Formation of Single-phase CuO Quantum Particles
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CuO nanocrystals of three different sizes 3.5, 6.5, and 10.0 nm were synthesized by a novel electrochemical route. Quantum size effects in these nanocrystals are evident from the optical absorption spectra. The optical absorption feature is observed to be blue shifted by about 1 eV with size reduction. The CuO q-particles were found to be single-phased and very stable as far as the size and phase is concerned.
I. INTRODUCTION
Nanoscale quantum dots have been extensively studied to understand the evolving electronic structure from atomic to bulk state. The properties of nanoclusters cannot be described simply as a straightforward extension of molecules or bulk solids. Understanding the fundamental properties of semiconducting quantum dots relies on the ability to synthesize nanocrystals having a narrow size distribution with well controlled surfaces and defects. Although extensive research is being carried out on developing methods for growth and characterization of II–VI semiconductor nanoparticles, semiconducting oxide nanoparticles have been comparatively less studied. There has been considerable interest in the study of CuO and other copper oxygen systems1–6 mainly because they form the basis of technologically important materials such as high-Tc superconductors and materials showing giant magnetoresistance. Cupric oxide is exceptional among the 3d transition metal oxides. The crystal structure of CuO is monoclinic7 whereas other 3d transition metal monoxides are cubic. The Cu–O bond is covalent, and it also depicts the many body complications in its electronic structure. CuO has an open 3d shell (3d 9 ). The electronic structure of single-crystalline and polycrystalline CuO has been investigated using electron spectroscopies.8–10 Nanocrystalline CuO, however, has not been studied in detail. It would be highly interesting to study the size dependence on correlation effects and antiferromagnetic ordering in CuO quantum particles. Recently, few reports on size-induced effects in CuO, NiO, and CoO nanoparticles11–24 have been published. Orel et al.17 have carried out structural studies on CuO nanoparticles having size 60 nm while Xu et al.18 have reported Raman studies on CuO nanoparticles. The mag-
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J. Mater. Res., Vol. 17, No. 5, May 2002 Downloaded: 25 Nov 2014
netic properties of oxide nanoparticles have attracted considerable attention.19–22 Oxide nanoparticles with size ranging from 6 to 10 nm have been investigated.19–22 X-ray photoelectron spectroscopic studies11,12,24 on CuO nanoparticles address the question of stability of the CuO phase. Here we discuss the formation of q-particles of copper oxide using a novel electrochemical route. Quantum size effects are visible in optical spectroscopic studies. Stable, single-phase CuO nanocrystals, having sizes 3.5, 6.5, and 10 nm, have been synthesized. Earlier,15 it has been proposed that CuO nanoparticles having size less than 25 nm are not stable; cubic cuprous oxide is forme
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