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Madison, WI, United States

Ryan K.E.,U.S. Naval Academy | Keating P.L.,U.S. Naval Academy | Jacobs T.D.B.,University of Pennsylvania | Grierson D.S.,systeMech | And 3 more authors.

The work of adhesion is an interfacial materials property that is often extracted from atomic force microscope (AFM) measurements of the pull-off force for tips in contact with flat substrates. Such measurements rely on the use of continuum contact mechanics models, which ignore the atomic structure and contain other assumptions that can be challenging to justify from experiments alone. In this work, molecular dynamics is used to examine work of adhesion values obtained from simulations that mimic such AFM experiments and to examine variables that influence the calculated work of adhesion. Ultrastrong carbon-based materials, which are relevant to high-performance AFM and nano- and micromanufacturing applications, are considered. The three tips used in the simulations were composed of amorphous carbon terminated with hydrogen (a-C-H), and ultrananocrystalline diamond with and without hydrogen (UNCD-H and UNCD, respectively). The model substrate materials used were amorphous carbon with hydrogen termination (a-C-H) and without hydrogen (a-C); ultrananocrystalline diamond with (UNCD-H) and without hydrogen (UNCD); and the (111) face of single crystal diamond with (C(111)-H) and without a monolayer of hydrogen (C(111)). The a-C-H tip was found to have the lowest work of adhesion on all substrates examined, followed by the UNCD-H and then the UNCD tips. This trend is attributable to a combination of roughness on both the tip and sample, the degree of alignment of tip and substrate atoms, and the surface termination. Continuum estimates of the pull-off forces were approximately 2-5 times larger than the MD value for all but one tip-sample pair. © 2014 American Chemical Society. Source

Jacobs T.D.B.,University of Pennsylvania | Ryan K.E.,U.S. Naval Academy | Keating P.L.,U.S. Naval Academy | Grierson D.S.,systeMech | And 4 more authors.
Tribology Letters

The effect of atomic-scale roughness on adhesion between carbon-based materials is examined by both simulations and experimental techniques. Nanoscale asperities composed of either diamond-like carbon or ultrananocrystalline diamond are brought into contact and then separated from diamond surfaces using both molecular dynamics simulations and in situ transmission electron microscope (TEM)-based nanoindentation. Both techniques allow for characterization of the roughness of the sharp nanoasperities immediately before and after contact down to the subnanometer scale. The root mean square roughness for the simulated tips spanned 0.03 nm (atomic corrugation) to 0.12 nm; for the experimental tips, the range was 0.18-1.58 nm. Over the tested range of roughness, the measured work of adhesion was found to decrease by more than an order of magnitude as the roughness increased. The dependence of adhesion upon roughness was accurately described using a simple analytical model. This combination of simulation and experimental methodologies allows for an exploration of an unprecedented range of tip sizes and length scales for roughness, while also verifying consistency of the results between the techniques. Collectively, these results demonstrate the high sensitivity of adhesion to interfacial roughness down to the atomic limit. Furthermore, they indicate that care must be taken when attempting to extract work of adhesion values from experimental measurements of adhesion forces. © 2013 Springer Science+Business Media New York. Source

Agency: NSF | Branch: Standard Grant | Program: | Phase: | Award Amount: 225.00K | Year: 2015

The broader impact/commercial potential of this Small Business Innovation Research (SBIR) Phase I is the development of a disruptive manufacturing technology that will enable a new class of nanomembrane-based electronic devices to be assembled and integrated on flexible substrates. This innovative technology promises to provide flexible electronics developers and manufacturers a new option for fabricating a wide range of flexible devices that require the integration of high-performance semiconductors. It is anticipated that printing tools and processes based on this core technology will significantly lower the technological barriers that are hindering the widespread manufacture of next-generation flexible devices.

This Small Business Innovation Research (SBIR) Phase I project aims to develop a direct printing tool that surpasses the available technologies in terms of both precision and scalability. Current flexible device manufacturing processes do not have the capabilities needed to realize high-performance flexible devices through the integration of high-quality semiconductor materials. Therefore, new strategies are required for fabricating and printing the thin device layers that are essential in emerging high-performance flexible electronics. This project will involve mechanics simulations,tool design and fabrication, process experiments to meet resolution and yield metrics, and establishment of design constraints and operating conditions for a manufacturing process.

Kim-Lee H.-J.,University of Wisconsin - Madison | Kim-Lee H.-J.,Samsung | Carlson A.,University of Illinois at Urbana - Champaign | Grierson D.S.,University of Wisconsin - Madison | And 4 more authors.
Journal of Applied Physics

Microtransfer printing is a versatile process for retrieving, transferring, and placing nanomembranes of various materials on a diverse set of substrates. The process relies on the ability to preferentially propagate a crack along specific interfaces at different stages in the process. Here, we report a mechanics-based model that examines the factors that determine which interface a crack will propagate along in microtransfer printing with a soft elastomer stamp. The model is described and validated through comparison to experimental measurements. The effects of various factors, including interface toughness, stamp geometry, flaw sizes at the interfaces, and nanomembrane thickness, on the effectiveness of transfer printing are investigated using a fracture-mechanics framework and finite element modeling. The modeling results agree with experimental measurements in which the effects of interface toughness and nanomembranes thickness on the transfer printing yield were examined. The models presented can be used to guide the design of transfer printing processes. © 2014 AIP Publishing LLC. Source

Agency: Department of Defense | Branch: Air Force | Program: STTR | Phase: Phase I | Award Amount: 100.00K | Year: 2011

The objective of this phase I STTR project is to develop and demonstrate a roll-to-roll process for printing semiconductor and metal nanostructures with lateral dimensions as small as 100 nm on flexible substrates. systeMech will collaborate with the University of Wisconsin-Madison (Prof. M.G. Lagally"s group) to develop and characterize a process for transferring semiconductor and metal nanomembranes, which have been patterned via nanoimprint lithography at the wafer-level, to flexible substrates. The transfer of nanostructures patterned at the wafer-level has significant advantages over direct nanoimprinting, including better etching capabilities and fewer distortion problems. The primary objectives for phase I are: (1) Demonstrating retrieval of patterned nanostructures using a rotating stamp, (2) Demonstrating printing of nanostructures on flexible substrates using a rotating stamp, and (3) Designing a complete roll-to-roll manufacturing process capable of patterning>0.1 square meters. These objectives will be accomplished through mechanical modeling of the manufacturing process, retrieval and printing experiments, and process characterization. systeMech is a newly-formed small business, and the founders have experience in semiconductor manufacturing, mechanics, and nanoengineering. Prof. Max Lagally at the University of Wisconsin-Madison is a leader in nanomembrane processing for electronic and photonic devices and currently leads an AFOSR-funded MURI on nanomembranes.

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