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19 Feb 2001

Volume 78, Issue 8, pp. 1023-1163

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Preparation and photoluminescence of highly ordered TiO2 nanowire arrays

Y. Lei, L. D. Zhang, G. W. Meng, G. H. Li, X. Y. Zhang, C. H. Liang, W. Chen, and S. X. Wang

Appl. Phys. Lett. 78, 1125 (2001); http://dx.doi.org/10.1063/1.1350959 (3 pages) | Cited 168 times

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Highly ordered TiO2 nanowire (TN) arrays were prepared in anodic alumina membranes (AAMs) by a sol-gel method. The TNs are single crystalline anatase phase with uniform diameters around 60 nm. At room temperature, photoluminescence (PL) measurements of the TN arrays show a visible broadband with three peaks, which are located at about 425, 465, and 525 nm that are attributed to self-trapped excitons, F, and F+ centers, respectively. A model is also presented to explain the PL intensity drop-down of the TN arrays embedded in AAMs: the blue PL band of AAMs arises from the F+ centers on the pore walls, and the TNs first form in the center area of the pores and then extend to the pore walls. © 2001 American Institute of Physics.
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81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
81.07.Bc Nanocrystalline materials
78.55.Mb Porous materials
61.46.-w Structure of nanoscale materials
71.35.Aa Frenkel excitons and self-trapped excitons

Large-scale production of nanocrystals by laser ablation of microparticles in a flowing aerosol

W. T. Nichols, J. W. Keto, D. E. Henneke, J. R. Brock, G. Malyavanatham, M. F. Becker, and H. D. Glicksman

Appl. Phys. Lett. 78, 1128 (2001); http://dx.doi.org/10.1063/1.1347385 (3 pages) | Cited 26 times

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We experimentally demonstrate the production of nanoparticles by laser ablation of microparticles entrained at high density in a flowing aerosol. The currently measured production rate of 20 grams per hour could be scaled to industrially useful rates. We have characterized the size distribution of particles and found nearly monodisperse distributions where mean sizes were smaller and varied less with laser fluence than was observed for ablation of microparticles held on flat plates. Mean size was controlled from 4–20 nm by varying the type and pressure of carrier gas. We found Ag and CdSe nanoparticles were crystalline having few dislocations. Materials tested included metals (Ag, Au, and W), semiconductors (Si, CdSe, GaN, and ZnO), ceramics (WC, SiC, and YBa2Cu3O7), and a ferroelectric. Two types of collection processes are described that preserve the nonagglomerated nature of the particles, even at high mass densities. © 2001 American Institute of Physics.
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52.38.Mf Laser ablation
79.20.Ds Laser-beam impact phenomena
81.20.Rg Aerosols in materials synthesis and processing
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
81.07.Bc Nanocrystalline materials

Stimulated blue emission in reconstituted films of ultrasmall silicon nanoparticles

M. H. Nayfeh, N. Barry, J. Therrien, O. Akcakir, E. Gratton, and G. Belomoin

Appl. Phys. Lett. 78, 1131 (2001); http://dx.doi.org/10.1063/1.1347398 (3 pages) | Cited 77 times

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We dispersed electrochemical etched Si into a colloid of ultrabright blue luminescent nanoparticles (1 nm in diameter) and reconstituted it into films or microcrystallites. When the film is excited by a near-infrared two-photon process at 780 nm, the emission exhibits a sharp threshold near 106 W/cm2, rising by many orders of magnitude, beyond which a low power dependence sets in. Under some conditions, spontaneous recrystallization forms crystals of smooth shape from which we observe collimated beam emission, pointing to very large gain coefficients. The results are discussed in terms of population inversion, produced by quantum tunneling or/and thermal activation, and stimulated emission in the quantum confinement-engineered Si–Si phase found only on ultrasmall Si nanoparticles. The Si–Si phase model provides gain coefficients as large as 103–105 cm−1. © 2001 American Institute of Physics.
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78.66.Db Elemental semiconductors and insulators
78.45.+h Stimulated emission
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Ap Elemental semiconductors
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