5 results
Formation of micro-mechanical interlocking sites by nanoscale sculpturing for composites or hybrid materials with stainless steel
- Chima Obobi Kalu, Mathias Hoppe, Iris Hölken, Melike Baytekin-Gerngross, Mark-Daniel Gerngross, Juergen Carstensen, Rainer Adelung
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- Journal:
- Journal of Materials Research / Volume 35 / Issue 23-24 / 14 December 2020
- Published online by Cambridge University Press:
- 29 October 2020, pp. 3145-3156
- Print publication:
- 14 December 2020
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The demands of modern materials are highly challenging as well as partially contradictory. For example, materials should be strong like steels but chemically inert like soft low-surface energy polymers. These conflicts can be overcome by effectively combining disparate materials in composites that allow fusing of the traditional material classes like ceramics, polymers, and metals. Such combinations require sufficient adhesion between the individual materials. If adhesion is based on mechanical interlocking, the chemistry and chemical compatibility of the individual materials play a negligible role for the adhesion, but the mechanical properties of the materials are exclusively important. This work focusses on a technologically relevant example of a micro-mechanical interlocking surface structure on grade 304 stainless steel (SST) by nanoscale sculpturing. Using a low aggressive/low toxic seawater-like and diluted HNO3-based electrolyte, the resulting structure is free from preferential grain-boundary etching. The sculptured surface is super hydrophilic with undercuts suitable for mechanical interlocking with polymers. In single-lap shear tests, different two-component adhesives failed cohesively on structured SST while showing more than a doubling of the ultimate shear strength compared to the state-of-the-art grit-blasted SST composites which only showed adhesive failure.
Piezotronic sensors
- Till Frömling, Roumeng Yu, Mona Mintken, Rainer Adelung, Jürgen Rödel
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- Journal:
- MRS Bulletin / Volume 43 / Issue 12 / December 2018
- Published online by Cambridge University Press:
- 10 December 2018, pp. 941-945
- Print publication:
- December 2018
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Piezotronics can not only afford control of electronic transport over potential barriers, but the attendant mechanical stress can also influence various physical properties of piezoelectric semiconductors. Stress significantly affects the optical properties of these materials as well as their response toward the chemical environment and magnetic fields. This article focuses on the utilization of piezotronics with regard to these physical parameters for sensor applications. Stress sensors, optical sensors (especially in the ultraviolet range), and sensors for chemicals in gas and liquid phases or magnetic fields via coupled magnetostrictive layers are discussed. The benefits of piezotronics for sensors are highlighted by discussing respective figures of merit.
Employing Thin Film Failure Mechanisms to Form Templates for Nano-electronics
- Rainer Adelung, Mady Elbahri, Shiva Kumar Rudra, Abhijit Biswas, Seid Jebril, Rainer Kunz, Sebastian Wille, Michael Scharnberg
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- Journal:
- MRS Online Proceedings Library Archive / Volume 863 / 2005
- Published online by Cambridge University Press:
- 01 February 2011, B7.3/O11.3
- Print publication:
- 2005
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Recently, we showed that thin film stresses can be used to form well aligned and complex nanowire structures [1]. Within this approach we used stress to introduce cracks in a thin film. Subsequent vacuum deposition of metal leads to the formation of a metal layer on the thin film and of metal nanowires in the cracks of the film. Removal of the thin film together with the excess metal cover finishes the nanowire fabrication on the substrate. As stress can be intentionally introduced by choosing an appropriate thin film geometry that leads to a stress concentration, the cracks and consequently the nanowires can be well aligned. Meanwhile, we have demonstrated how to form thousands of parallel aligned nanowires, x-and y-junctions or nanowires with macroscopic contacts for sensor applications, simply by applying fracture mechanics in thin films. Christiansen and Gösele called this approach “constructive destruction” in a comment in Nature Materials [2]. This gives a hint how to overcome some problems of the approach, arising from the limits of thin film fracture. A generalization of the fracture approach by being “more destructive” can overcome this limitations. For example, it is difficult to form pairs of parallel wires with a nanometer distance of the pair, but a micrometer separation between the individual pairs. Structures like this are useful for many contact applications including sensor arrays or field effect transistors. As well as thin film fracture, thin film delamination can be well controlled by fracture mechanics. Our latest experiments show that the combination of both, fracture and delamination, forms an ideal shadow mask for vacuum deposition. Cracks with delaminated sides were used as templates for the deposition of pairs of parallel wires consisting out of different materials with only a few 10 nm separation. First, a metal was sputter deposited under an angle of approx. 45° through the delaminated crack, which was used as a shadow mask. Afterwards, a second deposition metal is deposited under the opposite 45° angle with respect to the sample normal, having the crack located in the middle between both deposition sources. The angle, the delamination height and the crack width determine the separation of the nanowire contacts. We present several examples which show how these mechanisms of mechanical failure of thin films can be turned into useful templates for various nanostructures. We will focus here on two thin film systems, that can be easily deposited in every lab. These are wet chemically deposited photo-resist and flash evaporated amorphous carbon. These examples are compared with finite element simulations of the thin film stress with the ANSYS program. Moreover, we show how the delamination cracks can be also used as masks for the removal of material. Channals with a width down to 20 nm produced by ion beam sputtering are shown.
Radiotracer Diffusion Measurements of Noble Metal Atoms in Semiconducting Organic Films.
- Michael Scharnberg, Jörn Kanzow, Klaus Rätzke, Rainer Adelung, Franz Faupel, Stephan Meyer, Jens Pflaum
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- Journal:
- MRS Online Proceedings Library Archive / Volume 871 / 2005
- Published online by Cambridge University Press:
- 01 February 2011, I6.31
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- 2005
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The application of organic field effect transistors (OFETs) for large scale low-cost electronic devices has lead to intense research. Diindenoperylene (DIP) thin films on SiO2 are a prominent system due to their high structural out-of-plane order. While bottom contact OFET structures can be realized easily, preparation of top contacts might cause diffusion of metal atoms (typically Ag or Au) deep into the organic film changing the injection properties at the interface. These properties are of great importance for device fabrication. Therefore, only by understanding the diffusion behaviour of metals into the organic layer, formation of well defined interfaces and control of their properties will become possible. For a better understanding of the diffusion of noble metal atoms into crystalline organic films, a radiotracer technique has been used to obtain diffusion profiles for Ag and Au diffusion in crystalline DIP films. For Ag diffusion in DIP, the decrease in Ag concentration of four orders of magnitude within the first few nanometers indicates that most of the metal atoms remain near the surface while small amounts can penetrate deep into the thin film and can even accumulate at the interface between organic film and the silicon substrate. A comparison with diffusion profiles obtained for polymers indicates that the interplay between diffusion and immobilization by aggregation also determine the diffusion behaviour of metals in organic crystalline materials. Latest experiments support this interpretation of the diffusion profiles. Single atoms are highly mobile in the organic crystalline material due to the weak interaction between the metal and the organic material. Therefore, most of the single atoms that penetrate into the material do so during the initial phase of the deposition. When more and more atoms arrive at the surface, cluster formation sets in. Due to the high cohesive energy of the metal the atoms can not leave the cluster and become immobilized. After deposition of a closed surface layer no further metal diffusion should be observed. With the knowledge about the diffusion processes gained by the radiotracer measurements control of process parameters and development of barrier layers in sub-monolayer range should be possible.
A Production Method for Aligned Nanowires on Arbitrary Materials
- Rainer Kunz, Rainer Adelung
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- Journal:
- MRS Online Proceedings Library Archive / Volume 818 / 2004
- Published online by Cambridge University Press:
- 21 March 2011, M5.31.1
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- 2004
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We present a method that allows us to produce aligned metallic nanowires on almost any material. This method recently enabled us to produce interconnected platinum nanowire networks on polymeric Nafion® or gold nanowires on Teflon AF. We will explain the principle of this method by means of a reference material, the so called layered transition metal dichalcogenides (TMDC) crystals. The method is based on producing cracks in thin films as templates, using large sticking coefficient differences and long diffusion lengths. The underlying mechanism that forms the template cracks is mechanical stress. In the case of the TMDC crystals this stress is introduced in the substrate by an electronic interaction between the metal used for the nanowires and the TMDC-crystal. The large difference in the condensation coefficient is an immanent property of layered crystals for many different adsorbates. Obtained by cleavage along a so called “Van-der-Waals-gap”, surfaces of such crystals are atomically flat over hundreds of microns. As a consequence of their layered character the surfaces have no reconstruction and almost no step edges or other defects, which is the basis for the long diffusion length. In contrast, the rare defects have a very high sticking coefficient and act as excellent nucleation centers. Therefore, after metal evaporation on such surfaces in UHV, various structures can be formed in a self organized processes. We observed, e.g., clusters in fractal or geometric arrangements or large nanowire networks on the surfaces [1]. In order to understand, why the different structures form, a systematic study of the growth parameters, (nucleation, diffusion length, evaporated metal, influence of the substrate-crystal), is necessary. Therefore, we first carried out diffusion studies on these surfaces. We could show that in extreme cases (Cu on metallic TaS2) diffusion length of more than 50νm could be observed combined with a nucleation probability of almost zero. This is evident from a growth mode showing similarities with the DLA (Diffusion Limited Aggregation) growth process. In contrast, metal diffusion (Cu) on the geometrically similar surfaces on the semiconducting (WSe2) surface shows much a shorter diffusion length and no DLA growth. We suggest a model to explain the different diffusion behavior as a key to understand the different self organized structures. Learning from the TMDC crystals, we show the application on technological more important materials.