G. Beamson

Characterization of the oxide/hydroxide surface of aluminium using x‐ray photoelectron spectroscopy: a procedure for curve fitting the O 1s core level

The performance of coated and bonded aluminium relies heavily upon its surface chemistry and hence characterization of the aluminium surface is important. A method to quantify the hydroxide concentration at aluminium oxide/hydroxide surfaces by curve fitting the O 1s peak is developed and tested in this paper. Pseudoboehmite, AlO(OH), is formed at the surface of aluminium after immersion in boiling water. The surface of this material was used to determine the binding energy of the unresolved O 1s component peaks that were referenced to the binding energy of the Al 2p oxide component. In vacuo heating resulted in changes in the elemental and functional composition that were consistent with dehydration of the pseudoboehmite. It is proposed that the resultant film comprises γ-alumina with residual hydroxide groups. The O 1s curve-fitting method was applied to air-formed films with known atmospheric exposure histories before and after heating in vacuo. The change in both the elemental composition and functional stoichiometry of the films upon heating was consistent with significant but incomplete dehydration. The probable surface phases are determined from the functional and elemental composition. Copyright

XPS: binding energy calibration of electron spectrometers 5—re-evaluation of the reference energies

The binding energies of the calibration peaks for x-ray photoelectron spectroscopy—Cu 2p3/2, Ag 3d5/2 and Au 4f7/2—have been reassessed based on the traceable data recorded in 1984 using unmonochromated x-rays and an analyser resolution of 0.3 eV. The changes in those energies, for different x-ray sources and analyser resolutions, have been calculated and the results compared with further data. This includes work with monochromatic Al x-rays recorded at high energy resolution, allowing the binding energies to be referred to a new zero value set at the Fermi edge measured for Ag. A consistent set of data is presented for the calibration and assessment of photoelectron spectrometers with energy resolutions in the range 0.2–1.5 eV, when used with unmonochromated Al or Mg x-rays or monochromated Al x-rays.

Analysis of chemical vapour deposited diamond films by X-ray photoelectron spectroscopy

Abstract X-ray photoelectron spectroscopy (XPS) for elemental and phase analysis of diamond surfaces is reviewed, including both single crystal natural diamond and polycrystalline chemical vapour deposition (CVD) films. The core C1s peaks, plasmon losses and valence band spectra of sp2 graphite are compared with those of sp3 diamond, and briefly with mixed sp2/sp3 hard carbon films. Surface reconstructions are reviewed for diamond in the presence of hydrogen or following thermal annealing. Attention is drawn to the destructive effects of argon ion bombardment ‘cleaning’. The synthesis of CVD diamond, including the initial nucleation process, is described and the significance of hydrogen is explained. Chemical modification of the surface of diamond films is discussed, with relevance to sensors and field electron emission. XPS analysis of (111) polycrystalline films treated by atom beams of N, O, H, Cl is described and the influence of unwanted oxygen is emphasised. For both atom beam and furnace oxidation, the oxygen is incorporated into the (111) diamond surface as bridging C–O–C.

High resolution x-ray photoemission study of plasma oxidation of indium–tin–oxide thin film surfaces

The influence of plasma oxidation and other surface pretreatments on the electronic structure of indium–tin–oxide (ITO) thin films has been studied by high resolution x-ray photoemission spectroscopy. Plasma oxidation compensates n-type doping in the near surface region and leads to a reduction in the energy of plasmon satellite structure observed in In 3d core level spectra. In parallel, the Fermi level moves down within the conduction band, leading to a shift to low binding energy for both core and valence band photoemission features; and the work function increases by a value that corresponds roughly to the core and valence band binding energy shifts. These observations suggest that the conduction band of ITO is fixed relative to the vacuum level and that changes of work function are dominated by shifts of the Fermi level within the conduction band.

High resolution XPS investigation of photocured films containing perfluoropolyether acrylates

Abstract The paper reports an XPS investigation on films obtained by photopolymerising new perfluoropolyether methacrylates as pure products or added in low amounts to a typical UV-curable resin (Bisphenol A bis-ethylether diacrylate). The structure of the fluorinated monomers is Rf–Rh type, where Rh=–CH 2 O–CO–NH–CH 2 –CH 2 –OCOC(CH 3 ) CH 2 while Rf=CF 3 –CF 2 O–(CF 2 O) n (CF 2 –CF 2 O) m –CF 2 – for monomer 1 (PM 890, m / n =1.68), and Rf=Cl–CF 2 –CF(CF 3 )–O–(CF 2 CF(CF 3 )–O) 2 –CF 2 – for monomer 2 . Quantitative evaluation of the different atomic ratios was performed using take-off angles of 45 and 10° (very surface region) on both film sides, the one in contact with the glass substrate and the one exposed to air. The results obtained indicate strong fluorine enrichment on the air side of the films and a concentration gradient at the surface, while the glass side has a composition similar to the bulk.

A study of the ITO-on-PPV interface using photoelectron spectroscopy

Abstract Angle-dependent photoelectron spectroscopy has been used to study some details of the chemistry at the interface between indium-tinoxide, deposited by argon plasma sputtering, and poly( p -phenylene vinylene). We find chemical species corresponding to different oxidized states of poly( p -phenylene vinylene) and we discuss their assignment with reference to those produced in photo-oxidation experiments.

Observation of vibrational asymmetry in the high resolution monochromatized XPS of hydrocarbon polymers

Abstract High resolution C1s spectra are reported for polyethylene, polypropylene, hexatriacontane (n-C36H74) and polystyrene. Asymmetry is observed on the high binding energy side of the lineshape for the first three of these compounds, and is attributed to the excitation of CH stretching vibrations during core level photoionization. The effect only becomes apparent for experimental linewidths

Crystallisation of PET from the Amorphous State: Observation of Different Rates for Surface and Bulk Using XPS and FTIR

Crystalline regions of poly(ethylene terephthalate) (PET) are associated with the trans glycol conformation of the polymer repeat unit. Amorphous regions are largely associated with the gauche conformation. We describe experiments which follow the development of trans conformers at the surface and in the bulk of amorphous PET films (∼150 nm thick) annealed above the glass transition temperature T g . X-ray photoelectron spectroscopy was used to probe the surface region to a depth of ∼5 nm and Fourier transform infrared spectroscopy (FTIR) to examine changes in the bulk. For PET samples annealed at 90°C no conformational change was observed either at the surface or in the bulk after 120 min. At 95 and 110 °C the gauche to trans conformational change was over in ∼30 min (surface) and >120 min (bulk) and ∼15 minutes (surface) and ∼30 min (bulk), respectively. Hence the surface rearranges faster than the bulk, consistent with increased mobility at the surface due to the polymer chains being less constrained. This is analogous with the phenomenon of surface premelting in crystalline solids. A comparison of reflection-absorption infrared spectroscopy and transmission FTIR data demonstrates the occurrence of molecular reorientation in the bulk in addition to conformational change.

The screening response of a dilute electron gas in core level photoemission from Sb-doped SnO2

Abstract The variation of core lineshape with carrier concentration in Sb-doped SnO 2 has been studied by high-resolution X-ray photoemission spectroscopy. The Sn 3d core levels display an asymmetric lineshape which may be fitted with components associated with screened and unscreened final states. The separation between the two fitted peaks and the relative intensity of the screened component both increase with increasing carrier concentration. The satellite energies are of the order expected for a screening mechanism involving excitation of plasmons.

Enhanced stab resistance of armor composites with functionalized silica nanoparticles

Traditionally shear thickening fluid (STF) reinforced with Kevlar has been used to develop flexible armor. At the core of the STF-Kevlar composites is a mixture of polyethylene glycol (PEG) and silica particles. This mixture is often known as STF and is consisted of approximately 45 wt % PEG and 55 wt % silica. During rheological tests, STF shows instantaneous spike in viscosity above a critical shear rate. Fabrication of STF-Kevlar composites requires preparation of STF, dilution with ethanol, and then impregnation with Kevlar. In the current approach, nanoscale silica particles were dispersed directly into a mixture of PEG and ethanol through a sonic cavitation process. Two types of silica nanoparticles were used in the investigation: 30 nm crystalline silica and 7 nm amorphous silica. The admixture was then reinforced with Kevlar fabric to produce flexible armor composites. In the next step, silica particles are functionalized with a silane coupling agent to enhance bonding between silica and PEG. The ...