July 2020: ACS Applied Materials & Interfaces
Thermoelectric materials, which can directly convert heat to electricity, can effectively increase the sustainability of electricity production through the scavenging of waste heat. Although traditional thermoelectric generators with bulk metal chalcogenide thermoelements have been successfully used in power generation from heat sources, they cannot provide power generation in upcoming applications such as lab-on-a-chip devices or biomedical devices. Nanoscale patterning offers many advantages that could be of use for this endeavour, such as the ability to pattern diverse shaped structures with the potential for precisely positioning them in any area of a substrate. However, the direct patterning of thermoelectric metal chalcogenides can be challenging and is normally constrained to certain geometries and sizes. Here we report the direct writing of sub-10 nm wide bismuth sulphide (Bi2S3) and a proof-of-concept demonstration of the thermoelectric properties of directly-writable thin films using a single-source, spin-coatable, and electron-beam sensitive bismuth(III) ethylxanthate precursor. A self-doping strategy was deployed in order to increase the inherently low carrier concentration of pristine Bi2S3, achieved by selectively introducing sulphur vacancies in the films during vacuum annealing, which resulted in an electron rich material. We measured a room-temperature electrical conductivity of 6 S m−1 and a Seebeck coefficient of −21.41 μV K−1 for a directly patterned, substoichiometric Bi2S3 thin film. It is expected that with further optimization of structure and morphology, this approach can be useful to study nanostructured Bi2S3 and ultimately as fabrication technique for micro- thermoelectric generator for on-chip applications.
