Application of neutron interferometry to the measurement of thin film density

The application of neutron interferometry to the measurement of the atom de nsity of polymer thin films (<1 mu m thick) supported on silicon substrates is described. Polymer films were chosen primarily for their fixed, well-de fined stoichiometry; however, the technique is applicable to films of any e lemental composition. The wavelength-independent phase shift of a beam of t hermal neutrons passing through the sample gives a measure of the product o f the film atom density, the film thickness, the lattice spacing of the sil icon interferometer, and the scattering lengths of the constituent elements of the film. The film thickness was found by x-ray reflectivity while the other two parameters are well-defined quantities. The technique does not re ly on complex mathematical modeling of physical processes nor on thin film standards for data interpretation. With some refinements, neutron interfero metry is envisioned as an important tool in the creation of thin films havi ng well-defined densities which will be useful in the calibration of many a nalysis techniques. (C) 1999 American Institute of Physics. [S0003-6951(99) 00603-8].