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[en] A proof-of-concept of applying laser micro-machining to fabricate high performance GaN light-emitting diode (LED) was presented in this study. Laser micro-machining was applied to fabricate GaN LED chip with angled sidewalls (ALED). The inclined sapphire sidewalls were coated with highly reflective silver film which functions as an efficient light out-coupling medium for photons within the LED structure. Thus, more laterally-propagating photons can be redirected to the upward direction of the ALED with silver coating (Ag-ALED). Performances of the Ag-ALED, ALED and conventional planar GaN LED were evaluated. At an injection current of 30 mA, the light output intensity of Ag-ALED was significantly improved by 97% and 195% as compared to ALED and conventional planar LED, respectively. The corresponding wall-plug efficiency of Ag-ALED was remarkably increased by 95% and 193% as compared to ALED and conventional planar LED, respectively. The results of this study demonstrated that the Ag-ALED showed a pronounced increase in light output intensity compared to conventional planar LED, which may have many potential applications in the field of display engineering.
[en] Many 2D graphene-based catalysts for electrooxidation of glucose involved the use of binders and toxic reducing agents in the preparation of the electrodes, which potentially causes the masking of original activity of the electrocatalysts. In this study, a green method was developed to prepare binder-free 3D graphene aerogel/nickel foam electrodes in which bimetallic Pd-Pt NP alloy with different at% ratios were loaded on 3D graphene aerogel. The influence of Pd/Pt ratio (at%: 1:2.9, 1:1.31, 1:1.03), glucose concentration (30 mM, 75 mM, 300 mM, 500 mM) and NaOH concentration (0.1 M, 1 M) on electrooxidation of glucose were investigated. The catalytic activity of the electrodes was enhanced with increasing the Pd/Pt ratio from 1:2.9 to 1:1.03, and changing the NaOH/glucose concentration from 75 mM glucose/0.1 M NaOH to 300 mM glucose/1 M NaOH. The Pd1Pt1.03/GA/NF electrode achieved a high current density of 388.59 A g−1 under the 300 mM glucose/1 M NaOH condition. The stability of the electrodes was also evaluated over 1000 cycles. This study demonstrated that the Pd1Pt1.03/GA/NF electrode could be used as an anodic electrode in glucose-based fuel cells.
[en] Graphical abstract: Display Omitted Highlights: ► Cu2O doped p-type AZO films was first prepared by sol–gel method. ► AZO:Cu2O films showed a polycrystalline Cu2O (1 1 0) and Cu (2 0 0) phases. ► p-Type conductivity was achieved by annealing in N2/H2 forming gas at 400 °C. ► p–n junction (ITO/AZO:Cu2O) revealed rectifying I–V characteristics. ► The mean optical transmittance of AZO:Cu2Ofilms was >90%. -- Abstract: Highly transparent Cu2O-doped p-type Zn1−xAlxO (AZO; Al/Zn = 1.5 at%) conducting oxide films were synthesized on glass substrates using a cost effective low temperature sol–gel method. X-ray diffraction of the Cu2O-doped AZO (AZO:Cu2O) films revealed a polycrystalline Cu2O (1 1 0) peak. The I–V measurements of the p–n junction (ITO/AZO:Cu2O) revealed rectifying I–V characteristics, showing that these AZO:Cu2O films exhibit p-type conductivity. p-Type conductivity was achieved by annealing the AZO:Cu2O films in N2/H2 forming gas at 400 °C. The hole concentration, hole mobility and resistivity of the 0.5–2 mol% AZO:Cu2O films were 5.41 × 1018 to 1.99 × 1020 cm−3, 8.36–21.6 cm2/V s and 1.66 × 10−2 to 6.94 × 10−3 Ω cm, respectively. These results show that post-annealing in a forming gas is effective and practicable in producing p-type AZO.
[en] By engineering a new cohosting system of tris(8-hydroxyquinoline) and 4,7-diphenyl-1,10-phenanthroline in the electron transport layer, the current efficiency of the organic light emitting diode is improved by 34% to 4.3 cd/A as compared to the device with a single host of Alq3 as the electron transport layer. The maximum luminance is over 16,000 cd/m2 at the bias of 22 V and the current of 475 mA/cm2, which is ∼ 73% higher than the single host Alq3 device without optimizing the layer thickness. The reasons for the improvement will be investigated. The results strongly indicate that the knowledge of bulk conductivity engineering of organic n-type transporters shows practical significance in OLED applications
[en] Highlights: ► High-quality ZnO thin films were deposited at room temperature. ► Effect of O2 flow and RF sputtering voltages on properties of ZnO films were studied. ► O2/Ar ratios played a key role in controlling optical properties of ZnO films. ► Photoluminescence intensity of the ZnO films strongly depended on O2/Ar ratios. ► Crystallite size, stress and strain strongly depended on O2/Ar ratios. - Abstract: ZnO thin films were deposited onto quartz substrates by radio frequency (RF) reactive magnetron sputtering using a Zn target. The structural and optical properties of the ZnO thin films were investigated comprehensively by X-ray diffraction (XRD), ultraviolet–visible and photoluminescence (PL) measurements. The effects of the oxygen content of the total oxygen–argon mixture and sputtering voltage in the sputtering process on the structural and optical properties of the ZnO films were studied systemically. The microstructural parameters, such as the lattice constant, crystallite size, stress and strain, were also calculated and correlated with the structural and optical properties of the ZnO films. In addition, the results showed that the crystalline quality of ZnO thin films improved with increasing O2/Ar gas flow ratio from 2:8 to 8:2. XRD and PL spectroscopy revealed 800 V to be the most appropriate sputtering voltage for ZnO thin film growth. High-quality ZnO films with a good crystalline structure, tunable optical band gap as well as high transmittance could be fabricated easily by RF reactive magnetron sputtering, paving the way to obtaining cost-effective ZnO thin films transparent conducting oxides for optoelectronics applications
[en] We report the synthesized mixture of MXene and NiCo LDH on nickel foam by an electrodeposition technique. The specific capacitance of the mixture attained 983.6 F g−1 at a discharge current of 2 A g−1, which is greater than that of pure MXene. Compared to NiCo LDH, the sample created through electrodeposition provided a better rate capability of 983.6 F g−1 at 2 A g−1 and 536.6 F g−1 at 50 A g−1 and cycling stability with 76% retention after 5000 cycles at 30 A g−1. Moreover, a solid-state asymmetric supercapacitor with MXene-LDH as the positive electrode and multi-walled carbon nanotube coated on the nickel foam as the negative electrode delivers high energy density (36.70 Wh kg−1 at the power density of 1.44 kW kg−1), which outperforms the other devices reported previously.
[en] Highlights: • 3D Co(II) ions modified graphene aerogels were prepared by one-step hydrothermal process. • The aerogel electrodes showed hybrid supercapacitor behaviors. • The aerogel electrodes exhibited high rate capability and long-term cycling stability. - Abstract: Reduced graphene oxide (r-GO) aerogels decorated with divalent cobalt ions were synthesized via a one-pot hydrothermal self-assembly route. The interaction of Co(II) ions with 3D r-GO aerogels was investigated by spectroscopic techniques, including Raman, attenuated total reflectance infrared, and X-ray photoelectron spectroscopies. The excellent electrochemical properties of the aerogels were confirmed by cyclic voltammetry, galvanostatic charge/discharge tests, and electrochemical impedance spectroscopy in an acid electrolyte (1 M H2SO4). The Co(II) ion-modified r-GO aerogels can be used as high-performance hybrid supercapacitor materials with a specific capacitance of 387.2 F g–1 at 1 A g–1 current density and a good cycling stability without capacity decay over 1000 cycles. The mechanical integrity enhancement of the hybrid r-GO aerogel framework and the improvement in its unique capacitive performance are attributed to the efficient interconnection produced by electro-active Co(II) ions
[en] Ni–Al co-doped ZnO (NiAl:ZnO) thin films were deposited on glass substrates by DC magnetron sputtering in Ar using a single ceramic, spark-plasma-sintered target with 2 wt% Al and 5 wt% Ni. The effects of the sputtering power and gas pressure on the NiAl:ZnO films were studied. The structural, electrical, and optical properties of the films were characterized by X-ray diffraction, field emission scanning electron microscopy, Hall effect measurements and UV–vis transmission spectroscopy. As the sputtering power and gas pressure increased, the crystallinity, electrical properties and optical band gap of the films were improved. The NiAl:ZnO film deposited at 40 W at 6.0 mTorr had the strongest (0 0 2) XRD peak and the lowest resistivity of approximately 2.19 × 10−3 Ω cm with an optical transmittance of 90%.
[en] Graphical abstract: - Highlights: • Ni–Al co-doped ZnO (NiAl:ZnO) composite thin films were deposited by DC magnetron sputtering at room temperature. • All films showed a highly preferential (0 0 2) c-axis orientation. • XPS revealed the presence of metallic Ni, NiO, and Ni2O3 states, and Ni atoms were successfully doped in the NiAl:ZnO films. • NiAl:ZnO (3 wt% Ni) film showed the lowest electrical resistivity of 2.59 × 10−3 Ω cm. • Band gap widening (4.18 eV) was observed in the NiAl:ZnO films with 5 wt% Ni. - Abstract: Ni–Al co-doped ZnO (NiAl:ZnO) films with fixed Al content at 2 wt% and different Ni contents (2.5, 3, and 5 wt%) were deposited by DC magnetron sputtering in an argon atmosphere at room temperature. X-ray diffraction revealed that all films showed a highly preferential (0 0 2) c-axis orientation. XPS revealed the presence of metallic Ni, NiO, and Ni2O3 states, and Ni atoms were successfully doped in NiAl:ZnO films, which did not result in a change in ZnO crystal structure and orientation. The electrical resistivity of NiAl:ZnO film was decreased to 2.59 × 10−3 Ω cm at a Ni doping concentration of 3 wt% compared with undoped Al-doped ZnO film (5.58 × 10−3 Ω cm). The mean optical transmittance in the visible range was greater than 80% for all films. Band gap widening (4.18 eV) was observed in the NiAl:ZnO films with 5 wt% Ni, attributed to the Burstein–Moss shift due to the increase of carrier concentration
[en] Highlights: ► A novel porous carbon with rod-like pore structure was prepared using hydroxyapatite as templates. ► The N and O contained mesoporous carbon was obtained by modified by HNO3 solution. ► The role of hydroxyapatite as double-template and mechanism of surface modification were supposed. ► The modified mesoporous carbon exhibited good electrochemical performances. -- Abstract: Novel mesoporous carbon has been synthesized using rod-like nano-hydroxyapatite (HA) particles as templates, sucrose as carbon precursor by polymerizing, carbonizing and the removal of templates with HCl solution. In the process, HA not only acted as an endotemplate but also an exotemplate producing micropores and mesopores. Subsequently, mesoporous carbon was modified by HNO3 solution with different concentration. The morphology, pore structure, and surface functional groups of the as-obtained samples are analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer–Emmett–Teller method (BET), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). The electrochemical performance for electrochemical capacitors is evaluated in a 1 M H2SO4 aqueous solution. The results manifest that the structrue of resultant carbon with a high surface area (719.7 m2 g−1) and large pore volume (1.51 cm3 g−1) is the replica of HA. After modification, the surface area and pore volume mesoporous carbons slightly decrease, while their electrochemical performance have been significantly improved with the increase of the capacitance from 125.7 to 170.1 F g−1 and a non-decayed cycle life over 5000 cycles for HA-C-0.15N