Thickness calibration of carbon foils

The transmittance of normally incident, monochromatic light for self-supporting carbon foils is a well-known nondestructive procedure to determine their thickness. The relationship of transmittance and foil thickness can be described using the exact analytical equation for a single unsupported layer, where the only free parameter is the complex refractive index. Using this formula, calibration curves for various data from the literature could be fitted. Explanations are given as to why carbon foils prepared even by the same procedure but in different setups show different optical parameters. The newly developed carbon foils, prepared by laser plasma ablation-deposition, were thickness calibrated in the same manner. In this case, AT-cut quartz crystals coupled to a thickness monitor were used as substrates for the thickness standards. (orig.)