Measurement of polystyrene mean inner potential by transmission electron holography of latex spheres

This study describes the use of transmission electron holography to determine the mean inner potential of polystyrene. Spherical nanoparticles of amorphous polystyrene are studied so that the effect of specimen thickness on the phase shift of an incident electron wave can be separated from the intrinsic refractive properties of the specimen. A recursive four-parameter χ-squared minimization routine is developed to determine the sphere center, radius, and mean inner potential (φ₀) at each pixel in the phase image. Because of the large number of pixels involved, the statistics associated with determining a single φ₀ value characteristic of a given sphere are quite good. Simulated holograms show that the holographic reconstruction procedure and the χ-squared analysis method are robust. Averaging the φ₀ data derived from ten phase images from ten different polystyrene spheres gives a value of φ₀^PS = 8.5 V (σ) = 0.7 V). Specimen charging and electron-beam damage, if present, affect the measurement at a level below the current precision of the experiment.