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Correlative Microscopy Study of FIB Patterned Stainless Steel Surfaces as Novel Nano-Structured Stents for Cardiovascular Applications
- Michael Schmidt, Feroze Nazneen, Gregoire Herzog, Damien Arrigan, Paul Galvin, Calum Dickinson, Johann P de Silva, Declan Scanlan, Neal O’Hara, Graham L W Cross, Nikolay Petkov, Justin D Holmes
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- Journal:
- MRS Online Proceedings Library Archive / Volume 1466 / 2012
- Published online by Cambridge University Press:
- 20 July 2012, mrss12-1466-tt04-03
- Print publication:
- 2012
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- Article
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Coronary artery disease is a major problem worldwide causing 7.2 million deaths worldwide annually, resulting from vascular occlusion, myocardial infarction and its complications. Stent implantation is a percutaneous interventional procedure that mitigates vessel stenosis, providing mechanical support within the artery. However, stenting causes physical damage to the arterial wall. It is well accepted that a valuable route to reduce in-stent re-stenosis can be based on promoting cell response to nano-structured stainless steel (SS) surfaces such as, for example, by patterning nano-pits in SS. In this regard patterning by Focussed Ion-Beam (FIB) milling offers several advantages for flexible prototyping (i) practically any substrate material that is able to withstand high vacuum conditions of the microscope chamber can be used, (ii) there is high flexibility in the obtainable shapes and geometries by modulating the ion beam current and the patterning conditions, (iii) reduced complexity of the pattering process e.g. it is a single-step process with a possibility of real-time monitoring of the milling progression. On the other hand FIB patterning of polycrystalline metals is greatly influenced by channelling effects and re-deposition. Correlative microscopy methods present an opportunity to study such effects comprehensively and derive structure-property understanding that is important for developing improved pattering. In this report we present a FIB patterning protocol for nano-structuring features (concaves) ordered in rectangular arrays on pre-polished 316L Stainless Steel (SS) surfaces. An investigation based on correlative microscopy approach of the size, shape and depth of the developed arrays in relation to the crystal orientation of the underlying SS domains, is presented. The correlative microscopy protocol is based on cross-correlation of top-view Scanning Electron Microscopy (SEM), Electron Backscattered Diffraction (EBSD), and Atomic Force Microscopy (AFM).Various dose tests were performed, aiming at improved productivity by preserving nano-size accuracy of the patterned process. The optimal FIB patterning conditions for achieving reasonably high throughput (patterned rate of about 0.03 mm2 per hour) and nano-size accuracy in dimensions and shapes of the features, are discussed as well.
The Mechanics of Nanoimprint Forming
- Graham L. W. Cross, Richard M. Langford, Barry S. O'Connell, John B. Pethica
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- Journal:
- MRS Online Proceedings Library Archive / Volume 841 / 2004
- Published online by Cambridge University Press:
- 01 February 2011, R1.6
- Print publication:
- 2004
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- Article
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Nanoimprint and a number of other related techniques are a collection of surface patterning technologies that involve direct contact of a master template with the target surface. As such, they are governed by the laws of contacting bodies, and the mechanics involved can readily be investigated by existing indentation methods or close variants thereof. Among the many demonstrated applications of nanoimprint, lithographic resist processing has generated considerable interest due to its combination of high resolution with rapid throughput over wide areas. Pattern transfer can be achieved by the application of heat and pressure to the stamp (hot embossing), or solely by the generation of shear stress at the contact (cold forming.) In both cases we have found that elastic and viscoplastic strains are present during the forming process, the former of which can considerably alter the characteristics of the pattern transfer. The use of depth sensing instrumented indentation in conjunction with specially designed stamps and a variety of microscopy techniques has allowed us to isolate, control, and measure many of the stresses and strains directly during the imprint process. Further, in a more standard role, the indenter can be used to characterize the mechanical properties of imprinted structures. In this paper we summarize our experimental findings and conclusions on the role of important factors influencing the fidelity of the imprint process including elastic stresses, plastic deformation mechanisms, complexities in the confined deformation rheology, and choices in the form of applied stress. These are illustrated by a series of idealized experiments ranging from the squeeze flow of prepared coupons to the flat punch indentation of thin films and back extrusion into isolated cavities. A connection between these more localized experiments and the established findings and requirements of applications such as wide area lithography and functional polymer patterning will be made to establish the concept of “instrumented imprint”.
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