C. W. Leung

A Polyferroplatinyne Precursor for the Rapid Fabrication of L1 0 -FePt-type Bit Patterned Media by Nanoimprint Lithography

A polyferroplatinyne polymer can be patterned on the surface of Si wafer in ordered nanoline or nanodot shapes with PDMS molds through nanoimprint lithography (NIL), and subsequent thermal treatment gives rise to the nanopatterned arrays of L1(0) -FePt nanoparticles with the same periodicities. The method offers excellent potential to be utilized in the simple and rapid fabrication of bit patterned media for magnetic data recording.

Liver cancer immunoassay with magnetic nanoparticles and MgO-based magnetic tunnel junction sensors

We have demonstrated the detection of alpha-fetoprotein (AFP) labeled with magnetic nanoparticles (MNPs) using MgO-based magnetic tunnel junction (MTJ) sensors. AFP is an important hepatic tumor biomarker and the detection of AFP has significant applications for clinical diagnostics and immunoassay for early-stage liver cancer indications. In this work, MgO-based MTJ sensors and 20-nm iron-oxide magnetic nanoparticles (MNPs) were used for detecting AFP antigens by a sandwich-assay configuration. The MTJ sensors with a sensing area of 4 × 2 μm2 possess tunneling magnetoresistance (TMR) of 122% and sensitivity of 0.95%/Oe at room temperature. The target AFP antigens of three concentrations were successfully detected, and the experimental data indicate that the resistance variations of the MTJ sensor increased with the AFP concentration ratios proportionally. These results demonstrate that MgO-based MTJ sensors together with MNPs are a promising biosensing platform for liver cancer immunoassay.

Effect of the magnetic order on the room-temperature band-gap of Mn-doped ZnO thin films

Exchange interaction between localized magnetic moments mediated by free charge carriers is responsible for a non-monotonic dependence of the low-temperature energy band-gap in dilute magnetic semiconductors. We found that in weakly doped Mn-ZnO films, increasing the exchange interaction by increasing the concentration of free charge carriers results in a red-shift of the near-band-edge emission peak at room temperature. An increase of Mn concentration widens the band gap, and a blue-shift prevails. Exchange interaction can be used to tune the room-temperature optical properties of the wide-band gap semiconductor ZnO.

One-dimensional tunable ferroelectric photonic crystals based on Ba0.7Sr0.3TiO3/MgO multilayer thin films

Tunable photonic crystals (PCs) have attracted much attention in the past decade because of their various applications, such as ultrafast optical filters and optical waveguides with add–drop functionalities. One way of achieving tunability is to make use of ferroelectric materials since the refractive index of ferroelectric materials can be electrically tuned through the electro-optic effect. In this paper, we present our work on developing a tunable one-dimensional (1D) PC based on a Ba0.7Sr0.3TiO3/MgO multilayer structure. The photonic band structures and band gap maps of the PC were calculated by using the plane-wave expansion (PWE) method. It is found that the gap center linearly shifts with the change in the refractive index of Ba0.7Sr0.3TiO3. A ferroelectric 1D PC consisting of a Ba0.7Sr0.3TiO3/MgO multilayer thin film was epitaxially deposited on a MgO (001) single-crystal substrate by pulsed laser deposition. A photonic band gap in the visible region is observed in the transmission spectrum of the...

Formation of core/shell structured cobalt/carbon nanoparticles by pulsed laser ablation in toluene

Magnetic cobalt nanoparticles encapsulated in shells of layered structure have been produced by the technique of pulsed laser ablation in toluene. The morphology, microstructure, and magnetic properties of the prepared nanoparticles were characterized by electron microscopy, micro-Raman spectroscopy, and superconducting quantum interference device magnetometry, respectively. The results indicated that the cobalt nanoparticles fabricated are noncrystalline but coated with the graphitic carbon layers. It is believed that the formation of these carbon layers well-protect the cobalt nanoparticles to be oxidized thus maintaining the superparamagnetic property. This is an important feature that makes the cobalt nanoparticles a useful material for medical and many other magnetic based applications.

Investigation of pyrolysis temperature in the one-step synthesis of L10 FePt nanoparticles from a FePt-containing metallopolymer

Ferromagnetic (L10 phase) FePt alloy nanoparticles (NPs) with extremely high magnetocrystalline anisotropy are considered to be very promising candidates for the next generation of ultrahigh-density data storage systems. The question of how to generate L10 FePt NPs with high coercivity, controllable size, and a narrow size distribution is a challenge. We report here a single-step fabrication of L10 FePt NPs by employing one of the two new polyferroplatinyne bimetallic polymers as precursors. The influence of the pyrolysis temperature on the size and magnetic properties of the resulting FePt alloy NPs has been investigated in detail.

High-quality all-oxide Schottky junctions fabricated on heavily doped Nb: SrTiO3 substrates

We present a detailed investigation of the electrical properties of epitaxial

Nonvolatile organic transistor-memory devices using various thicknesses of silver nanoparticle layers

{\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}\mathrm{Mn}{\mathrm{O}}_{3}∕\mathrm{Sr}{\mathrm{Ti}}_{0.98}{\mathrm{Nb}}_{0.02}{\mathrm{O}}_{3}

Semitransparent organic solar cells with hybrid monolayer graphene/metal grid as top electrodes

Schottky junctions. A fabrication process that allows reduction of the junction dimensions to current electronic device size has been employed. A heavily doped semiconductor has been used as a substrate in order to suppress its series resistance. We show that, unlike standard semiconductors, high-quality oxide-based Schottky junctions maintain a highly rectifying behavior for doping concentration of the semiconductor larger than

Non-volatile, reversible switching of the magnetic moment in Mn-doped ZnO films

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