Guan Jianguo

Ion sensitive field effect transducer-based biosensors.

Ion-sensitive field effect transistors (ISFETs) have found growing interest in the rapidly developing field of biosensors. The principles, application and new developing techniques of ISFET-based biosensors are reviewed.

Preparation and characterization of monodisperse nickel nanoparticles by polyol process

Polymer-protected monodisperse nickel nanoparticles were synthesized by a modified polyol reduction method in the presence of poly (N-vinyl-2-pyrrolidone). These nanoparticles were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), selected area electron diffraction (SAED), as well as vibrating sample magnetometer (VSM). The experimental results show that the addition of PVP and the concentration of NaOH have strong influences on the size, agglomeration and uniformity of nanoparticles. In the presence of PVP and NaOH with low concentrations, monodisperse nickel nanoparticles with average diameters about 42 nm were obtained and characterized to be pure nickel crystalline with fee structure. Secondary structures such as clusters, loops, and strings resulted from magnetic interactions between particles were observed. The chemical interaction between the PVP and nickel nanoparticles was found by FTIR. The saturation magnetization (Ms), remarem magnetization (Mr) and coercivity (HC) of these nickel nanoparticles are lower than those of balk nickel.

THE MICRO–FABRICATING PROCESS AND ELECTROMAGNETIC PROPERTIES OF TWO KINDS OF Fe POWDERS WITH DIFFERENT GRAIN SIZES AND INTERNAL STRAINS

The micro-fabricating process and electromagnetic properties of two kinds of Fe pow- ders with different grain sizes and internal strains were studied. The results show that the homemade Fe powders with smaller grain size, larger internal strain and surface roughness than the carbonyl Fe powders, evolve into big and thin Fe flakes by micro-fabricating for 10 h with the help of the process control agent (PCA). When micro-fabrication for t=12 h, these Fe flakes will fracture and their av- erage width will reduce due to strong internal strain. When t is further prolonged to 24 h, these Fe flakes become thinner, finally, those with larger aspect ratio and smaller width can be obtained, which show high permeability and low permittivity. The epoxy resin-based microwave absorbing materials containing such Fe flakes of 20% (volume fraction) exhibit a reflection loss less than 10 dB in the 9.4—17.9 GHz frequency range with a minimal peak of 14.6 dB, whose average thickness is 1.5 mm.

Effect of interface-roughness scattering on mobility degradation in SiGe p-MOSFETs with a high-k dielectric/SiO2 gate stack

A physical model for mobility degradation by interface-roughness scattering and Coulomb scattering is proposed for SiGe p-MOSFET with a high-k dielectric/SiO2 gate stack. Impacts of the two kinds of scatterings on mobility degradation are investigated. Effects of interlayer (SiO2) thickness and permittivities of the high-k dielectric and interlayer on carrier mobility are also discussed. It is shown that a smooth interface between high-k dielectric and interlayer, as well as moderate permittivities of high-k dielectrics, is highly desired to improve carriers mobility while keeping a low equivalent oxide thickness. Simulated results agree reasonably with experimental data.

Electrorheological particles composed of polyaniline core and BaTiO3 layer shell

Composite particles consisting of polyaniline (PAn) core and barium titanate (BaTiO3) layer shell were synthesized. The PAn-BaTiO3 composites particles were characterized with TEM and XRD. The dielectric behavior of particles was tested and the electrorheological (ER) behavior of the suspensions of PAn/BaTiO3 particles in chlorinated paraffin oil with a 20 vol% was investigated under DC electric field. The results show that the ER effect of composite particle is far stronger than that of pure polyaniline and barium titanate which were synthesized by the same method. pH and thickness of BaTiO3 have an important influence on the ER effects.

XRD and HRTEM analyses of the ball milled nanocrystalline FeCo alloy

The nanostructures of the ball milled FeCo particles were characterized as functions of the ball milling time (t) using quantitative X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM) analysis techniques. The results show that the nanocrystalline bcc FeCo particles are available using carbonyl iron and cobalt powders as the start materials during the high-energy ball milling. At the early stage of ball milling, Co powders are easily mashed into nanocrystalllites, by which the surface of the larger Fe particles of about 80–150 nm is coated. With t increasing, the refinement of grain size and the incorporation of defects including dislocations, disclinations and grain boundaries happen, and then FeCo alloy with a certain layered structure is formed, finally the layered structure disappears with the formation of isotropic grains having a steadystate grain size in the nanometer regime after a certain period of t.

Microwave permeability change of FeCo nanocrystalline during high energy ball milling

The microwave magnetic properties of the ball milled FeCo particles were investigated as functions of ball milling time (t) using microwave electromagnetic parameters analysis techniques. The results show that the imaginary part of intrinsic dynamic permeability (μi) of the ball-milled particles is much bigger than that of raw powders. μi strongly depends on t and exhibits several slightly damped ferromagnetic resonances. These phenomena are in qualitative agreement with the formation of the corresponding microstructure or the Aharoni s model of non-uniform exchange resonance modes. The present microwave permeability behavior indicates that nanocrystalline materials with the same grain size may exhibit different properties that depend upon the microstructure, which provides a possibility for manufacturing high performance microwave absorber.

Study on electromagnetorheological fluid containing CuPc−Fe3O4 nanoparticles composite

Electromagnetorheological (EMR) fluids containing CuPc−Fe3O4 nanopareticles composite were prepared and their properties were studied. The results show that Δτ of this kind of EMR fluids increases with the increments of applied electric field, magnetic field and volume fraction of the nanoparticles composite. Δτ has an approximate linear relationship with γ. When an electric and magnetic field are applied simulateously, the EMR fluids have a synergistic effect. The EMR fluids have a good long-term stability.

Design strategies and structure simplification methods of self-propelled micro-/nanomotors

Self-propelled micro-/nanomotors (MNMs), which are defined as micro-/nanodevices capable of converting various energy into autonomous motion, can be used to pick up, transport, and release various cargoes within a liquid medium. They have important potential applications, for example, in drug delivery, biosensors, protein and cell separation, microsurgeries and environment remediation. This review comprehensively introduces the design strategies and structures of self-propelled MNMs along with an outlook for their future development. It starts with the summary of the propulsion mechanisms of self-propelled MNMs of bubble recoiling and self-phoresis induced by the asymmetric release of products or heat. For bubble recoiling propulsion, the continuous momentum change is caused by a jet of bubbles, while for self-phoresis propulsion, the MNMs move in a local electric field, concentration gradient, surface tension gradient, or temperature gradient, etc. After systematically and in-depth understanding these propulsion mechanisms, it has been pointed out that the key to design self-propelled MNMs is to construct an asymmetric field across micro-/ nanoparticles. Following this clue, the structures evolution and simplification methods of self-propelled MNMs are reviewed. Janus structures and multilayer-tubular structures, which are prepared through asymmetric modification process, electrochemical synthesis, template-assisted method, rolled-up nanotech, etc., have been firstly proposed to construct asymmetric fields across micro-/nanoparticles for their propulsion. However, the complicated structure and preparation process hinder the application of MNMs. Anisotropic single-component irregular particles, tubes and bowl-like MNMs, which are obtained by dry spinning method, “growing-bubble”-templated self-assembly, etc., have been subsequently achieved by utilizing their anomalous morphology and the nucleation preference of bubble molecules on different surfaces. This kind of MNMs show somewhat simple structure and can be easily fabricated, but the motion direction is still difficult to control because of the Brownian motion. Isotropic semiconducting MNMs have been recently developed by taking advantage of the limited light penetration depth in the isotropic photoresponsive particles, of which the motion is independent of the rotational Brownian motion. This suggests a remarkable breakthrough in design strategy of MNMs due to the simple isotropic structure of the motor and the controllability in both motion direction and speed by light. Besides the evolution of self-propelled MNMs from the complicated structure to the simplified one, some remarkable progresses have also been made on the motion control, functionalization, etc. For example, the speed and state of MNMs can so far be easily adjusted by the concentration of fuels, the intensity of external fields, etc. The direction can be controlled accurately by magnetic field, electric field, light, etc. Numerous complex tasks can also be performed effectively, such as protein separation, drug delivery, environmental detection and remediation, etc. Lastly, an outlook is also provided on the future development and main challenges of self-propelled MNMs. The future development of MNMs should be focused on improving energy conversion efficiency through optimization of structures, exploring new propulsion mechanisms and endowing MNMs with environmental responses for self-navigation, detection, and specific operations. In this way, MNMs will approach to the practical applications in biomedicine, environment treatment, microengineering, etc.

Thermal instability and microstructure of strontium M-type hexaferrite nanoparticles synthesized by citrate approach

The dried gel of SrFe12O19, prepared by citrate approach, was investigated by means of infrared spectroscopy (IR), thermograimetric analysis (TG), differential scanning calorinetry (DSC), X-ray diffraction (XRD) techniques, energy dispersive spectroscopy (EDS), and transmission electron microscopy (TEM). The thermal instability and the thermal decomposition of low-temperature strontium M-type hexaferrite crystallized at about 600°C were confirmed for the first time by XRD method. The decomposition of the low-temperature strontium M-type hexaferrite took place at about 688.6°C determined by DSC investigation. The low-temperature strontium M-type hexaferrite nanoparticles were decomposed into SrFeO2.5 with an orthorthombic cell and Fe2O3 with a tetragonal cell as well as possible α-Fe2O3. The agglomerated particles with sizes less than 200 nm obtained at 800°C were plesiomorphous to strontium M-type hexaferrite. The thermally stable strontium M-type hexaferrite nanoparticles with size less than 100 nm could take place at 900°C. Up to 1000°C, the phase transformation to form strontium M-type hexaferrite was ended, the calcinations with the sizes more than 1 μm were composed of α-Fe2O3 and strontium M-type hexaferrite. The method of distinguishing γ-Fe2O3 with a spinel structure from Fe2O3 with tetragonal cells by using powder XRD method was proposed. Fe2O3 with tetragonal cells to be crystallized before the crystallization of thermally stable strontium M-type hexaferrite was confirmed for the first time. The reason why α-Fe2O3 as an additional phase appears in the calcinations is the cationic vacancy of strontium M-type hexaferrite,SrFel2-x▭xO19(0⩽x⩽0.5). 3