Scanning thermal microscopy (SThM) uses micromachined thermal sensors integrated in a force sensing cantilever with a nanoscale tip that can be highly useful for exploration of thermal management of nanoscale semiconductor devices as well as mapping of surface and subsurface properties of related materials. Whereas SThM is capable to image externally generated heat with nanoscale resolution, its ability to map and measure thermal conductivity of materials has been mainly limited to polymers or similar materials possessing low thermal conductivity in the range from 0.1 to 1 W m−1 K−1, with lateral resolution on the order of 1 μm. In this paper, we use linked experimental and theoretical approaches to analyse thermal performance and sensitivity of the micromachined SThM probes in order to expand their applicability to a broader range of nanostructures from polymers to semiconductors and metals. We develop physical models of interlinked thermal and electrical phenomena in these probes and their interaction with the sample on the mesoscopic length scale of few tens of nm and then validate these models using experimental measurements of the real probes, which provided the basis for analysing SThM performance in exploration of nanostructures. Our study then highlights critical features of these probes, namely, the geometrical location of the thermal sensor with respect to the probe apex, thermal conductance of the probe to the support base, heat conduction to the surrounding gas, and the thermal conductivity of tip material adjacent to the apex. It furthermore allows us to propose a novel design of the SThM probe that incorporates a multiwall carbon nanotube or similar high thermal conductivity graphene sheet material with longitudinal dimensions on micrometre length scale positioned near the probe apex that can provide contact areas with the sample on the order of few tens of nm. The new sensor is predicted to provide greatly improved spatial resolution to thermal properties of nanostructures as well as to expand the sensitivity of the SThM probe to materials with heat conductivity values up to 100–1000 W m−1 K−1.

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Nanoscale spatial resolution probes for scanning thermal microscopy of solid state materials

Magnetic heterostructures that combine large spin-orbit torque efficiency, perpendicular magnetic anisotropy, and low resistivity are key to develop electrically-controlled memory and logic devices. Here we report on vector measurements of the current-induced spin orbit torques and magnetization switching in perpendicularly magnetized Pd/Co/AlO$_x$ layers as a function of Pd thickness. We find sizeable damping-like (DL) and field-like (FL) torques, of the order of 1~mT per $10^7$~A/cm$^2$, which have different thickness and magnetization angle dependence. The analysis of the DL torque efficiency per unit current density and electric field using drift-diffusion theory leads to an effective spin Hall angle and spin diffusion length of Pd larger than 0.03 and 7~nm, respectively. The FL SOT includes a significant interface contribution, is larger than estimated using drift-diffusion parameters, and is further strongly enhanced upon rotation of the magnetization from the out-of-plane to the in-plane direction. Finally, taking advantage of the large spin-orbit torques in this system, we demonstrate bipolar magnetization switching of Pd/Co/AlO$_x$ layers with similar current density as used for Pt/Co layers with comparable perpendicular magnetic anisotropy.

Interface enhanced spin-orbit torques and current-induced magnetization switching of Pd/Co/AlO$_x$ layers

Optical and electrical properties of hydrided palladium thin films studied by an inversion approach from transmittance measurements

The pulsed plasma polymerization of tetramethyltin monomer was studied as a function of the radio frequency (rf) duty cycle employed, all other plasma variables being held constant. Progressive increases in the relative tin content of the plasma deposited films were observed with systematic decreases in the rf duty cycles employed during film formation. The variations in tin content of these films were documented by XPS, FT-IR, TEM, AFM, and electrochemical analyses. A particularly interesting aspect of this work is the microstructure of the films which reveals spherical tin particles of essentially uniform diameters (20−30 nm) independent of the duty cycle during deposition. The increasing metal content in these films with decreasing duty cycle corresponds to increased aggregation of these nanosized particles into progressively larger sized clusters. The results obtained are supportive of the use of the variable duty cycle pulsed plasma deposition technique as a new route to improved nanoscale film chemi...

M.A. Angadi

Papers

Electrical properties of thin nickel films

Electrical resistivity of thin palladium films

Electrical resistivity and temperature coefficient of resistance of vacuum evaporated thin chromium films

The effect of the deposition rate on the electrical resistivity of thin tin films

Temperature coefficient of resistance of thin manganese films