Ulf O. Karlsson

Improved microscopical diagnosis of pulmonary tuberculosis in developing countries

The diagnosis of pulmonary tuberculosis (TB) relies on the bacteriological examination of sputum. However, microscopy of smears made directly from sputum has a low sensitivity and there is an urgent need for improved methods. We have compared microscopy of smears made directly from sputum with microscopy after liquefaction of sputum with household bleach (NaOCl) and concentration of bacteria by centrifugation. In 3 studies performed in Ethiopia and India, the use of the NaOCl method increased the number of samples positive for acid-fast bacilli by more than 100%. The technique is appropriate for developing countries and its application would increase the efficiency of TB control programmes. As a potent disinfectant, NaOCl also has the advantage of lowering the risk of laboratory infection.

Adsorption of Sn onSi(111)7 × 7: reconstructions in the monolayer regime

Different monolayer phases of Sn on Si(111)7 × 7 have been studied by means of scanning tunneling microscopy (STM), core-level photoelectron spectroscopy (XPS), and Rutherford backscattering spectrometry (RBS). The STM results show that 3 × 3 reconstructions are obtained for room-temperature deposition of 13 ML of Sn followed by sample annealing in a broad temperature range. A T4 Sn adatom 3 ×3 phase is formed for temperatures between 500 and 800°C, with a concentration of defects that is strongly dependent on the temperature and which is as high as 25% for the lowest temperatures. Above 825°C a second 3×3 adatom reconstruction is formed, a mosaic-like phase with a 1:1 mixture of Si and Sn atoms in T4 positions. The results from investigations of the higher coverage 23 × 23 reconstruction by XPS and RBS support the theory that this phase is a two-layer epitaxial Sn structure with all Si(111) dangling bonds saturated. The Sn coverage for this phase was determined to be between 1 and 1.2 ML.

Studies of highly oriented CeO2 films grown on Si(111) by pulsed laser deposition

Abstract CeO 2 is an interesting buffer layer material for the growth of YBa 2 Cu 3 O 7− δ overlayers on Si in devices, with the aim of preventing heat-diffusion due to its excellent lattice matching with Si and YBa 2 Cu 3 O 7− δ . Epitaxial CeO 2 -films have been synthesised on Si(111) by pulsed laser deposition. Stoichiometric changes of the Ce x O y -film depending on the ambient oxygen pressure during the deposition were studied by X-ray photoelectron spectroscopy. A method is presented for growing a sharp interface between CeO 2 and Si(111). The dependence of the in-plane orientation of the CeO 2 film on the substrate temperature was investigated by X-ray diffraction. The best films, grown at 700°C, showed full width at half maximum of the rocking curve close to 0.1°, but already at room temperature very highly oriented films with less than 0.2° were synthesised.

Oxygen structures on Fe(110)

The adsorption of oxygen on a Fe(110) single crystal has been studied by means of high resolution photoelectron spectroscopy (HRPES) and scanning tunneling microscopy (STM). Core level spectra were ...

Pro- and anti-inflammatory substances modulate expression of the leukotriene B4 receptor, BLT1, in human monocytes.

The high‐affinity leukotriene B4 (LTB4) receptor, BLT1, is a chemotactic receptor involved in inflammatory responses. In this study, we have explored the regulation of BLT1 expression in human monocytes by pro‐ and anti‐inflammatory cytokines, lipopolysaccharide (LPS), and dexamethasone. We found that proinflammatory mediators, such as interferon‐γ (IFN‐γ), tumor necrosis factor‐α, and LPS, down‐regulated expression, whereas the anti‐inflammatory cytokine, interleukin‐10, and dexamethasone up‐regulated BLT1 mRNA expression. The effect of IFN‐γ on BLT1 mRNA expression was rapidly detectable (<4 h) and concentration‐dependent (1–50 ng/ml) and seems to be exerted through a block in transcriptional activity. Alterations in mRNA expression were accompanied by changes in BLT1 surface expression, and receptor down‐modulation following IFN‐γ stimulation resulted in a diminished chemotactic response to LTB4. The regulation of BLT1 mRNA and receptor protein expression was similar to the regulation of the monocyte chemoattractant protein‐1 chemokine receptor, CC chemokine recptor 2 (CCR2). Flow cytometric analysis of fresh peripheral blood cells revealed that classical (CD14++CD16–) monocytes express high levels of BLT1 and CCR2 and that both receptors are down‐regulated on CD14+CD16+ monocytes. Apart from providing insight into the regulation of BLT1 in human monocytes, our results reveal a parallel expression and regulation of BLT1 and CCR2, which may help to understand monocyte trafficking during pathophysiological conditions.

Influence of oxygen and nitrogen on the growth of hot-filament chemical vapor deposited diamond films

The effect of incorporating oxygen and nitrogen into the feed gases on the texture and surface morphology of diamond film synthesized by hot filament chemical vapor deposition (HFCVD) is investigated. The reactant gas composition is determined by the gas flow rates. At a constant flow rate of hydrogen (33 sccm) and methane (0.68 sccm), the oxygen and nitrogen were varied in the O/(O 1 C) ratio from 0.05 to 0.43 and in the N/(N 1 C) ratio from 0.15 to 0.60. The films were grown under a constant pressure (20 Torr) and a constant substrate temperature (8008C). Clearly nitrogen in the reactant gases has a distinct tendency to promote the k100l texture and the corresponding {100} morphology, whereas oxygen promotes the development of k111l texture and {111} morphology. According to the Wulff theorem (Ga d100=d111a g100=g111) and the evolutionary selection of crystallites and the surface configurations of diamond, the results reveal that during growth nitrogen plays a critical role in activating the CD‐H surface site and consequently increases the surface free energy g 111, of the {111} surface. In contrast, oxygen activates the CDvH2 surface site and increases the surface free energy g 100, of the{100} surface. These results indicate that the texture and the surface morphology of polycrystalline diamond film can be completely controlled by the reactant gas composition. q 1999 Elsevier Science S.A. All rights reserved.

Growth of inclined boron nanowire bundle arrays in an oxide-assisted vapor-liquid-solid process

In the vapor-liquid-solid process typically employed for semiconductor nanowire growth, nucleation and anisotropic crystal growth of single nanowires are achieved with generation of a solid/liquid alloy interface using metal catalysts. The nucleation and growth mechanism of nanowires may be greatly altered when a second liquid is introduced into the solid/liquid alloy interface. In this work, we demonstrate bundled boron nanowire (BNW) array growth on Au coated Si substrates by introducing a second liquid of B2O3 onto the solid (B)/liquid alloy (Au-B) interface. The BNWs in each bundle are straight but highly inclined with respect to the normal of the substrate. A study of BNW morphology and chemical elemental distribution using electron microscopy and energy dispersive x-ray spectroscopy suggested that the catalyst Au provided the nucleation site for BNW bundles while the liquid B2O3 modified the initiation of BNWs from each nucleation site, resulting in multiple initiation of the BNWs from each site.

The adsorption of I2 on Si(111)-7×7 studied by soft X-ray photoemission

The adsorption Of I2 on Si(111)-7 x 7 at room temperature is studied with soft X-ray photoelectron spectroscopy. I2 adsorbs dissociatively, forming a mixture of SiI, SiI2 and SiI3 moieties, of whic ...

Epitaxial silicide formation in the Mg/Si(111) system

Abstract The silicide formation has been studied in the Mg/Si(111) system by low energy electron diffraction (LEED) and photoelectron spectroscopy. It has been found that an epitaxial Mg 2 Si silicide is responsible for the ( 2 3 √3 × 2 3 √3)R30° reconstru system. The thickness of the silicide is limited due to the very low formation temperature for this silicide. The Fermi level is positioned 0.59 ± 0.06 eV above the valence band maximum in the Si substrate and the valence band maximum in the epitaxial silicide is positioned 0.3 ± 0.1 eV below the Fermi level.

Misfit strain induced lattice distortions in heteroepitaxially grown LaxCa1−xMnO3 thin films studied by extended x-ray absorption fine structure and high-resolution x-ray diffraction

Mn-O and Mn-Mn interatomic distances were determined in LaxCa1-xMnO3 films grown heteroepitaxially on single crystal SrTiO3 and LaAlO3 substrates by molecular beam epitaxy. Mn-O bond lengths were f ...