Materials Science Concepts Research Articles

Dislocations in bilayer graphene

Dislocations represent one of the most fascinating and fundamental concepts in materials science. Most importantly, dislocations are the main carriers of plastic deformation in crystalline materials. Furthermore, they can strongly affect the local electronic and optical properties of semiconductors and ionic crystals. In materials with small dimensions, they experience extensive image forces, which attract them to the surface to release strain energy. However, in layered crystals such as graphite, dislocation movement is mainly restricted to the basal plane. Thus, the dislocations cannot escape, enabling their confinement in crystals as thin as only two monolayers. To explore the nature of dislocations under such extreme boundary conditions, the material of choice is bilayer graphene, the thinnest possible quasi-two-dimensional crystal in which such linear defects can be confined. Homogeneous and robust graphene membranes derived from high-quality epitaxial graphene on silicon carbide provide an ideal platform for their investigation. Here we report the direct observation of basal-plane dislocations in freestanding bilayer graphene using transmission electron microscopy and their detailed investigation by diffraction contrast analysis and atomistic simulations. Our investigation reveals two striking size effects. First, the absence of stacking-fault energy, a unique property of bilayer graphene, leads to a characteristic dislocation pattern that corresponds to an alternating AB B[Symbol: see text]AC change of the stacking order. Second, our experiments in combination with atomistic simulations reveal a pronounced buckling of the bilayer graphene membrane that results directly from accommodation of strain. In fact, the buckling changes the strain state of the bilayer graphene and is of key importance for its electronic properties. Our findings will contribute to the understanding of dislocations and of their role in the structural, mechanical and electronic properties of bilayer and few-layer graphene.

ChemInform Abstract: Liquid‐Crystalline Ordering as a Concept in Materials Science: From Semiconductors to Stimuli‐Responsive Devices

AbstractReview: <160 refs.

Liquid‐Crystalline Ordering as a Concept in Materials Science: From Semiconductors to Stimuli‐Responsive Devices

While the unique optical properties of liquid crystals (LCs) are already well exploited for flat-panel displays, their intrinsic ability to self-organize into ordered mesophases, which are intermediate states between crystal and liquid, gives rise to a broad variety of additional applications. The high degree of molecular order, the possibility for large scale orientation, and the structural motif of the aromatic subunits recommend liquid-crystalline materials as organic semiconductors, which are solvent-processable and can easily be deposited on a substrate. The anisotropy of liquid crystals can further cause a stimuli-responsive macroscopic shape change of cross-linked polymer networks, which act as reversibly contracting artificial muscles. After illustrating the concept of liquid-crystalline order in this Review, emphasis will be placed on synthetic strategies for novel classes of LC materials, and the design and fabrication of active devices.

Materials Engineering with a Social Context: A course on Materials, Ethics, & Society

ABSTRACTA sophomore level Materials Engineering course entitled, “Materials, Ethics, & Society” at Cal Poly analyzes the interactions between technology and society, and emphasizes the communication of societal and ethical impacts of technology to diverse audiences. Students study materials in a historical context, not only to highlight specific materials science concepts, but also to explore societal-technology connections. Starting from the Stone Age, advances in civilizations have come about through discoveries and new uses of materials. World geography, history, and culture become intertwined with the casting of metals, alloy development, ceramics, and phase diagrams. Students highlight the social relevancy of materials throughout history, and seek parallel themes in today’s world. While learning about the development of the atomic bomb, students also examine the ethical dilemmas of the scientists and the current NSPE Code of Ethics for Engineers. In addition, the role of the engineering profession is examined with the NAE Engineering Grand Challenges and current news items. Students investigate how materials engineering can help society through examples of appropriate technology solutions, such as designing porosity in ceramics for water filters and food storage pots. Students develop their analytical and communication skills by discussing C.P. Snow’s “two cultures” and debating a rationale for scientific literacy. Students are also trained in informal science learning in preparation for NanoDays with young and diverse audiences. At the same time, they learn about nano-scale science and technology principles, and the associated societal and ethical implications. The course culminates with student-created videos for the general public that highlight a material or technology of importance to society and integrates the material science with ethical, environmental, and societal dimensions.

How to translate materials science concepts into K–12 student outreach activities

Abstract

Fostering a Conceptual Understanding in Undergraduate Materials Education: A Multivariable Animated Spreadsheet Approach

ABSTRACTWe describe how students explore materials science concepts using animated interactive spreadsheets. An engaging pedagogy is created in the classroom using spreadsheets in a way that initially camouflages mathematical complexity, which can later be revealed and taught. Use of off-the-shelf spreadsheet software, including freeware makes these spreadsheets universally available.

An Atom is Known by the Company it Keeps: A Constructionist Learning Environment for Materials Science Using Agent-Based Modeling

This article reports on “MaterialSim”, an undergraduate-level computational materials science set of constructionist activities which we have developed and tested in classrooms. We investigate: (a) the cognition of students engaging in scientific inquiry through interacting with simulations; (b) the effects of students programming simulations as opposed to only interacting with ready-made simulations; (c) the characteristics, advantages, and trajectories of scientific content knowledge that is articulated in epistemic forms and representational infrastructures unique to computational materials science, and (d) the principles which govern the design of computational agent-based learning environments in general and for materials science in particular. Data sources for the evaluation of these studies include classroom observations, interviews with students, videotaped sessions of model-building, questionnaires, and analysis of artifacts. Results suggest that by becoming ‘model builders,’ students develop deeper understanding of core concepts in materials science, and learn how to better identify unifying principles and behaviors within the content matter.

Hierarchic concept of structural levels and structural engineering of inorganic materials

The paper considers the hierarchic concept of structural levels in inorganic materials. On the one hand, it reflects the hierarchic structure of matter and, on the other hand, plays a significant part in the well-known materials-science triad: chemical composition–structure–properties. It is the hierarchic concept of structure that may underlie the structural engineering of materials. Special significance of the concept in nanostructured materials science is emphasized.

Applications of combinatorial approach to the investigation of optical functional materials

Recent applications of combinatorial methodology to the investigation of optical functional materials are reviewed on the basis of the authors’ work. The content includes: basic concepts of combinatorial materials science, combinatorial investigations of UV/VUV excited photoluminescence, luminescent rear earth complex doped polymer and magneto-optical materials. The fundamental synthesis techniques and characterization methods in combinatorial methodology are also illustrated in the text.

Chiral imprinting of palladium with cinchona alkaloids

In the search for new materials and concepts in materials science, metallo-organic hybrids are attractive candidates; they can combine the rich diversity of organic molecules with the advantages of metals. Transition metals such as palladium are widely applied in catalysis, and small organic molecules such as those in the cinchona alkaloid family can control the stereochemistry of a number of organic reactions. Here, we show that reducing a metal salt in the presence of a cinchona alkaloid dopant gives a chirally imprinted metallo-organic hybrid material that is catalytically active and shows moderate enantioselectivity in hydrogenation. Furthermore, using photoelectron emission spectroscopy, we show that the metal retains some chiral character even after extraction of the dopant. This simple and effective methodology opens exciting opportunities for developing a variety of chiral composite materials.

Discovery Learning Tools in Materials Science: Concept Visualization with Dynamic and Interactive Spreadsheets

AbstractMany materials science concepts can be developed into animated, interactive spreadsheets to create engaging discovery learning tools. These Excel spreadsheets do not require programming expertise. Learning how to create and use these didactically useful spreadsheets is simple and new examples can be quickly created by teachers.

Conductive polymer composite materials and their utility in electromagnetic shielding applications

AbstractCommercial electronic devices require shielding solutions that ensure electromagnetic compatibility (EMC) while accounting for effects of specific enclosure structural features such as seams, vents, and port dimensions. In practice, suitable EMC materials combine with the device operating characteristics to determine an overall shielding response. To optimally couple plastic design practices with EMC requirements, both polymer materials science and electrical engineering concepts, must be considered. Use of extrinsically conductive polymer (ECP) formulations for electronic applications has advantages in that they can be directly molded to a desired shape and serve to provide the necessary shielding while also meeting mechanical integrity requirements. Shielding and mechanical performance can be varied via filler loading or altered through wall thickness changes to satisfy demands associated with a particular device. Injection‐moldable ECP polycarbonate‐based formulations can attain average shielding effectiveness (SE) levels of ∼50–60 dB through 2 GHz at 2‐mm thickness as measured using ASTM D 4935 procedures. These values vary with thickness, and SE improvements of ∼10–20 dB are observed when increasing from 1 to 2 mm. Additionally, resultant mechanical properties of shielding composites are strong functions of overall fiber content. These interrelated material and shielding characteristics, which form the basis for filled conductive polymer use within practical enclosure shielding designs, are described. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

The defining role of structure (including epitaxy) in the plausibility of homeopathy

The key stumbling block to serious consideration of homeopathy is the presumed “implausibility” of biological activity for homeopathic medicines in which the source material is diluted past Avogadro's number of molecules. Such an argument relies heavily on the assumptions of elementary chemistry (and biochemistry), in which the material composition of a solution, (dilution factors and ligand–receptor interactions), is the essential consideration. In contrast, materials science focuses on the three-dimensional complex network structure of the condensed phase of water itself, rather than the original solute molecules. The nanoheterogenous structure of water can be determined by interactive phenomena such as epitaxy (the transmission of structural information from the surface of one material to another without the transfer of any matter), temperature–pressure processes during succussion, and formation of colloidal nanobubbles containing gaseous inclusions of oxygen, nitrogen, carbon dioxide, and possibly the remedy source material. Preliminary data obtained using Raman and Ultra-Violet–Visible (UV–VIS) spectroscopy illustrate the ability to distinguish two different homeopathic medicines ( Nux vomica and Natrum muriaticum) from one another and to differentiate, within a given medicine, the 6c, 12c, and 30c potencies. Materials science concepts and experimental tools offer a new approach to contemporary science, for making significant advances in the basic science studies of homeopathic medicines.

(ii) Deformation of materials

Summary This article provides an overview of the mechanical properties of materials with particular emphasis placed upon orthopaedic biomaterials. Engineering concepts of stress, strain, shear, yielding and failure are introduced and through consideration of microstructural mechanisms, the behaviour of materials under loading is discussed. In providing a concise overview of the deformation of materials, the reader is introduced to fundamental concepts in engineering and materials science.

Teaching What You Can’t See: Museum Exhibits as a Bridge to Learning Materials Science

AbstractThe use of exhibits in informal science education venues such as science centers and museums is an integral part of engaging students in science, encouraging them to take science courses in school, and motivating them to pursue science and engineering careers. Through an Internships in Public Science Education Program funded by the National Science Foundation and in partnership with the education efforts of the Materials Research Science and Engineering Center (MRSEC) and the Discovery World Museum of Science, Economics and Technology, we have built and tested interactive components for museum exhibits on advanced materials science and nanotechnology concepts. Our front-end assessment revealed a gap in scientific understanding about objects smaller than can be seen by the naked eye. Facts learned through standard teaching methods were easily recalled, but in-depth, conceptual knowledge and application of those facts are lacking in both children and adults. We designed interactive exhibits to specifically address this disconnect in comprehension. By inviting the learner to actively participate in an interactive exhibit activity, he or she is able to develop a deeper understanding of advanced materials concepts that are difficult to teach with textbooks alone. Formative assessment of our exhibit prototypes show that students and adults not only participate in the interactive exhibit activity, but are able to learn and apply the concepts contained within them.

Solid-state reshaping of crystals: flash increase in porosity of zirconium phosphate-hypophosphite that contains polyethylenoxa diphosphonate pillars.

Engineering of crystals and solids is an active area of research that intertwines the concepts of supramolecular chemistry and materials science. The supramolecular construction of nanoporous solids with ample, open voids that can be freely accessed by other molecular species is quite a difficult task and pursued by a vast number of research groups. One common approach is the spontaneous aggregation of dissolved small-molecular building blocks. However, its success is rather limited because for the selfaggregation to render useful architectures, one should posses a profound predictive knowledge of the involved intermolecular forces, which implies the proposition and preparation of molecules (“aggregons”) with suitable geometries and functionalities. Yet, worse, once the crystal or solid is formed, there are few opportunities, if any, to further manipulate its structure. Layered g-zirconium phosphate (g-ZP) is a versatile and well-known structure in which the phosphates that reside in the surfaces of the lamellae are topotactically replaceable by phosphonates and diphosphonates, the latter leading to pillared, porous solids. Layered g-ZP can be thus used as a carving board in which appropriate organic molecules could be orderly grafted at a controlled, low density. Therefore, size and shape of interpillar spaces may be tuned by simply choosing organic moieties of appropriate length and flexibility and by controlling the degree of pillaring. Moreover, one may select a suitable chemical response of interpillar spaces by including sophisticated functionalities in the organic chain. These facts, together with the possibility of replacing all remaining superficial phosphates by other phosphorous functions of different polarity, make the prospects of this building-block combination to be limited only by the imagination of the researcher. We report herein that the chemical response to a simple acid–base reaction induces fast, sharp porosity changes in the microcrystals of the inorganic–organic material created by stepwise, double topotactic exchange of g-ZP by pentaethylenglycol derived diphosphonic acid and hypophosphite (see Scheme 1). Treatment of exfoliated g-ZP in 1:1 water/acetone at 80 8C with the diphosphonic acid in the appropriate molar ratio (step A) led to the pillared material I of empirical formula ZrPO4[O2P(OH)2]0.74[O2P(OH)-R-(OH)PO2]0.13·nH2O, R= CH2CH2(OCH2CH2)5OCH2CH2. Careful neutralization of I with methylamine followed by treatment with hypophosporous acid (Scheme 1 step B; see Experimental Section) yielded a new material II. Elemental and thermogravimetric analyses for II gave the empirical formula Zr(PO4)(O2PH2)0.74(C14H30P2O12)0.13·0.8H2O, thus showing that all exchangeable phosphates of I were replaced by hypophosphite without appreciable loss of diphosphonate. A sample of material II, dissolved in HF/D2O, gave a P NMR spectrum with signals at 0.0, 8.9, and 25.3 ppm attributable to phosphoric, hypophosphorous, and phosphonic acids, respectively. Their relative intensity (3.97:2.91:1) was in excellent agreement with the calculated ratios (3.84:2.85:1) for the empirical formula obtained from the other techniques. FTIR of II showed the expected stretching P H band at 2403 cm 1 while solid-state MAS P NMR revealed the presence of the nonexchangeable phosphates at 27.9 and the complete disappearance of the signal at 13.6 ppm arising from exchangeable phosphates of the starting material I. Both hypophosphite and phosphonate groups gave a broad signal at about 10 ppm, whose intensity heavily increased under cross-polarization conditions (contact time 2 ms). X-ray powder diffraction of II showed a reasonable degree of crystallinity and an interlayer distance of 1.28 nm, which was independent of the degree of humidity of the sample. The unexpectedly fast swelling of material II occurred when it reacted with a very small amount of methylamine. A comparative study of the titration of I and II with methylamine is depicted in Figure 1a. While I gradually increases its interlayer distance with increasing pH (see powder XRD patterns in Figure 1b), II shows a remarkable, sharp swelling from 1.28 nm to 2.14 nm in a very narrow pH range (ca. 4.2 to 5.0) corresponding to the addition of solely 0.2 equivalents of amine. It should be noted that II suffers extensive oxidation at pH> 7. Solid-state P NMR and elemental analysis indicate that phase II completely transforms into phase I at pH 9. The forces governing the piling of g-ZP and g-ZP/ hypophosphite (g-ZPH) layers are very different. In g-ZP the outer layer of exchangeable phosphates form a network of Scheme 1. Synthesis of I and II.

An Impact Study of the Implementation of a Materials Science and Engineering Module at the Fifth Grade Level

AbstractAn impact study of the implementation of a newly developed Materials Science and Engineering Module was conducted as part of a National Science Foundation funded GK-12 project at the University of South Florida. The objective of GK-12 STARS (Students, Teachers and Resources in the Sciences) program is to foster systemic change in elementary by enriching math and science curricula and encouraging long-term professional development for teachers in the K-5 band. The program also aims to decrease the current educational gap in science and math curricula prevalent among certain schools within the same school district, which is reflected in the outcome of the Florida Comprehensive Assessment Test (FCAT). The module was developed for the purpose of enhancing existing textbook driven science instruction and creating a fundamentally sound scientific exposure in elementary school students. As part of this activity, students from three different schools (one private, one suburban, and one urban) were introduced to basic concepts in materials science and engineering through hands-on experiments, presentations, and field trips to the university's material research related laboratories (i.e. polymer chemistry, microelectronics, nanotechnology, geotechnics, corrosion, etc.) The developed module offered information ranging from basic definitions to newly discovered cutting edge phenomenon in the field of nanotechnology. Subsequently, pre and post test instruments were administered to assess student performance. Results from the pretest showed that students from all participating schools performed within the standard deviation. The post assessment test showed that the experimental group had twice as many correct answers, as the control group from each school.

A guide for students

A lighthearted and chatty overview of the concepts of materials science, Navigating the Materials World is a helpful supplement to conventional textbooks, says George Whitesides.

Using Interdisciplinary Examples in Nanotechnology to Teach Concepts of Materials Science and Engineering

ABSTRACTThe National Science Foundation-supported Materials Research Science and Engineering Center (MRSEC) on Nanostructured Materials and Interfaces at the University of Wisconsin – Madison has an extensive education and outreach effort. One theme of this effort is the development of instructional materials based on cutting-edge research in nanoscale science and engineering. The Nanoworld Cineplex contains movies and demonstrations that can be brought into classes, and the Nanotechnology Lab Manual contains numerous experiments that can be used for virtual or actual laboratories. Also available are kits, software, teaching modules and articles. A hands-on kit for nontechnical audiences, “Exploring the Nanoworld,” has been produced in collaboration with the Institute for Chemical Education.In this paper, novel hands-on demonstrations and innovative laboratory experiments aimed at the college level will be highlighted. High-tech devices and materials such as light emitting diodes (LEDs), shape memory alloys, amorphous metal, and ferrofluids are discussed in the classroom and studied in the laboratory as illustrations of nanotechnology and its impact on energy, the environment and our quality of life. These examples illustrate interdisciplinary research that provides connections among materials science, chemistry, physics, engineering, and the life sciences. They also highlight the tools of nanotechnology, such as scanning probe microscopy, electron microscopy, x-ray diffraction, and chemical vapor deposition, which are associated with the preparation and characterization of nanostructured materials. Demonstrations of the incorporation of nanotechnology to teach fundamental materials science principles presented are summarized at http://www.mrsec.wisc.edu/edetc.

Managing Student Group Projects in an Introductory Materials Science Course

ABSTRACTIn an introductory materials science course for mechanical and industrial engineering sophomores, a term-long student team project is included as a graded activity. Successful completion of the project fulfills three course objectives where students learn 1) to compose professional reports in teams and demonstrate effective communication skills, 2) to apply introductory concepts of materials science well enough to follow technical articles on various topics, and 3) to locate resources to gather additional information related to a topic. To help students learn to research a topic, to write, to work in teams, and to speak publicly, the course includes guest lectures with various instructors with expertise in library research skills, technical writing, and communication studies. Course assessment indicates that sophomores find their projects interesting and they report learning a lot about the topics they selected. Interventions in the early stages of the curriculum allow the students to perform better during their senior year Capstone Design Project. The details of how the projects are managed will be described.