The solid state provides a richly varied fabric for intertwining chemical bonding, electronic structure, and magnetism. The discovery of superconductivity in iron pnictides and chalcogenides has revealed new aspects of this interplay, especially involving magnetism and superconductivity. Moreover, it has challenged prior thinking about high-temperature superconductivity by providing a set of materials that differ in many crucial aspects from the previously known cuprate superconductors. Here we review some of what is known about the superconductivity and its interplay with magnetism, chemistry, and electronic structure in Fe-based superconductors.

Indium tin oxide (ITO) is the most widely used transparent electrode material today. Although the material possesses a superior combination of high optical transparency and large conductance, conventional ITO thin-film deposition techniques are incompatible with the mechanical and thermal requirements associated with the emerging class of flexible electronic devices. To address this issue, the status of the development of ITO nanostructures such as nanowires and nanoparticles will be reviewed in this article. Two major achievements to be discussed are the growth of vertically oriented arrays of ITO nanowires and the synthesis of small diameter, monodisperse ITO nanoparticles. In addition, solutions of these materials can be deposited utilizing existing printed electronics manufacturing techniques to realize highly transparent, conductive, and flexible ITO thin films on a diverse range of substrates, including plastics. These nanomaterial-based approaches could one day help realize low-cost, flexible electronics based on transparent thin-film electrodes.

Bacteria often live in the form of surface-associated communities of cells termed biofilms. Within biofilms, there is a division of labor in which genetically identical cells differentiate to serve distinct functions. This cellular differentiation results from a response to extracellular signals that occur due to changes in the local environment of a cell or in response to signaling molecules that the cells themselves produce. In this review, we discuss differentiation in biofilms, focusing on the molecular mechanisms that regulate differentiation in the bacterium Bacillus subtilis. In this organism, there is a subpopulation of cells within a biofilm that produces a signal, while a different subpopulation of cells responds to it. Studying what signals cells use to communicate with each other within a biofilm will allow for better design of strategies to prevent and disrupt biofilms.

Laser-assisted bioprinting is one among several technologies that are being developed in the recent and growing field of bioprinting. Bioprinting is defined as the use of computer-aided transfer processes for patterning and assembling living and non-living materials with a prescribed 2D or 3D organization in order to produce bio-engineered structures serving in regenerative medicine, pharmacology, and basic cell biology studies. We describe the physical parameters that need to be tuned for laser-assisted bioprinting of materials and cells, with high throughput and controlled printing resolution. We present its applications for printing cells and tissue-relevant biomaterials, both in vitro and in vivo. Finally, we discuss how this technique may help in reproducing the local cell micro-environment and dealing with tissue complexity and heterogeneity for fabricating functional tissue-engineered 3D constructs.

This article is based on the Fred Kavli Distinguished Lectureship in Nanoscience presentation given by Harry Atwater (California Institute of Technology) on April 5, 2010 at the Materials Research Society Spring Meeting in San Francisco, CA. The Kavli Foundation supports scientific research, honors scientific achievement, and promotes public understanding of scientists and their work. Its particular focuses are astrophysics, nanoscience, and neuroscience.

Solar energy is currently enjoying substantial growth and investment, owing to worldwide sensitivity to energy security and climate change. Solar energy is an inexhaustible resource and is in abundant supply on all continents of the world. The power density of sunlight (~1000 W/m2) and the efficiency of photovoltaic devices (~10–25%) are high enough so that land use does not limit photovoltaic deployment at the terawatt scale. However solar photovoltaics are currently too expensive to achieve parity with other forms of electricity generation based on fossil fuels. This is largely due to the cost (and for some cases, the abundance) of materials used in photovoltaic modules and systems, and the cost of deploying in current form. This economic and social context has created the present situation where there is widespread interest in photovoltaic technology for power generation, but the cumulative installed world capacity for photovoltaics is <50 GW, and it appears to be very challenging for photovoltaics to play a very substantial role in large-scale (terawatt) electricity generation in the short term.

Thin-film photovoltaic technologies have an enormous potential to reduce the cost of solar electricity. However, because thin photoactive layers are used, optical absorption is incomplete unless light-trapping strategies are employed. Since conventional light-trapping approaches based on geometric scattering are less effective in thin-film cells, coherent light-trapping approaches that exploit the wave nature of light are being explored to enhance optical absorption. In this article, we look at the various strategies for coherent light trapping in thin-film solar cells, including photonic crystals, metal nanostructures, and multilayer stacks. The suitability of a particular strategy depends on factors such as configuration of the solar cell, process compatibility, cost, desired angular response, and materials usage. We also discuss the physical limits of light trapping in thin films.

A novel contact technique to reduce the effective Schottky barrier height on Ge and III–V high mobility semiconductors is described. Single metals are used in combination with an ultrathin dielectric to tune the metal/semiconductor barrier height toward zero by shifting or suppressing the strong Fermi-level pinning. Barrier height reduction in the metal-insulator-semiconductor (MIS) contact structure is verified through direct measurements and deduced from increased diode current and reduced contact resistance. Current demonstrations of the MIS contact have barriers as low as 0.05 eV for Er/SiN/n-Ge and 0.18 eV for Al/Al2O3/n-GaAs. The underlying physics is discussed along with the dependence of the minimum achievable contact resistance and barrier height on the metal, dielectric material, dielectric thickness, and substrate doping. For Ge, the MIS contact provides a possible solution to the low n-type Ge dopant solubility problem and allows for the fabrication of Schottky barrier field-effect transistors. For III–V semiconductors, the MIS contact allows for the use of a non-alloyed contact that is crucial for the scalability of III–V metal oxide semiconductor field-effect transistors.

Bio-based plastics, in which the fossil carbon is replaced by bio/renewable-based carbon, offer the intrinsic value proposition of a reduced carbon footprint and are in complete harmony with the rates and time scale of the biological carbon cycle. Identification and quantification of bio-based content is based on the radioactive C-14 signature associated with (new) biocarbon. Using experimentally determined biocarbon content values, one can calculate the intrinsic CO2 emissions reduction achieved by substituting petrocarbon with biocarbon—the material carbon footprint value proposition. The process carbon footprint arising from the conversion of feedstock to final product is computed using life-cycle assessment methodology. Biodegradability in conjunction with selected disposal systems such as composting and anaerobic digestion offers an end-of-life solution to completely remove the plastic substrate from the environment. Not all bio-based polymer materials are biodegradable, and not all biodegradable polymers are bio-based. Most importantly, complete biodegradability (complete utilization of the polymer by the microorganisms present in the disposal environment) is necessary as per ASTM and ISO standards, otherwise there could be serious health and environmental consequences.

Three-dimensional (3D) battery architectures have emerged as a new direction for powering microelectromechanical systems and other small autonomous devices. Although there are few examples to date of fully functioning 3D batteries, these power sources have the potential to achieve high power density and high energy density in a small footprint. This overview highlights the various architectures proposed for 3D batteries, the advances made in the fabrication of components designed for these devices, and the remaining technical challenges. Efforts directed at establishing design rules for 3D architectures and modeling are providing insight concerning the energy density and current uniformity achievable with these architectures. The significant progress made on the fabrication of electrodes and electrolytes designed for 3D batteries is an indication that a number of these battery architectures will be successfully demonstrated within the next few years.

Education research strongly indicates that students make decisions in their mid- to late adolescence that impact the general direction of their careers, including choices about pursuing studies in science and mathematics. Educators can play an important role in these student career choices. By creating and implementing teacher professional development programs that increase teachers’ awareness/understanding of materials science and providing materials science-based classroom materials, researchers can take concrete actions toward improving the number and quality of students entering materials science and engineering departments as undergraduate students. No matter where you live or work throughout the world, there is a school nearby and abundant opportunities for researchers to make a difference in K–12 science education.

Hydrogen is considered by some to be a promising non-CO2-emitting energy carrier for the future. However, to realize a hydrogen economy, there are several technological barriers to overcome. Currently, safe and efficient storage of hydrogen is a bottleneck in the practical usage of hydrogen for fuels. In this article, we present a review on the first-principles computational approach in designing hydrogen storage materials with an emphasis on molecular hydrogen storage in nanostructured materials. Given the limitation of pristine nanostructures for room-temperature hydrogen storage, the strategy of decorating the backbone structure of the nanostructure with transition metal atoms in order to enhance the hydrogen adsorption energy is addressed, and the interplay between the Coulomb interactions and the so-called Kubas interaction (nondissociative weak chemisorption via electron donation and back-donation channels) has been studied. The influence of electron spin on the hydrogen binding energy, problems of metal clustering and oxidation, and the structural instability that may arise during hydrogen sorption are also discussed. We address the limitations and challenges in the development of high-capacity hydrogen storage materials and provide perspectives for how computational materials design can help cope with those problems.

As applications of atomic layer deposition (ALD) in emerging areas such as nanoelectronics, photovoltaics, and flexible electronics expand beyond single-wafer semiconductor processing, there is a growing need for novel approaches to integrate new process designs, substrate materials, and substrate delivery methods. An overview is given of new means to extend the capabilities of ALD and to improve the speed and simplicity of ALD coatings using new reactor designs. These include energy-enhanced and spatial ALD schemes involving plasma, direct-write, atmospheric pressure, and roll-to-roll processing. The long-term goal of this work is to integrate viable high-throughput capabilities with ALD processes.

With exceptional carrier mobilities, mechanical strength, and optical transparency, graphene is a leading material for next-generation electronic devices. However, for most applications, graphene will need to be integrated with other materials, which motivates efforts to understand and tune its surface chemistry. In particular, the modification of graphene via organic functionalization holds promise for tuning the electronic properties of graphene, controlling interfaces with other materials, and tailoring surface chemical reactivity. Toward these ends, this article reviews recent work from our laboratory on noncovalent and covalent organic functionalization of graphene. Using ultrahigh vacuum scanning tunneling microscopy (UHV STM), the molecular ordering and electronic properties of organic adlayers on graphene are characterized at the molecular scale. In addition, UHV STM is employed to nanopattern these organic layers with sub-5 nm resolution, thus providing a pathway for producing graphene-based heteromolecular nanostructures.

Ionic motion and electrochemistry in bulk materials and at their surfaces have long been studied for their relevance in several areas of science and technology, ranging from ionic conductors to batteries to fuel cells. The ability to engineer materials at the nanometer scale, however, has made these concepts even more relevant. This is due to the large surface-to-volume ratios typical of nanostructures. This implies, for instance, that chemical reactivity and defect motion at surfaces or interfaces are enhanced or may be fundamentally different compared to their bulk counterparts. In addition, nominally modest voltages or differences in chemical potential when applied across nanoscale distances can produce large electric fields and diffusive forces. While all of this may complicate the interpretation of experimental results, it also presents us with new opportunities for materials engineering. In this article, we will briefly review the current research status of several systems where ionic motion and electrochemical effects are of particular importance. These include resistive switching systems, oxide heterostructures, ferroelectric materials, and ionic liquids. We will report on experimental results and also emphasize open questions regarding their interpretation. We will conclude by discussing future research directions in the field.

Bacteria living in surface-attached biofilm communities must maintain electrochemical gradients to support basic cellular functions, including chemo-osmotic transport and adenosine triphosphate synthesis. Central to this is the maintenance of electron flow to terminal electron acceptors. These acceptors can be soluble inorganic and organic molecules, such as oxygen, nitrate, sulfate, dimethyl sulfoxide, or fumarate, or solid metal oxides, such as Fe(III) and Mn(IV) oxides. When electrons are transferred to a solid substrate, they may be (1) carried directly to the acceptor via outer membrane cytochromes, (2) carried by electron shuttle molecules, (3) transferred along conductive protein nanowires, or (4) conducted through other extracellular matrices. No matter what the electron acceptor is, in the laboratory, bacterial biofilms are frequently studied while growing on inert surfaces, incapable of electron transfer. However, in natural environments, as well as many industrial and biotechnology settings, biofilms grow on electrically active surfaces. In this review, we propose that the study of bacterial biofilms on redox-active surfaces is important both for the development of industrial processes, such as microbial fuel cells and wastewater treatment systems, as well as for our understanding of how these communities of microbes affect global nutrient cycling, other geobiological processes, and even human disease.

Microchips have revolutionized biological analysis since they can be used to perform biochemical analysis with high efficiency and accuracy. Femtosecond laser direct writing followed by wet chemical etching can be used to fabricate hollow microstructures with almost any three-dimensional (3D) structure without stacking or bonding. This permits microfluidic systems to be integrated with micro-optical components (e.g., mirrors and lenses) and micromechanical components (e.g., valves and pumps) in a glass chip by a single continuous process. Furthermore, other micro-optical components such as optical waveguides and attenuators can be integrated by additional femtosecond laser direct writing. Thus, femtosecond laser direct writing can be used to fabricate functional microfluidics, optofluidics, lab-on-a-chip devices, and micro-total analysis systems. In this study, 3D femtosecond laser micromachining is used to fabricate microchips integrated with functional microcomponents for biological analysis. Optofluidic systems, in which microfluidic components are integrated with micro-optical components, are used to detect single cells and perform high-sensitivity analysis of liquid samples by optical methods. Another interesting microchip is introduced, namely nanoaquariums, which is used for performing dynamic observations of microorganisms and bacteria and allows the functions of microorganisms and bacteria to be determined, such as elucidation of the gliding mechanism of Phormidium to seedling roots for growth acceleration of vegetables.

The energy science of clathrate hydrates is a rapidly expanding field, with high-performance computing (HPC) playing an ever-growing role to help understand the molecular processes and properties that drive clathrate hydrates to nucleate and grow into crystalline, amorphous, or mixed structures, their non-stoichiometric nature upon formation, the formation mechanism from homogeneous and heterogeneous nucleation, and their stability and limits of metastability. Many of the questions that HPC can help to answer about hydrates are intractable experimentally because of the difficulty of measurements at the length (nanometers) and time (nanoseconds) scales imposed by the fundamental phenomena at the molecular level. At the same time, the length and time scales that are accessible by simulations pose limitations on what can be studied (e.g., phase equilibria and metastability, nucleation mechanisms, non-stoichiometry) and how it can be studied (e.g., Monte Carlo, molecular dynamics, metadynamics, transition path sampling, thermodynamic integration). Ultimately, the energy science of clathrate hydrates will benefit from HPC by gaining insight into the detailed mechanism for formation, dissociation, and stability.

Most K–12 outreach programs worldwide within materials science and beyond rely on scientists visiting K–12 classrooms and assisting teachers with instruction and development of classroom materials, as well as developing on-site professional development workshops. Due to the limited time materials scientists and teachers have available for participating in K–12 outreach programs, more creative approaches are necessary to accommodate the needs of a broader spectrum of teachers and students. Incorporating technology into K–12 outreach programs is one approach that can be used to overcome some of the obstacles currently faced. This article discusses different manners in which technology can be included in K–12 materials science outreach programs, such as K–12 educational software and tools as well as online professional development programs. This article also draws on broader educational technology research to identify known challenges of incorporating technology into outreach programs and possible ways to overcome such challenges.

Ultrafast science—the study of highly complex and extremely short-lived transient events—has become an area of significant interest in the materials sciences, physics, chemistry, and biology. This article focuses on the state-of-the-art instrumentation and a few of the available probes and techniques, and intends to give a brief overview of the possibilities and challenges for ultrafast materials sciences and for the instrumentation that is required. The pulsed laser-material interactions are briefly introduced, since they are the principal methods to access and trigger ultrafast processes in materials. The associated time and length scales and a few experimental possibilities in the materials sciences are discussed in the first part of this article. The second part deals with the two most applicable types of pulsed probes, x-rays and electrons, and the associated methods to interrogate ultrafast processes. Emphasis is on their differences, capabilities, and limitations.