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Granular and columnar nickel–carbon composites may exhibit large strain sensitivity, which makes them an interesting sensor material. Based on experimental results and morphological characterization of the material, we develop a model of the electron transport in the film and use it to explain its piezoresistive effect. First we describe a model for the electron transport from particle to particle. The model is then applied in Monte Carlo simulations of the resistance and strain properties of the disordered films that give a first explanation of film properties. The simulations give insights into the origin of the transverse sensitivity and show the influence of various parameters such as particle separation and geometric disorder. An important influence towards larger strain sensitivity is local strain enhancement due to different elastic moduli of metal particles and carbon matrix.

We have produced granular films based on carbon and different transition metals by means of plasma deposition processes. Some of the films possess an increased strain sensitivity compared to metallic films. They respond to strain almost linearly with gauge factors of up to 30 if strained longitudinally, while in the transverse direction about half of the effect is still measured. In addition, the film's thermal coefficient of resistance is adjustable by the metal concentration. The influence of metal concentration was investigated for the elements Ni, Pd, Fe, Pt, W, and Cr, while the elements Co, Au, Ag, Al, Ti, and Cu were studied briefly. Only Ni and Pd have a pronounced strain sensitivity at 55 ± 5 at. % (atomic percent) of metal, among which Ni–C is far more stable. Two phases are identified by transmission electron microscopy and X-ray diffraction: metal-containing nanocolumns densely packed in a surrounding carbon phase. We differentiate three groups of metals, due to their respective affinity to carbon. It turns out that only nickel has the capability to bond and form a stable and closed encapsulation of GLC around each nanoparticle. In this structure, the electron transport is in part accomplished by tunneling processes across the basal planes of the graphitic encapsulation. Hence, we hold these tunneling processes responsible for the increased gauge factors of Ni–C composites. The other elements are unable to form graphitic encapsulations and thus do not exhibit elevated gauge factors.

The strain sensitivity, i.e. the resistivity change due to mechanical strain of thin composite nano-cermet films of Pt–SiO2 was investigated. We prepared films with a thickness of 400 nm by means of co-sputtering processes at substrate temperatures around 400 °C. The specimens respond to uniform strain (ɛ = 0.2‰) with gauge factors up to 18. These gauge factors remained high at least up to 250 °C in air and also after further annealing up to 600 °C in vacuum. Therefore we state these functional films might be suitable for high temperature pressure and force sensors. The films have a relatively high film resistivity of some MΩ/sq and exhibit temperature coefficients of resistance (TCR) in the range of −2000 ppm/K up to −600 ppm/K. X-ray diffraction revealed a single crystalline fcc platinum phase while transmission electron microscopy proved a typical granular structure of the films. Pt-clusters sized 5–10 nm are embedded in an amorphous insulating matrix of silica. The composition of such nano-cermet films displaying high gauge factors is approx. 40 at% Pt, 20 at% Si and 40 at% of O.

Der Gesundheitsbereich ist eine der beschaftigungsstarksten und fur die Lebensqualitat und die gesellschaftliche Zukunftsentwicklung wichtigsten Themenfelder in Deutschland. Die Bedeutung wird in den kommenden Jahrzehnten weiter zunehmen, weil die gesundheitlichen Versorgungs- und Reorganisationsbedarfe im demografischen Wandel wachsen.

Nickel containing amorphous hydrogenated carbon (Ni:a-C:H) thin films prepared by reactive sputtering have a high potential for use as piezoresistive sensors. Investigations by means of X-ray diffraction (XRD), transmission electron microscopy, energy-dispersive X-ray spectroscopy, and magnetic characterizations indicate that sputtering parameters and heat treatment influence the film composition, the microscopic structure, and some relevant macroscopic physical properties. The films are heterogeneous in nature and consist of either nanometer sized hcp nickel, nickel carbide (these phases being indistinguishable by XRD), or fcc nickel clusters encapsulated by graphite-like carbon shells. The nature of the metal clusters in the thin films has a strong effect on its magnetic properties. For approximately 55 at.% Ni the electrical resistivity of the film is nearly temperature independent over a broad temperature range from 100 K to 400 K. The strain sensitivity, with a gauge factor of 20, is up to ten times higher than conventional temperature independent strain sensitive films. Compared to industry standard NiCr functional layers used for pressure sensors, Ni:a-C:H films provide a ten fold higher output signal.

Oriented SnO2 nanowire (NW) arrays were grown on TiO2(001) substrates by molecule-based chemical vapor deposition of Sn(OtBu)4. Preferred growth directions ([101], [−101], [011], and [0–11]) of SnO2 NWs were correlated to surface energy consideration and crystallographic relationship between the substrate and NW material by comprehensive electron microscopy and bulk tomographic studies. The proposed growth incubation model (tilting of catalyst/NW interface due to driving force of surface energy) explains the formation mechanism of oriented SnO2 NWs on TiO2 substrates. These results allowed us to also study the I–V characteristics and gas-sensing properties of individual SnO2 NWs grown with a perfectly defined crystal orientation ([101]).

Zusammenfassung Die Arbeit beschreibt die Entwicklung eines neuen Materials, das auf eine mechanische Belastung zehnmal empfindlicher reagiert als die heute genutzten metallischen DMS-Materialen. In diesem Kompositmaterial liegen mit Kohlenstoff umhüllte Nickelcluster mit einem Durchmesser zwischen 10 nm und 20 nm vor. Die Umhüllungen bestehen aus einigen gebogen Graphenlagen, die die Nickelcluster wie Zwiebelschalen umgeben. Elektronenmikroskopische Aufnahmen zeigten, dass die Metallcluster isoliert voneinander vorliegen, sich also nicht berühren, so dass der Stromtransport durch die Hüllen aus Kohlenstoff beeinträchtigt ist. Wird nun eine Dehnung oder Verzerrung dieses komplexen Materials zB durch einen äußeren Druck hervorgerufen, so beeinflusst dies den Stromtransport durch das Material, also seinen elektrischen Widerstand, sehr stark. Dies ermöglicht eine sehr empfindliche elektrische Messung des Drucks oder der Kraft. Neben einer um den Faktor elf erhöhten Dehnungsempfindlichkeit (k-Faktor bis zu 22) im Gegensatz zu herkömmlichen DMS-Materialen weisen diese Dünnschichten einen auf null einstellbaren Temperaturkoeffizienten des elektrischen Widerstands auf (TKR kleiner als ±25 ppm/K). Erste Prototypen in Form von Stahlmembran-Drucksensoren zeigen eindrucksvoll das Potenzial dieser Dünnschichten für Sensoranwendungen auf. Die hohe Dehnungsempfindlichkeit konnte bestätigt werden, auch viele weitere Sensorparameter wie zB das Kriechen, die Linearität der Kennlinie und das Signalrauschen konnten untersucht werden und liegen in für diese Sensoren typischen Bereichen.

In this paper we report on the influence of particle size distribution, particle substrate interaction, and drying behavior on the self-assembly process using ligand stabilized silver particles. Two-dimensional particle arrays were characterized using transmission electron microscopy and extensive image analysis. The formation of such structures was observed in situ using an environmental scanning electron microscope in WET-STEM mode. The results confirm that a small particle size distribution is crucial for the formation of regular particle patterns with long range order, but also the particle substrate interaction and the particle density have an influence on the degree of ordering. Additionally, we find that separated binary particle assemblies keep the orientation of their two-dimensional hexagonal lattices over alternating domains of small and big particles. This is probably enabled due to the formation of dislocations and a small change of the course of the lattice lines within the respective boundary.

Core/shell nanowires of Al/Al2O3 are obtained by decomposition of tert-butoxyalane on metal, silicon or glass substrates heated up to 650 °C without use of a noble metal seed. These biphasic nanowires are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), scanning energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM) and high-resolution TEM. They have uniform diameters of about 20–30 nm, are composed of an inner aluminium wire, wrapped up by aluminium oxide at a constant molar ratio, and have lengths of several micrometers. As the temperatures approach the melting point of Al (660.4 °C), we propose a growth mechanism for the nanowires which resembles to vapour-liquid-solid (VLS) growth of ceramic nanowires with a liquid metal phase catalyst seed which in this case is aluminium. The biphasic nature of the wires is due to the disproportionation of aluminium in the transient “AlO” and to Ostwald ripening.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Imaging single epidermal growth factor receptors (EGFR) in intact cells is presently limited by the available microscopy methods. Environmental scanning electron microscopy (ESEM) of whole cells in hydrated state in combination with specific labeling with gold nanoparticles was used to localize activated EGFRs in the plasma membranes of COS7 and A549 cells. The use of a scanning transmission electron microscopy (STEM) detector yielded a spatial resolution of 3 nm, sufficient to identify the locations of individual EGFR dimer subunits. The sizes and distribution of dimers and higher order clusters of EGFRs were determined. The distance between labels bound to dimers amounted to 19 nm, consistent with a molecular model. A fraction of the EGFRs was found in higher order clusters with sizes ranging from 32–56 nm. ESEM can be used for quantitative whole cell screening studies of membrane receptors, and for the study of nanoparticle-cell interactions in general.

High-yield synthesis of germanium nanowires (NWs) and core−shell structures is achieved by the chemical vapor deposition (CVD) of dicyclopentadienyl germanium ([Ge(C5H5)2]). The one-dimensional (1D) nanostructures are formed on an iron substrate following a base-growth model in which an Fe−Ge epilayer functions as a catalytic bed. The wire growth is selective and no catalyst particles are observed at the tip of the NWs, which is contrary to the characteristic feature of a 1D growth based on the vapor−liquid−solid (VLS) mechanism. The diameter and length of the NWs were in the ranges 15−20 nm and 25−40 μm, respectively, as found by high-resolution electron microscopy. Both axial and radial dimensions of the NWs can be controlled by adjusting the precursor feedstock, deposition temperature, and size of alloy nuclei in the Fe−Ge epilayer. High precursor flux produced coaxial heterostructures where single-crystalline Ge cores are covered with an overlayer of nanocrystalline Ge. Single-crystal Ge nanowires exh...

Dual specificity tyrosine-(Y)-phosphorylation regulated kinase 1A (DYRK1A) is encoded on human chromosome 21 and thus 1.5-fold overexpressed in Down syndrome (DS). Reports from animal models provide strong evidence that an altered DYRK1A gene dosage results in disturbed brain development. Neuronal differentiation is regulated by an accurate control of G1-G0 cell cycle exit, and a disturbed expression of DYRK1A is assumed to deregulate this process. Hence, normalization of elevated DYRK1A kinase activity is currently considered as a possible therapeutic option in DS. Nonetheless, the underlying mechanisms how DYRK1A affects cell cycle regulation and neuronal development remain largely unknown. Therefore, the main part of this study aimed to elucidate the hypothesis that DYRK1A overexpression alters neuronal cell cycle progression and differentiation, and to identify the underlying molecular mechanisms. To investigate effects of DYRK1A overexpression in neuronal cell cycle progression a human cell model with controllable overexpression of DYRK1A was developed. This study shows that DYRK1A overexpression arrested SH SY5Y neuroblastoma cells in G1-phase dependent on its kinase activity and expression levels. Long-term overexpression of DYRK1A led to G0 cell cycle exit and premature neuronal differentiation. Moreover, DYRK1A affected protein stability of the cell cycle regulators p27Kip1 and Cyclin D1 in G1-phase by phosphorylation of their regulatory sites Ser10 and Thr286, respectively. Furthermore, DYRK1A contributed to p27Kip1 Ser10 phosphorylation in differentiating primary mouse neurons and in developing embryonic mouse brain. In summary, the study provides new mechanistic evidence that DYRK1A mediates neuronal cell cycle progression by regulation of G1-S-phase transition and G0 cell cycle exit. The reported findings support the assumption that DYRK1A overexpression contributes to the neurodevelopmental alterations that are present in DS. Septins are a family of GTP-binding and filament forming proteins that fulfill important cellular functions by formation of scaffolds or diffusion barriers. Septin4 was found in neurodegeneration related protein aggregates and is required for proper migration of cortical neurons. Nonetheless, the functional regulation of Septin4 remains unclear. Therefore, the second part of this thesis reports a novel mechanism to regulate Septin4 function. It is shown that DYRK1A phosphorylated Septin4 at Ser107 and that Ser107 phosphorylation affected Septin4 protein stability. These findings strongly indicated a functional relation of DYRK1A and Septin4. Therefore, Septin4 fusion proteins for future analysis of Ser107 phosphorylation in the regulation of protein stability and filament assembly were constructed.

Imaging single epidermal growth factor receptors (EGFR) in intact cells is presently limited by the available microscopy methods. Environmental scanning electron microscopy (ESEM) of whole cells in hydrated state in combination with specific labeling with gold nanoparticles was used to localize activated EGFRs in the plasma membranes of COS7 and A549 cells. The use of a scanning transmission electron microscopy (STEM) detector yielded a spatial resolution of 3 nm, sufficient to identify the locations of individual EGFR dimer subunits. The sizes and distribution of dimers and higher order clusters of EGFRs were determined. The distance between labels bound to dimers amounted to 19 nm, consistent with a molecular model. A fraction of the EGFRs was found in higher order clusters with sizes ranging from 32-56 nm. ESEM can be used for quantitative whole cell screening studies of membrane receptors, and for the study of nanoparticle-cell interactions in general.

Structural, optical, electro and photoelectrochemical properties of amorphous and crystalline sol-gel Nb2O5 coatings have been determined. The coatings are n-type semiconductor with indirect allowed transition and present an overall low quantum efficiency (Ø < 4%) for UV light to electric conversion. The photoconducting behavior of the coatings is discussed within the framework of the Gärtner and Södergren models. Improvement can be foreseen if Nb2O5 coatings can be made of 10—20 nm size nanoparticles.

Metal containing carbon thin films can be prepared to exhibit piezoresistive properties with a high sensitivity to mechanical strain and with a temperature independent resistance. This unique combination of properties predisposes these films to be used in sensors for pressure, force, weight and torque. For the case of nickel containing carbon films (often termed as Ni containing hydrogen ated amorphous carbon , shortly Ni:a-C:H) we are able to demonstrate a strain sensitivity (gauge factor) of approx. 20 together with a temp erature coefficient of resistivity (TCR) below ±50 ppm/K in the wide temperature range of 100 K to 400 K. The sensitivity of our films is thus enhanced by a factor of 10 compared with standard metallic thin films in today’s sensors. The films consist of crystalline nanoclusters of nickel with a diameter of 10 – 20 nm which are encapsulated by only few atomic layers of graphene (or turbostratic graphite) as revealed by transmission electron microscopy (TEM). These carbon encapsulated clusters are embedded in a matrix of carbon. The new type of films are named nanoNi@C i.e. nano-Nickel clusters encapsulated by carbon. Keywords: gauge factor, strain gauge, TCR, Nickel clusters, gr aphite, carbon, encapsulated , pressure, force sensors

Single-step synthesis of one-dimensional Ge/SiCxNy core-shell nanocables was achieved by chemical vapor deposition of the molecular precursor [Ge{N(SiMe3)2}2]. Single crystalline Ge nanowires (diameter approximately 60 nm) embedded in uniform SiCxNy shells were obtained in high yields, whereby the growth process was not influenced by the nature of substrates. The shell material exhibited high oxidation and chemical resistance at elevated temperatures (up to 250 degrees C) resulting in the preservation of size-dependent semiconductor properties of germanium nanowires, such as intact transport of charge carriers and reduction of energy consumption, when compared to pure Ge nanowires.

Extended abstract of a paper presented at Microscopy and Microanalysis 2013 in Indianapolis, Indiana, USA, August 4 – August 8, 2013.

Single crystal Ge nanowires (NWs) were obtained in high yield by gas phase decomposition of germanium di-cyclopentadienylide ([Ge(C5H5)2]), at 325 °C on iron substrates. Highresolution electron microscopy (SEM/TEM) showed Ge NWs to be uniform in terms of diameter (20 nm) and length (> 25 μm). The wire growth is selective and appears to be governed by a Ge-Fe alloy epilayer formed by the reaction between Ge clusters and iron substrate, during the initial stages of the CVD process. The supersaturation of Ge-Fe solid-solution with respect to Ge content induces the spontaneous formation of single crystal germanium nuclei that act as templates for the nanowire growth. X-ray and electron diffraction revealed the NWs to be single crystals of cubic germanium with a preferred growth direction[11–2]. The proposed base-growth model on Fe substrate is supported by TEM, EDX and XPS studies.

Background: Surface bound proteins on colloid particles are widely used in biotechnological applications such as diagnostics or separation. Analysis of colloid surfaces by imaging methods provides information on the structure of these protein films, and an understanding of the functional relationships of biomolecules immobilised on solid surfaces. Methods: In order to visualise protein molecules organised in films on surfaces of nano-sized gold-particles, an electron-microscopic approach based on the scattering absorption contrast of the specimen was applied. Results: Analysing protein conjugated gold particles with a transmission electron microscope, protein films on gold particle surfaces cause a significant scattering absorption contrast based on the materials' electron density. Thus, the thickness of such films becomes directly measurable in planar projection and the shape of these films are visualised without negative staining methods. The insertion of Ruthenium-labelled antibodies instead of non-labelled antibodies as a marker with increased electron-density in these films yields a contrast enhancement of the whole film. Additional labelling with anti-Mouse IgG Gold conjugates localises the position of the surface bound antibodies in such protein films. Conclusions: The power of transmission electron microscopy to resolve protein-films on colloid surfaces without staining or labelling as a sample preparation procedure has been demonstrated. Thus, this direct method provides an analytical tool for studying protein films and their structural features on particle surfaces. Cytometry 37: 87–92, 1999. © 1999 Wiley-Liss, Inc.

Size and shape of metallic nanoparticles, which are embedded in sol-gel produced glass-like layers, are able to influence the optical properties of coatings on glass. Since the shape of the particles is determined by its crystalline structure, and the structure is modified significantly during the particle growth, the development of both was observed in dependence on the stage of growth appliying conventional and high resolution electron microscopy. These investigations carried out on Au and Ag particles have revealed different types of colloidal growth, a real structure often formed by dislocations and twins as well as a relatively high particle mobility.

A model of the Monte Carlo simulation is used for calculating profiles of the backscattered electron intensity and the secondary electron yield caused by the scanning electron beam. In order to get a fast yield calculation a simple procedure has been developed to describe the escape of secondary electrons. In the present paper first simulations are discussed with the aim of comparing backscattered electron and secondary electron profiles of wall and trench structures. Special attention is given to the influence of the shape of the target surface topography on the electron backscattering and secondary emission.