SIZE DISTRIBUTION ANALYSIS OF NANOPARTICLES USING SMALL ANGLE X-RAY SCATTERING TECHNIQUE

With recent improvements in nanotechnology, a large variety of nanoparticles have been synthesized. These particles are widely utilized in a large number of applications, including ultrafine wiring, light emitting devices, catalysts, fuel cells, covering materials, adhesion bond, abrasives, ink, medicines in drug delivery system (DDS), real-time PCR kit. However, techniques for evaluating nanoparticles are still in the developing stage. Although there are many techniques for size determination, each particular method usually has both advantages and disadvantages. Equipment must be selected that is appropriate to the shape, state, and size of the sample to be started. The most popular analytical technique is transmission electronic microscope (TEM), whose unique feature is the ability to give information on real images as well as size. However, understanding size distribution using TEM is difficult because a large number (hundreds) of particles is necessary to assure a reliable distribution. Further, manual procedures are usually necessary for the measurement of particles with sizes in 1 to 2 nm range or less, because it is very difficult to estimate the size distribution with image processing alone. Other techniques for particle size evaluation are: dynamic light scattering (DLS), laser diffraction, differential mobility analyzer (DMA), and time-of-flight secondary ion mass spectroscopy (TOF-SIMS). The advantages and the disadvantages of these techniques are listed in Table 1. This report introduces a new method of size distribution analysis: the small-angle X-ray scattering (SAXS) technique. SAXS is preferable to other methods because nondestructive and rapid measurements can be performed for a variety of samples such as thin films, powder, solution, bulk films, etc. SAXS can be readily applied to particles in the range from 1 to 100 nm, although measurements outside this range are also possible. Particles of size ca. 1 to 10 nm in particular can be analyzed with higher accuracy compared to other techniques. (Particles in this range will be referred to as “small” particles.) In this paper, the principle of size distribution analysis will be described, and SAXS results of various nanoparticles will be examined.