Graphene Wafers Research Articles

Tunable Adhesion for All-Dry Transfer of 2D Materials Enabled by the Freezing of Transfer Medium.

The real applications of chemical vapor deposition (CVD)-grown graphene films require the reliable techniques for transferring graphene from growth substrates onto application-specific substrates. The transfer approaches that avoid the use of organic solvents, etchants, and strong bases are compatible with industrial batch processing, in which graphene transfer should be conducted by dry exfoliation and lamination. However, all-dry transfer of graphene remains unachievable owing to the difficulty in precisely controlling interfacial adhesion to enable the crack- and contamination-free transfer. Herein, through controllable crosslinking of transfer medium polymer, the adhesion is successfully tuned between the polymer and graphene for all-dry transfer of graphene wafers. Stronger adhesion enables crack-free peeling of the graphene from growth substrates, while reduced adhesion facilitates the exfoliation of polymer from graphene surface leaving an ultraclean surface. This work provides an industrially compatible approach for transferring 2D materials, key for their future applications, and offers a route for tuning the interfacial adhesion that would allow for the transfer-enabled fabrication of van der Waals heterostructures.

Controlled Growth of Single-Crystal Graphene Wafers on Twin-Boundary-Free Cu(111) Substrates.

Single-crystal graphene (SCG) wafers are needed to enable mass-electronics and optoelectronics owing to their excellent properties and compatibility with silicon-based technology. Controlled synthesis of high-quality SCG wafers can be done exploiting single-crystal Cu(111) substrates as epitaxial growth substrates recently. However, current Cu(111) films prepared by magnetron sputtering on single-crystal sapphire wafers still suffer from in-plane twin boundaries, which degrade the SCG chemical vapor deposition. Here, it is shown how to eliminate twin boundaries on Cu and achieve 4 in. Cu(111) wafers with ≈95% crystallinity. The introduction of a temperature gradient on Cu films with designed texture during annealing drives abnormal grain growth across the whole Cu wafer. In-plane twin boundaries are eliminated via migration of out-of-plane grain boundaries. SCG wafers grown on the resulting single-crystal Cu(111) substrates exhibit improved crystallinity with >97% aligned graphene domains. As-synthesized SCG wafers exhibit an average carrier mobility up to 7284 cm2 V-1 s-1 at room temperature from 103 devices and a uniform sheet resistance with only 5% deviation in 4 in. region.

Rapid and crack-free transfer of large-area graphene wafers

Rapid and crack-free transfer of large-area graphene wafers

Rapid and Scalable Transfer of Large-area Graphene Wafers.

Recently, scalable production of large-area graphene films on metal foils with promising qualities has been successfully achieved by eliminating grain boundaries, wrinkles and adlayers. The transfer of graphene from growth metal substrates onto functional substrates remains one inescapable obstacle on the road to the real commercial applications of CVD graphene films. Current transfer methods still require time-consuming chemical reactions, which hinders its mass production, and produces cracks and contamination that strongly impede performance reproducibility. Therefore, graphene transfer techniques with fine intactness and cleanness of transferred graphene, and improved production efficiency would be ideal for the mass production of graphene films on destination substrates. Herein, through the engineering of interfacial forces enabled by sophisticated design of transfer medium, we realize the crack-free and clean transfer of 4-inch-sized graphene wafers onto silicon wafers within only 15min. The reported transfer method is an important leap over the long-lasting obstacle of the batch-scale graphene transfer without degrading the quality of graphene, bringing the graphene products close to the real applications. This article is protected by copyright. All rights reserved.

Crack-Free Transfer of Graphene Wafers <i>via</i> Photoresist as Transfer Medium

Crack-Free Transfer of Graphene Wafers <i>via</i> Photoresist as Transfer Medium

Biomedical domains of the as-prepared nanocomposite based on hydroxyapatite, bismuth trioxide and graphene oxide

In this work, mineral trioxide and graphene oxide manipulated the morphological and biological potential of hydroxyapatite-based nanocomposites. XRD, FTIR, XPS, and EDS were used to perform the structural and chemical composition of HAP, pure Bi2O3, HAP/Bi2O3, HAP/GO, and HAP/Bi2O3/GO composites. The morphological alteration is investigated by TEM and FESEM techniques, followed by roughness parameters calculations. TEM micrographs confirm that the encapsulation of HAP through GO nanosheets to form HAP/GO reduces the agglomeration of HAP grains to appear separately on graphene wafers with sizes ranging from 11.4 to 28.5 nm, while HAP grains are sized from 11.4 to 22.8 nm. FESEM micrographs show that the combination of the three gradients (HAP, Bi2O3, and GO) cause well-defined grains, besides leaving wide pores in-between grain bundles, besides hitting grain size in scope that starts from 20 to 35 nm. Triple composite (HAP/Bi2O3/GO) records a higher roughness average than binary composites (HAP Bi2O3, and HAP/GO) with a value of 33.3 nm. Moreover, integration of the three components boosts the cell viability potential to record the uppermost percentage of 98.7 ± 2%, with clear enhancement in anti-microbial activity with an inhibition area of 25.7 ± 1.9 mm against Escherichia coli and 24.8 ± 1.8 mm in case of Staphylococcus.aureus.

Estimation of electrode contact impedance and conductivity of single-layer graphene using electrical impedance tomography

The paper describes a novel method of detecting defects in the fabrication of graphene films which have many important applications due to their unique mechanical and electronic properties. The illustrative method is based upon electrical impedance tomography and is demonstrated using a testbed to obtain the conductivity profile across the entire graphene surface. Sensed data are processed using a described reconstruction procedure that estimates electrode contact impedances and spatial conductivity. The results are presented of numerical simulations and experiments with graphene wafers of size 2.5 cm. The results show that the proposed method can jointly estimate contact impedance at each electrode and conductivity distribution.

The effect of catalytic copper pretreatments on CVD graphene growth at different stages

The controllable synthesis of high-quality and large-area graphene by chemical vapor deposition (CVD) remains a challenge nowadays. The massive grain boundaries in graphene grown on polycrystalline Cu by CVD significantly reduce its carrier mobility, limiting its application in high-performance electronic devices. Here, we confirm that the synergetic pretreatment of Cu with electropolishing and surface oxidation is a more efficient way to further suppress the graphene nucleation density (GND) and to accelerate the growth rate of the graphene domain by CVD. With increasing the growth time, we found that the increasing amount of GND and growth rate of the graphene domain were both decreasing during the whole CVD process when the Cu surface was not oxidized. By contrast, they kept growing over time when the Cu surface was pre-oxidized, which suggested that the change trends of the effects on the GND and growth rate between the Cu surface morphology and oxygen were opposite in the CVD process. In addition, not only the domain shape, but the number of graphene domain layers were impacted as well, and a large number of irregular ellipse graphene wafers with dendritic multilayer emerged when the Cu surface was oxidized.

Batch synthesis of transfer-free graphene with wafer-scale uniformity

Scalable synthesis of transfer-free graphene over insulators offers exciting opportunity for next-generation electronics and optoelectronics. However, rational design of synthetic protocols to harvest wafer-scale production of directly grown graphene still remains a daunting challenge. Herein we explore a batch synthesis of large-area graphene with wafer-scale uniformity by virtue of direct chemical vapor deposition (CVD) on quartz. Such a controllable CVD approach allows to synthesize 30 pieces of 4-inch graphene wafers in one batch, affording a low fluctuation of optical and electrical properties. Computational fluid dynamics simulations reveal the mechanism of uniform growth, indicating thermal field and confined flow field play leading roles in attaining the batch uniformity. The resulting wafer-scale graphene enables the direct utilization as key components in optical elements. Our method is applicable to other types of insulating substrates (e.g., sapphire, SiO2/Si, Si3N4), which may open a new avenue for direct manufacture of graphene wafers in an economic fashion.

Effects of electrode placement position and tilt angles of a platform on voltage induced by NaCl electrolyte flowing over graphene wafer

The extraction of energy from water in the natural environment has attracted significant interest in energy-harvesting applications in recent years. This study investigates the effects of the electrode placement position and the tilt angle of a platform on the voltage induced by a flow of aqueous NaCl electrolyte solution over a two-dimensional graphene wafer. It is shown that an orthogonal arrangement of the electrodes relative to the electrolyte flow direction maximizes the induced voltage. Further experiments are performed in which the graphene wafers are positioned such that the electrolyte flows over the short and long sides of the electrodes, respectively. The results show that the higher voltage response is obtained when the electrolyte flows through the long side of the electrodes. Finally, an investigation is performed into the voltage induced for various tilt angles from 20° to 60° of the graphene wafers placed on a platform. The charging and discharging time are revealed from experiments for the first time for various tilt angles. Based on the cases studied, the 45° tilt angle induces the highest voltage. Overall, the results presented in this study provide a useful insight into the optimal electrode placement position and tilt angle of a platform for graphene energy harvesting from aqueous sodium chloride solutions.

Synthesis of Graphene Wafers: from Lab to Fab

Synthesis of Graphene Wafers: from Lab to Fab

Scalable and ultrafast epitaxial growth of single-crystal graphene wafers for electrically tunable liquid-crystal microlens arrays

The scalable growth of wafer-sized single-crystal graphene in an energy-efficient manner and compatible with wafer process is critical for the killer applications of graphene in high-performance electronics and optoelectronics. Here, ultrafast epitaxial growth of single-crystal graphene wafers is realized on single-crystal Cu90Ni10(1 1 1) thin films fabricated by a tailored two-step magnetron sputtering and recrystallization process. The minor nickel (Ni) content greatly enhances the catalytic activity of Cu, rendering the growth of a 4 in. single-crystal monolayer graphene wafer in 10 min on Cu90Ni10(1 1 1), 50 folds faster than graphene growth on Cu(1 1 1). Through the carbon isotope labeling experiments, graphene growth on Cu90Ni10(1 1 1) is proved to be exclusively surface-reaction dominated, which is ascribed to the Cu surface enrichment in the CuNi alloy, as indicated by element in-depth profile. One of the best benefits of our protocol is the compatibility with wafer process and excellent scalability. A pilot-scale chemical vapor deposition (CVD) system is designed and built for the mass production of single-crystal graphene wafers, with productivity of 25 pieces in one process cycle. Furthermore, we demonstrate the application of single-crystal graphene in electrically controlled liquid-crystal microlens arrays (LCMLA), which exhibit highly tunable focal lengths near 2 mm under small driving voltages. By integration of the graphene based LCMLA and a CMOS sensor, a prototype camera is proposed that is available for simultaneous light-field and light intensity imaging. The single-crystal graphene wafers could hold great promising for high-performance electronics and optoelectronics that are compatible with wafer process.

Application of Arduino Module to Research in Surface Physics

Abstract During the semiconductor or graphene wafers surface were investigated, the Arduino module was applied to control the impact point of the laser beam. While the pulse signal of laser beam impacts to surface selected material and the material is exposed to enough strong magnetic field, the photomagnetoelectric effect takes place. This causes the electrical signal in the measurement coil, which is connected to amplifiers. The paper presents application of Arduino UNO module to control the position in two dimensions (in the XY plane) of investigated silicon or graphene wafers while the photomagnetoelectric effect is measuring. The Arduino drive (through the integrated circuit with power transistors) the steps and shift of a dedicated table with a sample situated at the top of the table. Constructed equipment, based on Arduino board, allows for one step size of 1.25 μm in X-axis and Y-axis, and in effect, the each square millimeter contains 640000 measurement points. We are able also to modify the Arduino program for motors controller any moment. Moreover, it is also possible to apply the obtain method to investigate another semiconductor materials. The commercially available similar devices don’t have all need functions and they are incomparably more expensive.

Dewetting behavior of electron-beam-deposited Au thin films on various substrates: graphenes, quartz, and SiO2 wafers

We demonstrate the dewetting behavior of Au thin films on the following substrates: single- and multilayer mechanically exfoliated graphene, and SiO2 and ST-cut quartz wafers. The 1-nm-thick Au thin films were prepared by electron beam deposition. The mean sizes of the Au nanoparticles from as-deposited samples were 0.4, 0.9, 1.6, and 2.3 nm and increased after a 60-min annealing at 900 °C to 5.1, 6.4, 9.4, and 10.8 nm for SiO2, ST-cut quartz, mono- and bi-layer graphene, respectively. Conversely, the areal densities of the Au nanoparticles decreased in all substrates with increasing annealing time. The different sizes, areal densities, and morphological evolutions of the Au nanoparticles due to annealing on the different substrates imply different interfacial interactions between Au and each surface. In addition, it is worth noting that single-walled carbon nanotubes (SWNTs) can be grown using the dewetted Au nanoparticles on graphene-coated quartz substrates. Finally, the present work can contribute to not merely precise formation of Au nanoparticles via dewetting phenomenon but also surface modification of graphene and SWNT growth.

Invited Presentation: Covalent Functionalization of Carbon Nanotubes and Graphene: Chemistry, Electronic Structure and Physical Properties

We have demonstrated the covalent functionalization of carbon nanotubes and graphene with a variety of chemistries including the use of nitrophenyl groups, Diels-Alder reactions and organometallic derivatization. The chemical formation of covalent carbon-carbon bonds involving the basal plane carbon atoms modifies the electronic properties of graphene; the transformation of the carbon centers from sp2 to sp3 introduces a barrier to electron flow by saturating the carbon atoms and opening a band gap which potentially allows the generation of insulating and semiconducting regions in graphene wafers. In this talk I will discuss our recent results on the electronic and magnetic properties of chemically modified graphene, the observation of ferromagnetism, and the application of organometallic chemistry to facilitate the interconnection of single-walled carbon nanotubes.

CVD formation of graphene on SiC surface in argon atmosphere

We investigate the microscopic processes leading to graphene growth by the chemical vapor deposition of propane in an argon atmosphere at the SiC surface. Experimentally, it is known that the presence of argon fastens the dehydrogenation processes at the surface, at high temperatures of about 2000 K. We perform ab initio calculations, at zero temperature, to check whether chemical reactions can explain this phenomenon. Density functional theory and supporting quantum chemistry methods qualitatively describe formation of the graphene wafers. We find that the 4H-SiC(0001) surface exhibits a large catalytic effect in the adsorption process of hydrocarbon molecules, this is also supported by preliminary molecular dynamics results. The existence of the ArH(+) molecule, and an observation from the Raman spectra that the negative charge transfers into the SiC surface, would suggest that presence of argon atoms leads to a deprotonization on the surface, which is necessary to obtain a pure carbon adlayer. But the zero-temperature description shows that the cold environment is insufficient to promote argon-assisted surface cleaning.

ChemInform Abstract: Advances in the Chemical Modification of Epitaxial Graphene

AbstractReview: 118 refs.

Ultra-low resistance ohmic contacts in graphene field effect transistors

We report on an experimental demonstration of graphene-metal ohmic contacts with contact resistance below 100 Ω µm. These have been fabricated on graphene wafers, both with and without hydrogen intercalation, and measured using the transmission line method. Specific contact resistivities of 3 × 10−7 to 1.2 × 10−8 Ω cm2 have been obtained. The ultra-low contact resistance yielded short-channel (source-drain distance of 0.45 µm) HfO2/graphene field effect transistors (FETs) with a low on-resistance (Ron) of 550 Ω µm and a high current density of 1.7 A/mm at a source-drain voltage of 1 V. These values represent state-of-the-art (SOA) performance in graphene-metal contacts and graphene FETs. This ohmic contact resistance is comparable to that of SOA high-speed III–V high electron mobility transistors.

Advances in the chemical modification of epitaxial graphene

Chemistry will play an increasingly important role in the realization of graphene applications. The chemical formation of covalent carbon–carbon bonds involving the basal plane carbon atoms offers an alternative approach to the control of the electronic properties of graphene, and potentially allows the generation of insulating and semiconducting regions in graphene wafers. This review summarizes recent progress in the covalent modification of epitaxial graphene and the effect that chemistry has on the electronic and magnetic properties of the material.

Universal Segregation Growth Approach to Wafer-Size Graphene from Non-Noble Metals

Graphene has been attracting wide interests owing to its excellent electronic, thermal, and mechanical performances. Despite the availability of several production techniques, it is still a great challenge to achieve wafer-size graphene with acceptable uniformity and low cost, which would determine the future of graphene electronics. Here we report a universal segregation growth technique for batch production of high-quality wafer-scale graphene from non-noble metal films. Without any extraneous carbon sources, 4 in. graphene wafers have been obtained from Ni, Co, Cu-Ni alloy, and so forth via thermal annealing with over 82% being 1-3 layers and excellent reproducibility. We demonstrate the first example of monolayer and bilayer graphene wafers using Cu-Ni alloy by combining the distinct segregation behaviors of Cu and Ni. Together with the easy detachment from growth substrates, we believe this facile segregation technique will offer a great driving force for graphene research.