Hyperspectral Imaging of Structure and Composition in Atomically Thin Heterostructures

Precise vertical stacking and lateral stitching of two-dimensional (2D) materials, such as graphene and hexagonal boron nitride (h-BN), can be used to create ultrathin heterostructures with complex functionalities, but this diversity of behaviors also makes these new materials difficult to characterize. We report a DUV-vis-NIR hyperspectral microscope that provides imaging and spectroscopy at energies of up to 6.2 eV, allowing comprehensive, all-optical mapping of chemical composition in graphene/h-BN lateral heterojunctions and interlayer rotations in twisted bilayer graphene (tBLG). With the addition of transmission electron microscopy, we obtain quantitative structure-property relationships, confirming the formation of interfaces in graphene/h-BN lateral heterojunctions that are abrupt on a micrometer scale, and a one-to-one relationship between twist angle and interlayer optical resonances in tBLG. Furthermore, we perform similar hyperspectral imaging of samples that are supported on a nontransparent silicon/SiO2 substrate, enabling facile fabrication of atomically thin heterostructure devices with known composition and structure.11Nsciescopu

Origins of Charge Noise in Carbon Nanotube Field-Effect Transistor Biosensors

Determining the major noise sources in nanoscale field-effect transistor (nanoFET) biosensors is critical for improving bioelectronic interfaces. We use the carbon nanotube (CNT) FET biosensor platform to examine the noise generated by substrate interactions and surface adsorbates, both of which are present in current nanoFET biosensors. The charge noise model is used as a quantitative framework to show that insulating substrates and surface adsorbates are both significant contributors to the noise floor of CNT FET biosensors. Removing substrate interactions and surface adsorbates reduces the power spectral density of background voltage fluctuations by 19-fold

Single Electron Charge Sensitivity of Liquid-Gated Carbon Nanotube Transistors

Random telegraph signals corresponding to activated charge traps were observed with liquid-gated CNT FETs. The high signal-to-noise ratio that we observe demonstrates that single electron charge sensing is possible with CNT FETs in liquids at room temperature. We have characterized the gate-voltage dependence of the random telegraph signals and compared to theoretical predictions. The gate-voltage dependence clearly identifies the sign of the activated trapped charge

Small Molecule Injection into Single-Cell <i>C. elegans</i> Embryos via Carbon-Reinforced Nanopipettes

<div><p>The introduction of chemical inhibitors into living cells at specific times in development is a useful method for investigating the roles of specific proteins or cytoskeletal components in developmental processes. Some embryos, such as those of <i>Caenorhabditis elegans</i>, however, possess a tough eggshell that makes introducing drugs and other molecules into embryonic cells challenging. We have developed a procedure using carbon-reinforced nanopipettes (CRNPs) to deliver molecules into <i>C. elegans</i> embryos with high temporal control. The use of CRNPs allows for cellular manipulation to occur just subsequent to meiosis II with minimal damage to the embryo. We have used our technique to replicate classical experiments using latrunculin A to inhibit microfilaments and assess its effects on early polarity establishment. Our injections of latrunculin A confirm the necessity of microfilaments in establishing anterior-posterior polarity at this early stage, even when microtubules remain intact. Further, we find that latrunculin A treatment does not prevent association of PAR-2 or PAR-6 with the cell cortex. Our experiments demonstrate the application of carbon-reinforced nanopipettes to the study of one temporally-confined developmental event. The use of CRNPs to introduce molecules into the embryo should be applicable to investigations at later developmental stages as well as other cells with tough outer coverings.</p> </div

Effect of Latrunculin A on PAR-6 localization.

<p>(<b>a</b>) Control with injection buffer containing 3.75% DMSO (<i>N</i> = 9). (<b>b</b>) Injection of 60 µM (<i>N</i> = 10) and (<b>c</b>) 90 µM (<i>N</i> = 5) LatA. In each panel, DIC is on the left and PAR-6::mCherry is on the right.</p

Carbon-reinforced nanopipette (CRNP) fabrication.

<p>(<b>a</b>) CRNP fabrication procedure. Quartz capillaries were filled with Fe(NO₃)₃ catalyst and left to dry, then pulled into pipettes of desired geometry. Carbon was grown within the pipette using chemical vapor deposition (CVD). (<b>b</b>) A SEM image of the tip of a CRNP, scale bar is 20 nm.</p

CRNP injection characterization and experimental configuration.

<p>(<b>a</b>) Characterization of injection volume. A differential interference contrast (DIC) image of a CRNP and fluorescence images before injection of dextran-TxRed into a droplet of glycerol and immediately after the injection. (<b>b</b>) Histogram of injection volume from multiple injections using one representative CRNP. (<b>c</b>) A cartoon and a (<b>d</b>) DIC image of the experimental configuration for embryo injection. A quartz holding pipette was used to immobilize the embryo during injection. Light suction applied through the holding pipette also allowed for the withdrawal of the CRNP. In all figures, unless otherwise stated, <i>t</i> = 0 is defined as the beginning of meiosis II, injection occurs at t ^≈ 0: 15, anterior is to the left, and scale bars are 10 µm.</p