Recent advances in x-ray and neutron sources, optics, and scattering methods are heralding a new age in the study of the structure and properties of complex materials. By providing unprecedented resolution in real space, reciprocal space, and time, new techniques address materials characterization challenges beyond anything possible before, at length scales ranging from the atomic scale to the mesoscale, and at times as short as femtoseconds. The high degree of coherence of third-generation synchrotron sources permits a new level of precision in the quantitative description and analysis of diffraction and scattering and allows beams with sizes probing individual nanostructures to be produced. As a result, in situx-ray and neutron analysis techniques now provide insight into the structure of nanomaterials and yield a more precise set of metrics describing the nanometer-scale structure of materials. Time resolution and in situ studies allow application of these techniques to materials driven far from equilibrium and to the challenging environment associated with materials processing.

Surfaces and buried interfaces play critical roles in many environmental, catalytic, and tribological processes and in a wide variety of applications, including microelectronics and optoelectronics. Interfacial structure and composition are closely coupled to their surroundings, and probes that yield information about materials in situ are essential to obtain a thorough understanding of interface functions and properties. The highly brilliant, hard x-rays available from synchrotron light sources can easily penetrate through gas or liquid environments, or even solid thin-film overlayers, and enable real-time monitoring of the evolving chemistry and structure of the interface with atomic-scale resolution. Here we review the in situ study of interfaces by a variety of synchrotron x-ray scattering techniques and provide several examples of their application in electrochemical processes and thin-film island growth. We also discuss recent advances in analytical techniques and x-ray optics that are facilitating the in situ study of surfaces and buried interfaces with direct imaging.

Recent advances in pulsed x-ray sources have opened up new opportunities to study the dynamics of matter directly in the time domain with picosecond to femtosecond resolution. In this article, we present recent results from a variety of ultrafast sources on time-resolved x-ray scattering from elementary excitations in periodic solids. A few representative examples are given on folded acoustic phonons, coherent optical phonons, squeezed phonons, and polaritons excited by femtosecond lasers. Next-generation light sources, such as the x-ray-free electron laser, will lead to improvements in coherence, flux, and pulse duration. These experiments demonstrate potential opportunities for studying matter far from equilibrium on the fastest time scales and shortest distances that will be available in the coming years.

X-ray and neutron diffraction have been two key techniques for structural characterization of materials since their inception. If single crystals of the materials of interest cannot be synthesized, one has to resort to powder diffraction. This results in the loss of three-dimensional orientation information of the crystal, and one has to contend with the one-dimensional information that is inherent to powder diffraction, making it harder to analyze the data. The structural study of contemporary materials and their remarkable properties is a challenging problem, particularly when properties of interest result from interplay of multiple degrees of freedom. Very often these are associated with structural defects or relate to different length scales in a material. The signature of the defect-related phenomenon is visible as diffuse scattering in the diffraction pattern, and the signals associated with diffuse scattering are orders of magnitude smaller than Bragg scattering. Given these limitations, it is crucial to have high-resolution and high-intensity data along with the ability to carry out theoretical interpretation that goes beyond periodic lattice formalism of crystallography. Great advances have been achieved due to the advent of synchrotron and neutron sources, along with the availability of high-speed computational algorithms allowing materials scientists to work with a very small amount of sample (both single crystal and powder) and analyze vast amounts of data to unravel detailed structural descriptions that were not previously possible. This article presents some of these great advances in using scattering probes for materials characterization.

Advances in nanoscale directed assembly strategies have enabled researchers to analogize atomic assembly via chemical reactions and nanoparticle assembly, creating a new nanoscale “periodic table.” We are just beginning to realize the nanoparticle equivalents of molecules and extended materials and are currently developing the ground rules for creating programmable nanometer-scale coordination environments. The ability to create a diverse set of nanoscale architectures from one class of nanoparticle building blocks would allow for the synthesis of designer materials, wherein the physical properties of a material could be predicted and controlled a priori. Our group has taken the first steps toward this goal and developed a means of creating tailorable assembly environments using DNA-nanoparticle conjugates. These nanobioconjugates combine the discrete plasmon resonances of gold nanoparticles with the synthetically controllable and highly selective recognition properties of DNA. Herein, we elucidate the beneficial properties of these materials in diagnostic, therapeutic, and detection capabilities and project their potential use as nanoscale assembly agents to realize complex three-dimensional nanostructures.