Martin Gradhand

Preparation of nonconducting infrared-absorbing thin films

A simple procedure for preparing colloidal “black” bismuth films is introduced, which leaves the target cold and does not pollute the recipient. The Bi evaporation occurs in a closed box in the evaporation chamber with an internal radiation shield. The bismuth is evaporated from a tantalum boat at a residual air pressure of 2×102Pa. The resulting films with a thickness of about 10μm are structureless down to a spatial resolution of 5.6μm, they become electrically insulating after 48h storage time in air, and they show an IR absorbance of above 70% in the 3–5μm wavelength range. The films are easily removable in an ultrasonic water bath. Thus, these films are ideally appropriate to increase the IR emissivity of microelectronic structures in microthermal infrared failure analysis investigations such as lock-in thermography, as is demonstrated in an application example. The application of this film may improve the thermographic detection limit of heat sources below metallized areas by up to a factor of 10, l...

Skew Scattering Mechanism by an Ab Initio Approach: Extrinsic Spin Hall Effect in Noble Metals

We present a first-principles study of the extrinsic spin Hall effect due to skew scattering at substitutional defects in noble metals (Cu, Ag, and Au). The dependence of the spin Hall angle on the type of impurity atoms in the host materials is discussed. We perform a detailed analysis based on the consideration of the total angular momentum dependence on scattering phase shifts of the impurity and host atoms.

Thermoelectric transport in

The thermoelectric transport properties of

\text{Bi}_2\text{Te}_3/\text{Sb}_2\text{Te}_3

text{Bi}_2text{Te}_3/text{Sb}_2text{Te}_3

superlattices

superlattices are analyzed on the basis of first-principles calculations and semi-classical Boltzmann theory. The anisotropy of the thermoelectric transport under electron and hole-doping was studied in detail for different superlattice periods at changing temperature and charge carrier concentrations. A clear preference for thermoelectric transport under hole-doping, as well as for the in-plane transport direction was found for all superlattice periods. At hole-doping the electrical transport anisotropies remain bulk-like for all investigated systems, while under electron-doping quantum confinement leads to strong suppression of the cross-plane thermoelectric transport at several superlattice periods. In addition, insights on the Lorenz function, the electronic contribution to the thermal conductivity and the resulting figure of merit are given.

Thermoelectric transport in Bi₂Te₃/Sb₂Te₃ superlattices

The thermoelectric transport properties of

Extrinsic spin Hall effect from first principles.

text{Bi}_2text{Te}_3/text{Sb}_2text{Te}_3

Spin Hall angle versus spin diffusion length: Tailored by impurities

superlattices are analyzed on the basis of first-principles calculations and semi-classical Boltzmann theory. The anisotropy of the thermoelectric transport under electron and hole-doping was studied in detail for different superlattice periods at changing temperature and charge carrier concentrations. A clear preference for thermoelectric transport under hole-doping, as well as for the in-plane transport direction was found for all superlattice periods. At hole-doping the electrical transport anisotropies remain bulk-like for all investigated systems, while under electron-doping quantum confinement leads to strong suppression of the cross-plane thermoelectric transport at several superlattice periods. In addition, insights on the Lorenz function, the electronic contribution to the thermal conductivity and the resulting figure of merit are given.