Search Results - (Author, Cooperation:Jesser)

article

2021

Soziale Ungleichheit ; Kind ; Schule ; Übergang ; Soziale Arbeit ; Unterstützung ; Österreich

SIÖ : Fachzeitschrift für Soziale Arbeit in Österreich, (2021) H. 3, S. 20-25, 1019-7729

German

Online

1989

Forschung ; Computereinsatz ; Datenbank ; Melodie ; Musikpädagogik ; Volkslied ; Volksmusik ; Musikwissenschaft ; Analyse

Nauck-Börner, Christa (Hrsg.), Musikpädagogik zwischen Traditionen und Medienzukunft., Laaber: Laaber-Verl. (1989), S. 213-228, 3-89007-201-1

German

article

2017

Gemeinde (Kommune) ; Bewerbung ; Leitung ; Verfahren ; Zuständigkeit ; Verwaltung ; Beamter

Deutsche Verwaltungspraxis, Bd. 68 (2017) H. 5, S. 186-188, 0343-9496

0945-1196

German

Anmerkungen

article

2017

Recht ; Erwerbstätigkeit ; Vergütung ; Ehrenamtliche Arbeit ; Zweitberuf ; Definition ; Funktion (Struktur) ; Verwaltung ; Öffentlicher Dienst ; Beamter

Deutsche Verwaltungspraxis, Bd. 68 (2017) H. 12, S. 493-497, 0343-9496

0945-1196

German

Anmerkungen

Online

2022

Bewältigung ; Furcht ; Psychische Gesundheit ; Hilfe suchendes Verhalten ; Schüler ; COVID-19 ; Pandemie ; Schutzfaktor ; Jugendlicher

Healthcare, Bd. 10 (2022) H. 7, 14 S., 2227-9032

English

article

2019

Gemeinde (Kommune) ; Personalbeschaffung ; Bewerbung ; Innovation ; Internet ; Personal ; Informationstechnologie ; Online-Angebot ; Niedersachsen

Deutsche Verwaltungspraxis, Bd. 70 (2019) H. 9, S. 379-383, 0343-9496

0945-1196

German

Anmerkungen

2018-06-19

The American Society for Microbiology (ASM)

0099-2240

1098-5336

Biology

1089-7550

AIP Digital Archive

Physics

Epitaxial growth of compound semiconductors on the (001) exhibits an asymmetry in the dislocation morphology in the two 〈110〉 directions for thicknesses near the critical thickness. The source of the asymmetry has been investigated by growth of a thickness wedge of p- and n-type GaAs0.95 P0.05 on GaAs by metalorganic chemical vapor deposition. The effect of misorientation on the resolved shear stress for each slip system has been calculated and eliminated as the source of the asymmetry. The thickness gradient was also eliminated as the source. A definitive correlation can be made between the asymmetry and the differences in the Peierls barriers of the two types of dislocations. The asymmetry results in two different critical thicknesses, one for each type of dislocation. The Peierls barriers are more similar in p-type material than in n-type material. In agreement with this, a reduced amount of asymmetry was observed in the p-type overgrowth as compared to the n-type. The nucleation barrier differences between the two types of dislocations are shown to be an unlikely source of the asymmetry.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

A critical-thickness model is proposed for lattice-mismatched epitaxial layers which incorporates for the first time both the equilibrium and kinetic components of misfit accommodation. The model is an attempt to provide a physical basis for the discrepancy between the observed and calculated critical thickness in zinc-blende semiconductors. The equilibrium components of the model use a force balance and a Volterra description of the dislocation line tension with frictional forces includiing Peierls barriers and dislocation atmospheres. The effect of the frictional forces is to shift the critical thickness to a larger value and to produce a residual elastic strain which persists for large thicknesses. The frictional barriers are low in face-centered-cubic metals and produce minor changes from the previous theories; however, for semiconductors the frictional forces may be high and produce a substantial increase in the predicted critical thickness. The kinetic component of misfit accommodation has been addressed through a dynamic frictional force. The explicit form of the kinetic component of misfit accommodation depends on the operative mechanism of misfit-dislocation generation. A simple criterion is proposed to estimate whether the generation of misfit dislocations will be controlled by equilibrium or kinetic factors.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

Stoichiometric single crystal GaAs is grown at 75 °C by a migration-enhanced-epitaxy (MEE) technique. The stoichiometry of the GaAs films can be controlled by adjusting the arsenic monolayer deposition time. For Ga-rich compositions, epitaxy breaks down and polycrystalline GaAs results. For stoichiometric GaAs, and As-rich compositions, epitaxy proceeds and specular stoichiometric films can be grown to significant thicknesses. Reflection high-energy electron diffraction patterns indicated some surface roughness that increased for compositions closer to those which were Ga rich. This work suggests that low-temperature growth by MEE results in limited-thickness-epitaxy (LTE) behavior for GaAs that is very different from low-temperature growth by conventional molecular beam epitaxy. The results of this work indicate the importance of stoichiometry, surface roughening, and surface diffusion phenomena in determining regimes where epitaxy occurs at low temperature. A maximum LTE epitaxial thickness of 300 nm was obtained at 75 °C. © 1999 American Institute of Physics.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

A technique for the heteroepitaxy of GaAs/Si films having reduced threading dislocation density is presented. The important attribute of this technique is the suppression of three-dimensional Volmer–Weber island formation during initial deposition. This suppression is achieved by deposition of a stoichiometric GaAs buffer layer by a migration-enhanced epitaxy technique on silicon at 348 K to a thickness greater than the "monolithic thickness," hm. Subsequent GaAs films deposited by conventional molecular beam epitaxy on buffer layers of thickness greater than hm possess structural and optical characteristics that exceed those for state-of-the-art GaAs/Si layers: an x-ray full width at half maximum (FWHM) of 110 arcsec with a dislocation density at the film surface of 3×106 cm−2 and a concomitant 4 K photoluminescence FWHM of 2.1 meV. The p-i-n structures suitable for use as light-emitting diodes (LEDs) that were grown on the reduced threading dislocation density GaAs/Si and by means of forward- and reverse-bias measurements, demonstrated an ideality factor of n=1.5, an increased reverse-bias breakdown electric field of 2.1×107 V/m, and an intrinsic region resistivity of 4×107 Ω cm for LEDs of increasingly smaller mesa size. © 2001 American Institute of Physics.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

High-temperature microstructure of Si–Ge alloys containing 10–15 mole % GaP were studied. Quenching the 80/20 Si–Ge alloy (80 at. % Si) from above 1125 °C and the 50/50 Si–Ge alloy (50 at. % Si) from above 1025 °C resulted in a duplex microstructure. The two-phase regions consisted of a regular array of rodlike structures (GaP) in a Si–Ge matrix whereas the monophase regions were pure Si–Ge. These rodlike structures were found to lie along the [001] direction and result in {002} spots in a [100] electron diffraction pattern. The "rods'' were about 35 and 45 nm in diameter in the case of the 80/20 and 50/50 alloy, respectively. These structures are not stable on annealing and do not form when the solidification rate is decreased. © 1996 American Institute of Physics.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

In order to assess the relative contributions of glide and climb processes in the relaxation of misfit strain in heteroepitaxial layers, the glide and climb velocities of dislocations are compared at several temperatures. It is shown that the glide velocity is much greater than the climb velocity under normal conditions. For copper and silicon, about four orders of magnitude can exist at 3/4 of the melting temperature with lower temperatures leading to larger differences. One therefore expects relaxation of misfit strain to proceed primarily by glide mechanisms. Two cases are addressed here in which climb processes can be important: (i) by-passing of an obstacle and (ii) redistribution of an irregular array of interfacial misfit dislocations into a regular array of lower energy.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

An experimental investigation of misfit dislocation generation mechanisms at an InGaAs/GaAs heterointerface is reported. InGaAs epitaxial layers were grown by low-pressure organometallic vapor-phase epitaxy on patterned and unpatterned GaAs substrates having etch-pit densities (EPD) of 200, 1400, and 10 000 cm−2. After epitaxial growth, the samples were annealed at temperatures between 650 and 750 °C, and analyzed by optical and transmission electron microscopy. For the range of substrate EPD studied, it was found that the substrate EPD controls the onset of misfit dislocation generation for low-temperature epitaxy (〈600 °C) on unpatterned substrates. When epilayers were annealed at 750 °C, the density of misfit dislocations was independent of the substrate EPD. These studies also show that the dominant misfit dislocation generation mechanism for films grown on patterned substrates is nucleation at the growth-mesa edge. The density of preexisting threading dislocations has little influence on misfit dislocation generation for films selectively deposited within 100×100 μm2 growth windows. For selective heteroepitaxy, misfit dislocation generation strongly depends on the crystallographic orientation of the growth-mesa edge. © 1994 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

Three processing methods were employed to homogenize a Si0.80Ge0.20 alloy hot pressed with additions of approximately 2 a/o GaP. The melt-growth methods investigated include single-pass zero melting, zone leveling, and splat cooling. Energy dispersive spectroscopy was performed in conjunction with scanning electron microscopy and transmission electron microscopy along with x-ray diffractometer analysis to characterize the resultant ingots. The single-pass zone-melted ingot exhibited a higher GaP content than the zone-leveled ingot probably as a consequence of a higher growth temperature during zone melting. Both ingots had large regions of uniform average composition whereas the splat cooled alloy exhibited a marked inhomogeneity.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

In this paper we have extended the exact predictions of critical misfit fc and critical thickness hc —based on equilibrium suppositions and a parabolic interfacial potential of shear strength μ—in superlattices of layer pairs A and B introducing the thicknesses ha=ηac and hb=ηbc, and moduli μa, μb, and μ as variables. The extension involved an explicit relation between the homogeneous misfit strains e¯a and e¯b on the one hand and the thicknesses and moduli on the other in order to ensure lateral force balance. Analytical expressions for the energies ED and Ee¯ per unit area per interface for misfit dislocations and mistfit strains, respectively, have been derived and minimized to obtain the equilibrium value e¯m needed to predict fc and hc. The expression for ED is rather complicated. However, a variety of simplifying approximations were feasible, which not only facilitated numerical evaluation but also made it possible to draw various conclusions. The case of equal elastic constants but variable layer thicknesses shows that a maximum value of fc occurred when the superlattice layers have equal thickness and that the layers of equal thickness produced the minimum value of ED. Scaling relations were found that could be used to calculate ED values simply by selecting the appropriate combinations of thicknesses and elastic constants. The effect of changing elastic constants or the values of critical thickness or critical misft could also be represented through scaling relations.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

A parabolic interaction potential has been used to develop a model for calculating the misfit dislocation (MD) energy in the case of a superlattice of alternating layers of materials with equal elastic constants and thicknesses. The model, which is believed to be a good one for small misfits and to have some merit for covalent bonded materials, is exactly solvable for the critical thickness above which it is energetically favorable to lose coherency by the introduction of MDs into the interfaces. It was found, for a given misfit f, that the critical thickness for epitaxial superlattices free from their substrate is somewhat more than 4 times that for a single epilayer on a thick substrate. Furthermore, the critical thickness varies almost inversely with misfit to the power 1.22 when Poisson's ratio is 1/3. It was also shown that the critical misfit fc obtained by equating maximal misfit strain and MD energies is a significant overestimate of fc. The results for a superlattice are compared with those of a thin layer on a thick substrate.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

The coherency-incoherency transition in epitaxial crystals is said to take place at a critical misfit fc or, for a system in which a monolayer is subcritical, at a critical thickness hc. In this paper, we analyze the physical principles and models used to predict critical parameters and put them into perspective. We stress the dependence of the relevant principles on the equilibrium-nonequilibrium conditions under which the quantities are measured in practice. The advantages and disadvantages of the models used—essentially the Frenkel–Kontorowa and Volterra models—are highlighted.

Electronic Resource

1471-0528

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

High resolution imaging of gynaecological tissue offers the potential for identifying pathological changes at early stages when interventions are more effective. Optical coherence tomography (OCT) is a high resolution high speed optical imaging technology which is analogous to ultrasound B–mode imaging except reflections of light are detected rather than sound. The OCT technology is capable of being integrated with laparoscopy for real–time subsurface imaging. In this report, the feasibility of OCT for differentiating normal and pathologic laparoscopically–accessible gynaecologic tissue is demonstrated. Differentiation is based on architectural changes of in vitro tissue morphology. OCT has the potential to improve conventional laparoscopy by enabling subsurface imaging near the level of histopathology.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

Experimentally it has been found that twist bonding a thin layer of epitaxially grown material to a thick substrate of the same material has the properties of being compliant with respect to the growth of a heteroepitaxial layer onto the thin layer. The benefit of the compliant substrate is that the heteroepitaxial layer is of much higher perfection when compared to the same growth but on a bulk substrate, primarily due to a very low density of threading dislocations present in the heteroepitaxial deposit. This concept has been investigated experimentally and discussed in terms of what is the operative mechanism of the compliant substrate. However, there is still much to be explained about the mechanism by which the compliant substrate accommodates misfit between itself and the heteroepitaxial layer. How the structure of the interface between the compliant substrate and the thick substrate can be tailored to derive the maximal benefit in the epilayer is the subject of the present article. The importance of a high angle of twist between the compliant substrate and the bulk substrate is in providing a high density of interfacial dislocations. Closely spaced dislocations with overlapping cores approximate the conditions of a free-standing compliant substrate by providing an easy mechanism for the complaint substrate to elastically accommodate misfit between itself and the heteroepitaxial film grown onto it. In cases which exhibit strong atomic interaction between compliant substrate and bulk substrate the approximation to a free-standing compliant substrate is not as good and the interface can be reasonably described in terms of a dense array of pure screw dislocations. In this case accommodation of misfit between the heteroepitaxial film and the compliant substrate can be accomplished by elastically changing the lattice parameter of the compliant substrate to meet that of the heteroepitaxial film. The elastic deformation of the compliant substrate can cause the dense array of pure screw dislocations to reorient thereby introducing an edge component to the interfacial dislocations which accommodates the introduced misfit between the compliant substrate and the bulk substrate. The details of this mechanism and how it can be used to design compliant substrates show that exact coincidence angles of twist should be avoided. Further, good compliant substrates may be obtained by wafer bonding thin complaint substrates of a crystal similar to that of the heteroepitaxial film rather than of a material similar to that of the substrate. © 1999 American Institute of Physics.

Electronic Resource