The effect of the external lateral electric field on the luminescence intensity of InAs/GaAs quantum dots

We report on low-temperature microphotoluminescence (μ-PL) measurements of InAs/GaAs quantum dots (QDs) exposed to a lateral external electric field. It is demonstrated that the QDs’ PL signal could be increased severalfold by altering the external and/or the internal electric field, which could be changed by an additional infrared laser. A model which accounts for a substantially faster lateral transport of the photoexcited carriers achieved in an external electric field is employed to explain the observed effects. The results obtained suggest that the lateral electric fields play a major role for the dot luminescence intensity measured in our experiment—a finding which could be used to tailor the properties of QD-based optoelectronic applications. The text was submitted by the authors in English.     

Laser-induced ablation of polymers using a patterned dopant generated from a leuco-dye precursor via flood exposure: A “portable conformable mask” approach to laser ablation of PMMA at 351 nm

A two-stage laser ablation process is described, which initially generates a laser-light absorbing image from a conventional photolithographic mask via a UV-flood exposure step. For this purpose a colorless precursor of a dye, i.e., itsleuco form, is imbedded into the polymer to be ablated as a dopant. For poly(methyl methacrylate) as such a polymer, triphenylmethanol, the leuco precursor for the corresponding triphenylmethyl dye represents a good choice for ablation with excimer lasers operating at the wavelength 351 nm. In this fashion conventional masks and exposure tools of UV-photolithography may be used in combination with laser ablation. The resulting images are characterized by a good contrast and reasonably sharp contours. The photochemical mechanism and additional aspects of this two-step process, which resembles the portable conformal mask approach of photolithography, are outlined.     

Efficient and stereoselective synthesis of bicyclo[3.2.1]octan-8-ones: synthesis and palladium-catalyzed isomerization of functionalized 2-vinyl-2,3,3a,4,5,6-hexahydro-2,3-benzofurans

A new C,O-cyclodialkylation of dilithiated cyclic beta-keto esters and beta-keto sulfones with 1,4-dibromo-2-butene is reported which results in regio- and diastereoselective formation of 2-vinyl-2,3,3a,4,5,6-hexahydro-2,3-benzofurans. The products could be efficiently transformed into functionalized bicyclo[3.2.1]octan-8-ones by a palladium-catalyzed rearrangement reaction. In case of sulfone derivatives, this rearrangement proceeds with high stereospecifity to give exclusively the endo-configured diastereomers. The bicyclo[3.2.1]octane skeleton is present in a large number of pharmacologically important natural products.     

Modelling and design of a novel air-spring for a suspension seat

Air-springs used in conjunction with auxiliary volumes provide both spring stiffness and damping. The damping is introduced through the flow restriction connecting the two air volumes. This article presents a simplified model of an air-spring with an auxiliary volume derived from first principles for simulation and design of an air-spring coupled to an auxiliary volume for a suspension seat. Tests were performed on an experimental apparatus to validate the model. The simulation model of the air-spring and auxiliary volume followed the trend predicted by the literature but showed approximately 27% lower transmissibility amplitude and 21% lower system natural frequency than that obtained by tests when using large diameter flow restrictions. This inaccuracy is assumed to be introduced by the simplified mass transfer equations defining the flow restriction between air-spring and auxiliary volume. The model showed closer correlation to the experimental results when the auxiliary volume size was decreased by two-thirds of the volume actually used for the experiment. A procedure, using the developed simulation model, for the design of a prototype air-spring and auxiliary volume, is presented for application in a typical articulated or rigid frame dump truck. The goal of the study was to design a suspension seat for this application and to obtain a SEAT value below 1.1. The design was optimised by varying auxiliary volume size and flow restriction diameters for different loads. A SEAT value of less than 0.9 was achieved, clearly indicating the effectiveness of using an auxiliary volume with an air-spring as seat suspension.     

Linearly polarized photoluminescence from an ensemble of wurtzite GaN/AlN quantum dots

Microphotoluminescence from GaN/AlN quantum dots grown by molecular beam epitaxy on sapphire substrates along the (0001) axis has been studied. To produce quantum dots of different average sizes and densities, the nominal amount of deposited GaN has been varied from 1 to 4 ML. The density of the quantum dots was about 10¹¹ cm⁻², which corresponded to about 10³ quantum dots excited in the experiments. The photo-luminescence from the quantum dots was linearly polarized and the maximum polarization degree (15%) has been observed for the sample with the lowest amount of deposited GaN. The photoluminescence intensity from this sample under continuous laser excitation decreased by more than two orders of magnitude for about 30 min and then stabilized. The photoluminescence intensity from other samples under continuous excitation remained constant. We suggest that a rather high polarization degree is caused by anisotropy in the strain and shape of the quantum dots formed near the dislocations, which also act as the centers of nonradiative recombination.     

Fluidic and air-stable supported lipid bilayer and cell-mimicking microarrays

As drug delivery, therapy, and medical imaging are becoming increasingly cell-specific, there is a critical need for high fidelity and high-throughput screening methods for cell surface interactions. Cell membrane-mimicking surfaces, i.e., supported lipid bilayers (SLBs), are currently not sufficiently robust to meet this need. Here we describe a method of forming fluidic and air-stable SLBs through tethered and dispersed cholesterol groups incorporated into the bottom leaflet. Achieving air stability allows us to easily fabricate SLB microarrays from direct robotic spotting of vesicle solutions. We demonstrate their application as cell membrane-mimicking microarrays by reconstituting peripheral as well as integral membrane components that can be recognized by their respective targets. These demonstrations establish the viability of the fluidic and air-stable SLB platform for generating content microarrays in high throughput studies, e.g., the screening of drugs and nanomedicine targeting cell surface receptors.