Al2O3-doped ZnO Research Articles

Graphene Reinforced Anticorrosion Transparent Conductive Composite Film Based on Ultra-Thin Ag Nanofilm.

Transparent conductive films are widely used in electronic products and industrial fields. Ultra-thin Ag conductive nanofilm (ACF) was prepared on a soda lime silica glass (ordinary architectural glass) substrate with industrial magnetron sputtering equipment with AZO (Al2O3 doped ZnO) as the crystal bed and wetting layer. In order to improve the corrosion resistance and conductivity of the ACF, graphene nanosheets were modified on the surface of the ACF by electrospraying for the first time. The results show that this graphene modification could be carried out continuously on a meter scale. With the modification of the graphene layer, the corrosion rate of graphene-decorated ACF (G/ACF) can be reduced by 74.56%, and after 72 h of salt spray test, the conductivity of ACF samples without modification of graphene can be reduced by 34.1%, while the conductivity of G/ACF samples with modification of graphene can be reduced by only 6.5%. This work proves the potential of graphene modified ACF to prepare robust large-area transparent conductive film.

Location-Optoelectronic Property Correlation in ZnO:Al Thin Film by RF Magnetron Sputtering and Its Photovoltaic Application.

In this study, a radio-frequency magnetron sputter system was used to deposit Al2O3 doped ZnO (AZO) thin films at room temperature, and the soda lime glass (SLG) substrates were placed at different zones relative to the center of the sample holder under the target. The samples were then analyzed using an X-ray diffractometer, Hall-effect measurement system, UV-visible spectrophotometer, and X-ray photoelectron spectroscopy. It was found that the electrical, structural, and optical properties of AZO films strongly depend on the target racetrack. The AZO thin film grown at a location outside the racetrack not only has the most suitable figure of merit for transparent conductive films, but also retains the least residual stress, which makes it the most suitable candidate for use as a CZTSe transparent conductive layer. When applied to CZTSe solar cells, the photoelectric efficiency is 3.56%.

Impacts of light on switching properties of epitaxial (Pb0.9La0.1)(Zi0.4Ti0.6)O3 capacitor with Al2O3 doped ZnO top electrode

Epitaxial (001) (Pb0.9La0.1)(Zi0.4Ti0.6)O3(PLZT)/La0.5Sr0.5CoO3(LSCO)/SrTiO3(STO) heterostructure was prepared by radio frequency (RF) magnetron sputtering, and Al2O3 doped ZnO (AZO) film was used as the top electrode to fabricate AZO/PLZT/LSCO capacitors in order to investigate the influence of light on electrical and optical properties of the capacitors. It was found that remanent polarizations of the capacitor are 25.7 μC/cm2, 23.3 μC/cm2, 20.7 μC/cm2, 31.3 μC/cm2 under the light intensity of 80 mW/cm2, 100 mW/cm2, 120 mW/cm2, and the dark condition, respectively. Remanent polarization (Pr) is obviously reduced upon illumination, which is attributed to the pinning of captured photogenic carriers on ferroelectric domains. The leakage current densities are 2.1 ×10−4 A/cm2, 2.69 ×10−4 A/cm2, 3.60 ×10−4 A/cm2 and 4.82 ×10−4 A/cm2 at 250 kV/cm and 2.1 ×10−4 A/cm2, 2.57 ×10−4 A/cm2, 3.58×10−4 A/cm2 and 4.62 ×10−4 A/cm2 at −250 kV/cm, respectively. The leakage current density upon illumination is bigger than that under dark condition, and satisfies of the capacitors satisfy the limited space charge conduction under the condition of higher electric field, and Ohmic conduction mechanism under the condition of lower electric field. It is found that illumination does not change the leakage mechanism, but impacts the leakage current density.

Characterization of physical and mechanical properties of Al2O3-doped ZnO (AZO) thin films deposited on transparent polyimide supports with various ALD process parameters

Fabrication of Al2O3 doped ZnO (AZO) thin films on transparent polyimide substrates using ex-situ oxygen plasma-assisted atomic layer deposition (ALD) is studied. The alumina composition is controlled by adjusting the ALD cycle ratio in the reaction sequence from 9:1 to 49:1 (diethylzinc/H2O:trimethylaluminum/H2O). Nanoscratch and electromechanical tensile tests are performed to evaluate the mechanical reliability of the AZO thin films fabricated under various processing conditions. Conventionally deposited AZO shows the lowest sheet resistance of 294 Ω/sq at a doping ratio of 19:1 at 150 ℃. However, the resistance of AZO grown on a polymer surface modified by plasma is higher at 429 Ω/sq. Nanoscratch results reveal that the first critical load could be increased by surface hardening and strong adherence as a function of the process temperature and plasma treatment. Under a tensile strain, doping of alumina delayed the strain (%) at crack initiation from 0.58 to 0.82%. The initial elastic modulus of the AZO/transparent polyimide composites showed a transient decrease with an increase in the alumina content from 2.7 to 3.8 at.%. These results demonstrating the mechanical characteristics of thin films as a function of the processing conditions are significant for flexible display manufacturing.

Flash sintering activated by bulk phase and grain boundary complexion transformations

A naturally-occurring coupled thermal and electric runaway, resulted from an Arrhenius temperature-dependent specimen conductivity, can trigger flash sintering in many ceramics. This study reveals another possibility to activate flash sintering: a bulk phase transformation or a grain boundary (phase-like) complexion transition can cause an abrupt rise in the specimen conductivity to jump start flash sintering (prior to the occurrence of a natural thermal runaway). In undoped and Al2O3-doped ZnO, the flash sintering is activated by natural thermal runways that can be quantitively predicted from an Arrhenius extrapolation of low-temperature specimen conductivity. In contrast, a bulk eutectic reaction and the associated formation of premelting-like intergranular films (IGFs) in Bi2O3-doped ZnO can lead to a nonlinear rise in the specimen conductivity (above the Arrhenius extrapolation) to trigger flash sintering prior to the occurrence of the predicted natural thermal runaway. Yet, a natural thermal runaway can still take place in Bi2O3-doped ZnO before the occurrence of the interfacial and bulk transformation if the initial electric field is increased to a sufficiently high level. All five cases can be fully explained in a consistent framework so that this set of experiments systematically validate our theory of flash initiation. This work uncovers the roles of the bulk phase and interfacial (phase-like) complexion transformations in initiating flash sintering, thereby suggesting a new direction to understand and tailor the flash sintering process. An observation of ultra-fast field-induced migration of aliovalent cations during the flash sintering of Al2O3-doped ZnO is also reported.

Surface modification of Li1.3Al0.3Ti1.7(PO4)3 ceramic electrolyte by Al2O3-doped ZnO coating to enable dendrites-free all-solid-state lithium-metal batteries

Abstract The Na+ super-ionic conductor (NASICON) type solid electrolytes Li1.3Al0.3Ti1.7(PO4)3 (LATP) are of increasing interest because of their high total ionic conductivity and excellent stability against moist air. However, they are not stable when contacting with lithium metal because of the rapid Ti4+ reduction by Li metal, which greatly restrict their application in lithium batteries. Here, we propose a Al2O3-doped ZnO (AZO) surface coating method by magnetron sputtering to improve the stability of the Li1.3Al0.3Ti1.7(PO4)3 electrolyte against the attack of lithium-metal anode and to avoid the growth of lithium dendrite. The Al2O3-doped ZnO coating of the electrolyte Li1.3Al0.3Ti1.7(PO4)3 demonstrates high chemical stability against the attack of lithium-metal in a wide electrochemical potential ranges (>5 V), as well as an excellent performance of suppressing of lithium dendrites. Furthermore, the Al2O3-doped ZnO coated Li1.3Al0.3Ti1.7(PO4)3 was found to be the candidate electrolyte for the all-solid-state lithium battery. An all-solid-state Li/LiFePO4 battery with Al2O3-doped ZnO coated Li1.3Al0.3Ti1.7(PO4)3 as the solid electrolyte shows good cyclability and a high columbic efficiency for 50 charge/discharge cycles. Furthermore, the surface-modified electrolyte Li1.3Al0.3Ti1.7(PO4)3 by Al2O3-doped ZnO coating also enables the lithium metal battery to exhibit extremely long cycling for nearly 1000 h due to the ability of suppressing of lithium dendrites.

Al2O3-doped ZnO coating of carbon nanotubes as cathode material for lithium-sulfur batteries

Currently, lithium-sulfur (Li-S) batteries become increasingly attractive because of their high theoretical energy density and high theoretical specific capacity. In this work, high-sulfur-loading Al2O3 doping of a ZnO-modified carbon nanotube (AZO@S/CNT) composite is synthesized via the hydrothermal method and subsequent high-temperature solid-state reaction. Al2O3-doped ZnO (AZO) induces a strong chemical interaction between polysulfides to restrain the “shuttle effect.” In addition, we use a novel method to enhance the electronic conductivity of the cathode material. The Al2O3 doping of ZnO can increase the electron density in ZnO, and thus enhance its electronic conductivity. The initial discharge capacity of the cathode with 60-wt.% S reaches 1100 mAh g−1 and the recycle capacity still remains 700 mAh g−1 after 200 cycles at 0.2 C with a capacity fade rate of 0.18% per cycle, offering a potential candidate for practical application of high-energy-density Li-S batteries in the future.

Optical excitation-enhanced sensing properties of acetone gas sensors based on Al2O3-doped ZnO

PurposeThe purpose of this research is to synthesize Al2O3-ZnO thick films, study the effect of doping and optical excitation on their sensing properties and introduce an attractive candidate for acetone detection in practice.Design/methodology/approachZnO nanoparticles doped with Al2O3 were prepared by sol-gel method and characterized via X-ray diffraction and field-emission scanning electron microscopy. The sensing properties to acetone were investigated with an irradiation of UV. The sensing mechanism was also discussed with UV-Vis spectroscopy.FindingsThe doping of Al2O3 promoted the sensing response and stability of ZnO nanoparticles. The optimum performance was obtained by 4.96 Wt.% Al2O3-ZnO. The response to acetone (1,000 ppm) was significantly increased to 241.81, even just at an operating temperature of 64°C. It was also demonstrated that optical excitation with UV irradiation greatly enhanced the sensing response and the sensitivity can reach up to 305.14.Practical implicationsThe sensor fabricated from 4.96 Wt.% Al2O3-ZnO exhibited excellent acetone-sensing characteristics. It is promising to be applied in low power and miniature acetone gas sensors.Originality/valueIn the present research, the optimum performance was obtained by 4.96 Wt.% Al2O3-ZnO at a low operating temperature of 64°C. The sensing properties were enhanced significantly with optical excitation, and the sensing mechanism was discussed with UV-Vis spectroscopy which has been reported rarely before.

Effects of Ultra-Thin Al2O3-Doped ZnO Film as Anode Buffer Layer Grown by Thermal Evaporation for Organic Light-Emitting Diodes

In this study, the efficiency of organic light-emitting diodes (OLEDs) was enhanced by depositing an Al2O3-doped ZnO (AZO) film as a buffer layer by thermal evaporation. The enhancement mechanism was systematically investigated, the X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy results of which revealed the formation of the UV-ozone-treated AZO film. The work function increased from 4.8 eV (standard ITO electrode) to 5.24 eV (AZO with 1 wt% for 1 nm), while the surface roughness was smoother than that of the ITO electrode. UV-ozone-treated AZO film increased the surface energy and polarity of the ITO surface. The transmittance increased in the 325–375 nm when the UV-ozone treated AZO was deposited on the ITO substrate. Further, results from admittance spectroscopy showed that the inserted AZO film increased the capacitance and conductance. It was also found that the carrier injection increased in the space-charge region. Moreover, the turn-on voltage of the devices decreased from 4 V to 3.2 V at 0.5 mA/cm2, the luminance increased from 7588 cd/m2 to 31880 cd/m2, and the current efficiency increased from 3.2 cd/A to 4.7 cd/A when a 1 nm-thick UV-ozone-treated AZO film with 1 wt% was inserted as a buffer layer in the OLEDs.

Superior electrochemical performance of LiCoO2 electrodes enabled by conductive Al2O3-doped ZnO coating via magnetron sputtering

A conductive Al2O3-doped ZnO (AZO) layer is coated directly on the LiCoO2 (LCO) porous composite electrode by magnetron sputtering of an AZO target, offering more efficient electron transfer and a stabilized interface layer. Up to 90% of the initial capacity of the AZO-coated electrode can be retained (173 mAh g−1) after 150 cycles between 3.0 and 4.5 V vs. Li/Li+. Meanwhile, the rate performance is remarkably improved showing a reversible capacity of 112 mAh g−1 at 12 C. The formation of amorphous solid electrolyte interface (SEI) observed on the uncoated LCO electrode is effectively impeded on the AZO-coated one. Acting as an intermediate barrier, the AZO layer can prevent chemical dissolution of the active materials by forming a thin passivation layer on the electrode surface containing some metal fluorides which are chemically inactive and ionically conductive. The positive role of the AZO coating is still effective under a more severe condition tested with an upper cut-off potential of 4.7 V.

Cu2ZnSnS4 solar cells fabricated by short-term sulfurization of sputtered Sn/Zn/Cu precursors under an H2S atmosphere

Synthesis of Cu2ZnSnS4 (CZTS) thin films by short-term sulfurization of sputtered Sn/Zn/Cu precursors under ambient H2S is studied. The effect of the sulfurization processes on the film morphology, surface roughness, composition of the CZTS, and the crystallinity was investigated by using scanning electron microscopy, optical profiler, energy dispersive spectroscopy, and X-ray diffraction respectively. To further explore the CZTS layer, the following additional layers were deposited to complete the solar cells: CdS with chemical bath deposition; ZnO and Al2O3-doped ZnO with RF magnetron deposition; and, silver fingers as the front contact as the last layer. The optical and morphological properties of the CZTS films were investigated and compared. Subsequently, the electrical characteristics and the efficiencies of the regarding solar cells were analyzed. A maximum efficiency of 3.8% has been obtained for the fast sulfurization (30min at 580°C) and finally, the performance is compared with our best cell fabricated through the more common slow annealing.

Characteristics of AZO electrode with high transmittance in near infrared range.

We studied Al2O3-doped ZnO (AZO) thin film as a transparent conducting layer for photovoltaic cell operated in wide range of solar spectrum. Effects of substrate temperature on the optical, structural, and electrical properties of thin AZO film were investigated. AZO films were deposited on glass substrates by RF magnetron sputtering system using a 2 wt.% Al2O3 doped target at different temperature conditions. The grown AZO films at low deposition temperatures ranged from 100 degrees C to 300 degrees C show relatively low resistivity, while the samples deposited at 400 degrees C or room temperature are with higher resistivity of -8 x 10(-4) Ω x cm. The measurement by atomic force microscopy reveals that all AZO films possess very smooth surface morphologies with RMS values below 1 nm regardless of substrate temperature. Optical transmittance of the AZO films increases from 81% to 95% as the substrate temperature increases. The AZO films deposited at 200 degrees C condition shows the optimum value of figure-of-merit of 43.7 x 10(-3) Ω(-1), showing the resistivity of 3.4 x 10(-4) Ω x cm and the transmittance of 94%. Additionally, it is noted that the transmittance of the films at near infrared wavelength of 1250 nm exceeds 90%, demonstrating the feasibility as a transparent electrode for thin film solar cell with narrow band gap.

Evaluation of the optoelectronic properties and corrosion behavior of Al2O3-doped ZnO films prepared by dc pulsed magnetron sputtering

The main requirements for transparent conducting oxide (TCO) films acting as electrodes are a high transmission rate in the visible spectral region and low resistivity. However, in many cases, tolerance to temperature and humidity exposure is also an important requirement to be fulfilled by the TCOs to assure proper operation and durability. Besides improving current encapsulation methods, the corrosion resistance of the developed TCOs must also be enhanced to warrant the performance of optoelectronic devices.In this paper the performance of aluminum-doped zinc oxide (AZO) films deposited by pulsed dc magnetron sputtering has been studied. Structure, optical transmittance/reflectance, electrical properties (resistivity, carrier concentration and mobility) and corrosion resistance of the developed coatings have been analyzed as a function of the doping of the target and the coating thickness. Films grown from a 2.0 wt% Al2O3 target with a thickness of approximately 1 µm showed a very low resistivity of 6.54 × 10–4 Ωcm and a high optical transmittance in the visible range of 84%. Corrosion studies of the developed samples have shown very low corrosion currents (nanoamperes), very high corrosion resistances (in the order of 107 Ω) and very high electrochemical stability, indicating no tendency for electrochemical corrosion degradation.

Effects of Hydrogen on the Optical and Electrical Characteristics of the Sputter‐Deposited Al2O3‐Doped ZnO Thin Films

In this study, AZO thin films were deposited on glass by using a 98 mol% ZnO + 1 mol% Al2O3 (AZO, Zn : Al = 98 : 2) ceramic target and a r.f. magnetron sputtering system. At first, the effects of different H2 flow rates (H2/(H2 + Ar) = 0%~9.09%, abbreviated as H2‐deposited AZO thin films, deposition temperature was 200°C) added during the deposition process on the physical and electrical properties of AZO thin films were investigated. The optical transmittance at 400 nm~700 nm is more than 80% for all AZO thin films regardless of H2 flow rate and the transparency ratio decreased as the H2 flow rate increased. The Burstein‐Moss shift effect was used to prove that the defects of AZO thin films decreased with increasing H2 flow rate. Also, the 2% H2‐deposited AZO thin films were also treated by the H2 plasma at room temperature for 60 min (plasma‐treated AZO thin films). The value variations in the optical band gap (Eg) values of the H2‐deposited and plasma‐treated AZO thin films were evaluated from the plots of (αhν)2 = c(hν − Eg), and the Eg values increased with increasing H2 flow rate. The Eg values also increased as the H2‐plasma process was used to treat on the H2‐deposited Al2O3‐doped ZnO (AZO) thin films.

Studies on Ethanol Gas Sensing Properties of Al2O3-doped ZnO Thick Films

The thick films of undoped and Al2O3 - doped ZnO were prepared by screen printing technique. AR grade Zinc Oxide powder (99.9% pure) was mixed mechnochemically with different wt. %( 0.5, 1 and 3) of Aluminium Chloride (Hexahydrate) (AlCl3.6H2O) in Acetone medium to obtain Al2O3 - ZnO composite material. The prepared materials were sintered at 1000oC for 12h in air ambience and reground to ensure sufficiently fine particle size. The electrical, structural and morphological properties of the films were investigated. The X-ray diffraction analysis of undoped and Al2O3 - doped ZnO material showed the polycrystalline nature. The surface morphology of the films was studied by SEM indicating that the films are granular and porous. The final composition of each film was determined by EDAX analysis. The gas response of undoped and doped ZnO films was studied for different gases such as CO, H2, NH3, and Ethanol at operating temperature ranging from 50oC to 450oC. The undoped ZnO film showed the poor response to Ethanol gas, while the film doped with 1 wt. % Al2O3 gave the good response to ethanol gas (500ppm) at 400oC. The selectivity, response and recovery time of the sensor were measured and presented.

Investigation on AZO Films Deposited by Radio-Frequency Reactive Magnetron Sputtering

The Al2O3-doped ZnO(AZO) films were deposited on the glasses by means of RF magnetron sputtering technology. The films were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD) and Profile-system respectively. The effect of substrate temperature on the structure of the AZO films is investigated.As a result, the properties of the AZO thin films are remarkably influenced by the substrate temperature , especially in the range of 200°C to 500 °C. The film prepared at the substrate temperature of 400°C possesses the best crystalline.

Growth of Al-doped ZnO films with tilted nano-columns on r-cut sapphire substrates by pulsed laser deposition

2 wt.% Al2O3-doped ZnO (AZO) thin films in both single layer and bi-layer forms were deposited on α-Al2O3 (011¯2) (r-cut) and (0001) (c-cut) substrates by a pulsed laser deposition technique. Single layer AZO films were grown under either vacuum or 33.3 Pa of O2 pressure. Bilayer AZO films were grown with a sequential deposition of a uniform template layer under vacuum and a nano-column-structured layer under 33.3 Pa of O2 pressure. Interestingly, single layer AZO film grown on r-cut sapphire in high oxygen pressure (33.3 Pa) shows tilted grain boundaries along [1¯102¯]AZO. The bilayer film deposited on r-cut substrate shows tilted nano-column growth while the film grown on c-cut substrate has vertically grown nano-columns. The results of X-ray diffraction and cross-section transmission electron microscopy studies show a systematic variation of the d-spacing of (0002)AZO and (112¯0)AZO for all AZO films. Electrical resistivity was measured and found to be strongly dependent on the different microstructures achieved under different oxygen pressures and substrates.

Optical enhancement by back reflector with ZnO:Al2O3(AZO) or NiCr diffusion barrier for amorphous silicon germanium thin film solar cells

Different composite films, including Al, Ag/NiCr/Al and Al2O3-doped ZnO (AZO)/Ag/NiCr (AZO)/Al, were utilized as the back reflectors for p-i-n hydrogenated amorphous silicon germanium (a-SiGe:H) thin film solar cells. The experimental results indicated that the AZO leyer between silicon layers and Ag/NiCr/Al back reflector was effect in improving solar cell performance, mainly owing to an increase in short-circuit current density (Jsc) of the solar cells. In addition, the thickness of AZO film could strongly affect the Jsc. The highest solar cell performance was achieved at the AZO thickness of about 90 nm. A nickel-chromium (NiCr) or AZO film was inserted between Ag and Al as a diffusion barrier against mutual diffusion of them, the similar performances of solar cells were achieved. So AZO/Ag/NiCr (AZO)/Al could be utilized as an advanced AZO/metal back reflector for p-i-n a-SiGe:H solar cells.

Structural and electrical properties of transparent conducting Al2O3-doped ZnO thin films using off-axis DC magnetron sputtering

Structural and electrical properties of off-axis DC magnetron sputtered Al2O3-doped ZnO (AZO) films were systematically investigated as a function of deposition distance from the center. With increasing distance, the AZO films showed an enhanced crystallinity and a denser microstructure with a smooth surface. The AZO film sputtered at the edge of the deposition stage (∼6cm away from the center) showed the highest mobility (∼10.1cm2/Vs) and the lowest resistivity (∼2×10−3Ωcm) due to the high plasma and thermal power density, which was suitable for transparent conducting oxide applications.

Electrochemical Characteristics of Al2O3-Doped ZnO Films by Magnetron Sputtering

Al2O3-doped ZnO (AZO) films have been prepared by radio frequency (rf) magnetron sputtering. The electrical properties and electrochemical behavior are investigated by Hall measurements, galvanostic cycling, and cyclic voltammograms. The result demonstrates that doping with a small amount of Al2O3 (<3 wt %) can improve the electrochemical performance of ZnO significantly. Among all of the AZO films, AZO2 (2 wt % Al2O3) film shows the best behavior with a large reversible specific capacity around 590 mAh g–1 and excellent capacity retention. High-resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) measurements confirm the formation of LiAl and nanosized Al2O3 during the first discharge and charge processes, respectively. The electrochemical reaction mechanism of AZO with lithium is proposed. It is believed that the nanosized Al2O3 formed after the charge process in AZO films plays an important role in the improvement of electrochemical performance.