Elastic and inelastic deformations of ethylene-passivated tenfold decagonalAl−Ni−Coquasicrystal surfaces

Abstract

The adhesion and friction force properties between a tenfold Al-Ni-Co decagonal quasicrystal and a titanium nitride (TiN)-coated tip were investigated using an atomic force microscope in ultrahigh vacuum. To suppress the strong chemical adhesion found in the clean quasicrystal surfaces, the sample was exposed to ethylene that formed a protective passivating layer. We show that the deformation mechanism of the tip-substrate junction changes from elastic to inelastic at a threshold pressure of 3.8 to 4.0 GPa. Images of the indentation marks left above the threshold pressure indicate the absence of new steps, and indicate that surface damage is not accompanied by formation of slippage planes or dislocations, as found in plastically deforming crystalline materials. This is consistent with the lack of translational periodicity of quasicrystals. The work of adhesion in the inelastic regime is five times larger than in the elastic one, plausibly as a result of the displacement of the passivating layer. In the elastic regime, the friction dependence on load is accurately described by the Derjaguin-Müller-Toporov (DMT) model, consistent with the high hardness of both the TiN tip and the quasicrystal sample. Above the threshold pressure, the friction versus load curve deviates from the DMT model, indicating that chemical bond formation and rupture contribute to the energy dissipation. The adhesion and friction force properties between a tenfold Al-Ni-Co decagonal quasicrystal and a titanium nitride ͑TiN͒-coated tip were investigated using an atomic force microscope in ultrahigh vacuum. To suppress the strong chemical adhesion found in the clean quasicrystal surfaces, the sample was exposed to ethylene that formed a protective passivating layer. We show that the deformation mechanism of the tip-substrate junction changes from elastic to inelastic at a threshold pressure of 3.8 to 4.0 GPa. Images of the indentation marks left above the threshold pressure indicate the absence of new steps, and indicate that surface damage is not accompanied by formation of slippage planes or dislocations, as found in plastically deforming crystalline materials. This is consistent with the lack of translational periodicity of quasicrystals. The work of adhesion in the inelastic regime is five times larger than in the elastic one, plausibly as a result of the displacement of the passivating layer. In the elastic regime, the friction dependence on load is accurately described by the Derjaguin-Müller-Toporov ͑DMT͒ model, consistent with the high hardness of both the TiN tip and the quasicrystal sample. Above the threshold pressure, the friction versus load curve deviates from the DMT model, indicating that chemical bond formation and rupture contribute to the energy dissipation.

High-resolution scanning tunneling microscopy investigation of the (12110) and (10000) two-fold symmetricd-Al-Ni-Co quasicrystalline surfaces

“…Apart from the intrinsic aperiodic structure and the well known unusual physical bulk properties, 1 QC possess many interesting surface features such as good oxidation resistance compared to pure Al single crystals and a particularly low coefficient of friction. [2][3][4][5][6][7] In the research of surface properties and their relation to the aperiodic structure the twofold surfaces of the d-Al-Ni-Co quasicrystal are of special interest since they allow a simultaneous investigation of a periodic and perpendicular to it an aperiodic axis on same surface. An outstanding example for a simultaneous measurement of surface physical properties directly related to this two inequivalent surface directions of the clean ͑10000͒ d-Al-Ni-Co surface is the friction anisotropy measurement of Park et al 6 They reported a 7.8 times lower friction coefficient along the aperiodic compared to the periodic axis.…”

“…Both groups have their advantages and can be used complementary to reveal quasicrystalline surface structures. The STM results presented here are therefore compared with the results of surface diffraction methods, [11][12][13] STM measurements of the ͑10000͒ surface, 4,14 and are compared in all three dimensions with an appropriated bulk atomic model of the investigated crystals. 15 The structure of the low-index surface ͑10000͒ d-Al-Ni-Co was investigated by STM by Kishida et al 14 and Park et al, 4 by helium atom scattering ͑HAS͒ and SPA-LEED ͑Refs.…”

“…The STM results presented here are therefore compared with the results of surface diffraction methods, [11][12][13] STM measurements of the ͑10000͒ surface, 4,14 and are compared in all three dimensions with an appropriated bulk atomic model of the investigated crystals. 15 The structure of the low-index surface ͑10000͒ d-Al-Ni-Co was investigated by STM by Kishida et al 14 and Park et al, 4 by helium atom scattering ͑HAS͒ and SPA-LEED ͑Refs. 11 and 12͒ by Sharma et al, and by LEED and angle-resolved photoemission spectroscopy ͑ARPES͒ by Rotenberg et al 16 However, the findings of the local atomic arrangement by STM of Park et al 4 and Kishida et al 14 were not coherent with each other.…”

The surface science of quasicrystals

“…Friction is a complex phenomenon, with many channels contributing to energy dissipation. Park and co-workers used atomic force microscopy (AFM) and STM to study the twofold surface of d-Al-Ni-Co which contains both periodic and quasiperiodic directions [51,75,120]. By measuring the torsional response of the AFM cantilever, they could directly compare frictional effects along the periodic and aperiodic directions on the same surface.…”

“…At low temperatures, benzene (C 6 H 6 ) was found to adsorb in a disordered fashion on i-Al-Pd-Mn [74]. Ethylene (C 2 H 4 ) was used to passivate the tenfold surface of dAl-Ni-Co in measurements of the friction of the surface using atomic force microscopy [75].…”