(a) Doppler -parameter depth profiles for as-deposited Pd-capped Mg films and subsequent hydrogen loading (open and filled circles) or heat treatment under an inert He environment (dash-dotted and dashed lines). (b) Corresponding diagram, with positron implantation energy as the running parameter.
(a) Doppler -parameter depth profiles for Pd-capped films. (i) As-deposited film (hollow circles); (ii) hydrogen loaded film (filled circles); (iii) partially desorbed film after 6 days in vacuum (hollow squares); (iv) desorbed film (filled triangles). (b) Corresponding diagram; the running parameter is the positron implantation energy .
(a) Theoretical valence EMDs of Mg (Ref. 24, black full line) and (Ref. 25, blue dashed line) projected on the -axis and convoluted with the experimental Compton scattering resolution with a full width at half maximum (FWHM) of . (b) 1D-ACAR of an as-deposited Mg film (sample 1a) obtained at a positron implantation energy of 5 keV (thick solid line). The (red) thin line shows comparison with the free-electron contribution (inverted parabola, dash-dotted line) with a Fermi momentum of convoluted with the experimental resolution with a FWHM of plus the estimated (semi-)core contribution (dashed line).
(a) Coincidence Doppler distribution of an as-deposited film at 2 keV (blue full line) and 4 keV (red dashed line), respectively. The shaded areas denote the intervals used to determine the - and - parameters. (b) Logarithmic representation of these coincidence Doppler distributions, showing the ranges of predominant contributions by valence electrons and semicore plus core electrons, respectively.
XRD patterns of Pd-capped Mg film (bottom) after heating in a He environment (red), (top) fully desorbed after loading with , sample 1b (blue).
XRD patterns of Pd-capped Mg film (bottom) after loading with , sample 1c (red), (top) after subsequent partial desorption, sample 1c (blue).
(a) Doppler -parameter depth profiles for a Pd-capped Mg film, sample 1c. (i) As-deposited film (hollow circles); (ii) hydrogen loaded at 500 K (filled circles); (iii) first desorption up to 573 K (blue filled squares); (iv) second desorption up to 600 K (red filled triangles). (b) Corresponding diagram.
(a) Doppler -parameter depth profiles for a Pd-capped Mg film, sample 1b. (i) As-deposited film (hollow circles); (ii) hydrogen loaded at 480 K (filled circles); (iii) desorption up to 498 K (blue filled squares). (b) Corresponding diagram.
Ortho-positronium fraction as a function of average implantation depth for sample 1c (top) and 1b (bottom). The high o-Ps formation and its slow decay with positron implantation energy for sample 1c indicate a pronounced positronium formation at the interface of the Mg layer with the capping layer.
(a) Doppler -parameter depth profiles for Pd-capped Mg–Si (filled and hollow circles) and uncapped Si–Mg (filled and hollow triangles) bilayer films. (b) Corresponding diagram with positron implantation energy as running parameter.
(a) Doppler -parameter depth profiles for Pd-capped Mg–Si bilayer films; (i) as-deposited (filled and hollow circles), and after (ii) heating at 480 K in He, sample 2a (filled squares) and (iii) hydrogen loading at 480 K, sample 2b (hollow squares), respectively. (b) Corresponding diagram.
XRD patterns of Pd-capped Mg–Si bilayer films after hydrogen loading at 480 K, sample 2b (blue line, top), and heating at 480 K in He, sample 2a (red line, bottom), respectively, showing a clear formation in both cases.
Cross-sectional TEM images of Pd-capped Mg–Si bilayer films (a) after heating at 480 K in He (sample 2a) and (b) hydrogen loading at 480 K (sample 2b), respectively. Both samples show the presence of a layer on top of a remaining thinner Si layer and glass substrate, as evidenced by (c) SAED patterns. In addition, the presence of an amorphous presumably Mg-rich prelayer is seen on various parts of the heat treated sample 2a, as shown in (a).
Schematic drawing of the proposed evolution of Pd-capped Mg–Si bilayers on a glass substrate upon prolonged (i) heating at 480 K in an inert He gas environment or (ii) hydrogen loading at 480 K at a pressure of 0.8 MPa. The hydrogen loading leads to a higher local temperature and faster transformation to , and inhibits the formation of an amorphous Mg–Pd or Mg–Si prelayer. The initially formed releases all hydrogen when contact with is reached.
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