Deuterium depth profiles in metals using imaging field desorption

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Abstract
Depth profiles of 80‐eV deuterium ions implantedi n s i t u into (110) tungsten have been measured by imaging, field‐desorption mass spectrometry. The relative abundance of deuterium was measured from the surface to a depth of 300 Å with 2‐Å depth resolution by controlled field evaporation of the specimen, and time‐of‐flight mass spectroscopy. The measured position of the depth‐distribution maximum (49±2 Å from the surface), and structure in the distribution is consistent with a model which describes channeling of the deuterium in the near‐surface region following recoil implantation of impurity species from the tungstensurface. The depth distribution of these implantedsurface species has also been measured. For carbon and oxygen, penetration is limited to 22 Å, with abundance decreasing exponentially from the surface. The maximum measuredimplantation depths of these species are in agreement with those predicted theoretically, assuming a model where surfacecarbon and oxygen are channeled into the near‐surface region by the incoming deuterium. These results will be interpreted in the context of the CTR first‐wall impurity problem, and will be used to suggest a novel method for i n s i t u characterization of low‐energy plasma species in operating CTR devices.

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