An antireflection surface with sub-wavelength structure has been successfully fabricated on a fused silica substrate. The fabricated antireflection structured surface consists of a microcone array of fused silica with a period shorter than the wavelengths of visible light. The microcone array is made by a reactive ion etching method using fluorocarbon plasma. A microdisk array of chromium thin film, formed by an electron-beam lithography and lift-off process, is used as the etching mask. Since an electric field induced near the substrate was focused on the edges of the metal disks, these disks gradually shrank. Consequently, a conical shape was formed. The fabricated cone array has a period of 250 nm and a height of 750 nm. Measured reflectivity of the antireflection structured surface is less than 0.5% in the wavelength range of 400–800 nm for normal incidence.

Index-guided two-dimensional (2D) optical waveguides are numerically studied to investigate propagation properties of guided optical waves. The 2D optical waveguide consists of a dielectric thin film sandwiched between two semi-infinite metals. We demonstrate that vertically localized 2D optical waves can be laterally confined and guided by index guiding when the dielectric film has a high-refractive-index core and claddings of a lower index. The index guiding provides good optical power transmittance, otherwise optical power is rapidly attenuated due to lateral beam divergence.

Zinc stannate (Zn2SnO4) thin films were deposited by RF magnetron sputtering on silica substrates at various [O2/(Ar+O2)] flow ratios. The influences of the [O2/(Ar+O2)] flow ratio on the crystalline structure, and the optical and electrical properties have been investigated. No sharp X-ray diffraction (XRD) peaks were observed in as-deposited thin films. After postdeposition annealing in air at 750°C, the thin films showed a preferred orientation of (111). The thin films exhibited a high transmittance in the visible spectrum irrespective of the [O2/(Ar+O2)] flow ratio or postdeposition annealing. The optical band gap was estimated to be 4.1 eV by analyzing the optical spectra of thin films annealed at 750°C. The composition ratio of Zn/Sn for thin films deposited in an Ar/O2 mixture was 2.0 and their electrical resistivity was on the order of 105 Ω·cm. In contrast, the composition ratio of Zn/Sn for a thin film deposited in pure Ar was 1.5 and an electrical resistivity of 4.1 ×10-2 Ω·cm was observed.

We demonstrate feedback cooling of the center-of-mass motion of single charged nanoparticles to millikelvin temperatures in three dimensions via applying oscillating electric fields synchronized to their optically observed motion. The observed motional temperatures at weak feedback agree with a simple model and allow us to estimate the charge number of trapped nanoparticles. The agreement between our model and experiments is confirmed by independent measurements of the charge numbers based on a shift in the oscillation frequency induced by a constant electric field. The demonstrated temperature of below 10 mK at 4 × 10 −3 Pa is lower than that with the conventional optical cooling approach at this pressure by one to two orders of magnitude. Our results form the basis of manipulating cold charged nanoparticles and paves the way to quantum mechanical studies with trapped nanoparticles near their ground state.Manipulating the motion of objects near their quantum ground state has been a crucial subject in diverse fields from quantum simulations [1-3] and quantum information processing [4] to precision measurements [5,6]. Cooling atomic ions and ensembles of neutral atoms to their motional ground state has been successful [2,7]. Specific vibrational modes of nanoand micromechanical oscillators have been brought to their quantum ground state [8,9]. However, cooling the motion of particles including more than a few atoms to their motional ground state has been an elusive goal. The main difficulty lies in the absence of an efficient mechanism for cooling.Cold nanoparticles are expected to possess various applications such as testing quantum mechanics for macroscopic objects [10,11], ultrasensitive force and mass sensing [12][13][14][15][16][17][18], and the laboratory test of the collisional dynamics of interstellar materials [19]. Up to now, cooling the motion of nanoparticles to millikelvin temperatures has been demonstrated via all-optical approaches, where trapping, observing, and cooling them are all based on light scattering [20][21][22][23][24][25]. The lowest temperature achieved with all-optical approaches is finally limited by random photon recoils [26]. To overcome the limitation from photon recoils, an all-electrical approach for highly charged particles has been proposed [27].Here, we show that the motional temperature of single charged nanoparticles in an optical trap is efficiently lowered via the optical measurement of the nanoparticle's position and the application of oscillating electric fields synchronized to their motion. The observed motional temperatures with the electric feedback T eff agree with a simple model only when the mass of the nanoparticle is properly estimated through the time scale of the rethermalization of the motion after it is cooled. The agreement between our model and experimental results is confirmed by independent measurements of the charge number based on the electric-field-induced shift in the oscillation frequency.Compared to the conventional all-optical cooling method, param...

An epitaxial film of CuScO2, a transparent oxide semiconductor with a delafossite structure, was grown on an α−Al2O3(112¯0) substrate by a pulsed laser deposition method using a single-phase Cu2Sc2Oδ target. A two-dimensional x-ray reciprocal space mapping measurement revealed that the film was single phase with a rhombohedral crystal structure. The film showed six-fold rotational symmetry in the basal plane, indicating that the film had a twinned domain structure. The epitaxial growth of CuScO2[3R](0001) thin films on α−Al2O3(112¯0) substrates is caused by the uniaxial locked epitaxy mechanism along the ⟨1¯21¯0⟩ direction of the film, and the orientation relationships of the film with respect to the substrate were CuScO2[3R](0001)∕∕α−Al2O3(112¯0) and CuScO2[3R][1¯21¯0]∕∕α−Al2O3[88¯01]. The optical transmittance of the film was larger than 65% in the visible/near-infrared regions, while the energy gap for direct allowed transition was estimated as 3.7 eV. The resistivity of the film, 9.3×106Ωcm at room temperature, significantly decreased to 4.0 Ωcm after both substituting Mg2+ ions for Sc3+ and intercalating excess oxygen. The Mg-doped CuScO2+X(0001) thin film showed optical transmittance of larger than 65% in the visible region, and the Seebeck coefficient was positive, indicating a p-type conductivity.