Synthesis and characteristics of tungsten ultra-fine particles by Nd : YAGlaser irradiation

Tungsten ultra-fine particles were synthesized by the irradiation of two sy nchronized-pulse Nd: YAG lasers on a tungsten substrate in a low pressure i nert gas atmosphere. Two types of lasers, which include the main laser (max . power: 10 J/pulse, wavelength: 1064 nm, pulse width: 0.2 ms) and the assi st laser (max. power: 150 J/pulse, wavelength: 1064 nm, pulse width: 10 ms) , were used to form the tungsten ultra-fine particles. Pulsed irradiation o f the main laser was delayed 9 ms after the assist laser pulsed irradiation . In order to efficiently form ultra-fine particles, the laser irradiation conditions were a 10 J/pulse for the main laser power, and a 46.5-132 J/pul se for the assist laser. The ambient pressure was 1.3 x 10(3)-6.7 x 10(4) P a for the He gas atmosphere. TEM observations shows that the primary particles are several nm in diamete r under each condition. An agglomeration of the primary particles occurred under high pressure and high laser power conditions. It is concluded that t he size distribution and shape of the generated ultra-fine particles can be controlled by the pressure and laser power conditions. As for the electron diffraction of the tungsten ultra-fine particles, both the crystalline and amorphous phases were observed under this condition. The size distribution was measured by a low pressure differential mobility analyzer (LP-DMA) for each condition. The peak of the size distribution was shifted from the sev eral nm to the tens of nm level with increasing the high pressure and high laser power conditions.