Mixed Films Research Articles

Exceptional Electrical Detection of Trace NO2 via Mixed Metal MOF-on-MOF Film-Based Sensors.

The tunability of metal-organic frameworks (MOFs) makes them exceptional materials for the development of highly selective, low-power sensors for toxic gas detection. Herein, we demonstrate enhanced detection of NO2 gas by a MOF-based electrical impedance sensor made using a unique mixed metal MOF-on-MOF synthesis. A combined experimental and computational study was performed using the exemplar NixMg1-x-MOF-74 to understand the fundamental structure-property relationships behind metal mixing and MOF film synthesis methods on sensor performance. Density functional theory results indicated that the presence of Ni in Mg-MOF-74 increased framework stability and increased the electron density of states at lower energies near the HOMO, as well as enhanced the NO2-Mg adsorption interaction. Impedance data of the NixMg1-x-MOF-74 films with larger Ni contents showed greater impedance change after exposure to 1 ppm of NO2 gas. Furthermore, when synthesized through either a drop-cast or direct solvothermal film growth approach, the monometallic Ni-based sensors had the best performance. However, the mixed metal NixMg1-x-MOF-74 sensors synthesized through a MOF-on-MOF approach resulted in the highest impedance change, outperforming all monometallic Ni-based sensors. In particular, the mixed metal Ni-on-Mg-MOF-74 film was the best-performing sensor with an impedance change of 309 upon trace NO2 exposure. Change in impedance response after NO2 exposure was improved by 52% compared to the best monometallic Ni-on-Ni-MOF-74 sensor. Structural analysis of the Ni-on-Mg film showed that the first Mg-MOF-74 layer acts as a structural template controlling the structural features of the final film after metal exchange with Ni. This led to improved film quality, evidenced by the greater crystallinity and larger MOF grain sizes, and resulted in enhanced sensor performance which was not achievable through other metal mixing methods. Altogether, this study identifies structure-property relationships and synthetic templating methods that inform MOF-based sensor design, allowing for improved detection of toxic compounds.

Flexible Narrow Bandgap Sn-Pb Perovskite Solar Cells with 21% Efficiency Using N,N'-Carbonyldiimidazole Treatments.

Flexible tin-lead (Sn-Pb) mixed perovskite solar cells (PSCs) are among the promising flexible photovoltaics, owing to the narrow bandgap (NBG) of Sn-Pb perovskites, flexible and wearable features, and their role as a critical component in all-perovskite tandem photovoltaics. However, the flexible Sn-Pb PSCs suffer from a low power conversion efficiency, no higher than 18.5%, along with limited stability. Herein, we reported an efficient and stable flexible NBG Sn-Pb PSC via an N,N'-carbonyldiimidazole (CDI) passivation strategy. CDI, with strong adsorption energy, preferentially binds to Sn2+ compared with oxygen (O2), thus effectively inhibiting the adsorption of O2 on perovskite surfaces. The transfer of electron density around Sn2+ dramatically decreased, thus suppressing Sn2+ oxidation. The CDI treatments endowed the Sn-Pb mixed films with fewer defects, improved crystallinity, better morphology, and matched energy-level alignment. The flexible Sn-Pb devices exhibited a high PCE of 21.02%. Besides, the devices showed enhanced stability and promoted flexibility. This work provides a pathway to visibly increase the efficiency and stability of the flexible Sn-Pb mixed photovoltaic cells.

Cr2O3–NiO mixed oxides thin films for p-type transparent conductive electrodes

The Cr2O3–NiO mixed oxides’ thin films were formed by means of the layer-by-layer magnetron sputtering deposition of Cr2O3, NiO, and Cr2O3 layers on c-plane sapphire substrates. These thin-film structures, subjected to subsequent annealing, constituted a combination of the monocrystalline (0001) Cr2O3 and nonordered nickel oxide phase, which was a mixture of NiO and Ni2O3. The annealing at 900 and 1000 °С in air facilitated the diffusion of Ni and Cr atoms into the layers. Varying the annealing time allowed us to control the uniformity of the Ni and Cr distribution, the microrelief of the film surface, the transmittance in the visible region, and the sheet resistance of the Cr2O3–NiO thin-film structures. Thus, the films annealed at 900 °C during 30 min were characterized by a uniform distribution, a relatively weakly developed surface, a low sheet resistance, and the highest Haacke's Figure of Merit of 1.49 × 10–9 Ω–1. The formation of mixed Cr2O3–NiO oxides by the proposed approach was found to be an effective way to improve the performances of Cr2O3 based p-type transparent conductive electrodes.

Hetero-Nucleation Induced [111]-Oriented Mixed Halide Perovskite for Stable Pure Red Light-Emitting Diodes.

Mixed halide 3D perovskites are promising for bright, efficient, and wide-color gamut light-emitting diodes (LEDs) due to their excellent carrier transport, high luminescence, and easily tunable bandgaps. However, serious halide ion migration inside mixed halide 3D perovskite results in poor operational and spectral stability of the as-fabricated LEDs. Here, a hetero-nucleation crystallization strategy is reported to grow [111]-orientationpreferred mixed halide 3D perovskite CsPbI3-xBrx thin films for stable pure red LEDs. This hetero-nucleation crystallization is enabled by the addition of phosphoric acid (H3PO4) complexation, which promotes the growth of small perovskite grains into large grains with uniform [111]-orientation. The obtained [111]-orientation preferred film exhibits excellent stability under light or electric field stimulus as revealed by model analysis and experimental results compared to that of [001]-orientation preferred film. Thus, based on the [111]-orientationpreferred film, the fabricated LED exhibits an external quantum efficiency of 22.8%, a maximum brightness of 12000cdm-2, and a half-life time of 4080min under 1.5mA cm-2. More importantly, the electroluminescence spectrum of the device remains stable during the continuous operation of 4080min, showcasing the significant spectral stability improvement enabled by the hetero-nucleation induced [111]-orientation strategy.

Compositional Optimization of Sputtered SnO2/ZnO Films for High Coloration Efficiency

We performed an electrochromic investigation to optimize the composition of reactive magnetron-sputtered mixed layers of zinc oxide and tin oxide (ZnO-SnO2). Deposition experiments were conducted as a combinatorial material synthesis approach. The binary system for the samples of SnO2-ZnO represented the full composition range. The coloration efficiency (CE) was determined for the mixed oxide films with the simultaneous measurement of layer transmittance, in a conventional three-electrode configuration, and an electric current was applied by using organic propylene carbonate electrolyte cells. The optical parameters and composition were measured and mapped by using spectroscopic ellipsometry (SE). Scanning Electron Microscopy (SEM) and Energy-Dispersive X-ray Spectroscopy (EDS) measurements were carried out to check the SE results, for (TiO2-SnO2). Pure metal targets were placed separately from each other, and the indium–tin-oxide (ITO)-covered glass samples and Si-probes on a glass holder were moved under the two separated targets (Zn and Sn) in a reactive argon–oxygen (Ar-O2) gas mixture. This combinatorial process ensured that all the compositions (from 0 to 100%) were achieved in the same sputtering chamber after one sputtering preparation cycle. The CE data evaluated from the electro-optical measurements plotted against the composition displayed a characteristic maximum at around 29% ZnO. The accuracy of our combinatorial approach was 5%.

Exploring the influence of Al content on the optical and interface properties of HfAlOx mixed gate dielectric thin films and their applications in MOS devices

Exploring the influence of Al content on the optical and interface properties of HfAlOx mixed gate dielectric thin films and their applications in MOS devices

Fast-switching electrochromic smart windows based on WO3 doped NiO thin films

Nickel oxide (NiO) is a very promising material for the counter electrode in electrochromic devices (ECDs). In the current research, WO3 incorporated NiO thin films were fabricated via RF sputtering to enhance the electrochromic performance of NiO thin films. An XRD analysis revealed that the addition of WO3 to the cubic NiO thin film disrupts its long-range crystalline structure, resulting in an amorphous state. FESEM revealed the formation of columnar structure which favours ECDs. XPS analysis revealed that the addition of WO3 into NiO enhanced the hole concentration by creating nickel vacancies (nickel defects). Compared to pristine NiO, WO3 mixed NiO thin films showed enhanced optical modulation (66 %) with rapid switching speed (0.6 s/1.0 s for bleaching/colouring). This is mainly because the defect- induced amorphous structure of the nickel tungsten oxide thin film can provide large number of diffusion channels which facilitates the rapid ion intercalation process, and can accommodate large number of ions, and hence enhances the electrochromic performance. This advancement might have a substantial impact on the development of nickel tungsten oxide as a potential counter electrode in high-performance energy saving smart windows.

POLYETHYLENE TEREPHTHALATE (PET) COATED WITH CHITOSAN AND CYCLOSPORINE A LAYERS AS A POTENTIAL STENT MATERIAL AND DRUG-DELIVERY SYSTEM

The aim of this paper was to design, prepare and characterise chitosan (Ch) and cyclosporine A (CsA) mixed films deposited on a plasma-activated polyethylene terephthalate (PET) polymer surface to be used as a cover for implantable blood vessel stents. The PET polymer coated with Ch and CsA layers was immersed in simulated body fluid (SBF) to examine how the obtained layers can behave in the environment of human body fluids. Time-of-flight secondary ion mass spectrometry was employed to determine the chemical composition of the deposited films and to analyse the spatial distribution of molecules on the PET surface. The results showed the controlled release of CsA from the chitosan matrix. It can be concluded that the modification of the PET polymer with layers of chitosan and CsA has great application potential in the tissue engineering as a biocompatible stent of blood vessels with therapeutic properties.

Syntheses and performance study of three POM-viologen compounds with photo- and electric-stimulation response

In recent years, stimulus responsive materials have received widespread attention. Under solvothermal conditions, three polyoxometalates-viologen organic–inorganic hybrid compounds were successfully constructed by combining a viologen ligand 1-(3-Nitro-benzyl)-[4,4′]bipyridinyl-1-ium bromide (1,3-nibipy·Br) with octamolybdate, namely [Cu2(1,3-nibipy)4(H2O)2(β-Mo8O26)2]·2H2O (1), [Cu2(1,3-nibipy)4(H2O)4(β-Mo8O26)]·(β-Mo8O26) (2) and (1,3-Hnibipy)2·(β-Mo8O26) (3). These three compounds can exhibit color changing properties under both light and electrical stimulation. Through characterizations of PXRD, FT-IR, UV–vis spectra, XPS, EPR, CV, and other tests, the photochromic and electrochromic properties of these three compounds are caused by the generation of viologen radicals. Compounds 1–3 have a rapid photoresponse efficiency and can be made into mixed matrix films for use as ultraviolet detectors. In addition, coated filter paper synthesized from acetonitrile and compounds can serve as an innovative erasable ink-free printing material medium, which is suitable for various erasable ink-free printing and anti-counterfeiting fields. We further investigated the electrochromic devices prepared from compounds 1–3, which achieved color change at a voltage of around −0.2 V and exhibited good stability after 500 cycles.

Comparative study on the characterization of chitosan mixed natural phenolic aldehyde edible films

Comparative study on the characterization of chitosan mixed natural phenolic aldehyde edible films

Structure Properties Correlations on Nickel‐Iron Oxide Catalysts Deposited by Atomic Layer Deposition for the Oxygen Evolution Reaction in Alkaline Media

Thermal atomic layer deposition (ALD) is used for the first time to deposit iron‐nickel oxides onto carbon nanotubes in a ternary process to produce a wide range of mixed oxide thin films. When using ferrocene (FeCp2) and nickelocene (NiCp2) with ozone (O3) as metals and oxygen sources, respectively, a competition between the metal precursors and the growth modes is observed. Indeed, while ferrocene promotes a 2D‐growth, nickelocene prefers a 3D‐growth. Although both precursors are homoleptic metallocenes, they behave differently in the ALD of their respective metal oxide, leading to unexpected atomic ratios and films morphologies of the iron‐nickel oxides. The 2Fe:1Ni sample displays the best performances in the electrochemical water oxidation (oxygen evolution reaction) exhibiting an overpotential of 267 mV at a current density of 10 mA cm−1, a Tafel slope of 36.8 mV dec−1, as well as a good stability after 15 h of continuous operation.

Surface chemical polishing and passivation minimize non-radiative recombination for all-perovskite tandem solar cells

All-perovskite tandem solar cells have shown great promise in breaking the Shockley–Queisser limit of single-junction solar cells. However, the efficiency improvement of all-perovskite tandem solar cells is largely hindered by the surface defects induced non-radiative recombination loss in Sn–Pb mixed narrow bandgap perovskite films. Here, we report a surface reconstruction strategy utilizing a surface polishing agent, 1,4-butanediamine, together with a surface passivator, ethylenediammonium diiodide, to eliminate Sn-related defects and passivate organic cation and halide vacancy defects on the surface of Sn–Pb mixed perovskite films. Our strategy not only delivers high-quality Sn–Pb mixed perovskite films with a close-to-ideal stoichiometric ratio surface but also minimizes the non-radiative energy loss at the perovskite/electron transport layer interface. As a result, our Sn–Pb mixed perovskite solar cells with bandgaps of 1.32 and 1.25 eV realize power conversion efficiencies of 22.65% and 23.32%, respectively. Additionally, we further obtain a certified power conversion efficiency of 28.49% of two-junction all-perovskite tandem solar cells.

Thiourea-Induced Cocrystallization of Mixed-Halide Perovskite Thin Films for High-Performance Pure Blue Perovskite Light Emitting Diodes

Metal halide perovskite light-emitting diodes (PeLEDs) are gaining significant attention towards next-generation display materials owing to their advantageous properties, including color tunability, exceptionally narrow bandwidth, and high luminescence. Recent studies have successfully achieved over 20% external quantum efficiencies (EQE) in green and red PeLEDs. However, the blue PeLEDs lag far behind those of green or red PeLEDs because unstable phase stability in mixed halide perovskite thin films under high turn-on voltage (Von). In specific, the blue emission usually possesses halide ions with smaller ionic radius (Cl- or Br-), which easily migrates under high operative bias generating significant halogen vacancies and phase-transformation. In this context, we suggest thiourea as a promising additive for stabilizing defective perovskite thin films. Thiourea is a well-known hydrogen bond donor to halogens, which allows potential coordination complex of thiourea-halide ions to encompass well-dispersed mixed halides in co-crystallized perovskite lattices. In addition, the strong coordination of the C=S···Pb2+ was also demonstrated the thiourea-incorporated perovskite films, which effectively passivated undercoordinated Pb2+ antisites. Consequently, the thiourea-incorporated perovskite films exhibited stable deep-blue emission within 460 nm, demonstrating excellent luminance and quantum efficiency in pure blue PeLEDs. Moreover, the addition of thiourea achieved decreased Von and excellent spectral stability of pure blue PeLEDs at high applied bias, leading to significant advancements in pure blue perovskite display technology.

A low-cost and convenient route of fabricating GaN films with P-type mixed microcrystalline and amorphous structure deposited via Ga target of magnetron sputtering

GaN, a third-generation semiconductor, has gained widespread attention owing to its high temperature resistance, wide bandgap, and high critical breakdown electric fields. Magnetron sputtering has a broad potential in the field of low-cost growth of GaN on account of high efficiency, superior quality, and convenient operation. However, challenges caused from the pure Ga targets with a huge refrigeration system need to be resolved for wide practices. Here, a new and cost-effective Ga target for magnetron sputtering was fabricated by utilizing the wetting properties of CuGa2 and Ga. Mixed microcrystalline and amorphous GaN films were obtained via reactive magnetron sputtering employing the Ga target. The average deposition rate is about 1.68 nm/min, and the average roughness is ∼7.45 ± 0.26 nm under 100 W of sputtering power. In addition, the sputtered GaN films were found to be wide-bandgap and p-type semiconductors with high transmittance, as revealed by x-ray photoelectron spectroscopy and absorption spectra. The GaN films display a bandgap of ∼3.60 eV and a transmittance exceeding 88.5% in the visible range. Furthermore, field-effect transistors and metal–semiconductor–metal photodetectors have been fabricated using the obtained GaN films, demonstrating favorable response characteristics. The prospects of microcrystalline/amorphous GaN films in sensing, power devices, and flexible electronics were forecasted. Overall, a low-cost and pervasive route of target fabrication process expands the possibilities of using low melting point metals in magnetron sputtering.

Life cycle assessment of recycling metallised food packaging plastics using mechanical, thermal and chemical processes

Single treatment of metallised food packaging plastics waste (MFPW) has shown disappointing results with recycling rate <20 % due to its complex structure consisting of 10 % aluminium (Al) and 90 % mixed plastic films made of PE, PP, PS, PET, etc. Besides, it is generating many emissions and residues that must be landfilled making it difficult to integrate them into the circular economy. Therefore, a multi-stage recycling (MSR) approach has recently been developed using several sequential mechanical, thermal and chemical processes to recover energy and Al from MFPW with additional revenue for recycling plant operators. The thermal treatment helps to decompose the plastic fraction into wax or oil, gaseous, and solid residue (SR) composed of Al and coal, while the mechanical process can be used as a pre-treatment of MFPW feedstock and SR. Finally, the chemical treatment (leaching and functionalization) can be used to extract Al from SR and to refine coal into carbon microparticles (CPs), respectively. In order to investigate the environmental performance of the proposed MSR system, this research was developed. The investigation was performed using SimaPro life cycle analysis (LCA) tool according to ISO 14040/44 Standards and the impact assessment method is ReCiPe 2016. Five different scenarios were proposed in the constructed LCA layout, namely, conversion of MFPW to a) wax and gas (pyrolysis), b) wax, gas, and aluminium chloride (AlCl₃) (pyrolysis and leaching), c) wax, gas, AlCl₃, and CPs (pyrolysis, leaching, and functionalization), and d) oil, gas, AlCl₃, and CPs (catalytic pyrolysis, leaching, and functionalization). Besides, the oil produced from catalytic pyrolysis is used for generation of electricity (scenario e). The results showed that wax and gas recovery scenario (a) has better environmental potential and environmental benefits compared to incineration practice. The results did not change much after extraction of Al and CPs (scenario b, c), with a few increasing by 2–4% in the total score. While a lot of environmental burdens from upgrading and utilization (Scenario d, e) were recorded, reaching 79 % due to the huge amount of the catalyst was used. Thus, MSR systems have bigger environmental benefits, however, the chemical and catalytic processes still need to be further improved to reduce the effect of terrestrial acidification.

Joint experimental-computational: Revealing the role of sodium poly(heptazineimide) in the selective separation of CO2 in PEBAX-based mixed matrix membranes

Mixed matrix membranes (MMMs) with the dual properties of porous materials and polymer matrix membranes have become one of the most optimal solutions to the gas separation problem. However, the adapted porous material and the explicit transport mechanism of gases within the mixed matrix membrane hinder its further commercialization. Thanks to their porous nature and tunable gas adsorption properties, heteroatom-doped porous materials, especially nitrogen-doped porous materials, are widely used to design and prepare advanced CO2 separation membranes. Herein, a layered two-dimensional nano-sheet with a nitrogen content of 44.7 % was successfully synthesized via thermal polymerization. And nano-sheets were homogeneously dispersed in a Pebax matrix to make a composite film. Since the CO2 affinity of the nitrogen functional site and the PEO flexible chain, realizing the synergistic improvement of CO2 permeability and selectivity. A comprehensive combined permeation experimental/simulation characterization reveals the CO2 transport pathway within the membrane, indicating the mechanism of action of nitrogen-doped porous packing on CO2 diffusion. Among these, the CO2 permeability of the mixed matrix film containing 5 wt% sodium poly(heptazine imide) (NaPHI) reached 153 Barrer at a feed gas pressure of 9 bar, nearly 149 % compared to the pure Pebax film. The selectivity of CO2/N2 was enhanced to 105, exhibiting a remarkable increase of 159 % and exceeding the 2019 Robeson limit. Importantly, the present work further reveals and demonstrates the gas separation mechanism of nitrogen-doped porous filler/polymer hybrid matrix membranes, which provides new ideas for the design and application of heteroatom-doped porous fillers in the field of gas separation.

Unravelling Structural, Optical, and Band Alignment Properties of Mixed Pb-Sn Metal-Halide Quasi-2D Ruddlesden-Popper Perovskites.

Lead-tin (Pb-Sn) mixed-halide perovskites show potential for single-junction and tandem solar cells due to their adjustable band gaps, flexible composition, and superior environmental stability compared to three-dimensional (3D) perovskites. However, they have lower power conversion efficiencies. Understanding band alignment and charge carrier dynamics is essential for enhancing photovoltaic performance. In this view, herein we have prepared thin films of mixed Pb-Sn-based two dimensional (2D) Ruddlesden-Popper (RP) perovskites BA2FA(Pb1-xSnx)2I7 using a solution-based method. XRD study revealed the formation of orthorhombic phases for pristine (BA2FAPb2I7) and mixed Pb-Sn perovskite thin films. UV-vis analysis showed that different n = 2 and n = 3 phases are present in the pristine sample. In contrast, Pb-Sn-doped samples showed no signature of other phases with a prominent red-shift in the visible spectral region. Cyclic voltammetry showed peaks for electron transfers at the band edges. Additionally, electrochemical and optical band gap matching was observed, along with decreased peak intensity due to less reactant and altered electrolyte-perovskite interface stability. Density functional theory (DFT) calculations revealed that the reduced band gap is due to the alteration of electrostatic interactions and charge distribution within the lattice upon Sn substitution. Low-temperature PL analysis provided insights into charge carrier dynamics with Sn substitution and suggested the suppression of higher n phases and self-trapped excitons/carriers in mixed Pb-Sn quasi-2D RP perovskite thin films. This study sheds light on the electron transfer phenomena between TiO2 and SnO2 layers by estimating band offsets from valence band maximum (VBM) and conduction band minimum (CBM), which is crucial for future applications in fabricating stable and efficient 2D-Pb-Sn mixed perovskites for optoelectronic applications.

Morphological and Chemical Nanoscale Analysis of Mesoporous Mixed IrOx-TiOy Thin Films as Electrode Materials

Morphological and Chemical Nanoscale Analysis of Mesoporous Mixed IrOx-TiOy Thin Films as Electrode Materials

Naphthalene-embedded spiropyran derivative-A type of conjugated expanded material with solid-state photochromic properties and tunable color switching range

Due to the limited free volume in the solid state, spiropyrans generally exhibit photochromic properties in solution or mixed thin films. However, few spiropyrans can display the photoisomerization process in the solid state. One conventional solution for solid-state photochromism is to embed the spiropyran on polymer chains or introduce bulky groups to create an efficient free volume in the solid state. In this article, we attempt to introduce large conjugated fragments on the spiropyran backbone to construct a donor-acceptor (D-A) building block that not only possesses an enlarged π-electron system with enhanced electronic delocalization capability but also exhibits an improved free volume for efficient solid-state photoisomerization. Through this strategy, we have successfully embedded the naphthalene ring on the spiropyran backbone to obtain a novel D-A type conjugated building block, SP-Naph, which exhibits excellent solid-state photochromic performance and reversibility. Furthermore, the D-A structure of SP-Naph significantly tuned its photochromic color-switching range to blue. Consequently, SP-Naph was successfully applied in optical printing and invisible inks. The excellent solid photochromic properties make it exhibit remarkable photochromic effects, indicating significant potential for optical printing and anti-counterfeiting applications.

Nano-innovations in lubrication: Unveiling the synergistic boundary lubrication potential of zinc titanate with phosphonium ionic liquid

This study investigates the potential of Zinctitanate (ZnTiO3) nanoparticles (APS <100 nm) as nano-additives in lubricant formulations, in conjunction with phosphonium phosphate ionic liquids. Comparative analysis against well-established nano-additives highlights ZnTiO3's exceptional dispersion stability, enduring beyond 225 days. Tribological assessments unveil significant enhancements in antiwear, antifriction, and extreme pressure properties, with 1 wt% ZnTiO3 outperforming the base oil. The ZnTiO3 hybrid nanolubricants exhibited notable synergy, achieving a 49 % reduction in wear compared to hexagonal boron nitride (hBN) and Boehmite NPs. Surface characterization confirms the formation of a protective transfer film (≥100 nm thick), attributed to ZnTiO3's disintegration under tribostress. This results in the development of a mixed metallic metal oxide interfacial film composed of (FeTiO3, FePO4, and ZnO) domains on exposed nascent steel surfaces through tribochemical reactions. These findings suggest ZnTiO3 as a promising nano-additive for advanced lubricants, offering substantial improvements in dispersion stability and tribological performance.