Thickness Of Multilayer Films Research Articles

Significantly enhanced piezoelectric temperature stability of KNN-based ceramics through multilayer textured thick films composite

The temperature instability of piezoelectric properties in KNN-based ceramics has been a major bottleneck impeding them toward practical applications. Herein, we prepared multilayer composite ceramics using two kinds of textured thick films with different polymorphic phase transition temperatures. The composite ceramics simultaneously exhibited outstanding piezoelectric properties (d33 = 400 ± 20 pC/N; S = 0.18 % at 40 kV/cm) and piezoelectric temperature stability (d33 and S variation within 5 % and 2 %, respectively over the temperature range of room temperature to 180 °C). The synergistic contribution of slightly fluctuating εr·Pr values, the robust phase and domain structures, and the complementary effect of piezoelectric fluctuation between the two composite layers led to the outstanding temperature stability of piezoelectric properties. Furthermore, the piezoelectric energy harvester produced using KNN-T1/T2 composite ceramics exhibits a large power density of 5.4 mW/cm3. These results prove great potential of KNN-T1/T2 ceramics in high temperature piezoelectric devices.

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.

Measurement of Nanoscale Film Thickness Using Neutron Depth Profiling Technique.

Determination of geometric parameters for thin film materials has always been a critical concern in scientific research. This paper proposes a novel approach for high-resolution and nondestructive measurement of nanoscale film thickness. In this study, the neutron depth profiling (NDP) technique was employed to accurately measure the thickness of nanoscale Cu films, achieving an impressive resolution of up to 1.78 nm/keV. The measurement results exhibited a deviation from the actual thickness of less than 1%, highlighting the accuracy of the proposed method. Additionally, simulations were conducted on graphene samples to demonstrate the applicability of NDP in measuring the thickness of multilayer graphene films. These simulations provide a theoretical foundation for subsequent experimental measurements, further enhancing the validity and practicality of the proposed technique.

Adsorption structure of iron phthalocyanine and titanyl phthalocyanine on Cu(1 1 1)

The adsorption structure of iron phthalocyanine (FePc) and titanyl phthalocyanine (TiOPc) was studied by a combination of near edge X-ray absorption fine structure (NEXAFS) spectroscopy and normal incidence X-ray standing waves (NIXSW) technique. The FePc results demonstrate that the molecule adsorbs with the Fe metal centre at an adsorption height of 2.44 ± 0.09 Å, its macrocycle plane mostly parallel with the underlying surface and a single adsorption configuration. However, a small distortion of the isoindole groups, with respect to one another, is required to rationalise the results. The TiOPc results similarly indicate that the macrocycle plane is mostly parallel with the underlying surface up to thick multilayer films, yet, in the monolayer regime, the molecule must adsorb in multiple configurations. These configurations are nominally assigned to a mixture of adsorption configurations with some Ti=O bonds pointing towards the surface, and some pointing away. We determine that, in both configurations, the Ti metal centre sits at a similar adsorption height above the surface of 3.00 ± 0.20 Å.

75‐1: Real Time Doping Management of High‐Performance Organic Electroluminescence Displays

Recently, organic light emitting diode (OLED) and quantum dot (QD)‐OLED displays are attracting attention as representative displays ranging from mobile to tablet, laptop, and TV markets. In these OLED and QD‐OLED displays, the individual thickness and doping ratio of functional multilayer films of organic electroluminescence (EL) are the most important factors in device characteristics such as color coordinates, efficiency, and lifetime. In particular, unlike the thickness that can be measured up to the sub‐nanometer, quantified measurement methods have not been well prepared for the various dopant contents of EL. We proposed a method to quantify the doping ratio of individual functional thin films of EL using Raman spectroscopy. First, a unique signal of each layer material of the EL was found using Raman spectroscopy, and a significant signal was classified from the resultant signal. And by utilizing the intensity of the peak of the signal, we succeeded in quantifying the doping rate using partial least squares regression and artificial intelligence. In particular, quantification was very successful even in the thinnest thin film and the thin film with the lowest dopant content. Finally, as a result of evaluation by dividing the doping rate of the EL light emitting layer in the pixel of the actually completed OLED sample by dividing it from 0 to 6%, the linear regression of the average doping rate converged to 100% was obtained. Accordingly, it succeeded in real‐time monitoring and management of the doping ratio of the EL element, which is a major factor influencing the performance and quality of OLED and QD‐OLED displays, in mass production.

Competition Pathways of Energy Relaxation of Hot Electrons through Coupling with Optical, Surface, and Acoustic Phonons

The hot electrons in carbon-based materials exhibit interesting ballistic transport behaviors for designing high-performance single-electron transistors. However, the cooling of such hot electrons back to the equilibrium state may be slowed down by the excessively populated optical phonons, thus limiting their ballistic transport. Therefore, a thorough understanding of the coupling between hot electrons and optical phonons is of critical importance. Here, by varying the thickness of a multilayer graphene film on a supporting substrate, we investigated the competition pathways of the energy relaxation of the photoinduced hot electrons through coupling with the optical, surface, and acoustic phonons. The difference in the τ2 values indicates that thickness plays an important role in the optical phonon population. For the multilayer graphene film thickness less than 3 nm, the super-collision model describes the hot electron cooling dynamics that is strongly affected by the surface phonons from the supporting substrate. As the multilayer graphene film thickness increases from 3 to 20 nm, the accumulation of the optical phonons induces a hot optical phonon effect, resulting in a bottleneck of cooling of the hot electrons. As the multilayer graphene film thickness further increases from 20 to 40 nm, a direct coupling between the hot electrons and acoustic phonons starts to dominate. The surface states of the interfaces at the inner layers of the multilayer graphene film contribute to this direct coupling as an additional cooling channel. The quantitative understanding of the energy relaxation pathways of the hot electrons offers insights into designing high-performance single-electron transistors.

Exploitation of Nano-Crystalline Cupric Cxide (CuO) Doped Zinc Oxide (ZnO) Multilayer Thick Film as a CO2 Gas Sensor

Exploitation of Nano-Crystalline Cupric Cxide (CuO) Doped Zinc Oxide (ZnO) Multilayer Thick Film as a CO2 Gas Sensor

High Dielectric Breakdown Strength Nanoplatelet‐Based Multilayer Thin Films

AbstractDielectric materials that can withstand high voltages are of great interest due to the growing need for high‐performance insulation systems in electronics. Polymer nanocomposites have gained popularity as electrical insulators due to their processability, high operating voltage, and tortuous paths for current flow created by the nanoparticles in the polymer matrix. The dielectric breakdown strength of a relatively thick multilayer thin film containing polyethylenimine (PEI) and vermiculite clay (VMT), thickened with tris(hydroxymethyl)aminomethane (tris), is evaluated as a function of bilayers (BL) deposited. The resulting nanobrick wall structure of this clay‐based assembly is ideal for protective insulation. An 8 BL PEI+tris/VMT film achieves a dielectric breakdown strength of 245 kV mm−1, with a thickness of 5 µm. With increasing bilayers, the breakdown strength gradually decreases, but 20 BL of PEI+tris/VMT achieves a breakdown voltage of 2.36 kV. This nanoplatelet‐based system is the first “thick growing” layer‐by‐layer deposited film to be used as an insulating layer. Its unusually high breakdown strength can be useful for the protection of various high voltage electronics.

Formation of Fe–Co/glass multilayer films via pulsed laser deposition

Sputtering-made magnetic thin films with metal–ceramic multilayer structures have been reported to achieve excellent magnetic properties and/or new functions for various magnetic materials. However, sputtering-made magnetic films tend to have 10 or fewer layers because the main applications of thin films, such as magnetic sensors, recording heads and recording media, require thin films thinner than 1 μm. This paper reports an Fe–Co/glass multilayer thick-film that has an approximate thickness of 10 μm (above 100 layers). This thick-film was prepared via pulsed laser deposition using several composite targets (two- or three-layer targets) consisting of an Fe–Co alloy (or Fe–Co sheet) and a glass plate. The fabrication of an Fe–Co single-layer film and a glass single-layer film was examined to determine the optimal defocus rate for the composite target. Then, we confirmed that the use of a [glass plate]/[Fe–Co alloy] two-layer target enabled the local formation of a [20 nm thick Fe–Co]/[10 nm thick glass) laminated structure with approximately 130 layers. An Fe–Co/glass multilayer structure was formed by using a three-layer target of a [Fe–Co sheet]/[glass plate]/[metal alloy]. Nonetheless, the results also suggest that large glass droplets should be removed in future work to create homogeneous multilayer thick-films.

UV Ozone based rapid low temperature fabrication of flexible dye sensitized solar cells

Herein, we have developed a multilayer TiO2 film thickness of around 4 µm at lower temperature (120 °C) by spin coating and doctor blade technique on polyethylene terephthalate (ITO-PET) substrate. Further, the additional processing step Ultravoilet-Ozone (UVO3) treatment was performed on TiO2 electron transport layer (ETL) to enhance the performance of FDSSCs. UVO3 treatment significantly improved the crystallinity and charge transport characteristic of ETL by removing the organic impurities. The photovoltaic devices based on 4 h of UVO3 treated TiO2 film exhibited superior device performance with an overall power conversion efficiency (PCE) of 2.53% compared to 1.43% (without UVO3 treatment). Electrochemical impedance measurement indicated that TiO2 layer treated with UVO3 decreased series resistance, electron recombination and improved electron life substantially. The improved device properties, simple preparation procedure and low processing cost, enable this FDSSCs fabrication method to be a credible alternative of conventional techniques.

Magnetic and magnetoelectric properties of NixCu1–xFe2O4–PbZr0.52Ti0.48O3 single and multilayered thick films

Magnetic and magnetoelectric properties of NixCu1–xFe2O4–PbZr0.52Ti0.48O3 single and multilayered thick films

Single-shot spectrally resolved interferometry for the simultaneous measurement of the thickness and surface profile of multilayer films.

We present a single-shot spectrally-resolved interferometry for simultaneously measuring the film thickness and surface profile of each layer of a patterned multilayer film structure. For this purpose, we implemented an achromatic phase shifting method based on the geometric phase using the polarization characteristics of the light and obtained four phase-shifted interferograms in the spectrally-resolved fringe pattern at the same time by combining a pixelated polarizing camera with an imaging spectrometer. As a result, we could simultaneously measure the reflectance and phase of the sample over a wide wavelength range with a single measurement. To evaluate the validity of the proposed method, we measured a patterned five-layer film specimen and compared our measurement results with those from commercial instruments, an ellipsometer and a stylus profiler, respectively. We confirmed the results matched each other well.

Spin-speed independent thickness and molecular adsorption behaviour of polyelectrolyte multilayers

The science behind the build-up mechanism of polyelectrolyte multilayers is important for developing devices for various engineering applications. Here we, study the dependency of thickness of polyelectrolyte multilayer films, fabricated using spin-assisted layer-by-layer self-assembly of polyelectrolytes technique, with respect to varying spin-speed while keeping all other parameters of the fabrication process-window constant. The thickness measurements were performed using variable angle spectroscopic ellipsometry and atomic force microscopy. The experimentally observed results were validated mathematically using a Flory type theory. In addition, the bio-molecular adsorption studies on these polyelectrolyte multilayer films fabricated at various spin-speeds, were also quantitatively analyzed using fluorescence microscopy studies. It was seen that the effect of spin-speed on the thickness of polyelectrolyte multilayers was negligible. In addition, it was also observed that the bio-molecular adsorption modalities onto these substrates were also independent of the spin-speed. This finding prompts to develop low-cost alternative technologies for various biomedical engineering applications, like functionalized substrates for centrifugal assay for fluorescence-based cell adhesion, wherein stability of films against strong mechanical forces generated during spinning can play an important role.

Measuring the multilayer silicon based microstructure using differential reflectance spectroscopy.

The yield of a large-area ultra-thin display panel depends on the realization of designed thickness of multilayer films of all pixels. Measuring the thicknesses of multilayer films of a single pixel is crucial to the accurate manufacture. However, the thinnest layer is reaching the sub-20nm level, and different layers feature remarkable divergence in thickness with similar optical constants. This turns to a key obstruction to the thickness characterization by optical spectroscopy. Based on the tiny differences in absorptivity, a fast method for measuring the film thickness in a single pixel is proposed which combines the layer number reducing model and micro-area differential reflectance spectroscopy. The lower layers can be considered as semi-infinite in the corresponding spectral range whose thickness is infinite in the fitting algorithm. Hence, the thickness of the upper layer is fitted in a simplified layer structure. For demonstration, a multilayer silicon microstructure in a single pixel, p-Si/a-Si/n-Si (10nm/950nm/50nm) on complex substrate, is measured. The light spot diameter is about 60 microns with measuring-time in 2 seconds. The measurement deviation is 3% compared by a commercial ellipsometer. To conclude, the proposed method realizes the layer number reduction for fitting multilayer thickness with large thickness difference and similar optical constants, which provides a powerful approach for multilayer microstructure characterizations.

Microstructure, mechanical and tribological properties of multilayer Ti-DLC thick films on Al alloys by filtered cathodic vacuum arc technology

Low hardness and poor wear resistance are major limitations of Al alloys, which hinder their application in several fields, especially automotive moving parts. DLC can effectively improve hardness and wear resistance of Al alloys, but high residual stress and poor adhesion limit the film thickness. Multilayer thick films (~10 μm) composed of alternating Ti and Ti-DLC layers were successfully deposited on Al alloys. The influence of Ti content on the microstructure, mechanical and tribological properties of the film was emphasized. As the Ti content decreased from 10.42 to 1.35 at.%, the microstructure evolved from a polycrystalline composite film to a nanocrystalline composite film, and then to an amorphous film. The mechanical and tribological properties of the film depended on the microstructure. The amorphous composite film (Ti >6.06 at.%) exhibited better wear resistance than the polycrystalline composite film (Ti <6.06 at.%) due to the higher H/E⁎ (>0.1), H3/E⁎2 (>0.2) and elastic recovery (>60%). When the doped Ti content was 6.06 at.%, the nanocrystalline composite multilayer film showed superior comprehensive performance of high hardness (~23 GPa), high elastic recovery (~69%), low friction coefficient (~0.13) and low wear rate (1.0 × 10−7 mm3/Nm).

Sublimable Spin-Crossover Complexes: From Spin-State Switching to Molecular Devices.

Spin‐crossover (SCO) active transition metal complexes are an important class of switchable molecular materials due to their bistable spin‐state switching characteristics at or around room temperature. Vacuum‐sublimable SCO complexes are a subclass of SCO complexes suitable for fabricating ultraclean spin‐switchable films desirable for applications, especially in molecular electronics/spintronics. Consequently, on‐surface SCO of thin‐films of sublimable SCO complexes have been studied employing spectroscopy and microscopy techniques, and results of fundamental and technological importance have been obtained. This Review provides complete coverage of advances made in the field of vacuum‐sublimable SCO complexes: progress made in the design and synthesis of sublimable functional SCO complexes, on‐surface SCO of molecular and multilayer thick films, and various molecular and thin‐film device architectures based on the sublimable SCO complexes.

Role of Metal Ion-Linked Multilayer Thickness and Substrate Porosity in Surface Loading, Diffusion, and Solar Energy Conversion.

Metal ion-linked multilayers offer an easily prepared and modular architecture for controlling energy and electron transfer events on nanoparticle, metal oxide films. However, unlike with planar electrodes, the mesoporous nature of the films inherently limits both the thickness of the multilayer and subsequent diffusion through the pores. Here, we systematically investigated the role of TiO2 nanoparticle film porosity and metal ion-linked multilayer thickness in surface loading, through-pore diffusion, and overall device performance. The TiO2 porosity was controlled by varying TiO2 sintering times. Molecular multilayer thickness was controlled through assembling ZnII-linked bridging molecules (B = p-terphenyl diphosphonic acid) between the metal oxide and the Ru(bpy)2((4,4'-PO3H2)2bpy)]Cl2 dye (RuP), thus producing TiO2-(Bn)-RuP films. Using attenuated total reflectance infrared absorption and UV-vis spectroscopy, we observed that at least two molecular layers (i.e., TiO2-B2 or TiO2-B1-RuP) could be formed on all films but subsequent loading was dependent on the porosity of the TiO2. Rough estimates indicate that in a film with 34 nm average pore diameter, the maximum multilayer film thickness is on the order of 4.6-6 nm, which decreases with decreasing pore size. These films were then incorporated as the photoanodes in dye-sensitized solar cells with cobalt(II/III)tris(4,4'-di-tert-butyl-2,2'-bipyridine) as a redox mediator. In agreement with the surface-loading studies, electrochemical impedance spectroscopy measurements indicate that mediator diffusion is significantly hindered in films with thicker multilayers and less porous TiO2. Collectively, these results show that care must be taken to balance multilayer thickness, substrate porosity, and size of the mediator in designing and maximizing the performance of new multilayer energy and electron management architectures.

Layer-controlled single-crystalline graphene film with stacking order via Cu-Si alloy formation.

Multilayer graphene and its stacking order provide both fundamentally intriguing properties and technological engineering applications. Several approaches to control the stacking order have been demonstrated, but a method of precisely controlling the number of layers with desired stacking sequences is still lacking. Here, we propose an approach for controlling the layer thickness and crystallographic stacking sequence of multilayer graphene films at the wafer scale via Cu-Si alloy formation using direct chemical vapour deposition. C atoms are introduced by tuning the ultra-low-limit CH4 concentration to form a SiC layer, reaching one to four graphene layers at the wafer scale after Si sublimation. The crystallographic structure of single-crystalline or uniformly oriented bilayer (AB), trilayer (ABA) and tetralayer (ABCA) graphene are determined via nano-angle-resolved photoemission spectroscopy, which agrees with theoretical calculations, Raman spectroscopy and transport measurements. The present study takes a step towards the layer-controlled growth of graphite and other two-dimensional materials.

Di-anisotropic conductive Janus-type film endued with super-paramagnetism and enhancive red fluorescence

Fluorescent–conductive–magnetic multifunctional materials have wider applications than their counterpart single-functional materials. In this work, a newflexible twi-layer Janus-type film (TJF) with concurrence of di-anisotropic electrical conduction, super-paramagnetism and red fluorescence is designed and constructed via electrospinning. The unique TJF consists of two up-to-down layers closely bonded together; the up layer is an easily prepared non-array super-paramagnetic Fe3O4/polyvinylpyrrolidone nanofiber pellicle. The down layer is a Janus-type membrane with a left–right structure consisting of (polymethylmethacrylate (PMMA)/Eu(BA)3phen)║(PMMA/polyaniline (PANI)) Janus nanobelt arrays respectively used as the left and right halves. The conductive directions in the two halves are vertical, and the same is true with the insulative orientations, resulting in di-anisotropic conduction. The fluorescent color of the down layer is red under UV irradiation. In order to ensure high conductive anisotropy and enhancive red fluorescence, an exceptional Janus nanobelt is designed and applied as a conductive and building unit to construct the down layer. The critical thickness of the twi-layer multifunctional film is a vital parameter and studied for the first time. When the thickness of the up layer is determined, a corresponding critical thickness of the down layer will exist, and when the thickness of the down layer is fixed, a critical thickness of the up layer will also exist. No fewer than the critical thickness, the fluorescence properties of the down layer are not affected by the up layer. In this work,three kinds of special Janus structures are used to separate and confine different materials in their own domains at the microscopic and macroscopic levels, and microscopic and macroscopic partitions are simultaneously realized in TJF, leading to TJF with superior performance. Furthermore, TJF has excellent mechanical anisotropy. This work provides guidance for exploring the critical thickness and mutual effects of multi-layer multifunctional film.

Optimized optical design of thin-film transistor arrays for high transmittance and excellent chromaticity

Transmittance and chromaticity are essential requirements for optical performance of thin-film transistor (TFT) arrays. However, it is still a challenge to get high transmittance and excellent chromaticity at the same time. In this paper, optimized optical design by using antireflection film theory and optical phase modulation is demonstrated in low temperature poly-silicon (LTPS) TFT arrays. To realize high transmittance, the refractive index difference of adjacent films is modified by using silicon oxynitride (SiOxNy) with adjustable refractive index. To realize excellent chromaticity, the thicknesses of multilayer films are precisely regulated for antireflection of certain wavelength light. The results show that the transmittance and chromaticity have been improved by about 6% and 18‰, respectively, at the same time, which is a big step forward for high optical performance of TFT arrays. The device characteristics of the TFT arrays with the optimal design, such as threshold voltage and electron mobility, are comparable to those of conventional TFT arrays. The optimized optical design results in enhanced power-conversion efficiencies and perfects the multilayer film design on the basic theory, which has great practicability to be applied in TFT arrays.