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Positron depth profiling of the structural and electronic structure transformations of hydrogenated Mg-based thin films
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10.1063/1.3075762
/content/aip/journal/jap/105/4/10.1063/1.3075762
http://aip.metastore.ingenta.com/content/aip/journal/jap/105/4/10.1063/1.3075762
View: Figures

Figures

Image of FIG. 1.
FIG. 1.

(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.

Image of FIG. 2.
FIG. 2.

(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 .

Image of FIG. 3.
FIG. 3.

(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).

Image of FIG. 4.
FIG. 4.

(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.

Image of FIG. 5.
FIG. 5.

XRD patterns of Pd-capped Mg film (bottom) after heating in a He environment (red), (top) fully desorbed after loading with , sample 1b (blue).

Image of FIG. 6.
FIG. 6.

XRD patterns of Pd-capped Mg film (bottom) after loading with , sample 1c (red), (top) after subsequent partial desorption, sample 1c (blue).

Image of FIG. 7.
FIG. 7.

(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.

Image of FIG. 8.
FIG. 8.

(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.

Image of FIG. 9.
FIG. 9.

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.

Image of FIG. 10.
FIG. 10.

(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.

Image of FIG. 11.
FIG. 11.

(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.

Image of FIG. 12.
FIG. 12.

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.

Image of FIG. 13.
FIG. 13.

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).

Image of FIG. 14.
FIG. 14.

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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/content/aip/journal/jap/105/4/10.1063/1.3075762
2009-02-24
2014-04-25
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Positron depth profiling of the structural and electronic structure transformations of hydrogenated Mg-based thin films
http://aip.metastore.ingenta.com/content/aip/journal/jap/105/4/10.1063/1.3075762
10.1063/1.3075762
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