ISSN:0232-1300    

DOI:10.1002/crat.2170320103

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

ISSN:0232-1300    

DOI:10.1002/crat.2170320104

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractApplying a rotating magnetic field to an electrically conducting liquid, a Lorentz force is induced which generates a melt rotation of a certain angular velocity. A cylindrical gallium melt (aspect ratio 2.5) has been used as a model liquid. The melt has been heated from the bottom (Ra= 106) or from the top (Ra= −106) and the resulting temperature fluctuations in the melt have been measured in dependence on the rotating field strength (Bmax= 30 mT). In the case of the unstable gradient 0.8 mT are sufficient to dominate the buoyancy driven convection and to reduce the amplitude of the buoyancy caused temperature oscillations for more than one order of magnitude. At the same time, the fluctuation frequency increases with the field strength. In the case of the stabilizing temperature gradient, low amplitude/high frequency temperature fluctuations are generated by the rotating magnetic field, indicating the transition to a time‐dependent flow. In both cases we see an increase of the convective heat transport for magnetic inductions higher than approximately 5 m T.Applying the rotating magnetic field to the Bridgman growth of gallium doped germanium, the same behavior can be seen: Growing with a top‐seeded arrangement, the intensity of the dopant striations is decreased and their frequency is increased. Growing with a bottom‐seeded arrangement, the interface curvature changes from concave to convex and the flow becomes time‐

ISSN:0232-1300    

DOI:10.1002/crat.2170320105

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractIm Konzentrationsbereich von 0 bis 25 at% Germanium wurde das Segregationsverhalten von Sili‐zium‐Germanium‐Einkristallen gezüchtet mit Hilfe des HF‐beheizten tiegelfreien Zonenschmelzver‐fahrens untersucht. Vollstündig versetzungsfreie Kristalle mit bis zu 8 at% Germanium wurden gezüchtet. Störungen des einkristalline Wachstum waren im wesentlichen auf konstitutionelle Unterkühlung zurückzuführen. Mittels pyrometrischer Temperaturmessung wurde der Anstieg der axialen Temperaturverteilung ΔT/ΔZin der Nähe der Wachstumsphasengrenze bestimmt und daraus die kritische Ziehgeschwindigkeit abgeleitet. Die Messungen zeigten, daß mit zunehmenden Germaniumgehalt der Temperaturgradient im

ISSN:0232-1300    

DOI:10.1002/crat.2170320106

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractA systematic study of the metal‐organic vapour‐phase epitaxial growth of (GaIn)P and (AlIn)P layers deposited on GaAs substrates with (001) and (110) orientation is presented. Special attention has been paid to the growth on (001)‐oriented wafers with different misorientations to the growth direction. The influence of the growth conditions on the properties of the epitaxial layers such as lattice mismatch, alloy composition, photoluminescence (PL) wavelength, FWHMs of PL peaks and atomic ordering is discussed. Layers with mirrorlike surfaces and various degrees of order could be deposited at growth temperaturesTgranging from 595 °C to 750 °C for (GaIn)P and 720 °C to 800 °C for (AlIn)P. In addition to the influence ofTgon the Ga incorporation during the (GaIn)P growth we found the Ga distribution coefficientkGato be affected by the misorientation of the substrates.kGacorrelates presumably with the number of kinks and steps on the substrate surface.Transmission electron diffraction (TED) and PL investigations show that the degree of order — often described by the ordering paramter η — depends strongly onTgthe ordering is more pronounced when the layers are deposited on substrates misoriented towards the (111) lattice plane. Strong ordering has been observed for (GaIn)P samples grown at 680 °C on substrates 2° misoriented towards the [110] direction and at 650 °C on substrates 6° misoriented towards the same direction. For the (AlIn)P samples striking ordering has been found when they we

ISSN:0232-1300    

DOI:10.1002/crat.2170320107

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractPlots of crystal size distribution of the following crystallizer models are compared: an ideal continuous‐flow MSMPR (mixed suspension, mixed product removal) crystallizer with a zero as well as non‐zero initial crystal size, an MSMPR crystallizer with size dependent growth of crystals, an MSMPR crystallizer with missing fines, an MSMPR crystallizer with agglomerative growth, and a series of MSMPR crystallizers simulating a crystallizer with nonideal agitation. The shape of the individual size distribution curves can serve as a diagnostic criterion in determination of the most probable model of crystallizat

ISSN:0232-1300    

DOI:10.1002/crat.2170320108

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractThree new structural phase transformations in the Cs amidosulfonate were detected and studied by means of DSC, X‐ray diffraction, infrared spectroscopy and by measuring the temperature dependence of the dielectric constant of monocrystalline platelets. In the temperature range from 325 to 345 K a second‐order phase transition occurs. After completion of the second order‐phase transformation, a first‐order phase transformation proceeds. At higher temperatures (435 K) a lambda‐transition occurs. The transition temperatures, enthalpies and entropies of the above reactions as well the melting temperature and the heat of melting of the CsSO3NH2were obtained. By means of the methods of H. KISSINGER and T. OZAWA the activation energies of the first order phase transformation were d

ISSN:0232-1300    

DOI:10.1002/crat.2170320109

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractFor selected compounds with perfluorinated chains the structure of smectic phases was investigated by X‐ray diffraction measurements. For rod‐like compounds with only one terminal perfluorinated chain the incompatibility of the hydrocarbon and the fluorocarbon moieties leads to a segregation of both parts which can be considered as microphase separation.For swallow‐tailed compounds the structure of smectic phases depends on the position and the length of the perfluorinated chains. If the steric interaction dominates an antiparallel packing of the molecules within the smectic layers is favoured. If the incompatibility of the hydrocarbon and fluorocarbon moieties is of importance the smectic layers are distorted and at lower temperatures the layer structure is transformed into a columnar stru

ISSN:0232-1300    

DOI:10.1002/crat.2170320110

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractThe displacement fields of different kinds of both perfect and dissociated dislocations have been calculated for an isotropic continuum, and by means of linear elasticity. Additionally, the corresponding HRTEM images have been simulated by the well‐established EMS program package in order to predetermine the structural aspects of dislocations, and then to compare it with experimental HRTEM micrographs. The latter ones resulted from plastically deformed GaP single crystals and InAs/(001)GaAs single epitaxial layers. It could be established that using the simple approach of linear elasticity and isotropy results can be obtained which correspond well to the experimental images. So, the structure of various Shockley partial dislocations bounding a stacking fault can be detected unambiguously. The splitting behaviour of perfect 30° dislocations (separation into a 0° and 60° partial) and 90° dislocations (separation into two 60° partials) both with line direction along 〈112〉, 60° dislocations (separation into 30°/90° and 90°/30° configuration) and screw dislocations (separation into two 30° partials) along 〈110〉 are discussed in the more detail. Moreover, the undissociated sessile Lomer dislocation, glissile 60° dislocation and edge dislocation hav

ISSN:0232-1300    

DOI:10.1002/crat.2170320111

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractBy using an imaging plate, point defects and lattice distortion prior to and after plastic deformation has been studied with back reflection Laue method. This includes structure refinement with the intensity data extracted from back reflections only. Preliminary results show promising prospect. The intrinsic difficulties of Laue method have been addressed. Improvement possibilities will also be discussed.

ISSN:0232-1300    

DOI:10.1002/crat.2170320112

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY