(Top) XRD scan of a thin film grown using the same PLD parameters as for the thin film, except that the Si substrate was held at room temperature and no background gas was used during the growth. (Bottom) XRD scan of a LaS thin film deposited on a (100) MgO substrate. Miller indices of the most predominant reflection peaks from the cubic rocksalt phase of LaS are identified. Smaller peaks corresponding to , , and impurity phases are also indicated.
AFM scans over a area of (a) a LaS thin film grown on a (100) MgO substrate and (b) a LaS thin film grown on a (100) Si substrate. The PLD parameters for both films were identical, except that the Si substrate was held at room temperature and no background gas was used during the growth.
Three different line scans obtained from the AFM data of a thin film shown in Fig. 2(a) . The average grainlike feature size on the surface is estimated to be about .
HRTEM image of a LaS thin film grown on a MgO substrate. The film thickness is about .
HRTEM image of the interface.
HRTEM image of the LaS thin film in a region just above the interface.
HRTEM image in the middle of the thick LaS thin film.
HRTEM image of the top surface of the LaS thin film.
Experimental FE characteristics of planar and cathodes. Each of these plots represents an average over four or five different measurements at the same point and for the same distance . The total emission current for different values depend strongly on the distance (3.6 and ) between the probe ball and the cathode surface.
FE characteristics of planar and cathodes. To allow comparison, the FE characteristics are plotted using the current densities vs local electric fields obtained from a set of at different distance and an analysis presented in Ref. 8 .
Schematic of the patchwork model of the cathode surface. The emitting areas are preferentially limited to the outcropping (100) areas of the LaS nanocrystals which have a work function in the range of .
Fowler-Nordheim plot of FE of a and planar cathode. Also shown are the results of numerical simulations for a full area emitting cathode (Ref. 15 ).
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