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  • 1
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    Quorum sensing influences growth and photosynthetic membrane production in high-cell-density cultivations of Rhodospirillum rubrum (2013)
    BioMed Central
    Details
    Publication Date: 2013-08-09
    Description: Background: The facultative anoxygenic photosynthetic bacterium Rhodospirillum rubrum exhibits versatile metabolic activity allowing the adaptation to rapidly changing growth conditions in its natural habitat, the microaerobic and anoxic zones of stagnant waters. The microaerobic growth mode is of special interest as it allows the high-level expression of photosynthetic membranes when grown on succinate and fructose in the dark, which could significantly simplify the industrial production of compounds associated with PM formation. However, recently we showed that PM synthesis is no longer inducible when R. rubrum cultures are grown to high cell densities under aerobic conditions. In addition a reduction of the growth rate and the continued accumulation of precursor molecules for bacteriochlorophyll synthesis were observed under high cell densities conditions. Results: In the present work, we demonstrate that the cell density-dependent effects are reversible if the culture supernatant is replaced by fresh medium. We identified six N-acylhomoserine lactones and show that four of them are produced in varying amounts according to the growth phase and the applied growth conditions. Further, we demonstrate that N-acylhomoserine lactones and tetrapyrrole compounds released into the growth medium affect the growth rate and photosynthetic membrane expression in high cell density cultures. Conclusions: In summary, we provide evidence that R. rubrum possesses a Lux-type quorum sensing system which influences the biosynthesis of photosynthetic membranes and the growth rate and is thus likely to be involved in the phenotypes of high cell density cultures and the rapid adaptation to changing environmental conditions.
    Electronic ISSN: 1471-2180
    Topics: Biology
    Published by BioMed Central
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  • 2
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    Quorum sensing influences growth and photosynthetic membrane production in high-cell-density cultivations of Rhodospirillum rubrum (2013)
    BioMed Central
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    Publication Date: 2013-01-01
    Electronic ISSN: 1471-2180
    Topics: Biology
    Published by BioMed Central
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  • 3
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    Electric properties and carrier multiplication in breakdown sites in multi-crystalline silicon solar cells (2015)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2015-05-28
    Description: This paper studies the effective electrical size and carrier multiplication of breakdown sites in multi-crystalline silicon solar cells. The local series resistance limits the current of each breakdown site and is thereby linearizing the current-voltage characteristic. This fact allows the estimation of the effective electrical diameters to be as low as 100 nm. Using a laser beam induced current (LBIC) measurement with a high spatial resolution, we find carrier multiplication factors on the order of 30 (Zener-type breakdown) and 100 (avalanche breakdown) as new lower limits. Hence, we prove that also the so-called Zener-type breakdown is followed by avalanche multiplication. We explain that previous measurements of the carrier multiplication using thermography yield results higher than unity, only if the spatial defect density is high enough, and the illumination intensity is lower than what was used for the LBIC method. The individual series resistances of the breakdown sites limit the current through these breakdown sites. Therefore, the measured multiplication factors depend on the applied voltage as well as on the injected photocurrent. Both dependencies are successfully simulated using a series-resistance-limited diode model.
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 4
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    Interplay between crystallinity profiles and the performance of microcrystalline thin-film silicon solar cells studied by in-situ Raman spectroscopy (2015)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2015-12-08
    Description: The intrinsic microcrystalline absorber layer growth in thin-film silicon solar-cells is investigated by in-situ Raman spectroscopy during plasma enhanced chemical vapor deposition. In-situ Raman spectroscopy enables a detailed study of the correlation between the process settings, the evolution of the Raman crystallinity in growth direction, and the photovoltaic parameters η (solar cell conversion efficiency), J SC (short circuit current density), FF (fill factor), and V OC (open circuit voltage). Raman spectra were taken every 7 nm of the absorber layer growth depending on the process settings. The Raman crystallinity of growing microcrystalline silicon was determined with an absolute error of approximately ±5% for total absorber layer thicknesses 〉50 nm. Due to this high accuracy, inherent drifts of the Raman crystallinity profiles are resolvable for almost the entire absorber layer deposition. For constant process settings and optimized solar cell device efficiency Raman crystallinity increases during the absorber layer growth. To compensate the inhomogeneous absorber layer growth process settings were adjusted. As a result, absorber layers with a constant Raman crystallinity profile — as observed in-situ — were deposited. Solar cells with those absorber layers show a strongly enhanced conversion efficiency by ∼0.5% absolute. However, the highest FF , V OC , and J SC were detected for solar cells with different Raman crystallinity profiles. In particular, fill factors of 74.5% were observed for solar cells with decreasing Raman crystallinity during the later absorber layer growth. In contrast, intrinsic layers with favorable J SC are obtained for constant and increasing Raman crystallinity profiles. Therefore, monitoring the evolution of the Raman crystallinity in-situ provides sufficient information for an optimization of the photovoltaic parameters with surpassing depth resolution.
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 5
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    New insight into the microstructure and doping of unintentionally n-type microcrystalline silicon carbide (2016)
    American Institute of Physics (AIP)
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    Publication Date: 2016-05-07
    Description: Microcrystalline silicon carbide (μc-SiC:H) deposited by hot wire chemical vapor deposition (HWCVD) and plasma-enhanced chemical vapor deposition (PECVD) provide advantageous opto-electronic properties, making it attractive as a window layer material in silicon thin-film and silicon heterojunction solar cells. However, it is still not clear which electrical transport mechanisms yield dark conductivities up to 10 −3 S/cm without the active use of any doping gas and how the transport mechanisms are related to the morphology of μc-SiC:H. To investigate these open questions systematically, we investigated HWCVD and PECVD grown layers that provide a very extensive range of dark conductivity values from 10 −12 S/cm to 10 −3 S/cm. We found out by secondary ion mass spectrometry measurements that no direct correlation exists between oxygen or nitrogen concentrations and high dark conductivity σ d , high charge carrier density n , and low activation energy E a. Higher σ d seems to rise from lower hydrogen concentrations or/and larger coherent domain sizes L SiC . On the one hand, the decrease of σ d with increasing hydrogen concentration might be due to the inactivation of donors by hydrogen passivation that gives rise to decreased n . On the other hand, qualitatively consistent with the Seto model, the lower σ d and lower n might be caused by smaller L SiC , since the fraction of depleted grain boundaries with higher E a increases accordingly.
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 6
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    Role of oxygen and nitrogen in n-type microcrystalline silicon carbide grown by hot wire chemical vapor deposition (2016)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2016-12-09
    Description: N-type microcrystalline silicon carbide (μc-SiC:H(n)) deposited by hot wire chemical vapor deposition provides advantageous opto-electronic properties for window layer material in silicon-based thin-film solar cells and silicon heterojunction solar cells. So far, it is known that the dark conductivity (σ d ) increases with the increase in the crystallinity of μc-SiC:H(n)films. However, due to the fact that no active doping source is used, the mechanism of electrical transport in these films is still under debate. It is suggested that unintentional doping by atmospheric oxygen (O) or nitrogen (N) contamination plays an important role in the electrical transport. To investigate the impact of O and N, we incorporated O and N in μc-SiC:H(n) films and compared the influence on the microstructural, electronic, and optical properties. We discovered that, in addition to increasing the crystallinity, it is also possible to increase the σ d by several orders of magnitude by increasing the O-concentration or the N-concentration in the films. Combining a high concentration of O and N, along with a high crystallinity in the film, we optimized the σ d to a maximum of 5 S/cm.
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 7
    Electronic Resource
    Electronic Resource
    Electrical and optical characterization of semiconducting Ru2Si3 films and single crystals (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 3347-3352 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Recently, Ru2Si3 has been predicted to be a direct semiconductor with a band gap of (approximate)0.8 eV. Since the corresponding wavelength of this potential light emitter coincides with the absolute absorption minimum of glass fibers of 1.5 μm, considerable attention has been attracted. Measurements of the temperature dependence of the electrical resistivity of silicide films on insulating substrates were carried out in van der Pauw geometry. The results were explained by assuming carrier hopping over grain boundaries. The optical absorption coefficient was measured on thin films grown on various substrates, on self-sustaining films, where the substrate was partly removed and on a single crystal by photothermal deflection spectroscopy. A direct band gap at 0.84 eV was found. The absorption coefficient is very low up to (approximate)1.5 eV, likely due to a low density of states, and then strongly increases at higher energies. The experimental results qualitatively confirm the predictions of the band structure calculations. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1402965
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  • 8
    Electronic Resource
    Electronic Resource
    Hot electron impact excitation cross-section of Er3+ and electroluminescence from erbium-implanted silicon metal-oxide-semiconductor tunnel diodes (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 71 (1997), S. 2824-2826 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have demonstrated the 1.5 μm electroluminescence from implanted Er ions inside the SiO2 insulator of a silicon metal-oxide-semiconductor structure under forward bias. The Er ions are excited by the direct impact from electrons tunneling through the oxide at electric fields larger than 6 MV/cm. Under these conditions, we measured an excitation cross-section of 6±2×10−15 cm2 and a lifetime of the excited 4I13/2 level of 1.5 ms. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.120147
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  • 9
    Electronic Resource
    Electronic Resource
    Improvement of grain size and deposition rate of microcrystalline silicon by use of very high frequency glow discharge (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 65 (1994), S. 2588-2590 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The influence of the plasma excitation frequency on the growth conditions and the material properties of microcrystalline silicon prepared by plasma enhanced chemical vapor deposition at low deposition temperature is investigated. It is found that an increase of the plasma excitation frequency leads to a simultaneous increase of the growth rate, the grain size, and the Hall mobility of microcrystalline silicon. This is attributed to an effective selective etching of disordered material creating more space to develop crystalline grains, while also more species for faster growth of the crystallites are available. © 1994 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.112604
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  • 10
    Electronic Resource
    Electronic Resource
    Connection between hydrogen plasma treatment and etching of amorphous phase in the layer-by-layer technique with very high frequency plasma excitation (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 2991-2993 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The formation of microcrystalline silicon was investigated employing the layer-by-layer technique with very high frequency plasma excitation. Etching of the deposited layers was found to be a dominant effect during hydrogen plasma treatment. Microcrystalline growth occurred when the thickness of the deposited layer was reduced to a certain value in each cycle. The etching stopped when a noticeable crystalline volume fraction was produced; for long hydrogen treatment times no film growth was observed. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.369616
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