Electric-field-induced second harmonic generation from vacuuni-evaporated metallophthalocyanine film/metal electrode interface

The optical second harmonic generation (SHG) was used to study the redistribution of space charges, which was caused by photoillumination, at the nanosized interface between metal electrode and phthalocyanine (Pc) film. The redistribution of space charges was observed using the SHG spectra, where the space-charge-induced electric field (SCIEF) broke the centrosymmetry of the Pc molecule and gave rise to another effective second order nonlinear polarization aside from the one induced by the second order electric quadrupole. Furthermore, an external bias was applied to the sandwiched metal-copper phthalocyanine (CuPc)-meal sample to induce the second order nonlinear polarization. The quadratic relationship between SHG intensity and the external applied bias was observed. On the basis of the four-layer model, the electric-field-induced SHG (EFISHG) process was analyzed. The theoretical results showed good agreement with the experimental data.