Heat Transfer between a Self-Heated Scanning Thermal Microscopy Probe and a Cold Sample: Impact of the Probe Temperature
- PDF / 1,203,058 Bytes
- 6 Pages / 612.12 x 792.12 pts Page_size
- 84 Downloads / 173 Views
Heat Transfer between a Self-Heated Scanning Thermal Microscopy Probe and a Cold Sample: Impact of the Probe Temperature
Ali Assy1, Séverine Gomès1, Stéphane Lefèvre1 and Pierre-Olivier Chapuis1 1
Centre de Thermique de Lyon, CNRS-INSA de Lyon-UCBL, 9 rue de la Physique, Campus La Doua-LyonTech, 69621 Villeurbanne (Lyon), France.
ABSTRACT Scanning Thermal Microscopy measurements with a resistive microprobe electrically heated were performed for different probe temperatures, for probe free in air and in contact with various specimens. The measured relative difference of Joule power dissipated in the probe when tip is in contact with a sample and when it is free in air is studied for different magnitude of the electrical current that heats the probe. A variation of this signal, never outlined before, is observed. A predictive modeling is used to explain these results and identify from the experimental data the global thermal conductance of the probe-sample thermal exchange for experiments performed in ambient conditions.
INTRODUCTION Characterizing the thermal properties of a sample by Scanning Thermal Microscopy (SThM) requires first studying the heat transfer mechanisms between the heated probe-tip and the sample. Being out of contact, the probe transports heat to the sample due to air conduction and radiation for experiments under ambient conditions. A percentage of heat is also lost through natural convection. When the probe contacts the sample, two heat mechanisms are added to those cited above: solid to solid heat conduction, and heat transfer through water film. This film is developed on the sample surface due to capillary condensation of the ambient humidity. The contribution of these mechanisms is coupled and depends on different parameters: sample thermal conductivity, probe temperature, environmental conditions, probe size… In the last decade, researchers studied the heat transfer that operates between a SThM probe and a sample. Most of the studies were performed using a high probe temperature supposing that the water film disappears when the tip temperature is above 100 oC [1, 2]. The water film thickness does not exceed few nanometers [3], depending on the environment relative humidity (RH) [4] and the hydrophobic or hydrophilic character of surfaces. However, the heat transfer through the water film is complex and there are only few studies dealing with this heat f low and investigating the parameters that impact on its contribution. The aim of this work is monitoring the SThM signal while working at various probe temperatures and using different materials. An analytical model taking into account all the heat
transfer mechanisms is proposed. Based on this model description, an analysis of measurements versus the probe temperature and a discussion about various parameters that can explain these measurements are given. EXPERIMENTAL DETAILS The used SThM probe is the Wollaston wire probe [5]. It consists of a Pt 90%/ Rd 10% wire of 5 µm in diameter and 200 µm in length bent in a V-shape and covered wi
Data Loading...
