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A two-temperature semiconductor model was used to investigate the non-equilibrium thermal transport in Ge2Sb2Te5 thin films caused by an ultrashort laser pulse ranging from atto- to nanoseconds. In the model, photo-excited carriers were considered based on the semiconductor absorbing mechanism. As a general rule, shorter laser pulses led to shorter equilibration time between carrier and lattice systems. However, a minimum time to reach the thermal equilibrium (about 80 ps) was obtained for both the attosecond and femtosecond laser pulses, which was mainly determined by material properties instead of the pulse width. The carrier density had a strong influence on the temperatures of both the carrier and lattice systems, and photo-excited carriers played an important role in the first 40 ps under the attosecond and femtosecond laser irradiations. Besides, the ambipolar diffusion effect significantly reduced the density of free carriers and then extended the crystallization and amorphization times of Ge2Sb2Te5. [ABSTRACT FROM AUTHOR]

The correlation of microstructural development and the kinetics of film growth has been investigated during the epitaxial film growth of an ultrathin binary Ag0.93Al0.07 solid solution on a Si(111)-7?7 surface at 300K by the combination of high-resolution transmission electron microscopy, X-ray diffraction, scanning tunneling microscopy, low energy electron diffraction, and realtime in-situ stress measurements. Up to a film thickness of 6±2 nm, epitaxial Ag0.93Al0.07 film growth is characterized by the strikingly extensive formation of planar faults parallel to the film/ substrate interface, while at larger thickness the film grows practically defect-free. As revealed by real-time in-situ stress measurements, the extensive formation of planar faults at the very initial stage of growth is not driven by the reduction of the system's elastic strain energy but is rather caused by a striking thickness-dependence of the stacking-fault energy owing to a quantum size effect of the ultrathin metal alloy film, resulting in a frequent succession of fcc and hcp stackings of close-packed layers during the initial stage of film growth. The extensive development of planar faults at the initial stage of film growth (<6±2 nm) is associated with the occurrence of a high density of kinks and corners at thereby atomically rough surface ledges, which strongly enhances the downward transport of adatoms from higher to lower terraces (interlayer mass transport) by a reduction of the effective diffusion barrier at the edge of surface steps and by increasing the driving force for adatoms to attach to the surface ledges. As a result, the epitaxial Ag0.93Al0.07 film initially grows in a 2D layer-by-layer type of growth and thus establishes atomically smooth film surfaces. For the practically planar-fault-free growth at thicknesses beyond 6±2 nm, interlayer mass transport becomes distinctively limited, thereby inducing a transition from 2D to 3D type of film growth. [ABSTRACT FROM AUTHOR]

The interplay between structural properties and charge transfer in self-assembled quantum ring (QR) chains grown by molecular beam epitaxy on top of an InGaAs/GaAs quantum dot (QD) superlattice template is analyzed and characterized. The QDs and QRs are vertically stacked and laterally coupled as well as aligned within each layer due to the strain field distributions that governs the ordering. The strong interdot coupling influences the carrier transfer both along as well as between chains in the ring layer and dot template structures. A qualitative contrast between different dynamic models has been developed. By combining temperature and excitation intensity effects, the tuning of the photoluminescence gain for either the QR or the QD mode is attained. The information obtained here about relaxation parameters, energy scheme, interlayer and interdot coupling resulting in creation of 1D structures is very important for the usage of such specific QR-QD systems for applied purposes such as lasing, detection, and energy-harvesting technology of future solar panels. [ABSTRACT FROM AUTHOR]

During the deposition of polycrystalline thin films, often intrinsic compressive stresses develop, which reversibly change in tensile direction once the deposition process is interrupted. Up to date, the underlying mechanism of such reversible stress changes during growth interruptions have been controversially discussed, mainly because the correlations between the growth conditions, the developing film microstructure and the reversible stress change were still largely unclear. The present study has experimentally established the separate effects of the pre-interruption deposition rate and the average lateral film grain size on both the magnitude and the kinetics of the reversible tensile stress rise during polycrystalline film growth interruption. To this end, real-time in situ substrate-curvature measurements were performed during polycrystalline Ag growth and upon subsequent growth interruptions for well-defined and controlled adjusted microstructures. It is shown that the magnitude of the reversible tensile stress rise during growth interruption is predominantly governed by the grain-boundary density, while the rate of the tensile stress rise during growth interruption increases with increasing pre-interruption deposition rate and increasing (lateral) Ag grain size. These phenomena can be rationalized by taking deposition-rate and lateral-grain-size dependent surface morphological developments into account. [ABSTRACT FROM AUTHOR]

The aluminum-induced layer exchange (ALILE) process occurring upon annealing amorphous Si/polycrystalline Al bilayers (a-Si/c-Al) has been observed at a temperature as low as 165 °C. The diffusion length of Si along Al grain boundaries is proposed as a tool for determining the annealing conditions, i.e., temperature and time, for the occurrence of the c-Al→c-Si layer exchange. Analysis of the local and global energy changes upon layer exchange reveals that a tiny driving force controls the kinetics of layer exchange and leads to a general interpretation of the mechanism of the ALILE process. [ABSTRACT FROM AUTHOR]

Focuses on a study which determined the temperature of photoexcited carriers in semi-insulating gallium arsenic wafers. Background on photoluminescence topography; Experimental procedure; Calculation of carrier lifetime; Discussion.

Using (331)B GaAs templates with nanoscale fluctuations, we have fabricated InGaAs/GaAs quantum wires (QWRs) with a density of ∼2.0×10[sup 6] cm[sup -1] and the degree of polarization as high as ∼28%. In the samples with weak lateral confinement, we observed thermal delocalization of carriers from the one-dimensional QWR states to the two-dimensional quantum-well states with increasing temperature, which is almost absent in QWR samples with strong lateral confinement. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In perovskite manganites La[sub 0.7-x]Nd[sub x]Ca[sub 0.3]MnO[sub 3] (x=0, 0.05, 0.1, 0.15, and 0.20) prepared by the sol–gel technique, large magnetocaloric effects have been observed. The maximum of the magnetic entropy change peaks at the magnetic ordering temperature. Compared to La[sub 0.7]Ca[sub 0.3]MnO[sub 3], an enhancement of the magnetocaloric effect has been obtained in the samples with Nd[sup 3+] dopant (for La[sub 0.5]Nd[sub 0.2]Ca[sub 0.3]MnO[sub 3], the maximum of ΔS[sub M] is about -2.31 J/kg K). © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A La-deficient manganite perovskite sample La[sub 0.54]Ca[sub 0.32]MnO[sub 3-δ] was prepared by conventional solid-state reaction method. The Curie temperature T[sub C] is 272 K, about 10 K higher than that of La[sub 1-x]Ca[sub x]MnO[sub 3]. A large magnetic entropy change has been observed and the maximum -ΔS[sub M]approx. 2.9 J/kg K appears at its Curie temperature upon a 0.9 T magnetic field change. The easy fabrication and higher chemical stability make La[sub 0.54]Ca[sub 0.32]MnO[sub 3-δ] a suitable candidate as a working substance in magnetic refrigeration technology. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Provides information on a study which examined rare-earth element erbium, which was deposited onto (100) oriented Zn-doped p-type InP to form Schottky barriers. Material attractive for high-speed optoelectronic and high power microwave devices; Prerequisite essential for the development of advanced devices; Measurements in the I-V-T method; Technique used for measuring the reverse bias capacitance-voltage characteristics.