Quantitative electron phase imaging with high sensitivity and an unlimited field of view

As it passes through a sample, an electron beam scatters, producing an exit wavefront rich in information. A range of material properties, from electric and magnetic field strengths to specimen thickness, strain maps and mean inner potentials, can be extrapolated from its phase and mapped at the nanoscale. Unfortunately, the phase signal is not straightforward to obtain. It is most commonly measured using off-axis electron holography, but this is experimentally challenging, places constraints on the sample and has a limited field of view. Here we report an alternative method that avoids these limitations and is easily implemented on an unmodified transmission electron microscope (TEM) operating in the familiar selected area diffraction mode. We use ptychography, an imaging technique popular amongst the X-ray microscopy community; recent advances in reconstruction algorithms now reveal its potential as a tool for highly sensitive, quantitative electron phase imaging

Search engine optimization : a new literacy practice

Search Engine Optimization (SEO) is the technical practice of modifying a website to receive higher rankings on search engines such as Google. Computer programmers carefully place keywords within content of frequently updated websites such as blogs, social networks\u27 discussion boards, and company profile sites so the site will appear at a higher ranking on search engines and capture potential consumers\u27 attention. Search engines frequently change the algorithms that scan websites and display them on search results listings, meaning the writers and computer programmers who focus on this optimization must constantly adjust their tactics for new rhetorical situations. This technical writing focuses not only on content and keyword count but essentially the goal of constantly drawing attention to the information they produce and exchange. Following this conception of literacy, Search Engine Optimization writing as a literacy practice includes technical programming skills to create web content. This content is intended to reach a human audience but is mediated by the technical knowledge of search engine algorithms. New literacy practices describe not only new technical genres but reflect that the process of creating such genres and the social motives for creation are non-traditional or new. SEO writing involves new technical writing skills and styles of writing, as well as a new purpose, not just selling products or achieving recognition, but gaining the attention of search engines that often control web users access to information. Exploring the literacy practice of such writing will demonstrate how technical and professional communicators have adapted to new genres and rhetorical situations in a digital landscape

Search engine optimization: a new literacy practice

Search Engine Optimization (SEO) is the technical practice of modifying a website to receive higher rankings on search engines such as Google. Computer programmers carefully place keywords within content of frequently updated websites such as blogs, social networks\u27 discussion boards, and company profile sites so the site will appear at a higher ranking on search engines and capture potential consumers\u27 attention. Search engines frequently change the algorithms that scan websites and display them on search results listings, meaning the writers and computer programmers who focus on this optimization must constantly adjust their tactics for new rhetorical situations. This technical writing focuses not only on content and keyword count but essentially the goal of constantly drawing attention to the information they produce and exchange. Following this conception of literacy, Search Engine Optimization writing as a literacy practice includes technical programming skills to create web content. This content is intended to reach a human audience but is mediated by the technical knowledge of search engine algorithms. New literacy practices describe not only new technical genres but reflect that the process of creating such genres and the social motives for creation are non-traditional or new. SEO writing involves new technical writing skills and styles of writing, as well as a new purpose, not just selling products or achieving recognition, but gaining the attention of search engines that often control web users access to information. Exploring the literacy practice of such writing will demonstrate how technical and professional communicators have adapted to new genres and rhetorical situations in a digital landscape

Holographic imaging with a hard x-ray nanoprobe : Ptychographic versus conventional phase retrieval

We have performed near-field x-ray imaging with simultaneous object and probe reconstruction. By an advanced ptychographic algorithm based on longitudinal and lateral translations, full-field images of nanoscale objects are reconstructed with quantitative contrast values, along with the extended wavefronts used to illuminate the objects. The imaging scheme makes idealizing assumptions on the probe obsolete, and efficiently disentangles phase shifts related to the object from the imperfections in the illumination. We validate this approach by comparison to the conventional reconstruction scheme without simultaneous probe retrieval, based on the contrast transfer function algorithm. To this end, a set of semiconductor nanowires with controlled chemical composition (InP core, insulating SiO2 layer, and indium tin oxide cover) is imaged using the quasi-point source illumination realized by the hard x-ray nanofocus (26 nm x 39 nm spot size) of the ID16A Nano-Imaging beamline at the European Synchrotron Radiation Facility

Validity of the empty-beam correction in near-field imaging

Extended wavefronts are used for coherent full field imaging of objects based on solving the inverse Fresnel diffraction problem. To this end, the conventional data correction step is given by division of the recorded object image by the intensity pattern of the empty beam. This division of intensities in the detection plane is a rather crude approximation for the separation of the complex valued object and probing fields. Here we present a quantitative error estimate, along with its mathematical proof, and confirm the prediction with numerical simulations. Finally the problem is illustrated with experimental results

Near-field ptychography using lateral and longitudinal shifts

ISSN:1367-263