A modified single-stage low pressure impactor is described to measure the coefficient of normal restitution e(n) for nanoparticles. The device is analysed numerically using CFD, and the gas flow inside the structured impaction plate is studied. A formula for the calculation of e(n) is derived and first measurements of e(n) for spherical silver particles are presented together with numerical data obtained from force-based molecular dynamics simulations. Furthermore, the simulation data for e(n) and the sticking probability are investigated in detail for the elastic, and partly for the plastic impaction regime.