Showing papers by "Ludvik Martinu published in 2011"
TL;DR: In this article, a dye-sensitized solar cell was constructed with the as-synthesized porous anatase TiO2 spheres as photoanodes, which exhibited a 5% energy conversion efficiency.
Abstract: Porous anatase TiO2 spheres with sizes ranging from 150 to 250 nm were synthesized by a rapid microwave treatment of spherical titanium glycolate precursors preformed via an ethylene glycol-mediated sol–gel process. The effects of various experimental conditions on the formation of titanium glycolate precursors and final TiO2 spheres were investigated. A dye-sensitized solar cell (DSSC) assembled with the as-synthesized porous TiO2 spheres as photoanodes exhibits a 5% energy conversion efficiency, which is almost 40% higher than that made of the standard commercial Degussa P25 TiO2 nanopowders.
118 citations
TL;DR: In this paper, a two-step method was proposed to optimize the nanoporous characteristics of TiO2 samples, enabling a higher charge and discharge capacity and a larger rate capability compared to dense materials.
74 citations
TL;DR: In this article, the effect of porosity on the physical and electrochromic properties of WO3 was studied by radio frequency magnetron sputtering and the best performing films were combined into a 27 layer quarter-wave interference filter which is shown to cycle between bleached and colored states, while providing attractive transmission.
55 citations
TL;DR: A design methodology for metameric filters based on the luminous efficiency curve of the human eye results in filters with a lower number of layers and hence lower fabrication costs, and with a higher color difference sensitivity under various illuminants and for nonstandard observers.
Abstract: In order to increase the anticounterfeiting performance of interference security image structures, we propose to implement an active component using an electrochromic material. This novel device, based on metamerism, offers the possibility of creating various surprising optical effects, it is more challenging to duplicate due to its complexity, and it adds a second level of authentication. By designing optical filters that match the bleached and colored states of the electrochromic device, one can obtain two hidden images—one appearing when the device is tilted, and the other one disappearing when the device is colored under an applied potential. Specifically, we present an example of a filter that is metameric with the colored state of the electrochromic device, demonstrate how the dynamic nature of the device offers more fabrication flexibility, and discuss its performance. We also describe a design methodology for metameric filters based on the luminous efficiency curve of the human eye: this approach results in filters with a lower number of layers and hence lower fabrication costs, and with a lower color difference sensitivity under various illuminants and for nonstandard observers.
21 citations
TL;DR: A significant role of the substrate material, of the interfaces, and of the nature and microstructure of the deposited films in long term stability under everyday application conditions is underline.
Abstract: Optical security devices applied to banknotes and other documents are exposed to different types of harsh environments involving the cycling of temperature, humidity, chemical agents, and tribomechanical intrusion. In the present work, we study the stability of optically variable devices, namely metameric interference filters, prepared by dual ion beam sputtering onto polycarbonate and glass substrates. Specifically, we assess the color difference as well as the changes in the mechanical properties and integrity of all-dielectric and metal–dielectric systems due to exposure to bleach, detergent and acetone agents, and heat and humidity. The results underline a significant role of the substrate material, of the interfaces, and of the nature and microstructure of the deposited films in long term stability under everyday application conditions.
9 citations
TL;DR: In this paper, the authors report on time and species-resolved plasma imaging analysis of high-power impulse magnetron sputtering discharge operated above a Cr target in pure oxygen.
Abstract: We report on time- and species-resolved plasma imaging analysis of high-power impulse magnetron sputtering discharge operated above a Cr target in pure oxygen. It was found that the discharge emission is dominated by oxygen species. No metal-dominated sputtering has been detected, in contrast to the discharges in Ar, N2, and N2/Ar mixtures investigated previously.
8 citations
Patent•
03 Jun 2011
TL;DR: In this article, an integrated security structure is provided employing an external source of energy to change the appearance of the structure rendering the structure more challenging to duplicate due to its complexity; the security structure includes a substrate forming part of a bank note, identification document, or other security device; an active device within the substrate changing color between at least two colors.
Abstract: An integrated security structure is provided employing an external source of energy to change the appearance of the structure rendering the structure more challenging to duplicate due to its complexity. The security structure includes a substrate forming part of a bank note, identification document, or other security device; an active device within the substrate changing color between at least two colors wherein a color of the substrate surrounding the active device matches one of the at least two colors to form a metameric device. At least one Interference Security Image Structure (ISIS) is configured to be metameric with a bleached state of the active device and is therefore invisible at normal incidence. Another ISIS is metameric with the colored state of the electrochromic device and consequently becomes invisible during coloration. When the whole device is tilted, both ISIS's change color while the rest of the device essentially remains the same.
6 citations