Showing papers on "Quantum capacitance published in 2019"

Improving the Quantum Capacitance of Graphene-Based Supercapacitors by the Doping and Co-Doping: First-Principles Calculations.

Abstract: We explore the stability, electronic properties, and quantum capacitance of doped/co-doped graphene with B, N, P, and S atoms based on first-principles methods. B, N, P, and S atoms are strongly bonded with graphene, and all of the relaxed systems exhibit metallic behavior. While graphene with high surface area can enhance the double-layer capacitance, its low quantum capacitance limits its application in supercapacitors. This is a direct result of the limited density of states near the Dirac point in pristine graphene. We find that the triple N and S doping with single vacancy exhibits a relatively stable structure and high quantum capacitance. It is proposed that they could be used as ideal electrode materials for symmetry supercapacitors. The advantages of some co-doped graphene systems have been demonstrated by calculating quantum capacitance. We find that the N/S and N/P co-doped graphene with single vacancy is suitable for asymmetric supercapacitors. The enhanced quantum capacitance contributes to the formation of localized states near the Dirac point and/or Fermi-level shifts by introducing the dopant and vacancy complex.

The intrinsic volumetric capacitance of conducting polymers: pseudo-capacitors or double-layer supercapacitors?

Abstract: The capacitance of conducting polymers represents one of the most important material parameters that in many cases determines the device and material performances. Despite a vast number of experimental studies, the theoretical understanding of the origin of the capacitance in conducting polymers remains unsatisfactory and appears even controversial. Here, we present a theoretical method, based on first principle capacitance calculations using density functional theory (DFT), and apply it to calculate the volumetric capacitance of two archetypical conducting polymers: poly(3,4-ethylene dioxythiophene) (PEDOT) and polypyrrole (PPy). Our aim is to achieve a quantitate description of the volumetric capacitance and to provide a qualitative understanding of its nature at the atomistic level. We find that the volumetric capacitance of PEDOT and PPy is ≈100 F cm−3 and ≈300 F cm−3, respectively, which is within the range of the corresponding reported experimental results. We demonstrate that the capacitance of conducting polymers originates from charges stored in atomistic Stern layers formed by counterions and doped polymeric chains. The Stern layers have a purely electrostatic origin, since the counterions do not form any bonds with the atoms of the polymeric chains, and no charge transfer between the counterions and conducting polymer takes place. This classifies the conducting polymers as double-layer supercapacitors rather than pseudo-capacitors. Further, we analyze contributions to the total capacitance originating from the classical capacitance CC and the quantum capacitance CQ, respectively, and find that the latter provides a dominant contribution. The method of calculations of the capacitance developed in the present paper is rather general and opens up the way for engineering and optimizing the capacitive response of the conducting polymers.

Band Filling and Cross Quantum Capacitance in Ion-Gated Semiconducting Transition Metal Dichalcogenide Monolayers

Abstract: Ionic liquid gated field-effect transistors (FETs) based on semiconducting transition metal dichalcogenides (TMDs) are used to study a rich variety of extremely interesting physical phenomena, but ...

The Electronic Thickness of Graphene

Abstract: The van-der-Waals stacking technique enables the fabrication of heterostructures, where two conducting layers are atomically close. In this case, the finite layer thickness matters for the interlayer electrostatic coupling. Here we investigate the electrostatic coupling of two graphene layers, twisted by 22 degrees such that the layers are decoupled by the huge momentum mismatch between the K and K' points of the two layers. We observe a splitting of the zero-density lines of the two layers with increasing interlayer energy difference. This splitting is given by the ratio of single-layer quantum capacitance over interlayer capacitance C and is therefore suited to extract C. We explain the large observed value of C by considering the finite dielectric thickness d of each graphene layer and determine d=2.6 Angstrom. In a second experiment we map out the entire density range with a Fabry-Perot resonator. We can precisely measure the Fermi-wavelength in each layer, showing that the layers are decoupled. We find that the Fermi wavelength exceeds 600nm at the lowest densities and can differ by an order of magnitude between the upper and lower layer. These findings are reproduced using tight-binding calculations.

Adsorption of metal atoms on silicene: stability and quantum capacitance of silicene-based electrode materials.

Abstract: We explore the adsorption stability and quantum capacitance of transition metal atoms on silicene based on first-principles calculations. Silicene with a buckled atomic layer has a high surface/volume ratio and silicene-based materials are expected to have potential applications for supercapacitors. We find that the most favorable adsorption sites on pristine silicene are valley sites for Al and Ti, and hollow sites for Ag, Cu and Au, respectively. Among all these systems with the doping of metal atoms, silicene is modulated to possess a quasi-metallic characteristic, accompanied by an appreciable electron transfer and the formation of defect states near the Fermi level. Due to the low density of states near the Fermi level, the quantum capacitance of pristine silicene has been limited. By the doping of metal atoms, especially Ti atoms, with the introduction of localized defect states near the Fermi level, quantum capacitance is found to be enhanced significantly. In addition, the quantum capacitance is found to increase monotonically following the increase of doping concentrations.

Design and Modeling of High Efficiency Graphene Intensity/Phase Modulator Based on Ultra-Thin Silicon Strip Waveguide

Abstract: Based on the electro-absorption/electro-refraction effect of graphene, we present a high efficiency intensity/phase modulator by exploiting ultra-thin silicon strip waveguide (UTSSW) structure. Due to the special structure of UTSSW, the propagating transverse electric (TE) mode is less confined to the core of silicon and penetrate deeper into the cladding SiO2 layer, which makes the double-layer graphene closer to the maximum of electric field. The combination of UTSSW structure and double-layer graphene facilitate low insertion loss (IL) together with high modulation efficiency modulator. The graphene intensity/phase modulator performances are comprehensively studied in terms of attenuation, IL, modulation depth (MD), optical operation bandwidth, phase shift, energy per bit (Ebit) consumption, and 3-dB electro-optic bandwidth. With graphene chemical potential μ = 0 eV, the MD is about 0.297 dB/μm, 0.304 dB/μm, 0.306 dB/μm for typical incident light wavelength λ = 1310 nm, 1550 nm, 2000 nm, respectively. When the electro-refraction working region is set between 0.6 eV and 1.0 eV, the $\Delta {\rm{Re}}({{\rm{n}}_{{\rm{eff}}}})$ keeps >6.8 × 10−3 with the wavelength increasing from 1250 nm to 2000 nm, which can be used for phase modulation. The maximum value of $\Delta {\rm{Re}}({{\rm{n}}_{{\rm{eff}}}})$ is 8.055 × 10−3 at incident light wavelength of 1616 nm. The 3-dB electro-optic bandwidth of graphene intensity/phase optical modulator are estimated by using an RC circuit model. Moreover, performances metrics dependence on the distance between the capacitor plates d and the doping level (EF) of transferred graphene are quantitatively analyzed and described. Finally, the quantum capacitance of designed graphene-based intensity modulator with different charged impurity concentration are also discussed when graphene μ = 0 eV and μ = 0.6 eV, respectively.

Quantum supercapacitors

Abstract: Recently there has been a great deal of interest on the possibility to exploit quantum-mechanical effects to increase the performance of energy storage systems. Here we introduce and solve a model of a quantum supercapacitor. This consists of two chains, one containing electrons and the other one holes, hosted by arrays of double quantum dots, the latter being a building block of experimental architectures for realizing charge and spin qubits. The two chains are in close proximity and embedded in the same photonic cavity, which is responsible for long-range coupling between all the qubits, in the same spirit of the Dicke model. By employing a variational approach, we find the phase diagram of the model, which displays ferromagnetic and antiferromagnetic phases for suitable pseudospin degrees of freedom, together with phases characterized by collective superradiant behavior. Importantly, we show that when transitioning from the ferro/antiferromagnetic to the superradiant phase, the quantum capacitance of the model is greatly enhanced. Our work offers opportunities for the experimental realization of a novel class of quantum supercapacitors with an enhanced storing power stemming from exquisite quantum mechanical effects.

Graphitic carbon nitride decorated with FeNi3 nanoparticles for flexible planar micro-supercapacitor with ultrahigh energy density and quantum storage capacity

Abstract: Portable miniaturized energy storage micro-supercapacitors have attracted significant attention due to their power source and energy storage capacity, replacing batteries in ultra-small electronic devices. Fabrication with porous and 2D graphitic nanomaterials with high conductivity and surface area leads to high-performance micro-supercapacitors. In order to satisfy the fast-growing energy demands for the next generation, we report performance and design of a 2D heterostructured EDLC (g-C3N4) and pseudocapacitor (FeNi3) resulting in short ionic diffusion path and prominent charge storage based on synergic functionalities. This heterostructure system shows an enhanced quantum capacitance (38% enhancement) due to delocalized states near the Fermi level. Having achieved an areal capacitance of 19.21 mF cm-2, capacitive retention (94%), enhanced power density (17-fold), having ultrahigh energy density of 0.30 W h cm-3 and stability of the material even without any obvious degradation after 1000 cycles, this smart heterostructure acts as a new platform for designing high-performance in-plane micro-supercapacitors.

High resolution potassium sensing with large-area graphene field-effect transistors

Abstract: We demonstrate large-area graphene based ion sensitive field effect transistors (ISFETs) with potassium ionophore sensing layers. Graphene ISFETs encapsulated with an ultra-thin hydrophobic layer, parylene C, and active areas ∼0.4 cm2 are characterized by an rms current noise as low as 5 nA in a 60 Hz electrical bandwidth, field effect mobilities up to 5000 cm2 V−1 s−1 and quantum capacitance limited coupling. Real-time sensing of K+ was achieved with a detection limit of 10−9 M K+, equivalent to 39 ng/L, and a resolution of ∼2 ×10−3 log [K+]. The ISFETs exhibit reversibility under spiking experiments and long term stability with limited drift over a course of five months. The cross-sensitivity has been measured to be 2.5 mV/decade for Na+, 4.2 mV/decade for Ca2+, 1.5 mV/decade for Mg2+ and 9.0 mV/decade for NH 4 + . Experiments with a variety of specimens, including beverages and blood, confirm the suitability of graphene ISFETs for K+ sensing in fluids with multiple solutes. The graphene ISFET design can be extended to sensing of other ionic species by substitution of alternative ionophores within the sensing membrane.

Route to achieving enhanced quantum capacitance in functionalized graphene based supercapacitor electrodes

Abstract: We have investigated the quantum capacitance ([Formula: see text]) in functionalized graphene modified with ad-atoms from different groups in the periodic table. Changes in the electronic band structure of graphene upon functionalization and subsequently the [Formula: see text] of the modified graphene were systematically analyzed using density functional theory (DFT) calculations. We observed that the [Formula: see text] can be enhanced significantly by means of controlled doping of N, Cl and P ad-atoms in the pristine graphene surface. These ad-atoms are behaving as magnetic impurities in the system, generating a localized density of states near the Fermi energy which, in turn, increases charge (electron/hole) carrier density in the system. As a result, a very high quantum capacitance was observed. Finally, the temperature dependent study of [Formula: see text] for Cl and N functionalized graphene shows that the [Formula: see text] remains very high in a wide range of temperatures near room temperature.

Quantum capacitance mediated carbon nanotube optomechanics

Abstract: Cavity optomechanics allows the characterization of a vibration mode, its cooling and quantum manipulation using electromagnetic fields. Regarding nanomechanical as well as electronic properties, single wall carbon nanotubes are a prototypical experimental system. At cryogenic temperatures, as high quality factor vibrational resonators, they display strong interaction between motion and single-electron tunneling. Here, we demonstrate large optomechanical coupling of a suspended carbon nanotube quantum dot and a microwave cavity, amplified by several orders of magnitude via the nonlinearity of Coulomb blockade. From an optomechanically induced transparency (OMIT) experiment, we obtain a single photon coupling of up to $g_0=2\pi\cdot 95\,\textrm{Hz}$. This indicates that normal mode splitting and full optomechanical control of the carbon nanotube vibration in the quantum limit is reachable in the near future. Mechanical manipulation and characterization via the microwave field can be complemented by the manifold physics of quantum-confined single electron devices.

Enhancement of quantum capacitance by chemical modification of graphene supercapacitor electrodes: a study by first principles

Abstract: In this paper, we specify a powerful way to boost quantum capacitance of graphene-based electrode materials by density functional theory calculations. We performed functionalization of graphene to manifest high-quantum capacitance. A marked quantum capacitance of above $$420\,\upmu \mathrm{F}\,\mathrm{cm}^{-2}$$ has been observed. Our calculations show that quantum capacitance of graphene enhances with nitrogen concentration. We have also scrutinized effect on the increase of graphene quantum capacitance due to the variation of doping concentration, configuration change as well as co-doping with nitrogen and oxygen ad-atoms in pristine graphene sheets. A significant increase in quantum capacitance was theoretically detected in functionalized graphene, mainly because of the generation of new electronic states near the Dirac point and the shift of Fermi level caused by ad-atom adsorption.

Shedding Light on Pseudocapacitive Active Edges of Single-Layer Graphene Nanoribbons as High-Capacitance Supercapacitors

Abstract: In the field of energy storage by high-rate supercapacitors, there has been an upper limit for the total interfacial capacitance of carbon-based materials. This upper limit originates from both quantum and electric double-layer capacitances. Surpassing this limit has been the focus of intense research in this field. Here, we precisely investigate the effect of chemical functional groups and physical confinement on the electrochemical performance of graphene nanoribbons. We present the results of a quasi-one-dimensional single-layer graphene nanoribbon (120 nm in width and ∼100 μm in length) microelectrode fabricated by mechanical exfoliation of graphite, followed by electron beam lithography process and oxygen plasma etching treatment. We directly measure the interfacial capacitance as a function of frequency at different potentials in an aqueous electrolyte using a three-electrode electrochemical system. Electrochemical impedance spectroscopy and cyclic voltammetry tests show an average capacitance of 75...

Gate reflectometry for probing charge and spin states in linear Si MOS split-gate arrays

Abstract: We fabricated linear arrangements of multiple split-gate devices along an SOI mesa, thus forming a 2×N array of individually controllable Si quantum dots (QDs) with nearest neighbor coupling. We implemented two different gate reflectometry-based readout schemes to either probe spin-dependent charge movements by a coupled electrometer with single-shot precision, or directly sense a spin-dependent quantum capacitance. These results bear significance for fast, high-fidelity single-shot readout of large arrays of foundry-compatible Si MOS spin qubits.

Nanomechanical characterization of quantum interference in a topological insulator nanowire.

Abstract: Aharonov–Bohm conductance oscillations emerge as a result of gapless surface states in topological insulator nanowires. This quantum interference accompanies a change in the number of transverse one-dimensional modes in transport, and the density of states of such nanowires is also expected to show Aharonov–Bohm oscillations. Here, we demonstrate a novel characterization of topological phase in Bi2Se3 nanowire via nanomechanical resonance measurements. The nanowire is configured as an electromechanical resonator such that its mechanical vibration is associated with its quantum capacitance. In this way, the number of one-dimensional transverse modes is reflected in the resonant frequency, thereby revealing Aharonov–Bohm oscillations. Simultaneous measurements of DC conductance and mechanical resonant frequency shifts show the expected oscillations, and our model based on the gapless Dirac fermion with impurity scattering explains the observed quantum oscillations successfully. Our results suggest that the nanomechanical technique would be applicable to a variety of Dirac materials. The density of states (DOS) of a topological insulator nanowire is expected to show Aharonov-Bohm (AB) oscillations, but they are never observed so far. Here, Kim et al. reveal AB oscillations in the DOS of a Bi2Se3 nanowire via nanomechanical resonance measurements.

Influence of Quantum Capacitance on Charge Carrier Density Estimation in a Nanoscale Field-Effect Transistor with a Channel Based on a Monolayer WSe 2 Two-Dimensional Crystal Semiconductor

Abstract: A critical analysis of charge carrier statistics influenced by quantum capacitance is carried out in order to predict the electrical performance of a nanoscale metal–oxide–semiconductor field-effect transistor (MOSFET) with a channel made of a monolayer tungsten diselenide (WSe2) two-dimensional (2D) crystal semiconductor. Since quantum capacitance originating from two-dimensional electron gas in a quantum well or an inversion layer does not completely screen the quasistatic electric field during applied gate voltage, the partial penetration of an external electric field through the 2D semiconductor channel will generate excess charge carriers; thus quantum capacitance will play an important role in determining the overall charge carrier density in the channel. Therefore, common methods used to extract charge carrier density in the channel for three-dimensional (3D) crystal semiconductors will yield inaccurate results when used for 2D crystal semiconductors. To address this issue, this study proposes a modified approach for extracting charge carrier density in WSe2-based 2D semiconductors by combining the appropriate carrier statistics with consideration of quantum capacitance. In addition, the study investigates the effect of interface traps on overall capacitance, which may influence the electrical performance of a nanoscale MOSFET with monolayer WSe2 as a channel material.

Effects of the N/S codoping configuration and ternary doping on the quantum capacitance of graphene

Abstract: Heteroatom doping is considered to be a highly effective approach for changing the electronic properties of graphene. However, the effects of the doping mode and site have not been investigated in detail. We explored the effect of the N/S codoping configuration and ternary doping with other elements on the quantum capacitance of graphene. It was found that at the same doping concentration, the Fermi levels are both shifted to the conduction band for chain doping and distributed doping, enhancing the electronic properties of graphene and effectively improving the quantum capacitance. The newly introduced heteroatoms contribute less to the obtained quantum capacitance than nitrogen and sulfur. N/S codoping is still a relatively effective doping method, and the optimal quantum capacitance was obtained for the nitrogen to sulfur ratio of 1:2. This work sheds light on the effect of the N/S codoping on the carbon electrode and suggests an effective approach for optimizing the quantum capacitance.

First-principles calculation of quantum capacitance of metals doped graphenes and nitrogen/metals co-doped graphenes: designing strategies for supercapacitor electrodes

Abstract: In this paper, we investigated the quantum capacitance and the integrated charge of graphene-based materials based on first-principles density functional theory calculations. Transition metals doped in a graphene plane will not move out of the graphene plane and will finally form an accurate symmetrical structure. Meanwhile, for transition metals doped out of plane, regardless of the positions that the metals were placed, they will conform to the same stable M–MV complexes eventually. Meanwhile, the introduction of N atoms makes the Al atom hybridization state tend to be consistent. Al3–NNN (the Al-embedded, nitrogen doped monovacancy graphene-based complexes, and the number of N atoms represents the number of N atoms surrounding the Al) and Al4–NNNN (Al-embedded, nitrogen doped divacancy graphene-based complexes) have the same Al atom hybridization, but it is different in the Al doped monovacancy graphene complexes (Al–MV) and the Al doped divacancy graphene complexes (Al–DV). In addition, we also found that both the Sc doped monovacancy graphene and the Al4–N (Al-embedded, nitrogen doped divacancy graphene-based complexes) can be used as candidates for the negative electrode materials of asymmetric supercapacitors. The results can provide valuable insights into the design and preparation of electrodes for high-performance supercapacitors.

Macroscopic Salt Rejection through Electrostatically Gated Nanoporous Graphene.

Abstract: Atomically thin porous graphene is emerging as one of the most promising candidates for next-generation membrane material owing to the ultrahigh permeation. However, the transport selectivity relie...

Understanding the phase dependent energy storage performance of MnO2 nanostructures

Abstract: We demonstrate charge storage mechanisms of four kinds of MnO2 polymorphs (α, β, γ, and δ) both in micro- and nanodimensions successfully synthesized by hydrothermal and microwave irradiation techniques. We observed that layered δ-MnO2, comprised of self-assembled nanoflakes oriented in different directions, shows a significantly improved capacitive behavior. The maximum achieved specific capacitance is 518 F/g at a current density of 3 A/g in a 3M KOH electrolyte solution, exhibiting a large capacity retention of 83.95% over 2000 consecutive charge/discharge cycles at a current density of 10 A/g. State of the art Density Functional Theory (DFT) simulations have also been performed to support experimental data. The quantum capacitance presented from DFT simulations predicts that the δ phase exhibits highest quantum capacitance, whereas it is lowest for the β phase supporting the experimental trend. Also, the structural features of wide tunnel size (∼7 A) for the δ phase facilitates favorable insertion of cations, whereas narrow tunnel size (∼1.89 A) for the β phase restricts the diffusion of charge particles yielding poor capacitance performance.

Quantum Capacitance Model for Graphene FET-Based Gas Sensor

Abstract: Because of its extraordinary characteristics, this material has attracted researchers in various arenas. Among the numerous fields where this material can be applied is the gas sensor technology. The graphene experiences remarkable changes in its electrical and physical characteristics when exposed to different gases; and they are, therefore, the ideal candidates for gas sensing application. However, a deep understanding of the effects of gas molecules on the graphene energy band structure and its electronic properties, need to be further studied. In this paper, a new quantum capacitance model for the gas sensor employing the graphene field effect transistor platform is proposed. Hence, a general approach using the Tight-binding approximation based on the nearest neighbor incorporating Schrodinger equation is developed. Therefore, the adsorption effects of the CO, NO, and NH3 gases on the energy band structure, quantum capacitance, and I-V characteristics of the graphene FET are analytically modeled and investigated. The results indicated that, the gas adsorption can cause significant changes on the graphene band structure and quantum capacitance. The I-V characteristics evaluation indicated current decrement after gas adsorption because of the conductance decrement induced by the band gap increment. The proposed models for the capacitance were also compared with the published experimental data and a satisfactory agreement was achieved.

Two Dimensional heterostructure and its application in efficient quantum energy storage

Abstract: Portable miniaturized energy storage micro-supercapacitor has engrossed significant attention due to its power source and energy storage capacity, replacing batteries in ultra-small electronic devices. Fabrication with porous and 2D graphitic nanomaterials with high conductivity and surface area signify high performance of micro-supercapacitor. In order to satisfy the fast-growing energy demands for the next-generation, we report performance and design of a 2D heterostructure of EDLC (g-C$_3$N$_4$) & pseudocapacitive (FeNi$_3$) resulting low ionic diffusion path and prominent charge storage based on their synergic functionalities. This heterostructure system shows an enhanced quantum capacitance (38% enhancement) due to delocalized states near Fermi level. Having achieved the areal capacitance of 19.21 mFcm$^{-2}$, capacitive retention (94%), enhanced power density (17 fold) having ultrahigh energy density of 0.30 this http URL$^{-3}$ and stability of the material even without any obvious degradation after 1000 cycles, this smart heterostructure acts as a new platform for designing high-performance in-plane micro-supercapacitor.

Route to Achieving Enhanced Quantum Capacitance in Functionalized Graphene based Supercapacitor Electrodes

Abstract: We have investigated the quantum capacitance ($C_Q$) in functionalized graphene, modified with ad-atoms from different groups in the periodic table. Changes in the electronic band structure of graphene upon functionalization and subsequently the quantum capacitance ($C_Q$) of the modified graphene were systematically analyzed using density functional theory(DFT) calculations. We observed that the quantum capacitance can be enhanced significantly by means of controlled doping of N, Cl and P ad-atoms in the pristine graphene surface. These ad-atoms are behaving as magnetic impurities in the system, generates a localized density of states near the Fermi energy, which intern increases charge(electron/hole) carrier density in the system. As a result, a very high quantum capacitance was observed. Finally, the temperature dependent study of $C_Q$ for Cl and N functionalized graphene shows that the CQ remains very high in a wide range of temperature near the room temperature.

Origin of the anomalous size-dependent increase of capacitance in boron nitride–graphene nanocapacitors

Abstract: The anomalous size-dependent increase in capacitance in boron nitride–graphene nanocapacitors is a puzzle that has been initially attributed to the negative quantum capacitance exhibited by this particular materials system. However, we show in this work that the anomalous nanocapacitance of this system is not due to quantum effects but has pure electrostatic origin and can be explained by a parallel-plate (square) nanocapacitor model filled with a dielectric film characterized by a size/thickness-dependent relative permittivity. The model presented here is in excellent agreement with the experimentally measured capacitance values of recently fabricated graphene and hexagonal boron nitride nanocapacitors. The results obtained seem to suggest that the size-dependent increase of capacitance in the above-mentioned family of nanocapacitors can be explained by classical finite-size geometric electrostatic effects.

Quantum capacitance tuned flexible supercapacitor by UV-ozone treated defect engineered reduced graphene oxide forest

Abstract: A forest like 3D carbon structure formed by RGO was prepared to use as electrode material for highly power efficient supercapacitor. To improve the specific energy of the electrode, pore like defects were incorporated on the RGO forests by atomic oxygen etching, during the UV-ozone treatment. The modified surface helps to increase the net capacitance by permitting the electrolyte to the inner core of the active material and improving the minimal quantum capacitance. Density functional theory (DFT) based first principle studies were carried out to find DOS at the Fermi level of defect induced RGO sheet and hence to validate the effect of quantum capacitance on net capacitance. Specific capacitance of RGO forest was increased by almost 150 % after introduction of the defects. The best performing material exhibits 18.87 mFcmalt;supagt;-2alt;/supagt; areal capacitance at 2 mAcmalt;supagt;-2alt;/supagt; current density which is equivalent to 70 Fcmalt;supagt;-3alt;/supagt; at 3.7 Acmalt;supagt;-3alt;/supagt; current density, and it was used to fabricate the supercapacitor. Two super capacitors were fabricated, (i) on graphite sheet (non-flexible) and (ii) on scotch tape (flexible). Here PVA-KOH gel soaked filter paper was used as electrolyte-separator. Both the prepared supercapacitors on graphite sheet and scotch tape are able to transfer electrical energy with ultra high specific power (656.25 mWcmalt;supagt;-3alt;/supagt; and 164.06 mWcmalt;supagt;-3alt;/supagt; respectively) while maintaining moderate energy densities. The first device can withstand its primary capacitance by 90% even after 10K charge-discharge cycles and the flexible device was able to hold 96% of its capacitance after 1K bending cycles.

Investigating the electrical characteristics of a single electron transistor utilizing graphene nanoribbon as the island

Abstract: Single electron transistor (SET) is a fast device with promising features in nanotechnology. Its operation speed depends on the island material, so a carbon based material such as graphene nanoribbon (GNR) can be a suitable candidate for using in SET island. The GNR band gap which depends on its width, has a direct impact on the coulomb blockade and SET current. In this research, current–voltage characteristic for the SET utilizing GNR in its island is modelled. The comparison study shows the impact of GNR width and length on the SET current. Furthermore SET quantum capacitance is modeled and effect of GNR width and temperature on the quantum capacitance are investigated.

Nanomechanical characterization of quantum interference in a topological insulator nanowire

Abstract: The discovery of two-dimensional gapless Dirac fermions in graphene and topological insulators (TI) has sparked extensive ongoing research toward applications of their unique electronic properties. The gapless surface states in three-dimensional insulators indicate a distinct topological phase of matter with a non-trivial Z2 invariant that can be verified by angle-resolved photoemission spectroscopy or magnetoresistance quantum oscillation. In TI nanowires, the gapless surface states exhibit Aharonov-Bohm (AB) oscillations in conductance, with this quantum interference effect accompanying a change in the number of transverse one-dimensional modes in transport. Thus, while the density of states (DOS) of such nanowires is expected to show such AB oscillation, this effect has yet to be observed. Here, we adopt nanomechanical measurements that reveal AB oscillations in the DOS of a topological insulator. The TI nanowire under study is an electromechanical resonator embedded in an electrical circuit, and quantum capacitance effects from DOS oscillation modulate the circuit capacitance thereby altering the spring constant to generate mechanical resonant frequency shifts. Detection of the quantum capacitance effects from surface-state DOS is facilitated by the small effective capacitances and high quality factors of nanomechanical resonators, and as such the present technique could be extended to study diverse quantum materials at nanoscale.

Acoustic extraordinary transmission manipulation based on proximity effects of heterojunctions.

Abstract: Heterojunctions between two crystalline semiconductor layers or regions can always lead to engineering the electronic energy bands in various devices, including transistors, solar cells, lasers, and organic electronic devices. The performance of these heterojunction devices depends crucially on the band alignments and their bending at the interfaces, which have been investigated for years according to Anderson's rule, Schottky-Mott rule, Lindhard theory, quantum capacitance, and so on. Here, we demonstrate that by engineering two different acoustic waveguides with forbidden bands, one can achieve an acoustic heterojunction with an extraordinary transmission peak arising in the middle of the former gaps. We experimentally reveal that such a transmission is spatially dependent and disappears for a special junction structure. The junction proximity effect has been realized by manipulating the acoustic impedance ratios, which have been proven to be related to the geometrical (Zak) phases of the bulk bands. Acoustic heterojunctions bring the concepts of quantum physics into the classical waves and the macroscopic scale, opening up the investigations of phononic, photonic, and microwave innovation devices.