Laboratory Setup for Scanning-Free Grazing Emission X-ray Fluorescence.

Grazing incidence and grazing emission X-ray fluorescence spectroscopy (GI/GE-XRF) are techniques that enable nondestructive, quantitative analysis of elemental depth profiles with a resolution in the nanometer regime. A laboratory setup for soft X-ray GEXRF measurements is presented. Reasonable measurement times could be achieved by combining a highly brilliant laser produced plasma (LPP) source with a scanning-free GEXRF setup, providing a large solid angle of detection. The detector, a pnCCD, was operated in a single photon counting mode in order to utilize its energy dispersive properties. GEXRF profiles of the Ni-Lα,ß line of a nickel-carbon multilayer sample, which displays a lateral (bi)layer thickness gradient, were recorded at several positions. Simulations of theoretical profiles predicted a prominent intensity minimum at grazing emission angles between 5° and 12°, depending strongly on the bilayer thickness of the sample. This information was used to retrieve the bilayer thickness gradient. The results are in good agreement with values obtained by X-ray reflectometry, conventional X-ray fluorescence and transmission electron microscopy measurements and serve as proof-of-principle for the realized GEXRF setup. The presented work demonstrates the potential of nanometer resolved elemental depth profiling in the soft X-ray range with a laboratory source, opening, for example, the possibility of in-line or even in situ process control in semiconductor industry.

Diamond-Graphite Nanoplatelet Surfaces as Conductive Substrates for the Electrical Stimulation of Cell Functions.

The nanocarbon allotropes constitute valid alternatives when designing control and actuation devices for electrically assisted tissue regeneration purposes, gathering among them important characteristics such as chemical inertness, biocompatibility, extreme mechanical properties, and, importantly, low and tailorable electrical resistivity. In this work, coatings of thin (100 nm) vertically aligned nanoplatelets composed of diamond (5 nm) and graphite were produced via a microwave plasma chemical vapor deposition (MPCVD) technique and used as substrates for electrical stimulation of MC3T3-E1 preosteoblasts. Increasing the amount of N2 up to 14.5 vol % during growth lowers the coatings' electrical resistivity by over 1 order of magnitude, triggers the nanoplatelet vertical growth, and leads to the higher crystalline quality of the nanographite phase. When preosteoblasts were cultured on these substrates and subjected to two consecutive daily cycles of 3 µA direct current stimulation, enhanced cell proliferation and metabolism were observed accompanied by high cell viability. Furthermore, in the absence of DC stimulation, alkaline phosphatase (ALP) activity is increased significantly, denoting an up-regulating effect of preosteoblastic maturation intrinsically exerted by the nanoplatelet substrates.

A mixture toxicity approach to predict the toxicity of Ag decorated ZnO nanomaterials.

Nanotechnology is a rising field and nanomaterials can now be found in a vast variety of products with different chemical compositions, sizes and shapes. New nanostructures combining different nanomaterials are being developed due to their enhancing characteristics when compared to nanomaterials alone. In the present study, the toxicity of a nanostructure composed by a ZnO nanomaterial with Ag nanomaterials on its surface (designated as ZnO/Ag nanostructure) was assessed using the model-organism Daphnia magna and its toxicity predicted based on the toxicity of the single components (Zn and Ag). For that ZnO and Ag nanomaterials as single components, along with its mixture prepared in the laboratory, were compared in terms of toxicity to ZnO/Ag nanostructures. Toxicity was assessed by immobilization and reproduction tests. A mixture toxicity approach was carried out using as starting point the conceptual model of Concentration Addition. The laboratory mixture of both nanomaterials showed that toxicity was dependent on the doses of ZnO and Ag used (immobilization) or presented a synergistic pattern (reproduction). The ZnO/Ag nanostructure toxicity prediction, based on the percentage of individual components, showed an increase in toxicity when compared to the expected (immobilization) and dependent on the concentration used (reproduction). This study demonstrates that the toxicity of the prepared mixture of ZnO and Ag and of the ZnO/Ag nanostructure cannot be predicted based on the toxicity of their components, highlighting the importance of taking into account the interaction between nanomaterials when assessing hazard and risk.

Heat Dissipation Interfaces Based on Vertically Aligned Diamond/Graphite Nanoplatelets.

Crystalline carbon-based materials are intrinsically chemically inert and good heat conductors, allowing their applications in a great variety of devices. A technological step forward in heat dissipators production can be given by tailoring the carbon phase microstructure, tuning the CVD synthesis conditions. In this work, a rapid bottom-up synthesis of vertically aligned hybrid material comprising diamond thin platelets covered by a crystalline graphite layer was developed. A single run was designed in order to produce a high aspect ratio nanostructured carbon material favoring the thermal dissipation under convection-governed conditions. The produced material was characterized by multiwavelength Raman spectroscopy and electron microscopy (scanning and transmission), and the macroscopic heat flux was evaluated. The results obtained confirm the enhancement of heat dissipation rate in the developed hybrid structures, when compared to smooth nanocrystalline diamond films.

Luminescence studies on SnO2 and SnO2:Eu nanocrystals grown by laser assisted flow deposition.

Transparent conductive tin oxide materials have been a research topic extensively studied in recent years due to the great interest for many applications. However, in most of them, the pure form is rarely used, being usually modified by the incorporation of dopants. Selecting the most appropriate technique to develop nanocrystals of doped tin oxide and understanding the influence of dopant on the optical properties are the challenges that need to be addressed when envisaging devices. To fulfill this objective, the recently developed laser assisted flow deposition (LAFD) method is explored to grow SnO2 and SnO2:Eu nanocrystals. The morphology of these nanocrystals was investigated by scanning electron microscopy and well defined prismatic nanocrystals with sizes of ∼60 nm were identified. The crystalline quality assessed by X-ray diffraction measurements and Raman spectroscopy indicates that the produced nanocrystals are monophasic and crystallize in the tetragonal rutile structure. Steady state luminescence studies provide the information on the optical active centres in the SnO2 and SnO2:Eu nanocrystals. For the undoped samples only broad emission bands were observed by pumping the samples in the ultraviolet region. The broad emission was found to be an overlap of green and red optical centres as identified by temperature and excitation intensity dependent luminescence. The latter was found to exhibit an excitonic-related behaviour and the green emission was found to be of utmost importance to discuss the intraionic luminescence in the doped samples. For the SnO2:Eu nanocrystals the luminescence is dominated by the magnetic allowed (5)D0 → (7)F1 transition with the ions in almost undistorted centrosymmetric sites. The ion luminescence integrated intensity is found to increase with increasing temperatures being well accounted for a thermal population provided by the thermal quenching of the green band.

Stiff diamond/buckypaper carbon hybrids.

Given the specific properties of each carbon allotrope such as high electrical/thermal conductivity of multiwall carbon nanotubes (MWCNT) and extreme hardness and high inertness of nanocrystalline diamond (NCD), the integration of both carbon phases is highly desirable. Therefore, in the present work, buckypapers were produced from MWCNT suspensions and were used as free-standing substrates to be coated with NCD by microwave plasma chemical vapor deposition (MPCVD). The integration of both allotropes was successfully achieved, the CNTs being preserved after diamond growth as confirmed by µ-Raman spectroscopy and scanning electron microscopy (SEM). Additionally, a good linkage was observed, the CNTs remaining embedded within the NCD matrix, thus reinforcing the interface of the resulting hybrid structure. This was corroborated by bending tests in a modified nanohardness tester. The increase of the Young's modulus from 0.3 to 300 GPa after NCD growth enables the use of this material in a wide range of applications including microelectromechanical systems (MEMS). Additionally, a highly anisotropic electrical resistivity behavior was confirmed: low in-plane values were found for the CNT layer (1.39 × 10(-2) Ω.cm), while high transverse ones were measured for both the NCD coated and uncoated CNT buckypapers (8.13 × 10(5) and 6.18 × 10(2) Ω.cm, respectively).

Comparative study of multilayers used in monochromators for synchrotron-based coherent hard X-ray imaging.

A systematic study is presented in which multilayers of different composition (W/Si, Mo/Si, Pd/B(4)C), periodicity (from 2.5 to 5.5 nm) and number of layers have been characterized. In particular, the intrinsic quality (roughness and reflectivity) as well as the performance (homogeneity and coherence of the outgoing beam) as a monochromator for synchrotron radiation hard X-ray micro-imaging are investigated. The results indicate that the material composition is the dominating factor for the performance. By helping scientists and engineers specify the design parameters of multilayer monochromators, these results can contribute to a better exploitation of the advantages of multilayer monochromators over crystal-based devices; i.e. larger spectral bandwidth and high photon flux density, which are particularly useful for synchrotron-based micro-radiography and -tomography.

Identification of the receptor-binding regions of pb5 proteins of bacteriophages T5 and BF23.

The receptor-binding protein pb5(T5) of bacteriophage T5, when expressed from the oad gene cloned in pVK88 under the control of the phage T7 promoter/polymerase system, has been shown to bind to its FhuA receptor on the surface of E. coli, where it blocks FhuA for subsequent adsorption of T5 (Mondigler et al., FEMS Microbiol. Lett., 130, 293-300, 1995). In the present study the blocking assay has been applied to analyze the effects of several mutations within oad on the FhuA-binding properties of corresponding pb5 derivatives. Three classes of mutations were tested: (i) oad deletion derivatives, (ii) the oad mutation known to interfere with FhuA-binding of T5 (Heller and Bryniok, J. Virol., 49, 20-25, 1984), and (iii) linker-insertion mutations at a site very close to the oad mutation. Of the corresponding pb5 derivatives only one, a deletion derivative lacking the 153 C-terminal amino acids, was as active in the blocking assay as wild-type pb5(T5). All other derivatives were inactive or almost inactive. Isolation and molecular characterization of phenotypic revertants of T5oad showed that all revertants were true genotypic revertants of the oad mutation. The oad mutation has been identified as a G to T exchange resulting in a substitution of Gly for Trp at position 166 of pb5(T5). DNA sequencing of the hrs gene of bacteriophage BF23 and comparing the deduced amino acid sequence of pb5(BF23) with that of pb5(T5) revealed distinct regions of similarity and nonsimilarity. We propose that the receptor-binding region of pb5(T5) (pb5(BF23)) is formed by the region of nonsimilarity extending from amino acid position 89 (88) to position 305 (283).

Characterization of ultra smooth interfaces in Mo/Si-multilayers.

The interface structure of Mo/Si-multilayers prepared by Pulsed Laser Deposition (PLD) on Si substrates at room temperature has been investigated. Already the in-situ ellipsometer data acquired during film growth indicate a particular behaviour of this material system that is caused by reaction/diffusion processes of the condensing atoms. MoSi(x) interlayers are formed both at the Mo on Si- and at the Si on Mo-interfaces. The results of multilayer characterization carried out by SNMS and RBS show similar concentration profiles for both types of the interlayers. More detailed information about interface structure and morphology can be provided by HREM investigations. In the TEM micrographs of various multilayers prepared for different laser light wavelengths an improvement of layer stack quality, i.e. formation of abrupt interfaces, with increasing photon energy is observed. Layer stacks having almost ideally smooth interfaces were synthesized by UV-photon ablation. HREM micrographs of these multilayers show a pronounced separation of spacer and absorber layers. The roughness sigma(R) of the interfaces between the amorphous Si- and MoSi(x)-layers was determined by image analysis. On the average a level sigma(R) approximately 0.1 nm is found. There is no indication for roughness replication or amplification from interface to interface as it is known from the appropriate products of conventional thin film technologies.