Jörg Meyer

Azobenzene at coinage metal surfaces: Role of dispersive van der Waals interactions

We use different semiempirical dispersion correction schemes to assess the role of long-range van der Waals interactions in the adsorption of the prototypical molecular switch azobenzene

Chirality Change of Chloronitrobenzene on Au(111) Induced by Inelastic Electron Tunneling

({\text{C}}_{6}{\text{H}}_{5}{\text{-N}}_{2}{\text{-C}}_{6}{\text{H}}_{5})

Stabilizing a molecular switch at solid surfaces: A density functional theory study of azobenzene at Cu(111), Ag(111), and Au(111)

at the coinage metal surfaces Cu(111), Ag(111), and Au(111). Compared to preceding density-functional theory results employing a semilocal exchange and correlation functional we obtain partly sizable changes in the computed adsorption geometry and energetics. The discomforting scatter in the results provided by the different schemes is largely attributed to the unknown form of the damping function in the semiempirical correction expression. Using the congeneric problem of the adsorption of benzene as a vehicle to connection with experiment, we cautiously conclude that the account of dispersive interactions at the metal surfaces provided by the various schemes is in the right ballpark, with the more recent, general schemes likely to overbind.

Electron–hole pairs during the adsorption dynamics of O2 on Pd(100): exciting or not?

Chirality chameleon: Inelastic electron tunneling manipulation can be used to change a single chloronitrobenzene (ClNB) molecule, randomly adsorbed on Au(111), into its desired enantiomeric form (r or l, see STM images and ball-and-stick representation) and to vary its rotational orientation. The different threshold voltages for chirality change (260 mV) and rotation (380 mV) allow these processes to be induced separately.

Non-adiabatic effects during the dissociative adsorption of O2 at Ag(111)? A first-principles divide and conquer study

We present a density-functional theory trend study addressing the binding of the trans-cis conformationalswitch azobenzene C6H5-N= N-C6H5 at three coinage-metal surfaces. From the reported detailed energetic-, geometric-, and electronic-structure data we conclude that the governing factor for the molecule-surface interaction is a competition between covalent bonding of the central azo -N= N- bridge on the one hand and the surface interaction of the two closed-shell phenyl -C6H5 rings on the other. With respect to this factor the cis conformer exhibits a more favorable gas-phase geometric structure and is thus more stabilized at the studied surfaces. With the overall binding still rather weak the relative stability of the two isomers is thereby reduced at Ag111 and Au111. This is significantly different at Cu111, where the cis bonding is strong enough to even reverse the gas-phase energetic order at the level of the employed semilocal electronic exchange and correlation xc functional. While this actual reversal may well be affected by the deficiencies due to the approximate xc treatment, we critically discuss that the rationalization of the general effect of the surface on the metastable molecular states is quite robust. This should equally hold for the presented analysis of recent tip-manipulation and photoexcitation isomerization experiments from the view point of the derived bonding mechanism.

Enzyme-linked immunosorbent assays based on peroxidase labels and enzyme-amplified lanthanide luminescence detection.

During the exothermic adsorption of molecules at solid surfaces, dissipation of the released energy occurs via the excitation of electronic and phononic degrees of freedom. For metallic substrates, the role of the non- adiabatic electronic excitation channel has been controversially discussed, as the absence of a band gap could favour an easy coupling to a manifold of electron-hole pairs of arbitrarily low energies. We analyse this situation for the highly exothermic showcase system of molecular oxygen dissociating at Pd(100), using time-dependent perturbation theory applied to first-principles electronic-structure calculations. For a range of different trajectories of impinging O2 molecules, we compute largely varying electron-hole pair spectra, which underlines the necessity to consider the high-dimensionality of the surface dynamical process when assessing the total energy loss into this dissipation channel. Despite the high Pd density of states at the Fermi level, the concomitant non-adiabatic energy losses nevertheless never exceed about 5% of the available chemisorption energy. While this supports an electronically adiabatic description of the predominant heat dissipation into the phononic system, we critically discuss the non-adiabatic excitations in the context of the O2 spin transition during the dissociation process.

Peroxidase enhanced lanthanide luminescence—a new technique for the evaluation of bioassays

We study the gas-surface dynamics of O2 at Ag(111) with the particular objective to unravel whether electronic non-adiabatic effects are contributing to the experimentally established inertness of the surface with respect to oxygen uptake. We employ a first-principles divide and conquer approach based on an extensive density-functional theory mapping of the adiabatic potential energy surface (PES) along the six O2 molecular degrees of freedom. Neural networks are subsequently used to interpolate these grid data to a continuous representation. The low computational cost with which forces are available from this PES representation allows then for a sufficiently large number of molecular dynamics trajectories to quantitatively determine the very low initial dissociative sticking coefficient at this surface. Already these adiabatic calculations yield dissociation probabilities close to the scattered experimental data. Our analysis shows that this low reactivity is governed by large energy barriers in excess of 1.1eV very close to the surface. Unfortunately, these

Electronic Friction-Based Vibrational Lifetimes of Molecular Adsorbates : Beyond the Independent-Atom Approximation

The enzyme-amplified lanthanide luminescence (EALL) detection is developed and applied for the determination of peroxidase as marker in enzyme-linked immunosorbent assays (ELISA). The detection scheme is based on the peroxidase catalysed dimerization of 4-hydroxyphenylpropionic acid (pHPPA) and the subsequent formation of a ternary complex with Tb(III)EDTA. Quantum yields and fluorescence lifetimes of the luminescent species are presented to give an estimate of the potential of this procedure. Two different ELISA were performed with the EALL detection scheme. For the first, a model ELISA for the determination of goat anti-rabbit IgG, a limit of determination of 3 micrograms dm-3 (2 fmol) of the antibody could be achieved. As second model assay, a commercial ELISA kit was successfully validated for the new detection scheme. Photometric and EALL detection were in good agreement for the determination of human anti-gliadin IgA in serum.

Quantification of finite-temperature effects on adsorption geometries of π-conjugated molecules : Azobenzene/Ag(111)

A new technique for the enzyme-amplified lanthanide luminescence (EALL) quantification of peroxidase in bioassays is introduced. Several phenolic peroxidase substrates may be used. These are dimerised in the course of the enzymatic reaction and subsequently form luminescent ternary complexes with terbium(III) EDTA. The luminescence signals are enhanced by addition of CsCl and can be read out in a time resolved type of measurement. With the substrate p-hydroxyphenylpropionic acid, a detection limit for horseradish peroxidase of 2 × 10−12 mol dm−3 could be achieved.

Electron-induced isomerisation of dichlorobenzene on Cu(111) and Ag(111)

We assess the accuracy of vibrational damping rates of diatomic adsorbates on metal surfaces as calculated within the local-density friction approximation (LDFA). An atoms-in-molecules (AIM) type charge partitioning scheme accounts for intramolecular contributions and overcomes the systematic underestimation of the nonadiabatic losses obtained within the prevalent independent-atom approximation. The quantitative agreement obtained with theoretical and experimental benchmark data suggests the LDFA-AIM scheme as an efficient and reliable approach to account for electronic dissipation in ab initio molecular dynamics simulations of surface chemical reactions.