Quantitative temperature measurement of an electrically heated carbon nanotube using the null-point method

Department of Mechanical Engineering, Korea University, Seoul 136-701, Republic of Korea.
The Review of scientific instruments (Impact Factor: 1.61). 11/2010; 81(11):114901. DOI: 10.1063/1.3499504
Source: PubMed


Previously, we introduced the double scan technique, which enables quantitative temperature profiling with a scanning thermal microscope (SThM) without distortion arising from heat transfer through the air. However, if the tip-sample thermal conductance is disturbed due to the extremely small size of the sample, such as carbon nanotubes, or an abrupt change in the topography, then quantitative measurement becomes difficult even with the double scan technique. Here, we developed the null-point method by which one can quantitatively measure the temperature of a sample without disturbances arising from the tip-sample thermal conductance, based on the principle of the double scan technique. We first checked the effectiveness and accuracy of the null-point method using 5 μm and 400 nm wide aluminum lines. Then, we quantitatively measured the temperature of electrically heated multiwall carbon nanotubes using the null-point method. Since the null-point method has an extremely high spatial resolution of SThM and is free from disturbance due to the tip-sample thermal contact resistance, and distortion due to heat transfer through the air, the method is expected to be widely applicable for the thermal characterization of many nanomaterials and nanodevices.

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    • "Scanning Thermal Microscopy (SThM) [13] [14] [15] [16] [17] [18], that while showing good performance in studies of polymeric and organic materials, has limited ability to differentiate between high thermal conductivity materials such as used in the semiconductor industry, thermoelectrics or optical devices [19] [20]. The main reasons are – spatial resolution on the range of few tens of nanometres remains well below other scanning probe microscopy (SPM) approaches, low sensitivity to thermal properties of materials of high thermal conductance, worsened by the unstable and weak thermal contact between the thermal sensor and the studied object. "
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    ABSTRACT: Scanning thermal microscopy (SThM) - a type of scanning probe microscopy that allows mapping thermal transport and temperatures in nanoscale devices, is becoming a key approach that may help to resolve heat dissipation problems in modern processors and develop new thermoelectric materials. Unfortunately, performance of current SThM implementations in measurement of high thermal conductivity materials continues to me limited. The reason for these limitations is two-fold - first, SThM measurements of high thermal conductivity materials need adequate high thermal conductivity of the probe apex, and secondly, the quality of thermal contact between the probe and the sample becomes strongly affected by the nanoscale surface corrugations of the studied sample. In this paper we develop analytical models of the SThM approach that can tackle these complex problems - by exploring high thermal conductivity nanowires as a tip apex, and exploring contact resistance between the SThM probe and studied surface, the latter becoming particularly important when both tip and surface have high thermal conductivities. We develop analytical model supported by the finite element analysis simulations and by the experimental tests of SThM prototype using carbon nanotube (CNT) at the tip apex as a heat conducting nanowire. These results elucidate vital relationships between the performance of the probe in SThM from one side and thermal conductivity, geometry of the probe and its components from the other, providing pathway for overcoming current limitations of SThM.
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    ABSTRACT: We develop and demonstrate the theory and method of null-point scanning thermal microscopy, which can obtain quantitative temperature profiles even when the heat conductance between the tip and the sample is disturbed due to abrupt changes in the surface topography or properties. Due to its generality, it would be widely applicable for a variety of problems associated with the thermal characterization of nanomaterials and nanodevices.
    International Journal of Thermal Sciences 01/2011; 62. DOI:10.1016/j.ijthermalsci.2011.11.012 · 2.63 Impact Factor
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    ABSTRACT: A method is described to quantify thermal conductance and temperature distributions with nanoscale resolution using scanning thermal microscopy. In the first step, the thermal resistance of the tip-surface contact is measured for each point of a surface. In the second step, the local temperature is determined from the difference between the measured heat flux for heat sources switched on and off. The method is demonstrated using self-heating of silicon nanowires. While a homogeneous nanowire shows a bell-shaped temperature profile, a nanowire diode exhibits a hot spot centered near the junction between two doped segments.
    Nano Letters 01/2012; 12(2):596-601. DOI:10.1021/nl203169t · 13.59 Impact Factor
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