Trilayer Films Research Articles

Mechanically stable ultrathin flexible metallic Au/Pt/Au tri-layer as an alternative transparent conducting electrode for optoelectronic device applications

Indium tin oxide (ITO) is a ubiquitous transparent conducting oxide employed in several modern optoelectronic devices. However, due to limited availability and fast depletion of indium, there is an urge to supplement its use with suitable alternatives in appropriate sheet resistance range, depending on the application requirement. In this scenario, an alternative flexible transparent conducting Au/Pt/Au ultrathin metallic tri-layer electrode sputter-deposited on PET substrate is explored. The tri-layer shows maximum transmittance of 55% at 500 nm and it presents a nearly flat behavior in the entire visible spectrum. Electrical transport properties of Au/Pt/Au layer show sheet resistance of 66 Ω/□ and mobility of 8.32 cm2V−1s−1, respectively. The contact angle measurement indicates that plain hydrophilic PET (62.6°) turns hydrophobic (94.2°) upon coating with Au/Pt/Au tri-layer. The surface properties analyzed using atomic force microscopy and optical profilometry indicate a crack-free, densely packed homogenous film. The tri-layer film shows mechanical stability up to 50,000 bending and twisting cycles. The obtained surface work function of Au/Pt/Au tri-layer film is 4.97 eV. The ultrathin flexible Au/Pt/Au tri-layer explored as top electrode in a piezoelectric generator and as top and bottom electrodes in an alternating current driven electroluminescent device exhibits appreciable performance.

Effects of Electron Irradiation on the Properties of ZnO/Au/ZnO Films Deposited on Poly-Imide Substrates

Transparent and conductive ZnO 50 nm/Au 8 nm/ZnO 50 nm tri-layer films were deposited on poly-imide films by radio frequency (RF) and direct current (DC) magnetron sputtering at room temperature, and then the effect of electron irradiation on the crystallization, electrical resistivity and optical properties of the films was considered with X-ray diffraction, UV-visible spectrometer, Atomic force microscope and Hall measurement system. All the films were deposited at a fixed sputtering power, Ar gas flow rate, and distance between target and substrate, while the post-deposition electron irradiation energy was varied from 300 to 900 eV. The electron irradiated films exhibited a flatter surface than the as deposited films that were not electron irradiated, and the XRD patterns also revealed that the electron irradiated films had larger grain sizes than that of as deposited films. The films electron irradiated at 900 eV also showed a higher visible transmittance of 79.8% and a lower sheet resistance of 56.0 Ω/□. Post-deposition films electron irradiated at 900 eV showed a higher figure of merit of 1.86×10-3 Ω-1 than that of the as deposited film of 1.29×10-3 Ω-1. The optical band gap was also enhanced by electron irradiation. The films electron irradiated at 900 eV showed a higher optical band gap of 4.07 eV.

Ultra-thin corrugated metamaterial film as large-area transmission dynode

Large-area transmission dynodes were fabricated by depositing an ultra-thin continuous film on a silicon wafer with a 3-dimensional pattern. After removing the silicon, a corrugated membrane with enhanced mechanical properties was formed. Mechanical metamaterials, such as this corrugated membrane, are engineered to improve its strength and robustness, which allows it to span a larger surface in comparison to flat membranes while the film thickness remains constant. The ultra-thin film consists of three layers (Al2O3/TiN/Al2O3) and is deposited by atomic layer deposition (ALD). The encapsulated TiN layer provides in-plane conductivity, which is needed to sustain secondary electron emission. Two types of corrugated membranes were fabricated: a hexagonal honeycomb and an octagonal pattern. The latter was designed to match the square pitch of a CMOS pixel chip. The transmission secondary electron yield was determined with a collector-based method using a scanning electron microscope. The highest transmission electron yield was measured on a membrane with an octagonal pattern. A yield of 2.15 was achieved for 3.15 keV incident electrons for an Al2O3/TiN/Al2O3 tri-layer film with layer thicknesses of 10/5/15 nm. The variation in yield across the surface of the corrugated membrane was determined by constructing a yield map. The active surface for transmission secondary electron emission is near 100%, i.e. a primary electron generates transmission secondary electrons regardless of the point of impact on the corrugated membrane.

A smart tri-layered nanofibrous hydrogel thin film with controlled release of dual drugs for chemo-thermal therapy of breast cancer

A tri-layered nanofibrous hydrogel thin film with temperature sensitivity is introduced as a new controlled drug release system to treat breast cancer. A simultaneous heat generation with the tunable release of dual drugs is observed in response to visible light radiation. A tri-layered nanofibrous sheet was fabricated through sequential electrospinning the blends of Au@Chit@DOX-loaded poly(N-isopropylacrylamide-co-N-methylol acrylamide) (poly (NIPAAm-co-NMA)) and Curcumin-loaded poly (vinyl alcohol) (Cu-loaded PVA), where the Cu-loaded PVA nanofibers (NFs) are sandwiched between two layers of Au@Chit@DOX-loaded poly (NIPAAm-co-NMA) NFs. After thermal crosslinking of the tri-layered nanofibrous sheet, the nanofibrous hydrogel thin film is obtained. FTIR/ATR, UV–Vis, Photoluminescence, and PXRD analyses were used for characterizing. PVA NFs and poly (NIPAAm-co-NMA) NFs were observed in the average diameters of 358 and 212 nm, respectively, and Au@Chit@DOX nanoparticles (NPs) appeared as local thickening inside the NFs. The distribution of drugs was visualized with confocal images. The thermal stability up to 295 °C and tensile strength of 0.65 MPa with 99.36% elongation were reported for the nanofibrous hydrogel thin film. Unlike the fast release of drugs from the nanofibrous sheet, a controlled release of drugs was observed from the nanofibrous hydrogel thin film at 45 °C and under visible light radiation. 52% at 45 °C and 55% under light radiation were reported for the Cur release and 86% at 45 °C and 88% under light radiation were observed for the release of DOX within 18 h. The in vitro cell viability results under light radiation displayed a chemo-thermal therapy over breast cancer cells.

Comment on “ZnO/Ag/graphene transparent conductive oxide film with ultrathin Ag layer” [J. Vac. Sci. Technol. B 39, 052208 (2021)

In the paper [Fang et al., J. Vac. Sci. Technol. B 39, 052208 (2021)], structure and transparent conductive properties of ZnO/Ag/graphene trilayer films with different thicknesses of the Ag layer were investigated. It was found that a continuous Ag layer could be formed at a layer thickness of 10.5 nm, and thus the ZnO/Ag (10.5 nm)/graphene trilayer film could achieve better transparent conductive properties. However, unfortunately, the data of carrier concentration and mobility obtained by the Hall effect for single-layer Ag and ZnO films as well as ZnO/Ag (10.5 nm)/graphene trilayer films have some clear errors that need to be addressed. The authors may consider correcting these errors, perhaps in an erratum.

Improved Dielectric Permittivity and Energy Density of Layered Polymer Composites through the Incorporation of Ultralow Amounts of RGO@BTO Hybrid Nanosheets

Polymer dielectric composites are extensively used in modern electronic devices because of their extremely high power density. However, unfavorable coupling between breakdown strength and dielectric permittivity can make achieving high energy density a challenge. In this study, reduced graphene oxide @ barium titanate (RGO@BTO) hybrid nanosheets have been fabricated and utilized as fillers in the design of RGO@BTO/P(VDF-HFP) single-layer films. An increase in permittivity to 24.8@10 kHz, i.e., equivalent to 253% of the P(VDF-HFP) (∼9.8@10 kHz) matrix, has been achieved with only 1 wt % RGO@BTO nanofillers due to the formation of microcapacitors. Furthermore, the RGO@BTO/P(VDF-HFP) film is hot-pressed with a PEI film and a P(VDF-HFP) film, forming a trilayer structure. Consequently, this trilayer film displays a high breakdown strength of 478 kV/mm, a high energy density of 8.25 J/cm3, and a satisfactory efficiency of 64.3%. Thus, this study provides an efficient route for designing polymer composites that combine high energy density with high permittivity.

Theoretical approach and experimental investigation of spin current tunnelling in Ni80Fe20/Si3N4/Fe40Co37Zr11N12 magnetically collinear trilayer films with defined in-plane uniaxial anisotropy

Ferromagnetic trilayer film systems with nonferromagnetic Si3N4 interface layers were fabricated by using magnetron sputtering. A post-annealing process was carried out at 400 °C for 2 h in a static magnetic field, in order to induce an in-plane uniaxial anisotropy. The present study introduces the exchange interaction between ferromagnetic layers which influences the static magnetisation properties as well as the natural resonance frequency behaviour and its damping features, i.e., damping and anti-damping effects. This is expressed by the total damping parameter αitot = αGi ± αspi, which is enhanced or reduced by a spin transfer torque damping parameter ± αspi whereupon Gilbert bulk damping αGi is considered to be independent. The static polarisation loops are slightly but noticeably different, caused by an interface with thickness up to 100 nm, which reflects a decreasing exchange interaction. With varying the interface thickness, the films also show a distinct variation in their frequency spectra. This leads to the conclusion that spin currents caused by spin pumping arise, and tunnelling within a Si3N4 insulating barrier generates spin transfer torque. This can be assumed because the observed ferromagnetic resonance dual lines show remarkable changes in their Full Width at Half Maxima (FWHM) at frequencies of approximately 600 MHz caused by the Ni80Fe20 layers and 2.32 GHz caused by the Fe40Co37Zr11N12 layers. Regarding the FWHM of the resonance frequency spectra in association with the damping constant αeff on the dependence of the interface layer thickness, one can observe an exponential curve shape for both ferromagnetic layers, which is obviously a sign for the interaction between the layers through a spin current tunnelling mechanism.

Transition-edge sensors using Mo/Au/Au tri-layer films

The proximity effect to reduce the transition temperature of a superconducting film is frequently used in transition-edge sensors. Here, we develop these transition-edge sensors using Mo/Au/Au tri-layer films to detect soft x-rays. They are equipped with an overhanging photon absorber. We reduce the fabrication complexity by integrating the sensor patterning with the tri-layer film formation. We determine the electro-thermal parameters of the sensors through a series of resistance vs. temperature and current vs. voltage measurements. We also demonstrate their energy-resolving capability by using a 55Fe radioactive x-ray source. The best energy resolution was approximately 6.66 eV at 5.9 keV, with a theoretical count rate of 500 Hz.

Symmetrical SnO2/W-doped VO2/SnO2 sandwich structures with high luminous transmittance, excellent solar modulation ability and low phase transition temperature

Until now, it is still a challenging task to obtain VO2-based smart windows with high luminous transmittance (Tlum), satisfactory solar modulation ability (ΔTsol) and low phase transition temperature (Tc) close to room temperature. In this work, symmetrical SnO2(d nm)/W doped VO2 (W-VO2, 60 nm)/SnO2(d nm) (d = 0, 90, 150, 230, 260, 330) multilayer films were proposed and deposited on quartz glass substrates by pulsed laser deposition. The bottom SnO2 layer acted as buffer to improve the crystallinity of VO2, while the top SnO2 layer served as antireflection layer to enhance the optical properties. When SnO2 layer reached a certain thickness, the crystallinity of W-VO2 interlayer was significantly improved, and therefore the optical properties of the obtained tri-layer films were greatly increased. In comparison with the W-VO2 monolayer film, Tlum and ΔTsol of the tri-layer film with d = 260 nm increased from 45.0% to 54.4% and from 2.6% to 10.7%, respectively, while maintaining a low Tc of 39.0 °C. Interestingly, the prepared SnO2/W-VO2/SnO2 tri-layer films showed lively golden yellow or iridescent colors. The results provide a possibility for the design of VO2-based smart windows with low phase transition temperature and excellent thermochromic properties.

Enhancement of Damping-Like Field and Field-Free Switching in Pt/(Co/Pt)/PtMn Trilayer Films Prepared in the Presence of an In Situ Magnetic Field.

The current-induced magnetization switching and damping-like field in Pt/(Co/Pt)/PtMn trilayer films prepared with and without an in situ in-plane field of 600 Oe have been studied systematically. In the presence of the in situ field, a small in-plane bias field (HEB) is observed for films with PtMn thickness ≥5 nm, while there is no observable HEB for PtMn thickness ≤3 nm. Nevertheless, a field-free switching of perpendicular magnetization of Co/Pt is observed for all the films with the PtMn thickness of 1-7 nm. On the other hand, without the presence of the in situ field, HEB and field-free switching are not seen. Furthermore, the damping-like fields (HDL) are much enhanced in the presence of the in situ field, and the increasement can be up to 47%. We further revealed that the spin current is mainly from the Pt layer, while the noncollinear spin configuration at the interface caused by the in situ in-plane field may play a role in the HDL enhancement. Micromagnetic simulations indicate that the canting of antiferromagnet PtMn spins plays an important role in the field-free switching. Our findings clarify the source of spin current in the trilayer films and provide an easier approach to field-free switching and HDL enhancement for future low-power spintronic devices.

Cyclic nanoindentation of ITO/Ag/ITO multilayer films: Hysteresis behavior and cyclic deformation response

The poor evaluation of the cyclic deformation response has been a main challenge for extensive applications and developments of ITO/Ag/ITO (IAI) multilayer films. In this paper, the effects of tri-layer film structure on hysteresis behavior and cyclic deformation response were investigated for IAI multilayer films via nanoindentation. The results indicate that the decreased density of picture-frame cracks and the enhanced mechanical performances for 300°C-IAI multilayer films are compared with those of ITO single-layer films under cyclic nanoindentation. Additionally, according to the energy-based method, the values of fracture toughness for 300°C-IAI multilayer films and ITO single-layer films are 3.49–4.17 MPa m0.5 and 3.04–3.18 MPa m0.5, respectively. Consequently, the structural design of ceramic/metal/ceramic tri-layer films are expected to be a potential method to enhance the resistance of cyclic deformation damage for transparent conducting films.

TiOx/Ti/TiOx Tri-Layer Film-Based Waveguide Bolometric Detector for On-Chip Si Photonic Sensor

In this article, we experimentally demonstrate an on-chip optical power monitoring at the near-infrared spectral region (1520&#x2013;1600 nm) using the waveguide bolometric detector with a TiO_<i>x</i>/Ti/TiO_<i>x</i> tri-layer film based on the silicon-on-insulator (SOI) platform. For the incident light absorption causing a heat generation, a heavily doped (<inline-formula> <tex-math notation="LaTeX">${n}^{+}$ </tex-math></inline-formula>) Si waveguide is introduced to utilize the mechanism of free-carrier absorption (FCA), and a metal (Au) strip is deposited onto the <inline-formula> <tex-math notation="LaTeX">${n}^{+}$ </tex-math></inline-formula> Si waveguide to further enhance the light absorption. A bolometric material of TiO_<i>x</i>/Ti/TiO_<i>x</i> tri-layer film is integrated for the thermal-to-electrical conversion. As a result, it exhibits superior performances, which are the temperature coefficient of resistance (TCR) of &#x2212;2.296&#x0025;/K and the maximum sensitivity of &#x2212;46.45&#x0025;/mW with a low wavelength-dependency. In addition, a rapid response time is obtained with the rise/fall time of <inline-formula> <tex-math notation="LaTeX">$24.6 ~\mu \text{s}/29.8 ~\mu \text{s}$ </tex-math></inline-formula>, which is enough for a variety of optical sensing applications. This work demonstrates the waveguide-based bolometric photodetection using the FCA effect, for the first time to our knowledge, which can also be simply extended for the operation wavelength range to the mid-infrared (MIR) spectral region for bio/chemical sensing applications.

Polymorphism, Structure, and Nucleation of Cholesterol·H2O at Aqueous Interfaces and in Pathological Media: Revisited from a Computational Perspective.

We revisit the important issues of polymorphism, structure, and nucleation of cholesterol·H2O using first-principles calculations based on dispersion-augmented density functional theory. For the lesser known monoclinic polymorph, we obtain a fully extended H-bonded network in a structure akin to that of hexagonal ice. We show that the energy of the monoclinic and triclinic polymorphs is similar, strongly suggesting that kinetic and environmental effects play a significant role in determining polymorph nucleation. Furthermore, we find evidence in support of various O–H···O bonding motifs in both polymorphs that may result in hydroxyl disorder. We have been able to explain, via computation, why a single cholesterol bilayer in hydrated membranes always crystallizes in the monoclinic polymorph. We rationalize what we believe is a single-crystal to single-crystal transformation of the monoclinic form on increased interlayer growth beyond that of a single cholesterol bilayer, interleaved by a water bilayer. We show that the ice-like structure is also relevant to the related cholestanol·2H2O and stigmasterol·H2O crystals. The structure of stigmasterol hydrate both as a trilayer film at the air–water interface and as a macroscopic crystal further assists us in understanding the polymorphic and thermal behavior of cholesterol·H2O. Finally, we posit a possible role for one of the sterol esters in the crystallization of cholesterol·H2O in pathological environments, based on a composite of a crystalline bilayer of cholesteryl palmitate bound epitaxially as a nucleating agent to the monoclinic cholesterol·H2O form.

Realization of high luminous transmittance and solar modulation ability of VO2 films by multistep deposition and in-situ annealing method

Novel VO2(x nm)/VO2(x nm)/VO2(x nm) (x = 10, 14, 16, 20) trilayer films are proposed and prepared on quartz glass substrates via multistep devotion and in-situ annealing by pulsed laser deposition. The bottom, intermediate and top VO2 layers are distinguished by different thickness and annealing time. The characterization of FESEM and AFM showed that grain size and surface roughness of VO2 films increase gradually from the bottom to top layer. The trilayer structure has little effect on phase transition temperature of VO2, but hysteresis width can be tuned in the range of 11–27 °C. The luminous transmission and solar modulation ability of VO2(16 nm)/VO2(16 nm)/VO2(16 nm) trilayer film were remarkably enhanced to 55.7% and 8.0%. The results suggested that such an enhancement can be attributed to the well matching of grain size of the bottom, intermediate and top VO2 layers. The study in this work provide a simple and promising strategy for designing high-quality VO2-based smart windows without additional functional layers.

Multilayered mucoadhesive hydrogel films based on Ocimum basilicum seed mucilage/thiolated alginate/dopamine-modified hyaluronic acid and PDA coating for sublingual administration of nystatin

The present study establishes an experimental design for the preparation of new bi and tri-layer mucoadhesive sublingual films based on basil (Ocimum basilicum L.) seed mucilage (OBM) as novel plant-polysaccharide for oromucosal administration of nystatin (Nys). The films formulation consists of a drug reservoir-mucoadhesive layer cross-linked via CaCl2, with protective mucoadhesive layers based on thiolated alginate (TA) and polydopamine (PDA). OBM served as a new mucoadhesive polysaccharide in second layers, where the dopamine-modified-hyaluronic acid (DHA) improved the mucoadhesive strength and swelling rate properties. The drug-loaded formulations of trilayer film with PDA coating, and bilayer film with DHA/OBM (1:1) in the second layer, showed the desired mucoadhesion properties (about 69 and 75.3% respectively). The obtained results revealed that the bilayer film containing DHA had a superior swelling degree in the range of 15–19 (g/g). While the PDA coating sample showed the highest resistance to water uptake and erosion. The bilayer film (DHA/OBM with 1:1 ratio) provided a maximum drug release of 86% after 4 h. The selected formulations indicated good mechanical properties with no cytotoxicity.

High-performance indium-free flexible transparent ATO/Au/ATO tri-layer films by magnetron sputtering

Due to the scarcity of indium (In) in the earth and its potential harm to individuals, the development of In-free transparent conductive film is considered crucial. In this work, In-free SnO 2 :Sb/Au/SnO 2 :Sb (ATO/Au/ATO, SAS) tri-layer films with high transparency and conductivity were successfully prepared on polycarbonate (PC) substrates by RF and DC magnetron sputtering at room temperature. The influence of the Au layer thickness on microstructure, electrical and optical performances was systematically studied after fixing the ATO thickness to 50 nm. It was indicated by X-ray diffraction patterns that ATO is amorphous and Au is oriented along (111). The trend of increasing and then decreasing light transmission with Au layer thickness was observed in both experimental and simulation results. The improved figure of merit (FoM, 1.89 × 10 −2 Ω −1 ) was achieved in SAS tri-layer film, the resistivity and average transmittance of which was lowered to 7.50 × 10 −5 Ω cm and 81.4%, respectively, when Au layer thickness is 11 nm. Moreover, the mechanism of the variation of optical and electrical properties at different Au layer thickness was proposed. Particularly, the SAS tri-layer films also exhibit superior flexibility, durability and adhesion. These results demonstrate SAS tri-layer films are promising alternative to ITO in flexible electronics applications.

Effect of gas composition during Pt sputtering on structural and magnetic properties of CoFeB thin films.

Ultrathin Ta/CoFeB/Pt trilayer structures are relevant to a wide range of spintronic applications, from magnetic tunnel junctions to skyrmionics devices. Controlling the perpendicular magnetic anisotropy, Gilbert damping and Dzyaloshinskii-Moriya interaction in the CoFeB layer is key for these applications. We examine the role of sputter gas composition during the Pt overlayer deposition of a Ta/CoFeB/Pt trilayer in Ar, Kr and Xe working gas environments during direct current magnetron sputtering. Decreasing density of the Pt layer (from 21 g/cm3 to 15 g/cm3) was apparent in specular x-ray reflectivity measurements of the trilayer films when increasing the molecular weight of the sputtering gas from Ar to Kr to Xe. Significant effects on the Gilbert damping and the interfacial Dzyaloshinskii-Moriya interaction (DMI) energy were observed, with increases in the damping from 0.037(1) to 0.042(1) to 0.048(1), and reductions in the interfacial DMI from 0.47(4) mJ/m2 to 0.45(5) mJ/m2 to 0.39(4) mJ/m2. The ability to control the perpendicular magnetization and DMI strength of these materials through judicious interfacial control is a means toward magnetic devices with better stability at smaller lateral dimension, key to device scaling for spintronic device arrays.

Ultrahigh energy storage capability of trilayered polyetherimide/poly(vinylidenefluoride-trifluoroethylene-chlorofluoroethylene) with low loading of boron nitride nanosheets

We developed a trilayer film with linear PEI as outer layers and P(VDF-TrFE-CFE) composite as middle layer. Trilayer architecture contributes to the redistribution of local field, thereby greatly improving breakdown strength and energy density.

Preparation and properties of AZO/PS/AZO tri-layer transparent conductive film with a light-trapping structure

The light-trapping structure is an effective method to increase solar light capture efficiency in the solar cells. In this study, Al-doped ZnO (AZO)/polystyrene (PS)/AZO tri-layer transparent conductive film with light-trapping structure was fabricated by magnetron sputtering and liquid phase methods. The structural, optical and electrical properties of the AZO films could be controlled by different growth conditions. When the sputtering pressure of the under-layer AZO film was 0.2 Pa, the discharge voltage was around 80 V, which was within the optimal process window for obtaining AZO film with high crystallinity. The optimal under-layer AZO film had a large surface roughness and a very low static water contact angle of 75.71°, promoting the relatively uniform distribution of PS spheres. Under this sputtering condition, the prepared AZO/PS/AZO tri-layer film had the highest crystallinity and least point defects. The highest carrier concentration and Hall mobility are 3.0 × 1021 cm-3and 5.39 cm2 V-1 s-1, respectively. Additionally, a transparent conductive film with the lowest resistivity value (3.88 × 10-4 Ω cm) and the highest average haze value (26.5%) was obtained by optimizing the process parameters. These properties were comparable to or exceed the reported values of surface-textured SnO2-based as well as ZnO-based TCOs films, making our films suitable for transparent electrode applications, especially in thin-film solar cells.

Optimized hydration dynamics in mucoadhesive xanthan-based trilayer vaginal films for the controlled release of tenofovir

Karaya gum, pectin and xanthan gum have been tested as candidates for manufacturing mucoadhesive trilayer films containing ethylcellulose and chitosan for the vaginal administration of the antiviral Tenofovir (TFV). The swelling profile correlated with the amount of mobile dipoles determined by impedance spectroscopy allows the determination of the hydration dynamics of these films. The fast water penetration has been demonstrated to favor the formation of polyelectrolyte complexes (PEC) via hydrogen or ionic bonds which would favor a controlled release. The incorporation of an inorganic drug release regulator induces the weakness of the polymeric chains thus enhancing the ionic mobility via the formation of low molecular weight PECs in films manufactured with karaya gum. Due to the different mechanical properties of the individual components, pectin-based films failed for a potential pharmaceutical formulation. However, mucoadhesive trilayer films produced with xanthan gum have demonstrated a moderate swelling, improved wettability and a controlled release of TFV.