Crystalline Films Research Articles

Indirect Enhancement of ALD Thin-Film Properties Induced by the ECAP Modification of an As-Extruded Mg-Ca Alloy.

The purpose of this study is to investigate the indirect effects on the properties of ZrO2 films deposited by atomic layer deposition (ALD) when an Mg-Ca alloy is modified through equal-channel angular pressing (ECAP) following extrusion. The study aims to understand how the increase in CaO content in the native oxide layer of the Mg-Ca alloy influences the crystallinity and defect density of the ZrO2 film. Consequently, the corrosion protection performance of the ZrO2 film is enhanced by 1.2 to 1.5 times. A reduction in the anti-scratch property of the ZrO2 film was also observed, with a critical load reduction of 34 μN. This research provides a detailed analysis of the modifications induced by ECAP on the as-extruded Mg-Ca alloy and its subsequent impact on the properties of the ZrO2 film.

Effect of linear antenna chemical vapor deposition process parameters on the growth of nanocrystalline diamond-on-GaN films

The present work will systematically study the effect of different linear antenna microwave plasma enhanced chemical vapor deposition (LACVD) processing parameters on the optimal deposition of the diamond films. The low pressure and low temperatures of LACVD growth conditions is expected to deposit diamond films on otherwise reactive gallium nitride (GaN) surfaces, without any intermediate nitride buffer layer. First, the distances between the quartz tube and the samples put on the stage are varied (3–15 cm), which has a direct impact on the substrate temperature (415°–300 °C). Thereafter, the microwave input power was also altered (1.5–2.8 kW) to attain low substrate temperatures. It was found that 300 °C is the temperature limit, which can be attained by heating only with microwave plasma when the substrates are kept farthest (15 cm) away from the liner antenna quartz tube. An additional heater was used under the stage for rapidly achieving such minimum substrate temperature of 300 °C. Substrate heater was used for efficient growth of the diamond phase while using pulse mode frequency of microwave power input for optimization of the diamond films. The microstructure (plate-like and cauliflower-like) of the deposited nanocrystalline diamond (NCD) films and the cross-sectional images for thickness measurements was observed under the scanning electron microscope and the elemental analysis of the film surfaces was done by electron diffraction spectroscopy. Moreover, the diamond film quality and crystallinity were evaluated by Raman spectroscopy with 488 nm laser light. Diamond-on-GaN film results were compared with conventional Si substrate. Different LACVD reactor parameters like, antenna to stage distances, microwave input power in continuous wave mode, and growth temperatures have significant impacts on the grown films, both in terms of their quality and microstructure. It was found that the optimum deposition of nanocrystalline diamond film on GaN substrates without its surface etching was possible, under pulse mode (20 kHz, 45 % duty cycle) with 2 kW average input microwave power.

The role of thickness on the structural and luminescence properties of Y2O3:Ho3+, Yb3+ upconversion films

The structural, surface, and upconversion (UC) luminescence properties of Y2O3:Ho3+,Yb3+ films grown by pulsed laser deposition, for different numbers of laser pulses, were studied. The crystallinity, surface, and UC luminescence properties of the thin films were found to be highly dependent on the number of laser pulses. The X-ray powder diffraction analysis revealed that Y2O3:Ho3+,Yb3+ films were formed in a cubic structure phase with an Ia 3¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\overline{3 }$$\\end{document} space group. The thicknesses of the films were estimated by using cross-sectional scanning electron microscopy, depth profiles using X-ray photoelectron spectroscopy (XPS), and the Swanepoel method. The high-resolution XPS was used to determine the chemical composition and oxidation states of the prepared films. The UC emissions were observed at 538, 550, 666, and 756 nm, assigned to the 5F4 → 5I8, 5S2 → 5I8, 5F5 → 5I8, and 5S2 → 5I7 transitions of the Ho3+ ions. The power dependence measurements confirmed the involvement of a two-photon process in the UC process. The color purity estimated from the Commission International de I’Eclairage coordinates confirmed strong green UC emission. The results suggested that the Y2O3:Ho3+,Yb3+ UC transparent films are good candidates for various applications, including solar cell applications.

Plasma‐assisted Surface Engineering to Stabilize Mn3+ in Electrodeposited Manganese Oxide Films for Water Oxidation

Manganese oxide is a unique type of transition metal oxide that effectively functions as a catalyst for the oxygen evolution reaction (OER). Here, manganese oxide (MnOx) polymorphs are synthesized through electrochemical deposition and treated with an atmospheric pressure plasma jet (APPJ). The APPJ surface treatment can generate numerous oxygen vacancies and modify the crystallinity of the MnOx films, which can enhance the long‐term stability of the MnOx films by stabilizing the Mn3+ content in the highly oxidizing environment. The increase in Mn3+ content and concentration of oxygen vacancies in the material synergistically increase the adsorption capacity of OH* and the electron‐transferring capacity of MnOx films in the OER process, making them more stable and effective for OER. MnOx films treated with APPJ exhibit significantly higher activity, better stability, and lower Tafel slopes for OER than untreated MnOx films. The MnOx films treated with APPJ can remain stable for up to 92 hours during OER with a current density of 10 mA cm‐2, with an onset overpotential of 310 mV. This strategy, which combines APPJ surface treatment techniques with electrodeposition methods, is innovative in the surface modification of manganese oxides with mixed valences to create OER catalysts with stable Mn3+ content.

Defect Passivation Strategies in Two‐Dimensional Organic–Inorganic Hybrid Perovskites for Enhanced Photoelectric Performance

AbstractThe polycrystalline perovskite films treated with solutions inevitably are subjected to high‐density crystal defects, significantly affecting the performance and stability of perovskite‐based photodetectors. In this research, a reasonably designed organic small molecule using piperazine iodide (PI) as an additive is employed to modify the perovskite films. The results indicate that this designed molecule not only improves the crystallinity of the perovskite film but also effectively passivates defects by modifying the local electron density. Consequently, recombination of non‐radiation charges is inhibited, improving the optoelectronic performance and stability of the device. The modified flexible photoelectric device exhibits a responsivity of 3.07 mA W−1 under 405 nm laser illumination. Notably, it maintains a high responsivity even after 7000 bending cycles. Furthermore, generality of the strategy is verified by applying it to various types of two‐dimensional organic–inorganic hybrid perovskite. Additionally, another small molecular amine phthalimide (PTM) is selected as an additive to further verify the universality of this strategy, which reveals that it demonstrates the same passivation as PI. This strategy provides a novel idea for defect passivation of two‐dimensional organic–inorganic hybrid perovskite, signifying a practical application significance for developing flexible wearable devices with optimized performance, perovskite light‐emitting diodes, and solar cells.

High‐Stability van Der Waals Structures of GeTe/Sb2Te3 Superlattices for 100× Increased Durability Phase‐Change Memory (PCM) by Low‐Temperature Atomic Layer Deposition

AbstractThe superlattices phase‐change memory (SL‐PCM), based on GeTe/Sb2Te3 superlattices (SLs), garners considerable attention within the academic community owing to its exceptional electrical properties. While the exact mechanism remains a topic of ongoing debate, researchers widely acknowledge that the presence of van der Waals (vdW) gap structures within SLs plays a pivotal role. However, the formation of vertical nanoparticles (VNPs) from the random orientation of Sb2Te3 and the substantial intermixing between GeTe and Sb2Te3 due to high‐temperature fabrication processes leads to pronounced elemental intermixing during electrical operations, causing a loss of SLs properties. This investigation uses atomic layer deposition techniques, specifically Sb‐atomic seed layer and periodic quintuple layers stacking, to address issues from random orientation Sb2Te3 grains and anomalous VNPs. This approach yields Sb2Te3 crystalline films with a high‐stability vdW gap structures. By leveraging these films, SLs with a preferred crystallographic orientation at a notable low temperature of 90 °C are successfully fabricated. The optimized SLs exhibit remarkable structural stability and mitigate alloy phase emergence during electrical operations, resulting in a 100‐fold enhancement in device durability. This work advances reliable SL‐PCM understanding and implementation, propelling this memory technology into the next generation.

Simulation Study of Crystalline Al2O3 Thin Films Prepared at Low Temperatures: Effect of Deposition Temperature and Biasing Voltage

In this paper, classical molecular dynamics simulations were used to explore the impact of deposition temperature and bias voltage on the growth of Al2O3 thin films through magnetron sputtering. Ion energy distributions were derived from plasma mass spectrometer measurements. The fluxes of deposited particles (Ar+, Al+, and O−) were categorized into low, medium, and high energies, and the results show that the films are dominated by amorphous Al2O3 at low incident energies without applying bias. As the deposition temperature increased, the crystallinity of the films also increased, with the crystals predominantly consisting of γ-Al2O3. The crystal content of the deposited films increased when biased with −20 V compared to when no bias was applied. Crystalline films were successfully obtained at a deposition temperature of 773 K with a −20 V bias. When biased with −40 V, crystals could be obtained at a lower deposition temperature of 573 K. Increasing the bias enables the particles to have higher energy to overcome the nucleation barrier of the crystallization process, leading to a greater degree of film crystallization. At this stage, the average bond length between Al-O is measured to be approximately 1.89 Å to 1.91 Å, closely resembling that of the crystal.

Preparation of polyimide films with ultralow dielectric loss at high frequency by reducing intermolecular friction

Due to the rapid development of high frequency and high rate communication technology, polyimide (PI) films with ultra-low dielectric loss (Df) at high frequency, excellent thermal and mechanical properties are urgently needed. A series of PI films with ultra-low Df were prepared by introducing different mesogen units. Among them, one novel PI film with biphenyl liquid-crystal-like units (BAHQ-TFMB) achieve a recorded low Df of 0.00169 (10 GHz) which surpasses previous studies on pure PI bulk films. Importantly, the high degree of collinearity of the friction work (Wf) and Df of PI films (Pearson's r = 0.992) was confirmed, which indicate that Wf among PI macromolecules plays an important role in determining Df of PI films. To reveal underlying reason for reducing the Wf and Df of PI films, the contribution of the degree of orientation and crystallinity of PI films with or without liquid-crystal-like structures were comparative studied. Through a two-dimensional orientation determinant, it is found that increasing the crystallinity of liquid-crystal-like PI films is the main contribution to reducing Wf and corresponding Df of PI films while the orientation of PI films seems to have weak effect. Moreover, BAHQ-TFMB PI film exhibits excellent mechanical properties. The tensile strengths is 145.5 ± 12.0 MPa and Young's moduli is 4.76 ± 0.28 GPa.

Synthesis of nitrogen-doped crystalline Ga2O3 thin films via trimethylgallium doped NH3/H2/N2/O2 premixed stagnation flames

This study presents a novel and cost-effective technique for fabricating nitrogen-doped crystalline α-Ga2O3 and β-Ga2O3 thin films under atmospheric pressure conditions through flame synthesis for the first time. We employ metal–organic ammonia (NH3)-assisted flame synthesis (MO-NAFS) in a quasi-one-dimensional trimethylgallium (TMG) doped NH3/H2/N2/O2 flat flame to achieve a one-step deposition of Ga2O3 onto c-plane α-Al2O3 substrates. We found that hydrogen (H2) addition directly impacts the crystallinity of the Ga2O3 thin film. When only NH3 is employed as the fuel, a thin-film single-crystal nitrogen-doped β-Ga2O3 was observed. Blending the NH3 with 5 % of H2 yields a single-crystal nitrogen-doped α-Ga2O3, while a further increase of H2 fraction up to 10 % results in a mixture of both α-Ga2O3 and β-Ga2O3 crystals. Remarkably, the nitrogen doping through MO-NAFS was found to persistently result in an N/O atomic ratio as high as 1.12, as determined by the XPS analysis. This approach paves the way to a simple and scalable means for producing crystalline nitrogen-doped Ga2O3 thin films with potential control of crystal phase composition through parameter adjustments.

Synthesis of nano-diamond film on GaN surface with low thermal boundary resistance and high thermal conductivity

Joule self-heating is the main obstacle limiting the performance of GaN power devices. A nano-diamond (NCD) film for near-junction heat transfer has been approved as an effective approach to overcome this issue. In the present study, we developed a scheme to deposit a smooth NCD film with high thermal conductivity (TC) over the surface of GaN. First, a 10-nm Si3N4 was deposited as the protective layer of GaN, followed by electrostatic seeding to improve nucleation density and particle distribution uniformity. Second, argon and gradient methane gas were introduced to prepare the NCD film based on nucleation and the growth period. The resulting thickness of the NCD film was 150 nm with a roughness of about 20 nm. The thermal boundary resistance (TBReff) between GaN and NCD film was only 12.8 ± 0.64 m2K/GW, whereas the TC of the NCD film was 200 ± 40 W m−1 K−1, which was similar to the theoretical prediction. Thus, it could be inferred that the high crystallinity of the NCD film contributes to the low TBReff and high TC through the whole NCD layer.

Using a Flexible Fountain Pen to Directly Write Organic Semiconductor Patterns with Crystallization Regulated by the Precursor Film.

Organic semiconductor (OSC) films fabricated by meniscus-guided coating (MGC) methods are suitable for cost-effective and flexible electronics. However, achieving crystalline thin films by MGC methods is still challenging because the nucleation and crystal growth processes are influenced by the intertwined interactions among solvent evaporation, stochastic nucleation, and the fluid flow instabilities. Herein, a novel flexible fountain pen with active ink supply is designed and used to print OSCs. This direct-write method allows the flexible pen tip to contact the substrate, maintaining a robust meniscus by eliminating the gap found in conventional MGCs. An in situ optical microscopy observation system shows that the precursor film plays a critical role on the crystallization and the formation of coffee rings and dendrites. The computational fluid dynamics simulations demonstrate that the microstructure of the pen promotes extensional flows, facilitating mass transport and crystal alignment. Highly-aligned ribbon-shaped crystals of a small organic molecule (TIPS-pentacene), as well as a semiconducting polymer (N2200) with highly-ordered orientations, have been successfully printed by the flexible fountain pen. Organic field-effect transistors based on the flexible pen printed OSCs exhibit high performances and strong anisotropic mobility. In addition, the flexible fountain pen is expandable for printing multiple lines or large-area films.

Discovery of Crystallizable Organic Semiconductors with Machine Learning.

Crystalline organic semiconductors are known to have improved charge carrier mobility and exciton diffusion length in comparison to their amorphous counterparts. Certain organic molecular thin films can be transitioned from initially prepared amorphous layers to large-scale crystalline films via abrupt thermal annealing. Ideally, these films crystallize as platelets with long-range-ordered domains on the scale of tens to hundreds of microns. However, other organic molecular thin films may instead crystallize as spherulites or resist crystallization entirely. Organic molecules that have the capability of transforming into a platelet morphology feature both high melting point (Tm) and crystallization driving force (ΔGc). In this work, we employed machine learning (ML) to identify candidate organic materials with the potential to crystallize into platelets by estimating the aforementioned thermal properties. Six organic molecules identified by the ML algorithm were experimentally evaluated; three crystallized as platelets, one crystallized as a spherulite, and two resisted thin film crystallization. These results demonstrate a successful application of ML in the scope of predicting thermal properties of organic molecules and reinforce the principles of Tm and ΔGc as metrics that aid in predicting the crystallization behavior of organic thin films.

Effect of plasma discharge pulse length for GaN film crystallinity on sapphire substrate by high density convergent plasma sputtering device

Effect of plasma discharge pulse length for GaN film crystallinity on sapphire substrate by high density convergent plasma sputtering device

Reactively Processed Poly(butylene adipate terephthalate) Composite–Based Multilayered Films with Improved Properties for Sustainable Packaging Applications: Structural Characterization and Biodegradation Mechanism

AbstractIn this study, it is attempted to enhance the properties and biodegradability of poly(butylene adipate terephthalate) (PBAT) using nanocomposite technology to meet the demand for sustainable packaging applications. Two nanoclays containing PBAT composites are reactively processed and integrated into the multilayered films. Reactive processing facilitates the dispersion and distribution of nanoclay particles in the PBAT matrix. The multilayered films comprising reactively processed PBAT composites exhibited a 24.5%–31.5% reduction in the oxygen transmission rate and improved dimensional stability and tensile properties. Moreover, the degradability of the multilayered film comprising reactively processed PBAT composites reached 82% in 180 days. In contrast, a neat PBAT film of similar thickness attained only 53% degradation in the same period. The biodegradation mechanism is proposed based on the topology of the disintegrated films studied using scanning electron microscopy, chemical bond vibrations determined by Fourier‐transform infrared spectroscopy, and structural evolution by small‐ and wide‐angle X‐ray scattering (SWAXS). The SWAXS analysis is used to understand the changes in the degree of crystallinity, long‐range periodic order, and crystalline and amorphous layer thickness of the multilayered films before and after degradation. Such multilayered films can find applications where packaging or biomedical devices cannot be recycled.

Enhanced intrinsic thermal conductivity of liquid crystalline polyester dispersed films through hydrogen bond interaction

Polymer-dispersed liquid crystal (MHxFy) films comprising liquid crystal polymer (LCPH and LCPF) were successfully obtained by the method of solution casting & thermal compressing. At a LCPH mass fraction of 67 %, thermal conductivity (λ) value in through-plane (λ⊥) and in-plane (λ∥) direction of MH2F1 films reach up to 0.305 W/(m·K) and 2.879 W/(m·K), respectively. In comparison to pure LCPF, the thermal conductivity of MH2F1 exhibited an increase of 4.42 times, which is 14.4 times than that of conventional thermoplastics. Meanwhile, the crystallinity of MHxFy films around 50 % which is indicate the crystal phase become more integrated and regular. The FTIR spectra reveals a significant blue shift (3432 cm−1 to 3421 cm−1) in the absorption peak of the –OH group in MH2F1, suggesting a robust interaction between LCPF and LCPH. The primary cause of elevated thermal conduction in these films was determined to be the consistent presence of “thermal bridges” and a high degree of crystallinity. Furthermore, the T5%, Tmax and residual carbon at 800 °C of MH2F1 were 347.8 °C, 409.4 °C and 8 %, respectively. This is attributed to the ordered distribution of LCPH in LCPF matrix through hydrogen bonding interaction, forming an interpenetrating network of LCPF-LCPH. The result show that MHxFy films demonstrating superior intrinsic thermal conductivities, thermal stabilities, and mechanical properties.

Tailoring the surface topography and crystallinity of EuMnO3 films: A study on sintering effects

We obtained EuMnO3 films through a sol-gel process at varying temperatures, aiming to investigate spatial layout variations influenced by different sintering temperatures. Our results indicate that films adopt an orthorhombic structure when sintered between 800 °C and 850 °C, accompanied by a reduction in nanocrystal size during annealing. Surface analysis reveals that films processed at higher temperatures exhibit increased roughness, negative asymmetry, heightened kurtosis, elevated peak densities, and more distinct peak forms. Furthermore, these films display surfaces with greater anisotropy and lower spatial frequencies compared to those sintered at lower temperatures. Nevertheless, fractal analysis uncovers that both the EuMnO800 and EuMnO850 samples showcase heightened spatial complexity, a more uniform nanotexture, optimal surface porosity, and improved topographic consistency. The findings suggest that films sintered at 800 °C display a spatial arrangement with superior topographic qualities, rendering them potentially valuable for the advancement of semiconductor films derived from perovskite rare-earth oxides for various technological applications.

Role of anionic surfactant addition in improving thermoelectric properties of PEDOT:PSS free-standing films

Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) has recently gained interest as a potential candidate for small-scale thermoelectric conversion because of the facile doping, solution processability, and flexibility. However, the practical applications of PEDOT:PSS are limited by its comparatively low figure of merit (ZT) compared with inorganic thermoelectric materials. Herein, to further improve the thermoelectric properties of PEDOT:PSS, we investigated the role of the addition of surfactants, sodium dodecyl sulfate, sodium dodecyl benzenesulfonate (SDBS) or Triton X-100, to the PEDOT:PSS free-standing films on their thermoelectric properties. We showed that the addition of the surfactant improved the film crystallinity, significantly improving the electrical conductivity. The highest conductivity was obtained for anionic surfactant SDBS at a 0.94 wt% concentration. Moreover, the inclusion of the surfactant reduced the thermal conductivity while maintaining a relatively constant Seebeck coefficient, consequently improving the ZT value. Furthermore, a flexible thermoelectric device crafted from the as-fabricated PEDOT:PSS/SDBS sheets was developed to explore the potential applications of wearable electronics using low-grade thermal energy. Overall, we indicate the significance of surfactants in enhancing the thermoelectric properties of free-standing PEDOT:PSS films in this study.

Characterization and ohmic contact properties of indium tin-oxide films prepared on p-type GaN using electron-cyclotron-resonance plasma-sputter deposition

The optical and electrical properties of indium tin oxide (ITO) films deposited using electron cyclotron resonance (ECR) plasma-sputter deposition and the ohmic contact properties between the ITO films and p-type gallium nitride (p-GaN) were evaluated. The electrical properties of the ITO films were evaluated in terms of the dependence on the tin (IV) oxide (SnO2) content of the ITO target and radio frequency (RF) power. The ohmic contact properties between the ITO films and p-GaN were also characterized by varying the top-surface Mg concentration of the p-GaN substrate. An ohmic contact was achieved without post-annealing treatment by depositing the film on a p-GaN high-dope substrate with a top-surface Mg concentration of 2.0 × 1020 cm−3 under low RF-power deposition using an ITO sputter target with 10 wt.% SnO2. The interface between the ITO films and p-GaN that achieved an ohmic contact was observed using scanning transmission electron microscopy (STEM) and was very smooth with no crystal disorder. This indicates that the crystallinity of the ITO films and p-GaN surface is a factor affecting ohmic-contact properties. The inter-diffusion between the ITO films and p-GaN surface was also evaluated using transmission electron microscopy energy dispersive X-ray spectroscopy (TEM-EDS), and no inter-diffusion was observed.

A novel Se-diffused selenization strategy to suppress bulk and interfacial defects in Sb2Se3 thin film solar cell

In recent years, vacuum-based deposition of antimony selenide (Sb2Se3) thin films has garnered significant attention owing to its easy and impurity-free fabrication, along with exceptional power conversion efficiency (PCE). However, the necessary post-selenization process comes with a shortcoming of instigating buried Sb2Se3/molybdenum (Mo) back-contact interface defects. This study introduces a novel Se-diffusion post-selenization technique to precisely regulate the selenium reaction atmosphere, preventing void formation on the Sb2Se3 thin film surface and maintaining film quality for enhanced device efficiency. An optimized selenization condition with a precise Se precursor film thickness led to obtaining highly crystalline, preferentially (hk1) oriented, and large-grained Sb2Se3 films. Furthermore, a meticulous Se diffusion in Sb2Se3 film reduced the inevitable MoSe2 layer thickness at the Mo surface, thereby enhancing the quality of the back contact interface. The Sb2Se3 solar cell that was selenized to optimal level showed significant enhancements, raising the fill factor from 40.06 % to 45.12 % and improving the device efficiency from 2.89 % to 3.57 %. Our newly developed selenization strategy establishes a successful approach to regulate the Sb2Se3 film quality by addressing a crucial challenge in improving the efficiency of antimony chalcogenide solar cells.

Growth of α-Ga2O3 from Gallium Acetylacetonate under HCl Support by Mist Chemical Vapor Deposition.

α-Ga2O3 films were grown on a c-plane sapphire substrate by HCl-supported mist chemical vapor deposition with multiple solution chambers, and the effect of HCl support on α-Ga2O3 film quality was investigated. The growth rate monotonically increased with increasing Ga supply rate. However, as the Ga supply rate was higher than 0.1 mmol/min, the growth rate further increased with increasing HCl supply rate. The surface roughness was improved by HCl support when the Ga supply rate was smaller than 0.07 mmol/min. The crystallinity of the α-Ga2O3 films exhibited an improvement with an increase in the film thickness, regardless of the solution preparation conditions, Ga supply rate, and HCl supply rate. These results indicate that there is a low correlation between the improvement of surface roughness and crystallinity in the α-Ga2O3 films grown under the conditions described in this paper.