We have realized a high-detection-efficiency photon number resolving detector at an operating wavelength of about 850 nm. The detector consists of a titanium superconducting transition edge sensor in an optical cavity, which is directly coupled to an optical fiber using an approximately 300-nm gap. The gap reduces the sensitive area and heat capacity of the device, leading to high photon number resolution of 0.42 eV without sacrificing detection efficiency or signal response speed. Wavelength dependent efficiency in fiber-coupled devices, which is due to optical interference between the fiber and the device, is also decreased to less than 1% in this configuration. The overall system detection efficiency is 98%±1% at wavelengths of around 850 nm, which is the highest value ever reported in this wavelength range.

Thin films of multiferroic (Bi0.6Tb0.3La0.1)FeO3 were grown on Pt∕Ti∕SiO2∕Si substrate under various oxygen pressures by pulsed laser deposition technique. X-ray diffraction patterns show that the crystallinity of the thin film is improved with decreasing depositing oxygen pressure and the thin film grown at a lower oxygen pressure of 0.01torr exhibits a single perovskite phase with preferred (001) orientation. Leakage current of the as-deposited thin films decreases with decreasing grown oxygen pressure. Significantly, the leakage current of the thin films can be reduced largely by an annealing process at 800°C with flowing oxygen. The annealed thin films show a relatively high resistivity and stable polarization loops with double remnant polarization of about 3μC∕cm2. The conduction properties of the thin films have been well analyzed, and it is indicated that the dominant conduction mechanism is the space-charge-limited conduction for the thin film grown at higher oxygen pressure and the Poole-Frenkel conduction for the thin films grown at lower oxygen pressure.

Photon number resolving detectors based on titanium-transition edge sensors with high speed and high quantum efficiency have been developed for quantum sensors in the fields of quantum information and quantum radiometry. The two devices optimized at wavelengths of interest showed 81% and 64% system detection efficiencies at 850 nm and 1550 nm, respectively. The response speed of the device optimized for a high counting operation is 190 ns, which corresponds to a counting rate over 1 MHz.

Modulated structure of incommensurate composite crystal (Sr 2 Cu 2 O 3 ) 0.70 CuO 2 , ''Sr 14 Cu 24 O 41 ,'' has been investigated by single-crystal x-ray-diffraction method using centrosymmetric (3ϩ1)-dimensional superspace group. In (Sr 2 Cu 2 O 3 ) 0.70 CuO 2 , displacive modulation of O atom in the CuO 2 chain is fairly large. Considering the modulation of bond angles, it has been found that the Cu-O bond in the CuO 2 chain is tilting toward the Cu 2 O 3 ladder in order that the O atom in the chain plays as apical oxygen for the CuO 4 square in the ladder. The bond-valence sum ͑BVS͒ method has been applied to investigate the hole distribution in the modulated structure of (Sr 2 Cu 2 O 3 ) 0.70 CuO 2 . It is indicated that the valence of Cu atom in the Cu 2 O 3 ladder is ϩ2.04, where about 0.03 holes are certainly transferred from the CuO 2 chain through the modulated O atom in the CuO 2 . The BVS calculation has demonstrated that almost all of the holes are prepared in the CuO 2 chain by the large modulation of the Cu-O bond. Cu atoms in the modulated CuO 2 chain have been proved to form hole-ordered structure with next-nearest-neighbor Cu 2ϩ ions separated by Cu 3ϩ ion on the Zhang-Rice singlet site. The periodicity of the hole-ordered structure is five times of the average CuO 2 lattice along the crystallographic c axis, which is compatible with the spin-dimerized state at low temperature. The new model of the two-dimensional hole-ordered structure in the CuO 2 plane has been obtained by the BVS calculation. Furthermore, the two-dimensional configuration of the spin dimers has been successfully derived from the holeordered structure in the CuO 2 plane. It has been concluded that the valences of Cu atoms both in the Cu 2 O 3 ladder and in the CuO 2 chain are well controlled by the modulated O atom in the CuO 2 chain.

We have measured the cathodoluminescence (CL) spectra of silicon dioxide (SiO2) films prepared by a variety of methods and observed peaks at 280, 445, 480, 520, and 640 nm. A comparison of the CL and electron spin resonance spectra of Si-doped quartz glass showed that the 445 and 480 nm peaks originated from oxygen vacancy centers, which were different from E′ centers. From CL measurement of a cross section of thermally grown SiO2 film deposited on a Si substrate, we found that the relative intensities of the 445 and 480 nm peaks were stronger than that of the CL peak at 640 nm. This CL peak was attributed to the nonbridging oxidation hole centers or their precursors. Furthermore, CL measurement of a cross section of a 16 M dynamic random-access memory device revealed that the relative intensity in the gate oxide film was stronger than that in the interlayer oxide film. These data suggest that the content of oxygen vacancy centers increases in the vicinity of the interface between the SiO2 film and the Si substrate relative to that of the nonbridging oxidation hole centers. CL spectroscopy provides us with a large amount of data on defects in the SiO2 film of Si-based electronic devices at the 0.1 μm level.