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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 this work we address the dynamics and stability of calcium/PPV and barium/PPV interfaces during and after deposition of the metal. Diffusion of calcium and barium into OC/sub 1/C/sub 10/ PPV is studied with low energy ion scattering (LEIS) and x-ray photoelectron spectroscopy (XPS). During metal deposition the diffusivity is found to be orders of magnitude higher than after deposition and the diffusion coefficient was found to be dependent on the metal concentration in the PPV. Furthermore, the amount of metal inside the polymer films was found to depend on the deposition rate. These observations were explained in a two-stage diffusion model. In the first stage atoms land on the surface and diffuse fast into the polymer and in the second stage metal ionizes and is trapped and diffusion is strongly decreased. The diffusion coefficient of barium into PPV at T=298 K is found to be almost an order of magnitude lower than the diffusion coefficient of calcium into PPV [(0.35+or-0.05)*10/sup -23/m/sup 2//s and (2.7+or-0.4)*10/sup -23/ m/sup 2//s, respectively]. Furthermore, the activation energy of the diffusion process of barium into PPV (0.75+or-0.07eV) is significantly higher than the activation energy of the diffusion process of calcium into PPV (0.62+or-0.05 eV). The difference in diffusion coefficient and activation energy between calcium and barium are discussed in terms of an Arrhenius law of diffusion. Finally, polymer LED performance was studied as a function of the amount of metal diffused into the polymer layer. It was observed that the light output and the efficiency decreased as the amount of metal in the PPV increased. This indicates that the metal ions form charge carrier traps and exciton quenching sites in the PPV

A combination of low- and high-energy ion beam analysis techniques was used to determine the distribution of indium chloride compounds in model polymeric light-emitting diodes (p-LEDs). Parts of polymeric LEDs (poly-dialkoxyphenylenevinylene (OC/sub 1/C/sub 10/-PPV) on indium-tin-oxide (ITO) substrates) were exposed to a HCl/Ar flow to simulate the processes occurring during conversion of precursor PPVs and acid treatment of polymers. Samples with variable exposure times as well as pristine samples were studied with Rutherford backscattering spectrometry (RBS), low energy ion scattering (LEIS), X-ray photoelectron spectroscopy (XPS) and particle induced X-ray emission (PIXE). The RBS measurements show that after HCl exposure indium is distributed throughout the OC/sub 1/C/sub 10/-PPV layer. LEIS and XPS measurements indicate that the indium and chlorine are present at the outermost surface of the OC/sub 1/C/sub 10/-PPV layer. PIXE measurements in combination with the RBS data demonstrate that the indium chloride in the OC/sub 1/C/sub 10/-PPV layer is distributed in blisters ( phi = 50 mu m) which are orientated perpendicular to the sample surface. To study the OC/sub 1/C/sub 10/-PPV/ITO interface, samples were delaminated by peeling the polymeric layer of the ITO using Scotch tape. LEIS measurements on the fracture planes demonstrate the formation of an interfacial layer between the ITO and the PPV. The implications for p-LEDs are discussed

The effect of controlled exposure to O on the stability of Ca cathode of polymeric light emitting diodes (pLEDs) was studied. The LEDs were fabricated with ITO as anode, poly[2-methoxy-5-(3',7'-dimethyloctyloxy)-1,4-phenylenevinylene] [OC1C10-PPV] as electroluminescent polymer, Ca as cathode and Al as protecting layer. The polymer layers of the LEDs were spin coated under dry N atm. and transported directly into an UHV chamber where the metal electrodes were deposited by evapn. To study the effects of exposure to O of the Ca cathode, deposition of the Ca layer was interrupted in some cases and the samples were exposed to 30-1000 mbar of O. The amt. of O in the layers of the pLEDs was detd. from current-voltage data and elastic recoil detection and was correlated with device performance parameters. Exposing a part of the Ca layer to O at layer thicknesses equal to or less than 10 nm led to a total loss of brightness. The failure of pLEDs is attributed to oxidative degrdn. of OC1C10-PPV in contact with oxidized Ca and O at the interface. The damage and failure can be prevented if fabrication of the devices is carried out in a totally inert atm

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.

The energy loss distribution of ions transmitted through a 5.7±0.2 μm thick Si crystal was measured and simulated with the Monte Carlo channeling simulation code FLUX . A general resemblance between the measured and simulated energy loss distributions was obtained after incorporation of an energy dependent energy loss in the simulation program. The energy loss calculations are used to investigate the feasibility to detect the presence of light element dopant clusters in a host crystal from the shape of the energy loss distribution, with transmission ion channeling. A curved crystal structure is used as a model for a region in the host crystal with clusters. The presence of the curvature does have a large influence on the transmitted energy distribution, which offers the possibility to determine the presence of dopant clusters in a host crystal with transmission ion channeling.

Low energy ion implantation at high doses of boron (>1015 cm–2) in Si is necessary for the fabrication of ultrashallow junctions but can result in the undesirable presence of boron clusters. Values for the dimensions of the lattice distortions in the implanted Si are obtained by comparing the enhanced dechanneling and the direct scattering peak in the region with clusters in a channeled Rutherford backscattering spectrometry spectrum to those from Monte Carlo calculations on a curved crystal structure. Values of about 0.17 and 65 nm are found for the maximum deformation and the length of the distortions in the crystal, respectively, which implies that the lattice distortions extend significantly outside the layer in which the B clusters are supposed to be present. ©2001 American Institute of Physics.

We have measured axially channeled Rutherford backscattering spectra of Si1-xGex nanofilms in silicon(001). A step in the yield of the host crystal was found for off-normal axes at the depth of the nanofilm. The step was measured as a function of the angle between the incoming beam and the [011] axis and shows two maxima. It is found that Monte Carlo simulations assuming tetragonal distortion reproduce the experimental results. A universal curve was derived which enables determination of the tetragonal distortion from ion-channeling experiments, for a given film thickness. The results are compared with XRD measurements.

The influence of gallium ions on the development of the mineralization process in a cell culture model was investigated. To determine the elemental composition the proton microprobe in combination with proton induced X-ray emission (micro-PIXE) and energy-dispersive X-ray fluorescence (XRF) were used. Micro-PIXE allows a precise quantification of elements combined with their accurate localization. In contrast, the XRF results may be used as a rough estimate of the mineralization process development. It was found that gallium influences the mineralization process in a dose-dependent manner. At low doses an increased while at high doses an impaired mineralization was observed. The amount of deposited gallium correlates with the concentration of the element in the cell culture medium. © 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.

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.

We investigated the elemental composition of different layers of polymeric light-emitting diode (pLED) model structures. Of special concern have been poly-(3,4-ethylenedioxythiophene) (PEDOT)/polystyrenesulfonate (PSS) and poly-phenylenevinylene (PPV) films, which are used widely in pLEDs. We found halogen compounds as impurities: bromine in the PEDOT/PSS and chlorine in the PPV layer. It is argued that the presence of halogen containing compounds could be an important reason for the degradation of pLEDs.

The proton microprobe in combination with proton induced X-ray emission (micro-PIXE) and with proton induced gamma-ray emission (micro-PIGE) are used to determine quantitatively the modulation of inorganic deposits formation by Sr and F ions in a cell culture model. The results indicate that the process may be investigated by the micro-PIXE determination of the amount of calcium deposited. It was found that F-treatment stimulate bone formation at doses much lower than Sr. At high doses an impaired mineralization is found for both elements. It was found that the mechanisms responsible for of F and Sr incorporations are different. The minimal F and Sr concentrations in the medium at which the incorporation may be investigated by micro-PIGE and micro-PIXE amount to ∼0.02 mg/l and

In the study of interfacial diffusion processes in polymer light-emitting diodes, the use of high-energy ion-scattering techniques can be of great value due to the possibility of quantitative elemental depth profiling. However, ion irradiation of polymers is known to cause various degradation effects, including the loss of hydrogen. Since the hydrogen loss determines the accuracy of depth profiling, it is an interesting subject for study in order to define experimental conditions hi which the degradation is suppressed. The loss of hydrogen from porphyrins (organic solar cells) has been measured by means of elastic recoil detection analysis with 2, 4, and 7.6 MeV He+ beams. A theoretical model is proposed in which the hydrogen loss is described through the formation and recombination of free hydrogen radicals. A distinct difference is introduced between direct recombination processes and the diffusion of radicals out of the ion track.

Stopping powers for channeled He ions have been calculated with a modified version of the Monte Carlo code LAROSE [J.H. Barrett, Phys. Rev. B 3 (1971) 1527]. The spatial distribution of the valence electron density in Si was obtained from bandstructure calculations. The stopping power was calculated using Lindhard's free-electron gas approach within the framework of the local density approximation. Spatial variations of the electron density along individual trajectories produce a significant contribution to the energy loss distribution. The average energy loss of 4 MeV He ions channeled in the axial 〈100〉, 〈111〉 and 〈110〉 directions have been calculated and compared with measured values. The contribution of the core electrons to the energy loss is investigated by adding the spherically symmetric Hartree-Fock-Slater electron densities of the closed shells to the valence electron density. Calculations show a high energy loss tail in the spectrum qualitatively in agreement with published experimental results.

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.

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).

A cause for degradation of polymer light-emitting diodes is the oxidation of the polymer by oxygen diffusing out of the indium-tin-oxide (ITO) anode. This problem can be solved by the introduction of an organic hole-injecting film, poly-(3,4-ethylenedioxythiophene) (PEDOT) doped with poly(styrenesulfonate) (PSS), between the ITO and the emissive polymer. Indeed, a dramatic improvement of the lifetime and also the luminous efficiency has been observed. However, our Rutherford backscattering (RBS) studies show that the ITO/PEDOT:PSS interface is not stable. In as prepared glass/ITO/PEDOT:PSS samples 0.02 at. % indium was found in the PEDOT:PSS film. Annealing in a nitrogen atmosphere at 100 °C during 2500 h increased the indium concentration to 0.2 at. %. Upon exposure to air much faster degradation of the ITO/PEDOT:PSS interface was observed; after several days in air the amount of indium reached a saturation concentration of 1.2 at. %. The degradation of the interface can be explained by etching of the ITO due to the strong acidic nature of PEDOT:PSS. ©2000 American Institute of Physics.

We investigated the influence of the presence of oxygen during the deposition of the calcium cathode on the structure and on the performance of polymeric light emitting diodes (pLEDs). The oxygen background pressure during deposition of the calcium cathode of polymeric LEDs was varied. Subsequently, the oxygen depth distribution was measured and correlated with the performance of the pLEDs. The devices have been fabricated in a recently built ultraclean setup. The polymer layers of the pLEDs have been spincoated in a dry nitrogen atmosphere and transported directly into an ultrahigh vacuum chamber where the metal electrodes have been deposited by evaporation. We used indium–tin–oxide as anode, OC1C10 PPV as electroluminescent polymer, calcium as cathode, and aluminum as protecting layer. We achieved reproducibility of about 15% in current and brightness for devices fabricated in an oxygen atmosphere of less than or equal to 10 -9 mbar. For further investigations the calcium deposition was carried out in an oxygen atmosphere from 10 -8 to 10 -5 mbar. We determined the amount of oxygen in the different layers of the current–voltage-light characterized pLEDs with elastic recoil detection analysis and correlated it with the characteristics of the devices. The external efficiency of the pLEDs decreases continuously with increasing oxygen pressure, the current shows a pronounced minimum. The brightness mostly decreases with increasing oxygen with an indication of a slight minimum. PLEDs with completely oxidized calcium are not operational. The first contact of the pLEDs with the dry glove box environment leads to an immediate reduction of current and brightness which is caused by the cooling of the devices by several degrees. Determining reproducible characteristics of pLEDs in the vacuum requires the measurement of their temperature.

Reactive ion etching of Si wafers with a CF4 plasma results in the formation of a very thin layer of SiFx. Quantification of the fluorine areal density as a function of plasma parameters is important for models describing the etching process. The Eindhoven AVF cyclotron has been used to quantify the amount of deposited fluorine using the 19F(p,p'¿)19F reaction detecting the 110 and 197 keV ¿-lines with a hyperpure Ge detector. The energy of the proton beam was chosen to be 2.76 MeV thereby limiting the Compton background by suppressing excitation of the fourth excited state (5/2+) of 29Si. Quantification was obtained through the use of an implantation standard. A detection limit of 1 × 1014 F/cm2 was obtained and two series of pilot experiments were carried out in which gas discharge pressure and plasma power density have been varied.

High-spin states in the odd-odd nucleus 148 Eu, populated by a carbon-13 induced reaction on a lanthanum target, were investigated with several different tools of in-beam nuclear spectroscopy. The low-energy levels show collective excitations, interpreted as 3 − octupole-phonon couplings to multi-particle-hole states. A probable two-octupole-phonon state is identified. Otherwise most 148 Eu high-spin levels are interpreted in terms of fully aligned multi-particle-hole states rather well described both by a semi-empirical shell model and a deformed independent-particle model.

Ion-implanted silicon detectors which are specially developed for timing experiments show timing response variations of a few times 100 ps as a function of the position of the detector. These variations are caused by resistivity fluctuations up to 50%. To quantify these resistivity variations, depletion depth studies have been performed for a set of detectors. The timing results are obtained with a high-resistivity overdepleted detector. Different detectors are produced from one wafer. Some of these detectors show very low resistivity variations (10%) whereas others show strong resistivity variations (50%). No correlation between the originating place on the wafer and the magnitude of the resistivity variations has been found yet. Therefore, detectors should be scanned at least for homogeneous depletion depth to ensure homogeneous behavior when optimum performance in time of flight experiments and pulse shape experiments is desired. >

The presence of oxygen during the deposition of the calcium electrode of polymeric light-emitting diodes is investigated. The devices are fabricated in an ultraclean setup. We used ITO as anode, OC1C10 PPV as electroluminescent polymer, calcium as cathode and aluminium as protecting layer. The influence of the presence of dry oxygen during deposition is investigated and the exposure of the calcium layer to dry oxygen subsequently to the deposition on the polymer. The change of the structure due to the exposure to oxygen is determined with elastic recoil detection analysis (ERDA) and correlated to the I-V-light characteristics of the devices. Exposure of the devices to oxygen during deposition leads to a decrease in brightness and current with increasing oxygen pressure. The exposure of the calcium to oxygen subsequently to the deposition does not affect the performance of the devices except at calcium layer thicknesses less than 10 nm.

A method for determination of the concentration of mercury in the gaseous phase is described. In the first step of the method a stable sulphur-mercury complex is formed. For this purpose sulphur is deposited on a filter and the investigated gas flows through the filter. Millipore filters and the deposition of sulphur from Na2S2O3 * 5H2O solution were found to be most suitable. The amount of Hg absorbed on the filter was determined by PIXE or by NAA in the second step of the method. An optimization of proton energy was performed in the PIXE analysis to obtain the maximal signal-to-background ratio. The detection limit of the method, expressed as the minimal amount of Hg which has to flow through the filter equals to 30 and 2 ng for PIXE and NAA techniques, respectively. Applications of the method are also described.

Binding and excitation energies, electromagnetic transition rates and multipole moments have been calculated for 57–66 Ni from many-particle shell-model wave functions with neutrons in the 2 p 3 2 , 1 f 5 2 and 2 p 1 2 orbits outside the 56 Ni core. The efiective two-body matrix elements are obtained from the modified surface delta interaction. The average absolute deviation between the calculated and experimental binding and excitation energies is 0.11 MeV (with the exclusion of 66 Ni). Electric quadrupole transition rates and moments are calculated with an effective neutron charge e n = (1.70±0.08) e , obtained from a least-squares fit to experimental data. Magnetic dipole transition rates and moments follow from five fitted effective reduced singleparticle matrix elements. The average absolute deviations between theory and experiment for the strongest E2 transitions (1–15 W.u.) and for the strongest M1 transitions (0.01–0.14 W.u.) are 3.5 and 0.03 W.u., while the average measured strengths are 7.0 and 0.07 W.u., respectively.