a b s t r a c tWe report a single-step growth process of graphene nanostripes (GNSPs) by adding certain substituted aromatics (e.g., 1,2-dichlorobenzene) as precursors during the plasma enhanced chemical vapor deposition (PECVD). Without any active heating and by using low plasma power ( 60 W), we are able to grow GNSPs vertically with high yields up to (13 ± 4) g/m 2 in 20 min. These GNSPs exhibit high aspect ratios (from 10:1 to >~130:1) and typical widths from tens to hundreds of nanometers on various transitionmetal substrates. The morphology, electronic properties and yields of the GNSPs can be controlled by the growth parameters (e.g., the species of seeding molecules, compositions and flow rates of the gases introduced into the plasma, plasma power, and the growth time). Studies of the Raman spectra, scanning electron microscopy images, ultraviolet photoelectron spectroscopy, transmission electron microscopy images, energy-dispersive x-ray spectroscopy and electrical conductivity of these GNSPs as functions of the growth parameters confirm high-quality GNSPs with electrical mobility~10 4 cm 2 /V-s. These results together with residual gas analyzer spectra and optical emission spectroscopy taken during PECVD growth suggest the important roles of both substituted aromatics and hydrogen plasma in the rapid vertical growth of GNSPs with large aspect ratios.

The realization of many promising technological applications of graphene and graphenebased nanostructures depends on the availability of reliable, scalable, high-yield and low-cost synthesis methods. Plasma enhanced chemical vapor deposition (PECVD) has been a versatile technique for synthesizing many carbon-based materials, because PECVD provides a rich chemical environment, including a mixture of radicals, molecules and ions from hydrocarbon precursors, which enables graphene growth on a variety of material surfaces at lower temperatures and faster growth than typical thermal chemical vapor deposition (T-CVD). Here we review recent advances in the PECVD techniques for synthesis of various graphene and graphene-based nanostructures, including horizontal growth of monolayer and multilayer graphene sheets, vertical growth of graphene nanostructures (VG-GNs) such as graphene nanostripes (GNSPs) with large aspect ratios, direct and selective deposition of monolayer and multi-layer graphene on nanostructured substrates, and growth of multi-wall carbon nanotubes (MWCNTs). By properly controlling the gas environment of the plasma, it is found that no active heating is necessary for the PECVD growth processes, and that highyield growth can take place in a single step on a variety of surfaces, including metallic, semiconducting and insulating materials. Phenomenological understanding of the growth mechanisms are described. Finally, challenges and promising outlook for further development in the PECVD techniques for graphene-based applications are discussed.

Selectively pyridinic type nitrogen-doped graphene is fabricated and applied as a lithium ion battery anode including post mortem characterization.

We present the generation of THz radiation by focusing ultrafast laser pulses with three incommensurate wavelengths to form a plasma. The three colors include 800 nm and the variable IR signal and idler outputs from an optical parametric amplifier. Stable THz is generated when all three colors are present, with a peak-to-peak field strength of ~200 kV/cm and a relatively broad, smooth spectrum extending out to 6 THz, without any strong dependence on the selection of signal and idler IR wavelengths (in the range from 1300-2000 nm). We confirm that 3 colors are indeed needed, and comment on the polarization characteristics of the generated THz, some of which are challenging to explain with plasma current models that have had success in describing two-color plasma THz generation. a Contributed equally to this work.

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We show experimentally that the terahertz (THz) emission of a plasma, generated in air by a two-color laser pulse (containing a near IR frequency and its second harmonic), can be enhanced by the addition of an 800-nm pulse. We observed enhancements of the THz electric field by a factor of up to 30. This provides a widely accessible means for researchers using optical parametric amplifiers (OPA) to increase their THz yields by simply adding the residual pump beam of the OPA to the plasma generating beam. We investigate the dependence of the THz electric field enhancement factor on the powers of the two-color beam as well as the 800-nm enhancement beam. Numerical calculations using the well-known photocurrent model are in excellent agreement with the experimental observations.

Graphene has received much attention as a supercapacitor electrode material due to its chemical inertness in preventing reaction with electrolytes and the large surface area due to its two-dimensional nature. However, when graphene sheets are processed into electrodes, they tend to stack together and form a turbostratic graphite material with a much reduced surface area relative to the total surface area of individual graphene sheets. Separately, electrochemical exfoliation of graphite is one method of producing single-layer graphene, which is often used to produce graphene for supercapacitor electrodes, although such exfoliated graphene still leads to reduced surface areas due to stacking during electrode fabrication. To utilize the large surface area of graphene, graphene must be exfoliated in situ within a supercapacitor device after the device fabrication. However, graphitic electrodes are typically destroyed upon exfoliation, which is largely due to the loss of electrical connectivity among small exfoliated graphene flakes. Here, we report successful in situ exfoliation of graphene nanostripes, a type of quasi-one-dimensional graphene nanomaterial with large length-to-width aspect ratios, as the anode material in supercapacitors. We find that the in situ exfoliation leads to over 400% enhancement in capacitance as the result of retaining the electrical connectivity among exfoliated quasi-one-dimensional graphene nanostripes in addition to increasing the total surface area, paving ways to fully realizing the benefit of graphene electrodes in supercapacitor applications.

A standard approach for confirming the stability of thin films consists of probing them over an extended period of time by spectroscopic ellipsometry (SE) and plotting the resulting psi (Ψ) and delta (Δ) values versus time at a few selected wavelengths across the spectral range. In general, if Ψ and Δ remain constant with time, or essentially constant, the material is deemed to be stable. Here, we suggest that in addition to this ‘eyeball’ approach, a statistical analysis of the data may often be appropriate. In particular, we reevaluate a set of Ψ/Δ versus time data from a sputtered bismuth–tellurium–selenium film that appear to remain essentially constant by the traditional approach, subjecting it to a distance analysis, a principal components analysis, and a cluster analysis. The application of these statistical tools, especially to range‐selected data (300–989 nm), reveals previously unobserved changes, suggesting that either the film in question or the analytical approach itself had changed during the course of the measurements. Weighted distance formulas for Ψ and Δ were also applied so that the data did not need to be range selected for the key effects to be observed. The distance approach was similarly applied (i) to a set of SE data from a thin carbon film, which revealed consistent changes in the material that were not apparent in the standard approach, and (ii) to samples that were deliberately contaminated or improperly measured. Thus, we recommend a more rigorous, statistical approach to the analysis of SE Ψ/Δ versus time data. Copyright © 2016 John Wiley & Sons, Ltd.