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- ItemCharacteristics of austenitic stainless steel nitrided in a hybrid glow discharge plasma(New York, NY : Springer, 2009) Oliveira, R.M.; Ueda, M.; Silva, L.L.G.; Reuther, H.; Lepienski, C.M.A nitriding process based on two distinct nitrogen glow discharge modes, with sample temperatures ranging from 380 °Cto480°C, was employed to treat the surface of austenitic stainless steel (SS 304). The temperature is controlled exclusively by switching the operation conditions of the discharges. First mode of operation is the conventional one, named cathodic, which runs at higher pressure values (1 mbar) in comparison to the second mode, named anodic, which runs at the pressure range of 10-3 -10-2 mbar. Cathodic mode is used to quickly heat the sample holder, by the high ion flux. On the other hand, in the anodic mode, due to the lower operation pressure, higher effective ion acceleration takes place, which allows deeper ion implantation into the sample surface. This hybrid process was thoroughly explored regarding the duty cycle and conditions of operation, to achieve optimal performance of the treatments, which led to the attainment of surface hardness for samples of AISI SS 304 as high as 20 GPa and improvements including higher elastic modulus and resistance against corrosion. Detailed comparison among samples treated by this process with others treated by conventional method was done using nanoindentation, Auger Electron Spectroscopy (AES) and corrosion resistance testing.
- ItemCarbon nanotubes filled with ferromagnetic materials(Basel : MDPI, 2010) Weissker, Uhland; Hampel, Silke; Leonhardt, Albrecht; Büchner, BerndCarbon nanotubes (CNT) filled with ferromagnetic metals like iron, cobalt or nickel are new and very interesting nanostructured materials with a number of unique properties. In this paper we give an overview about different chemical vapor deposition (CVD) methods for their synthesis and discuss the influence of selected growth parameters. In addition we evaluate possible growth mechanisms involved in their formation. Moreover we show their identified structural and magnetic properties. On the basis of these properties we present different application possibilities. Some selected examples reveal the high potential of these materials in the field of medicine and nanotechnology.
- ItemPhase transition and anomalous low temperature ferromagnetic phase in Pr 0.6Sr 0.4MnO 3 single crystals(New York, NY : Springer Science + Business Media B.V., 2009) Rößler, S.; Harikrishnan, S.; Naveen Kumar, C.M.; Bhat, H.L.; Elizabeth, S.; Rößler, U.K.; Steglich, F.; Wirth, S.We report on the magnetic and electrical properties of Pr 0.6Sr 0.4MnO 3 single crystals. This compound undergoes a continuous paramagnetic-ferromagnetic transition with a Curie temperature T C301 K and a first-order structural transition at T S64 K. At T S, the magnetic susceptibility exhibits an abrupt jump, and a corresponding small hump is seen in the resistivity. The critical behavior of the static magnetization and the temperature dependence of the resistivity are consistent with the behavior expected for a nearly isotropic ferromagnet with short-range exchange belonging to the Heisenberg universality class. The magnetization (M-H) curves below T S are anomalous in that the virgin curve lies outside the subsequent M-H loops. The hysteretic structural transition at T S as well as the irreversible magnetization processes below T S can be explained by phase separation between a high-temperature orthorhombic and a low-temperature monoclinic ferromagnetic phase.
- ItemLarge superplastic strain in non-modulated epitaxial Ni-Mn-Ga films(Amsterdam : Elsevier, 2010) Yeduru, S.R.; Backen, A.; Fahler, S.; Schultz, L.; Kohl, M.The phase transformation and superplastic characteristics of free-standing epitaxial Ni-Mn-Ga stripes are reported. The stripes are prepared by micromachining a 1 μm thick Ni-Mn-Ga film sputter-deposited on a single crystalline MgO (100) substrate using optical lithography and a Chromium-based sacrificial layer technology. The stripes are oriented at angles of 0 and 45 degrees with respect to the Ni-Mn-Ga unit cell. Electrical resistance versus temperature characteristics reveal a reversible thermally induced phase transformation between 169°C and 191°C. Stress-strain measurements are performed with the stress applied along the [100]Ni-Mn-Ga as well as [110]Ni-Mn-Ga direction. Depending on the orientation, the twinning stress ranges between 25 and 30 MPa, respectively. For the [100] Ni-Mn-Ga and [110]Ni-Mn-Ga directions, superplastic behaviour with a strain plateau of 12 % and 4% are observed, respectively, indicating stress-induced reorientation of non-modulated martensite variants.
- ItemGain of a 500-fold sensitivity on an intravital MR Contrast Agent based on an endohedral Gadolinium-Cluster-Fullerene-Conjugate: A new chance in cancer diagnostics(Sydney : Ivyspring, 2010) Braun, Klaus; Dunsch, Lothar; Pipkorn, Ruediger; Bock, Michael; Baeuerle, Tobias; Yang, Shangfeng; Waldeck, Waldemar; Wiessler, ManfredAmong the applications of fullerene technology in health sciences the expanding field of magnetic resonance imaging (MRI) of molecular processes is most challenging. Here we present the synthesis and application of a GdxSc3-xN@C80-BioShuttle-conjugate referred to as Gd-cluster@-BioShuttle, which features high proton relaxation and, in comparison to the commonly used contrast agents, high signal enhancement at very low Gd concentrations. This modularly designed contrast agent represents a new tool for improved monitoring and evaluation of interventions at the gene transcription level. Also, a widespread monitoring to track individual cells is possible, as well as sensing of microenvironments. Furthermore, BioShuttle can also deliver constructs for transfection or active pharmaceutical ingredients, and scaffolding for incorporation with the host's body. Using the Gd-cluster@-BioShuttle as MRI contrast agent allows an improved evaluation of radio- or chemotherapy treated tissues.
- ItemTowards deterministically controlled InGaAs/GaAs lateral quantum dot molecules(College Park, MD : Institute of Physics Publishing, 2008) Wang, L.; Rastelli, A.; Kiravittaya, S.; Atkinson, P.; Ding, F.; Bof Bufon, C.C.; Hermannstädter, C.; Witzany, M.; Beirne, G.J.; Michler, P.; Schmidt, O.G.We report on the fabrication, detailed characterization and modeling of lateral InGaAs quantum dot molecules (QDMs) embedded in a GaAs matrix and we discuss strategies to fully control their spatial configuration and electronic properties. The three-dimensional morphology of encapsulated QDMs was revealed by selective wet chemical etching of the GaAs top capping layer and subsequent imaging by atomic force microscopy (AFM). The AFM investigation showed that different overgrowth procedures have a profound consequence on the QDM height and shape. QDMs partially capped and annealed in situ for micro- photoluminescence spectroscopy consist of shallow but well-defined quantum dots (QDs) in contrast to misleading results usually provided by surface morphology measurements when they are buried by a thin GaAs layer. This uncapping approach is crucial for determining the QDM structural parameters, which are required for modeling the system. A single-band effective-mass approximation is employed to calculate the confined electron and heavy-hole energy levels, taking the geometry and structural information extracted from the uncapping experiments as inputs. The calculated transition energy of the single QDM shows good agreement with the experimentally observed values. By decreasing the edge-to-edge distance between the two QDs within a QDM, a splitting of the electron (hole) wavefunction into symmetric and antisymmetric states is observed, indicating the presence of lateral coupling. Site control of such lateral QDMs obtained by growth on a pre-patterned substrate, combined with a technology to fabricate gate structures at well-defined positions with respect to the QDMs, could lead to deterministically controlled devices based on QDMs. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.
- ItemNanostructured silver substrates with stable and universal sers properties: Application to organic molecules and semiconductor nanoparticles(New York, NY [u.a.] : Springer, 2010) Chursanova, M.V.; Dzhagan, V.M.; Yukhymchuk, V.O.; Lytvyn, O.S.; Valakh, M.Y.; Khodasevich, I.A.; Lehmann, D.; Zahn, D.R.T.; Waurisch, C.; Hickey, S.G.Nanostructured silver films have been prepared by thermal deposition on silicon, and their properties as SERS substrates investigated. The optimal conditions of the post-growth annealing of the substrates were established. Atomic force microscopy study revealed that the silver films with relatively dense and homogeneous arrays of 60-80-nm high pyramidal nanoislands are the most efficient for SERS of both organic dye and inorganic nanoparticles analytes. The noticeable enhancement of the Raman signal from colloidal nanoparticles with the help of silver island films is reported for the first time. © 2009 The Author(s).
- ItemOn the efficiency of bile salt for stable suspension and isolation of single-walled carbon nanotubes-spectroscopic and microscopic investigations(Berlin : Springer Verlag, 2010) Lukaszczuk, P.; Borowiak-Palen, E.; Rümmeli, M.H.; Kalenczuk, R.J.In this contribution we present a systematic study on the dispersion of SWCNTs in a water-based solution of biocompatible detergent: sodium deoxycholate (DOC). By avoiding harsh chemical conditions, which are known to damage nanotubes structure, a stable SWCNTs suspension was created. Long term stirring of the solution led to preparation of a stable transparent solution, containing welldispersed isolated SWCNTs. The as-prepared dispersion remained stable and clear for two months. Optical absorption spectroscopy was employed to measure SWCNTs suspension stability. Nanotube aggregation was evaluated through the tangential mode (G mode) present in the Raman spectrum. High-resolution transmission electronmicroscopy was employed to observe the mechanism of debundling process. © 2010 Springer-Verlag.
- ItemShort Communication: the Influence of Air-Abrasive Trimming on the Current Noise of Thick Film Resistors(London [u.a.] : Gordon & Breach, 1984) Wolf, M.[No abstract available]
- ItemOn Experimental Data of the Tcr of Tfrs and Their Relation to Theoretical Models of Conduction Mechanism(London [u.a.] : Gordon & Breach, 1985) Storbeck, I.; Wolf, M.Any theory of electrical conduction in TFRs encounters mainly two problems: (i) explanation of the dependence of R□ on properties of conducting component (volume fraction, grain size, resistivity), (ii) explanation of the temperature dependence of R□ taking into account (i). In order to achieve this one has to fit some microscopic parameters to experimental R□-and TCR-values, and to check if they are reasonable or not. The aim of the following discussion is to show, that such a fitting by means of experimental TCR-values is not correct. This is due to the fact that TCR-behaviour, as is well known, is determined also by the dependence of resistivity on strain. But any theoretical model neglects strains, also those who are induced by thermal strains. By means of published experiments concerning the strain dependence of resistance, the magnitude is estimated by which the TCR-values have to be corrected for the described fit.