Junen Yao

Microstructure-dependent dielectric properties of TbMnO3 in Au∕TbMnO3∕YBa2Cu3O7−x capacitors

Au∕TbMnO3(TMO)∕YBa2Cu3O7−x(YBCO) capacitors were fabricated on LaAlO3 (LAO) and SrTiO3 (STO) substrates under identical conditions. Dielectric properties were measured in the temperature range from 20to350K. High dielectric constants and single dielectric transition peaks were found in both TMO films. The dielectric constants of TMO film on STO substrate were larger than those of TMO film on LAO substrate; correspondingly, the transition temperature of TMO film on STO substrate was higher than that of TMO film on LAO substrate. Although x-ray diffraction showed both TMO films had the same epitaxial orientation, atom force microscopy revealed that the films had different surface morphologies, which originated from the YBCO layers on different substrates. The good surface morphology of YBCO layer and the element diffusion between TMO and YBCO layers may be suggested to be responsible for the significant improvement in the dielectric properties of TMO thin film.

A Highly Sensitive Resonance Scattering Spectral Assay for Hg2+ Based on the Aptamer-Modified AuRu Nanoparticle-NaClO3-NaI-Cationic Surfactant Catalytic Reaction

Gold ruthenium (AuRu) nanoparticles were modified by single strand DNA (ssDNA) to prepare an aptamer AuRu nanoprobe (AuRussDNA) for Hg2+. The nanoprobe reacted with Hg2+ to form double-stranded T-Hg2+-T mismatches, and the released AuRu nanoparticles aggregated to big particles, which induced an increase in the resonance scattering (RS) signal at 592 nm. The RS signal was linear to the concentration of Hg2+ in the range of 0.0067–3.3 nmol L−1. Using the AuRussDNA in filtration solution as a catalyst, a new catalytic RS assay was proposed for detection of trace Hg2+. This method was applied for the determination of Hg2+ in real samples.

Multi-characterization of LiCoO 2 cathode films using advanced AFM-based techniques with high resolution

AbstarctThe thin film Li-ion batteries have been extensively used in micro-electronic devices due to their miniaturization, high capacity density and environmental friendliness, etc. In order to further prolong the lifetime of the film batteries, one of important tasks is to explore the aging mechanisms of the cathode films. In this paper, we especially focused on the multi-characterization of the LiCoO2 film in nanoscale, which is carried out by combining advanced AFM-based techniques with capacity measurement. The surface morphology, contact stiffness as well as surface potential were measured by amplitude modulation-frequency modulation (AM-FM) and kelvin probe force microscope (KPFM), respectively. Remarkable changes after different numbers of charge/discharge cycling were observed and the intrinsic reasons of them were discussed in detail. To acknowledge the relationship with these microscopic changes, the macro-capacity of the thin films was also measured by the galvanostatic charge/discharge method. These comprehensive results would provide a deep insight into the fading mechanism of the cathode film, being helpful for the design and selection of the cathode film materials for high performance batteries.

Dielectric characteristics of Fe-doped LaTiO3+δ and visible light modulation

Fe-doped La1−xFexTiO3+δ (x = 0.05, 0.1, and 0.3, 0.4) ceramic samples are prepared via a traditional solid-state reaction route. The low temperature (77 K ≤ T ≤ 360 K) dielectric properties of the samples have been systematically investigated in the frequency range from 100 Hz to 1 MHz. It is clearly observed that extraordinarily high low-frequency dielectric constants appear at room temperature in La0.6Fe0.4TiO3+δ, which is ∼1000 times larger than that of La0.95Fe0.05TiO3+δ. Interestingly, the dielectric characteristics of the samples have obvious light dependence at room temperature within the measured frequency range. The results have demonstrated that visible light improves the dielectric properties of the ceramics by means of I–V and complex impedance analysis.

A novel optical beam deflection detection system based on asphericlens for high-speed atomic force microscope

The optical lever detection method has been widely used to detect the cantilever deflection in atomic force microscope (AFM) due to its simple mechanism and high sensitivity. The deflection detection of very small cantilever is a key and difficult issue in the development of a high-speed AFM. In this paper, a specially designed optical beam deflection detection system based on an aspheric lens is presented. The aspheric lens is fixed on an adjustable metal tube above the cantilever to focus the laser beam with a small spot. Two laser line beamsplitter cubes are installed symmetrically and oppositely over the aspheric lens with separately mounting a diode laser and a position sensitive detector (PSD) on two translation stages at the same height. The collimated laser beam is reflected down by one cube and focused by the aspheric lens at an off-centered position. The focused beam is then incident upon the cantilever and reflected back onto the opposite off-centered position. Change in the reflection angle caused by the cantilever deflection results in a parallel shift of the outgoing laser beam after the aspheric lens. The laser beam is finally reflected onto the PSD by the other cube. Experimental results show that the laser beam can be focused with a spot of less than 16 μm in diameter. With above system, the deflection detection of the small cantilever can be realized, which meets the requirement for the use in a high-speed AFM.

An alternative flat scanner and micropositioning method for scanning probe microscope

An alternative flat scanner used for combining a scanning probe microscope with an inverted optical microscope is presented. The scanner has a novel structure basically consisting of eight identical piezoelectric tubes, metal flexure beams, and one sample mount. Because of the specially designed structure, the scanner is able to carry a sample of more than 120 g during imaging. By applying voltages of ±150 V, scanning range of more than 30 μm in three dimensions can be achieved. To improve the reliability of the stick-slip motion, a new method for sample micropositioning is proposed by applying a pulsed voltage to the piezotubes to produce a motion in the z-axis. Reliable translation of the sample has been thus accomplished with the step length from ∼700 nm to 9 μm over a range of several millimeters. A homemade scanning probe microscope-inverted optical microscope system based on the scanner is described. Experimental results obtained with the system are shown.

Oscillatory Motions of a Cantilever in High-Speed Atomic Force Microscopy in Constant-Height Mode

The dynamic behavior of a rectangular cantilever in high-speed atomic force microscopy (AFM) in constant-height mode is studied. Experiments were first performed to observe how the AFM cantilever responds to a surface steplike structure. Oscillatory motions of the cantilever tip occuring in the structure were then simulated based on the damped point-mass model. Simulation results are in agreement with the experimental observation. The effects of resonance frequency and spring constant on oscillation were simulated as important parameters of the cantilever. Those results would be helpful for the understanding and analysis of the dynamic behavior of a cantilever in high-speed AFM.