Over decades of effort, investigations of the intrinsic phase transition behavior of nanoscale ferroelectric structures have been greatly complicated by materials processing variations and by the common and uncontrolled occurrence of spacecharge, which interacts directly with the polarization and can obscure fundamental behavior. These challenges have largely been overcome, and great progress in understanding the details of this class of phase transitions has been made, largely based on advances in the growth of high-quality, epitaxial ferroelectric films and in the theory and simulation of ferroelectricity. Here we will discuss recent progress in understanding the ferroelectric phase transition in a particular class of model systems: nanoscale perovskite thin-film heterostructures. The outlook for ferroelectric technology based on these results is promising, and extensions to laterally confined nanostructures will be described.

An overview is given on scientific and device advances for InGaAs metal oxide semiconductor heterostructures and inversion channel metal oxide semiconductor field-effect transistors (MOSFETs), with emphasis on results using ultrahigh vacuum-deposited Ga2O3(Gd2O3) [GGO] as high-κ dielectrics. Regardless of the approaches used to deposit high-κ dielectrics on InGaAs, critical material and electrical parameters of fabricating inversion channel InGaAs MOSFETs must be ready for complementary MOS technology beyond the 16-nm node, and some of these parameters have been achieved. These parameters include low interfacial density of states; low electrical leakage currents; high-temperature (800–900°C) thermal stability for high-κ dielectrics/InGaAs heterostructures, where the amorphous oxide structure and atomically smooth and sharp interfaces are retained; and oxide scalability with a capacitance equivalent thickness of ≤1 nm. Interfacial chemical properties and band parameters, which are important for device design in the high κs/InGaAs, have been thoroughly studied. Representative enhancement-mode InGaAs MOSFETs are compared and correlated with the interfacial structures. Deposition methods and electrical characteristics of high-κ dielectrics on InGaA are discussed. The inversion channel InGaAs MOSFETs of 0.4–1.0 μm gate length have exhibited excellent device performance in terms of drain current and transconductance.

Controlled pore glasses are formed through selective etching of one phase of a spinodally decomposed borosilicate glass, an old technique that is the basis of the porous Vycor synthesis technique developed in the 1920s. This technique is receiving renewed attention as these glasses find new applications as substrates for biosensing, bioreactors, precise filtration, and chromatography. Analogous techniques are being applied to crystalline ceramics, such as directed cooling of ZrO2/MgO and MgAl2O4/Al2O3 eutectics to drive phase separation with the subsequent dissolution of one phase. Pyrolytic reactive sintering is a combination of the phase separation method and the reactive sintering method to obtain a 3D porous structure network. For example, dolomite (CaMg[CO3]2) and ZrO2 yield a uniformly porous CaZrO3/MgO composite that utilizes evolved CO2 as a “pore-forming agent.” This article gives an overview of recent developments on meso- and macroporous ceramics based on phase separation and reactive sintering technologies.

Nanowires are among the most exciting one-dimensional nanomaterials because of their unique properties, which result primarily from their chemical composition and large surface area to volume ratio. These properties make them ideal building blocks for the development of next generation electronics, opto-electronics, and sensor systems. In this article, we focus on the unique mechanical properties of nanowires, which emerge from surface atoms having different electron densities and fewer bonding neighbors than atoms lying within the nanowire bulk. In this respect, atomistic simulations have revealed a plethora of novel surface-driven mechanical behavior and properties, including both increases and decreases in elastic stiffness, phase transformations, shape memory, and pseudoelastic effects. This article reviews such atomistic simulations, as well as experimental data of these phenomena, while assessing future challenges and directions.

Truly proton-conducting materials would have an immense impact on sustainable energy technologies for the 21st century, through efficient fuel cells, electrolyzers, and gas-separation membranes. However, proton conduction combined with materials stability seems difficult to achieve, and some hurdles and pathways are outlined in this article. Problems, possibilities, and artifacts of transport across and along interfaces are discussed, linked mainly to space-charge layer properties and engineering of the grain-boundary core and to water in nanovoids. The importance of protons in many semiconducting functional oxides is also explained. At lower temperatures and in humid environments, the presence of protonated cation vacancies (Ruetschi defects) is predicted and is expected to play an important role in photoelectrochemistry, catalysis, and surface transport.

Aluminum nitride (AlN) and gallium nitride (GaN) play an essential role in modern electronics, particularly in optoelectronics. Highly efficient light-emitting devices covering the ultraviolet to green spectral region are fabricated from these materials. Despite all efforts, the growth of large-size and high-quality AlN and GaN crystals for substrates, which are thermally and lattice-matched to the AlGaN-based device structures, is still in its infancy. This is due to the high equilibrium vapor pressure of nitrogen above these compounds, which requires growth techniques employing either the vapor phase or liquid solutions. The best commercially available GaN substrates show a high dislocation density of >105 per cm2 and strong bowing with a radius of curvature smaller than 10 m. This article reviews current growth techniques that look promising and may become commercially viable.

The development of laser-assisted atom-probe tomography (APT) analysis and new sample preparation approaches have led to significant advances in the characterization of semiconductor materials and device structures by APT. The high chemical sensitivity and three-dimensional spatial resolution of APT makes it uniquely capable of addressing challenges resulting from the continued shrinking of semiconductor device dimensions, the integration of new materials and interfaces, and the optimization of evolving fabrication processes. Particularly pressing concerns include the variability in device performance due to discrete impurity atom distributions, the phase and interface stability in contacts and gate dielectrics, and the validation of simulations of impurity diffusion. This overview of APT of semiconductors features research on metal-silicide contact formation and phase control, silicon field-effect transistors, and silicon and germanium nanowires. Work on silicide contacts to silicon is reviewed to demonstrate impurity characterization in small volumes and indicate how APT can facilitate defect mitigation and process optimization. Impurity contour analysis of a pFET semiconductor demonstrates the site-specificity that is achievable with current APTs and highlights complex device challenges that can be uniquely addressed. Finally, research on semiconducting nanowires and nanowire heterostructures demonstrates the potential for analysis of materials derived from bottom-up synthesis methods.

The continuous improvement in luminous efficacy of “white” light-emitting-diode (LED) sources offers the potential of considerable energy savings in general lighting applications. Recent experiments at UCSB have demonstrated 117 lumens per watt (lm/W) in white LEDs, with further improvements expected in the near future. Considerable progress has also been achieved using nonpolar GaN, such as a-plane {1120} and m-plane {1100} GaN, or semipolar GaN substrates. Such devices avoid the deleterious effects of charge separation due to spontaneous and piezoelectric polarization inherent in most c-axis-oriented devices.

Carbon dioxide (CO2) is arguably the most high-profile molecule of recent times. Although much of its bad press comes from environmental concerns associated with greenhouse gas emissions, there exists the possibility to harness this abundant resource for application to the synthesis and processing of useful materials. This article describes a selection of recent successes in using supercritical carbon dioxide (scCO2) as a solvent for polymerizations. Further, the uses of compressed CO2 as a processing tool in the fabrication of materials for applications such as coatings and biomaterials are discussed. Finally, the application of scCO2 to photolithography is demonstrated, with particular focus on CO2 as a processing solvent for the patterning of organic electronic devices.

This article provides a brief overview of recent progress in the synthesis and functionalization of magnetic nanoparticles and their applications in the early detection of malignant tumors by magnetic resonance imaging (MRI). The intrinsic low sensitivity of MRI necessitates the use of large quantities of exogenous contrast agents in many imaging studies. Magnetic nanoparticles have recently emerged as highly efficient MRI contrast agents because these nanometer-scale materials can carry high payloads while maintaining the ability to move through physiological systems. Superparamagnetic ferrite nanoparticles (such as iron oxide) provide excellent negative contrast enhancement. Recent refinement of synthetic methodologies has led to ferrite nanoparticles with narrow size distributions and high crystallinity. Target-specific tumor imaging becomes possible through functionalization of ferrite nanoparticles with targeting agents to allow for site-specific accumulation. Nanoparticulate contrast agents capable of positive contrast enhancement have recently been developed in order to overcome the drawbacks of negative contrast enhancement afforded by ferrite nanoparticles. These newly developed magnetic nanoparticles have the potential to enable physicians to diagnose cancer at the earliest stage possible and thus can have an enormous impact on more effective cancer treatment.

Cells are ion conductive gels surrounded by a ∼5-nm-thick insulating membrane, and molecular ionic pumps in the membrane establish an internal potential of approximately −90 mV. This electrical energy store is used for high-speed communication in nerve and muscle and other cells. Nature also has used this electric field for high-speed motor activity, most notably in the ear, where transduction and detection can function as high as 120 kHz. In the ear, there are two sets of sensory cells: the “inner hair cells” that generate an electrical output to the nervous system and the more numerous “outer hair cells” that use electromotility to counteract viscosity and thus sharpen resonance to improve frequency resolution. Nature, in a remarkable exhibition of nanomechanics, has made out of soft, aqueous materials a microphone and high-speed decoder capable of functioning at 120 kHz, limited only by thermal noise. Both physics and biology are only now becoming aware of the material properties of biomembranes and their ability to perform work and sense the environment. We anticipate new examples of this biopiezoelectricity will be forthcoming.

Fuels for advanced nuclear reactors differ from conventional light water reactor fuels and also vary widely because of the specific architectures and intended missions of the reactor systems proposed to deploy them. Functional requirements of all fuel designs for advanced nuclear energy systems include (1) retention of fission products and fuel nuclides, (2) dimensional stability, and (3) maintenance of a geometry that can be cooled. In all cases, anticipated fuel performance is the limiting factor in reactor system design, and cumulative effects of increased utilization and increased exposure to inservice environments degrade fuel performance. In this article, the current status of each fuel system is reviewed, and technical challenges confronting the implementation of each fuel in the context of the entire advanced reactor fuel cycle (fabrication, reactor performance, recycle) are discussed.

In this article, we briefly review a particular approach to fabricate light-emitting diode (LED) structures on the semipolar side facets of triangular GaN stripes grown by selective area epitaxy. This approach enables a significant reduction of the internal piezoelectric fields in the LED's active area, while still maintaining the well-established c-direction as the main epitaxial growth direction for GaN-based devices on large area substrates. For the latter, these internal fields are responsible for the lower efficiency of GaN-based LEDs in the longer (green) wavelength range. The reduced internal fields of such semipolar LEDs can be directly determined by photoluminescence (PL) investigations on pre-biased LED structures and further confirmed by time-resolved PL studies. The epitaxial growth behavior is strongly facet-dependent, leading to different surface flatnesses on different semipolar facets formed by this procedure and different – indium incorporation efficiencies. An increased indium uptake on semipolar {1101} facets as compared to conventional c-plane layers can help to shift the LED emission to longer wavelengths near 500 nm, despite the significantly reduced field-dependent Stark shift, which helps to reach the green wavelength range in polar LEDs.

Novel nanoionics devices, atomic switches, have been developed using a solid-electrochemical reaction to control the formation and annihilation of the metal filament between two electrodes. The switching operation can be achieved simply by the application of a bias voltage to precipitate metal atoms in a nanogap between the two electrodes or to dissolve them onto one of the electrodes. The small size of atomic switches enables rapid switching even though atomic motion is required. They also have several novel characteristics in that they are nonvolatile, consume less power, and have a simple structure and a low on-resistance. Logic gates and 1 kbit nonvolatile memory chips have been developed using atomic switches in order to demonstrate the possibilities for improving present-day electronic devices. Their characteristics also enable the fabrication of new types of electronic devices, such as high-performance programmable logic devices that may achieve a multitude of functions on a single chip.

For decades, a kind of nanoscale microstructure, known as the premartensitic “tweed structure” or “mottled structure,” has been widely observed in various martensitic or ferroelastic materials prior to their martensitic transformation, but its origin has remained obscure. Recently, a similar nanoscale microstructure also has been reported in highly doped ferroelastic systems, but it does not change into martensite; instead, it undergoes a nanoscale freezing transition—“strain glass” transition—and is frozen into a nanodomained strain glass state. This article provides a concise review of the recent experimental and modeling/simulation effort that is leading to a unified understanding of both premartensitic tweed and strain glass. The discussion shows that the premartensitic tweed or strain glass is characterized by nano-sized quasistatic ferroelastic domains caused by the existence of random point defects or dopants in ferroelastic systems. The mechanisms behind the point-defect-induced nanostructures and glass phenomena will be reviewed, and their significance in ferroic functional materials will be discussed.

The micro-pulling-down technique is a crystal growth method that has been mostly developed since 1992. The general scheme of the growth system is relatively simple: the melt (oxide, fluoride, metal) residing in a crucible is transported in downward through microcapillary channel(s) made in the bottom of the crucible. Two driving forces (capillary action and gravity) support the delivery of the melt to the liquid/solid growth interface formed under the crucible due to a properly established temperature gradient. Appropriate configuration of the crucible bottom allows for controlling of the crystal shape (fibers, rods, tubes, plates) and the dimensions of the crystals' cross sections that range approximately from 0.1 to 10 mm. A great number of scientifically and industrially important optical crystal fibers have been successfully produced using this method.

The scaling of transistors to smaller dimensions and the exploration of devices with III–V and Ge channels for digital logic places serious demands on the ohmic contacts used in these devices. Contacts with extremely low specific contact resistances are required to take full advantage of the performance promised by alternative semiconductor materials. In addition, device processes and contact morphologies must be compatible with the geometry and feature sizes of the transistors. In this article, we begin by reviewing what is known about contacts to Ge, InGaAs, InAs, and InSb, including the role of Fermi level pinning on the Schottky barrier that is often formed at the metal/semiconductor interface and common strategies for forming ohmic contacts. Then we turn our attention to the additional challenges faced when preparing ohmic contacts for the many types of field-effect transistors now under development for Ge and III–V complementary field-effect transistor technology.

Internal microstructural length scales play a fundamental role in the strength and ductility of a material. Grain boundaries in nanocrystalline structures and heterointerfaces in nanolaminates can restrict dislocation propagation and also act as a source for new dislocations, thereby affecting the detailed dynamics of dislocation-mediated plasticity. Atomistic simulation has played an important and complementary role to experiment in elucidating the nature of the dislocation/interface interaction, demonstrating a diversity of atomic-scale processes covering dislocation nucleation, propagation, absorption, and transmission at interfaces. This article reviews some atomistic simulation work that has made progress in this field and discusses possible strategies in overcoming the inherent time scale challenge of finite temperature molecular dynamics.

Many of the porous materials used in laboratory and industrial processes do not have simple regular or crystalline structures. This greatly complicates efforts to characterize them and to understand and optimize their performance for particular applications. This review surveys recent efforts to use simulation and modeling to better understand the structure and performance of several classes of materials, including phase-separated glasses, sol-gel–derived materials, templated silica materials, and activated carbons. Approaches to modeling these materials fall generally into two classes: reconstructions, which generate models based on experimental measurements, and mimetic simulations, which attempt to model the preparation of the materials. While significant progress has been made in many respects, both reconstructive and mimetic transferred currently available are often computationally intensive and not easily transferable between different classes of materials. Finally, since gas adsorption is used widely as a characterization tool for amorphous porous materials and is often the focus of the materials' application, recent developments in simulation and theory appropriate to the study of capillary phenomena in amorphous porous materials are reviewed.

The merits of atom-probe tomography (APT) of inorganic materials are well established, as described in this volume. However, one of the long-held aspirations of atom-probe scientists, structural and chemical characterization of organic and biological materials at near-atomic resolution, has yet to be fully realized. A few proof-of-concept type investigations have shown that APT of organic materials is feasible, but a number of challenges still exist with regard to specimen preparation and conversion of raw time-of-flight mass spectrometry data into a three-dimensional map of ions containing structural and chemical information at an acceptable resolution. Recent research aided by hardware improvements and specimen preparation advances has made some progress toward this goal. This article reviews the historical developments in this field, presents some recent results, and considers what life science researchers might expect from this technology.