Aligned Films Research Articles

Extreme Polarization Anisotropy in Resonant Third-Harmonic Generation from Aligned Carbon Nanotube Films.

Carbon nanotubes (CNTs) possess extremely anisotropic electronic, thermal, and optical properties owing to their 1D character. While their linear optical properties have been extensively studied, nonlinear optical processes, such as harmonic generation for frequency conversion, remain largely unexplored in CNTs, particularly in macroscopic CNT assemblies. In this work, macroscopic films of aligned and type-separated (semiconducting and metallic) CNTs are synthesized and polarization-dependent third-harmonic generation (THG) from the films with fundamental wavelengths ranging from 1.5 to 2.5µm is studied. Both films exhibited strongly wavelength-dependent, intense THG signals, enhanced through exciton resonances, and third-order nonlinear optical susceptibilities of 2.50×10-19 m2 V-2 (semiconducting CNTs) and 1.23×10-19 m2 V-2 (metallic CNTs), respectively are found, for 1.8µm excitation. Further, through systematic polarization-dependent THG measurements, the values of all elements of the susceptibility tensor are determined, verifying the macroscopically 1D nature of the films. Finally, polarized THG imaging is performed to demonstrate the nonlinear anisotropy in the large-size CNT film with good alignment. These findings promise applications of aligned CNT films in mid-infrared frequency conversion, nonlinear optical switching, polarized pulsed lasers, polarized long-wave detection, and high-performance anisotropic nonlinear photonic devices.

(Invited) Macroscopically Aligned Carbon Nanotubes for Photonics, Electronics, and Thermoelectrics

The remarkable flexibility, stable chemical structure, and extraordinary thermal, electrical, and optical properties of carbon nanotubes (CNTs) are promising for a variety of applications in flexible and/or high-temperature electronics, optoelectronics, and thermoelectrics, including wearables, refractory photonics, and waste heat harvesting. However, the long-standing goal in the preparation of CNT ensembles is how to maintain the extraordinary properties of individual CNTs on a macroscopic scale. The polydispersity and randomness remain two main challenges. Here, we will discuss different methods for creating macroscopically aligned CNTs, including spontaneous formation of wafer-scale aligned CNT films via controlled vacuum filtration and production of ultrahigh-conductivity CNT fibers and films through solution spinning and coating. We will then describe the optical, dc and ac electrical, thermal, and thermoelectric properties of these materials. These results are promising for device applications in various fields such as flexible CNT broadband detectors, spectrally selective thermal emitters, and thermoelectric devices.

Super-strong and high-performance electrical film heater derived from silver nanowire/aligned bacterial cellulose film

High-performance electrical Joule heaters with high mechanical properties, low driving voltage, rapid response, and flexibility are highly desirable for portable thermal management. Herein, by using aligned bacterial cellulose (BC) and silver nanowire (AgNW), we fabricated a novel film heater based on Joule heating phenomena. The aligned BC film prepared by stretching BC hydrogel and hot-pressing drying technology showed outstanding mechanical properties and flexibility. The ultrahigh strength of up to 1018 MPa and the toughness of 20 MJ/m3 were obtained for the aligned BC film with 40% wet-stretching (BC-40). In addition, the aligned BC film could be folded into desirable shapes. The AgNW was spray-coated on the surface of aligned BC-40 film and then covered with polydimethylsiloxane to form a P@AgNW@BC heater. P@AgNW@BC heater showed excellent conductivity, which endowed the film heater with an outstanding Joule heating performance. P@AgNW@BC heater could reach ~ 98 ℃ at a very low driving voltage of 4 V with a rapid heating response (13 s) and long-term temperature stability. The P@AgNW@BC heater with such an outstanding heating performance can be used as a flexible heating device for different applications in daily life like deicing/defogging device, wearable thermotherapy, etc.Affiliations: Please check and confirm that the authors and their respective affiliations have been correctly identified and amend if necessary.yes, we confirmed the affiliations are correct.Article title: Kindly check and confirm the edit made in the article title.Thanks, the title is no problem.Graphical

Liquid crystal alignment effect and electro-optical characteristics of rubbing-atmospheric plasma coprocessing in ZnO alignment film according to concentration

Liquid crystal alignment effect and electro-optical characteristics of rubbing-atmospheric plasma coprocessing in ZnO alignment film according to concentration

Mannitol enhanced thermal conductivity and environmental stability of highly aligned MXene composite film

Multifunctional thermal management materials with high flexibility are urgently required to tackle the heat dissipation issues of highly integrated electronics. MXene is considered a promising two-dimensional (2D) material for preparing composite with high thermal conductivity. However, there still is a challenge to prepare highly aligned MXene composite for simultaneously achieving high thermal performance and excellent mechanical properties. Herein, a novel MXene composite film was synthesized by vacuum-assisted filtering MXene nano-sheets suspension containing non-toxic and pollution-free mannitol. Under the connection of mannitol, MXene nano-sheets in the MXene/mannitol composite film form a highly aligned structure, resulting in outstanding thermal and mechanical properties. In-plane and through-plane thermal conductivities are 36.3 and 1.06 W m−1 K−1 for the MXene/mannitol composite film prepared using MXene suspension with a mannitol content of 0.2 mol/L, which are higher by 172% and 193% than those of pure MXene film, respectively. As the heat sink for a high-power LED, the MXene/mannitol composite film also demonstrated an excellent heat dissipation efficiency outperforming pure MXene film. Moreover, the MXene/mannitol composite film exhibited noteworthy mechanical property and stable thermal conductivity after bending for 300 times. Our findings provide a promising approach to prepare high-performance heat spreader for the thermal management of modern electronic components.

P‐94: Enhancement of the reliability of TFT‐LCD displays by focusing on study of RDC

In this paper, the test of residual DC voltage was carried out on the test cells with different combinations of liquid crystal (LC), polyimide alignment film (PI) and color resist flat layer (PFA). Combined with the circuit simulation results, the residual DC voltage was comprehensively analyzed, it is its characteristics of "fast accumulation" and "slow release" that lead to the decrease in the reliability of TFT‐LCD display. By analyzing the characteristic parameters of related materials, we have given the optimal combination of materials to reduce the residual DC voltage. As various application scenarios require higher and higher panel performance and their material combinations become more and more complex, the research results in this article will be of great significance for improving the reliability of TFT‐LCD displays.

Perpendicular Alignment of Covalent Organic Framework (COF) Pore Channels by Solvent Vapor Annealing

Covalent organic frameworks (COFs) have showcased great potential in diverse applications such as separation and catalysis, where mass transfer confined in their pore channels plays a significant role. However, anisotropic orientation usually occurs in polycrystalline COFs, and perpendicular alignment of COF pore channels is ultimately desired to maximize their performance. Herein, we demonstrate a strategy, solvent vapor annealing, to reorient COF pore channels from anisotropic orientation to perpendicular alignment. COF thin films are first synthesized to have flexible N-H bonds in their skeletons, thus having structural mobility to enable molecular rearrangement. A solvent with low relative permittivity and a conjugated structure is then identified to have a strong affinity toward the COFs, allowing its vapor to easily penetrate into the COF interlayers. The solvent vapor weakens the π-π interaction and consequently allows the COF monolayers to dissociate. The COF monolayers undergo a reorientation process that converts from random stacking into the face-on stacking fashion, in which the through COF pores are perpendicularly aligned. The aligned COF film exhibits high separation precision toward ions featuring a size difference down to 2 Å, which is 8 times higher than that of the anisotropically oriented counterpart. This work opens up an avenue for COF orientation regulation by solvent vapor annealing and reveals the essential role of the perpendicular alignment of COF pore channels to enable precision separations.

Measurement of azo dye film with large photo-induced birefringence and complex refractive index

Azo dyes are valuable functional materials due to their sensitive response to and effective modulation of polarized light. It is essential to find out not only the optical anisotropy but also the complex refractive index of azo dye materials for photonics applications. We report here such measurements of highly ordered photoaligned azo dye films. The film has an apparent dichroic ratio of about 60. We model the photoaligned azo dye film systems using the Berreman transfer matrix. By means of regression fitting of the polarization dependent transmittance and reflectance data, we were able to determine the complex refractive indices of the aligned film at the wavelength range of 400–1000 nm. This material is found to have exceptionally large optical birefringence (Δn ∼ 0.75 at 632.5 nm and Δn ∼ 0.48 at 850.6 nm). The aligned azo dye film is valuable to applications such as coatable polarizers and optical modulation devices.

Femoral-Physeal-Sparing ACL Reconstruction With Lateral Extra-articular Tenodesis and Inside-Out Repair of Lateral Meniscus in a Skeletally Immature Patient

Background: Anterior cruciate ligament (ACL) reconstructions in skeletally immature patients have an increased risk of graft failure and a decreased rate of successful return to sports. Anterior cruciate ligament reconstructions (ACLRs) combined with lateral extra-articular tenodesis (LET) procedures are reported to limit anterolateral rotary instability of the knee, decreasing tension on the ACL graft. However, the open physes found in pediatric patients present unique challenges for ACLR. This video demonstrates a technique to avoid the femoral physis and necessary precautions for performing an ACLR with LET in a skeletally immature patient. Indications: The indications for combined ACLR and LET, as opposed to ACLR alone, mainly center on the risk factors for graft failure. These include the following: posterior tibial slope >12°, revision ACLR, high-grade pivot shift on physical examination, meniscal deficiency, generalized ligamentous hyperlaxity, and—especially pertinent to this procedure—skeletally immature patients. Technique Description: Standard plain radiographs and long-leg alignment films, along with a magnetic resonance imaging (MRI) study, are necessary to assess for malalignment, bone age, and concomitant meniscal and chondral pathology. This technique describes the senior author’s preferred technique for pediatric ACLR with LET. The senior author’s preferred order of operations includes performing the autologous hamstring graft harvest and LET before performing the diagnostic arthroscopy. This is followed by the intra-articular work including the ACLR. It is also the senior author’s preference to perform physeal-sparing femoral tunnels, using fluoroscopy for tunnel placement. Results: Getgood et al reported that an ACLR with an LET in young patients with a high risk of graft failure had a significant reduction in graft rupture compared to an ACLR alone. Furthermore, Noyes et al reported a significantly lower rate of graft failure and a higher rate of return to sports in those who received LET in addition to ACLR compared with those who received ACLR alone. Discussion: An ACLR combined with an LET has been reported to reduce graft failure rates and improve clinical outcomes in high-risk patients. An ACLR with LET may also be considered in skeletally immature patients with appropriate indications and extra precautions to avoid growth arrest or deformity. Patient Consent Disclosure Statement: The author(s) attests that consent has been obtained from any patient(s) appearing in this publication. If the individual may be identifiable, the author(s) has included a statement of release or other written form of approval from the patient(s) with this submission for publication.

Angular Dependence of Guest–Host Liquid Crystal Devices with High Pretilt Angle Using Mixture of Vertical and Horizontal Alignment Materials

To date, devices exhibiting incidence-angle-dependent transmittance have been fabricated by imparting an angle to a bulk liquid crystal (LC) by aligning the LC in the vicinity of one substrate horizontally (with respect to the substrate) while aligning the LC in the vicinity of another substrate vertically. Another approach has been to control LC angles near substrates by blending or layering horizontal and vertical alignment films. In this study, we control LC angles near substrates by controlling the pretilt angles of blended alignment films; for specific angles, we use dichroic dyes to characterize the incidence angle dependence of these LC devices. Using a guest/host LC device with a pretilt angle near 45°, we successfully construct an LC element with a transmittance peak near a polar angle of 45°.

Self-Assembly of Silver Nanowire Films for Surface-Enhanced Raman Scattering Applications.

The development of SERS detection technology is challenged by the difficulty in obtaining SERS active substrates that are easily prepared, highly sensitive, and reliable. Many high-quality hotspot structures exist in aligned Ag nanowires (NWs) arrays. This study used a simple self-assembly method with a liquid surface to prepare a highly aligned AgNW array film to form a sensitive and reliable SERS substrate. To estimate the signal reproducibility of the AgNW substrate, the RSD of SERS intensity of 1.0 × 10-10 M Rhodamine 6G (R6G) in an aqueous solution at 1364 cm-1 was calculated to be as low as 4.7%. The detection ability of the AgNW substrate was close to the single molecule level, and even the R6G signal of 1.0 × 10-16 M R6G could be detected with a resonance enhancement factor (EF) as high as 6.12 × 1011 under 532 nm laser excitation. The EF without the resonance effect was 2.35 × 106 using 633 nm laser excitation. FDTD simulations have confirmed that the uniform distribution of hot spots inside the aligned AgNW substrate amplifies the SERS signal.

Comparative study of liquid crystal variable retarder with rubbed polyimide and SiO2 thin films by glancing angle deposition

A comparative study on the optical, morphological and laser-induced damage characteristics of rubbed polyimide, SiO2 thin films by glancing angle deposition, and the corresponding liquid crystal (LC) retarders, is presented in this paper. SiO2 inorganic thin films were prepared with a deposition angle of 45[Formula: see text], and traditional polyimide (PI) films were prepared by spin coating and rubbing. The experimental results indicate that the SiO2 thin films have a good transmittance and resistance to laser damage. The transmittance of the SiO2 thin films was above 92% in the wavelength range 400–1200 nm, and that of the corresponding LC retarder was approximately 90% in the wavelength range 800–1200 nm. The laser-induced damage threshold of the SiO2 thin films reached 32.6 J/cm2, and that of the corresponding LC retarder was 1.84 J/cm2. These results are better than those of the PI alignment films. SiO2 thin films have potential for use in the LC optical devices for laser applications.

Temperature-switched orientation properties through physicochemically constructed aluminum zirconium oxide films

In general, it has one of the characteristics of homeotropic alignment and homogeneous alignment depending on the material and manufacturing process of the liquid crystal alignment layer. However, in this study, we propose a new type of alignment film that has the characteristics of changing the liquid crystal alignment direction according to the curing temperature. The AlZrO alignment film produced by the solution process and brush coating method showed homeotropic alignment characteristics when cured at low temperatures and homogeneous alignment characteristics when cured at high temperatures. These switching characteristics according to the curing temperature showed stable LC alignment, respectively, and the threshold voltages were 0.81 V and 0.857 V in vertical alignment (VA) mode and twisted nematic (TN) mode, respectively, demonstrating excellent electro-optical properties. The mechanism of these switching characteristics was analyzed through surface modification analysis. This study introduces new insights into liquid crystal alignment films that satisfy all of the high-efficiency fabrication process, various application possibilities due to their switching properties, and excellent electro-optical properties.

Elucidating the Origins of High Preferential Crystal Orientation in Quasi‐2D Perovskite Solar Cells (Adv. Mater. 5/2023)

Perovskite Solar Cells In article 2208061, Lukas E. Lehner, Martin Kaltenbrunner, and co-workers report the controlled nucleation of quasi-2D perovskites at the liquid–air interface of the precursor solution. Restricting the initial crystal growth to the surface of the liquid results in highly aligned perovskite thin films with improved charge transport, enabling efficient solar cells with excellent stability.

Orientation and mobility control of 4HCB organic film for flexible X-ray detectors with high performance

• The space-confined melt process is used to produce highly orientated organic semiconducting crystalline films with a large area. • Confined molecular packing significantly improves the hole mobility. • The 4HCB based X-ray detectors can achieve a high sensitivity with low dark current, result in outstanding direct imaging capabilities. • The device shows steady flexibility, with no degradation in detecting function after 100 cycles of bending. In comparison to inorganic counterparts, organic semiconducting (OSC) crystalline films are promising for building large-area and flexible ionizing radiation detectors for X-ray imaging or dosimetry due to their tissue equivalence, simple processing and large-scale production accessibility. Fabrication processes, however, hinder the ability to generate aligned and large-area films with high carrier mobility. In this work, the space-confined melt process is used to produce highly orientated 4HCB (4-hydroxycyanobenzene) OSC films with a large area of 15 × 18 mm 2 . The out-of-plane direction of the 4HCB film is <001>, and the benzene rings are found to be extensively overlapped inside the in-plane direction, according to the XRD patterns. The film exhibits a high resistivity up to 10 12 Ω cm, and high hole mobility of 10.62 cm 2 V −1 s −1 . Furthermore, the 4HCB (80-μm-thick film) based X-ray detectors can achieve a sensitivity of 93 μC Gyair −1 cm −2 and on/off ratio of 157. The device also shows steady flexibility, with no degradation in detecting function after 100 cycles of bending. Finally, the proposed 4HCB film detectors demonstrated a high-resolution X-ray imaging capability. The imaging of several materials with sharp edges (copper and polytetrafluoroethylene) has been obtained. This work has developed a fast but efficient approach for producing large-area, highly oriented OSC films for high-performance X-ray detectors.

Nematic liquid crystalline polymer films for gas separation

ABSTRACT The gas separation performances of free-standing planar aligned nematic LC polymer films were investigated for gas separations of He, CO2, CH4 and Xe. The films consist of derivatives of 1,4-phenylene bis(4-((6-(acryloyloxy)hexyl)oxy)benzoate)s with respective cyano, chloro, methyl and phenyl substituents on the central aromatic cores. Two new LC derivatives of 1,4-phenylene bis(4-((6-(acryloyloxy)hexyl)oxy)benzoate)s were successfully synthesised and fully characterised. Single gas permeation and sorption data show increasing gas permeabilities with increasing steric size of the substituents while the ideal gas selectivity of He over CH4 and He over CO2 decreases. The sorption coefficient of all films is independent of the LC substituents, while the subsequently extracted diffusion coefficient for the films with a phenyl substituent is three times higher compared to the films with a cyano substituent, demonstrating that the steric size of the LC substituents mainly affects the diffusion of gasses rather than the solubility of the gases. Irrespective of a methyl or a phenyl substituent, a larger kinetic diameter of Xe gives a 20 times lower diffusion coefficient compared to the smaller species (CO2).

Low aberration and fast response liquid crystal lens with optically compensated bend structures

A hole-patterned electrode (HPE) liquid crystal (LC) lens with positive (0 D – 0.7 D) and negative focal lengths (0 D - −1.1 D) is demonstrated. The lens uses an optically compensated bend (OCB) cell filled with dual-frequency LC materials and alignment films with an intermediate pretilt angle. Better reduction in tilt and coma aberration can be achieved using this simple one-layer structure with its symmetric LC orientation in an OCB cell than can be obtained with a complicated two-layer HPE LC lens. The use of dual-frequency switching together with the reduction of the backflow effect in the OCB cell also improves the response by about 7 times compared with the conventional HPE LC lens.

Ultrahigh thermal conductive graphite film via the in-situ construction of aligned nanographene skeleton using chemical vapor deposition

Both high thermal conductivity (K) and large cross-sectional area are essential for thermal dissipation materials to maximize their heat transfer capability. However, the drastic decrease of K values with the increased thickness makes the existing graphite/graphene films less favored for practical applications. In this work, graphite film with both large thickness and high K value is produced based on an in-situ composition strategy between nanographene (G) and pyrocarbon (PyC) via chemical vapor deposition (CVD) using CH3OH/C2H5OH mixed precursors. It's found that an optimized O/C ratio of precursors facilitates the construction of ordered G skeletons within the deposited G/PyC composites. Such G/PyC composites can be completely graphitized at a lower temperature than the existing products. After 2400 °C annealing, dense, thick, and highly aligned graphite films were prepared. Their K values reach 1350 and 1010 W m–1 K–1 at the thickness of 40 and 120 μm, respectively, surpassing the existing records with similar thicknesses. More importantly, the proposed method is insensitive to the deposition substrates, and the G/PyC can be infiltrated into large-size fiber preforms as a matrix for preparing centimeter-thick high K materials. Besides, the G/PyC also exhibits better mechanical and electromagnetic shielding performances than the existing products, indicating a promising multifunctional application prospect.

Induction of Highly Ordered Liquid Crystalline Phase of an Azobenzene Side Chain Polymer by Contact with 4'-Pentyl-4-cyanobiphenyl: An In Situ Study.

The orientation of liquid crystal (LC) molecules is significantly governed by solid interfaces and free surfaces, and a variety of functional materials have been developed using these properties. Although LC materials are already in industrial use, particularly for LC display panels, various studies have been conducted in recent years to better grasp the interface behavior of LC molecules. In this work, we succeeded in in situ observations of induction of higher ordered LC phases at the interface between a side-chain LC azobenzene polymer film with a thickness of ∼400 nm and a low-molecular-mass nematic LC, 4'-pentyl-4-cyanobiphenyl of 35 μm thickness, using small-angle X-ray scattering measurements and polarized optical microscopy. It is revealed that the two different mesogens cooperatively form hybrid higher ordered smectic LC phases probably through weak electron transfer immediately after interfacial contact. The induction process consists of three stages in terms of dynamic structure evolutions. Upon UV irradiation, the hybrid smectic LC structure diminished. This study provides new insights into the behavior of LC molecules near the alignment film on the solid substrate.

Highly Aligned Graphene Oxide for Lithium Storage in Lithium‐Ion Battery Through A Novel Microfluidic Process: The Pulse Freezing

AbstractThe modification of carbon‐based lithium‐ion batteries electrodes is required for the growing need of more reliable electric vehicles. Herein, a new method is introduced to fabricate vertically aligned graphene oxide (GO) films as free‐standing carbon lithium hosts for lithium‐ion batteries with enhanced performance. Vertical alignments are induced of GO in a microfluidic channel by controlling flow rates and patterns of GO suspensions. The vertical alignments are preserved and spontaneously form porous microstructures by Pulse Freezing the GO solutions inside the channel. This combined process results in the increase of levels of microstructure porosity and vertical alignment of GO films. The alignment and porous microstructures increase both electron and ion transfer capabilities across the prepared film. The half‐cell performance of aligned GO films shows a specific capacity of 440 mAh g−1 at a current density of 0.5 A g−1 after 150 cycles. This is a 190% specific capacity increase compared to the performance of a half‐cell prepared with GO without the high level of vertical alignment and microporosity. The significant increase in the value and stability of specific capacity and higher rates of charge transfer favor the promising application of carbon‐based lithium‐ion batteries for electric transportation industries.