Thermal Conductivity Measurements in Atomically Thin Materials and Devices

In this chapter, I will provide a brief overview of atomically thin materials that are formed by layers held together by van der Waals forces or weak covalent bonding. These materials provide a unique and cheap way of studying plethora of phenomena. Perhaps, the relative simplicity of the methods that are commonly used in the studies of two dimensional (2D) materials are one of the main reasons why they attracted attention at this level since the advent of graphene. After an introduction to the properties of 2D materials, I will talk about the methods to obtain 2D materials and conclude the chapter with the possibilities of heterostructures of 2D materials.

Measuring the thermal conductivity of materials is a very important field as the continuation of the improvement in modern electronics and optoelectronics heavily depends on the thermal management. Both high thermal conductivity and low thermal conductivity materials are required in the device design. Besides the fields mentioned above, excess heat scavenging via thermoelectric devices is an ever-growing field. Thermoelectric devices performance is determined by the figure of merit \(Z=S^2 \sigma \kappa \) where S is the Seebeck coefficient, \(\sigma \) is the electrical conductivity and \(\kappa \) is the thermal conductivity. Materials that are good electrical conductors and thermal insulators are needed for efficient thermoelectric devices.

In this chapter I will introduce the measurement of thermal conductivity using the bolometric effect. The bolometric effect is defined as the resistivity change of a material due to heating. Indeed, the bolometric effect forms the basis of many modern technological sensors and devices. For instance, most commonly used integrated circuit thermometers are based on the well calibrated resistivity change of a Pt strip. Another example is the thermal imaging sensors. A cooled array of high temperature coefficient of resistance material can sensitively detect the infrared spectrum due to the change in the electrical resistance of the active material.