Differential alternating current chip calorimeter for in situ investigation of vapor-deposited thin films

Abstract

Physical vapor deposition can be used to produce thin films with interesting material properties including extraordinarily stable organic glasses. We describe an ac chip calorimeter for in situ heat capacity measurements of as-deposited nanometer thin films of organic glass formers. The calorimetric system is based on a differential ac chip calorimeter which is placed in the vacuum chamber for physical vapor deposition. The sample is directly deposited onto one calorimetric chip sensor while the other sensor is protected against deposition. The device and the temperature calibration procedure are described. The latter makes use of the phase transitions of cyclopentane and the frequency dependence of the dynamic glass transition of toluene and ethylbenzene. Sample thickness determination is based on a finite element modeling of the sensor sample arrangement. In the modeling, a layer of toluene was added to the sample sensor and its thickness was varied in an iterative way until the model fit the experimental data.