Sign-inverted response of aluminum work function to tangential strain

Abstract

We have investigated the response of the work function, W, of low-index aluminum surfaces to tangential strain by using first-principles calculations based on density functional theory. This response parameter is a central quantity in electrocapillary coupling of metal electrodes relating to the performance of porous metal actuators and surface stress based sensing devices. We find that Al surfaces exhibit a positive response for all orientations considered. By contrast, previous studies reported negative-valued response parameters for clean surfaces of several transition metals. We discuss separately the response of W to different types of strain and the impact of the strain on the Fermi energy and the surface dipole. We argue that the reason for the abnormal positive sign of the Al response parameter lies in its high valence electron density.

Electrocapillary Coupling at Metal Surfaces from First Principles: On the Impact of Excess Charge on Surface Stress and Relaxation

“…The calculation of W and ς was performed along the lines of our previous work, where more details can be found. We evaluate the work function W as where the dipole barrier V dip = V vac – V̅ bulk corresponds to the difference between the vacuum potential and the average potential in the bulk region of the slab and E f is the Fermi energy (also with respect to V̅ bulk ).…”

“…Because the electrode potential and the work function of the metal surface are closely linked, , the electrocapillary coupling parameter near the potential of zero charge (i.e., for q = 0) may be determined in terms of the response of the electronic work function, W , to an applied in-plane strain . The variation in W with strain is readily accessible via ab initio computation. − …”

“…There have been hopes that analyzing simple metals would be the first step toward that goal. In this spirit, the work function strain response of the sp-bonded metal Al was investigated, which was revealed to have an unexpected positive sign …”

Ab-initio modeling of electromechanical coupling at Si surfaces

“…62 Following this definition, the vacuum level V vac equals the surface dipole potential V dip , which is the same convention as used in Ref. 31. Figure 1 illustrates the determination of the two quantities whose response to strain was investigated in this work, namely the IP n and the electron affinity v. They represent the difference between the surface dipole potential, V dip , and the energy of the VBM, E VBM , or the CBM, E CBM , respectively…”

“…In contrast to the negative response parameters found for transition metals, a positive work function strain response was obtained for Al surfaces via density functional theory (DFT) calculations. 31 This was attributed to the high electron density of Al.…”