Scanning thermal microscopy

Over the past thirty years, nanoscience and nanotechnology have led to a growing need for fundamental knowledge of thermal and energetic properties at ever smaller scales, from micrometers to nanometers. In particular, the development of new materials and systems depends on significant progress in understanding energy transport at these scales. The technological and commercial activities of many industrial sectors, such as semiconductors, aeronautics, aerospace and information technology, are profoundly affected.

Precise thermal measurements on scales of less than 30 nm, for example, are undoubtedly needed to characterize and optimize the properties of nanostructured materials such as interphases and superlattices (nanoscale multilayers), nanoporous materials, nano-objects and nanomaterials such as graphene, carbon nanotubes or nanowires, which are already being integrated into composites and components. The aim is also to gain a better understanding of failure mechanisms in electronic and optoelectronic components, whose design is often based on theoretical analyses without appropriate experimental verification. These measurements will also improve the accuracy and validity of simulation tools for ultra-integrated technologies.

In addition to energy transport, any phenomenon involving exchanges of energy and entropy with the environment, such as changes in atomic structures or magnetic domains, requires or induces heat dissipation or cooling in some way. This includes phase changes and chemical and biochemical reactions. Nanoscale thermal analysis should enable us to study these ultra-localized phenomena.

In this context, SThM (Scanning Thermal Microscopy) is a promising method for thermal imaging, thermal measurements and the study of thermal transport phenomena at micro and nano scales. Its lateral thermospatial resolution can be as low as 50 nm. Microscopy is based on the principle of bringing a very small probe into contact or proximity with the object to be characterized, with the probe and object having different temperatures.

Currently mainly based on AFM (Atomic Force Microscopy), it benefits from its ability to position the probe very precisely in relation to the structure under study, while controlling the force between the two objects. The vector of information of interest is the heat flux exchanged between the tip and the sample, this flux being dependent on the temperature difference between the probe and the sample, as well as on the latter's thermophysical properties.

In SThM, the AFM probe is therefore used not only as a force sensor, but also as a detector of the amount of heat exchanged between the probe and the sample. While various physical phenomena and/or thermally-dependent...