Takafumi Matsuda

Cathodoluminescence Property of ZnO Nanophosphors Prepared by Laser Ablation

ZnO nanophosphors with a diameter of 7?50 nm have been fabricated under an oxygen gas atmosphere at room temperature by evaporating ZnO powder or Zn targets using pulsed laser ablation. The size and uniformity of ZnO nanophosphors strongly depend on oxygen gas pressure. Results of cathodoluminescence analysis show strong ultraviolet, blue, green, and green-yellow emissions from ZnO nanophosphors excited by a ?150 eV low-energy electron beam emitted from carbon nanotubes, depending upon the target material and oxygen gas pressure. Ultraviolet, blue, green, and green-yellow emissions can be attributed to the transitions from the conduction band to the valence band, the Zni level to the VZn level or the valence band, the VO level to the valence band, and the Zni level to the Oi level, respectively.

Aqueous nanosilica dispersants for carbon nanotube.

Nanosilicas can disperse single-wall carbon nanotube (SWCNT) in aqueous solution efficiently; SWCNTs are stably dispersed in aqueous media for more than 6 months. The SWCNT dispersing solution with nanosilica can produce highly conductive transparent films which satisfy the requirements for application to touch panels. Even multiwall carbon nanotube can be dispersed easily in aqueous solution. The highly stable dispersion of SWCNTs in the presence of nanosilica is associated with charge transfer interaction which generates effective charges on the SWCNT particles, giving rise to electrostatic repulsion between the SWCNTs in the aqueous solution. Adhesion of charged nanosilicas on SWCNTs in the aqueous solution and a marked depression of the S11 peak of optical absorption spectrum of the SWCNT with nanosilicas suggest charge transfer interaction of nanosilicas with SWCNT. Thus-formed isolated SWCNTs are fixed on the flexible three-dimensional silica jelly structure in the aqueous solution, leading to the uniform and stable dispersion of SWCNTs.

Role of Negative Electric Field Biasing on Growth of Vertically Aligned Carbon Nanotubes Using Chemical Vapor Deposition

Vertically aligned carbon nanotubes (CNTs) were grown on a Si substrate by thermal chemical vapor deposition (CVD) and direct current plasma-enhanced CVD with a negative electric field. By contrast, under a positive electric field, CNTs grew randomly. The morphologies of the CNTs grown on Si and quartz substrates were compared to clarify the mechanism of aligned CNT growth. CNTs grown on quartz showed a random structure regardless of the polarity and amplitude of applied electric field. It is noted that the Fe catalysts on the tips of aligned CNTs were apparently elongated compared with those of randomly grown CNTs. The present observations suggest that aligned CNT growth might be due to the electrostatic force acting on the electrons drawn toward the tips of CNTs by negative electric field.

Essential Role of Viscosity of SWCNT Inks in Homogeneous Conducting Film Formation

Newly developed inorganic single-wall carbon nanotube (SWCNT) inks of the Zn/Al complex and colloidal silica give a quite homogeneous SWCNT film on the polyethylene terephthalate (PET) substrate by the bar-coating method, whereas the surfactant-based SWCNT inks of sodium dodecyl sulfonate (SDS) and sodium dodecyl benzene sulfonate (SDBS) cannot give a homogeneous film. The key properties of SWCNT inks were studied for the production of homogeneous SWCNT films. The contact angle and surface tension of the inorganic dispersant-based SWCNT inks were 70° and 72 mN m(-1), respectively, being close to those of water (71.5° and 71 mN m(-1)). The viscosity was significantly higher than that of water (0.90 mPa·s), consequently, providing sufficient wettability, spreadability, and slow drying of the ink on the substrate, leading to homogeneous film formation. On the other hand, the surfactant dispersant-aided SWCNT inks have the contact angle and surface tension twice lower than the inorganic dispersant-based SWCNT inks, guaranteeing better wettability and spreadability than the inorganic dispersant-based inks. However, the small viscosity close to that of water induces a heterogeneous flow of SWCNT ink on rapid drying, leading to inhomogeneous film formation.

Air pressure profile and voidage change within vibrating particle beds

Abstract Measurements were made of air pressure beneath and along one side of vibrating particle beds consisting of glass beads of mean diameter 99 μm. In the span of one vibratory cycle, the peak air pressure at 25 mm from the bed surface was found to be higher than that at the bottom (100 mm from the surface) regardless of the magnitudes of vibratory intensity and frequency. A modified compressible gas model, involving variations of voidage in space and time, was proposed to explain the cause of this unusual air pressure reversal.

Field emission properties of zinc oxide-coated vertically aligned carbon nanotube emitter array

Carbon nanotubes (CNTs) are one of candidate materials for field emission applications, including field emission display (FED), or X ray tubes, because of excellent physical features. In our previous work, in order to develop nano-sized CNT field emitters, vertically aligned CNT (VACNT) field emitters with 100 nm-dot array structures have been fabricated using direct-current plasma enhanced chemical vapor deposition (dc-PECVD) and showed the turn on voltages as low as 1.1 V/μm [1]. In addition, ZnO nanoparticle as phosphor materials have been fabricated by pulsed laser ablation method, where ultraviolet, blue, green, and yellow emission were observed from ZnO nano-phosphors in cathodoluminescence (CL) property using CNT emitters [2]. Recently, ZnO nanostructures such as nanowires, or nanoneedles have been grown on CNTs as a field emitter material, which improved their field emission properties [3, 4]. On the other hand, ZnO also act as a phosphor material. Until now, ZnO phosphor/CNT composite materials have not been reported yet. In this work, therefore, we investigated the field emission property of ZnO coated CNTs and luminescence property.

ZnO nanopowder induced light scattering for improved visualization of emission sites in carbon nanotube films and arrays

We report on ZnO nanopowder induced light scattering for improved visualization of emission sites in carbon nanotube films and arrays. We observed a significant reduction of the internal multiple light scattering phenomena, which are characteristic for ZnO micropowders. The microsized grains of the commercially available ZnO:Zn (P 15) were reduced to the nanometre scale by pulsed laser ablation at an oxygen ambient pressure of 10 kPa. Our investigations show no crystalline change and no shift of the broad green emission peak at 500 nm for the ZnO nanopowder. For the application in field emission displays, we demonstrate the possibility of achieving cathodoluminescence with a fine pitch size of 100 microm of the patterned pixels without requiring additional electron beam focusing and without a black matrix. Moreover, the presented results show the feasibility of employing ZnO nanopowder as a detection material for the phosphorus screen method, which is able to localize emission sites of carbon nanotube films and arrays with an accuracy comparable to scanning anode field emission microscopy.

Air pressure reversal within vibrating particle beds

Abstract Measurements were made of the air pressure at the bottom and along one side of vibrating particle beds. Glass beads of mean diameters of 99, 227 and 332 μm were used, and the static bed height was varied between 60 and 150 mm. Over one vibratory cycle, the peak air pressure at about 40-50 mm from the top (in beds of 99 μm glass beads) was always the highest; higher than that at the vessel base; the position of the maximum air pressure moved upward with increasing bed height. This unusual pressure reversal was observed to occur in beds of greater heights with larger glass beads. In conjunction with this air pressure reversal, the dependence of the instability of vibrating particle beds on particle size was examined through calculations of the interparticular normal vertical stress.