International audienceThermal imaging of individual silicon nanowires (Si NWs) is carried out by a scanning thermal microscopy (SThM) technique. The vertically aligned 1.7 (micro)m long Si NWs are fabricated combining nanosphere lithography and metal-induced wet chemical etching. A thermal model for the SThM probe is then presented with two steps: a model out of contact which enables a calibration of the probe, and a model in contact to extract thermal parameters from the sample under study. Using this model and the experimental thermal images, we finally determine a mean value of the tip-to-sample thermal contact resistance and a mean value of the Si NWs thermal conductivity. No significant thermal conductivity reduction in comparison with bulk Si is observed for Si NWs with diameters ranging from 200 to 380 nm. However, the technique presented here is currently the only one available to perform thermal measurements simultaneously on an assembly of individual one-dimensional nanostructures. It enables to save time and to make a statistical processing of the thermal data in order to deduce a reliable mean thermal conductivity, even when the tip-to-sample thermal contact resistance cannot be considered neither negligible in comparison with the Si NW intrinsic thermal resistance nor constant from one Si NW to another

We have developed a technique using a photothermal microscope from which we can make a thermal image of an electronic component working at a “high frequency” using a charge coupled device (CCD) camera and a multichannel lock-in scheme. To do this, we have created an electronic “stroboscope”: the frequency F of the thermal signal induced by a high frequency electrical excitation and the frequency of the light F+f that illuminates the device are next to each other; the signal reflected at the surface of the device whose amplitude is proportional to the variation of reflectivity and hence to the variation of temperature and whose frequency is the blinking one f is analyzed by a visible CCD camera. Amplitude and phase images of the high frequency thermal phenomenon can then be made. Moreover, this technique presents a great advantage: the spatial resolution is better than 1 μm. The amplitude and phase images presented show, with a very good spatial resolution, Joule and Peltier heating of a polycrystalline silicon 2.5 kΩ resistor across which a sinusoidal current is forced.

Thermal conductivity reduction is observed in P3HT nanowires inside porous alumina, upon size confinement due to a change in crystal orientation.

In scanning thermal microscopy (SThM) techniques, the thermal exchange radius between tip and sample is a crucial parameter. Indeed, it limits the lateral spatial resolution but, in addition, an accurate value of this parameter is necessary for a precise identification of thermal properties. But until now, the thermal exchange radius is usually estimated but not measured. This paper presents an experimental procedure, based on the 3omega-SThM method, to measure its value. We apply this procedure to evaluate the thermal exchange radius of two commercial probes: the well-known Wollaston one and a new probe constituted of a palladium film on a SiO(2) substrate. Finally, presenting silicon nanowire images, we clearly demonstrate that this new probe can reach a spatial resolution better than 100 nm whereas the Wollaston probe hardly reaches a submicronic spatial resolution.