Structural,optical, and electrical properties of conducting p-type transparent Cu–Cr–O thin films

Cu–Cr–O films were prepared by DC magnetron co-sputtering using Cu and Cr targets on quartz substrates. The films were then annealed at temperatures ranging from 400 °C to 900 °C for 2 h under a controlled Ar atmosphere. The as-deposited and 400 °C-annealed films were amorphous, semi-transparent, and insulated. After annealing at 500 °C, the Cu–Cr–O films contained a mixture of monoclinic CuO and spinel CuCr₂O₄ phases. Annealing at 600 °C led to the formation of delafossite CuCrO₂ phases. When the annealing was further increased to temperatures above 700 °C, the films exhibited a pure delafossite CuCrO₂ phase. The crystallinity and grain size also increased with the annealing temperature. The formation of the delafossite CuCrO₂ phase during post-annealing processing was in good agreement with thermodynamics. The optimum conductivity and transparency were achieved for the film annealed at approximately 700 °C with a figure of merit of 1.51×10⁻⁸ Ω⁻¹ (i.e., electrical resistivity of up to 5.13 Ω-cm and visible light transmittance of up to 58.3%). The lower formation temperature and superior properties of CuCrO₂ found in this study indicated the higher potential of this material for practical applications compared to CuAlO₂.     

Orientation control and electrical properties of PZT/LNO capacitor through chemical solution deposition

This paper describes the deposition of PZT/lanthanum nickel oxide (LNO) electrode thin-film capacitor on a Si(1 0 0) substrate with a chemical solution deposition (CSD). Highly (1 0 0)-oriented LNO film with a perovskite structure was deposited by annealing at 700 °C from a precursor solution of La(NO₃)₃ and Ni(CH₃COO)₂. In addition, highly (1 0 0)&(0 0 1)-oriented PZT/LNO capacitor was deposited on LNO/Si substrate by annealing at 600 °C, showing P_r = 18 μC/cm² and E_c = 36 kV/cm. Furthermore, the resultant PZT/LNO thin-film capacitor exhibited no fatigue up to 10⁸ switching cycles.     

Reprint of "Palladium Ohmic contact on hydrogen-terminated single crystal diamond film"

Contact properties of Palladium (Pd) on the surface of hydrogen-terminated single crystal diamond were investigated with several treatment conditions. 150 nm Pd pad was deposited on diamond surface by thermal evaporation technique, which shows good Ohmic properties with the specific contact resistivity (ρ_c) of 1.8 × 10^− 6 Ω cm² evaluated by Transmission Line Model. To identify the thermal stability, the sample was annealed in Ar ambient from 300 to 700 °C for 3 min at each temperature. As the temperature increased, ρ_c firstly decreased to 4.93 × 10⁻⁷ Ω cm² at 400 °C and then increased. The barrier height was evaluated to be − 0.15 eV and − 0.03 eV for as-deposited and 700 °C annealed sample by X-ray photoelectron spectroscopy analysis. Several surface treatments were also carried out to determine their effect on ρ_c, among which HNO₃ vapor treated sample indicates a lower value of 5.32 × 10⁻⁶ Ω cm².     

Structural and optoelectronic properties of transparent conductive c-axis-oriented ZnO based multilayer thin films with Ru interlayer

ZnO and Ru multilayer thin films are deposited using the sputtering deposition technique at room temperature. The effects of the Ru interlayer thickness and annealing temperature on the properties of multilayer thin films have been studied. An X-ray diffraction study reveals that ZnO layers are highly c-axis-oriented. The use of an Ru interlayer improves the crystalline quality of the subsequently deposited ZnO layers. Moreover, the crystalline quality of the entire structure is further enhanced through thermal annealing in a vacuum. Atomic force microscopy images show that the surface roughness of the multilayer thin films increases with a Ru interlayer thickness greater than 6 nm. The roughness of the film surface increases in correlation with annealing temperatures. This accounts for the decreased optical transmittance of the multilayer thin films annealed at temperatures higher than 450 °C. The electrical resistivity of multilayer thin films decreases with an increase in the metallic interlayer thickness. Thermal annealing at 450 °C causes low resistivity in multilayer thin films. The lowest resistivity reached ～5.4 × 10^?4 Ω cm for multilayer films with a 10-nm-thick Ru interlayer annealed at 450 °C.     

Transparent semiconductor zinc oxide thin films deposited on glass substrates by sol–gel process

Transparent semiconductor ZnO thin films were spin-coated onto alkali-free glass substrates by a sol–gel process. The influence of ZnO sols synthesized via different solvents (2-ME, EtOH or IPA) on the surface morphologies, microstructures, optical properties and resistivities of the obtained films were investigated. The as-coated films were annealed in ambient air at 500 °C for 1 h. X-ray diffraction results showed all polycrystalline ZnO thin films to have preferred orientation along the (0 0 2) plane. The surface morphologies, optical transmittances and resistivity values of the sol–gel derived ZnO thin films depended on the solvent used. The ZnO thin films synthesized with IPA as the solvent exhibited the highest average transmittance 92.2%, an RMS roughness of 4.52 nm and a resistivity of 1.5 × 10⁵ Ω cm.     

Improving the electrical properties of niobium-doped titania sputtering targets by sintering in oxygen-deficient atmospheres

Niobium-doped titania (TNO) film can be used as a transparent conductive oxide (TCO) film due to its excellent conductivity and visible transparency. The performances of TNO sputtering targets are thus critical issues in optimizing sputtered films. This study clarifies the influences of inert and reducing atmospheres on the microstructure, densification, crystal structure, and electrical properties of TNO sputtering targets. The results indicate that a sintering atmosphere of 90% Ar–10% H₂ can result in a lower sintered density, larger grain size, and lower resistivity than can an atmosphere of Ar, followed by one of air. Sintering in 90% Ar–10% H₂ or Ar obviously decreases the resistivity of TiO₂, from >10⁸ Ω cm to <10⁻¹ Ω cm, and the TNO target, from >10¹ Ω cm to <10⁻¹ Ω cm. The resistivity of TNO target sintered at 1200 °C in 90% Ar–10% H₂ is as low as 1.8×10⁻² Ω cm.     

Tailoring of morphology and orientation of LaNiO3 films from polymeric precursors

The aim of this work was to prepare lanthanum nickel oxide (LaNiO₃, LNO) thin films of different morphology and orientation. The precursor solutions were prepared by a chemical method from citric salts of lanthanum and nickel. Films were deposited using spin-on technique on Si (1 0 0) substrates. Tailoring of the films orientation and morphology has been attained through two thermal treatment processes with different heating devices: tubular furnace (process 1) and hot plate (process 2). Films were annealed at 600 and 700 °C, with heating rates: 20 °C/min (process 1) and 1 °C/min (process 2). Annealing times were from 30 min to 20 h. LNO films were characterized by AFM and X-ray diffraction analysis. Depending on the heating process applied, the obtained films showed very different structures, from completely amorphous to well crystallized and highly oriented. Films treated by process 1 were polycrystalline, had smaller oval grains and lower roughness parameters than films heated on a hot plate. Due to the low heating rate and heating from the substrate side, films obtained through process 2 were highly (1 1 0) oriented with elongated grains aligned along one direction.     

Heteroepitaxial ZnO/sapphire (0 0 0 1) structure prepared by sol–gel process

ZnO thin films were grown on sapphire (0 0 0 1) substrates by sol–gel process and their structural and optical properties were characterized in detail. High-quality texture was obtained by using precursor solution of zinc acetate and ethanolamine in 2-methoxyethanol, pyrolyzed at 300 °C, then heated at 500 °C, and finally annealed at 750 °C. Highly c-axis oriented ZnO films were confirmed by X-ray θ–2θ scan. A relatively high transmittance in the visible spectra range and clear absorption edge of the film were observed. Epitaxial relationship between ZnO and sapphire and photoluminescence of the film were examined by using a X-ray pole-figure analysis and He–Cd laser. Near-band-edge emission with a deep-level emission was observed.     

Electrochemical performance of La2NiO4+δ cathode for intermediate-temperature solid oxide fuel cells

The application of the La₂NiO_4+δ (LNO), one of the Ruddlesden–Popper series materials, as a cathode material for intermediate temperature solid oxide fuel cells is investigated in detail. LNO is synthesized via a complex method using ethylenediaminetetraacetic acid (EDTA) and citric acid. The effect of the calcination temperature of the LNO powder and the sintering temperature of the LNO cathode layer on the anode-supported cell, Ni–YSZ/YSZ/GDC/LNO, is characterized in view of the charge transfer resistance and the mass transfer resistance. Charge transfer resistance was not significantly affected by calcination and sintering temperature when the sintering temperature was not lower than the calcination temperature. Mass transfer resistance was primarily governed by the sintering temperature. The unit cell with the LNO cathode sintered at 1100 °C with 900 °C-calcined powder presented the lowest polarization resistance for all the measured temperatures and exhibited the highest fuel cell performances, with values of 1.25, 0.815, 0.485, and 0.263 W cm⁻² for temperatures of 800, 750, 700, and 650 °C, respectively.     

Ce0.9Gd0.1O1.95 supported La0.6Sr0.4Co0.2Fe0.8O3−δ cathodes for solid oxide fuel cells

Lanthanum-based iron- and cobalt-containing perovskite has a high potential as a cathode material because of its high electro-catalytic activity at a relatively low operating temperature in solid oxide fuel cells (SOFCs) (600–800). To enhance the electro-catalytic reduction of oxidants on La_0.6Sr_0.4Co_0.2Fe_0.8O_3?δ (LSCF), Ga doped ceria (Ce_0.9Gd_0.1O_1.95, GDC) supported LSCF (15LSCF/GDC) is successfully fabricated using an impregnation method with a ratio of 15 wt% LSCF and 85 wt% GDC. The cathodic polarization resistances of 15LSCF/GDC are 0.015 Ω cm², 0.03 Ω cm², 0.11 Ω cm², and 0.37 Ω cm² at 800 °C, 750 °C, 700 °C, and 650 °C, respectively. The simply mixed composite cathode with LSCF and GDC of the same compositions shows 0.05 Ω cm², 0.2 Ω cm², 0.56 Ω cm², and 1.20 Ω cm² at 800 °C, 750 °C, 700 °C, and 650 °C, respectively. The fuel cell performance of the SOFC with 15LSCF/GDC shows maximum power densities of 1.45 W cm^?2, 1.2 W cm^?2, and 0.8 W cm^?2 at 780 °C, 730 °C, and 680 °C, respectively. GDC supported LSCF (15LSCF/GDC) shows a higher fuel cell performance with small compositions of LSCF due to the extension of triple phase boundaries and effective building of an electronic path.     

Annealing effect on temperature coefficient of resistivity in La1−xSrxMnO3 ceramics

We investigated annealing effects of La_1?xSr_xMnO₃ (x = 0–0.6) on electrical resistivity and the temperature coefficient of resistivity (TCR). The annealed samples’ resistivity was lower than those of non-annealed samples. For example, annealing changed the resistivity of x = 0.3 at 25 °C from 4.50 × 10^?5 to 3.71 × 10^?5 Ω m. Remarkable difference in TCR was observed after annealing, for x = 0.3, 0.45, and 0.5. For x = 0.3, the TCR after annealing was 4000 ppm/°C, which was 1250 ppm/°C greater than that before annealing. We investigated (1) crystal phase, (2) Mn average valence, (3) Mott insulator–metal transition temperature, and (4) microstructure. The microstructure was remarkably varied for annealed x = 0.3 and 0.5. The average grain size of the x = 0.3 increased from 1.60 up to 2.38 μm. Results show that annealing affects resistivity and TCR because of grain growth during annealing.     

Electrochemical and microstructural characteristics of nanoperovskite oxides Ba0.2Sr0.8Co0.8Fe0.2O3−δ (BSCF) for solid oxide fuel cells

Nanoperovskite oxides, Ba_0.2Sr_0.8Co_0.8Fe_0.2O_3?δ (BSCF), were synthesized via the co-precipitation method using Ba, Sr, Co, and Fe nitrates as precursors. Next, half cells were fabricated by painting BSCF thin film on Sm_0.2Ce_0.8O_x (samarium doped ceria, SDC) electrolyte pellets. X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and electrochemical impedance spectroscopy (EIS) measurements were carried out on the BSCF powders and pellets obtained after sintering at 900 °C. Investigations revealed that single-phase perovskites with cubic structure was obtained in this study. The impedance spectra for BSCF/SDC/BSCF cells were measured to obtain the interfacial area specific resistances (ASR) at several operating temperatures. The lowest values of ASR were found to be 0.19 Ω cm², 0.14 Ω cm² 0.10 cm², 0.09 Ω cm² and 0.07 Ω cm² at operating temperatures of 600 °C, 650 °C, 700 °C, 750 °C and 800 °C, respectively. The highest conductivity was found for cells sintered at 900 °C with an electrical conductivity of 153 S cm^?1 in air at operating temperature of 700 °C.     

Growth of highly c-axis oriented LaNiO3 films with improved surface morphology on Si substrate using chemical solution deposition and rapid heat treatment process

LNO (LaNiO₃) thin films were directly deposited onto Si substrates with a thin layer of amorphous natural oxide (SiO₂) using three different precursor solutions. Effects of the constitution of precursor solution and the annealing heating rate on the surface morphology and the orientation were investigated. The LNO film derived from the mixture of a methanol solvent and an acetylacetone chelating agent had the flat surface with no cracks and pinholes. The heating rate of rapid annealing process had a critical effect on the oriented growth of the LNO film, and its c-axis orientation degree increased with the annealing heating rate. The LNO film with the heating rate of 40 ℃/s exhibited the highest degree of c-axis orientation (99.57%) and the lowest resistivity (9.35 × 10^?4 Ω cm). It would be a potential bottom electrode and/or seed layer to integrate perovskite-type films on it for functional devices.     

Coating of nano-sized ionically conductive Sr and Ca doped LaMnO3 films by sol–gel route

In this study, Sr and Ca doped LaMnO₃ thin ceramic films were coated on Al₂O₃ substrates by using a sol–gel route as the cathode material for SOFC. Nitrate precursors were used for the preparation of the thin film coating solution, and methanol and acetyl acetone were also used as the solvent and chelating agent, respectively. After the solution was prepared, an Al₂O₃ single crystal substrate was dipped into the solution. Then it was fired at 500 °C and annealed at 1025 °C for the crystallization. Coated films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), focused ion beam (FIB) and atomic force microscopy (AFM). Conductivity of the coated films was measured by the four probe Van der Pauw method. XRD, SEM, AFM and FIB characterizations of the coated film showed that the LaMnO₃ phase was formed, surface of the films was uniform and had homogenously distributed pores sized about 10 nm, mean grain size was about 60–80 nm and the film thickness was about 180 nm. The specific resistivity of the film was calculated to be 0.524 Ω m.     

Properties of solution-processed MgInZnO semiconductor thin films and photodetectors fabricated at a low temperature using UV-assisted thermal annealing

Ultraviolet (UV) irradiation-assisted thermal annealing is used for the fabrication of Mg doped InZnO (MIZO) semiconductor thin films and metal-semiconductor-metal (MSM) type photodetectors on alkali-free glasses at a low temperature of 300 °C. In this study, the effects of UV irradiation time on the structural features and the optical and electrical properties of sol-gel derived MIZO thin films were investigated, and the photoresponse properties of MIZO photodetectors fabricated using UV-assisted thermal annealing (UV-TA) and conventional thermal annealing (CTA) were compared. The molar ratio of In:Zn was fixed at 3:2, and the Mg content was maintained at 20 at% ([Mg]/[In+Zn]) in the precursor solution. After a spin-coating and drying procedure was performed twice, the dried sol-gel films were heated on a hotplate at 300 °C and exposed to UV irradiation in ambient air. The UV irradiation time was adjusted to 1, 2, 3, and 4 h. All annealed MIZO thin films had a dense microstructure, uniform film thickness, and flat surface and exhibited good optical transmittance (> 86.0%). The mean resistivity decreased with increasing irradiation time, and the samples irradiated for 4 h exhibited the lowest mean resistivity of 4.4×10² Ω-cm. Current-voltage (I-V) characteristics showed that the MIZO photodetectors operated in the photoconductive mode. Under illumination with UVC light, the MIZO photodetectors exhibited an I_light-to-I_dark ratio of 7.7 × 10² and had a photoresponsivity of 5.0 A/W at a bias of 5 V.     

The sheet resistance of graphene under contact and its effect on the derived specific contact resistivity

It is normally assumed that the sheet resistances under and outside the metal contact are identical when deriving specific contact resistivity of graphene from transmission line model. We considered the contact end resistance and obtained the sheet resistance under contact of 670 Ω/□, which is much different from that outside the contact of 1840 Ω/□. Considering the difference, the value of specific contact resistivity is determined to be 3.3 × 10⁻⁶ Ω cm², which is three times as large as the unmodified value. This indicates that the difference between the sheet resistances under and outside the contact affects the derived specific contact resistivity of graphene significantly.     

Study of Cu-based Al-doped ZnO multilayer thin films with different annealing conditions

AZO/Cu/AZO multilayer thin films produced under different annealing conditions are studied in this paper, to examine the effects of atmosphere and annealing temperature on their optical and electrical properties. The multilayer thin films are prepared by simultaneous RF magnetron sputtering (for AZO) and DC magnetron sputtering (for Cu). The thin films were annealed in a vacuum or an atmosphere of oxygen at temperatures ranging from 100 to 400 °C in steps of 100 °C for 3 min. High-quality multilayer films (at Cu layer thickness of 15 nm) with resistivity of 1.99×10⁻⁵ Ω-cm and maximum optical transmittance of 76.23% were obtained at 400 °C annealing temperature in a vacuum. These results show the films to be good candidates for use as high quality electrodes in various displays applications.     

Novel nano-crystalline Er2O3 hydrogen isotopes permeation barriers

Hydrogen Isotopes permeation barriers (HIPB) are used to reduce hydrogen isotopes permeation and leakage in the fields such as thermonuclear fusion energy, hydrogen energy, petroleum industry and vacuum solar receiver. In this study, nano-crystalline Er₂O₃ HIPB with about 5–10 nm grain size were made by sol-gel method. Their performances, including deuterium-permeation reduction factor (D-PRF), micro-structure, mechanical property and electrical property were reported. The D-PRF of 0.2 μm nano-crystalline Er₂O₃ HIPB reached 300 at 700 °C and did not deteriorate after 128 h deuterium permeation. The bonding strength and the nano-hardness steadily remained about 13 N and 10 GPa after 128 h deuterium permeation at 700 °C, respectively. The morphology and micro-structures of the nano-crystalline Er₂O₃ HIPB showed no measurable changes after 128 h deuterium permeation, which ensured the stable D-PRF and mechanical properties. However, the electrical resistivity of the nano-crystalline Er₂O₃ HIPB decreased after deuterium permeation at 700 °C. The electrical resistivity decreased from 9 × 10⁹ Ω cm by over three orders of magnitude and then tended to be stable, which might be attributed to oxygen loss or deuterium invasion.     

Large-size graphene microsheets as a protective layer for transparent conductive silver nanowire film heaters

A new strategy is reported for the fabrication of silver nanowire (AgNW) film heaters using reduced small/or large-size graphene oxide (rSGO or rLGO) sheets as an over-coating protective layer. The results show that ultrathin rLGO microsheets provide the best combination of protective effect and electrical properties on AgNW networks and thus could enable the design of high-performance transparent film heaters. As a consequence, good optical transparency and electrical conductivity, good oxidation resistance and thermal stability, and good heating performances are achieved with as-made rLGO/AgNW film heaters. Specifically, the rLGO/AgNW hybrid film annealed at 700 °C shows a low sheet resistance of 27 Ω sq⁻¹ and a good optical transparency of 80%. Furthermore, it exhibits good heating characteristics and defrosting performance at low voltages. The results presented here may pave the way for a new promising application of rLGO/AgNW hybrid film in transparent film heaters and other electrical devices.     

Performance and stability of Ruddlesden-Popper La2NiO4+δ oxygen electrodes under solid oxide electrolysis cell operation conditions

Ruddlesden-Popper La₂NiO_4+δ (LNO) oxygen electrodes were investigated under solid oxide electrolysis cell (SOEC) operation conditions. The electrochemical performance of LNO was measured in both solid oxide fuel cell (SOFC) and SOEC modes at 750 °C in air. The results suggest that LNO oxygen electrodes exhibit high electrochemical activity and the processes related to oxygen adsorption, dissociation and diffusion dominate the oxygen evolution reaction on the electrodes. Electrical conductivity relaxation (ECR) measurements imply that LNO shows better oxygen surface exchange performance than conventional LSM and LSCF electrodes, because of its special crystal structure with flexible non-stoichiometric oxygen. Significant performance degradation was observed during polarization at 500 mA cm⁻² and 750 °C in the SOEC mode for 48 h. XRD and XPS results confirmed that high-order Ruddlesden-Popper La₃Ni₂O₇ and La₄Ni₃O₁₀ phases have great contributions to the performance degradation of LNO oxygen electrodes related to anodic current polarization at 500 mA cm⁻² and 750 °C.