Faceting and defaceting phase transitions ofPd∕W(111)

Abstract

We have studied the faceting and defaceting phase transitions of Pd/ W͑111͒. In apparent agreement with results of recent theoretical simulation ͓C. Oleksy, Surf. Sci. 549, 246 ͑2004͔͒, we find the fastest way to create the largest facets is to anneal at a temperature right below the temperature that the defaceting transition occurs. On the other hand, while the paths of faceting transitions show normal retardation as the cooling rate is increased, the paths of defaceting transitions show negligible dependence on the heating rate even if increased by 64-fold. Another notable observation is a phase separation of the surface into defaceted and faceted regions after long annealing time while there is more than enough Pd remaining to induce faceting of the whole surface. This leads us to the proposal that instead of thermal disorder, the observed defaceting transition of the Pd/ W͑111͒ system is mainly driven by local loss of Pd, which is due to thermal desorption. Such desorption loss could be effectively replenished via surface diffusion at the vicinity of the Pd 3d islands. The observed independence of the defaceting transition path on the heating rate is rationalized as the consequence of a balance in between the loss and the supply of Pd, which can establish very quickly as the temperature rises.

Hydrogen adsorption promoted perpendicular magnetic anisotropy in nano-structured Fe coverage on Pd/W{112} faceting surface

“…In previous report of Liao et al, 1000 K-annealed Pd/W{112} surface reveals sharper LEED spots, indicating larger average facet size relative to 800-K results. 7 In Fig. 5, the H 2 induced H C enhancement is similar for 800 and 1000 K-faceted surface, implying that the facet size seems insignificant.…”

“…Previous studies show that Pd can be used to induce the faceting of W(111) and the size of 3-sided pyramids ranges from several to tens of nanometers, depending on the annealing process. [5][6][7] Pd is also one of the extensively studied materials for hydrogen storage and gas sensor, because of its high efficiency in catalyzing hydrogen dissociation. 8 Thus, the nano-scale faceted Pd/ W(111) surface is an unexplored functional template either from magnetism's and metal-hydride's point of view.…”

Core-level spectroscopy of the Pd/W(110) interface: Evidence of long-range Pd-island–W interactions at submonolayer Pd coverages

“…This is most dramatically illustrated in the phenomenon of overlayer-induced faceting of bcc(111) surfaces (Ta, Mo, and W) [25][26][27][28][29][30][31][32][33][34][35][36]. Recently, more subtle overlayer-induced effects have been investigated.…”

Oxygen-induced nano-faceting of Re(112¯1)

“…Adsorbate-induced faceting of metal surfaces, which include both planar and curved (tip) metal surfaces [11][12][13][14][15][17][18][19][20][21][22][23][24][25][26][27], has been studied extensively in recent years. However, among the previous studies, an atomic-level understanding of how the mass transport necessary to form facets occurs is lacking.…”