Thermal conductivity of benzothieno-benzothiophene derivatives on a nanometric scale

GROUPE DE RECHERCHE : NCM

GROUPE DE RECHERCHE : NCM

GROUPE DE RECHERCHE : NCM

Thermal conductivity of benzothieno-benzothiophene derivatives on a nanometric scale

Thermal phenomena on nano-objects can be measured quantitatively and observed on a nanometric scale thanks to the Scanning Thermal Microscope. Using this local probe microscope, we are able to differentiate the thermal conductivity of nanometre-thick films made of two types of molecules of the same type.my family. This experimental and theoretical study makes it possible to correlate thermal conductivity with the atomic structure of molecules and their organisation in a thin film.

There is growing interest in measuring thermal properties at the nanometre scale to characterise nano-objects (individual molecules, monolayers, 2D materials or 1D materials), but also to monitor the operation of nano-electronic components (transistors). We used the Scanning Thermal Microscope (SThM), a microscope from the large family of local probe microscopes, to thermally characterise organic films with a thickness of between 40 and 400 nm on a nanometre scale. Two types of film were characterised, each consisting of a different molecule; one composed of four rings and named BTBT, the other molecule has in addition to BTBT two alkyl chains of 8 carbon atoms added on either side of the molecule (named C8-BTBT-C8).

These molecules, which are not commercially available, have been synthdeveloped by a partner chemist at the Université Libre de Bruxelles (Belgium). Already known for their performance in organic transistors with electronic mobilities sometimes reaching 200 cm² V^-1 s^-1Here we explore the thermal properties of these promising molecules. Few studies have focused on their thermal properties, despite the fact that these molecules are good candidates for applications in thermoelectricity (low thermal conductivity)..

SThM studies of these materials enable us toaccéder Both the topography of the surface at nanometre scale and the thermal conductivity of the film at a precise point on the surface. This conductivity value is obtained directly after a calibration phase on samples of known thermal conductivity. BTBT and C8-BTBT films have thermal conductivities of 0.6 - 1.3 W m^-1 K^-1 and 0.3 - 0.7 W m^-1 K^-1 respectively, showing the impact of the alkyl chain on the vibration modes of the molecules and therefore on thermal conductivity. These differences in thermal conductivity were linked to the organisation of the molecules in the film using theoretical calculations carried out at the University of Mons (Belgium), the Catalan Institute of Nanosciences and Nanotechnologies (Barcelona, Spain) and the University of Cagliari (Italy). This work opens up opportunities for the use of SThM in nanotechnology, but also for the study of these organic materials for thermoelectricity.

Find out more :

https://dx.doi.org/10.1039/D0NR08619C
https://hal.archives-ouvertes.fr/hal-03135025v1

Dominique Vuillaume

Stephane Lenfant