School of Physical and Chemical Sciences Te Kura Matū Seminar Series

Covalently-Bound Organic Modifiers on ZnO: Effects on the Electronic and Chemical Surface Properties

Speaker

Alexandra McNeil, Supervised by Professor Alison Downard (SPCS) and Associate Professor Martin Allen (Department of Electrical Engineering)

Institute

School of Physical and Chemical Sciences, University of Canterbury

Time & Place

Mon, 19 Nov 2018 11:00:00 NZDT in Jack Erskine Lecture Theatre 031

All are welcome

Abstract

Zinc oxide (ZnO) is an earth-abundant semiconductor with a wide band gap, high transparency, and high electron mobility. As such, it is of increasing interest for use in transparent electronic devices such as thin film transistors and ultraviolet photodiodes. Unfortunately, its high surface sensitivity means that in its native state, ZnO is electronically unreliable. Hydroxyl groups on the surface create downwards bending of the conduction and valence bands at the ZnO-air interface, and results in an accumulation of electrons.1 Species such as oxygen and water molecules can physisorb to this hydroxyl layer and further change the electronic properties at the surface. However, through the deliberate attachment of molecular layers to thin films and single crystals of ZnO, the surface band bending can be manipulated, and the rate of adsorption of atmospheric contaminants slowed.

This talk will outline two approaches for ZnO surface modification, namely phosphonic acids2 and aryldiazonium ion chemistry.3 It will discuss the use of atomic force microscopy and X-ray photoelectron spectroscopy to determine the degree of modification success and the corresponding effects on surface band bending. Some differences between the main ZnO crystal faces will be highlighted alongside the challenges of performing electrochemistry at semiconducting surfaces.

 1 Heinhold, R.; Williams, G. T.; Cooil, S. P.; Evans, D. A.; Allen, M. W. Phys. Rev. B 2013, 88 (23), 235315.

2McNeill, A. R.; Hyndman, A. R.; Reeves, R. J.; Downard, A. J.; Allen, M. W. ACS Appl. Mater. Interfaces 2016, 8 (45), 31392–31402.

3 McNeill, A. R.; Bell, K. J.; Hyndman, A. R.; Gazoni, R. M.; Reeves, R. J.; Downard, A. J.; Allen, M. W. J. Phys. Chem. C 2018,122 (24), 12681–12693.