An apparatus for depth profile analysis of a material composition of a workpiece, the apparatus comprising: a reduced pressure chamber; an etching beam source within the reduced pressure chamber for providing a Neutral Beam having a trajectory, the etching beam source comprising a gas cluster ion beam source for forming a gas cluster ion beam; accelerating means for accelerating the gas cluster ion beam; means for dissociating the gas cluster ion beam; and means for separating ionized components of the accelerated gas cluster ion beam from neutral components to form the Neutral Beam, whereby the gas cluster ion beam is substantially completely dissociated; the apparatus further comprising holding means for disposing the workpiece within the reduced pressure chamber and within the trajectory of the Neutral Beam for etching a surface region of the workpiece; control means for etching a controlled depth of the workpiece at a selected region of the surface of the workpiece, using the Neutral Beam to form an etched surface region; a probe beam source for directing a probe beam at the etched surface region of the workpiece to induce emission of radiation from the etched surface region, whereby, optionally, the Neutral Beam or the gas cluster ion beam may be used as a probe beam in place of the probe beam source and the probe beam; an analytical sensor for detecting radiation emitted from the etched surface region and for analyzing the composition of the region; and control means for repeatedly etching, probing, sensing, and analyzing the etched surface region to form a depth profile analysis of the material composition of the workpiece. a reduced pressure chamber; an etching beam source within the reduced pressure chamber for providing a Neutral Beam having a trajectory, the etching beam source comprising a gas cluster ion beam source for forming a gas cluster ion beam; accelerating means for accelerating the gas cluster ion beam; means for dissociating the gas cluster ion beam; and means for separating ionized components of the accelerated gas cluster ion beam from neutral components to form the Neutral Beam, whereby the gas cluster ion beam is substantially completely dissociated; the apparatus further comprising holding means for disposing the workpiece within the reduced pressure chamber and within the trajectory of the Neutral Beam for etching a surface region of the workpiece; control means for etching a controlled depth of the workpiece at a selected region of the surface of the workpiece, using the Neutral Beam to form an etched surface region; a probe beam source for directing a probe beam at the etched surface region of the workpiece to induce emission of radiation from the etched surface region, whereby, optionally, the Neutral Beam or the gas cluster ion beam may be used as a probe beam in place of the probe beam source and the probe beam; an analytical sensor for detecting radiation emitted from the etched surface region and for analyzing the composition of the region; and control means for repeatedly etching, probing, sensing, and analyzing the etched surface region to form a depth profile analysis of the material composition of the workpiece. a gas cluster ion beam source for forming a gas cluster ion beam; accelerating means for accelerating the gas cluster ion beam; means for dissociating the gas cluster ion beam; and means for separating ionized components of the accelerated gas cluster ion beam from neutral components to form the Neutral Beam, whereby the gas cluster ion beam is substantially completely dissociated;