The thermoelectric properties of a nanoscale germanium segment connected by aluminium nanowires are studied using scanning thermal microscopy.

On-chip temperature sensing on a micro-to nanometer scale is becoming more desirable as the complexity of nanodevices keeps increasing and their downscaling continues. The continuation of this trend makes thermal probing and management more and more challenging. This highlights the need for scalable and reliable temperature sensors, which have the potential to be incorporated into current and future device structures. Here, it is shown that U-shaped graphene stripes consisting of one wide and one narrow leg form a single material thermocouple that can function as a self-powering temperature sensor. It is found that the graphene thermocouples increase in sensitivity with a decrease in leg width, due to a change in the Seebeck coefficient, which is in agreement with previous findings and report a maximum sensitivity of ΔS ≈ 39 μV K −1 .

We report heat transport measurements on suspended single-layer graphene disks with radius of 150–1600 nm using a high-vacuum scanning thermal microscope. The results of this study revealed a radius-dependent thermal contact resistance between tip and graphene, with values between 1.15 and 1.52  ×  108 KW−1. The observed scaling of thermal resistance with radius is interpreted in terms of ballistic phonon transport in suspended graphene discs with radius smaller than 775 nm. In larger suspended graphene discs (radius  >775 nm), the thermal resistance increases with radius, which is attributed to in-plane heat transport being limited by phonon–phonon resistive scattering processes, which resulted in a transition from ballistic to diffusive thermal transport. In addition, by simultaneously mapping topography and steady-state heat flux signals between a self-heated scanning probe sensor and graphene with 17 nm thermal spatial resolution, we demonstrated that the surface quality of the suspended graphene and its connectivity with the Si/SiO2 substrate play a determining role in thermal transport. Our approach allows the investigation of heat transport in suspended graphene at sub-micrometre length scales and overcomes major limitations of conventional experimental methods usually caused by extrinsic thermal contact resistances, assumptions on the value of the graphene’s optical absorbance and limited thermal spatial resolution.

We have extracted temperature-dependent thermal conductivity values from scanning thermal microscopy measurements of a self-heated multiwalled carbon nanotube supported on a silicon substrate. A deliberately introduced segment of amorphous carbon served as an integrated nanoheater. Kelvin probe force microscopy was used to supplement the thermometry data with values for the nanotube’s electrical resistivity. This way, both the spatially resolved temperature rise and the Joule heating power density were available for further analysis. A one-dimensional heat diffusion model was fitted to the data to extract values for the thermal conductivity along the nanotube axis and the thermal conductance between the nanotube and supporting substrate. We found thermal conductivity values that continuously increase from 200 to 400 W m–1 K–1 in a temperature range of 100 to 400 K above room temperature. The values obtained are about one order of magnitude lower compared to values reported for the freely suspended case. We attribute this observation to the increased phonon scattering and quenching of acoustic phonon modes due to the substrate interaction.

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