Characteristics of microdomains and microdomain patterns recorded by electron beam irradiation on Y-cut LiNbO_3 crystals

摘要

We present the results of investigations of planar domain patterns (isolated domains and domain gratings) fabricated by irradiation of the nonpolar Y-surface of LiNbO_3 crystals by an electron beam (EB) incident normally onto the surface. The EB recorded domains were investigated using atomic force microscopy, confocal second harmonic generation microscopy, and chemical etching as an auxiliary method. The dependence of the domain characteristics on irradiation conditions (acceleration voltage U, EB current I, and irradiation time t_(irr)) were determined. The length L_d of both isolated domains and domain gratings along the polar axis Z grows linearly with t_(irr) (at U, I = const) with no tending to saturation. The plots L_d(t_(irr)) obtained for U = 10 and 15 kV are practically identical, whereas the values of L_d for U = 5 kV are essentially lower. The domain thickness T_d along the Y-direction, i.e., the depth of the switched layer grows with acceleration voltage U. These results are discussed in terms of space-charge fields formation arising under EB irradiation of insulators. The linearity of L_d(t_(irr)) is accounted for by the frontal domain growth via the viscous friction law. The experimental dependence of T_d on U supports the suggestion that the domain thickness is determined by the penetration depth R_e of primary electrons, which in turn is governed by U. The difference in L_d(t_(irr)) plots for different U is accounted for by different electron emission σ. Indirect evidences of a defect structure modification in a thin surface layer with respect to the crystal bulk are obtained.