Linear electro-optic tensor ratio determination and quadratic electro-optic modulation of electrostatically self-assembled CdSe quantum dot films

摘要

A new class of CdSe quantum dot-doped polymer films are synthesized using electrostatic layer-by-layer self-assembly processing technique. Transmission electron spectroscopy and electron beam diffraction results show that the diameter of the CdSe quantum dots is 2-3 nm and that the CdSe clusters possess a hexagonal structure. X-ray photoelectron spectroscopy allows determination of the concentration of the CdSe quantum dots within the resulting films. Linear electro-optic (Pockels) and quadratic electro-optic (Kerr) effect behavior of the films are investigated by using Mach-Zenhder interferometric and ellipsometric techniques, respectively. Linear electro-optic tensor ratios r_333/r_113 of 4.3 (+-) 0.2 were determined. Theoretical calculations of the quadratic electro-optic coefficients are proposed for the conventional ellipsometric technique. The orientational enhancement effect originating from the permanent dipole moment and induced dipole moment of the CdSe clusters is also discussed. From the analysis of experimental data, we determine that the typical reorientational time for a CdSe dot in these films to respond to a sinusoidal electric field is 17.5 ms.