The cluster size dependence of thermal stabilities of both molybdenum and tungsten nanoclusters

We measured, for the first time, the oxidation enthalpies of both molybdenum (Mo) and tungsten (W) nanoclusters at several cluster sizes. We observed that the oxidation enthalpies of both Mo and W nanoclusters went down to the corresponding bulk values, respectively, with increasing cluster size. By using the oxidation enthalpies, we estimated the formation enthalpies by using H-nanocluster = O-nanocluster - O-bulk. The formation enthalpies of both Mo and W nanoclusters were all positive and went down to the bulk value (defined as 0 kcal/mol), indicating that the thermal stabilities of both Mo and W nanoclusters improved toward the bulk state with increasing cluster size. (C) 2002 Elsevier Science B.V. All rights reserved.