The effects of dielectric decrement and finite ion size on differential capacitance of electrolytically gated graphene

The final publication is available at Elsevier via http://dx.doi.org/10.1016/j.cplett.2018.04.030 © 2018. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/We analyze the effects of dielectric decrement and finite ion size in an aqueous electrolyte on the capacitance of a graphene electrode, and make comparisons with the effects of dielectric saturation combined with finite ion size. We first derive conditions for the cross-over from a camel-shaped to a bell-shaped capacitance of the diffuse layer. We show next that the total capacitance is dominated by a V-shaped quantum capacitance of graphene at low potentials. A broad peak develops in the total capacitance at high potentials, which is sensitive to the ion size with dielectric saturation, but is stable with dielectric decrement.Natural Sciences and Engineering Research Council of Canada (ZLM: Grant No. 2016-03689

Insights on the Excitation Spectrum of Graphene Contacted with a Pt Skin

The excitation spectrum in the region of the intraband (Dirac plasmon) and interband ( π plasmon) plasmons in graphene/Pt-skin terminated Pt 3 Ni(111) is reproduced by using an ab-initio method and an empirical model. The results of both methods are compared with experimental data. We discover that metallic screening by the Pt layer converts the square-root dispersion of the Dirac plasmon into a linear acoustic-like plasmon dispersion. In the long-wavelength limit, the Pt d electron excitations completely quench the π plasmon in graphene at about 4.1 eV, that is replaced by a broad peak at about 6 eV. Owing to a rather large graphene/Pt-skin separation (≈3.3 Å), the graphene/Pt-skin hybridization becomes weak at larger wave vectors, so that the π plasmon is recovered with a dispersion as in a free-standing graphene

Stopping force acting on a charged particle moving over a drift-current biased supported graphene

In our recent publication we investigated the impact of plasmon-phonon hybridization on the stopping force acting on a charged particle moving parallel to a sandwich-like structure consisting of two graphene sheets separated by a layer of sapphire. In this work we evaluate the stopping force on a charged particle moving parallel to a graphene layer biased with a drift electric current supported by an insulating substrate. The dielectric function of the system is written in terms of the response function of graphene and the bulk dielectric function of the substrate. Focusing on the range of frequencies from THz to mid-infrared, the response function is expressed in terms of a frequency-dependent conductivity of graphene. The conductivity with a drift current is evaluated using the Galilean Doppler shift model. The energy loss function (the imaginary part of the negative value of the inverse dielectric function) and the stopping force are presented in the cases without and with drifting electrons, showing the effects of the drift velocity on the plasmon-phonon hybridization. The stopping force is also calculated when the drift and electron beam velocities have the same and opposite signs.Catalysts for water splitting and energy storage, April 3-5th, 2024 ; Vienna, AustriaLink to the conference website: [https://web.archive.org/web/20240409120751/http://dollywood.itp.tuwien.ac.at/~florian/Vienna_April2024/

Energy loss and deflection of fast ions moving parallel to the graphene sheet

We investigate the interactions of fast ions with graphene, describing the excitations of the electron gas in graphene by a two-dimensional hydrodynamic model. By linearizing the hydrodynamic equations, we derive general expressions for the induced potential, the stopping force and the image force for an ion moving parallel to the graphene sheet. Moreover, the Barkas effect on the stopping force and the analogous corrections to the induced potential and the image force are evaluated within the second-order perturbation approach to the hydrodynamic equations. The numerical results of the linear and nonlinear theories are obtained showing the influence of the ion position and its velocity on the stopping force and the image force.YUCOMAT 2007 : 9th Annual Conference YUCOMAT 2007 : Programme and the book of abstracts; September 10-14, 2007; Herceg Novi, Montenegr

Wake effect in interactions of ions with graphene-sapphire-graphene structure

In our recent publication1 we have studied the wake potential induced by an external charged particle that moves parallel to various sy1-Al2O3-sy2 composites, where syi (with i=1,2) may be vacuum, pristine graphene, or doped graphene. Several important parameters were fixed at their respective typical values: the distance of the charged particle from the closest surface, the thickness of the sapphire (aluminum oxide, Al2O3) layer, and the doping density (i.e., Fermi energy) of graphene. In this work we present a detailed study of the effects due to variations of all those parameters in the case of the wake potential produced by charged particle moving parallel to the graphene-Al2O3- graphene composite system, by using the dynamic polarization function of graphene within the random phase approximation for its π electrons described as Dirac’s fermions and by using a local dielectric function for the sapphire layer2 . For the velocity of the charged particle below the threshold for excitations of the Dirac plasmon in graphene, given by its Fermi velocity vF, strong effects are observed due to variation of the particle distance, while for the velocity of the charged particle above vF strong effects are observed due to varying the thickness of the Al2O3 layer, as well as due to graphene doping

Theoretical modeling of experimental EELS data for monolayer graphene supported by different metal substrates

We present a theoretical modeling of the electron energy loss spectroscopy data for monolayer graphene supported by Pt(111), Ru(0001), and Ni(111) substrates. In order to reproduce the experimental loss function, we have used a two-dimensional, two-fluid hydrodynamic model for inter-band transitions of graphene’s π and σ electrons and an empirical Drude-Lorentz model in the local approximation for metal substrates. The agreement between the theoretical curves and the experimental data is very good in the cases of graphene supported by Pt and Ru substrates. Conversely, the agreement is less satisfactory for the case of graphene/Ni, presumably due to the strong hybridization between the π states of graphene and the d bands of Ni, which is not accounted for in the model

Resolving the Mechanism of Acoustic Plasmon Instability in Graphene Doped by Alkali Metals

Graphene doped by alkali atoms (ACx) supports two heavily populated bands (π and σ) crossing the Fermi level, which enables the formation of two intense two-dimensional plasmons: the Dirac plasmon (DP) and the acoustic plasmon (AP). Although the mechanism of the formation of these plasmons in electrostatically biased graphene or at noble metal surfaces is well known, the mechanism of their formation in alkali-doped graphenes is still not completely understood. We shall demonstrate that two isoelectronic systems, KC8 and CsC8, support substantially different plasmonic spectra: the KC8 supports a sharp DP and a well-defined AP, while the CsC8 supports a broad DP and does not support an AP at all. We shall demonstrate that the AP in an ACx is not, as previously believed, just a consequence of the interplay of the π and σ intraband transitions, but a very subtle interplay between these transitions and the background screening, caused by the out-of-plane interband C(π)→A(σ) transitions

Energijski gubitak naelektrisane čestice koja se kreće iznad površine grafena

12. Kongres fizičara Srbije : Apr 28 - Maj 2, Vrnjačka Banja, 2013

Theoretical modeling of experimental EELS data for free-standing and supported graphene

Firstly, we present a theoretical modeling of the experimental electron energy loss (EEL) spectra of free-standing films consisting of N graphene layers in a scanning transmission electron microscope (STEM) [1]. We treat the multi-layer graphene (MLG) as layered electron gas with in-plane polarizability modeled by a two-dimensional (2D), two-fluid hydrodynamic (HD) model [2] for the inter-band transitions of ʌ DQGı electrons of single-layer graphene (SLG), and find good agreement (as shown in Fig. 1) with the experimental EEL spectra [3] for N<10 graphene layers. Secondly, we present a theoretical modeling of the experimental EEL spectroscopy (EELS) data for monolayer graphene supported by Pt(111), Ru(0001), and Ni(111) substrates [4], as well as for high-quality graphene grown on peeled-off epitaxial Cu(111) foils [5]. To reproduce the experimental loss function, we use the same version of the HD model for graphene’s ʌ DQG ı HOHFWURQV in conjunction with an empirical Drude-Lorentz model for metal substrate. Finally, we present an analytical modeling of the experimental EELS data for free-standing graphene obtained by STEM using an ab initio method and the 2D, two-fluid extended HD (eHD) model [6]. We use an optical approximation based on the conductivity of graphene given in the local, i.e., frequency-dependent form derived by these two methods and find very good agreement with the EEL spectra from three independent experiments [3,7,8], especially in the case of the eHD modelMini-workshop REST in Paris : December 7-8, Paris, 2017