Application of neutron interferometry to the measurement of thin film density

Abstract

The application of neutron interferometry to the measurement of the atom density of polymer thin films (<1 μm thick) supported on silicon substrates is described. Polymer films were chosen primarily for their fixed, well-defined stoichiometry; however, the technique is applicable to films of any elemental composition. The wavelength-independent phase shift of a beam of thermal neutrons passing through the sample gives a measure of the product of the film atom density, the film thickness, the lattice spacing of the silicon 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 rely on complex mathematical modeling of physical processes nor on thin film standards for data interpretation. With some refinements, neutron interferometry is envisioned as an important tool in the creation of thin films having well-defined densities which will be useful in the calibration of many analysis techniques.

Thermal Expansion of Supported Thin Polymer Films: A Direct Comparison of Free Surface vs Total Confinement

“…2,31 Using the relationship (∂T g /∂F) ) (∂T g /∂P)-(∂P/∂F) ) (∂T g / ∂P) (1/Fκ), where κ is the isothermal compressibility κ ) 2.2 × 10 -10 Pa -1 , 32 a density increase of 1.25-2.50% over bulk values is required for a 20-40°C rise in T g . This shift is improbable, especially in light of recent measurements of bulk average densities to within 1.0% 33,34 and, in the case of neutron interferometry measurements, 35 within 0.5% of the bulk value for polystyrene thin films.…”

A new polarized neutron interferometry facility at the NCNR

“…neutron phase effects (see Table 1). fisherThese include demonstration of the 4π periodicity of neutron wave function [3], precision coherent and incoherent scattering length measurements [4][5][6][7], measuring vertical coherence [8], demonstrating contrast in the presence of zero entanglement but non-zero Quantum Discord [9], and more applied experiments including phase contrast imaging [10,11] and measuring the density of thin films [12]. More recently, proposed experiments have needed both high neutron polarization and precise spin manipulation.…”

The photo-neutronrefractive effect

“…amplitude and phase, in contrast to standard scattering or diffraction techniques where only the intensity is measured. The successful development of a neutron interferometer [8] has hence led to a boost in neutron optics opening up completely new experimental possibilities in applied [45,46,47] and fundamental physics [48,49,50,51,52,53,54], e.g. extremely accurate measurements of scattering lengths [55,56,57,58,59,60,61,62,63,64] or tests of quantum mechanics [65,66,67,68].…”

“…amplitude and phase, in contrast to standard scattering or diffraction techniques where only the intensity is measured. The successful development of a neutron interferometer [8] has hence led to a boost in neutron optics opening up completely new experimental possibilities in applied [45,46,47] [65,66,67,68]. For an excellent, complete and recent review on neutron interferometry see Ref.…”