For the first time, the latent heat of fusion DH m for Sn particles formed by evaporation on inert substrate with radii ranging from 5 to 50 nm has been measured directly using a novel scanning nanocalorimeter. A particle-size-dependent reduction of DH m has been observed. An "excluded volume" is introduced to describe the latent heat of fusion from the enhanced surface melting of small particles. Melting point depression has also been found by our nanocalorimetric technique. [S0031-9007(96)00495-4]

The melting behavior of 0.1-10-nm-thick discontinuous indium films formed by evaporation on amorphous silicon nitride is investigated by an ultrasensitive thin-film scanning calorimetry technique. The films consist of ensembles of nanostructures for which the size dependence of the melting temperature and latent heat of fusion are determined. The relationship between the nanostructure radius and the corresponding melting point and latent heat is deduced solely from experimental results ͑i.e., with no assumed model͒ by comparing the calorimetric measurements to the particle size distributions obtained by transmission electron microscopy. It is shown that the melting point of the investigated indium nanostructures decreases as much as 110 K for particles with a radius of 2 nm. The experimental results are discussed in terms of existing melting point depression models. Excellent agreement with the homogeneous melting model is observed.

This work investigates the thermodynamic properties of small structures of Al using an ultrasensitive thin-film differential scanning calorimeter. Al thin films were deposited onto a Si 3 N 4 surface via thermal evaporation over a range of thicknesses from 6 to 50 Å. The Al films were discontinuous and formed nanometer-sized clusters. Calorimetry measurements demonstrated that the melting point of the clusters is lower than the value for bulk Al. We show that the melting point of the clusters is size dependent, decreasing by as much as 140°C for 2 nm clusters. The results have relevance in several key areas for Al metallization in microelectronics including the early stages of film growth and texture formation, the Al reflow process, and the dimensional stability of high aspect ratio Al lines.

We introduce a high sensitivity (1J/m2) scanning microcalorimeter that can be used at high heating rates (104 °C/s). The system is designed using ultrathin SiN membranes that serve as a low thermal mass mechanical support structure for the calorimeter. Calorimetry measurements of the system are accomplished via resistive heating techniques applied to a thin film Ni heating element that also serves as a thermometer. A current pulse through the Ni heater generates heat in the sample via Joule heating. The voltage and current characteristics of the heater were measured to obtain real-time values of the temperature and the heat delivered to the system. This technique shows potential for measuring irreversible heat of reactions for processes at interfaces and surfaces. The method is demonstrated by measuring the heat of fusion for various amounts of thermally evaporated Sn ranging from 50 to 1000 Å.

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