Measurement of refractive index variation of liquids by surface plasmon resonance and wavelength-modulated heterodyne interferometry

In this study an alternative method based on surface plasmon resonance is proposed for in-situ monitoring of variation in the refractive index of a test sample. A wavelength-modulated light source and an unequal-path-length optical configuration heterodyne interferometer are used to detect the phase difference change, which can then be used to estimate the change in the refractive index of a test sample. The experimental results demonstrate a phase stability of 0.02°. The resolution power of the refractive index is 1.5 × 10^− 6 RIU. This method has several advantages over previously used methods such as simple optical setup, easier operation in real time, and low cost.     

Applications of vertically oriented TiO2 micro-pillars array on the electrode of dye-sensitized solar cell

In this research, dye-sensitized solar cells based on TiO₂ micro-pillars fabricated by inductive couple plasma etcher were investigated by analyses of X-ray diffraction (XRD), scanning electron microscopy (SEM), contact angle, ultraviolet-visible absorption spectra (UV-vis), and current-voltage characteristics. X-ray diffraction patterns show that the TiO₂ anatase phase forms while sintering at 450 °C for 30 min. The SEM images reveal that the diameter and height of TiO₂ micro-pillars are about 3 and 0.8 μm, respectively. The measurements of contact angle between TiO₂ micro-pillars and deionized water (DI water) reveal that the TiO₂ micro-pillars is super-hydrophilic while annealed at 450 °C for 30 min.The absorption spectrum of TiO₂ micro-pillars is better than TiO₂ thin film and can be widely improved in visible region with N3 dye adsorbed. The results of current-voltage (I-V) characteristics analysis reveal that dye-sensitized solar cell with TiO₂ micro-pillars electrode has better I-V characteristics and efficiency than TiO₂ film electrodes. This result may be due to the annealed TiO₂ micro-pillars applied on the electrode of dye-sensitized solar cell can increase the contact area between TiO₂ and dye, resulting in the enhancement of I-V characteristics and efficiency for dye-sensitized solar cell.     

Ferromagnetic films with magnon bandgap periodic structures: Magnon crystals

A new type of photonic crystals is proposed. The new crystals have a forbidden gap in the microwave spectrum of magnetostatic spin waves, and, by analogy with photonic crystals, they are called magnon crystals. Specimens of such crystals were fabricated on the basis of yttrium iron garnet films. The surfaces of ferromagnetic films containing two-dimensional etched hole structures were studied by atomic force and magnetic force mag-netometry. The propagation of spin waves through the magnon crystals was investigated.     

An axial flow cyclone to remove nanoparticles at low pressure conditions

In this study, the axial flow cyclone used in Tsai et al. (2004) was further tested for the collection efficiency of both solid (NaCl) and liquid (OA, oleic acid) nanoparticles. The results showed that the smallest cutoff aerodynamic diameters achieved for OA and NaCl nanoparticles were 21.7 nm (cyclone inlet pressure: 4.3 Torr, flow rate: 0.351 slpm) and 21.2 nm (5.4 Torr, 0.454 slpm), respectively. The collection efficiencies for NaCl and OA particles were close to each other for the aerodynamic diameter ranging from 25 to 180 nm indicating there was almost no solid particle bounce in the cyclone. The 3-D numerical simulation was conducted to calculate the flow field in the cyclone and the flow was found to be nearly paraboloid. Numerical simulation of the particle collection efficiency based on the paraboloid flow assumption showed that the collection efficiency was in good agreement with the experimental data with less than 15% of error. A semi-empirical equation for predicting the cutoff aerodynamic diameter at different inlet pressures and flow rates was also obtained. The semi-empirical equation is able to predict the cutoff aerodynamic diameter accurately within 9% of error. From the empirical cutoff aerodynamic diameter, a semi-empirical square root of the cutoff Stokes number, , was calculated and found to be a constant value of 0.241. This value is useful to the design of the cyclone operating in vacuum to remove nanoparticles.     

Structural, electrical, optical and magnetic properties of Co0.2AlxZn0.8−xO films

Co_0.2Al_xZn_0.8−xO films prepared with different molar ratio of aluminum nitrate to zinc acetate were deposited on substrates by the sol-gel technique. X-ray diffraction, photoluminescence and ferromagnetism measurements were used to characterize the Co_0.2Al_xZn_0.8−xO diluted magnetic semiconductors. The authors found that the intensity of the acceptor-related photoluminescence increased with increasing aluminum concentration and an increase in the number of the acceptor-like defects (zinc vacancies especially) in the Co_0.2Al_xZn_0.8−xO film might lead to the enhancement of the magnetic properties. This implies that controls of the aluminum concentration and the number of the acceptor-like defects are important factors to produce strong ferromagnetism Co_0.2Al_xZn_0.8−xO films prepared by the sol-gel method.     

Phonon–replica transitions in InGaN/GaN quantum well structures

A side-bump feature in a photoluminescence (PL) spectrum of an InGaN compound was widely observed. With reasonable fitting to PL spectra with three Gaussian distributions, the temperature variations of the peak positions, integrated PL intensities, and peak widths of the main and first side peaks of three InGaN/GaN multiple quantum well samples with different nominal indium contents are shown and interpreted. The existence of the side peaks is attributed to phonon–replica transitions. The variations of the peak position separations and the decreasing trends of the first side peak widths beyond certain temperatures in those samples were explained with the requirement of phonon momentum condition for phonon–replica transitions. In the sample with 25% nominal indium content, the phonon–replica transition could become stronger than the direct transition of localized states.     

Improvement of photoluminescence mechanism of CTA-treated Si-implanted SiO2 films by using RTA

In this paper, a shift in the photoluminescence (PL) peak from blue to near-infrared region was observed in the Si⁺-implanted 400-nm-thick SiO₂ films with the rapid thermal annealing (RTA) method only. As the Si⁺-fluence was 1×10¹⁶ ions/cm², a blue band was observed in the films after RTA at 1050 °C for 5 s in dry-N₂ atmosphere; then, the band shifted from blue to orange upon increasing the holding temperature of RTA to 1250 °C in the films after the isochronal RTA in dry N₂. Furthermore, while the fluence was increased to 3×110¹⁶ ions/cm² and the holding temperature was at the same range between 1050 and 1250 °C, the PL peak occurred between red and near-infrared regions. Although the RTA and conventional thermal annealing (CTA) methods produce a similar mechanism, the CTA method needs a much longer annealing-time and a higher Si⁺-implanted dose than the RTA method for producing the same shift and intensity of PL peak from the as-implanted sample. Therefore, the RTA method can produce the mechanism in the Si⁺-implanted sample with the PL energy between blue and near-infrared band in place of the CTA method.     

Transition from disorder to order in thin metallic films studied with angle-resolved photoelectron spectroscopy

The transition from disorder to order in Ag film grown on Au(111) was investigated by monitoring the quantum well states using angle-resolved photoelectron spectroscopy. Our results show that the binding energies do not alter, but the in-plane dispersion alters from flat to parabolic when the film is annealed. We suggest that there are isolated and ordered patches scattered across the film at an early stage of the transition and that atoms inside the patches are fully ordered along the surface normal. These ordered patches grow and merge together as the annealing temperature increases.     

Using photoelectron emission microscopy with hard-X-rays

We present several successful test cases of using photoelectron emission microscopy (PEEM) for photon energy up to 25 keV. First, the full extended X-ray absorption fine structure analysis was implemented in areas as small as 100 μm² for transition-metal K edge absorption spectra and, therefore, demonstrated the feasibility of combining structural and chemical analysis with hard-X-ray absorption spectroscopy with high lateral resolution. We also show that PEEM can be used in a transmission (radiography) mode as an imaging detector for hard-X-ray. This approach again leads to the unprecedented 0.3 μm lateral resolution, particularly critical for the use of coherence-based phase contrast techniques in real time X-ray radiology.