Production of III-V Nanocrystals by Picosecond Pulsed Laser Ablation
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Production of III-V Nanocrystals by Picosecond Pulsed Laser Ablation M. H. Wu, R. Mu, A. Ueda and D. O. Henderson Department of Physics, Fisk University Nashville, TN 37208
ABSTRACT InAs nanoparticles have been produced by picosecond pulsed laser ablation of bulk targets in the presence of an inert backing gas. Atomic force microscopy measurements show particles ranging in size from one to ten nm. Stoichiometry of the targets, determined by Rutherford backscattering measurements, are typically preserved within ten percent. Optical absorption and raman scattering data help confirm the crystalline, quantum confined nature of the nanoparticles. INTRODUCTION Laser ablation has many properties which make it an attractive technique for the production of nanoparticles. The growth of nanoparticles produced by laser ablation has been shown to occur largely in the plume, before deposition on the substrate.1 Virtually any type of nanoparticle can thus be deposited on any type of substrate, with no regard to lattice parameters or other properties. Laser ablation has been shown to produce extremely small particles, with sizes less than five nanometers commonly reported. In addition, laser ablation by short pulses does not require introduction of an inert backing gas, reducing the potential for introduction of impurities. An inert backing gas may be used, however, to affect particle size distributions. In these cases, ablation is still a relatively clean technique, since impurities are restricted to those found in the backing gas and those in the target (i.e. no precursor material is necessary). Many parameters, such as laser pulse energy, laser wavelength, backing gas pressure, back gas type and sampling distance from the plume center can be used to control the size of particles resulting from laser ablation. Ablation does have some drawbacks, most notably the relatively broad size distributions obtained compared to chemical synthetic techniques and lack of long range order in the deposited particles compared to self – assembled systems.2 Most of the studies of semiconductor nanoparticle production by laser ablation have focused on the single element semiconductor Si and Ge,3 with relatively few reports concerning the formation of multi element semiconductors, such as III-V or II-VI semiconductors, by the pulsed laser ablation process.4 It is thus of interest to study production of binary semiconductors to examine both the “portability” of experimental parameters from single element to binary semiconductors and to examine the preservation of stoichiometry in binary element targets. We report here on studies of formation of InAs nanoparticles by laser ablation, concentrating on the stoichiometry and morphology of the resulting particles. As an initial study, ablation experiments have
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