Session: 14-01: Measurement Techniques and Thermophysical Properties in Micro/Nanoscale

Paper Number: 132727

132727 - Sub-Micron Resolution Mapping of Thermal Properties in Cvd and Mbe-Grown Molybdenum Disulfide via Nanoscale Thermoreflectance Microscopy 

Abstract: 

As with most other functional properties of 2D materials, thermal energy transport via phonons can be impacted quite dramatically through their scattering by a variety of material defects. These phonon scattering events in 2D systems arise from the plethora of defects and interfaces that arise from both the growth parameters and post-processing steps that are often required to manipulate the 2D materials functionalities.  The thermal transport properties of 2D materials at and around these defect phonon scattering sites, which often have length scales and spacings on the order of a few to 10’s of nanometers, are difficult to isolate and measure individually with the thermal measurement techniques available previously.  For example, optical based techniques for measuring thermal properties of 2D materials (e.g., Raman, TDTR) are ultimately diffraction limited and thus restricted in-practice to areal spatial resolution on the order of single micrometers.  Techniques using lasers coupled with AFM-tips (e.g., Nano-FTIR) have shown promise in achieving sub-diffraction limited areal resolution to qualitatively interrogate optically excited surfaces, but lack the opto-thermal transduction power afforded by thermoreflectance-based methods to ensure accurate measurement of local temperature and thermal wave modulation.

Here, we introduce a novel approach called Nanoscale Thermoreflectance Microscopy (NTM), capable of characterizing the thermal properties of 2D materials with ~10 nm areal spatial resolution. NTM combines the principles of steady-state thermoreflectance (SSTR) with the superior spatial resolution made possible through physical-aperturing of the heat flow from tip-to-sample via contact mode scanning probe methods. Thermal maps of CVD and MBE-grown molybdenum disulfide (MoS₂) grown on SiO₂/Si and Al₂O₃ substrates are presented, quantifying the impact of the chosen growth method and substrate on material quality through direct visualization of how the thermal resistance increases near defects such as wrinkles/boundaries, adlayer nucleation sites, etc.  These local increases in resistance are attributed to the impact of the defect in question on phonon transport.  As a result, this new capability enables an estimation of the length scales over which various defect structures exert influence over phonon transport in these 2D materials, providing important thermal insight to guide future synthesis, processing and device-integration efforts using this important family of materials.  Examples of areas where this novel ability to characterize local thermal transport phenomena can have a disruptive impact include development of single-photon emitters (SPEs) using dichalcogenides for quantum applications, as well as novel transistor, memory and sensor device architectures leveraging 2D heterostructures or stand-alone layers to realize new avenues for advanced computing.

Presenting Author: Brian Foley Laser Thermal

Presenting Author Biography: Brian Foley is the Vice President of Research and Development at Laser Thermal. Brian completed his doctorate in Mechanical Engineering in 2016 at the University of Virginia advised by Prof. Patrick Hopkins, followed by his post-doctoral research with Prof. Samuel Graham while at Georgia Tech. He brings over 15 years of experience in research and product development in Thermal Transport and RF/Microwave/Terahertz electronics.

Authors:

Brian Foley Laser Thermal
Andrew Jones Laser Thermal
Patrick Hopkins Laser Thermal
John Gaskins Laser Thermal