Naoyuki Ohnishi

Ultra-Precision Float Polishing of Calcium Fluoride Single Crystals for Deep Ultra Violet Applications

Abstract High purity calcium fluoride (111) single crystals were float polished to a flatness of 32 nm p-v on 90-mm-diameter samples that had a surface roughness of 0.72 nm Ry, and 0.077 nm rms, as measured with a Scanning Probe Microscope (SPM). By observing an area of a float-polished surface with a high resolution transmission electron microscope, it was determined that the float-polished surface had a perfect (111) lattice with small atomic steps, and no subsurface damage. The polished surface roughness depends on the mismatch between the sample surface and the (111) plane. This result was also verified by SPM observation.

Epitaxial growth and characterization of stoichiometric LiNbO3 films prepared by the sol-gel method

After stoichiometric LiNbO3 thick films were deposited on z-cut LiNbO3 substrates using the sol-gel method from a precursor solution containing various polyvinyl alcohol (PVA) concentrations, their characteristics were investigated. The film thickness increased linearly with the increase in PVA and precursor concentrations. The orientation relationships between films and substrates were determined by x-ray diffraction, Raman spectroscopy, and transmission electron microscopy, and the results showed that (006) oriented LiNbO3 epitaxial layers with parallel epitaxial relationships could be grown on a z-cut LiNbO3 substrate. The refractive indexes of the films were n0=2.28±0.02 and ne=2.19±0.02 at a wavelength of 632.8nm, and their transmission loss was 0.50±0.04dB∕cm.

Epitaxial Growth of Er, Ti Doped LiNbO3 Films Prepared by Sol–Gel Method

Erbium (Er3+) doped lithium niobate (LiNbO3) thick films were deposited on z-cut congruent LiNbO3 (LN) substrate by the sol–gel method from the 0.20 mol/dm3 precursor solution containing various Er3+ concentration and 0.10 mol/dm3 poly(vinyl alcohol) (PVA), and their crystal characteristics were evaluated. The Er3+ concentration in the LN film was controlled by the Er3+ concentration in the starting solution. The orientation relationships between Er doped LN films and substrates were determined by X-ray diffraction, Raman spectroscopy, and transmission electron microscopy, and (006) oriented Er doped LN epitaxial layers with parallel epitaxial relationships could be grown on the z-cut LN wafer. Moreover, it was made clear from the electron beam diffraction measurements that the film came to be polycrystalline, when the Er concentration was over 3 mol %. The refractive index of Er-doped LN films decreased with increasing Er concentration. 1.5 mol % Ti:1.0 mol % Er LN films, which acted as a waveguide, were prepared by our sol–gel method. It showed the 1530 nm emission by 980 nm excitation, which was considered to be due to the Er3+ corresponding to the 4I13/2 →4I15/2 transition.

HRTEM analysis of Pt/C multilayers

High-resolution transmission electron microscopy (HRTEM) studies were performed on Pt/C multilayers fabricated for x-ray mirror optics. The multilayers with d-spacing of about 4 nm were deposited either by dc-magnetron sputtering or by ion-beam sputtering on commercially available Si wafer substrates. Atomic resolution TEM observations and selected area electron diffraction (SAED) of cross-sections of multilayers were made by using several TEM apparatus including an ultra-high-voltage TEM with theoretical point resolution of 0.10 nm. The HRTEM and SAED studies showed that the multilayer consisted of amorphous C layers and polycrystalline Pt layers having a texture with the Pt <111> axes oriented normal to the interface. The Pt grain size perpendicular to the layers was of about the layer thickness, while the grain size along the layers varied in a range up to 10 nm. Detailed analysis of the HRTEM images indicated that the interface of the multilayer was basically defined as surface of the Pt crystal grains, and the interface roughness originated in an arrangement of the grains. Interface broadening observed in the image was primarily attributed to the averaging of the roughness due to Pt grains.