Study On Specific Heat Capacities Of Nanometer Thin Films With Molecular Dynamics Simulation And Microstructure Testing

The specific heat capacities of thin films are no longer intrinsic material properties at some cases as they are for bulk samples. Due to the microscale effect, they depend on the thickness meanwhile varied from different parparation methods. The abnormal thermophysical properties are key parameters that are very difficult to get in the researches of micro-devices or nano-devices. In this article the algorithm of molecular dynamics is adopted to study the specific heat capacities of several kinds of thin films used widely in MEMS of which some are measured in experiments. Also some facts that may have influences on the calculations and the precision of testings are discussed.In the paper models of thin solid films are constructed based on experimental values and reliable potential function is chosen to present the interaction of atoms. Specific heat capacities of films of aluminium, copper, silicon and silicon dioxide in the thickness range of 1nm to 5nm at 100-600K are calculated by melocular dynamics method in canonical ensemble. The results show that the specific heat capacities of the thin films have large deviations and are much smaller than their bulk materials; and the values are in agreement with some theoretical analysis that proposed in others' literatures. The results disclose the importance of the potential function to the simulation, because it is significantly meaningful to determine whether the calculation is right or not to some extent. The influence of defects on specific heat capacity is studied and results show that defects can enlarge the value of heat capacity due to the increasing of desity of state in forbidden band.Surface machining microcalorimeters are fabricated and proper schemes are designed for the test of heat capacity of Al thin films. The comparisons between the results of measurement and simulation are made. The former is larger than the latter and the reasons for their deviation are analysed.