Sung Hwan Heo

Synthesis and visible-light-induced catalytic activity of Ag2S-coupled TiO2 nanoparticles and nanowires

We present the synthesis and visible-light-induced catalytic activity of Ag(2)S-coupled TiO(2) nanoparticles (NPs) and TiO(2) nanowires (NWs). Through a simple wet chemical process from a mixture of peroxo titanic acid (PTA) solution, thiourea and AgAc, a composite of Ag(2)S NPs and TiO(2) NPs with sizes of less than 7 nm was formed. When the NP composite was further treated with NaOH solution followed by annealing at ambient conditions, a new nanocomposite material comprising Ag(2)S NPs on TiO(2) NWs was created. Due to the coupling with such a low bandgap material as Ag(2)S, the TiO(2) nanocomposites could have a visible-light absorption capability much higher than that of pure TiO(2). As a result, the synthesized Ag(2)S/TiO(2) nanocomposites exhibited much higher catalytic efficiency for the decomposition of methyl orange than commercial TiO(2) (Degussa P25, Germany) under visible light.

Transmission-type microfocus x-ray tube using carbon nanotube field emitters

A microfocus x-ray tube that can generate x rays with the focal spot size less than 5μm has been demonstrated using carbon nanotube (CNT) field emitters. A CNT cathode on a sharp tungsten tip, a magnetic solenoid lens, and a transmission-type x-ray target were adopted for the microfocus x-ray tube. The design characteristics and the operation performance of the microfocus x-ray tube are presented. Due to the small focal spot size, clear x-ray radiographic images of 6μm bars and x-ray images with the magnification factor of higher than 230 were obtained.

Synthesis and Photocatalytic Activity of Anatase TiO2 Nanoparticles-coated Carbon Nanotubes

A simple and straightforward approach to prepare TiO2-coated carbon nanotubes (CNTs) is presented. Anatase TiO2 nanoparticles (NPs) with the average size ~8 nm were coated on CNTs from peroxo titanic acid (PTA) precursor even at low temperature of 100 °C. We demonstrate the effects of CNTs/TiO2 molar ratio on the adsorption capability and photocatalytic efficiency under UV–visible irradiation. The samples showed not only good optical absorption in visible range, but also great adsorption capacity for methyl orange (MO) dye molecules. These properties facilitated the great enhancement of photocatalytic activity of TiO2 NPs-coated CNTs photocatalysts. The TiO2 NPs-coated CNTs exhibited 2.45 times higher photocatalytic activity for MO degradation than that of pure TiO2.

Well-aligned zinc sulfide nanobelt arrays: Excellent field emitters

Large-scale, well-aligned and oriented wurtzite ZnS nanobelt arrays are fabricated by a simple solvothermal reaction and subsequent heat treatment. The nanobelts grow along the [0001] direction perpendicularly on a zinc substrate, which are about 30nm in thickness, several hundreds of nanometers in width, and up to 4μm in length. Importantly, such nanostructured arrays show a good field emission property with low turn-on field (3.8Vμm−1) and high field enhancement factor (∼1800), which is ascribed to the top edges and corners of the freestanding and well aligned nanobelts, and good electric contact with the conducting substrate where they grow.

A vacuum-sealed miniature X-ray tube based on carbon nanotube field emitters

A vacuum-sealed miniature X-ray tube based on a carbon nanotube field-emission electron source has been demonstrated. The diameter of the X-ray tube is 10 mm; the total length of the tube is 50 mm, and no external vacuum pump is required for the operation. The maximum tube voltage reaches up to 70 kV, and the X-ray tube generates intense X-rays with the air kerma strength of 108 Gy·cm2 min−1. In addition, X-rays produced from the miniature X-ray tube have a comparatively uniform spatial dose distribution.

Stable Field Emitters for a Miniature X-ray Tube Using Carbon Nanotube Drop Drying on a Flat Metal Tip

Stable carbon nanotube (CNT) field emitters for a vacuum-sealed miniature X-ray tube have been fabricated. The field emitters with a uniform CNT coating are prepared by a simple drop drying of a CNT mixture solution that is composed of chemically modified multi-walled CNTs, silver nanoparticles, and isopropyl alcohol on flat tungsten tips. A highly thermal- and electrical-conductive silver layer strongly attaches CNTs to the tungsten tips. Consequently, the field emitters exhibit good electron emission stability: continuous electron emission of around 100 μA at 2.3 V/μm has stably lasted over 40 h even at non-high vacuum ambient (~10−3 Pa).

Improvement in the photoelectrochemical responses of PCBM/TiO2 electrode by electron irradiation.

The photoelectrochemical (PEC) responses of electron-irradiated [6, 6]-phenyl-C61-butyric acid methyl ester (PCBM)/TiO2 electrodes were evaluated in a PEC cell. By coating PCBM on TiO2 nanoparticle film, the light absorption of PCBM/TiO2 electrode has expanded to the visible light region and improved the PEC responses compared to bare TiO2 electrode. The PEC responses were further improved by irradiating an electron beam on PCBM/TiO2 electrodes. Compared to non-irradiated PCBM/TiO2 electrodes, electron irradiation increased the photocurrent density and the open-circuit potential of PEC cells by approximately 90% and approximately 36%, respectively at an optimum electron irradiation condition. The PEC responses are carefully evaluated correlating with the optical and electronic properties of electron-irradiated PCBM/TiO2 electrodes.

Small-sized flat-tip CNT emitters for miniaturized x-ray tubes

Small tip-type CNT emitters with the diameter of 0.8 mm were fabricated for miniaturized X-ray tubes. The CNT emitters were prepared by dropping CNTs and silver nanoparticles on a flat surface of a W metal tip followed by annealing at 800°C for 2h under vacuum. The CNT emitters exhibit good field emission properties with the threshold electric field of 1.15 V/µm and the field enhancement factor of 12,050. CNTs were well attached to a flat W tip surface without coating on the side plane of the tip, and thus beam divergence could be minimized. Consequently, a miniaturized X-ray tube with the inner diameter of 5mm was successfully demonstrated using the tip-type CNT emitter.

SU‐E‐T‐79: Fabrication of Miniature X‐Ray Tube Using Carbon Nanotube Field Emitter for Electronic Brachytherapy

Purpose: A miniature x‐ray tube with the diameter of 10 mm has been fabricated using a carbon nanotube(CNT)field emitter, optimal design of electron optics and x‐ray target, and vacuum sealing of the x‐ray tube. The CNT emitter with nm∼μm scale and simpler cathode structure was used for miniaturization of x‐ray tube. A truncated conical shaped beryllium (Be) and thin tungsten (W) coating were adopted to emit 3‐dimensionally uniform x‐ray as an isotropic radiation source. Anode grounded high voltage (HV) connection and vacuum sealed x‐ray tube structure within 10 mm diameter are advantages for intra‐cavitary or skin surface electronic brachytherapy. Methods: The miniature x‐ray tube consisted with a tip‐shaped CNT emitter with the diameter of 0.25∼0.8 mm, a focusing electrode, a transmission‐type x‐ray target, getter film and a metalized HV isolation ceramic. The CNT emitter has been fabricated by coating and sintering of CNT and Silver nano particle mixture on the flat W tip. The miniature x‐ray tube is brazed in a 3×10−6 torr of vacuum furnace. The electron and x‐ray emission are calculated by EGN2 and MCNP5 program, and measure using a precision current meter (Fluke multimeter 189), a soft x‐ray chamber (PTW 34013), and x‐ray spectrometer (Amptek XR‐100t‐CdTe). Results: The CNT emitter emitted electron current over 1 mA at −9.8 kV/5 mm, and 0.1 mA was continued for over 3000 minutes with decrease ratio of −0.01 μA/min. The diode‐type miniature x‐ray tube is started to emit less than 5 Gy/min x‐ray at cm air depth from −20 kV to −50 kV following the gate to CNTcathode gap, and applying cathode voltage. Conclusions: The miniature x‐ray tube using CNTfield emitter has been demonstrated. The CNT based x‐ray tube can be more miniature, and is expected to apply various field of electronic brachytherapy, soon. This work was supported by the R&D Program of MKE/KEIT (10035553, Development of multi‐direction X‐ray emitting super‐miniature X‐ray tube for intra‐cavity imaging system) and the National Research Foundation of Korea (NRF) grant funded by the Korea government (MEST) (No. 2010‐0020387).