Junmo Koo

Raman spectroscopy of copper phosphate glasses

Abstract Raman spectra of binary copper phosphate glass samples, xCuO · (1 − x)P2O5, having x = 0.4, 0.5, and 0.55 and various [Cu2+]/[Cutotal] ratios have been measured. The Raman spectra of the samples changed with changing [Cu2+]/[Cutotal] ratio as well as CuO content. The smaller ionic size and the greater charge of the Cu2+ ion than those of the Cu1+ ion create larger in-chain POP bond angles and smaller out-of-chain PO2 angle as well as greater CuO field strength. Differing local structures of Cu1+ and Cu2+ ions in phosphate glass results in a variation of Raman spectra of the glasses depending on the [Cu2+]/[Cutotal] ratio. Also, a decrease in phosphate chain length with increasing CuO content affected the Raman spectra of the glasses. Although the crystallization of the samples is not detected in the X-ray diffraction, the overlapping bands in the Raman spectra of the 0.55 CuO samples are attributed to crystalline phases.

Effect of heat treatment on formation of sol-gel (Pb, La)TiO3 films for optical application

Lead lanthanum titanate [(Pb,La)TiO{sub 3}] sol-gel films have been prepared to investigate the effect of heat treatment on the fabrication of uniform and crack-free thick films by applying different heating schedules. The surface morphology as well as the optical properties such as refractive index, optical transmission, and optical propagation loss of the films was examined depending on the film thickness. Because the slower and longer heating is enough to remove the organic and nitrate residues and diminish the thermal shock during heating the films, the slower and longer heating can produce the uniform and crack-free thick films having higher refractive index as well as lower optical propagation loss. Also, the drying and heating the films on hot plate in every coating resulted in the fabrication of thick films having above 8000 {Angstrom} without any defects and microcracks. This film presented the highest refractive index as well as the lowest optical propagation loss which grows exponentially with increasing the film thickness due to the scattering of defects in the film. {copyright} {ital 1997 Materials Research Society.}

Synthesis and Characterization of Highly Oriented Sol-Gel (Pb, La) TiO3 Thin Film Optical Waveguides

The preparation and the optical characteristics of highly oriented PLT thin films are investigated. PLT films fabricated on MgO(100) and c-plane sapphire substrates have highly grown in (100) and (111) orientations, respectively. PLT films with high La content have a near cubic structure and weak anisotropy of refractive indices. The optical propagation losses of PLT films decrease as the La content of the films increases due to a complex interaction of surface roughness reduction and a reduction in the anisotropy refractive index. However, optical scattering in thicker sol-gel PLT thin film waveguides occurs by the internal scattering mechanism from the defects and the interfaces rather than by the surface scattering mechanism.

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.

Preparation and waveguiding properties of sol-gel derived lathanum modified lead titanate slab waveguides

Abstract Using sol-gel processing method, thin films of lathanum modified lead titanate (PLT) on Corning 7059 glass were prepared. Differential thermal analysis (DTA/TG) curve of gel powder and infrared spectra (FT-IR) of the films were measured to estimate proper heating schedule. Microstructures of the films were observed using a scanning electron microscope (SEM). The waveguiding properties and the propagation loss were measured using the prism coupling method. Effects of the drying conditions on the refractive indices and the propagation losses of the films were investigated. Experimental results showed that the grain size and the content of residual organics in the film decreased as the drying temperature of the film increased. As the drying temperature increased, the refractive index increased and the propagation loss decreased.