Pt-induced faceting of W field emitter tips

Diffusion and desorption of submonolayer platinum deposited on the multi-faceted surface of a tungsten micro-crystal

“…4) shows that after spreading the adlayer was stable during heating to about 1100 K and that Pt started to desorb at about 1780 K. The latter value is in good correlation with previous measurements on the surfaces of W(1 1 2) [11], W(0 1 1) [18] and W emitter tip [8]. The activation energy for Pt desorption 5.19-5.55 eV is relatively low but it corresponds well to E des obtained for the desorption of 'zero coverage' Pt from W(1 1 0) quoted in Table 1.…”

“…The calculated (apparent) work function f was compared to the adsorption curve presented in Ref. [8] (Fig. 6, page 89), maximum of which corresponded to around 1 geometrical monolayer (ML) of platinum.…”

“…Platinum is known to cause a massive faceting of the (1 1 1) plane of tungsten [1][2][3][4], but usually the faceting processes required a much higher concentration of adsorbate (around 1 physical monolayer = 3 geometrical ML in the case of bcc (1 1 1) plane) than the average coverage used in this work. Works, conducted on the curved and diversified surfaces of emitter tips [6,8], dealt so far with relatively high Pt concentrations, where extensive faceting after annealing the Pt covered tip at temperatures T ! 1750 K was reported, but any increase of emission from the region near {1 1 1} pole was not found.…”

“…Works were carried out both on plane W(1 1 1) crystals (e.g. [1][2][3][4][5]) and curved surfaces of W emitter tips [5][6][7][8][9][10]. Accordingly, the growth, alloying and segregation of transition metals (including Pt) deposited on tungsten (1 1 1) and (1 1 2) planes were studied [11][12][13][14].…”

Simulation of adsorbate-induced faceting on curved surfaces

“…Interesting results have been obtained for faceting on curved surfaces of W and Mo in FIM (field ion microscopy) [10][11][12] and FEM (field emission microscopy) experiments [13][14][15]. Initially a spherical surface comprises macroscopic crystal facets.…”