Thermoelectric Properties of Substoichiometric Electron Beam Patterned Bismuth Sulfide

July 2020: ACS Applied Materials & Interfaces

https://pubs.acs.org/doi/abs/10.1021/acsami.0c06829

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.

Anas & Pawan correlate charge and TE transport to paracrystallinity in conducting polymers

Jan 2020: Nature Communications https://www.nature.com/articles/s41467-020-15399-2

The conceptual understanding of charge transport in conducting polymers is still ambiguous due to a wide range of paracrystallinity (disorder). Here, we advance this understanding by presenting the relationship between transport, electronic density of states and scattering parameter in conducting polymers. We show that the tail of the density of states possesses a Gaussian form confirmed by two-dimensional tight-binding model supported by Density Functional Theory and Molecular Dynamics simulations. Furthermore, by using the Boltzmann Transport Equation, we find that transport can be understood by the scattering parameter and the effective density of states. Our model aligns well with the experimental transport properties of a variety of conducting polymers; the scattering parameter affects electrical conductivity, carrier mobility, and Seebeck coefficient, while the effective density of states only affects the electrical conductivity. We hope our results advance the fundamental understanding of charge transport in conducting polymers to further enhance their performance in electronic applications.

Pepe's demonstration of nanoscale patterning of Bi2S3 thermoelectric films and devices

Direct patterning of thermoelectric metal chalcogenides can be challenging and is normally constrained to certain geometries and sizes. Here we report the synthesis, characterization, and direct writing of sub-10 nm wide bismuth sulfide (Bi2S3) using a single-source, spin-coatable, and electron-beam-sensitive bismuth(III) ethylxanthate precursor. In order to increase the intrinsically low carrier concentration of pristine Bi2S3, we developed a self-doping methodology in which sulfur vacancies are manipulated by tuning the temperature during vacuum annealing, to produce an electron-rich thermoelectric material. We report 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. We expect that our demonstration of directly writable thermoelectric films, with further optimization of structure and morphology, can be useful for on-chip applications.