Renhuai Wei

Facile chemical solution synthesis of p-type delafossite Ag-based transparent conducting AgCrO2 films in an open condition

Recent progress in transparent conducting components stimulates the extensive exploration of p-type transparent conducting oxide (TCO) materials. Here, we report the synthesis of a class of p-type delafossite Ag-based TCO thin films, AgCrO2 (ACO), using a facile chemical solution route in an open condition. Firstly, the evolution of microstructure, morphology, and optical properties with respect to annealing temperature is reported. The stoichiometric ACO thin films show self-assembled c-axis orientation. The 500 °C-annealed ACO thin film presents a relatively high quality, dense surface and good optical transmittance amongst all the derived thin films. Then, to improve the conductivity, Mg doping effects are investigated. Upon Mg doping, p-type conductivity is obtained for thin films of AgCr1−xMgxO2 (0.04 ≤ x ≤ 0.20). The conductivity initially increases from 3.1 × 10−3 to 67.7 × 10−3 S cm−1 with x increasing from 0.04 to 0.12 and then slightly decreases with further increasing Mg concentration. The Hall results display that the hole concentration gradually increases with increasing Mg dopant concentration, and the carrier mobility first increases with x increasing from 0.04 to 0.12, while decreases with x further increasing from 0.12 to 0.20. A high magnitude of optical transmittance near 60% in the visible region and wide optical bandgaps (3.41–3.66 eV) of the AgCr1−xMgxO2 thin films are observed. The facial fabrication of ACO thin films in an open condition will provide a start for the synthesis of Ag-based delafossite thin films.

Annealing temperature effects on (111)-oriented BiFeO3 thin films deposited on Pt/Ti/SiO2/Si by chemical solution deposition

As the most-studied multiferroic material, (111)-oriented BiFeO3 (BFO) thin films are desirable due to the highest polarization in the (111) plane. The difficulty of achieving large-area (111)-oriented BFO films on silicon wafers towards implementation with silicon technology has hindered the development of BFO films. Herein, we report the annealing temperature effects on chemical solution deposition (CSD) derived BFO films on Pt(111)/Ti/SiO2/Si substrates without any buffer layer. The derived BFO films shows a strong (111) orientation with a distorted rhombohedral structure and R3c space group. The annealing temperature effects on the microstructures as well as the properties were investigated. A dense and crack-free surface was obtained in the low-temperature annealed films. Relatively high room-temperature remnant polarization 2Pr (120–140 μC cm−2) could be obtained with low leakage (∼10−5 A cm−2 at 200 kV cm−1). Scanning electron microscopy and transmission electron microscopy showed that this is an available route for fabricating large-area (111)-oriented BFO films on silicon-based wafers with high 2Pr using low-cost solution processing.

BiFeO3(00l)/LaNiO3/Si thin films with enhanced polarization: an all-solution approach

Multiferroic BiFeO3 (BFO) thin films with a thickness larger than 400 nm are grown on solution-derived LaNiO3 coated Si substrates via chemical solution deposition. The prepared BFO/LaNiO3/Si thin films are strongly (00l)-oriented with a distorted rhombohedral structure of R3c symmetry. The effects of the annealing temperature within the temperature range of 500–650 °C on the microstructures and properties are investigated. With an annealing temperature increasing to 600 °C, the (00l) orientation is enhanced and the grain size is increased, whereas a higher annealing temperature will lead to the deterioration of the orientation and microstructures. The annealing temperature dependent dielectric, leakage and ferroelectric properties are investigated, showing excellent properties for the low temperature annealed BFO thin films. The mechanisms about annealing temperature effects are discussed. The results will provide an effective route to realize the integration of large-area BFO thin films on Si wafers by an all-solution approach with low cost.

Self-assembled c-axis oriented antiperovskite soft-magnetic CuNCo3 thin films by chemical solution deposition

Preparation of antiperovskite thin films is challenging work due to their complex phase diagram and easy decomposition during processing, which hinder the fundamental studies and applications. Herein, we report the preparation of antiperovskite CuNCo3 (CNC) thin films on several different single crystal substrates by chemical solution deposition. The results show that the derived CNC thin films are c-axis oriented regardless of the substrate orientation, suggesting the self-assembled c-axis orientation. The microstructures as well as the physical properties are investigated, showing that the CNC thin films are metallic and can be considered as a new type of soft-magnet with a ferromagnetic Curie temperature higher than 650 K. The results will provide an effective route for fabricating antiperovskite cobalt-based thin films as well as provide a prototype for the investigation of the growth mechanisms of complex metal nitride thin films by solution methods.

Ca3Co4O9/polycrystalline Al2O3: an effective template for c-axis oriented layered cobaltate thin films by chemical solution deposition

In this paper, Bi2Sr2Co2Oy and Bi2Ba2Co2Oy thin films were prepared on Ca3Co4O9/polycrystalline Al2O3 thin films by chemical solution deposition. The results show that both of the bismuth-based cobaltate thin films are self-assembled c-axis oriented, which confirms that Ca3Co4O9/polycrystalline Al2O3 thin film can be used as an effective template to induce c-axis oriented grain growth in layered cobaltate thin films. The annealing temperature effects on Bi2Sr2Co2Oy thin films were investigated, and the resistivity and Seebeck coefficient decrease with the increasing annealing temperature. The results will provide an effective template to realize self-assembled c-axis oriented layered cobaltate thin films on polycrystalline substrates by chemical solution deposition.

Facile chemical solution deposition of nanocrystalline CrN thin films with low magnetoresistance

CrN thin films are first prepared by a facile chemical solution deposition method. The results show that the derived CrN thin films are nanocrystalline with the grain size of 30–60 nm. X-ray photoelectron spectroscopy measurement shows the stoichiometry of the derived thin film. The temperature dependent resistivity within the range of 2–300 K shows a semiconductor-like behavior with dρ/dT < 0 and a discontinuity in resistivity at 253 K is observed due to the antiferromagnetic transition. At 10 K the magnetoresistance is as low as −0.06% under 45 kOe. The first growth of CrN thin films by the facile chemical solution deposition will provide an alternative route to prepare CrN thin films, especially for large-area CrN thin films with low-cost.

Dwell time effects on high coercivity CoFe2O4 thin films deposited by the solution processing

High room temperature coercivity CoFe2O4 (CFO) thin films are desirable in view of many applications, which is seldom achieved over 3 kOe in solution deposited CFO thin films. Herein, grain growth kinetic is investigated in the solution derived CFO thin films with coercivity larger than 4 kOe, showing a relaxation mechanism. The coercivity and magnetization increase initially and then decrease with increasing dwell time. The high coercivity is originated mainly from the critical grain size and the growth strain induced by the small crystallites and poorly developed grains. The results will provide a route to fabricate larger-area CFO thin films with high coercivity on silicon wafers by low-cost solution processing.

Unipolar resistive switching characteristics and scaling behaviors in La2Mo2O9 thin films for nonvolatile memory applications

La2Mo2O9 (LMO) thin films have been deposited on Pt/Ti/SiO2/Si substrates by pulsed laser deposition and the resistive switching (RS) characteristics of the Au/LMO/Pt devices has been investigated. The Au/LMO/Pt devices show excellent unipolar RS characteristics with high resistance ratio between high resistance state and low resistance state (LRS), good endurance, and retention performances. The results of temperature dependence of resistance and x-ray photoelectron spectroscopy suggest that the observed RS characteristics can be explained by the formation and rupture of conducting filaments composed of oxygen vacancies. Furthermore, the plot of the reset current (IR) as a function of the third harmonic coefficient (B0) caused by Joule heating during the reset process shows scaling behavior with a power law of I R ∝ B 0 − δ. The IR and reset power (PR) can also be scaled to the resistance in LRS (R0), i.e., I R ( P R ) ∝ R 0 − α ( β ). The observed scaling behaviors indicate the importance of the Joule h...

Upper critical field and vortex phase diagram of polycrystalline δ-Mo1-xZrxN thin films by sol-gel

Upper critical field of polycrystalline δ-Mo1-xZrxN (0 ≤ x ≤ 0.3) thin films by sol-gel was investigated. It showed that the upper critical field was continuously improved with Zr doping content, and the improvement of ∼10 T in upper critical field was mainly attributed to the combined effects of obvious enhancements in normal-state resistivity with slight changes in Tc, obvious decrease in crystallite/grain size and enhanced microstrains. Flux jump was observed in low-level doped thin films due to enhanced critical current density by Zr doping. Finally, the vortex phase diagram of δ-Mo0.95Zr0.05N thin films was presented, which will provide guidance for investigation about the vortex mechanisms of δ-Mo1-xZrxN thin films.

p-type transparent conductivity in high temperature superconducting Bi-2212 thin films

In this study, hole-type high-temperature superconductor Bi2Sr2CaCu2Oy (Bi-2212) with strong electronic correlation is proposed as a p-type transparent conducting oxide (TCO) candidate. Phase-pure and c-axis oriented Bi-2212 thin films with different thicknesses were prepared to investigate the optoelectronic properties. High room-temperature conductivity between 1064 and 200 S/cm with visible transmittance over 50% is obtained for the prepared Bi-2212 thin films. The results will provide an arena to search for p-type TCOs in high-temperature superconductors with strong electronic correlation and give a potential application in the field of transparent metallic contacts as well as transparent correlated metal/n-type semiconductor Schottky diodes.In this study, hole-type high-temperature superconductor Bi2Sr2CaCu2Oy (Bi-2212) with strong electronic correlation is proposed as a p-type transparent conducting oxide (TCO) candidate. Phase-pure and c-axis oriented Bi-2212 thin films with different thicknesses were prepared to investigate the optoelectronic properties. High room-temperature conductivity between 1064 and 200 S/cm with visible transmittance over 50% is obtained for the prepared Bi-2212 thin films. The results will provide an arena to search for p-type TCOs in high-temperature superconductors with strong electronic correlation and give a potential application in the field of transparent metallic contacts as well as transparent correlated metal/n-type semiconductor Schottky diodes.