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The requirements for high performance and low energy consumption call for novel light-weight high-temperature structural materials. A possible answer can be intermetallic γ-TiAl-based alloys, which—in terms of weight—clearly outperform the classical Ni based alloys. However, not only their mechanical properties, such as high specific strength and high creep resistance, are important for device design and use, but also their electrical behavior is of significant importance. In order to correctly interpret the results of electrical material testing techniques, such as eddy current testing, a profound knowledge on the electrical properties is essential. In this study, local-probe techniques, such as conductive atomic force microscopy (CAFM) and micro four-point probe (μ4PP) measurements, were used to determine the specific resistivity of the constituent phases of a Ti-43.5Al-4Nb-1Mo-0.1B (at. %) TNM γ-TiAl based alloy. It turned out that the different phases exhibit noticeably different resistivity values, which vary over two orders of magnitude, whereas the βo phase has the smallest resistivity and the α2 phase the highest. CAFM and μ4PP results were in rather good agreement for the α2 and γ phases with resistivity values of ρα2,CAFM = (1.0 ± 0.7) × 10−5 Ω m and ρα2,4PP = (1.5 ± 1.5) × 10−5 Ω m for the α2-phase, and ργ,CAFM = (6.5 ± 2.1) × 10−6 Ω m, and ργ,4PP = (1.4 ± 1.2) × 10−6 Ω m for the γ-phase. For the βo phase, μ4PP measurements resulted in ρβo,4PP = (9.0 ± 5.0) × 10−7 Ω m. In this case, CAFM values are not reliable due to the formation of a contact barrier that deteriorates the measurements. [ABSTRACT FROM AUTHOR]

Visualization of functionally different domains in bulk heterojunction (BHJ) solar cells is of paramount importance to understand the routes of optimization of their structure for best performance. In this work, a concept of detecting n-type and p-type semiconductor domains in BHJ structures by methods based on atomic force microscopy (AFM) is proposed. It assigns an active role to the semiconducting coating of the AFM probe tip which is able to form different junctions, i.e., p-n anisotype or p+-p, n+-n isotype, with the surfaces inspected. Here, we illustrate this concept on the example of BHJ structures composed of the n-type inorganic microcrystalline semiconductor CdS and mechanochemically prepared p-type kesterite nanopowder and two types of AFM probe tip coatings, i.e., p-type boron-doped diamond and n-type nitrogen-doped diamond coating, respectively. Conductive AFM (CAFM) measurements demonstrated unequivocally the different diode behavior when contacting n- or p-type semiconductor domains in the BHJ structures. Simulation of the energy level alignment at the probe-sample interfaces allowed us to explain the formation of anisotype or isotype junctions depending on the sample domain and probe used. Kelvin probe force microscopy measurements were consistent with the CAFM results and indicated the different contact potentials from the diverse types of domains in the BHJ structure. [ABSTRACT FROM AUTHOR]

We have investigated the growth and stability of molecular ultra-thin films, consisting of rod-like semiconducting para-hexaphenyl (6P) molecules vapor deposited on ion beam modified TiO2(110) surfaces. The ion bombarded TiO2(110) surfaces served as growth templates exhibiting nm-scale anisotropic ripple patterns with controllable parameters, like ripple depth and length. In turn, by varying the ripple depth one can tailor the average local slope angle and the local step density/terrace width of the stepped surface. Here, we distinguish three types of substrates: shallow, medium, and deep rippled surfaces. On these substrates, 6P sub-monolayer deposition was carried out in ultra-high vacuum by organic molecular beam evaporation (OMBE) at room temperature leading to the formation of islands consisting of upright standing 6P molecules, which could be imaged by scanning electron microscopy and atomic force microscopy (AFM). It has been found that the local slope and terrace width of the TiO2 template strongly influences the stability of OMBE deposited 6P islands formed on the differently rippled substrates. This effect is demonstrated by means of tapping mode AFM, where an oscillating tip was used as a probe for testing the stability of the organic structures. We conclude that by increasing the local slope of the TiO2(110) surface the bonding strength between the nearest neighbor standing molecules is weakened due to the presence of vertical displacement in the molecular layer in correspondence to the TiO2 atomic step height. [ABSTRACT FROM AUTHOR]