Production and Characterisation of Thermoelectrically Efficient Thin Films for Green Energy Applications
Creators: name: Penhale-Jones, Becky
Publisher: name: Lancaster University
Year: 2024

description: Molecular electronics focuses on using molecules or their monolayers as
 electrical devices. Within this, the field of molecular thermoelectronics
 hones in on using these same building blocks for improvement of
 thermoelectric properties, or conversion of waste heat into useful
 electricity. Specifically designing molecules enables fine tuning of these
 properties to produce devices that are capable of effectively harnessing
 previously wasted energy. For example, adding side chains to a molecular
 backbone will impact phonon transport within it, as well as changing the
 packing density once the molecule forms into a monolayer. Furthermore,
 altering where the electrodes in a junction contact these molecules and
 their monolayers will influence quantum interference (QI)
 
 effects. These characteristics consequently shift other properties of the
 materials such as electrical conductance and figure of merit (FOM). This,
 in turn, enables advancements in the devices utilising such materials to
 produce useful products with greater efficiency. In this research,
 monolayers were formed via Langmuir-Blodgett (LB) deposition and
 selfassembled monolayers (SAMs) from specially designed molecules for
 improved QI and thermoelectric efficiency. Techniques including atomic
 force microscopy (AFM) and x-ray photoelectron spectroscopy (XPS) were
 used to determine whether these formed uniform monolayers with reasonable
 electrical conductance.
 
 
 In this research, monolayers were formed via Langmuir-Blodgett (LB)
 deposition and selfassembled monolayers (SAMs) from specially designed
 molecules for improved QI and thermoelectric efficiency. Techniques
 including atomic force microscopy (AFM) and x-ray photoelectron
 spectroscopy (XPS) were used to determine whether these formed uniform
 monolayers with reasonable electrical conductance.
 
 
 Graphene-coated AFM probes were wear-tested. Standard non-conductive AFM
 probes were coated in graphene via Langmuir-Schaefer (LS), in an attempt
 to prolong their lifetime. Conductive probes have been coated previously,
 with the conclusion that this improves conductance for tailored molecules
 in a junction. However, this study viewed the potential benefit of
 increased usability of the probes with minimal reduction in attainable
 detail.
 
 
 Furthermore, tetrapodal molecules were investigated, building on previous
 work on the possibility of decoupling the electrical conductance of the
 molecular backbone from its anchors, creating stable yet conductive
 monolayers. The aim was to understand if varying the ‘tail’ group of the
 molecule influenced its interaction within the molecular junction,
 therefore changing its electrical
 
 conductance.
 
 
 Finally, several dithiolenates were studied, with one anchor point and two
 thiol groups for substrate binding. Thiols have been extensively studied
 due to their affinity for gold, however, the role of dithiolenates is
 largely unknown. Two molecules were tested, both with protected and
 deprotected forms. Greater electrical conductance was anticipated for the
 deprotected forms than
 
 their protected counterparts. 
 
 
 This thesis concludes that LS and self-assembly produce good monolayers
 with the desired properties per their molecular design. As such, the
 techniques present promising methods for fabricating useful
 thermoelectrically efficient thin films.