Masayasu Soga

High performance of hydrogen peroxide detection using Pt nanoparticles-dispersed carbon electrode prepared by pulsed arc plasma deposition

We propose novel electrodes with platinum nanoparticles dispersed on a glassy carbon (Pt-NPs/GC) prepared using a pulsed arc plasma deposition (APD) method. The method could coat Pt-NPs on a base material directly with a single-step process in a very short deposition time. The characteristics of the electrodes were discussed in detail. The detection of hydrogen peroxide was performed as an example for application of the electrodes. The distribution of nanoparticles was controlled easily by the number of pulse. The surface morphology changed with the pulse number and the annealing except for the sample prepared by 5 pulses deposition (APD(5)), implying that the APD(5) remained as NPs after the annealing. Average particle size was 2.7 nm on the Pt-NPs/GC. Catalyst activity for oxidizing hydrogen peroxide per Pt loading was excellent on the Pt-NPs/GC. When the Pt-NPs/GC was used as a detector for hydrogen peroxide on a flow injection analysis, the Pt-NPs/GC showed high sensitivity without deterioration. Oxidation current increased linearly with the concentration of hydrogen peroxide from 10nM to 100 μM. This fast and easily prepared electrode showed the capability to replace a conventional bulk metal electrode.

Optimizing coverage of metal oxide nanoparticle prepared by pulsed laser deposition on nonenzymatic glucose detection.

Metal oxide nanoparticles prepared by pulsed laser deposition (PLD) were applied to nonenzymatic glucose detection. NiO nanoparticles with size of 3 nm were deposited on glassy carbon (GC) and silicon substrates at room temperature in an oxygen atmosphere. Transmission electron microscope (TEM) image showed nanoparticles with the size of 3 nm uniformly scattered on the Si(001) substrate. Unlike co-sputtering nanoparticle and carbon simultaneously, the PLD method can easily control the surface coverage of nanoparticles on the surface of substrate by deposition time. Cyclic voltammetry was performed on the samples deposited on the GC substrates for electrochemical detection of glucose. The differences between peak currents with and without glucose was used to optimize the coverage of nanoparticles on carbon electrode. The results indicated that optimal coverage of nanoparticles on carbon electrode.

Room-Temperature Epitaxial Growth of (Li,Ni)O Thin Film with Li Content up to 60 mol %

NiO thin films containing up to 60 mol % Li were deposited on an ultra smooth sapphire (0001) substrate at room-temperature (RT) by the pulsed laser deposition (PLD) process. From in situ reflection high-energy electron diffraction (RHEED) and ex situ X-ray diffraction (XRD), it was found that the cubic NiO thin film containing 60 mol % Li, deposited at RT, could be epitaxially grown with (111) orientation; however the film became polycrystalline when deposited at 200 °C under the same atmosphere. These results indicate the possible exploration of novel growth of the oxide films using RT PLD process.

Electrochemical Response of Platinum Ultrathin Layer Formed by Pulsed Laser Deposition

Ultrathin layer of platinum (ULPt) was deposited on glassy carbon (GC) substrate by using pulsed laser deposition (PLD) method, and electrochemical properties of the ULPt were discussed. The deposition was simply performed at room temperature with short deposition time. Atomic force microscopy and scanning electron microscopy images showed the flat surface of the ULPt. X-ray photoelectron spectroscopy (XPS) characterized the ULPt in the Pt(0) state, and biding energy of ULPt was positively shifted. These results indicated that nanostructure of Pt thin layer was formed. The electrochemical activity of the prepared ULPt on GC substrate was superior to a bulk Pt electrode regarding the potential and the magnitude of current on oxidizing hydrogen peroxide. This fast and easily prepared low-cost electrode had the potential to replace a conventional bulk metal electrode.

Growth of Nanocubic MgO on Silicon Substrate by Pulsed Laser Deposition

Magnesium oxide (MgO) prepared by both pulsed laser deposition and sputtering methods showed constriction of lattice constants. To emphasize the effect of the constriction of lattice constants, MgO prepared at high oxygen atmosphere and high substrate temperature, resulted in the growth of cubic-shaped magnesium oxide (MgO) nanoparticles on a Si substrate. In oxygen atmosphere, the nanocubic MgO was scattered on the substrate without the Si surface being covered by a MgO thin film. Interestingly, the growth of nanocubic MgO was restrained on the samples prepared in nitrogen atmosphere. The formation of nanocubic MgO is related to the deposition pressure as well as the etching effect provided by oxygen atmosphere.

Epitaxial Indium Tin Oxide Film Deposited on Sapphire Substrate by Solid-Source Electron Cyclotron Resonance Plasma

Indium tin oxide (ITO) thin films were epitaxially grown on sapphire substrates by solid-source electron cyclotron resonance (ECR) plasma deposition. Compared with the other methods such as sputtering and evaporation methods, the ECR plasma method resulted in a flat surface and a low resistivity with a relatively low substrate temperature. The surface roughness was strongly dependent on the ratio of oxygen gas flow during deposition. With optimal deposition conditions, the ITO thin film epitaxially grew on a c-plane sapphire substrate with twelvefold symmetry. The surface roughness and resistivity were estimated to be 0.4 nm and 1.4×10-4 Ωcm, respectively. The X-ray rocking curve revealed 0.025° of full width at half maximum (FWHM) on the epitaxial ITO thin film. The ITO film deposited on an epitaxial GaN(001) layer on a c-plane sapphire substrate showed sixfold in-plane symmetry, indicating the epitaxial growth of ITO(111) on the GaN(001)/c-plane sapphire substrate.

Large Lattice Misfit on Epitaxial Thin Film: Coincidence Site Lattice Expanded on Polar Coordinate System

The growth of an epitaxial film with a large lattice misfit to substrates is interpreted as domain growth with domain matching by the coincidence site lattice (CSL), in which it is assumed that (m×n) film lattice units are superimposed on (k×l) substrate lattice units. The domain matching with all combinations of two lattice units was expanded on a polar coordinate system (polar CSL figure), where the radius and angle are indicative of the domain size and the lateral angle between two superimposed lattices, respectively. The polar CSL figure enable us to visualize the domain matching of all combinations between the two lattice units (k×l) and (m×n). The cubic-on-cubic growth of magnesium oxide on a silicon substrate and the lateral rotation of bismuth cuprate oxide were taken as examples of visualization using the polar CSL figure.

Effect of post annealing on MgO thin film prepared on silicon(001) substrate in high oxygen pressure and high substrate temperature by pulsed laser deposition

Epitaxial growth of MgO was verified with the relation of MgO(100) parallel to Si(100) (cubic on cubic growth) even with a large mismatch of lattice constants ~ 22%, instead of 9% mismatch in 45° rotation growth. MgO films prepared at higher deposition temperature showed (001) preferred orientation on Si(001) substrate. After post-annealing the MgO thin films, the pole figure of X-ray diffraction verified the epitaxial growth of cubic on cubic relation. Fe3Si thin film was deposited on Si(001) substrate with the MgO film as buffer layer.

Heavy Doping of Li + -ion into NiO Epitaxial Thin Films via Unequilibrium Room-temperature Processing for New Functionalization

NiO is a typical material for new p-type oxide semiconductors. Conductivity of NiO can be raised with Li + doping. In case of Li-heavy doping, we can obtain Li x NiO 2 (0.5 2 has been increased as an electrode material for rechargeable lithium cells. In this work, we tried to fabricate a novel NiO material with Li + -heavily doped by applying the pulsed laser-induced room temperature (R.T.) film process. Previously, we have succeeded in the epitaxial growth of various oxide thin films at R.T. such as Sn-doped In 2 O 3 transparent electrodes [1]. Although the many studies have been made on the deposition of NiO epitaxial thin film at low temperatures [2], there are few reports on fabrication and the conductive characteristic for Li-heavily doped NiO epitaxial films. The film deposition at R.T., which is the unequilibrium vapor phase process, is expected to result in different crystal structure and characteristics from the films grown at high-temperatures. A composition-adjusted thin film of Li x Ni 1-x O(0.10 2 O 3 )(0001) or MgO(100) substrates by pulsed laser deposition (PLD) technique in 10 −6 Torr of oxygen at R.T. and the high temperatures of 350 and 515°C. Crystalline properties of thin films deposited at R.T. or high temperatures were examined using reflection high energy electron diffraction (RHEED) and X-ray diffraction. For the Li-heavily doped NiO films(x>0.30) grown at R.T., a clear streak RHEED pattern showing epitaxial growth was observed. But the Li-heavily doped NiO films grown at high temperatures, exhibited the ring RHEED pattern, which indicates the policrystal growth of films. Electric conductivity of various Li-doped NiO thin films deposited at R.T. or high temperatures on sapphire (0001) substrates were measured by two-probe method. The interesting results were obtained that conductivity of the film was increased remarkably with an increase of Li-doping for R.T. deposition, but was not changed so much regardless of Li-doping for high-temperature depositions.