Methods A thin gold film of 200-nm thickness was initially deposited onto a 0.02-Ω cm p-type silicon (100) wafer using an evaporator
(e-beam) in the AMPEL Nanofabrication laboratory at the University of British Columbia (UBC). Four sets of these gold-silicon samples of 10 mm × 10 mm size were precisely cut using a dice saw and used for the present experiment. In order to obtain a large number of Nec-1s nanoparticles for analysis without Selleckchem MGCD0103 damaging the surface of the target, laser cycles were gradually increased (2, 3, 4, and 5 cycles). The laser source is an all-diode-pumped, direct-diode-pumped Yb-doped fiber oscillator/amplifier system capable of producing variable pulse energies up to 10 mJ with a pulse frequency range between 200 kHz and 25 MHz. Average power
varies between 0 and 20 W. In order to ablate the target material and create nanoparticles, the laser beam scanned the surface of the gold-sputtered silicon wafer in a 40 × 40 dot-array pattern. The laser beam dwell time at each dot point can be set at 0.5, 0.75, or 1.0 ms. The laser-irradiated samples were then characterized by scanning electrical microscopy (SEM), transmission electron microscopy (TEM), and energy-dispersive X-ray (EDX) analyses. A spectrophotometer (Ocean Optics, Dunedin, FL, USA) was used to measure the reflectance of the laser-irradiated samples by illumination with a wavelength in the range of 200 to 2,200 nm. Results and discussion Characterization of this website nanoparticle aggregation Figure 1 shows a TEM image of a gold-silicon nanofiber, accompanied with EDX analysis results. The figure shows that nanofibers consist of agglomerated silicon oxide nanoparticles with individual gold nanoparticles or a small cluster of gold nanoparticles dispersed in the cloud of silicon oxide nanoparticle agglomerates. It is also evident from the image that the diameter of gold particles is a fraction of that of silicon oxide particles. Figure 1 TEM and EDX
analyses. TEM and EDX analyses show that a dense cloud of gold atoms (plume) firstly assembled in different laser spots of the gold target. The basic mechanism of femtosecond laser synthesis of nanoparticles could be Amylase explained in terms of the dynamic formation mechanism postulated by Sivakumar et al. [17] and Tan and Venkatakrishnan [18]. In brief, a dense cloud of atoms (plume) accumulated around the laser spot of the gold target during the course of ablation. This core was made up of a number of small gold atoms aggregated randomly due to the density fluctuation to form embryonic nanoparticles. Even when the ablation process had been terminated, at the end of the cycle, the aggregation continued, per se at a significantly slower growth rate with every new cycle until all atoms in the vicinity of the embryonic nanoparticles were depleted.