[en] The formation of small gold clusters at the initial stage of the metal growth on a thin film of the conjugated organic semiconductor diindenoperylene (DIP) leads to charging during ultraviolet photoemission spectroscopy (UPS) investigations. Additional irradiation of the sample with visible light was successfully applied to re-establish charge neutrality on the sample surface. By varying the light energy, we demonstrate that the optical formation of excitons and/or polarons results in efficient electron transfer from DIP to the positively charged Au clusters and thus the elimination of charging in UPS. This allows the collection of reliable information on the interface electronic structure

[en] A series of random copolymers of styrene and methyl methacrylate was prepared on a silicon substrate by RF pulsed inductively coupled plasma. The plasma gas phase was investigated by optical emission spectroscopy (OES). The physico-chemical characteristics of the deposited copolymer films were analyzed by several surface techniques: X-ray photoelectron spectroscopy (XPS), Fourier-Transform infrared absorption (FT-IR), Time-of-flight secondary ion mass spectrometry (ToF-SIMS), etc. OES of the plasma and FT-IR spectra of the films are predictive: plasma emitting a higher relative benzyl radical signal results in the deposition of a more aromatic plasma polymer. The functional thin films can be deposited by selection of the co-monomers.

[en] The infrared dielectric response of UO₂ has been determined by reflection electron energy-loss spectroscopy. One resonance frequency, ωsub(TO), is found at 278 cm^-1 with oscillator strength Δepsilon = 16.8 and damping γ = 38 cm^-1. Resonant scattering from the 5f unoccupied orbitals is observed in the energy-loss intensities. (author)

[en] Full text: Conjugated organic molecules are increasingly being used as active materials in novel (opto-) electronic devices (e.g., light emitting diodes, transistors, solar cells). Frequently, electron injection barriers between a metal contact and the organic layer can be reduced by the introduction of alkali metal atoms. Therefore, knowledge of the interaction between alkali metals and organics, as well as of the resulting energy level alignment at the interface is needed. We present an ultraviolet photoelectron spectroscopy study (Hasylab, Hamburg) on Rb-intercalated thin films of the organic semiconductor N,N-bis-(1-naphthyl)- N,N-diphenyl1-1,1-biphenyl1-4,4-diamine (-NPD). The formation of new occupied electronic states in the otherwise empty energy gap of -NPD is observed, accompanied by a significant shift of the Fermi-level. By varying the organic film thickness we can identify alkali metal atom diffusion as a key parameter for the establishment of thermodynamic equilibrium between substrate and sample surface. Furthermore, experimental results indicate that even for -NPD thickness as small as 100 Angstroms, equilibrium is not established for low Rb intercalation levels. This is deduced from the observation of filled electronic states at and even above the substrate Fermi-level

[en] The combined information of complementary physical analysis techniques is applied to obtain a full characterisation of the important material parameters of new high-k layers, i.e. the layer thickness, density, composition and interlayer thickness and nature, and to optimise the measurement methodologies of the different techniques

[en] Ultraviolet-ozone (UV-O₃) treatment of polyarylene, a semiconductor dielectric polymer, has been characterized using contact angle measurements, x-ray photoelectron spectroscopy, spectroscopic ellipsometry (SE), and ellipsometric porosimetry. Significant modification of the film surface composition is already observed after a short exposure time (30 s). Longer treatment time leads to further increase in oxygen concentration and formation of an oxidized surface layer and densification of the film as evidenced by solvent adsorption data. Results obtained from SE indicate few changes in optical parameters, thickness, and refractive index (RI) of the film, up to 5 min of UV-O₃ treatment. Increasing the exposure time further leads to a substantial change in film thickness and an increase in RI. The same trend was observed for porous polyarylene but to a stronger extent. A dense layer at the porous polymer surface is only formed after 20 min of treatment. Under these conditions, the optical properties of the material are strongly modified, with a substantial thickness shrinkage and increase in RI

[en] In this work, covalent modification of mono- and bilayer graphene is achieved using tetrafluoromethane (CF₄), oxygen and hydrogen RF plasma. Controlled modification of graphene is usually difficult to achieve, in particular with oxygen plasma, which is rather aggressive and usually leads to etching of graphene. Here we use x-ray photoelectron spectroscopy and Raman spectroscopy to show that mild plasma conditions and fine tuning of the number of functional groups can be obtained in all plasmas by varying parameters such as exposure time and sample position inside the chamber. We found that even for the usual harsh oxygen treatment the defect density could be lowered, down to one defect for 3.5 × 10⁴ carbon atoms. Furthermore, we show that CF₄ plasma leads to functionalization without etching and that graphene becomes an insulator at saturation coverage. In addition, the reactivity of mono- and bilayer graphene was studied revealing faster modification of monolayer in oxygen and CF₄ plasma, in agreement with previous works. In contrast, similar modification rates were observed for both mono- and bilayer during hydrogenation. We attribute this discrepancy to the presence of more energetic species in the hydrogen plasma such as positive ions that could play a role in the functionalization process. (paper)

[en] Plasma hydrogenation of graphene has been proposed as a tool to modify the properties of graphene. However, hydrogen plasma is a complex system and controlled hydrogenation of graphene suffers from a lack of understanding of the plasma chemistry. Here, we correlate the modifications induced on monolayer graphene studied by Raman spectroscopy with the hydrogen ions energy distributions obtained by mass spectrometry. We measure the energy distribution of H⁺, H₂⁺, and H₃⁺ ions for different plasma conditions showing that their energy strongly depends on the sample position, pressure, and plasma power and can reach values as high as 45 eV. Based on these measurements, we speculate that under specific plasma parameters, protons should possess enough energy to penetrate the graphene sheet. Therefore, a graphene membrane could become, under certain conditions, transparent to both protons and electrons.

[en] High quality Aluminium-doped Zinc Oxide (AZO) films have been obtained by suitably controlling the magnetron sputtering parameters and the substrate temperature. The X-ray diffraction studies showed that a transition of orientation from (002) plane to (103) plane, versus substrate temperature. The surface morphology characterized by scanning electron microscopy and atomic force microscopy exhibited a dense and compact structure at higher temperature. For 200 nm thick AZO films deposited at temperature 530°C, using a ZnO target with an Al₂O₃ content of 3 wt%, the lowest electrical resistivity is 6.8×10⁻⁴ Ω.cm and transmittance is over 85% in the visible spectral region. The conductivity improvement of AZO films was closely related to the crystallanity characterized by the (103) orientation and the densely packed structure.

[en] To optimize the adhesion of layers presenting strong barrier properties on low-density polyethylene (LDPE) surfaces, we investigated the influence of argon and argon–oxygen atmospheric pressure post-discharges. This study was performed using x-ray photoelectron spectroscopy, atomic force microscopy, optical emission spectroscopy (OES) and dynamic water contact angle (WCA) measurements. After the plasma treatment, a slight increase in the roughness was emphasized, more particularly for the samples treated in a post-discharge supplied in oxygen. Measurements of the surface roughness and of the oxygen surface concentration suggested the competition of two processes playing a role on the surface hydrophilicity and occurring during the post-discharge treatment: the etching and the activation of the surface. The etching rate was estimated to about 2.7 nm s⁻¹ and 5.8 nm s⁻¹ for Ar and Ar–O₂ post-discharges, respectively. The mechanisms underlying this etching were investigated through experiments, in which we discuss the influence of the O₂ flow rate and the distance (gap) separating the plasma torch from the LDPE surface located downstream. O atoms and NO molecules (emitting in the UV range) detected by OES seem to be good candidates to explain the etching process. An ageing study is also presented to evidence the stability of the treated surfaces over 60 days. After 60 days of storage, we showed that whatever the O₂ flow rate, the treated films registered a loss of their hydrophilic state since their WCA increased towards a common threshold of 80°. This ‘hydrophobic recovery’ effect was mostly attributed to the reorientation of induced polar chemical groups into the bulk of the material. Indeed, the relative concentrations of the carbonyl and carboxyl groups at the surface decreased with the storage time and seemed to reach a plateau after 30 days. (paper)