Hydrogen plasma treatment can create defects such as sulfur vacancies in single layer MoS2. A single layer graphene's protection can effectively reduce the defects formation as confirmed by Raman spectroscopy. © 2019 The Author(s)

Spin coating and drop casting are viable methods for rapid and low-cost additive manufacturing of components for flexible devices and sensors. We investigated the cumulative effects of layering a conductive polymer composite 2 wt% MWCNT filler in PEDOT:PSS on a Mylar substrate for application to electromagnetic interference (EMI) shielding. The optical transmittace of spin coated composite layers is 90%, 45%, and 20% with a thickness of 0.05 µm, 0.15 µm, and 0.45 µm respectively. Drop cast composite layers have 0% transmittance due to their much greater starting thickness of 4.4 µm. The addition of isopropyl alcohol (IPA) to the solution mixture and substrate heating to 40 °C improves the conductivity, and drying time of the cured composite layers to 10 min. This study shows that the cumulative effects of composite layering are additive, but the electrical properties do not scale the same way. A significant increase in the EMI SE is mainly attributed to the enhanced electrical conductivity of the composite. The insertion of a 50 µm gap in between two 15 µm composite layers accentuates the EMI shielding effectiveness (SE) significantly to a peak of 21 dB within a narrow frequency range in the Ku-band tested.

Sputter-prepared nickel (Ni) films can lose more than half their starting thickness due to evaporation in hydrogen (H2) annealing environments. The loss rate of the sputtered Ni films during the chemical vapor deposition growth of graphene has not been reported earlier. The evaporation rate of sputtered Ni film with the amorphous, mixed, preferred ⟨111⟩ texture was experimentally determined to be 20, 11, and 6 nm/m, respectively. An increase of argon mixture in H2 was found to reduce pitting defects in the films during annealing. The quality of grown graphene on top of the Ni improved when the growth temperature was raised from 900 to 1000 °C, as monitored by Raman spectroscopy. More importantly, loss in the starting Ni film thickness can inhibit the growth of graphene layers. By maintaining the growth of the graphene to two layers or less, a high optical transparency of 95% or better can be achieved.

Graphene has amazing abilities due to its unique band structure characteristics de‐ fining its enhanced electrical capabilities for a material with the highest characteris‐ tic mobility known to exist at room temperature. The high mobility of graphene occurs due to electron delocalization and weak electron–phonon interaction, mak‐ ing graphene an ideal material for electrical applications requiring high mobility and fast response times. In this review, we cover graphene’s integration into infra‐ red (IR) devices, electro-optic (EO) devices, and field effect transistors (FETs) for ra‐ dio frequency (RF) applications. The benefits of utilizing graphene for each case are discussed, along with examples showing the current state-of-the-art solutions for these applications. Graphene has many outstanding properties due to its unique bonding and subse‐ quently band gap characteristics, having electronic carriers act as “massless” DiracFermions. The material characteristics of graphene are anisotropic, having phenomenal characteristic within a single sheet and diminished material character‐ istics between sheet with increasing sheet number and grain boundaries. We will discuss the integration of graphene into many electronic device applications. Graphene has the highest mobility values measured in a material at room tempera‐ ture, allowing integration into fast response time devices such as a high electron mobility transistor (HEMT) for RF applications. Graphene has shown promise in IR detectors by utilizing graphene in thermal-based detection applications.

Trace level identification of explosive molecules are very important not only for security screening but also for the environment and human health. Driven by the need, the current article reports for the first time gold nanocage–graphene oxide hybrid platform for the spectral fingerprint and the trace level identification of RDX and TNT. Reported experimental data using RDX show that the surface-enhanced Raman spectroscopy (SERS) enhancement factor for graphene oxide (GO) attached gold nanocage assembly is 4 orders of magnitude higher than only nanocage, and it is due to the enormous field enhancement for the nanocage assembly. The current article demonstrates that label-free nitro-explosive identification limits using hybrid platform can be as low as 10 fM for TNT and 500 fM for RDX, which indicate that gold nanocage–graphene oxide assembly can be very attractive for a variety of practical applications.

This review will highlight recent research underlying the design of novel nanodevices and nanosensors that incorporate graphene, nanodots, nanowires, and biomolecules including DNA aptamers and peptides. The emphasis is on models and theory that guide the design of these nanodevices and nanosensors. In selected cases, research designed to test the usefulness of these designs is highlighted in this chapter.

This study investigated the effectiveness of a graphene- and aptamer-based field-effect-transistor-like (FET-like) sensor in detecting lead and potassium ions. The sensor consists of a graphene-covered Si/SiO2 wafer with thrombin binding aptamer (TBA) attached to the graphene layer and terminated by a methylene blue (MB) molecule. K(+) and Pb(2+) both bind to TBA and cause a conformational change, which results in MB moving closer to the graphene surface and donating an electron. Thus, the abundance of K(+) and Pb(2+) can be determined by monitoring the current across the source and drain channel. Device transfer curves were obtained with ambipolar field effect observed. Current readings were taken for K(+) concentrations of 100 μM to 50 mM and Pb(2+) concentrations of 10 μM to 10 mM. As expected, I d decreased as ion concentration increased. In addition, there was a negative shift in V Dirac in response to increased ion concentration.

: Parylene film is attractive for hermetic encapsulation of porous surfaces, including energetic materials, and for the protection of integrated circuits on large-diameter silicon substrates. Achieving uniformity and repeatability of chemical vapor deposited (CVD) parylene film on large-diameter wafers in a batch system is challenging. The difficulties are related to improper selection of the wafer attachment apparatus in the chamber, and the poor coating repeatability from run to run is attributed to wafer volume changes in the CVD chamber. We discuss hardware modifications and preparation methods that improve the predictability, uniformity, and adhesion of the parylene film on nanoporous silicon surfaces. Atomic force microscopy (AFM) can determine surface roughness and distinguish differences in nanoporous silicon etched surfaces. Energetic materials that are hygroscopic in nature need to be protected from the environment during storage to improved ignition lifetime. Parylene film is an effective moisture barrier for nanoporous-scale material applications. We tested the adequacy and lifetime of parylene protection layer for a nanoenergetic device and found the shelf life can be extended in environments with greater than 80% humidity.

The growth of large-area bilayer graphene has been of technological importance for graphene electronics. The successful application of graphene bilayers critically relies on the precise control of the stacking orientation, which determines both electronic and vibrational properties of the bilayer system. Toward this goal, an effective characterization method is critically needed to allow researchers to easily distinguish the bilayer stacking orientation (i.e., AB stacked or turbostratic). In this work, we developed such a method to provide facile identification of the stacking orientation by isotope labeling. Raman spectroscopy of these isotopically labeled bilayer samples shows a clear signature associated with AB stacking between layers, enabling rapid differentiation between turbostratic and AB-stacked bilayer regions. Using this method, we were able to characterize the stacking orientation in bilayer graphene grown through Low Pressure Chemical Vapor Deposition (LPCVD) with enclosed Cu foils, achieving almost 70% AB-stacked bilayer graphene. Furthermore, by combining surface sensitive fluorination with such hybrid (12)C/(13)C bilayer samples, we are able to identify that the second layer grows underneath the first-grown layer, which is similar to a recently reported observation.

Understanding of nickel (Ni) grain size, distribution, and structure are critical parameters in a sputter-deposited Ni catalyst for achieving the desired number of graphene layers [1] grown by atmospheric pressure chemical vapor deposition (APCVD). The size and distribution of grains can be controlled by variations in sputtering parameters, but the final crystal structure and defects are not apparent until after the high temperature annealing. We analyzed the x-ray diffraction patterns in the Ni catalyst to determine effect of thermal annealing on the Ni grain size, orientation, and structural defects. Experiments have shown that in-situ sputter-deposited Ni films at 250 °C are highly oriented in the direction [111] that produced the high yield of graphene films with desired number of layers. Low defect density in a sputtered nickel (Ni) catalyst is a necessary ingredient for achieving precision number of graphene layers. These sputtering parameters can accelerate or postpone the final preferred orientation of the Ni film. A sputter temperature of 250 °C achieved complete transformation from polycrystalline film to the preferred [111] orientated film.

Electronic structures and properties of nanocontacts involving the Ag-n-C-60-Ag-n system were explored. Molecular geometries of the studied species were optimized at the DFT level using the B3LYP functional and the 6-31G(d) basis set for carbon atoms and the LANL2DZ effective core potential (ECP) for the silver atoms. The C-60 was placed between the silver clusters of different sizes and the C-2h, symmetry was assumed in the calculations. In these complexes the top of the center of fused six-membered rings of C-60 interacted with silver clusters. Interaction energies between the silver clusters and C-60 were corrected for the basis set superposition error and were computed at the same theoretical level using various the 6-31G(d) and 6-311G(d) basis sets for carbon and LANL2DZ and Stuttgart RSC 1997 effective core potentials for the silver atoms. The obtained results were compared with those of the corresponding Au-n-C-60-Au-n systems obtained at the same theoretical level. It is expected that electronic structure at the interface will play an important role for the performance of nano devices.

This paper reports for the first time the development of a large-scale SERS substrate from a popcorn-shaped gold nanoparticle-functionalized single walled carbon nanotubes hybrid thin film for the selective and highly sensitive detection of explosive TNT material at a 100 femtomolar (fM) level.

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: Significant progress has been made in growing and characterizing graphene and fabricating and testing graphene-based devices. Growth parameters have been optimized for producing large area single- and bilayer graphene. These materials have been characterized using Raman spectroscopy methods developed in this program for determining layer number, stacking order, and defects in graphene. Device processing methods have also been developed, including atomic layer deposition of gate dielectrics with fabricated field-effect transistors (FETs) demonstrating 3-GHz threshold frequencies. A large measured device data set has been produced for circuit design and device modeling validation. Models have been developed to assist in the electrical characterization of the graphene/substrate interface that takes into account interface defects. Graphene FETs will find applications in high frequency communication and radar systems. The U.S. Army Research Laboratory (ARL) has demonstrated inkjet printed flexible graphene supercapacitors with the Stevens Institute of Technology. ARL has also used unique high-speed supercapacitors developed by an ARL Small Business Innovation Research (SBIR) performer, JME Inc., to demonstrate energy storage for a munitions energy harvesting system under development by the Armament Research, Development and Engineering Center (ARDEC). ARL developed supercapacitor technology will enable size, weight, shelf life, and reliability improvements for munitions' electronic systems.

The structural quality of graphene films is of immense importance both in improving growth procedures and understanding the resulting films' electronic properties. The graphene film needs to be atomically smooth with low defects, low roughness, and high electronic mobility for high performance Field Effect Transistor (FET) devices. Because of graphene's high optical transmittance and conductivity, it is also being considered as a transparent conductive electrode [1]. Multilayer graphene prepared by diluted methane-based CVD at 1 atm on nickel (Ni) films deposited over Si/SiO2 wafers has been shown in various colours, sizes, and shapes [2]. Their preferred nucleation sites in relation to the Ni grain boundaries are not well understood. In this study, we prepared a variety of Ni templates having grain structures ranging from small to large and with mixed distribution across the surface. This was achieved through evaporation and sputter deposition methods. We found the greatest variety of Ni grains was achieved by changing the sputter deposition temperature (100 and 250°C), and pressure (2 and 20 mT). The ability to grow single- and few-layer graphene on top of the Ni catalyst depended on the highly diluted methane gas in CVD, as confirmed by micro-Raman spectroscopy. Methane ratios from 0.5 vol.% to 0.41 vol.% exhibited a strong presence of graphene, 0.36 vol. % produced mixed results, and 0.24 vol.% or less produced no evidence of graphene on a Ni template after the anneal and CVD. Annealing temperatures with as small as a 25°C difference had a great influence on final size of graphene. The grains grew almost double in size when annealed at 975°C as compared to 950°C. So it is advantageous to perform annealing followed by growth at the highest possible temperature and then combine it with an optimized cooling rate.

We report on electrically-induced heating and mixing of multilayered nickel/aluminum (Ni/Al) laminates observed by streak camera emission spectroscopy. Past experiments probing the kinetic energy of material ejected from the reaction zone indicate that additional kinetic energy originates from Ni/Al samples, presumably from exothermic mixing between the two metals. Here we examine streak spectrographs of similar experiments to determine the presence of expected elements and their temperatures. We conducted these experiments in rough vacuum, but found the emission to be dominated by argon (Ar) and nitrogen (N) lines in addition to the expected emission of Al and Ni, which were also present. Using the spectral information of Ar, we analyzed the relative intensities of four Ar peaks between 425 and 455nm, with respect to their expected Boltzmann distributions to yield temperatures as a function of time. These temperatures were 2.24–2.59eV for Al samples, and 2.93–3.27eV for both Ni and Ni/Al samples, and were within estimates based on the measured electrical energy delivered to each device. The higher Ni/Al sample temperatures seemed to validate our past measurements of increased kinetic energy and the apparent rapid exothermic mixing between Ni and Al, although Ni samples yielded surprisingly high temperatures as well. These results may be important for future nanomanufacturing techniques involving localized heating from reactive Ni/Al multilayers, where the precise control of spatial temperatures may necessitate an equally precise temporal control of the reaction.