Structural evolution of W nano clusters with increasing cluster size

We have recorded the x-ray diffraction (XRD) patterns of nanometer-size W metal clusters prepared at different average cluster sizes. Nanometer-size W metal clusters were produced through a collision induced clustering mechanism of W metal atoms generated by decomposing W(CO)(6) vapors. The XRD patterns clearly showed that structure changed from amorphous --> face- centered-cubic (fcc)--> body-centered-cubic (bcc) with increasing average cluster size. This implies that W metal clusters do not simply approach the bulk bcc structure but pass through an intermediate fcc structure before they reach the bulk structure, as predicted by Tomanek, Mukherjee, and Bennemann [Phys. Rev. B 28, 665 (1983)]. (C) 1999 American Institute of Physics. [S0021-9606(99)02540-4].