Life in the Atacama — Year 2: Geologic reconnaissance through long-range roving and implications on the search for life

The Life in the Atacama-2004 project, which included geological, morphological, and mineralogical mapping through combined satellite, field-based, and microscopic perspectives and long-range roving, led to the localization of potential habitats

Spectroscopic results from the Life in the Atacama (LITA) project 2004 field season

Analysis of spectroscopy datasets from rover field tests in the Atacama Desert (Chile), focusing on the composition of the surface and identification of potential habitats for life

A Picture of the Research Field of Doctoral Education from the Students’ Perspectives : Studies Using Questionnaires and Scales

Peer reviewe

PHOTOELECTRIC EFFECTS IN HIGH-RESISTIVITY EuSe

On a étudié les propriétés des monocristaux d'EuSe rouge transparent de haute résistivité au moyen de la photoconductivité et de la tension de photodiffusion avec des photons d'energie plus basse ou égale à celle-ci de la bande interdite Eg. Les pointes principales des spectres obtenus par la phoconductiuité ou photovoltaïque se trouvent à l'énergie de 1,85 eV équivalente à Eg dans EuSe. On a trouvé deux niveaux de défaut aux énergies 1,3 eV et 1,67 eV respectivement.The properties of red- transparent high-resistivity EuSe single crystals have been studied by means of the photoconductivity and photodiffusive voltage with photon energies less or equal to the forbidden energy gap Eg. In both the photoconduction and photovoltage spectra the main peak is situated at a photon energy of 1.85 eV corresponding to Eg in EuSe. Two defect levels were found at photon energies 1.3 and 1.67 eV

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

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

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

Electric field redistribution and electroluminescence response time in polymeric light-emitting diodes

The electric field redistribution due to injected and trapped charge carriers in Langmuir-Blodgett (LB) films of poly(3-hexylthiophene) (P3HT) sandwiched between indium tin oxide and aluminum (Al) electrodes as function of applied voltage has been studied using charge collection measurements by the time-of-flight technique. For μ tE<d (the drift distance shorter than the interelectrode distance) the amount of the collected photocharge is a function of electric field near the Al electrode and has been used to probe the time evolution of it. The response time for the field to redistribute inside the P3HT LB film was found to be of the order of 5-200 μs, in good agreement with the delay time observed in time-resolved electroluminescence measurements in light-emitting diodes (LED) of similar LB films. We suggest a model for the response times in organic LEDs based on these results