Decomposition of Ferrocene on Pt(111) and Its Effect on Molecular Electronic Junctions

© 2019 American Chemical Society. From dilute vapor, ferrocene encountering Pt(111) decomposes, producing bound cyclopentadienyl rings, in contrast to its legendary stability in solution electrochemistry. We propose that decomposition occurs through initial chemisorption, making a Pt-C bond to a ferrocenium hydride, followed by step-edge catalyzed decomposition leading to migration of the Fe atom inside the Pt bulk. These conclusions are based on results from density functional theory (DFT) calculations. When Pt(111) approaches ferrocene tethered to a self-assembled monolayer, only the first, spontaneous but mechanically reversible chemisorption is predicted. Nonequilibrium Green's function calculations utilizing DFT predict that chemisorption increases molecular junction conductivities by a factor of 2-5. This could contribute to the extremely high conductivities observed in junctions supporting rectification up to unprecedented high-frequency cutoffs of ∼520 GHz, though squashed junctions at half monolayer coverage are predicted to conduct 104 times better

Electrical Transport Properties Based on Silicon-1,6-hexadithiol-Silicon Molecular Devices

Self-assembly of a single-molecule membrane (Self-assembled monolayers,SAMs) has been widely used in nanotechnology, biological sensors, and molecular electronics in the past two decades. However, the microscopic geometric information on the electrode-molecular-electrode conformation is inaccessible experimentally, and the connection between the microstructure of the silicon electrode surface in the real chemical environment and the connection mode of the silicon-sulfur and the electrical transport properties is not clear, and the theoretical calculations will be the main means of clarifying these problems. In this paper, based on the experimental reported silicon-1-6-hexadithiol-silicon molecular devices of density functional theory (DFT), combined with the nonequilibrium Green function (NE GF) method, we perform quantum transport calculations for the zero bias conductance of the model and electron transmission spectra. It is shown that silicon-sulfur molecular junctions have some significantly different properties compared to metal-based molecular junctions. The structural details of silicon-sulfur molecular junctions have a crucial influence on their electrical transport propertie

Silicon - single molecule - silicon circuits.

In 2020, silicon - molecule - silicon junctions were fabricated and shown to be on average one third as conductive as traditional junctions made using gold electrodes, but in some instances to be even more conductive, and significantly 3 times more extendable and 5 times more mechanically stable. Herein, calculations are performed of single-molecule junction structure and conductivity pertaining to blinking and scanning-tunnelling-microscopy (STM) break junction (STMBJ) experiments performed using chemisorbed 1,6-hexanedithiol linkers. Some strikingly different characteristics are found compared to analogous junctions formed using the metals which, to date, have dominated the field of molecular electronics. In the STMBJ experiment, following retraction of the STM tip after collision with the substrate, unterminated silicon surface dangling bonds are predicted to remain after reaction of the fresh tips with the dithiol solute. These dangling bonds occupy the silicon band gap and are predicted to facilitate extraordinary single-molecule conductivity. Enhanced junction extendibility is attributed to junction flexibility and the translation of adsorbed molecules between silicon dangling bonds. The calculations investigate a range of junction atomic-structural models using density-functional-theory (DFT) calculations of structure, often explored at 300 K using molecular dynamics (MD) simulations. These are aided by DFT calculations of barriers for passivation reactions of the dangling bonds. Thermally averaged conductivities are then evaluated using non-equilibrium Green's function (NEGF) methods. Countless applications through electronics, nanotechnology, photonics, and sensing are envisaged for this technology

Spontaneous S-Si bonding of alkanethiols to Si(111)-H: Towards Si-molecule-Si circuits

© The Royal Society of Chemistry 2020. We report the synthesis of covalently linked self-assembled monolayers (SAMs) on silicon surfaces, using mild conditions, in a way that is compatible with silicon-electronics fabrication technologies. In molecular electronics, SAMs of functional molecules tethered to goldviasulfur linkages dominate, but these devices are not robust in design and not amenable to scalable manufacture. Whereas covalent bonding to silicon has long been recognized as an attractive alternative, only formation processes involving high temperature and/or pressure, strong chemicals, or irradiation are known. To make molecular devices on silicon under mild conditions with properties reminiscent of Au-S ones, we exploit the susceptibility of thiols to oxidation by dissolved O2, initiating free-radical polymerization mechanisms without causing oxidative damage to the surface. Without thiols present, dissolved O2would normally oxidize the silicon and hence reaction conditions such as these have been strenuously avoided in the past. The surface coverage on Si(111)-H is measured to be very high, 75% of a full monolayer, with density-functional theory calculations used to profile spontaneous reaction mechanisms. The impact of the Si-S chemistry in single-molecule electronics is demonstrated using STM-junction approaches by forming Si-hexanedithiol-Si junctions. Si-S contacts result in single-molecule wires that are mechanically stable, with an average lifetime at room temperature of 2.7 s, which is five folds higher than that reported for conventional molecular junctions formed between gold electrodes. The enhanced “ON” lifetime of this single-molecule circuit enables previously inaccessible electrical measurements on single molecules