Indium coverage of the Si(111)- 7×3 -in surface

The indium coverage of the Si(111)-√7 × √3-In surface is investigated by means of x-ray photoelectron spectroscopy and first-principles density functional theory calculations. Both experimental and theoretical results indicate that the In coverage is a double layer rather than a single layer. Moreover, the atomic structure of the Si(111)-√7 × √3-In surface is discussed by comparing experimental with simulated scanning tunneling microscopy (STM) images and scanning tunneling spectra with the calculated density of states. Our structural assignment agrees with previous studies, except for the interpretation of experimental STM images

Donor–acceptor co-adsorption ratio controls the structure and electronic properties of two-dimensional alkali–organic networks on Ag(100)

P.T.P.R. and P.J.B. acknowledge financial support from Diamond Light Source and EPSRC. G.C. acknowledges financial support from the EU through the ERC Grant “VISUAL-MS” (Project ID: 308115). B.S. and R.J.M. acknowledge doctoral studentship funding from the EPSRC and the National Productivity Investment Fund (NPIF). R.J.M. acknowledges financial support via a UKRI Future Leaders Fellowship (MR/S016023/1).The results are presented of a detailed combined experimental and theoretical investigation of the influence of coadsorbed electron-donating alkali atoms and the prototypical electron acceptor molecule 7,7,8,8-tetracyanoquinodimethane (TCNQ) on the Ag(100) surface. Several coadsorption phases were characterized by scanning tunneling microscopy, low-energy electron diffraction, and soft X-ray photoelectron spectroscopy. Quantitative structural data were obtained using normal-incidence X-ray standing wave (NIXSW) measurements and compared with the results of density functional theory (DFT) calculations using several different methods of dispersion correction. Generally, good agreement between theory and experiment was achieved for the quantitative structures, albeit with the prediction of the alkali atom heights being challenging for some methods. The adsorption structures depend sensitively on the interplay of molecule–metal charge transfer and long-range dispersion forces, which are controlled by the composition ratio between alkali atoms and TCNQ. The large difference in atomic size between K and Cs has negligible effects on stability, whereas increasing the ratio of K/TCNQ from 1:4 to 1:1 leads to a weakening of molecule–metal interaction strength in favor of stronger ionic bonds within the two-dimensional alkali–organic network. A strong dependence of the work function on the alkali donor–TCNQ acceptor coadsorption ratio is predicted.Publisher PDFPeer reviewe

Bovine ischaemic teat necrosis: a further potential role for digital dermatitis treponemes

A recent outbreak of ischaemic teat necrosis (ITN) on mainland UK has resulted in large economic losses for dairy farmers. Typical cases start as an area of dry, thickened and encrusted skin on the medial aspect of the base of the teat, where the teat joins the udder, often with a fetid odour. The erosion spreads down the teat, often causing intense irritation, which in turn leads to more severely affected animals removing the entire teat. Due to the severity of ITN and the substantial economic costs to the industry, analyses were undertaken to ascertain if an infectious agent might be involved in the pathology. The study has considered a role for digital dermatitis (DD) treponemes in the aetiopathogenesis of ITN because, as well as being the prime bacteria associated with infectious lameness, they have been associated with a number of emerging skin diseases of cattle, including udder lesions. A high association between presence of DD-associated treponemes and incidence of ITN (19/22), compared with absence in the control population is reported. Furthermore, sequencing of the 16S rRNA gene of treponeme isolates supports the hypothesis that the identified treponemes are similar or identical to those isolated from classical foot DD lesions in cattle (and sheep). Further studies are required to allow effective targeted prevention measures and/or treatments to be developed

Indium coverage of the Si(111)- 7×3 -In surface

The indium coverage of the Si(111)-√7×√3-In surface is investigated by means of x-ray photoelectron spectroscopy and first-principles density functional theory calculations. Both experimental and theoretical results indicate that the In coverage is a double layer rather than a single layer. Moreover, the atomic structure of the Si(111)-√7×√3-In surface is discussed by comparing experimental with simulated scanning tunneling microscopy (STM) images and scanning tunneling spectra with the calculated density of states. Our structural assignment agrees with previous studies, except for the interpretation of experimental STM images

Direct experimental evidence for substrate adatom incorporation into a molecular overlayer

While the phenomenon of metal substrate adatom incorporation into molecular overlayers is generally believed to occur in several systems, the experimental evidence for this relies on the interpretation of scanning tunnelling microscopy (STM) images, which can be ambiguous and provides no quantitative structural information. We show that surface X- ray diffraction (SXRD) uniquely provides unambiguous identification of these metal adatoms. We present the results of a detailed structural study of the Au(111)-F4TCNQ system, combining surface characterisation by STM, low energy electron diffraction and soft X-ray photoelectron spectroscopy with quantitative experimental structural information from normal incidence X-ray standing waves (NIXSW) and SXRD, together with dispersion corrected density functional theory (DFT) calculations. Excellent agreement is found between the NIXSW data and the DFT calculations regarding the height and conformation of the adsorbed molecule, which has a twisted geometry rather than the previously supposed inverted bowl shape. SXRD measurements provide unequivocal evidence for the presence and location of Au adatoms, while the DFT calculations show this reconstruction to be strongly energetically favoured.Comment: 38 pages, 10 figure

Direct quantitative identification of the "surface trans-effect"

The strong parallels between coordination chemistry and adsorption on metal surfaces, with molecules and ligands forming local bonds to individual atoms within a metal surface, have been established over many years of study. The recently proposed "surface trans-effect" (STE) appears to be a further manifestation of this analogous behaviour, but so far the true nature of the modified molecule-metal surface bonding has been unclear. The STE could play an important role in determining the reactivities of surface-supported metal-organic complexes, influencing the design of systems for future applications. However, the current understanding of this effect is incomplete and lacks reliable structural parameters with which to benchmark theoretical calculations. Using X-ray standing waves, we demonstrate that ligation of ammonia and water to iron phthalocyanine (FePc) on Ag(111) increases the adsorption height of the central Fe atom; dispersion corrected density functional theory calculations accurately model this structural effect. The calculated charge redistribution in the FePc/H2O electronic structure induced by adsorption shows an accumulation of charge along the σ-bonding direction between the surface, the Fe atom and the water molecule, similar to the redistribution caused by ammonia. This apparent σ-donor nature of the observed STE on Ag(111) is shown to involve bonding to the delocalised metal surface electrons rather than local bonding to one or more surface atoms, thus indicating that this is a true surface trans-effect

Optimal control for a phase field system with a possibly singular potential

In this paper we study a distributed control problem for a phase field system of Caginalp type with logarithmic potential. The main aim of this work would be to force the location of the diffuse interface to be as close as possible to a prescribed set. However, due to the discontinuous character of the cost functional, we have to approximate it by a regular one and, in this case, we solve the associated control problem and derive the related first order necessary optimality conditions

Direct experimental evidence for substrate adatom incorporation into a molecular overlayer

While the phenomenon of metal substrate adatom incorporation into molecular overlayers is generally believed to occur in several systems, the experimental evidence for this relies on the interpretation of scanning tunneling microscopy (STM) images, which can be ambiguous and provides no quantitative structural information. We show that surface X-ray diffraction (SXRD) uniquely provides unambiguous identification of these metal adatoms. We present the results of a detailed structural study of the Au(111)-F4TCNQ system, combining surface characterization by STM, low-energy electron diffraction, and soft X-ray photoelectron spectroscopy with quantitative experimental structural information from normal incidence X-ray standing wave (NIXSW) and SXRD, together with dispersion-corrected density functional theory (DFT) calculations. Excellent agreement is found between the NIXSW data and the DFT calculations regarding the height and conformation of the adsorbed molecule, which has a twisted geometry rather than the previously supposed inverted bowl shape. SXRD measurements provide unequivocal evidence for the presence and location of Au adatoms, while the DFT calculations show this reconstruction to be strongly energetically favored

Direct experimental evidence for substrate adatom incorporation into a molecular overlayer

While the phenomenon of metal substrate adatom incorporation into molecular overlayers is generally believed to occur in several systems, the experimental evidence for this relies on the interpretation of scanning tunneling microscopy (STM) images, which can be ambiguous and provides no quantitative structural information. We show that surface X-ray diffraction (SXRD) uniquely provides unambiguous identification of these metal adatoms. We present the results of a detailed structural study of the Au(111)-F4TCNQ system, combining surface characterization by STM, low-energy electron diffraction, and soft X-ray photoelectron spectroscopy with quantitative experimental structural information from normal incidence X-ray standing wave (NIXSW) and SXRD, together with dispersion-corrected density functional theory (DFT) calculations. Excellent agreement is found between the NIXSW data and the DFT calculations regarding the height and conformation of the adsorbed molecule, which has a twisted geometry rather than the previously supposed inverted bowl shape. SXRD measurements provide unequivocal evidence for the presence and location of Au adatoms, while the DFT calculations show this reconstruction to be strongly energetically favored

Direct Experimental Evidence for Substrate Adatom Incorporation into a Molecular Overlayer

While the phenomenon of metal substrate adatom incorporation into molecular overlayers is generally believed to occur in several systems, the experimental evidence for this relies on the interpretation of scanning tunneling microscopy (STM) images, which can be ambiguous and provides no quantitative structural information. We show that surface X-ray diffraction (SXRD) uniquely provides unambiguous identification of these metal adatoms. We present the results of a detailed structural study of the Au(111)-F4TCNQ system, combining surface characterization by STM, low-energy electron diffraction, and soft X-ray photoelectron spectroscopy with quantitative experimental structural information from normal incidence X-ray standing wave (NIXSW) and SXRD, together with dispersion-corrected density functional theory (DFT) calculations. Excellent agreement is found between the NIXSW data and the DFT calculations regarding the height and conformation of the adsorbed molecule, which has a twisted geometry rather than the previously supposed inverted bowl shape. SXRD measurements provide unequivocal evidence for the presence and location of Au adatoms, while the DFT calculations show this reconstruction to be strongly energetically favored