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This course text provides comprehensive coverage for fundamental and advanced courses in nanoelectronics. It provides insight into the future of electronics, emerging devices, logic and memory, sensors, systems architecture, nanofabrication, and the fundamental physics behind nanoelectronics.

A new source of softening Conventional metals gain much of their strength through the interaction of dislocations with obstacles such as grain boundaries, whereas the geometrical constraints prevailing in nanostructured materials limit such effects. Huajian Gao and colleagues now report molecular dynamics simulations which reveal that the strength of ultrafine grained copper containing twin boundaries can be controlled by a dislocation nucleation mechanism activated below a critical twin thickness. The motion of the new dislocations leads to the migration of twin planes, and as a result the material becomes softer. The smaller the grains, the smaller the twin-boundary spacing and the higher the maximum strength of the material. The strength of conventional metals is determined by the interaction of dislocations with obstacles such as grain boundaries. Molecular dynamics simulations reveal that the strength of ultrafine-grained copper containing twin boundaries can be controlled by a dislocation nucleation mechanism activated below a critical twin thickness. Below this thickness the material becomes softer. The smaller the grains, the smaller the critical twin boundary spacing, and the higher the metal's maximum strength. In conventional metals, there is plenty of space for dislocations—line defects whose motion results in permanent material deformation—to multiply, so that the metal strengths are controlled by dislocation interactions with grain boundaries 1 , 2 and other obstacles 3 , 4 . For nanostructured materials, in contrast, dislocation multiplication is severely confined by the nanometre-scale geometries so that continued plasticity can be expected to be source-controlled. Nano-grained polycrystalline materials were found to be strong but brittle 5 , 6 , 7 , 8 , 9 , because both nucleation and motion of dislocations are effectively suppressed by the nanoscale crystallites. Here we report a dislocation-nucleation-controlled mechanism in nano-twinned metals 10 , 11 in which there are plenty of dislocation nucleation sites but dislocation motion is not confined. We show that dislocation nucleation governs the strength of such materials, resulting in their softening below a critical twin thickness. Large-scale molecular dynamics simulations and a kinetic theory of dislocation nucleation in nano-twinned metals show that there exists a transition in deformation mechanism, occurring at a critical twin-boundary spacing for which strength is maximized. At this point, the classical Hall–Petch type of strengthening due to dislocation pile-up and cutting through twin planes switches to a dislocation-nucleation-controlled softening mechanism with twin-boundary migration resulting from nucleation and motion of partial dislocations parallel to the twin planes. Most previous studies 12 , 13 did not consider a sufficient range of twin thickness and therefore missed this strength-softening regime. The simulations indicate that the critical twin-boundary spacing for the onset of softening in nano-twinned copper and the maximum strength depend on the grain size: the smaller the grain size, the smaller the critical twin-boundary spacing, and the higher the maximum strength of the material.

A shining example of doping Many technological materials are intentionally 'doped' by the introduction of trace amounts of foreign elements to impart new and useful properties — a classic example is the doping of semiconductors. Feng Wang et al . describe a system in which lanthanide doping can be used to control the growth of NaYF 4 nanocrystals, making it possible to simultaneously tune the size, crystallographic phase and optical properties of the resulting materials. These findings increase our understanding of doping-induced structural transformations, and provide a straightforward route for the controlled synthesis of luminescent nanocrystals for many applications. Many technological materials are intentionally 'doped' with foreign elements to impart new and desirable properties, a classic example being the doping of semiconductors to tune their electronic behaviour. Here lanthanide doping is used to control the growth of nanocrystals, allowing for simultaneous tuning of the size, crystallographic phase and optical properties of the hybrid material. Doping is a widely applied technological process in materials science that involves incorporating atoms or ions of appropriate elements into host lattices to yield hybrid materials with desirable properties and functions. For nanocrystalline materials, doping is of fundamental importance in stabilizing a specific crystallographic phase 1 , modifying electronic properties 2 , 3 , 4 , modulating magnetism 5 as well as tuning emission properties 6 , 7 , 8 , 9 . Here we describe a material system in which doping influences the growth process to give simultaneous control over the crystallographic phase, size and optical emission properties of the resulting nanocrystals. We show that NaYF 4 nanocrystals can be rationally tuned in size (down to ten nanometres), phase (cubic or hexagonal) and upconversion 10 , 11 , 12 emission colour (green to blue) through use of trivalent lanthanide dopant ions introduced at precisely defined concentrations. We use first-principles calculations to confirm that the influence of lanthanide doping on crystal phase and size arises from a strong dependence on the size and dipole polarizability of the substitutional dopant ion. Our results suggest that the doping-induced structural and size transition, demonstrated here in NaYF 4 upconversion nanocrystals, could be extended to other lanthanide-doped nanocrystal systems for applications ranging from luminescent biological labels 12 to volumetric three-dimensional displays 13 .

HighlightsA core–sheath structured phase change nanocomposite (PCN) with aligned and overlapping interconnected BNNS networks were successfully fabricated.The PCN has an ultrahigh in-plane thermal conductivity (28.3 W m−1 K−1), excellent flexibility and high phase change enthalpy (101 J g−1).The PCN exhibits intensively potential applications in the thermal management of 5G base stations and thermoelectric generators.Thermal management has become a crucial problem for high-power-density equipment and devices. Phase change materials (PCMs) have great prospects in thermal management applications because of their large capacity of heat storage and isothermal behavior during phase transition. However, low intrinsic thermal conductivity, ease of leakage, and lack of flexibility severely limit their applications. Solving one of these problems often comes at the expense of other performance of the PCMs. In this work, we report core–sheath structured phase change nanocomposites (PCNs) with an aligned and interconnected boron nitride nanosheet network by combining coaxial electrospinning, electrostatic spraying, and hot-pressing. The advanced PCN films exhibit an ultrahigh thermal conductivity of 28.3 W m−1 K−1 at a low BNNS loading (i.e., 32 wt%), which thereby endows the PCNs with high enthalpy (> 101 J g−1), outstanding ductility (> 40%) and improved fire retardancy. Therefore, our core–sheath strategies successfully balance the trade-off between thermal conductivity, flexibility, and phase change enthalpy of PCMs. Further, the PCNs provide powerful cooling solutions on 5G base station chips and thermoelectric generators, displaying promising thermal management applications on high-power-density equipment and thermoelectric conversion devices.

This article introduces in archival form the Nanolithography Toolbox, a platform-independent software package for scripted lithography pattern layout generation. The Center for Nanoscale Science and Technology (CNST) at the National Institute of Standards and Technology (NIST) developed the Nanolithography Toolbox to help users of the CNST NanoFab design devices with complex curves and aggressive critical dimensions. Using parameterized shapes as building blocks, the Nanolithography Toolbox allows users to rapidly design and layout nanoscale devices of arbitrary complexity through scripting and programming. The Toolbox offers many parameterized shapes, including structure libraries for micro- and nanoelectromechanical systems (MEMS and NEMS) and nanophotonic devices. Furthermore, the Toolbox allows users to precisely define the number of vertices for each shape or create vectorized shapes using Bezier curves. Parameterized control allows users to design smooth curves with complex shapes. The Toolbox is applicable to a broad range of design tasks in the fabrication of microscale and nanoscale devices.

HighlightsFundamental principles for designing high-performance thermally conductive graphene-based polymer composites are reviewed in detail.The reasoning behind using the preconstructed graphene 3D networks for fabricating thermally conductive composites and recent progress are discussed in-depth.Insight into the existing bottlenecks and opportunities in developing preconstructed 3D networks of graphene and their thermally conductive composites is also presented.Electronic devices generate heat during operation and require efficient thermal management to extend the lifetime and prevent performance degradation. Featured by its exceptional thermal conductivity, graphene is an ideal functional filler for fabricating thermally conductive polymer composites to provide efficient thermal management. Extensive studies have been focusing on constructing graphene networks in polymer composites to achieve high thermal conductivities. Compared with conventional composite fabrications by directly mixing graphene with polymers, preconstruction of three-dimensional graphene networks followed by backfilling polymers represents a promising way to produce composites with higher performances, enabling high manufacturing flexibility and controllability. In this review, we first summarize the factors that affect thermal conductivity of graphene composites and strategies for fabricating highly thermally conductive graphene/polymer composites. Subsequently, we give the reasoning behind using preconstructed three-dimensional graphene networks for fabricating thermally conductive polymer composites and highlight their potential applications. Finally, our insight into the existing bottlenecks and opportunities is provided for developing preconstructed porous architectures of graphene and their thermally conductive composites.

Dendrimers are nano-sized, radially symmetric molecules with well-defined, homogeneous, and monodisperse structure that has a typically symmetric core, an inner shell, and an outer shell. Their three traditional macromolecular architectural classes are broadly recognized to generate rather polydisperse products of different molecular weights. A variety of dendrimers exist, and each has biological properties such as polyvalency, self-assembling, electrostatic interactions, chemical stability, low cytotoxicity, and solubility. These varied characteristics make dendrimers a good choice in the medical field, and this review covers their diverse applications.

van der Waals heterostructures constitute a new class of artificial materials formed by stacking atomically thin planar crystals. We demonstrated band structure engineering in a van der Waals heterostructure composed of a monolayer graphene flake coupled to a rotationally aligned hexagonal boron nitride substrate. The spatially varying interlayer atomic registry results in both a local breaking of the carbon sublattice symmetry and a long-range moiré superlattice potential in the graphene. In our samples, this interplay between short-and long-wavelength effects resulted in a band structure described by isolated superlattice minibands and an unexpectedly large band gap at charge neutrality. This picture is confirmed by our observation of fractional quantum Hall states at ±5/3 filling and features associated with the Hofstadter butterfly at ultrahigh magnetic fields.

HighlightsThe state-of-the-art progress of flexible thermally conductive films with ultrahigh in-plane isotropic thermal conductivity (k) and potential application are summarized.The heat transfer mechanism, processing methods to enhance k, optimization strategies to reduce interface thermal resistance of flexible thermally conductive films are reviewed.The limitations and opportunities for the future development of flexible thermally conductive films are proposed.Effective thermal management is quite urgent for electronics owing to their ever-growing integration degree, operation frequency and power density, and the main strategy of thermal management is to remove excess energy from electronics to outside by thermal conductive materials. Compared to the conventional thermal management materials, flexible thermally conductive films with high in-plane thermal conductivity, as emerging candidates, have aroused greater interest in the last decade, which show great potential in thermal management applications of next-generation devices. However, a comprehensive review of flexible thermally conductive films is rarely reported. Thus, we review recent advances of both intrinsic polymer films and polymer-based composite films with ultrahigh in-plane thermal conductivity, with deep understandings of heat transfer mechanism, processing methods to enhance thermal conductivity, optimization strategies to reduce interface thermal resistance and their potential applications. Lastly, challenges and opportunities for the future development of flexible thermally conductive films are also discussed.

Majorana fermions are particles identical to their own antiparticles. They have been theoretically predicted to exist in topological superconductors. Here, we report electrical measurements on indium antimonide nanowires contacted with one normal (gold) and one superconducting (niobium titanium nitride) electrode. Gate voltages vary electron density and define a tunnel barrier between normal and superconducting contacts. In the presence of magnetic fields on the order of 100 millitesla, we observe bound, midgap states at zero bias voltage. These bound states remain fixed to zero bias, even when magnetic fields and gate voltages are changed over considerable ranges. Our observations support the hypothesis of Majorana fermions in nanowires coupled to superconductors.