K.-M. Källman

Transient electroluminescence: Mobility and response time in quinquethiophene Langmuir–Blodgett films

Transient characteristics of organic light-emitting diodes with Langmuir–Blodgett films of quinquethiophene as the emitting material have been studied. Field and thickness dependence of the response time have been studied. From the time lag between the voltage pulse and the first appearance of electroluminescence emission, the mobility parallel to the chain of the molecules has been calculated. In thicker films, anisotropy in mobility has been observed when compared with previous results obtained from field-effect studies. The interfaces have been found to play an important role in thinner films.

High-frequency response of polymeric light-emitting diodes

The frequency dependence of alternating-current polymeric light-emitting diodes has been studied. Langmuir–Blodgett (LB) films of poly(3-hexylthiophene) have been used as the active emitting material sandwiched between LB films of emeraldine base polyaniline to form the device. We have shown that by reducing the thickness of the emitting layer using the LB deposition technique, one can increase the high-frequency operating limit of the device. From the −3 dB frequency, we have calculated the carrier mobility in the emitting polymer layer, and compared it with the Poole–Frenkel model. The electroluminescence and photoluminescence spectra have been studied.

Frequency response of molecularly thin alternating current light-emitting diodes

The frequency response of molecularly thin alternating-current polymeric light-emitting diodes has been studied. Langmuir–Blodgett (LB) films of poly(3-hexylthiophene) (PHT) were used as the active emitting material and the device was formed by sandwiching PHT films between LB films of emeraldine base polyaniline. As a step towards molecular electronic devices, we have shown that even two molecular layers of PHT (≈6 nm) are sufficient for light emission. The high frequency operation limit of the device has been discussed in terms of a charge accumulation process at the polymer–polymer interface. The electroluminescence (EL) spectra of different structures have been compared with corresponding photoluminescence spectra. A significant blueshift in EL has been observed in thinner structures and its origin has been discussed.

Origin of Photocurrent in Poly(3-hexylthiophene)

Abstract We have measured the steady state (SS) and pulsed photoconductive response in Langmuir-Blodgett (LB) films of poly(3-hexylthiophene) (P3HT) in order to clarify the origin of the photocurrent in P3HT sandwiched between indiumtin oxide and aluminum (Al) electrodes. We have shown that the Al electrode is important for the observed photosignal. The spectral response of the SS signal follows, however, the absorption spectrum of P3HT, and therefore we attribute the photosignal to hole injection from the Al electrode due to electron transfer from the photo-excited polymer close to the interface.

ALPHA CLUSTERS IN MEDIUM LIGHT NUCLEI: RECENT RESULTS AND OPEN QUESTIONS

The presence of alpha cluster structures in light nuclei is well established. This paper concentrates on the medium light nuclei between 16O and 44Ti. Especially the nucleus 32S has been examined in detail and new data is presented. The elastic scattering data of alpha particles on 28Si forming 32S shows a peculiar disappearance of cross section at 31 MeV excitation energy and above. Also, the energy versus J(J + 1) plot shows at least one clear rotational-like band of alpha cluster states, with the main energy levels split into many narrow and closely lying levels with the same spin. Furthermore, few experiments have been carried out investigating the alpha cluster structure of non-nα nuclei, especially on the proton rich side of stability. The evidence at hand indicates that adding neutrons retains some alpha cluster structures and in some cases might even enhance them, but adding protons seems to destroy the structures.

Demonstrating the conservation of angular momentum using spherical magnets

10.1119/1.5002548.1An experimental setup for demonstrating the conservation of angular momentum of rotating spherical magnets is described. Two spherical Nd-Fe-B magnets are placed on a double inclined plane and projected towards each other with pre-selected impact parameters ranging from zero to a few tens of millimeters. After impact, the two magnets either revolve vigorously around the common center of mass or stop immediately, depending on the value of the impact parameter. Using a pick-up coil connected to an oscilloscope, the angular frequency for the rotating magnets was measured, and an estimate for the angular momentum was obtained. A high-speed video camera captured the impact and was used for measuring linear and angular velocities of the magnets. A very good agreement between the initial angular momentum before the impact and the final angular momentum of the revolving dumbbell is observed. The two rotating magnets, and the rotating electromagnetic field emanating from them, can also be viewed...

Crossing the dripline to N-11 using elastic resonance scattering

The level structure of the unbound nucleus N-11 has been studied by C-10+p elastic resonance scattering in inverse geometry with the LISE3 spectrometer at GANIL, using a C-10 beam with an energy of 9.0 MeV/ nucleon. An additional measurement was done at the A1200 spectrometer at MSU. The excitation function above the C-10+p threshold has been determined up to 5 MeV. A potential-model analysis revealed three resonance states at energies 1.27(-0.05)(+0.18) MeV (Gamma = 1.44 +/- 0.2 MeV), 2.01(-0.05)(+0.15) MeV (Gamma = 0.84 +/- 0.2 MeV), and 3.75 +/- 0.05 MeV (Gamma = 0.60 +/- 0.05 MeV) with the spin-parity assignments I-pi=1/2+,1/2,-,5/2+, respectively. Hence, N-11 is shown to have a ground state parity inversion completely analogous to its mirror partner Be-11. A narrow resonance in the excitation function at 4.33 +/- 0.05 MeV was also observed and assigned spin parity 3/2-.