Friction and energy dissipation mechanisms in adsorbed molecules ...

More documents

Recommendations

Info

Table 12. Slip time data for adsorption on Ag substrates.Advances in Physics 277 = 1 = 1Adsorbate Substrate type Technique T (K) Reference = 0.2 = 0.5 (liquid) (solid) = 2τ (ns)Downloaded by [North Carolina State University] at 09:24 22 April 20134 He(helium) Amorphous QCM [479] 10Ag (111) textured Resistivity [447] 0.1(E)H2O (water) (111) textured Resistivity 300 [87,473] 0.1(E)CO(carbon monoxide) (111) textured Resistivity [447] 0.36(E)C2H4 (ethylene) (111) textured Resistivity 50 [447] 0.72(E)C6H6 (benzene) (111) textured Resistivity 50 [447] 1.4(E)C2H12 (cyclohexane) (111) textured Resistivity [447] 1.7(E)Xe (xenon) (111) textured Resistivity 10 [447] 3(E)Xe (xenon) (111) textured Resistivity 77.4 [164] 3.3(E) 4(E) 6(E)C2H6 (ethane) (111) textured Resistivity 50 [447] 3.6(E)Xe (xenon) (111) textured Theory [115,323] 200(E)C2H12 (cyclohexane) (111) textured QCM 300 [508] 0 2 1.5O2 (oxygen) (111) textured QCM 300 [511] 0 0 0 0Xe (xenon) (111) textured QCM 77.4 [164] 0.25 0.8 1Xe (xenon) (111) textured QCM 77.4 [352] 2.3 1.2 1.1 1.8Xe (xenon) (111) textured QCM 77.4 [353] 2.3 1.2 1.1 1.8Xe (xenon) (111) textured QCM 77.4 [356] 2Ar (argon) (111) textured QCM 77.4 [87,473] 1.5Kr (krypton) Fractal QCM 77.4 [33,34] 1.5Kr (krypton) (111) textured QCM 77.4 [355] 2.1 2.7H 2 O (water) (111) textured QCM 300 [508] 7 3 4 8H 2 O (water) (111) textured QCM 300 [87,473] 4C 2 H 4 (ethylene) (111) textured QCM 77.4 [511] 15 5C 2 H 6 (ethane) (111) textured QCM 77.4 [511] 15 9C 7 H 8 (toluene) (111) textured QCM 300 [537] 10 15Table 13. QCM slip time data for Au substrates.Adsorbate Substrate type T (K) Reference = 0.2 = 0.5 = 1 (liquid) = 1 (solid) = 24 He(helium) Amorphous 0.5–2 [480] >0Kr (krypton) (111) terraced 85 [185] 0&1.5 0&1 0.1 0.2Kr (krypton) (111) terraced 85 [181] 0&7 0&2 0&1 0Kr (krypton) (111) textured 77.4 [355] 1 5Kr (krypton) (111) textured 77.4 [173] 1 5Kr (krypton) (111) textured 77.4 [176] 1.5 4Kr (krypton) (111) textured 77.4 [33,34] 1.5 2 10Kr (krypton) Amorphous 77.4 [404] 4 50 100Xe (xenon) (111) textured 80 [33] 1.2 4Xe (xenon) (111) textured 113.6 [33] 1 2 5Xe (xenon) (111) textured 110 [508] 1.7 1.1 0.7N 2 (nitrogen) (111) textured 77.4 [508] 3 4 8N 2 (nitrogen) (111) textured 77.4 [176] 4 7τ (ns)Bruschi [181]. Bruschi and coworker observed that by slowly increasing the amplitude of thesubstrate oscillations, they could induce a sharp transition from a film locked to the substrate to asliding one, thus two values are reported for the slip time in Table 13, corresponding to the pinnedand sliding state. The group also observed sharp pinning transitions separating a low-coverageregion, characterized by slippage at the surface, from a high-coverage region where the film islocked to the oscillating electrodes. The role of the step edges in the pinning remains a matter of
278 J. KrimTable 14. Slip time data for fiber textured Cu(111) and Ni(111) substrates. = 1 = 1Adsorbate Substrate Technique T (K) Reference = 0.2 = 0.5 (liquid) (solid) = 2τ (ns)Downloaded by [North Carolina State University] at 09:24 22 April 2013H(hydrogen) Ni Resistivity [447] 0.001(E)O 2 (oxygen) Cu Resistivity [447] 0.007(E)CO(carbon Ni Resistivity [447] 0.014(E)monoxide)CO(carbon Cu Resistivity [447] 0.039(E)monoxide)N 2 (nitrogen) Ni Resistivity [447] 0.046(E)C 6 H 5 ICu(111) STM-QCM 300 [272] 0 0 0 0(iodobenzene)C 6 H 6 (benzene) Cu(111) STM-QCM 300 [272] >0 >0Xe (xenon) Ni(111) QCM 77.4 [356] 0.4 0.47 0.2Kr (krypton) Ni(111) QCM 77.4 [355] 0.26 0.78C 8 H 18 (n-octane) Cu(111) QCM 300 [623] 1.5 0.9 0.8Kr (krypton) Cu(111) QCM 77.4 [355] 7 11Xe (xenon) Cu(111) QCM 77.4 [356] 15.5 30great interest, as it must be accounted for in all realistic treatments of sliding friction. Liquid filmsappear much less susceptible to variations in slip time attributable to pinning.4.5.3. Cu(111) and Ni(111) substrates (Table 14)Slip time data for adsorption on Cu(111) and Ni (111) substrates are summarized in Table 14.Slip times followed by (E) denote electronic contributions only. Cu(111) and Ni(111) are veryclose in lattice spacing (0.4414 and 0.0441 nm, respectively), but have very different potentialcorrugations (U o = 1.9 and 14 meV, respectively). The systems have received attention on accountof the fact that their binding potential energies have been reported in the literature [355,356] andalso for the numerous resistivity measurements that have been reported for adsorbates on thesesubstrates [447]. Resistivity measurements indicate very high levels of electronic friction, andQCM measurements show relatively high levels of friction, and low slip times for the majority ofsystems studied. The exception is Xe/Cu(111): although the system is commensurate, the potentialcorrugation is evidently too low to pin the layer [356]. This result was predicted numericallyby Cieplak et al. [35], who reported a lack of static friction in commensurate systems with lowpotential corrugation amplitudes. Reguzzoni [61] have very recently examined the size dependenceof pinning in Kr clusters adsorbed on Cu(111) and Si substrates by numerical methods, as describedabove . When the size of the contact was reduced below a critical value, they observed domainsto coalesce and the interfaces to become commensurate (Figure 7). The behavior is interpreted interms of the competing effects of interfacial and elastic interactions.To explore this effect in more detail, Bortolani et al. performed an MD study of the slip timeand static friction for a slab of Xe deposited on a slab of Cu [163,501]. In order to model therole played by the phonons in the two blocks, they compared results obtained with a substrateformed by fixed atoms with one formed by mobile atoms. In the latter case, the scattering betweenXe and Cu mobile atoms was found to be inelastic and there was an exchange of momentum andenergy between the two blocks. This in turn produced disorder in the interface plane, which acted todecrease the static friction also increase the slip time. The authors describe the interaction betweenXe and Cu with a phenomenological multi-ion potential which gave rise to anticorrugation of thecharge distribution and reproduced their ab initio density functional calculations. Since the model
Page 5 and 6:
158 J. KrimDownloaded by [North Car
Page 7 and 8:
Page 9 and 10:
162 J. KrimFigure 1. Simplest geome
Page 11 and 12:
Page 13 and 14:
Page 15 and 16:
Page 17 and 18:
170 J. Krimexperimental values are
Page 19 and 20:
172 J. Krim1.3.8. Statistical mecha
Page 21 and 22:
Page 23 and 24:
Page 25 and 26:
178 J. KrimFigure 15. Schematic of
Page 27 and 28:
180 J. Krimemission current depends
Page 29 and 30:
182 J. Krimdiffusion. PEEM thus bri
Page 31 and 32:
184 J. Krimdrift mobility can be re
Page 33 and 34:
Page 35 and 36:
Page 37 and 38:
190 J. KrimAgain, assuming a thin-f
Page 39 and 40:
Page 41 and 42:
Page 43 and 44:
196 J. Krimand the substrate at the
Page 45 and 46:
Page 47 and 48:
Page 49 and 50:
Page 51 and 52:
Page 53 and 54:
206 J. KrimFigure 32. Few-asperity
Page 55 and 56:
Page 57 and 58:
210 J. Krimthe shuttle’s amplitud
Page 59 and 60:
212 J. Krimapparent macroscopic are
Page 61 and 62:
Page 63 and 64:
Page 65 and 66:
Page 67 and 68:
220 J. KrimFigure 43. Schematic of
Page 69 and 70:
Page 71 and 72:
224 J. Krimliquid monolayers, a res
Page 73 and 74: 226 J. KrimDownloaded by [North Car
Page 77 and 78: Downloaded by [North Carolina State
Page 85 and 86: 238 J. KrimFigure 55. Schematic of
Page 87 and 88: 240 J. Krim(58). Although the subst
Page 93 and 94: 246 J. Krimlayer to reproduce the D
Page 95 and 96: 248 J. Krimfree energy with respect
Page 103 and 104: 256 J. KrimTable 3. QCM slip time d
Page 105 and 106: 258 J. KrimTable 5. QCM slip time d
Page 107 and 108: 260 J. KrimTable 6. Slip time data
Page 123: 276 J. KrimDownloaded by [North Car
Page 129 and 130: 282 J. Krimand friction forYBCO (T
Page 131 and 132: 284 J. Krimincreased as the number
Page 169 and 170: Downloaded by [North Carolina State
show all

Friction and energy dissipation mechanisms in adsorbed molecules ...

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?