Condensation of isolated metal clusters studied with a calorimeter

We describe the combination of molecular beam techniques with a calorimeter in order to investigate thermal properties of isolated metal clusters. A size distribution of neutral Sn-N clusters with 6 less than or equal to N less than or equal to 600 is deposited on a bimetallic micromechanical sensor and the released heat during the cluster deposition can be determined from the time-dependent bending of the sensor. The size distribution of the deposited clusters coming from the pulsed source has been probed with a quasicontinuous time-of-flight mass spectrometer. The formation enthalpy per atom of the investigated Sn-N cluster size distribution is obtained from the measured calorimetric heat to Delta h(f,298)=0.45-0.53 eV. (C) 1999 American Institute of Physics. [S0021-9606(99)02619-7].