The differential sputter yields of tantalum grains during argon ion magnetron sputtering were measured and found to correlate with the atomic packing density in the uppermost atomic layer. Grains with their (110) planes aligned within 15 degrees of the sputtering surface had the highest sputtering yield (0.95 at./ion at 400 eV). Simultaneously, grains oriented so that their (111) planes were within 15 degrees of the sputtering surface had sputtering yields of around two times lower (0.47 at./ion at 400 eV). These results are consistent with the surface sputtering rather than the channeling model. A correlation was found between the number of free atoms on the surface, as determined using a facetted surface model and the measured sputtering yield. (c) 2006 American Vacuum Society.