A dark mode in scanning thermal microscopy

Abstract

The need for high lateral spatial resolution in thermal science using Scanning Thermal Microscopy (SThM) has pushed researchers to look for more and more tiny probes. SThM probes have consequently become more and more sensitive to the size effects that occur within the probe, the sample, and their interaction. Reducing the tip furthermore induces very small heat flux exchanged between the probe and the sample. The measurement of this flux, which is exploited to characterize the sample thermal properties, requires then an accurate thermal management of the probe-sample system and to reduce any phenomenon parasitic to this system. Classical experimental methodologies must then be constantly questioned to hope for relevant and interpretable results. In this paper, we demonstrate and estimate the influence of the laser of the optical force detection system used in the common SThM setup that is based on atomic-force microscopy equipment on SThM measurements. We highlight the bias induced by the overheating due to the laser illumination on the measurements performed by thermoresistive probes (palladium probe from Kelvin Nanotechnology). To face this issue, we propose a new experimental procedure based on a metrological approach of the measurement: a SThM "dark mode." The comparison with the classical procedure using the laser shows that errors between 14% and 37% can be reached on the experimental data exploited to determine the heat flux transferred from the hot probe to the sample.

Improving accuracy of nanothermal measurements via spatially distributed scanning thermal microscope probes

“…S1). Therefore, as initially observed by our group and later confirmed elsewhere 22 , conducting measurements in absence of laser can greatly improve the stability of SThM measurements. In all experiments reported below, the laser was shut off.…”

“…These temperature variations -often referred to as "ambient temperature" -arise mainly from electrical effects arising from SThM operation, such as the feedback control of the position and laser illumination for positioning. In particular, the temperature variations due to laser illumination on the SThM probe are difficult to quantify 22 as they vary depending on: i) the position of the laser beam on the cantilever which affects reproducibility of the measurements; ii) the laser source-cantilever distance which is not constant and thus causes variations of the probe temperature as it approaches the sample surface and iii) laser influenced artefacts arising from high topographical features and change of the sample reflectance. Indeed, in our experiments below, a rise of 0.5 K was typically observed over a 30 minutes timescale.…”

Quantitative Mapping of Nanothermal Transport via Scanning Thermal Microscopy

“…5). Therefore, as initially observed by our group[122] and later confirmed elsewhere[123], conducting measurements in the absence of a laser can greatly improve the stability of SThM measurements. In all experiments reported below, the laser was shut off during thermal measurements.In standard AFM Force-Spectroscopy, the laser deflection on the cantilever is related to the spring constant of both probe and sample.…”

“…-arise mainly from electrical effects arising from SThM operation, such as the feedback control of the position and laser illumination for positioning. In particular, the temperature variations due to laser illumination on the SThM probe [122] are difficult to quantify [123] as they vary depending on: i) the position of the laser beam on the cantilever which affects reproducibility of the measurements; ii) the laser source-cantilever distance which is not constant and thus causes variations of the probe temperature as it approaches the sample surface and iii) laser influenced artefacts arising from high topographical features and change of the sample reflectance. Indeed, a rise of 0.1 K was typically observed over a 30 minute timescale in our experiments as shown below.…”

Quantitative Measurement of the Thermal Contact Resistance between a Glass Microsphere and a Plate

“…It has also been used to investigate the thermal contact resistance between the probe tip and a planar substrate [14][15][16][17][18] and to measure the thermal resistance due to a water meniscus formed around the probe-substrate contact region [19]. Most SThM studies use a thermal sensor placed in direct contact with the sample, which raises subtle metrological issues [12,20]. In recent studies a microsphere was glued on the probe of a SThM to study the near-field radia-tive heat transfer in a sphere-plate geometry on a phase transition material [21] or on a photovoltaic cell [22].…”