Raman micro-spectroscopy for quantitative thickness measurement of nanometer thin polymer films

The sensitivity of far-field Raman micro-spectroscopy was investigated to determine quantitatively the actual thickness of organic thin films. It is shown that the thickness of organic films can be quantitatively determined down to 3 nm with an error margin of 20% and down to 1.5 nm with an error margin of 100%. Raman imaging of thin-film surfaces with a far-field optical microscope establishes the distribution of a polymer with a lateral resolution of ~400 nm and the homogeneity of the film. Raman images are presented for spin-coated thin films of polysulfone (PSU) with average thicknesses between 3 and 50 nm. In films with an average thickness of 43 nm, the variation in thickness was around 5% for PSU. In films with an average thickness of 3 nm for PSU, the detected thickness variation was 100%. Raman imaging was performed in minutes for a surface area of 900 µm2. The results illustrate the ability of far-field Raman microscopy as a sensitive method to quantitatively determine the thickness of thin films down to the nanometer range

Calcium Carbonate Nucleation Investigated in a Double Pulse Experiment

The nucleation rate is essential in a number of research fields in order to control crystal formation. The purpose of this study is to test and optimize the double pulse procedure as a method to investigate nucleation of calcium carbonate. The induction time, interpreted as time of formation of postcritical nuclei, was used to separate a stage in which nucleation is the main process from a stage in which formed nuclei mainly grow. The induction time was defined for a model mineralization solution by recording the pH profile of the supersaturated solution representing the desaturation curve. In the double pulse procedure nucleation was quenched during the induction time at several time points, and existing nuclei could grow until a size detectable by scanning electron microscopy. It was observed, under applied supersaturation conditions S = 4, that postcritical nuclei formed directly when the saturation level of the solution was achieved. It is proposed here that the growth of crystals occurs due to the agglomeration of nuclei