Prof. Graham L.W. Cross "Polymer Deformation during Nanostructure Fabrication by Mechanical Processing: Size Effects and Novel Flow Mechanisms"

Mechanics-based fabrication methods now provide a comprehensive means to realize scalable nanoscale device fabrication.  Functional elements of the mechanical assembly line required for the massively parallel production of nanoscale structures and devices, including mastering, replication and transfer, have been demonstrated and in some instances even commercialized.  As the efficiency and reliability of these methods is improved, an increasing penetration to more traditional fields of research is enabled.  My group seeks to make a connection between fundamental materials physics and these emerging nanofabrication methods. 

In this talk, I will discuss the mechanical generation of shape and organization of structure at the nanoscale, with an emphasis on the deformation of thin film polymers in quasi-two dimensional flow fields that arise during thermal imprint. Molecular scale squeeze flow in this process presents significant challenges to understanding and controlling the mass transport necessary for high fidelity replication of patterned dies[1]. We discuss recent developments in the use of a modified nanoindentation technique[2] to measure glassy forging and viscous melt moulding flows in ultrathin polymer films, on 10, 100, and 1000 nm length scales. A surprising scaling of stress vs. strain relationships as system size is reduced to dimensions below the statistical size of the polymer molecule is revealed[3] and its connection to chain network topology is discussed. In addition, a brief review of a novel mass transport mechanism[4] for planar geometries arising from the deliberate injection of small amplitude oscillatory shear stress during forming will be given. Connection and contrast to the growing body of confined-molecule polymer physics measurements and concepts are made.
 

[1] G. L. W. Cross, The production of nanostructures by mechanical forming, Journal of Physics D: Applied Physics, 39 R363-R386 (2006).
[2] W. McKenzie, W., J. B. Pethica, G. L. W. Cross, A direct-write resistless hard mask for rapid nanoscale patterning of diamond, Diamond and Related Materials, 20, 707 (2011);  G. L. W. Cross, B. S. O Connell, and J. B. Pethica, H. D. Rowland, and W. P. King, Variable Temperature Thin Film Indentation with a Flat Punch, Review of Scientific Instruments, 79 013904 (2008).
[3] Rowland, H. D., W. P. King, J. B. Pethica, and G. L. W. Cross, Molecular Confinement Accelerates Deformation of Entangled Polymers During Squeeze Flow, Science, 322, 720-724, (2008); Rowland, H. D., G. L. W. Cross, B. S. O Connell, J. B. Pethica, and W. P. King, Measuring Glassy and Viscoelastic Polymer Flow in Molecular-Scale Gaps using a Flat Punch Mechanical Probe, ACS Nano, 2:3, 419-428, (2008).
[4] G. L. W. Cross, B. S. O Connell, H. O. Ozer, and J. B. Pethica, Room Temperature Mechanical Thinning and Imprinting of Solid Films, Nano Letters 7 357-362 (2007).