Quantum capacitance

About: Quantum capacitance is a research topic. Over the lifetime, 954 publications have been published within this topic receiving 24165 citations.

Band tail interface states and quantum capacitance in a monolayer molybdenum disulfide field-effect-transistor

Abstract: Although MoS2 field-effect transistors (FETs) with high-k dielectrics are promising for electron device applications, the underlying physical origin of interface degradation remains largely unexplored. Here, we present a systematic analysis of the energy distribution of the interface state density (D it) and the quantum capacitance (C Q) in a dual-gate monolayer exfoliated MoS2 FET. The C Q analysis enabled us to construct a D it extraction method as a function of E F. A band tail distribution of D it with the lowest value of 8 × 1011 cm−2 eV−1 suggests that D it is not directly related to the sharp peak energy distribution of the S vacancy. Therefore, the Mo–S bond bending related to the strain at the interface or the surface roughness of the SiO2/Si substrate might be the origin. It is also shown that ultra-thin 2D materials are more sensitive to interface disorder due to the reduced density of states. Since all the constituents for the measured capacitance are well understood, I–V characteristics can be reproduced by utilizing the drift current model. As a result, one of the physical origins of the metal/insulator transition is suggested to be the external outcome of interface traps and quantum capacitance.

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.

A manufacturable process integration approach for graphene devices

Abstract: In this work, we propose an integration approach for double gate graphene field effect transis- tors. The approach includes a number of process steps that are key for future integration of graphene in microelectronics: bottom gates with ultra-thin (2 nm) high-quality thermally grown SiO2 dielectrics, shallow trench isolation between devices and atomic layer deposited Al2O3 top gate dielectrics. The com- plete process flow is demonstrated with fully functional GFET transistors and can be extended to wafer scale processing. We assess, through simulation, the effects of the quantum capacitance and band bend- ing in the silicon substrate on the effective electric fields in the top and bottom gate oxide. The proposed process technology is suitable for other graphene-based devices such as graphene-based hot electron transistors and photodetectors.

Charging the quantum capacitance of graphene with a single biological ion channel.

Abstract: The interaction of cell and organelle membranes (lipid bilayers) with nanoelectronics can enable new technologies to sense and measure electrophysiology in qualitatively new ways. To date, a variety of sensing devices have been demonstrated to measure membrane currents through macroscopic numbers of ion channels. However, nanoelectronic based sensing of single ion channel currents has been a challenge. Here, we report graphene-based field-effect transistors combined with supported lipid bilayers as a platform for measuring, for the first time, individual ion channel activity. We show that the supported lipid bilayers uniformly coat the single layer graphene surface, acting as a biomimetic barrier that insulates (both electrically and chemically) the graphene from the electrolyte environment. Upon introduction of pore-forming membrane proteins such as alamethicin and gramicidin A, current pulses are observed through the lipid bilayers from the graphene to the electrolyte, which charge the quantum capacitance of the graphene. This approach combines nanotechnology with electrophysiology to demonstrate qualitatively new ways of measuring ion channel currents.

Quantum capacitance as a reagentless molecular sensing element

Abstract: The application of nanoscale capacitance as a transduction of molecular recognition relevant to molecular diagnostics is demonstrated. The energy-related signal relates directly to the electron occupation of quantized states present in readily fabricated molecular junctions such as those presented by redox switchable self-assembled molecular monolayers, reduced graphene oxide or redox-active graphene composite films, assembled on standard metallic or micro-fabricated electrodes. Sensor design is thus based on the response of a confined and resolved electronic density of states to target binding and the associated change in interfacial chemical potential. Demonstrated herein with a number of clinically important markers, this represents a new potent and ultrasensitive molecular detection enabling energy transducer principle capable of quantifying, in a single step and reagentless manner, markers within biological fluid.