Papers by Ferdinand Hofer
Imaging & Microscopy, 2009
Imaging & Microscopy, 2008
Materials Chemistry and Physics, 2015
ABSTRACT We present a study on the formation mechanism of copper zinc tin sulphide (CZTS) nanopar... more ABSTRACT We present a study on the formation mechanism of copper zinc tin sulphide (CZTS) nanoparticles prepared from metal salts and 1-dodecanethiol in oleylamine. The nanoparticle sample exhibits two kinds of crystals, large ones with a size of about 70 nm and smaller ones with a diameter of about 25 nm. Analysis of the chemical composition of single nanoparticles revealed that the small nanoparticles consist of copper sulphide, while the larger ones are CZTS nanoparticles. A thorough investigation of the formation process of the nanoparticles revealed that the presence of the copper sulphide nanoparticles originates from the formation of copper sulphide nanopartides in the initial nucleation step. These initial copper sulphide nanoparticles are converted to copper tin sulphide before the final CZTS nanoparticles are obtained.
Solar Energy Materials and Solar Cells, 2013
ABSTRACT Solution processable small molecules are an alternative to conjugated polymers in organi... more ABSTRACT Solution processable small molecules are an alternative to conjugated polymers in organic photovoltaics and have recently been in the focus of intense research. In this work, organic–inorganic hybrid solar cells with active layers consisting of the solution-processable small-molecule p-DTS(FBTTh2)2 and copper indium sulfide nanoparticles are presented. The copper indium sulfide nanoparticles are formed in situ directly in the small molecule matrix from metal xanthate precursors. The prepared nanocomposite small molecule/copper indium sulfide films are very smooth, highlighting the good compatibility of p-DTS(FBTTh2)2 with the in situ preparation of metal sulfide nanoparticles. The formed nanoparticles have diameters of about 3 nm. Hybrid solar cells, exhibiting power conversion efficiencies of 1.3%, are characterized by IV curves, EQE spectra and electron microscopy.
2013 IEEE 39th Photovoltaic Specialists Conference (PVSC), 2013
ABSTRACT Besides active materials the choice of suitable cathodes is crucial for a good overall p... more ABSTRACT Besides active materials the choice of suitable cathodes is crucial for a good overall performance in solar cells. A cathode modification utilizing a thin silver interlayer followed by an aluminum layer can largely enhance the fill factor of polymer: CIS (copper indium sulfide) solar cells in comparison to pure Al or Ag cathodes. In this work, we investigate if this concept can also be applied to polymer: fullerene solar cells to enhance their overall power conversion efficiency. The organic solar cells examined consisted of blends of low band-gap donor polymers (PCDTBT and PSiF-DBT) as well as PCBM as acceptor.
2010 35th IEEE Photovoltaic Specialists Conference, 2010
Bulk heterojunction hybrid solar cells with a CuInS2-poly(pphenylene vinylene) active layer are p... more Bulk heterojunction hybrid solar cells with a CuInS2-poly(pphenylene vinylene) active layer are presented in this contribution. The acceptor phase is obtained in-situ within the matrix of the polymer by the reaction of the metal ions with the decomposition products of a sulfur source (thioacetamide) using a moderate heating step. As prepared donor-acceptor nanocomposites were used as active layers in hybrid solar cells. Structural characterization was performed using XRD and TEM methods, solar cell performance and optical properties were explored by j-V-, absorbance-and IPCEmeasurements.
Inorganic Chemistry, 2011
The formation of copper indium disulfide nanoparticles via the oleylamine route using copper iodi... more The formation of copper indium disulfide nanoparticles via the oleylamine route using copper iodide, indium chloride, and elemental sulfur has been investigated by applying conventional thermal heating as well as microwave irradiation. Oleylamine thereby acts as a capping ligand as well as a solvent. In an initial set of experiments, the onset of the reaction was determined to be around 115°C by an in situ X-ray study using Synchrotron radiation. Using comparatively low synthesis temperatures of 120°C, it is already possible to obtain nanoparticles of 2-4 nm with both heating methods but with irregular shape and size distribution. By applying higher temperatures of 220°C, more crystalline and larger nanoparticles were obtained with slight differences in crystallite size and size distribution depending on the synthesis route. The size of the nanoparticles is in the range of 3-10 nm depending on the heating time. Using microwave irradiation, it is possible to obtain nanoparticles in only 90 s of total synthesis time. Control experiments to probe a nonthermal microwave effect were carried out ensuring an identical experimental setup, including the heating profile, the stirring rate, and the volume and concentration of the solutions. These experiments clearly demonstrate that for the preparation of CuInS 2 nanoparticles described herein no differences between conventional and microwave heating could be observed when performed at the same temperature. The nanoparticles obtained by microwave and thermal methods have the same crystal phase, primary crystallite size, shape, and size distribution. In addition, they show no significant differences concerning their optical properties.
Cheminform, 2010
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was e... more ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
Microscopy Microanalysis Microstructures, 1993
2014 Electron energy-loss spectrometry enables the detection of Li and Be via the K ionization ed... more 2014 Electron energy-loss spectrometry enables the detection of Li and Be via the K ionization edges. However, the detection and quantification of these low energy edges present several problems, like low edge-to-background ratios, problems with background extrapolations, overlapping of edges and multiple scattering in case of thicker specimens. All these problems can be overcome by careful application of well known procedures: Spectra have to be recorded from very thin specimen regions (t/03BB 0.5) and subsequently deconvoluted by the Fourier-log-method. This procedure improves the background in front of the edges, so that the conventional A . E-r model can be used for background fitting without problems. The Li and Be K edges overlap with other edges e.g. the L23 edges of elements Mg to P and the M23 edges of the elements Ca to Cu. In such a situation quantitative analysis is only possible by a multiple-least-square fit with reference spectra and if experimentally determined partial cross-sections are used. The successful application of these methods is demonstrated for inorganic materials like phenacite, beryl, spodumene, Be-phosphate and Li-Cr-oxide. The quantification and detection limits for Li and Be in typical material science specimens are discussed. Microsc. Microanal. Microstruct. 4 (1993) DECEMBER 1993, PAGE 539 Classification Physics Abstracts 07.80 1. Introduction.
Physical Review B, 2014
ABSTRACT We report on the formation of one-dimensional Au/Ag core-shell nanostructures in superfl... more ABSTRACT We report on the formation of one-dimensional Au/Ag core-shell nanostructures in superfluid helium nanodroplets (He-N) and their subsequent surface deposition under soft landing conditions. In vortex charged He-N, dopant atoms and clusters prefer to agglomerate along vortex cores, which serve as personal cryo-templates for each nanowire. A sequential pickup scheme enables the fabrication of Au/Ag structures with either Au as core and Ag as shell or vice versa. The core-shell structure is in both cases shown by energy-dispersive x-ray spectroscopy (EDX) in a scanning transmission electron microscope (STEM). The inherent spatial resolution and element sensitivity of this method allows a direct observation of the two different phases. High resolution STEM studies elucidate morphological details of the Au/Ag nanostructures and, together with the EDX analysis, indicate that the nanowires are formed in a multicenter aggregation process.
Micron and Microscopica Acta, 1988
... caused by chromatic aberrations of the post specimen lenses as pointed out by Egerton (1984) ... more ... caused by chromatic aberrations of the post specimen lenses as pointed out by Egerton (1984) and by Malis et a!. Ferdinand Hofer and ... Unless allowance for the chromatic aberration effects of the post specimen lenses is made (Craven et a!., 1981), the implication appears to be ...
Journal of the Chemical Society, Dalton Transactions, 1988
ABSTRACT
AHN:TRANSM.ELECTRON EN.2E O-BK, 2004
... In this Chapter, we will focus on fixed beam EFTEM and its specific use in addressing questio... more ... In this Chapter, we will focus on fixed beam EFTEM and its specific use in addressing questions regarding the micro-and nanochemistry of various ... Additionally, we intend for this chapter to provide a literature survey including most materials science applications of EFTEM. ...
Ultramicroscopy, 1996
Quantitative microanalysis by electron energy-loss spectrometry requires knowledge of partial inn... more Quantitative microanalysis by electron energy-loss spectrometry requires knowledge of partial inner-shell ionization cross-sections. Data for the L23-edges of the elements strontium to molybdenum are not well known. We have therefore measured cross-section ratios (k-factors) for the L23-edges of the elements Sr to Mo using thin film oxide-standards. The experimental values are compared with calculations derived from a modified hydrogenic and
Electroactive Materials, 2001
Summary. Thin-film electrodes allow the manufacturing of flat batteries of variable design. The... more Summary. Thin-film electrodes allow the manufacturing of flat batteries of variable design. Their electric performance is better than that of customary cells because of a larger contact area between anode and cathode and better utilization of the electrochemically active materials. Bipolar thin-film electrodes for the rechargeable alkaline zinc/manganese dioxide system were assembled using graphite-filled plastics (high-density polyethylene and polyisobutylene). In a
Electroactive Materials, 2001
Summary. Energy-filtering transmission electron microscopy (EFTEM) and electron energy-loss spe... more Summary. Energy-filtering transmission electron microscopy (EFTEM) and electron energy-loss spectrometry (EELS) have been used to measure the distribution of titanium in titanium-doped electrolytic manganese dioxide, which consists of large particle agglomerates of some micrometer diameter. In contrast to previous investigations, where the distribution of the doping elements can only be investigated at the thinnest regions of the agglomerates, we describe an
Ultramicroscopy, 1996
Energy-filtering transmission electron microscopy (EFTEM) has been used for imaging of secondary ... more Energy-filtering transmission electron microscopy (EFTEM) has been used for imaging of secondary phases in materials, e.g. precipitates and grain boundary phases. The investigations have been performed with a Philips CM20 equipped with a Gatan imaging filter at 200 kV acceleration voltage. In order to visualize the secondary phases in a steel sample we have recorded jump ratio images using the
Microscopy Microanalysis Microstructures, 1991
2014 Quantitative microanalysis using the EELS technique requires the knowledge of partial scatte... more 2014 Quantitative microanalysis using the EELS technique requires the knowledge of partial scattering cross-sections to relate the measured intensities to the concentrations in the compounds. Partial scattering cross-sections can be determined either theoretically or empirically by means of standards. Cross-sections for K, L23 and M45 ionization edges can be calculated by the hydrogenic model and by the Hartree-Slater-model and with these models elements ranging from Li to W can be quantified. Alternatively, the ratio of two cross-sections (k-factor) can be used for quantification.
Microscopy Microanalysis Microstructures, 1996
2014 Electron energy-loss spectrometry enables the detection of Li and Be via the K ionization ed... more 2014 Electron energy-loss spectrometry enables the detection of Li and Be via the K ionization edges. However, the detection and quantification of these low energy edges present several problems, like low edge-to-background ratios, problems with background extrapolations, overlapping of edges and multiple scattering in case of thicker specimens. All these problems can be overcome by careful application of well known procedures: Spectra have to be recorded from very thin specimen regions (t/03BB 0.5) and subsequently deconvoluted by the Fourier-log-method. This procedure improves the background in front of the edges, so that the conventional A . E-r model can be used for background fitting without problems. The Li and Be K edges overlap with other edges e.g. the L23 edges of elements Mg to P and the M23 edges of the elements Ca to Cu. In such a situation quantitative analysis is only possible by a multiple-least-square fit with reference spectra and if experimentally determined partial cross-sections are used. The successful application of these methods is demonstrated for inorganic materials like phenacite, beryl, spodumene, Be-phosphate and Li-Cr-oxide. The quantification and detection limits for Li and Be in typical material science specimens are discussed. Microsc. Microanal. Microstruct. 4 (1993) DECEMBER 1993, PAGE 539 Classification Physics Abstracts 07.80 1. Introduction.
Journal of Materials Science Letters, 1996
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Papers by Ferdinand Hofer