The diffusivity of spherical colloidal particles close to a planar hard wall is studied by dynamic light scattering with evanescent illumination. A novel setup allows us to independently vary the scattering vector components parallel $Q_{\Vert }$ and normal $Q_{\perp }$ to the wall. An expression for the initial decay rate $\Gamma$ of the time autocorrelation functions is derived as a function of both $Q_{\Vert }$ and $Q_{\perp }$, as well as the penetration depth of the evanescent wave, where hydrodynamic interactions of particles with the wall are included. This makes it possible to study the viscous wall drag effect quantitatively for particles as small as $85\mathrm{nm}$ in radius.

The dynamics of colloidal spheres near to a wall is studied with an evanescent wave scattering setup that allows for an independent variation of the components of the scattering wave vector normal and parallel to the wall. The correlation functions obtained with this novel instrumentation are interpreted on the basis of an expression for their short time behavior that includes hydrodynamic interactions between the colloidal spheres and the wall. The combination of the evanescent wave scattering setup and the exact expression for the short time behavior of correlation functions allows for an unambiguous measurement of the particle mobility parallel and normal to the wall by means of light scattering. It is possible to measure the viscous wall drag effect on the dynamics of particles with radii as small as $27\mathrm{nm}$ , where, however, the method reaches its limits due to the low scattering intensities of such small particles.