Spatially Resolved Determination of Thermal Conductivity by Raman Spectroscopy

We review the Raman shift method as a non-destructive optical tool to investigate the thermal conductivity and demonstrate the possibility to map this quantity with a micrometer resolution by studying thin film and bulk materials for thermoelectric applications. In this method, a focused laser beam both thermally excites a sample and undergoes Raman scattering at the excitation spot. The temperature dependence of the phonon energies measured is used as a local thermometer. We discuss that the temperature measured is an effective one and describe how the thermal conductivity is deduced from single temperature measurements to full temperature maps, with the help of analytical or numerical treatments of heat diffusion. We validate the method and its analysis on 3- and 2-dimensional single crystalline samples before applying it to more complex Si-based materials. A suspended thin mesoporous film of phosphorus-doped laser-sintered Si78Ge22 nanoparticles is investigated to extract the in-plane thermal conductivity from the effective temperatures, measured as a function of the distance to the heat sink. Using an iterative multigrid Gauss-Seidel algorithm the experimental data can be modelled yielding a thermal conductivity of 0.1 W/m K after normalizing by the porosity. As a second application we map the surface of a phosphorus-doped 3-dimensional bulk-nanocrystalline Si sample which exhibits anisotropic and oxygen-rich precipitates. Thermal conductivities as low as 11 W/m K are found in the regions of the precipitates, significantly lower than the 17 W/m K in the surrounding matrix. The present work serves as a basis to more routinely use the Raman shift method as a versatile tool for thermal conductivity investigations, both for samples with high and low thermal conductivity and in a variety of geometries.Comment: accepted in Semicond. Sci. Technol., 8 figure

Combining conductive atomic force microscopy with electrically detected magnetic resonance

We present the design and implementation of a scanning probe microscope, which combines electrically detected magnetic resonance (EDMR) and (photo-)conductive atomic force microscopy ((p)cAFM). The integration of a 3-loop 2-gap X-band microwave resonator into an AFM allows the use of conductive AFM tips as a movable contact for EDMR experiments. The optical readout of the AFM cantilever is based on an infrared laser to avoid disturbances of current measurements by absorption of straylight of the detection laser. Using amorphous silicon thin film samples with varying defect densities, the capability to detect a spatial EDMR contrast is demonstrated. Resonant current changes as low as 20 fA can be detected, allowing the method to realize a spin sensitivity of 8×106spins/√Hz at room temperature

Laser-sintered thin films of doped SiGe nanoparticles

We present a study of the morphology and the thermoelectric properties of short-pulse laser-sintered (LS) nanoparticle (NP) thin films, consisting of SiGe alloy NPs or composites of Si and Ge NPs. Laser-sintering of spin-coated NP films in vacuum results in a macroporous percolating network with a typical thickness of 300 nm. The Seebeck coefficient is independent of the sintering process and typical for degenerate doping. The electrical conductivity of LS films rises with increasing temperature, best described by a power-law and influenced by two-dimensional percolation effects.Comment: 4 pages, 4 figure

Herstellung und thermoelektrische Eigenschaften gesinterter Gruppe-IV Nanopartikel

Laser-sintered Si, Ge and SiGe nanoparticle thin films are investigated concerning their applicability to thermoelectrics. A mesoporous meander-like structure is the characteristic feature of the resulting films. To adjust the doping in the films a new wet-chemical method is developed. The complex structure of the films requires advanced methods for the determination of the thermal conductivity, for which spatially resolved Raman spectroscopy is used. The thermoelectric figures of merit obtained for the laser-sintered films are at least comparable to other SiGe materials.Lasergesinterte Si-, Ge- oder SiGe-Nanopartikel-Dünnfilme mit einer charakteristischen mesoporösen Mäander-artigen Struktur werden auf ihre Eignung als thermoelektrische Materialien untersucht und bewertet. Zur Einstellung der Dotierung der Filme wird eine neuartige nasschemische Methode entwickelt. Die komplexe Struktur der Filme stellt besondere Anforderungen an die Messung der thermischen Leitfähigkeit, die mittels einer auf Raman-Spektroskopie basierenden Methode vorgenommen wird

Yeast growth and survival assays as a pre-screening method for quantitative in vitro protein characterization

For in-vitro protein characterization of HpUreI, the channel protein is purified with a hexameric His-tag. However, the tag position might interfere with protein properties like gating or permeability. Thus, the functionality of UreI constructs with a His-tag at the C-terminus (UTH) and N-terminus (HTU, UreIpcl) uncleaved or cleaved and in the PL1 loop is tested with in-vivo yeast complementation assays. The in-vivo assays are designed and established for three different solutes, urea, ammonia/ammonium and water. The functional assays are performed on solid media as spotting assay and in liquid media as liquid assay. With these assays the permeability and pH gating are determined for these solutes and are compared to an untagged WT HpUreI. For the functionality of the tagged UreI constructs first findings can be presented for urea permeability. UreIpcl and PL1 showed the same permeability and pH gating pattern for urea. For the other two solutes, ammonia/ammonium and water, the assays must be optimized further. Comparing spotting and liquid assay, the liquid assay solves most of the drawbacks which spotting assays showed like unequal nutrient supply and depletion. In conclusion, the functional assays for the three different solutes urea, ammonia/ammonium and water are designed, established and after further optimization may represent a first step towards developing an enrichment method for membrane channels for multiplexed assays for variant effects (MAVE).Author Anna Stoiber, B.Sc.Masterarbeit Universit\ue4t Linz 202

The electrically detected magnetic resonance microscope: Combining conductive atomic force microscopy with electrically detected magnetic resonance

We present the design and implementation of a scanning probe microscope, which combines electrically detected magnetic resonance (EDMR) and (photo-)conductive atomic force microscopy ((p)cAFM). The integration of a 3-loop 2-gap X-band microwave resonator into an AFM allows the use of conductive AFM tips as a movable contact for EDMR experiments. The optical readout of the AFM cantilever is based on an infrared laser to avoid disturbances of current measurements by absorption of straylight of the detection laser. Using amorphous silicon thin film samples with varying defect densities, the capability to detect a spatial EDMR contrast is demonstrated. Resonant current changes as low as 20 fA can be detected, allowing the method to realize a spin sensitivity of 8×106spins/Hz−−−√ at room temperature