Istraživanje površine V(100) upotrebom sinkrotronskog zračenja

The electronic structure of V(100) has been studied by means of synchrotron radiation. Normal emission (n.e.) spectra, taken in the energy range between 15 and 100 eV, were analysed in terms of existing band structure calculations. The obtained data support our previous reports suggesting that the peak at the Fermi level has a bulk and surface component. The variation of the intensity at the Fermi level was measured in the constant initial state (CIS) mode. In the photon energy range between 40 and 100 eV the variation of the intensity at the Fermi level is generally following the energy dependence of the resonant spectrum of vanadium films. However, the resonant spectrum obtained from V(100) appears to be significantly narrower than the spectra reported for films.U ovom se radu prikazuju rezultati istraživanja V(100) upotrebom sinkrotronskog zračenja. Spektri okomite fotoemisije u području fotonskih energija između 15 i 100 eV uspoređuju se s postojećim teorijskim proračunima za strukturu valentne vrpce vanadija. Dobiveni rezultati potvrđuju našu prije iznijetu tezu, da se maksimum fotoemisijskog intenziteta na Fermijevom nivou sastoji od dvije komponente, volumne i površinske. Promjena intenziteta na Fermijevom nivou mjerila se je u modu konstantnog početnog stanja. U području fotonskih energija između 40 i 100 eV, promjene fotoemisijske struje s Fermijevog nivoa vrlo su slične rezonantnom spektru vanadijevih tankih slojeva. Međutim, rezonantni spektar površine V(100) je značajno uži od rezonantnog spektra vanadijevih tankih filmova

Structure Determination of F 4 TCNQ on Ag(111):A Systematic Trend in Metal Adatom Incorporation

A structure determination of the commensurate phase formed by 7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (F4TCNQ) absorbed on Ag(111) is reported. Initial characterization was performed using low-energy electron diffraction and synchrotron radiation photoelectron spectroscopy, with quantitative structural data being provided by normal incident X-ray standing waves (NIXSW) and surface X-ray diffraction (SXRD). NIXSW data show the F4TCNQ molecule to adopt a “twisted” conformation on the surface, previously found to be associated with metal adatom incorporation into a 2d-metal–organic framework for F4TCNQ on Au(111), Ag(100), and Cu(111). SXRD results provide direct evidence of the presence of Ag adatoms that are found to occupy near-bridge or fcc hollow sites with respect to the underlying surface, at an adsorption height of 2.69 ± 0.10 Å. The results show a consistent pattern of behavior for F4TCNQ adsorption on the (111) surfaces of Cu, Ag, and Au

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

Surface adsorption structure determination using backscattering photoelectron diffraction

Following a brief historical introduction, the distinction between two modes of photoelectron diffraction, high-energy forward scattering and low energy backscattering, and two modes of data collection, angle-scan and energy-scan, is explained. This is followed by a review of energy-scan backscattering photoelectron diffraction (PhD). Examples are presented of atomic adsorption and molecular adsorption on metal surfaces and molecular adsorption on oxide surfaces. The paper ends with a brief survey of future prospects for the application of the PhD technique

Modern techniques of surface science

This fully revised, updated and reorganised third edition provides a thorough introduction to the characterisation techniques used in surface science and nanoscience today. Each chapter brings together and compares the different techniques used to address a particular research question, including how to determine the surface composition, surface structure, surface electronic structure, surface microstructure at different length scales (down to sub-molecular), and the molecular character of adsorbates and their adsorption or reaction properties. Readers will easily understand the relative strengths and limitations of the techniques available to them and, ultimately, will be able to select the most suitable techniques for their own particular research purposes. This is an essential resource for researchers and practitioners performing materials analysis, and for senior undergraduate students looking to gain a clear understanding of the underlying principles and applications of the different characterisation techniques used in the field today

Growth and Evolution of TCNQ and K Coadsorption Phases on Ag(111)

Alkali-doping is a very efficient way of tuning the electronic properties of active molecular layers in (opto-)electronic devices based on organic semiconductors. In this context, we report on the phase formation and evolution of charge transfer salts formed by 7,7,8,8-tetracyanoquinodimethane (TCNQ) in coadsorption with potassium on a Ag(111) surface. Based on an in-situ study using low energy electron microscopy and diffraction we identify the structural properties of four phases with different stoichiometries, and follow their growth and inter-phase transitions. We label these four phases α to δ, with increasing K content, the last two of which (γ and δ-phases) have not been previously reported. During TCNQ deposition on a K-precovered Ag(111) surface we find a superior stability of δ phase islands compared to the γ phase; continued TCNQ deposition leads to direct transition from the δ to the β-phase when the K:TCNQ ratio corresponding to this phase regime is reached, with no intermediate γ-phase formation. When, instead, K is deposited on a surface precovered with large islands of the low density commensurate (LDC) TCNQ phase that are surrounded by a TCNQ 2D-gas, we observe two different scenarios: On the one hand, in the 2D-gas phase regions, very small α-phase islands are formed (close to the resolution limit of the microscope, 10-15 nm), which transform to β-phase islands of similar size with increasing K deposition. On the other hand, the large (micrometer-sized) TCNQ islands transform directly to similarly large single-domain β-phase islands, the formation of the intermediate α-phase being suppressed. This frustration of the LDC-to-α transition can be lifted by performing the experiment at elevated temperature. In this sense, the morphology of the pure TCNQ submonolayer is conserved during phase transitions

PCCP - ordered growth of VOPc on FePC monolayer

<p>Full experimental data can be found in the corresponding manuscript.</p> <p>Here are all the raw data corresponding to the paper.</p> <p>STM images and LEED patterns of:</p> <p>ML FePc/Au (111)</p> <p>ML VOPc/ML FePc/ Au (111)</p