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We propose an approach for the characterization of scanning thermal microscopy (SThM) probe response using a sample with silicon dioxide steps. The chessboard-like sample provides a series of nine surfaces made of the same material, with identical roughness, but consisting of different thicknesses of silica layers standing on a single silicon wafer. The nine regions have different effective thermal conductivities, allowing the calibration of SThM probes within a given set of surface conditions. A key benefit is the possibility of comparing the spatial resolution and the sensitivity to vertical inhomogeneities of the sample for different probes. A model is provided to determine the thermal contact area and contact thermal resistance from the experimental data. The results underline that ballistic heat conduction can be significant in crystalline substrates below the top thin films, especially for film thicknesses lower than 200 nm and effective thermal contact radius lower than 200 nm. They also highlight the sensitivity of SThM to ultrathin films, as well as the substrate below micrometric films under in-air conditions but not when in vacuum. This work advances quantitative nanometer-scale thermal metrology, where usual photothermal methods are more difficult to implement. [ABSTRACT FROM AUTHOR]

The thermoelectric and physical properties of superlattices consisting of modulation doped Ge quantum wells inside Si1-yGey barriers are presented, which demonstrate enhancements in the thermoelectric figure of merit, ZT, and power factor at room temperature over bulk Ge, Si1-yGey, and Si/Ge superlattice materials. Mobility spectrum analysis along with low temperature measurements indicate that the high power factors are dominated by the high electrical conductivity from the modulation doping. Comparison of the results with modelling using the Boltzmann transport equation with scattering parameters obtained from Monte Carlo techniques indicates that a high threading dislocation density is also limiting the performance. The analysis suggests routes to higher thermoelectric performance at room temperature from Si-based materials that can be fabricated using micro- and nano-fabrication techniques. [ABSTRACT FROM AUTHOR]

Nominally identical permalloy nanowires, with widths down to 150 nm, were fabricated onto a single-electron transparent Si3 N4 membrane using electron beam lithography (EBL) and focused ion beam (FIB) milling. Transmission electron microscopy (TEM) experiments were performed to compare the nanostructures produced by these two techniques in what we believe is the first direct comparison of fabrication techniques for nominally identical nanowires. Both EBL and FIB methods produced high quality structures with edge roughness being of the order of the mean grain size 5-10 nm observed in the continuous films. However, significant grain growth was observed along the edges of the FIB patterned nanowires. Lorentz TEM in situ imaging was carried out to compare the magnetic behavior of the domain walls in the patterned nanowires with anti-notches present to pin domain walls. The overall process of domain wall pinning and depinning at the anti-notches showed consistent behavior between nanowires fabricated by the two methods with the FIB structures having slightly lower characteristic fields compared to the EBL wires. However, a significant difference was observed in the formation of a vortex structure inside the anti-notches of the EBL nanowires after depinning of the domain walls. No vortex structure was seen inside the anti-notches of the FIB patterned nanowires. Results from micromagnetic simulations suggest that the vortex structure inside the anti-notch can be suppressed if the saturation magnetization (Ms) is reduced along the nanowire edges. A reduction of Ms along the wire edges may also be responsible for a decrease in the domain wall depinning fields. Whereas the two fabrication methods show that well-defined structures can be produced for the dimensions considered here, the differences in the magnetic behavior for nominally identical structures may be an issue if such structures are to be used as conduits for domain walls in potential memory and logic applications. [ABSTRACT FROM AUTHOR]

Lorentz microscopy has been used to study the micromagnetic processes occurring during the reversal of multiscale single and multilayer CoFe elements. The elements, which have similar dimensions to write heads used in magnetic recording, typically have length scales varying from 10 μm in the element “core” down to 100 nm in the element “tip.” Marked differences both in the core and the tip regions are observed between single and multilayer elements. The results demonstrate clearly how the role played by shape anisotropy in complex elements can be effectively reduced by multilayering, allowing any anisotropy induced in the film during deposition to play a greater role in defining the resulting behavior. [ABSTRACT FROM AUTHOR]

Lorentz microscopy has been used to explore the structure variation of domain walls in thin Permalloy nanowires in the vicinity of symmetric triangular antinotches. The antinotches present a complex potential landscape to domain walls. Walls can be trapped in front of, partly enter, or be trapped inside the antinotches according to the geometry of the latter and, in the case of vortex domain walls, the chirality. In all cases, the magnetization distribution was determined. Of particular note was the structure the wall assumed during depinning from the antinotch, complex forms extending over distances several times the wire width being observed. [ABSTRACT FROM AUTHOR]