Ladislav Fekete

Growth and characterization of nanodiamond layers prepared using the plasma-enhanced linear antennas microwave CVD system

Industrial applications of plasma-enhanced chemical vapour deposition (CVD) diamond grown on large area substrates, 3D shapes, at low substrate temperatures and on standard engineering substrate materials require novel plasma concepts. Based on the pioneering work of the group at AIST in Japan, the high-density coaxial delivery type of plasmas has been explored (Tsugawa et al 2006 New Diamond Front. Carbon Technol. 16 337–46). However, an important challenge is to obtain commercially interesting growth rates at very low substrate temperatures. In this work we introduce the concept of novel linear antenna sources, designed at Leybold Optics Dresden, using high-frequency pulsed MW discharge with a high plasma density. This type of pulse discharges leads to the preparation of nanocrystalline diamond (NCD) thin films, compared with ultra-NCD thin films prepared in (Tsugawa et al 2006 New Diamond Front. Carbon Technol. 16 337–46). We present optical emission spectroscopy data for the CH4–CO2–H2 gas chemistry and we discuss the basic properties of the NCD films grown.

Ultrashort pulse laser ablation of dielectrics: Thresholds, mechanisms, role of breakdown

In this paper, we establish connections between the thresholds and mechanisms of the damage and white-light generation upon femtosecond laser irradiation of wide-bandgap transparent materials. On the example of Corning Willow glass, evolution of ablation craters, their quality, and white-light emission were studied experimentally for 130-fs, 800-nm laser pulses. The experimental results indicate co-existence of several ablation mechanisms which can be separated in time. Suppression of the phase explosion mechanism of ablation was revealed at the middle of the irradiation spots. At high laser fluences, air ionization was found to strongly influence ablation rate and quality and the main mechanisms of the influence are analysed. To gain insight into the processes triggered by laser radiation in glass, numerical simulations have been performed with accounting for the balance of laser energy absorption and its distribution/redistribution in the sample, including bremsstrahlung emission from excited free-electron plasma. The simulations have shown an insignificant role of avalanche ionization at such short durations of laser pulses while pointing to high average energy of electrons up to several dozens of eV. At multi-pulse ablation regimes, improvement of crater quality was found as compared to single/few pulses.

High photocarrier mobility in ultrafast ion-irradiated In0.53Ga0.47As for terahertz applications

Optical pump–terahertz (THz) probe spectroscopy was used for investigation of electron dynamics in In0.53Ga0.47As films irradiated by heavy ions (Br+) at doses from 109 to 1012 cm−2. From the transient conductivity spectra, photoexcited electron lifetimes and mobilities were determined; their decrease is observed upon increase in the irradiation dose. At the highest dose, the material combines an electron lifetime of 0.46 ps with an exceptionally high photoexcited electron mobility of 3600 cm2 V−1 s−1. This last value is even higher than those reported for low-temperature-grown GaAs with similar electron lifetime. Due to its rather low band gap, heavy-ion irradiated In0.53Ga0.47As shows promising properties for the development of THz systems using telecommunication based technology.

Electrochemical Platform for the Detection of Transmembrane Proteins Reconstituted into Liposomes

The development of new methods and strategies for the investigation of membrane proteins is limited by poor solubility of these proteins in an aqueous environment and hindered by a number of other problems linked to the instability of the proteins outside lipid bilayers. Therefore, current research focuses on an analysis of membrane proteins incorporated into model lipid membrane, most frequently liposomes. In this work, we introduce a new electrochemical methodology for the analysis of transmembrane proteins reconstituted into a liposomal system. The proposed analytical approach is based on proteoliposomal sample adsorption on the surface of working electrodes followed by analysis of the anodic and cathodic signals of the reconstituted proteins. It works based on the fact that proteins are electroactive species, in contrast to the lipid components of the membranes under the given experimental conditions. Electroanalytical experiments were performed with two transmembrane proteins; the Na(+)/K(+)ATPase that contains transmembrane as well as large extramembraneous segments and the mitochondrial uncoupling protein 1, which is a transmembrane protein essentially lacking extramembraneous segments. Electrochemical analyses of proteoliposomes were compared with analyses of both proteins solubilized with detergents (C12E8 and octyl-PoE) and supported by the following complementary methods: microscopy techniques, protein activity testing, molecular model visualizations, and immunochemical identification of both proteins. The label-free electrochemical platform presented here enables studies of reconstituted transmembrane proteins at the nanomolar level. Our results may contribute to the development of new electrochemical sensors and microarray systems applicable within the field of poorly water-soluble proteins.

Adamantane substitutions: a path to high-performing, soluble, versatile and sustainable organic semiconducting materials

Novel ethyladamantyl solubilization side groups were found to induce π–π interactions between the conjugated cores through adamantyl–adamantyl stacking in soluble diketopyrrolopyrrole (DPP) derivatives. The closeness of the DPP cores amplifies charge transfer in the material, as far as the π–π interaction is a dominant charge-hopping pathway. As a result, tenfold enhancement of hole mobilities exceeding those obtained for insoluble derivatives was reached. Moreover, due to high crystallinity and co-planarity of the conjugated cores, electron transfer was preserved with a mobility of 0.2 cm2 V−1 s−1 for dithiophene-DPP. At the same time, the material remained soluble, which is a significant advantage for purification and processing. This approach can be universally applied for many types of semiconducting organic materials containing the imide motif, where solubilization is achieved by side-group substitution.

Molecular Adjuvants Based on Nonpyrogenic Lipophilic Derivatives of norAbuMDP/GMDP Formulated in Nanoliposomes: Stimulation of Innate and Adaptive Immunity

ABSTRACTPurposeThe aim of this work was to demonstrate an immunostimulatory and adjuvant effect of new apyrogenic lipophilic derivatives of norAbuMDP and norAbuGMDP formulated in nanoliposomes.MethodsNanoliposomes and metallochelating nanoliposomes were prepared by lipid film hydration and extrusion methods. The structure of the liposomal formulation was studied by electron microscopy, AF microscopy, and dynamic light scattering. Sublethal and lethal γ-irradiation mice models were used to demonstrate stimulation of innate immune system. Recombinant Hsp90 antigen (Candida albicans) bound onto metallochelating nanoliposomes was used for immunisation of mice to demonstrate adjuvant activities of tested compounds.ResultsSafety and stimulation of innate and adaptive immunity were demonstrated on rabbits and mice. The liposomal formulation of norAbuMDP/GMDP was apyrogenic in rabbit test and lacking any side effect in vivo. Recovery of bone marrow after sublethal γ-irradiation as well as increased survival of mice after lethal irradiation was demonstrated. Enhancement of specific immune response was demonstrated for some derivatives incorporated in metallochelating nanoliposomes with recombinant Hsp90 protein antigen.ConclusionsLiposomal formulations of new lipophilic derivatives of norAbuMDP/GMDP proved themselves as promising adjuvants for recombinant vaccines as well as immunomodulators for stimulation of innate immunity and bone-marrow recovery after chemo/radio therapy of cancer.

Resistance to protein adsorption and adhesion of fibroblasts on nanocrystalline diamond films: the role of topography and boron doping

Boron-doped nanocrystalline diamond (BNCD) films exhibit outstanding electrochemical properties that make them very attractive for the fabrication of electrodes for novel neural interfaces and prosthetics. In these devices, the physicochemical properties of the electrode materials are critical to ensure an efficient long-term performance. The aim of this study was to investigate the relative contribution of topography and doping to the biological performance of BNCD films. For this purpose, undoped and boron-doped NCD films were deposited on low roughness (LR) and high roughness (HR) substrates, which were studied in vitro by means of protein adsorption and fibroblast growth assays. Our results show that BNCD films significantly reduce the adsorption of serum proteins, mostly on the LR substrates. As compared to fibroblasts cultured on LR BNCD films, cells grown on the HR BNCD films showed significantly reduced adhesion and lower growth rates. The mean length of fibronectin fibrils deposited by the cells was significantly increased in the BNCD coated substrates, mainly in the LR surfaces. Overall, the largest influence on protein adsorption, cell adhesion, proliferation, and fibronectin deposition was due to the underlying sub-micron topography, with little or no influence of boron doping. In perspective, BNCD films displaying surface roughness in the submicron range may be used as a strategy to reduce the fibroblast growth on the surface of neural electrodes.Graphical Abstract

Thiophene-free diphenyl-amino-stilbene-diketo-pyrrolo-pyrrole derivatives as donors for organic bulk heterojunction solar cells

An extended study on a group of four soluble diphenyl-amino-stilbene based diphenyl-diketopyrrolo- pyrrole molecules has been carried out. Using the materials in thin-film transistors it was shown that the above-mentioned compounds can be successfully used as donors in organic photovoltaic devices. Influence of the molecular symmetry and solubilizing chain on the morphology and solar cell performance are described. It was shown that a shorter and non-branched ethyl acetate chain leads to higher charge carrier mobility, short circuit current, and better fill factor. After the basic optimization, a power conversion efficiency of about 1.5 % was reached. This, to the best of our knowledge, is the highest reported efficiency of thiophene-free small-molecule diketo-pyrrolopyrroles.

Ultrafast carrier response of Br+-irradiated In0.53Ga0.47As excited at telecommunication wavelengths

We present results of infrared pump—terahertz probe experiments applied to a set of In0.53Ga0.47As films irradiated with heavy ions (Br+) at doses from 109 to 1012 cm−2. Photoexcitation at 1400 nm (0.89 eV) allowed us to characterize the response close to telecommunications’ wavelengths whilst avoiding the intervalley carrier scattering observed when a shorter wavelength excitation is used. The excitation fluence was varied in our experiments in order to characterize the dynamics in detail: the lifetimes and mobilities of both electrons and holes were retrieved, and the trap filling and carrier diffusion were clearly observed. The In0.53Ga0.47As film irradiated by the dose of 1012 cm−2 exhibits simultaneously ultrashort electron lifetime (∼300 fs) and very high electron mobility (2800 cm2V−1s−1). These findings are particularly important for the design of terahertz emitters controlled by lasers operating at standard telecommunication wavelengths.

Ultrashort-pulse laser processing of transparent materials: insight from numerical and semi-analytical models

Interaction of ultrashort laser pulses with transparent materials is a powerful technique of modification of material properties for various technological applications. The physics behind laser-induced modification phenomenon is rich and still far from complete understanding. We present an overview of our models developed to describe processes induced by ultrashort laser pulses inside and on the surface of bulk glass. The most sophisticated model consists of two parts. The first part solves Maxwell’s equations supplemented by the rate and hydrodynamics equations for free electrons. The model resolves spatiotemporal dynamics of free-electron population and yields the absorbed energy map. The latter serves as an initial condition for thermoelastoplastic simulations of material redistribution. The simulations performed for a wide range of irradiation conditions have allowed to clarify timescales at which modification occurs after single laser pulses. Simulations of spectrum of laser light scattered by laser-generated plasma revealed considerable blueshifting which increases with pulse energy. To gain insight into temperature evolution of a glass material under the surface irradiation conditions, we employ a model based on the rate equation describing free electron generation coupled with the energy equations for electrons and lattice. Swift heating of electron and lattice subsystems to extremely high temperatures at fs timescale has been found at laser fluences exceeding the threshold fluence by 2-3 times that can result in efficient bremsstrahlung emission from the irradiation spot. The mechanisms of glass ablation with ultrashort laser pulses are discussed by comparing with the experimental data. Finally, a model is outlined, developed for multi-pulse irradiation regimes, which enables gaining insight into the roles of defects and heat accumulation.