Experimental evidence of structural transition from fcc to bulk bcc in nanophase metal clusters of (Fe)n, (Cr)n, (Mo)n and (W)n produced by CO2 laser multiphoton decomposition of metal carbonyls

We have produced nanophase metal clusters, (Fe)(n), (Cr)(n), (Mo)(n) and (W)(n), by multiphoton decomposition of the corresponding metal carbonyls with a 10.6 mu m CO2 laser in the presence of Ar and SF6. The size distribution was narrow and the average diameter was 6, 3.5, 2 and similar to 1 nm for Fe, Cr, Mo and W clusters, respectively. The structure was found to be bcc for both Fe and Cr clusters, fee for Mo clusters, and amorphous for W dusters (note that all the bulk metals have bce structure). Considering the cluster sizes (9630, 1870, 230 and similar to 30 for Fe, Cr, Mo and W clusters, respectively) estimated from their average diameters, it is likely that there exists a structural transition from fee to bulk bcc with increasing cluster size in these metal clusters. (C) 1998 Elsevier Science B.V.