Abstract: The α-Fe₂O₃ ultrafine particles coated with a layer of stearic acid(ST) were prepared by phase transfer method.There is a significant red shift of optical absorption band edge with the decrease of size particles which exhibits the dielectric confinement effect. The effect of dielectric confinement on the electrochemical and photoelectrochemical properties of α-Fe₂O₃ ultrafine particles was investigated by using cyclic voltammetry and photocurrent measurement.The coating layer with smaller dielectric constant decreases the shielding to the electric lines,so that the platinum electrode deposed by the coated particles is more electrochemically reversible than by the naked particles.Acathodic photocurrent is observed with both kinds of particles in the region of-600～267 mV,but there is a fine distinction in the cathodic photocurrent of two kinds of electrodes,which comes from the dielectric confinement effect.Aweak anodic photocurrent is observed in the potential region of>260 mV.

Key words: α-Fe₂O₃ ultrafine particles, Dielectric confinement effect, Photoelectrochemistry