Final Electrical Properties Research Articles

Cross-Scale Industrial Manufacturing of Multifunctional Glass Fiber/Epoxy Composite Tubes via a Purposely Modified Filament Winding Production Line.

In the present research work is demonstrated a cross-scale manufacturing approach for the production of multifunctional glass fiber reinforced polymer (GFRP) composite tubes with a purposely redesigned filament winding process. Up until now, limited studies have been reported towards the multiscale reinforcement direction of continuous fibers for the manufacturing of hierarchical composites at the industrial level. This study involved the development of two different multi-walled carbon nanotube (MWCNT) aqueous-based inks, which were employed for the modification of commercial glass fiber (GF) reinforcing tows via a bath coating unit in a pilot production line. The obtained multifunctional GFRP tubes presented a variety of characteristics in relation to their final mechanical, hydrothermal aging, electrical, thermal and thermoelectric properties. Results revealed that the two individual systems exhibited pronounced differences both in crushing behavior and durability performance. Interestingly, for lateral compression the MWCNT coatings comprising a polymeric dispersant minorly affected the mechanical response of the produced tubes. The crashworthiness indicators of the multifunctional tubes displayed a slight 5% variation to the respective reference values, combined with a more ductile behavior. Moreover, regarding the bulk electrical and thermal conductivity values, as well as the Seebeck coefficient factor, the corresponding tubes displayed a variance of 233% and 19% and an opposite semi-conducting sign denoting a p- and n-type character, respectively.

Study of Ge‐Rich Ge–Sb–Te Device‐Dependent Segregation for Industrial Grade Embedded Phase‐Change Memory

Ge‐rich Ge–Sb–Te (GGST) alloys are the most promising materials for phase‐change memory in embedded applications, being able to fulfill the tough data retention requirements of automotive and consumer markets. GGST alloys are sensitive to thermal budgets and spatial confinement; thus, memory device process integration and architecture can strongly impact their final electrical properties and reliability. Herein, exploiting a statistical methodology capable to extract quantitative metrics for evaluating by‐process segregation, the inhomogeneity of out‐of‐fab GGST material in function of process parameters is studied such as architecture and alloy composition. The present results with the already known source of segregation, namely the back‐end‐of‐line thermal budget, are compared providing a comprehensive description of the main modulating factors of segregation among these different process parameters.

Compaction pressure effect on the dielectric, DC and AC conductivity of C-130 porcelain

Porcelain insulators can be prepared in a variety of compositions using several different preparation techniques. In the frame of the present work the effect of the applied compaction pressures on the C-130 grade electroporcelain was studied in terms of electrical and dielectric properties. Compaction is a widely used preparation process, nevertheless, a little is known about the effect of the compaction pressure on the final electrical properties of the material. Samples prepared with different compaction pressures (from 70 MPa to 110 MPa; 10 MPa step size) were subjected to a measurement of DC conductivity up to 1200 °C, and a measurement of dielectric properties at room temperature after different firing temperatures. The DC conductivity of the raw samples ranged from ∼10−10 S/m at room temperature to <10−3 S/m at 1100 °C. Temperature dependence of the DC conductivity revealed that the dominant charge carriers were H+ and OH− ions (initial stages of heating) and alkali ions (at high temperatures and during second heating). The DC conductivity of the previously fired samples (at 1100 °C) ranged from ∼10−12 S/m (room temperature) to ∼10−3 S/m (1200 °C). The AC conductivity of the samples ranged from ∼10−7 S/m (samples fired at 1300 °C, measured at low frequencies) to ∼10−3 (raw sample, measured at high frequencies). AC conductivity measurements and dielectric analysis confirmed that the conduction occurred through ion hopping and the bulk boundary conductivity was dominant. The relative permittivity reached 7–8 after firing at 1300 °C at frequencies above 2 MHz.

In operando characterization of the ionic conductivity dependence on liquid transient phase and microstructure of cold-sintered Bi2O3-doped Li1.3Al0.3Ti1.7(PO4)3 solid-state electrolyte

A disruptive sintering technique, Cold Sintering Process (CSP), has been used to produce cold-sintered samples of Bi2O3-doped Li1.3Al0.3Ti1.7(PO4)3 (LATP) as solid-state electrolyte (SSE). An in operando impedance study has been performed to shed light on this sintering process. In this work, Bi2O3 and 3 m acetic acid solution sintering aids were synergistically added to LATP powders to sinter at low temperature. Effects of Transient Liquid Phase (TLP) content on the sintering behavior, phase composition, microstructure, and electrochemical properties were all investigated for a LATP doped with 2 wt% Bi2O3 (optimal content) solid-state electrolyte (SSE). The data revealed that the final electrical properties, which are the key parameter decisive for their application, are defined by the following sintering parameters: Transient Liquid Phase (TLP) content, temperature, pressure, and dwell time. Using acetic acid 3 m as TLP, LATP-based samples can be cold-sintered at optimized sintering conditions of 150 °C and 700 MPa of uniaxial pressure for 90 min. The resultant SSE shows a high ionic conductivity (4.5·10−5 S cm−1) at room temperature (RT) and relative density (∼95%), which demonstrates the effectiveness of the low-temperature sintering process by optimizing the ionic conductivity of LATP-based SSE, also reducing preparation costs and CO2 emissions.

Molecule Clustering Dynamics in the Molecular Doping Process of Si(111) with Diethyl-propyl-phosphonate.

The molecular doping (MD) process is based on the deposition of dopant-containing molecules over the surface of a semiconductor substrate, followed by the thermal diffusion step. Previous studies suggest that, during the deposition, the molecules nucleate clusters, and at prolonged deposition times, they grow into self-assembled layers on the sample to be doped. Little is known about the influence of nucleation kinetics on the final properties of these layers and how they change when we modify the solution properties. In this work, we examine the nucleation rate and the molecular surface coverage kinetics of diethyl-propyl phosphonate on silicon at different solution concentrations and how these conditions influence the final electrical properties of the doped samples. We present a high-resolution morphological characterization of the as-deposited molecules together with the electrical results of the final doped samples. The experimental results show a non-obvious behavior, explained through understanding of the competition between the molecules' physisorption and chemisorption mechanisms. As a consequence, due to the deeper knowledge of the deposition phase, a finer tuning of the conductive properties of MD-doped samples is achieved.

Cold Atmospheric Plasma-Assisted Direct Deposition of Polypyrrole-Ag Nanocomposites for Flexible Electronic Sensors

Conductive polymers and their composite materials have attracted considerable interest due to their potential applications in sensors, actuators, drug delivery systems, and energy storage devices. Despite their wide range of applications, many challenges remain primarily with respect to the complex synthesis and time-consuming manufacturing steps that are often required in the fabrication process of various devices with conductive polymers. Here, we demonstrate the novel use of cold atmospheric plasma (CAP)-assisted deposition technologies as a solvent-free and scalable approach for in situ polymerization and direct deposition of conductive polypyrrole-silver (PPy-Ag) nanocomposites onto the desired substrates under atmospheric conditions. In this study, a systematic approach with different precursor composition mixtures containing pyrrole as the monomer and AgNO3 as the photoinitiator was investigated to assess the effect of precursor composition on the final chemical, electrical, and mechanical properties of the PPy-Ag nanocomposite thin-film coatings which were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, and cyclic bending tests. The characterizations indicated the possibility of fabricating PPy-Ag nanocomposite films with tunable degrees of polymerization and Ag nanoparticle loading by simply varying the percentage of AgNO3 in precursor composition mixtures. Finally, as a proof of concept, the potential use of the PPy-Ag nanocomposite films with different Ag nanoparticle loading percentages was assessed for humidity sensing by measuring their level of change in electrical resistance in the relative humidity range of 12-60%. It is envisioned that the developed CAP-assisted deposition technology can provide a new stepping stone toward scalable additive manufacturing of various functional nanocomposite films for different low-cost and flexible electronic applications.

Tuning the Self-Assembled Morphology of Ti3C2Tx MXene-Based Hybrids for High-Performance Electromagnetic Interference Shielding.

Hybrid materials based on transition metal carbide and nitride (MXene) nanosheets have great potential for electromagnetic interference (EMI) shielding due to their excellent electrical conductivity. However, the performance of final products depends not only on the properties of constituent components but also on the morphology of the assembly. Here, via the controlled diffusion of positively charged poly(allylamine hydrochloride) (PAH) chains into the negatively charged Ti3C2Tx MXene suspension, MXene/PAH hybrids in the forms of thin films, porous structures, and fibers with distinguished internal morphologies are obtained. Our results confirm that PAH chains could effectively enhance the oxidation stability and integrity of wet and dry MXene structures. The flexibility to tune the structures allows for a thorough discussion of the relations between the morphology, electrical conductivity, and EMI shielding mechanism of the hybrids in a wide range of electrical conductivity (2.5 to 3347 S·cm-1) and thickness (7.7 to 1900 μm) values. The analysis of thin films shows the direct impact of the polymer content on the alignment and compactness of MXene nanosheets regulating the films' electrical conductivity/EMI shielding effectiveness. The colloidal behavior of the initial MXene suspension determines the interconnection of MXene nanosheets in MXene/PAH porous assemblies and the final electrical properties. In addition to the internal morphology, examining the laminated MXene/PAH fibers with geometrically different arrangements demonstrates the role of conductive network configuration on EMI shielding performance. These findings provide insights into tuning the EMI shielding effectiveness via the charge-driven bottom-up assembly of electrically conductive MXene/polyelectrolyte hybrids.

Structural and morphological properties of contacts to a (111) orientation monosilicon substrate based on aluminum with a Ti and w – 10 % Ti barrier layer

The paper presents the results of studies on the formation of ohmic contacts to monosilicon from aluminum in the presence of a thin-film barrier layer based on titanium and tungsten.&#x0D; The purpose of reseach: to study the mechanism of solid-phase interaction in Al/Ti/Si and Al/Ti/SiOx/Si systems during the formation of contacts to (111) orientation silicon based on aluminum with a Ti and W 10% Ti barrier layer, their structural and morphological properties and ways to manage this mechanism. The study revealed relationships between the structure and properties of the films, which can lead to marriage or a decrease in the service characteristics of the IC due to a violation of the structure of the film composition.&#x0D; Methods and objects of research: It is shown that the difference in the behavior of thick and thin oxides is consistent with the thermodynamic data for bulk materials. In this case, the formation and final electrical properties of the silicidesilicon interface region depend on the presence of unavoidable impurities present during the deposition of the reacting metal.&#x0D; As a result of electron microscopic studies of the Al/WTi/Si system, it was found that the tungsten10 % (wt.) titanium barrier layer is reliably thermally stable up to a temperature of 773 K, regardless of the layer thickness (0.050.12 m).

Formamidinium halide salts as precursors of carbon nitrides

Pyrolysis of formamidinium halide salts (FAI, FABr) results in a new type of amorphous carbon nitride materials with a mass fraction of 40–50% nitrogen content. Pyrolysis temperature drives final chemical composition, morphology, optical and electrical properties of the material independently of the halide precursor and identifying triazine ring, instead of typical heptazine unit, as the main building block of this material. We elaborated a temperature dependent mechanism of formation for these materials and foresee its potential value as native passivation layer in the field of perovskite solar cells.

Honeywell develops new technology for production of green hydrogen

Composites of high density polyethylene, HDPE, filled with submicrometric particles of BaTiO3, BT, have been prepared. Uniform dispersion of the particles was achieved by high energy ball milling and subsequent hot pressing. Using SEM, FTIR, TGA-DTA and stress-strain tests, studies of the structural, morphological and mechanical features of the composites have been carried out. Frequency response analysis, dielectric strength and resistivity measurements were also performed to evaluate the final electrical properties as a function of the processing and the amount of BaTiO3 particles. From the analysis of the microscopic structure, it can be deduced that any change in the properties of the materials must be solely ascribed to the presence of the BT particles. A balance between an enhancement of space charge polarization with the presence of BT and the existence of permanent dipoles associated to them might explain an initial increase in the dielectric losses with the BT content, and its later decrease at higher BT content. The observed decrease in resistivity and breakdown voltage when increasing the amount of BaTiO3 can be explained by the lower resistivity of BT particles at room temperature and the growing accumulation of space charge.

Development of a multifunctional self-sensing composite structure

In the present work, a model of electrical properties of composites with inherent sensing properties is proposed. More specifically, the effect of both geometry and dispersion procedure is analyzed for carbon nanostructured polimers, exploring their influence in its electromechanical properties by developing simple analytical methods. In this context, it is observed that a better CNT distribution (by reducing the aggregate ratio) leads to a higher electrical conductivity as well as a higher electrical sensitivity to mechanical deformation. Therefore, the proposed model allows to get a deepr knoweledge about the influence of different processing parametrs in the final electrical properties of the nanocomposite. Moreover, the experimetal testing of self-sensing structures has been carried out by using a carbon nanotube doped adhesive film. More specifically, it has been observed that the proposed nanostructured adhesive presnts an outstanding capability for early damage detection and propagation, being a promising technique in order to complement other available inspection methods. This tests have been validated at coupon level, as well as a subelement one, by using stiffened panels. In addition, it has been proved a higher capability for detecting the presence of possible weak interfaces, demonstrating the applicability of the developed technique.

Enhanced tensile strength, fracture toughness and piezoresistive performances of CNT based epoxy nanocomposites using toroidal stirring assisted ultra-sonication

The importance of proper CNT dispersion is still the main challenge in CNTs doped epoxy nanocomposites. Therefore, this study was aimed to investigate the effect of toroidal stirring-assisted sonication on final mechanical, electrical and electromechanical properties of the nanocomposites. Two different samples were produced i.e. one with just sonication (M1 batch) and the other was produced using a combination of sonication and high toroidal stirring in an iterative approach (M2 batch). While piezoresistivity performance of the CNT based nanocomposites were mainly investigated in the literature for tensile mode and less attempts were conducted in presence of a pre-crack, both tensile and fracture tests were performed in this study to measure mechanical and electromechanical properties of the nanocomposites. SEM and FESEM were used for the microstructural characterizations. Results showed that M2 batch resulted in a better mechanical, electrical, and piezoresistivity performance than the M1 batch resulting from a better CNT dispersion and less amount of voids in the former compared to the latter. In fact, tensile strength and fracture toughness was increased by 70% and 17%, respectively for M2 batch with respect to M1 batch . Moreover, piezoresistive-sensitivity of the M2 batch increased 14%, compared to M1 batch. Finally, different trends in piezoresistivity was revealed in the fracture test before the occurrence of macroscopic damage, attributed to state of CNT dispersion and manifesting as a negative and positive trend for the M2 and M1 batches, respectively.

Electrical behavior of RuO2-glass composites: The effect of RuO2 particle size on the percolation threshold

Even small amounts of the fission byproduct ruthenium can increase the overall electrical conductivity of nuclear glasses by several orders of magnitude. In this context, the main goal of the present work is to evaluate the dependence of RuO2 particle size on the electrical behavior and percolation threshold of RuO2-glass composites. For this purpose, a set of sodium borosilicate glasses with different RuO2 content or distinct particle size is synthesized and characterized by X-ray diffraction and scanning electron microscopy. The electrical properties of these composites are assessed by impedance spectroscopy in a temperature range below the glass transition. The obtained results expose a transition in the electrical behavior of the RuO2-glass composites in the vicinity of the percolation threshold. The composites are mostly ionic conductors for low RuO2 content, but they become predominantly electronic conductors for RuO2 contents beyond the percolation threshold. The dependence of their electrical conductivity on temperature is also revealing. The composites showing ion-conducting behavior exhibit a strong and crescent dependence of the conductivity on temperature, while the electron-conducting composites show a metal-like conductivity. Even more noteworthy, the dependence of the electrical behavior on the RuO2 particle size unveils an extremely low percolation threshold (~1% vol.) and consequently higher conductivity for the glass composites synthesized with the nanometric RuO2 powder. These results bring new insights into the discussion of why these composites present such a low percolation threshold and suggest that the particle size of precursor powders play a crucial role in their final electrical properties.

Effect of the N/P/S and transition-metal co-doping on the quantum capacitance of supercapacitor electrodes based on mono- and multilayer graphene

The effect of co-dopants (N, P, and S) and transition metals (TMs = Ti, V, Cr, Mn, Co, Ni) presence in mono- and multilayer graphene on the final material geometry, stability, electrical and magnetic properties, and quantum capacitance was systematically investigated using density functional theory (DFT) calculations. The simultaneous presence of dopants and vacancies is more effective than doping alone in enlarging the quantum capacitance of graphene. Incorporation of N, P, and S co-dopants and TMs -dopants significantly improved the quantum capacitance and surface charge storage of graphene. The co-doping of Ti and N/P/S systems are the most outstanding, with the highest quantum capacitance of 239.84 μF/cm2. However, due to the interaction between layers, the quantum capacitance of multilayered co-doped graphene is lower than the capacitance of similarly-doped monolayered graphene. The results demonstrated in this work provide insights on the effective approach of the quantum capacitance enhancement of graphene-based supercapacitor.

Process Chain Optimization for SWCNT/Epoxy Nanocomposite Parts with Improved Electrical Properties

Electrically conductive nanocomposites present opportunities to replace metals in several applications. Usually, the electrical properties emerging from conductive particles and the resulting bulk values depend on the micro/nano scale morphology of the particle network formed during processing. The final electrical properties are therefore highly process dependent. In this study, the electrical resistivity of composites made from single-walled carbon nanotubes in epoxy was investigated. Three approaches along the processing chain were investigated to reduce the electrical resistivity of nanocomposites-the dispersion strategy in a three-roll mill, the curing temperature, and the application of electric fields during curing. It was found that a progressive increase in the shear forces during dispersion leads to a more than 50% reduction in the electrical resistivities. Higher curing temperatures of the nanocomposite resin also lead to a decrease of around 50% in resistivity. Furthermore, a scalable resin transfer molding set-up with gold-coated electrodes was developed and tested with different mold release agents. It has been shown that curing the material under electric fields leads to an electrical resistivity approximately an order of magnitude lower, and that the properties of the mold release agent also influence the final resistivity of different samples in the same batch.

Intra-Cycle Elastic Nonlinearity of Nitrogen-Doped Carbon Nanotube/Polymer Nanocomposites under Medium Amplitude Oscillatory Shear (MAOS) Flow.

This study seeks to unravel the effect of carbon nanotube’s physical and chemical features on the final electrical and rheological properties of polymer nanocomposites thereof. Nitrogen-doped carbon nanotubes (N-CNTs) were synthesized over two different types of catalysts, i.e., Fe and Ni, employing chemical vapor deposition. Utilizing this technique, we were able to synthesize N-CNTs with significantly different structures. As a result, remarkable differences in the network structure of the nanotubes were observed upon mixing the N-CNTs in a polyvinylidene fluoride (PVDF) matrix, which, in turn, led to drastically different electrical and rheological properties. For instance, no enhancement in the electrical conductivity of poorly-dispersed (N-CNT)Ni/PVDF samples was observed even at high nanotube concentrations, whereas (N-CNT)Fe/PVDF nanocomposites exhibited an insulative behavior at 1.0 wt%, a semi-conductive behavior at 2.0 wt%, and a conductive behavior at 2.7 wt%. In terms of rheology, the most substantial differences in the viscoelastic behavior of the systems were distinguishable in the medium amplitude oscillatory shear (MAOS) region. The stress decomposition method combined with the evaluation of the elastic and viscous third-order Chebyshev coefficients revealed a strong intra-cycle elastic nonlinearity in the MAOS region for the poorly-dispersed systems in small frequencies; however, the well-dispersed systems showed no intra-cycle nonlinearity in the MAOS region. It was shown that the MAOS elastic nonlinearity of poorly-dispersed systems stems from the confinement of N-CNT domains between the rheometer’s plates for small gap sizes comparable with the size of the agglomerates. Moreover, the intra-cycle elastic nonlinearity of poorly-dispersed systems is frequency-dependent and vanished at higher frequencies. The correlation between the microstructure and viscoelastic properties under large shear deformations provides further guidance for the fabrication of high-performance 3D-printed electrically conductive nanocomposites with precisely controllable final properties for engineering applications.

Self-Organized In-Depth Gradients in Highly Ti-Doped ZnO Films: Thermal Versus MW Plasma Annealing

Highly Ti-doped ZnO films have been produced by a spin-casting sol-gel process. The spin-casted films show high in plane homogeneity and optical quality. However, when inspected in depth, the surface composition is Ti rich. We show that two possible annealing processes can be considered depending on the properties to exploit. To promote in-depth homogenization, thermal annealing processes have been applied. Meanwhile, the gradients can be exacerbated, thanks to a non-negligible surface sputtering, by applying microwave (MW) plasma treatments with Ar discharges at different pressures. The microstructural properties of the differently processed films have been obtained prior to a study by grazing incidence X-ray fluorescence (GI-XRF) spectroscopy, which reveals the in-depth composition trends induced by the two alternative annealing procedures. The final wetting, electrical and optical properties of the films are described in accordance with the Ti distribution pattern revealed by GI-XRF. The study underlines for the first time how MW plasma annealing processes can be used to exacerbate self-induced atomic gradients in sol-gel films with potential implications in catalytic and biomedical applications.

Electrical and Chemical Properties of Graphene over Composite Materials: A Technical Review

Graphene is a material that has superior mechanical, electrical, and thermal properties. It has drawn the attention of many scientific researchers for this purpose. In this paper, three different types of fillers, GNPs, MWCNTs and EG reinforced epoxy nanocomposites were mainly studied. Different shear mixing speeds and shear mixing times were considered during the study of the nanocomposites with 0.1 wt% loading of the fillers. The effects of various types of fillers and different shear mixing speeds and durations on mechanical and electrical properties of the final composites were examined. The GNPs-reinforced epoxy nanocomposite was the only one that showed a 13% improvement in elastic modulus as compared to pure epoxy when the shear mixing conditions were 3000 rpm for 2 hours. The research also studied the effects of different loadings of GNPs and the addition of acetone as a solvent on the final mechanical, electrical and thermal properties of the composites (with the fixed shear mixing speed and time). The tensile strength of the composites reduced drastically when the loading of GNPs increased while the elastic modulus shows some increase with the growth in GNP loading. The study found that GNPs reinforced composites did not show the percolation threshold even with 5 wt% (with the ratio to the weight of epoxy) loading of the GNPs. The GNPs-reinforced epoxy composites showed an 116% improvement in the thermal conductivity as compared to the pure epoxy samples when the GNPs loading was 5 wt%. The results from the studied literatures also showed that the samples prepared with the addition of acetone had higher thermal diffusivity than the samples prepared without acetone.

Variation of Vanadium Incorporation in Semi-Insulating SiC Single Crystals Grown by PVT Method

Two SiC crystals were grown using SiC source powder with different level of purity and then the effect of the purity of SiC source materials on the final electrical properties has been systematically observed. Furthermore, the variation of vanadium amount according to the growth direction of vanadium doped semi-insulated SiC single crystals has been investigated. The quality of SiC crystal grown using SiC source powder with higher purity was definitely better than SiC crystal with lower purity. SiC crystals having an average resistivity value of about 1×1010 Ωcm were successfully obtained. In the result of COREMA measurement, the use of high purity SiC powder was revealed to obtain wafers with better uniformity in resistivity value.

Polymorphism Control of Layered MoTe2 through Two-Dimensional Solid-Phase Crystallization

Two-dimensional (2D) molybdenum ditelluride (MoTe2) exhibits an intriguing polymorphic nature, showing stable semiconducting 2H and metallic 1T′ phases at room temperature. Polymorphism in MoTe2 presents new opportunities in developing phase-change memory, high- performance transistors, and spintronic devices. However, it also poses challenges in synthesizing homogeneous MoTe2 with a precisely controlled phase. Recently, a new yet simple method using sputtering and 2D solid-phase crystallization (SPC) is proposed for synthesizing high-quality and large-area MoTe2. This study investigates the polymorphism control of MoTe2 synthesis using 2D SPC. The Te/Mo ratio and oxygen content in the as-sputtered films correlate strongly with the final phase and electrical properties of SPC MoTe2. Furthermore, the SPC thermal budget may be exploited for stabilizing a deterministic phase. The comprehensive experiments presented in this work demonstrate the versatile and precise controllability on the MoTe2 phase by using the simple 2D SPC technique.