| AVS 55th International Symposium & Exhibition | |
| Electronic Materials and Processing | Tuesday Sessions |
| Session EM-TuM |
| Session: | ZnO Materials and Devices |
| Presenter: | J.E. Whitten, University of Massachusetts Lowell |
| Authors: | J. Singh, University of Massachusetts Lowell J. Im, University of Massachusetts Lowell J.E. Whitten, University of Massachusetts Lowell J.W. Soares, U.S. Army Natick Soldier Center D.M. Steeves, U.S. Army Natick Soldier Center |
| Correspondent: | Click to Email |
Zinc oxide has a unique bimodal photoluminescence spectrum consisting of UV and visible emission peaks, with the latter believed to originate from surface dependent processes. Possibilities exist to tailor the optical properties of ZnO by appropriate surface functionalization. Adsorption of a variety of silanes on nanocrystalline and single crystal zinc oxide surfaces has been investigated toward the goal of modifying the valence electronic structure and photoluminescence spectrum. Adsorbates include various fluorinated, electron-withdrawing silanes and 3-mercaptopropyltrimethoxysilane (MPS). In the case of nanocrystalline ZnO, adsorption has been carried out from solution, and XPS and FTIR confirm successful covalent attachment to the surface. Comparative studies have also been carried out in which sputter-cleaned ZnO(0001) has been dosed in ultrahigh vacuum (UHV) with model silane molecules. MPS has a high enough vapor pressure to be dosed in UHV, and angle-resolved XPS demonstrates adsorption with the sulfur at the vacuum interface, with minimal polymerization of the MPS monolayer. The effect of coadsorbed water has also been investigated by simultaneously exposing clean ZnO(0001) to water and silane vapors. Ultraviolet photoelectron spectroscopy (UPS) has been used to measure the valence electronic spectra and differences between nanocrystalline and ZnO(0001), and the effect of nanoscale dimensions on the ionization energy of the HOMO valence band (mainly due to nonbonding O 2p orbitals) has been studied. The effects of silane adsorption on the UPS spectra has also been investigated, and attempts have been made to correlate these with changes in photoluminescence.