That's amoir
Moir patterns are often unwanted artifacts in digital imaging. The commensurate/incommensurate beating of two spatially-periodic patterns (e.g., pixels in the image and pixels on a display) creates an extra superlattice that detracts from the image quality. In multilayer graphene, moir patterns signal the presence of rotational stacking faults between graphene layers; a desired product produced when multilayer graphene is grown on the carbon face of silicon carbide. Researchers at the Georgia Institute of Technology and the National Institute of Standards and Technology, show that the analysis of the resulting atomic moir patterns in epitaxial graphene can be used to determine not only the rotation angles between layers, but the strain in the layers.
When grown on the carbon-terminated (000 -1) surface of hexagonal silicon carbide, graphene layers grow in a non-graphitic form where each layer is rotated with respect to the previous one. Remarkably, as shown in a number of experiments [2-4], this configuration typically results in an electronic structure indistinguishable from single-layer graphenewith apparently little influence of the substrate. In this paper, we analyze in detail scanning tunneling micrographs of this unique material, and show that moir patterns due to as many as 4 layers are visible in the imaging. Using Fourier methods to investigate the relative periods and phases of these patterns, the authors extracted the small relative strain between layers. The methods are analogous to those employed for strain measurement via optical moir interferometry, but the periodic pattern is the atomic lattice of graphene itself. Strains less than 0.37% were detected, and strain variations could be resolved over a size scale comparable to the moir superlattice cell. The method should prove to be useful for studies of the influence of strain on the electronic and transport properties of graphene.
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LK12221E
Sucking Genes
Flexible polymers, such as long DNA, RNA molecules and proteins, can pass through a narrow pore whose size is
comparable to their molecular thickness. We highlight the richness and complexity involved in the dynamics of this
unique mode of molecular transport, called "translocation", actively driven by external forces. We show that a key
to understanding this important process lies in the response property of a chain-like flexible object to a pulling
(sucking) force, i.e., it cannot respond all at once, a fact familiar to anyone who has pulled a flexible rope in
daily life. The underlying physical picture is now starting to be unveiled, and we believe its essential character
will prove interesting to a general audience. The proposed molecular picture provides a first ever generic theory
consistent with various experimental reports, hence should be indispensible for the design of new experiments
towards an ultimate goal: a rapid, innovative method of biopolymer sequencing as well as the deeper insight into
the cellular transport of biopolymers.
