• PDF / 2,658,895 Bytes
• 8 Pages / 420.48 x 639 pts Page_size
• 42 Downloads / 271 Views

DOWNLOAD

REPORT

---

NATURE AND APPLICATION OF PARTICULATE MATTER PRODUCED BY PULSED LASER ABLATION LI-CHYONG CHEN, and ERNEST L. HALL General Electric Corporate Research and Development, Schenectady, NY12301 ABSTRACT Particulates produced by 248 nm KrF excimer laser ablation were investigated in two systems: Nb-Al and Cr-Nb. Both systems contain intermetallics which are potentially useful high temperature materials. While the melting temperature of Nb is three times higher than that of Al, the melting temperature difference between Nb and Cr is less substantial. This work focuses on the effects of melting temperature difference between the terminal elements in binary alloy systems on the nature of the particulate matter formed by laser ablation. Transmission (TEM) and scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), and optical image analysis were used to characterize the products. The particulate generation rate and the size distribution depend on various growth parameters. In both Nb-Al and Cr-Nb systems, the particulates are all enriched in Nb, with the smallest particulates richest in Nb. Single phase particulates containing barely detectable Al were found in Nb-Al system. In the Cr-Nb system, electron diffraction patterns indicate two types of particulates: one exhibiting a new metastable diamond cubic structure and the other being a two phase mixture of bcc Cr and bcc Nb. A plausible mechanism whereby the lower melting temperature element is depleted as well as the correlation of the particulate size and the overall composition of individual particulate will be discussed. Stoichiometric studies of the particulates generated in the Nb-Al and Cr-Nb systems using the pulsed laser deposition (PLD) technique help illustrate the merits and limitations of the same. One example of the potential applications of the particulate-containing films will be demonstrated. INTRODUCTION Pulsed laser deposition is rapidly emerging as one of the leading techniques for producing high quality thin films of varying composition such as high temperature superconducting material [1]. The technique is particularly useful because of the possibility of retaining stoichiometry in going from the target to the deposited film. However, the presence of the particulates in deposited films has been considered to be one of the major factors that impeded the more widespread application of the PLD method. A concise overview on the attributes of the PLD generated particulates will be published in a forthcoming reference book [2]. Most of the work reported to date emphasized the relationship of the density and size of the particulates and processing parameters, such as the laser fluence and wavelength [3-7]. The characteristic velocity of the particulates has also been investigated in a number of laboratories [8-11]. The condensation process of the particulates, including the resultant chemical composition and the microstructure of the particulates, were hardly addressed, however. Briefly speaking, particulates generated by pulsed laser ablat