Laser Manipulation of Single Nanoparticles
Nanoparticles have received much attention and have been investigated as one of the representative materials in nanoscience and nanotechnology. They show interesting properties originating from their intermediate size between single atoms and bulk. For ex
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10.1
Introduction
Nanoparticles have received much attention and have been investigated as one of the representative materials in nanoscience and nanotechnology. They show interesting properties originating from their intermediate size between single atoms and bulk. For example, it is reported by Nakanishi et al. as described in Chap. 14 that colloidal solutions of perylene and 4'-dimethylamino-Nmethylstilbazolium p-toluensulfonate nanoparticles show size-dependent extinction spectra. Also, it is well known that gold particles of several decades of nanometers show a distinct absorption band in the visible region as a result of surface plasmon resonance. In many cases, studies of nanoparticles have been conducted for an ensemble of many particles, so that distributions in size, shape, defect, and so on, are usually neglected in consideration of their physical and chemical properties. This was of course due to the difficulty in manipulating, spectroscopically investigating, and fabricating individual nanoparticles. There is a strong need to develop methods for manipulating, spectroscopically investigating, and fabricating nanoparticles one by one. Indeed, it is recognized that the manipulation and fixation method is one of the key techniques for various fields of nanoscience and nanotechnology. Selforganization [1,2] and surface modification of substrates [3] are useful for pattern formation of nanoparticles, particularly to arrange many nanoparticles spatially on a substrate. In principle, however, these methods cannot control individual nanoparticles. It is also quite common to apply a scanning probe microscope (SPM) for nanomanipulation at the present stage of investigation. The SPM manipulation method enables one to manipulate particles with size from a few nanometers to a few tens of nanometers on certain substrates at room temperature in ambient air [4,5]' while three-dimensional manipulation, spectroscopic characterization, and chemical fixation of individual nanoparticles in solution at room temperature is considered to be difficult. Laser manipulation is a very useful method to handle fine objects in small domains. Indeed application of laser manipulation enables us to trap, manipulate, characterize, modify, and fabricate small particles in solution under an optical microscope at room temperature [6-9]. Most studies have been concentrated on Jlm sized objects such as polymer beads, crystals, biocells, H. Masuhara et al. (eds.), Single Organic Nanoparticles © Springer-Verlag Berlin Heidelberg 2003
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and so forth, while application for nanometer-sized objects has been rarely explored because of the difficulty of identifying invisible nanometer-sized objects. However, it has been recently demonstrated that 10-20 nm sized polymer chains could be trapped and assembled in solution at the focal point of a trapping beam [10]. Also, Svoboda and Block have shown how to trap a single 36 nm diameter gold particle in water [11]. Furthermore methods for fixing micrometer-sized particles [12] and nanopa
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