Improvement Of Electrical Properties Research Articles

Improvement of electrical and energy harvesting properties of new lead-free BST modified 0.995BNKT–0.005LN ceramics

ABSTRACT New lead-free (1-y)[0.995Bi0.5(Na0.80K0.20)0.5TiO3-0.005LiNbO3]-y[(Ba0.7Sr0.3)TiO3] or (1-y)[0.995BNKT-0.005LN]-y[BST] (where y = 0, 0.01, 0.02, 0.03, 0.04 and 0.05 mol fraction) ceramics were fabricated by a conventional sintering method with two calcination steps. All ceramics sintered at 1125°C for 2 hours showed an optimum relative density of ~98% and a linear shrinkage of ~18%. X-ray diffraction patterns indicated that all ceramics possessed a pure perovskite phase with coexisting rhombohedral and tetragonal structures. Electrical and energy harvesting properties of 0.995BNKT–0.005LN ceramics were improved with 0.03 mol fraction BST addition (d 33 = 287 pC/N, d*33 = 440 pm/V, g33 = 13.40 × 10−3 V/mN and FoM = 3.85 pm2/N). From the observed results, the 0.97[0.995BNKT-0.005LN]-0.03[BST] ceramic is a promising candidate for lead-free piezoelelectric sensor-actuator and energy harvester.

Process temperature-dependent interface quality and Maxwell-Wagner interfacial polarization in atomic layer deposited Al2O3/TiO2 nanolaminates for energy storage applications.

Considering the excellent tunability of electrical and dielectric properties in binary metal oxide based multi-layered nanolaminate structures, a thermal atomic layer deposition system is carefully optimized for the synthesis of device grade Al2O3/TiO2 nanolaminates with well-defined artificial periodicity and distinct interfaces, and the role of process temperature in the structural, interfacial, dielectric and electrical properties is systematically investigated. A marginal increase in interfacial interdiffusion in these nanolaminates, at elevated temperatures, is validated using X-ray reflectivity and secondary ion mass spectrometry studies. With an increase in deposition temperature from 150 to 300 °C, the impedance spectroscopy measurements of these nanolaminates exhibited a monotonic increment in dielectric constant from ∼95 to 186, and a decrement in dielectric loss from ∼0.48 to 0.21, while the current-voltage measurements revealed a subsequent reduction in leakage current density from ∼2.24 × 10-5 to 3.45 × 10-7 A cm-2 at 1 V applied bias and an improvement in nanobattery polarization voltage from 100 mV to 700 mV, respectively. This improvement in dielectric and electrical properties at elevated processing temperature is attributed to the reduction in impurity content along with the significant enhancement in sublayer densities and the conductivity contrast driven Maxwell-Wagner interfacial polarisation. Additionally, the devices fabricated at 300 °C exhibited a higher capacitance density of ∼22.87 fF μm-2, a low equivalent oxide thickness of ∼1.51 nm, and a low leakage current density of ∼10-7 A cm-2 (at 1 V bias), making this nanolaminate a promising material for high-density energy storage applications. These findings highlight the ALD process temperature assisted growth chemistry of Al2O3/TiO2 nanolaminates for superior dielectric performance and multifaceted applications.

Improvement of structural, optical and electrical properties of indium-doped ZnO nanoparticles synthesized by Co-precipitation method

Improvement of structural, optical and electrical properties of indium-doped ZnO nanoparticles synthesized by Co-precipitation method

Significant increase of the photoresponse range and conductivity for a chalcogenide semiconductor by viologen coating through charge transfer.

Widening the photoresponse range while enhancing the electrical properties of semiconductors could reduce the complexity and cost of photodetectors or increase the power conversion efficiency of solar cells. Surface doping through charge transfer with organic species is one of the most effective and widely used approaches to achieve this aim. It usually features easier preparation over other doping methods but is still limited by the low physicochemical stability and high cost of the used organic species or low improvement of electrical properties. This work shows unprecedented surface doping of semiconductors with highly stable, easily obtained, and strong electron-accepting viologen components, realizing the significant improvement of both the photoresponse range and conductivity. Coating the chalcogenide semiconductor KGaS2 with dimethyl viologen dichloride (MV) yields a charge-transfer complex (CTC) on the surface, which broadens the photoresponse range by nearly 300 nm and improves the conductivity by 5 orders of magnitude. The latter value surpasses all records obtained by surface doping through charge transfer with organic species.

Electrical and Gas Sensor Properties of Nb(V) Doped Nanocrystalline β-Ga2O3.

A flame spray pyrolysis (FSP) technique was applied to obtain pure and Nb(V)-doped nanocrystalline β-Ga2O3, which were further studied as gas sensor materials. The obtained samples were characterized with XRD, XPS, TEM, Raman spectroscopy and BET method. Formation of GaNbO4 phase is observed at high annealing temperatures. Transition of Ga(III) into Ga(I) state during Nb(V) doping prevents donor charge carriers generation and hinders considerable improvement of electrical and gas sensor properties of β-Ga2O3. Superior gas sensor performance of obtained ultrafine materials at lower operating temperatures compared to previously reported thin film Ga2O3 materials is shown.

Simultaneous improvement of leakage, electric, and magneto-dielectric properties due to the reduction in grain size

(1-x)Ga0.8Fe1.2O3 – xGd3Ga5O12 composites have been studied for different concentrations (0.0 ≤ x ≤ 0.2) at two different annealing temperatures (1300 °C and 1350 °C). Increasing concentration of Gd3Ga5O12 (GGG) is observed to reduce grain size from 2.8 μm for x = 0.0 to 903 nm for x = 0.2, annealed at 1300 °C. Annealing at 1350 °C keeping the concentration same at x = 0.2, further reduces the grain size to ∼ 669 nm. Consistent with the grain size reduction, a reduction of leakage current by five orders of magnitude has been achieved. Using high resistive GGG enhanced the dielectric constant of all the composites along with a significant reduction in conductivity. An enhancement of the magnetodielectric factor observed in all the composites indicates improved coupling between magnetic and electrical parameters.

Parasitic behavior of different V/III ratios on the properties of InGaN/GaN heterostructures by MOCVD technique

In this study, InGaN/GaN heterostructures were grown on a c-plane flat sapphire substrate (FSS) by using the metalorganic chemical vapor deposition (MOCVD) technique. The flow rates of the ammonia gas varied from 9 SLM to 24 SLM for the growth of InGaN thin film, which was equivalent to the V/III ratio of 6211–16562. Results indicated that a higher V/III ratio promotes parasitic behavior by hydrogen dissociated from ammonia. The parasitic behavior from hydrogen species etches the InN away from the growing surface and transforms the growth morphology from 3D islands to 2D growth mode. A slight reduction in indium composition was observed when increasing the V/III ratio. Next, more stable bandgap energy was observed for the InGaN thin films grown at higher V/III ratios. Improvements in electrical properties in terms of electron mobility and sheet resistance were observed at a higher V/III ratio which is associated with the improvement of crystalline quality and less defect density at a higher V/III ratio. The correlation of strain and carrier density of the thin films was further discussed. It was concluded that the growth of high crystalline quality and thick InGaN thin film was possible for solar cell applications at higher V/III ratio growth conditions.

Improvement of Electrical Properties of Silver Nanowires Transparent Conductive by Metal Oxide Nanoparticles Modification

At present, silver nanowire transparent conductive films (AgNWs-TCFs) still have problems such as high resistance of AgNWs network nodes, uneven distribution of resistance and poor electrical performance stability, which restrict their commercial application. Different from chemical modification, in this paper, a method of modifying AgNWs-TCFs with metal oxide nanoparticles (MONPs) is proposed, that is, ZnO, SnO2, Al2O3 and TiO2 etc., four transparent metal oxides are used as targets respectively in a magnetron sputtering process, modifying the silver nanowire network wire–wire junctions and silver nanowire in AgNWs-TCFs using active MONPs generated by magnetron sputtering. A series of AgNWs@MONPs for the AgNWs@ZnO-TCFs, AgNWs@SnO2-TCFs, AgNWs@Al2O3-TCFs and AgNWs@TiO2-TCFs were obtained. A significant decrease in the resistance of AgNWs-TCFs through the modification of MONPs was shown. Respectively, the reduction of resistance was 75.6%, 70.4%, 53.2% and 59.8% for AgNWs@ZnO-TCFs, AgNWs@SnO2-TCFs, AgNWs@Al2O3-TCFs and AgNWs@TiO2-TCFs. Correspondingly, its non-uniformity of resistance distribution was 12.5% (18.2% before), 10.0% (17.1% before), 10.1% (24.3% before) and 10.6% (13.4% before), respectively, which markedly improved the uniformity of electrical property. Respectively, their failure voltages reach 16, 16, 15 and 16 (V), so accordingly, the electrical stability is considerably enhanced. In addition, the uniformity of temperature distribution was also significantly optimized with its temperature non-uniformity of 10.4%, 8.7%, 10.3% and 9.6%, respectively. Contrast that with AgNWs@MONPs, and the failure voltages and temperature non-uniformity of AgNWs-TCFs are 12 V and 40.6%.

High Thermoelectric Performance of p-Type Bi0.4Sb1.6Te3+x Synthesized by Plasma-Assisted Ball Milling.

The exploration of new synthesis methods is important for the improvement of the thermoelectric property of a material for the different mechanisms of microstructure fabrication, surface activity modulation, and particle refinement. Herein, we prepared p-Bi2Te3 bulk materials by a simple synthesis method of the plasma-assisted ball milling, which yielded finer nanopowders, higher texture of in-plane direction, and higher efficiency compared to the traditional ball milling, favoring the simultaneous improvement of electrical and thermal properties. When combined with the Te liquid sintering, nano-/microscale hierarchical pores were fabricated and the carrier mobility was also increased, which together resulted in the low lattice thermal conductivity of 0.52 W·m-1·K-1 and the high power factor of 43.4 μW·cm-1·K-2 at 300 K, as well as the ranking ahead zT of 1.4@375 K. Thus, this work demonstrated the advantages of plasma-assisted ball milling in highly efficient synthesis of p-type Bi2Te3 with promising thermoelectric performance, which can also be utilized to prepare other thermoelectric materials.

Multiple stability of electrical properties for oxides-modified (K,Na)NbO3-based ceramics

Lead-free potassium sodium niobate (KNN) ceramics have become crucial advanced functional materials with conspicuous performance. Although continuous improvements of electrical properties were achieved via various strategies these years, the poor stability leads to the bottleneck for application. Herein, the stability of electrical properties under different conditions (i. e. electric field, frequency and temperature) were emphasized on in KNN-based ceramics with addition of oxides based on the availability for optimizing properties. With addition of Fe2O3, high ferroelectric, piezoelectric and dielectric properties remain due to the maintained rhombohedral-orthorhombic-tetragonal (R-O-T) phase boundary at room temperature and little changed Curie temperature (TC), while deterioration happens with excess Fe2O3 attributing to the pinning effect from replacement of Fe3+ in crystal lattice. Furthermore, the elevated beginning electric field for stable ferroelectricity and negative strain under increasing electric field are gained with elevating Fe2O3 along with little changed piezoelectricity. Stable strain maintains with increasing frequencies when Fe2O3 content changes, as an enhancement are discovered for residual polarization (Pr) and coercive electric field (EC) at 0.5–1 Hz for x ≥ 1.0%. Moreover, improved temperature stability for piezoelectricity and strain as well as remained high ferroelectricity is presented with increasing Fe2O3, originating from the increasing diffusion behavior of R-O-T phase boundary and non-declined TC, respectively. Thus, this work provides an effectively strategy to optimize the stability of electrical properties for application of KNN-based materials.

A new approach to simultaneously reducing, nitrogen doping and noble metal coating of graphene oxide via active-screen plasma

Graphene is widely used for various applications, especially after nitrogen doping and incorporation with metal nanoparticles. Herein, a simultaneous approach to reducing, nitrogen doping and noble metals coating of graphene oxide (GO) is reported using an advanced active-screen plasma (ASP) technique. With a noble metal plate added as an extra lid of active screen cage, the corresponding noble metal, mainly or fully in pure metal state, depending on the noble metal type, as well as a minority of Fe and Cr, is deposited on GO with simultaneous reduction and nitrogen doping. The ASP treated GO exhibits varying levels of improvement in electrical property depending on the type of noble metal nanoparticles hybridized with. Specifically, ASP treated GO incorporated with Pt or Au revealed 2–4 orders of magnitude of improvement in electrical property.

Improvement of Electrical Properties of Sn-Doped Indium Tin Oxide by In-Situ Annealing

Improvement of Electrical Properties of Sn-Doped Indium Tin Oxide by In-Situ Annealing

Hybrid Bisphenol A non-isocyanate polyurethane composite with Mica powder: A new insulating material

Non-isocyanate polyurethanes (NIPU) or hydroxyurethanes from CO2 sourced monomers were prepared via a non-toxic route, which avoided the toxic isocyanate utilization with an excellent conversion ratio of cyclic carbonate, higher than 95%. The hybrid NIPU was prepared in the presence of aminosilylated-mica, used as reinforcement to improve mechanical properties, besides keeping the charge dissipation. The improvement of mechanical, thermal and electrical properties by silylated mica is attributed to higher crosslinking density in the organosilicate network. (attributed to the interfacial urethane linkage between the -NH2 on the surface of the mica and the cyclocarbonates). It has been demonstrated the feasibility to produce candidate materials for replacing epoxy-mica paper hybrid system by an alternative CO2 derived non-isocyanate hydroxyurethane-mica powder system. This system holds two advantages: CO2 long-term capture and a more simplified hybrid formation, since no vacuum pressure impregnation (VPI) is necessary, does resulting on lower energy consumption.

Fabrication and Conductivity of Graphite Nanosheet/Nylon 610 Nanocomposites Using Graphite Nanosheets Treated with Supercritical Water at Different Temperatures.

In this study, water at high temperatures (150, 175, 200 °C) and in a vacuum state (-0.1 MPa) was applied to graphite nanosheets to enhance surface activity to promote the formation of oxygen-containing functional groups through supercritical water treatment. Nylon 610 nanocomposites (with treated or untreated nanosheets as nanofillers) were then synthesized using interfacial polymerization. X-ray diffraction (XRD) analysis showed that the water treatment did not alter the crystal structure of the carbon nanosheets. Additionally, Fourier transform infrared spectroscopy (FTIR) analysis showed the presence of amide peaks within the nanocomposites, indicating the presence of hydrogen bonding between the nanosheets and the polymer matrix. The intensity of the amide peaks was higher for nanocomposites combined with treated nanosheets than untreated ones. This hydrogen bonding is beneficial to the conductivity of the nanocomposites. The conductivity of treated nanosheets/nylon nanocomposites generally decreased with increasing wt%, while the conductivity of untreated nanosheets/nylon nanocomposites increased with increasing wt%. The decrementing of conductivity in the treated nanosheets/nylon nanocomposites is due to the agglomeration of the nanosheets within the composite. This is in in line with scanning electron microscopy (SEM) results which showed that at higher wt%, the aggregation condition tended to occur. The highest conductivity obtained is 0.004135 S/m, as compared to the conductivity of neat nylon 610, which is 10-14 S/m. This improvement in electrical properties can be attributed to the intact structure of the nanosheets and the interaction between the nanofillers and the nylon 610 matrix. The optimum nylon 610 nanocomposite synthesized was the one incorporated with 0.5 wt% graphite nanosheets treated at 200 °C and -0.1 MPa, which possess the highest conductivity.

Thermal neutrons effect on improvement of electrical properties at CIGS thin film derived by sol-gel dip coating technique

The thermal neutron effect on the copper indium gallium (di)selenide thin film synthesized by the sol-gel dip-coating technique has explained the novel use of this film under extreme conditions (such as neutron irradiation fields). The thin film samples were treated by using the reactor neutrons to obtain the optimum neutron treatment for the determination of the variations in the structural characteristics. The gamma filter system has provided the evaluation of the high thermal neutron flux effect on the thin film samples by using the tangential beam tube of ITU TRIGA Mark–II reactor. The influence of the neutron effect on the electrical and optical features was explained by the rise of selenium amount in the thin film. The neutron-treated thin film samples (at 50 at. % Se) had a significant effect on the lowest electrical resistivity depending on the increase of the film density. The equivalent gamma dose of the neutron-treated thin film was determined as a 0.024 Gy dose level for neutron irradiation. The neutron treatment was significant to evaluate the decrease in the sheet resistivity of the thin film at this dose level. The neutron dose has led to a slight decrease in the optical band gap as the result of the thermal and epithermal neutrons' effects on the thin film.

Impact polypropylene copolymers containing multifold H-shape long-chain-branching structures: Effect on dielectric and electrical properties

This paper discusses the dielectric and electrical properties of novel impact polypropylene copolymers containing multifold H-shape long-chain-branching structures (LCB-IPCs), i.e. PP-H-PP, PP-H-EPC (EP copolymer), and EPC-H-EPC. Dielectric spectroscopy study indicates that the LCB structures tend to decrease the dielectric constant of IPC increased from that of net PP due to EPC alloying. Electron trap distribution study reveals that the LCB structures have the effect of deepening the electron traps of IPC shallowed from those of net PP by EPC alloying. Similar effect of LCB structures extends to electrical breakdown properties. Compared to LCB structure-free pristine IPC, which is reduced on electrical breakdown strength under both AC and DC electrical voltage as compared to net PP, LCB-IPCs are on the contrary measured continuously increased breakdown strengths in both occasions. The improvements in electrical properties of LCB-IPCs are mainly attributed to the crystalline morphology alterations, i.e. decreasing in spherulite size and increasing in spherilite density, due to PP-H-PP structure exercising effective nucleation for PP crystallization.

(Invited, Digital Presentation) Advanced Passivating Contacts for Silicon Photovoltaics

Carrier selective passivating contacts, which provide dual functions of surface defect passivation and extracting one type of charge carriers, is a key enabler for high efficiency Si solar cells. Here we introduce two passivating contact materials developed in our lab: one is the hydrogenated nanocrystalline silicon (nc-Si:H) and the other is the metal-oxide (non-silicon) material. For the nc-Si:H, it is demonstrated that the use of the (p)nc-Si:H/(i)a-Si:H stack instead of the conventional (p)a-Si:H/(i)a-Si:H in silicon heterojunction solar cells provides not only a mitigation of the parasitic absorption loss but also improvements in passivation and electrical contact properties. This results in an efficiency increase by 0.3-0.6% absolute compared to our reference cell, and a best cell efficiency of 23.5%. For metal-oxide material, we have developed an atomic-layer-deposited titanium oxide (TiOx) that functions as an efficient and transparent hole-selective passivating contact without using buffer layer, leading to the proof-of-concept solar cells with efficiencies above 20%. An example of applying the developed contact material as a recombination junction layer of the perovskite/Si tandem solar cell will be presented.

The development and characterization of carbon nanofiber/polylactic acid filament for additively manufactured piezoresistive sensors

In this work, an investigation into the effects of manufacturing parameters on carbon nanofiber (CNF)/polylactic acid (PLA) filament for fused filament fabrication (FFF) additive manufacturing (AM)-produced strain sensors was conducted. A design of experiments (DOE) approach was undertaken to explore the impact of CNF weight fraction, extrusion temperature, and number of extrusions on sensor performance. The initial extrusion combined pulverized PLA material and CNFs via a dry melt-mixing process. Through the DOE process, it was found that extruding CNF/PLA material at 185 °C for two total extrusions yielded material with dramatic improvements in electrical properties compared to unmodified material. Using the optimal manufacturing procedure, piezoresistive dog-bone shaped sensors were manufactured via FFF with 5.0, 7.5, and 10.0 wt % CNF/PLA filament and three different sizes. Piezoresistive testing under monotonic and cyclic loading conditions revealed strong and repeatable behavior from the piezoresistive AM sensors produced with 7.5 and 10.0 wt % CNFs. In general, 7.5 wt % CNF/PLA sensors showed greater strain sensitivity than 10.0 wt % CNF/PLA sensors for monotonic loading. Additionally, sensor size appeared to contribute significantly to the performance of 7.5 wt % CNF/PLA sensors. However, the 10.0 wt % CNF/PLA sensors exhibited greater repeatability in their piezoresistive response, and sensor size had much less impact on strain sensing performance. The printed sensors also exhibited a strong response under cyclic loading, however, variability in their piezoresistive response was significantly higher than under monotonic loading conditions. The results of this study are an important step towards the realization of low-cost, easily produced, and highly customizable strain sensors produced via FFF technology.

Cu2Te Incorporation-Induced High Average Thermoelectric Performance in p-Type Bi2Te3 Alloys.

p-Type (Bi, Sb)2Te3 alloys are attractive materials for near-room-temperature thermoelectric applications due to their high atomic masses and large spin-orbit interactions. However, their narrow band gaps originating from spin-orbit interactions lead to bipolar excitation, thereby limiting average thermoelectrics within a local temperature region (300-400 K). Here, we introduce Cu2Te into the Bi0.3Sb1.7Te3 (BST) lattice to implement high thermoelectrics over a wide temperature range. The carrier concentration is synergistically modulated via Cu substitution and the evolution of intrinsic point defects (antisites and vacancies). Furthermore, the chain effect caused by Cu2Te incorporation in BST is reflected in the improvement of the weighted mobility μW, thereby enhancing the power factor in the whole temperature range. Extrinsic and intrinsic defects due to the incorporation of Cu2Te lead to a significant reduction in the lattice thermal conductivity κL, which is further demonstrated by Raman spectroscopy. Combining κL and μW, the quantity factor B increases from 0.5 to 1 with increasing Cu2Te content due to not only the reduction of κL but also a significant improvement in electrical properties. Eventually, a peak figure of merit (zT) of ∼1.15 at 423 K is achieved in BST-Cu2Te samples, and an average figure of merit (zTave) of ∼1.12 (350-500 K) surpasses other excellent p-type Bi2Te3-based thermoelectrics. Such a synergistic effect can facilitate near-room-temperature thermoelectric applications of Bi2Te3-based alloys and provide chances for the technology space in thermoelectrics.

High Linearity Synaptic Devices Using Ar Plasma Treatment on HfO2 Thin Film with Non-Identical Pulse Waveforms.

We enhanced the device uniformity for reliable memory performances by increasing the device surface roughness by exposing the HfO2 thin film surface to argon (Ar) plasma. The results showed significant improvements in electrical and synaptic properties, including memory window, linearity, pattern recognition accuracy, and synaptic weight modulations. Furthermore, we proposed a non-identical pulse waveform for further improvement in linearity accuracy. From the simulation results, the Ar plasma processing device using the designed waveform as the input signals significantly improved the off-chip training and inference accuracy, achieving 96.3% training accuracy and 97.1% inference accuracy in only 10 training cycles.