Guangyi Shang

Cantilevered bimorph-based scanner for high speed atomic force microscopy with large scanning range

A cantilevered bimorph-based resonance-mode scanner for high speed atomic force microscope (AFM) imaging is presented. The free end of the bimorph is used for mounting a sample stage and the other one of that is fixed on the top of a conventional single tube scanner. High speed scanning is realized with the bimorph-based scanner vibrating at resonant frequency driven by a sine wave voltage applied to one piezolayer of the bimorph, while slow scanning is performed by the tube scanner. The other piezolayer provides information on vibration amplitude and phase of the bimorph itself simultaneously, which is used for real-time data processing and image calibration. By adjusting the free length of the bimorph, the line scan rate can be preset ranging from several hundred hertz to several kilohertz, which would be beneficial for the observation of samples with different properties. Combined with a home-made AFM system and a commercially available data acquisition card, AFM images of various samples have been obtained, and as an example, images of the silicon grating taken at a line rate of 1.5 kHz with the scan size of 20 microm are given. By manually moving the sample of polished Al foil surface while scanning, the capability of dynamic imaging is demonstrated.

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.

Catalytic effect of ReAu nanoalloy on the Te particle reaction and its application to resonance scattering spectral assay of CA125.

ReAu nanoparticles with a molar ratio of 2:8 Re and Te nanoparticles were prepared by NaBH₄ reduction. In HCl medium at 65°C, ultratrace Re, Te and ReAu bimetallic nanoparticles strongly catalyzed the slow reaction between Sn(II) and Te(VI) to form Te particles, which exhibited the strongest resonance scattering (RS) peak at 782 nm. As the amount of nanocatalyst increased, the RS intensity at 782 nm (I(782 nm) ) increased linearly, and the increase in intensity ΔI(782 nm) was linear to the ReAu, Re and Te concentrations in the ranges 0.07-9.0, 0.01-4.5 and 30-1200 nM, respectively. As a model, a ReAu immunonanoprobe catalytic Te-particle resonance scattering spectral (RSS) method was established for detection of CA125, using ReAu nanoparticle labeling CA125 antibody (CA125Ab) to obtain an immunonanoprobe (ReAuCA125Ab) for CA125. In pH 7.6 citric acid-Na₂HPO₄ buffer solution, ReAuCA125Ab aggregated nonspecifically. Upon addition of CA125, the immunonanoprobe reacted with it to form ReAuCA125Ab-CA125 dispersive immunocomplex in the solution. After the centrifugation, the supernatant containing the immunocomplex was used to catalyze the reaction of Te(VI)-Sn(II) to produce the Te particles that resulted in the I(782 nm) increasing. The ΔI(782 nm) was linear to CA125 concentration (C(CA125)) in the range 0.1-240 mU/mL. The regression equation, correlation coefficient and detection limit were ΔI(782 nm) = 1.61 C(CA125) + 1.5, 0.9978 and 0.02 mU/mL, respectively. The proposed method was applied to detect CA125 in serum samples, with satisfactory results.

Piezoelectric bimorph-based scanner in the tip-scan mode for high speed atomic force microscope.

A piezoelectric bimorph-based scanner operating in tip-scan mode for high speed atomic force microscope (AFM) is first presented. The free end of the bimorph is used for fixing an AFM cantilever probe and the other one is mounted on the AFM head. The sample is placed on the top of a piezoelectric tube scanner. High speed scan is performed with the bimorph that vibrates at the resonant frequency, while slow scanning is carried out by the tube scanner. The design and performance of the scanner is discussed and given in detailed. Combined with a commercially available data acquisition system, a high speed AFM has been built successfully. By real-time observing the deformation of the pores on the surface of a commercial piezoelectric lead zirconate titanate (PZT-5) ceramics under electric field, the dynamic imaging capability of the AFM is demonstrated. The results show that the notable advantage of the AFM is that dynamic process of the sample with large dimensions can be easily investigated. In addition, this design could provide a way to study a sample in real time under the given experimental condition, such as under an external electric field, on a heating stage, or in a liquid cell.

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.

Resonance-type bimorph-based high-speed atomic force microscopy: Real-time imaging and distortion correction

Resonance-type bimorph-based high-speed atomic force microscopy (HSAFM) capable of operating in the sample-scan and tip-scan modes is presented in this paper. The working principle of the high-speed scanner, the experimental setup, and the data collection system are described in detail. The main characteristic of the high-speed scanner is the use of a piezoelectric bimorph, where one of the piezoelectric layers is used to drive the bimorph beam to scan at a high speed and the other monitors the bimorph vibration. Image distortions due to the phase-lag and sinusoidal scanning are analyzed and simulated. The correction methods for the compensation of the phase-lag and nonlinear movement are proposed based on data shift and nonlinear mapping relations, respectively. The HSAFM imaging at the maximum rate of ~30 frames per second is demonstrated with our data collection and correction program. The image distortions caused by the phase-lag and sinusoidal scanning are effectively eliminated in real-time. This work would provide useful methods for the development of HSAFM and applications in the observation of dynamic processes at nanoscale.

Electrochemical Behavior of LiFePO4 Thin Film Prepared by RF Magnetron Sputtering in Li2SO4 Aqueous Electrolyte

LiFePO4 films were deposited on Au/Si substrate by radio-frequency magnetron sputtering. The effect of annealing on the crystallization and morphology of LiFePO4 thin film has been investigated. X-ray diffraction revealed that the films through annealing were well crystallized compared with as-deposited films. The surface morphology of the thin film was also observed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Electrochemical tests in 1M Li2SO4 showed that the annealed thin film in 500°C exhibits larger Li-ion diffusion coefficient (3.46 × 10-7 cm2s-1) than as-deposited film and powder. Furthermore, cyclic voltammetry demonstrate a well-defined lithium intercalation/deintercalation reaction at around 0.45 V versus SCE (i.e., 3.6 V versus Li+/Li), suggesting that the annealed LiFePO4 thin film is a promising candidate cathode film for lithium microbatteries.

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.