Laser ablation single target

Pulsed laser deposition (PLD) [1-3] uses high-power laser pulses with an energy density of more than 108 W cm 2 to melt, evaporate, excite, and ionize material from a single target. This laser ablation produces a transient, highly luminous plasma plume that expands rapidly away from the target surface. The ablated material is collected on an appropriately placed substrate surface upon which it condenses and a thin film nucleates and grows. 

It is also possible to characterize accurately the composition of new thin fihn materials using RBS. RBS analysis of the Sri xCaxCu02 materials demonstrates that the single-phase infinite-layer thin films have the same average composition as the multiphase targets from which they were prepared by laser ablation. These compositional analysis results demonstrate that PLD can be used to prepare readily a specific stoichiometry material even when the target is not single phase. 

MWNT can also be prepared by laser ablation. Contrary to the synthesis of single-walled nanotubes, no catalyst is added here, but a pure graphite target is vaporized by means of a focused laser beam. The resulting MWNT are precipitated at cooler positions within the reactor. Here as well, the operating temperature is about 1200 °C because the number of defects increases and the yields of MWNT decrease at lower temperatures. Below 200 °C then, no growth of carbon nanotubes is observed anymore. The process produces a considerable portion of amorphous carbon, fullerenes, and carbon nanoparticles besides the desired MWNT. These impurities have to be removed before further use. The yields of multiwalled nanotubes usually range about 40%. 

Figure 1. Optical absorption spectra of Ag colloidal solutions produced by the repetitive (10 Hz) single-pulse 1064 nm (/) and double-pulse (1064 nm + 1064 nm, 7 ps pulse separation) laser ablation (2) of silver target in water. 

Both single and multiple targets do not guarantee the deposition of stoichiometric films because different elements will evaporate or sputter at different rates, except with the laser ablation method Low to medium deposition temperatures... 

A laser ablation technique for the preparation of boron nanowires was published almost contemporary to the previous work. Crystalline boron nanowires with tetragonal structure have been reported to form via laser treatment on boron rods, doped with 10% of a half-and-half mixture of Ni and Co metal powders. A Nd/YAG laser of 532 nm wavelength, 10 Hz frequency, and 3.5 W power was applied on the B/NiCo target. It was then kept in a furnace at 1250°C, under flowing argon gas for 30 min. The x-ray diffraction data predicted that nanowires with crystalline structure and crystals are mostly single crystal in nature. The role of the catalyst in formation of the nanostructure has also been examined and proven to be vital. 

CO2. laser ablation of a carbon rod (graphite pure or doped) at room temperature (no oven is needed) in an argon inert flow. A single continuous CO2 laser (wavelength 1064 nm power 400-900W) was directed to the above carbon target with the growth of carbon nanotubes. 

Yudasaka, M., Sensui, N., Takizawa, M., Bandow, S., Ichihashi, T., lijima, S. - Formation of single wall carbon nanotubes catalyzed by Ni separation from Y in laser ablation or in arc discharge using a C target containing a NiY catalyst , Chem. 

Zhang, M., Yudasaka, M., lijima, S. - Single wall carbon nanotubes a high yield of tubes through laser ablation of a crude-tube target , Chem. Phys. Lett. 336 (2001) 196-200... 

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