Dominant Conduction Research Articles

Structural study and temperature dependent relaxation and conduction mechanism of orthorhombic tungsten bronze Ba4La28/3(Zr0.05Ti0.95)18O54 ceramic

In this study, the Ba4La28/3(Zr0.05Ti0.95)18O54 ceramic was prepared using the solid-state technique. The X-ray diffraction technique was used in this study to investigate the Ba/La order in the solid solution Ba4La28/3(Zr0.05Ti0.95)18O54. We have developed a structural model, to represent the order within the structure. The formula of model [Ba4−a□a]A2[La8+2b3□2−2b3]A1,A1′(Zr0.05Ti0.95)18O54 is described as perovskite layers with a thickness of 3 octahedral parallel to the xOz plane. Scanning electron microscopy (SEM) showed that Ba4La28/3(Zr0.05Ti0.95)18O54 ceramic exhibits a typical columnar grain with a heterogeneous distribution over the entire surface. Complex impedance spectroscopy was used to analyze the dielectric and electrical properties of Ba4La28/3(Zr0.05Ti0.95)18O54 materials over a frequency range of 10 Hz to 1 MHz and a temperature range of 350°C to 400°C. An appropriate equivalent electrical circuit was also used to investigate the contributions of grains and grain boundaries. The AC-conductivity data was analyzed using Jonscher's universal power law. The thermal behavior of the exponent parameter "s" indicates that the dominant conduction mechanism in our compound is the non-overlapping small polaron tunneling (NSPT) model. The activation energies calculated from the conduction and relaxation mechanisms are nearly identical for the Ba4La28/3(Zr0.05Ti0.95)18O54 ceramic.

Ba2NiMoO6-δ as a potential electrode for protonic ceramic electrochemical cells

A novel layered double perovskite-based electrode of composition Ba2NiMoO6-δ (BNMO) is proposed for application in Protonic Ceramic Electrochemical Cells (PCECs). Structural characterization by X-ray diffraction (XRD) revealed good chemical compatibility with a BaCe0.7Zr0.1Y0.2O3-δ (BCZY712) electrolyte and phase stability in oxidizing atmospheres. In this study, symmetrical cells of both the pure BNMO electrode and a composite electrode with 50 vol% of BCZY712 material were prepared by screen printing and sintering in air at 950 °C. Microstructural characterization by Scanning Electron Microscopy (SEM) showed good adhesion of the electrode films with the substrate, while Energy-dispersive Spectroscopy (EDS) revealed good percolation of both phases in the case of the composite electrode. Electrochemical studies made by Electrochemical Impedance Spectroscopy (EIS) on the pure BNMO electrode demonstrated that the total polarization resistance was lower in wet conditions in the case of N2 atmospheres, corroborating a potential protonic contribution, while in O2 atmospheres this term was similar between wet and dry conditions, due to dominant p-type electronic conductivity. Conversely, performance was aggravated by the addition of the BCZY712 composite phase; a result clarified to be due to an insufficient level of electronic conductivity in the composite electrode. To the best of our knowledge this is the first study of BNMO for proton conducting applications, providing important information on preparation, compatibility and electrochemical performance, as required for its further optimization.

The prevalence of permanent pacemaker implantation after open-heart surgeries; eight years of experience in Tehran heart center

BackgroundWe aimed to evaluate the prevalence of permanent pacemaker implantation (PPI) among open-heart surgery patients.MethodsWe reviewed data from 23 461 patients undergoing open-heart surgeries between 2009 and 2016 in our heart center in Iran. A total of 18 070 patients (77%) had coronary artery bypass grafting (CABG), 3 598 (15.3%) valvular surgeries, and 1 793 (7.6%) congenital repair procedures. Finally, 125 patients who received PPI following open-heart surgeries were enrolled in our study. We defined the demographic and clinical characteristics of all these patients.ResultsPPI was required in 125 (0.53%) patients with an average age of 58 ± 15.3 years. The average hospitalization time after surgery and waiting time for PPI were 19.7 ± 10.2 and 11.4 ± 6.5 days, respectively. Atrial fibrillation was the dominant pre-operative cardiac conduction abnormality (29.6%). Also, the primary indication for PPI was complete heart block in 72 patients (57.6%). Patients in the CABG group were significantly older (P = 0.002) and were more likely to be male (P = 0.030). The valvular group longer bypass and cross-clamp times and had more left atrial abnormalities. In addition, the congenital defect group was younger and had longer ICU stay times.ConclusionsBased on our study findings, PPI was required in 0.53% of patients following open-heart surgery due to damage to the cardiac conduction system. The current study paves the way for future investigations to identify possible predictors of PPI in patients undergoing open-heart surgeries.

Transport Properties of Intergrowth Structures Ba5In2Al2ZrO13 and Ba7In6Al2O19

The development of solid oxide fuel cells operating at medium temperatures (500–700 °C and even lower) requires the search for proton conductors based on complex oxides that would have a wide range of required properties. This task stimulates the search for new promising phases with proton conductivity. The new hexagonal perovskite-related compound Ba7In6Al2O19 was synthesized by the solid-state method. The phase was characterized by powder X-ray diffraction, thermogravimetric analysis, FT-IR spectroscopy, and impedance spectroscopy (in a wide range of temperatures, and partial pressures of oxygen at various atmospheric humidities). The investigated phase had a hexagonal structure with a space group of P63/mmc; the lattice parameters for Ba7In6Al2O19 are a = 5.921(2) Å, c = 37.717(4) Å. The phase is capable of reversible hydration and incorporates up to 0.15 mol H2O. IR-data confirmed that protons in the hydrated compound are presented in the form of OH–-groups. Electrical conductivity data showed that the sample exhibited dominant oxygen-ion conductivity below 500 °C in dry air and dominant proton conductivity below 600 °C in wet air.

Impact of the split-off band on the tunneling current at metal/heavily-doped p-type SiC Schottky interfaces

Ni/p-type SiC Schottky barrier diodes with various acceptor densities (N A = 5 × 1015 to 3 × 1019 cm−3) are fabricated and the measured current–voltage characteristics are analyzed by numerical calculation of tunneling current. The tunneling current is calculated taking account of multiple valence bands. It is revealed that tunneling of holes in the split-off band, which has a light effective mass (0.21m 0), is the dominant conduction mechanism at metal/heavily-doped p-type SiC Schottky interfaces.

Polyimide-Derived Supramolecular Systems Containing Various Amounts of Azochromophore for Optical Storage Uses.

The progress of digital technologies demands more speed and larger storage capacity. Optical storage systems have the advantage of being cheap, fast and capacious. This article explores the potential use of polyimide-based films as a recording medium for optical storage devices. The materials were designed through a host-guest approach that involves a cyano-containing polyimide precursor and an azochromophore combined in the following ratios: 1:0.25, 1:0.5, 1:0.75 and 1:1. After thermal treatment up to 200 °C, polyimide systems were formed with supramolecular structures constructed via hydrogen bonding as shown by molecular modeling and FTIR at around 3350 cm-1. The aspects arising from the variation of the azo-dye content in the polyimide samples and their impact on the vitrification temperature, colorimetric features, refractive index, band gap, non-linear optical susceptibility and birefringence were investigated for the first time. The thermal analysis indicated a slight decrease in the vitrification temperature from 190.84 °C for the sample without azo dye to 163.91 °C for the film containing the highest leading of azo dye. The morphology images revealed the occurrence of periodic structures in azo-derived materials exposed to a UV laser, which is accentuated by the addition of more azo dye molecules. Optical tests allowed observation of the increase in the dominant wavelength, refractivity and optical conductivity of the samples, produced by the incorporation of azochromophore and laser irradiation. The photo-generated birefringence increased from 0.014 (sample with 1:0.25) to 0.036 (sample with 1:1), which in combination with the created regular topography pattern, is essential for the use of these materials as recording media in optical storage applications.

Nonequilibrium noise as a probe of pair-tunneling transport in the BCS-BEC crossover.

The detection of elementary carriers in transport phenomena is one of the most important keys to understand nontrivial properties of strongly correlated quantum matter. Here, we propose a method to identify the tunneling current carrier in strongly interacting fermions from nonequilibrium noise in the Bardeen-Cooper-Schrieffer to Bose-Einstein condensate crossover. The noise-to-current ratio, the Fano factor, can be a crucial probe for the current carrier. Bringing strongly correlated fermions into contact with a dilute reservoir produces a tunneling current in between. The associated Fano factor increases from one to two as the interaction becomes stronger, reflecting the fact that the dominant conduction channel changes from the quasiparticle tunneling to the pair tunneling.

Elucidating Polaron Dynamics in Cs2AgBiBr6 Double Perovskite.

Lead-free Cs2AgBiBr6 double perovskites have recently emerged as a possible alternative to lead-based halide perovskites for photovoltaic and optoelectronic applications. Significant research efforts have been devoted toward device engineering to enhance the performance of Cs2AgBiBr6 double-perovskite-based photovoltaic and optoelectronic devices; however, less attention has been paid to address their intrinsic photophysical properties. In this work, we have shown that the small polaron formation under photoexcitation and polaron localization limits the carrier dynamics in Cs2AgBiBr6 double halide perovskites. Furthermore, temperature-dependent ac conductivity measurement reveals that single polaron hopping is the dominant conduction mechanism. Ultrafast transient absorption spectroscopy reveals that a deformed lattice under photoexcitation leads to the formation of small polarons which act as self-trapped states (STSs) and lead to the ultrafast trapping of charge carriers. Our findings provide an in-depth understanding of intrinsic limitations of Cs2AgBiBr6 perovskites, which can be applicable for other bismuth-based semiconductors.

Investigation of conduction mechanism and UV light response of vertically grown ZnO nanorods on an interdigitated electrode substrate.

Vertically aligned zinc oxide nanorod (ZnO-NR) growth was achieved through a wet chemical route over a comb-shaped working area of an interdigitated Ag-Pd alloy signal electrode. Field-emission scanning electron microscopy images confirmed the formation of homogeneous ZnO-NRs grown uniformly over the working area. X-ray diffraction revealed single-phase formation of ZnO-NRs, further confirmed by energy-dispersive X-ray spectroscopy analysis. Temperature-dependent impedance and modulus formalisms showed semiconductor-type behavior of ZnO-NRs. Two electro-active regions i.e., grain and grain boundary, were investigated which have activation energy ∼0.11 eV and ∼0.17 eV, respectively. The conduction mechanism was investigated in both regions using temperature-dependent AC conductivity analysis. In the low-frequency dispersion region, the dominant conduction is due to small polarons, which is attributed to the grain boundary response. At the same time, the correlated barrier hopping mechanism is a possible conduction mechanism in the high dispersion region attributed to the bulk/grain response. Moreover, substantial photoconductivity under UV light illumination was achieved which can be attributed to the high surface-to-volume ratio of zinc oxide nanorods as they provide high density of trap states which causes an increase in the carrier injection and movement leading to persistent photoconductivity. This photoconductivity was also facilitated by the frequency sweep applied to the sample which suggests the investigated ZnO nanorods based IDE devices can be useful for the application of efficient UV detectors. Experimental values of field lowering coefficient (βexp) matched well with the theoretical value of βS which suggests that the possible operating conduction mechanism in ZnO nanorods is Schottky type. I-V characteristics showed that the significantly high photoconductivity of ZnO-NRs as a result of UV light illumination is owing to the increase in number of free charge carriers as a result of generation of electron-hole pairs by absorption of UV light photons.

Electronic properties of single-crystalline Fe4O5.

We synthesized single and polycrystals of iron oxide with an unconventional Fe4O5 stoichiometry under high-pressure high-temperature (HP-HT) conditions. The crystals of Fe4O5 had a CaFe3O5-type structure composed of linear chains of iron with octahedral and trigonal-prismatic oxygen coordinations. We investigated the electronic properties of this mixed-valence oxide using several experimental techniques, including measurements of electrical resistivity, the Hall effect, magnetoresistance, and thermoelectric power (Seebeck coefficient), X-ray absorption near edge spectroscopy (XANES), reflectance and absorption spectroscopy, and single-crystal X-ray diffraction. Under ambient conditions, the single crystals of Fe4O5 demonstrated a semimetal electrical conductivity with nearly equal partial contributions of electrons and holes (σn ≈ σp), in line with the nominal average oxidation state of iron as Fe2.5+. This finding suggests that both the octahedral and trigonal-prismatic iron cations contribute to the electrical conductivity of Fe4O5via an Fe2+/Fe3+ polaron hopping mechanism. A moderate deterioration of crystal quality shifted the dominant electrical conductivity to n-type and considerably worsened the conductivity. Thus, alike magnetite, Fe4O5 with equal numbers of Fe2+ and Fe3+ ions can serve as a prospective model for other mixed-valence transition-metal oxides. In particular, it could help in the understanding of the electronic properties of other recently discovered mixed-valence iron oxides with unconventional stoichiometries, many of which are not recoverable to ambient conditions; it can also help in designing novel more complex mixed-valence iron oxides.

Remarkable Reduction in IG with an Explicit Investigation of the Leakage Conduction Mechanisms in a Dual Surface-Modified Al2O3/SiO2 Stack Layer AlGaN/GaN MOS-HEMT.

We demonstrated the performance of an Al2O3/SiO2 stack layer AlGaN/GaN metal-oxide semiconductor (MOS) high-electron-mobility transistor (HEMT) combined with a dual surface treatment that used tetramethylammonium hydroxide (TMAH) and hydrochloric acid (HCl) with post-gate annealing (PGA) modulation at 400 °C for 10 min. A remarkable reduction in the reverse gate leakage current (IG) up to 1.5×10-12 A/mm (@ VG = -12 V) was observed in the stack layer MOS-HEMT due to the combined treatment. The performance of the dual surface-treated MOS-HEMT was significantly improved, particularly in terms of hysteresis, gate leakage, and subthreshold characteristics, with optimized gate annealing treatment. In addition, an organized gate leakage conduction mechanism in the AlGaN/GaN MOS-HEMT with the Al2O3/SiO2 stack gate dielectric layer was investigated before and after gate annealing treatment and compared with the conventional Schottky gate. The conduction mechanism in the reverse gate bias was Poole-Frankel emission for the Schottky-gate HEMT and the MOS-HEMT before annealing. The dominant conduction mechanism was ohmic/Poole-Frankel at low/medium forward bias. Meanwhile, gate leakage was governed by the hopping conduction mechanism in the MOS-HEMT without gate annealing modulation at a higher forward bias. After post-gate annealing (PGA) treatment, however, the leakage conduction mechanism was dominated by trap-assisted tunneling at the low to medium forward bias region and by Fowler-Nordheim tunneling at the higher forward bias region. Moreover, a decent product of maximum oscillation frequency and gate length (fmax × LG) was found to reach 27.16 GHz∙µm for the stack layer MOS-HEMT with PGA modulation. The dual surface-treated Al2O3/SiO2 stack layer MOS-HEMT with PGA modulation exhibited decent performance with an IDMAX of 720 mA/mm, a peak extrinsic transconductance (GMMAX) of 120 mS/mm, a threshold voltage (VTH) of -4.8 V, a higher ION/IOFF ratio of approximately 1.2×109, a subthreshold swing of 82 mV/dec, and a cutoff frequency(ft)/maximum frequency of (fmax) of 7.5/13.58 GHz.

Effective role of vacuum annealing in improving structural, optical, and electrical properties of SiO2/Ag/ZnO multilayers deposited by RF sputtering for optoelectronic applications

Transparent conductive thin films require multilayer coatings involving metals and dielectrics with high refractive indices. Radiofrequency (RF) magnetron sputtering technique was used to accurately fabricate the SiO2/Ag/ZnO multilayers on the corning glass substrates at 298 K to be used in Concentrating Solar Power (CSP) reflectors, solar cell, and photovoltaic applications. This method optimizes coating processes in a uniform, homogeneous manner, resulting in improved optical and electrical properties, thermal endurance, and long-term stability. The technique was used to synthesize highly translucent and conductive multilayers. The structural, optical, and electrical properties as a function of temperature in the range from 25 °C to 450 °C were detailed. The crystallite size (D cry ), lattice microstrain (ε), dislocation density (δ), and crystallites per unit surface area (N) were calculated. The values of (D cry ) increased while the other parameters decreased with increasing temperature. The linear optical parameters were calculated. The optical results demonstrated that temperature had an impact on the studied multilayers’ optical properties. The dielectric constants, the loss factor, the AC electrical conductivity, the exponential factor, and the activation energy for the dominant conductivity mechanism were all calculated using the capacitance and conductance pathways.

Surface and interfacial conduction using gadolinium-doped ceria electrolyte for advanced low temperature 400–500 °C fuel cell

Lowering the operating temperature with enhanced performance and better efficiency is considered a universal R&D bottleneck for the progress of low-temperature (<520 °C) solid oxide fuel cells (SOFCs) or ceramic fuel cells (CFCs) to avail the opportunities of commercialization. Bulk doping is the primary ionic conduction mechanism in traditional electrolyte materials for CFC, mainly influenced by the operating temperature and bulk density, thus resulting in high operational temperature. Herein, we proposed a new mechanism for tunning Ce0.9Gd0.1O2-δ (GDC) electrolyte based on a nanocrystalline structure from surface or grain boundary conduction to interfacial conduction by introducing the carbonates to form the heterostructure, exhibiting an extremely high ionic conductivity of (0.2 S·cm−1) at 520 °C. At first, we noticed that the grain boundary conduction of GDC is causing to enhance the charge carrier leading to establishing surface conduction. We further modify the GDC with carbonates to form the core–shell heterostructure to boost ionic conduction. The constructed cell with core–shell heterostructure has exhibited a remarkable performance of 968 mW/cm2.In contrast, 578 mW/cm2 was achieved from the surface conduction of GDC, and at the same time, we observed immensely low grain-boundary resistance from the impedance analysis. The mechanism of core–shell structure formation has been discussed in detail, and the ionic conduction at the surface and interfaces can be considered the dominant conduction mechanism for GDC electrolytes. This work has explored a new approach by tuning the ionic property from surface to interface to develop advanced CFCs, significantly improving the state-of-art GDC electrolyte via enhancing surface/interface conductions. This may be developed as a more functional approach for advanced energy materials, e.g., battery and electrolysis devices.

Polyimide-based ultraviolet-operated nonvolatile photomemory device

Organic nonvolatile photomemory devices have drawn considerable attention in the field of optical computing. However, most organic nonvolatile photomemory devices use a charge-trap-type architecture that is complex and difficult to miniaturize. This paper proposes a nonvolatile polyimide (PI) resistive photomemory device with a simple metal–PI–metal configuration; its resistance can be altered using pulsed ultraviolet (UV) irradiation and can be maintained at the altered level even after irradiation has ceased. The resistance can also be returned to the initial state by subsequent irradiation with UV light. The memory window is around 7 order of magnitude. Fourier-transform infrared spectroscopy and UV–visible/near-infrared spectroscopy demonstrated that UV irradiation caused a high-energy-gap (Eg) aromatic form of PI to transform into low-Eg quinoid form, prompting the dominant conduction mechanism of the photomemory device to change from hopping conduction to ohmic conduction. A model characterizing the PI-based photomemory device was also developed and is discussed herein.

Boosting visible light driven gas–solid phase photocatalytic reduction of CO2 on BiOCl microspheres by enhanced carrier transportation through lattice structure modification

BiOCl powders with different amounts of thiourea addition (0, 25 mg, 50 mg, 100 mg versus 8 mmol Bi(NO3)3, denoted as BOC, BOC-S1, BOC-S2, BOC-S3) in precursor were prepared by solvothermal method. In this work, thiourea generated modification of lattice structure, stimulating shrinkable Bi-O bond rather than S element doping or composite structure forming. Shrinkable Bi-O bond generated enhanced interaction between [Bi2O2]2+ and adjacent Cl-, causing stronger inner electric field. Shorter Bi-O bond endows valence band(VB) more Cl 3p component, enhancing Cl 3p dominance. With intrinsic Bi 6p dominant conduction band, holes could be transferred to VB on Cl while electrons be transferred to CB on Bi under stronger inner electric field, performing heterojunction like efficient charge separation and transfer. Prominent promotion on CO2 photocatalytic reduction was thus achieved due to improved charge separation and transfer efficiency, where BOC-S2 reach about 5.6 times higher CH4 yield than BOC with CH4 selectivity increasing from 80.673 % (BOC) to 96.473 % (BOC-S2), certifying successful CO2 reduction ability promotion through lattice structure modulation.

Thermal transport properties of IrSbSe

We report a thermal transport study of IrSbSe, which crystallizes in a noncentrosymmetric cubic structure with the $P2_13$ space group and shows a narrow-gap semiconducting behavior. The large discrepancy between the activation energy for conductivity [$E_\rho$ = 128(2) meV] and for thermopower [$E_S$ = 17.7(9) meV] from 200 to 300 K indicates the polaronic transport mechanism. Electrical resistivity varies as $exp(T_0/T)^{1/4}$ and thermopower varies as $T^{1/2}$ at low temperatures, indicating that it evolves into the Mott's variable-range hopping dominant conduction with decreasing temperature. IrSbSe shows relatively low value of thermal conductivity ($\sim$ 1.65 W/K$\cdot$m) and thermopower of about 0.24 mV/K around 100 K, yet poor electrical conductivity. On the other hand, high vacancy defect concentration on both Ir and Sb atomic sites of up to 15\%, suggests high defect tolerance and points to possibility of future improvement of carrier density by chemical substitution or defect optimization.

Study of Co-Doped K2Ti6O13 Lead-Free Ceramic for Positive Temperature Coefficient Thermistor Applications

Cobalt-doped potassium hexa-titanate (Cox:K2Ti6O13 (x = 0.05, 0.10, 0.15 mole%)) ceramics were synthesized by the solid-state reaction method. The XRD patterns confirmed single-phase development in a monoclinic symmetry of various samples, and they were used for different structural calculations of Cox:K2Ti6O13 ceramics. The dielectric constant, tanδ, electrical modulus, and ac conductivity of Co-doped K2Ti6O13 were studied in the temperature range of 100–500 °C. Anomalies were observed in graphs of the dielectric constant versus temperature, showing the transition phase in the studied samples. Dielectric peaks at transition temperature decreased with an increasing frequency, and the peaks shifted toward higher temperatures, illustrating the relaxation of the dielectric materials. The composition with x = 0.10 showed low dielectric loss and a higher dielectric constant and can be utilized for high-temperature dielectric material. Small doping of cobalt improved the ac conductivity of K2Ti6O13 ceramics due to the increase in the spin–phonon interaction and dominant electron hopping conduction; however, the conductivity diminished with substantial doping because of the contraction of the tunnel space and ambushing of conduction electrons. The uniqueness of this study is in the high dielectric optimization of lead-free ceramic Cox:K2Ti6O13 and the discovery of positive temperature coefficients of the resistivity of these ceramic samples.

Mixed Ionic and Electronic Conduction in TeO2-ZnO-V2O5 Glasses towards Good Dielectric Features.

The melt-quenching technique was used to synthesize tellurite glasses of the chemical composition 80TeO2-(20-x) ZnO-xV2O5. X-ray diffraction (XRD) patterns indicate the amorphous nature of the prepared glasses. Raman and FTIR measurements demonstrate a progressive substitution of the Te-O-Te linkages by the Te-O-V bridges and the formation of VO4 and VO5 units by a change of the vanadium coordination due to the higher number of oxygens incorporated by further addition of V2O5. The AC conductivity was investigated in the frequency range of 40 Hz to 107 Hz between 473 K to 573 K. A good coherence of the AC conductivity was found using a model correlating the barrier hopping (CPH) and the dominant conduction process changes from ionic to polaronic with the addition of V2O5. The dielectric constant exhibits high values in the range of lower and medium frequencies. Both variations of the electric modulus and the dielectric loss parameters with frequency and temperature showed a relaxation character mainly assigned to the vanadate phases. The electric modulus displays a non-Debye dielectric dispersion and a relaxation process. The present results open the door to future zinc-tellurite glasses-doped vanadium exploitation as a potential electrolyte-based material for solid-state batteries.

Impact of interfacial engineering on MgO-based resistive switching devices for low-power applications

In this work, the resistive switching characteristics of MgO/Al2O3-based resistive random-access memory (ReRAM) devices have been reported. Analysis shows the change in dominant conduction mechanism from space-charge-limited conduction to Schottky emission owing to the incorporation of an Al2O3 insertion layer. The MgO/Al2O3 bilayer ReRAM devices exhibit lower power operation (50.6% reduction) and better switching uniformity as compared to single-layer devices, depending on the stack configuration. This can be attributed to the lower oxygen vacancy accumulation and filament confinement at the MgO/Al2O3 interface, resulting in a more controllable switching operation. Further X-ray photoelectron spectroscopy (XPS) depth profile analysis of the bilayer device reveals that the switching dynamics are correlated directly with the oxygen vacancy concentrations. These findings indicate the importance of interfacial layer engineering in improving the resistive switching properties of MgO-based memory devices, thus allowing for low-power applications.

Reactive co-sputtering of ternary Au–Ta–O films with tunable electrical resistivity

Heavy-metal-based films with high electrical resistivity are needed for hohlraums for magnetically assisted inertial confinement fusion. Here, we study ternary Au–Ta–O films deposited by reactive direct-current magnetron co-sputtering from elemental Au and Ta targets in an oxygen containing atmosphere. By varying the O content, the electrical resistivity of films can be tuned in a wide range of ∼100–40 000 μΩ cm. With increasing O content, a drastic increase in resistivity occurs at ∼45 at. % of O, separating regimes with two different dominant conduction mechanisms attributed to metallic conduction through the Au–Ta alloy matrix (for ≲45 at. % of O) and tunneling across insulating Ta2O5 layers separating conducting islands (for ≳45 at. % of O). Post-deposition annealing at 300 °C leads to the segregation of Au into ∼50-nm islands, sharply decreasing the resistivity for films with ≳45 at. % of O but not for the metal-like films with lower O content.