Ferromagnetism in Co-doped ZnO films grown by molecular beam epitaxy: magnetic, electrical and microstructural studies

We studied structural, optical and magnetic properties of high-quality 5 and 15% Co-doped ZnO films grown by plasma-assisted molecular beam epitaxy (MBE) on (0001)-sapphire substrates. Magnetic force microscopy (MFM) and magnetic measurements with SQUID magnetometer show clear ferromagnetic behavior of the films up to room temperature whereas they are antiferromagnetic below 200 K approximately. Temperature dependence of the carrier mobility was determined using Raman line shape analysis of the longitudinal-optical-phonon-plasmon coupled modes. It shows that the microscopic mechanism for ferromagnetic ordering is coupling mediated by free electrons between spins of Co atoms. These results bring insight into a subtle interplay between charge carriers and magnetism in MBE-grown Zn(1-x)CoxO films.Comment: 10 pages, 9 figures, 2 table

Non stoichiometry effect and disorder in Cu2ZnSnS4 thin films obtained by flash evaporation Raman scattering investigation

The cation disorder in Cu2ZnSnS4 thin films grown by flash evaporation of ZnS, CuS and SnS binary compounds has been studied by Raman spectroscopy. Process parameters such as the substrate temperature during the evaporation and the Ar pressure in the post-thermal treatment determined the samples' composition and Raman spectra. As a measure of cation disorder, the half-width and relative intensity of the Raman band peaking at 331-332 cm-1 is analysed. Comparison of the spectra for different samples of known composition showed that the relative intensity of the 331 cm-1 defect peak correlates with the previously reported theoretical prediction about enhancement of antisite defect formation in Cu2ZnSnS4 under "Cu-poor, Zn-rich" conditions. For "Cu-rich, Zn-poor" films, further experimental confirmation was obtained of the previously detected effect of the enhancement of cation disorder under intense optical excitationThis research is supported by the People Programme (Marie Curie Actions) of the European Union’s Seventh Framework Program FP7/2007-2013/ under REA grant greement 269167 (PVICOKEST), the Spanish MINECO project (KEST- PV, ENE2010-21541-C03) and the OPTEC grant. RC acknowledges financial support from Spanish MINECO within the program Ramon y Cajal (RYC-2011-08521

RIM promotes calcium channel accumulation at active zones of the Drosophila neuromuscular junction

Synaptic communication requires the controlled release of synaptic vesicles from presynaptic axon terminals. Release efficacy is regulated by the many proteins that comprise the presynaptic release apparatus, including Ca(2+) channels and proteins that influence Ca(2+) channel accumulation at release sites. Here we identify Drosophila RIM and demonstrate that it localizes to active zones at the larval neuromuscular junction. In Drosophila RIM mutants, there is a large decrease in evoked synaptic transmission, due to a significant reduction in both the clustering of Ca(2+) channels and the size of the readily releasable pool of synaptic vesicles at active zones. Hence, RIM plays an evolutionarily conserved role in regulating synaptic calcium channel localization and readily releasable pool size. Since RIM has traditionally been studied as an effector of Rab3 function, we investigate whether RIM is involved in the newly identified function of Rab3 in the distribution of presynaptic release machinery components across release sites. Bruchpilot (Brp), an essential component of the active zone cytomatrix T bar, is unaffected by RIM disruption, indicating that Brp localization and distribution across active zones does not require wild type RIM. In addition, larvae containing mutations in both RIM and rab3 have reduced Ca(2+) channel levels and a Brp distribution that is very similar to that of the rab3 single mutant, indicating that RIM functions to regulate Ca(2+) channel accumulation but is not a Rab3 effector for release machinery distribution across release sites

Development of a high-resolution spatial inventory of greenhouse gas emissions for Poland from stationary and mobile sources

Greenhouse gas (GHG) inventories at national or provincial levels include the total emissions as well as the emissions for many categories of human activity, but there is a need for spatially explicit GHG emission inventories. Hence, the aim of this research was to outline a methodology for producing a high-resolution spatially explicit emission inventory, demonstrated for Poland. GHG emission sources were classified into point, line, and area types and then combined to calculate the total emissions. We created vector maps of all sources for all categories of economic activity covered by the IPCC guidelines, using official information about companies, the administrative maps, Corine Land Cover, and other available data. We created the algorithms for the disaggregation of these data to the level of elementary objects such as emission sources. The algorithms used depend on the categories of economic activity under investigation. We calculated the emissions of carbon, nitrogen sulfure and other GHG compounds (e.g., CO2, CH4, N2O, SO2, NMVOC) as well as total emissions in the CO2-equivalent. Gridded data were only created in the final stage to present the summarized emissions of very diverse sources from all categories. In our approach, information on the administrative assignment of corresponding emission sources is retained, which makes it possible to aggregate the final results to different administrative levels including municipalities, which is not possible using a traditional gridded emission approach. We demonstrate that any grid size can be chosen to match the aim of the spatial inventory, but not less than 100 m in this example, which corresponds to the coarsest resolution of the input datasets. We then considered the uncertainties in the statistical data, the calorific values, and the emission factors, with symmetric and asymmetric (lognormal) distributions. Using the Monte Carlo method, uncertainties, expressed using 95% confidence intervals, were estimated for high point-type emission sources, the provinces, and the subsectors. Such an approach is flexible, provided the data are available, and can be applied to other countries

Band-gap engineering of Cu2ZnSn1-xGe xS4 single crystals and influence of the surface properties

Thin film solar cells based on Cu2ZnSn(S,Se)4 are very promising, because they contain earth-abundant elements and show high absorptivity. However, the performance of these solar cells needs to be improved in order to reach efficiencies as high as that reported for Cu(In,Ga)Se 2-based devices. This study investigates the potential of band-gap engineering of Cu2ZnSn1-xGexS 4 single crystals grown by chemical vapour transport as a function of the [Ge]/([Sn] + [Ge]) atomic ratio. The fundamental band gap E0 is found to change from 1.59 to 1.94 eV when the Ge content is increased from x = 0.1 to x = 0.5, as determined from spectroscopic ellipsometry measurements. This knowledge opens a route to enhancing the performance of kesterite-based photovoltaic devices by a Ge-graded absorber layer. Furthermore, the formation of GeO2 on the surface of the as-grown samples was detected by X-ray photoelectron spectroscopy, having an important impact on the effective optical response of the material. This should be also taken into account when designing photovoltaic solar cellsRC acknowledges financial support from Spanish MINECO within the program Ramón y Cajal (RYC-2011-08521). This work was supported by the Marie Curie-IRSES project (PVICOKEST, GA: 269167), MINECO projects (KEST-PV, ENE2010-21541-C03-01/-02/-03) and Marie Curie-ITN project (KESTCELL, GA: 316488

Towards the growth of Cu2ZnSn1-xGexS4 thin films by a single-stage process: Effect of substrate temperature and composition

Cu2ZnSn1-xGexS4 (CZTGS) thin films prepared by flash evaporation of a Zn-rich Cu2ZnSn0.5Ge0.5S4 bulk compound in powder form, and a subsequent thermal annealing in S containing Ar atmosphere are studied. The effect of the substrate temperature during evaporation and the initial composition of the precursor powder on the growth mechanism and properties of the final CZTGS thin film are investigated. The microstructure of the films and elemental depth profiles depend strongly on the growth conditions used. Incorporation of Ge into the Cu2ZnSnS4 lattice is demonstrated by the shift of the relevant X-ray diffraction peaks and Raman vibrational modes towards higher diffraction angles and frequencies respectively. A Raman mode at around 348-351 cm-1 is identified as characteristic of CZTGS alloys for x = [Ge]/([Sn]+[Ge]) = 0.14-0.30. The supply of Ge enables the reduction of the Sn loss via a saccrifical Ge loss. This fact allows increasing the substrate temperature up to 350º C during the evaporation, forming a high quality kesterite material and therefore, reducing the deposition process to one single stageRC acknowledges financial support from Spanish MINECO within the Ramón y Cajal programme (RYC-2011-08521) and VIR for the Juan de la Cierva fellowship (JCI-2011-10782). GB also acknowledges the CSIC-JAE pre-doctoral program, co-funded by the European Social Fund. This work was supported by the Marie Curie-IRSES project (PVICOKEST, GA: 269167), Marie Curie-ITN project (KESTCELL, GA: 316488), DAAD project (INTERKEST, Ref: 57050358), and MINECO projects (SUNBEAM, ENE2013-49136-C4-3-R) (TEC2012-38901-C02-01). A. Scheu is acknowledged for GDOES measurement

Towards the growth of Cu2ZnSn1 xGexS4 thin films by a single-stage process: Effect of substrate temperature and composition

9 págs.; 7 figs.; 2 tabs.Cu2ZnSn1-xGexS4 (CZTGS) thin films prepared by flash evaporation of a Zn-rich Cu2ZnSn0.5Ge0.5S4 bulk compound in powder form, and a subsequent thermal annealing in S containing Ar atmosphere are studied. The effect of the substrate temperature during evaporation and the initial composition of the precursor powder on the growth mechanism and properties of the final CZTGS thin film are investigated. The microstructure of the films and elemental depth profiles depend strongly on the growth conditions used. Incorporation of Ge into the Cu2ZnSnS4 lattice is demonstrated by the shift of the relevant X-ray diffraction peaks and Raman vibrational modes towards higher diffraction angles and frequencies respectively. A Raman mode at around 348-351 cm-1 is identified as characteristic of CZTGS alloys for x = [Ge]/([Sn]+[Ge]) = 0.14-0.30. The supply of Ge enables the reduction of the Sn loss via a saccrifical Ge loss. This fact allows increasing the substrate temperature up to 350º C during the evaporation, forming a high quality kesterite material and therefore, reducing the deposition process to one single stage & 2015 Elsevier B.V. All rights reserved.RC acknowledges financial support from Spanish MINECO within the Ramón y Cajal programme (RYC-2011-08521) and VIR for the Juan de la Cierva fellowship (JCI-2011-10782). GB also acknowledges the CSIC-JAE Pre-doctoral Program, co-funded by the European Social Fund. This work was supported by the Marie Curie-IRSES Project (PVICOKEST, GA: 269167), Marie Curie-ITN project (KESTCELL, GA: 316488), DAAD project (INTERKEST, Ref: 57050358), and MINECO projects (SUNBEAM, ENE2013-49136-C4-3-R) (TEC2012- 38901-C02-01). A. Scheu is acknowledged for GDOES measurements.Peer Reviewe

Towards the growth of Cu2ZnSn1 xGexS4 thin films by a single stage process Effect of substrate temperature and composition

Cu2ZnSn1-xGexS4 (CZTGS) thin films prepared by flash evaporation of a Zn-rich Cu2ZnSn0.5Ge0.5S4 bulk compound in powder form, and a subsequent thermal annealing in S containing Ar atmosphere are studied. The effect of the substrate temperature during evaporation and the initial composition of the precursor powder on the growth mechanism and properties of the final CZTGS thin film are investigated. The microstructure of the films and elemental depth profiles depend strongly on the growth conditions used. Incorporation of Ge into the Cu2ZnSnS4 lattice is demonstrated by the shift of the relevant X-ray diffraction peaks and Raman vibrational modes towards higher diffraction angles and frequencies respectively. A Raman mode at around 348-351 cm-1 is identified as characteristic of CZTGS alloys for x = [Ge]/([Sn]+[Ge]) = 0.14-0.30. The supply of Ge enables the reduction of the Sn loss via a saccrifical Ge loss. This fact allows increasing the substrate temperature up to 350º C during the evaporation, forming a high quality kesterite material and therefore, reducing the deposition process to one single stageRC acknowledges financial support from Spanish MINECO within the Ramón y Cajal programme (RYC-2011-08521) and VIR for the Juan de la Cierva fellowship (JCI-2011-10782). GB also acknowledges the CSIC-JAE pre-doctoral program, co-funded by the European Social Fund. This work was supported by the Marie Curie-IRSES project (PVICOKEST, GA: 269167), Marie Curie-ITN project (KESTCELL, GA: 316488), DAAD project (INTERKEST, Ref: 57050358), and MINECO projects (SUNBEAM, ENE2013-49136-C4-3-R) (TEC2012-38901-C02-01). A. Scheu is acknowledged for GDOES measurement

Properties of SiGe/Si heterostructures fabricated by ion implantation technique

A comprehensive electrical characterisation of the SiGe/Si heterostructures has been performed in the wide temperature range (10270 K). Four structures fabricated by the Ge⁺ ion implantation technique at different substrate temperatures (room temperature, 150°C, 450°C and 600°C) have been studied. The diode I-V characteristics, thermally stimulated capacitance and currents were measured and the presence and parameters of shallow trap levels were determined in dependence on the substrate temperature. The sample implanted at 450°C shows the best diode operation reflecting the higher quality of the surface silicon layer as compared to RT- and 150°C-implanted samples. Implantation-induced mechanical stresses have been investigated by Raman spectroscopy. For the first time the cryogenic TSCR technique has been applied to this system which makes it possible to investigate strain in the silicon layer due to SiGe layer formation