Qinwei Shi

Analytical study of electronic structure in armchair graphene nanoribbons

We present the analytical solution of the wave function and energy dispersion of armchair graphene nanoribbons (GNRs) based on the tight-binding approximation. By imposing the hard-wall boundary condition, we find that the wave vector in the confined direction is discretized. This discrete wave vector serves as the index of different subbands. Our analytical solutions of wave function and associated energy dispersion reproduce the results of numerical tight-binding and the solutions based on the

Average density of states in disordered graphene systems

\mathbf{k}∙\mathbf{p}

Electronic structure of bilayer graphene: A real-space Green's function study

approximation. In addition, we also find that all armchair GNRs with edge deformation have energy gaps, which agrees with recently reported first-principles calculations.

Emerging nanodevice paradigm: Graphene-based electronics for nanoscale computing

In this paper, the average density of states (ADOS) with a binary alloy disorder in disordered graphene systems are calculated based on the recursion method. We observe an obvious resonant peak caused by interactions with surrounding impurities and an anti-resonance dip in ADOS curves near the Dirac point. We also find that the resonance energy (Er) and the dip position are sensitive to the concentration of disorders (x) and their on-site potentials (v). An linear relation, not only holds when the impurity concentration is low but this relation can be further extended to high impurity concentration regime with certain constraints. We also calculate the ADOS with a finite density of vacancies and compare our results with the previous theoretical results.

Excluded volume effect on confined polymer translocation through a short nanochannel

In this paper, a real-space analytical expression for the free Green’s function propagator of bilayer graphene is derived based on the effective-mass approximation. Green’s function displays highly spatial anisotropy with threefold rotational symmetry. The calculated local density of states LDOS of a perfect bilayer graphene produces the main features of the observed scanning tunneling microscopy STM images of graphite at low bias voltage. Some predicted features of the LDOS can be verified by STM measurements. In addition, we also calculate the LDOS of bilayer graphene with vacancies by using the multiple-scattering theory scatterings are localized around the vacancy of bilayer graphene. We observe that the interference patterns are determined mainly by the intrinsic properties of the propagator and the symmetry of the vacancies.

Shape of disorder-broadened Landau subbands in graphene.

The continued miniaturization of silicon-based electronic circuits is fast approaching its physical limitations. It is unlikely that advances in miniaturization, following the so-called Moores Law, can continue in the foreseeable future. Nanoelectronics has to go beyond silicon technology. New device paradigms based on nanoscale materials, such as molecular electronic devices, spin devices and carbon-based devices, will emerge. In this article, we introduce a nanodevice paradigm: graphene nanoelectronics. Due to its unique quantum effects and electronic properties, researchers predict that graphene-based devices may replace carbon nanotube devices and become major building blocks for future nanoscale computing. To manifest its unique electronic properties, we present some of our recent designs, namely a graphene-based switch, a negative differential resistance (NDR) device and a random access memory array (RAM). Since these basic devices are the building blocks for large-scale circuits, our findings can help researchers construct useful computing systems and study graphene-based circuit performance in the future.

Graphene nanoribbon field-effect transistors

We simulated the translocation process of a polymer chain from a source container to a drain container through a short nanochannel. We utilized the bond fluctuation model coupled with Monte Carlo dynamics in our simulations. The calculation results show that the excluded volume effect significantly affects the polymers translocation time tau. This time depends nonmonotonically on the polymer length N. For a fixed nanochannel length, tau decreases when the polymer length increases. tau, however, increases when the polymer length exceeds a certain threshold. This observation differs from those predicated for a Gaussian chain. In this paper, we will further present our findings to explain this phenomenon. The knowledge we gain from this research can enhance the understanding of complex transport processes in many biological systems.

Emerging nanocircuit paradigm: Graphene-based electronics for nanoscale computing

In this Letter, we calculate the density of states of graphene under a highly uniform magnetic field and white-noise random potential. We discover that the disorder-broadened zero-energy Landau band has a Gaussian shape and its width is proportional to the random potential variance and the square root of magnetic field. We also use the Wegner-type calculation to justify our simulation results.

Vacancy-induced splitting of the Dirac nodal point in graphene

We demonstrated that an electronic field-effect transistor (FET) can be made from patterned monolayer or bilayer graphene nanoribbons. The FET performance can be achieved regardless of structural defects (either edge defects or topological defects). The I-V characteristics of resulting FETs are similar to those made from single-walled carbon nanotubes. This one-dimensional functional device is very useful for future nanoscale electronics.

Quantum Dot Based on Z-shaped Graphene Nanoribbon: First-principles Study

The continued miniaturization of silicon-based electronic circuits is fast approaching the physical and geometrical limits over the past decades. It is unlikely that these advances in miniaturization can continue in the new millennium. Future nanoelectronics will go beyond the silicon technology. New circuit paradigms based on novel nanoscale materials, such as molecular electronic circuits and carbon-based circuits, will be employed. In this paper, we introduce an emerging nanocircuit paradigm, graphene nanoelectronics. Due to its unique quantum effects and electronic properties, researchers predict that graphene-based circuits will replace carbon nanotube circuits and become major building blocks for future nanoscale computing. To manifest its unique electronic properties, we present some of our recent designs, namely a switch, a field-effect transistor and a random access memory array (HAM). We also provide a common platform to simulate the circuit behavior and the platform can be used to design functional graphene-based computing system in future.