To expand the possible applications, chemical vapor deposition grown graphene needs to be transferred to appropriate substrates such as a silicon wafer. Although enormous efforts have been devoted to transfer graphene to various substrates using many different methods, the quality of the final product is still insufficient. We develop a new process named semi-dry transfer, which combines wet etching and dry transfer to obtain graphene with a clean interface with the substrate. For this purpose, an adhesive tape is attached to a sacrificial polymer deposited on the synthesized graphene, which allows the graphene to be easily manipulated so that it can be carefully cleaned before being precisely transferred onto target substrates, here silicon (Si) surfaces. We used this technique to transfer up to 4 × 4 cm2 of graphene onto SiO2/Si substrates. Using various analysis techniques such as low energy electron diffraction, scanning electron microscopy, scanning tunneling microscopy/spectroscopy, Raman, Auger electron and X-ray photoelectron spectroscopies, we demonstrate that our transferred graphene on Si is continuous, clean and that it is very promising for device fabrication. Graphene transistors show transport properties comparable with the state-of-the-art.

Copper foil impurities are hampering scalable production of high-quality graphene by chemical vapor deposition (CVD). Here, we conduct a thorough study on the origin of these unavoidable contaminations at the surface of copper after the CVD process. We identify two distinct origins for the impurities. The first type is intrinsic im-purities, originating from the manufacturing process of the copper foils, already present at the surface before any high-temperature treatment, or buried into the bulk of copper foils. The buried impurities diffuse towards the copper surface during high-temperature treatment and precipitate. The second source is external: silica contamination arising from the quartz tube that also precipitate on copper. The problem of the extrinsic silica contamination is readily solved upon using an adequate confinement the copper foil samples. The intrinsic impurities are much more difficult to remove since they appear spread in the whole foil. Nevertheless, elec-tropolishing proves particularly efficient in drastically reducing the issue.

This work introduces a new measurement methodology for enhancing gas detection by tuning the magnitude and polarity of back-gate voltage of a field-effect transistor (FET)-based sensor. The aim is to simultaneously strengthen the sensor response and accelerate the sensor recovery. In addition, this methodology can consume less energy compared with conventional measurements by direct current bias. To illustrate the benefits of the proposed methodology, we fabricated and characterized a polypyrrole/graphene (PPy/G) FET sensor for ammonia (NH3) detection. Our experiment, simulation and calculation results demonstrated that the redox reaction between the NH3 molecules and the PPy/G sensitive layer could be controlled by altering the polarity and the magnitude of the back-gate voltage. This proof-of-principle measurement methodology, which solves the inherent contradiction between high response and slow recovery of the chemiresistive sensor, could be extended to detect other gases, so as to improve global gas measurement systems. It opens up a new route for FET-based gas sensors in practical applications.

Previous theoretical works suggested that superhydrophobicity could be enhanced through partial inhibition of the quantum vacuum modes at the surface of a broadband-absorber metamaterial which acts in the extreme ultraviolet frequency domain. This effect would then compete with the classical Cassie-Baxter interpretation of superhydrophobicity. In this article, we first theoretically establish the expected phenomenological features related to such a kind of "quantum" superhydrophobicity. Then, relying on this theoretical framework, we experimentally study patterned silicon surfaces on which organosilane molecules were grafted, all the coated surfaces having similar characteristic pattern sizes but different profiles. Some of these surfaces can indeed freeze quantum photon modes while others cannot. While the latter ones allow hydrophobicity, only the former ones allow for superhydrophobicity. We believe these results lay the groundwork for further complete assessment of superhydrophobicity induced by quantum fluctuations freezing.

The use of protective barriers to isolate a metal surface from an aggressive environment is a common-way to inhibit its degradation. We used ambient pressure x-ray photoelectron spectroscopy to assess in real time the evolution of the copper surface and the contextual protective action of 2D material coatings (graphene and hexagonal boron nitride) towards copper oxidation. In an isobaric experiment with 2 mbar of oxygen, the bare copper oxidizes near room temperature, while both 2D materials can retard the onset temperature for the first oxidation of copper by more than 120 degrees C. However, their protection mechanism is different: boron nitride behaves more straightforwardly, forming an effective barrier to copper oxidation until it is etched away at high temperatures, leading to a rapid oxidation to cuprous and then cupric oxide. On the other hand, graphene reveals to be a more interesting playground underneath oxygen intercalates and begins a slower undercover oxidation of copper. The coexistence between graphene and cuprous oxide, not observed in boron nitride, protects the copper from further oxidation to cupric oxide. (C) 2020 Elsevier Ltd. All rights reserved.

The growth of single-layer graphene (SLG) by chemical vapor deposition (CVD) on copper surfaces is very popular because of the self-limiting effect that, in principle, prevents the growth of few-layer graphene (FLG). However, the reproducibility of the CVD growth of homogeneous SLG remains a major challenge, especially if one wants to avoid heavy surface treatments, monocrystalline substrates and expensive equipment to control the atmosphere inside the growth system. We demonstrate here that backside tungsten coating of copper foils allows for the exclusive growth of SLG with full coverage by atmospheric pressure CVD implemented in a vacuum-free furnace. We show that the absence of FLG patches is related to the suppression of carbon diffusion through copper. In the perspective of large-scale production of graphene, this approach constitutes a significant improvement to the traditional CVD growth process since (1) a tight control of the hydrocarbon flow is no longer required to avoid FLG formation and, consequently, (2) the growth duration necessary to reach full coverage can be drastically shortened.

We present an ultra-thin lateral SOI PIN photodiode with transferred monolayer graphene as the transparent gate, to provide enhanced ultraviolet (UV) performance and mechanical flexibility beyond standard Si-based devices. The device dark current shows intact characteristics after the post-CMOS thinning and graphene transfer processing steps. The device responsivity presents high potential in UV and visible wavelength detections (i.e. within the 200-900 nm range) under monochromatic light illumination. A maximum responsivity of 0.18 A W-1 has been experimentally achieved at 390 nm wavelength and validated by simulation, for a diode with intrinsic length L-i of 20 mu m. Additionally, the similar to 5 mu m-thick device chip with direct board assembly paves the way towards the development of hybrid flexible electronics.

We performed spatially resolved near-ambient-pressure photoemission spectromicroscopy on graphene-coated copper in operando under oxidation conditions in an oxygen atmosphere (0.1 mbar). We investigated regions with bare copper and areas covered with mono- and bi-layer graphene flakes, in isobaric and isothermal experiments. The key method in this work is the combination of spatial and chemical resolution of the scanning photoemission microscope operating in a near-ambient-pressure environment, thus allowing us to overcome both the material and pressure gap typical of standard ultrahigh-vacuum X-ray photoelectron spectroscopy (XPS) and to observe in operando the protection mechanism of graphene toward copper oxidation. The ability to perform spatially resolved XPS and imaging at high pressure allows for the first time a unique characterization of the oxidation phenomenon by means of photoelectron spectromicroscopy, pushing the limits of this technique from fundamental studies to real materials under working conditions. Although bare Cu oxidizes naturally at room temperature, our results demonstrate that such a graphene coating acts as an effective barrier to prevent copper oxidation at high temperatures (over 300 °C), until oxygen intercalation beneath graphene starts from boundaries and defects. We also show that bilayer flakes can protect at even higher temperatures. The protected metallic substrate, therefore, does not suffer corrosion, preserving its metallic characteristic, making this coating appealing for any application in an aggressive atmospheric environment at high temperatures.

Graphene decorated by palladium (Pd) nanoparticles has been investigated for hydrogen sensor applications. The density of Pd nanoparticles is critical for the sensor performance. We develop a new chemical method to deposit high-density, small-size and uniformly-distributed Pd nanoparticles on graphene. With this method, Pd precursors are connected to the graphene by π-π bonds without introducing additional defects in the hexagonal carbon lattice. Our method is simple, cheap, and compatible with complementary metal-oxide semiconductor (CMOS) technology. This method is used to fabricate hydrogen sensors on 3-inch silicon wafers. The sensors show high performance at room temperature. Particularly, the sensors present a shorter recovery time under light illumination. The sensing mechanism is explained and discussed. The proposed deposition method facilitates mass fabrication of the graphene sensors and allows integration with CMOS circuits for practical applications.

Inserting 2D conducting material between dielectrics modifies the Brewster angle. We theoretically and experimentally demonstrate this influence using mono-, bi- and trilayer graphene samples. It provides an original optical measurement of 2D materials' conductivity.

Insertion of two-dimensional (2D) materials in optical systems modifies their electrodynamical response. In particular, the Brewster angle undergoes an up-shift if a substrate is covered with a conducting 2D material. This work theoretically and experimentally investigates this effect related to the 2D induced current at the interface. The shift is predicted for all conducting 2D materials and tunability with respect to the Fermi level of graphene is evidenced. Analytical approximations for high and low 2D conductivities are proposed and avoid cumbersome numerical analysis of experimental data. Experimental demonstration using spectroscopic ellipsometry has been performed in the UV to NIR range on mono-, bi-and trilayer graphene samples. The non-contact measurement of this modified Brewster angle allows to deduce the optical conductivity of 2D materials. Applications to telecommunication technologies can be considered thanks to the tunability of the shift at 1.55 mu m.

Graphene’s high susceptibility to adsorbed (nano-)particles makes it of great interest for sensing applications, and it provides schemes to tailor graphene’s properties for example for spintronics and catalysis. Ultrasmall metallic clusters are interesting candidates in this perspective. Their physico-chemical properties, which greatly differ from the element’s single atom or bulk characteristics, strongly depend on the exact number of atoms. It is expected that these size-specific cluster properties will transpire in graphene’s electronic properties. Thus on the one hand, graphene can act as a sensor to clusters, while on the other, the virtually endless possibilities to tune a cluster’s properties, greatly expands the opportunities for graphene-based cluster devices.

Densely populated edge-terminated vertically aligned two-dimensional MoS 2 nanosheets (NSs) with thicknesses ranging from 5 to 20 nm were directly synthesized on Mo films deposited on SiO 2 by sulfurization. The quality of the obtained NSs was analyzed by scanning electron and transmission electron microscopy, and Raman and X-ray photoelectron spectroscopy. The as-grown NSs were then successfully transferred to the substrates using a wet chemical etching method. The transferred NSs sample showed excellent field-emission properties. A low turn-on field of 3.1 V/μm at a current density of 10 µA/cm 2 was measured. The low turn-on field is attributed to the morphology of the NSs exhibiting vertically aligned sheets of MoS 2 with sharp and exposed edges. Our findings show that the fabricated MoS 2 NSs could have a great potential as robust high-performance electron-emitter material for various applications such as microelectronics and nanoelectronics, flat-panel displays and electron-microscopy emitter tips.

Graphene's sensitivity to adsorbed particles has attracted widespread attention because of its potential sensor applications. Size-selected few-atom clusters are promising candidates as adparticles to graphene. Due to their small size, physicochemical properties are dominated by quantum size effects. In particular, few-atom gold clusters demonstrate a significant catalytic activity in various oxidation reactions. In this joint experimental and computational work, size-selected gold clusters with 3 and 6 atoms adsorbed on graphene field-effect transistors and their interaction with molecular oxygen are investigated. While oxygen adsorbs at both cluster sizes, there is a pronounced cluster size dependence in the corresponding doping, as demonstrated via first-principle calculations and electronic transport measurements. Furthermore, the doping of gold cluster decorated graphene changes sign from n- to p-doping upon oxygen adsorption, directly evidencing electron transfer to the oxygen molecules and hence their activation. These observations pinpoint graphene as a valuable platform to investigate and exploit size-dependent cluster properties.

We investigated the interaction between size-selected Au-2 and Au-3 clusters and graphene. Hereto preformed clusters are deposited on graphene field-effect transistors, a novel approach which offers a high control over the number of atoms per cluster, the deposition energy and the deposited density. The induced p-doping and charge carrier scattering indicate that a major part of the deposited clusters remains on the graphene flake as either individual or sub-nm coalesced entities. This is independently confirmed by scanning electron microscopy on the same devices after current annealing. Our novel approach provides perspectives for the electronic sensing of metallic clusters down to their atom-by-atom size-specific properties, and exploiting the tunability of clusters for tailoring desired properties in graphene.

The influence of chemical vapor deposition (CVD) graphene grain size on the electromagnetic (EM) shielding performance of graphene/polymethyl methacrylate (PMMA) multilayers in K-a-band was studied both experimentally and theoretically. We found that increasing the average graphene grain size from 20 to 400 mu m does not change the EM properties of heterostructures consisting of graphene layers sandwiched between submicron thick PMMA spacers. The independence of EM interference shielding effectiveness on the graphene grain size between 20 and 400 mu m allows one to use cheaper (or more convenient regimes of CVD) graphene samples with low crystallinity and small grain size in the development of new graphene-based passive EM devices operated at high frequencies. (C) 2017 Society of Photo-Optical Instrumentation Engineers (SPIE)

Suspended graphene is exposed to different fluorine-containing species produced by a plasma source fed with CF4 precursor gas. We investigate the fluorination process by selecting two different kinetic energies for the ions striking the graphene surface. The chemical-bonding environment is discussed, and the control of the graphene-fluorination homogeneity is investigated at the individual graphene sheets. The modifications of the electronic and structural properties are examined by scanning photoelectron microscopy, micro-Raman analysis, and scanning electron microscopy. The results are compared with those obtained for supported graphene on copper. Suspended graphene provides a quasi-ideal model for investigating the intrinsic properties of irradiated carbon nano-systems while avoiding damage due to backscattered atoms and recoil due to a supporting substrate.