We describe a toolbox, implemented in Matlab, for the computational modelling of optical tweezers. The toolbox is designed for the calculation of optical forces and torques, and can be used for both spherical and nonspherical particles, in both Gaussian and other beams. The toolbox might also be useful for light scattering using either Lorenz-Mie theory or the T-matrix method.

First measurements of oxygen grain boundary diffusion coefficients in nanocrystalline yttria-doped ZrO2 (n-ZrO2⅐6.9 mol % Y2O3) are presented. The 18 O diffusion profiles measured by secondary ion mass spectroscopy are much deeper in the nanocrystalline specimens than in single crystals. An oxygen diffusivity, D B, in the grain boundaries can be deduced, which is Ϸ3 orders of magnitude higher than in single crystals. From the present data the temperature variation of the oxygen grain boundary diffusivity, D B ‫؍‬ 2.0 ؋ 10 ؊5 exp (؊0.91 eV͞kBT) m 2 ͞s, and the oxygen surface exchange coefficient, k ‫؍‬ 1.4 ؋ 10 ؊2 exp (؊1.13 eV͞kBT) m͞s, are derived. Y ttria stabilized zirconia (ZrO 2 ⅐Y 2 O 3 ) is widely used as an electrolyte material in solid oxide fuel cells or oxygen sensors. The technological importance of the material arises from its extraordinary oxygen transport properties, which are attributed to an oxygen vacancy mechanism. The replacement of quadrivalent Zr by trivalent Y gives rise to a high concentration of structural oxygen vacancies for charge compensation and stabilizes the cubic phase (1). The structural vacancies dramatically increase the mobility of oxygen ions, and the highest ionic conductivities were reported for Y 2 O 3 concentrations of 7-10 mol % (2).There is a broad interest in reducing the high operating temperatures of solid oxide fuel cells, typically 900-1,000°C, and resulting degradation effects by increasing the oxygen ion conductivity of the electrolyte. In undoped monoclinic nanocrystalline ZrO 2 it was found that the diffusion of oxygen in interfaces is 10 3 to 10 4 times faster than in the bulk of the crystallites (3). The question arises as to whether the high oxygen diffusivities of ZrO 2 ⅐Y 2 O 3 upon doping can be further enhanced by the introduction of a large number of crystallite interfaces. A reason for an enhanced oxygen diffusion could be a loosely packed grain boundary structure, which is well established for pure metals (4), or easy formation of vacancy-type free volumes within the grain boundaries (5). On the other hand, there are reports that oxygen transport across grain boundaries could be impeded by a blocking effect due to space charge layers in the grain boundary region (6) or silica-containing grain boundary phases (7). In the present study, we present direct measurements of the grain boundary diffusion coefficients in nanocrystalline ZrO 2 ⅐Y 2 O 3 , which are accomplished by using 18 O as a tracer and secondary ion mass spectroscopy for depth profiling.Fully dense nanocrystalline ZrO 2 ⅐Y 2 O 3 bulk specimens were synthesized by dc sputtering of a ZrY metal target and crystallite condensation in an argon atmosphere at 240 Pa. Subsequent oxidation by slow exposure to an oxygen atmosphere (2,000 Pa) and in situ uniaxial compaction at high pressures (2 GPa) yielded disk-shaped specimens 5 mm in diameter with a relative mass density ͞ 0 Ϸ89% of the green body and a mean crystallite size Ͻ5 nm. From the sputter target with the composition of Zr 84 Y 16 , speci...

We integrate the optical elements required to generate optical orbital angular momentum into a microdevice. This allows the rotation of either naturally occuring microparticles or specially fabricated optical rotors. We use a two photon photopolymerization process to create microscopic diffractive optical elements, customized to a wavelength of choice, which are integrated with micromachines in microfluidic devices. This enables the application of high optical torques with off-the-shelf optical tweezers systems.

We present a controlled stress microviscometer with applications to complex fluids. It generates and measures microscopic fluid velocity fields, based on dual beam optical tweezers. This allows an investigation of bulk viscous properties and local inhomogeneities at the probe particle surface. The accuracy of the method is demonstrated in water. In a complex fluid model ͑hyaluronic acid͒, we observe a strong deviation of the flow field from classical behavior. Knowledge of the deviation together with an optical torque measurement is used to determine the bulk viscosity. Furthermore, we model the observed deviation and derive microscopic parameters.