@article{wang2024enhancing,

title = {Enhancing the Pressure-Sensitive Electrical Conductance of Self-Assembled Monolayers},

author = {Xintai Wang and Asma Alajmi and Zhangchenyu Wei and Mohammed Alzanbaqi and Naixu Wei and Colin Lambert and Ali Ismael},

url = {https://pubs.acs.org/doi/full/10.1021/acsami.4c15796},

doi = {https://doi.org/10.1021/acsami.4c15796},

year  = {2024},

date = {2024-11-19},

urldate = {2024-01-01},

journal = {ACS Applied Materials & Interfaces},

publisher = {ACS Publications},

abstract = {The inherent large HOMO–LUMO gap of alkyl thiol (CnS) self-assembled monolayers (SAMs) has limited their application in molecular electronics. This work demonstrates significant enhancement of mechano-electrical sensitivity in CnS SAMs by external compression, achieving a gauge factor (GF) of approximately 10 for C10S SAMs. This GF surpasses values reported for conjugated wires and DNA strands, highlighting the potential of CnS SAMs in mechanosensitive devices. Conductive atomic force microscopy (cAFM) investigations reveal a strong dependence of GF on the alkyl chain length in probe/CnS/Au junctions. This dependence arises from the combined influence of molecular tilting and probe penetration, facilitated by the low Young’s modulus of alkyl chains. Theoretical simulations corroborate these findings, demonstrating a shift in the electrode Fermi level toward the molecular resonance region with increasing chain length and compression. Introducing a rigid graphene interlayer prevents probe penetration, resulting in a GF that is largely independent of the alkyl chain length. This highlights the critical role of probe penetration in maximizing mechano-electrical sensitivity. These findings pave the way for incorporating CnS SAMs into mechanosensitive and mechanocontrollable molecular electronic devices, including touch-sensitive electronic skin and advanced sensor technologies. This work demonstrates the potential of tailoring mechanical and electrical properties of SAMs through molecular engineering and interface modifications for optimized performance in specific applications.},

keywords = {AFM, Atomic Force Microscopy, Gauge factor, openQCM, Penetration, QCM, Quartz Crystal Microbalance, Self-Assembled Monolayers (SAMs), Tunnelling decay},

pubstate = {published},

tppubtype = {article}

}

@article{wang2023determination,

title = {Determination of electric and thermoelectric properties of molecular junctions by AFM in peak force tapping mode},

author = {Xinati Wang and Angelo Lamantia and Michael Jay and Hatef Sadeghi and Colin J Lambert and Oleg V Kolosov and Benjamin Robinson},

url = {https://iopscience.iop.org/article/10.1088/1361-6528/acdf67/meta},

doi = {https://doi.org/10.1088/1361-6528/acdf67},

year  = {2023},

date = {2023-06-19},

urldate = {2023-06-19},

journal = {Nanotechnology},

abstract = {Molecular thin films, such as self-assembled monolayers (SAMs), offer the possibility of translating the optimised thermophysical and electrical properties of high-Seebeck-coefficient single molecules to scalable device architectures. However, for many scanning probe-based approaches attempting to characterise such SAMs, there remains a significant challenge in recovering single-molecule equivalent values from large-area films due to the intrinsic uncertainty of the probe-sample contact area coupled with film damage caused by contact forces. Here we report a new reproducible non-destructive method for probing the electrical and thermoelectric properties of small assemblies (10 – 103) of thiol-terminated molecules arranged within a SAM on a gold surface, and demonstrate the successful and reproducible measurements of the equivalent single-molecule electrical conductivity and Seebeck values. We have used a modified thermal-electric force microscopy (TEFM) approach, which integrates the conductive-probe atomic force microscope, a sample positioned on a temperature-controlled heater, and a probe-sample peak-force feedback that interactively limits the normal force across the molecular junctions. The experimental results are interpreted by density functional theory calculations allowing quantification the electrical quantum transport properties of both single molecules and small clusters of molecules. Significantly, this approach effectively eliminates lateral forces between probe and sample, minimising disruption to the SAM while enabling simultaneous mapping of the SAMs nanomechanical properties, as well as electrical and/or thermoelectric response, thereby allowing correlation of the film properties.},

keywords = {Functional Theory (DFT) Calculations, Molecular Thin Films, openQCM, openQCM Q-1, QCM, QCM-D, Self-Assembled Monolayers (SAMs)},

pubstate = {published},

tppubtype = {article}

}