Growth of multineedles of tungsten caused by reaction of tungsten oxide with acetone

Abstract

The growth of crystalline needles of tungsten on the tungsten substrate through chemical reaction between vacuum-deposited tungsten oxide and acetone vapors of (3–5) ×10−6 Torr was investigated with the aid of a field emission and a transmission electron microscope. A large number of tungsten needles were found to be grown by heating the substrate, onto which tungsten oxide had been deposited, initially at a temperature in the range ∼1500–1800 °K in acetone and then at a temperature between ∼2300 and ∼2600 °K in acetone-free vacuum. The needles were mostly [110] oriented and their number density amounted to ∼107/cm2. It is believed that the needle growth was closely related to the reduction of the oxide by carbon provided from acetone through the thermal cracking.