Single Molecule Electronics

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)

Abstract

Single molecule electronics represents a rapidly growing area of interest within the electronics community. As the size of electronics continue to miniaturise, the use of metal-molecule-metal junctions has the potential to provide a useful step in this process via the bottom-up approach. The majority of previous work in the molecular electronics field has focused on junctions using gold as the contact metal. However, alternative contact materials such as the ferromagnetic 3d transition metals provide an exciting opportunity to probe new effects including spin-dependent transport.

Here, a mechanically controllable break junction technique has been developed and used to measure the conductance of single molecules using both gold and ferromagnetic (nickel and cobalt) electrodes. A scanning tunnelling microscope break junction technique was also employed to provide a comparison between measurements using both methods.
To date, work on single-molecule junctions incorporating 3d transition metals has been limited due to the tendency of these metals to oxidize under ambient conditions. It has been observed within, that it can be possible to measure the conductance of single molecule junctions without using techniques such as electrochemical control to protect the metal contacts from oxidation. A number of metal-molecule-metal junctions have been studied to determine their most probable value of conductance. Several further techniques such as 2D histograms, I-V curves, 2D correlation histograms and conditional histograms have been used to expand on this analysis.

Magnetoresistance measurements using the mechanically controllable break junction method were explored for Co|pentanedithiol|Co junctions by comparing the conductance obtained with and without the presence of a magnetic field. A magnetoresistance of 567% was measured. Anisotropic magnetoresistance experiments were performed on the same junction and an anisotropic magnetoresistance of 77% was measured. Magnetoresistance measurements were also performed using the scanning tunnelling microscope break junction method on Ni|1,4-benzenedithiol|Ni junctions. However, no magnetoresistance effect was observed.
Date of Award29 Sep 2020
Original languageEnglish
Awarding Institution
  • The University of Bristol
SupervisorWalther Schwarzacher (Supervisor)

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