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To examine the origin of spontaneous noncentrosymmetric molecular dipole orientation of an evaporated film of tris(8-hydroxyquinolinolato) aluminum (Alq 3), overlayer deposition of Alq 3 on the backside of a peeled Alq 3 film was investigated. Although the surface potential (SP) of the backside of the Alq 3 film was negative, the SP showed a positive shift by overlayer deposition of Alq 3. This means that the spontaneous dipole orientation of Alq 3 molecules in the overlayer is opposite to that in the underlayer. A molecular geometric effect due to a bulky molecular shape is proposed as the origin of the noncentrosymmetry.

Long-term measurement of noncentrosymmetric molecular orientation of vacuum-evaporated tris(8-hydroxyquinolinato) aluminum (III) (Alq 3 ) thin film was performed by means of first-order electroabsorption (EA) spectroscopy. This molecular orientation is responsible for the giant surface potential of Alq 3 film, and it might be utilized to nonlinear optical devices. Although the EA response presented reduction, the relaxation time constant was on the order of year. Possible mechanisms for the reduction are discussed.

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We report an instrument with the combination of solution jet beam deposition method and ultraviolet photoelectron spectroscopy (UPS). The solution jet beam method is a novel technique to fabricate organic thin films in vacuum, where solution of the organic material is sprayed in vacuum. This method can be applied to organic materials which cannot be vacuum evaporated due to thermal decomposition, e.g., ionic organic solids such as cyanine dyes. The present instrument combines this method with UPS, which is a powerful method for investigating the electronic structure of solids. Using this instrument, the UPS spectra of cyanine dye films deposited by the solution jet beam method were measured without exposure to air. The observed spectra were clearer than those of spin-coated films exposed to air.

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We report ultraviolet photoelectron spectroscopy (UPS) measurements of cyanine dye films fabricated by solution jet beam method without exposure to air. The solution jet beam method is a novel technique to fabricate organic thin films in vacuum, where solution of the organic material is sprayed in vacuum. This method can be applied to organic materials which cannot be vacuum-evaporated due to thermal decomposition, as in the case of cyanine dyes. The observed spectra were sharper than those of spin-coated films exposed to air, demonstrating the advantage of the present approach. The spectra were compared with the results of density functional theory (DFT) calculations.