ALBERT

Notes: The phase formation and the morphological stability of ε1-Cu3Ge and ε1-Cu3(Si1−xGex) in Cu/epitaxial-Ge(e-Ge)/(111)Ge, Cu/(001)Ge, Cu/e-Ge/(111)Si, and Cu/(001)Si–Ge alloys have been investigated by transmission electron microscopy in conjunction with the energy dispersive spectrometry as well as by sheet resistance measurement. Epitaxial Cu and epitaxial ζ-Cu5Ge were found to form in as-deposited Cu/e-Ge/(111)Ge and Cu/e-Ge/(111)Si. On the other hand, textured Cu was found to form in the other systems. Polycrystalline ε1-Cu3Ge and ε1-Cu3(Si1−xGex) were the only phases formed in 150–500 °C annealed Cu/Ge and (Cu/e–Ge/Si and Cu/Si–Ge alloys) systems, respectively. They were found to agglomerate at 550 °C. The room-temperature oxidation of substrate in the presence of Cu3(Si1−xGex) was found only in the Cu/Si0.7Ge0.3 system. From the sheet resistance measurement, ε1-Cu3Ge has the lowest resistivity of 7 μΩ cm after 400 °C annealing. The electrical resistivity was found to decrease with the Ge content. © 2000 American Institute of Physics.

Notes: The growth kinetics of amorphous interlayers (a interlayers) formed by solid-state diffusion in ultrahigh vacuum deposited polycrystalline Ti thin films on germanium and epitaxial Si1−xGex (x=0.3, 0.4 and 0.7) alloys grown on (001) Si and (111) Ge has been investigated by transmission electron microscopy and Auger electron spectroscopy. The growth of a interlayers in all systems was found to follow a linear growth behavior initially. The activation energies for the linear growth of a interlayers were found to decrease with the Ge content and are 1.0±0.2, 0.95±0.2, 0.85±0.2, and 0.7±0.2 eV for Ti/Si0.7Ge0.3, Ti/Si0.6Ge0.4, Ti/Si0.3Ge0.7, and Ti/Ge systems, respectively. The maximum thickness of a interlayer was found to increase with the Ge content with x≤0.4. On the other hand, the formation temperature of crystalline phase was observed to decrease with the Ge content. Essential factors for the formation and growth of a interlayer are discussed. The results are compared with the Ti/Si system. © 2001 American Institute of Physics.

Notes: The effects of alloy composition on the formation temperature and electrical resistivities of C54 titanium germanosilicide formed during the Ti/Si1−xGex (x=0, 0.3, 0.4, 0.7, 1) solid state reaction have been investigated. Ti5(Si1−yGey)3, C49– and C54–Ti(Si1−zGez)2 were observed to form in the Ti/Si1−xGex (x≥0.4) systems. On the other hand, Ti6(Si1−yGey)5 and C54–Ti(Si1−zGez)2 were found in the Ti/Si1−xGex (x[greater, double equals]0.7) systems. For both cases, the relationship of x〉y〉z was found. The appearance and agglomeration temperature of low-resistivity C54–Ti(Si1−zGez)2 were both found to decrease with the Ge concentration. The resistivities of C54–Ti(Si1−zGez)2 were measured to be 15–20 μΩ/cm. The segregation of Si1−wGew (w〉x) was found in all samples annealed above 800 °C. The effects of thermodynamic driving force, kinetic factor, and composition of the micro-area are discussed. © 1999 American Institute of Physics.

Notes: The effects of growth temperature, substrate offcut, and dislocation pileup formation on threading dislocation density (TDD) in compositionally graded SiGe buffers are explored. To investigate dislocation glide kinetics in these structures, a series of identical samples graded to 30% Ge were grown at temperatures between 650 and 900 °C on (001)-, (001) offcut 6° towards an in-plane 〈110〉-, and (001) offcut 6° towards an in-plane 〈100〉-oriented Si substrates. The field threading dislocation density (field TDD) in the on-axis samples varied exponentially with temperature, from 3.7×106 cm−2 at 650 °C to 9.3×104 cm−2 at 900 °C. The activation energy for dislocation glide in this series, calculated from the evolution of field TDD with growth temperature, was 1.38 eV, much lower than the expected value for this composition. This deviation indicates that strain accumulating during the grading process at low growth temperatures is forcing further dislocation nucleation, resulting in a deviation from pure glide-limited relaxation. The TDD of samples grown on offcut substrates exhibited a more complicated temperature dependence, likely because films grown on offcut substrates have an increased tendency towards saturation in dislocation reduction reactions at high temperature. Dislocation reduction processes were further explored by initiating compositional grading up to 15% Ge at 650 °C and continuing the grade to 30% Ge at 900 °C. The low temperature portion of this growth provided an excess concentration of threading dislocations which could subsequently be annihilated during the high temperature portion of the growth, enabling a comparison of reduction rates for different substrate offcuts. Combining these results with threading dislocation densities in a variety of other samples, a complete picture of strain relaxation kinetics in compositionally graded SiGe/Si emerges. Generally, strain relaxation in these structures is limited by dislocation glide, and threading dislocation densities are independent of final Ge content. However, we theorize that dislocation pileup formation inhibits the strain relaxation process and is therefore accompanied by a rise in field threading dislocation density. Based on these results, we now have a predictive model for TDD in compositionally graded SiGe/Si over a wide range of growth conditions. © 2001 American Institute of Physics.

Notes: Thermocouple cantilever probes are used in the atomic force microscope (AFM) to simultaneously obtain thermal and topographical images of surfaces with submicrometer scale spatial resolution. Three designs of thermocouple AFM probes and the thermal images obtained by each of them are presented here. Experiments show that the dominant mechanism for sample-probe heat transfer is gas conduction. If probes are not properly designed, this could lead to image distortion and loss of temperature and spatial resolution. The steady state probe behavior is dominated by the gas thermal conductivity whereas the transient effects are dominated by the thermal mass of the probe. Thermal images of single transistors show their thermal characteristics under different biasing conditions. In addition, hot spots created by short-circuit defects within a transistor can be located by this technique. Efforts are underway to improve the spatial resolution from 0.4 to 0.05 μm by careful probe design. The results suggest that this can be achieved when the size of the thermal sensor at the tip of an AFM cantilever probe is of the order of the tip radius. © 1995 American Institute of Physics.

Notes: Investigation on magnetocaloric effects, magnetic entropy, Curie temperature, and specific heat of nanocomposite binary gadolinium alloys Gd–Tb, Gd–Zn, and Gd–Y has been carried out with an applied magnetic field of 1 T and in a temperature range of 233–313 K. Compared with the respective bulk alloys, the as-prepared nanocomposite alloys were found to have higher specific heat and lower Curie temperature. The nanocomposite Gd–Y alloy exhibited distinctive enhancement of both magnetocaloric effect and magnetic entropy over that of the bulk alloy. The finding is of importance for developing new materials for magnetic refrigeration at room temperature. A discussion concerning the enhanced magnetic entropy in nanometer superparamagnetic systems is presented in detail. © 1996 American Institute of Physics.

Notes: New derivation of the kinetics of isothermal phase transformation by using probability calculation has been introduced and demonstrated for the simple one-dimensional case, which yields conclusions for transformation with preferred nucleation at line defects. In contrast to the classical treatments, the present derivation starts from a finite discrete system and follows direct logic. With this method it is possible to determine the distribution function of nuclei and to investigate problems such as the many-nuclei correlation, superposition of more than one process, and various boundary conditions. Further analysis yields formulation for the rate of impingement and other details about the transformation. Combined with the analytical treatment, the specialized algorithm for Monte Carlo simulation of nucleation and growth has been developed. From the results of simulation the limitation of the continuous approach has been detected. © 1995 American Institute of Physics.

Notes: The formation of amorphous interlayers (a-interlayers) by solid-state diffusion in ultrahigh-vacuum-deposited polycrystalline Ti thin film on germanium and epitaxial Si1−xGex (x=0.3, 0.4, and 0.7) alloys grown on (001)Si has been investigated by transmission electron microscopy and Auger electron spectroscopy. Amorphous interlayers, less than 2 nm in thickness, were observed to form in all as-deposited samples. The growth of the a-interlayers was found to vary nonmonotonically with the composition of Si–Ge alloys in annealed samples. On the other hand, the formation temperature of crystalline phase was found to decrease with the Ge content. The results are compared with those of the Ti/Si system. © 1995 American Institute of Physics.

Notes: Theoretical results on the kinetics of transformations with nucleation and growth mechanisms in homogeneous systems during isothermal annealing are reported. The present derivations start from a probability calculation in a finite discrete assembly. In the simplest case with a constant growth rate the results of the formulation agree with the classical Avrami equation for two- and three-dimensional systems. Furthermore, by calculating the survival probability step by step for separate occurrences, the relationships between interfering processes and the effects of neighboring nuclei are revealed. In particular, the distribution of nuclei pairs with distance is determined. Various cases of preferred nucleation in specialized regions, such as linear zones (e.g., dislocations), planar areas (e.g., grain boundaries), or three-dimensional partial volumes, are analytically solved and these solutions can be directly used for the interpretation and evaluation of experimental measurements. © 1996 American Institute of Physics.