Slow DNA transport through nanopores in hafnium oxide membranes.

<p>We present a study of double- and single-stranded DNA transport through nanopores fabricated in ultrathin (2-7 nm thick) freestanding hafnium oxide (HfO2) membranes. The high chemical stability of ultrathin HfO2 enables long-lived experiments withhours, in which we observe >50 000 DNA translocations with no detectable pore expansion. Mean DNA velocities are slower than velocities through comparable silicon nitride pores, providing evidence that HfO2 nanopores have favorable physicochemical interactions with nucleic acids that can be leveraged to slow down DNA in a nanopore.</p

Volatility Measurements of Sustainable Aviation Fuels: A Comparative Study of D86 and D2887 Methods

The volatility and evaporation rate of aviation fuels impact combustion efficiency at some operating conditions as well as the jet-engine combustor operability, including ignition, lean blowout, and combustion dynamics. To help characterize the volatility of jet fuel, one experimental approach utilizes a one-plate atmospheric distillation (ASTM D86), while the other employs a close to infinite plate system in a gas chromatogram (GC) and the corresponding elution time of n-alkanes to simulate a distillation curve (ASTM D2887). The simulated distillation has been more repeatable historically, but with the advent of sustainable aviation fuels, the interpretation of this GC data and its correlation to the traditional one-plate approach are not clear. Here, we measured the one-plate (D86) and simulated (ASTM D2887) distillations of neat SAF candidates, their blends, and several conventional fuels. A total of 66 and 4 samples were measured in the simulated distillation and one-plate experiments, respectively. A simulated distillation curve blend rule is reported here as well as the impact of blending high concentrations of single components in HEFA. Significant disagreements between the calculation of D86 correlated data from D2887 data and the directly measured D86 data are discussed

Direct Imaging of Atomic-Scale Ripples in Few-Layer Graphene

Graphene has been touted as the prototypical two-dimensional solid of extraordinary stability and strength. However, its very existence relies on out-of-plane ripples as predicted by theory and confirmed by experiments. Evidence of the intrinsic ripples has been reported in the form of broadened diffraction spots in reciprocal space, in which all spatial information is lost. Here we show direct real-space images of the ripples in a few-layer graphene (FLG) membrane resolved at the atomic scale using monochromated aberration-corrected transmission electron microscopy (TEM). The thickness of FLG amplifies the weak local effects of the ripples, resulting in spatially varying TEM contrast that is unique up to inversion symmetry. We compare the characteristic TEM contrast with simulated images based on accurate first-principles calculations of the scattering potential. Our results characterize the ripples in real space and suggest that such features are likely common in ultrathin materials, even in the nanometer-thickness range

Synthetically encoded ultrashort-channel nanowire transistors for fast, pointlike cellular signal detection.

Nanostructures, which have sizes comparable to biological functional units involved in cellular communication, offer the potential for enhanced sensitivity and spatial resolution compared to planar metal and semiconductor structures. Silicon nanowire (SiNW) field-effect transistors (FETs) have been used as a platform for biomolecular sensors, which maintain excellent signal-to-noise ratios while operating on lengths scales that enable efficient extra- and intracellular integration with living cells. Although the NWs are tens of nanometers in diameter, the active region of the NW FET devices typically spans micrometers, limiting both the length and time scales of detection achievable with these nanodevices. Here, we report a new synthetic method that combines gold-nanocluster-catalyzed vapor-liquid-solid (VLS) and vapor-solid-solid (VSS) NW growth modes to produce synthetically encoded NW devices with ultrasharp (nm) n-type highly doped (n(++)) to lightly doped (n) transitions along the NW growth direction, where n(++) regions serve as source/drain (S/D) electrodes and the n-region functions as an active FET channel. Using this method, we synthesized short-channel n(++)/n/n(++) SiNW FET devices with independently controllable diameters and channel lengths. SiNW devices with channel lengths of 50, 80, and 150 nm interfaced with spontaneously beating cardiomyocytes exhibited well-defined extracellular field potential signals with signal-to-noise values of ca. 4 independent of device size. Significantly, these "pointlike" devices yield peak widths of ∼500 μs, which is comparable to the reported time constant for individual sodium ion channels. Multiple FET devices with device separations smaller than 2 μm were also encoded on single SiNWs, thus enabling multiplexed recording from single cells and cell networks with device-to-device time resolution on the order of a few microseconds. These short-channel SiNW FET devices provide a new opportunity to create nanoscale biomolecular sensors that operate on the length and time scales previously inaccessible by other techniques but necessary to investigate fundamental, subcellular biological processes.</p

Slow DNA Transport through Nanopores in Hafnium Oxide Membranes

We present a study of double- and single-stranded DNA transport through nanopores fabricated in ultrathin (2–7 nm thick) freestanding hafnium oxide (HfO₂) membranes. The high chemical stability of ultrathin HfO₂ enables long-lived experiments with <2 nm diameter pores that last several hours, in which we observe >50 000 DNA translocations with no detectable pore expansion. Mean DNA velocities are slower than velocities through comparable silicon nitride pores, providing evidence that HfO₂ nanopores have favorable physicochemical interactions with nucleic acids that can be leveraged to slow down DNA in a nanopore

Synthetically Encoded Ultrashort-Channel Nanowire Transistors for Fast, Pointlike Cellular Signal Detection

Nanostructures, which have sizes comparable to biological functional units involved in cellular communication, offer the potential for enhanced sensitivity and spatial resolution compared to planar metal and semiconductor structures. Silicon nanowire (SiNW) field-effect transistors (FETs) have been used as a platform for biomolecular sensors, which maintain excellent signal-to-noise ratios while operating on lengths scales that enable efficient extra- and intracellular integration with living cells. Although the NWs are tens of nanometers in diameter, the active region of the NW FET devices typically spans micrometers, limiting both the length and time scales of detection achievable with these nanodevices. Here, we report a new synthetic method that combines gold-nanocluster-catalyzed vapor–liquid–solid (VLS) and vapor–solid–solid (VSS) NW growth modes to produce synthetically encoded NW devices with ultrasharp (<5 nm) n-type highly doped (n⁺⁺) to lightly doped (n) transitions along the NW growth direction, where n⁺⁺ regions serve as source/drain (S/D) electrodes and the n-region functions as an active FET channel. Using this method, we synthesized short-channel n⁺⁺/n/n⁺⁺ SiNW FET devices with independently controllable diameters and channel lengths. SiNW devices with channel lengths of 50, 80, and 150 nm interfaced with spontaneously beating cardiomyocytes exhibited well-defined extracellular field potential signals with signal-to-noise values of ca. 4 independent of device size. Significantly, these “pointlike” devices yield peak widths of ∼500 μs, which is comparable to the reported time constant for individual sodium ion channels. Multiple FET devices with device separations smaller than 2 μm were also encoded on single SiNWs, thus enabling multiplexed recording from single cells and cell networks with device-to-device time resolution on the order of a few microseconds. These short-channel SiNW FET devices provide a new opportunity to create nanoscale biomolecular sensors that operate on the length and time scales previously inaccessible by other techniques but necessary to investigate fundamental, subcellular biological processes

Cu₂IrO₃: A New Magnetically Frustrated Honeycomb Iridate

We present the first copper iridium binary metal oxide with the chemical formula Cu₂IrO₃. The material is synthesized from the parent compound Na₂IrO₃ by a topotactic reaction where sodium is exchanged with copper under mild conditions. Cu₂IrO₃ has the same monoclinic space group (<i>C</i>2/<i>c</i>) as Na₂IrO₃ with a layered honeycomb structure. The parent compound Na₂IrO₃ is proposed to be relevant to the Kitaev spin liquid on the basis of having Ir⁴⁺ with an effective spin of 1/2 on a honeycomb lattice. Remarkably, whereas Na₂IrO₃ shows a long-range magnetic order at 15 K and fails to become a true spin liquid, Cu₂IrO₃ remains disordered until 2.7 K, at which point a short-range order develops. Rietveld analysis shows less distortions in the honeycomb structure of Cu₂IrO₃ with bond angles closer to 120° compared to Na₂IrO₃. Thus, the weak short-range magnetism combined with the nearly ideal honeycomb structure places Cu₂IrO₃ closer to a Kitaev spin liquid than its predecessors

Nanocomposite gold-silk nanofibers.

Cell-biomaterial interactions can be controlled by modifying the surface chemistry or nanotopography of the material, to induce cell proliferation and differentiation if desired. Here we combine both approaches in forming silk nanofibers (SNFs) containing gold nanoparticles (AuNPs) and subsequently chemically modifying the fibers. Silk fibroin mixed with gold seed nanoparticles was electrospun to form SNFs doped with gold seed nanoparticles (SNF(seed)). Following gold reduction, there was a 2-fold increase in particle diameter confirmed by the appearance of a strong absorption peak at 525 nm. AuNPs were dispersed throughout the AuNP-doped silk nanofibers (SNFs(Au)). The Young's modulus of the SNFs(Au) was almost 70% higher than that of SNFs. SNFs(Au) were modified with the arginine-glycine-aspartic acid (RGD) peptide. Human mesenchymal stem cells that were cultured on RGD-modified SNF(Au) had a more than 2-fold larger cell area compared to the cells cultured on bare SNFs; SNF(Au) also increased cell size. This approach may be used to alter the cell-material interface in tissue engineering and other applications.</p

Facet-Selective Epitaxy of Compound Semiconductors on Faceted Silicon Nanowires

Integration of compound semiconductors with silicon (Si) has been a long-standing goal for the semiconductor industry, as direct band gap compound semiconductors offer, for example, attractive photonic properties not possible with Si devices. However, mismatches in lattice constant, thermal expansion coefficient, and polarity between Si and compound semiconductors render growth of epitaxial heterostructures challenging. Nanowires (NWs) are a promising platform for the integration of Si and compound semiconductors since their limited surface area can alleviate such material mismatch issues. Here, we demonstrate facet-selective growth of cadmium sulfide (CdS) on Si NWs. Aberration-corrected transmission electron microscopy analysis shows that crystalline CdS is grown epitaxially on the {111} and {110} surface facets of the Si NWs but that the Si{113} facets remain bare. Further analysis of CdS on Si NWs grown at higher deposition rates to yield a conformal shell reveals a thin oxide layer on the Si{113} facet. This observation and control experiments suggest that facet-selective growth is enabled by the formation of an oxide, which prevents subsequent shell growth on the Si{113} NW facets. Further studies of facet-selective epitaxial growth of CdS shells on micro-to-mesoscale wires, which allows tuning of the lateral width of the compound semiconductor layer without lithographic patterning, and InP shell growth on Si NWs demonstrate the generality of our growth technique. In addition, photoluminescence imaging and spectroscopy show that the epitaxial shells display strong and clean band edge emission, confirming their high photonic quality, and thus suggesting that facet-selective epitaxy on NW substrates represents a promising route to integration of compound semiconductors on Si