3 results
Variable sequence of events during the past seven terminations in two deep-sea cores from the Southern Ocean
- Aya Schneider Mor, Ruth Yam, Cristina Bianchi, Martina Kunz-Pirrung, Rainer Gersonde, Aldo Shemesh
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- Journal:
- Quaternary Research / Volume 77 / Issue 2 / March 2012
- Published online by Cambridge University Press:
- 20 January 2017, pp. 317-325
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The relationships among internally consistent records of summer sea-surface temperature (SSST), winter sea ice (WSI), and diatomaceous stable isotopes were studied across seven terminations over the last 660 ka in sedimentary cores from ODP sites 1093 and 1094. The sequence of events at both sites indicates that SSST and WSI changes led the carbon and nitrogen isotopic changes in three Terminations (TI, TII and TVI) and followed them in the other four Terminations (TIII, TIV, TV and TVII). In both TIII and TIV, the leads and lags between the proxies were related to weak glacial mode, while in TV and TVII they were due to the influence of the mid-Pleistocene transition. We show that the sequence of events is not unique and does not follow the same pattern across terminations, implying that the processes that initiated climate change in the Southern Ocean has varied through time.
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.
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.