Synthesis of Nanoscaled Powders by Laser-Evaporation of Materials
- PDF / 2,563,528 Bytes
- 12 Pages / 414.72 x 648 pts Page_size
- 27 Downloads / 188 Views
particles is narrow and can be adjusted by the laser parameters. The particle surfaces can be kept free of contaminations or subsequently can be conditioned. With a high power laser available the device is easily built up. Moreover the technique of nanopowder synthesis by laser evaporation is easy to use. EXPERIMENTAL RESULTS The creation of powders in the nanometre range can be investigated with a simple experimental arrangement if a high power laser is available [10]. The pulsed light of a Nd:YAG-Laser (X= 1060 nm) with an average light power of 20 W, a pulse energy of 0.2 mJ and a pulse time of 200 ns is focused onto the surface of a solid sample. To avoid oxidation of the material the experiment is performed under ambient pressure in an open container which is floated by argon. Various materials like metals, oxide ceramics and other ceramics can be used. For inert metals like gold or platinum and for oxide ceramics the experiments can be carried out under ambient air. A part of the ablated material is collected on different holders for subsequent investigations in a scanning electron microscope (SEM), a transmission electron microscope (TEM) and a X-ray diffractometer (XRD). During the pulsed laser operation small plasma plumes can be observed on the surface of the sample marking the points where the focused infrared laser beam interacts with the sample. The repeated expansions of the small plasma plumes lead to a noise having the frequency of the laser pulse repetitions. From the lasered points on the samples surface smoke arises indicating that material has been ablated. The smoke dissolves in the ambient gas and forms an aerosol. A SEM micrograph of the samples surface after laser operation (figure 1) shows a small crater from where material has been ablated 0, 11
.........................
Figure 1: SEM - micrograph of a iron sample after interaction with pulsed Nd:YAG laser light The roll-like borders around these craters and incomplete droplet formation show that some material has been melted during the interaction with the laser light. The diameters of the craters correspond approximately to the focus area of the used laser. Figure 2 shows SEM micrographs of the material collected by a flat SEM holder which has been positioned beneath an iron (bcc) target (figure 2a) and a gold target (figure 2b) respectively. Spheres in the 1- 10 ptm rage are visible. Energy dispersive X-ray microanalysis shows that these spheres have the same chemical composition as the target. Depending on the ablated material and the position of the SEM holder during the laser ablation process these spheres are covered with a diffuse layer that cannot be further resolved in the used SEM (see figure 2b). 4
a) b) Figure 2: SEM - micrographs of material that has been deposited on the SEM holder during the laser ablation of a) iron (bcc) and b) gold TEM investigations show that these diffuse layers are formed by spherical particles with diameters of about 10 nm [11]. A TEM micrograph of a sample (figure 3) that has been prepared by ho
Data Loading...
