Table of contents

The economically viable production of piezoelectric nanomaterials that can efficiently convert low-level mechanical signals into electrical power promises to revolutionize the emerging self-powered technologies in wearable sensors, consumer electronics, and defense applications. Here, we report the scalable nanomanufacturing and assembly of tellurium (Te) nanowires with chiral-chain structure into wearable piezoelectric devices, and explore the feasibility of such devices for self-powered sensing applications, e.g. cardiovascular monitoring. The ultrathin device can be conformably worn onto the human body, effectively converting the imperceptible time-variant mechanical vibration from the human body, e.g. radial artery pulse, into distinguishable electrical signals through straining the piezoelectric Te nanowires. We further uncover the process-structure-property relationships in designing, manufacturing, and integrating the Te nanowire piezoelectric devices. Our results suggest the potential of solution-synthesized Te nanowire as a new class of piezoelectric nanomaterial for self-powered devices and may lead to new opportunities in energy, electronics, and sensor applications.

Controlling trapped charges at the interface between a two-dimensional (2D) material and SiO₂ is crucial for the stable electrical characteristics in field-effect transistors (FETs). Typically, gate-source bias has been used to modulate the charge trapping process with a narrow dielectric layer with a high gate electric field. Here, we observed that charge trapping can also be affected by the lateral drain-source voltage (V_DS) in the FET structure, as well as by the gate-source bias. Through multiple V_DS sweeps with increasing measurement ranges of the V_DS, we demonstrated that the charge trapping process could be modulated by the range of the applied lateral electric field. Moreover, we inserted a hexagonal boron nitride (h-BN) layer between the MoS₂ and SiO₂ layer to explore the charge trapping behavior when a better interface is formed. This study provides a deeper understanding of controlling the electrical characteristics with interface-trapped carriers and lateral electrical fields in 2D material-based transistors.

The exceptional intrinsic properties of aligned nanofibers, such as carbon nanotubes (CNTs), and their ability to be easily densified by capillary forces motivates their use as shape-engineerable materials. While a variety of self-assembled CNT structures, such as cell networks, micropillars, and pins have previously been fabricated via the capillary-mediated densification of patterned CNT arrays, predicting the critical pattern size (s_cr) that separates cell versus pin formation and the corresponding process-morphology scaling relations within the micrometer range are outstanding. Here, facile and scalable mechanical patterning and capillary densification techniques are used to establish s_cr by elucidating how the effective elastic modulus of aligned CNT arrays during densification governs the resulting pin geometries. Experiments and modeling show that this effective modulus scales with CNT height and is about an order of magnitude smaller for pins as compared to cell networks formed from bulk-scale (i.e. non-patterned) CNT arrays. Patterning therefore results in pins with a lower packing density (commensurate with double the wall thickness) and a larger characteristic length scale than bulk cell networks (i.e. s_cr ∼ 5 ×  cell width). CNT arrays with the initial randomly-oriented carbon 'crust' removed via oxygen plasma etching yield a higher degree of structural uniformity and better agreement with the proposed elasto-capillary model, which enables the use of capillary densification to predictively design hierarchical and shape-tunable materials for advanced thermal, electronic, and biomedical devices.

Conventional microchip fabrication is energy and resource intensive. Thus, the discovery of new manufacturing approaches that reduce these expenditures would be highly beneficial to the semiconductor industry. In comparison, living systems construct complex nanometer-scale structures with high yields and low energy utilization. Combining the capabilities of living systems with synthetic DNA-/protein-based self-assembly may offer intriguing potential for revolutionizing the synthesis of complex sub-10 nm information processing architectures. The successful discovery of new biologically based paradigms would not only help extend the current semiconductor technology roadmap, but also offer additional potential growth areas in biology, medicine, agriculture and sustainability for the semiconductor industry. This article summarizes discussions surrounding key emerging technologies explored at the Workshop on Biological Pathways for Electronic Nanofabrication and Materials that was held on 16–17 November 2016 at the IBM Almaden Research Center in San Jose, CA.

In this review, we begin by discussing the need for harnessing renewable energy resources in the context of global energy demands. A summary of first- and second-generation solar cells, their efficiency and grid parity is provided, followed by the need to reduce material and installation costs, and achieve higher efficiencies beyond the Shockley–Queisser limit imposed on single junction cells. We also discuss the specific advantages offered by nanomaterials in enhanced energy harvesting, what design platforms comprise nanostructured photovoltaics, and list the prominent categories of nanomaterials used in the design of third generation solar cells. We review the significant nanostructured photovoltaic platforms that have encouraging power conversion efficiencies, have the potential for long term stability (both structural and functional) and have received attention in the field. In addition to their operational principle, we highlight both their advantages and shortcomings, along with insights into possible improvements. We include alternate routes to improving power conversion efficiency, not by tuning material properties to match the solar spectrum but using additives and/or structural modifications to allow more efficient harvesting of sunlight, either by reducing losses or by altering the spectral properties. The properties of nanomaterials that make them well-suited as active materials in photovoltaic devices (broadband absorption, high quantum yield, etc.) also make them ideal candidates for luminescent solar concentrators (LSCs). These devices also harvest solar energy, but instead of directly allowing charge generation, they act as downconverters for other photovoltaic cells. We review dye, thin film, and quantum dot based LSCs that have garnered a lot of attention in recent years as these devices face a resurgence given the advances in materials science and engineering which have led to novel quantum dots and hybrid semiconductors. The review ends with where the future of nanostructured photovoltaics is headed, what device designs and materials development are needed to achieve efficiencies beyond the Shockley–Queisser limits and fulfil the goal of the 3rd and 4th generation photovoltaics.

Borophene, a new two-dimensional (2D) structure of boron atoms, has aroused a great deal of attention and research recently. However, research on the thermal conductivity of borophene is still scarce, although this is critical for the potential application of borophene. Accordingly, we investigate the in-plane and cross-plane thermal conductivities of single- and multi-layer borophene using the non-equilibrium molecular dynamics simulations. The effect on the thermal conductivity with respect to sample length, temperature, layer number and mechanical strain is systematically examined. It is found that the in-plane thermal conductivity of infinite-size single-layer borophene exhibits strong anisotropy, which is calculated to be 102.5 ± 1.9 (along the zigzag direction) and 233.3 ± 2.1 W m⁻¹K⁻¹ (along the armchair direction). Notably, we found that both the in-plane and cross-plane thermal conductivities of borophene are affected by temperature variations, which is the same as other 2D materials. Surprisingly, the in-plane thermal conductivity of multi-layer borophene is insensitive to the layer number. This is attributed to the out-of-plane flexural phonons mode vibration being maintained by the intrinsic bi-layer structure (buckled structure), resulting in a negligible effect of interlayer vdW interactions of the multi-layer structure on the out-of-plane flexural phonons mode. In particular, the cross-plane strain was found to be effective in modulating the cross-plane thermal conductivity of multi-layer borophene in our research. Our findings here are of significance for understanding the thermal transport behavior of single- and multi-layer borophene and promoting their future applications in thermal management and nanodevices.

Low pressure (<20 Torr) non-thermal plasma flow tube reactors are commonly used for the synthesis of high purity nanoparticles (NPs) via nucleation and subsequent growth from vapor phase precursors. In spite of their utility, process monitoring (i.e. output NP size characterization) in such reactors is difficult, as there is a dearth of techniques available for online NP size distribution function measurement. In this study, we developed and applied an ion mobility spectrometry (IMS) system consisting of a low pressure differential mobility analyzer (LPDMA) and electrical detector to determine the collision cross section distribution functions of Si NPs synthesized in a radio frequency non-thermal SiH₄–Ar plasma operated at ∼2 Torr (266 Pa). The collision cross section, roughly proportional to projected area, is a parameter quantifying the size and structure of nanometer scale species in the vapor phase. We introduce the collision cross section distribution function as a metric for potential use in online process monitoring in NP synthesis. Proper inversion of the collision cross section distribution function requires a priori knowledge of the LPDMA transfer function. We utilized a tandem differential mobility analyzer approach, coupled with a Twomey–Markwoski based scheme to determine LPDMA transfer functions. Subsequent application of these transfer functions in collision cross section distribution function determination showed that at the outlet of the non-thermal plasma flow tube reactor, both negatively and positively charged Si NPs persisted with nearly identical collision cross section distribution functions. NPs were found to have mode 'mobility equivalent' diameters near 10 nm, and via TEM analysis were found to persist at the reactor outlet as small aggregates composed of ∼5 nm diameter primary particles. Size distribution functions inferred from collision cross section measurements were compared to size distribution functions inferred from TEM images; excellent agreements were found between IMS and TEM for both mean mobility equivalent diameter and distribution function width. In total, this study shows that (1) IMS is a viable approach for process monitoring in non-thermal plasma NP flow tube synthesis systems, (2) although NPs are modestly aggregated at low-pressure plasma reactor outlets, the extent of aggregation is considerably less than observed in most atmospheric pressure and equilibrium NP synthesis systems (e.g. flames), and (3) after exiting the plasma reactor, the decharging of NPs from highly negative charge levels to a bipolar charge distribution likely drives aggregation on the plasma boundary.

The dielectric function of the intermetallic compound PtAl₂ is assessed and found to be comparable to that of titanium nitride, suggesting that nanostructures of PtAl₂ may be suitable for plasmonic devices. In order to probe this further, the optical properties of experimentally produced arrays of nanoscale PtAl₂ semi-shells of about 300 nm diameter were examined and compared to the results of numerical simulations. The structures showed a broad localized surface plasmon resonance centered on ∼1.3 eV (∼950 nm), which matched the simulations. Calculations showed that a ten-fold enhancement of the electric field of the incident light will be achieved around the rim of suitably oriented PtAl₂ semi-shells. The phase of the oscillation induced by 1060 nm light will be retarded by π/2 relative to the incident light. This is indicative of a resonant condition. These observations suggest that it could be worthwhile to investigate possible applications for this and other intermetallic compounds in nanoscale plasmonic devices.