Rinsing microstructures on a patterned semiconductor wafer is modeled. The simulation results are presented for two cases when the surfaces of a trench as the microstructure are made of a single material, or two different materials. The dynamics of contaminant removal from the microstructure surfaces and its dependence on the geometrical structure, physical characteristics of the surfaces, and contaminant diffusivity are presented. The results show that in the case of a trench with two different materials, the cleaning dynamics of the trench bed strongly depends on the stacking order of the materials. When the upper material has a smaller desorption rate coefficient, the dynamics of contaminant transport develops a smaller rate at some point in time that depends on the thickness of the layers. (C) 2014 Elsevier Ltd. All rights reserved.

We demonstrate a variable focal length achromatic lens that consists of a flat liquid crystal diffractive lens and a pressure-controlled fluidic refractive lens. The diffractive lens is composed of a flat binary Fresnel zone structure and a thin liquid crystal layer, producing high efficiency and millisecond switching times while applying a low ac voltage input. The focusing power of the diffractive lens is adjusted by electrically modifying the sub-zones and re-establishing phase wrapping points. The refractive lens includes a fluid chamber with a flat glass surface and an opposing elastic polydimethylsiloxane (PDMS) membrane surface. Inserting fluid volume through a pump system into the clear aperture region alters the membrane curvature and adjusts the refractive lens' focal position. Primary chromatic aberration is remarkably reduced through the coupling of the fluidic and diffractive lenses at selected focal lengths. Potential applications include miniature color imaging systems, medical and ophthalmic devices, or any design that utilizes variable focal length achromats.

We demonstrate an innovative variable-focus flat liquid-crystal diffractive lens (LCDL) with 95% diffraction efficiency and millisecond switching times using a +/-2.4 V ac input. This lens is based on the electrical modulation of a 3 mum layer of nematic liquid-crystal sandwiched between a Fresnel zone electrode structure and a reference substrate. Each zone is divided into 12 subzones to digitize the phase profiles and define the phase wrapping points. The focusing power can rapidly be switched by electrically changing the number of subzones and re-establishing the wrapping points. Potential applications include zooms with no moving parts and autofocus lenses for compact imaging devices.

Non-mechanical variable lenses are important for creating compact imaging devices. Various methods employing dielectrically actuated lenses, membrane lenses, and/or liquid crystal lenses were previously proposed(1-4). Here we present tunable-focus flat liquid crystal diffractive lenses (LCDL) employing binary Fresnel zone electrodes fabricated on Indium-Tin-Oxide using conventional micro-photolithography. The phase levels can be adjusted by varying the effective refractive index of a nematic liquid crystal sandwiched between the electrodes and a reference substrate. Using a proper voltage distribution across various electrodes the focal length can be changed. Electrodes are shunted such that the correct phase retardation step sequence is achieved. If the number of 2 pi zone boundaries is increased by a factor of m the focal length is changed from f to f/m based on the digitized Fresnel zone equation: f = r(m)(2)/2m lambda, where r(m) is m(th) zone radius, and lambda is the wavelength.The lenses operate at very low voltage levels (+/- 2.5V ac input), exhibit fast switching times (20-150 ms), can have large apertures (> 10 mm), and small form factor, and are robust and insensitive to vibrations, gravity, and capillary effects that limit membrane and dielectrically actuated lenses. Several tests were performed on the LCDL including diffraction efficiency measurement, switching dynamics, and hybrid imaging with a refractive lens. Negative focal lengths are achieved by adjusting the voltages across electrodes. Using these lenses in combination, magnification can be changed and zoom lenses can be formed. The promising results make LCDL a good candidate for non-mechanical auto-focus and zoom lenses.

We report on a novel zoom lens with no moving parts in the form of a switchable Galilean telescope. This zoom telescope consists of two flat liquid-crystal diffractive lenses with apertures of 10mm that can each take on the focal lengths of -50 and +100cm, with a spacing of 50cm and, hence, a zoom ratio of 4x. The lenses are driven using a low-voltage ac source with 1.6V and exhibit millisecond switching times. The spectral characteristic of this diffractive zoom system is evaluated for light sources of various bandwidths. Potential applications for this technology include a zoom lens with no moving parts for camera phones and medical imaging devices.

Mechanical testing of collagenous tissues at different length scales will provide improved understanding of the mechanical behavior of structures such as skin, tendon, and bone, and also guide the development of multiscale mechanical models. Using a microelectromechanical-systems (MEMS) platform, stress-strain response curves up to failure of type I collagen fibril specimens isolated from the dermis of sea cucumbers were obtained in vitro. A majority of the fibril specimens showed brittle fracture. Some displayed linear behavior up to failure, while others displayed some nonlinearity. The fibril specimens showed an elastic modulus of 470 ± 410 MPa, a fracture strength of 230 ± 160 MPa, and a fracture strain of 80% ± 44%. The fibril specimens displayed significantly lower elastic modulus in vitro than previously measured in air. Fracture strength/strain obtained in vitro and in air are both significantly larger than those obtained in vacuo, indicating that the difference arises from the lack of intrafibrillar water molecules produced by vacuum drying. Furthermore, fracture strength/strain of fibril specimens were different from those reported for collagenous tissues of higher hierarchical levels, indicating the importance of obtaining these properties at the fibrillar level for multiscale modeling.

Collagen, a molecule consisting of three braided protein helices, is the primary building block of many biological tissues including bone, tendon, cartilage, and skin. Staggered arrays of collagen molecules form fibrils, which arrange into higher-ordered structures such as fibers and fascicles. Because collagen plays a crucial role in determining the mechanical properties of these tissues, significant theoretical research is directed toward developing models of the stiffness, strength, and toughness of collagen molecules and fibrils. Experimental data to guide the development of these models, however, are sparse and limited to small strain response. Using a microelectromechanical systems platform to test partially hydrated collagen fibrils under uniaxial tension, we obtained quantitative, reproducible mechanical measurements of the stress-strain curve of type I collagen fibrils, with diameters ranging from 150-470 nm. The fibrils showed a small strain (epsilon < 0.09) modulus of 0.86 +/- 0.45 GPa. Fibrils tested to strains as high as 100% demonstrated strain softening (sigma(yield) = 0.22 +/- 0.14 GPa; epsilon(yield) = 0.21 +/- 0.13) and strain hardening, time-dependent recoverable residual strain, dehydration-induced embrittlement, and susceptibility to cyclic fatigue. The results suggest that the stress-strain behavior of collagen fibrils is dictated by global characteristic dimensions as well as internal structure.

Dielectric properties of a novel liquid crystal with direct transition from isotropic to twist grain boundary (TGB) phase were studied. Measurements were performed over a wide range of temperature in the isotropic phase, TGB(A), TGB(C) and SmC* phases. The Arrhenius plot of the relaxation frequency of the molecular process around the short axis shows a variation in the activation energy in the isotropic phase. This is attributed to smectic-like fluctuations in the isotropic phase. The dielectric relaxation strength in the TGBC phase has anomalous behaviour in the vicinity of TGB(C)-SmC* transition. The single cellective process observed in the TGB(C) phase splits into two processes in the SmC* phase.

Electro-optic measurements were performed on a lamellar nematic phase in which the mesogenic moieties lie in lamellae that are separated by partially perfluorinated side groups. The twist elastic constant K22, viscosity gamma(1), and the quadratic and quartic anchoring strength coefficients are reported. K22 and gamma(1) are found to be considerably smaller than that of typical three-dimensional nematics. The small K22 is due to the greatly weakened interactions between the spatially separated lamellae.

Small quantities of the bent-core mesogen P-7PIMB were dissolved in an anticlinic liquid crystal consisting of a mixture of left- and right-handed TFMHPOBC, with enantiomer excess X=0.2. For bent-core concentrations above C=3 wt %, differential scanning calorimetry shows the disappearance of the higher temperature synclinic phase, as well as the appearance of a new peak at a low temperature T c. Polarized infrared absorption measurements indicate that the new DSC peak is due to an orientational transition of the bent-core molecules, analogous to the transition previously observed in a smectic A matrix. For T>T c the plane of the bent-core molecules lies in the tilt plane of the anticlinic matrix, with the arrow (the symmetry axis) of the bent-core molecules parallel to the smectic layers. For T<T c we deduce that the bent-core molecules lie within a single smectic layer, with the polar tilt of the arrow approximately equal to the polar tilt of the TFMHPOBC molecule and the vector connecting the two ends of the bent-core molecule perpendicular to the anticlinic tilt plane. Additionally, T c was found to be an increasing function of bent-core concentration.

Quasielastic light scattering measurements were performed in the nematic phase of mixtures consisting of the calamitic mesogen 8OCB doped with small concentrations of the bent-core molecule P-7PIMB. It was found that the regular part of the bend elastic constant decreases strongly with dopant concentration X. Close to the nematic-smectic-A phase transition temperature, the divergent part of the bend elastic constant, which is proportional to the bare correlation length xi(0)(||) parallel to the layer normal, also decreases rapidly with X. The effect of the dopant on xi(0)(||) is examined in brief theoretically.

Two cylindrical liquid bridges, with a conduit to facilitate flow of liquid from one bridge to the other, were levitated against gravity in a magnetic field gradient. The stability limit of the bridges subjected to near zero total body force was measured as a function of their slenderness ratios, and found to be in good agreement with theoretical predictions.

Freedericksz measurements were performed on mixtures of a nematic mesogen and a V-shaped molecule. The bend elastic constant was found to decrease significantly with increasing concentration of the V-shaped molecule. The results are discussed theoretically, taking into account the detailed structure of the molecules.

The interlayer interaction coefficient U in the anticlinic phase of enantiomeric binary mixtures was determined by measuring the threshold electric field for the onset of solitary waves. U was found to increase with decreasing temperature in the anticlinic phase for a given enantiomer excess X. The ratio U(X,straight theta)/U(X=1,straight theta), where straight theta is the polar angle, was found to be significantly smaller for mixtures with low enantiomer excess than for the optically pure material. The observed behavior is analyzed using a mean-field model for dipole-dipole interactions in adjacent layers.