Nanocomposite Multilayer Films Research Articles

Attainment of high critical current in thick BaZrO3-doped YBa2Cu3O7 multilayer nanocomposite films

High critical current (Ic) in high magnetic fields (B) with minimal variations with respect to the orientation of the B field is demanded by many applications such as high-field magnets for fusion systems. Motivated by this, this work studies 6 vol. % BaZrO3/YBa2Cu3O7 (BZO/YBCO) multilayer nanocomposite films by stacking two 10 nm thick Ca0.3Y0.7Ba2Cu3O7 (CaY-123) spacers with three BZO/YBCO layers of thickness varied from 50 to 330 nm to make the total film thickness of 150–1000 nm. The Ca diffusion from the spacers into BZO/YBCO was shown to dramatically enhance pinning efficiency of c-axis aligned BZO nanorods, which yields high and almost thickness independent critical current density (Jc) in the BZO/YBCO multilayer nanocomposite films. Remarkably, enhanced Jc was observed in these multilayer samples at a wide temperature range of 20–80 K and magnetic fields up to 9.0 T. In particular, the thicker BZO/YBCO multilayer films outperform their thinner counterparts in both higher value and less anisotropy of Jc at lower temperatures and higher fields. At 20 K and 9.0 T, Ic is up to 654 A/cm-width at B//c in the 6% multilayer (1000 nm) sample, which is close to 753 A/cm-width at B//ab due to the intrinsic pinning. This result illustrates the critical role of the Ca cation diffusion into the YBCO lattice in achieving high and isotropic pinning in thick BZO/YBCO multilayer films.

A novel approach to obtain superior microwave absorption using Non-Conducting polymer jacket coated Multi-Layer Hexaferrite-TMDC nanocomposite film

This article represents the imposing electromagnetic interference (EMI) shielding behaviour of non-conducting polymer jacket-coated Co2Y-hexaferrite-MoS2 binary nanofillers incorporated PVDF multi-layer nanocomposite films. The presence of Co2Y-hexaferrite inside PVDF enhanced the magnetic permeability, whereas the incorporation of semiconducting transition metal dichalcogenide (TMDC), MoS2, inside the PVDF matrix improves the polarization effects of the nanocomposite films. The crystalline phases corresponding to Co2Y-hexaferrite, MoS2 nanoparticles and the multi-phase nanocomposite films have been justified using XRD analysis and Rietveld refinement study. FESEM micrographs confirm the hexagonal and cotton-ball structures of Co2Y-hexaferrite and MoS2 nanoparticles, respectively; in addition, the presence of Co2Y-MoS2 binary nanofillers inside the PVDF matrix has been confirmed. The stability of the nanocomposite films against electrical breakdown is clearly demonstrated by the minimum leakage current observed at 90 kV/m under J-E characteristics. The room temperature maximum magnetization of 33.32 emu/g of Co2Y-hexaferrite at an external magnetic field of 50,000 Oe helps in incurring magnetic losses and the corresponding improvement of shielding effectiveness due to absorption (SEA) of the nanocomposite films. This article demonstrates the modulation of SEA of the nanocomposite films depending on both the binary nanofillers loading percentage inside PVDF and the thickness of the nanocomposite films. Also, a unique mechanism corresponding to the coating of a non-conducting polymer jacket over a multi-layer structure has been opted herein to improve SEA in the frequency range of 12–18 GHz. This unique mechanism demonstrates that the maximum SEA for the non-conducting polymer jacket-coated multi-layer nanocomposite film is −51.23 dB at 14.03 GHz, and the corresponding total shielding effectiveness (SET) is −74.51 dB at 13.23 GHz, along with > 99.9999 % attenuation.

Synthesis, microstructure and micro-mechanical characterization of metal (Nb, Ti) – MAX phase (Ti2AlC) nanolaminates

We utilize elevated temperature physical vapor deposition (PVD) techniques to design metal/MAX multilayered nanocomposite thin films with alternating nanoscale metallic (Nb, Ti) and MAX phase (Ti2AlC) layer thicknesses. These metal/MAX nanolaminate architectures attempt to exploit a unique hierarchical topology – as interfaces between the layers are expected to be in direct competition with the internal interfaces within the MAX layers, to drive their tunable macroscopic mechanical behavior. Two metal/MAX nanolaminates – Nb/Ti2AlC and Ti/Ti2AlC – were deposited. The Nb/Ti2AlC metal/MAX system showed highly diffused layer interfaces with distinct Ti – rich and Nb–Al – rich layers, with the presence of MAX phase alongside TiC and other Ti–Al and Nb–Al intermetallic phases. The Nb/Ti2AlC system possessed a layered architecture, though the MAX phases were not found to be continuously present in each alternating layer. The second Ti/Ti2AlC system showed a non-lamellar nanocomposite microstructure and the formation of mixed Tin+1AlCn phases (a mix of n = 1, 2), and no indication of layering. Diffusion occurring between the metal/MAX layers in both cases, likely due to the elevated temperatures during the deposition process, is speculated as the likely cause of these resultant microstructures. The mechanical properties of both systems were evaluated using micromechanical (nanoindentation and micro-pillar compression) techniques, which demonstrated high strengths for both systems (Nb system: yield and instability strengths of 4.88 ± 0.1 GPa and 5.57 ± 0.03 GPa, Ti system: yield and instability strength of 5.61 ± 0.28 GPa and 6.21 ± 0.25 GPa). This work highlights the promising mechanical properties of metal/MAX multilayered depositions and summarizes the challenges in PVD synthesis of metal/MAX multilayered nanolaminates.

Enhancement of corrosion resistance and superparamagnetic property by structural modulation in (Co-DLC)/DLC multilayered nanocomposite films

A structure of {[(Co-DLC)/DLC]X}n Multilayered Nanocomposite Films (MNF) is designed by inserting pure DLC high-resistance layers into Co-DLC nanocomposite film, which consists of alternating Co-DLC and DLC layers were prepared by magnetron sputtering. The electrochemical behavior and magnetic property of the films are modulated by varying the number of deposition cycles (n) and the thickness of one single-cycle (X). The electrochemical results show that this MNF structure significantly improves the corrosion resistance of the films owing to the clear interfaces, which block the micropores penetrating the films. Compared to the co-sputtering film, as the number of cycles n increases to 7, the corrosion resistance is enhanced by one order of magnitude from 2.3 × 104 to 2.2 × 105 Ω·cm2. However, the interfaces between the Co-DLC and DLC layer become blurred when the thickness of one single-cycle X is lower than 30 nm, and the corrosion resistance decreases to 3.7 × 104 Ω·cm2. In terms of magnetism, the multilayer structure helps to regulate the homogeneity of Co particle size. As X increases from 30 to 100 nm, the Co particle size increases from 2.7 to 4.7 nm, and the saturation magnetization intensity (Ms) of superparamagnetic property in the films increases from 2.8 to 8.2 mT. As X increases, the remanent magnetization ratio (Mr/Ms) decreases and reaches 0.011 at X = 100 nm, which is about one order of magnitude smaller than that of the co-sputtering film. This result indicates that the MNF have better superparamagnetic property. It is noteworthy that {[(Co-DLC)/DLC]X}n MNF with X ranging from 100 to 40 nm and n ranging from 3 to 7 can achieve high corrosion resistance and superparamagnetic property, simultaneously.

An effective microwave absorber using multi-layer Design of carbon allotrope based Co2Z hexaferrite-Polymer nanocomposite film for EMI shielding applications

This report shows impressive electromagnetic interference (EMI) shielding efficiency of laminated nanocomposites of PVDF containing binary nanofillers of rGO and Co2Z hexaferrite. These rGO layers in the PVDF matrix in association with magnetic nanofillers have been considered to improve interfacial polarization by accumulating charges at the interfaces of rGO-Co2Z hexaferrite-PVDF system. The crystallographic phase, chemical composition, and successful incorporation of the binary nanofillers into PVDF have been verified using XRD, XPS, RAMAN, and FESEM analysis. The J-E analysis of rGO-Co2Z hexaferrite-PVDF nanocomposite films confirm that the current density of all the nanocomposite films is very less and found in the order of 10-5 A/m2 under the maximum electric field of 70 kV/m. This indicates the emergence of polarization effect in the nanocomposite films when subjected to high external electric field without having electrical breakdown. The significant magnetization of ∼8.9 emu/g for nanocomposite films, at room temperature is beneficial for boosting the EMI shielding effectiveness due to absorption (SEA). The combination of magnetization and electrical polarization in nanocomposite film helps to attain significantly high total shielding effectiveness (SET) in the frequency range of 12–18 GHz. The shielding effectiveness study of both mono-layer and multi-layer nanocomposite films have been investigated. Improvement of SEA has also been achieved by the elevation of the thickness of the nanocomposite film within the range of 0.8 to 1.0 mm, which in turn improves SET to a value of −54.09 dB at 15.70 GHz for multi-layer system of thickness 0.861 mm with >99.999 % of attenuation whereas the mono-layer film of thickness 0.180 mm shows the SET of −47.03 dB at 14.76 GHz with an attenuation of >99.99 %.

One-Step Synthesis of TiO2/SiO2-np Nanocomposite Photocatalytic Multilayer Films: Effect of Incorporation Time Sequences of SiO2 Nanoparticles during the TiO2 Film Growth.

In this article, the TiO2/SiO2-np nanocomposite multilayer films were synthesized in a single step by reactive magnetron sputtering combined with a nanoparticle aerosol jet. The SiO2 nanoparticles (SiO2-np) were introduced into a growing TiO2 thin film with different time sequences during deposition for a fixed duration. The SiO2-np acting as impurities are introduced into the TiO2 to willingly disturb its growth and to cause growth defects in order to increase the specific surface area of the photocatalytic film. In reason of the non-photoactive properties of the SiO2 nanoparticles, their introduction allows us to study only the effects induced on the film morphology, microstructure, and photocatalytic properties by their incorporation. The fractographies and topographies reveal strong changes in the morphologies depending on the time sequence of the nanoparticle introduction in the thin films. The introduction of SiO2-np from the beginning of the TiO2 film growth leads to the formation of high and large growth defects resulting in a highly diffusive surface. In addition, XRD analysis shows that the crystallite size tends to decrease as the composite film layer gets closer to the surface. Their photocatalytic performance is obtained by following the degradation of orange G dye under UV-visible irradiation. The photocatalytic performance is not only related to the specific surface area of the catalyst film, and the coverage of the photoactive phase on the surface, but also to the crystal quality of the photoactive phase. Furthermore, the samples exhibit good photostability, maintaining the same activity after four degradation cycles. In the specific case of TiO2/SiO2-np, it is demonstrated that the introduction of the nanoparticles only at the beginning of the film growth is more efficient than a continuous introduction. This result suggests that this original process allows the use of a relevant strategy for the nanoparticle introduction according to the required functionality.

Sandwiched film of graphene/silver nanowire conductive layer reinforced by hydroxyethyl cellulose bond layer

Multilayer nanocomposite film made of different materials has multifunctional properties and is applied in the field of flexible electronic devices. Herein, hydroxyethyl cellulose (HEC) and boron nitride nanosheets (BNNS) were used as the matrix and thermal conductivity material of the HEC/BNNS (HB) insulation layer and were combined with conductive blade structure graphene/silver nanowires (GA) film to prepare a three-layer HB/GA20/HB film. Using the high mechanical properties of the HEC based film, the tensile strength of the three-layer film is increased to 22.0 MPa, 633 % higher than that of the pure conductive film. The sensor prepared by multilayer film has good bending sensing performance (1500 cycles) and electromagnetic shielding performance (29.3 dB). The heating temperature of HB/GA20/HB film heater is up to 107.9 °C at 20 V. In the HB/GA20/HB film, the external HB layer provides insulation, thermal conductivity and physical support, and the internal GA layer with good conductive and sensing properties is combined to build a multi-functional sensor, which can be applied as a mobile sensor, heater and electromagnetic shielding material in the flexible wearable field.

Electrochemical assembly of single-walled carbon nanotube/polypyrrole/tellurium/lead telluride multi-layer nanocomposite films for room-temperature flexible thermoelectric application

With the complexity and diversification of thermoelectric (TE) application scenarios, it becomes increasingly difficult for single-component thermoelectric materials to satisfy practical demands. Therefore, recent researches have largely focused on the development of the multi-component nanocomposites, which are probably a good solution for the TE application of some materials that are not eligible when used alone. In this work, a seires of single-walled carbon nanotube (SWCNT)/polypyrrole (PPy)/tellurium (Te)/lead telluride (PbTe) multi-layer flexible composite films were fabricated via the successive electrodeposition of the flexible PPy layer with a low thermal conductivity, the ultra-thin Te induction layer, and the brittle PbTe layer with a large Seebeck coefficient over the pre-fabricated SWCNT membrane electrode with a high electrical conductivity. Through the complementary advantages between different components and the multiple synergies of the interface engineering, the SWCNT/PPy/Te/PbTe composites harvested the excellent TE performance with a maximum power factor (PF) of 929.8 ± 35.4 µW m−1 K−2 at room temperature, outperforming those of most of the electrochemically-prepared organic/inorganic TE composites reported previously. This work evidenced that the electrochemical multi-layer assembly is a feasible tactic for constructing special thermoelectric materials to meet customized requirements, which could also be applied to other material platforms.

The benefit of Ca in improving pinning of BaZrO3-Y2O3 doubly-doped YBa2Cu3O7-x/Ca0.3Y0.7Ba2Cu3O7-x multilayer nanocomposite films

This work examines the pinning enhancement in BaZrO 3 (BZO) +Y2O3 doubly-doped (DD) YBa2Cu3O7 (YBCO) nanocomposite multilayer (DD-ML) films. The film consists of two 10 nm thin Ca0.3Y0.7Ba2Cu3O7-x (CaY-123) spacers stacking alternatively with three BZO + Y2O3/YBCO layers of 50 nm each in thickness that contain 3 vol% of Y2O3 and BZO doping in the range of 2–6 vol%. Enhanced magnetic vortex pinning and improved pinning isotropy with respect to the orientation of magnetic field (B) have been achieved in the DD-ML samples at lower BZO doping as compared to that in the single-layer counterparts (DD-SL) without the CaY-123 spacers. For example, the pinning force density (F p ) of ∼58 GNm−3 in 2 vol.% of DD-ML film is ∼110% higher than in 2 vol% of DD-SL at 65 K and B//c-axis, which is attributed to the improved pinning efficiency by c-axis aligned BZO nanorods through diffusion of Calcium (Ca) along the tensile-strained channels at BZO nanorods/YBCO interface for improvement of the interface microstructure and hence pinning efficiency of BZO nanorods. An additional benefit is in the considerably improved J c (θ) and reduced J c anisotropy in the former over the entire range of the B orientations. However, at higher BZO doping, the BZO nanorods become segmented and misoriented, which may change the Ca diffusion pathways and reduce the benefit of Ca in improving the pinning efficiency of BZO nanorods.

Macroscopic mapping of the linear in-plane anisotropy of nanocellulosic thin films by Mueller matrix polarimetry

The present work focuses on the characterization of the macroscopic optical anisotropy of cellulose nanocomposite multilayer thin films prepared by grazing incidence spraying. The polarization properties of such films composed of in-plane aligned cellulose nanofibrils embedded in a polyelectrolyte multilayer are investigated by Mueller matrix polarimetry (MMP). Linear birefringence is the predominant polarization property resulting from the unidirectional organization of the cellulose nanofibrils, thus, the differential decomposition of the Mueller matrix measured on the films allows the determination of their actual structural birefringence, ⟨Δn⟩=0.032. Moreover, modeling the sample as an effective medium provides a parametrized expression that describes its linear birefringence as a function of the optical constants of the components, the volume fraction of nanofibrils, the distribution of orientation, and the film thickness. Therefore, MMP provides a fast, simple, and non-destructive method to characterize both the structural characteristics and the optical birefringence/dichroism of the films over large areas, which is of great interest for various optoelectronic applications.

Microstructure, Mechanical and Tribological Properties of Arc Ion Plating NbN-Based Nanocomposite Films.

NbN, NbN-Ag and NbN/NbN-Ag multilayer nanocomposite films were successfully deposited by an arc ion plating system (AIP), and their microstructures, mechanical and tribological properties were systematically investigated. The results show that all the films had a polycrystalline structure, and the Ag in the Ag-doped films existed independently as a face-centered cubic phase. The content of Ag in NbN-Ag and NbN/NbN-Ag films was 20.11 and 9.07 at.%, respectively. NbN films fabricated by AIP technique had excellent mechanical properties, and their hardness and critical load were up to 44 GPa and 34.6 N, respectively. The introduction of Ag into NbN films obviously reduced the friction coefficient at room temperature, while the mechanical properties and wear resistance were degraded sharply in comparison with that of NbN films. However, the NbN/NbN-Ag films presented better hardness, H/E*, H3/E*2, adhesive strength and wear resistance than NbN-Ag films. Additionally, analysis of wear surfaces of the studied films and Al2O3 balls using 3D images, depth profiles, energy dispersive spectrometry (EDS) and Raman spectra indicated that the main wear mechanisms of NbN and NbN/NbN-Ag films were adhesive and oxidation wear with slight abrasive wear, while the severe abrasive and oxidation wear were the dominant wear mechanism for NbN-Ag films.

Ultrathin nanocomposite films with asymmetric gradient alternating multilayer structures exhibit superhigh electromagnetic interference shielding performances and robust mechanical properties

Conductive polymer composites achieve high electromagnetic interference (EMI) shielding performances mainly by utilizing large amounts of conductive fillers, which increases the thickness of the composites and leads to a sharp decrease in their mechanical properties. Herein, for the first time, we fabricated an ultrathin and flexible cellulose nanofiber/reduced graphene oxide@Fe3O4&cellulose nanofiber/silver nanowires (CNF/rGO@Fe3O4&CNF/AgNWs) nanocomposite film that utilized an asymmetric gradient alternating multilayer structure to improve the EMI shielding performance and mechanical properties of the film. In particular, the CNF/rGO@Fe3O4&CNF/AgNWs-37 wt%-6L asymmetric gradient alternating 6-layer nanocomposite film with a thickness of 67 μm achieved an EMI shielding effectiveness (EMI SE) of up to 112.9 dB (the average EMI SE in the X-band was 104 dB), which was enabled by the high electrical conductivity and a novel shielding mechanism, which entailed the electromagnetic waves undergoing gradient absorption and gradient reflection in the layers of the film. Furthermore, the CNF/rGO@Fe3O4&CNF/AgNWs-37 wt%-6L asymmetric gradient alternating 6-layer nanocomposite film also exhibited robust mechanical properties (tensile strength of 115.2 MPa and fracture strain of 8.1%) and excellent thermal conductivity (11.02 W·m−1·K−1). Interestingly, although the conductivity of the asymmetric gradient alternating multilayer nanocomposite films decreased with increasing number of layers, the EMI shielding properties showed the opposite trend.

High-strength, flexible and superhydrophobic graphene/aramid nanofiber nanocomposite films for electromagnetic interference shielding application

Electromagnetic interference (EMI) shielding composite materials exhibit many amazing characteristics, including low density, excellent flexibility and corrosion resistance, compared with metals. However, it is a long-standing challenge for EMI shielding materials to overcome inferior mechanical properties and limited hydrophobic characteristics. In this work, the high-strength, flexible and superhydrophobic graphene nanosheet/aramid nanofiber (GNS/ANF) nanocomposite films with layered microstructure were prepared by the sol-gel transformation and spray coating process. The resultant film exhibits excellent mechanical properties with a high tensile strength (131.17 ± 2.77 MPa), large fracture strain (9.58 ± 0.58%), and favorable toughness (8.84 ± 0.74 MJ m−3), which are 26.2 times, 7.5 times and 221.0 times higher than those of pure GNS films. These results are attributed to synergistic effect between intensive stretching of three dimensional (3D) nanofiber network and extensive sliding of GNS produced effective energy dissipation. Moreover, the film with content of 70 wt% GNS has EMI shielding effectiveness of 31.3 dB, and its reflection coefficient is more than 0.89, revealing a reflection-dominant shielding mechanism. Meanwhile, the film possesses superhydrophobic property (158.7° ± 1.1°) and flame retardancy. The multilayered nanocomposite films have excellent potential for high-performance EMI shielding applications under some outdoor conditions.

Enabling coherent BaZrO3 nanorods/YBa2Cu3O7−x interface through dynamic lattice enlargement in vertical epitaxy of BaZrO3/YBa2Cu3O7−x nanocomposites

One-dimensional c-axis-aligned BaZrO3 (BZO) nanorods are regarded as strong one-dimensional artificial pinning centers (1D-APCs) in BZO-doped YaBa2Cu3O7−x (BZO/YBCO) nanocomposite films. However, a microstructure analysis has revealed a defective, oxygen-deficient YBCO column around the BZO 1D-APCs due to the large lattice mismatch of ∼7.7% between the BZO (3a = 1.26 nm) and YBCO (c = 1.17 nm), which has been blamed for the reduced pinning efficiency of BZO 1D-APCs. Herein, we report a dynamic lattice enlargement approach on the tensile strained YBCO lattice during the BZO 1D-APCs growth to induce c-axis elongation of the YBCO lattice up to 1.26 nm near the BZO 1D-APC/YBCO interface via Ca/Cu substitution on single Cu-O planes of YBCO, which prevents the interfacial defect formation by reducing the BZO/YBCO lattice mismatch to ∼1.4%. Specifically, this is achieved by inserting thin Ca0.3Y0.7Ba2Cu3O7−x (CaY-123) spacers as the Ca reservoir in 2–6 vol.% BZO/YBCO nanocomposite multilayer (ML) films. A defect-free, coherent BZO 1D-APC/YBCO interface is confirmed in transmission electron microscopy and elemental distribution analyses. Excitingly, up to five-fold enhancement of J c (B) at magnetic field B= 9.0 T//c-axis and 65 K–77 K was obtained in the ML samples as compared to their BZO/YBCO single-layer (SL) counterpart’s. This has led to a record high pinning force density F p together with significantly enhanced B max at which F p reaches its maximum value F p,max for BZO 1D-APCs at B//c-axis. At 65 K, the F p,max ∼158 GN m−3 and B max ∼ 8.0 T for the 6% BZO/YBCO ML samples represent a significant enhancement over F p,max ∼ 36.1 GN m−3 and B max ∼ 5.0 T for the 6% BZO/YBCO SL counterparts. This result not only illustrates the critical importance of a coherent BZO 1D-APC/YBCO interface in the pinning efficiency, but also provides a facile scheme to achieve such an interface to restore the pristine pinning efficiency of the BZO 1D-APCs.

Adhesion strength of Tii_xCx – DLC multilayer nanocomposite thin films coated by ion-plasma deposition on martensitic stainless steel produced by selective laser melting followed by plasma-nitriding and burnishing

[Ti0.2C0.8/a-C]40 multilayer thin films composed of forty pairs of TiC and pure carbon layers were formed on a selective laser melted (SLM) martensitic stainless steel by means of ion-plasma deposition process. SLM steel was pre-treated by one of the two following schemes: (1) oil quenching from 1040°C followed by heating to 480°C for 4 hours and air cooling (HT), finish milling (FM); (2) HT, FM, ion-plasma nitriding followed by burnishing. Mechanical failure mode and critical load Lc for damaging the coatings were determined using linear scratch tests performed at linearly-increased normal force. Indentation by conical diamond tip were carried out in order to asses an elastic recovery and energy dissipation coefficient defined as the ratio of plastic to total deformation energy. The scratch test results showed that the post-processing of the substrate strongly influenced the failure mode of the coating and increased the critical load from 320 mN to 920 mN. Indentation revealed that nitriding and burnishing before coating deposition increase the elastic recovery of the [Ti0.2C0.8/a-C]40 coating-substrate system from 24% to 68%. The energy dissipation coefficient drops from 79% to 45%.

Steady-State Conduction Current Performance for Multilayer Polyimide/SiO2 Films.

The steady-state electrical conduction current for single and multilayer polyimide (PI) nanocomposite films was observed at the low and high electric field for different temperatures. Experimental data were fitted to conduction models to investigate the dominant conduction mechanism in these films. In most films, space charge limited current (SCLC) and Poole–Frenkel current displayed dominant conduction. At a high electric field, the ohmic conduction was replaced by current–voltage dependency. Higher conduction current was observed for nanocomposite films at a lower temperature, but it declined at a higher temperature. PI nanocomposite multilayer films showed a huge reduction in the conduction current at higher electric fields and temperatures. The conclusions derived in this study would provide the empirical basis and early breakdown phenomenon explanation when performing dielectric strength and partial discharge measurements of PI-based nanocomposite insulation systems of electric motors.

Growth of out-of-plane standing MoTe2(1-x)Se2x/MoSe2 composite flake films by sol–gel nucleation of MoOy and isothermal closed space telluro-selenization

This study describes the sol–gel processing of MoOy on Si (100) to subsequently achieve out-of-plane MoTe2/MoSe2 flake composite films by an isothermal closed space vapor transformation. The oxide precursor films have been prepared from a Mo isopropoxide solution in isopropanol and acid catalysis induced by HCl. Thermal annealing at 200, 400 and 600 °C enhanced the condensation after xerogel formation. An x-ray absorption analysis demonstrates that films condensed at 200 °C are at an intermediate chemical state between MoO3 and MoO2. To achieve MoTe2/MoSe2 composite films, the precursor oxide films were reduced in H2 and exposed to the chalcogenides by isothermal closed space vapor transport at 600 °C. The multilayered nanocomposite films grow with an out-of-plane flake-like structure and an evident integration of Se in the MoTe2 phase according to a MoTe2(1-x)Se2x alloy, with an estimation of x of 0.25. The alloy and the orientation of the flakes are consistent with the bands present in the Raman spectrum. These films are attractive for applications requiring high surface area interfaces favoring gas or ion exchange reactions with transition metal dichalcogenides.

Multilayer polyimide nanocomposite films synthesis process optimization impact on nanoparticles dispersion and their dielectric performance

AbstractThe preparation of polyimide (PI)/nanocomposite films and their thickness are a complex process with some ambiguous variables that are involved in the synthesis process. Therefore, it is crucial to understand those variables and reveal the chemistry behind them. Several methods have been probed until an optimal synthesis process was found. A detailed synthesis process optimization is described in this article to understand all variables, which can influence the molecular weight of polyamic acide (PAA) solution, the thickness of films, and nanoparticles dispersion. The spin coating technique was used to control the thickness of single and multilayer PI/nanocomposite films, which reveals that the thickness of the casted PI film depends on several factors, such as the viscosity, molecular weight of the PAA solution, and the spin speed of spin coater. Factors, which can influence the molecular weight of PAA solution, are discussed in detail. After completing the synthesis process, the single and multilayer PI nanocomposite films are characterized experimentally. The results reveal that using a thin layer of nanocomposite on PI film in the form of a multilayer structure improves the nanoparticles dispersion and thereafter its dielectric properties.

Energy storage performance in polymer dielectrics by introducing 2D SrBi4Ti4O15 nanosheets

Polymer-based dielectric energy storage materials have been playing critical roles in high-performance energy storage capacitors due to their high breakdown electric fields and facile processability. However, the low energy density and efficiency of polymer-based film capacitors limit their widespread application in various electronics products. In this contribution, we synthesized the SrBi4Ti4O15 (SBT) nanosheets with large aspect ratio by using the molten salt method and introduced them into the PVDF matrix to prepare a multilayer nanocomposite film, of which the discharge energy density and discharge efficiency were much improved. Finite element simulation results show that the addition of 2D SBT nanosheets can significantly improve the local electric field distribution of nanocomposite films. Finally, a high discharge energy density of 11.69 J cm−3 and an excellent discharge efficiency of 78.95% were simultaneously achieved in the 0/5/0 sample. This work provides a reference for polymer-based dielectrics with excellent comprehensive energy storage performance.

Layer-by-layer assembly of graphene oxide and 12-molybdosilicate composite films for the electrocatalytic reduction of chloroform in neutral aqueous solution

Graphene oxide-based nanocomposite multilayer films with polyethylene imine (PEI) and H4[SiMo12O40]4- POM interface have been investigated for their electrocatalytic reduction of chloroform in water. Resulting thin films were characterized by both electrochemical and surface based techniques. Cyclic voltammetry was employed to show the layer growth and redox behaviour of the modified electrode system with redox chemistry of the incorporated POM being present. AC impedance gave insights into the porosity and conductivity of the constructed multilayer POM system. Surface characterisation by XPS, AFM and SEM of the modified electrode was also performed to gain insights into the surface morphology and elemental composition of the modified electrode. The constructed multilayer system exhibited an electrocatalytic response to chloroform in water.