Theory Of Graphene Research Articles

A Comprehensive Study on the Theory of Graphene Solution‐Gated Field Effect Transistor: Simulations and Experiments

Graphene solution-gated field effect transistors (G-SgFETs) have been widely developed in the field of biosensors, but deficiencies in their theories still exist. A theoretical model for G-SgFET, including the three-terminal equivalent circuit model and the numerically calculating method, is proposed by the comprehensive analyses of the graphene-liquid interface and the FET principle. Not only the applied voltages on the electrode-pairs of gate-source and drain-source, but also the nature of graphene and its derivatives are considered by analysing their influences on the Fermi level, the carriers’ concentration and mobility, which may consequently affect the output drain-source current. To verify whether it is available for G-SgFETs based on different method prepared graphene, three kinds of graphene materials which are liquid-phase exfoliated graphene, reduced graphene oxide (rGO), and tetra (4-aminophenyl) porphyrin hybridized rGO are used as examples. The coincidences of calculated output and transfer feature curves with the measured ones are obtained to confirm its adaptivity for simulating the basic G-SgFETs’ electric features, by modulating Fermi level and mobility. Furthermore, the model is exploited to simulate G-SgFETs’ current responding to the biological functionalization with aptamer and the detections for circulating tumor cells, as a proof-of-concept. The calculated current changes are compared with the experimental results, to verify the proposed G-SgFETs’ model is also suitable for mimicking the bio-electronic responding, which may give a preview of some conceived G-SgFETs’ biosensors and improve the design efficiency.

Anomalous screening in narrow-gap carbon nanotubes

The screening of Coulomb interaction controls many-body physics in carbon nanotubes, as it tunes the range and strength of the force that acts on charge carriers and binds electron-hole pairs into excitons. In doped tubes, the effective Coulomb interaction drives the competition between Luttinger liquid and Wigner crystal, whereas in undoped narrow-gap tubes it dictates the Mott or excitonic nature of the correlated insulator observed at low temperature. Here, by computing the dielectric function of selected narrow- and zero-gap tubes from first principles, we show that the standard effective-mass model of screening systematically underestimates the interaction strength at long wavelength, hence missing the binding of low-energy excitons. The reason is that the model critically lacks the full three-dimensional topology of the tube, being adapted from graphene theory. As ab inito calculations are limited to small tubes, we develop a two-band model dielectric function based on the plane-wave expansion of Bloch states and the exact truncated Coulomb cutoff technique. We demonstrate that our -- computationally cheap -- approach provides the correct screening for narrow-gap tubes of any size and chirality. A striking result is that the screened interaction remains long-ranged even in gapless tubes, as an effect of the microscopic local fields generated by the electrons moving on the curved tube surface. As an application, we show that the effective electron-electron force that is felt at distances relevant to quantum transport experiments is super Coulombic.

PHỔ PLASMON TRONG HỆ 3 LỚP GRAPHENE LỚP KÉP

Các nghiên cứu gần đây đã chỉ ra rằng graphene có những tính chất đặc biệt và có nhiều tiềm năng ứng dụng trong các lĩnh vực công nghệ khác nhau. Bài báo này trình bày các kết quả về phổ kích thích tập thể, một đặc tính quan trọng của vật liệu, trong một cấu trúc ba lớp graphene lớp kép trên nền điện môi không đồng nhất trong gần đúng pha ngẫu nhiên ở nhiệt độ không tuyệt đối. Kết quả giải số cho thấy, một nhánh quang học và hai nhánh âm học tồn tại trong hệ khảo sát. Nhánh quang nhanh chóng biến mất do bị hấp thụ mạnh còn hai nhánh âm học tiếp tục kéo dài hơn cho đến khi tiếp xúc với đường biên vùng kích thích đơn hạt của hệ. Sự không đồng nhất của điện môi nền làm giảm tần số các nhánh quang phổ tần số cao nhưng lại có thể làm tăng tần số của nhánh phổ tần số thấp. Ảnh hưởng của khoảng cách giữa các lớp lên các nhánh phổ cũng không khác nhiều so với các cấu trúc nhiều lớp đã được khảo sát trước đây. Các kết quả thu được có thể có cung cấp thêm thông tin, góp phần hoàn thiện lý thuyết về vật liệu mới graphene.

Quantization of non-Abelian gauge theory in graphene

A time-dependent strain induces non-Abelian gauge field in a sheet of graphene. We discuss the effective field theory of this system of graphene subjected to a general form of time-dependent strain. We study the modifications to this effective field theory as a result of breaking Lorentz symmetry down to its sub-group, [Formula: see text], employing the VSR formalism. As the effective theory describing the graphene system has gauge symmetry; to quantize this theory, we add a suitable ghost and gauge fixing terms to the original action. The resultant action is observed to be invariant under a BRST symmetry. We have studied the BRST symmetry of the resultant theory, and explicitly constructed the BRST transformations.

On the classes of explicit solutions of Dirac, dynamical Dirac and Dirac–Weyl systems with non-vanishing at infinity potentials, their properties and applications

We construct explicitly potentials, Darboux matrix functions and corresponding solutions of Dirac, dynamical Dirac and Dirac–Weyl systems using generalised Bäcklund-Darboux transformation (GBDT) in the important case of nontrivial initial systems. In this way, we construct explicit solutions of systems with non-vanishing at infinity potentials, including steplike and power-law growth potentials. Thus, the constructed potentials (systems) differ fundamentally from the actively studied case of GBDT for the trivial initial systems.Generalised matrix eigenvalues A (not necessarily diagonal) and corresponding generalised matrix eigenfunctions Π(x) of the nontrivial initial systems are used in the GBDT constructions in this paper. Explicit expressions for these Π(x) are new and the method of deriving these expressions may be applied to various other important problems.The case of Dirac–Weyl system, which is of interest in electron dynamics and graphene theory is studied in greater detail, and generalised separation of variables appears in our approach to the study of this system.Explicit expressions for Weyl–Titchmarsh functions (in the form of pseudo-realisations) are derived.

Preparation and Test of NH3 Gas Sensor Based on Single-Layer Graphene Film.

The ammonia sensing properties of single-layer graphene synthesized by chemical vapor deposition (CVD) were studied. The Au interdigitated electrode (IDE) was prepared by microelectromechanical systems (MEMS) technology, and then, the single-layer graphene was transferred to the IDE by wet transfer technology. Raman spectroscopy was used to monitor the quality of graphene films transferred to SiO2/Si substrates. Moreover, the theory of graphene’s adsorption of gases is explained. The results show that gas sensing characteristics such as response/recovery time and response are related to the target gas, gas concentration, test temperature, and so on. In the stability test, the difference between the maximum resistance and the minimum resistance of the device is 1 ohm without ammonia, the change is less than 1% of its initial resistance, and the repeatability is up to 98.58%. Therefore, the sensor prepared with high quality single-layer graphene has good repeatability and stability for ammonia detection.

Cooperative Motion of Electrons on the Graphene Surface

Introduction. Today, the development of the graphene theory to control its physical and mechanical properties is a relevant objective. The paper deals with the conducting properties of graphene. In particular, the paper investigates the linear law of electron dispersion and traces its corollaries. Materials and Methods. The development of the theory is based on the verified experimental data and on the foundamental principles of the solid body theory and quantum mechanics. The study follows the universal synergetic principle according to which, there have been developed two split-level mathematical models of the quasi-particle motion in graphene on exposure to the electric field. On the macroscopic level, we suggest that graphene should be analyzed as a crystal consisting of three parallel planes. Two of them are electron gas. The remaining one is the main body of the crystal. On the microscopic level, the quasi-particle motion of the electron wave is described through the Schroedinger equation. Results. The study has developed the alternative method for the explanation of the linear dispersion law in graphene on the macroscopic level. Basing on the analysis of the model, the paper provides a hypothesis of the cooperative motion of the electron pairs, which make up a boson particle. The given hypothesis is different from the traditional one. In accordance with the latter, quasi-particles in graphene are Dirac fermions. To prove the hypothesis consilience, the study examines Hall’s effect in grapheme. The linear dispersion law for a pair of electrons is also deduced from the Schroedinger equation. Both the macroscopic and microscopic models are in a reasonable agreement with the experimental data. Discussion and Conclusion. The main result of the research is the development of the multi-level mathematical model which properly features the conducting properties of graphene (linear dispersion law, anomalous Hall effect). The practical relevance consists in revealing the possibility to control the conducting properties of graphene through impacts on electron pairs.

Synthesis and patterning of graphene: Strategies and prospects

The extraordinary success of graphene in various applications has led to the quest to innovate techniques for production and patterning of nanomaterials. Numerous techniques such as vapor deposition, epitaxial growth, mechanical and chemical exfoliation have been explored to achieve this goal. These new methods have enabled the synthesis of a monolayer to a few layer graphene structures, in various forms such as films, nanoribbons, and 3D nanocomposites that are dispersed in solutions, suspended or deposited on substrates. However, several challenges still exist in processing graphene for futuristic device fabrication. Thus, there is a need to review the traditional processing and synthesis techniques developed for obtaining graphene. This review will provide a solid foundation on technology development for achieving economical and high throughput synthesis of high quality graphene for scalable applications. In this review, we provide a brief discussion on the theory of graphene, discuss synthesis techniques along with conventional and recent approaches to pattern graphene structures, and conclude with an emphasis on direct patterning methods. Discussions on the properties of graphene produced using different techniques and their emerging applications will assist in selecting an appropriate methodology for achieving desired properties in graphene. This is expected to be instrumental in the development of new strategies for fabrication of futuristic graphene-based devices.

Phase transition in three-dimensional quantum electrodynamics at T ≠ 0

Dynamic mass generation in 3D quantum electrodynamics (QED3) is considered at T ≠ 0. To solve the Schwinger–Dyson equation for the Matsubara electron Green’s function, the ladder approximation is used and the corresponding photonic function is taken in the Landau gauge. In this case, the instant approximation is used for the photonic function. It is established that the process of dynamical mass generation in QED3 at T ≠ 0 is accompanied by a phase transition. Formal analogy of transitions in the coupling constant is revealed at T ≠ 0 in QED3, at T = 0 in QED4, and in graphene theory. Critical values of the coupling constant and temperature, calculated numerically based on an approximate analytical solution of the Schwinger–Dyson equation are of the same orders of magnitude.

Symmetry of standing waves generated by a point defect in epitaxial graphene

Using scanning tunneling microscopy (STM) and Fourier Transform STM (FT-STM), we have studied a point defect in an epitaxial graphene sample grown on silicon carbide substrate. This analysis allows us to extract the quasiparticle energy dispersion, and to give a first experimental proof of the validity of Fermi liquid theory in graphene for a wide range of energies from -800 meV to +800 meV. We also find evidence of a strong threefold anisotropy in the standing waves generated by the defect. We discuss possible relations between this anisotropy, the chirality of the electrons, and the asymmetry between graphene's two sublattices. All experimental measurements are compared and related to theoretical T-matrix calculations.