Biaxial Film Research Articles

Radiative heat transfer between biaxial hyperbolic film in the far-field and near-field

Thin films demonstrate considerable potential in the realms of radiative heat transfer and play a major role in thermal rectification and energy conversion. Hyperbolic materials can effectively promote radiative heat transfer due to the ability to excite hyperbolic polaritons in a wide range of hyperbolic bands. However, the potential of biaxial hyperbolic film in radiative heat transfer remains insufficiently explored. In this work, the radiative heat transfer between α-phase molybdenum trioxide (α-MoO3) is theoretically investigated, considering separations ranging from 20 nm to 2 μm. When considering radiative heat flux along the [010] direction, the near-field radiative heat flux of α-MoO3 with a thickness of 10 nm is only 8 % less than that of the bulk material and exceeds the blackbody limit by approximately three orders of magnitude at a separation of 20 nm. This phenomenon is attributed to the excitation of hyperbolic polaritons. Conversely, when the gap distance is 1000 nm, the heat flux between films is an order of magnitude lower than that between bulk materials. These findings help study radiative heat transfer between thin films at micro- and nano-scale.

Effects of electrothermal ageing on dielectric performance of metallised biaxial orientation polypropylene film capacitors in strong magnetic fields

Effects of electrothermal ageing on dielectric performance of metallised biaxial orientation polypropylene film capacitors in strong magnetic fields

Negative biaxial retarder made from reactive molecules with X-shaped core structure

Although biaxial retarder films have merits of optical applications, limited numbers of the biaxial retarder have been developed using reactive mesogen (RM) materials. New X-shaped RM (XRM) molecules were synthesized and optical retarder films were fabricated using mixtures of a rodlike RM and the XRM. The in-plane retardation, the out-of-plane retardation and the NZ coefficient of the retarder films were investigated. The retarder films represented negative biaxial property or z-plate property depending on the chemical structure and the concentration of XRM.

Large spatial shifts of reflected light beam off biaxial hyperbolic materials

Many optical systems that deal with polarization rely on the adaptability of controlling light reflection in the lithography-free nanostructure. In this study, we explore the Goos–Hänchen (GH) shift and Imbert–Fedorov (IF) shift in a biaxial hyperbolic film on a uniaxial hyperbolic substrate. This research statistically calculates and analyzes the GH shift and IF shift for the natural biaxial hyperbolic material (NBHM). We select the surface with the strongest anisotropy within the NBHM and obtain the complex beam-shift spectrum. By incorporating the NBHM film, the GH shift caused by a transversely magnetic incident-beam on the surface increases significantly compared with that on the uniaxial hyperbolic material. The maximum of GH shift can reach 86λ 0 at about 841 cm−1 when the thickness of NBHM is 90 nm, and the IF shift can approach 2.7λ 0 for a circularly-polarized beam incident on a 1700-nm-thick NBHM. It is found that the spatial-shift increases when a highly anisotropic hyperbolic polariton is excited in hyperbolic material, where the shift spectrum exhibits an oscillating behaviour accompanied with sharp shift peak (steep slope). This large spatial shift may provide an alternative strategy to develop novel sub-micrometric optical devices and biosensors.

A biaxial stretchable, flexible electric heating composite film for de-icing

Icing on some flexible components which generally arises large deformation in work, such as air spring of high-speed rail and helicopter rotor, greatly threatens the safety of operation. Thus, flexible and stretchable de-icing capability are demanded to prevent ice accumulation on these flexible components. In this study, a novel flexible, biaxial stretchable electric heating film (BSF) with fast thermal response is developed for de-icing. The BSF was fabricated by combining conductive rubber materials with stretchable electrode which was prepared by silver plating on fiber cloth. To further reduce the tensile stress and resistance change of BSF, BSF with biaxial kirigami structure (BK-BSF) was explored, with excellent stretchable electro thermal performance, i.e., Joule heat can be generated when stretched by 40% along and perpendicular to the electrode directions. This study provides a feasible technical scheme for the anti-icing of flexible components.

Design and Analysis of a Mandrel Process to Control the Properties of Poly(p-Phenylene Terephthalamide) Films

Abstract Kinematic and rheological considerations have been used to design and analyze the processing steps for obtaining biaxial chain orientation in poly(p-phenylene terephthalamide) (PPTA) films. A semi-quantitative approach to the mandrel design allows one to predict the type and degree of molecular orientation obtained. For the case of PPTA dissolved in H2SO4, the basic steps are extrusion of the liquid crystalline solution through an annular die followed by expansion and elongational flow over a mandrel. The mandrels used include conical, hyperbolic and ogival shapes. Molecular orientation as well as mechanical properties were found to be dependent on mandrel shape and presence. Wide angle x-ray diffraction (WAXS) techniques using White-Spruiell orientation factors and pole figures were used to characterize the films. Mechanical properties as well as the above techniques indicate a high degree of biaxial orientation can be obtained with a bias in certain film directions depending on the mandrel used. Tensile strength and Young's modulus values were found to be on the order of 30 000 psi and one million psi respectively. They also can be equally distributed in the film plane depending on mandrel shape. White-Spruiell orientation factors were as high as 0.49 and 0.5 for f 1 B a n d f 2 B $f_{1}^{B}\text{ }and\text{ }f_{2}^{B}$ respectively. Scanning electron microscopy was used to observe the film superstructure as a function or processing conditions. All films exhibited a skin-core structure. Uniaxially drawn films are fibillar while the biaxial films appear to be more homogeneous.

Biaxial film bulk acoustic resonator magnetic sensor based on the Fe80Ga20 anisotropic ΔE effect

With the increasing application of personal navigation systems in consumer electronics, the demand for multi-axis magnetic sensors based on MEMS is growing. We report a biaxial MEMS DC magnetic sensor consisting of an Mo/AlN/Fe80Ga20 film bulk acoustic resonator, with anisotropy ΔE effect-based sensing principle. Different from the previously reported 1D magnetic sensor based on the ΔE effect, the anisotropic ΔE effect was used to realize in-plane and out-of-plane 2D magnetic field responses on a discrete sensor, and the sensor had two readout methods: resonant frequency f and return loss S11. The magnetic sensor realized the resonant frequency f shifted by 1.03 MHz and 0.2 MHz in the 567 Oe in-plane magnetic field and 720 Oe out-of-plane magnetic field, respectively, and the S11 changes by −30.2 dB and −0.92 dB. As the applied magnetic field increases, the −3 dB bandwidth quality factor Q 3dB of the S11 curve gradually increases, and its maximum values in the in-plane and out-of-plane magnetic fields are 77 143 and 1828, respectively, which reduces the detection limit of the magnetic sensor. The resonant magnetic sensor has stable high linear temperature and frequency drift characteristics, and its temperature frequency coefficient is −48.7 ppm °C−1.

Crosslinking effect on polyvinyl alcohol resin for barrier properties of barrier biaxial orientation films

A novel barrier chemical coating was formulated and developed by using an organic and inorganic sol-gel process. In this work, a hybrid solution was prepared using different percentages of cross-linker into a polyvinyl alcohol and Tetraethyl orthosilicate to improve the barrier properties of biaxial oriented polypropylene (BOPP) films. The TGA results showed that thermal stability had been enhanced after incorporating tetraethyl orthosilicate as inorganic materials. The transparency of coated films showed enhanced e.g. haze percentage, which improved about 12% and gloss properties were for 90 GU. The coated side and plain side COF were measured at about 0.4, COF is an important slip property at the end-use application. After coating, printing properties were checked and found that the thickness and particle size of pigment were uniform and color strength was also suitable for the packaging applications. The oxygen transmission rate (OTR) properties have been improved from 1880 cc/m2/day to 0.9 cc/m2/day compared to a plain film. The water vapor transmission rate (WVTR) properties have been improved from 10 g/m2/day to 5.9 g/m2/day a plain film. The application of the films showed an excellent barrier for bread packed in coated film and checked for nine days. The results showed that micro-organism was reduced by enhancing the barrier properties by applying the coating on film.

The intrinsic Josephson effect of Bi-2212 superconducting thin films prepared by sol-gel method

In this paper, Bi2Sr2Ca1Cu2O8+σ (Bi-2212) superconducting thin films was prepared by using a sol-gel method on a LaAlO3 (LAO) single crystal substrate, with acetates of bismuth, strontium, calcium, and copper as the starting raw materials. A step structure was specifically designed to measure the intrinsic Josephson effect. The microstructure of the Bi-2212 thin films and their epitaxial growth on the LAO substrate were analyzed by a Cs-corrected transmission electron microscope (Cs-TEM) with an atomic-level resolution and the electrical properties were measured. The results showed that the prepared Bi-2212 thin films had good epitaxial growth characteristics and good in-plane and out-plane growth texture and that its critical transition temperature, Tc, was 87 K. The interface between the substrate and the film was well-defined; the films grow epitaxially on the substrate from the CuO layer, with a highly ordered atom arrangement. The I–V characteristic curve of the prepared step micro-bridging sample showed zero-voltage overcurrent phenomenon, and the critical current was 2.3 mA. In addition, multiple current-voltage jumps were observed on the curve, indicating that the prepared biaxial texture thin films showed the intrinsic Josephson effect.

Highly epitaxial YBa2Cu3O7−δ films grown on gradient La2−x Gd x Zr2O7-buffered NiW-RABiTS using all sol–gel process

The overall purpose of this work is to develop a reliable and low-cost technique for fabrication of coated conductors (CCs) on the flexible substrates, and to understand the effects of oriented growth and microstructure on the superconducting performance of CCs in-depth. The investigations of gradient La2−x Gd x Zr2O7 buffer architecture and YBa2Cu3O7−δ (YBCO) film on Ni-5at%W rolling-assisted biaxially textured substrate using all sol–gel process are reported. Combining x-ray diffraction and transmission electron microscopy (TEM) analysis, it is revealed that the gradient buffer architecture with increased lattice constant along the direction of film growth has an excellent c-axis orientation, while the inversed gradient architecture with decreased lattice constant shows the deteriorated orientation, indicating that the highly epitaxial growth mechanism most likely related to the interfacial lattice matching degree. The detailed analysis of YBCO films grown on gradient La2−x Gd x Zr2O7 under different deposition parameters, and the influence of microstructure on electrical properties are systematically discussed using x-ray diffraction, rocking curve test, scanning electron microscopy and TEM observations. Finally, the excellent biaxial texture YBCO film on gradient La2−x Gd x Zr2O7 buffer architecture is prepared at a proper heat-treatment temperature of 780 °C, and the full width at half maximum of ϕ-scan and ω-scan are 5.9° and 6.4°, respectively. The critical transition temperature T c,onset of the as-prepared YBCO film is 90 K. With elevating the temperatures, the appearance of a large number of weak-link and amorphous regions, being indicative of the microstructural collapse, is mainly responsible for the reduced superconductivity.

Magneto-Seebeck microscopy of domain switching in collinear antiferromagnet CuMnAs

Antiferromagnets offer spintronic device characteristics unparalleled in ferromagnets owing to their lack of stray fields, THz spin dynamics, and rich materials landscape. Microscopic imaging of antiferromagnetic domains is one of the key prerequisites for understanding physical principles of the device operation. However, adapting common magnetometry techniques to the dipolar-field-free antiferromagnets has been a major challenge. Here we demonstrate in a collinear antiferromagnet a thermoelectric detection method by combining the magneto-Seebeck effect with local heat gradients generated by scanning far-field or near-field techniques. In a 20-nm epilayer of uniaxial CuMnAs we observe reversible 180∘ switching of the Néel vector via domain wall displacement, controlled by the polarity of the current pulses. We also image polarity-dependent 90∘ switching of the Néel vector in a thicker biaxial film, and domain shattering induced at higher pulse amplitudes. The antiferromagnetic domain maps obtained by our laboratory technique are compared to measurements by the established synchrotron-based technique of x-ray photoemission electron microscopy using x-ray magnetic linear dichroism.Received 5 June 2020Accepted 12 August 2020DOI:https://doi.org/10.1103/PhysRevMaterials.4.094413©2020 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasAntiferromagnetismMagnetic domainsSeebeck effectSpintronicsPhysical SystemsAntiferromagnetsTechniquesAtomic force microscopyNear-field optical spectroscopyScanning techniquesCondensed Matter, Materials & Applied Physics

Enhanced Dispersion and Mechanical Behavior of Polypropylene Composites Compounded Using Extension-Dominated Extrusion

Abstract The process of dispersing filler in polymer matrix is vital to the behavior of polymer composites. The current study involves understanding the extent of dispersion of filler by only varying the nature of mixing during the process. Identical polymer composite materials are processed via two different kinds of mixing sections on the screw in a twin-screw extruder, differing in the type and amount of stress they impose on the filler agglomerate. An aggressive (900) Kneading Block (KB) mixing section is compared with recently developed Extensional Mixing Elements (EMEs), which impart extension dominated mixing while KB imparts shear dominated mixing. Various EME geometries of different levels of aggressiveness were computationally studied and validated. Composites obtained from KB are compared with composites processed using five different EME geometries. Three composites of Polypropylene (PP) filled with carbon black, graphene nano platelets and carbon nanotubes were studied independently. Composites processed through EMEs display about an order of magnitude better dispersion of filler agglomerate over the composites processed through KB. In addition, enhanced modulus and yield stress is observed for composites processed through EMEs. An improvement of 63% to 266% in the strain achieved for EME processed composites is seen under biaxial film stretching.

Correlation between the wafer curvature and fluorescence of pulsed laser deposited ruby thin films stressed to ∼2 GPa

Here, the room temperature piezospectroscopic response of highly-fluorescent, ∼330 nm-thick pulsed laser deposited crystalline ruby (0.05 wt. % Cr3+ doped α-Al2O3) thin films on either (001)-oriented sapphire or (001)-oriented yttria-stabilized zirconia wafers was investigated and calibrated against biaxial film stress measurements obtained from a multibeam optical stress sensor or profilometry-determined wafer curvature measurements. The piezospectroscopic frequency shift from 0 to 1.9 GPa of compressive biaxial stress for the phase-pure (001)-oriented ruby films produced here had the same piezospectroscopic Π11 and Π22 tensor coefficient values as bulk ruby over its previously calibrated 0–0.9 GPa range. This extended calibration may be useful when using ruby to measure the amount of biaxial stress in a variety of multilayer devices and coatings.

Research on fast self-learning improvement of ADRC control algorithm for film thickness control system

In the biaxially stretched film (BOPP) thickness control system, the traditional PID and Active-Disturbance Rejection Controller (ADRC) can’t achieve the ideal control effect. The Smith prediction method is used in the essay to establish a discretization model for the BOPP thickness control system. Combining with BP self-learning algorithm, a fast self-learning improved ADRC control algorithm (FSADRC) is proposed. By means of the additional momentum term and the adaptive learning rate method, the nonlinear combination of the ADRC system is adjusted in real time, the optimal control parameters are found, and the parameters are self-tuned. As a consequence, the improved algorithm is applied to the biaxial tensile film thickness control model. The simulation results show that the method has the advantages of high response speed and strong self-adaptive ability, which can effectively improve the control performance of the BOPP thickness control system.

Experimental Analyses on Multiscale Structural and Mechanical Properties of ε-Si/GeSi/C-Si Materials

Strained silicon (ε-Si) is a promising material that could extend Moore’s law by enhancing electron mobility. A ε-Si material is usually composed of multiscale, multilayer heterostructures, where the strained-silicon film or strap is tens-of-nanometers thick, and its buffer layers are of the micrometer scale. The structural properties determine the electrical performance and reliability of ε-Si-based devices. Inhomogeneous residual stress is induced during the preparation, which induces ε-Si structure failure. In this work, biaxial strained-silicon films that contain graded and relaxed germanium-silicon buffer layers were prepared on monocrystalline silicon wafers through reduced-pressure chemical-vapor epitaxy. The layer components and thicknesses were measured using energy-dispersive spectroscopy and scanning-electron microscopy. Crystal and lattice characters were observed by using high-resolution transmission-electron microscopy and micro-Raman spectroscopy. The residual stress distribution along cross-sections of the ε-Si multilayer structures was examined by using micro-Raman mapping. The experimental results showed that, with a gradual increase in germanium concentration, the increasing residual stress was suppressed owing to dislocation networks and dislocation loops inside the buffer layers, which favored the practical application.

Narrowing of the Boolchand intermediate phase window for amorphous hydrogenated silicon carbide

Intermediate phases represent the so called “sweet spot” in amorphous material systems where the bond stretching and bond bending constraint forces are equally balanced by the total degrees of freedom in the system. They are sometimes also referred to as “Boolchand” phases in recognition of the seminal contributions of Dr. Punit Boolchand to the study of these materials. In a prior publication (King et al., J. Non-Cryst. Solids 379 (2013) 67), we presented possible evidence for the existance of an intermediate (i.e. “Boolchand”) phase in amorphous hydrogenated silicon carbide (a-SiC:H) with a wide range in mean atomic coordination (〈r〉 = 2.4 − 2.7). Support for such a wide phase window was based primarily on a correlation between the post plasma deposition bi-axial film stress and 〈r〉. However, we demonstrate in the present article that the apparent width of the Boolchand intermediate phase window in the prior study was inflated due to two competing film stress contributions, and that the true range in 〈r〉 for the phase window is substantially narrower. Specifically, opposing tensile and compressive film stress components were identified to arise during the plasma enhanced chemical vapor deposition (PECVD) of a-SiC:H. The tensile film stress component was attributed to film/substrate thermal contraction mismatch on cooling from the deposition temperature, while the compressive stress component was attributed to ion bombardment of the a-SiC:H growth surface during PECVD. In the prior study, the energy of the ions during PECVD was primarily modulated by the addition of a low frequency bias to the plasma and was intentionally utilized to produce films with varying compressive stress and 〈r〉. In the present study, the low frequency bias was removed from the PECVD of a-SiC:H and instead the deposition pressure was varied to produce films with varying 〈r〉 and exclusively tensile stress. Through detailed analysis of the tensile bi-axial film stress and Young's modulus dependence on 〈r〉, we found conclusive evidence that the film-substrate thermal contraction mismatch was the dominant film stress component in this case and that the magnitidue of the tensile stress was purely due to rigidity percolation in the a-SiC:H film. We therefore conclude that in our previous study the balance of the tensile and compressive stress components resulted in the deceptive appearance of a potentially wide Boolchand intermediate phase window for a-SiC:H. Based on the a-SiC:H films generated in the present study where only the tensile stress component was significant, we have found the window for a possible intermediate phase to be greatly narrowed at Δ〈r〉 ≤ 0.05.

The Effect of Different Additives in the in-Situ Stress of Thin Co Films

Fe, Co and Ni (and their alloys) are widely used due to their interesting ferromagnetic, chemical, and physical properties. Electrodeposited thin films tend to develop sizable mechanical stresses as a result of the nucleation and growth process. Often, these stresses can approach or exceed the yield stress of the bulk material and can lead to loss of adhesion and the generation of bulk and surface defects. Models have been developed that treat steady-state stress as a dynamic competition between tensile and compressive stress generation mechanisms that are largely governed by atomic mobility, microstructure, and deposition rate. Although additives are often used to mitigate residual stress during thin film growth, the exact mechanisms by which these additives influence residual stress is an active area of research. In this talk, we examine the growth stress associated with electrodeposition of Co thin films onto (111)-textured Au cantilever electrodes from 0.5 M Na2SO4 containing 0.1 M CoSO4 and 0.5 M H3BO3. The stress was measured with an optical cantilever curvature technique that can be used during deposition to determine the real-time stress evolution. Deposition was also examined using an electrochemical quartz crystal microbalance (EQCM) in order to determine the current efficiency as a function of both overpotential and deposition time. We have measured the average biaxial film stress as a function of overpotential and observe a significant increase in tensile stress as the deposition potential is made more negative. These results are discussed in the context of stress generating models that appear in the literature. The growth stress was also examined from 0.5 M Na2SO4 + 0.1 M CoSO4 electrolyte with controlled additions of glycine and boric acid. Each additive was studied under a specific potential window, as determined by the observed influence the additives have on Co deposition. Glycine acts as a buffer, maintaining a stable H+ concentration. The buffering product glycinate (Gly-) complexes with Co2+, thereby shifting the deposition window. Baths with boric acid have an average current efficiency between 40 and 90%, produce deposits with high tensile stress which undergo little postdeposition relaxation. Current efficiency from glycine baths range between 20 and 70%. Deposits generally have lower tensile stress and exhibit additional post-deposition stress relaxation.

Blue-phase liquid crystal display with insulating protrusion

ABSTRACTIn order to lower the saturation voltage and enhance the transmittance of in-plane switching blue-phase liquid crystal display (IPS-BPLCD), IPS-BPLCD with insulating protrusion is proposed. The single-protrusion (only set on the top of pixel electrode) and double-protrusion (set on the top of pixel and common electrodes) structures are investigated in this work. The potential distribution changes when the protrusion is used. There is a thicker transverse electric field in BPLC range, because the stronger electric field at the edges of the electrodes is decentralised into BPLC range. As a result, the saturation voltage is reduced from 36.3 V to 28.9 V when the double-protrusion structure is used, and transmittance is increased by ~20%. The contrast ratio is larger than 1000:1 in 60° viewing cone using a half-wave biaxial film. Both single-protrusion and double-protrusion structures have the uniform gamma curves at large oblique viewing angles. Moreover, the off-axis image distortion index is 0.1590 at 60º polar angle when zigzag electrodes are used.

Growth of magnetic nanowires along freely selectable \u2329hkl\u232a crystal directions

The production of nanowire materials, uniformly oriented along any arbitrarily chosen crystal orientation, is an important, yet unsolved, problem in material science. Here, we present a generalizable solution to this problem. The solution is based on the technique of glancing angle deposition combined with a rapid switching of the deposition direction between crystal symmetry positions. Using iron–cobalt as an example, we showcase the simplicity and capabilities of the process in one-step fabrications of 〈100〉, 〈110〉, 〈111〉, 〈210〉, 〈310〉, 〈320〉, and 〈321〉-oriented nanowires, three-dimensional nanowire spirals, core–shell heterostructures, and axial hybrids. Our results provide a new capability for tailoring the properties of nanowires, and should be generalizable to any material that can be grown as a single-crystal biaxial film.

Ambient contrast ratio of LCDs and OLED displays

We systematically analyze the ambient contrast ratio (ACR) of liquid crystal displays (LCDs) and organic light-emitting diode (OLED) displays for smartphones, TVs, and public displays. The influencing factors such as display brightness, ambient light illuminance, and surface reflection are investigated in detail. At low ambient light conditions, high static contrast ratio plays a key role for ACR. As the ambient light increases, high brightness gradually takes over. These quantitative results set important guidelines for future display optimization. Meanwhile, to improve an OLED’s ACR at large oblique angles, we propose a new broadband and wide-view circular polarizer consisting of one linear polarizer and two biaxial films. Good performance is realized.