Several selective growth methods had been used, such as nanosphere lithography [20], electron-beam lithography [21, 22], and conventional photolithography [19]. In this regard, we present a selective area growth of single crystalline Sn-doped ITO NWs to improve the field emission properties owing to the reduction of the screen effect. In our previous study, the conductive properties of ITO NWs have been investigated, which is compatible with that

of the high quality ITO thin films [23, 24]. A periodically arrayed Au film prepared via a copper grid mask is used to control the growth area of ITO NWs in order to investigate the screen effect. Importantly, the length of ITO NWs was found to significantly see more influence the field emission properties. As a result, the reduced turn-on fields from 9.3 to 6.6 V μm−1 and improved β values from 1,621 to 1,857 could be found

after the selective area growth of Sn-doped ITO NWs at 3 h. Methods Growth of LY2835219 Sn-doped ITO nanowires The ITO nanowires were grown by the hydrogen thermal reduction vapor transport method. Indium (99.9%) and tin (99.9%) were mixed as source powders with the weight ratio of 9:1 and placed in an alumina boat (Al2O3). The 5-nm-thick Au film as the catalyst was deposited on the silicon substrate by a sputter process and patterned by a copper grid mask. The alumina boat was placed in the center of the alumina tube and then the substrates were put into the low region very (several center meters) next to the source powder. The system was heated up to 600°C with a heating rate of 5°C/min. Consequently, the ITO NWs were grown at 600°C for 10 and 3 h with a constant flow of mixed Ar/H2 gas (10% H2) at 90 sccm. Another oxygen gas was flowed into the furnace with 0.5 sccm as a source of oxygen to form ITO NWs. After the furnace had been cooled down to room temperature, gray products were found on the surface of the silicon substrate. Characterization

Structures of products were analyzed by X-ray diffractometer (XRD, Shimadzu XRD 6000, Nakagyo-ku, Kyoto, Japan) and transmission electron microscope (TEM, JEOL-2010, JEOL Ltd., Akishima, Tokyo, Japan). The morphology was analyzed by field emission scanning electron microscope (SEM, JEOL-6500). The X-ray photoelectron spectroscopy (XPS, ULVAC-PHI, PHI Quantera SXM, Chanhassen, MN, USA) was used to examine the chemical composition of nanowires. Field emission measurement of ITO NW arrays was performed with a parallel plate as the cathode and a circular steeliness tip as the anode (1-mm diameter). A high voltage–current instrument, Keithley 237 (Cleveland, OH, USA), was operated to perform the field emission characteristics. All emission measurements were carried out in a vacuum chamber with a pressure kept under 10−6 Torr The applied voltage between the electrodes was increased to a maximum of 1,000 V by 20-V step.