Four-layer Films Research Articles

Multilayer thin film mid-infrared broadband absorber with high visible light transmittance

Few reports on absorbers achieve both high transmittance of visible light and strong absorption of mid-infrared light. Here a multilayered absorber with high visible light transmittance and strong broadband absorption in the mid-infrared band is proposed. The absorber is four-layer films of ITO/SiO2/ITO/SiO2 successively deposited on single-sided conductive glass by electron beam evaporation technology. The experiment shows that the integral transmittance in the 400–800 nm range is 82.8 %, and the integral absorption in the 3–5 μm band is 88.2 %.

Low energy ion irradiation induced Au/Ag multilayer nanostructured substrates for SERS-based molecular sensing

Au and Ag are the most prominent plasmonic materials to study Surface-Enhanced Raman Spectroscopy (SERS) because of their wide tuning of localized surface plasmon resonance in the broad wavelength range. In the present work, the formation of nanostructures of Au single-layer, Au/Ag bi-layer, and Au/Ag/Au/Ag four-layer thin films on silicon substrates by low energy Kr++ ion irradiation with fluences of 1 × 1015 and 3 × 1015 ions/cm2 was systematically studied and were used for the detection of dye molecules. The surface morphology and microstructural analysis indicated the formation of different nanostructures with different ion fluences by atomic force microscopy and field emission scanning electron microscopy. Rutherford backscattering spectrometry results indicate a considerable change in film thickness after ion irradiation, mainly due to the removal of surface atoms due to sputtering. The maximum enhancement in Raman intensity of R6G was observed in the Bi-layer Au–Ag substrate compared to other substrates with an enhancement factor of 4.78 × 106 corresponding to a 1516 cm−1 characteristic peak in SERS analysis. Coumarin 343 molecules trace amount were detected to determine the versatility of the substrate. A finite-difference time-domain simulation was performed to provide a better understanding of the nanostructure hot-spots formation and support the obtained SERS results.

Improving the quality of multi-layer films based on furcellaran by immobilising active ingredients and impact assessment of the use of a new packaging material.

To improve the quality of multi-layer film, four-layer films based on furcellaran and active ingredients: gelatin hydrolysate, curcumin, capsaicin, montmorillonite and AgNPs, were produced in an innovative manner. The films were characterised by SEM and AFM analysis. Along with an increase in the concentration of active ingredients, the structure of the film becomes less homogeneous, which may affect the functional properties. The objective of the study was to analyse changes in the functional properties of the newly-obtained films and to verify their potential as packaging materials for fish products. With the increase in active ingredient concentration, water properties also improved, but there were no noticeable significant effects on mechanical properties. For antioxidant properties, the obtained values were within 1.04-2.74mM Trolox/mg (FRAP) and 7.67-40.49% (DPPH). The obtained multi-layer films were examined with regard to the shelf-life of salmon. For this purpose, salmon fillets were packed in films having good antioxidant and functional properties. The films were effective in microorganism growth inhibition responsible for fillet spoilage during storage. The microorganism number in the active film-stored samples was lower by 0.13 log CFU/g on day 12 versus the control. However, film application did not retard lipid oxidation in the salmon fillets. Nonetheless, the films show great potential as active packaging materials, extending the shelf-life of the packed foods.

Active and Intelligent Four-Layer Films Based on Chitosan, Gelatin, Furcellaran and Active Ingredients—Preparation, Characterisation and Application on Salmon

Innovatively, four-layer, active biopolymer films based on furcellaran, chitosan and gelatin as well as active compounds (curcumin, capsaicin, AgNPs, montmorillonite and gelatin hydrolysate) were obtained. The films showed strong antioxidant effects. Adding active ingredients caused increased enthalpy change value (ΔH) and thermal stability. The potential application of the film was analysed by storing Atlantic salmon fillets in the material. The films showed an active effect. This effect was the strongest during the first 3 days of storage. Compared to the synthetic LDPE film, the active film showed a total 0.81 log/CFU lower microbial count on the 12th day of storage. Lipid oxidation was not delayed in the salmon. Nonetheless, the results indicate high applicative potential of the composites.

The oxidation behavior and reaction thermodynamics and kinetics of the Mg-X (X = Ca/Gd/Y) binary alloys

Oxidation behavior of the Mg-X (X = Ca/Gd/Y) alloys at 500 ℃ was studied and had been clarified using thermodynamics and kinetics. The improved high-temperature oxidation resistance by reactive elements was attributed to the formation of compact reactive-element-rich oxide film. The oxides formation priority is determined by the critical concentration of reactive elements based on thermodynamics. A four-layered structure film was formed on Mg-Ca alloys, which was proposed to be caused by alternating enrichment of Ca and Mg atoms at metal/oxide interface. Hydrides was formed in the matrix during oxidation process, resulting from the decomposition of H2O and continues inward diffusion of H.

Design and development of four-layer anti-reflection coating stacks (ZnS and YF3 thin films) for HgCdTe-based mid-wave infrared detectors

The four-layer anti-reflection coating (ARC) film stacks (consisting of four layers of zinc sulphide (ZnS) and yttrium fluoride (YF3) materials with an optimized thickness of 699 ± 2.6 nm) were grown on the backside of the HgCdTe (mercury cadmium telluride)-CdZnTe (cadmium zinc telluride) assembly (i.e., CdZnTe substrate) using the thermal-evaporation deposition technique. Successively, the characterization tools like atomic force microscope, X-ray diffractometer, energy dispersive X-ray spectrometer, and scanning electron microscope were utilized to realize the optimized ARC film stacks. ARC stacks (ZnS/YF3/ZnS/YF3) with cubic zinc blende phase and preferred orientation (111) were confirmed. The desired surface morphology (dense and low roughness), elemental composition (purity), and micro-structural features (reasonable grain size and material continuity) of ARC films were achieved. The optimized films were further examined through their utilization in the fabrication of two similar ARC stacks/structures with a configuration of YF3/ZnS/YF3/ZnS/CdZnTe–HgCdTe and Fourier Transform infrared spectrometer was used to measure their reflectance. ARC film stacks (with remarkably thin film thickness and good repeatability) have reduced the reflection of HgCdTe–CdZnTe assembly to a minimum value from 22% to < 1.0% within the mid-wave infrared spectral region, which further validates theoretically. Thus, the four-layer ARC film stacks are the effective reflection agent that could be used to fabricate high-performance HgCdTe infrared detectors.

Experimental investigation of mechanical behavior at the microstructure of copper-graphene thin films

Graphene reinforcements in the metal matrix cause improvement in mechanical properties. The interaction of graphene depends on the microstructure and deformation of the metal matrix. At the nano and micro scale, metal graphene composites are mainly evaluated by indirect techniques like nanoindentation, which only induces specific deformation and failure mechanisms. In this work, nanolayered copper–graphene composites are fabricated to study the impact of graphene particles’ reinforcements on the mechanical behavior during uniaxial tensile loading. The stress required for film cracking increases in the ten-layer copper films (channel cracks) by 50% and the four-layer copper films (microcracks) by 121% with graphene reinforcement. Electron microscopy reveals that the graphene particles’ presence at the interfaces causes deflections in the crack paths leading to improved mechanical performance. The graphene particles also affect the grain boundary sliding (cause of microcracks) in the four-layer samples, increasing the crack onset strain from 1.3% to 2.4%. Comparing the energy release rate ratio of deflection and penetration to the fracture toughness ratio of the copper–graphene interface and graphene particle shows that crack deflection is expected. Molecular dynamics simulations also show that the deflection of cracks is due to graphene stopping the growth of plastic zones, which leads to delaminations at the interface.

Comparative study of perhydropolysilazane protective films

ABSTRACT Silicon dioxide thin films are a promising alternative to protective glass in solar cells. In this work, one-layer and four-layer thin films of a perhydropolysilazane (PHPS) were spin-coated from solution in dibutyl ether and cured by exposure to moderate temperatures or ultraviolet (UV) light to obtain glassy SiOx layers. Optical and morphological properties as well as their long-term stability were studied using XPS, FTIR, UV-Vis spectroscopy, and SEM microscopy with EDX analysis. The results showed that the process of converting PHPS layers to SiOx continues after the completion of the curing procedure for both methods. However, the composition of the thermally cured films is similar to silicon oxide, while the UV-cured samples demonstrate a composition similar to silicon dioxide due to differences in the reactions occurring during the curing process. The prolonged transformation process opens up possibilities for creating self-improving protective coatings based on PHPS.

Wear-resistant surface coloring by ultrathin optical coatings

We design, fabricate, optically and mechanically characterize wearable ultrathin coatings on various substrates, including sapphire, glass and silicon wafer. Extremely hard ceramic materials titanium nitride (TiN), aluminium nitride (AlN), and titanium aluminium nitride (TiAlN) are employed as reflective, isolated and absorptive coating layer, respectively. Two types of coatings have been demonstrated. First, we deposit TiAlN after TiN on various substrates (TiAlN-TiN, total thicknesses <100 nm), achieving vivid and viewing-angle independent surface colors. The colors can be tuned by varying the thickness of TiAlN layer. The wear resistance of the colorful ultrathin optical coatings is verified by scratch tests. The Mohs hardness of commonly used surface coloring made of Si-/Ge-metals on substrates is <2.5, as soft as fingernail. However, the Mohs hardness of our TiAlN-TiN on substrates is evaulated to be 7-9, harder than quartz. Second, Fano-resonant optical coating (FROC), which can transmit and reflect the same color as a beam split filter is also obtained by successively coating TiAlN-TiN-AlN-TiN (four-layer film with a total thickness of 130 nm) on transparent substrates. The FROC coating is as hard as glass. Such wearable and color-tunable thin-film structural colors and filters may be attractive for many practical applications such as sunglasses.

Spectral and dosimetric properties of multilayer structures of radiochromic absorbed dose reference materials

The paper considers a method for extending ionizing radiation absorbed dose measurement range by multilayer technology of one-, two-, three- and four-layer radiochromic films. It shows that this technology expands the AD measurement range to the small dose region of 10-1000 Gy.

Breakdown field enhancement and energy storage performance in four-layered Aurivillius films

In dielectric capacitors, ferroelectric thin films with slim polarisation electric (P-E) hysteresis loops, which are mainly characterised by small residual polarisation (Pr) and large saturation polarisation (Ps) are expected to obtain high recoverable energy density (Ur) and efficiency (η). However, a lower breakdown in ferroelectric thin films usually impedes this result. Here, through the co-doping of La3+ and Pr3+ ions, a larger Ur of 54.27 J/cm3 and high η of 85.6% were obtained in four-layered Aurivillius phase ferroelectric thin films capacitors due to the enhanced breakdown electric field. The doped films annealed at relatively low temperatures showed similar energy storage properties compared with those of the prototype and higher energy storage efficiency compared with that of higher annealing films. In addition, the obtained thin film shows excellent energy storage properties in a wide frequency range, fatigue durability and good thermal stability. These results indicated that four-layered Aurivillius films are promising candidate materials for dielectric energy storage capacitors. The co-doping of double ions was an effective way to improve energy storage performance.

Studies of magnesium - hydroxyapatite micro/nano film for drug sustained release

It is challenging to fabricate the bioactive films containing magnesium (Mg) particles to take full advantage of this characteristic of Mg to obtain a film with porous structure. Mg-doped hydroxyapatite (Mg-HA) film with uniform distribution of Mg particles are obtained by pulsed laser deposition. In the simulated body fluids, the Mg in the Mg-HA film is preferentially degraded for ion exchange, and the microporous structures are formed into the surface of the Mg-HA film after 7 days. These microporous structures facilitate the diffusion of the drug covered by the Mg-HA film to achieve sustainable drug release. Herein, ciprofloxacin hydrochloride (CIP) film as the drug representative is obtained by low energy electron beam deposition (LEBD) to verify the sustained release effect of Mg-HA film. Therefore, the four-layer composite films with a distribution of the CIP are obtained using the layered growth of CIP film and Mg-HA film by the PLD-LEBD coupling technology. The results showed that Mg-HA film not only prolonged the CIP release period, but also enhanced the drug release in the middle and late stage. Furthermore, the application of Mg-HA film to implant surface modification can not only exert excellent antibacterial effect, but also promote bone healing.

In-plane interfacial phonon transport through multi-layer thin films by theoretical analyses and Monte Carlo simulations

This work studies the in-plane phonon transport through double-layer, superlattice, and four-layer thin films by theoretical analyses and Monte Carlo simulations. The spectral diffuse mismatch model and the adiabatic diffuse scattering are taken as the interface and surface boundary conditions respectively. The results indicate that the number of thin-film layers has little impact on the heat flux distribution within each layer and there is a heat flux discontinuity at the interface. Indentical in-plane thermal conductivities are obtained for double-layer, superlattice, and four-layer thin films with a uniform thickness of each layer. This means that the number of thin-film layers has negligible impacts on the in-plane thermal conductivity, which can provide the first explicit explanation to the observation in a recent experiment. Finally, the minimum in-plane thermal conductivity is found in thin films when varying thickness ratios. The extreme points are also analytically obtained. This law is completely different from that for the cross-plane thermal conductivity or that predicted by the Fourier's law of heat conduction for in-plane heat transport which leads to a monotonic relation between the thermal conductivity and the thickness ratio.

Internal Stress Prediction and Measurement of Mid-Infrared Multilayer Thin Films.

We present an experimental method for evaluating interfacial force per width and predicting internal stress in mid-infrared band-pass filters (MIR-BPF). The interfacial force per width between the two kinds of thin-film materials was obtained by experimental measurement values, and the residual stress of the multilayer thin films was predicted by the modified Ennos formula. A dual electron beam evaporation system combined with ion-assisted deposition was used to fabricate mid-infrared band-pass filters. The interfacial forces per width for Ge/SiO2 and SiO2/Ge were 124.9 N/m and 127.6 N/m, respectively. The difference between the measured stress and predicted stress in the 23-layer MIR-BPF was below 0.059 GPa. The residual stresses of the four-layer film, as well as the 20-layer and 23-layer mid-infrared band-pass filter, were predicted by adding the interface stress to the modified Ennos formula. In the four-layer film, the difference between the predicted value and the measured stress of the HL (high–low refractive index) and LH (low–high refractive index) stacks were −0.384 GPa for (HL)2 and −0.436 GPa for (LH)2, respectively. The predicted stress and the measured stress of the 20-layer mid-infrared filter were −0.316 GPa and −0.250 GPa. The predicted stress and the measured stress of the 23-layer mid-infrared filter were −0.257 GPa and −0.198 GPa, respectively.

Synthesis and evaluation of high-performance diamond films with multilayer structure on printed circuit board drills

Printed Circuit Board (PCB) filled with a large amount of Alumina ceramics has broad application prospects in the fifth-generation industry but is hard to drill. This work focuses on high-performance diamond films to improve the working life of drilling tools and holes quality of products. By utilizing hot filament chemical vapor deposition (HFCVD) methods, the monolayer microcrystalline diamond (MCD), bilayer micro-nanocrystalline diamond (MNCD), and four-layer diamond (MNMNCD) are coated on commercial PCB drills (WC-6% Co). Solid particle erosion tests are conducted to study erosive wear mechanism of diamond films impacted by ceramic powders/particles. Besides, cutting performances of diamond coated drilling tools are evaluated by performing high-speed drilling tests with PCB as workpieces. In Erosion tests, the monolayer MCD film presents intergranular fracture and shows the lowest erosive resistance. The MNCD and MNMNCD films have similar fracture forms, where curved boundaries and steps between layers indicate their discontinuous fracture, and minor deep cone holes on the surfaces demonstrate their high resistance to crack growth. Moreover, only one minor deep cone hole is observed on the four-layer film which indicates it has the best resistance to particle impinging. In drilling tests, the number of holes drilled by the diamond coated tools before failure is regarded as criteria of working life. Then surface and sectional morphologies of holes are also observed to evaluate the quality of products. The results indicate the number of holes machined by the four-layer MNMNCD coated drills reaches 10,000, while that of the monolayer and the bilayer MNCD ones are 3000– 4000 and 6000 respectively. More importantly, different from the other two types of diamond coated tools, almost no burrs with a height of over 20 μm are observed on the hole entrance using the four-layer diamond coated tools. Therefore, considering both the working life and holes quality, the MNMNCD films excel in the cutting performance of the new type of PCB drilling.

Deposition of high-transmittance ITO thin films on polycarbonate substrates for capacitive-touch applications

In this study, a dual-power (RF-superimposed DC) with four-target magnetron sputtering system was used to deposit transparent, conducting indium-tin-oxide (ITO) films on polycarbonate (PC) substrates at low-temperatures process (25–120 °C). A sheet resistance of 350–500 Ω/sq, resistivity of ~10−4 Ω-cm, and light transmittance of 88% in the visible range were achieved. In addition, the simulation and experimental results showed that the deposited 20-nm-thick ITO film with two- and four-layer anti-reflective film (SiO2/TiO2 and SiO2/TiO2/SiO2/TiO2) structures could improve the light penetration characteristics. The transmittance of the multilayer stack (ITO/anti-reflective films/PC) can reach 91% which is ~3% higher than that of the bare ITO-on-PC sample. The experimental results also showed that the low turbidity (haze < 0.08%), excellent adhesion (ASTM class is 5B), and hardness (2H–4H) of ITO/anti-reflection films/PC structure could be suitable for capacitive touch panel applications.

Microstructural evolution in chemical solution deposited PbZrO3 thin films of varying thickness

Compared to the bulky ceramic counterparts, antiferroelectric (AFE) thin films exhibit higher energy-storage performance. It has been demonstrated that the performance of the AFE thin films is strongly affected by the thickness. However, possible changes in the phase structures and microstructures accompanied by varying thicknesses have been less known, which makes it hard to fully understand the physical insight of the thickness effect. Herein, we fabricate a series of PbZrO3 (PZ) thin films by chemical solution deposition whose thickness is approximately proportional to the number of deposition layers, i.e., one to four layers with each layer of about 60 nm in thickness. The detailed structural characterization has been performed by using x-ray diffraction, a scanning electron microscope, and a transmission electron microscope. The films are composed of nanorods oriented normal to the films in which each nanorod maintains single crystalline though segmented by the horizontal interfaces between each of the two neighboring layers, suggesting nearly perfect epitaxy during multilayer growth. The multidomain state is found in three-/four-layer PZ thin films while the one-/two-layer PZ films always present a monodomain state. Meanwhile, incommensurate phases with different modulation periods have been observed in the four-layer PZ films. By comparing the as-observed structural features with the measured electrical properties of different films, it seems that microstructural evolution with the film thickness should not be negligible in evaluating the structure–property relation of PZ-based thin films.

The effect of different turbulent flow on failure behavior in secondary loop of the pressurized water reactor

To investigate the effect of different two-phase turbulent flow on the failure behavior, two areas with different distances from the orifice, which suffered from different degrees of two-phase turbulent flow, were studied by transmission electron microscope (TEM) and computational fluid dynamic (CFD). The results indicated that the two-phase turbulent flow affected the wall thinning by accelerating increase of the mass transfer rate. The Erosion at pipe head adjacent to the orifice was found to form cavitation, forming a single layer of nanocrystalline Fe3O4 film on the ferrite matrix; while a moderate Flow accelerated corrosion (FAC) was found in the middle of the pipe, producing a four-layer Fe3O4 film, which consisted of an inner thin nanocrystalline oxide layer, a second dense blocky-shaped oxide layer, a third loose particle layer, an outermost layer deposited large particle layer. Obviously, the four-layer oxide film structure had better protection than the single layer oxide film due to low mass transfer rate.

CONDENSER STRUCTURES BASED ON BARIUM TITANATE FILMS FORMED BY SOL-GEL METHOD

The objective of the work is investigation the dielectric permittivity and dielectric loss tangent of BaTiO3 films in a capacitor structure formed by sol – gel method on a Si/TiOx/Pt substrate. The basis of this capacitor is a four-layer film of barium titanate xerogel with a thickness of about 200 nm. The film was synthesized by sol-gel method at a final annealing temperature 750 °C. The problems related to the development of method of forming multilayer capacitor structures, the analysis of the morphology and phase composition of BaTiO3 film, and also the measurement of the capacitance-voltage characteristics in the frequency range 10 kHz – 2 MHz have been solved. Morphology of the films was analyzed using a Hitachi S-4800 scanning electron microscope. X-ray diffraction spectra was recorded using a DRON-3 automated diffractometer, using monochromatic CuKα radiation. Capacitance-voltage characteristics were obtained using a B1500A semiconductor analyzer. Dielectric constant and dielectric loss tangent, calculated for capacitance measurements, are changed as follows: for a bias voltage of U = 0 V, the change in ε is 232–214, and tanδ 0.022–0.16, and for a bias voltage of U = 10 V, ε occurs in the range 135–124 and tanδ from 0.02 to 0.1. The obtained frequency dependences of the dielectric constant of BaTiO3 films show a decrease in the dielectric constant in the range of 10 kHz – 2 MHz. It was found that, with a BaTiO3 film thickness of less than 100 nm, a thin-film capacitor with a lower platinum electrode is not always formed, which is probably caused by shunting of the structure.

Testing of aluminium and its alloys as structural materials for a MEMS switch

An important step in the MEMS switch fabrication is the formation of a suspended micron-sized beam. Typically, the beam is made of gold due to its high electrical conductivity and chemical inertness. However, the fabrication process is complicated by poor suitability of Au for chemical etching and deformation of the beam under residual mechanical stress. An additional disadvantage is a high price of gold. Aluminium and its alloys are considered as a promising alternative. In this work, the magnetron-sputtered Al 99.99%, Al–1% Si and Al–1.5% Ti are tested as structural materials for a MEMS switch. We fabricate 1 μm thick beams and investigate surface morphology, electrical resistivity and mechanical properties. Single-layer films of Al 99.99% and Al–1% Si have coarse-grained microstructure with the root-mean-square roughness higher than 50 nm. The multi-step deposition reduces this value to 15 nm without significant deterioration of the resistivity and Young’s modulus. However, multilayer films of Al 99.99% have interlayer voids, which may degrade the switch reliability. Al–1.5% Ti provides much smoother and fine-grained film with plain sidewalls, which results in a higher quality factor of the beams. But this alloy has three times higher electrical resistivity than pure Al. Therefore, fabrication of the beam and transmission line from Al–1.5% Ti will increase insertion loss of the switch. A four-layer film of Al–1% Si is more preferable, since it also has fine microstructure and does not contain interlayer voids, but is close to pure aluminium in terms of resistivity.