Multilayer Thin Films Research Articles

High transparent conductive Ga-doped ZnO-based multilayer thin films with embedded ultrathin TiN layer deposited in oxygen-containing atmosphere.

To avoid metal layer oxidation during the deposition of transparent conductive oxide (TCO)/metal/TCO multilayer films in an oxygen-containing atmosphere, the ultra-thin (<10 nm) titanium nitride (TiN) layer has been proposed to replace metal embedding in gallium-doped zinc oxide (GZO) film for the development of indium-free transparent electrodes. The effects of TiN thickness on the structure, morphology, electrical, and optical properties of GZO/TiN/GZO multilayer thin films deposited in argon-oxygen mixtures on glass substrates by magnetron sputtering are investigated. The experimental results reveal that multilayers with the 8 nm-thick TiN layer have the optimal performance (figure of merit of 2.75 × 10-1 Ω-1): resistivity of 4.68 × 10-5 Ω cm, and optical transmittance of above 91% in the visible region, which is superior to the sandwich film with the metal embedded layer.

High dielectric temperature stability in the relaxor ferroelectric thin films via using a multilayer heterostructure

The temperature stability of the relaxor ferroelectrics (RFEs) mainly originates from the diffuse phase transition (DPT). Higher atomic disorder degrees, more inhomogeneous lattice distortion and polymorphic phases could increase the compositional inhomogeneity for a stronger DPT. This work aims to enhance this compositional inhomogeneity for a high dielectric temperature stability by preparing the multicomponent RFE-based multilayer heterostructure polycrystalline thin films. The as-prepared RFE thin films show a relatively high dielectric constant (∼165.14), and a very high dielectric temperature stability with a very low relative variation ratio of dielectric constant (∼1.7 %) from -55 °C to 150 °C which can be comparable to most linear dielectric thin films. Meanwhile, the dielectric loss and leakage current densities were also optimized. This work brings the potential application of the RFE thin films in the thin-film capacitor with high temperature stability requirements.

Modelling the propagation of electromagnetic plane waves in lossless, nonmagnetic multilayer thin films using polynomial model

Modelling the propagation of electromagnetic plane waves in lossless, nonmagnetic multilayer thin films using polynomial model

Improved performance of AZO/Ag/AZO transparent conductive films by inserting an ultrathin Ti layer

Multilayer thin films of titanium-embedded Al-doped ZnO/Ag/Al-doped ZnO (AZO/Ag/AZO) structures have been designed and deposited onto polyethylene terephthalate (PET) substrates to develop an indium-free transparent flexible electrode. The effect of Ti layer on the morphological, structural, optical and electrical properties of multilayer thin films was investigated. The insertion of ultra-thin Ti layers enhances the near-infrared transmittance of AZO/Ag/AZO thin films, widens the spectral transmission window of AZO/Ag/AZO thin films, and improves the conductivity and surface roughness of AZO/Ag/AZO thin films. As the Ag thickness increases from 8 nm to 12 nm, the sheet resistance of the AZO/Ti/Ag/AZO thin film decreases from 16.22 Ω sq-1 to 7.17 Ω sq-1. AZO/Ti/Ag/AZO with an Ag thickness of 8 nm exhibits excellent optoelectronic properties with an average transmittance of 80.3 % and 61.7 % in the wavelength range of 400–1100 nm and 400–2000 nm, as well as a sheet resistance of 16.22 Ω Sq-1. It is demonstrated that AZO/Ti/Ag/AZO multilayer flexible films have great potential in various fields.

Distributions of easy axes and reversal processes in patterned MRAM arrays

The distribution of the easy-axes in an array of MRAM cells is a vital parameter to understand the switching and characteristics of the devices. By measuring the coercivity as a function of applied-field angle, and remaining close to the perpendicular orientation, a classic Stoner-Wohlfarth approximation has been applied to the resulting variation to determine the standard deviation, sigma , of a Gaussian distribution of the orientation of the easy-magnetisation directions. In this work we have compared MRAM arrays with nominal cells sizes of 20 nm and 60 nm and a range of free layer thicknesses. We have found that a smaller diameter cell will have a wider switching-field distribution with a standard deviation sigma = {9.5}^{circ }. The MRAM arrays consist of pillars produced by etching a multilayer thin film. This value of sigma is dominated by pillar uniformity and edge effects controlling the reversal, reinforcing the need for ever-improving etch processes. This is compared to larger pillars, with distributions as low as sigma = {5.5}^{circ }. Furthermore we found that the distribution broadens from sigma = {5.5}^{circ } to sigma = {8.5}^{circ } with free layer thickness in larger pillars and that thinner films had a more uniform easy-axis orientation. For the 20 nm pillars the non-uniform size distribution of the pillars, with a large and unknown error in the free-layer volume, was highlighted as it was found that the activation volume for the reversal of the free layer 930 nm^3 was larger than the nominal physical volume of the free layer. However for the 60 nm pillars, the activation volume was measured to be equal to one fifth of their physical volume. This implies that the smaller pillars effectively reverse as one entity while the larger pillars reverse via an incoherent mechanism of nucleation and propagation.

β-FeSi2: A high refractive index candidate material for infrared bandpass filters

Bandpass filters (BPFs) are optical filters with significantly high transmittance in a specific wavelength range and low transmittance on both sides. Infrared BPFs can reduce system losses and overheating caused by other light wavelengths owing to their ability to selectively transmit infrared light of the desired wavelength. This article discusses the potential of using a high refractive index material, β-FeSi2, in BPFs. To the best of our knowledge, no studies have applied β-FeSi2 to infrared BPFs. Simulation results showed that its high refractive index allows the excellent performance of the BPF to be achieved using a multilayer thin film structure with only three layers. Fourier transform infrared spectroscopy and x-ray photoelectron spectroscopy results showed that the β-FeSi2 thin film exhibited the lowest absorptance of approximately 0 when the correct stoichiometry (Fe:Si = 1:2) was achieved through co-sputtering. Based on these findings, a β-FeSi2/SiO2/β-FeSi2 multilayer thin film was designed to fabricate the BPF. The fabricated BPF exhibited a narrow peak and achieved a peak transmittance exceeding 80%. This suggested that β-FeSi2 is a promising material for fabricating infrared BPFs. Utilizing these filters is expected to yield significant efficiency improvements and reduce losses across various applications, including thermophotovoltaics and infrared heaters.

Quantification of Unsupported Thin-Film X-ray Spectra Using Bulk Standards.

A quantification model which uses standard X-ray spectra collected from bulk materials to determine the composition and mass thickness of single-layer and multilayer unsupported thin films is presented. The multivariate model can be iteratively solved for single layers in which each element produces at least one visible characteristic X-ray line. The model can be extended to multilayer thin films in which each element is associated with only one layer. The model may sometimes be solved when an element is present in multiple layers if additional information is added in the form of independent k-ratios or model assumptions. While the algorithm is suitable for any measured k-ratios, it is particularly well suited to energy-dispersive X-ray spectrometry where the bulk standard spectra can be used to deconvolve peak interferences in the thin-film spectra. The algorithm has been implemented and made available in the Open Source application National Institute of Standards and Technology DTSA-II. We present experimental data and Monte Carlo simulations supporting the quantification model.

Efficient PFOA removal from drinking water by a dual-functional mixed-matrix-composite nanofiltration membrane

Drinking water contamination by per- and polyfluorinated alkyl substances (PFAS) is a global concern. Nanofiltration is a promising PFAS removal technology due to its scalability and cost-effectiveness. However, nanofiltration cannot typically reduce PFAS concentrations below current drinking water recommendations. To enhance PFAS removal, we developed mixed-matrix-composite nanofiltration (MMCNF) membranes—an active nanofiltration layer on porous adsorptive support that synergetically combines filtration and adsorption. We synthesized MMCNF membranes comprising thin polyelectrolyte multilayer films deposited on thick (~400 µm) polyethersulfone supports incorporating β-cyclodextrin microparticles. These membranes achieved near complete removal (>99.9%) of model PFAS (PFOA: perfluorooctanoic acid) for significantly longer filtration times compared to a control membrane without β-cyclodextrin, but otherwise identical. The spent MMCNF membrane was regenerated using ethanol, and high PFOA removal performance was regained during three filtration cycles. Perfluorooctanoic acid was concentrated 38-fold in the ethanol eluent. Further concentration by evaporation is straightforward and can enable eluent recycling and effective PFAS removal.

Facile Fabrication and Characterization of Oriented and Multilayer Thin Films of Solution Processable Conjugated Polymer

Fabrication of multilayer thin films of solution‐processable organic semiconductors has great potential in organic electronics, but adopting existing thin‐film techniques to attain this is highly cumbersome. Herein, a unique unidirectional floating film transfer method has been utilized, which allows the facile fabrication of large area and oriented thin films of conjugated polymers. This method has successfully fabricated and characterized multilayer and oriented thin films of regioregular poly(3‐hexylthiophene) without having any adverse effect on the underlying layers. Optical characterizations reveal that fabricated thin films are anisotropic with a dichroic ratio of 2.2 having a single layer thickness of 14.5 nm. X‐ray diffraction results demonstrate uniformity in the crystallinity of the multilayered thin film with comparable crystallite size and interplanar spacing with purely edge‐on molecular orientation. The organic field effect transistor fabricates using multilayer thin films and also exhibits a uniform and saturated charge carrier mobility of about 0.1 cm2 V−1 s−1.

Near-infrared tunable Tamm plasmons high-performance hot electron photodetector based on Ag/Ge2Sb2Te5 low Schottky barrier

Hot electron photodetector is a typical hot electron optoelectronic device, which can realize the narrow band photoelectric detection with high tunability and sensitivity. The Tamm plasmons (TPs) based on the planar metal film/distributed Bragg reflector (DBR) has the advantages of simple structure, low manufacturing cost, and high absorption efficiency. A multilayer thin film device structure for high-performance near-infrared hot electron metal-semiconductor-metal photodetectors is proposed. The structure is based on Ag/Ge2Sb2Te5 (GST) Schottky barrier and TPs formed by SiO2/MoS2 DBR. The simulation results of hot electron emission theory show that DBR can effectively extend the absorption spectrum of Ag film and the response spectrum of the device, and enhance the absorption rate of Ag film and the response of the device. The responsivity which is up to 53 mA/W can be obtained by adjusting the structure parameters of the DBR, the thickness of the Ag film, and the GST layer. At the same time, we also propose a digital display system based on the arrangement of crystalline GST and amorphous GST. It provides a new way for the realization of high-performance near-infrared hot electronic devices and is conducive to expanding the application field of hot electronic photodetectors.

Research on bending and low resistance drift behavior of In2Se3/Sb composite multilayer films based on flexible substrates

In this paper, the research on bending and low resistance drift of In2Se3/Sb composite multilayer films based on flexible substrate were investigated. The flexible film can still complete the phase transition after being at different bending radius for 24 h and bending 2 × 104 times. With the increase of bending times, the crystalline resistance of the film increased gradually, the band gap widened. Compared with the flat film, the stretched and pressed films had a lower resistance drift. External forces such as bending, stretching and pressing will reduce the surface roughness of the flexible film. The stability of the multilayer structure for flexible thin film was checked by transmission electron microscopy. The devices based on In2Se3/Sb composite multilayer thin film were prepared on a flexible substrate polyether ether ketone. The device can achieve Set and Reset operation in the states of flat, bending and after bending 100 times. It had low power consumption. This study could provide a potential option for flexible information storage.

Thickness-controlled porous NiO films by Ni(OH)2/alginate layer-by-layer assembly

Ni(OH)2/alginate multilayer thin films were prepared directly by dip-coating using Layer-by-Layer assembly method. β-Ni(OH)2 nanoplatelets were first synthetized by chemical precipitation from nickel nitrate in ammonia under ultrasound. These particles, stabilized at pH ≈ 8, present an equivalent diameter of ≈ 250 nm and a zeta potential of ≈ + 35 mV. Sodium alginate was used as a negatively charged polyelectrolyte. In this work, the multilayer growth was first investigated in situ using optical fixed-angle reflectometry showing that particles/polyelectrolyte multilayer film can be successfully carried out. Ni(OH)2/alginate multilayer thin films were elaborated using several parameters: number of adsorbed bilayers, alginate and Ni(OH)2 particles concentrations, showing that multilayer films thickness can be mainly controlled by the number of adsorbed bilayers. The elaborated films were then heated at 325 °C in air for 1 h to calcinate the incorporated polyelectrolyte and to form NiO films. Thermal treatment experiments show an alginate content-dependent film adhesion. Indeed, multilayer films are more adherent and homogeneous with low alginate concentration (< 0.2 g.L−1). Finally, the specific surface area (SSA) of the NiO films was determined by adsorption-desorption of nitrogen gas using BET method.

Modelling structural colour from helicoidal multi-layer thin films with natural disorder.

A coupled mode theory based on Takagi-Taupin equations describing electromagnetic scattering from distorted periodic arrays is applied to the problem of light scattering from beetles. We extend the method to include perturbations in the permittivity tensor to helicoidal arrays seen in many species of scarab beetle and optically anisotropic layered materials more generally. This extension permits analysis of typical dislocations arising from the biological assembly process and the presence of other structures in the elytra. We show that by extracting structural information from transmission electron microscopy data, including characteristic disorder parameters, good agreement with spectral specular and non-specular reflectance measurements is obtained.

Improved thermoelectric power factor of multilayered poly(3,4-ethylenedioxythiophene) polystyrene sulfonate and Cu2Se thin films

Cu2Se is a promising thermoelectric material due to its superionic behavior with superior transport properties. Here we report a facile method of spin coating for the fabrication of multilayers of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) and Cu2Se thermoelectric materials for mid-temperature range applications. The synthesis of multilayered thin films with a unique organic-inorganic hybrid framework could be used in flexible thermoelectric devices. The detailed investigation of PEDOT:PSS and Cu2Se multilayered thin films reveals interaction between organic and inorganic material as inferred by AFM and FTIR. The electronic transport properties were investigated for all specimens, with the highest PF of 20.1 µW/m. K2 at 450 K was achieved from the bilayer stacking of Cu2Se and PEDOT:PSS, which is about 82 % higher as compared to that of pure PEDOT:PSS at the same temperature. These improved transport properties are the combined effect of energy filtering and interface effects. The proposed strategy opens up an avenue for research on chalcogenide based composite materials with an organic framework for flexible thermoelectric device applications.

Solution processed multi-layered thin films of Ge20Sb5S75 and Ge20Sb5Se75 chalcogenide glasses

Solution processed non-toxic Ge20Sb5Se75 chalcogenide glass thin films were deposited using spin-coating method from n-propylamine—methanol solvent mixture in specular optical quality. Optical properties, composition, structure, and chemical resistance were studied in dependence on the annealing temperature. Significant increase of refractive index and chemical resistance caused by thermoinduced structural polymerization and release of organic residua were observed. The high chemical resistance of hard-baked thin films allowed repeated direct depositions by spin-coating, increasing total thickness. Multilayered thin films of amorphous Ge20Sb5Se75 and Ge20Sb5S75 were also successfully prepared by direct deposition for the first time. Solution based deposition of non-toxic Ge20Sb5Se75 thin films in specular optical quality significantly widens the applicability of solution processed chalcogenide glass thin films. Moreover, solution based direct deposition of different glasses on hard-baked thin films opens the way to simple and cost-effective preparation of more sophisticated optical elements (e.g. beam splitters, photonic mirrors).

High-performance of laser annealed ITO/Cr-Ag/ITO multilayered thin film for transparent conducting application.

A novel laser annealing treatment was used to enhance the optoelectronics, and the morphological properties of ITO/Cr-Ag/ITO (ICAI) thin film are presented. The multilayer thin film was deposited using the RF magnetron sputtering technique and annealed using an Nd:Yag laser. The ICAI properties were characterized using X-ray diffraction, an atomic force microscope, field emission scanning electron microscope, energy dispersive X-ray, UV–visible spectroscopy, four and two-probe point probe. These techniques show the high quality of the thin film and the improvement of the properties caused by the laser annealing. The XRD shows that laser annealing improves the crystalline quality of the film. The AFM and FESEM exhibit uniform and high surface quality, where the roughness was decreased, and the grain size was enlarged. The optical transmittance was increased from 80 to 90 %, similar to the bandgap from 3.35 to 3.79 eV The electrical measurements show a significant decrease in the resistivity, and an Ohmic contact improved with laser annealing. The annealed structure has recorded a high figure of merit of 174 × 10−3 Ω−1. These results demonstrate that laser annealing treatment significantly enhances the thin film's properties. Therefore. The ICAI structure can replace the other transparent conducting material with a low annealing temperature and low energy.

Simultaneously low resistance drift and ultra‐fast phase change speed based on GeSb/Sb multilayer thin films

AbstractThermal stability and phase transition rate are two important issues that restrict the engineering applications of phase change memories. In this paper, GeSb/Sb multilayer films were prepared by multilayer stacking, and their phase transition properties were investigated. GeSb/Sb multilayer films had higher crystallization temperature, better data retention, and lower resistance drift than pure Sb films, which indicated that they had excellent thermal stability and accuracy of resistance identification. The test results of X‐ray diffraction and atomic force microscopy showed that GeSb spacer layers could inhibit grain growth of Sb film layers, thus reducing the roughness and potential fluctuation of the film surface. X‐ray reflectivity experiments showed that the GeSb/Sb multilayer films before and after crystallization had small volume changes. The devices based on [GeSb(7 nm)/Sb(3 nm)]8 multilayer films could achieve reversible resistive transition operation between SET and RESET at a pulse width of 10 ns, showing satisfactory transition rate and operational power consumption. The low resistance drift and ultra‐fast phase transition speed make GeSb/Sb multilayer films one of the promising choices for phase change memories.

Mapping strain across Co80Ta7B13 / Co62Ta6B32 glassy interfaces

While multilayered thin film metallic glasses offer promising mechanical properties due to their interfaces, the correlation between chemical composition and and strain at the interfaces has not been investigated so far. Hence, atomic distance and composition variations across glassy Co80Ta7B13 / Co62Ta6B32 interfaces are revealed by correlative transmission electron microscopy, nanobeam precession electron diffraction (NBPED) mapping and atom probe tomography (APT). A composition dependent mean atomic distance is identified for the individual layers. At the interfaces, a chemically graded region of 4 nm thickness is observed with APT, while the mean atomic distance gradient - investigated by NBPED mapping - extends over 9 nm and cannot solely be explained by chemical composition changes. Instead, the excess thickness of the atomic distance gradient compared to the chemical gradient can be rationalized by the presence of strain at the interface.

In situ visualization of LbL-assembled film nanoscale morphology using scanning ion conductance microscopy

The layer-by-layer (LbL) technique is a simple method employed to fabricate multi-layered thin films by alternately adsorbing anionic and cationic polyelectrolytes through the electrostatic interactions. In order to fabricate thin films with desirable structures and properties, it is crucial to understand how different fabricate conditions direct the thin film formation. In this study, we performed the In situ characterization of thin firm using scanning ion conductance microscopy (SICM), where the thickness as well as the surface roughness are evaluated for films with different layer numbers. Moreover, the effects of the pH and ionic strength on the fabrication of the thin films were investigated. SICM enabled the determination of the film thickness with a single layer level and the comprehension of the relationship between the surface morphology and fabrication conditions.

Magnetron sputtering process for deposition of multilayered thin diamond-like carbon films with silver nanoparticles for anti-reflective coatings and refractometric sensing

Multilayered film stacks serving optical applications usually require multiple target sources for deposition. In this work, we present a convenient method for the deposition of single- and multilayered thin films with varying diamond-like carbon (DLC) and silver content employing a single magnetron in the deposition system. For this, a reactive magnetron sputtering system was utilized and the silver target was poisoned based on desired structure: clean target and argon gas resulted in a pure silver film, completely poisoned target and acetylene and argon gas resulted in a DLC film, and anything in between resulted in a nanocomposite DLC:Ag film. The films were deposited on fused quartz, crystalline silicon, and porous anodized aluminum oxide substrates. We investigated the optical properties of these films and showed their applications for anti-reflective, black-appearing coatings and refractometric sensors, both experimentally and by simulation methods.