Molecular-level understanding of transport and optic properties of doped oxide nanoclusters
EMSL Project ID
19595
Abstract
In this proposal, a research plan to investigate ferromagnetic zinc oxide (ZnO) nanoclusters is outlined. ZnO is a widely studied material due to its wide-band gap energy of 3.3 eV at room temperature that has attracted tremendous interest as a blue light emitting material, a buffer layer for GaN-based devices and a transparent conductor in solar cells. As we go into the nano regime of ZnO, band gap energy increases due to confinement and a large blue shift in photoluminescence is observed. ZnO can be doped with variety of transition metals to form a diluted magnetic semiconductor (DMS). Even though pure ZnO is not magnetic, ZnO doped with transition metals like Co, in very small concentration as 2% of the total volume is ferromagnetic at room temperature. The ferromagnetic semiconductor has an application in non-volatile memory storage devices and spintronics. By manipulating spins, rather than charge, it is anticipated that more energy-efficient memory storage will be developed. We prepare pure ZnO and doped ZnO nanoparticles by a technique that is a combination of magnetron sputtering and gas-aggregation and study their transport, optic, and magnetic properties. The Zn atoms along with transition metal atoms are sputtered out of metallic Zn-transition metal target into the oxygen atmosphere, where they form clusters by aggregation. Cluster size is observed using transmission electron microscopy (TEM). The sizes of the nanoclusters should be small such that quantum confinement and surface effects will play dominant roles in the optical properties. Ultraviolet-photoluminescence (UV-PL) measurements done on pure ZnO nanocluster samples, showed a blue shift of the PL energy in comparison with bulk samples. Ferromagnetism and UV-PL are both observed at room temperature for transition metal-doped ZnO nanocluster films. Magnetic measurements are conducted using SQUID magnetometer. The properties vary with the dopant element and the concentration of dopants. The optical and ferromagnetic properties of the clusters needs to be studied as a function of size and concentration. In order to improve our understanding and control of molecular-level structural, optical, and transport properties of nanoclusters interfaces for applications of solid-oxide fuel cell, chemical sensors, and solid-state lighting, we will need to pursue further studies on the interfacial phenomena studies of surface and atomic composition for doped nanoclusters. To understand the semiconducting oxides and cluster interfaces, specific tools with high resolution are required to probe the clusters. The study on oxidation states of our doped cluster oxides are necessary as the oxygen plays a major role in the characteristics of the samples. For characterization of the samples, we would like to make use of the facilities at EMSL like XRD, XPS, AFM, TEM, PL and Accelerator measurements.
Project Details
Project type
Large-Scale EMSL Research
Start Date
2006-08-24
End Date
2009-09-30
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members
Related Publications
Antony J, and Y Qiang. 2007. "Cathodoluminescence from a device of carbon nanotube-field emission display with ZnO nanocluster phosphor." Nanotechnology 18(29):295703. doi:10.1088/0957-4484/18/29/295703
Wang CM, LV Saraf, and Y Qiang. 2008. "Microstructures of ZnO films deposited on (0001) and r-cut α-Al2O3 using MOCVD." Thin Solid Films 516(23):8337-8342. doi:10.1016/j.tsf.2008.04.001