Morphology of Ni ultrathin films on Mo(110) and W(100) studied by LEED and STM

Abstract

The morphology of ultrathin Ni films on Mo(110) and W(100) has been studied by low-energy electron diffraction and scanning tunneling microscopy. Ni films grow pseudomorphically on Mo(110) at 300 K for a coverage of 0.15 ML. A (8 × 1) structure is found at 0.4 ML, which develops into a (7×1) structure by 0.8 ML as the film undergoes a structural change to fcc Ni(111) at 6 ML. The growth mode switches from layer-by-layer to Stranski-Krastanov between 4 ML and 6 ML. Annealing at around 850 K results in alloying of submonolayer films with the substrate, while for higher coverages the Ni agglomerates into nanowedge islands. Ni films grow pseudomorphically on W(100) up to a coverage of around 2 ML at 300 K, above which there is a structural change from bcc to hcp Ni with the epitaxial relationship (1120) N i || (100) W . This is accompanied by the formation of orthogonal domains of uniaxial strain-relieving dislocations from the third layer of the film. For coverages up to 1 ML the growth proceeds by formation of two-dimensional islands, but shifts to three-dimensional growth by 2 ML with rectangular islands aligned along the 011 substrate directions. Annealing at around 550 K results in agglomeration of Ni into larger islands and increasing film roughness.

Interactions of Ni Nanoparticles with Reducible CeO2(111) Thin Films

“…The slight shift in the Ni 2p 3/2 peak position to a higher binding energy value at 300 K compared to that from the bulk Ni can be contributed to the initial and final state effects resulting from the low coordination of the Ni atoms in very small clusters. ,− As shown in the STM image (Figure b), at room temperature, very small Ni particles that are less than 2.0 nm wide and 0.5 nm high are formed on the ceria surface. These particles are two-dimensional considering the height for an atomic layer of Ni in STM is between 2 and 3 Å . On the basis of the thermodynamics, the formation of two-dimensional islands on an oxide surface should occur if the interfacial energy between the metal and the oxide (γ m/o ) is smaller than the difference between the surface free energy for the metal (γ v,m ) and the oxide (γ v,o ) .…”

“…These particles are two-dimensional considering the height for an atomic layer of Ni in STM is between 2 and 3 Å. 35 On the basis of the thermodynamics, the formation of twodimensional islands on an oxide surface should occur if the interfacial energy between the metal and the oxide (γ m/o ) is smaller than the difference between the surface free energy for the metal (γ v,m ) and the oxide (γ v,o ). 36 Although the surface free energy of Ni (∼1.7 J/m 2 ) is larger than that of ceria (0.7 J/m 2 ), Ni tends to wet the ceria surface which indicates a strong interaction between the two.…”

Understanding the Role of Metal-Modified Mo(110) Bimetallic Surfaces for C–O/C═O and C–C Bond Scission in C3 Oxygenates

“…Characterization of the Ni/Mo(110) and Co/Mo(110) surfaces has been extensively studied via LEED, STM, and AES; the investigations of the growth of Ni − and Co − overlayers on Mo(110) show that both Ni and Co grow layer by layer on Mo(110) at room temperature and form 3D islands upon annealing to >600 K. Reactions of alcohols on clean Mo(110) and modified Mo(110) have been largely reported by Friend’s group via surface science studies. − However, the investigation of reactions of aldehydes on Mo(110) is limited; Mei et al studied the reaction pathways of acetaldehyde via periodic spin-polarized density functional theory (DFT) simulations, and Queeney et al reported the reaction of formaldehyde on Mo(110) using temperature-programmed reactions and infrared reflectance absorbance spectroscopy . To the best of our knowledge, there has been no experimental UHV study of C3 aldehyde on pure Mo(110) and/or metal-modified Mo(110) surfaces.…”

Growth morphology of thin films on metallic and oxide surfaces

“…Until now, the surface structures and growth modes of various adsorbate metals (e.g. Cu [3], Co [4], Fe [5], Ni [6], Mg [7], Ba [8], K [9], S [10], In [11], Ag [12][13][14][15][16][17], Au [18][19], Sn [20][21], Pb [22][23][24][25], etc.) on the Mo (110) substrates have been investigated by a variety of experimental and theoretical methods in a number of works.…”

“…Until now, the surface structures and growth modes of various adsorbate metals (e.g. Cu [3], Co [4], Fe [5], Ni [6], Mg [7], Ba [8], K [9], S [10], In [11], Ag [12][13][14][15][16][17], Au [18,19], Sn [20,21], Pb [22][23][24][25], etc) on Mo (110) substrates have been investigated by a variety of experimental and theoretical methods in a number of works. Recently, the formation of oxide layers on transition metal (TM) surfaces has also received considerable attention [26][27][28][29], including the Mo (110) surface [30,31].…”