Energetics and Vibrational States for Hydrogen on Pt(111)

Bădescu, Ştefan C.; Salo, Petri; Ala-Nissilä, Tapio; Ying, S. C.; Jacobi, K.; Wang, Yuemin; Bedürftig, Kolja; Ertl, G.

doi:10.1103/physrevlett.88.136101

Cited by 112 publications

(113 citation statements)

References 33 publications

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“…The activation energy of D is found larger than that of H by 15 meV, and the prefactor is roughly the same as that of H within the experimental uncertainty. According to theoretical calculations, the zero point energy difference between H and D on Pt(111) is about 45 meV [26,42]. Considering that there is a difference of zero point energy at the saddle point, our measured value is quite reasonable.…”

Section: Prl 97 166101 (2006) P H Y S I C a L R E V I E W L E T T E supporting

confidence: 51%

Quantum Diffusion of H on Pt(111): Step Effects

2006

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Using a linear optical diffraction technique, we have systematically investigated the defect effects on quantum surface diffusion of hydrogen on Pt(111) surfaces. The quantum tunneling effect was clearly observed for hydrogen diffusion at low temperatures as manifested by a leveling off of the diffusion coefficient on flat surfaces. The strong influence of surface defects on the quantum diffusion is in good agreement with the creation of an inhomogeneous surface with adsorption sites of different binding energies. DOI: 10.1103/PhysRevLett.97.166101 PACS numbers: 68.35.Fx, 68.35.Dv, 68.43.Jk, 82.20.Xr Because of the small mass of the hydrogen atom and the weakly corrugated potential energy surface, diffusion of hydrogen on metal surfaces may take both classical overbarrier hopping and quantum mechanical under-barrier tunneling. Quantum effects in surface diffusion are of broad interest and have been intensively studied both experimentally [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] and theoretically [16 -26]. The first observation of a nearly temperature independent surface (chemical) diffusivity of H on W(110) in the low temperature regime by Gomer and coworkers [1] using field emission microscopy (FEM) has stimulated a great theoretical effort [16 -26] because of the observed unexpected different behavior from the light atom diffusion in bulk metals, for which a much stronger temperature dependence was found [27]. Experimentally, while similar behaviors were observed by the same group using the same technique for H on a number of other metal surfaces [2 -7], only one report using a different technique, scanning tunneling microscopy (STM), has confirmed the weak temperature dependence of surface (tracer) diffusivity for H on Cu(100) [13], but at a diffusion rate about 6 -9 orders of magnitude slower (10 ÿ19 cm 2 = sec vs 10 ÿ10 -10 ÿ13 cm 2 = sec). Using a linear optical diffraction (LOD) technique that probes diffusion over a length scale of microns, Zhu and his coworkers found an activated quantum diffusion with a strong temperature dependence for H on Ni(111) [11,12] and Ni(100) [8], drastically different from what has been observed by Gomer and his coworkers on the same systems [7]. These differing and apparently contradictory observations, using different techniques, need to be resolved in order to remove any doubts on the experimental observation of quantum surface diffusion.Recognizing that different techniques detect different physical properties of a system, and that such properties might be influenced by different processes, we studied the quantum effects in surface diffusion using one of the above techniques, the linear optical diffraction technique [28][29][30]. The system we have chosen is H on Pt(111), because there is a theoretical prediction for this system [26], and we have extensively studied the over-barrier diffusion of this system [31]. Compared to FEM and STM, which detect the H diffusion only within a single well-ordered terrace, the linear optical diffraction technique probes...

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Section: Prl 97 166101 (2006) P H Y S I C a L R E V I E W L E T T E supporting

confidence: 51%

Quantum Diffusion of H on Pt(111): Step Effects

2006

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“…1 The range of the calculated activation energy from theoretical models is likewise rather broad, ranging from 200 to ϳ80 meV. 19,[26][27][28] The difference in the measured diffusion activation energy by LOD and by QHAS may come from the different diffusion length scale involved in these techniques. 50 Due to the macroscopic diffusion length scale of ϳ5 m used in LOD, the effect of surface steps on H diffusion is unavoidable.…”

Section: Comparison With Previous Resultsmentioning

confidence: 99%

“…The interaction of hydrogen with transition metal surfaces, in particular, platinum, has received extensive experimental [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] and theoretical [18][19][20][21][22][23][24][25][26][27][28] attention, primarily because platinum is an important heterogeneous catalyst in the hydrogenation reactions, and the hydrogen atom is the simplest chemisorption species which provides the ideal model system for testing the theoretical models and dynamical concepts. Hydrogen is also interesting due to its small mass that opens the possibility of observation of crossover from classical dynamics to quantum dynamics.…”

Section: Introductionmentioning

confidence: 99%

Step effects and coverage dependence of hydrogen atom diffusion onPt(111)surfaces

2004

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Step effects on surface diffusion of hydrogen on stepped Pt͑111͒ have been studied by linear optical diffraction technique over a temperature range from 90 to 150 K. Diffusion anisotropy on stepped Pt͑111͒ surfaces has been observed: the unexpected enhanced diffusion perpendicular to steps cannot be explained within the lattice gas model on stepped substrates, indicating a nonlocal and directional step effect. The coverage-dependent diffusion coefficient on flat Pt͑111͒ surface was also measured over a wide coverage range from 0.1 to 0.8 ML. They were analyzed within the framework of the lattice gas model using quasichemical approximation, indicating that H-H repulsive interaction can significantly affect the energy of saddle point as well as that at the adsorption sites.

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“…This would mean that the additional atoms are probably bound in three-fold hole sites, as reported for the Pt(111) surface. 7,8 As outlined in the introduction, vibrations of H atoms bound at these sites should be expected at wavenumbers well below 1300 cm 1 . Unfortunately this range is masked by the absorption of the zeolite.…”

Section: Resultsmentioning

confidence: 99%

“…3 Up to 3 H atoms per Pt were also reported for small size (1 nm) -Al 2 O 3 -supported Pt nanoparticles, albeit at temperatures of 166-188 K. 5 It is known that the HPt binding energy depends considerably on the type of support. 6 Thus, the H 2 desorption energy from the Pt 13 clusters amounts to 2.10 eV in LTL zeolite, 6 1.36 eV in Y zeolite, 4 but only 0.8 eV from Pt(111) single crystal surfaces, 7 and while the preferred binding site on the (111) surface is the three-fold hole the large number of adsorbed H per cluster suggests that H forms preferentially a bridging bond between two neighbouring atoms (edge site). In some cases, terminal bonding to single atoms has been observed (on-top site).…”

Section: Introductionmentioning

confidence: 99%