J. Liesegang

Is there a universal mean-free-path curve for electron inelastic scattering in solids?

Abstract On the basis of a recent modification to dielectric theory, it is shown that the mean free path for inelastic electron scattering in a wide range of materials is described by a formula giving a dependence on electron energy of the form AE 0.75 where A is, however, sample-dependent.

Surface modification of poly(tetrafluoroethylene) by gas plasma treatment

Abstract Poly(tetrafluoroethylene) (PTFE) samples were surface modified in gas plasma atmospheres of air, oxygen, argon and water vapour in order to increase the surface energy. Its dispersive and polar components were determined by contact angle measurements after various treatment times. Plasma treatment times of only 15s were sufficient in all gases studied for substantial surface modification of PTFE. The chemical composition of the surfaces was studied by X-ray photoelectron spectroscopy (X.p.s.). The main results of all the plasma treatments were the abstraction of fluorine and the production of surface crosslinks, whereas only a low level of oxygen-containing groups was attached into the surface layer.

An Analysis of the Transmission Properties of Spherical Electrostatic Electron Spectrometers

A detailed analysis of the transmission properties of low‐energy spherical electrostatic electron spectrometers employing preacceleration or preretardation is presented, which shows that the transmission efficiency of such instruments is not necessarily related inversely to electron energy nor directly to analyzer pass energy. A prescription, which enables observed spectra to be corrected over a wide energy range for intensity variations resulting from instrumental effects, is provided, and a detectable shift (≤ 0.1 eV) in the apparent position of electron lines under certain conditions is predicted. The theory is applied to the design and performance of two spherical photoelectron spectrometers employing ultraviolet and soft x‐ray sources. The analysis may readily be extended to other forms of electrostatic spectrometers employing preacceleration or preretardation.

Electronegativity as a unifying concept in the determination of Fermi energies and photoelectric thresholds

Abstract The method proposed by Nethercot for the determination of the Fermi energies and photoelectric thresholds of simple binary compounds has been successfully applied to some AB 2 compounds and metals.

Contact angle measurement and surface energetics of sized and unsized paper

Abstract Determining the surface free energy of paper from contact angle data for various liquids is not straight forward and the results can sometimes be misleading. For insufficiently sized paper, errors may arise from rapid penetration of liquid probes into the sheet, which prevents accurate measurement of contact angles. For well-sized paper, errors may arise from factors associated with the roughness of the sheet. Despite the fact that some of the sources of error are well known, contact angle methods are still favoured for determining the surface free energy of paper. In this study, we focus on some factors associated with the topographical and chemical heterogeneity of paper (particularly sized sheets) that may cause contact angle data to lead to incorrect prediction of surface energetics. Whatman filter paper with and without calendering and AKD sizing treatment was used as a model system for studying the effect of sheet surface heterogeneity. To evaluate the sheet surface roughness at an interfibre pore level, the contact area between a water drop and the sized sheet surface was studied using confocal laser-scanning microscopy (CLSM). For well-sized sheets the actual contact area between the drop and the sheet was much smaller than the apparent contact area. The chemical heterogeneity of the sized filter paper sheets was studied using XPS and IGC. Both techniques again showed that the surfaces of well sized papers still possess acid and base polarities that are capable of interacting with liquid or vapour probes with acid and base functionality. Poor liquid–sheet contact area, however, acts as a factor that limits the number of acid–base adducts formed across the liquid–sheet interface. A possible way of correcting for the effect of sheet surface roughness on the apparent liquid–sheet contact angle using the Cassie–Baxter equation was tested.

The electronic structure of the valence bands of solid NH3 and H2O studied by ultraviolet photoelectron spectroscopy

Abstract The results of a photoelectron study using ultraviolet 40.81 eV photons (UPS) of the outermost bands of the molecular solids NH 3 and H 2 O are reported. The binding energies, the energy separation, the band widths and the branching ratio of the two outermost bands of solid NH 3 are found not to be significantly different from the 3a l and 1e molecular orbital states of the gaseous NH 3 UPS spectrum. This implies that hydrogen bonding has not produced any significant change in the electronic structure of the valence bands of solid NH 3 . Because of a much smaller intermolecular hydrogen bond length in solid H 2 O compared to that in solid NH 3 , the hydrogen bond does, however, produce a significant change in the valence bands of H 2 O on solidification, and because of the orbital geometry it predominantly affects the 3a l molecular orbital state.

DIFFRACTION AND HOLOGRAPHY WITH PHOTOELECTRONS AND FLUORESCENT X-RAYS

Abstract We consider studies of the atomic and magnetic structure near surfaces by photoelectron diffraction and by the holographic inversion of both photoelectron diffraction data and diffraction data involving the emission of fluorescent x-rays. The current status of photoelectron diffraction studies of surfaces, interfaces, and other nanostructures is first briefly reviewed, and then several recent developments and proposals for future areas of application are discussed. The application of full-solid-angle diffraction data, together with simultaneous characterization by low energy electron diffraction and scanning tunneling microscopy, to the epitaxial growth of oxides and metals is considered. Several new avenues that are being opened up by third-generation synchrotron radiation sources are also discussed. These include site-resolved photoelectron diffraction from surface and interface atoms, the possibility of time-resolved measurements of surface reactions with chemical-state resolution, and circular dichroism in photoelectron angular distributions from both non-magnetic and magnetic systems. The addition of spin to the photoelectron diffraction measurement is also considered as a method for studying short-range magnetic order, including the measurement of surface magnetic phase transitions. This spin sensitivity can be achieved through either core-level multiplet splittings or circular-polarized excitation of spin-orbit-split levels. The direct imaging of short-range atomic structure by both photoelectron holography and two distinct types of x-ray holography involving fluorescent emission is also discussed. Both photoelectron and x-ray holography have demonstrated the ability to directly determine at least approximate atomic structures in three dimensions. Photoelectron holography with spin resolution may make it possible also to study short-range magnetic order in a holographic fashion. Although much more recent in its first experimental demonstrations, x-ray fluorescence holography should permit deriving more accurate atomic images for a variety of materials, including both surface and bulk regions.

An electron spectroscopic study of the adsorption of benzenethiol and 1,2-benzenedithiol on the Cu(110) surface

Abstract The adsorption of benzenethiol and 1,2-benzenedithiol on Cu(110) is studied over wide exposure and temperature ranges using UPS, Δφ, XPS and vibrational-EELS. Both compounds lose their thiol hydrogen atom(s) when chemisorbed on Cu, forming monoand di-phenyl mercaptide respectively. At room temperature and low surface coverage the chemisorbed phenyl mercaptide species further undergoes limited desulfurization, with the build-up of the resulting chemisorbed atomic sulfur on the surface self-inhibiting continued C-S bond dissociation. At low exposure the phenyl ring of both the adsorbates lies flat on the Cu surface, but takes a standing-up (though not strictly perpendicular) orientation at high exposures. Whereas the monomercaptide adsorbate appears highly ordered, the dimercaptide does not. UPS was employed to monitor the adsorbate thermo-evolution. Although direct observation of the interaction between the first adsorbate monolayer and the substrate was not possible, analysis of the spectral changes indicates that the loss of the thiol hydrogen of the first layer benzenethiol and 1,2-benzenedithiol were complete at −112 and −90°C, respectively, significantly below the final multilayer desorption temperatures of −89 and −46°C.

Electron mean free paths in ge in the range 70–1400 eV

Abstract Accurate values of the electron inelastic scattering mean free path, λ( E ), in amorphous germanium have been measured in the electron energy range 70–1400 eV and are compared with other experimental values for Si, GeO 2 , and SiO 2 . The data are also compared with predictions from a variety of theoretical models.

The development of x-ray photoelectron spectroscopy: 1900–1960

Abstract A review of the historical development of the technique of X-ray photo-electron spectroscopy is presented, from the discovery of the photoelectric effect by Hertz in 1887 to the early stages of the present day revitalization of the technique by K. Siegbahn and his associates, that is, up to 1960. It is shown that the technique has undergone an almost continuous process of development and utilization, with a small number of able and dedicated workers providing major contributions and stimuli at various times throughout this long period.