Surface Tilt Angle Research Articles

Determination of surface tilt angle of splay and bend liquid crystal cells

This study presents and demonstrates an approach for determining the surface tilt angles of parallel-aligned liquid crystal cells. The relationships between the incident angles and the corresponding phase retardations in the splay and the bend configurations are analyzed. The equations for the surface tilt angles are derived accordingly, and their accuracy is discussed. This method does not require knowledge of the cell thickness and is easily applied to assembled pi-cells.

AFM Observation of Microstructural Changes in Fe-Mn-Si-Al Shape Memory Alloy

We analyzed the surface relief caused by stress-induced hcp martensitic transformation in Fe-30Mn-5Si-lAl shape memory alloy by atomic force microscopy. The alloy exhibits a good shape memory effect and an improved ductility due to a small addition of Al to a conventional Fe-30Mn-6Si shape memory alloy. The orientation of an austenite matrix was determined with surface traces of four {111} f planes, which enabled us to determine the surface tilt angles for all twelve variants of hcp martensites and deformation twins. On the basis of these values, stress-induced martensite and deformation twin coexisting in the same grain were identified by studying the surface tilt angles. The surface relieves caused by the stress-induced martensite recovered after heating above the reversed transformation temperature, however some relieves originating from the deformation twin remained.

Fe-30Mn-5Si-1Al 形状記憶合金の原子間力顕微鏡組織観察

The surface relief caused by stress-induced fcc/hcp martensitic transformation in an Fe-30Mn-5Si-1Al shape memory alloy, which exhibited a good shape memory effect and an improved ductility due to a small addition of aluminum to a conventional Fe-30Mn-6Si shape memory alloy, was quantitatively analyzed by atomic force microscopy. The orientation of an austenite grain was determined with surface traces of four {111}f planes, which made it possible to determine the surface tilt angles for all 12 variants of hcp martensite and deformation twins. On the basis of these values, the stress-induced martensite and deformation twin, coexisting in a grain, were identified by investigating the surface tilt angles. The surface relief caused by the stress-induced martensite recovered after heating above the reverse transformation temperature, but that due to the deformation twin remained unaltered.

Decentration Error Analysis Using Optical Centering Device and Skew Ray Tracing

Any small decentering of a lens's surface can be resolved into an angular tilt of the surface about its intersection with the optical axis. The decentration error of an optical lens has a significant effect on the quality of the image it produces. This paper presents a simple method based on skew ray tracing and an optical centering device to calculate the decentration error resulting from the surface tilt of an optical lens. The results reveal that the decentration error and the radius of the spot circle traced out on the detector of the optical centering device as the sample of interest is rotated are related via a linear approximation when the decentration error is small. Furthermore, it is found that for small surface tilt angles, an approximate value of the decentration error can be obtained simply by taking the first-order differentiation of the mathematical expression for the decentration error.

Design, Simulation, Fabrication, and Characterization of a Digital Variable Optical Attenuator

In this paper, we present the design, simulation, fabrication, and some measurement and characterization of a novel 16-bit digital variable optical attenuator (VOA) that attenuates by switching individual mirror of an array as an attempt to achieve input voltage variation independence and output linearization. The design was aided by a simulation package that features coupled electrostatic and mechanical solver. The mirror array spans an area of 1500times1500 mum <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2 </sup> and contains 16 equal-length rectangular micromirrors. Each mirror is suspended by two torsion beams. Experiments on beam design and width variations are conducted. Assuming Gaussian distribution, the mirror widths computed by an iteration algorithm vary from about 40 to 250 mum. Based on silicon-on-insulator (SOI) technology, two fabrication schemes to open the backside optical entrance were investigated. A hydrofluoric (HF) acid vapor-phase-etching (VPE) setup built to release the microstructure anhydrously is the key to achieve high yield especially for fragile components. Surface flatness, resonance frequencies, and tilt angles of selected mirrors were characterized. Quartz chips patterned with aluminum electrodes and 10 mum-high SU8 spacer columns were fabricated and assembled to corresponding device chips. Optical performance adversely affected by mirror bending is believed to originate from the intrinsic stress of the SOI wafer

Direct optical observation of magnetic domains in Ni–Mn–Ga martensite

This letter reports the direct optical observation, i.e., without polarization, of the magnetic domain structure explained by a large surface relief in Ni–Mn–Ga martensite. The authors suggest that the relief is due to the different straining of the surface and the bulk caused by the internal stresses associated with the magnetic shape memory effect. As a result of the relief the projection of the (011) twin traces upon the (010) plane creates the observed zigzag pattern. The surface tilt angle calculated from the zigzag pattern is ∼3°.

Growth of InGaN multiple quantum wells and GaN eplilayer on GaN substrate

We investigated that the surface morphology of GaN epilayers was significantly affected by the surface tilt orientation of GaN substrate. Surface morphologies of GaN epilayers on GaN substrates show three types: mirror, wavy, and hillock. These surface morphologies are dependent on the surface orientation of GaN substrates. It is found that the hillock morphology of GaN epilayer was formed on the GaN substrate with surface tilt orientation less than 0.1°. As the surface tilt angle increased to 0.35°, the surface morphology varied from hillock to wavy morphology. Above a surface tilt angle of 0.4°, surface morphology changed to the mirror-like type morphology. Additionally, these three types of GaN surface morphology also affected the optical quality of GaN epilayers as well as InGaN multiple quantum wells on GaN substrates by non-uniform In incorporation on the different surface morphologies of GaN epilayers.

A noncontact sensor for measurement of distal residual-limb position during walking

A simple noncontact device was implemented for measuring the position of the distal residual limb relative to the prosthetic socket during ambulation. The device was a small and lightweight photoelectric sensor positioned within a frame mounted immediately beneath the socket. Calibration tests showed that the sensor had a displacement range of 60.0 mm. The root-mean-square error for all sources of error considered (different reflective surfaces, peak-to-peak signal noise, drift, nonlinearity, different surface tilt angles, surface curvature, and wetness [simulating sweating]) was <1.95% full-scale output. We used the sensor in a preliminary study on a unilateral, transtibial amputee with diabetes to assess pistoning during ambulation. Results showed an average 41.7 mm proximal displacement during swing phase relative to stance phase. When the subject was walking on a flat surface, pistoning was significantly less (p = 0.000) with a supracondylar strap compared with no supracondylar strap, although the difference was not substantial (0.8 mm). A 5 min rest period caused the limb to displace proximally in the socket approximately 4.8 mm during subsequent walking trials, possibly reflecting limb enlargement and thus a more proximal position in the socket after the rest period. The device can potentially be used in prosthetics research for evaluating clinical features that may affect limb position and pistoning and thus fit.

Step control of vicinal 6H–SiC(0001) surface by H2 etching

Anisotropic step bunching on vicinal 6H–SiC(0001) surface induced by H2 etching was investigated. Step structures were observed using atomic force microscopy and high-resolution transmission electron microscopy at off angle &amp;lt;2°. The etched surfaces exhibited three types of step bunching: (1) straight six-bilayer steps, (2) straight six-bilayer steps and nanofacets, and (3) zigzag three-bilayer steps. The step height and density can be controlled by a tilt angle and direction of a vicinal surface. Mechanisms of the step bunching processes are discussed at points of an anisotropy of lateral-etching rates and surface-free energies.

コンパクト化を目指したＭｕｌｔｉ‐ｐｏｌｅ Ｗｉｇｇｌｅｒ用放射光アブソーバの開発

A compact photon absorber for the accelerator diagnosis beamline #2 of the SPring-8 storage ring, which withstands high heat load of the synchrotron radiation from a multi-pole wiggler, has been developed. In order to make the absorber compact, two absorber blocks made of GlidCop with a different tilt angle of surface have been arranged in tandem in the vacuum chamber. The front absorber intercepts upper and lower parts of the synchrotron radiation, and the rear one absorbs central part of the synchrotron radiation. Wirecoils made of copper have been inserted in the water-cooling channels of each absorber block to increase the heat transfer coefficient. The result of thermal and stress analysis with the ABAQUS code shows that the absorber has the fatigue strength of more than 5000 times at the maximum heat load of the synchrotron radiation from the wiggler.

Design optimization of a large scale rooftop photovoltaic system

Abstract This paper presents the optimization process of a grid connected photovoltaic (PV) system, which is intended to replace a large-scale thermal solar system on the rooftop of a Federal office building. A PV energy conversion model is described. Based on this model, array surface tilt angle and array size are optimized. The optimization method is based on maximizing the utilization of the array output energy, and, at the same time, minimizing the electricity power sold to grid. An effectiveness factor is introduced that takes into account both of these parameters. The array configuration and the output parameters are determined by comparing several PV modules. A 43.2 kW PV system is designed and operational problems such as harmonic effects and anti-islanding are discussed. Finally, the system performance is simulated and through economic analysis it has shown that the cost of PV system can be recouped in 13 years under the current renewable energy incentive program by the state of Illinois.

Ocean surface determination from X‐band radar‐image sequences

An empirical inversion method is presented for determination of time series of ocean surface elevation maps from nautical radar‐image sequences. The method is based on the determination of the surface tilt angle in antenna look direction at each pixel of the radar images. Thereby in situ sensors are not required. An external calibration is not necessary. A conventional nautical X‐band radar, operating at grazing incidence and horizontal polarization in transmit and receive, is used as a sensor. Radar‐image sequences, with their high spatial resolution and large coverage, offer a unique opportunity to derive and study individual waves and wave fields in space and time and therefore allow the measurement of individual wave parameters and wave groups. For validation of the inversion scheme, the significant wave heights derived from the inverted radar data sets and from colocated wave records are compared. It is shown that the accuracy of the radar‐retrieved significant wave height is within the accuracy of the in situ sensors. Furthermore, a wave elevation time series is directly compared to a buoy record to show the capabilities of the proposed method.

Computer Simulation of Transition Processes between Bistable States in Bistable Nematic Liquid Crystal Cell Using Breaking Phenomenon of Surface Anchoring

The transition process between bistable states in the bistable nematic (Bi-Nem) cell based on the anchoring breaking phenomenon has been strictly simulated by computer. In our simulation, the surface tilt angle dependence of the contribution of azimuthal anchoring to the surface free energy density has been taken into account. This leads to successful reproduction of the bistable operation of the Bi-Nem cells by the computer simulation. As a result, it has been clarified that in the transition process from the uniform state to the twisted state, the molecular orientation takes the 270 deg. twisted state at first and then changes toward to the 180 deg. twisted state. From our simulations, it is confirmed that the bistable transition occurs in limited regions of polar and azimuthal anchoring energy on the slave plate.

Influence of the surface tilt angle on the spatially periodic distortions in super-twisted nematic displays

Periodic deformation arising as parallel stripes in super-twisted nematic displays are studied numerically. The role played by a surface tilt angle δ in their appearance and structure is determined. It is found that the stripes exist in a narrow voltage range between two thresholds. The lower threshold at which they arise is practically independent of the tilt angle. The higher threshold at which the homogeneous deformation occurs decreases with δ. For relatively small twist angles (e.g., 180°) the transition to the homogeneously deformed structure is continuous. If the twist angle is high (e.g., 270°) this transition becomes discontinuous. The stripes are eliminated if the tilt angle exceeds some critical value which increases with the twist angle and may be larger than 30°.

Formation Mechanisms and Packing Structures of Alkoxyl and Alkyl Monolayers on Si(111): Theoretical Studies with Quantum Chemistry and Molecular Simulation Models

Quantum chemistry and molecular mechanics calculations are performed to study formation mechanisms and packing structures of octadecanal and octadecene monolayers on Si(111). The radical chain mechanism is investigated by density functional theory with cluster models. Transition states of key steps involving abstracting a neighboring hydrogen atom from the surface are confirmed with the six-membered ring structures. Energy barriers for abstractions of the surface H to form new reactive surface Si radicals in the substitution of Si(111) via Si−O and Si−C linkages are 18.05 and 14.97 kcal/mol, respectively. Based on the radical chain mechanism, we investigate the linear and zigzag packing structures of alkoxyl chains on Si(111) with substitution percentages of 50%, 66.7%, and 75% using a series of two-dimensional repeating cells. By comparison of packing energies of octadecanoyl chains at different substitution percentages, 66.7% is predicted to be an optimal substitution percentage, which agrees with experimental observations. At this surface substitution, packing structures of the monolayer such as tilt angles and film thickness are well correlated with experimental data. The difference in packing structures between monolayers on Si(111) via Si−O and Si−C linkages is rationalized by their different van der Waals radii of surface linkage groups and tilt angles of chains.

Residual stress measurement in textured thin film by grazing-incidence X-ray diffraction

Measurements of residual stresses in textured thin films have always been problematic. In this article, a new experimental method using grazing-incidence X-ray diffraction is presented with its principles based upon the conventional sin 2ψ method. Instead of using the Bragg–Brentano (B-B) or Seemann–Bohlin geometry, the proposed method utilizes an asymmetrical diffraction geometry for which the X-ray beam is incident at a grazing angle γ to the sample surface, while the angle ψ is the tilt angle of the sample surface as defined by the conventional sin 2ψ method. Basic equations involved in the X-ray residual stress analysis are described, along with exemplified experimental data. Analysis shows that, for an isotropic medium, strain measured using this grazing-incidence geometry assumes a linear relationship with the geometrical parameter cos 2α sin 2ψ, where the angle α is a constant and is defined as the Bragg angle at ψ=0°, θ o, minus the grazing incidence angle γ, i.e. α=θ o−γ. The grazing-incidence diffraction geometry effectively increases the irradiation volume from a thin-film specimen, thereby giving rise to higher intensity for high-angle Bragg peaks than the conventional B-B geometry. The proposed analysis has another advantage, in that the inhomogeneous sample casts little effect on the residual stress results when compared to the traditional sin 2ψ method.

Nematic Film Under Electric Field: Total Internal Reflection, Surface Tilt Angle and Anchoring Energy

In this paper, we first analyze an existing anchoring energy measurement technique in terms of accuracy and surface tilt angle value as an electric field is applied to the nematic cell initially planarly aligned. We thus perform a simulation of the film behavior using a pure elastic model and derive from it a possible new method for polar anchoring coefficient measurement, based on the surface tilt angle dependence on the applied voltage. We propose an experimental setup to perform this measurement. The reported preliminary experiment (5CB nematic film aligned using a polyimid layer) shows on one hand the feasibility of the measurement and in an other hand that - in that specific case - the pure elastic model is too restrictive and extra surface phenomena have to be accounted for.

On the saturation behaviour of twisted nematic liquid crystal cells with a nonzero pretilt angle

Equations are obtained for the surface tilt angle and the twist angle of the director in a twisted nematic liquid crystal cell under a high magnetic field. Under a zero pretilt angle, the two equations reduce to those obtained by Sugimura et al[2,3]. This fact has also been demonstrated numerically. With finite field strength and nonzero pretilt angle, no saturation transition exists.

Investigation of surface topography using a multidetector system in a SEM

The backscattered electron (BSE) signal is widely used for examination of surface topography in a scanning electron microscope (SEM). For detection of this signal both the standard configuration of two detectors as well as a multidetector system are employed. In the BSE mode, the sum of signals becomes less dependent on the surface inclination whereas the difference signal becomes proportional to the local surface tilt angle. One can see, that the signal from the two-detector system is influenced by an artefact. A successful combination of several independent detector signals to improve the topographical image has been proposed. For an investigation of the topographic mode in SEM, six p–i–n diodes of small surface area were placed opposite to each other. The digital BSE signal processing system enabled realization of different algorithms of mixing signals coming from several detectors. Some ways for eliminating the artefacts were proposed. For example, a method to form images without a shadow effect was used. It is useful for distinguishing between artefacts and real features. Moreover, the experimental results indicate that the real topography of a specimen can be obtained if the specimen is rotated. The aim of this work was to use a multidetector system and to develop models to allow the data to be interpreted.

Homeotropic polar anchoring energy of a nematic liquid crystal using the fully leaky waveguide technique

Optical excitation of a series of fully leaky guided modes has been used to explore the director distortion of a hybrid-aligned nematic liquid crystal with a negative dielectric anisotropy (Merck-BDH, MLC 6608) under application of an ac electric field. Hybrid alignment is realized by the use of a lecithin film on the top glass plate and rubbed polyimide on the bottom plate, both plates having indium–tin–oxide coatings. Continuum theory is used to model the director profile through the cell. Fitting the fully leaky guided mode data both in transmission and reflection using optical multilayer theory together with continuum modeling gives the director profile both with and without applied fields. From this fitting the changes in the surface tilt angle and its gradient are obtained. Using this information the polar anchoring coefficient of the homeotropic surface Wθ is deduced. At 23.1 °C we find Wθ=(4.6±0.2)×10−4 J m−2.