Thin Films Research Articles

Boron Trioxide-Assisted Post-Annealing Enables Vertical Oriented Recrystallization of Sb2Se3 Thin Film for High-Efficiency Solar Cells.

Crystallization process is critical for enhancing the crystallinity, regulating the crystal orientation of polycrystalline thin films, as well as repairing defects within the films. For quasi-1D Sb2Se3 photovoltaic materials, the preparation of Sb2Se3 thin films still faces great challenges in adjusting orientation and defect properties, which limits the device performance. In this study, a novel post-treatment strategy is developed that uses a low melting point B2O3 coating layer as a flux to drive the recrystallization of Sb2Se3, thereby regulating the micro-orientation of thermal evaporation-derived Sb2Se3 films and optimizing their electrical properties. Mechanistic investigations show that B2O3 exhibits stronger adsorption with (hk1) planes of Sb2Se3 to induce a vertical orientation growth of the film, while blocking the volatilization channels of Se and inhibiting Se vacancy defects by interacting with Sb2Se3. The Sb2Se3 film with [hk1] preferential orientation and suppressed deep-level defects promotes the effective transport of charge carriers in solar cells. As a result, the B2O3-treated device delivers a champion efficiency of 9.37% without MgF2 anti-reflection coating, which is currently the highest efficiency in Sb2Se3 solar cells achieved by thermal evaporation method. This study provides a new method and mechanism for regulating optical and electrical properties of low-dimensional inorganic thin films.

Crystal and Electronic Structure of β‐Nb2N Thin Films Grown by Molecular Beam Epitaxy

AbstractNiobium nitrides have garnered significant research interest since their discovery due to their exceptional properties and broad applications. In this study, NbNx thin films are successfully grown on 4H(6H)‐SiC(001) substrates using nitrogen‐assisted molecular beam epitaxy. Through scanning transmission electron microscopy and X‐ray diffraction, it is confirmed that the crystal structure of the thin films corresponds to the β‐Nb2N. Different from the previously reported structure of the βA phase (P63/mmc) of β‐Nb2N, the results clearly match with the βB phase (). Resistivity measurements reveal that β‐Nb2N exhibits superconductivity at ≈10 K with an upper critical field of ≈5 T. Its 3D electronic structure is further elucidated using angle‐resolved photoemission spectroscopy combined with theoretical calculations. The observed superconductivity in β‐Nb2N is attributed to its relatively high electron–phonon coupling strength and density of states at Fermi level. Interestingly, it is found that the sample is close to a Lifshitz transition, suggesting potential for tunable physical properties. The results provide a comprehensive understanding of the crystal and electronic structures of β‐Nb2N, facilitating its future applications.

Tuning Self-Polarization of Epitaxial BiFeO3 Thin Films through Interface Effects.

Interface effects and strain engineering have emerged as critical strategies for modulating polarization and internal electric fields in ferroelectric materials, playing a vital role in exploring coupling mechanisms and developing ferroelectric diode devices. In this study, we selected BiFeO3 as a representative ferroelectric material and utilized interface engineering to control its polarization. By precisely manipulating the atomic stacking sequence at the interface, we influenced the electrostatic potential step across the interface, resulting in a bias voltage in the ferroelectric hysteresis loops that defined the ferroelectric state. The introduction of strain and strain gradients through a lattice mismatch between the film and substrate generated a flexoelectric field of approximately 3 MV/m, significantly impacting the internal electric field. Additionally, we successfully modified the Schottky barrier height within BiFeO3 films through the synergy and competition between interfacial and flexoelectric effects. This work expands the potential applications of thin-film flexoelectricity in Schottky diodes, sensors, and memory devices.

Free‐Radical Polymerization of Liquid Hydroxyethyl Methacrylate Layers Using Nanosecond Plasma Pulses

ABSTRACTPromoting both high functional group preservation and high deposition rates is a major challenge in plasma deposition. This study explores a dynamic method using nanosecond pulsed plasma discharges to polymerize thin liquid layers of 2‐hydroxyethyl methacrylate (HEMA). The influence of plasma pulse frequency (200 ns) and liquid layer thickness on chemical structure retention, polymeric growth, and thin film growth rate is examined. High‐resolution mass spectrometry (HRMS) highlights that plasma curing of liquid monomer layers achieves significantly better chemical structure preservation and polymeric growth, along with deposition rates an order of magnitude higher than traditional vapour‐phase methods. This work provides valuable insights and guidelines for plasma‐induced free‐radical polymerization of liquid layers into functional thin solid films.

Annealing Temperature Effect on the Properties of CoCe Thin Films Prepared by Magnetron Sputtering at Si(100) and Glass Substrates

This study explores cobalt–cerium (Co90Ce10) thin films deposited on silicon (Si) (100) and glass substrates via direct current (DC) magnetron sputtering, with thicknesses from 10 nanometer (nm) to 50 nm. Post-deposition annealing treatments, conducted from 100 °C to 300 °C, resulted in significant changes in surface roughness, surface energy, and magnetic domain size, demonstrating the potential to tune magnetic properties via thermal processing. The films exhibited hydrophilic behavior, with thinner films showing a stronger substrate effect, crucial for surface engineering in device fabrication. Increased film thickness reduced transmittance due to photon signal inhibition and light scattering, important for optimizing optical devices. Furthermore, the reduction in sheet resistance and resistivity with increasing thickness and heat treatment highlights the significance of these parameters in optimizing the electrical properties for practical applications.

Cannabichromene (CBC) Shows Matrix-Dependent Thermal Configurational Stability.

The optical purity of cannabichromene (CBC, 1a) is affected by the matrix in which it is generated by thermolysis from its native carboxylated form (cannabichromenic acid, CBCA, 1b). Thus, thermolysis at 130 °C in planta caused a marked decrease of the enantiomeric excess (ee), while, under the same conditions, only a modest decrease of optical purity was observed when thermolysis was carried out in extracto. To rationalize these puzzling observations, the kinetics of thermal (100 °C) racemization of enantiopure cannabichromene (1a) was evaluated by enantioselective ultrahigh performance liquid chromatography in solvents (decalin and isopropyl alcohol, neat and acidified with TFA) and surfaces (native and silanized borosilicate glass) of complementary polarity. Optical stability was more than halved in isopropanol compared to decalin (t1/2 50 h vs 135 h), but acidification had no effect on racemization. However, contact with a solid surface dramatically accelerated the process, with a t1/2 of only 6 h on both glass surfaces. The overall extent of racemization of enantiopure CBC (1a) was compared under conditions commonly used for decarboxylation (heating at 130 °C) between a decalin solution and a thin film on three different surfaces (native and silanized borosilicate glass and powdered blank cannabis biomass). In line with the kinetic data, a significant erosion of enantiopurity was observed on all solid surfaces compared to the solution. These observations suggest that discrepancies in the reported enantiomeric purity of natural CBC could be not only of biogenetic derivation but also be associated with the decarboxylation protocol of cannabichromenic acid (1b). These findings, while relevant for the exploitation of the bioactivity of natural CBC for human health, should also prompt the adoption of a standardized decarboxylation protocol for the studies on the configurational status of CBC (1a) in cannabis and, in general, of cannabinochromanoids in nature.

Electron-Beam-Evaporated Nickel Oxide Thin Films for Application as a Hole Transport Layer in Photovoltaics

We present the growth of nickel oxide (NiO) thin films as a hole transport material in photovoltaic devices using the e-beam evaporation technique. The metal oxide layers were reactively deposited at a substrate temperature of 200 °C using an electron beam evaporator under an oxygen atmosphere. The oxide films reactively grown through electron-beam evaporation were optimized for carrier transport layers. Optical and structural characterizations were performed using ultraviolet–visible (UV–Vis) spectrometry, X-ray diffraction, contact angle measurements, scanning electron microscopy, and Hall effect measurements. The study of these films confirmed that the NiO layer is a suitable candidate for use as a hole transport layer based on Hall effect measurements. A morphological study using field-emission scanning electron microscopy confirmed the growth of compact, uniform, and defect-free metal oxide layers. Contact angle measurements revealed that the films possessed semi-hydrophilic properties, contributing to improved stability by repelling water from their surfaces. The stoichiometry of the films was influenced by the oxygen pressure during deposition, which affected both their morphological and optical features. The NiO films exhibited a transmittance exceeding 80% in the visible spectrum. These findings highlight the potential applications of such nickel oxide films as hole transport material layers.

Ga2O3-Based Optoelectronic Memristor and Memcapacitor Synapse for In-Memory Sensing and Computing Applications

This study presents the fabrication and characterization of a dual-functional Pt/Ga2O3/Pt optoelectronic synaptic device, capable of operating as both a memristor and a memcapacitor. We detail the optimized radio frequency (RF) sputtering parameters, including a base pressure of 8.7 × 10−7 Torr, RF power of 100 W, working pressure of 3 mTorr, and the use of high-purity Ga2O3 and Pt targets. These precisely controlled conditions facilitated the formation of an amorphous Ga2O3 thin film, as confirmed by XRD and AFM analyses, which demonstrated notable optical and electrical properties, including light absorption properties in the visible spectrum. The device demonstrated distinct resistive and capacitive switching behaviors, with memory characteristics highly dependent on the wavelength of the applied light. Ultraviolet (365 nm) exposure facilitated long-term memory retention, while visible light (660 nm) supported short-term memory behavior. Paired-pulse facilitation (PPF) measurements revealed that capacitance showed slower decay rates than EPSC, suggesting a more stable memory performance due to the dynamics of carrier trapping and detrapping at the insulator interface. Learning simulations further highlighted the efficiency of these devices, with improved memory retention upon repeated exposure to UV light pulses. Visual encoding simulations on a 3 × 3 pixel array also demonstrated effective multi-level memory storage using varying light intensities. These findings suggest that Ga2O3-based memristor and memcapacitor devices have significant potential for neuromorphic applications, offering tunable memory performance across various wavelengths from ultraviolet to red.

Impacts of O2/(O2+Ar) Flow Ratio on the Properties of Li‐Doped NiO Thin Films Fabricated by Pressure‐Gradient Radiofrequency Magnetron Sputtering

Herein, Li‐doped NiO thin films are deposited on glass substrates using pressure‐gradient radiofrequency magnetron sputtering, with Ar and O2 as sputtering gases. Following film fabrication, their crystal structures, optical features, and electrical properties are investigated as functions of O2 flow rate to the total flow rate (O2/(O2 + Ar)) of 10 sccm. The deposited films are also annealed at 600 °C for 1 h in an oxygen atmosphere. Notably, the resistivity of the as‐deposited films decreases significantly by three orders of magnitude from 106 to 0.0232 Ω cm when the sputtering gas is changed from pure Ar to pure O2. However, the transmittance decreases with increasing oxygen flow rate. Investigations on the temperature dependence of conductivity reveal hole conduction in the range of ≈320–420 K owing to small polaron hopping.

Harnessing Defects in SnSe Film via Photo-Induced Doping for Fully Light-Controlled Artificial Synapse.

2D-layered materials are recognized as up-and-coming candidates to overcome the intrinsic physical limitation of silicon-based devices. Herein, the coexistence of positive persistent photoconductivity (PPPC) and negative persistent photoconductivity (NPPC) in SnSe thin films prepared by pulsed laser deposition provides an excellent avenue for engineering novel devices. It is determined that surface oxygen is co-regulated by physisorption and chemisorption, and the NPPC is attributed to the photo-controllable oxygen desorption behavior. The dominant behavior of chemisorption induces high stability, while physisorption provides room for adjusting NPPC. A simple fully light-modulated artificial synaptic device based on SnSe film is constructed to operate various synaptic plasticity and reversible modulation of conductance by applying 430 and 255nm illuminations. A three-layer artificial neural network structure with a high accuracy of 95.33% to recognize handwritten digital images is implemented based on the device. Furthermore, the pressure-related cognition response of humans while climbing and the foraging and recognition behaviors of anemonefish are mimicked. This work demonstrates the potential of 2D-layered materials for developing neuromorphic computing and simulating biological behaviors without additional treatment. Furthermore, the one-step method for preparation is highly adaptable and expected to realize large-area growth and integration of SnSe-based devices.

Modulation of Energy Band Positions in Sb2S3 Thin Films for Enhanced Photovoltaic Performance of FTO/TiO2/Sb2S3/P3HT/Au Solar Cell

Antimony sulfide (Sb2S3) has the potential as an absorber material in photovoltaics due to its suitable bandgap and favorable optoelectronic properties. However, its energy band positions are not extensively explored which are essential for effective charge separation and transfer. This study examines the energy band positions of Sb2S3 thin films as a function of annealing temperature. Sb2S3 thin films are grown by a combination of successive ionic layer adsorption and reaction (SILAR) and chemical bath deposition (CBD) method to enhance the crystallinity, tune the bandgap, and overall quality of Sb2S3 films to enhance the photovoltaic performance. Optical bandgap decreases from 2.41 to 1.67 eV from the as‐deposited films to annealed at 300 °C due to changes in interatomic distances. Energy band positions of Sb2S3 films are measured both by cost‐effective electrochemical cyclic voltammetry and Mott–Schottky analysis and validated the findings using ultraviolet photoelectron spectroscopy (UPS). The conductivity of Sb2S3 is found to be n‐type. Thin‐film solar cells are then fabricated by employing Sb2S3 as an absorber layer in an FTO/TiO2/Sb2S3/P3HT/Au structure, achieving an enhanced power conversion efficiency, increasing from 0.4 to 2.8% after annealing. These findings demonstrate the potential of Sb2S3 as a low‐cost absorber material for thin‐film photovoltaics.

Heterochiral Self‐Discrimination Driven Dimerization of Polynuclear Gold(I)‐Sulfido Complexes with Enhanced Phosphorescence

Decanuclear chiral gold(I) sulfido clusters (SSDP‐Au10 and RSDP‐Au10) have been assembled by taking advantage of the judiciously selected SDP ligands (SDP = 7,7’‐bis(diphenylphosphino)‐1,1’‐spirobiindane). Interestingly, an achiral heterodimer icosanuclear meso‐cluster (mesoSDP‐Au20) has been obtained by simply mixing SSDP‐Au10 and RSDP‐Au10 in a 1:1 ratio. These gold(I) complexes have been found to display intense near‐infrared (NIR) luminescence with an emission maximum at around 750 nm in the solid state. The photoluminescence quantum yield (PLQY) of mesoSDP‐Au20 in drop‐cast solid‐state thin film has been found to show a significant enhancement from 8% in the SSDP‐Au10 and RSDP‐Au10 to 25%. In addition, the dimerization process with heterochiral self‐discrimination has been found to be sensitive to the solvent polarity and configuration of the diphosphine ligand. This work has provided a platform for the investigation and mechanistic understanding of heterochiral self‐sorting and assembly processes.

Dual Interfacial Design Enables Efficient and Stable Semitransparent Wide‐Bandgap Perovskite Solar Cells With Scalable‐Coated Silver Nanowire Contact for Tandem Applications

ABSTRACTSemitransparent perovskite solar cells (PSCs) hold great potential for applications in aesthetic building facades and top‐illuminated tandem devices. Indium tin oxide is currently the frequently used top transparent contact, which would degrade the underlying perovskites during sputter process. Here, we report low‐temperature, scalable solution‐processed silver nanowires (AgNWs) as top window electrodes for fabricating efficient and stable semitransparent PSCs. As a decisive step, an impermeable SnO2 thin film deposited by atomic layer deposition (ALD) is applied to prevent chemical reactions between AgNWs and halides of perovskites. In parallel, the molecular absorption of propylenediamine iodine (PDADI) on perovskite surface, instead of forming two‐dimensional (2D) perovskite capping layer, is found to effectively passivate the perovskite surface, which simultaneously leads to remarkably enhanced thermal stability, thus affording the processing window for ALD‐SnO2 deposition. Eventually, the prepared semitransparent PSCs with a bandgap of 1.71 eV achieve a champion efficiency of 17.5%, being the highest efficiency for semitransparent PSCs with AgNWs top contacts. On these bases, we constructed a four‐terminal perovskite/copper indium gallium diselenide (CIGS) tandem cell, giving a state‐of‐the‐art efficiency of 26.85%.

Band edge engineering of lead halide perovskites using carboxylic‐based self‐assembled monolayer for efficient photovoltaics

AbstractPerovskite solar cells are promising candidates for low‐cost and efficient photovoltaic markets, but their efficiency is usually limited by the non‐radiative recombination losses at the mismatched interface of perovskite and transport layers. Herein, we show that the band edges of perovskite thin films can be on‐demand engineered by a series of carboxylic‐based self‐assembled monolayers. Experimental and theoretical studies indicate that the functionalized perovskite inherits the polarity of the monolayer with linear dependence of work function on the molecular dipole moments, which enables the management of interfacial charge transport process. Solar cells with 4‐bromophenylacetic acid SAMs achieve about 6.48% enhancement in power conversion efficiency with the champion values over 23%.

Heterochiral Self-Discrimination Driven Dimerization of Polynuclear Gold(I)-Sulfido Complexes with Enhanced Phosphorescence.

Decanuclear chiral gold(I) sulfido clusters (SSDP-Au10 and RSDP-Au10) have been assembled by taking advantage of the judiciously selected SDP ligands (SDP = 7,7'-bis(diphenylphosphino)-1,1'-spirobiindane). Interestingly, an achiral heterodimer icosanuclear meso-cluster (mesoSDP-Au20) has been obtained by simply mixing SSDP-Au10 and RSDP-Au10 in a 1:1 ratio. These gold(I) complexes have been found to display intense near-infrared (NIR) luminescence with an emission maximum at around 750 nm in the solid state. The photoluminescence quantum yield (PLQY) of mesoSDP-Au20 in drop-cast solid-state thin film has been found to show a significant enhancement from 8% in the SSDP-Au10 and RSDP-Au10to 25%. In addition, the dimerization process with heterochiral self-discrimination has been found to be sensitive to the solvent polarity and configuration of the diphosphine ligand. This work has provided a platform for the investigation and mechanistic understanding of heterochiral self-sorting and assembly processes.

Characterization of the Microstructure of Sr0.75Ba0.25Nb2O6 Thin Films by Brillouin Light Scattering

Strontium-barium niobate (SrxBa(1−x)Nb2O6) films can be considered as a promising material for microwave applications due to high dielectric nonlinearity and relatively low losses. Since strontium-barium niobate has a disordered structure that determines its unique electrical properties, the identification of structural features of the SrxBa(1−x)Nb2O6 films is the key to their successful use. The SrxBa(1−x)Nb2O6 films were synthesized on a sapphire substrate by magnetron sputtering. The structure of the films was studied by both traditional methods of electron microscopy, X-ray diffraction, and the rarely used for thin films investigation Brillouin light scattering method, which was the focus of our study. We show that Brillouin light scattering is an excellent nondestructive method for studying the structural features of thin ferroelectric strontium-barium niobate films. An analysis of the features of the Brillouin light scattering spectra in thin-film structures and their comparison with the spectra of bulk crystals allowed us to determine with high accuracy the thickness of the films under study and their structural features determined by the resonant scattering of acoustic waves.

Potentiality of chitosan/titanium oxide nanocomposite for removing iron and chromium from hydrous solutions.

The present study involved the preparation of a nano-polymer based on shrimp wastes as a biodegradable chitosan nanoparticle (Cs) incorporated into titanium oxide nanoparticles (TiO2) in an aqueous medium and carried on the specific polymer to form thin films. The spectroscopic properties of chitosan/TiO2/Polymer thin films were estimated by transmission electron microscopy (TEM) and Fourier transform infrared (FTIR) spectroscopy. The fabricated films were then examined for their potential to eliminate iron (Fe) and chromium (Cr) from solutions. The adsorption efficiency was also evaluated along various contact times. In general, the results illustrated that the heavy metals removal increases with increasing the different ratios of chitosan and TiO2 nanoparticles incorporated in polymer thin films. Removal efficiency increased with an increase in contact time. More than 70% of Fe and Cr ions were removed in the first 30min of contact time using different thin films examined. The maximum removal for metal ions after 90min for the pest thin film (0.08 TiO2) was 97.1 and 88.8% for Fe and Cr, whereas the lowest thin film removal efficiency (PVC) was 29.5 and 8.07% for Fe and Cr, respectively. In conclusion, the fabricated thin film composed of polyvinylidene chloride and chitosan plus 0.08 g titanium oxide nanoparticles had a heavy metal removal capacity three times greater than that of basic polyvinylidene chloride.

Thin film sputter-deposition of AlN crystals in oxygenated chamber: A pilot study

Abstract Aluminium nitride (AIN) is a promising thin film electrical insulation material layer in electronic devices. The magnetron sputtering method is usually employed to sputter-deposit AlN thin film on silicon (Si) substrate using a pure aluminium (Al) metallic target in a low base pressure vacuum condition. In many cases, the thin film deposition of high quality AlN crystals requires the application of heat and bias to the substrate, highly pure nitrogen reactant gas, argon sputtering gas and Al target, low sputtering pressure, high sputtering power, post-deposition AlN annealing, ultra-low base pressure of the sputtering chamber and a distinctive crystal orientation of the nucleation layer or substrate underneath. In our work, the utilisation of AlN ceramic target instead of pure Al metallic target has allegedly facilitated the growth of AlN crystals without the need to conform to these requirements. Non-amorphous AlN〈100〉 and AlN〈002〉 thin film crystals have been successfully sputtered from AlN ceramic target on Si〈100〉 substrate in a relatively high sputtering chamber base pressure and at a moderate 200 W - 250 W of sputtering power. Additionally, 250 W of sputtering power has been observed to assist in the growth of AlN〈002〉 crystals. The presence of AlN〈002〉 may have reduced the leakage/tunnel current density in AlN thin film layer to 46.33 pA/cm2 and modified the small-scale surface height characteristics. A high degree of AlN〈002〉 crystallisation may suggest good electrical insulating properties in AlN thin film layer, which can be applied in electronic devices that critically require a low leakage current specification.

Lead-free dielectric thin films: Synthesis of Ag(Nb1−xTax)O3 via reactive dc magnetron sputtering

Growing environmental concerns have driven the switch from lead-containing dielectric perovskite ceramics to lead-free alternatives such as silver niobate tantalate [Ag(Nb1−xTax)O3], where tantalum (Ta) substitution for niobium (Nb) enhances energy-storage density. Thin film deposition presents a promising way for fabricating these materials for use in capacitors. In this study, Ag(Nb1−xTax)O3 (0 ≤ x ≤ 0.5) thin films are synthesized via combinatorial reactive dc magnetron sputtering from metallic targets. The chemical and phase compositions of the films are comprehensively analyzed using scanning electron microscopy coupled with energy dispersive x-ray spectroscopy, elastic recoil detection analysis, Rutherford backscattering spectrometry, x-ray diffraction, Raman spectroscopy, and x-ray photoelectron spectroscopy. The findings demonstrate that reactive dc magnetron sputtering is a feasible technique for producing complex perovskite oxide thin films with customized chemical composition and microstructure. By enhancing the understanding of the Ag(Nb1−xTax)O3 material system, this study aims to contribute to the development of environmentally benign high-performance dielectrics that could replace lead-based ceramics in energy-storage applications.

Influence of the Ag Content on the Natural and Thermal Induced Oxidation of Cu Thin Films

In this paper, we studied the deposition and characterization of monolithic and silver-doped copper coatings using RF magnetron sputtering. The main objective was to examine the impact of different Ag contents on natural and thermally induced aging when compared with monolithic copper coatings. For this purpose, the as-deposited surfaces were left exposed to normal temperature and humidity conditions during one year (natural) and were annealed at 200 °C in a non-controlled atmosphere. To evaluate the results of these treatments, the films were characterized in terms of surface and cross-section morphology, structure, chemical composition, wettability, and surface energy. The as-deposited monolithic copper films exhibit a clear face-centered cubic structure with a very strong preferential crystallographic orientation according to the (111) diffraction plane. The presence of Ag in the as-deposited coatings decreased the ability of the films to be wetted, increasing their hydrophobicity and jeopardizing crystallographic orientation development according to the (111)-Cu diffraction plane, particularly after annealing, when compared to Cu films. Through annealing, Cu2O and Ag2O were formed, leading to a significant decrease in surface energy and reduced wettability. These results can help elucidate and estimate the life span of smart windows, batteries, and solar panels, which are some of the many applications for these coatings.