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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.

The piezoresistive effects of nickel–carbon thin films, i.e., the sensitivity to hydrostatic pressure and uniform strain, are investigated in this study. Thin films, which were obtained by reactive sputtering processes with thicknesses up to 1200 nm, exhibit pressure sensitivity coefficients ( PCR ) about −20 ppm/bar and gauge factors up to 30 on Si/SiO 2 substrates. A linear change of the thin film's resistance in respect to the applied hydrostatic pressure was observed. Additionally, the temperature coefficients of resistance were determined in the range of −300 to 0 ppm/K, while the temperature coefficient of the PCR s was obtained as good as 0 ppm/K.

Ni:a-C:H thin films obtained by reactive sputtering processes were investigated using EXAFS and subsequent wavelet analysis. Depending on overall thin film deposition conditions, the clusters of Ni in Ni:a-C:H can appear as fcc-Ni or as a non-fcc-Ni phase, such as hcp-Ni or Ni3C. While hcp-Ni and Ni3C are hardly distinguishable by XRD, the EXAFS analysis can reveal if carbon is the nearest neighbour of Ni or not, thus if Ni3C is present or hcp-Ni. Our study showed that wavelet transformation analysis of the EXAFS data is necessary to discriminate clearly between hcp-Ni and Ni3C regarding the presence or absence of carbon coordination shells around the X-ray absorbing Ni atoms. Furthermore, we are confident to have identified Ni3C in our thin films, however, we cannot exclude the possibility of the co-existence of hcp-Ni. Finally, calculations of XRD peaks of hcp-Ni and Ni3C showed that a discrimination of these two crystal phases might be feasible when the crystallite size is increased beyond 40 nm.

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.

The influence of charge carrier traps on charge carrier transport is studied in a small molecule organic semiconductor model system by means of an optical time-of-flight method. The model system consists of the hole transport material N,N'-di(1-naphtyl)-N,N'-diphenylbenzidine (α-NPD, sometimes denoted as α-NPB) either undoped or doped with various concentrations of the small molecule 4,4',4”-tris-[N-(1-naphtyl)-N-(phenylamino)]-triphenylamine (1-NaphDATA), which is known to create hole traps in α-NPD.In case of undoped α-NPD, non-dispersive hole transport is observed and the hole mobility is determined as 6·10−4cm2/Vs in the examined electric field range, being in good agreement with published data. Depending on the intensity of the laser light employed for optical charge carrier generation, current transients both in the space-charge regime and in the small signal case are obtained. In the small signal case the current transients do not exhibit the expected flat current plateau before the characteristic kink that marks the transit time, but feature a cusp instead. A tentative mechanism for its formation is proposed.The influence of the trap concentration on charge carrier transport is studied by introducing 1-NaphDATA as a molecular dopant. It is demonstrated that the hole transport in α-NPD can be controlled by varying the doping concentration of 1-NaphDATA. Increasing the trap concentration, a transition from non-dispersive transport in undoped α-NPD to non-dispersive but trap-controlled transport with reduced mobility and further to dispersive transport is observed.