| AVS 54th International Symposium | |
| Nanometer-scale Science and Technology | Wednesday Sessions |
| Session NS2+EM-WeA |
| Session: | Nanoscale Devices and Nanowires II |
| Presenter: | R.A. Rosenberg, Argonne National Laboratory |
| Authors: | R.A. Rosenberg, Argonne National Laboratory G.K. Shenoy, Argonne National Laboratory P.S.G. Kim, University of Western Ontario, Canada T.K. Sham, University of Western Ontario, Canada |
| Correspondent: | Click to Email |
Due to quantum confinement effects nanostructures often exhibit unique and intriguing fluorescence behavior. X-ray excited optical luminescence (XEOL) provides the capability to chemically map the sites responsible for producing low energy (1-6 eV) fluorescence. By taking advantage of the time structure of the x-ray pulses at the Advanced Photon Source (APS, ~80 ps wide, 153 ns separation) it also possible to determine the dynamic behavior of the states involved in the luminescence. In this presentation we show how this technique can be utilized to understand the XEOL from silicon nanowires (~50 nm diameter). Analysis of the XEOL spectra revealed the presence of three peaks at 475, 540, and 640 nm whose breadth increased with increasing wavelength. To gain insight into the dynamic nature of the luminescence, time-gated spectra were obtained as the x-ray energy was varied through the Si K edge. Data were obtained using 15-140 ns and a 0-10 ns gates. For the long time gate the areas are roughly evenly distributed among each of the peaks. However, in the short time gated data the 640 nm peak is dominant. This clearly demonstrates that the relative lifetime of this state is shorter than the other two. This is in contrast to the conventional wisdom for homo-structured and single component materials, for which the lifetime usually increases with wavelength. By extracting the intensity of each peak as the x-ray energy is scanned thru the Si K edge we are able to demonstrate that the 540 nm luminescence emanates from the Si nano crystallites imbedded in the wire, the 475 nm peak originates from the oxide shell, and the 640 nm peak comes from defects located near the Si-SiO interface.
*Use of the Advanced Photon Source was supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.