Search

Abstract This paper describes an experimental study on field emission characteristics of individual graphene layers for vacuum nanoelectronics. Graphene layers were prepared by mechanical exfoliation from a highly oriented pyrolyzed graphite block and placed on an insulating substrate, with the resulting field emission behavior investigated using a nanomanipulator operating inside a scanning electron microscope. A pair of tungsten tips controlled by the nanomanipulator enabled electric connection with the graphene layers without postfabrication. The maximum emitted current from the graphene layers was 170 nA and the turn-on voltage was 12.1 V.

Flexible and wearable sensors increasingly draw attention owing to their advantages of providing lightweight, portable, wearable, or implantable capabilities. Along with the development of flexible materials toward wearable devices, flexible sensors operating via electrochemical and mechanical stimuli demonstrate promise to fulfill potential healthcare and robotics applications, including artificial muscles, health monitoring, human motion detection, soft robotic skin, and human–machine interfaces. This review focuses on carbon nanotube (CNT)-based flexible sensors to detect diverse chemical species and mechanical forces. Often, combined with polymers to imbue flexibility, CNT-based flexible sensors enable specific and stable detections of mechanical deformations and electrochemical analytes while withstanding various mechanical loads, including stretching, bending, and twisting. [ABSTRACT FROM AUTHOR]

The ubiquitous presence of wrinkles in two-dimensional materials alters their properties significantly. It is observed that during the growth process of graphene, water molecules, sourced from ambient humidity or transferred method used, can get diffused in between graphene and the substrate. The water diffusion causes/assists wrinkle formation in graphene, which influences its properties. The diffused water eventually dries, altering the geometrical parameters and properties of wrinkled graphene nanoribbons. Our study reveals that the initially distributed wrinkles tend to coalesce to form a localized wrinkle whose configuration depends on the initial wrinkle geometry and the quantity of the diffused water. The movement of the localized wrinkle is categorized into three modes—bending, buckling, and sliding. The sliding mode is characterized in terms of velocity as a function of diffused water quantity. Direct bandgap increases linearly with the initial angle except the highest angle considered (21°), which can be attributed to the electron tunneling effect observed in the orbital analysis. The system becomes stable with an increase in the initial angle of wrinkle as observed from the potential energy plots extracted from MD trajectories and confirmed with the DOS plot. The maximum stress generated is less than the plastic limit of the graphene. [ABSTRACT FROM AUTHOR]

We have demonstrated a three-dimensional composite structure of graphene and carbon nanotubes as electrodes for super-capacitors. The goal of this study is to fabricate and test the vertically grown carbon nanotubes on the graphene layer acting as a spacer to avoid self-aggregation of the graphene layers while realizing high active surface area for high energy density, specific capacitance, and power density. A vertical array of carbon nanotubes on silicon substrates was grown by a low-pressure chemical vapor deposition process using anodized aluminum oxide nanoporous template fabricated on silicon substrates. Subsequently, a graphene layer was grown by another low-pressure chemical vapor deposition process on top of a vertical array of carbon nanotubes. The Raman spectra confirmed the successful growth of carbon nanotubes followed by the growth of high-quality graphene. The average measured capacitance of the three-dimensional composite structure of graphene-carbon nanotube was 780 mFcm[sup -2] at I00mVs[-l]. [ABSTRACT FROM AUTHOR]

In this paper, nanoscale anodic oxidation lithography using an atomic force microscope (AFM) is systematically studied on carbon nanotubes (CNTs). Trends between the produced feature size and the corresponding process parameters, such as applied voltage, water meniscus length, tip speed during oxidation (hold time), and humidity are observed. By methodically varying these process parameters, the appropriate working ranges have been found to create features of various sizes based on the oxidation of the CNT structure. We have obtained feature sizes down to 58 nm by setting oxidation time per pixel to 20 ms corresponding to a tip speed of 1.50 μ m/s. Optimizing the tip speed during line scans was found to be critical in maintaining the presence of the water meniscus, which was often found to break above the tip speeds of 1 μm/s. In addition, a comparison of the results from employing this technique between CNT and graphene patterning is illustrated. Other factors affecting the reproducibility of the results are addressed in an endeavor to make the oxidization process more robust and repeatable. [ABSTRACT FROM PUBLISHER]

We observe conductivity oscillations with aperiodic spacing to only one side of the tunneling current in a dual-gated graphene field effect transistor with an n-p-n type potential barrier. The spacing and width of these oscillations were found to be inconsistent with pure Fabry-Perot-type interferences, but are in quantitative agreement with theoretical predictions that attribute them to resonant tunneling through quasibound impurity states. This observation may be understood as another signature of Klein tunneling in graphene heterojunctions and is of importance for future development and modeling of graphene based nanoelectronic devices. [ABSTRACT FROM AUTHOR]

Flexible energy‐storage devices increasingly attract attention owing to their advantages of providing lightweight, portable, wearable, or implantable capabilities. Many efforts are made to explore the structures and fabrication processes of flexible energy‐storage devices for commercialization. Here, the most recent advances in flexible energy‐storage devices based on graphene, graphene oxide (GO), and carbon nanotubes (CNTs), are described, including flexible supercapacitors and batteries. First, properties, synthesis methods, and possible applications of those carbon‐based materials are described. Then, the development of carbon‐nanotube‐based flexible supercapacitors, graphene/graphene‐oxide‐based flexible supercapacitors, and graphene‐ and carbon‐nanotube‐based flexible battery electrodes are discussed. Finally, the future trends and perspectives in the development of flexible energy‐storage devices are highlighted. [ABSTRACT FROM AUTHOR]

We present an overview of our research on nanoelectronics and nanomechanics based on low-dimensional materials, including carbon nanotubes and graphene. Our primary research focus is on carbon nanotube and graphene architectures for electronics, energy harvesting, and sensing applications. We are also investigating an atomically precise graphene nanomachining method as well as a high-throughput desktop nanolithography process. In addition, we are exploiting nanomechanical actuators and nanoscale measurement techniques for reconfigurable arrayed nanostructures with applications in THz antennas, remote detectors, and biomedical nanorobots. Last, we are studying the effect of antibody functionalized nickel nanowires to improve cell separation techniques. These design, nanofabrication, manipulation, and characterization processes will enable next-generation nanoelectronics that have a wide range of applications including sensors, detectors, system-on-a-chip, system-in-a-package, programmable logic controls, energy storage systems, and all-electronic systems. [ABSTRACT FROM AUTHOR]

Abstract: The impact of polymer removal by forming gas and vacuum annealing on the doping, strain, and morphology of chemical vapor deposited (CVD) and mechanically exfoliated (ME) graphene is investigated using Raman spectroscopy and atomic force microscopy (AFM). The behavior of graphene exposed and unexposed to polymer is compared. It is found that the well-known doping effect after forming gas annealing is induced in CVD–ME graphene by polymeric residue/hydrogen-functionalization. Further, forming gas annealing of ME graphene is shown to induce strain via pinning of the graphene layer to the substrate. It is found that vacuum annealing removes most polymeric residue, with minor doping and strain effects. Finally, a study of AFM step height and roughness measurements provides a comprehensive understanding of those annealing-based processes which create morphological changes and directly influence doping and strain in the graphene layer, such as removal of polymer, removal of the interfacial graphene–substrate water layer, environmental doping effects and deformation of the graphene layer. [Copyright &y& Elsevier]

We investigate the quantum transport dynamics of electrons in a multi-path Aharonov–Bohm interferometer comprising several parallel graphene nanoribbons. At low magnetic field strengths, the conductance displays a complex oscillatory behavior stemming from the interference of electron wave functions from different paths, reminiscent of the diffraction grating in optics. With increasing magnetic field strength, certain nanoribbons experience transport blockade, leading to conventional Aharonov–Bohm oscillations arising from two-path interference. We also discuss the impact of edge effects and the influence of finite temperature. Our findings offer valuable insights for experimental investigations of quantum transport in multi-path devices and their potential application for interferometry and quantum sensing. • Simulating quantum transport dynamics of multi-path graphene interferometer. • Observing blockade of certain transport channels and its potential application for quantum sensing. • Systematic investigation of electric conductance for different geometries, Fermi energies, and magnetic field strengths. [ABSTRACT FROM AUTHOR]

Inmost envisioned applications, the full utilization of a graphene-carbonnanotube (CNT) construct requires maintaining the integrity of thegraphene layer during the CNT growth step. In this work, we exhibitan approach toward controlled CNT growth atop graphene substrateswhere the reaction equilibrium between the source hydrocarbon decompositionand carbon saturation into and precipitation from the catalyst nanoparticlesshifts toward CNT growth rather than graphene consumption. By utilizingC2H4feedstock, we demonstrate that the low-temperaturegrowth permissible with this gas suppresses undesirable catalytichydrogenation and dramatically reduces the etching of the graphenelayer to exhibit graphene-CNT hybrids with continuous, undamaged structures. [ABSTRACT FROM AUTHOR]