Superior energy storage performance of all-inorganic flexible antiferroelectric-insulator multilayer thin films

In this work, we develop an all-inorganic flexible capacitor films that by growing antiferroelectric Pb_0.94(Li_0.5Al_0.5)_0.06ZrO₃ (PLAZO) and insulating Al₂O₃ (AO) layer by layer on the flexible mica substrates. The results show that the low-annealing temperature below 600°C endows the PLAZO films to have low polarization loss and high breakdown strength, conversely, the high-annealing temperature above 650°C gives rise to large maximum polarization at the expense of breakdown strength. The insulating AO layers are introduced to reconcile the polarization and breakdown strength, achieving a remarkable improvement in the energy storage density of 41.78 J/cm³ with an efficiency of 91.2% in the AO/PLAZO/AO/PLAZO/AO (APAPA) multilayer films, which can be attributed to the significant improvement in breakdown strength and suppression of polarization loss by introducing AO insulator layer. Moreover, the energy storage performance of the APAPA flexible thin film capacitors possesses excellent frequency stability as well as bending cyclic endurance.     

Fabrication of highly efficient TiO2/Ag/TiO2 multilayer transparent conducting electrode with N ion implantation for optoelectronic applications

Fabrication of highly conductive and transparent TiO₂/Ag/TiO₂ (referred hereafter as TAT) multilayer films with nitrogen implantation is reported. In the present work, TAT films were fabricated with a total thickness of 100 nm by sputtering on glass substrates at room temperature. The as-deposited films were implanted with 40 keV N ions for different fluences (1×10¹⁴, 5×10¹⁴, 1×10¹⁵, 5×10¹⁵ and 1×10¹⁶ ions/cm²). The objective of this study was to investigate the effect of N⁺ implantation on the optical and electrical properties of TAT multilayer films. X-ray diffraction of TAT films shows an amorphous TiO₂ film with a crystalline peak assigned to Ag (111) diffraction plane. The surface morphology studied by atomic force microscopy (AFM) and field emission scanning electron microscope (FESEM) revealed smooth and uniform top layer of the sandwich structure. The surface roughness of pristine film was 1.7 nm which increases to 2.34 nm on implantation for 1×10¹⁴ ions/cm² fluence. Beyond this fluence, the roughness decreases. The oxide/metal/oxide structure exhibits an average transmittance ~80% for pristine and ~70% for the implanted film at fluence of 1×10¹⁶ ions/cm² in the visible region. The electrical resistivity of the pristine sample was obtained as 2.04×10⁻⁴ Ω cm which is minimized to 9.62×10⁻⁵ Ω cm at highest fluence. Sheet resistance of TAT films decreased from 20.4 to 9.62 Ω/□ with an increase in fluence. Electrical and optical parameters such as carrier concentration, carrier mobility, absorption coefficient, band gap, refractive index and extinction coefficient have been calculated for the pristine and implanted films to assess the performance of films. The TAT multilayer film with fluence of 1×10¹⁶ ions/cm² showed maximum Haacke figure of merit (FOM) of 5.7×10⁻³ Ω⁻¹. X-ray photoelectron spectroscopy (XPS) analysis of N 1s and Ti 2p spectra revealed that substitutional implantation of nitrogen into the TiO₂ lattice added new electronic states just above the valence band which is responsible for the narrowing of band gap resulting in the enhancement in electrical conductivity. This study reports that fabrication of multilayer transparent conducting electrode with nitrogen implantation that exhibits superior electrical and optical properties and hence can be an alternative to indium tin oxide (ITO) for futuristic TCE applications in optoelectronic devices.     

Preparation and electrochemical properties of gold nanoparticles containing carbon nanotubes-polyelectrolyte multilayer thin films

Multi-walled carbon nanotubes (MWCNT)/polyelectrolyte (PE) hybrid thin films were fabricated by alternatively depositing negatively charged MWCNT and positively charged (diallyldimethylammonium chloride) (PDDA) via layer-by-layer (LbL) assembly technique. The stepwise growth of the multilayer films of MWCNT and PDDA was characterized by UV–vis spectroscopy. Scanning electron microscopy (SEM) images indicated that the MWCNT were uniformly embedded in the film to form a network and the coverage density of MWCNT increased with layer number. Au nanoparticles (NPs) could be further adsorbed onto the film to form PE/MWCNT/Au NPs composite films. The electron transfer behaviour of multilayer films with different compositions were studied by cyclic voltammetry using [Fe(CN)₆]^3−/4− as an electrochemical probe. The results indicated that the incorporation of MWCNT and Au NPs not only greatly improved the electronic conductivity of pure polyelectrolyte films, but also provided excellent electrocatalytic activity towards the oxidation of nitric oxide (NO).     

Study of Cu-based Al-doped ZnO multilayer thin films with different annealing conditions

AZO/Cu/AZO multilayer thin films produced under different annealing conditions are studied in this paper, to examine the effects of atmosphere and annealing temperature on their optical and electrical properties. The multilayer thin films are prepared by simultaneous RF magnetron sputtering (for AZO) and DC magnetron sputtering (for Cu). The thin films were annealed in a vacuum or an atmosphere of oxygen at temperatures ranging from 100 to 400 °C in steps of 100 °C for 3 min. High-quality multilayer films (at Cu layer thickness of 15 nm) with resistivity of 1.99×10⁻⁵ Ω-cm and maximum optical transmittance of 76.23% were obtained at 400 °C annealing temperature in a vacuum. These results show the films to be good candidates for use as high quality electrodes in various displays applications.     

Functionalization of polymer multilayer thin films for novel biomedical applications

The design of functional polymer multilayer thin films with nanometer scale control is of great interest for biomedical applications such as tissue engineering, targeted drug delivery, controlled release system, and regenerative medicine. Various functions and properties of polymer thin films can be easily programmed and realized by the layer-by-layer assembly strategy, which is a facile and versatile deposition method to prepare well-defined biomedical multilayer platforms due to its benign process to prepare films under mild conditions and the capability of incorporating bioactive materials at a desired location within the films. Particularly, the fine tuning of physicochemical and biological properties of multilayer thin films is significantly important for designing novel biomedical platforms capable of adjusting the cellular functions. In this review, we focus on the overall background of the layer-by-layer assembly as well as the tuning of multilayer film properties and the programming of biological functions into the polymer thin films with a view on the control of cellular functions. Furthermore, we highlighted the recent achievements toward the design of novel biomedical platforms based on functionalized polymer multilayer thin films.     

Dielectric and ferroelectric properties of multilayer BaTiO3/NiFe2O4 thin films prepared by solution deposition technique

In this work different lead-free multilayered structures, composed of perovskite BaTiO₃ and spinel NiFe₂O₄ thin layers, were obtained by solution deposition method. Structural characterization of the sintered thin films confirmed the well-defined layered structure with overall thickness from 160 to 600 nm, crystalline nature of perovskite BaTiO₃ and spinel NiFe₂O₄ phases without secondary phases (after sintering below 900 °C) and grains on nanometer scale. Dielectric properties of the multiferroic multilayer BaTiO₃/NiFe₂O₄ thin films were analyzed in temperature and frequency range from 30 °C to 200 °C and 100 Hz to 1 MHz, respectively. In comparison to the pure BaTiO₃ films, the introduction of ferrite layer reduces dielectric response and increases low frequency permittivity dispersion of the multilayer thin films. The multilayer samples have shown relatively low dielectric loss with stronger contribution of conductivity at higher temperatures, and characteristic broad peak representing “relaxation” of the interface charge accumulation.     

Fabrication and bio-functionalization of tetrahedral amorphous carbon thin films for bio sensor applications

Tetrahedral amorphous carbon (ta-C) thin films are a promising material for use as biocompatible interfaces in applications such as in-vivo biosensors. However, the functionalization of ta-C film surface, which is a pre-requisite for biosensors, remains a big challenge due to its chemical inertness. We have investigated the bio-functionalization of ta-C films fabricated under specific physical conditions through the covalent attachment of functional biomolecular probes of peptide nucleic acid (PNA) to ta-C films, and the effect of fabrication conditions on the bio-functionalization. The study showed that the functional bimolecular probes such as protected long-chain ω-unsaturated amine (TFAAD) can be covalently attached to the ta-C surface through a well-defined structure. With the given fabrication process, electrochemical methods can be applied to the detection of biomolecular interaction, which establishes the basis for the development of stable, label-free biosensors.     

Synthesis of highly ordered mesoporous silica thin films for nano-fabrication of platinum nanodot arrays

Mesoporous silica thin films with highly ordered cubic Pm-3n and three dimensional hexagonal P6₃/mmc symmetries were synthesized by evaporation induced self assembly (EISA) method controlling the ratio of HCl and tetramethoxysilane in the initial sol solution and the humidity in the dip-coating chamber. Using these optimized mesoporous silica thin films, highly ordered Pt nanodot arrays with cubic and three dimensional hexagonal symmetries were synthesized by simple immersion in a Pt precursor solution and photoreduction. These periodic nanodot arrays in the silica thin film have a potential to be applied to single-electron devices mediated by coupling interactions with neighboring nanodots.     

Fabrication and characterization of low temperature sintered hard piezoelectric ceramics for multilayer piezoelectric energy harvesters

In this study, 0.65Pb(Zr_0.465Ti_0.545)O₃-0.35Pb(Zn_1/6Ni_1/6Nb_2/3)O₃, doped with 3.0 mol% MnCO₃ and 1.0 mol% CuO (M3.0C1.0PZT-PZNN), was investigated as a hard piezoelectric ceramic for multilayer ceramic piezoelectric energy harvesters (MLC-PEHs). These PEHs showed a high output performance that was partly ascribed to the hardening effect of MnCO₃. In contrast, a single-layer ceramic piezoelectric energy harvester (SLC-PEH), containing M3.0C1.0PZT-PZNN, exhibited a higher output power density than that containing an analogous non-Mn-doped soft piezoelectric ceramic (C1.0PZT-PZNN), especially at high accelerations. In the fabricated MLC-PEH, containing an M3.0C1.0PZT-PZNN-based five-layer ceramic and a pure Ag inner electrode, no interdiffusion was observed between the electrode and the ceramic layers, and the corresponding interface was clear and smooth. This MLC-PEH, which exhibited a high output power density and a relatively large current, was used to charge a 0.22 F capacitor at its resonance frequency and an acceleration of 1.5 G, achieving a charging rate higher than that of the SLC-PEH.     

Quantitative analysis on the adsorbed amount and structural characteristics of spin self-assembled multilayer films

In this study, we demonstrate that the adsorbed amount of respective layers in spin self-assembled multilayer films can be controlled and predictable using an empirical power-law equation in terms of spin speed and initial solution concentration. The amount of a pair of polyelectrolytes deposited per bilayer rapidly increases with increasing polyelectrolyte concentration up to 12.5 mM while the solution concentration above 16 mM has no appreciable effect on the adsorbed amount. The adsorbed film thickness per bilayer is shown to be easily controlled from about 5 to 40 Å and proportional to constant power exponents of −0.34 and 0.78 with respect to the spinning speed (Ω) and the mole concentration of polyelectrolytes, respectively. We also demonstrate with synchrotron X-ray reflectivity measurement that the alternating organic/inorganic ultrathin films fabricated by the spin self-assembly process contain highly ordered internal structure and retain unique optical characteristics determined by the boundary condition at both the substrate/multilayer film interface as well as the multilayer/air interface.     

High conducting multilayer films from poly(sodium styrenesulfonate) and graphite nanoplatelets by layer-by-layer self-assembly

Exfoliated graphite (G) nanoplatelet was modified with hexadecyltrimethylammonium bromide (C₁₆TAB) and was constructed as multilayer films by electrostatic self-assembly. A [poly(sodium styrenesulfonate)/graphite]_n (PSS/G)_n multilayer film was self-assembled by alternate adsorption of polyanionic PSS and cationic graphite nanoplatelets G. An uniform deposition process was detected by UV-vis absorption spectra. The (PSS/G)_n multilayer film exhibits an excellent electrical conductivity in the range of 50-200 S cm⁻¹, when bilayer number (n) exceeds a threshold value four, the conductivity of the multilayer film increases dramatically. Cyclic voltammogram measurement reveals that the (PSS/G)_n film with more bilayer has small charge-transfer resistance and high electrocatalytic activity.     

Antiferroelectric titanium-doped zirconia thin films deposited via HiPIMS for highly efficient electrocaloric applications

In this study, the antiferroelectric (AFE) and electrocaloric (EC) characteristics of lead-free titanium (Ti)-doped zirconia (ZrO₂) thin films deposited via high-power impulse magnetron sputtering (HiPIMS) were investigated. The argon-to-oxygen ratio was initially optimized during deposition to obtain a more stoichiometric ZrO₂ film for enhanced antiferroelectricity. Furthermore, enhanced crystallinity was achieved through the incorporation of Ti atoms into ZrO₂ thin films as confirmed via grazing incidence X-ray diffraction and high-resolution transmission electron microscopy. For metal-insulator-metal capacitors with Ti-doped ZrO₂ thin films, the AFE behaviors were significantly improved because of the excellent crystallinity of the tetragonal phase. Based on a fast polarization response and robust fatigue resistance under a 10⁶-cycle endurance test, the EC effect was successfully explored, and an adiabatic temperature change (ΔT) of ?14.8 K was realized. With competitive EC properties, Ti-doped ZrO₂ thin films deposited via HiPIMS are proposed as promising candidates for use in future cooling systems.     

Fabrication of highly conducting and transparent graphene films

Graphene-based transparent conducting films were prepared using the following method. A chemically-reduced graphene dispersion was synthesized and graphene films were prepared from it by transfer printing, followed by thermal treatment. The resulting graphene films possessed an excellent electrical conductivity with a high transparency. A sheet resistance lower than ∼2 KΩ/sq and a transparency well over 80% were achieved at a typical wavelength of 550 nm. These properties are considered quite sufficient for many applications, such as transparent conductor films for touch panels.     

Sintering behavior,microstructure and thermoelectric properties of calcium cobaltite thick films for transversal thermoelectric multilayer generators

The sintering behavior and the thermoelectric performance of Ca₃Co₄O₉ multilayer laminates were studied, and a multilayer thermoelectric generator was fabricated. Compacts and multilayer samples with anisotropic microstructure and residual porosity were obtained after conventional sintering at 920 °C, whereas dense and isotropic multilayer samples were prepared by firing at 1200 °C and reoxidation at 900 °C. A hot-pressed sample has a dense and anisotropic microstructure. Samples sintered at 920 °C exhibit low electrical conductivity due to the low density, whereas the Seebeck coefficient is not sensitive to preparation conditions. However, thermal conductivity of multilayers is very low, and, hence acceptable ZT values are obtained. A transversal multilayer thermoelectric generator (TMLTEG) was fabricated by stacking layers of Ca₃Co₄O₉ green tapes, AgPd conductor printing, and co-firing at 920 °C. The TMLTEG has a power output of 3 mW at ΔT = 200 K in the temperature interval of 25 °C to 300 °C.     

Fabrication of highly ordered pore array in anodic aluminum oxide

Highly ordered pore array in anodic aluminum oxide was fabricated by anodizing pure aluminum. The order of a pore array was affected by anodizing voltage, electrolyte temperature, and first anodizing time. A regular pore array with mean diameter of 24 nm and interpore distance of 109 nm could be formed by two-step anodization at 40 V., oxalic acid concentration of 0.3 M and electrolyte temperature of 15 ‡C. The measured interpore distance showed linearity with anodizing voltage. The diameter of pores was adjusted by pore widening treatment in a 5 wt% phosphoric acid solution at 30 ‡C after two step anodization. The mechanism of self-arrangement of pores could be explained by the repulsive interaction between the pore walls.     

Fabrication of short carbon fibre reinforced SiC multilayer composites by tape casting

Silicon carbide multilayer composites containing short carbon fibres (C_sf/SiC) were prepared by tape casting and pressureless sintering. C fibres were dispersed in solvents and then mixed with SiC slurry to make green C_sf/SiC tape. Triton X-100 was found to be the best one for Toho Tenax HTC124 fibres (with water soluble coating) among BYK-163, BYK-410, BYK-2150, BYK-9076, BYK-9077 and Triton X-100 dispersants. C_sf/SiC multilayer composites containing 5 vol.% fibre (mean fibre length of 3, 4.5, and 6 mm) were obtained. Addition of short C fibres seems to worsen the densification process in the C_sf/SiC multilayer composites, whereas anisotropy shrinkage in C_sf/SiC was also observed. Open pores size was increased slightly after the addition of C fibre but it decreased with the mean fibre length. Mechanical properties were affected by high residual porosity. The addition of short C fibre has not changed the crack deflection at weak interfaces. C_sf/SiC multilayer composites containing longer fibres (4.5 and 6 mm) presented higher elastic modulus, bending strength and Vickers hardness as compared to shorter fibres (3 mm). Improved sintering performance and fibre content are necessary to improve mechanical properties.     

Elaboration and mechanical properties of monolithic and multilayer mullite-alumina based composites devoted to ballistic applications

Both monolithic and multilayer mullite-alumina ceramic composites dedicated to ballistic applications were produced by uni-axial pressing and tape casting before being sintered at 1510 °C. The compositions combining andalusite and kaolin in addition to α-alumina exhibit the more promising mechanical properties, reaching the performances of pure ballistic alumina. However, for a given bulk density value, a significant improvement of the performances (Young's modulus and ballistic impedance) only by varying the composition of the monoliths is limited. The second approach reported in this work has consisted in the development of judicious multilayer materials based on the generation of internal residual stresses in thinner layers. Compared to the monolithic materials, the most efficient multilayer configurations exhibit a failure stress improved by +35% and a fracture energy increased by +60%. Indeed, the layers subjected to compressive stress promote a significant crack bifurcation during rupture.     

A novel approach to assess the mechanical reliability of thin,ceramic-based multilayer architectures

Many substrates for microelectronic systems contain ceramic/glass layers and metal features (e.g. electrodes, vias, metal pads) built up in a complex 3D architecture. The combination of different materials with distinct thermo-elastic properties may yield significant (local) internal stresses, which are to be superimposed to external thermo-mechanical loads in service. Due to the various material junctions, interfaces, etc, failure of these multilayer systems can hardly be predicted. In this work, a strategy is proposed to quantify the effect of architecture and loading conditions on the mechanical reliability of ceramic-based substrates. Model ceramic structures containing important design features (e.g. inner electrode, via, top metallization) were fabricated and tested in different environments (i.e. humid or dry conditions) under uniaxial as well as biaxial bending. Significant difference in the characteristic strength between ∼260 MPa and ∼620 MPa were measured, associated with the particular architectural feature, type of loading, and/or environment.     

Fabrication of highly ordered P3HT:PCBM nanostructures and its application as a supercapacitive electrode

In this paper, we successfully demonstrated the fabrication of highly ordered and large-scale P3HT:PCBM nanowires via a slow-drying method, which allows for the convenient and cost-effective preparation of well-defined P3HT:PCBM nanostructures with large domains. The formation of the organic nanowires can be explained by the self-organization of polymer chains under favorable thermodynamic conditions in the slow-drying process. Furthermore, the C-V measurements revealed that the P3HT:PCBM nanowires possess high capacitance. This supercapacitive behavior of the nanowires is related to their large surface area and open structure, which can facilitate ion transport and accumulation. Owing to their extremely easy preparation and excellent capacitance performance, the P3HT:PCBM nanowires offer a promising electrode material for supercapacitor devices.     

Fabrication of highly transparent CsPbBr3 quantum-dot thin film via bath coating for light emission applications

Metal halide perovskite is not easy to form a film due to its high crystallinity, which makes it unfavourable for its application in self-luminous LED. Herein, we propose a film synthesis process for perovskite quantum dots (PeQDs) based on bath coating. The proposed method is low in cost, can be performed in an atmospheric environment at room temperature, and is suitable for the rapid mass production of closely stacked PeQDs on the deposition substrate with excellent luminous characteristics. By controlling the deposit time and rotation speed, the monolayer QD film can be achieved. The deposited monolayer QD film shows a high transmittance of up to 86% and a narrow FWHM of 18 nm. The device fabricated by monolayer QD film shows a low threshold voltage of 3 V, the maximum luminance of 150 cd/m², the maximum current efficiency of 0.085 cd/A, the maximum EQE of 0.027%, and the high color purity of 87%. Due to the above properties, monolayer QD film elements have potential in smart home appliances and wearable devices, especially AR glasses.