DEPTH PROFILING OF HYDROGEN USING THE HIGH-EFFICIENCY ERD-TOF TECHNIQUE

The hydrogen detection efficiency using the ERD-TOF technique, based on the use of 10-mu-g/cm2 carbon foil as a start detector, was measured with respect to the second conventional ERD detector with an absorber placed at nearly comparable geometry in the same experiment. The probing beams were 30 MeV Cl-35 and 4 MeV He-4, with a detection angle of 30-degrees with equal entrance and exit angles with respect to the target surface. From the studies of films of Mylar, Kapton and deuterated polyethylene as well as PECVD a-Si:H, Si3N4, and a-C:H targets, the ERD-TOF hydrogen efficiency was found to be approximately 40% at 2.43 MeV hydrogen recoils, which increased gradually at lower energies. The hydrogen detection efficiency was also studied as a function of the MCP detector bias by scattering 1 and 3 MeV protons from a thin (100 angstrom) Au film. The energy variation in the efficiency using nearly saturated MCP detector bias was found to be proportional to the energy loss (dE/dx) of protons in the carbon. A considerable improvement in the efficiency was noted by coating the carbon foil with a thin low density MgO layer. The hydrogen depth profiles using the ERD-TOF technique show better depth resolution and an increased accessible depth than the ERD using absorber. The improved depth resolution, along with the intrinsic ability of the ERD-TOF technique to completely resolve the light element recoils, can be applied in many fields such as the study of hydrogen diffusion in double layer LPCVD Si3N4 structures and polymer diffusions with lower diffusion coefficients.