[en] The blue emission and near-infrared (NIR) up-conversion photoluminescence and dielectric relaxation of Tm³⁺/Yb³⁺ co-doped (Bi, Y)₂Ti₂O₇ pyrochlore thin films prepared by a chemical solution deposition method have been investigated. The pyrochlore phase has been maintained for all compositions. Intense blue and NIR emission can be detected on the thin films on fused silica substrates excited by a 980 nm diode laser. Three UC emission bands centered at 480 nm, 665 nm, and 800 nm in the spectra can be assigned to ¹G₄→³H₆, ¹G₄→³F₄ and ³H₄→³H₆ transitions of Tm³⁺ ions, respectively. The dependence of UC emission intensity on pumping power indicates that the blue emission of the thin films follows a three-photon process while the NIR emission is a two-photon process. The thin films also exhibit a relatively high dielectric constant and a low loss as well as good bias voltage stability. Temperature and frequency dependent dielectric relaxation has been investigated. This study suggests that Tm³⁺/Yb³⁺ co-doped (Bi, Y)₂Ti₂O₇ thin films can be applied to new multifunctional photoluminescence dielectric thin-film devices. -- Highlights: • Tm³⁺/Yb³⁺ co-doped (Bi, Y)₂Ti₂O₇ films were prepared by chemical solution deposition. • Intense blue and near-infrared (NIR) emission can be detected under 980 nm excitation. • Blue emission is a three-photon process while NIR emission a two-photon process. • The thin films have a relatively high dielectric constant and a low loss. • The thin films exhibit temperature and frequency dependent dielectric relaxation

[en] We report abnormal ferroelectric properties of compositionally graded Pb(Zr,Ti)O₃ thin films on LaNiO₃-coated SiO₂/Si substrates, where Pb(Zr,Ti)O₃ and LaNiO₃ films were prepared by a metalorganic decomposition technique and a sol - gel technique, respectively. It was found that the hysteresis loops of the Pb(Zr,Ti)O₃ graded films measured by the conventional Sawyer - Tower method shifted along the polarization axis, i.e., they showed polarization offsets when applied by an alternating electric field. The polarization offsets were 82.5 μC/cm² at 270 kV/cm and 62.5 μC/cm² at 185 kV/cm for the up-graded film and the down-graded film, respectively. The absolute magnitude of the polarization offsets was closely related to the magnitude of the driving electric field, and the direction of the polarization offsets depended on the direction of the composition gradient with respect to the substrate. Analysis indicated that the polarization offsets did not originate from asymmetric contact effects, oxygen vacancies, alignment of defect dipoles, and/or electron injection. These results showed that polarization offsets in hysteresis loops were the intrinsic characteristic of the compositionally graded Pb(Zr,Ti)O₃ thin films. [copyright] 2001 American Institute of Physics

[en] Photoluminescent (PL) and dielectric properties of La_1−xEu_xAlO₃ thin films were investigated in terms of Eu doping content (x = 0, 0.02, 0.04, 0.06, 0.08, and 0.1) and annealing temperature. The La_1−xEu_xAlO₃ thin films were prepared by a chemical solution deposition method and characterized by X-ray diffraction, field emission scanning electron microscopy, photoluminescence and dielectric measurement. The thin films were dense with a uniform thickness, and showed bright red-orange emissions, originated from the ⁵D₀ → ⁷F₂ and ⁵D₀ → ⁷F₁ transitions of Eu³⁺ ions. A stronger emission of ⁵D₀ → ⁷F₂ than that of ⁵D₀ → ⁷F₁ was attributed to Eu³⁺-doping induced structural distortion. The strongest PL intensity was observed in the thin films with a Eu³⁺-doping content x of 0.06, indicating the existence of concentration quenching effect of photoluminescence. Further lifetime study of photoluminescence indicated that the concentration quenching effect was due to the lifetime decrease of ⁵D₀ → ⁷F₁ and ⁵D₀ → ⁷F₂ transitions when Eu³⁺-doping content x increased. In addition, highly stable dielectric-bias electric field properties of Eu³⁺-doped LaAlO₃ thin films have been confirmed. Our study suggests that Eu³⁺-doped LaAlO₃ thin films have potential applications in integrated thin-film optoelectronic devices.

[en] (200)-oriented Eu-doped cerium oxide thin films were fabricated, on fused silica substrates by a chemical solution deposition method. The thin films obtained were characterized by X-ray diffraction, field emission scanning electron microscopy, X-ray photoelectron spectroscopy, and photoluminescence measurements. Ce with valence state 4 + is confirmed to be predominant in Eu-doped CeO_2 thin films. All the thin films were dense and crack-free, and showed bright orange-red emissions under ultraviolet light excitation, originated from the "5D_0 → "7F_1 and "5D_0 → "7F_2 transitions of Eu"3"+ ions. Structure distortions induced by Eu-doping affected the light emission of electric dipole transition "5D_0 → "7F_2. The strongest photoluminescent intensity was observed in the thin films with a Eu-doping content x of 0.08, indicating the existence of concentration quenching effect of photoluminescence. Lifetime study of photoluminescence indicated that the decrease of lifetime was originated from augmented pathway for deactivating excited Eu"3"+ ions. Our study suggests that Eu"3"+-doped CeO_2 thin films have potential applications in optoelectronic devices. - Highlights: • Ce_1_−_xEu_xO_2 thin films were prepared by chemical solution deposition. • The thin films show strong red-orange emission. • There is concentration quenching effect of photoluminescence. • Eu-doping leads to structure distortion of the thin films. • The thin films have potential applications in optoelectronic devices

[en] Highly c-axis oriented Bi_2−xEu_xVO_5.5 (x = 0, 0.05, 0.10, 0.15, and 0.20) thin films were prepared on Pt(111)/Ti/SiO₂/Si and fused silica substrates by using chemical solution deposition method, and characterized by X-ray diffraction, scanning electron microscopy, and optical and electrical measurements. Under 356 nm UV irradiation, a bright red photoluminescence can be observed in the thin films with x = 0.10, 0.15, and 0.20. The emission spectra included two strong peaks which originated from ⁵D₀ → ⁷F₁ (595 nm) and ⁵D₀ → ⁷F₂ (619 nm) transitions of Eu³⁺ ions. With increasing Eu³⁺-doping content x, the dielectric dispersion weakened, and dielectric loss decreased. Eu³⁺ doping can also decrease the leakage current of the thin films. These results demonstrate that Bi_2−xEu_xVO_5.5 thin films are a kind of multifunctional material with potential applications in luminescent ferroelectric devices. - Highlights: • c-axis oriented Bi_2−xEu_xVO_5.5 films were prepared by chemical solution deposition. • The thin films show bright red emission. • Eu³⁺-doping leads to weakened dielectric dispersion and decreased dielectric loss. • The thin films have potential applications in luminescent ferroelectric devices

[en] Eu"3"+-doped Bi_2Ti_2O_7 pyrochlore structure thin films were prepared by a chemical solution deposition method. The red-orange photoluminescence and dielectric relaxation of Bi_2_−_xEu_xTi_2O_7 thin films have been investigated in terms of Eu"3"+ doping content (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5, and 0.6) and annealing temperature. The crystallinity and surface morphology of the thin films were evaluated by X-ray diffractometer and field emission scanning electron microscopy. It was shown that the thin films annealed at 600 °C were well crystallized in pyrochlore structure without other impurity phases. Intense visible red-orange photoluminescence, originated from doubly split electric-dipole "5D_0→"7F_2 and magnetic-dipole "5D_0→"7F_1 transitions of Eu"3"+ ions, could be observed under ultraviolet excitation. The quenching concentration for photoluminescence of Bi_2_−_xEu_xTi_2O_7 thin films is about x = 0.5. In addition, the Bi_2_−_xEu_xTi_2O_7 thin films had a relatively low dielectric loss and a high dielectric constant as well as highly stable bias electric field properties. Meanwhile, the thin films exhibited dielectric relaxation based on the temperature and frequency dependence of dielectric properties. Our study suggested that Eu"3"+-doped Bi_2Ti_2O_7 thin films have potential applications in new multifunctional optoelectronic thin-film devices. - Highlights: • Bi_2_−_xEu_xTi_2O_7 pyrochlore films were prepared by chemical solution deposition. • The red-orange photoluminescence from Eu"3"+ ions was observed. • Dielectric relaxation of the thin films was confirmed. • The films had relatively low dielectric loss and good bias electric field stability. • The films have potential applications in multifunctional optoelectronic devices

[en] Highlights: • High-performance resistive switching Pt/TiO₂/Pt memory cells were obtained. • Amorphous TiO₂ layer was prepared by low-temperature photochemical deposition. • Pt/TiO₂/Pt memory cells exhibited excellent resistive switching parameters. • UV irradiation led to the formation of enhanced metal-oxide bonds. • Resistive switching corresponded to the formation/rupture of conductive filaments. - Abstract: High-performance resistive switching Pt/TiO₂/Pt memory cells were fabricated. The amorphous TiO₂ active layer was prepared by using a low-temperature photochemical solution deposition method—a simple preparation process combining first chemical solution deposition of the TiO₂ film layer and subsequent ultraviolet (UV) irradiation treatment. The obtained Pt/TiO₂/Pt memory cells exhibited excellent resistive switching parameters, such as centralized distribution of set and reset voltages, stable current values at high and low resistance states, and long retention time. The conductive mechanisms of high resistance state and low resistance state were Schottky emission and Ohmic conduction, respectively. The X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and scanning electron microscopy characterization of the TiO₂ thin films indicated that the UV irradiation treatment can lead to decomposition of the residual organics and the formation of enhanced metal-oxide bonds in the thin films. On the basis of the analysis of current–voltage characteristics and the temperature dependence of resistance, we explained the resistive switching phenomenon for Pt/TiO₂/Pt devices by using the model of formation/rupture of conductive filaments. Our study also suggested that the simple photochemical solution deposition method can be used for preparing some other oxide thin films with good resistive switching properties at low processing temperature which is promising to be extended to flexible resistive switching devices

[en] Particle separation is of great importance for a wide range of applications, such as biochemistry and biomedicine, and has been demonstrated using various techniques. Generally, these techniques necessitate carefully microfabricated devices and the assistance of microfluidics, thus making the separation difficult to accomplish. Here, we report a flexible, handy, and highly efficient optical method for particle separation using two tapered optical fibers, avoiding the use of complicated devices. By launching a laser beam with a power of 80 mW and wavelength of 1.55 μm into the first tapered fiber, particles of SiO₂ with a size of 3.14 μm and poly(methyl methacrylate) (PMMA) with a size of 10 μm were trapped and collected. As the laser (330 mW) was switched to the second fiber for 29 s, SiO₂ and PMMA particles were separated with separation efficiencies of 89.1% and 92.4%, respectively, because of their different photophoretic velocities. The separation performance was further demonstrated using different mixtures, with all separation efficiencies higher than 78%. The separation mechanism was explained by numerical simulations. (letter)

[en] We report uniform bipolar resistive switching characteristic with self-compliance effect of Pt/TiO₂/p-Si devices in which TiO₂ thin films were prepared directly on p-Si substrates by chemical solution deposition method. The resistive switching parameters of the Pt/TiO₂/p-Si cell obtained, such as distribution of threshold voltages, retention time, as well as resistance variation of high resistance state (HRS) and low resistance state (LRS), were investigated, and the conduction mechanisms of HRS and LRS were analyzed. The conductive mechanism at LRS and low voltage region of HRS was dominated by Ohmic law. At the high voltage region of HRS, the conductive mechanism followed the space charge limited current theory. The resistive switching phenomenon can be explained by electron trapping and de-trapping process, in which the defects (most probably oxygen vacancies) act as electron traps. Our study suggests that using p-type silicon as bottom electrode can provide a simple method for fabricating a resistive random access memory with self-compliance function. In addition, the Pt/TiO₂/p-Si configuration is compatible with complementary metal oxide semiconductor process

[en] A stable ECR plasma was produced and sustained in HER mirror using 2450MHz Whistler wave. The parameters of the ECR plasma and their chaining characters were studied in detail and were compared with those of the DC discharge plasmas. The conclusion is that the ECR plasma is a high ionizability, low temperature, middle density plasma, its peak density may much exceed the cutoff density of the pump wave (when ω = ω_pe) and arrive at the order of 10¹²cm^-3. The ECR plasma includes some high energy hot electrons (20Kev-200Kev) and middle energy warm electrons (< 20Kev). Those two kinds of electron created some strong X-ray emissions in a wide frequency range. The ECR plasma has higher edge density and can strongly interact with the wall. (author). 9 refs, 17 figs