Jae Hyeok Jang

Measurement of the linear electro-optic coefficients of sol-gel derived strontium barium niobate thin films using a two-beam polarization interferometer

A two-beam polarization interferometer in a reflection configuration is used to measure the electro-optic coefficients of highly oriented strontium barium niobate thin films prepared by a sol-gel method. The technique enables the determination of the electro-optic coefficients of films using a strong Fabry–Perot effect with automatic adjustment and maintenance of the operation point of the interferometer. The linear electro-optic coefficients increase with increasing Sr content in the films.

Photosensitivity of germanium oxide and germanosilicate glass sol-gel films

Abstract Germanium oxide and germanosilicate glass films were fabricated using a sol–gel spin coating method. The formation and photobleaching of the optical absorption band of the films in the 5-eV region were measured as a function of annealing under a reducing atmosphere and ultraviolet (UV) illumination. A greater amplitude in the 5-eV absorption band was observed with increasing annealing time due to the formation of more germanium-related oxygen vacancies in the films. Also, the photobleaching of the absorption band increased with increasing illumination time. Although the amplitude of the absorption band in 50GeO2–50SiO2 glass films is greater than that in germanium oxide glass films because of higher annealing temperature, germanium oxide glass films are more photosensitive due to the greater photobleachable neutral oxygen monovacancy (NOMV) concentration than non-photobleachable neutral oxygen divacancy (NODV) concentration in the films.

Highly oriented (Pb, La)TiO3 thin films prepared by sol-gel process

Highly oriented lead lanthanum titanate (PLT) thin films on MgO (100) and c-plane sapphire single-crystal substrates have been prepared using the sol-gel process. The orientation and the mechanism of the highly preferred oriented PLT films derived sol-gel process have been investigated. The sol-gel PLT films fabricated on MgO (100) and c-plane sapphire substrates grow preferentially with (100) and (111) crystallographic orientations respectively, regardless of the film thickness and La content. In addition, it is confirmed that the tetragonality of the PLT perovskite structure decreases with an increase of La content. The a-axis orientation of the sol-gel PLT film on MgO (100) substrate is controlled only by formation of the intrinsic tensile stress during the crystallization of the film.

Photobleaching of sol-gel-derived germanium oxide glass thin films

Photobleaching of the optical absorption band in the 5-eV region of sol-gel-derived germanium oxide glass thin films was examined with the irradiation of the 5-eV light. The photobleaching represented by the saturated absorption coefficient change (− Da) and the ratio of the neutral oxygen monovacancies to neutral oxygen divacancies concentrations for the germanium oxide were 175 cm −1 and 0.113, respectively. These values are larger than those of the pure germanium oxide bulk glass as well as germanosilicate thin films. The changes in bonding configuration around Ge atom by ultraviolet illumination were analyzed using x-ray photoelectron spectroscopy.

Optical and electrical properties of ferroelectric SBN thin films prepared by sol-gel process

Strontium barium niobate thin films were prepared by sol-gel method on various substrates using an improved process, two-step heating process. The two-step heating process applies an additive heat-treatment before crystallization for enhancement of the densification and the nucleation of films. Also, highly c-axis oriented SBN thin films with various compositions were obtained on MgO(100) and Pt(100)/MgO(100) substrates. Their optical and electrical properties such as optical propagation loss, refractive index, P-E hysteresis, and dielectric constant, were characterized as a function of the film composition.

Preparation and characteristics of seeded epitaxial (Sr,Ba)Nb2O6 optical waveguide thin films using sol-gel method

This work was financially supported by Korea Science and Engineering Foundation, under Grant No. 981-0803-019-2 and partly by the Brain Korea 21 Project.

Nonlinear optical characteristics of sol-gel-derived highly oriented ferroelectric strontium barium niobate thin films

Highly c-axis oriented SBN films with various compositions were obtained on MgO(100) substrates using sol-gel process. Although the sol-gel process has been developed for ferroelectric thin films, it is known as being hard to fabricate highly oriented films. Thus, the preferential orientation of the films was enhanced by two methods: (1) poling the film by a high dc electric field (greater than Ec) and (2) growing the film on an SBN-seeded MgO substrate. The mechanisms of these methods were discussed. For their optical applications, second-harmonic generation (SHG) effect of SBN films was studied. Fundamental beam of Nd:YAG laser with 1064 nm was used as a pump beam. From Maker fringe measurements with a quartz reference, second- order nonlinear optical (NLO) coefficients d of the films were obtained. The second-order NLO coefficients of the films could be enhanced to considerable extent by applying the electric poling and using a self-seeds layer. These phenomena indicate that the SHG effect is sensitive to crystallographic structure as well as ferroelectric polarization. Mathematical equation was derived to correlate this microstructure to the SHG effect of SBN films.