Multilayer Film Structures Research Articles

Peculiar Properties of Charge Transfer in a Multilayered Film Structure upon Selective Pulsed Photoexcitation

Vectorial charge transfer upon pulsed laser excitation in three-layer Langmuir–Schafer structures consisting of 100% photoactive molecules of porphyrin-fullerene dyad, phthalocyanine and polythiophene was studied. The behavior of the photovoltaic responses of the structures changed significantly upon selective optical excitation of monolayers. The mechanisms of the vectorial charge transfer in samples depending on the individual components photoexcitation of the structure are discussed.

Multilayer thin-film flake dispersion gel for surface-enhanced Raman spectroscopy

Ag nanorod arrays/dielectrics/mirror-structured multilayer thin-film are well known, highly sensitive surface-enhanced Raman scattering (SERS) substrates that enhance the Raman scattering cross-section by the interference of light. However, extracting biomarkers directly from human skin using these solid substrates is difficult. To overcome this problem, we propose a multilayer thin-film flake dispersion gel by centrifugal mixing of the multilayer thin-film and hydroxyethyl cellulose (HEC) gel. The multilayer thin-film was prepared by serial bideposition using the dynamic oblique angle deposition technique. The mixing process was optimized to obtain flakes of ~10 {\mu}m so that the optical properties of the multilayer film can be preserved, and there is no risk of adverse effects on humans. The SERS features of the flakes dispersion gel were tested using 4, 4'-bipyridine (BPY). The BPY molecules diffused through the highly porous gel within a few seconds, generating significant SERS signals. The multilayer film flakes dispersion gel showed a SERS signal about 20 times better than the gel-dispersed Ag nanorod arrays without a multilayer film structure. These SERS active flakes dispersion gel can be used directly on the skin surface to collect body fluids from sweat, for biomarker sensing.

Effect of ZnTe transition layer to the performance of CdZnTe/GaN multilayer films for solar-blind photodetector applications

High quality CdZnTe films were prepared on GaN substrates by a close-spaced sublimation method and ZnTe transition layers were introduced to decrease the lattice mismatch between substrates and CdZnTe films for the first time. The morphology and structure of multilayer films were measured by x-ray diffraction and scanning electron microscopy. The crystalline quality of CdZnTe films based on ZnTe transition layers is obviously optimized and the best full width at half maximum and grain size of CdZnTe films are 0.149° and 10.4 μm, respectively. A surface defect analysis of multilayer films was studied by x-ray photoelectron spectroscopy and low temperature photoluminescence, which indicated that the introduction of ZnTe transition layer can reduce the Cd vacancy ratio of CdZnTe films from 22.9% to 13.3%. It is also found that the electrical properties of GaN/ZnTe/CdZnTe multilayer films show a similar PN junction effect and the best photo-dark current ratio reaches 38.8. The responsivity of multilayer films under 254 nm light is about 69.1 times more than that to 400 nm, which improves the detection of CdZnTe films in the solar-blind region effectively.

Demagnetization Processes in Multilayered Permalloy-Based Film Structures

By examples of multilayered film structure Cu/[FeNi/Cu]10 deposited by the method of ion-plasma sputtering, a comparative analysis of the magnetic hysteresis loops measured on a vibrating magnetometer, a magnetic measuring complex with primary converter on the basis of SQUID (SQUID magnetometer), and a magneto-optical Kerr microscope is carried out. The use of a SQUID magnetometer made it possible to detect the step-by-step nature of remagnetization of the film structure, the presence of which was confirmed by observations on the Kerr microscope in the quasi-static remagnetization mode.

Effect of l-ascorbic acid on electrochemically deposited FeCoCu/Cu magnetic multilayer granular films: structural, magnetic and magnetoresistance properties

The FeCoCu/Cu multilayer granular films were prepared by the electrochemical deposition technique, and the effect of the l-ascorbic acid molarity on their structural, magnetic, and magnetoresistance properties was investigated. The structure of multilayer granular films is a face-centered cubic at room temperature, and the crystallite size increases from 5 to 14 nm with increasing the molarity of the l-ascorbic acid in the electrolyte. The recorded current-time curves indicate that 0.06 M l-ascorbic acid causes high current (200 mA) in the deposition of the magnetic layer during the electrochemical deposition process. The compositional analysis indicates that Fe deposition amount increases with increasing the l-ascorbic acid for the 0.04 and 0.06 M. The saturation magnetization decreases in the thin films due to increasing the molarity of l-ascorbic acid in the electrolyte. However, some of the Co and Fe reduces as a form of their oxide in the multilayer granular films containing a high amount of magnetic materials, and the antiferromagnetic behavior suppresses the ferromagnetic behavior. The multilayer granular film produced from the electrolyte with 0.04 M l-ascorbic acid exhibits both high magnetoresistance as 12% and 3.5% anisotropic magnetoresistance effect, and also, about 1 nm particle size.

Fabrication stacking faults and its influence on the delamination behavior of SuperPower (SCS4050®) tapes

In this study, the authors investigated the evolution of the stacking faults (local defects) during film deposition and its influence on the delamination behavior (mechanisms) of SuperPower (SCS4050®) tapes using the DEM approach. The DEM approach was developed explicitly for the characterization of the evolution of the local defect in multilayered film structures. According to the study, major local defects in a multilayered film structure emerge from interlayer interactions as a function of temperature and time during the deposition of films unto the substrate. The interlayer interactions include the thermal coefficient of expansion mismatch and different eigenstates of layers in the tape. Also, the influence of the major film deposition methods (chemical and physical vapor deposition methods) on the evolution of the stacking faults in the tape was investigated. Under the given parameters, the results showed that the most vulnerable to the evolution of the local defects in the SuperPower (SCS4050®) tapes are the yttrium barium copper oxide (YBCO) interfaces and silver (Ag) layer. A comparison of the computed loss of bonding energy in the tape shows that, if a delamination test is carried out on the tape, above 80% of the delamination would occur around YBCO interfaces. Also, according to the stacking faults distribution with different film deposition method, it is practicable to minimize or localize stacking faults to a particular region of the tape. According to this study and previous studies, the computed results on the DEM approach are consistent with those on several valuable experiments and models in the literature.

Structure evolution during deposition and thermal annealing of amorphous carbon ultrathin films investigated by molecular dynamics simulations

The evolution of the structure of amorphous carbon (a-C) films during deposition and thermal annealing is of significant interest from both the materials science and application perspectives. However, despite the voluminous literature of studies dealing with the deposition and physical properties of a-C films, basic understanding of the structure evolution due to phase change during film growth and heating is fairly sparse and empirical, presumably due to the lack of high-resolution instruments that can probe structural changes at the atomic and molecular levels in real time. Molecular dynamics (MD) is a powerful computational method for studying atomic/molecular-scale movement and interactions. Thus, the objective of this study was to perform MD simulations that provide insight into changes in the structure of ultrathin a-C films during deposition and annealing. Simulation results reveal a multi-layer film structure, even for a-C films as thin as ~20 Å, the existence of a deposition energy that yields a-C films with the highest sp3 content, the transient and steady-state stages of the structure evolution during annealing at different temperatures, and the changes in the hybridization state (mainly in the bulk layer) encountered during annealing at elevated temperatures. The MD results of this study are of particular importance to applications where the deposition conditions and operation temperature affect the structure and, in turn, the physical properties of ultrathin a-C films used as protective overcoats.

Characterization of the low temperature behavior of thin Titanium/Titanium Nitride multilayer films

Titanium and titanium nitride layers were alternately sputtered on a high resistivity silicon wafer to obtain a multilayer film structure, for a total thickness ranging between 34 and 180 nm. The electrical resistance of the Ti/TiN film was characterized from room temperature down to the superconducting transition. Both the resistivity just above the transition and the critical temperature were investigated as a function of the total film thickness and the single TiN layer thickness, respectively. The obtained resistivity range is 67–312 μΩ cm. Exploiting the proximity effect, we were able to tune the critical temperature in the 0.29–4.5 K range. A comparison between experimental data and theoretical models is proposed in order to facilitate the a priori design of superconducting detectors.

LSPR optical fiber biosensor based on a 3D composite structure of gold nanoparticles and multilayer graphene films.

In this paper, a localized surface-plasmon resonance (LSPR) biosensor, which uses a U-shaped multi-mode fiber (U-MMF), is introduced and investigated. It is modified with a complex of three-dimensional (3D) gold nanoparticles and multilayer graphene as spacer: n*(Au/G)@U-MMF, where n denotes the layer number of gold nanoparticles. The gold nanoparticles were synthesized by reducing chloroauric acid. Graphene films were formed using a liquid/chemical method. The number of gold-nanoparticle layers was found to be critical for the performance of the sensor. Moreover, using the finite-difference time domain, 3D nanostructures, with a wide range of gold-nanoparticle layers, were explored. The sensor showed the sensitivity of 1251.44 nm/RIU, as well as high stability and repeatability; for the measurement-process of time- and concentration-dependent DNA hybridization kinetics with detection concentrations, ranging from 0.1nM to 100 nM, the sensor displayed excellent performance, which points towards a vast potential in the field of medical diagnostics.

Interface crack growth rate and fatigue life of multilayer-coated conductor tapes

Rare-earth barium copper oxide (REBCO) coated conductor (CC) tapes in high-field magnet applications usually experience fatigue due to a variety of cyclic mechanical and thermal loads. Therefore, estimation of the fatigue life of a particular REBCO CC is vital for the successful development and applications of high-field magnets devices, which are crucial components for aerospace, automotive, and maglev train transportation. For these needs, the authors evaluated the interfaces fatigue crack growth rate, and fatigue life of multilayered yttrium barium copper oxide (YBCO) coated conductor (CC) tape at room temperature via a displacement-energy model (DEM) approach. The DEM approach can measure the damage initiation and propagation rate in specific interfaces of a multi-layer film structure simultaneously. It assumed transverse intrinsic tensile/compressive cyclic loading and adopted the linear-elastic damage law with the maximum normal stress failure criterion to characterize the degradation in the tape. With an initial Eigenfunction (W0) (a parameter equivalent to the stress loading amplitude range) set as 2.30 × 10-12 m, the computed results show a strain (ε) range from 0.35 to 0.46 % and fatigue ratio range from 0.002 to 0.07 in the interfaces of the tape. Under the given parameters, it was found out that the tape has a critical interface fatigue crack growth rate of 2.54 pm/cycle corresponding to fatigue life of 3.9372 × 105 cycles. According to our previous studies, the results on the DEM approach has good agreement with those on the Finite Element Method (FEM) counterpart model, closed-form solution (CFS) model, and X-ray diffraction method (XRD). This technique can help to avoid enormous resources usually spent experimentally on the calculation of fatigue life of REBCO CC tapes.

Investigation of crystallization behavior and structure of nanocomposite multilayer phase change thin films with zinc antimony and germanium antimony

Multilayer Zn50Sb50/Ge8Sb92 (ZS/GS) thin films were proposed and fabricated by alternate sputtering. The crystallization behaviors of nanocomposite ZS/GS thin films induced by heating were investigated by in situ resistance measurement. The crystallization behaviors of ZS/GS thin films can be regulated by tuning the thickness ratio and periods. The multilayer [ZS (8 nm)/GS (4 nm)]4 ([ZS(8)/GS(4)]4) thin film exhibits a high crystallization temperature (~ 245 °C), a large crystallization activation energy (2.61 eV), and high data retention ability (168 °C). The phase structure and thickness variation of the [ZS(8)/GS(4)]4 thin film were analyzed through x-ray diffraction (XRD) and x-ray reflection (XRR), respectively. The volume shrinkage during crystallization was as small as 3.9%. The multilayer structure and interface stability were confirmed by using transmission electron microscopy (TEM). A picosecond laser pump-probe system was used to evaluate the transition speed. The crystallization and amorphization periods of the [ZS(8)/GS(4)]4 thin film were only about 6.2 ns and 3.9 ns, respectively.

Определение конструкторско-технологических параметров намотки герметичных топливопроводов из полимерной пленки

The paper considers issues related to technology of manufacturing pipelines by winding polymer film materials and assessing their tightness with respect to gaseous and liquid fuel components. The shell is made by winding the required number of layers of continuous film tape with a given width, thickness and overlap on a rigid removable mandrel. The multilayer film structure of the shell made by winding a narrow polymer tape is considered as a computational model of the sealing shell of the pipeline. The tightness of the polymer pipeline shell is determined both by the physical and chemical parameters of the film material (permeability and diffusion coefficients) and by the structural and technological parameters of the wound shell. The simulation results allowed determining the main structural and technological parameters of the winding process as applied to the polyimide-fluoroplastic film PMF-352, which provide the total leakage of the film fuel lines within the requirements.

Modeling of magnetoimpedance effect in nanostructured multilayered films

The magnetoimpedance effect in nanostructured multilayers is studied theoretically. The multi-layered film structure consists of highly conductive non-magnetic central layer and two external multilayers containing soft magnetic layers of the same thickness separated either by magnetic spacers of different kind or by non-magnetic spacers. In order to describe the magnetoimpedance in the multilayer an electrodynamic model is proposed. The influence of geometric parameters and physical properties of the layers on the magnetoimpedance response is analyzed. The results obtained could be useful both for better understanding of high-frequency behavior of nanostructured multilayers and for optimization of multilayer parameters aiming to enhance the magnetoimpedance effect for practical applications.

Effect of Cr Dopants on the Structure and Failure Mechanism of TiAlN Multilayered Films

Effect of Cr Dopants on the Structure and Failure Mechanism of TiAlN Multilayered Films

Dual-channel ultra-narrowband mid-infrared filter based on bilayer metallic grating

Traditional dual-channel ultra-narrowband filters are mainly fabricated by multilayered thin films in accordance with interference effect, with the multilayered film structure being so thick that the environment adapatability can not be guaranteed as a problem especially for the infrared dual-band-pass filter which is as thick as ten times of micrometers. Based on this problem, we designed an ultra-thin dual-channel mid-infrared ultra-narrowband filter with fewer layers and bilayer metallic gratings here by integrating the interference effect with Fabry-Perot-like cavity resonance effect, of which the filter has a thickness of 5 um, one third of the tranditional ones, and the minimum half bandwidth is only 0.015 nm. The results reported provide a new approach for designing ultra-thin dual-channel mid-infrared ultra-narrowband filters.

Effect of bilayer period on the oxidation and corrosion resistance of Pb-Ti/MoS2 nanoscale multilayer films

The Pb-Ti/MoS2 nanoscale multilayer films are synthesized by unbalanced magnetron sputtering. The effect of bilayer period on the structure, oxidation, and corrosion resistance of the nanoscale multilayer films has been investigated. For the Pb-Ti/MoS2 nanoscale multilayer films, the basal (002) planes of MoS2 are oriented parallel to the substrate, and the crystallite size gradually increases with the bilayer period, obtaining a maximum value when the bilayer period is 17.1 nm. A further increase in the bilayer period results in a decrease in the crystallite size. The oxidation resistance of the Pb-Ti/MoS2 nanoscale multilayer films is systematically evacuated by sliding against the GCr15 pair under humid air. The anticorrosion properties are investigated by electrochemical measurements and sliding against the GCr15 pair after the salt spray tests. The results indicate that oxidation and corrosion resistance of the nanoscale multilayer films first increases with an increase of the bilayer period, and the nanoscale multilayer film with a period of 17.1 nm obtains the best antioxidation and anticorrosion resistance. This benefits us to select the MoS2-based multilayer films for different operating conditions.

Controlling luminescence and quenching mechanisms in subnanometer multilayer structure of europium titanium oxide thin films

We have investigated how layered structures of TiO2 and Eu2O3 on the subnanometer scale control the optical absorption, energy transfer, emission and quenching mechanisms in sensitized lanthanide luminescence systems. By using atomic layer deposition (ALD) as a tool for designing materials with sub nanometer precision, we have been able to make structures ranging from separate (TiO6)8- clusters to bulk TiO2, and series of samples showing transitions from 3D to 2D energy migration. Photoluminescence, excitation and decay measurements have been used alongside transmission electron microscopy (TEM) to investigate how the different structures affect the luminescence. We show that it is possible to drastically suppress concentration quenching compared to solid solutions by designing materials as multilayered structures that confines energy migration in 2D planes. This allows for application of higher concentrations of lanthanides and more defected structures, also enabling use of less pure reactants during synthesis.

Fully automatic modulation for broadband sunlight based on YOxHy/VO2 hybrid structures

Vanadium dioxides (VO2) thermochromic materials could exhibit reversible change in optical transmittance in response to external temperature. However, traditional VO2-based smart window is limited to an insufficient solar modulation ability as well as excessive transition temperature. Herein, we designed an all-solid form of YOxHy/VO2 multilayer film structure on quartz glass substrate, which can separately regulate visible and NIR light transmittance responding to environmental light and temperature, respectively. The hybrid film exhibits transparency under normal condition of room temperature and weak illumination, and solar energy transmittance can be dynamically regulated from 43% to 28%, 16% and finally 14% by controlling the conditions of temperature and illumination. Also, the optical and electrical transition temperature of m-VO2 shows an obvious decline. This hybrid film features high solar modulation ability and great conditional responsiveness with zero-energy consumption and low transition temperature. Our current results would supply new opportunities for smart-window applications, and also provide a new strategy for solar transmittance modulation.

Enhanced Adjustable Photovoltaic Response in Multilayer BiFeO3 Films

In this paper, the photovoltaic effect of BiFeO3 (BFO) film prepared by spin-coating was investigated. The photovoltaic effect of the multilayer BFO film is significantly enhanced compared to the single layer BFO film. The short-circuit current density increases to 62.6 μA/cm2 while the open-circuit voltage is 0.29 V, which is due to the efficient transport of carriers by the electron transport layer and the hole transport layer in the multilayer film structure. In addition, it is also possible to control the photovoltaic effect of BFO film by applying an external electric field, and a possible mechanism model is proposed to explain this phenomenon. This work found a simple way to enhance the photovoltaic effect of BFO and also achieved precise control of the BFO film photovoltaic effect.

Development of multilayer films with improved aroma barrier properties for durian packaging application

The symmetrical A/B/A structure of multilayer blown films was fabricated in this study. The immiscible low‐density polyethylene/polylactic acid (LDPE/PLA) blend was set as a core (B) layer and LDPE was used as skin (A) layers. The compositions of PLA in the core layer were varied from 20 to 50 wt%. The thickness of each layer was 10 μm (total film thickness of ~ 30 μm). In a blown film co‐extrusion process, the morphology of the fiber/ribbon‐like structures of LDPE/PLA blend was developed. Such structures had interesting effects on gas permeability and aroma barrier properties of the films. For instance, multilayer LDPE films containing 40 and 50 wt% PLA (P40 and P50) showed the reduction of oxygen permeability (PO2) approximately 20% and 43%, respectively, compared with the neat LDPE film. A long tortuous path for gas and aroma transportation through film thickness was created from the developed ribbon‐like structures of the PLA minor phase. For durian packaging application, fresh‐cut durian of 300 g was packed in the developed multilayer films, LDPE, and HDPE (Control), stored at 4°C for 7 days. Results demonstrated that the steady‐state condition of 10% to 13% O2 and 8% to 10% CO2 was achieved in all packages except in the HDPE. Moreover, the P40 and P50 films exhibited an outstanding aroma barrier property for three major durian volatiles: diethyl sulfide, ethyl propanoate, and 2‐ethyl‐1‐hexanol. Overall results clearly indicated that the multilayer LDPE films containing PLA exhibited a significantly improved aroma barrier performance with optimum gas permeability desirable for modified atmosphere packaging to retain quality of fresh‐cut durian throughout the storage period.