Non-Destructive Nanoscale Resolution using a Carbon Nanotube Scanning Thermal Probe

Lead Research Organisation: Lancaster University
Department Name: Physics


Accurate energy transport measurement in materials and devices is at the heart of recent developments of electronics in the polymer, bio-medical and pharmaceutical industries. For example, the measurement of the time-temperature profile in a decaying cancer cell conveys critical information on biochemical composition and metabolism, essential for diseased cell screening. However, as the dimensions of electronic devices reduce to the nanoscale, classical techniques for measuring electrical and thermal transport become less accurate. To achieve a better understanding of transport mechanisms, it is essential to develop new nanoscale tools to measure energy transport without causing damage to the samples analysed or to the measuring apparatus itself. Despite recent progress in small scale thermal transport measurements, known as Local Thermal Analysis (LTA), the performance is severely limited by measurement probe size, probe wear and damage caused to materials, such as cells, by the probe tip. To address these problems, this collaborative proposal between Durham University and Lancaster University will integrate carbon nanotubes (CNT) into the structure of an LTA probe tip, using conventional integrated circuit (IC) fabrication technology. CNTs are extremely small graphite-like carbon tubes with a diameter of about one nanometre (one hundred thousandth that of a human hair) and length of a few microns (the diameter of a human hair). CNTs' exceptional properties make them ideal for the design of nanoscale probes. The proposal aims to develop a non-destructive, CNT, scanning, thermal probe having a resolution better than 20 nm and capable of recording simultaneously the thermal transport properties and response of materials undergoing optical energy excitation. This research will lead to new applications across a wide range of industries from electronics to biomedicine, crossing traditional interdisciplinary boundaries. For example, it will be possible to monitor the performance of nanoscale electronic circuitry, essential to produce cheaper, faster and reliable devices; and also to assist the accurate screening of biological samples and even to monitor drug delivery to bio-cells.


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Description As at the onset of this project a very little was known on how such would operate and how to engineer it, we built a comprehensive multi-scale computational physical model of a probe operating in various environments. The immediate result of such study was a novel design of the thermal probe, not anticipated a priori, where multiwall CNT is attached to the side of a thermal sensor. Simultaneously, the modeling of SThM for the key materials used in semiconductor industry and nanotechnology such as Si, suggested that thermal resolution below 50 nm may not be beneficial, due to a large mean-free-path of thermal carriers, whereas an efficient and stable thermal contact between the probe apex and the sample is of a paramount importance.

These findings prompted development of a dedicated nanofabricated thermal transport test samples, "staircases" of few atomic layer materials, new IP on nanoscale sections of heterostructures that is now being considered for commercial exloitation, and trenched substrates where thermally probed layered materials can be suspended. We built unique variable environment SThM setup operating from a high vacuum of 10-7 torr (ten billionth of the atmospheric pressure) to ambient air and even liquid environments, that also allowed independent monitoring of nanoscale tip-sample contact via nanomechanical measurements. Using this system, we for the first time mapped thermal conductivity of graphene (a relative to CNT in terms of material nature and thermal conductivity) and directly compared nanoscale diffusive and ballistic heat transfer regimes. We also, for the first time, were able to correlate thermal transport between the probe apex with contact area measured via nanomechanical tests, paving the way for novel quantitative approaches in nanoscale thermal measurements. Finally, the prototypes of CNT-SThM probes manufactured jointly with Durham University, according to the new design rules, indicated a notable improvement of a thermal contrast and lateral thermal resolution below 50 nm, as well as superior topography resolution, thus accomplishing a key objective of the current project.

An unexpected benefit of this study was a development of a fully "immersed" SThM - iSThM. Such probe can significantly improve the thermal contact between the SThM tip and the sample, and its stability, but until our study, it was considered impossible due to perceived direct heat dissipation from the thermal sensor into the surrounding liquid, and degradation of lateral resolution. Notwithstanding, guided by our modeling, we tested such iSThM and successfully demonstrated nanoscale thermal mapping with 50 nm lateral resolution on the polymer-ceramic-metal Ultra Large Scale Integration interconnects. Such iSThM, would be of extreme interest for biotechnology, and functioning of nanoscale catalysts, to mention a few.
Exploitation Route The novel efficient nanoscale thermal microscopy methods will be of extremely wide use in the industrial laboratories and in teh production quality control environments. Novel approach to preparation of samples for nanoscale probe microscopy and scanning thermal microscopy is explored for exploitation via companies producing sample preparation equipment for SEM and related studies, as well via service companies and instrumentation companies.
Sectors Education,Electronics,Healthcare

Description The finding were used in the EU FP7 project QUANTIHEAT where they have been applied to the study nanothermal properties of various industrial materials including semiconductor processing and compound semiconductors.
First Year Of Impact 2017
Sector Digital/Communication/Information Technologies (including Software),Electronics,Energy
Impact Types Economic

Description European Commission (EC)
Amount £38,000 (GBP)
Organisation European Commission 
Sector Public
Country European Union (EU)
Start 06/2011 
End 06/2015
Description FP7 QUANTIHEAT
Amount € 586,000 (EUR)
Funding ID 604668 
Organisation European Commission 
Sector Public
Country European Union (EU)
Start 12/2013 
End 11/2017
Company Name Lancaster Materials Analysis 
Description Services to the industry and implementation of IP based on Lancaster patent US9082587 
Year Established 2014 
Impact Demonstrated potential for replacing TEM and SEM methods by less expensive in the characterization of semiconductor and optoelectronic structures