Stress Relief in Reconstruction

Abstract

We report on the first direct measurement of the change of the surface stress in the reconstruction of the Au(111) and the Au(100) surfaces. For both surfaces the reconstruction relaxes the intrinsic tensile stress, by 22% and 5%, respectively. A discussion of the data on the Au(111) surface in the FrenkelKontorova model shows that the energy gain due to the surface stress is not quite large enough to make the reconstructed phase energetically favored without the formation of the secondary herringbone structure of the solitons. On the Au(100) surface, the gain in elastic strain energy is clearly insufficient to cause the surface to reconstruct. [S0031-9007(97) The reconstruction has been discussed frequently using the Frenkel-Kontorova (FK) model [7][8][9][10]: In the onedimensional (1D) version, a chain of atoms (representing the top layer) linked by springs with nearest-neighbor force constant w 00 and "natural" spacing b is placed in a sinusoidal potential with amplitude W ͞2 representing a rigid substrate with periodicity a. The prime feature of the reconstruction, the soliton domain wall, results from energy minimization. Further minimization of a (very small) strain energy associated with the anisotropy of the stress relief in the soliton reconstruction leads to a secondary ("herringbone") structure of the solitons [11]. Despite the general consensus that the soliton reconstruction is driven by the large tensile stress [12,13] on the Pt(111) [4][5][6]14] and the Au(111) surfaces, there is no direct experimental evidence, e.g., by measurements on the stress relief in the reconstruction.On the reconstructed (100) surfaces of Ir, Pt, and Au, the surface atoms form quasi-hexagonal (hex) commensurate and incommensurate overlayers. The atom density in the surface layer is higher by (20-25)%. From firstprinciples calculations, Fiorentini et al. [15] find the surface stress for the unreconstructed (100) surfaces of Ir, Pt, and Au to be even larger than for the (111) surfaces. Furthermore, the stress on the (100) surfaces of the 5d fcc metals Ir, Pt, and Au is also significantly larger than for the (100) surfaces of the corresponding 4d metals. They [15] identify the tensile stress as driving the reconstruction of the (100) surfaces on the 5d metals. Indirect experimental evidence for stress relief in the reconstruction was obtained for the Ir(100) surface [16]. However, neither theory nor experiment could determine the change in the surface stress quantitatively. Without direct information about the actual amount of stress energy relieved in the reconstruction of the (100) surfaces, this interpretation of the origin of the reconstruction is questionable. We dispute it below.In this Letter we report the first measurements of the change in surface stress which accompanies the reconstruction of both the Au(111) and the Au(100) surfaces. The stress measurements were performed in an electrochemical cell, with the crystals immersed in a 0.1 M HClO 4 solution, using the cantilever bending method [17][18][19]; the bendin...

Electrochemical properties of atomic-scale metal wires

“…We may therefore attribute the conductance jumps in our experiment to an potential induced surface stress that change the atomic configurations of the nanowires. For Au electrodes, a 0.1 V potential causes a surface stress change of Â/0.05 N/m, [40,41], which can change the surface atom packing structure or reconstruction. In the case of atomic-scale metal wires, every atom is a surface atom and the stress built up at negative potentials can trigger a rearrangement in the atomic configuration of the wire.…”

Stress and structure of Ni monolayers on W(110): The importance of lattice mismatch

“…In spite of the fundamental issues related to stress during heteroepitaxial growth, experimental determinations of film stress with submonolayer sensitivity are rare. [4][5][6] In this paper we present direct experimental evidence for the intimate relation between film stress and structural transitions for the growth of Ni on W͑110͒ from the combination of low-energy electron diffraction ͑LEED͒, scanning tunneling microscopy ͑STM͒, and stress measurements. For coverages below 0.5 ML we measure considerable compressive film stress in the pseudomorphic Ni film while, based on lattice mismatch arguments, tensile stress is expected.…”

“…Recently, even the tunnel junction of a STM was used to measure surface stress effects in an electrochemical cell. 6 All these experiments are performed in a way to ensure film growth or adsorption only at the front surface of a thin substrate, whereas the backside remains unaffected. We measure film stress during growth with an optical bending beam technique, which we described previously.…”

“…In stress measurements, the absolute value of the surface stress cannot be determined, but its change due to adsorption is measured. Therefore, instead of strain in the growing layer, it is the sum of the surface free energy and its strain derivative of the adsorbate-substrate system, the absolute surface stress, 6 which governs the stress in the submonolayer range. Applying this approach to the interpretation of our stress measurements, it is the difference between the absolute surface stress of the adsorbate covered and the clean substrate that determines the resulting stress in the nearsurface region.…”

Stress induced grain boundaries in thin Co layer deposited on Au and Cu

“…The Ackland-Jones bond-angle method allows us to determine the type of the crystalline structure of each atom. The X-ray diffraction technique is a powerful method widely used for the structural characterisation of real materials [23]. This technique was also been employed for interpreting the data obtained from simulation, in particular to establish the arrangement of atoms or to determine the lattice constant [24].…”