Heat transfer processes in micro- and nanoscale devices have become more and more important during the last decades. Scanning thermal microscopy (SThM) is an atomic force microscopy (AFM) based method for analyzing local thermal conductivities of layers with thicknesses in the range of several nm to µm. In this work, we investigate ultrathin films of hexagonal boron nitride (h-BN), copper iodide in zincblende structure (γ-CuI) and some test sample structures fabricated of silicon (Si) and silicon dioxide (SiO2) using SThM. Specifically, we analyze and discuss the influence of the sample topography, the touching angle between probe tip and sample, and the probe tip temperature on the acquired results. In essence, our findings indicate that SThM measurements include artefacts that are not associated with the thermal properties of the film under investigation. We discuss possible ways of influence, as well as the magnitudes involved. Furthermore, we suggest necessary measuring conditions that make qualitative SThM measurements of ultrathin films of h-BN with thicknesses at or below 23 nm possible.
New micro- and nanoscale devices require electrically isolating materials with specific thermal properties. One option to characterize these thermal properties is the atomic force microscopy (AFM)-based scanning thermal microscopy (SThM) technique. It enables qualitative mapping of local thermal conductivities of ultrathin films. To fully understand and correctly interpret the results of practical SThM measurements, it is essential to have detailed knowledge about the heat transfer process between the probe and the sample. However, little can be found in the literature so far. Therefore, this work focuses on theoretical SThM studies of ultrathin films with anisotropic thermal properties such as hexagonal boron nitride (h-BN) and compares the results with a bulk silicon (Si) sample. Energy fluxes from the probe to the sample between 0.6 µW and 126.8 µW are found for different cases with a tip radius of approximately 300 nm. A present thermal interface resistance (TIR) between bulk Si and ultrathin h-BN on top can fully suppress a further heat penetration. The time until heat propagation within the sample is stationary is found to be below 1 µs, which may justify higher tip velocities in practical SThM investigations of up to 20 µms−1. It is also demonstrated that there is almost no influence of convection and radiation, whereas a possible TIR between probe and sample must be considered.
Conductive atomic force microscopy (CAFM) is a powerful technique to investigate electrical and mechanical properties of materials and devices at the nanoscale. However, its main challenge is the reliability of the probe tips and their interaction with the samples. The most common probe tips used in CAFM studies are made of Si coated with a thin (∼20 nm) film of Pt or Pt-rich alloys (such as Pt/Ir), but this can degrade fast due to high current densities (>10 2 A/cm 2 ) and mechanical frictions. Si tips coated with doped diamond and solid doped diamond tips are more durable, but they are significantly more expensive and their high stiffness often damages the surface of most samples. One growing alternative is to use solid Pt tips, which have an intermediate price and are expected to be more durable than metal-coated silicon tips. However, a thorough characterization of the performance of solid Pt probes for CAFM research has never been reported. In this article, we characterize the performance of solid Pt probes for nanoelectronics research by performing various types of experiments and compare them to Pt/Ir-coated Si probes. Our results indicate that solid Pt probes exhibit a lateral resolution that is very similar to that of Pt/Ir-coated Si probes but with the big advantage of a much longer lifetime. Moreover, the probe-to-probe deviation of the electrical data collected is small. The use of solid Pt probes can help researchers to enhance the reliability of their CAFM experiments.
A well-known method for measuring thermal conductivity is the 3-Omega (3ω) method. A prerequisite for it is the deposition of a metal heater on top of the sample surface. The known design rules for the heater geometry, however, are not yet sufficient. In this work, heaters with different lengths and widths within the known restrictions were investigated. The measurements were carried out on SiO2 thin films with different film thicknesses as a reference. There was a significant difference between theoretical deposited heater width and real heater width, which could lead to errors of up to 50% for the determined thermal conductivity. Heaters with lengths between 11 and 13 mm and widths of 6.5 µm or more proved to deliver the most trustworthy results. To verify the performance of these newfound heaters, additional investigations on Al2O3 thin films were carried out, proving our conclusions to be correct and delivering thermal conductivity values of 0.81 Wm−1 K−1 and 0.93 Wm−1 K−1 for unannealed and annealed samples, respectively. Furthermore, the effect of annealing on Al2O3 was studied, revealing a significant shrinking in film thickness of approximately 11% and an increase in thermal conductivity of 15%. The presented results on well-defined geometries will help to produce optimized heater structures for the 3ω method.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.