Preparation Of Tungsten Micro / Nanowire Arrays And Their Field Emission Properties

It is metals (such as W, Mo, Ta, etc.) that were first studied as field emission cathode material, whose launch mechanism is clearly and preparation is mature, and are used most widely in this field currently. Though having high processing ability and high emission current, to effectively boost the electric field, a micro-tip cathode with array structure is required due to the high work function. This requires large-area micro-tip preparation process or the synthesis of its one-dimensional nanomaterialsThe synthesis of one-dimensional structure and the study of field emission properties of metal tungsten, which is the most widely-used electron emission material, have become a widespread-concerned topic. It is difficult to obtain its quasi-one-dimensional nano-structure using traditional preparation methods due to its ultra-high melting point and ultra-low vapor pressure. At present, the methods of preparing metal tungsten nanowire universally require very demanding and hard-controlled reaction conditions and complicated process, thus synthesizing nanowire with large quantities has been restricted. The present work has synthesized metal tungsten single-crystalline micro/nano-array with uniform diameter using catalyst-free gas-assisted method at a relatively low temperature and studied its field emission properties.(1) Micro/nanowire array of refractory metallic W has been successfully synthesized using a non-catalyst and non-template assisted vapor transport method at relatively low temperature (900～1000℃). The synthesized W whiskers have nano-sized tips (<50 nm) and high aspect ratio (>100).(2) The present work have studied the effects of growth conditions(temperature, time, supersaturation etal) on the growth of single-crystalline W micro/nanowires and analysed its growth mechanism, indicating that this method is connected with the VS mechanism.(3) Single-crystal W micro/nanowires synthesized in this work have excellent field emission properties and their F-N curve has approximatly linear relationship with the Fowler-Nordheim theory.(4) The turn-on voltage of W micro/nanowires with average diameter 180 nm,350 nm,1100 nm is 4.0 Vμm-1,5.6 Vμm-1 and 7.1 Vμm-1, respectively, and the field enhancement factor of the nanowire array with average diameter 180 nm is 1904, which is comparable to CNTs and ZnO nanoneedles. W micro/nanowires have good thermal stability and the fluctuation in the current density (defined as AJ/Javerage) is less than 3.6%.