Although the thermal properties of millimeter-sized carbon nanotube mats and packed carbon nanofibers have been readily measured, measurements for a single nanotube are extremely difficult. Here, we report a novel method that can reliably measure the thermal conductivity of a single carbon nanotube using a suspended sample-attached T-type nanosensor. Our experimental results show that the thermal conductivity of a carbon nanotube at room temperature increases as its diameter decreases, and exceeds 2000 W/mK for a diameter of 9.8 nm. The temperature dependence of the thermal conductivity for a carbon nanotube with a diameter of 16.1 nm appears to have an asymptote near 320 K. The present method is, in principle, applicable to any kind of a single nanofiber, nanowire, and even single-walled carbon nanotube.

Thermal rectification is a fundamental phenomenon for active heat flow control. Significant thermal rectification is expected to exist in the asymmetric nanostructures, such as nanowires and thin films. As a one-atom-thick membrane, graphene has attracted much attention for realizing thermal rectification as shown by many molecular dynamics simulations. Here, we experimentally demonstrate thermal rectification in various asymmetric monolayer graphene nanostructures. A large thermal rectification factor of 26% is achieved in a defect-engineered monolayer graphene with nanopores on one side. A thermal rectification factor of 10% is achieved in a pristine monolayer graphene with nanoparticles deposited on one side or with a tapered width. The results indicate that the monolayer graphene has great potential to be used for designing high-performance thermal rectifiers for heat flow control and energy harvesting.

Semiconductor nanowires (NWs) are a developing platform for electronic and photonic technologies, and many demonstrated devices utilize a p-type/n-type (p-n) junction encoded along either the axial or radial directions of the wires. These miniaturized junctions enable a diverse range of functions, from sensors to solar cells, yet the physics of the devices has not been thoroughly evaluated. Here, we present finite-element modeling of axial and radial Si NW p-n junctions with total diameters of ~240 nm and donor/acceptor doping levels ranging from 10(16) to 10(20) cm(-3). We evaluate the photovoltaic performance of horizontally oriented NWs under 1 sun illumination and compare simulated current-voltage data to experimental measurements, permitting detailed analysis of NW performance, limitations, and prospect as a technology for solar energy conversion. Although high surface-to-volume ratios are cited as detrimental to NW performance, radial p-n junctions are surprisingly insensitive to surface recombination, with devices supporting open-circuit voltages (V(OC)) of ~0.54 V and internal quantum efficiencies of 95% even with high surface recombination velocities (SRVs) of 10(5) cm/s. Axial devices, in which the depletion region is exposed to the surface, are far more sensitive to SRV, requiring substantially lower values of 10(3)-10(4) cm/s to produce the same level of performance. For low values of the SRV (<100 cm/s), both axial and radial NWs can support V(OC) values of >0.70 V if the bulk minority carrier lifetime is 1 μs or greater. Experimental measurements on NWs grown by a vapor-liquid-solid mechanism yield V(OC) of 0.23 and 0.44 V for axial and radial NWs, respectively, and show that axial devices are limited by a SRV of ~7 × 10(3) cm/s while radial devices are limited by a bulk lifetime of ~3 ns. The simulations show that with further development the electrical characteristics of 200-300 nm Si NWs are sufficient to support power-conversion efficiencies of 15-25%. The analysis presented here can be generalized to other semiconductor homo- and heterojunctions, and we expect that insights from finite element modeling will serve as a powerful method to guide the design of advanced nanoscale structures.

Semiconductor nanowires (NWs) often exhibit efficient, broadband light absorption despite their relatively small size. This characteristic originates from the subwavelength dimensions and high refractive indices of the NWs, which cause a light-trapping optical antenna effect. As a result, NWs could enable high-efficiency but low-cost solar cells using small volumes of expensive semiconductor material. Nevertheless, the extent to which the antenna effect can be leveraged in devices will largely determine the economic viability of NW-based solar cells. Here, we demonstrate a simple, low-cost, and scalable route to dramatically enhance the optical antenna effect in NW photovoltaic devices by coating the wires with conformal dielectric shells. Scattering and absorption measurements on Si NWs coated with shells of SiN(x) or SiO(x) exhibit a broadband enhancement of light absorption by ∼ 50-200% and light scattering by ∼ 200-1000%. The increased light-matter interaction leads to a ∼ 80% increase in short-circuit current density in Si photovoltaic devices under 1 sun illumination. Optical simulations reproduce the experimental results and indicate the dielectric-shell effect to be a general phenomenon for groups IV, II-VI, and III-V semiconductor NWs in both lateral and vertical orientations, providing a simple route to approximately double the efficiency of NW-based solar cells.

This paper reports on measurements of the effective thermal conductivity and thermal diffusivity of various nanofluids using the transient short-hot-wire technique. To remove the influences of the static charge and electrical conductance of the nanoparticles on measurement accuracy, the short-hot-wire probes are carefully coated with a pure Al 2 O 3 thin film and only those probes that are coated well are used for measurements. In the present study, the effective thermal conductivities and thermal diffusivities of Au/toluene, Al 2 O 3 /water, and carbon nanofiber ͑CNF͒/water nanofluids are measured and the effects of the volume fraction and thermal conductivity of the nanoparticles and temperature are clarified. The average diameters of Au and Al 2 O 3 spherical particles are 1.65 and 20 nm, respectively. The average length and diameter of CNFs are 10 m and 150 nm, respectively. The uncertainty of the present measurements is estimated to be within 1% for the thermal conductivity and 5% for the thermal diffusivity. The measured results demonstrate that the effective thermal conductivities of the nanofluids show no anomalous enhancements and can be predicted accurately by the model equation of Hamilton and Crosser ͓Ind. Eng. Chem. Fundam. 1, 187 ͑1962͔͒ for the spherical nanoparticles and by the unit-cell model equation of Yamada and Ota ͓Waerme-Stoffuebertrag. 13, 27 ͑1980͔͒ for carbon nanofibers.

This letter reports on the measurements of the in-plane thermal conductivity and the electrical conductivity of a microfabricated, suspended, nanosized platinum thin film with the width of 260nm, the thickness of 28nm, and the length of 5.3μm. The experimental results show that the electrical conductivity, the resistance-temperature coefficient and the in-plane thermal conductivity of the nanofilm are greatly lower than the corresponding bulk values from 77to330K. The comparison results indicate that the relation between the thermal conductivity and the electrical conductivity of this nanofilm might not follow the Wiedemann–Franz law that describes the relation between the thermal conductivity and the electrical conductivity of a bulk metallic material.

Single-particle cryo-electron microscopy (cryo-EM) has become one of the most essential tools to understand biological mechanisms at molecular level. A major bottleneck in cryo-EM technique is the preparation of good specimens that embed biological macromolecules in a thin layer of vitreous ice. In the canonical cryo-EM specimen preparation method, biological macromolecules tend to be adsorbed to the air–water interface, causing partial denaturation and/or preferential orientations. In this work, we have designed and produced a new type of cryo-EM grids using bioactive-ligand functionalized single-crystalline monolayer graphene membranes as supporting films. The functionalized graphene membrane (FGM) grids exhibit specific binding affinity to histidine (His)-tagged proteins and complexes. In cryo-EM, the FGM grids generate relatively low background for imaging and selectively anchor 20S proteasomes to the supporting film surface, enabling near-atomic-resolution 3D reconstruction of the complex. We envision that the FGM grids could benefit single particle cryo-EM specimen preparation with high reproducibility and robustness, therefore enhancing the efficiency and throughput of high-resolution cryo-EM structural determination.

MoS2 has emerged as a promising alternative electrocatalyst for the hydrogen evolution reaction (HER) due to high intrinsic per‐site activity on its edge sites and S‐vacancies. However, a significant challenge is the limited density of such sites. Reducing the size and layer number of MoS2 and vertically aligning them would be an effective way to enrich and expose such sites for HER. Herein, a facile self‐limited on‐site conversion strategy for synthesizing monolayer MoS2 in a couple of nanometers which are highly dispersed and vertically aligned on 3D porous carbon sheets is reported. It is discovered that the preformation of well‐dispersed MoO3 nanodots in 1–2 nm as limited source is the key for the fabrication of such an ultrasmall MoS2 monolayer. As indicated by X‐ray photoelectron spectroscopy and electron spin resonance data, these ultrasmall MoS2 monolayers are rich in accessible S‐edge sites and vacancies and the smaller MoS2 monolayers the more such sites they have, leading to enhanced electrocatalytic activity with a low overpotential of 126 mV at 10 mA cm−2 and 140 mV at 100 mA mg−1 for HER. This state‐of‐the‐art performance for MoS2 electrocatalysts enables the present strategy as a new avenue for exploring well‐dispersed ultrasmall nanomaterials as efficient catalysts.