Key Engineering Materials Vol. 748

Abstract: Quaternary AlInGaN/AlInGaN multiquantum-well (MQW) structures were grown by metal-organic vapour-phase epitaxy (MOVPE). The influence of QW pairs and QW barrier width on the optical properties of the samples is investigated by means of temperature and incident-power dependent photoluminescence (PL) measurements. The PL emission peaks redshift and the PL peak intensities increase as the number of QW pairs increases. On the other side, a blueshift of the PL peak energy and reduction of the PL peak intensity are observed for the sample with thinner barrier width. These results are explained by carrier localization effect. The S-shaped temperature-dependence of the PL peak energies indicates the existence of localized states induced by the potential fluctuations. The estimated degree of localization effect is found to be enhanced for the sample with more QW pairs and thicker barrier layers. Observing the incident-power dependent PL spectra, the estimated amounts of localization effect of the samples are consistent with the incident-power induced blueshifts of PL peak energies and the slope exponents of power-law form of integrated PL intensity.

Abstract: In this work, a series of novel polymer gel electrolytes with 3D network as ion channels were extensively investigated. Four type polyesters, which are poly (glutaric acid pentaerythritol ester) (PGAPE), poly (adipic acid pentaerythritol ester) (PAAPE), poly (suberic acid pentaerythritol ester) (PSAPE) and poly (pentanedioic acid pentaerythritol ester) (PPAPE), were successfully developed for quasi-solid-state dye-sensitized solar cells (DSCs) with a maximum PCE of 5.32% under AM 1.5 illumination. Photoelectrochemical measurements of the DSCs were conducted by using electrochemical workstation. The present findings indicate that the 3D network structure of polyesters can facilitate the ionic transport and improve the PCE of the DSCs.

Abstract: Temperature effect on the I-V characteristics of tin monoxide thin film transistors (SnO TFTs) has been analyzed. The result shows that the drain current of the SnO TFT obeys the Meyer-Neldel rule under low temperature, where current conduction is a thermally activated process. The carrier transport would be dominated by multiple trapping conduction, while, percolation conduction mechanism holds as the temperature increase.

Abstract: The quasi-regular arrangements porous silicon was fabricated by by electrochemical process using organic solutions with front-side illumination, and SEM showed that the morphology of porous silicon was dependent sensitively on the current density, organic electrolytes and their concentration. The results indicate that N-dimethylformamide (DMF) is the best organic solution and quasi-regular arranged pores can be well organized in 20%HF/DMF solution. The luminescence shows fresh porous silicon can emit the red luminescence at room temperature and quench after nanoporous layer destroyed.

Abstract: Novel application of graphene combined with light emitting materials has been proposed recently due to the plasmonic effects of graphene. Here, we report our investigations on the structural and optical properties of two graphene/ZnO hybrid structures that fabricated based on different ZnO supports. Plasmon-enhanced ultraviolet photoluminescence has been observed from both samples. The combined Raman and photoluminescence studies suggest a strong interaction between ZnO and graphene, which is affected by the surface structures of ZnO. Our results develop insights about the influence of ZnO supports on the PL enhancement and interfacial coupling in graphene/ZnO hybrid structures, which provides a reference for the design and fabrication of optoelectronic devices with high efficiency.

Abstract: In this article, the low-firing Li_2+xNb_3xTi_1-4xO₃(x = 0.01, 0.02, 0.04, 0.06) ceramics with monoclinic structure have been obtained by the traditional solid solution method and their microwave dielectric properties were investigated in detail. The ceramics were finely densified at lower temperatures around 1100 °C and demonstrated favorable dielectric performances including relatively low permittivities (ε_r) ranging from 19 to 24, high Q×f values up to 60,000 GHz (f_res = 7.89GHz) and small temperature coefficients of the resonate frequency (for x = 0.02, τ_f = 10.4 ppm/ °C; x = 0.06, τ_f = -11.5 ppm/ °C). Furthermore, the ceramics could be densified at around 900°C with adding low-amount of B₂O₃. Especially, the 1wt.% B₂O₃-doped Li_2+xNb_3xTi_1-4xO₃ (x = 0.06) ceramics was sintered well-densified at 900°C and presented good microwave dielectric properties with ε_r ∼ 22.2, Q×f ∼ 44,000 GHz. In addition, these ceramics have luminescence properties, which indicated that the ceramics would be applied in LTCC and/or luminescence applications as new luminescence LTCC (low temperature co-fired ceramics) materials.

Abstract: In this paper ZnSb thin films were prepared by radio frequency magnetron sputteringfrom a stoichiometric Zn₄Sb₃ target followed by thermal annealing. The influence of sputteringconditions on microstructure, surface morphology, crystallinity and electrical transport propertieswere investigated. For the range of sputtering power of 50 W to 125 W and working pressure of 0.7Pa, it was found that the content of compound ZnSb phase in the films as well as film crystallinitycould be enhanced greatly by increasing the sputtering power, and this effect may be reinforced bydecreasing the working pressure to 0.2 Pa. At 0.7 Pa, A maximum value of 2.99 μW/cmK² of powerfactor measured at room temperature was obtained at 100 W. The sample prepared at the samepower and lower pressure of 0.2 Pa has a room temperature power factor of 5.46 μW/cmK² which isalmost doubled.

Abstract: Glutaraldehyde cross-linked silk sericin films were successfully prepared. FTIR was applied to characterize the chemical structure of films. Compared to pure silk sericin, cross-linked silk sericin film with 3% glutaraldehyde was found a new peak at 1620 cm^-1 and the peak intensity of cross-linked film decreased markedly, which indicating cross-linking reaction has been occurred. Thermal and swelling behavior of cross-linked films was investigated. The cross-linking reaction increased the thermal decomposition temperature. The swelling ratio of glutaraldehyde cross-linked silk sericin films went up with increasing glutaralehyde loading to 3wt%.

Abstract: We have synthesyzed TiO₂ nanotubes by an anodization method. The cathode was titanium (Ti) sheets and anode was platinum (Pt). The electrolytes were mixtures of ethylene glycol (EG), ammonium fluoride (NH₄F) and deionized water (DI water). The anodizing voltage was set to 50 V and the process was carried out for 2 h. The titanium foils were anodized at room temperature. Then Ag nanoparticles were loaded in TiO₂ nanotube arrays by immersed in 50 ml solutions containing of AgNO₃ (1.0, 1.5 and 2.0 mM) for 24 h. The morphology, structure, and optical properties of the prepared nanotubes were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and and UV-vis spectroscopy (UV-vis) respectively. The structures of TiO₂ nanotubes obtained from the nanotube arrays were crystallized by annealing at 450 °C for 2 h before immersed in solution and immersed in solution before crystallized by annealing are similar. When the concentration of silver nitrate (AgNO₃) increases, the TiO₂ nanotube arrays cracked and are not well arranged.

Abstract: A rotating horizontal electrode is used to substitute the classic vertical electrode in fabrication of anodic TiO₂ nanotube membrane, which alleviates the uneven length distribution. TiO₂ nanotube arrays membrane with more uniform length is thereby obtained and the mechanical property is improved. The CO₂ photoreduction ability of TiO₂ nanotube membrane was then tested.