Transmission Electron Microscopy and Electron Energy-Loss Spectroscopy Studies of Hole-Selective Molybdenum Oxide Contacts in Silicon Solar Cells.

In this study, substochiometric hole-selective molybdenum oxide (MoOx) contacts in crystalline silicon (c-Si) solar cells were investigated by a combination of transmission electron microscopy (TEM) and spatially resolved electron energy-loss spectroscopy (SR-EELS). It was observed that a ≈ 4 nm SiOx interlayer grows at the MoOx/c-Si interface during the evaporation of MoOx over a c-Si substrate. SR-EELS analyses revealed the presence of a 1.5 nm diffused MoOx/indium tin oxide (ITO) interface in both as-deposited and annealed samples. Moreover, the presence of a 1 nm thin layer with a lower oxidation state of Mo was detected at the SiOx/MoOx interface in an as-deposited state, which disappears upon annealing. Overall, it was evident that no hole-blocking interlayer is formed at the MoOx/ITO interface during annealing and homogenization of the MoOx layer takes place during the annealing process. Furthermore, device simulations revealed that efficient hole collection is dependent on MoOx work function and that reduction in the work function of MoOx results in loss of band bending and negatively impacts hole selectivity.

Tin gallium oxide solar-blind photodetectors on sapphire grown by molecular beam epitaxy.

We report on tin gallium oxide ((SnxGa1-x)2O3) solar-blind metal-semiconductor-metal (MSM) photodetectors grown by plasma-assisted molecular beam epitaxy on c-plane sapphire substrates with varying tin content up to XSn=10%. Incorporation of Sn into Ga2O3 was found to shift the optical bandgap of the epilayers from 5.0 eV (248 nm) for 0% Sn to 4.6 eV (270 nm) for 10% Sn content. Varying of the Sn concentration was also found to enable controlled tuning of the peak responsivity and cutoff wavelengths of MSM devices fabricated from the epilayers, with peak responsivity ranging from 0.75 A/W to nearly 16 A/W as the Sn concentration was increased from 0% to 10%. The high responsivity is attributed to photoconductive gain that increases for higher Sn concentrations and is accompanied by a slowing of the temporal response of the MSM detectors.

Transmission Electron Microscopy Studies of Electron-Selective Titanium Oxide Contacts in Silicon Solar Cells.

In this study, the cross-section of electron-selective titanium oxide (TiO2) contacts for n-type crystalline silicon solar cells were investigated by transmission electron microscopy. It was revealed that the excellent cell efficiency of 21.6% obtained on n-type cells, featuring SiO2/TiO2/Al rear contacts and after forming gas annealing (FGA) at 350°C, is due to strong surface passivation of SiO2/TiO2 stack as well as low contact resistivity at the Si/SiO2/TiO2 heterojunction. This can be attributed to the transformation of amorphous TiO2 to a conducting TiO2-x phase. Conversely, the low efficiency (9.8%) obtained on cells featuring an a-Si:H/TiO2/Al rear contact is due to severe degradation of passivation of the a-Si:H upon FGA.

High-Performance TiO2 -Based Electron-Selective Contacts for Crystalline Silicon Solar Cells.

Thin TiO2 films are demonstrated to be an excellent electron-selective contact for crystalline silicon solar cells. An efficiency of 21.6% is achieved for crystalline silicon solar cells featuring a full-area TiO2 -based electron-selective contact.

Glycated hemoglobin is not an accurate indicator of glycemia in rainbow trout.

Glycation occurs when glucose reacts non-enzymatically with proteins. This reaction depends upon time, ambient glucose concentration, and the molecular conformation of reactive amino acids. Little is known about protein glycation in fishes and the main objective of this study was to measure glycated hemoglobin (GHb) in rainbow trout, a glucose-intolerant species, under normoglycemic and hyperglycemic conditions. We also identified GHb isoforms in vivo and analyzed the structural environment surrounding potential glycation sites. Despite similar glycemia to healthy humans, GHb was an order of magnitude lower in rainbow trout (0.6%) compared with humans (6%) and was not affected by long-term hyperglycemia. Species differences in GHb appear to be related to differences in erythrocyte glucose, and differential expression and glycation of hemoglobin (Hb) isoforms may explain intraspecific differences in rainbow trout GHb. Computer analysis of glucose isomers (ringed-open and α- and ß-pyranoses) interacting with the ß-chain of rainbow trout HbI and HbIV, and human HbA did not reveal structural or energetic constraints for glucose binding (the initial step of glycation) for rainbow trout Hbs. Overall, there are significant differences between Hb glycation in humans and rainbow trout, and GHb does not appear to be an accurate indicator of glycemia over time in rainbow trout.

Spatially resolved measurement of femtosecond laser induced refractive index changes in transparent materials.

We present a practical method to determine femtosecond laser induced refractive index changes in transparent materials. Based on an iterative Fourier transform algorithm, this technique spatially resolves the refractive index of complex structures by combining the dimensions of the modified region with the corresponding phase change extracted from far-field intensity measurements. This approach is used to characterize optical waveguides written by a femtosecond laser in borosilicate glass.

Comparative magneto-photoluminescence study of ensembles and of individual InAs quantum dots.

We report on magneto-photoluminescence studies of InAs/GaAs quantum dots (QDs) of considerably different densities, from dense ensembles down to individual dots. It is found that a magnetic field applied in Faraday geometry decreases the photoluminescence (PL) intensity of QD ensembles, which is not accompanied by the corresponding increase of PL signal of the wetting layer on which QDs are grown. The model suggested to explain these data assumes considerably different strengths of suppression of electron and hole fluxes by a magnetic field. This idea has been successfully checked in experiments on individual QDs, where the PL spectra allow to directly monitor the charge state of a QD and, hence, to conclude about relative magnitudes of electron and hole fluxes toward the QD. Comparative studies of different individual QDs have revealed that the internal electric field in the sample (which was altered in the experiments in a controllable way) together with an external magnetic field will determine the charge state and emission intensity of the QDs.

Enhancement of the luminescence intensity of InAs/GaAs quantum dots induced by an external electric field.

InAs/GaAs quantum dots have been subjected to a lateral external electric field in low-temperature microphotoluminescence measurements. It is demonstrated that the dot PL signal could be increased several times depending on the magnitude of the external field and the strength of the internal (built-in) electric field, which could be altered by an additional infrared illumination of the sample. The observed effects are explained by a model that accounts for the essentially faster lateral transport of the photoexcited carriers achieved in an electric field.

Effects of separate carrier generation on the emission properties of InAs/GaAs quantum dots.

Individual quantum dots have been studied by means of microphotoluminescence with dual-laser excitation. The additional infrared laser influences the dot charge configuration and increases the dot luminescence intensity. This is explained in terms of separate generation of excess electrons and holes into the dot from the two lasers. With increasing dot density and/or sample temperature, the increase of the luminescence intensity vanishes progressively, while the possibility to control the dot charge remains.

Matrix metalloproteinase gelatinase B (MMP-9) coordinates and effects epithelial regeneration.

We studied the role of the matrix metalloproteinase gelatinase B (gelB; MMP-9) in epithelial regeneration using the gelB-deficient mouse. We report the novel finding that, in contrast to other MMPs expressed at the front of the advancing epithelial sheet in wounds of cornea, skin, or trachea, gelB acts to inhibit the rate of wound closure. We determined this to be due to control of cell replication, a novel capacity for MMPs not previously described. We also found that gelB delays the inflammatory response. Acceleration of these processes in gelB-deficient mice is correlated with a delay in signal transduction through Smad2, a transcription factor that inhibits cell proliferation, and in accumulation of epithelial-associated interleukin-1alpha, a cytokine that inhibits Smad2 signaling and promotes the inflammatory response. GelB-deficient mice also reveal defects in remodeling of extracellular matrix at the epithelial basement membrane zone, in particular, failure to effectively remove the fibrin(ogen) provisional matrix. We conclude that gelB coordinates and effects multiple events involved in the process of epithelial regeneration.

Induction and detection of cell-mediated reactions with different Blastomyces dermatitidis antigenic preparations.

Blastomyces dermatitidis yeast-phase antigens (killed cell, KWY; lysate, Lys; and filtrate, Fil) from canine isolate T-58 were compared with respect to the induction and detection of cellular immune responses in mice. The antigens exhibited good sensitivity and specificity when used to detect a delayed-type hypersensitivity (DTH) response in mice previously immunized with T-58 or Histoplasma capsulatum antigens. Greater reactivity was observed with the KWY and Lys antigens as DTH-inducing agents (immunogens) than with the Fil antigen. The antigens were also compared with regard to the induction and detection of a lymphoproliferative reaction using splenocytes from normal and sensitized mice, and optimal reactivity was demonstrated with the KWY and Fil antigen preparations both as immunogens (absorbance values 0.22-1.60 and 0.20-0.90, respectively) and as in vitro testing antigens (absorbance values 0.60-1.60 and 0.35-1.00 respectively) (P < 0.01). Peritoneal macrophages from mice sensitized with Fil and KWY antigens showed the greatest in vitro replication inhibition (RI) of B. dermatitidis yeast cells (RI values of 53% and 50% respectively) (P < 0.05). When mitogenic or antigenic lymphocytic supernatants were compared with respect to their ability to enhance the phagocytic activity of unelicited macrophages from normal mice to kill yeast cells, the T-cell mitogens (concanavalin A and phytohaemagglutinin) optimally activated the naive macrophages (45% and 44% RI respectively) compared with the B-cell mitogen (LPS) (23% RI) (P < 0.05). Similar results were obtained with the lymphocytic supernatants from mice immunized with KWY cells when activated using KWY or Fil antigens (46% and 40% RI respectively) (P < 0.05).

Characterization of a new bacteriophage which infects bacteria of the genus Acidiphilium.

A novel bacteriophage, termed phi AC1, that infects strains of the genus Acidiphilium (acidophilic, heterotrophic, aerobic, Gram-negative eubacteria) most commonly isolated from acidic mine drainage environments, has been discovered and several of its properties have been determined. This is the first report of a bacteriophage infecting such cells. The virion has a lambdoid morphology and is larger than lambda, as shown by electron microscopy and sucrose gradient centrifugation. The sedimentation coefficient of the virion is approximately 615S. The nucleic acid of phi Ac1 is dsDNA, approximately 102 kb in length. Several experimental results show that phi Ac1 is a temperate phage. The plaques are turbid, and most cells isolated from plaques produced on sensitive cells by filter-sterilized phage preparations contain the phage and are resistant to further phage infection. Southern blot analysis shows that phi Ac1 prophage DNA is integrated into the bacterial genome during the temperature growth phase.

Detection of infectious hematopoietic necrosis virus in an invertebrate (Callibaetis sp).

Infectious hematopoietic necrosis virus (IHNV) was detected in the common Mayfly (Callibaetis sp) by western immunoblot assay and was propagated in fish cells (CHSE-214) in culture. When propagated in cell culture, cytopathic effect characteristic of IHNV infection was observed. Antibody specific for IHNV was used to detect all of the major proteins of IHNV in the western immunoblot assay. When the crude lysate was subjected to electron microscopy, bullet-shaped particles (84 nm x 194 nm) characteristic of IHNV were observed. The data suggested that the Mayfly may be a factor in the dissemination of IHNV.

Use of a polynomial exponential function to describe migration of proteins on sodium dodecyl sulfate-polyacrylamide gels.

Standard mixtures of proteins were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Polynomial regression analysis was used to fit curves to the data points obtained by plotting log10 of protein molecular weight versus electrophoretic mobility. Polynomials with orders ranging from 1 to 4 were generated. The coefficients of each equation were analyzed for statistical significance. It was found that a third order polynomial was the highest-order equation in which all coefficients contributed significantly to the prediction of molecular weights. Using this equation, it was possible to estimate the molecular weights of known proteins in the range from 97,400 to 14,400 with a maximum error of 1%, compared with a maximum error of 17% when a first-order equation was used to describe the migration of the standards.

Neutralizing antibodies for infectious hematopoietic necrosis virus in eggs of steelhead trout (Salmo gairdneri).

Neutralizing antibodies specific for infectious hematopoietic necrosis virus (IHNV) were isolated from eggs of spawning Steelhead trout (Salmo gairdneri), using sodium sulfate precipitation. The isolated material was used in place of the primary antibody (rabbit anti-IHNV) in a protein immunoblotting assay to detect IHNV proteins specifically. The egg component that bound specifically to IHNV proteins was determined to be trout antibody by using antiserum toward trout immune globulins as the second antibody conjugate in the protein immunoblotting assay. The antibody recovered from eggs neutralized IHNV infectivity in cell culture. An average of 87.5% decrease in infectivity was observed.

Detection of infectious pancreatic necrosis virus using an inhibition enzyme-linked immunosorbent assay.

An inhibition enzyme-linked immunosorbent assay was used to detect infectious pancreatic necrosis (IPN) virus. In this assay the presence of virus was determined by measuring the decrease in titer of a known antiserum after incubation with a sample suspected to contain virus. The titer of the antiserum was measured with an indirect enzyme-linked assay. Compared to the double antibody sandwich method this assay required fewer reagents (only one anti-IPN serum was required). This assay was also sensitive enough to detect virus at levels of 1 X 10(2) TCID 50/ml. of purified virus and was able to detect virus in samples obtained in the field.

An improved plaque assay for viruses infecting poikilothermic cells; use of ultralow-gelling-temperature agarose.

The conventional plaque assay for viruses infecting poikilothermic cells is difficult because the cells are easily damaged at temperatures needed to keep the agarose overlay from solidifying prematurely. A modification of the assay in which these problems were solved by use of a new type of agarose (SeaPrep 15/45) that remains liquid above 15 degrees C, was developed. Use of this agarose made it easy to obtain smooth agar overlays without the risk of thermal damage to the cells.

Isolation and characterization of polyoma uncoating intermediates from the nuclei of infected mouse cells.

A method was developed which enabled the efficient recovery of polyoma uncoating intermediates from the nuclei of infected cells at early times after infection (15 min to 12 h). Cells were infected with radiolabeled virus and lysed with the detergent Nonidet P-40. The nuclei were then collected and sonicated, and the products were analyzed on sucrose gradients. The uncoating intermediate sedimented at 190S and was a viral DNA-protein complex closely associated with a structure of host origin. The host material associated with the 190S uncoating intermediate was determined by polyacrylamide gel electrophoresis and visualized by electron microscopy. The amount of 190S uncoating intermediate found in the nucleus increased with time after infection. The viral DNA was predominantly for I. All of the viral proteins were present in the 190S uncoating intermediate in amounts similar to those found in viral DNA-protein complex cores.