Enabling low-noise null-point scanning thermal microscopy by the optimization of scanning thermal microscope probe through a rigorous theory of quantitative measurement

Abstract

The application of conventional scanning thermal microscopy (SThM) is severely limited by three major problems: (i) distortion of the measured signal due to heat transfer through the air, (ii) the unknown and variable value of the tip-sample thermal contact resistance, and (iii) perturbation of the sample temperature due to the heat flux through the tip-sample thermal contact. Recently, we proposed null-point scanning thermal microscopy (NP SThM) as a way of overcoming these problems in principle by tracking the thermal equilibrium between the end of the SThM tip and the sample surface. However, in order to obtain high spatial resolution, which is the primary motivation for SThM, NP SThM requires an extremely sensitive SThM probe that can trace the vanishingly small heat flux through the tip-sample nano-thermal contact. Herein, we derive a relation between the spatial resolution and the design parameters of a SThM probe, optimize the thermal and electrical design, and develop a batch-fabrication process. We also quantitatively demonstrate significantly improved sensitivity, lower measurement noise, and higher spatial resolution of the fabricated SThM probes. By utilizing the exceptional performance of these fabricated probes, we show that NP SThM can be used to obtain a quantitative temperature profile with nanoscale resolution independent of the changing tip-sample thermal contact resistance and without perturbation of the sample temperature or distortion due to the heat transfer through the air.

AFM-thermoreflectance for simultaneous measurements of the topography and temperature

“…1,17 Accordingly, the need to understand thermal transport on the sub-100 nm scale, which is comparable to the width of the ne electrodes in a transistor, necessitates the development of a temperature-sensing method with a sub-100 nm spatial resolution. 1,[13][14][15][16][18][19][20][21][22][23][24][25][26][27] Further, nanoscale thermometry with a high spatial resolution is paramount for accurate thermal characterizations of nanomaterials (e.g., graphene, carbon nanotubes, or nanowires), which have recently drawn enormous amounts of attention. [11][12][13][14][27][28][29][30][31][32][33][34] Related research has been carried out with micro-Raman spectroscopy, 35 thermoreectance (TR), [36][37][38][39][40] near-eld scanning optical microscopy (NSOM), 41 scanning thermal microscopy (SThM), [12][13][14][18][19][20][21][22][23]…”

“…To meet the demands of nanoscale thermometry with sub-100 nm resolutions, recent studies focus on scanning probebased thermometries. 1,13,14,[18][19][20][21][22][23][24][25][30][31][32][33][34]41,47 Among these technique, in the case of NSOM which measures temperature in near-eld, 41 the spatial resolution is determined by the size of the probe aperture. Accordingly, it requires a very small aperture as well as a complex optical system for high spatial resolutions.…”

“…Also, SThM, which is contact nanothermometry based on the atomic force microscope (AFM) platform, employs a temperature-sensing probe. 1,6 In order to obtain the temperature distribution on the sample surface, the resistance change of a conductor embedded in a probe 13,14,20,21,30 or the thermoelectric voltage generated at a thermocouple junction placed at the tip end of a probe 18,19,[22][23][24][31][32][33][34] must be measured, meaning that an additional system is required to process the signal. Further, these temperature-sensor-integrated probes are produced through a complex MEMS fabrication process, making them expensive and fragile.…”

Investigating the origin of efficiency droop by profiling the temperature across the multi-quantum well of an operating light-emitting diode

“…12 Furthermore, Hwang et al developed a highly sensitive SThM probe whose performance is significantly improved through a systematic design based on quantitative measurement theory; using this highperformance SThM probe, they demonstrated the functionalities of NP SThM with low noise and high spatial resolution. 13 According to Hwang et al, since the spatial resolution of a SThM probe is affected by the intrinsic parameters determined by the design of a probe as well as the extrinsic factors unrelated to the performance of the probe, it is difficult to simply specify a certain value as the spatial resolution of a SThM probe. However, for the SThM probe newly developed by Hwang et al and used in the study reported here, its spatial resolution had been maximized by optimizing the intrinsic parameters so that it was much higher than the previously reported value ($50 nm).…”

“…A more detailed description of the principles and experimental procedures involved can be found elsewhere. 12,13 When Kim et al derived Eqs. (2) and (3), they did not consider the effect of heat generated in the probe by light.…”