L.J. van IJzendoorn

Stability of the interface between indium-tin-oxide and poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) in polymer light-emitting diodes

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 IT...

Controlled torque on superparamagnetic beads for functional biosensors

We demonstrate that a rotating magnetic field can be used to apply a controlled torque on superparamagnetic beads which leads to a tunable bead rotation frequency in fluid. Smooth rotation is obtained for field rotation frequencies many orders of magnitude higher than the bead rotation frequency. A quantitative model is developed, based on results from a comprehensive set of experiments at different field strengths and frequencies. At low frequencies (<10Hz), rotation is due to a small permanent magnetic moment in the bead. At high frequencies (kHz-MHz), the torque results from a phase lag between the applied field and the induced magnetic moment, caused by the non-zero relaxation time of magnetic nanoparticles in the bead. The control of torque and rotation will enable novel functional assays in bead-based biosensors.

Microstructure of heteroepitaxial Si/CoSi2/Si formed by Co implantation into (100) and (111) Si

Heteroepitaxial Si/CoSi2/Si structures have been synthesized by high‐dose implantation of Co into (100) and (111) Si at an energy of 170 keV and subsequent annealing. In the as‐implanted state the implanted Co is found to be present as CoSi2. For a dose of 2×1017 Co/cm2, the Co is present in the form of epitaxial precipitates, which exhibit both the aligned (A‐type) CoSi2 and twinned (B‐type) orientation. For a higher dose of 3×1017 Co/cm2, a monocrystalline epitaxial CoSi2 layer near the top of the implanted Co distribution is formed during the implantation. The heteroepitaxial structures that are formed in this way are fully aligned. In contrast, when these structures are formed by sequential surface deposition techniques, twinning occurs at every Si/CoSi2 interface. The formation of the aligned orientation of the buried CoSi2 layer can be attributed to the larger stability of aligned precipitates as compared to twin‐oriented precipitates.

Deposition of inorganic salts from solution on flat substrates by spin-coating: theory, quantification and application to model catalysts

The theory of spin-coating is applied to predict the amount of inorganic material that is deposited from a solution on a flat substrate on the basis of concentration, density, viscosity and evaporation rate of the solution and the spin speed applied during spin-coating. Measurements by Rutherford backscattering spectrometry (RBS) and inductively coupled plasma optical emission spectroscopy (ICP-OES) confirm the validity of the theory. Applications of the method in the preparation of model catalysts are discussed.

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.

Optical and mechanical properties of plasma‐beam‐deposited amorphous hydrogenated carbon

Amorphous hydrogenated carbon films have been deposited on crystalline silicon and on glass from an expanding thermal plasma. Two deposition parameters have been varied: the electric current through the plasma source and the admixed acetylene flow. No energetic ion bombardment has been applied during deposition. Ex situ analysis of the films yields the infrared refractive index, hardness, Young’s modulus, optical band gap, bonded hydrogen content, and the total hydrogen and mass density. The infrared refractive index describes the film properties independent of which plasma deposition parameter ~arc current or acetylene flow ! has been varied. The hardness, Young’s modulus, sp 2 / sp 3 ratio, and mass density increase with increasing refractive index. The optical band gap and hydrogen content of the films decrease with increasing refractive index. It is demonstrated that plasma-beam-deposited diamondlike a-C:H has similar properties as material deposited with conventional plasma-enhanced chemical-vapor-depositions techniques under energetic ion bombardment.

A model for ion-irradiation induced hydrogen loss from organic materials

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 in 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.

In-situ compositional and structural analysis of plastic solar cells

Bulk-heterojunction photovoltaic cells consisting of a photoactive layer of poly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV) and a C60 derivative, (1-(3-methoxycarbonyl)propyl-1-phenyl-[6,6]-methanofullerene), (PCBM), sandwiched between an indium tin oxide (ITO) anode covered with poly(ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), and an aluminum cathode have been analyzed using transmission electron microscopy (TEM) and cryogenic Rutherford backscattering spectrometry (RBS) to assess the structural and elemental composition of these devices. TEM of cross sections of fully processed photovoltaic cells, prepared using a focused ion beam, provide a clear view of the individual layers and their interfaces. RBS shows that during preparation diffusion of indium into the PEDOT:PSS occurs while the diffusion of aluminum into the polymer layers is negligible. An iodinated C60 derivative (I-PCBM) was used to determine the concentration profile of this derivative in the vertical direction of a 100 nm active layer.

Germanium diffusion and strain relaxation in Si/Si1−xGex/Si structures

Abstract The thermal stability of strained Si1−xGex layers grown by molecular beam epitaxy on Si(100) was measured using Rutherford backscattering spectrometry, secondary ion mass spectroscopy and high resolution X-ray diffractometry (HRXRD). Diffusion experiments were carried out on Si1−xGex layers 50 nm thick (x = 0.07, 0.16 and 0.33) annealed at temperatures between 775 and 1010 °C for different times. The diffusion of germanium was evaluated from the broadening of the RBS and SIMS germanium profiles, while the strain relaxation was deduced from the angular shift of the (400) reflection in HRXRD. The diffusion coefficient thus measured proved to be strongly dependent on the local germanium concentration in the film. In the tails of the profile, the diffusion coefficient was comparable with the value for germanium in bulk silicon while in the centre of the film an enhanced diffusion was found. Both the initial germanium fraction x in the as-grown film and the presence of misfit dislocations hah only minor influence on the diffusion behaviour. It is concluded that safe thermal processing of these structures is possible up to 850 °C for several hours.

Surface analysis of reactive ion‐etched InP

A dry‐etch process for InP is developed using a mixture of Cl2, Ar, CH4, and H2. This process results in a high etch rate and good anisotropy. The induced damage is investigated by surface characterization after etching, using x‐ray photoelectron spectroscopy, Rutherford backscattering spectrometry, photoluminescence measurements, and transmission electron microscopy. The etch mechanism is briefly discussed.