Role of valence states of adsorbates in inelastic electron tunneling spectroscopy: A study of nitric oxide on Cu(110) and Cu(001)

Abstract

We studied nitric oxide (NO) molecules on Cu(110) and Cu(001) surfaces with low-temperature scanning tunneling microscopy (STM) and density functional theory (DFT). NO monomers on the surfaces are characterized by STM images reflecting 2π * resonance states located at the Fermi level. NO is bonded vertically to the twofold short-bridge site on Cu(110) and to the fourfold hollow site on Cu(001). When NO molecules form dimers on the surfaces, the valence orbitals are modified due to the covalent bonding. We measured inelastic electron tunneling spectroscopy (IETS) for both NO monomers and dimers on the two surfaces, and detected characteristic structures assigned to frustrated rotation and translation modes by density functional theory simulations. Considering symmetries of valence orbitals and vibrational modes, we explain the intensity of the observed IETS signals in a qualitative manner.

Insight into Trimeric Formation of Nitric Oxide on Cu(111): A Density Functional Theory Study

“…The stable structures of NO monomer (NO) and dimer [(NO) 2 ] and metastable and stable structures . 24 This dimeric species on the Cu surfaces are different from the gas-phased one 63−66 and several adsorbed NO dimers, 6 for example, those in Cu-ZSM-5, 67 on the Cu clusters, 27,68 on the Co-dimer/γ-alumina catalyst, 28 and on other noble metal surfaces (Ag, Au), 25,29 where the intermolecular interaction arises from ON−NO bonding. For the NO trimeric adsorption, both trimer structures have triangular shapes composed of three NO molecules at three adjacent fcc-hollow sites in N-down configurations surrounding the hcp-hollow and atop site, respectively.…”

“…13−29 The open-shell structure of the 2π* orbitals is retained upon the monomeric adsorption on the noble metal surfaces, leading to a further intermolecular bonding between two adsorbed NO molecules to form a NO dimer. 14,24−32 The dimeric (NO) 2 formation was verified by (i) the detection of the N 2 O desorption because the NO dimer is an intermediate for N 2 O production; 13−17 by (ii) real-time observations of the NO dimer by scanning tunneling microscopy (STM); 23,24 and by (iii) first-principles calculations. 25−29 Generally speaking, on low-index Cu surfaces, molecularly adsorbed NO is assumed to be either monomer or dimer.…”

“…Understanding the adsorption and reactivity of nitric oxide (NO) on metal surfaces is essential from fundamental as well as practical application points of view. − As an important step for catalytic NO reduction in automotive exhaust gas conversion, NO adsorption on metal surfaces has been extensively studied in the last two decades. − Unlike CO adsorption, − the NO adsorption on the metal surfaces exhibits a complicated behavior because of its open shell structure of 2π* orbitals. − On the metal surfaces, NO undergoes molecular or dissociative adsorption depending on coverage, surface temperature, and the nature of the metals. − At low temperature, molecular adsorption of NO − mainly takes place where NO adsorbs as a monomer in many different binding geometries, namely upright, − side-on, ,, tilted ones; − or as a dimer in a high-coverage regime owing to the intermolecular interaction. − Furthermore, NO can be dissociated into N and O adatoms at higher temperatures, but whether dissociation occurs strongly depends also on surface coverage. − The origin of NO adsorption on metal surfaces is the back-donation process where 2π* orbitals of NO hybridize with the d band of the metal surfaces. − …”

Effect of local geometry on magnetic property of nitric oxide on Au(110)−(1×2)

“…4(a), 4(f), and 4(g)]. This can be rationalized by the inelastic process in which the initial state is 5σ or 6σ * , and the final state is 2π * e [50,52], which supports that the ν 3 (hindered rotation) is more plausible as the origin of the dI/dV peaks at ±35 meV.…”

“…A series of dI/dV spectra in Fig. 4 We consider the spatial distribution and assignment of the satellite peaks based on the IET propensity rule [49][50][51][52]. The t-NO belongs to the C s point group with the mirror plane (σ v ) along [001] and [110] (surface normal).…”