Novel nanoscale thermal property imaging technique: The 2ω method. I. Principle and the 2ω signal measurement

In this and the following companion articles, the authors present the 2ω method, a novel ac mode local thermal property imaging technique with nanoscale spatial resolution. To demonstrate the use of the thermoelectric probe as an active one that can function as both a heater and a temperature sensor, the authors develop and implement the 2ω signal measurement technique, which can extract thermoelectric signals from a thermocouple junction while electrically heating it simultaneously. The principle of the 2ω signal measurement technique is explained by a steady periodic electrothermal analysis. The authors use a specially designed test pattern to experimentally verify that the 2ω signal is caused by the temperature oscillation induced by Joule heating. In addition, based on the results from an experiment using a cross-shaped pattern, the measurement accuracy of the 2ω method depends on the junction size of the thermoelectric probe. The 2ω method is implemented and compared with other methods in the following companion paper.