PURPOSE: To perform modification of surface of fine particles obtg. a surface contg. scarce anisotropic part without requiring a drying stage nor heating stage by decomposing molecules of gas adsorbed to the surface of fine particles at low temp. and causing deposition of decomposed product on the surface by irradiating the surface with electron beams.

CONSTITUTION: A sample 10 is prepd. by sticking fine particles such as fine Si particles having about 100nm particle size which has been prepd. separately by evaporating Si in gas utilizing arc discharge, to the surface of a collodion film. The sample 10 is mounted between magnetic poles 50 in a sample chamber 40 and gaseous WF6 20 is introduced to near the sample 10. A layer of absorbed W formed on the surface of fine Si particles is irradiated with electron beams generated by an electron beam source 1 such as transmission electron microscope. Thus, W cluster is formed. The size and the film thickness of the cluster during the growth of the cluster are adjusted by confirming on a fluorescent screen provided in a camera chamber 30.