摘要:

AbstractThin film solar cells represent the major option for photovoltaic electricity production at economically acceptable costs. Especially cells and modules based on amorphous silicon can be produced on cheap large area substrates and are presently the choice to enter mass production. The understanding of the physical properties of amorphous silicon and amorphous silicon alloys forms the basis for an optimized cell design and the use of appropriate deposition processes. Stacked cell structures and improved interfaces in each single cell minimize the effect of light induced degradation. Multi junction cells of different band gap absorber materials are being developed and are already used which utilize the solar spectrum even better, and lead to higher stabilized efficiencies.

ISSN:0370-1972    

DOI:10.1002/pssb.2221920202

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractThis paper refers to the perspectives of the use of hydrogenated amorphous germanium and its alloys (deposited by the rf sputtering method). It is shown that considerable progress has been made in the optimization of aGe: H films. The deposition conditions leading to a good quality material and the corresponding properties are discussed. The problem of material stability, as well as recent progress in the understanding of the n‐ and p‐type doping mechanisms in the aGe: H network are presented. The main issues and perspectives of hydrogenated GeSi, GeN, and GeSn alloys are analyzed. Finally, results in the aGe: H device are

ISSN:0370-1972    

DOI:10.1002/pssb.2221920203

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractThe chemical situation of the Si atoms at the surface of Si3N4ultrathin films thermally grown onto Si(001) substrates 2 × 1 reconstructed in a NH3atmosphere has been recently studied in detail by core‐level spectroscopy using synchrotron radiation, as well as the chemical situation of the Si atoms at the film/substrate interface. The Si atoms at the surface are assigned to be either bonded to N atoms that are located in the layer just below the surface and having one dangling bond, or terminated by NH2. The Si atoms at the interface present intermediate oxidation states. Also recently high resolution isotopic tracing studies of N and H showed that nitrogeneous species (most probably NHxradicals,x<3) are mobile during thermal growth of silicon nitride films, while isotopic tracing of Si showed that this species appears to be immobile during growth. This newly built experimental scenario for the nanostructure of the surface and interface, and for the atomic transport processes taking place during nitride growth, led us to develop a model for the mechanism of thermal growth of Si3N4ultra‐thin films on Si(100), that is capable to explain the self‐limited character which makes them extremely attractive for applications in the VLSI and ULSI technologies for microfabrication of silicon d

ISSN:0370-1972    

DOI:10.1002/pssb.2221920204

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractStrong visible luminescence of porous silicon has triggered renewed general interest in the optical properties of silicon nanostructures. In addition to porous Si itself, Si‐based molecules, nanometer‐size Si particles, one‐dimensional Si chains, two‐dimensional Si layers, and many Si alloys are known to exhibit optical properties (absorption and luminescence) which strongly deviate from those of bulk crystalline Si. Here, we review and compare the main properties of the above‐mentioned systems and present a brief discussion of the experimental observations in terms of existing theories. Current prospects for Si‐based optoelectronic applications are als

ISSN:0370-1972    

DOI:10.1002/pssb.2221920205

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractIn a short introduction limitations of present semiconductor microelectronics are discussed. At the beginning of the next century both technological and physical limits will severely affect further miniaturisation of integrated circuits (IC) into the deep submicron, i.e. below 100nm feature size range. Several novel device concepts being based on the use of quantum effects in nanostructures are discussed which might open new pathways to faster, lower consumption, and more compact semiconductor ICs: Resonant tunneling structures might play an important role as multifunctional devices which allow the integration of more complex logical functions in one and the same device under more relaxed lithography conditions. A further approach in quantum electronics is focussed on electron interference in high mobility two‐dimensional electron gases (2DEG) at semiconductor heterointerfaces. Novel processor concepts might be possible by use of quantum dot arrangements and single electron tunneling. The underlying physics is explained and several experimental approaches for the realisation of quantum dots and wires are presente

ISSN:0370-1972    

DOI:10.1002/pssb.2221920206

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractThe interaction of energetic molecules with surfaces is of interest for nuclear fusion experiments, for the erosion of space vehicles, and for the understanding of basic charge exchange phenomena between metal surfaces and molecules. For the latter reason experiments with hyperthermal molecules are also of interest for catalytic processes and for the functioning of solid state sensors. In many cases the interaction of molecules with surfaces is governed by charge exchange processes. An obvious case is the catalytic oxidation of CO at surfaces where a negative carbon dioxide species is identified as an intermediate of the reaction. Negative carbon dioxide species are also found in beam experiments. Their yield and the correlated dissociation probabilities show the expected dependencies on e.g. the coverage of the metal with alkali metal layers. In the case of hydrogen molecules the influence of alkali layers is quite different. In chemisorption experiments alkalis cause a decrease of the dissociative chemisorption of hydrogen. In our beam experiments an increase of the molecular survival with alkali coverage is found accordingly. The interpretation of the findings gives more detailed insight into the dissociation mechanisms of small molecules.

ISSN:0370-1972    

DOI:10.1002/pssb.2221920207

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractOur present experiences in manipulating single atoms and molecules on solid surfaces by using the tip of a scanning tunneling microscope (STM) are reviewed. The construction and performance characteristics of our temperature variable STM is shortly described, which allows investigations in the temperature range between 15 and 300 K. As example for horizontal manipulation, in which the adatoms or admolecules are pulled along the surface by the STM tip, and the formation of man‐made surface structures, the formation of the letters ‘F’ and ‘U’, which form the logo of our university is presented. The adspecies used in these experiments are CO molecules and the substrate a Cu(211) surface. An example of vertical manipulation, in which an adparticle is picked up by the tip, carried to another place and released back to the surface, concerns Xe on the same substrate. The latter technique allows also to vary the chemical composition of the tip apex in a well‐defined manner. Consequences in imaging the surface with tips of different compositions are presented and discussed. Finally, STM observations of ordered high density phases of CO on the Cu(211) substrate ar

ISSN:0370-1972    

DOI:10.1002/pssb.2221920208

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractA relativistic Green function theory of the layer‐KKR type has been applied to calculate the electronic structure and its manifestation in valence‐band photoemission of ferromagnetic layer systems of the form Co/Cu/Co(001) and Cu/Co/Cu(001). The spin‐ and layer‐resolved density of states in Co films of one to ten monolayers on Cu(001) is almost mirror symmetric with respect to the central Co plane. For Cu films on Co(001), minority spin “quantum well states” have constant weights in the Cu monolayers and a stronger weight in the first Co monolayer. For all systems, spin‐resolved photoemission spectra mostly reflect the spin character of the initial states with modifications by spin‐orbit coupling. As a consequence, the spin‐averaged photocurrent by p‐polarized light from films with in‐plane magnetization shows a pronounced dependence on the magnetization direction, i.e. magnetic linear dichroism. For perpendicular magnetization, circularly polarized light produces sizeable magnetic circular dichr

ISSN:0370-1972    

DOI:10.1002/pssb.2221920209

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractIn two‐photon photoemission a photon from a pulsed laser excites an electron from a state below the Fermi level to an unoccupied intermediate state below the vacuum level. A second photon of the same pulse ionizes the intermediate state. The energy distribution of the photoelectrons yields information on the position and the lifetime of both the initial and, in particular, the intermediate state. Most of the work in two‐photon photoemission spectroscopy has been devoted to the investigation of image potential states (image states). They are bound states of electrons in front of metal surfaces in the potential well built by the image potential and the surface. The situation is analogous to the hydrogen atom, with a binding energy of the lowest state of 850 meV in first approximation. Up to four members of the Rydberg series are detected. Experimental results on the binding energy of image states in (111) and (100) surfaces of Ag, Au, Cu, and Pd agree with calculations by a one‐dimensional scattering model. The results for Co, Ni, and Fe are not yet understood. The effective mass is close to unity except for Ag(111). Lifetimes between 5 and 170 fs are measured. They can be explained by decay via electron‐hole pair creation in the bulk. Image states on metal overlayers yield information on film growth and surface morphology. Dielectric overlayers are been investigated. Adsorbate states of atoms and molecules adsorbed on metal substrates can also be studied by two‐photon photoemission spectroscopy. Results for Na, O, CO, and NO on Cu(111) are

ISSN:0370-1972    

DOI:10.1002/pssb.2221920210

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractLow‐energy ion backscattering and scanning tunneling microscopy (STM) can be used in combination to study the surface crystallography of single crystals, in particular also for alloy and ordered intermetallic compound systems. The elemental composition as well as the location of the atoms is determined by low‐energy noble gas impact collision ion scattering spectroscopy with neutral detection (NICISS). Microscopic information on an atomic scale is obtained with the help of STM. The influence of adsorption‐induced surface modifications is investigated at Cu3Au and compared with Cu surfaces. From the NICISS investigation the AuCu termination is inferred for clean Cu3Au(100) and (110). After careful preparation of the clean Cu3Au(110) surface the prominent (2 × 1) LEED superstructure changes into a pronounced (4 × 1) LEED pattern. The (4 × 1) structure can be explaining by row pairing of CuCu and AuAu rows in the topmost layer. Upon oxygen exposure of the Cu3Au compounds, Cu tends to segregate to the surface. In case of Cu3Au(110) a (2 × 1)O superstructure appears which is in part similar to the known added row structure obtained for Cu(110)(2 × 1)O. Comparison with the Cu(110)O surface shows, however, that the known periodically ordered structure of CuO stripes at undersaturation with oxygen does n

ISSN:0370-1972    

DOI:10.1002/pssb.2221920211

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY