Film Speed Research Articles

Investigation of structural, optical and magnetic characteristics of Co3O4 thin films

Nano-structured Co3O4 thin film are synthesized by dip coating and their structural, surface, optical and magnetic properties have been studied. The X-ray diffraction of film shows that the crystalline Co3O4 has cubic structure with preferrd orientation along the (400) plane which makes them advantageous for optoelectronic devices. The scanning electron microscopy micrograph reveals that the film has a porous structure. The transmission of the films gradually decreases with the decrease of the wavelength in the 900–300 nm region. Upon enhancing the withdrawal speed of the substrate, the transmission shows decrement due to increase in film thickness. From the investigation of the transmission spectra of Co3O4 films, the band-gap is found to lie between 2.12 and 2.30 eV. Magnetic characteristic of thin films relies on the withdrawal speed and thickness of thin films. With the increase of withdrawal speed saturation magnetization increases while coercivity of thin films decreases.

Archaeologies of post-socialist temporalities: Documentary experiments and the rhetoric of ruin gazing

Focusing on the independent documentary movement that is also a movement of digital filmmaking in China, this essay examines documentary’s mediation of post-socialist conceptions of time through digital filmmaking aesthetics, including ruin gazing, forwarding and reversing, and accelerating and decelerating film speed. In a comparative study of experimental documentaries on post-socialist temporalities in Eastern Europe and China—including the work of Chantal Akerman, Cong Feng, and Huang Weikai—the essay unravels documentary’s representation of time that illustrates the “post” as a locus of desires and anxieties, backward and forward glances that create heterogeneous relationships—with their own economy of stasis, velocity, and speed—in relation to the homogeneous and teleological time of Capital.

Evaluation of the oil film thickness for journal bearings supporting a rotating shaft under sinusoidal load condition

In this work, the oil film thickness of journal bearings is evaluated under dynamic-load condition by the numerical and experimental methods. The numerical method is based on the Reynolds equation with Reynolds boundary condition. The oil film is measured with eddy-current displacement sensors. It is confirmed that the numerical and experimental results agree qualitatively in terms of the relationship between rotating speed and average oil film thickness.

Particle Image Velocimetry (PIV) measurements in a water film, application to a tire rolling through a puddle

A measurement method based on Particle Image Velocimetry (PIV) with refraction of the laser sheet at a window/water interface is proposed for the measurement of the velocity field of a flow, inside a water puddle, due to a tire rolling on. This study focuses on the feasibility and repeatability of this optical measurement method. The characterization of the optical properties of this measurement technique defines its accuracy. The analysis of the overall features of the flow is focused on two main flow zones in front of and around the tire. The flow inside the first zone is characterized by a global velocity of the water displaced in an area located in front of the tire. In the second zone a velocity representative of the flow in the vicinity of the tire shoulder is also defined. Correlations of both characteristic velocities with the car speed and water film height are established. New and the corresponding worn tires were tested in this work.

Characteristics of Modified Spiral Thrust Bearing through Geometries and Dimension Modifications

This research focuses on the optimum design of fluid dynamic bearing (FDB) named modified spiral design. The objective is to improve the pressure and velocity distribution inside the FDB. In this paper, the current spiral design has 12 number of grooves while the modified spiral design has 24 number of grooves. Both design can be classified into two, bearing with seal and without seal. Air was chosen to replace the oil as the lubricant. Results show that the modified spiral bearing design has comparable characteristics compared to conventional spiral design in terms of pressure and velocity distribution. Modified spiral geometries also shows a tendency to replace the function of seals in FDB. This makes it possible to simplify bearing design without using any seal just by modifying its geometries based on novel modified spiral geometries. Experimental verifications also proved that the modified spiral bearing design has better air leakage control compared to the conventional ones. This phenomenon occurs in both design parameters, where when the designs are compared with respect to increase of rotational speed and air film thickness.

Investigation of radiation-protection knowledge, attitudes, and practices of North Queensland dentists.

Queensland has current radiation-protection guidelines; however, with the absence of data exploring compliance and implementation, the efficacy is unknown. The aim of the present study was to investigate the knowledge and attitudes on radiation protection among private North Queensland (NQ) dentists. A quantitative methodology was employed in an observational and descriptive study using questionnaires for data collection. Of the 154 questionnaires distributed, 63 were completed and returned. The respondents' knowledge concerning the technical details of their equipment was limited, with 31.5% and 47% not knowing the tube voltage and current utilized for their machines, respectively. In total, 23.8% of dentists had limited knowledge about the speed of the conventional film they used, 90.5% of respondents agreed that the role of imaging in dentistry is important, and 75.8% dentists reported the thyroid as the most important organ to protect during dental radiography. Their knowledge regarding position-distance rule was reasonably adequate; 80.3% of the dental practices appeared to follow the Australian Radiation Protection and Nuclear Safety Agency guidelines, 95.2% preferred taking radiographs if it was only urgent, and 69.8% identified a need for spreading awareness regarding radiation protection. An opportunity and need for further continuing education was identified among NQ dentists to ensure safety of patients.

Testing for low-speed skid resistance of road pavements

Low-speed skid resistance tests provide useful information not available from the normal high-speed skid resistance testing of road pavements. There are known limitations of the two commonly used measuring devices of low-speed skid resistance, i.e. British Pendulum Tester (BPT) and Dynamic Friction Tester (DFT). This study develops a Walking Friction Tester (WFT) to offer a practical alternative to measure low-speed pavement skid resistance. This paper compares WFT with BPT and DFT measurements in the following three aspects: correlation relationship, measurement variability, and speed comparison of field tests. Tests were also performed to examine the variability of WFT test results with respect to walking speed and water film thickness, respectively. The study showed that there was a good correlation coefficient of 0.80 between BPT and WFT measured data, and 0.70 between DFT and WFT friction coefficients. WFT measured data were found to have smaller variability than those of BPT and DFT. In field tests performed over a length of pavement section, WFT generated continuous friction data in much shorter times compared with the spot measurement mode of either BPT or DFT. The results also showed that WFT tests were independent of changes in walking speeds of operators and variations of water film thickness applied.

Process optimization and device variation of Mg-doped ZnO FBARs

Thin film bulk acoustic resonator (FBAR) plays a very important role in radio frequency (RF) filters used in cell phone and other wireless systems. Although FBAR is commercialized, the design/process interactions on the frequency response variation in FBAR device are still lacking. Design and fabrication are two crucial aspects affecting FBAR device performance. In this report, various solidly mounted resonators (SMR) were designed, fabricated and analyzed to study wafer-level site-to-site RF variation on design and fabrication process. As a key process step for SMR FBAR, the optimization process of Mg-doped ZnO piezoelectric thin film deposition was studied by varying thin film sputtering conditions using various sputtering targets and by post annealing treatment after the deposition. The quality of this crucial layer was verified by XRD on its (0 0 2) crystallization and wafer-level FBAR RF characterization. FBAR devices with high quality were fabricated with an excellent resonant behavior near 2 GHz and a maximum return loss of −15 to 25 dB. Quality factor Q ranges from 400 to 800, with a coupling coefficient keff2 of 1.5–3%. Wafer-level and wafer-to-wafer variation of central frequency are within 1.8–2.1 GHz. Computer simulation verified that this frequency variation correlates to the piezoelectric film variation of 1.6–1.9 μm. Process control on this piezoelectric thin film is essential to maintaining the resonator frequency-controlled value when building duplexer RF circuits. The dependency of RF performance on FBAR size, density and orientation is not obvious, compared to that of the wafer-level FBAR device variation on fabrication process. Regarding to the Mg-doping effect in MgxZn1-xO piezoelectric film, the amount of Mg in MgxZn1-xO film during the sputtering process must be properly controlled within 30% to keep the piezoelectric quality. The average acoustic speed of the Mg-doped ZnO film is 6870 m/s with the estimated range of 5760–7980 m/s, which is better than that of pure ZnO film (6330 m/s).

Elastic dynamics modelling and analysis for a valve train including oil film stiffness and dry contact stiffness

An elastic dynamics model for a valve train including combined stiffness of oil film and dry contact between a cam and a tappet, is proposed. Multi-directional elastic deformations of the valve train are solved by discretizing slender components into Rayleigh beam and bar elements. The oil film stiffness is determined by non-Newtonian elastohydrodynamic lubrication in the line contact, whereas the dry contact stiffness is achieved by using finite element contact analysis. A numerical solution for the dynamic model is developed and verified by conducting a dynamic stress experiment. The influences of rotation speed on the oil film stiffness and contact force between the cam and the tappet are discussed, and the combined effects of rotation speed and oil film stiffness on a dynamic transmission error of the valve train are analyzed. Results show that the oil film stiffness decreases when the cam rotation speed increases within a certain range, whereas the sharp increased contact force may enlarge the oil film stiffness when the speed exceeds a critical value. The oil film stiffness variation slight influences the contact force, but such variation significantly affects the dynamic transmission error.

Spiral Groove Face Seal Behavior and Performance in Liquid Lubricated Applications

ABSTRACTA series of experiments was conducted to study the behavior and performance of a spiral groove mechanical face seal in liquid lubricated applications. The seal's ability to contain water from ambient to near saturation conditions was tested. A comparison of experimental results with a numerical solution of the Reynolds equation under isothermal conditions was done. Two-phase and non-laminar flows were observed because of high speed, high temperature and high film thickness. Different lubrication regimes, such as mixed and hydrodynamic, were also reached. The results show that the spiral groove face seal can work for a large operating range with a lower friction factor but a higher leakage than the smooth face seal configuration.

Roll-to-Roll Mechanical Peeling for Dry Transfer of Chemical Vapor Deposition Graphene

Scaling up graphene fabrication is a critical step for realizing industrial applications of chemical vapor deposition (CVD) graphene, such as large-area flexible displays and solar cells. In this study, a roll-to-roll (R2R) graphene transfer system using mechanical peeling is proposed. No etching of graphene growth substrate is involved; thus, the process is economical and environmentally benign. A prototype R2R graphene transfer machine was developed. Experiments were conducted to test the effects of relevant process parameters, including linear film speed, separation angle, and the guiding roller diameter. The linear film speed was found to have the highest impact on the transferred graphene coverage, followed by the roller diameter, while the effect of separation angle was statistically insignificant. Furthermore, there was an interaction effect between the film speed and roller diameter, which can be attributed to the competing effects of tensile strain and strain rate. Overall, the experimental results showed that larger than 98% graphene coverage could be achieved with high linear film speed and large guiding roller diameter, demonstrating that a large-scale dry graphene transfer process is possible with R2R mechanical peeling.

Dynamic Characteristics Analysis of Spiral Groove Liquid Lubricated Seal Considering Centrifugal Inertia

A three degree of freedom model of spiral groove liquid lubricated seal was established for studying the effects of centrifugal inertia on dynamic characteristics. The dynamic stiffness and damping coefficients of liquid lubricated seal with centrifugal inertia and those without centrifugal inertia were obtained by means of finite element method, and then comparative analysis was carried out. Results indicate that dynamic stiffness and damping coefficients are increased linearly with the increase of rotating speed. Dynamic stiffness and damping coefficients decrease with the increasing film thickness. The effects of centrifugal inertia on axial stiffness coefficient and angular coupling stiffness coefficient can be neglected under different rotating speed and different film thickness. When the values of rotating speed and film thickness are large, the effect of centrifugal inertia on angle stiffness coefficient cannot be ignored. Centrifugal inertia has no effects on dynamic damping coefficients with the variation of rotating speed and film thickness.

Optimization of Growth Temperature of β-Ga₂O₃ Thin Films for Solar-Blind Photodetectors.

Monoclinic gallium oxide thin films were deposited on c-plane sapphire substrates at various substrate temperatures ranging from 450 °C to 700 °C by radio frequency magnetron sputtering technology. X-ray diffraction results showed that the deposited β-Ga2O3 films were oriented at (<mml:math display="block"> <mml:mover accent="true"> <mml:mn>2</mml:mn> <mml:mo>¯</mml:mo> </mml:mover></mml:math>01) direction. As the substrate temperature increased, the intensity of β-Ga2O3 peaks increased and bandgap decreased accordingly. Metal/semiconductor/metal structured solar-blind photodetectors based on β-Ga2O3 thin films growing at various substrate temperatures had been fabricated. The growth temperatures of thin films had no obvious influence on dark current and response to 365 nm light illuminations. The photoelectric properties such as responsivity and response speed of the thin films to 254 nm light illuminations were growth temperature dependent. At an applied bias of 50 V, the photodetectors prepared with 450 °C grown film had the highest responsivity of 2.18 A/W, and the photodetectors prepared with 700 °C grown film had the shortest rising time of 0.95 s under 254 nm light illuminations.

Asymptotic theory of fluid entrainment in dip coating

When a contact line moves with a sufficiently large speed, liquid or gas films can be entrained on a solid depending on the direction of contact-line movement. In this work, the contact-line dynamics in the situation of a generic two-fluid system is investigated. We demonstrate that the hydrodynamics of a contact line, no matter whether advancing or receding, can formally reduce to that of a receding one with small interfacial slopes. Since the latter can be well treated under the classical lubrication approximation, this analogy allows us to derive an asymptotic solution of the interfacial profiles for arbitrary values of contact angle and viscosity ratio. For the dip-coating geometry, we obtain, with no adjustable parameters, an analytical formula for the critical speed of wetting transition, which in particular predicts the onset of both liquid and gas entrainment. Moreover, the present analysis also builds a novel connection between the Cox–Voinov law and classical lubrication theory for moving contact lines.

Two-photon actuation of crosslinked liquid-crystalline polymers utilizing energy transfer system

ABSTRACTWe prepared crosslinked azotolane liquid-crystalline polymer (LCP) films doped with a stilbene derivative (two-photon chromophore) utilizing an interpenetrating polymer network (IPN) structure. The IPN films bend toward the light source upon irradiation with femtosecond laser pulses at 600 nm, which can excite the stilbene derivative by two-photon absorption. The bending speed of the IPN films increases with the square of the laser pulse intensity, which is compelling evidence for the two-photon processes.

Hollow Spherical Nanoshell Arrays of 2D Layered Semiconductor for High‐Performance Photodetector Device

AbstractWell‐defined hollow spherical nanoshell arrays of 2D transitional metal dichalcogenide (TMDC) nanomaterials for MoSe2 and MoS2 are grown via chemical vapor deposition technique for the first time. The hollow sphere arrays display the uniform dimensions of ≈450 nm with the shell thickness of ≈10 nm. The unique hollow sphere architecture with increased active surface area is forecasted to supply more efficient route to improve light‐harvesting efficiency through repeated light reflection and scattering inside the hollow structure without decay of response and recovery speed, because exceptional “SP–SP” junction barriers conducting mechanism can facilitate carriers tunneling and transport during the electron transfer procedure within the present particular structure. The MoSe2 hollow sphere photodetector exhibits an outstanding responsivity (8.9 A W−1), which is tenfold higher than that for MoSe2 compact film (0.9 A W−1), fast response and recovery speed, and good durability under illumination wavelength of 365 nm. Meanwhile, MoSe2 hollow sphere arrays on flexible polyethylene terephthalate substrates reveal excellent bending stability. Therefore, this research indicates that unique hollow sphere architecture of 2D TMDC materials will be an anticipated avenue for efficient photodetector devices with far‐ranging capability.

Mechanical behaviour of graphdiyne film: experimental and molecular dynamics simulation

AFM experiments and molecular dynamics simulation of rectangular graphdiyne films are performed in this paper. The force-deflection curves are obtained, and the elastic modulus is calculated as 218.5 GPa and 482.615 GPa, respectively. The simulated maximum stress and pre-tension of graphdiyne film are 33.088 GPa and 0.551 GPa, respectively. It is observed that the graphdiyne film fractured in the central point once the indentation depth over the critical depth. Also, the obviously elastic behaviour has found during the loading-unloading-reloading process. The deformation mechanisms and fractured behaviour of the graphdiyne film are discussed in detail during the loading process. Moreover, the effects of various factors including loading speed and indenter radii of the graphdiyne film by the MD simulation are discussed.

The numerical simulation and experiment on extrusion roller embossing of light diffusion plate with micro-structure

Extrusion roller embossing process has demonstrated the ability to produce polymer film with micro-structure. However the influence of various parameters on the forming quality has not been understood clearly. In this paper, a light diffusion plate with semi cylindrical micro-structure array as the research object, the influence of the main processing parameters such as roller speed, pressuring distance and polymer film temperature to the rolling quality was investigated in detail by simulation and experimental methods. The results show that the thickness of the light diffusion plate and the micro-structure fitting diameter increases with the increasing of the roll speed and the polymer film temperature, and decreases with the increasing of the pressing distance. Besides, the simulation results conformed well to the experimental results.

Graphene quantum dots enhance UV photoresponsivity and surface-related sensing speed of zinc oxide nanorod thin films

Thin films of almost vertically-grown zinc oxide nanorods (ZnO NR) were prepared via a solvothermal method, and graphene quantum dots (GQDs) were synthesized by pyrolyzing citric acid. Various amounts of GQDs were loaded onto ZnO NR thin films by applying a dip-coating process for different times. Field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), transmission electron microscopy (TEM), and X-ray diffractometry (XRD) were employed to characterize the structures. UV–visible spectra of the thin films showed no significant change in the bandgap (~3.3eV) after incorporating GQDs, which is appropriate for visible-blind UV sensing applications. Photoluminescence (PL) spectra showed a significant decrease in the PL intensity of the ZnO NR thin film after incorporating GQDs, suggesting that the generated electrons can be better separated from their hole counterparts and hence contribute to the generated photocurrent. Finally, UV sensing analysis was performed, indicating that GQDs can enhance both the UV-induced photocurrent and the sensing speed of ZnO NR thin films; however, the improvement in the surface-related UV sensing was higher than in the bulk-related one, which could be attributed to the numerous active sites and edge effects of GQDs. The enhanced photocurrent was discussed based on the band diagram.

ZnSe quantum dots downshifting layer for perovskite solar cells

To date, the instability of organometal halide perovskite solar cells (PSCs) has become the focus issue that limits the development and long-term application of PSCs. Both the ultraviolet (UV) rays in sunlight and moisture in air can significantly accelerate the disintegration of the perovskite. Here, we introduced a ZnSe quantum dots layer as downshifting materials, which was spin-coated onto the backside of PSCs. This layer converted the UV rays into visible light to prevent the destruction of PSCs as well as increase the light harvesting of the perovskite layer. Under the UV irradiation in the moisture ambient (40%), the destruction speed of the unencapsulated perovskite films were also delayed evidently. In addition, the power conversion efficiency (PCE) of the PSCs was increased from 16.6% to 17.3% due to the increase of the visible light absorbance of the perovskite.