230 research outputs found
Direct observations of the vacancy and its annealing in germanium
Weakly n-type doped germanium has been irradiated with protons up to a fluence of 3×10 exp 14 cm exp −2 at 35 K and 100 K in a unique experimental setup. Positron annihilation measurements show a defect lifetime component of 272±4 ps at 35 K in in situ positron lifetime measurements after irradiation at 100 K. This is identified as the positron lifetime in a germanium monovacancy. Annealing experiments in the temperature interval 35–300 K reveal two annealing stages. The first at 100 K is tentatively associated with the annealing of the Frenkel pair, the second at 200 K with the annealing of the monovacancy. Above 200 K it is observed that mobile neutral monovacancies form divacancies, with a positron lifetime of 315 ps.Peer reviewe
Low-dimensional structures generated by misfit dislocations in the bulk of Si1 - xGex/Si heteroepitaxial systems
Lattice diffusion and surface segregation of B during growth of SiGe heterostructures by molecular beam epitaxy: effect of Ge concentration and biaxial stress
Si1-xGex/Si1-yGey/Si(100) heterostructures grown by Molecular Beam Epitaxy
(MBE) were used in order to study B surface segregation during growth and B
lattice diffusion. Ge concentration and stress effects were separated. Analysis
of B segregation during growth shows that: i) for layers in epitaxy on
(100)Si), B segregation decreases with increasing Ge concentration, i.e. with
increased compressive stress, ii) for unstressed layers, B segregation
increases with Ge concentration, iii) at constant Ge concentration, B
segregation increases for layers in tension and decreases for layers in
compression. The contrasting behaviors observed as a function of Ge
concentration in compressively stressed and unstressed layers can be explained
by an increase of the equilibrium segregation driving force induced by Ge
additions and an increase of near-surface diffusion in compressively stressed
layers. Analysis of lattice diffusion shows that: i) in unstressed layers, B
lattice diffusion coefficient decreases with increasing Ge concentration, ii)
at constant Ge concentration, the diffusion coefficient of B decreases with
compressive biaxial stress and increases with tensile biaxial stress, iii) the
volume of activation of B diffusion () is positive for biaxial stress while it
is negative in the case of hydrostatic pressure. This confirms that under a
biaxial stress the activation volume is reduced to the relaxation volume
Si nanoparticle interfaces in Si/SiO2 solar cell materials
Novel solar cell materials consisting of Si nanoparticles embedded in SiO2 layers have been studied using positron annihilation spectroscopy in Doppler broadening mode and photoluminescence. Two positron-trapping interface states are observed after high temperature annealing at 1100 °C. One of the states is attributed to the (SiO2/Si bulk) interface and the other to the interface between the Si nanoparticles and SiO2. A small reduction in positron trapping into these states is observed after annealing the samples in N2 atmosphere with 5% H2. Enhanced photoluminescence is also observed from the samples following this annealing step.Peer reviewe
Electrical and structural properties of In-implanted Si1−xGex alloys
We report on the effects of dopant concentration and substrate stoichiometry on the electrical and structural properties of In-implanted Si1−xGex alloys. Correlating the fraction of electrically active In atoms from Hall Effect measurements with the In atomic environment determined by X-ray absorption spectroscopy, we observed the transition from electrically active, substitutional In at low In concentration to electrically inactive metallic In at high In concentration. The In solid-solubility limit has been quantified and was dependent on the Si1−xGex alloy stoichiometry; the solid-solubility limit increased as the Ge fraction increased. This result was consistent with density functional theory calculations of two In atoms in a Si1−xGex supercell that demonstrated that In–In pairing was energetically favorable for x ≲ 0.7 and energetically unfavorable for x ≳ 0.7. Transmission electron microscopy imaging further complemented the results described earlier with the In concentration and Si1−xGex alloy stoichiometry dependencies readily visible. We have demonstrated that low resistivity values can be achieved with In implantation in Si1−xGex alloys, and this combination of dopant and substrate represents an effective doping protocol
Recommended from our members
Annexins-a family of proteins with distinctive tastes for cell signaling and membrane dynamics
Annexins are cytosolic proteins with conserved three-dimensional structures that bind acidic phospholipids in cellular membranes at elevated Ca2+ levels. Through this they act as Ca2+-regulated membrane binding modules that organize membrane lipids, facilitating cellular membrane transport but also displaying extracellular activities. Recent discoveries highlight annexins as sensors and regulators of cellular and organismal stress, controlling inflammatory reactions in mammals, environmental stress in plants, and cellular responses to plasma membrane rupture. Here, we describe the role of annexins as Ca2+-regulated membrane binding modules that sense and respond to cellular stress and share our view on future research directions in the field.Work in our laboratories was supported by grants from the German Research Foundation to V.G. (CRC1348/A04, GE514/6-3) and U.R. (CRC1009/A06, CRC1348/A11); the Interdisciplinary Center for Clinical Research of the Münster Medical School to U.R. (Re2/022/20); the Danish Council for Independent Research (6108-00378A, 9040-00252B), Scientific Committee Danish Cancer Society (R90-A5847-14-S2, R269-A15812), and the Novo Nordisk Foundation (NNF18OC0034936) to J.N.; the Royal Society and Wolfson Foundation (RSWF\R3\183001) to F.N.E.G.; the National Institute of Health (NIH R01AR055686) to J.K.J.; the Ara Parseghian Medical Research Fund (G217137) to T.G
Immunotherapeutic targeting of membrane Hsp70-expressing tumors using recombinant human granzyme B
Background: We have previously reported that human recombinant granzyme B (grB) mediates apoptosis in membrane heat shock protein 70 (Hsp70)-positive tumor cells in a perforin-independent manner
- …