CNTs in Optoelectronic Devices: New Structural and Photophysical Insights on Porphyrin‐DWCNTs Hybrid Materials

The preparation and physical characterization of diverse porphyrin‐derived double‐walled carbon nanotubes (DWCNTs) conjugates are described. A porphyrin molecule is covalently linked and physically adsorbed to COOH‐derived DWCNTs. The photophysical properties of all porphyrin‐CNTs derivatives are studied in solution and in polymeric matrices. Definitive experimental evidence for photoinduced electron and/or energy transfer processes involving the porphyrin chromophores and the CNT wall is not obtained, but solid‐state UV‐vis absorption profiles display electronic transitions fingerprinting J‐ and H‐ type aggregates, where porphyrin molecules intermolecularly interact “head‐to‐tail” and “face‐to‐face”, respectively. In parallel, molecular modeling based on force‐field simulations is performed to understand the structure of the porphyrin‐CNTs interface and the nature of the interactions between the porphyrins and the DWCNTs. Finally, multilayered ‐ type devices are fabricated with the aim of investigating the interaction of the porphyrin‐derived DWCNTs with poly(3‐hexylthiophene)‐pyrene matrices containing small amounts of 1‐[3‐(methoxycarbonyl)propyl]‐1‐phenyl‐[6.6]C₆₁.     

Toward forced assembly of in situ low‐density polyethylene composites reinforced with low‐Tg phosphate glass fibers: Effects of matrix crystallization and shear deformation

This study is aimed at investigating the feasibility of using facile forced assembly methods (temperature and shear strain‐induced orientation of the dispersed phase) to create novel “in situ” low‐density polyethylene (LDPE) composites containing fibrillar inorganic phosphate glass (P‐glass) reinforcing phase during the composite fabrication. Clearly, the experimental results show that unique thermo‐rheological conditions exist under which the “in situ” LDPE composites containing fibrillar P‐glass with potential enhanced benefits can be prepared. DSC results showed that the P‐glass has a moderate nucleating effect on the LDPE crystallization that restricts in situ deformation of the P‐glass during the composite fabrication. Rheo‐optical data showed that a 5% P‐glass/95% LDPE hybrid composition, subjected to a shear rate of 20 s^?1 in the parallel plate configuration and 130°C gave “in situ” LDPE composite samples with the largest amount of P‐glass fibers in the limited range of experimental conditions used. This study may spur interests in a better understanding of the potential for the “in situ” reinforcement of engineering plastics with inorganic P‐glasses, at the molecular level, to produce novel “in situ” polymer composites with very high aspect ratios of the reinforcing inorganic phase. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Electrostatic-spray ionization mass spectrometry

An electrostatic-spray ionization (ESTASI) method has been used for mass spectrometry (MS) analysis of samples deposited in or on an insulating substrate. The ionization is induced by a capacitive coupling between an electrode and the sample. In practice, a metallic electrode is placed close to but not in direct contact with the sample. Upon application of a high voltage pulse to the electrode, an electrostatic charging of the sample occurs leading to a bipolar spray pulse. When the voltage is positive, the bipolar spray pulse consists first of cations and then of anions. This method has been applied to a wide range of geometries to emit ions from samples in a silica capillary, in a disposable pipet tip, in a polymer microchannel, or from samples deposited as droplets on a polymer plate. Fractions from capillary electrophoresis were collected on a polymer plate for ESTASI MS analysis.     

Aberration-free ultrathin flat lenses and axicons at telecom wavelengths based on plasmonic metasurfaces

The concept of optical phase discontinuities is applied to the design and demonstration of aberration-free planar lenses and axicons, comprising a phased array of ultrathin subwavelength-spaced optical antennas. The lenses and axicons consist of V-shaped nanoantennas that introduce a radial distribution of phase discontinuities, thereby generating respectively spherical wavefronts and nondiffracting Bessel beams at telecom wavelengths. Simulations are also presented to show that our aberration-free designs are applicable to high-numerical aperture lenses such as flat microscope objectives.     

Electro-elastic tuning of single particles in individual self-assembled quantum dots

We investigate the effect of uniaxial stress on InGaAs quantum dots in a charge tunable device. Using Coulomb blockade and photoluminescence, we observe that significant tuning of single particle energies (≈-0.22 meV/MPa) leads to variable tuning of exciton energies (+18 to -0.9 μeV/MPa) under tensile stress. Modest tuning of the permanent dipole, Coulomb interaction and fine-structure splitting energies is also measured. We exploit the variable exciton response to tune multiple quantum dots on the same chip into resonance.     

Hue discrimination, unique hues and naming

The hue discrimination curve (HDC) that characterizes performances over the entire hue circle was determined by using sinusoidally modulated spectral power distributions of 1.5 c/300 nm with fixed amplitude and twelve reference phases. To investigate relationship between hue discrimination and appearance, observers further performed a free color naming and unique hue tasks. The HDC consistently displayed two minima and two maxima; discrimination is optimal at the yellow/orange and blue/magenta boundaries and pessimal in green and in the extra-spectral magenta colors. A linear model based on Müller zone theory correctly predicts a periodical profile but with a phase-opponency (minima/maxima at 180° apart) which is inconsistent with the empirical HDC's profile.     

Nonradiative recombination at dislocations in III–V compound semiconductors

Carrier recombination at individual dislocations is investigated for the case of misfit dislocations at a heterojunction between Ga_1–xAl_xAs_1–yP_y epitaxial layers. Through the combined use of scanning transmission electron microscopy, electron beam induced current and cathodoluminescence analysis, it is shown that the non-radiative and radiative recombination properties of dislocations are associated with their fine crystallographic configuration. The edge Lomer-Cottrell dislocation is found to be electrically neutral. The absence of carrier recombination strongly suggests that core reconstruction may be important in eliminating dangling bonds and kink sites along the core of these dislocations. An undissociated dislocation with a Burgers vector b =1/2a〈110〉 is proposed as the more likely configuration for the edge Lomer-Cottrell dislocation. An asymmetry in the nonradiative recombination properties and crystallographic structure of the 60° dislocation is also reported and discussed.     

New methodology for localizing faults in programmable and commercial circuits

Localizing faults in integrated circuits when the CAD information is unavailable is a critical operation for failure analysis. IFA (Image Fault Analysis), a method based on the comparison of voltage contrast images is capable of offering a positive result. However, the time required for the localization can be excessive. For this reason, we have developed a methodology to insure the minimal time necessary for localization. We will present this new methodology and an application on an Altera programmable circuit.