ENERGY STRAGGLING FOR MEDIUM-ENERGY H+ BEAMS PENETRATING CU, AG, AND PT

The electronic-energy-straggling values for 50-250-keV H+ beams penetrating Cu, Ag, and Pt have been measured using backscattering. The Cu, Ag, and Pt layers with a thickness of about 30 nm were deposited onto Si, SiO2, Al2O3, and ZrO2 substrates with electron beams or by sputtering. The uniformity and grain growth of the thin films were observed by cross-section transmission electron microscopy (TEM) and diffraction. The thickness fluctuation determined by TEM is less than 2 nm. The backscattering spectra were obtained with an electrostatic toroidal analyzer with an energy resolution (standard deviation) of 150-200 eV, and the computer-simulated spectrum analysis has given the best-fit values of the energy straggling. The derived straggling values are compared with the theoretical values calculated from the extended Lindhard-Winther theory using the local electron density of the Hartree-Fock-Slater atomic model. Discussion is also made in terms of the short-range correlation effect proposed by Sigmund [Phys. Rev. A 26, 2497 (1982)].