A. W. Denier van der Gon

The effects of solvents on the morphology and sheet resistance in poly(3,4-ethylenedioxythiophene)–polystyrenesulfonic acid (PEDOT–PSS) films

The effects of solvents on the morphology and sheet resistance in poly(3,4-ethylenedioxythiophene)-polystyrenesulfonic acid (PEDOT-PSS) films

Melting of al surfaces

The thermal disordering of Al(110) and Al(111) surfaces was studied up to temperatures of 0.5 and 1.2 K below the bulk melting point Tm, respectively. With the use of medium energy ion scattering it was found that surface melting is present on the (110) face but not on the (111) face. The (110) disordered layer thickness increases with temperature as ln[Tm(T>m − T)]. The result in terms of a thermodynamic model that was presented earlier to explain the melting of Pb surfaces.

Indium diffusion in model polymer light-emitting diodes

The diffusion of indium into poly-(phenylenevinylene) (PPV) in model polymer light-emitting diodes (p-LEDs) was studied with Rutherford backscattering spectrometry (RBS), X-ray photoelectron spectroscopy (XPS), low energy ion scattering spectroscopy (LEIS) and particle induced X-ray emission (PIXE). The model p-LEDs consisted of a glass substrate, an indium–tin-oxide (ITO) electrode, a PPV layer obtained by thermal conversion of sulfonium precursor PPV, and a patterned aluminium electrode. From RBS measurements it was concluded that about 0.01 at.% indium was present in the PPV, homogeneously distributed in depth. Annealing at 230°C for 19 h caused the amount of In in the PPV layer to increase by roughly an order of magnitude. Under the patterned aluminium electrode, the annealing treatment resulted in accumulation of In at the PPV/Al interface, whereas the depth distribution of In remained homogeneous in the uncovered region of the model LEDs. XPS spectra on annealed model LEDs show that In was present in the near surface region of the PPV films, although LEIS analysis showed that In was not situated in the outermost atomic layer. LEIS measurements on as-prepared model LEDs showed that the patterned Al electrode had caused surface contamination of the uncovered PPV film with Al, which can have impact on the diffusion of In to the outermost surface during annealing treatments.

Subsurface segregation of yttria in yttria stabilized zirconia

a special precipitation method at a low temperature. The segregation to the outermost surface layer is dominated by impurities. The increased impurity levels are restricted to this first layer, which underlines the importance of the use of LEIS for this study. For temperatures of 1000 °C and higher, the oxides of the impurities Na, Si, and Ca even cover the surface completely. The performance of a device like the solid oxide fuel cell which has an YSZ electrolyte and a working temperature around 1000 °C, will, therefore, be strongly hampered by these impurities. The reduction of impurities, to prevent accumulation at the surface, will only be effective if the total impurity bulk concentration can be reduced below the 10 ppm level. Due to the presence of the impurities, yttria cannot accumulate in the outermost layer. It does so, in contrast to the general belief, in the subsurface layer and to much higher concentrations than the values reported previously. The difference in the interfacial free energies of Y 2O3 and ZrO2 is determined to be 22163 kJ/mol.

The structure of Si(111)-(3×3)R30°-Ag determined by surface X-ray diffraction

The Ag-induced (√3 × √3)R30° reconstruction on Si(111) has been investigated by surface X-ray diffraction. The in-plane projected structure is found from the structure factors near zero perpendicular momentum transfer. The height of the atoms in the unit cell is determined from rod profiles. The unit cell contains three Ag atoms (saturation coverage 1 monolayer) and eight Si atoms. The Ag atoms are located below a top layer of Si atoms that form a honeycomb. Large displacements from bulk positions occur. The structure is discussed in comparison with other measurements and previously proposed models.

Surface-induced melting and freezing I. Medium-energy ion scattering investigation of the melting of Pb{hkl} crystal faces

Abstract Ion-shadowing and -blocking experiments on cylindrically shaped single crystals of Pb reveal a strongly orientation-dependent disordering (melting) of the surface as the temperature T increases toward the bulk melting point T m . Most of the crystal faces become strongly disordered, but not the faces with orientations around the {111} and {100} planes. On the disordered surfaces the melted layer thickness is found to diverge logarithmically with increasing temperature. The disordering is shown to be driven by the orientation-dependent interface free energy which the ordered solid surface has in excess of a surface completely wetted with a liquid layer.

Composition and structure of the Cu85Pd15(110)-(2×1) surface determined by low-energy ion scattering

The composition and structure of the Cu85Pd15(110)-(2×1) surface has been determined by low-energy ion scattering. From time-of-f forward scattering and recoiling measurements it is concluded that the surface is unreconstructed. The equilibrium composition of the first two atomic layers is determined by comparing the energy and azimuthal distribution of backscattered 2 keV Ne+ ions as obtained with the EARISS (energy and angle-resolved ion scattering spectrometer) with three-dimensional ion trajectory simulations. For the first layer, a slight depletion in Pd is found (11±2 at%), whereas the second layer is strongly enriched in Pd (40±8 at%). These results are in reasonable agreement with an earlier proposed model [D.J. Holmes, D.A. King and C.J. Barnes, Surf. Sci. 227 (1990) 179]. In addition, the thermal segregation after sputtering at room temperature was investigated which showed similar behavior as was recently reported on Pt10Ni90(110) [P. Weigand, B. Jelinek, W. Hofer and P. Varga, Surf. Sci. 295 (1993) 57].

The electronic structure of n- and p-doped phenyl-capped 3,4-ethylenedioxythiophene trimer

A study was conducted on the effects of chemical doping on the chemical and electronic structure of condensed molecular solid films of the ethylenedioxythiophene (EDOT) trimer using ultraviolet pho ...

Modification of PEDOT-PSS by low energy electrons

The stability of conjugated organic materials under electron transport is of great importance for the lifetime of devices such as polymer light-emitting diodes (PLEDs). Here, the modification of thin films of poly(3,4-ethylenedioxythiophene) oxidized with poly(4-styrenesulfonate) (known as PEDOT–PSS, often used in the fabrication of PLEDs) by low-energy electrons has been studied using X-ray photo-electron spectroscopy. Thin films of PSSH and molecular solid films of EDOT molecules also have been studied. We find that electrons with kinetic energies as low as 3 eV result in significant modification of the chemical structure of the materials. For thin films of PSSH, the electron bombardment leads to a strong loss of oxygen and a smaller loss of sulfur. In addition, a large amount of the sulfur atoms that remain in the films exhibits a different binding energy because of scissions of the bonds to oxygen atoms. For condensed molecular solid films of EDOT molecules, we find that the carbon atoms bonded to oxygen react and form additional bonds, as evidenced by a new component in the C(1s) peak at a higher binding energy. In the PEDOT–PSS blend, we find both effects. The importance of these observations for light-emitting diodes incorporating PEDOT–PSS films is discussed. This work demonstrates that the combination of in situ low-energy electron bombardment in combination with photo-electron spectroscopy is a powerful method to simulate and study certain processes, associated with low-energy electrons, occurring in organic based devices, which cannot be studied directly otherwise.

Domain structure, segregation and morphology of the Pt3Sn(111) surface

Abstract Using spot-profile analysis low-energy electron diffraction, we have studied the domain structure and morphology of the Pt3Sn(111) surface after sputtering at room temperature and subsequent anneal treatments which result in the formation of the previously reported ( 3 × 3 ) R30° and (2×2) structures. In addition, we present new results on the temperature-dependent composition of the outermost layer and the subsurface region that is obtained from quantitative analysis of low-energy ion scattering and Auger electron spectroscopy experiments. The combination of these results and previous experiments yields a detailed picture of the evolution of the surface region during the anneal treatments. Finally, we propose the existence of a phase transition at high temperatures between the (2×2) phase and a (2×2)′ phase (not previously observed) on the basis of reversible changes in the SPA–LEED, LEIS and AES data.