Structural Relationship Between a Titanium Deuteride Film and a Thin Protecting Pd Toplayer

EG Keim, W Lisowski
2006 Microscopy and Microanalysis  
Thin films of titanium hydride (deuteride) have a number of possible applications as hydrogen (deuteride) storage material used in catalytic or energetic reactions (see [1] and Refs. therein). Application of such films under atmospheric pressure leads, however, to a partial decomposition of titanium hydride (deuteride) material due to interaction with oxygen [1]. In order to prevent interaction with air, titanium hydride (deuteride) films are covered by a protective layer such as Pd. In this
more » ... h as Pd. In this work titanium deuteride films (TiD y ) were obtained by the interaction of spectroscopically pure deuterium with thin Ti films evaporated in situ onto a Si(100) substrate within a glass UHV system [2], by evaporation of a fine Ti wire wound around a tungsten heater. During deposition of the films, the Si substrate was maintained at 273 K. The films were annealed for 60 min at 650 K. Deuterium was introduced in successive, calibrated doses at 298 K until an equilibrium pressure of 1 Pa was reached. Following this adsorption procedure, TiD y films were routinely obtained with y ≈ 2 [3]. The TiD y films were then covered in situ by evaporation of a 10 -12 nm thick Pd layer. The TEM specimens of the Pd/TiD y films were prepared in cross-section (XS) according to the recipe described in Ref. [4], and TEM examination of the Pd/TiD y films was performed ex situ. XS-TEM analysis was performed to obtain information regarding the bulk structure of corresponding films and to reveal the nanostructures formed at the Pd/TiD y interface. The results show the TiD y film to be plastically deformed leading to an increase in the roughness of the top Pd layer (Fig. 1a) . Selected Area Diffraction (SAD) analysis allowed the crystal phases in the bulk of the Pd/TiD y film to be identified (Fig. 1b) . By analysis of the cross-sectional TEM images the Pd/TiD y interface was identified and structures which are the result of a crystallographic relationship between adjacent grains of the TiD y top-layer, and between these grains and the Pd protecting layer could be characterized (Fig. 2) . Complex structures, including Moiré patterns, have been identified (Fig. 2) . The origin of these structures was determined by measuring the interplanar distances of the fringes in the lattice image [5], using well known formulas describing translational (d T ) and rotational (d R ) Moiré fringe spacing [6]. Selected Moiré structures, representing various lattice planes interfering within the Pd/TiD y interface, are shown in Fig. 2 (spots A, B and C). Moiré fringes (A) (d R = 1.48 nm) reveal the overlap of two TiD 2 (111) lattices rotated through 10°. Moiré superstructure (B) (d T = 1.73 nm) is produced by the overlap of TiD 2 (111) and Pd(111). Moiré fringes (C) (d T = 0.99 nm) disclose the cubic PdTi(111) transient phase [5], superimposed with the growth into the Pd(111) structure.
doi:10.1017/s1431927606061150 fatcat:tdoih4nf7faupcxidqxefrppku