Pt3Zr(0001): A substrate for growing well-ordered ultrathin zirconia films by oxidation

Abstract

We have studied the surface of pure and oxidized Pt3Zr(0001) by scanning tunneling microscopy (STM), Auger electron microscopy, and density functional theory (DFT). The well-annealed alloy surface shows perfect long-range chemical order. Occasional domain boundaries are probably caused by nonstoichiometry. Pt3Zr exhibits ABAC stacking along [0001]; only the A-terminated surfaces are seen by STM, in agreement with DFT results showing a lower surface energy for the A termination. DFT further predicts a stronger inward relaxation of the surface Zr than for Pt, in spite of the larger atomic size of Zr.A closed ZrO2 film is obtained by oxidation in 10 −7 mbar O2 at 400 • C and post-annealing at ≈ 800 • C. The oxide consists of an O-Zr-O trilayer, equivalent to a (111) trilayer of the fluorite structure of cubic ZrO2, but contracted laterally. The oxide forms a ( √ 19 × √ 19)R23 • superstructure. The first monolayer of the substrate consists of Pt and contracts, similar to the metastable reconstruction of pure Pt(111). DFT calculations show that the oxide trilayer binds rather weakly to the substrate. In spite of the O-terminated oxide, bonding to the substrate mainly occurs via the Zr atoms in the oxide, which strongly buckle down towards the Pt substrate atoms, if near a Pt position. According to DFT, the oxide has a bandgap; STM indicates that the conduction band minimum lies ≈ 2.3 eV above EF. PACS numbers: 68.55.A-, 68.35.bd, 68.37.Ef, 81.65.Mq

Substoichiometric ultrathin zirconia films cause strong metal–support interaction

“…Figure 2a shows a zirconia film of ≈ 5 ML thickness deposited on Pt(111) and annealed at 640 • C in UHV directly after sputter deposition, leading to the formation of zirconia islands and an ultrathin zirconia film in between. The ultrathin zirconia film shows a Zr-Zr distance of 0.350 ± 0.003 nm, as also observed for Pt 3 Zr(0001) 26 and Pd 3 Zr(0001). 21 The moiré pattern shown in the inset of Figure 2a 26 The creation of the ultrathin film can be reversed by annealing at 640 • C in 5 × 10 −7 mbar O 2 , see Figure 2b.…”

“…The ultrathin zirconia film shows a Zr-Zr distance of 0.350 ± 0.003 nm, as also observed for Pt 3 Zr(0001) 26 and Pd 3 Zr(0001). 21 The moiré pattern shown in the inset of Figure 2a 26 The creation of the ultrathin film can be reversed by annealing at 640 • C in 5 × 10 −7 mbar O 2 , see Figure 2b.…”

“…A closer look at the ultrathin film reveals a hexagonal lattice with interatomic distances of 0.35 nm, as is typical for ultrathin zirconia films, 21,26 see the Fourier transform (FFT) in Figure 1e. When comparing two domains rotated by a multiple of ≈ 60 • , their lattices agree within 1%, demonstrating that the deviations from an exactly hexagonal structure are small.…”

First-principles study of a new structure and oxidation mechanism of Pt3Zr

“…[19][20][21] Recently, the oxidation behavior of Pt 3 Zr (0001) surface was studied by the experiment and rst-principles calculations. 22 They found that the weak localized hybridization between Pt and Zr is benecial to oxidation of Zr metal. Note that the metal addition will accelerate the growth of ZrO 2 lm on the Pt 3 Zr (0001) surface.…”

From two- to three-dimensional alumina: Interface templated films and formation of γ−Al2O3 (111) nuclei

“…A viable approach for the synthesis of ultrathin oxide films is based on the selective oxidation of suitable bimetallic alloys [18][19][20][21][22]. The prototypical example is an ultrathin alumina film on the NiAl(110) substrate [18,23], which has been widely used as a support in model catalytic studies [1,[24][25][26].…”