A vacuum bearing structure comprises a combination of a planar gas bearing with a differentially-pumped vacuum seal. The bearing surface and the vacuum seal surfaces are formed of a porous material divided into a first outer region through which bearing gas can percolate to provide support and an inner second region providing the vacuum seal. An exhaust groove separates the two regions so that bearing gas can flow to atmosphere. The resulting structure can operate at a lower fly height to reduce loading on the differentially-pumped vacuum seal. The structure is particularly useful for motion feedthroughs into vacuum processes such as ion implantation.