Crystal Films Research Articles

Annual Energy-Saving Smart Windows with Actively Controllable Passive Radiative Cooling and Multimode Heating Regulation.

Smart windows with radiative heat management capability using the sun and outer space as zero-energy thermodynamic resources have gained prominence, demonstrating a minimum carbon footprint. However, realizing on-demand thermal management throughout all seasons while reducing fossil energy consumption remains a formidable challenge. Herein, an energy-efficient smart window that enables actively tunable passive radiative cooling (PRC) and multimode heating regulation is demonstrated by integrating the emission-enhanced polymer-dispersed liquid crystal (SiO2@PRC PDLC) film and a low-emission layer deposited with carbon nanotubes. Specifically, this device can achieve a temperature close to the chamber interior ambient under solar irradiance of 700W m-2, as well as a temperature drop of 2.3°C at sunlight of 500W m-2, whose multistage PRC efficiency can be rapidly adjusted by a moderate voltage. Meanwhile, synchronous cooperation of passive radiative heating (PRH), solar heating (SH), and electric heating (EH) endows this smart window with the capability to handle complicated heating situations during cold weather. Energy simulation reveals the substantial superiority of this device in energy savings compared with single-layer SiO2@PRC PDLC, normal glass, and commercial low-E glass when applied in different climate zones. This work provides a feasible pathway for year-round thermal management, presenting a huge potential in energy-saving applications.

Investigation on thermoelectric properties of SnSe thin films as prepared by RF magnetron sputtering

In this work, we investigated the thermoelectric properties of SnSe (Tin Selenide) thin films onto SiO2/Si-wafer substrates as prepared by RF (radio frequency) magnetron sputtering technique. The sputtering conditions used base pressure below 5.5 10−4 Pa and working pressure at 0.93 Pa within the Ar atmosphere as a flow rate fixed 40 sccm. The RF sputtering power was applied at 80 W and sputtering time for 30 min. After thin film deposition, as-deposited thin films were annealed by the vacuum annealing method at 300–450 °C. The crystal structure, morphology and film thickness, and atomic composition of SnSe thin film were carried out by X-ray diffraction (XRD), the field emission scanning electron microscope (FE-SEM), and energy-dispersive X-ray spectroscopy (EDS) techniques, respectively. The thermoelectric properties (electrical resistivity; ρ) and Seebeck coefficient; S) were measured by the ZEM-3 method to calculate the power factor (PF) value. The results showed that the as-deposited thin films had improved the crystallography of SnSe from amorphous to crystalline phases after thin films were annealed at a temperature range of 300–400 °C. At room temperature, the maximum power factor of 0.35 mW m˗1 K˗2 (ρ = 202 mΩ m and S = 165 μV K˗1) could be found to estimate the dimensionless Figure of Merit (ZT) values around 0.44 for annealing thin film sample at 400 °C.

The effect of Fe content on the dielectric properties of TlGa(0,999)Fe(0,001)S2 thin films

0,1 % iron containing Thallium Gallium Sulfide (TlGaS2 and TlGa(0,999)Fe(0,001)S2) thin films were deposited by thermal evaporation in the thickness range 20–200 nm. Raw bulk TlGaS2 and TlGa(0,999)Fe(0,001)S2 crystals were produced using the Bridgman technique. Iron (Fe) content was free, and the bonding content of a polarized charged group in the crystal and thin films was detected in the X-ray diffraction patterns. The dielectric characteristics of the thin films were determined by dielectric spectroscopy. The dielectric results showed Fe content polarizing in space-charge characteristics in the 1–100 Hz frequency range. Besides, the position and magnitude of dipolar polarization supported the presence of dipolar polarized charged groups having Fe content. In addition, it was realized that the void density explicitly affects the dielectric constant. The void density decreased toward higher thicknesses, whereas the dielectric constant increased. The ac conductivity results contributed to evaluating the effect of thickness for each thin film. The overall analysis indicated that even a small percentage of Fe (0,1 %) has a remarkable impact on the dielectric properties and electrical conduction of TlGa(0,999)Fe(0,001)S2 thin films. This analysis can provide opportunities to improve the electrical abilities of Thallium Gallium Sulfide (TlGaS2) thin films, which have applications as receivers of visible and infrared emission, X-ray and gamma-ray detectors, neutron detectors, barometers, and piezoelectric photoresistors if the presence of Fe is considered as investigated in TlGa1−xFexS2 thin films.

Effects of growth temperature on phase transformation and crystal quality of Ga2O3 films grown on Si/AlN composite substrates by MOCVD

High-quality ε-phase Ga2O3 thin film with a FWHM of 0.68° for the (002) plane in omega scan is grown on Si/AlN composite substrate by MOCVD. The crystal phase evolution and microstructure of Ga2O3 thin films at different temperatures are studied systematically. It is found that Ga2O3 changes from amorphous at 400 °C to ε-phase at 500 °C. As the temperature further rises to 600 °C, it eventually transforms into β-phase. Due to the difference of lattice mismatch, ε-Ga2O3 is crystalline with high crystallinity on the surface of the film, but amorphous at the interface, while β-Ga2O3 is polycrystalline. In addition, ε-Ga2O3 thin films not only have the smoothest surface with roughness of 2.63 nm, but also the content of point defects (such as oxygen vacancies) is significantly reduced compared with that of amorphous and β-Ga2O3 thin films. This work provides important references for the hetero-integration of Si and Ga2O3 by MOCVD, and is beneficial for the development of low cost and high crystal quality Ga2O3 thin films which are suitable for high voltage and ultraviolet optoelectronics.

Toughening mechanism in superstructure Hf6Ta2O17 thin film

Fracture toughness is a key indicator to estimate the anti-peeling performance of thermal barrier coatings (TBCs). A unique superstructure endows Hf6Ta2O17 with an outstanding phase stability and mechanical property, which also poses great challenges for studying its intrinsic toughening mechanism. Here, the superstructure Hf6Ta2O17 single crystal film was epitaxially grown on YSZ(011) substrate by pulsed laser deposition. An uncommon ripple pattern near the Vickers indentation crack tips was first reported. The pop-in signals in the load-displacement curve indicated it may be relevant to ferroelastic domain transformation, which was further confirmed by spontaneous strain distribution in HRTEM. The transformation path, predicted by DFT, was conducted in b→c ferroelastic domain through in-plane rotation of Hf–O/Ta–O polyhedrons. The corresponding critical stress for domain transformation was up to 5.83 GPa. In addition, an intrinsic ductility was confirmed with a high Pugh ratio B/G of 2.49, much larger than the critical value (1.75) for brittle-ductile transition. These two mechanisms make contribution to the superior fracture toughness of Hf6Ta2O17. This work provides a deep insight into the toughening mechanism of ceramics and paves the way to design of next-generation TBCs.

Atomistic insights into chemical vapor deposition process of preparing silicon carbide materials using ReaxFF-MD simulation

SiC is a kind of key advanced coating material used widely. The in-depth understanding of the CVD process of preparing SiC materials at the atomic scale is beneficial for studying the CVD mechanism and then optimizing the materials. Here, a CVD model of preparing SiC materials is established based on ReaxFF-MD considering the whole pyrolysis-adsorption-desorption-growth mechanism. The accuracy of the ReaxFF potential and its parameters is verified by DFT at first. Then an energy-based Monte Carlo (EMC)-MD-CVD model is proposed based on the bonding formation energy originating from DFT. It is used to simulate the CVD process of preparing SiC materials. The CVD of MTS is studied by deposition efficiency and deposited film components at different temperatures, and it can be found it in good agreement with experimental results. Finally, the crystallization of SiC film prepared by the CVD of MTS is studied by energy evolution and atomic structure evolution. The results are helpful to understand the CVD mechanism for preparing coatings and it can be used to optimize the CVD parameters of preparing SiC materials in the future.

Performance enhancement of Sb2(S,Se)3 solar cells through neodymium ion flow doping

Doping the light absorber layer of antimony chalcogenides with extrinsic ions is an effective approach for improving their photovoltaic quality. These dopant ions generally reside at positions other than the crystal lattice or form an alloy (e.g., AgSb(S,Se)3) with a poor device performance. Therefore, incorporating such ions into an antimony chalcogenide lattice such that there is a positive influence on device quality would be highly useful. Herein, doping of Nd3+ for Sb2(S,Se)3 is carried out via a modified hydrothermal deposition process. Notably, these ions are incorporated into the crystal lattice and migrate to the CdS/Sb2(S,Se)3 interface after doping, which are characterized using X-ray diffraction, X-ray photoelectron spectroscopy, and time-of-flight secondary ion mass spectrometry. Nd3+ doping produces benign effects on the crystal orientation, film morphology, optoelectronic properties, and defect passivation of the Sb2(S,Se)3 films. Consequently, all the photoelectrical parameters of Sb2(S,Se)3 solar cells doped with Nd3+ are enhanced, delivering a remarkable efficiency of 8.24 %. Furthermore, the best device stored in air only shows a slight decrease in efficiency in the 2400-h aging test. Overall, this study provides an effective doping strategy to improve the photovoltaic quality of Sb2(S,Se)3 films.

Use of polymer dispersed liquid crystal (PDLC) film as a greenhouse cover material

Use of polymer dispersed liquid crystal (PDLC) film as a greenhouse cover material

Axial Phenoxylation of Aluminum Phthalocyanines for Improved Cannabinoid Sensitivity in OTFT Sensors.

Cannabis producers, consumers, and regulators need fast, accurate, point-of-use sensors to detect Δ9-tetrahydrocannabinol (THC) and cannabidiol (CBD) from both liquid and vapor source samples, and phthalocyanine-based organic thin-film transistors (OTFTs) provide a cost-effective solution. Chloro aluminum phthalocyanine (Cl-AlPc) has emerged as a promising material due to its unique coordinating interactions with cannabinoids, allowing for superior sensitivity. This work explores the molecular engineering of AlPc to tune and enhance these interactions, where a series of novel phenxoylated R-AlPcs are synthesized and integrated into OTFTs, which are then exposed to THC and CBD solution and vapor samples. While the R-AlPc substituted molecules have a comparable baseline device performance to Cl-AlPc, their new crystal structures and weakened intermolecular interactions increase sensitivity to THC. Grazing-incidence wide-angle X-ray scattering (GIWAXS) and atomic force microscopy (AFM) are used to investigate this film restructuring, where a significant shift in the crystal structure, grain size, and film roughness is detected for the R-AlPc molecules that do not occur with Cl-AlPc. This significant crystal reorganization and film restructuring are the driving force behind the improved sensitivity to cannabinoids relative to Cl-AlPc and demonstrate that analyte-semiconductor interactions can be enhanced through chemical modification to create more responsive OTFT sensors.

Controlled Crystallization of Hybrid Perovskite Films from Solution Using Prepared Crystal Centers

Controlled Crystallization of Hybrid Perovskite Films from Solution Using Prepared Crystal Centers

High‐Quality Additive‐Free α‐FAPbI3 Film Fabricated by Alkane/Nanocrystals Method and Surface Chemistry Modulation for Efficient Perovskite Solar Cell

AbstractIt's still a scientific issue to synthesize exotic amines‐free and pure‐phase FAPbI3 film because most FAPbI3 films are synthesized by adding MACl‐like exotic amines salts in their precursor solution to reduce the phase transition barrier. In this work, high‐quality and additive‐free phase‐pure α‐FAPbI3 films are successfully fabricated via the sustainable Alkane/Nanocrystals method. FAPbI3 nanocrystals (NCs) are performed as the heterogeneous nuclei to promote the nucleation and crystallization of FAPbI3 films. Cryogenic‐TEM and in situ GIWAXS evidence the seed function and interesting phase evolution of FAPbI3 NCs. The whole phase transition course of pure FAPbI3 film is systematically studied. IR‐AFM and ToF‐SIMS reveal ligands capped on NCs are extruded to the film surface. PbAc‐IPA solution treating the film surface can effectively wash off the surplus ligands at the surface and modulate the surface chemistry and energy levels. As a result, an average power conversion efficiency (PCE) of 21.45% is achieved for MA‐free pure α‐FAPbI3 perovskite solar cells (PSCs), as well as the best light‐soaking stability record of retaining 95% of the initial PCE after 800 h. This work paves a new way to fabricate MA‐free pure α‐FAPbI3 PSCs.

Three Effective Methods for Passivation of Perovskite Solar Cell Defects

Perovskite solar cells have garnered significant attention due to their outstanding photoelectric properties. However, the majority of widely used perovskite polycrystalline ion crystal films are prepared through solution treatment processes, which often lead to the formation of high-density defects during the crystallization process. These defects within the device can be quite severe and are a major contributor to non-radiative recombination, limiting the enhancement of photovoltaic performance and stability of solar cell devices. In this paper, we review the latest advancements in defect passivation strategies for perovskite crystals, encompassing Lewis acid, Lewis base, and Lewis acid-base synergy approaches. We delve into the regulatory mechanisms and passivation effects of these various strategies on perovskite surface/interface defects. Furthermore, we anticipate the application of these defect passivation techniques in future studies, hoping to further enhance the performance and stability of perovskite solar cells.

Ultra-sensitive optical fiber ethanol gas sensor based on Vernier effect in cascaded Mach-Zehnder interferometer and Sagnac interferometer

Optical fiber-based sensors, which show the merits of high sensitivity, real-time, and rapid detection, have important research value in the detection of volatile organic compounds (VOCs). In this paper, a novel ethanol gas sensor was experimentally investigated based on the cascaded optical fiber-based Sagnac interferometer and Mach-Zehnder interferometer. The Sagnac interferometer was constructed with an anisotropic nematic liquid crystal (NLC) film which acted as the reactor with ethanol gas. A tapered single-mode fiber (SMF) was used to build the Mach-Zehnder interferometer (MZI). The two interferometers were parallelly and tandemly cascaded respectively to achieve the magnification of measurement sensitivity. Experimental results showed that the sensitivities were 8.561 pm/ppm with a magnification factor of 3.76 for the parallel cascaded structure and 7.924 pm/ppm with a magnification factor of 3.48 for the tandemly cascaded structure. The designed optical fiber-based ethanol gas sensor, showing the advantages of compact structure, high sensitivity, small size, and low cost, could be a competitive candidate for the detection of ethanol gas leakage.

Plasma‐Based Technologies for Halide Perovskite Photovoltaics

Plasma‐based technologies are at the frontier of material processing for several applications, from packaging to agronomy to photovoltaics. These processes allow for a fine‐tuning of material properties by engineering deposition, interaction with the substrate, and final surface characteristics at the atomistic level. As metal halide perovskite (MHP) solar cells enter the path toward commercialization, plasma processing can be seen as a powerful material manipulation tool already settled within industrially relevant procedures. In this perspective, the impact that these methods can have on different aspects of perovskite solar cells technology is envisioned, focusing on the direct interaction between plasma and MHPs. The use of plasma processes is foreseen for the deposition or crystallization of MHPs films, for treating their surface, as well as for the creation of suitable coatings either on top of perovskite layer and/or as encapsulants of the whole solar converting devices.

The fundamental role of Ta diffusion on the high coercivity of Ta/SmCo5/Ta and Ta/Sm2Co17/Ta films

The fundamental contribution of the Ta layer to the highly coercive Ta/SmCo / Ta films was investigated. A room temperature coercivity value of 4.5 T was achieved in film with 60% SmCo5 and 40% Sm2Co17. In films, in which only the Sm2Co17 phase was observed in XRD (X-ray diffraction), a high coercivity of 2 T was also obtained. All films were obtained by codeposition at temperature environment of Sm and Co atoms on a Ta layer, followed by annealing to promote the crystallization of the Sm-Co film. The following results were observed: (i) the presence of voids in the Sm-Co layer, observed in the cross- section STEM (Scanning Transmission Electron Microscope) images, (ii) the presence of stable Taα phase, observed in the XRD analysis, (iii) Ta diffusion in the Sm-Co layer, identified in the XPS (X-ray Photoelectron Spectroscopy) deep profile and, (iv) the initial magnetization curve, typical of a magnetization reversal controlled by pinning that led us to conclude that the voids produced during annealing by the diffusion of Ta in the Sm-Co layer, and they act as a pinning for the magnetization inversion, resulting in highly coercive films. Ta diffusion promoted the transition from the metastable Taβ phase to the stable Taα phase, at temperatures below 800 ◦C. Another important result was the strong exchange interaction between the grains reflected in the square hysteresis with Mr/Ms≈1.

Ultrasensitive Biomimetic Skin with Multimodal and Photoelectric Dual-Signal Sensing.

Mimicking biological skin enabling direct, intelligent interaction between users and devices, multimodal sensing with optical/electrical (OE) output signals is urgently required. Owing to this, this work aims to logically design a stretchable OE biomimetic skin (OE skin), which can sensitively sense complex external stimuli of pressure, strain, temperature, and localization. The OE skin consists of elastic thin polymer-stabilized cholesteric liquid crystal films, an ion-conductive hydrogel layer, and an elastic protective membrane formed with thin polydimethylsiloxane. The as-designed OE skin exhibits customizable structural color on demand, good thermochromism, and excellent mechanochromism, with the ability to extend the full visible spectrum, a good linearity of over 0.99, fast response speed of 93 ms, and wide temperature range of 119 °C. In addition, the conduction resistance variation of ion-conductive hydrogel exhibits excellent sensing capabilities under pressure, stretch, and temperature, endowing a good linearity of 0.99998 (stretching from 0 to 150%) and high thermal sensitivity of 0.86% per °C. Such an outstanding OE skin provides design concepts for the development of multifunctional biomimetic skin used in human-machine interaction and can find wide applications in intelligent wearable devices and human-machine interactions.

Crystallization of Germanium-SiO2 composite films via nanosecond laser pulse irradiation

Germanium (Ge)-SiO2 composite films fabricated by using radio frequency magnetron co-sputtering were subjected to nanosecond (ns) laser pulse irradiation. The intense laser irradiation effects on as deposited composite films lead to the modification and the formation of Ge nanocrystals (NCs) embedded in SiO2. The as-deposited and laser treated samples have been characterized with X-ray diffraction (XRD) and micro-Raman spectroscopy to understand the formation of Ge NCs due to laser irradiation. The respective Ge NCs related peaks in XRD pattern as well as the Ge-Ge related optical phonon vibrational peaks in micro-Raman spectra confirm the formation of Ge NCs. Transmission electron microscopy images indicate the formation of Ge NCs after the laser irradiation. The effects of laser pulse energy and the irradiation time play a vital role in the crystallization of the as-deposited films. The changes in the Ge NCs size related shifts in the peak position of Ge optical phonons from the Raman spectra of the respective samples are explained with Ge-Ge optical phonon vibrational model. The observed photoluminescence emission in the green and red region of the visible spectrum from the laser treated samples are explained using the phenomenon of creation of Ge NCs in the Ge+SiO2 composite films and the oxygen defects created in SiO2 during the ns laser treatment.

Non-iridescent magnetite photonic crystal films and pigments with enhanced magnetic coupling effect

Non-iridescent structural color films and pigments with novel enhanced microwave absorption characteristics are successfully fabricated at room temperature for the first time. The quasi-uniform magnetite nanoparticles (CV = 0.10 ∼ 0.20) with high refractive index (n = 2.42) and broad light absorption provide evident low-angle-independent property for the structural color pigments. More importantly, a universal technical protocol is developed for preparation of photonic crystals with inorganic nanoparticles, i.e., through designing of the binding strength between nanoparticles and mediated molecules, the slurry modulus is increased to 105 Pa, which effectively drives the nanoparticles to rapidly assemble into closely packed ordered arrays by our-designed powerful assembly technique. Additionally, the structural color materials are subjected as photonic crystal pigments (∼20 wt%) embedding in a transparent polymer matrix to form color coatings. Remarkably, the photonic crystal pigments exhibit strong magnetic coupling effect and enhanced microwave absorption performance due to the regular arrangement, with superior reflection loss (RLmin) values of −14.97 dB (increase by 65.8 % compared with randomized magnetic nanoparticles), and the effective absorption bandwidth (EAB) of 2.15 GHz. This new kind of photonic crystal pigment, combining visual color and radar wave absorption, provides a novel idea for developing of multi-wave-band high-performance stealth materials.

Influence of NaOH Concentration on Structural, Morphological, Optical, and Electrical Characterization of Perovskite Sodium Bismuth Titanate Prepared by Hydrothermal Method

The hydrothermal method successfully prepares a lead-free sodium bismuth titanate (NBT) perovskite film. The prepared films were studied structurally, and morphologically using X-ray diffraction, and field-emission scanning electron microscopy (FESEM), respectively. Varying the concentration of NaOH showed a noticeable effect on the properties studied. Good crystallization of NBT perovskite films without impurities was obtained at 18 and 20 M concentrations, where the crystalline size was 14 nm according to the Scherer equation. Also, when varying the concentration of NaOH, a similar film thickness was obtained through a cross-section of the FESEM images. It was observed that there was a difference in the intensity of the peaks of the photoluminescence spectra of the prepared films with a change in the concentration of NaOH, which confirms a change in the concentration of oxygen vacancies. The activation energy of the prepared films was deduced from the Arrhenius plot, as it showed small values in the films prepared with a low concentration of NaOH. The results showed that the maximum value of mobility of NBT films was at 20 M of NaOH concentration through the Hall Effect.

Tailoring stress relaxation for dopant-free ZnO thin films with high thermoelectric power factor

In this study, the effects of stress relaxation on the thermoelectric properties (carrier concentration n, Hall mobility μH, weighted mobility μW, density-of-state mass md*, Seebeck coefficient S, and thermopower factor PF) of undoped ZnO films were rationalized in terms of native defects (VO-related defects and Zni-related donors) induced through the deposition temperature (TD) during the sputtering process. All investigated ZnO films exhibited compressive stress and tended to become less compressive with increasing TD. The stress relaxation at high TD resulted in improved film crystallization and decreased native defect concentration, thus significantly enhancing md* through the reduction of intrinsic lattice defects, while less carriers were trapped and scattered by defects. Therefore, n and μ increased simultaneously (by 28 times and one order of magnitude, respectively), markedly enhancing the PF of dopant-free ZnO films.