Atom Probe Tomography (APT) was applied to analyze the silicidation reaction between a titanium metal film, capped by a TiN layer, and a boron-implanted silicon substrate. The concentration depth profile observed by APT, depicts low concentrations of B in titanium silicide itself and the B accumulation at the interface between the TiSi2 and the TiN capping layer. Moreover the three dimensional atomic reconstruction from APT revealed a laterally inhomogeneous B distribution along the interface as well as B precipitation. APT enables the stoichiometric identification of TiB2 precipitates smaller than 7nm in diameter.

An epitaxial CoSi2 process is presented, which allows the self-aligned formation of bitlines with only a few tens of nanometer width for Twin Flash memory cells in the 63nm generation. The bitlines show a good thermal stability and low resistance for widths down to 35nm, where polycrystalline CoSi2 is known to exhibit a strong narrow linewidth effect. Transmission electron microscopy studies revealed a cube-on-cube epitaxy with only a few twins depending on the annealing conditions. The low bitline resistance results in a linear drain voltage dependence of the programing characteristics and a suppression of secondary electron injection during programing.

We have presented systematic cross-plane thermal conductivity (λ) data for the undoped strain-symmetrized Si/Ge superlattices grown on Si(111) with superlattice (SL) period thickness varying from 3.6 to 16 nm. In thin SL period (L⩽7 nm) samples, the data have shown considerable reductions of λ, by more than 50% and 30% compared to the SiGe alloy and to the earlier reported values in (100)-oriented Si/Ge superlattice structures (SLS), respectively. For the thick SL period samples (L>10 nm), λ has shown a tendency to saturate at the SiGe alloy value. This is understood as, with increasing L, the SLS breaks and the SiGe alloying starts to grow. This structural behavior is clearly observed in the cross-plane transmission electron microscope images as well. In addition to these, for the thin SL period (L⩽7 nm) samples, the data have shown a shallow minimum which is attributed to the competing behavior of the wave nature and the classical particle nature of the localized phonons. Nevertheless, the present study of thermal conductivity on undoped strain-symmetrized Si/Ge SLs in (111) orientation suggests that an enhancement of thermoelectric figure-of-merit Z is possible.

The structure of nanocrystalline rhenium-silicon composite ReSix films with 1.4 <x <2.2 has been studied as a function of the time by means of high temperature x-ray diffraction and transmission electron microscopy. Simultaneously, the thermoelectric transport properties were measured during the heat treatment. The nanocrystallization was achieved by annealing of amorphous films deposited onto oxidized Si wafers by magnetron cosputtering. The crystallization process is characterized by a decreasing average crystallite size in the range between 7 and 19 nm. An unknown mechanism limits the grain growth after reaching a maximum size, which decreases with increasing Si content. In the final state the films contain only two phases: the amorphous phase and the nanocrystalline ReSi1.75 phase. The electrical conductivity and the thermoelectric power of these thin film composites show nonmonotonic dependence on the volume fraction of the nanocrystalline phase and depend on different parameters, which suggests a way to optimize the thermoelectric efficiency. (C) 2001 American Institute of Physics.

The use of Multi Quantum Well structures has been shown to provide a promising strategy for improving the thermoelectric figure of merit. In a recent paper the concept of carrier pocket engineering has been applied to strain symmetrized Si/Ge-superlattices leading to a ZT of 0.96 at room temperature for (111) orientation. Since the strain of the individual layers is crucial for the desired modification of their band structures, their experimental determination will be of importance. We have prepared a series of (111) oriented, 100 period (Si 2nm / Ge 2nm) superlattices on a graded Si0.5Ge0.5-buffer by sputter deposition. Deposition temperature and buffer thickness have been varied, the superlattices were characterized by AFM and XRD. The technique of XRD reciprocal space mappings of asymmetric reflections has been applied to describe the strain state of the superlattice. We found a buffer thickness of 1.1μm sufficient for more than 90% strain relaxation. XRD-data of 4nm-period superlattices are consistent with complete strain symmetrization.

Torque magnetometry was used to investigate the magnetic anisotropy of epitaxial Fe3O4 films of thicknesses 420 and 40 nm grown by pulsed laser deposition on (0 0 1) MgO substrates. Torque measurements at 130 K in the (1 1̄ 0) plane allow us to evaluate the influence of shape and stress anisotropy. As in bulk material field-cooled measurements performed at T=5 K show that the magnetic anisotropy is strongly influenced by the direction of the magnetic field applied above the Verwey temperature. In contrast to bulk magnetite we find smaller effective contributions of the magneto-crystalline anisotropy. In zero-field-cooled films our measurements suggest a tendency to a preferential out-of-plane orientation of the magnetic easy axis, but the dominating shape anisotropy favours an in-plane orientation of the magnetization.

Thermoelectric power and electrical conductivity have been investigated of thin films and single crystals of ReSi/sub 1.75/, a small gap semiconductor with E/sub g/=0.15 eV. The single crystals have been prepared by a modified Czochralski method, the films by facing target sputtering and reactive deposition epitaxy. The substrates used include SOS (silicon on sapphire) and Si(111) wafers. With both methods epitaxial stoichiometric ReSi/sub 1.75/ films were obtained. The films undergo a formation process during annealing up to 1000 K. They exhibit a negative thermoelectric power of about -100 /spl mu/V/K within a broad temperature range characteristic for degenerate semiconductors. The single crystals with a composition ReSi/sub 1.8/ show p-type conductivity as polycrystalline films with excess of Si. The quality of the single crystals has still to be improved to get a reference system for thin films.