025 g; Premabraze

616, Lucas-Milhaupt, Inc., Cudahy, CA, USA). The metal mixture binder is composed of 61.5 wt.% silver, 24 wt.% copper, and 14.5 wt.% indium micro- and nanoparticles. Metal wires such as copper, kovar, stainless steel (SUS), tungsten, silver, and titanium with a diameter of 1 mm were used as substrates of the emitters. One end of the metal wires was mechanically polished buy PD0332991 to have a flat surface. Around 0.5 μl of the CNT/metal binder mixture was put on a metal tip substrate. The CNT/metal binder mixture dried out very quickly in approximately 5 min due to high volatility of dichlorobenzene. Subsequently, an annealing process was carried out under LDN-193189 purchase vacuum at approximately 10−6 Torr at different temperatures. For comparison, a CNT emitter was prepared using silver nanoparticles (NPs; DGH, Advanced Nano Products Co., Ltd., Buyong-myeon, South Korea) under similar conditions. Figure 1 Schematics of the (a) CNT emitter fabrication process Ilomastat purchase and (b) experimental

setup for the characterization. The morphologies of the fabricated CNT emitters were characterized using a field emission scanning electron microscope (FESEM; Hitachi S-4800, Chiyoda-ku, Japan). The adhesive force of the CNT/metal binder coating on a substrate was measured by a pencil hardness test, which is described in American Society for Testing and Materials (ASTM) D3363. Field emission properties of the fabricated CNT emitters were characterized in a vacuum chamber, which is schematically shown in Figure  1b. A diode

type with a copper disc (diameter, 30 mm) acting as an anode was employed for the field emission test. A negative high voltage of 0 ~ −70 kV was applied to the CNT emitter while the Cu anode was grounded. The distance between the CNT emitter and the anode was fixed to 15 mm. In order to protect the high-voltage power supply due to high-voltage arcing, a current-limiting resistor (resistance, 10 MΩ) Vitamin B12 was installed between the power supply and the emitter. Results and discussion The role of metal binders is to attach CNTs to substrates. Silver NPs have been widely used for a metal binder due to good electrical conductivity and good contact with CNTs [3, 4, 28]. To investigate the performance as a binder, we prepared a CNT emitter on a tungsten metal tip (diameter, 1 mm) using silver NPs (Figure  2a). The annealing temperature to melt silver NPs was 750°C. As shown in Figure  2b, the fabricated CNT emitters exhibited very poor stability. Electron current density emitted from the emitter was initially 57.3 mA/cm2 at the applied voltage of 35.5 kV; however, the current density was dramatically reduced to 13.6 mA/cm2 for a 70-min operation (Figure  2b). Frequent arcing was observed during the test, and the emission current density was slowly decreased with the increase in the arcing events.