Kian Keat Lee

α-Fe2O3 nanotubes-reduced graphene oxide composites as synergistic electrochemical capacitor materials

We present a facile approach for the fabrication of a nanocomposite comprising α-Fe(2)O(3) nanotubes (NTs) anchored on reduced graphene oxide (rGO) for electrochemical capacitors (ECs). The hollow tubular structure of the α-Fe(2)O(3) NTs presents a high surface area for reaction, while the incorporation of rGO provides an efficient two-dimensional conductive pathway to allow fast, reversible redox reaction. As a result, the nanocomposite materials exhibit a specific capacitance which is remarkably higher (~7 times) than α-Fe(2)O(3) NTs alone. In addition, the nanocomposites show excellent cycling life and large negative potential window. These findings suggest that such nanocomposites are a promising candidate as negative electrodes in asymmetrical capacitors with neutral electrolytes.

Cobalt-based compounds and composites as electrode materials for high-performance electrochemical capacitors

Transition metal compounds (oxides, hydroxides, etc.) are emerging electrode materials for electrochemical capacitors (ECs) due to their rich redox properties involving multiple oxidation states and different ions. Pseudocapacitance derived from the reversible faradaic reactions can be ten times higher than those of the state-of-the-art carbon-based electric double layer capacitors (EDLCs). As one of the most well-known electroactive inorganic materials, extensive studies of cobalt-based compounds (Co3O4, Co(OH)2, CoOOH, CoS, etc.) for ECs have mushroomed, and the relevant literature has grown exponentially in the past ten years. This review consolidates and evaluates the recent progress, achievements, weaknesses and challenges in the research of cobalt-based compounds and nanocomposites for ECs. The triangular relationship between synthesis strategies, tailored material properties and the electrochemical performances is thoroughly assessed, unveiling the advanced electrode material design and development.

CoOOH nanosheet electrodes: Simple fabrication for sensitive electrochemical sensing of hydrogen peroxide and hydrazine

Cobalt oxyhydroxide, CoOOH, nanosheets were prepared via a surface alkaline treatment of cobalt foil at room temperature without using templates and catalysts. The morphology, chemical composition and structures of the nanosheets were characterized by XRD, FTIR and Raman spectroscopy, FESEM and TEM. These oriented and nanostructured arrays can be used directly as electrodes, thus simplifying the electrode fabrication process, as well as offering advantages such as enhanced electrode-electrolyte contact area, minimum diffusion resistance and direct active material-current collector connection for fast electron transport. The electrode was used as an electrochemical sensor towards non-enzymatic detection of hydrogen peroxide and hydrazine in alkaline solution. The amperometric detection of H(2)O(2) and N(2)H(4) was carried out at low potential (0V and 0.1V). At 0.1V, the amperometric signals are linearly proportional to H(2)O(2) concentration up to 1.6mM (R(2)=0.995), showing a detection limit (S/N=3) of 40μM and a high sensitivity of 99μA mM(-1)cm(-2). For N(2)H(4), the amperometric signals are linearly proportional to concentration up to 1.2mM (R(2)=0.99), showing a detection limit (S/N=3) of 20μM and a high sensitivity of 155μA mM(-1)cm(-2) at 0.1V.

Controllable unzipping for intramolecular junctions of graphene nanoribbons and single-walled carbon nanotubes

Graphene is often regarded as one of the most promising candidates for future nanoelectronics. As an indispensable component in graphene-based electronics, the formation of junctions with other materials not only provides utility functions and reliable connexions, but can also improve or alter the properties of pristine graphene, opening up possibilities for new applications. Here we demonstrate an intramolecular junction produced by the controllable unzipping of single-walled carbon nanotubes, which combines a graphene nanoribbon and single-walled carbon nanotube in a one-dimensional nanostructure. This junction shows a strong gate-dependent rectifying behaviour. As applications, we demonstrate the use of the junction in prototype directionally dependent field-effect transistors, logic gates and high-performance photodetectors, indicating its potential in future graphene-based electronics and optoelectronics.

Surface and interface studies of titanium silicide formation

Abstract Secondary ion mass spectrometry (SIMS), Rutherford backscattering spectroscopy (RBS) and X-ray photoelectron spectroscopy (XPS) are used to investigate Ti silicide formation mechanisms on a series of Ti on Si thin-films annealed in ultrahigh vacuum (UHV) at different temperatures and durations. The competition between oxygen diffusion and the silicide formation reaction (the so-called ‘snowplough’ effect) is observed directly, as well as a TiSiO layer. The results from these controlled experiments are compared with those from Ti-silicide films formed under rapid thermal annealing (RTA) conditions in a production furnace, with and without a TiW barrier layer. The TiW layer is shown to act as an effective barrier to silicon and oxygen out-diffusion, as well as the incorporation of ambient gases.

The effect of external fields and slit scattering on the beam spot profile of the coupled triplet system

Abstract The effect of external AC magnetic fields and slit scattering on the beam spot profile of the high excitation coupled triplet focusing system has been investigated. A 2 MeV proton beam has been exposed to an AC magnetic field generated from an air-cored solenoid positioned at various positions along the beam line. The resultant increase in beam spot size due to this external field was observed to be highly dependent on the field position along the beam line, with the region encompassing the collimation apertures found to be the most sensitive to stray fields. The effects of slit scattering was more pronounced for small aperture dimensions, but overall the beam quality at these small dimensions (1 μm) was satisfactory, with only a small fraction of the beam showing energy loss.

Polarizable energy-storage membrane based on ionic condensation and decondensation

Electrical energy storage and management is an urgent issue due to climate change and energy shortage. Dielectric and double-layer capacitors are the two basic energy-storage devices currently available. However, the application of the dielectric capacitor is very limited due to its low capacitance, while the double-layer capacitor suffers from difficult scaling-up and high fabrication cost, even though its capacitance is high. In this work, we present the first energy-storage membrane which stores charge when simply sandwiched between two metal plates. With an ionic conductivity of 2.8 × 10−4 S cm−1, the membrane is highly polarizable, and its energy-storage mechanism is based on the condensation–decondensation of mobile cations in the membrane negative matrix. The capacitance of a 1.0 cm2 area membrane is 0.2 F cm−2, and it can be readily scaled up simply by using larger membrane pieces. In view of its extreme simplicity, excellent scalability and practical viability, the novel game-changing membrane reported here may provide a sustainable solution to energy storage.

A surface and interface study on the InSb/GaAs heterostructures

Abstract This paper reports a surface and interface study of indium antimonide epitaxially grown on gallium arsenide using metalorganic magnetron sputtering technique. X-ray photoelectron spectroscopy analysis shows that the original surface of InSb is composed of InSb, In 2 O 3 , and Sb 2 O 3 , and the binding energy of Sb 3d 5/2 decreases when an antimony atom is surrounded by more indium atoms. The interdiffusion phenomenon is studied by both Auger electron spectroscopy depth profiling and Rutherford backscattering spectroscopy, the results of which are in good agreement. The width of the interdiffusion region is around 900 ± 100 A, and independent of epilayer thickness. X-ray diffraction study indicates that the crystallinity of the InSb epilayer becomes better with the increase of epilayer thickness. It is also demonstrated that the crystal orientation relationship between the InSb epilayer and GaAs substrate is (100) InSb//(100) GaAs, and the (100) crystal planes of InSb and GaAs are parallel to the macro-surface of the InSb/GaAs heterostructure.

Nuclear microscopy of Fe substituted 2212 BiSrCaCuO superconducting crystals

Abstract Crystals of the new generation BiSrCaCuO superconductors represent challenging materials to grow and fabricate into useful devices. Analysis of the material is also challenging. However the nuclear microprobe offers a possible solution to the problem of measurement of the stoichiometry, including oxygen, and sensitive mapping of micro-structures in single crystals. In the present paper we describe the results of nuclear microscopy of 2212 crystals, both as pure material and with up to 0.02 Fe substituted for Cu. We show evidence that the Fe is fully substituted into the crystal lattice.