Manufactured gadgets, throughout their lifespan, should operate with some determined electrical attributes. This however imposes the same need on all nanomaterial components. Developments in the analytical as well as experimental methods have enabled researchers to effectively analyze structurally as well as chemically driven modifications that dictate the electrical attributes of 1-dimensional nanostructures. Groundbreaking effects have been reported such as those relating to the modification of nanowires and migration of gold catalysts through Germanium nanowires, amongst many others.
The gold catalyst promotes the growth of nanowires and its application as a nanocontact to zinc oxide nanowires indicates that electrical transport attributes can be modified or switched from ohmic to Schottky owing to quantum-mechanical tunneling at the edge of the contact. This can be achieved by choosing an appropriate nanocontact comparable in diameter to the proposed nanowire.
In a recent paper published in Nano Letters Alex Lord and his colleagues investigated nanoscale modifications at the gold-zinc oxide nanowire interface and related the transport behavior to the form of the interface edge and its structure employing aberration-corrected scanning transmission electron microscopy. They selected the gold-zinc oxide nanowire system owing to its prototypical and abrupt nature of the interface between the metal and semiconductor.
Dr Lord said: “The experiments had a simple premise but were challenging to optimise and allow atomic-scale imaging of the interfaces. However, it was essential to this study and will allow many more materials to be investigated in a similar way.”
“This research now gives us an understanding of these new effects and will allow engineers in the future to reliably produce electrical contacts to these nanomaterials which is essential for the materials to be used in the technologies of tomorrow.
“In the near future this work can help enhance current nanotechnology devices such as biosensors and also lead to new technologies such as Transient Electronics that are devices that diminish and vanish without a trace which is an essential property when they are applied as diagnostic tools inside the human body.”
The authors synthesized zinc oxide through high-temperature vapor phase method. They used a thin layer of gold on the substrate in order to initiate the required growth and develop the one-step electrical nanocontacts on the tips of the nanowire.
The authors loaded the nanowires in the experimental scanning transmission electron microscopy configuration in a chamber of an ultrahigh-vacuum. Tungsten probes that were thermally annealed were lowered to the nanowires and one probe with a small bias of 0.2v was brought into contact with the gold particle located at one tip of the nanowire.
Over long storage periods the authors collected data related to the aging of the nanowires. They also realized that zinc oxide atoms shifted approximately 20 nm from the surface of the nanowire, and coated the gold leaving a defective zinc oxide surface. The results of the microscopy analysis confirmed catalyst encapsulation via a strong metal-support interaction, a heterogeneous catalysis phenomenon. It was, however, interesting as this was the first time for the phenomena to be observed in a transition metal oxide gold system at atmospheric pressure and room temperature.
By removing the extraneous material at the interface, the authors eliminated the edge-tunneling path, which yielded a range of transport characteristics dependent on the quality of the final interface.
This study provided an understanding of the zinc oxide diffusion around gold particles owing to a strong metal-support interaction. This created defective edges and the ability to switch between ohmic transport or Schottky transport behavior with simple modifications to a few zinc oxide atoms near the edge of the electrical gold contact. The potential mechanism discussed in this study provides unique possibilities for reactive circuit breakers as well as transient electronics that need materials that will diminish with time and eventually vanish.
Alex M. Lord1, Quentin M. Ramasse2, Despoina M. Kepaptsoglou2, Jonathan E. Evans3, Philip R. Davies4, Michael B. Ward5, and Steve P. Wilks6. Modifying the interface edge to control the electrical transport properties of nanocontacts to nanowires. Nano Letters, volume 17 (2017), pages 687−694. (DOI: 10.1021/acs.nanolett.6b03699)Show Affiliations
- Centre for NanoHealth, College of Engineering, University of Swansea, Singleton Park SA2 8PP, United Kingdom
- SuperSTEM Laboratory, SFTC Daresbury Campus, Keckwick Lane, Daresbury WA4 4AD, United Kingdom
- Centre for NanoHealth, College of Science, University of Swansea, Singleton Park SA2 8PP, United Kingdom
- Cardiff Catalysis Institute, School of Chemistry, Cardiff University, Park Place, Cardiff CF10 3AT, United Kingdom
- Institute for Materials Research, University of Leeds, Leeds, LS2 9JT United Kingdom
- Multidisciplinary Nanotechnology Centre, Department of Physics, College of Science, University of Swansea, Singleton Park SA2 8PP, United Kingdom
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