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Thermal conductivity of soils is a key parameter in determining the heat transfer and temperature field in thermal engineering. This paper developed a thermal conductivity model of soils with a consideration of the thermo-hydro-deformation interaction during a freezing process. The model was proposed based on the concept of normalized thermal conductivity, and integrated the temperature, volumetric unfrozen water content, porosity, mineralogy, solid particle type and frost heave. Then, the steps to calculate thermal conductivity of soils during a freezing process were illustrated. Additionally, compared with the other two widely used empirical models, i.e., model based on the apparent heat capacity method and model based on the Heaviside function, the proposed model was more effective and reasonable, while the other two models had some limitations in calculating thermal conductivity of soils during a freezing process. Moreover, the proposed model was comprehensively verified by the 32 soil samples, and the good agreements between the measured and model-calculated thermal conductivities of soils confirmed that the proposed model can be used to calculate the thermal conductivity of soils in the numerical simulations, and could also well reflect the effect of phase transition of water-ice on thermal conductivity of soils during a freezing process.

Amorphous oxide semiconductors (AOS) have unique advantages in transparent and flexible thin film transistors (TFTs) applications, compared to low-temperature polycrystalline-Si (LTPS). However, intrinsic AOS TFTs are difficult to obtain field-effect mobility (μ FE) higher than LTPS (100 cm2/(V·s)). Here, we design ZnAlSnO (ZATO) homojunction structure TFTs to obtain μ FE = 113.8 cm2/(V·s). The device demonstrates optimized comprehensive electrical properties with an off-current of about 1.5 × 10–11 A, a threshold voltage of –1.71 V, and a subthreshold swing of 0.372 V/dec. There are two kinds of gradient coupled in the homojunction active layer, which are micro-crystallization and carrier suppressor concentration gradient distribution so that the device can reduce off-current and shift the threshold voltage positively while maintaining high field-effect mobility. Our research in the homojunction active layer points to a promising direction for obtaining excellent-performance AOS TFTs.

Thermal conductivity of soils is significant on the thermal simulations in cold region engineering. Based on the generalized thermal conductivity for geotechnical materials, a thermal conductivity model for saline soil was proposed in this paper. At the micro level, the microstructure composition of sodium sulfate soils in the proposed model was redefined. Macroscopically, the variation of salt crystals and ice crystals with temperature and the relationship between the arrangements of components (i.e., liquid water, ice, soil particles) of saline soil were studied. Shape parameters α, β, τ were adopted to define the volume proportion of needle shape soil particles, spherical shape soil particles and disk shape soil particles, respectively. Besides, the proposed thermal conductivity model considered the heat loss due to the heat radiation in the measurement process. Furthermore, the accuracy of the proposed model was verified by the experimental data. The results showed that the soil particles can be defined as SWCA (i.e., soil particles, water, crystals mixture of salt and ice, air) four-layer concentric structure in the calculation of the thermal conductivity model of saline soil. Shape parameters have significant influence on simulation results. By comparing test data with calculated values, it can be found that at positive temperature, silty clay soil particles are mainly spherical (β = 0.5) and disc-shaped (τ = 0.5), while the sandy soil and soil-rock particles are more similar to the needle shape (α = 1.0). With the decrease of temperature, the particle parameters of silty clay soil change, β decreases to 0, τ increases to 0.75, and α increases to 0.25. However, at negative temperature, the soil particles of sandy soil and loess are still mainly needle-shaped (α = 1.0).

Significant efforts have been made to seek technologies to resolve water shortages. Among these efforts, seawater desalination and wastewater purification are considered mainstream strategies. Photothermal materials and adsorbents are the main components of solar-driven seawater desalination and wastewater purification, respectively. Herein, we propose MoO3-x (0

Memristors based on amorphous oxide semiconductors (AOSs) have attracted considerable attention recently. Here we present the study of amorphous ZnSnO (a-ZTO) memristors. The a-ZTO memristors were fabricated with Al layers as the bottom and top electrodes. The a-ZTO thin films, deposited by pulsed laser deposition, could be formed on the Al layer uniformly, and the Al layers were effective electrodes for a-ZTO memristors. It was verified that the a-ZTO memristors had obvious resistive switching (RS) behaviors, with a high ratio (∼103) of high-resistance and low-resistance states. Almost the same current-voltage curves were observed for five cycles, revealing the stable and reliable nature of devices. Our study demonstrated the a-ZTO memristors is a potential candidate to produce high-quality resistive random-access memories, which may open a path to applications of memristors based on indium-free AOSs.

The thermal conductivity of soils is a key factor in calculating soil heat transfer and analyzing temperature fields of geotechnical engineering in cold regions. We measured the thermal conductivity of a silty clay by a QuickLine-30 Thermal Properties Analyzer during a freezing-thawing process, and analyzed the variation of the thermal conductivity. We then calculated the thermal conductivity under the same experimental conditions using the three general models, i.e. weighted arithmetic mean model, weighted harmonic mean model, and weighted geometric mean model. The results show that for the thawed or frozen soils with little variation of unfrozen water content, the thermal conductivity is slightly influenced by temperature; however, for the soils in the major phase transition zone, the variation of the thermal conductivity with temperature is significant. After a freezing-thawing process, the thermal conductivities of the soils with higher initial dry densities become smaller, while those with lower initial dry densities become larger. We also found that the variation of porosity and hysteresis effect of unfrozen water content cause the difference of the thermal conductivity of soils between freezing and thawing processes, however the variation of porosity acts as the primary role. Furthermore, the three general models can all be used to calculate the thermal conductivity of soils; however, the weighted geometric mean model agrees best with the experimental data.

In the study, a three-parameter model was presented to calculate the thermal conductivity at full range of degree of saturation (S) for fine-grained soils based on the Fredlund and Xing model and the normalized thermal conductivity method. Three parameters (a, b, c) of the new model are determined by two equations and a measured point at a certain S. Two equations were obtained by the correlations between the parameters a, b, c and the basic properties of 30 Canadian soils by regression analysis. Moreover, the relationship between the thermal conductivity and S at full range of S was defined as the thermal conductivity curve (TCC) and was divided into 3 regions for the improvement of the calculation result. According to the sensitivity analysis, it is found that the calculated TCC is the most reliable when a point is measured in the Region 2. In addition, the new calculation model was also verified by 6 Chinese soils, suggesting the new model could present a good calculation result (R2 = 0.97) for the TCC.

In the study, a model matrix, based on the combinations of 1 thermal conductivity model for saturated soils (λsat), 4 thermal conductivity models for dried soils (λdry) and 4 Kersten number models for soils (Ke), was proposed to calculate the thermal conductivity of soils. 16 calculation models were included in the matrix. The matrix could be used to investigate the effects of the λdry models and Ke models on the calculational results of the 16 calculation models for the thermal conductivity of soils. The matrix was evaluated by 40 Canadian soils, and it is found that the He et al. model for λdry performs best among the 4 λdry models, the Cote and Konrad model for Ke performs best among the 4 Ke models. It also shows that the results of the calculation models in the matrix are different significantly, but the JCM (combination of the geometric mean model for λsat, the Johansen model for λdry, and the Cote and Konrad model for Ke) performs best among the calculation models for the thermal conductivity of soils. The effects of the λdry models and Ke models on the calculational results of calculation models for the thermal conductivity were evaluated by the modified difference index (MDI), showing that the Ke models have much larger effect on the calculational results than the λdry models. Besides, the calculation models containing the Cote and Konrad model for Ke were recommended to calculate the thermal conductivity of soils for its high accuracy.

The rapid development of wearable electronics demands for high-safety and stretchable lithium-ion batteries which are closer to the human skin, then accelerating the requirement for all-solid-state electrolytes with high stretchability and ion conductivity. Here, we proposed a decoupling strategy to effectively overcome the theoretical tradeoff between mechanical properties and ion conductivity of all-solid-state polymer electrolytes. The prepared stretchable all-solid-state polymer electrolyte (SSPE) via UV polymerization exhibits outstanding elastic tensile properties with elongation at break around 160.38%. The most interesting thing is that the SSPE membrane maintain high ion conductivity under external stress, the ion conductivity is 4.65 × 10−4 S cm−1 (0% strain) and 4.24 × 10−4 S cm−1 (75% strain) at room temperature. In addition, the SSPE membrane shows an excellent electrochemical stability window up to 5.2 V (vs. Li+/Li). The practicality of the SSPE was also investigated, including cell performance, deformation tests and destruction experiments. Therefore, the reported design of decoupling dual-function networks provides a promising approach for creating all-solid-state polymer electrolytes with high safety for stretchable energy storage applications.

Self-supporting three-dimensional (3D) transition metal electrodes have been considered for designing high-performance non-noble metal oxygen evolution reaction (OER) catalysts owing to their advantages such as binder-free, good mass transfer, and large specific surface area. However, the poor conductivity of ((oxy)hydr)oxides and the difficulty in adjusting their electronic structure limit their application. As an alternative strategy, instead of constituting the array electrode by the active components themselves, we herein report 3D Co(OH)2@MnO2 heterostructure decorated carbon nanoarrays grown directly on carbon paper (Co(OH)2@MnO2-CNAs). This unique structure can not only enhance electrical conductivity but also provide a larger specific surface area, and facilitate electrolyte diffusion and ion transport. The heterostructured Co(OH)2@MnO2 formed via incorporation with MnO2 facilitates the transition of CoII to CoIII in Co(OH)2 and it increases the storage of oxidative charge in the catalyst, leading to an OER activity matching with benchmark RuO2 and good stability. Density functional theory calculations suggest that the improved OER performance can be attributed to the formation of the heterojunction structure, resulting in the modulation of the electronic structure of Co atoms and the reduction of the free energy barrier of the rate-determining step for the OER.

Design of new materials with sophisticated nanostructure has been proven to be an efficient strategy to improve their properties in many applications. Herein, we demonstrate the successful combination of high electron conductive materials of NiCo2O4 with high capacitance materials of MnMoO4 by forming a core–shell nanostructure. The NiCo2O4@MnMoO4 core–shell nanoarrays (CSNAs) electrode possesses high capacitance of 1169 F g–1 (4.24 F cm–2) at a current density of 2.5 mA cm–2, obviously larger than the pristine NiCo2O4 electrode. The asymmetric supercapacitors (ASCs), assembled with NiCo2O4@MnMoO4 CSNAs as binder-free cathode and active carbon (AC) as anode, exhibit high energy density of 15 Wh kg–1 and high power density of 6734 W kg–1. Cycle performance of NiCo2O4@MnMoO4 CSNAs//AC ASCs, conducted at current density of 20 mA cm–2, remain 96.45% of the initial capacitance after 10,000 cycles, demonstrating its excellent long-term cycle stability. Kinetically decoupled analysis reveals that the capacitive ...

Magnesium doping is successfully utilized to enhance the electrochemical performance of Na2FeP2O7 for sodium-ion batteries (SIBs). A series of morphological and electrochemical tests indicate that Mg doping does not affect the structures of the host phase and the abundant defects in carbon coating are beneficial for electronic conductivity. A new peak at ~2.70 V during the first few cycles in CV curves is observed, which is related to the increase of specific capacity during the lifespan test. DFT calculation results reveal the enhanced electronic conductivity in Mg doped Na2FeP2O7, which is consistent with experimental observations. The Na2FeP2O7 with an appropriate Mg doped of 5% exhibits an initial reversible capacity of 90 mAh g−1 at 0.1 C without an obvious decline after 2000 cycles at 9 C. The specific capacity of Mg doped Na2FeP2O7 does not decrease fatally even the amount of Mg doped comes to 20%. The Coulombic efficiency is very high, close to 100% in all samples. The excellent electrochemical performance of Mg doped Na2FeP2O7 presents great potential as cathodes for advanced SIBs.

We report effect of oxygen vacancies on band gap narrowing, enhancement in electrical conductivity and room temperature ferromagnetism of SnO2 nanoparticles synthesized by simple chemical precipitation approach. As the calcination temperature is elevated from 400 to 800 °C, the average particle size increases from 12.26 to 34.43 nm, with enhanced grain growth and crystalline quality. At low temperatures, these nanoparticles are in a rather oxygen-poor state revealing the presence of many O vacancies and Sn interstitials in SnO2 nanoparticles as in this case Sn+2 is not oxidized completely to Sn+4 and small sized nano particles have more specific surface area, hence defects are more prominent. The oxygen content increases steadily with increasing temperature, with the Sn:O atomic ratio very near to the stoichiometric value of 1:2 at high temperatures suggesting the low density of defects. The optical band gap energies of all SnO2 nanoparticles are in the visible light region, decreasing from 2.89 to 1.35 eV, while room temperature ferromagnetism and electrical conductivity are enhanced with reduced temperatures. The dielectric constant (er) exhibited dispersion behaviour and the Debye’s relaxation peaks were observed in tanδ. The variation of dielectric properties and ac conductivity revealed that the dispersion is due to Maxwell–Wagner interfacial polarization and hopping of charge carriers between Sn+2/Sn+4. The narrowed band gap energies and enhanced ferromagnetism are mainly attributed to the increase of defects density (e.g., oxygen vacancies). The presence of oxygen vacancies is confirmed by EDX, Raman, PL, XPS, and UV–Vis spectra. The band gap of 1.35 eV is the smallest value for SnO2 reported so far. This rather small band gap, enhanced conductivity and room temperature ferromagnetism demonstrate that SnO2 nanoparticles are very promising in the visible light photo catalysis and optoelectronic devices.

Amorphous AlSnO ( a -ATO) thin films have been synthesized by a combustion solution process at low temperatures, with the Al:Sn molar ratio of 1: x ( x = 11 − 7) in the precursors. The influence of compositions on the structural, optical, and electrical properties of AlSnO (ATO) films were investigated in detail. The X-ray diffraction patterns revealed that all the ATO films are amorphous in nature. All elements were distributed uniformly over the films, regardless of holes formed in the matrix with increasing Al contents. The a -ATO films had an average transmittance over 80% in the visible region, with enlarged optical band gap energies from 3.42 to 3.67 eV at elevated Al contents. Hall-effect measurements identified that weak p -type conductivity could be obtained at the high Al doping levels with Al:Sn ratios higher than 1:9. The realization of p -type a -ATO films by the combustion solution method may open a door to design p -type amorphous-oxide-semiconductor thin-film transistors for transparent electronics.

Optical bandgap narrowing is observed in Sn0.94 Zn0.05Co0.01O2, Sn0.92 Zn0.05Co0.03O2 and Sn0.90 Zn0.05Co0.05O2 nanoparticles synthesized by the chemical co- precipitation method. The estimated particle size and optical band gap of Sn0.94 Zn0.05Co0.01O2, Sn0.92 Zn0.05Co0.03O2 and Sn0.90 Zn0.05Co0.05O2 nanoparticles are 16.51, 11.75 and 6.6 nm and 1.45, 1.36 and 0.93 eV, respectively. A red shift is noticed for all samples as compared to band gap value (3.6 eV) for bulk SnO2. Increasing Co content results in decreased particle size, narrowed band gap and enhanced emission intensities in visible range of light. Small sized nano particles have larger surface areas and these large surface areas lead to more defects (oxygen vacancies, tin interstitials). The increasing defects concentration (especially oxygen vacancies, tin interstitials) results to narrow the band gap. With increasing Co content, the particles are in oxygen-poor state indicating the presence of many O vacancies and Sn interstitials. The oxygen content decreases steadily with increasing Co content, with the Sn:O atomic ratio increases suggesting the high density of defects. Large number of defects (oxygen vacancies) creates several donor levels within the forbidden energy gap to narrow the band gap and these defects in the band gap act as luminescent centers to enhance the emission intensities in visible spectrum.

Zn doped Tin oxide (SnO2:Zn) nanoparticles have been synthesized by the chemical precipitation route with different thermal decomposition temperatures having emission intensities in visible light and narrowed bandgap. Band gap narrowing and emission intensities can be controlled by doping and calcination. The average particle sizes estimated by TEM agree with those calculated by XRD to be around 18.48 and 21.44 nm and the optical bandgap values found to be 1.30 and 2.52 eV in SnO2:Zn annealed at 400 and 600 °C, respectively. Blue shift in bandgap and decrease in photoluminescence intensity is noticed in (SnO2:Zn) nanoparticles with high annealing temperature, which is due to large grain sizes. As the grain sizes grow so defect density decreases and crystallanity increases. These defects act as luminescent centers and cause decrease in emission intensity and increase in band gap.

The doping of semiconductor nanocrystals (NCs) is crucial for the optimization of the performance of devices based on them. In contrast to recent progress on the doping of compound semiconductor NCs and silicon NCs, the doping of germanium (Ge) NCs has lagged behind. Here it is shown that Ge NCs can be doped with phosphorus (P) during synthesis by a nonthermal plasma. It is found that there are more P atoms in the NC near-surface region than in the NC core. P doping modifies the surface state of Ge NCs. Compressive strain can be incuced in Ge NCs by P which can explain the P-doping-enhanced oxidation resistance of Ge NCs. Stable dispersions of P-doped Ge NCs in acetonitrile can be cast to produce films for field-effect transistors (FETs). FET analysis shows that the electrical conductivity and electron mobility of a Ge-NC film increase with the increase of the P doping level, although the electrical activation efficiency of P in the Ge-NC film is low. Finally, atomic layer deposition of aluminum oxide at the surface of P-doped Ge NCs is shown to improve the performance of the FETs.

Thermal conductivity of freezing soils is an important parameter for the geotechnical engineering in cold regions. During a freezing process, unfrozen water freezes into ice. It changes soil components and induces frost heave, which will significantly increase the thermal conductivity of freezing soils. This study presents a generalized model for calculating the thermal conductivity of freezing soils with a consideration of soil components and frost heave. The generalized model for freezing soils was developed by different connections (e.g. series connection and parallel connection) between soil pores and solid grain and between unfrozen water and ice in the pores. This model was a function of unfrozen water content, frost heave, porosity, and initial water content. The proposed model was verified by measured data of eight silty clay samples with different dry densities and initial water contents. Results show that the calculated thermal conductivities agree well with measured data.

In this paper, all-inorganic CsPbIBr2 thin films were annealed by a two-step temperature-control process. All-inorganic, hole-transporting-layer-free, carbon-based planar perovskite solar cells (PSCs) with these CsPbIBr2 thin films (FTO/c-TiO2/CsPbIBr2/C) were fabricated. The effect of different first-step annealing temperatures during the two-step temperature-control process (50 °C/280 °C, 80 °C/280 °C, 100 °C/280 °C, 150 °C/280 °C, 180 °C/280 °C) on the photovoltaic conversion efficiency (PCE) of PSCs was investigated for the first time. When the first-step annealing temperature was 150 °C and the second-step annealing temperature was 280 °C, the highest efficiency of 8.31% was obtained. Without encapsulation, the solar cell could retain 97% of the initial PCE, when it was stored at 80 °C and zero humidity for 8 days. For comparison, solar cells with CsPbIBr2 films annealed by a one-step temperature-control process were fabricated. The highest PCE was 4.98%. From this, we could see that there is an increase of 66.9% in PCE, through using a two-step temperature-control annealing process. And also, in order to investigate why the PSCs by a two-step temperature-control annealing process has a higher PCE, all kinds of measurements were done for the first time. According to the results of the measurements, the perovskite film annealed by a two-step temperature-control process has a bigger crystal size, fewer grain boundaries, stronger PL and UV–vis absorption intensities, longer lifetime of minority carriers, less energy loss for hole transporting.

Amorphous zinc-tin oxide ( a -ZTO) films are fabricated using a combustion solution process. Utilization of a -ZTO films as the novel active layers, ultraviolet (UV) and ethanol sensors are prepared for the first time. The sensor performances are strongly related to the film resistance, which is determinated by the surface O 2 − formed by O 2 + e = O 2 − during UV and ethanol detections. During UV exposure, the resistivity of a -ZTO films decreases from 6.50 × 10 5 Ω cm to 56.85 Ω cm, which are very sensitive towards UV (365 nm) light and the photodetectors own a sensitivity value of 650 from 0 to 30 V. While for ethanol gas, the detection regions can be in a wide range from 20 ppm to 500 ppm. The gas response can achieve a value of 31.18 at 500 ppm ethanol and good response/recovery speed (6 s and 3 s), which can be comparable with that of the common used nanomaterials. The novel a -ZTO film based UV and gas sensors are very promising researches for future UV and gas sensor applications.

Post Ar/H2 plasma etching method is used to fabricate the texture surface of RF-sputtered ZnO:Al (AZO) transparent conductive films. Different plasma pressures (50 Pa, 100 Pa, 150 Pa and 200 Pa) are adopted during the etching process. The crystallinity improves with increasing the plasma pressure to 150 Pa. Surface morphology varies substantially by the bombardment of high energy Ar and H plasma atoms. Reduction of the mean free path of the plasma atoms and increment of the effective plasma atoms at high pressure will lead to the reduction of RMS after reaching to the largest value of 10.3 nm at 50 Pa. Lowest resistivity of 4.88 × 10−4 Ω cm and largest carrier concentration of 8.87 × 1020 cm−3 are obtained at 50 Pa due to the incorporation of hydrogen donors (passivation defects and grain boundary). The enhanced optical scattering ability by the texture structure (a pit size of ∼200 nm) results in a largest diffuse transmittance value of 1.68% and a best haze value of 2.00% at 550 nm at 50 Pa.

Generally, optoelectronic devices are fabricated at a high temperature. So the stability of properties for transparent conductive oxide (TCO) films at such a high temperature must be excellent. In the paper, we investigated the thermal stability of Ga-doped ZnO (GZO) transparent conductive films which were heated in air at a high temperature up to 500 °C for 30 min. After heating in air at 500 °C for 30 min, the lowest sheet resistance value for the GZO film grown at 300 °C increased from 5.5 Ω/sq to 8.3 Ω/sq, which is lower than 10 Ω/sq. The average transmittance in the visible light of all the GZO films is over 90%, and the highest transmittance is as high as 96%, which is not influenced by heating. However, the transmittance in the near-infrared (NIR) region for the GZO film grown at 350 °C increases significantly after heating. And the grain size of the GZO film grown at 350 °C after annealing at 500 °C for 30 min is the biggest. Then dye-sensitized TiO2 NPs based solar cells were fabricated on the GZO film grown at 350 °C (which exhibits the highest transmittance in NIR region after heating at 500 °C for 30 min) and 300 °C (which exhibits the lowest sheet resistance after heating at 500 °C for 30 min). The dye-sensitized solar cell (DSSC) fabricated on the GZO film grown at 350 °C exhibits superior conversion efficiency. Therefore, transparent conductive glass applying in DSSCs must have a low sheet resistance, a high transmittance in the ultraviolet–visible–infrared region and an excellent surface microstructure.

Transparent p -Li 0.07 Ni 0.93 O(111)/ n -ZnO ( 11 2 ¯ 0 ) heterojunctions with and without a Mg 1− x Zn x O ( x =0.4) intermediate layer were fabricated on r -plane sapphire substrates by pulsed laser deposition (PLD). The crystallinity of a -plane pure ZnO has been improved and the defect-related luminescence was restrained by introducing a thin Mn–Na codoped ZnO layer prior to the pure ZnO deposition. Both the heterojunctions show obvious rectifying properties and the introduction of Mg 1− x Zn x O layer facilitates the reduction in leakage current and shows improvement in junction characteristics. This work provides a feasible heterostructure based on the nonpolar ZnO which can potentially be used in the ZnO ultraviolet light-emitting or detecting devices.

The synthesis of graphene on Cu foils has been carried out using a low-pressure chemical vapor deposition (LPCVD) process. Under certain growth conditions apart from the graphene flakes, undesired CuxO nanodots appear. The samples were characterized by scanning electron microscopy, atomic force microscopy, Raman spectroscopy and X-ray photoemission spectroscopy. On the basis of the results, we investigated the effect of growth parameters such as pressure, methane-to-hydrogen ratio and cooling atmosphere on the growth rate, the composition, especially the cleanliness of graphene by scanning electron microscopy in detail. It is shown that the obtained film is quite sensitive on the preparation conditions and the appearance of CuxO nanodots is preventable.

Zn 0.989 Cu 0.01 Li 0.001 O thin films have been deposited on c- plane sapphire substrates by pulsed laser deposition (PLD). The films deposited at 500 °C and the oxygen pressures ( P O 2 ) ranging from 0.04 to 40 Pa were of good crystallinity with a (0002) preferential orientation. Three conductivity regimes were observed for the films with varying the P O 2 . The n -type film obtained at 0.04 Pa had a low resistivity of 1.95×10 −2 Ω cm, Hall mobility of 14.8 cm 2 V −1 s −1 , and carrier concentration of 2.16×10 19 cm −3 . The p -ty p e Zn 0.989 Cu 0.01 Li 0.001 O film could achieve when oxygen ambient reached as high as 40 Pa and with a hole concentration of 1.12×10 18 cm −3 . Films grown at P O 2 between 0.4 and 4 Pa commonly exhibited insulating behavior. All the Zn 0.989 Cu 0.01 Li 0.001 O films had a high transmittance above 80% in visible regions and the red-shift in optical band gap (E g ) happened as the P O 2 increased. Magnetic measurements showed that only the film fabricated at 0.04 Pa with n -type conduction exhibited room temperature ferromagnetism (RTFM) of 0.25 μ B /Cu while others obtained at higher P O 2 were paramagnetic. Oxygen vacancies ( V O ) are speculated that would play a crucial role for the ferromagnetic behavior observed.

Flexible optoelectronic devices are attractive because of light weight, small volume, flexibility and easy transport. Transparent conductive oxide thin films deposited on polymer substrates could satisfy the flexibility for optoelectronic devices. Ga-doped ZnO (GZO) films have been prepared on polycarbonate substrates by radio frequency magnetron sputtering at room temperature. The dependence of the structural, electrical, optical and adhesive properties for films on the sputtering powers was investigated. We also investigated the stability of the electrical property through doing Hall-effect measurements 18 months later. The lowest sheet resistance was 5.8 Ω/sq. After 18 months, the lowest sheet resistance was 6.5 Ω/sq. The stability of the electrical property is excellent. The average transmittance in the visible region of all the films was as high as 85 %, using air as reference. The good transparency-conducting property, excellent stability and room-temperature deposition on polymeric substrates enable GZO films to be widely used in optoelectronic devices.

Non-polar ZnO thin films were deposited on m-plane sapphire substrates by pulsed laser deposition at various temperatures from 300 to 700 °C. The effects of growth temperature on surface morphology, structural, electrical, and optical properties of the films were investigated. All the films exhibited unique m-plane orientation indicated by X-ray diffraction and transmission electron microscopy. Based on the scanning electron microscopy and atomic force microscopy, the obtained films had smooth and highly anisotropic surface, and the root mean square roughness was less than 10 nm above 500 °C. The maximum electron mobility was ∼18 cm2/V s, with resistivity of ∼0.26 Ω cm for the film grown at 700 °C. Room temperature photoluminescence of the m-plane films was also investigated.

Li-doped ZnCoO (ZnCoO:Li) diluted magnetic semiconductor thin films were prepared on SiO 2 substrates by pulsed laser deposition. In ZnCoO:Li films, Co 2+ substituted Zn 2+ and Li occupied the interstitial sites behaving as donors. The ZnCoO:Li films are of high electron concentration in the 10 20 cm −3 order and acceptable crystal quality with a hexagonal wurtzite structure. No cluster, precipitate, or second phase was found from the X-ray diffraction pattern and Co k -edge X-ray absorption near-edge structure measurements. The sp–d exchange interactions between the band electrons and the localized d electrons of Co ions substituting Zn ions were observed. The magnetization of ZnCoO:Li film is 0.61 μB/Co, higher than that of the ZnCoO film (0.49 μB/Co). The enhanced defect density and electron concentration due to the introduced Li donors may answer for the improvement of ferromagnetism at room temperature.

Fe-doped and Fe–Ga co-doped ZnO diluted magnetic semiconductor thin films on quartz substrate were studied. Rapid annealing enhanced the ferromagnetism (FM) of the films grown in Ar/O 2 . All the films grown in Ar are n-type and the carrier concentration could increase significantly when Ga is doped. The state of Fe in the films was investigated exhibiting Fe 3+ . Magnetic measurements revealed that room temperature ferromagnetism in the films were doping concentration dependent and would enhance slightly with Ga doping. The origin of the observed FM is interpreted by the overlapping of polarons mediated through oxygen vacancy based on the bound magnetic polaron model.

Cu-based Al-doped ZnO multilayer films were deposited on glass substrates by DC magnetron sputtering at room temperature. Three kinds of multilayer structures (AZO/Cu, AZO/Cu/AZO, and Cu/AZO) were designed for comparison, and the effects of the Cu layer thickness on photoelectrical properties of the multilayer films were investigated. The results revealed that the transparent-conductive property and near-infrared reflectance of the films are closely correlated with the Cu layer thickness, and among the three structures, AZO/Cu bi-layer films exhibited preferable photoelectrical properties. The AZO/Cu bi-layer film with a Cu layer thickness of 7 nm displayed the highest figure of merit of 4.82 × 10−3 Ω−1, with a low sheet resistance of 21.7 Ω/sq and an acceptable visible transmittance of 80%. The near infrared reflectance above 50% can be simultaneously obtained. The good performance of the coatings indicates that they are promising for coated glasses, thin film solar cells and heat-reflectors.

Ga-doped ZnO (ZnO:Ga) transparent conductive films were deposited on glass substrates by DC reactive magnetron sputtering. Taguchi method was used to find the optimal deposition parameters including oxygen partial pressure, argon partial pressure, substrate temperature, and sputtering power. By employing the analysis of variance, we found that the oxygen and argon partial pressures were the most influencing parameters on the electrical properties of ZnO:Ga films. Under the optimized deposition conditions, the ZnO:Ga films showed acceptable crystal quality, lowest electrical resistivity of 2.61 × 10 −4 Ω cm, and high transmittance of 90% in the visible region.

ZnO thin films were prepared by pulsed laser deposition at room temperature on glass substrates with oxygen pressures of 10–30 Pa. The structural, electrical, and optical properties of ZnO films were studied in detail. ZnO films had an acceptable crystal quality with high c -axis orientation and smooth surface. The resistivity was in the 10 2 Ω cm order for ZnO films, with the electron concentration of 10 16 –10 17 cm −3 . All the films showed a high visible transmittance ∼90% and a high UV absorption about 90–100%. The UV emission ∼390 nm was observed in the photoluminescence spectra. The oxygen pressures in the 10–30 Pa range were suitable for room temperature growth of high-quality ZnO films.

Al-doped ZnO (AZO) thin films have been prepared on glass substrates by pulsed laser deposition. The structural, optical, and electrical properties were strongly dependent on the growth temperatures. The lowest resistivity of 4.5 × 10−4 Ωcm was obtained at an optimized temperature of 350 °C. The AZO films deposited at 350 °C also had the high optical transmittance above 87% in the visible range and the low transmittance (

The CH3NH3PbI3 films were synthesized by a facile low-cost solution process and were used to fabricate photoconductive detectors. The perovskite photodetector is very sensitive to light, with a high responsivity of 5.51[Formula: see text]mA/W and a sensitivity of 50 at 5[Formula: see text]V under 350[Formula: see text]nm light illumination. The device exhibits the fast rise and decay processes with similar appearance, and the relaxation time constants are 270 and 300[Formula: see text]ms, respectively. The photo-current shows an evident saturation, without further increase for prolonging the illumination period. The perovskite photodetectors display high responsive performances to short-wavelength lights. This study is expected to provide a fundamental knowledge of perovskite photodetectors with high speed and repeatability for practical applications.

Quasi-aligned (Zn,Cd)O nanorods with highly faceted morphology were synthesized by a simple catalyst-free thermal evaporation method. The crystal structure and optical properties of the as-synthesized nanorods were thoroughly investigated. The results indicate that the (Zn,Cd)O nanorods are single crystals of wurtzite structure, having 12 side planes, namely, {0110} and {1120} planes. The presence of Cd is essential for obtaining these highly faceted nanorods. Room-temperature photoluminescence measurements indicated that the green emission of the products was attributed to both the surface-related defects and oxygen vacancies. These highly faceted nanorods possess significantly large surface-to-volume ratios and would be applicable in the fields of surface chemistry, photonics, and catalysis.

Ga-doped ZnO (ZnO:Ga) transparent conductive films were deposited on glass substrates by DC reactive magnetron sputtering. The structural, electrical, and optical properties of ZnO:Ga films were investigated in a wide temperature range from room temperature up to 400 °C. The crystallinity and surface morphology of the films are strongly dependent on the growth temperatures, which in turn exert an influence on the electrical and optical properties of the ZnO:Ga films. The film deposited at 350 °C exhibited the relatively well crystallinity and the lowest resistivity of 3.4 × 10−4 Ω cm. More importantly, the low-resistance and high-transmittance ZnO:Ga films were also obtained at a low temperature of 150 °C by changing the sputtering powers, having acceptable properties for application as transparent conductive electrodes in LCDs and solar cells.

N-doped p-type ZnO films were grown by plasma-free metal-organic chemical vapor deposition (MOCVD). The effect of substrate temperature on the electrical, optical, and structural properties of the N-doped ZnO films was investigated by Hall-effect, photoluminescence, X-ray diffraction measurements. The electrical properties of the films were extremely sensitive to the substrate temperature and the conduction type could be reversed in a narrow range from 380 °C to 420 °C. Based on X-ray photoelectron spectroscopy, a high compensation effect in the N-doped ZnO films grown by plasma-free MOCVD was suggested to explain the temperature-dependent phenomenon.

ZnO nanorods and nanonails have been synthesized on silicon wafers by a three-step catalyst-free thermal evaporation method in oxygen atmosphere. All the samples were hexagonal phase ZnO with highly c-axis preferential orientation. Different morphologies of ZnO nanostructures, i.e. ZnO nanorods and two kinds of nanonails, were observed at various temperature regions. Photoluminescence, transmission electron microscopy, and energy-dispersive X-ray spectroscope were employed to elucidate the reason for the formation of such different rod-like structures. The analysis results demonstrated that the caps of nanonails possess a large number of oxygen vacancies, which may play a key role in determining the formation of nanonails and the high intensity of green emission.

The authors report growth of stable Na-doped p-type ZnO films through pulsed laser deposition. Magnetic field dependent Hall-effect measurements demonstrate the firm p-type conductivity of the Na-doped films. The Na related acceptor level was estimated to be ∼164 meV by temperature-dependent photoluminescence and low temperature photoluminescence excitation spectra. ZnO p–n homojunction light-emitting diode consisting of Al-doped n-type ZnO and Na-doped p-type ZnO was fabricated on Si substrates. The diode showed evident rectification behavior with threshold voltage of ∼3.3 eV. The electroluminescence from the diode was observed at 110 K, consisting of three emission bands of 2.24 eV, 2.52 eV, and 3.03 eV from the radiative recombinations in the p-type layer. This work firmly demonstrates that Na could be a good dopant to create stable p-type ZnO.

Li–N dual-doped p-type ZnO (ZnO:(Li,N)) thin films have been prepared by pulsed laser deposition. The introduction of Li and N was confirmed by secondary ion mass spectrometry measurements. The structural, electrical, and optical properties as a function of growth temperature were investigated in detail. The lowest room-temperature resistivity of 3.99 Ω cm was achieved at the optimal temperature of 450 °C, with a Hall mobility of 0.17 cm2/V s and hole concentration of 9.12 × 1018 cm−3. The ZnO:(Li,N) films exhibited good crystal quality with a complete c-axis orientation, a high transmittance (about 90%) in the visible region, and a predominant UV emission at room temperature. The two-layer-structure p-ZnO:(Li,N)/n-ZnO homojunctions were fabricated on a sapphire substrate. The current–voltage characteristics exhibited the rectifying behavior of a typical p–n junction.

N-doped ZnO (ZnO:N) thin films were prepared by magnetron sputtering using NH3 as the N-doping source. The as-grown ZnO:N films showed high resistivity ∼103 Ω cm due to the hydrogen passivation effect. The properties of ZnO:N films under various annealing conditions (e.g., temperature, environment, and duration) were systematically studied with the aim of achieving p-type conductivity. The lowest room-temperature resistivity was found to be 7.73 Ω cm for p-type ZnO films annealed at 500 ∘C for 10 min in N2, with the hole concentration of 9.36×1017 cm−3 and Hall mobility of 0.86 cm2 V −1 s−1. Optical absorption spectra were performed to analyze the behaviors of hydrogen and nitrogen in p-type doping of ZnO. The NO–H complexes were largely present in as-grown ZnO films, which could be dissociated by thermal annealing resulting in activated N acceptors. Thus, the p-type conductivity was achieved in annealed ZnO:N films. A hydrogen-assisted nitrogen-acceptor doping mechanism was proposed as an answer for the achievement of p-type ZnO.