants into semiconductor lattice sites is an essential process in the manufacture of solid state electronic devices. Dopants also have a profound effect upon the semiconductor surface physics, since these species introduce both charge and strain into lattice. The surface must accommodate these effects by adopting structures which minimize the surface free energy. For example, Pashley and Haberern [1] have shown that silicon-doped GaAs(001) films produce highly disordered (2 × 4) surfaces with a large number of kinks in the As dimer rows. These kinks are presumed to be acceptors which neutralize the Si donor atoms in the surface depletion layer. Wang et al. [2] found that adsorbed boron on Si(100) migrates to subsurface lattice sites to relieve the strain induced by its smaller atomic size. The subsurface boron induces significant changes in the silicon surface reconstruction.We are curious whether the phenomena described above are a general property of doped semiconductor surfaces, or pertain only to the specific systems studied. Of particular interest to us is p-type doping of GaAs and InGaAs with carbon. * Corresponding author In the metalorganic vapor-phase epitaxy (MOVPE) and metalorganic molecular beam epitaxy (MOMBE) of III/V compounds, carbon tetrachloride (CCl 4 ) is an efficient source for incorporating carbon into the growing films [3][4][5][6][7][8]. Therefore we have investigated the decomposition of CCl 4 on As-and Ga-rich surfaces of GaAs(001) in ultrahigh vacuum. The important findings of this study are described below.

Residual strain and threading dislocation density in InGaAs layers grown on Si substrates by metalorganic vaporphase epitaxy Appl. Phys. Lett. 78, 93 (2001); 10.1063/1.1338502Dynamic study of the surfaces of (001) gallium arsenide in metal-organic vapor-phase epitaxy during arsenic desorption Structure and composition of the c(4×4) reconstruction formed during gallium arsenide metalorganic vapor-phase epitaxy Appl.

Introduction: Pancreatic ductal adenocarcinoma (PDAC) is projected to rise to the second leading cause of U.S. cancerrelated deaths by 2020. Novel therapeutic targets are desperately needed. MicroRNAs (miRs) are small noncoding RNAs that function by suppressing gene expression and are dysregulated in cancer. miR-21 is overexpressed in PDAC tumor cells (TC) and is associated with decreased survival, chemoresistance and invasion. Dysregulation of miR regulatory networks in PDAC tumor-associated fibroblasts (TAFs) have not been previously described. In this study, we show that miR-21 expression in TAFs promotes TC invasion.

Herein, we summarize our studies of the surface chemistry of gallium arsenide as it pertains to the metalorganic chemical-vapor deposition of compound semiconductors. It has been found by scanning tunneling microscopy and vibrational spectroscopy that the adsorption of reactant molecules on reconstructed GaAs (001) surfaces is "site-specific." Trimethylgallium dissociatively adsorbs only on arsenic sites, whereas arsine dissociatively adsorbs only on gallium sites. The decomposition of one precursor molecule (Ga(CH 3) 3 or AsH 3) creates the site for the decomposition of the other molecule (AsH 3 or Ga(CH 3) 3 , respectively). In this fashion, the crystal grows one atomic layer at a time. Studies of carbon doping with carbon tetrachloride have shown that adsorbed chlorine attacks the exposed gallium and generates volatile GaCl x species. The sitespecific nature of this reaction leads to a dramatic change in the film morphology, with the formation of 30nm etch pits randomly distributed over the surface.