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We studied the stability of metal/polymer interfaces by measuring the diffusion of calcium into a polymer (OC 1 C 10 PPV) layer during and after deposition of the metal using low energy ion scattering (LEIS) and X-ray photoelectron spectroscopy (XPS). During deposition the calcium diffusion depth in the PPV was found to be comparable for untreated samples and samples prepared in oxygen ambient (10 −7 mbar). In both cases diffusion depths up to ∼7 nm were observed. For PPV layers treated with atomic oxygen, the diffusion depth during deposition was slightly smaller. After deposition, it was observed that calcium diffusion in OC 1 C 10 PPV continues for several hours. When oxygen was present during calcium deposition or during the spin coating of the PPV, the diffusion coefficient for calcium in PPV was decreased considerably. In these cases accumulation of oxygen (adsorbed in the PPV during deposition or spin coating) at the calcium/PPV interface continued for several hours after deposition. Treatment of the PPV with atomic oxygen before calcium deposition resulted in a strong decrease of the calcium diffusion coefficient after deposition. From XPS measurements it was observed that calcium interacts with the chemically bonded oxygen in the PPV and also with the oxygen absorbed in the PPV layer. It can be concluded that oxygen, either chemically bonded to the PPV chain or adsorbed in the film, reduces the calcium diffusion coefficient. The initial performance of PLEDs with atomic oxygen treated PPV layers and PLEDs with calcium deposited in oxygen ambient was worse than the performance of untreated devices, but the stability in the life-test was better.

In polymer light emitting diodes (PLEDS) with an (ITO/PPV/Ca) structure we obsd. a significant redn. of both the current and the light output at const. voltage after heat treatment for only 30 min at 65 DegC. Electroluminescence spectroscopy expts. showed that the shape as well as the amplitude of the spectra were changed.The redn. of current and light output was investigated by measuring I-V and E-V (current-voltage and brightness-voltage) characteristics of PLEDs, I-V characteristics of single carrier devices, and by performing low energy ion scattering and XPS expts. on the Ca/PPV interface.It was concluded that the current and light output redn. could be ascribed to the degrdn. of the Ca/PPV and the ITO/PPV interfaces. The degrdn. of the ITO/PPV interface resulted in a redn. of the zero field hole mobility and a small increase of the field dependence of the mobility. The degrdn. of the Ca/PPV interface, probably by diffusion of calcium into the PPV, resulted in carrier traps and quenching sites, which influenced the field dependent electron mobility

The influence of oxygen exposure on three chemically different poly para -phenylene vinylene (PPV) derivatives used in polymeric light emitting devices (PLEDs) has been investigated. During device preparation, PPV layers have been exposed to oxygen either in the dark or during the irradiation with visible light, before the cathode was applied. Device efficiency was studied by electrical and optical characterisation and correlated to oxygen depth profiles measured with Elastic Recoil Detection Analysis (ERDA). Treatment with oxygen during light exposure leads to a decrease in current, light output and efficiency. It was found that two different PPV derivatives show the same current and light output reduction with different oxygen uptake. This behaviour is explained in terms of a different chemical structure and the number of structural defects (tolane-bisbenzyl moieties (TBBs)) incorporated. For two PPV derivatives treated with oxygen in the dark a reduction in current and light output was found, while the efficiency was unchanged. Another PPV derivative, however, shows a shift in the on-set voltage of the light output accompanied by an increased oxygen level at the PPV/Ca interface. It is concluded that after exposure in the dark, oxygen is incorporated in the PPV by Van der Waals interaction. During evaporation of the cathodes, oxygen will diffuse to the cathode and will be gettered by the calcium, which results in the formation of an electron injection barrier.

Planar MeV ion-channeling measurements on 2.2 nm thick Si1-xGex nano-films buried in Si are presented. The presence of the nano-film leads to a step in the yield of the host crystal in a {0 1 1} planar channeled RBS spectrum. In previous work we showed that with the help of Monte Carlo (MC) simulations the step height in axial channeling measurements provides useful information on the tetragonal distortion in buried nano-films. Since the step height is larger for planar channeling measurements, we extend this method to planar channeling in the present work. The measurements show that the flux distribution of channeled ions is not in statistical equilibrium, but still oscillates at the depth of the buried films (about 280 nm), This is confirmed by simulations performed with the MC simulation code FLUX and a qualitative understanding is obtained for the observed phenomena. The accuracy of the calculated step height curves appears much more sensitive to the choice of ion-atom potential than those from axial channeling, which can be attributed to the non-equilibrium distribution of channeled ions between the planes. Consequently, from planar channeling measurements, the tetragonal distortion can be determined with about the same accuracy as from axial channeling measurements in spite of the higher steps. (C) 2001 Elsevier Science B.V. All rights reserved.

The chemical composition and crystalline nature of inorganic deposits present in the human aortic wall were investigated. A proton microprobe in combination with proton induced X-ray emission and proton induced gamma-ray emission were used to determine quantitatively the elemental composition of the inorganic deposits while their structure was studied with the use of an X-ray microprobe in combination with X-ray diffraction and Fourier transform infrared microscopy. It was found that deposits in the aortic wall are composed of Ca–P compounds. Fluorine is accumulated in the inorganic phase. However, the mechanism of F deposition awaits further investigations. The only phase detected by the X-ray diffraction was a defective hydroxyapatite. The relative intensities of reflexes indicate that the c axis of the crystallites is parallel to the long axis of the vessel. IR microscopy revealed that the crystals were contaminated with carbonate groups. Moreover, the band characteristic for octacalcium phosphate was detected.

Two alternative detector types have been studied for use in the Eindhoven Scanning Ion Microprobe set-up. First, the applicability of a Charge Coupled Device (CCD) system for X-ray spectroscopy has been explored. Second, some properties of the SiTek type 1L30 Position Sensitive Detector (PSD) for charged-particle spectroscopy have been studied. A literature survey shows that excellent X-ray spectroscopy with a CCD system is feasible, particularly with a deep-depletion backside-illuminated CCD and low speed read-out. If, however, high-speed CCD read-out is required, such as for scanning microprobe experiments, a CCD system cannot be used for spectroscopy due to excess read-out noise. For the PSD, noise theory calculations are presented, which result in a noise shaping time for optimal energy and position resolution. In practice, however, a much longer time is needed to obtain sufficient energy and position linearity. Characterization measurements of the PSD using our 4 MeV He+ microprobe are also described. A position resolution of 0.47 mm and a position linearity of better than 0.15% detector length are found. In addition, an energy linearity better than 0.3% and an energy resolution of 36 keV are measured. The latter will have to be improved, to make the PSD suitable for charged-particle spectroscopy applications.

Ion channeling for materials analysis is usually carried out with He ion beam energies less than 3 MeV. The AVF-cyclotron at Eindhoven University of Technology allows the use of higher beam energies (3–30 MeV) which is of potential interest due to a high angular resolution, a large analysable depth range and the application of nuclear reactions or resonant scattering cross-sections. In this paper the enhanced angular resolution for 12.6 MeV He ions is demonstrated by angular scans from a buried Si 1− x Ge x layer. The enhanced analysable depth range is shown by quantitative defect depth profiling of a 4 μm thick relaxed SiGe multilayer buffer. Finally, a study on vibrational amplitudes in bulk InP was carried out by a combination of channeling and nuclear reaction analysis using the 31 P(α,p) 34 S reaction.

The use of electron irradiation in polymer research for polymer modification is a well known method. Recently the technique of pulsed electron beam polymerization has been introduced as a tool for investigations into the kinetics and mechanisms of free radical polymerization. The technique can be applied to homogeneous and in particular to heterogeneous polymerization systems such as an emulsion polymerization. The major advantages are: (1) no limitation to optical transparency of the system; (2) no additional initiator is required. The 6 MeV linear accelerator (linac) at the Cyclotron Laboratory of the Eindhoven University of Technology is used for the present investigations. In this contribution, the accelerator set-up will be described and pulsed electron beam polymerization experiments will be used to illustrate the new technique. The irradiation set-up operates with pulse repetition rates between 1 and 50 Hz at a monitored dose per pulse adjustable between 0.1 and 3 Gy. The reaction temperature can be varied up to 100°C. Results of the current investigations in the polymerization of styrene in bulk and methyl methacrylate in emulsion will be presented.

The deconvolution procedure based on the maximum-entropy method is applied to improve both resolution and noise characteristics of micro-PIXE maps. The procedure is simple to execute, fast, easily automated and assumes no a priori information. The best improvement is observed for data with low statistics. Special emphasis is given to the difficulties and limitations of processing micro-PIXE data. Examples of applications for biomedical samples are presented.

In elastic recoil detection analysis (ERDA) with a-particles, recoils can be separated from scattered projectiles by using detectors with a thin depletion layer and a pulse shape discrimination (PSD) circuit [S.S. Klein and H.A. Rijken, Nucl. Instr. and Meth. B 66 (1992) 393]. Improved performance is obtained with a multi-parameter data acquisition system; recoil events are more easily and accurately selected and sensitivity is improved by a factor of 5 to 1 X 1014 at/cm2 for oxygen on amorphous silicon. The typical surface depth resolution is 10 nm. Two alternative PSD circuits are proposed neither of them using fast electronics. Examples are given of profiling carbon and oxygen in thin films of Si, C and SiOxNy.

An improved coincidence time-of-flight recoil spectrometer is described. The use of alpha-particles instead of heavy ions to eject the recoils has the advantages of larger depth range and smaller target damage. Multi-element analysis and element-selective depth profiling on thin and moderately thick targets are demonstrated. A surface depth resolution of 3 nm has been obtained for 12C in carbon at a recoil angle φ of 30°. Resolution down to 1 nm is predicted when further compensation of kinematic effects is realized; using very well defined beams it might be possible to obtain atomic layer resolution. Strategies to extend the present sensitivity of about 1014 atoms cm2 by one or two orders of magnitude are discussed.

Elastic recoil detection (ERD) of carbon, nitrogen and oxygen from thin films on thick substrates was demonstrated using 10-15 MeV He2+ ions and thin films detectors. Non-Rutherford scattering was used to alter the relative sensitivities for carbon, nitrogen and oxygen by selecting specific recoil angles and incident energies. A depth resolution of 15 nm near the surface can be easily achieved as well as probing depths up to approximately 500 nm.

Detector limitations to the energy resolution can be avoided by measuring the time of flight over a sufficient distance. For 6 MeV 12C ions the energy resolution has been improved from 70 to 20 keV on a 3 m flight path. The depth resolution obtained in CERDA (coincident elastic recoil detection analysis) with a 12.6 MeV beam from the Eindhoven AVF cyclotron improves by a smaller factor (from 50 to 30 nm) because the depth resolution is now dominated by kinematic effects of beam emittance and detection solid angle. Without sensitivity loss the depth resolution may be further improved to 15 nm selecting the beam in a more effective way.

The energy resolution of ion-implanted charged particle detectors may be improved by decreasing the thickness of the implanted detector window to minimize energy straggling. Because of the resistance of this layer, however, the timing depends on the position of entry. Two solutions to this conflict between energy resolution and time resolution are studied: evaporating a very thin aluminum layer on the detector window and fabricating a rectangular detector. Both solutions are shown to be successful with a total time resolution in the low subnanosecond region (< 200 ps).