This article describes various techniques for applying strain to current and future complementary metal–oxide–semiconductor (CMOS) channels to boost CMOS performance. A brief history of both biaxial and uniaxial strain engineering in planar CMOS technology is discussed. Scalability challenges associated with process-induced uniaxial strain in sub-22 nm CMOS is highlighted in view of shrinking device dimensions and 3D device architecture (such as fin field-effect transistors [FinFETs]). Non-uniform strain relaxation in patterned geometries in tight pitch two- and three-dimensional devices is addressed. A case is made that the future scalable strain platform will require a combination of biaxial strain at wafer level in conjunction with local uniaxial strain. Finally, potential application of strain engineering to advanced III–V metal oxide semiconductor FET channels will be examined.

Elastic strain engineering offers a new route to enable high-performance catalysts, electrochemical energy conversion devices, separation membranes and memristors. By applying mechanical stress, the inherent energy landscape of reactions involved in the material can be altered. This is the so-called mechano-chemical coupling. Here we discuss how elastic strain activates reactions on metals and oxides. We also present analogies to strained polymer reactions. A rich set of investigations have been performed on strained metal surfaces over the last 15 years, and the mechanistic reasons behind strain-induced reactivity are explained by an electronic structure model. On the other hand, the potential of strain engineering of oxides for catalytic and energy applications has been largely underexplored. In oxides, mechanical stress couples to reaction and diffusion kinetics by altering the oxygen defect formation enthalpy, migration energy barrier, adsorption energy, dissociation barrier, and charge transfer barrier. A generalization of the principles for stress activated reactions from polymers to metals to oxides is offered, and the prospect of using elastic strain to tune reaction and diffusion kinetics in functional oxides is discussed.

The evolution of elastic strain engineering in nanostructures and devices requires characterization tools that can be used to not only observe but also quantify the actual strain in a sample, whether this strain is intrinsic or applied. Strain contrast in crystalline samples has always been one of the primary contrast mechanisms used for imaging the microstructure of a material in a transmission electron microscope (TEM). In this regard, TEM is a particularly powerful tool due to its ability to spatially resolve strain information with high precision and spatial resolution. This article reviews the techniques currently available for directly measuring strain in the TEM. Examples are given for measuring strain in semiconductor devices using imaging, diffraction, and holographic techniques. For strain measurement during in situ mechanical testing, two general methods are presented: the conversion of displacement from an actuation device or the direct measurement of strain using image features during deformation.

“Smaller is stronger.” Nanostructured materials such as thin films, nanowires, nanoparticles, bulk nanocomposites, and atomic sheets can withstand non-hydrostatic (e.g., tensile or shear) stresses up to a significant fraction of their ideal strength without inelastic relaxation by plasticity or fracture. Large elastic strains, up to ∼10%, can be generated by epitaxy or by external loading on small-volume or bulk-scale nanomaterials and can be spatially homogeneous or inhomogeneous. This leads to new possibilities for tuning the physical and chemical properties of a material, such as electronic, optical, magnetic, phononic, and catalytic properties, by varying the six-dimensional elastic strain as continuous variables. By controlling the elastic strain field statically or dynamically, a much larger parameter space opens up for optimizing the functional properties of materials, which gives new meaning to Richard Feynman’s 1959 statement, “there’s plenty of room at the bottom.”

Deformation is one of the most fundamental aspects of materials. While mechanical failure is an outcome of deformation to be avoided, elastic deformation can have a pronounced and positive impact on materials properties. The effect of elastic deformation becomes even more evident at low dimensions, because at the micro/nanoscale, materials and structures can usually sustain exceptionally high elastic strains before failure. The purpose of this overview is to present a summary of recent progress on elastically strained nanowires and atomic sheets. First, we will demonstrate that nanowires can sustain large elastic strains, and their bending modulus increases exponentially as the nanowire diameter decreases. Second, the elastic strain has been found to significantly modify the electronic structure of semiconductor nano/microwires to induce a metal–insulator transition at room temperature and to efficiently transform the mechanical energy into electricity. These recent developments point to potential future applications based on the elastic strain engineering of nanoscale materials.

Commonly used techniques for cleaning copper substrates before graphene growth via chemical vapor deposition (CVD), such as rinsing with acetone, nitric, and acetic acid, and high temperature hydrogen annealing still leave residual adventitious carbon on the copper surface. This residual carbon promotes graphene nucleation and leads to higher nucleation density. We find that copper with an oxidized surface can act as a self-cleaning substrate for graphene growth by CVD. Under vacuum conditions, copper oxide thermally decomposes, releasing oxygen from the substrate surface. The released oxygen reacts with the carbon residues on the copper surface and forms volatile carbon monoxide and carbon dioxide, leaving a clean copper surface free of carbon for large-area graphene growth. Using oxidized electropolished copper foil leads to a reduction in graphene nucleation density by over a factor of 1000 when compared to using chemically cleaned oxygen free copper foil.

The magnetic properties of Sr3SnO (SSO) epitaxial thin films prepared under various post-growth annealing treatments are reported. The SSO films are grown on cubic yttria-stabilized zirconia Si (001) platform by pulsed laser deposition. Post-growth vacuum annealing is found to enhance the room-temperature ferromagnetism (RTFM), whereas oxygen annealing reduces it. The results are explained through the oxygen vacancy constituted bound magnetic polarons (BMP) model. An empirical relationship between the extracted BMP concentration and the oxygen vacancy concentration is shown using X-ray photoelectron spectroscopy data. The results indicate a promising way to tune RTFM by manipulating oxygen vacancies and related defects.

Two-dimensional crystals are an important class of materials for novel physics, chemistry, and engineering. Germanane (GeH), the germanium-based analogue of graphane (CH), is of particular interest due to its direct band gap and spin–orbit coupling. Here, we report the successful co-deposition growth of CaGe2 films on Ge(111) substrates by molecular beam epitaxy and their subsequent conversion to germanane by immersion in hydrochloric acid. We find that the growth of CaGe2 occurs within an adsorption-limited growth regime, which ensures stoichiometry of the film. We utilize in situ reflection high energy electron diffraction (RHEED) to explore the growth temperature window and find the best RHEED patterns at 750 °C. Finally, the CaGe2 films are immersed in hydrochloric acid to convert the films to germanane. Auger electron spectroscopy of the resulting film indicates the removal of Ca, and RHEED patterns indicate a single-crystal film with an in-plane orientation dictated by the underlying Ge(111) substrate. X-ray diffraction and Raman spectroscopy indicate that the resulting films are indeed germanane. Ex situ atomic force microscopy shows that the grain size of the germanane is on the order of a few micrometers, being primarily limited by terraces induced by the miscut of the Ge substrate. Thus, optimization of the substrate could lead to the long-term goal of large area germanane films.

Sodium dodecyl sulfate (SDS) was chosen as the structure controller and surface modifier for hydrothermal preparation of surfactant-modified goethite (α-FeOOH) nanorods. The as-synthesized samples were characterized by transmission electron microscopy, x-ray diffraction, Fourier transform infrared spectroscopy, Brunauer, Emmett and Teller technique, and potentiometric titration. Adsorption study using methylene blue (MB) as a model pollutant was conducted onto the surfactant-modified goethite surface. The results showed that the surfactant-modified α-FeOOH nanorods had high adsorption capacity. MB could be efficiently removed from the solution at pH 5, initial MB concentration 200 mg/L, α-FeOOH dosage 0.5 g/L, and temperature 30 °C, with 96% removal ratio. The adsorption capacity was found to be as high as 385 mg/g. The adsorption kinetic data could be described well by the pseudo-second-order model. The isothermic data were highly fitted to Langmuir isotherm. High adsorption capacity and simple reaction conditions give this novel material good prospects in future applications.

The effects of electropulsing treatment (EPT) on the recrystallization and texture of Ni9W alloy were investigated using micro-hardness and electron backscattered diffraction patterns. It is found that compared with conventional annealing, EPT tremendously accelerates the recrystallization process of Ni9W alloy. Moreover, the full recrystallization temperature of EPT is decreased by ∼180 °C. The rapid recrystallization process is attributed to the substantial increase in the atomic flux resulting from the athermal effect. EPT also significantly reduces the intensity of cube texture after full recrystallization. The evolution of recrystallization microstructure and texture reveals that EPT greatly increases the proportion of noncube oriented nuclei but has little effect on the size advantage of cube grains. It is suggested that the change of recrystallization texture results from the different effects of EPT on cube band nucleation and shear band nucleation.