An inorganic bonding method providing 100% light transmittance at the bonded interface was proposed for fabricating devices with high optical density. First, we fabricated 5000 nm-thick SiO2 oxide underlayers on synthetic quartz glass wafers. After the film surfaces were polished to reduce surface roughness, the wafers with oxide underlayers were bonded using thin Ti films in vacuum at room temperature as a usual atomic diffusion process. After post annealing at 300 °C, 100% light transmittance at the bonded interface with the surface free energy at the bonded interface greater than 2 J/m2 was achieved. Dissociated oxygen from oxide layers probably enhanced Ti films oxidation, resulting in high light transmittance with high bonding strength attributable to the annealing. Using this bonding process, we fabricated a polarizing beam splitter and demonstrated that this bonding process is useful to fabricate devices with high optical density.

Atomic diffusion bonding of quartz glass wafers using thin Ti films, with SiO 2 underlayers on wafer surfaces, provides 100% light transmittance at the bonded interface along with strong bonding energy, after post-bonded low-temperature annealing. Cross-section images obtained using transmission electron microscopy show that the bonded interface after annealing at 350 °C consists of amorphous structure including nanocrystalline grains. Structural analysis using electron energy loss spectroscopy shows that post-bonded annealing enhances oxidation of Ti with oxygen dissociated from SiO 2 underlayers, and that Ti oxides form close to TiO 2 or Ti 4 O 7 . This oxidation provides 100% light transmittance with high bonding strength attributable to the annealing. Moreover, we applied this technique for bonding glass and sapphire wafers using SiO 2 -Nb 2 O 5 underlayers, demonstrating that 100% light transmittance and control of refractive index matching are achieved simultaneously at the

We study elementary excitations of spin-1 bosons with antiferromagnetic interaction in an optical lattice by applying the Gutzwiller approximation to the spin-1 Bose-Hubbard model. There appear various excitations associated with spin degrees of freedom in the Mott-insulator (MI) phase as well as in the superfluid (SF) phase. In this system, the ground state in the MI phase is known to exhibit a remarkable effect of even-odd parity of particle filling, in which even fillings stabilize the MI state due to formation of spin-singlet pairs. We find that excitation spectra in the MI phase exhibit characteristic features that reflect the even-odd parity effect of the ground state. We clarify evolution of elementary excitations across the quantum critical point of the SF-MI transition.

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