Small Tilt Angles Research Articles

Theoretical Study on Factors Influencing the Efficiency of D–π′–A′–π–A Isoindigo-Based Sensitizer for Dye-Sensitized Solar Cells

We investigated metal-free dyes based on isoindigo by performing density functional theory and Time-dependent density functional theory calculations to improve the efficiency of dye-sensitized solar cells. The D–π′–A′–π–A organic dyes (TIDP and TIDT) used triphenylamine as donor, thiophene as the π′-linker between the donor and auxiliary acceptor, and a phenyl or thiophene ring as the π-linker between the auxiliary acceptor and acceptor. TIDP and TIDT exhibit good charge-transfer properties. The TIDP-based device provides better device performance with a PCE of 4.11%. Calculated results reveal that the phenyl ring directly linking the auxiliary acceptor and acceptor causes a small tilt angle in the TiO2–adsorped dye, resulting in enhanced electron-injection rates, more efficient packing of adsorbed dye molecules, and slow charge recombination at the TiO2 surface. The performance of the TIDT-based device (η = 2.46%), arises from decreased electron-injection rates and fast charge recombination caused by the large dihedral angle of the adsorbed dye. This research identifies a potential π′-linker group and reveals the influence of the π-linker on photovoltaic performance in organic dyes. The phenyl ring directly linking the auxiliary acceptor and acceptor causes a smaller tilt angle in the TiO2-absorbed dye compared to thiophene ring resulting in enhanced electron-injection rates with increasing short-circuit current density (Jsc) as well as slow charge recombination at the TiO2 surface with increasing open-circuit voltage (Voc).

Oblique angle deposition of nickel thin films by high-power impulse magnetron sputtering.

Background: Oblique angle deposition is known for yielding the growth of columnar grains that are tilted in the direction of the deposition flux. Using this technique combined with high-power impulse magnetron sputtering (HiPIMS) can induce unique properties in ferromagnetic thin films. Earlier we have explored the properties of polycrystalline and epitaxially deposited permalloy thin films deposited under 35° tilt using HiPIMS and compared it with films deposited by dc magnetron sputtering (dcMS). The films prepared by HiPIMS present lower anisotropy and coercivity fields than films deposited with dcMS. For the epitaxial films dcMS deposition gives biaxial anisotropy while HiPIMS deposition gives a well-defined uniaxial anisotropy.Results: We report on the deposition of 50 nm polycrystalline nickel thin films by dcMS and HiPIMS while the tilt angle with respect to the substrate normal is varied from 0° to 70°. The HiPIMS-deposited films are always denser, with a smoother surface and are magnetically softer than the dcMS-deposited films under the same deposition conditions. The obliquely deposited HiPIMS films are significantly more uniform in terms of thickness. Cross-sectional SEM images reveal that the dcMS-deposited film under 70° tilt angle consists of well-defined inclined nanocolumnar grains while grains of HiPIMS-deposited films are smaller and less tilted. Both deposition methods result in in-plane isotropic magnetic behavior at small tilt angles while larger tilt angles result in uniaxial magnetic anisotropy. The transition tilt angle varies with deposition method and is measured around 35° for dcMS and 60° for HiPIMS.Conclusion: Due to the high discharge current and high ionized flux fraction, the HiPIMS process can suppress the inclined columnar growth induced by oblique angle deposition. Thus, the ferromagnetic thin films obliquely deposited by HiPIMS deposition exhibit different magnetic properties than dcMS-deposited films. The results demonstrate the potential of the HiPIMS process to tailor the material properties for some important technological applications in addition to the ability to fill high aspect ratio trenches and coating on cutting tools with complex geometries.

Monitoring algorithm of tilt angle based on sub-block plane fitting for high-resolution imaging

The limitation of mechanical structure and misoperations can result in a small tilt angle formed by the sample and the focal plane, which will decrease the resolution of the imaging system. Moreover, the small tilt angle is difficult to be observed. In order to solve this problem, a monitoring algorithm of tilt angle based on sub-block plane fitting for high-resolution imaging systems has been proposed, which is used to measure the initial angle of most 2D samples before imaging and assist users to determine the tilt degree of the sample. Experiments demonstrate that the proposed method can measure the tilt angle with a high measurement precision of 0.007° and a low residual tilt angle of 0.004°, indicating that the algorithm has high measurement precision and stability. Further results show that the quality of the image will be improved by 20%-27% when the tilt angle is 0.3056°, which means that the small degree of tilt of the sample can seriously damage the image quality. Therefore, the study of tilt angle measurement has great significance for high-resolution imaging systems.

Condition Monitoring and Failure Prediction of Gear Rotation Using a Contactless RF Magnetic Sensor

Development of sensor devices that can precisely detect small tilt angles of an anomalously rotating gear is in great demand for real-time condition monitoring and predictive maintenance of gear-based machines. The utility of a high-frequency giant magnetoimpedance (GMI)-based sensor for real-time monitoring of a rotating gear has been demonstrated. The rotation speed and tilt position of a magnetically labeled rotating gear were measured remotely from a distance of 14 cm. Small changes in magnetic field, down to mOe level, were detected using an optimized Co69.25Fe4.25Si13B12.5Nb1 microwire sensor. The sensing element exhibited remarkable field sensitivity ( $$ \eta $$ ) and GMI ratio of 230%/Oe and 300%, respectively. This contactless magnetic sensor is useful for future development of real-time condition monitoring and predicting failure of a rotating object.

Friction stir welding of glass fiber-reinforced polyamide 6: Analysis of the tensile strength and fiber length distribution of friction stir welded PA6-GF30

Friction stir welding (FSW) is a solid state welding process that is preferably used for aluminum alloys. In the study described here, FSW was applied to glass fiber-reinforced polyamide 6 (PA 6) and evaluated in terms of weld strength and fiber length distribution in the weld seam. For this purpose, the main effects on the tensile strength for friction stir welded specimens with a stationary shoulder were investigated. It could be shown that small tilt angles in combination with high contact pressures are advantageous. Using the optimum settings, a tensile strength of 50% of the base material strength could be achieved. Furthermore, an optical measuring method for large-volume fiber length measurement is introduced and evaluated. It has been demonstrated that the fibers shorten during the process. However, this has only a minor influence on the strength, while the influence of the tilt angle, the contact pressure, and the feed rate are significant.

Heat transfer characteristic of an ultra-thin flat plate heat pipe with surface-functional wicks for cooling electronics

A novel ultra-thin aluminum flat plate heat pipe (UAFHP) with dimensions of 120 × 120 × 2 mm was developed for the thermal management of concentrated electronic equipment. An evaporator container with support posts and a filling hole was manufactured integrally by the stamping method. The surface-functional wicks, which were fabricated by a micro-milling method, consisted of array orthogonal microgrooves and the groove surfaces were covered with grain-like microstructures. The effects of heat load, cooling-water temperature, and tilt angle on the heat transfer characteristic of UAFHP, including its thermal response performance, temperature distribution and thermal resistance, were investigated experimentally. The results showed that UAFHP exhibits a favorable thermal response performance and heat transfer performance. It can effectively dissipate 160 W and has a minimum thermal resistance of 0.156 °C/W in the horizontal orientation. Moreover, when the cooling-water temperature decreases, the wall temperature of UAFHP decreases while the thermal resistance of UAFHP increases. In addition, small tilt angles (θ ≤ 30°) have a negligible effect on the heat transfer characteristic of UAFHP. Compared with the flat plate heat pipes reported in the literature, UAFHP could significantly meet the requirements of thermal management of concentrated ultra-slim portable electronic equipment because of its advantages such as light weight, favorable heat transfer characteristic, ease of fabrication and low cost.

Pore Forming Properties of Alamethicin in Negatively Charged Floating Bilayer Lipid Membranes Supported on Gold Electrodes.

Electrochemical impedance spectroscopy (EIS), atomic force microscopy (AFM), and photon polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) were employed to investigate the formation of alamethicin pores in negatively charged bilayers composed of a mixture of 1,2-dimyristoyl- sn-glycero-3-phosphocholine (DMPC) and egg-PG floating at gold (111) electrode surfaces modified by self-assembled monolayers of 1-thio-β-d-glucose (β-Tg). The EIS data showed that the presence of alamethicin decreases the membrane resistivity by about 1 order of magnitude. PM-IRRAS measurements provided information about the tilt angles of peptide helical axis with respect to the bilayer normal. The small tilt angles obtained for the peptide helical axis prove that the alamethicin molecules were inserted into the DMPC/egg-PG membranes. The tilt angles decreased when negative potentials were applied, which correlates with the observed decrease in membrane resistivity, indicating that ion pore formation is assisted by the transmembrane potential. Molecular resolution AFM images provided visual evidence that alamethicin molecules aggregate forming hexagonal porous 2D lattices with periodicities of 2.0 ± 0.2 nm. The pore formation by alamethicin in the negatively charged membrane was compared with the interaction of this peptide with a bilayer formed by zwitterionic lipids. The comparison of these results showed that alamethicin preferentially forms ion translocating pores in negatively charged phospholipid membranes.

Probing Molecular Structures of Buried Interfaces in Thick Multilayered Microelectronic Packages

The fast development of flip-chip (FC) devices has helped to keep ICs on pace for Moore's law. FC devices have many buried interfaces, the structures of which all need to be investigated in order to optimize them. It is extremely difficult to examine molecular structures of buried interfaces in samples with multiple layers due to the lack of appropriate analytical tools. In this paper, real FC-on-leadframe devices, manufactured by Texas Instruments Incorporated, were investigated using the intrinsically interface-sensitive technique and sum-frequency generation (SFG) vibrational spectroscopy. By milling down the Si wafer, we can probe the polyimide (PI)/mold compound (MC) interface. By milling down further, we can examine the air/MC and the MC/leadframe (LF) interfaces. Methylene and methyl groups were detected from each of the three interfaces, and the orientation of methyl groups was determined at each interface. It was calculated that at the PI/MC interface, the methyl group tilt angle was 20° (from the surface normal). For the air/MC interface, the tilt angle was 43.5°, and for the LF/MC interface, the tilt angle was measured to be 45°. The deduced different methyl orientations at the two buried solid/solid interfaces can be interpreted by the interfacial interactions. The PI surface is more hydrophobic than the LF surface; therefore, it has more favorable interactions with the hydrophobic methyl groups, leading to a more “standing up” (smaller tilt angle) position for the methyl groups at the PI/MC interface. In this paper, SFG was successfully applied to study the buried interfaces in real devices. The SFG method used in this paper is general and can be applied to other real-world, complicated thick systems.

Experimental analysis of the evaporation regimes of an axially grooved heat pipe at small tilt angles

Using a high-speed digital microscope, visualization experiments of the vapor-liquid two-phase flow and heat transfer in an axially grooved heat pipe are conducted to investigate the evaporation regimes that occur at small tilt angles. The effects of the heat load and tilt angle on these evaporation regimes are analyzed. The evaporation regimes are further quantitatively characterized with a regime diagram developed based on the Bond number and Weber number. The results indicate that, unlike in a horizontal position, the evaporation regime of a grooved heat pipe with a small tilt angle can include corner-film evaporation induced by the combination of gravity and capillary force in addition to pool-surface evaporation and fin-film evaporation. Corner-film evaporation is the characteristic evaporation regime of an axially grooved heat pipe with a small tilt angle, and it exhibits random oscillatory motion of the vapor-liquid interface. Pool-surface evaporation is observed at small Weber numbers, corner-film evaporation occurs at large Weber numbers when the Bond number is approximately greater than 0.003, and fin-film evaporation occurs at medium Weber numbers.

Lubricant-infused coating by double-layer ZnO on aluminium and its anti-corrosion performance

In this study, double-layer zinc oxide was synthesized on an aluminium substrate by combining a sol-gel and a hydrothermal method. The bottom layer was flower-like and the upper layer was rod-shaped. The aluminium sheet coated with zinc oxide was infiltrated into a lubricating oil for 2 h to obtain an aluminium-based double-layer ZnO super-slippery surface. Testing showed that the surface demonstrated a good anti-fouling effect. The coating was hydrophobic and oleophobic, and even fruit juice and jam slipped down the surface at a small tilt angle (<5°). The corrosion resistance was also four orders of magnitude higher than that of the untreated aluminium sheet, and after three months, the anti-corrosion performance did not change significantly. Such good performance in the metal's corrosion resistance provides numerous potential application prospects.

2D Dipolar Bosons with Non-zero Tilt Angles

Recent experimental advances in creating stable dipolar systems, including polar molecules with large electric dipole moments, have led to vigorous theoretical activities. Here we discuss our work on homogeneous 2D dipolar bosons with dipoles oriented at an angle to the direction perpendicular to the confining 2D plane, i.e. for non-zero tilt angles. Using Bogoliubov-de Gennes equations, we obtain T=0 excitation spectrum of the dipolar Bose gas, and explore instabilities at varying tilt angle, density and dipolar coupling. We map out a phase diagram a function of tilt angle, dipole strength and density. We find the development of maxon-roton behavior leading to roton instabilities at large densities for small tilt angles, and at low densities for large tilt angles. The behavior is anisotropic in k-space; accordingly the roton instabilities occur in the ky direction, suggestive of inhomogeneity and stripe phase, with density mode becoming soft in the y direction. Our results compare favorably with existing Quantum Monte Carlo calculations for non-zero tilt angles.

Self-assembly, conductivity and chemosensor behavior of biphenylsulfone based Janus polycatenar

A novel Janus polycatenar JP-I bearing a bisphenylsulfone central core, with a hydrophobic 3,4,5-tridodecyloxybenzylether unit at one side and a hydrophilic trioligoethylene oxide benzyl triazoly unit at another side has been synthesized via copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction. JP-I can display SmA2 phase triggered by the addition of alkali metal ions. The LC property of the doped system was well demonstrated by polarized optical microscopy (POM), differential scanning calorimetry (DSC) and X-ray diffraction (XRD) experiments. The conductivity of the doped system (JP-I:LiOTf) is 4.0 × 10−8 S cm−1. JP-I could gel both in ethanol and aqueous ethanol. Such gel which formed in ethanol showed a helical nanostructure. The XRD displayed that the JP-I could self-assemble into a monolayer structure which had a small tilt angle in the layers. Furthermore, the gel system could be established to remove iodine from water. Additionally, JP-I could recognize Fe3+ with lower detection limit in aqueous ethanol. Finally, JP-I could self-assemble into micelles in aqueous solution and the critical micelle concentration CMC was determined to be 0.002 mg/ mL with the diameter of the spherical micelles about 15–20 nm.

Charge deposition dependence of electron transmission through PET nanocapillaries and a tapered glass microcapillary

Abstract Charge deposition dependences of electron transmission through insulating PET nanocapillaries and a tapered glass microcapillary are reported and differences with HCI transmission are noted. Investigations were conducted for electrons with incident energies 500–1000 eV, corresponding to energies per charge similar to those used for HCI studies, incident on (1) an array of PET nanocapillaries (density ∼5 × 108/cm2) with diameters 100 nm in a foil of thickness 12 μm, and (2) on a tapered glass microcapillary with inlet/outlet diameters of 800/100 μm and a length of ∼35 mm. The transmission was measured for incident electrons at small sample tilt angles ranging from 0° to 5° with respect to the beam direction. For most angles, including those near zero degrees, there was an initial quiet period during which essentially no transmission was observed, followed by large rises in the transmission during relatively short periods of charge deposition before equilibrium of the transmission was reached. The resulting equilibrium was stable, blocked or had frequent oscillations depending on the incident energy and the capillary used. Observations for both capillaries show that a negative charge patch is needed to guide incident electrons through the capillaries similar to the manner in which HCIs are guided through capillaries.

Numerical calculations of temperature dependence of dielectric constant for an ordered assembly of BaTiO3 nanocubes with small tilt angles

The dielectric constant of an ordered assembly of BaTiO3 nanocubes is numerically calculated as a function of temperature assuming a distribution of tilt angles of attached nanocubes. As the phase transition temperature from the tetragonal crystal structure to the cubic crystal structure of a BaTiO3 nanocube decreases as the tilt angle increases, the temperature at the peak of the dielectric constant of an ordered assembly is considerably lower than the Curie temperature of a free-standing BaTiO3 crystal. The peak of the dielectric constant as a function of temperature for an ordered assembly becomes considerably broader than that for a single crystal owing to the contribution of nanocubes with various tilt angles.

Quantum-enhanced sensing from hyperentanglement

Hyperentanglement --- simultaneous entanglement between multiple degrees of freedom of two or more systems --- has been used to enhance quantum information tasks such as quantum communication and photonic quantum computing. Here we show that hyperentanglement can lead to increased quantum advantage in metrology, with contributions from the entanglement in each degree of freedom, allowing for Heisenberg scaling in the precision of parameter estimation. Our experiment employs photon pairs entangled in polarization and spatial degrees of freedom to estimate a small tilt angle of a mirror. Precision limits beyond shot noise are saturated through a simple binary measurement of the polarization state. The broad validity of the dynamics considered here implies that similar strategies based on hyperentanglement can offer improvement in a wide variety of metrological tasks.

Nanoscale tilt measurement using a cyclic interferometer with polarization phase stepping and multiple reflections.

High-accuracy tilt or roll angle measurement is required for a variety of engineering and scientific applications. A cyclic interferometer with multiple reflections has been developed to measure small tilt angles. To accomplish this task, a novel and simple method, phase shift by polarization, was developed. The results of these studies show that the multiple reflection cyclic interferometers can be used to measure object tilts on the order of 0.2 nano-radians. We develop the theory for polarization phase step and show that accurate measurements can be made with the cyclic interferometer.

Cascaded Mirror Array: design and demonstration of low-cost light-weight digital scanning

A new digital scanning approach is proposed and its feasibility is demonstrated. The Cascaded Mirror Array applies an array of reflectors, with each reflector movable between discretized angular positions controlled by digitized electrical signals, to process a light beam by cascaded reflections to generate desired deflections of a light beam. An Uneven-Leg Tilting mechanism was devised to provide a very significant mechanical reduction ratio so that it can be used to generate very small tilt angles by comparatively large, finite displacements that can be easily created. A 4-bit 1D scanner prototype, built by simple non-MEMS methods, demonstrated point-to-point scanning at 0.0125° resolution from 1 to several hundred Hz. Studies based on finite element simulations suggest that by increasing electromagnetic driving force and reducing the size and mass of the prototype construction operating frequency up to several thousand Hz can be achieved. The new approach has the potential of making low-cost light-weight robust high speed scanners.

Thermal Convection in a Tilted Rectangular Cell with Aspect Ratio 0.5**Supported by the National Natural Science Foundation of China under Grant Nos 11572314, 11232011 and 11621202, and the Fundamental Research Funds for the Central Universities.

Thermal convection in a three-dimensional tilted rectangular cell with aspect ratio 0.5 is studied using direct numerical simulations within both Oberbeck–Boussinesq (OB) approximation and strong non-Oberbeck–Boussinesq (NOB) effects. The considered Rayleigh numbers Ra range from to , the working fluid is air at 300 K, and the corresponding Prandtl number Pr is 0.71. Within the OB approximation, it is found that there exist multiple states for and hysteresis for . For a relatively small tilt angle β, the large-scale circulation can either orient along one of the the vertical diagonal planes (denoted by mode) or orient parallel to the front wall (denoted by mode). Which of the two modes transports heat more efficiently is not definitive, and it depends on the Rayleigh number Ra. For and , the time-averaged flow field contains four rolls in the upper half and lower half of the cell, respectively, and modes only developing in tilted cells. By investigating NOB effects in tilted convection for fixed , it is found that the NOB effects on the Nusselt number Nu, the Reynolds number Re and the central temperature for different β ranges are different. NOB effects can either increase or decrease Nu, Re and when β is varied.

Interactions between lattice dislocation and Lomer-type low-angle grain boundary in nickel

Symmetric tilt Lomer-type low-angle grain boundaries (LLAGBs) are distinct grain boundaries formed by Lomer dislocation locks in face-centered cubic (fcc) metals. To reveal their mechanical behaviors, interactions between lattice dislocation and LLAGB are studied with molecular dynamics simulations. Dislocation reaction and slip transmission depend on the tilt angle of LLAGB, the character of incident dislocation and the particular glide planes inhabiting the incoming slip. For LLAGBs with relatively small tilt-angles, a free slip-transmission zone can be identified where dislocations can be forced to penetrate through the LLAGB without inducing dislocation reaction. Otherwise, the incident slip tends to be trapped, triggering a number of dislocation reactions and leading to indirect slip transmission across the boundary in the reaction zone. Critical strains for dislocation reactions are examined. Raising up the temperature will widen the dislocation reaction zone and the free transmission zone tends to disappear.

The impact of adjusting auxiliary donors on the performance of dye-sensitized solar cells based on phenothiazine D-D-π-A sensitizers

Three new D-D-π-A sensitizers ZHG5, ZHG6 and ZHG7 have been prepared by gradually improving the steric hindrance of auxiliary donors and the power conversion efficiencies (PCE) are 5.64%, 5.32% and 2.74%. UV–Vis absorption indicates that the molar extinction coefficients decrease with the increased steric hindrance of auxiliary donors. X-ray photoelectron spectroscopy (XPS) indicates that the tilt angles of ZHG5 and ZHG6 anchored on the TiO2 film are similar and ZHG7 is almost standing rather vertical on the TiO2 film with the smallest tilt angle. The results of dye desorption and XPS experiments indicate that the dye loading amount of ZHG6 with larger steric hindrance is lower than that of ZHG5, ZHG7 with largest auxiliary donor has the maximum loading amount probably due to its smallest tilt angle. Larger auxiliary donor of ZHG6 leads to higher open circuit voltage (Voc = 734 mV) but lower shorter circuit current (Jsc = 12.63 mA cm−2) compared with that of ZHG5 (Voc = 730 mV, Jsc = 12.06 mA cm−2). However, dense packing of dye ZHG7 anchored on the TiO2 leads to more serious intermolecular π-π aggregation effects. Perhaps this effect and lowest molar extinction coefficient are the reason that DSSC based on ZHG7 have the lowest PCE. So above results indicate that auxiliary donor with overlarge steric hindrance will have smaller tilt angle of dye anchored on TiO2 and may lead to more dye loading amount but serious intermolecular π-π aggregation effects.