Deposited Graphene Layers Research Articles

On the mechanism of electrochemical deposition of graphene on Al foils and AlSi10MgCu particles

The graphene synthesis via the electrochemical method and electrochemical deposition of graphene on Al foils and AlSi10MgCu particles were studied. The thickness of deposited graphene layers was varied from 3 to 20 layers and, thus, they were classified as multi-graphene. The chemically pure sucrose C12H22O11 was used as a raw material for graphene synthesis. It was shown that the deposition of graphene layers was affected mainly by the pH values of electrolyte mediums. In the electrochemical reaction at H2SO4 water solution at pH < 7, the graphene was deposited on Al foils and on AlSi10MgCu particles from the electrolyte. The microstructure and composition of graphene formed on Al foils and AlSi10MgCu particles' surface were studied by Raman spectroscopy, SEM, EDX, and TEM methods. The chemical mechanism of graphene formation was defined as follows: the sucrose was recovered via the reaction route C12H22O11 → C6H12O6 → Cgraphene in acidic aqueous media. An increase in the H2SO4 concentration from 0.05 M to 0.80 M has resulted in the formation of graphene layers with up to 6 μm thickness on AlSi10MgCu particles.

Effect of incidence and size of graphite particle on the formation of graphene on Ni surfaces

In this paper, we surveyed the effect of graphite thickness, impact velocity, substrate temperature, angle tilt of particle, incident angle, and Ni crystalline faces on the formation of graphene flakes, temperature, von Mises stress, and deformation. In the deposition process, graphene flakes are formed due to the impaction and attaching between the Ni substrate and graphite particles. The results reveal that there is a critical impact velocity leading to the graphene flakes that separated from the graphite particle and attached to the Ni substrate. The critical impact velocity decreases as increasing the thickness of graphite particles from 9 to 18 layers. In addition, the substrate temperature of the impact region and numbers of deposited graphene layers rise with the impact velocity increases. Notably, the elastic and plastic deformations of Ni substrate happen in the deposition process with high impact velocity. Furthermore, some dislocations are formed during and after the impact of the particle. The high-stress regions concentrate in the deposited graphene flakes and interfacial zone. The deposited graphene layer on Ni(001) creates a more stable structure than on surfaces Ni(111) and Ni(110). The graphene layer is successfully formed in the deposition process at an angle tilt from 0° to 10°.

Highly sensitive room temperature liquefied petroleum gas sensor based on CoSnO2 nanoislands deposited graphene layers

In this present work, an effective Liquefied Petroleum Gas (LPG) detecting nanocomposite of r-GO-CoSnO2 operable at room temperature was exhibited. Nanoparticles of Cobalt (Co) doped Tin Oxide (SnO2) nanoparticles were decorated uniformly over the reduced graphene oxide (rGO) layers. Reduction of graphene oxide (GO) into rGO and combination of metal oxide decoration was synthesized by one step using cost effective hydrothermal method using reductant hydrazine hydrate. Nanoparticles of CoSnO2 were self assembled over rGO via high pressure built inside the Teflon autoclave chamber. Structural and surface morphological characterizations confirmed the structure, size and shape of the prepared materials with distinct properties which are essential for a reliable sensing device. Distribution of metal oxide throughout the graphene layers act as an active site for the LPG molecules adsorption and desorption processes. For selectivity various analyte gases such as Hydrogen, Oxygen and Ammonia were examined. The proposed unique nanocomposite has exhibits low level detection of 2 ppm with quick response time of 4 s and recovery time of 5 s at room temperature. From these results it suggests that the proposed material will be a promising potential candidate for the fabrication of LPG sensor devices.

Robust Spin Interconnect with Isotropic Spin Dynamics in Chemical Vapor Deposited Graphene Layers and Boundaries.

The utilization of large-area graphene grown by chemical vapor deposition (CVD) is crucial for the development of scalable spin interconnects in all-spin-based memory and logic circuits. However, the fundamental influence of the presence of multilayer graphene patches and their boundaries on spin dynamics has not been addressed yet, which is necessary for basic understanding and application of robust spin interconnects. Here, we report universal spin transport and dynamic properties in specially devised single layer, bilayer, and trilayer graphene channels and their layer boundaries and folds that are usually present in CVD graphene samples. We observe uniform spin lifetime with isotropic spin relaxation for spins with different orientations in graphene layers and their boundaries at room temperature. In all of the inhomogeneous graphene channels, the spin lifetime anisotropy ratios for spins polarized out-of-plane and in-plane are measured to be close to unity. Our analysis shows the importance of both Elliott-Yafet and D’yakonov-Perel’ mechanisms with an increasing role of the latter mechanism in multilayer channels. These results of universal and isotropic spin transport on large-area inhomogeneous CVD graphene with multilayer patches and their boundaries and folds at room temperature prove its outstanding spin interconnect functionality, which is beneficial for the development of scalable spintronic circuits.

Unraveling absorptive and refractive optical nonlinearities in CVD grown graphene layers transferred onto a foreign quartz substrate

Absorptive and refractive optical nonlinearities in chemical vapor deposited graphene layers, transferred onto a foreign quartz substrate was studied by performing Z-scan experiment under continuous wave excitation. Open aperture Z-scan results exhibit two shoulder peaks along with a valley at the focal plane and is interpreted in terms of combined effect of saturation absorption (SA) and reverse saturation absorption (RSA). Self-defocusing effect and hence negative nonlinear refraction was observed from the closed aperture Z-scan experiment. Optical nonlinearity is found to decrease upon annealing of graphene layers at 250 °C. Reduction in optical nonlinearity as a consequence of annealing is attributed to the variation of sp2/sp3 fraction and higher crystallite size (decreased structural disorderness) as revealed from the Raman spectroscopy. sp3 carbon atoms support two photon absorption, leading to RSA behavior while sp2 structure displays SA behavior. Our study suggests that annealing paves a way to manipulate sp2/sp3 fraction which can alter the structural disorderness in graphene layers and hence the optical nonlinearities.

Fast, Noncontact, Wafer-Scale, Atomic Layer Resolved Imaging of Two-Dimensional Materials by Ellipsometric Contrast Micrography.

Adequate characterization and quality control of atomically thin layered materials (2DM) has become a serious challenge particularly given the rapid advancements in their large area manufacturing and numerous emerging industrial applications with different substrate requirements. Here, we focus on ellipsometric contrast micrography (ECM), a fast intensity mode within spectroscopic imaging ellipsometry, and show that it can be effectively used for noncontact, large area characterization of 2DM to map coverage, layer number, defects and contamination. We demonstrate atomic layer resolved, quantitative mapping of chemical vapor deposited graphene layers on Si/SiO2-wafers, but also on rough Cu catalyst foils, highlighting that ECM is applicable to all application relevant substrates. We discuss the optimization of ECM parameters for high throughput characterization. While the lateral resolution can be less than 1 μm, we particularly explore fast scanning and demonstrate imaging of a 4″ graphene wafer in 47 min at 10 μm lateral resolution, i.e., an imaging speed of 1.7 cm2/min. Furthermore, we show ECM of monolayer hexagonal BN (h-BN) and of h-BN/graphene bilayers, highlighting that ECM is applicable to a wide range of 2D layered structures that have previously been very challenging to characterize and thereby fills an important gap in 2DM metrology.

Plasmon-enhanced scattering and charge transfer in few-layer graphene interacting with buried printed 2D-pattern of silver nanoparticles

Hybrid structures combing silver nanoparticles and few-layer graphene have been synthetized by combining low-energy ion beam synthesis and stencil techniques. A single plane of metallic nanoparticles plays the role of an embedded plasmonic enhancer located in dedicated areas at a controlled nanometer distance from deposited graphene layers. Optical imaging, reflectance and Raman scattering mapping are used to measure the enhancement of electronic and vibrational properties of these layers. In particular electronic Raman scattering is shown as notably efficient to analyze the optical transfer of charge carriers between the systems and the presence of intrinsic and extrinsic defects.

Improved Nanoindentation Phase Transformation in Functional Structure of NiTi SMA and Graphene

Graphene layers were deposited on the surface of NiTi shape memory alloy (SMA) to enhance the spherical indentation depth and the phase transformed volume through an extra nanoscale cooling. The graphene-deposited NiTi SMA showed deeper nanoindentation depths during the solid-state phase transition, especially at the rate dependent loading zone. Larger superelastic deformation confirmed that the nanoscale latent heat transfer through the deposited graphene layers allowed larger phase transformed volume in the bulk and, therefore, more stress relaxation and depth can be achieved. During the indentation loading, the temperature of the phase transformed zone in the stressed bulk increased by ~12-43°C as the loading rate increased from 4,500 μN/s to 30,000 μN/s. The layers of graphene enhanced the cooling process at different loading rates by decreasing the temperature up to ~3-10°C depending on the loading rate.

Doping of cathodically polarized glassy carbon by natural graphite. A simple procedure for overlaying different carbons with electrochemically modifiable graphene layers

The reduction of graphite (at ca. −2V vs. Ag/AgCl, in DMF containing tetraalkylammonium salts) deposited onto smooth glassy carbon leads to intense graphite exfoliation that can be monitored through voltammetric scans or by fixed-potential electrolyses (E<−1.8V). These simple and extremely efficient processes result in very stable modified carbon surfaces exhibiting simple and astonishingly reproducible voltammetric responses (both in nature and intensity). The reduction peaks assigned to the cathodic doping of deposited graphene layers are found to be proportional to the scan rate. The modification of these graphene-like surface structures in two types or reactions: with a series of organic electrophiles (in the reaction with doped graphene that acts as a poly-nucleophile) or with in situ generated benzyl-type radicals was successfully achieved and compared with the results obtained on smooth carbon surfaces. Striking examples with additions of hexylferrocene, benzylic derivatives of anthraquinone, anthracene and perylene, and of para-substituted benzyls (R=NO2, I, Br, F) certainly underline the interest for these new materials.

Free-standing semipolar III-nitride quantum well structures grown on chemical vapor deposited graphene layers

We report the synthesis and optical characterization of semipolar-oriented III-nitride quantum well (QW) structures obtained by growth on chemical vapor deposited graphene layers using metalorganic vapor phase epitaxy. Various multi-quantum well stacks of GaN(QW)/AlGaN(barrier) and InGaN (QW)/GaN (barrier) were grown. Growth on graphene not only helps achieve a semipolar orientation but also allows facile transfer of the QW multilayer stack to other cheap, flexible substrates. We demonstrate room-temperature photoluminescence from layers transferred to flexible Kapton films.

Temperature variations at nano-scale level in phase transformed nanocrystalline NiTi shape memory alloys adjacent to graphene layers

The detection and control of the temperature variation at the nano-scale level of thermo-mechanical materials during a compression process have been challenging issues. In this paper, an empirical method is proposed to predict the temperature at the nano-scale level during the solid-state phase transition phenomenon in NiTi shape memory alloys. Isothermal data was used as a reference to determine the temperature change at different loading rates. The temperature of the phase transformed zone underneath the tip increased by ∼3 to 40 °C as the loading rate increased. The temperature approached a constant with further increase in indentation depth. A few layers of graphene were used to enhance the cooling process at different loading rates. Due to the presence of graphene layers the temperature beneath the tip decreased by a further ∼3 to 10 °C depending on the loading rate. Compared with highly polished NiTi, deeper indentation depths were also observed during the solid-state phase transition, especially at the rate dependent zones. Larger superelastic deformations confirmed that the latent heat transfer through the deposited graphene layers allowed a larger phase transition volume and, therefore, more stress relaxation and penetration depth.

Applications of Graphene Electrophoretic Deposition. A Review

This Review summarizes research progress employing electrophoretic deposition (EPD) to fabricate graphene and graphene-based nanostructures for a wide range of applications, including energy storage materials, field emission devices, supports for fuel cells, dye-sensitized solar cells, supercapacitors and sensors, among others. These carbonaceous nanomaterials can be dispersed in organic solvents, or more commonly in water, using a variety of techniques compatible with EPD. Most deposits are produced under constant voltage conditions with deposition time also playing an important role in determining the morphology of the resulting graphene structures. In addition to simple planar substrates, it has been shown that uniform graphene-based layers can be deposited on three-dimensional, porous, and even flexible substrates. In general, electrophoretically deposited graphene layers show excellent properties, e.g., high electrical conductivity, large surface area, good thermal stability, high optical transparency, and robust mechanical strength. EPD also enables the fabrication of functional composite materials, e.g., graphene combined with metallic nanoparticles, with other carbonaceous materials (e.g., carbon nanotubes) or polymers, leading to novel nanomaterials with enhanced optical and electrical properties. In summary, the analysis of the available literature reveals that EPD is a simple and convenient processing method for graphene and graphene-based materials, which is easy to apply and versatile. EPD has, therefore, a promising future for applications in the field of advanced nanomaterials, which depend on the reliable manipulation of graphene and graphene-containing systems.

Graphene as a diffusion barrier for Al and Ni/Au contacts on silicon

The insertion of chemically vapor deposited graphene layers between Al metallization and Si substrates and between Au and Ni metal layers on Si substrates is shown to provide a significant reduction in spiking and intermixing of the metal contacts and reaction with the Si, where the bilayer graphene was transferred to the samples after the Cu-foil was etched. The graphene prevents reaction between Al and Si up to the temperatures of 700 °C and the intermixing of Au and Ni up to the temperatures of at least 600 °C. The outstanding performance of the graphene as a metal diffusion barrier will be very useful to improve the stability of the metallizations at elevated temperatures.

Synthesis of a tunable MgB2/Nano-Graphene/MgB2–Josephson junction-like structure for electronic devices

The present investigations show a new trend, introducing the possibility of forming superconductor/conductor/superconductor Josephson junction-like structure using MgB2 as a model for the superconducting species and layered graphene for the conducting species. The MgB2/Graphene/MgB2 junction was synthesized in three steps, firstly MgB2 was synthesized by a conventional solid state reaction in a nitrogenated sealed tantalum ampoule. Secondly, a chemical vapor deposition (ICVD) technique was applied to deposit a few layers of graphene on the surfaces of two identical smoothly polished pellets of MgB2 with the same diameter and thickness. Thirdly, the two pellets with deposited graphene layers were formulated into one pellet using a hydrostatic compressor at 4 Ton cm−2. The structural and nano-structural features of the resulting interference junction were investigated by Raman spectra, XRD, AFM/STM and SE-microscopy with EDX-analysis. It was concluded that the manufactured MgB2/Graphene/MgB2 junction was controlled by many parameters.

Optical Absorption and Raman Scattering Studies of Few-Layer Epitaxial Graphene Grown on 4H-SiC Substrates

Optical absorption and Raman scattering studies of few-layer epitaxial graphene obtained by high temperature annealing of carbon terminated face of 4H-SiC(000-1) on-axis substrates are presented. Changing the pressure and annealing time, different stages of the graphene formation were achieved. Optical absorption measurements enabled us to establish average number of graphene layers covering the SiC substrate. Raman scattering experiments showed that integrated intensity of the characteristic 2D peak positively correlated with the number of graphene layers deposited on the SiC substrate. The spectral width of the 2D peak was found to decrease with the number of the deposited graphene layers.