A low-noise measurement system for scanning thermal microscopy resistive nanoprobes based on a transformer ratio-arm bridge

Abstract

Atomic force microscopy (AFM) is a widely used technology for the investigation and characterization of nanomaterials. Its functionality can be easily expanded by applying dedicated extension modules, which can measure the electrical conductivity or temperature of a sample. In this paper, we introduce a transformer ratio-arm bridge setup dedicated to AFM-based thermal imaging. One of the key features of the thermal module is the use of a low-power driving signal that prevents undesirable tip heating during resistance measurement, while the other is the sensor location in a ratio-arm transformer bridge working in the audio frequency range and ensuring galvanic isolation of the tip, enabling contact-mode scanning of electronic circuits. The proposed expansion module is compact and it can be integrated onto the AFM head close to the cantilever. The calibration process and the resolution of 11 mK of the proposed setup are shown.

Transformer bridge-based metrological unit for scanning thermal microscopy with resistive nanoprobes

“…Only in such a setup will the entire system respond to the nanoprobe resistance changes induced by the heat transfer from and to the investigated surface. In our previous experiments we used the AC measurement electronics in configuration of the Wheatstone bridge, in which the power dissipated in each bridge arm is monitored [7,8].…”

“…This effect is especially efficient, when the bridge is biased with LF signals. In our previous transformer bridge based electronics we operated with the bias frequency of 10 kHz and probe bias current of 1 mA [8]. Moreover, the bridge was balanced manually by the modification of the reference resistor, which due to the complex balancing procedure was of limited efficiency.…”