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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.

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.

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)

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...

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.

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.