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Optical constants of graphene measured by spectroscopic ellipsometry

Weber, J.W. (author), Calado, V.E. (author), Van de Sanden, M.C.M. (author)

A mechanically exfoliated graphene flake ( ? 150×380??m2) on a silicon wafer with 98 nm silicon dioxide on top was scanned with a spectroscopic ellipsometer with a focused spot ( ? 100×55??m2) at an angle of 55°. The spectroscopic ellipsometric data were analyzed with an optical model in which the optical constants were parameterized by B...

journal article 2010

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Quantum pumping in graphene with a perpendicular magnetic field

Tiwari, R.P. (author), Blaauboer, M. (author)

We consider quantum pumping of Dirac fermions in a monolayer of graphene in the presence of a perpendicular magnetic field in the central pumping region. The two external pump parameters are electrical voltages applied to the graphene sheet on either side of the pumping region. We analyze this pump within scattering matrix formalism and...

journal article 2010

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Influence of carrier density on the electronic cooling channels of bilayer graphene

Limmer, T. (author), Houtepen, A.J. (author), Niggebaum, A. (author), Tautz, R. (author), Da Como, E. (author)

We study the electronic cooling dynamics in a single flake of bilayer graphene by femtosecond transient absorption probing the photon-energy range 0.25–1.3 eV. From the transients, we extract the carrier cooling curves for different initial temperatures and densities of the photoexcited electrons and holes. Two regimes of carrier cooling,...

journal article 2011

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Mechanical cleaning of graphene

Goossens, A.M. (author), Calado, V.E. (author), Barreiro, A. (author), Watanabe, K. (author), Taniguchi, T. (author), Vandersypen, L.M.K. (author)

Contamination of graphene due to residues from nanofabrication often introduces background doping and reduces electron mobility. For samples of high electronic quality, post-lithography cleaning treatments are therefore needed. We report that mechanical cleaning based on contact mode atomic force microscopy removes residues and significantly...

journal article 2012

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Formation and control of wrinkles in graphene by the wedging transfer method

Calado, V.E. (author), Schneider, G.F. (author), Theulings, A.M.M.G. (author), Dekker, C. (author), Vandersypen, L.M.K. (author)

We study the formation of wrinkles in graphene upon wet transfer onto a hydrophilic target substrate, whereby draining of water appears to play an important role. We are able to control the orientation of the wrinkles by tuning the surface morphology. Wrinkles are absent in flakes transferred to strongly hydrophobic substrates, a further...

journal article 2012

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Graphene based piezoresistive pressure sensor

Zhu, S.E. (author), Ghatkesar, M.K. (author), Zhang, C. (author), Janssen, G.C.A.M. (author)

We present a pressure sensor based on the piezoresistive effect of graphene. The sensor is a 100?nm thick, 280??m wide square silicon nitride membrane with graphene meander patterns located on the maximum strain area. The multilayer, polycrystalline graphene was obtained by chemical vapor deposition. Strain in graphene was generated by applying...

journal article 2013

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I-V characteristics of in-plane and out-of-plane strained edge-hydrogenated armchair graphene nanoribbons

Cartamil-Bueno, S.J. (author), Rodriguez-Bolivar, S. (author)

The effects of tensile strain on the current-voltage (I-V) characteristics of hydrogenated-edge armchair graphene nanoribbons are investigated by using DFT theory. The strain is introduced in two different ways related to the two types of systems studied in this work: in-plane strained systems (A) and out-of-plane strained systems due to bending...

journal article 2015

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Temperature dependence of atomic vibrations in mono-layer graphene

Allen, C.S. (author), Liberti, E. (author), Kim, J.S. (author), Xu, Q. (author), Fan, Y. (author), He, K. (author), Robertson, A.W. (author), Zandbergen, H.W. (author), Warner, J.H. (author), Kirkland, A.I. (author)

We have measured the mean square amplitude of both in- and out-of-plane lattice vibrations for mono-layer graphene at temperatures ranging from ?100 K to 1300?K. The amplitude of lattice vibrations was calculated from data extracted from selected area electron diffraction patterns recorded across a known temperature range with over 80...

journal article 2015

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Colorimetry Technique for Scalable Characterization of Suspended Graphene

Cartamil Bueno, S.J. (author), Steeneken, P.G. (author), Centeno, Alba (author), Zurutuza, Amaia (author), van der Zant, H.S.J. (author), Houri, S. (author)

Previous statistical studies on the mechanical properties of chemical-vapor-deposited (CVD) suspended graphene membranes have been performed by means of measuring individual devices or with techniques that affect the material. Here, we present a colorimetry technique as a parallel, noninvasive, and affordable way of characterizing suspended...

journal article 2016

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Performance enhancement of reduced graphene oxide-modified carbon electrodes for vanadium redox-flow systems

Chakrabarti, B. (author), Nir, D. (author), Yufit, V (author), Tariq, F (author), Rubio-Garcia, J. (author), Maher, R. (author), Kucernak, A. (author), Aravind, P.V. (author), Brandon, N. (author)

Reduced graphene oxide (rGO) suspended in an N,N′-dimethylformamide (DMF) solvent underwent electrophoretic deposition (EPD) on carbon paper (CP) electrodes. X-ray computed micro-tomography (XMT) indicates a 24 % increase in the specific surface area of CP modified with rGO in comparison to the untreated sample. Furthermore, XMT confirms that...

journal article 2017

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Effects of Graphene Monolayer Coating on the Optical Performance of Remote Phosphors

Yazdan Mehr, M. (author), Vollebregt, S. (author), van Driel, W.D. (author), Zhang, Kouchi (author)

A graphene monolayer has been successfully coated on one side of a bisphenol-A-polycarbonate (BPA-PC) plate, used as a substrate for remote phosphor applications in light-emitting diode (LED)-based products. Using a photoresist transferring method, graphene sheet has been coated on BPA-PC plates. The results show that this graphene monolayer...

journal article 2017

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A guide to and review of the use of Multiwavelength Raman Spectroscopy for characterizing defective aromatic carbon solids: From graphene to amorphous carbons

Merlen, A. (author), Buijnsters, J.G. (author), Pardanaud, C. (author)

sp2 hybridized carbons constitute a broad class of solid phases composed primarily of elemental carbon and can be either synthetic or naturally occurring. Some examples are graphite, chars, soot, graphene, carbon nanotubes, pyrolytic carbon, and diamond-like carbon. They vary from highly ordered to completely disordered solids and detailed...

journal article 2017

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Distortion of DNA Origami on Graphene Imaged with Advanced TEM Techniques

Kabiri, Y. (author), Ananth, A.N. (author), van der Torre, J. (author), Katan, A.J. (author), Hong, Jin Yong (author), Malladi, S.R.K. (author), Kong, Jing (author), Zandbergen, H.W. (author), Dekker, C. (author)

While graphene may appear to be the ultimate support membrane for transmission electron microscopy (TEM) imaging of DNA nanostructures, very little is known if it poses an advantage over conventional carbon supports in terms of resolution and contrast. Microscopic investigations are carried out on DNA origami nanoplates that are supported...

journal article 2017

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Thermophoretically driven water droplets on graphene and boron nitride surfaces

Rajegowda, Rakesh (author), Kannam, Sridhar Kumar (author), Hartkamp, Remco (author), Sathian, Sarith P. (author)

We investigate thermally driven water droplet transport on graphene and hexagonal boron nitride (h-BN) surfaces using molecular dynamics simulations. The two surfaces considered here have different wettabilities with a significant difference in the mode of droplet transport. The water droplet travels along a straighter path on the h-BN sheet...

journal article 2018

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Graphene gas pumps

Davidovikj, D. (author), Bouwmeester, Damian (author), van der Zant, H.S.J. (author), Steeneken, P.G. (author)

We report on the development of a pneumatically coupled graphene membrane system, comprising of two circular cavities connected by a narrow trench. Both cavities and the trench are covered by a thin few-layer graphene membrane to form a sealed dumbbell-shaped chamber. Local electrodes at the bottom of each cavity allow for actuation of each...

journal article 2018

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Toward nanomechanical models of liquid-phase exfoliation of layered 2D nanomaterials: Analysis of a π − peel model

Botto, L. (author)

In liquid-phase exfoliation for the production of 2D nanomaterials fluid forces are used to gently overcome adhesive interlayer forces, leading to single- or few-layer 2D nanomaterials. Predicting accurately the critical fluid shear rate for exfoliation is a crucial challenge. By combining notions of fluid mechanics and fracture mechanics, we...

journal article 2019

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High-frequency stochastic switching of graphene resonators near room temperature

Dolleman, R.J. (author), Belardinelli, P. (author), Houri, S. (author), van der Zant, H.S.J. (author), Alijani, F. (author), Steeneken, P.G. (author)

Stochastic switching between the two bistable states of a strongly driven mechanical resonator enables detection of weak signals based on probability distributions, in a manner that mimics biological systems. However, conventional silicon resonators at the microscale require a large amount of fluctuation power to achieve a switching rate in the...

journal article 2019

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Analysis of a calibration method for non-stationary CVD multi-layered graphene-based gas sensors

Ricciardella, F. (author), Polichetti, Tiziana (author), Vollebregt, S. (author), Alfano, Brigida (author), Massera, Ettore (author), Sarro, Pasqualina M (author)

Limitations such as lack of detected stationary signal and slow signal recovery after detection currently affect graphene-based chemi-sensors operating at room temperature. In this work, we model the behavior of a sensor in a test chamber having limited volume and simulating the environmental conditions. From this model, we mathematically derive...

journal article 2019

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Sealing graphene nanodrums

Lee, M. (author), Davidovikj, D. (author), Sajadi, B. (author), Siskins, M. (author), Alijani, F. (author), van der Zant, H.S.J. (author), Steeneken, P.G. (author)

Despite theoretical predictions that graphene should be impermeable to all gases, practical experiments on sealed graphene nanodrums show small leak rates. Thus far, the exact mechanism for this permeation has remained unclear, because different potential leakage pathways have not been studied separately. Here, we demonstrate a sealing method...

journal article 2019

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Compact Graphene-Based Spiking Neural Network with Unsupervised Learning Capabilities

Wang, He (author), Cucu Laurenciu, N. (author), Jiang, Y. (author), Cotofana, S.D. (author)

To fully unleash the potential of graphene-based devices for neuromorphic computing, we propose a graphene synapse and a graphene neuron that form together a basic Spiking Neural Network (SNN) unit, which can potentially be utilized to implement complex SNNs. Specifically, the proposed synapse enables two fundamental synaptic functionalities,...

journal article 2020