Dielectric elastomer actuator (DEA) based flexible and stretchable electronics have attracted considerable attention over the past decades. The electrode components play an important role in the DEA performance. In this work, we studied how the incorporation of soft matrices in the electrodes affects the DEA actuation. The ultrasonic spraying was used to fabricate multiwall carbon nanotube (MWCNT) based electrodes for DEA. The results indicated that the addition of a water-soluble block polymer and silicone gel (acting as the soft matrices) could improve the actuation of the DEA with neat MWCNT electrodes by ~10% and ~24%, respectively. An inkjet printing ink, consisting of polydimethylsiloxane (PDMS), carbon black (CB) and chlorobenzene, was further developed. The stability, particle size, resistance, and morphology of 1-3 printing layers were characterized. The DEA with the inkjet-printed CB/PDMS electrodes showed 50% area stain at 2500 V, which is higher than the actuation with neat CB powder or CNT electrodes reported previously. Both results of the ultrasonic spraying and inkjet printing confirmed that the incorporation of soft matrices in the electrodes is helpful for DEA actuation.
Networks of silver nanowires (AgNWs) are promising candidates for transparent conducting electrodes in organic photovoltaics (OPV), as they achieve similar performance as the commonly used indium tin oxide (ITO) at lower cost and increased flexibility. The initial sheet resistance (Rs) of AgNW electrodes typically needs to be reduced by a post-annealing step (90 min@200 °C), being detrimental for processing on polymeric substrates.
We present novel low temperature-based methods to integrate AgNWs in organic small molecule-based photovoltaics, either as transparent and highly conductive bottom-electrode or, for the first time, as spray-coated AgNW top-electrode. The bottom-electrodes are prepared by organic matrix assisted low-temperature fusing. Here, selected polymers are coated below the AgNWs to increase the interaction between NWs and substrate. In comparison to networks without these polymeric sublayers, the Rs is reduced by two orders of magnitude.
AgNW top-electrodes are realized by dispersing modified high-quality AgNWs in inert solvents, which do not damage small molecule layers. Accordingly, our AgNW dispersion can be spray-coated onto all kind of OPV devices. Both bottom- and top-electrodes show a Rs of <11 Ω/ at >87 % transparency directly after spray-coating at very low substrate temperatures of <80 °C. We also demonstrate the implementation of our AgNW electrodes in organic solar cells. The corresponding devices show almost identical performance compared to organic solar cells exploiting ITO as bottom or thermally evaporated thin-metal as top-electrode.
Further improvement of infrared single photon sources is a major challenge for future implementations of quantum information and quantum communication applications. In this paper, we give further insight into a recently presented, conceptually novel method for the generation of single photons.1 The method is of particular interest for spectral domains where stable room temperature single photon sources are not available. For example, this is the presently the case for the near-infrared. This wavelength regime is important for data transfer over long distances where optical losses in fibers are minimal. The presented method is based on the following idea. The fundamental key requirement for single photon generation is the generation of a single excitation in an optically active system. It is not the presence of a single quantum system. The presented method is applied to realize a stable, non-blinking, room temperature infrared single photon source by converting visible single photons from a defect center in diamond to the near infrared. For the presented implementation, the theoretical conversion efficiency was estimated to be 26 %. In a first prove of principle experiment, a conversion efficiency of 0.1 % was achieved.
In this work, we demonstrate optical functionalities obtained with CdTe nanocrystals embedded in polystyrene.
These functionalities are based on our experimentally observed large, saturable, and controlled nonlinear optical
properties of CdTe nanocrystals, in the case of strong quantum confinement and near resonant interaction with the
excitation light. Our investigation considers the optical limiting functionality, presenting experimental proof of concepts.
These types of functionalities are of special interest for integrated optical quantum dots devices with applications in
imaging and telecommunications.
A general synthetic strategy for the synthesis of nanocrystals of both visible and near infrared emitting materials is
introduced. Further, the potential for these materials to be employed in a wide variety of applications is discussed.
The synthesis of strongly luminescing semiconductor nanocrystals reported is based on a wet-chemical approach. The
use of aqueous solutions and the avoiding of dangerous and unstable precursors make this synthetic approach to be easily
up-scaleable. The reaction yields are approaching gram amounts of the dried product and are limited solely by the
laboratory facilities and thus may be further increased by using industrial equipments. The nanocrystals obtained by this
route are strongly luminescing and suitable for various assembling procedures allowing the creation of core-shell
spherical and thin-film composites, that are promising for photonic and optoelectronic applications. New assembly
procedures allowing template-based formations of different types of metal-dielectric and porous metal nanostructures are
presented.
A general synthetic strategy for the synthesis of the near-infrared emitting materials, colloidal HgTe and PbX (where X = S, Se, Te) nanocrystals (NCs) is introduced. Further, the potential for these materials to be employed in applications such as light emitting diodes is discussed.
We describe how two different kinds of ordered bimetallic nanostructures (Au/Pt, Au/Ag) with hierarchical porosity, such as macroporous nanostructures and nanostructures constructed from hollow spheres, can be selectively and conveniently fabricated by a general template technique on silicon wafers and on glass substrates, and how such nanostructures can find application in catalyst or surface-enhanced Raman scattering (SERS) substrates.
A heterojunction between two 3-dimensional photonic crystals has been realized by interfacing two opal films of different lattice constants. The interface-related transmission minimum has been observed in the frequency range between two directional lowest-order bandgaps of the hetero-opal constituents. The interface transmission minimum has been modelled numerically and tentatively explained by formation of the standing wave across the photonic hetero-crystal due to matching of group velocities of optical modes in both parts at this frequency.
We present a photoluminescence and photoluminescence excitation study of CdTe quantum dots, prepared via a novel organometallic approach. The global photoluminescence (excited at the energy above the absorption edge) showed a red shift of 75 meV with respect to the first absorption peak. This band edge emission was found to be strongly dependent on the excitation photon. Resonant emission spectra showed a pronounced spectral shift and line narrowing with decreasing excitation energy. The resonant Stokes shifts were extracted from photoluminescence and photoluminescence excitation data. The minimum magnitude of the resonant Stokes shift of 14 meV was obtained at room temperature.
By applying a simple phenomenological model in the analysis of transient photocurrents arising in particulate ZnO films, several information are gained concerning the transport of electrons through the nanoporous network. From the results of experiments using electrodes with different thicknesses of the ZnO film, the driving force of the transport is identified as a gradient in the electrochemical potential across the electrode. Furthermore, since no effect of the ambient temperature on the transport dynamics at positive potentials is observed, an tunneling mechanism is proposed for the basic electron exchange between adjacent particles. By changing the average size of the ZnO particles, information about the height and the width of the potential barrier are drawn for the different ensembles of nanoparticles.
Mesoscopic structures with characteristic size either of the order of an electron de Broglie wavelength in semiconductors (1 - 10 nm) or close to the optical photon wavelength (100 - 1000 nm) exhibit non-trivial properties due to modified electron or photon density of states. 3D spatial confinement of electrons in nanocrystals (quantum dots) results in size- dependent energies and probabilities of optical transitions. The photon density of states can be modified in structures with strong modulation of the refractive index in three dimensions (photonic crystals) and in microcavities. Because of the essentially different electron and photon wavelengths, electron and photon densities of states can be engineered separately within the same mesostructure. We report here on synthesis and properties of semiconductor quantum dots corresponding to the strong confinement limit embedded either in a photonic crystal exhibiting a pseudogap or in a planar microcavity. We show that the interplay of electron and photon confinement within the same structure opens a way towards novel light sources with controllable spontaneous emission. Spontaneous emission which is not an inherent property of quantum systems but a result of their interaction with electromagnetic vacuum can be either promoted or inhibited depending on the modification of the photon density of states in a given mesostructure.
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