A zinc oxide (ZnO) nanorod array exhibiting an intense deep-level emission (DLE) was probed at the Zn K edge (9659 eV) using extended x-ray absorption fine structure (EXAFS) analysis. X-ray excited optical luminescence was used to obtain site-specific information around the absorbing Zn atom using optically detected EXAFS (ODXAS). The visible-emission corresponds to defects in ZnO crystal lattice introduced during growth. A comparative study between red (660 nm) and green (500 nm) DLE was conducted by collecting specific wavelength emissions of the optically detected x-ray absorption spectra. It was shown that red emission primarily originates from the nanorod surface, and green emission was linked to disorder occurring on Zn sites. We show that ODXAS can distinguish between two emission regions and provides a platform to link defect emission with specific crystal structures.
Both angle-dispersive and EXAFS experiments have been carried out to investigate the structural ordering of the high-pressure (hp) and high-pressure high-temperature (hp/ht) phases of GaSb. The diffraction patterns of all the different phases of GaSb have shown an absence of long-range order, while the EXAFS studies have demonstrated the lack of complete short-range order. GaSb is the only semiconductor compound among the III–V and II–VI systems to present such behaviour in all of its different hp and hp/ht phases.
We demonstrate a spectroscopic imaging based super-resolution approach by separating the overlapping diffraction spots into several detectors during a single scanning period and taking advantage of the size-dependent emission wavelength in nanoparticles.This approach has been tested using off-the-shelf quantum dots (Invitrogen Qdot) and inhouse novel ultra-small (~3 nm) Ge QDs.Furthermore, we developed a method-specific Gaussian fitting and maximum likelihood estimation based on a Matlab algorithm for fast QD localisation.This methodology results in a three-fold improvement in the number of localised QDs compared to non-spectroscopic images.With the addition of advanced ultrasmall Ge probes, the number can be improved even further, giving at least 1.5 times improvement when compared to Qdots.Using a standard scanning confocal microscope we achieved a data acquisition rate of 200 ms per image frame.This is an improvement on single molecule localisation super-resolution microscopy where repeated image capture limits the imaging speed, and the size of fluorescence probes limits the possible theoretical localisation resolution.We show that our spectral deconvolution approach has a potential to deliver data acquisition rates on the ms scale thus providing super-resolution in live systems.
We have developed new concepts and successfully prepared large area, ordered, and compact nanowire arrays for surface-enhanced Raman scattering applications. These nanowire films were synthesized via electrodeposition using porous alumina templates of varying order, thickness and pore diameters. Mechanical polishing has been shown to be a very effective method to prepare nanowire arrays with monodisperse length over comprehensively large dimensions. On the other hand, a convenient synthesis route has been suggested that allows the formation of nanoparticle arrays using very thin and/or large area porous alumina films. It is reckoned that even films with the smallest obtainable pore sizes can be utilized to prepare large area, fine nanoparticle arrays. Such arrays may also find use in other areas, such as solar cells and electrochemistry. Preliminary Raman experiments indicated that the nanowire/nanoparticle arrays are indeed surface-enhanced Raman scattering-active. Finally, the potentials offered by the reported processing methods for fabricating substrates with predictable and high Raman amplifications are discussed.
The study of the G-mode pressure coefficients of carbon nanotubes, reflecting the stiff sp2 bond pressure dependence, is essential to the understanding of their extraordinary mechanical properties as well as fundamental mechanics. However, it is hindered by the availability of carbon nanotubes samples only as bundles or isolated with surfactants. Octadecylamine functionalized carbon nanotubes are mostly of a single diameter and can be stably dispersed in 1, 2-dichloroethane and chloroform without surfactants. Here we perform high pressure Raman spectroscopy on these tubes and obtain their experimental G-mode pressure coefficients for individual tubes and bundles. The G-plus pressure coefficient for bundles is only about half of that for individual tubes in 1, 2-dichloroethane and is about two-thirds in chloroform. The G-minus pressure coefficient for bundles is about one-third of G-plus in 1, 2-dichloroethane and about the same in chloroform. These results for the first time provide unambiguous experimental evidence of the significant effect of bundling on carbon nanotubes' G-mode pressure coefficients, identifying it as one of the major reasons for the lack of consensus on what the values should be in the literature.
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