Effect of Impurity Adsorption on the Electronic and Transport Properties of Graphene Nanogaps

Graphene stands out as a versatile material with several uses in fields that range from electronics to biology. In particular, graphene has been proposed as an electrode in molecular electronics devices that are expected to be more stable and reproducible than typical ones based on metallic electrodes. In this work, we study by means of first principles, simulations and a tight-binding model the electronic and transport properties of graphene nanogaps with straight edges and different passivating atoms: Hydrogen or elements of the second row of the periodic table (boron, carbon, nitrogen, oxygen, and fluoride). We use the tight-binding model to reproduce the main ab-initio results and elucidate the physics behind the transport properties. We observe clear patterns that emerge in the conductance and the current as one moves from boron to fluoride. In particular, we find that the conductance decreases and the tunneling decaying factor increases from the former to the latter. We explain these trends in terms of the size of the atom and its onsite energy. We also find a similar pattern for the current, which is ohmic and smooth in general. However, when the size of the simulation cell is the smallest one along the direction perpendicular to the transport direction, we obtain highly non-linear behavior with negative differential resistance. This interesting and surprising behavior can be explained by taking into account the presence of Fano resonances and other interference effects, which emerge due to couplings to side atoms at the edges and other couplings across the gap. Such features enter the bias window as the bias increases and strongly affect the current, giving rise to the non-linear evolution. As a whole, these results can be used as a template to understand the transport properties of straight graphene nanogaps and similar systems and distinguish the presence of different elements in the junction.

LoGHeD: An effective approach for negative differential resistance effect suppression in negative capacitance transistors

A negative capacitance transistor (NCFET) with fully depleted silicon-on-insulator (FDSOI) technology (NC-FDSOI) is one of the promising candidates for next-generation low-power devices. However, it suffers from the inherent negative differential resistance (NDR) effect, which is very detrimental to device and circuit designs. Aiming at overcoming this shortcoming, this paper proposes for the first time to use local Gaussian heavy doping technology (LoGHeD) in the channel near the drain side to suppress the NDR effect in the NC-FDSOI. The technical computer-aided design (TCAD) simulation results have validated that the output conductance (GDS) with LoGHeD, which is used to measure the NDR effect, increases compared to the conventional NC-FDSOI counterpart and approaches zero. With the increase in doping concentration, the inhibitory capability of the NDR effect shows a monotonously increasing trend. In addition, the proposed approach maintains and even enhances performances of the NC-FDSOI transistor regarding the electrical parameters, such as threshold voltage (VTH), sub-threshold swing (SS), switching current ratio (ION/IOFF), and drain-induced barrier lowering (DIBL).

Achieved negative differential resistance behavior of Si/B-substituted into a C6 chain sandwiched between capped carbon nanotube junctions

Multi negative differential resistance (NDR) with large peak to valley ratio (PVR) and rectifying actions were observed for a CNT|C–(B–C)2–C|CNT molecular device.

High performance and gate-controlled GeSe/HfS2 negative differential resistance device

A novel and astonishing p-GeSe/n-HfS2 NDR device shows a high value for the peak-to-valley current ratio in the range of 5.8.

Hybrid superconducting heterostructures with magnetic interlayers

Electron transport processes in oxide superconducting heterostructures with epitaxially grown magnetic thin-film interlayers, in which the interaction of superconducting correlations and magnetic ordering occurs due to superconducting and magnetic proximity effects, have been studied experimentally. Hybrid mesa-heterostructures were prepared from thin-film bottom cuprate superconductor (S), magnetic (M) interlayer made of manganite or an antiferromagnetic cuprate, and the upper electrode made from an ordinary superconductor. When the cuprate antiferromagnetic material was replaced by a ferromagnetic manganite interlayer, the superconducting current was suppressed, although the thin magnetic film was several times thinner, 5 nm, and the temperature was lowered to 0.3 K. At low temperatures dependences of differential resistance vs. voltage for mesa-heterostructures with manganite interlayer featured mini-gap low-energy states.

Edge Doping Engineering of High-Performance Graphene Nanoribbon Molecular Spintronic Devices

We study the quantum transport properties of graphene nanoribbons (GNRs) with a different edge doping strategy using density functional theory combined with nonequilibrium Green’s function transport simulations. We show that boron and nitrogen edge doping on the electrodes region can substantially modify the electronic band structures and transport properties of the system. Remarkably, such an edge engineering strategy effectively transforms GNR into a molecular spintronic nanodevice with multiple exceptional transport properties, namely: (i) a dual spin filtering effect (SFE) with 100% filtering efficiency; (ii) a spin rectifier with a large rectification ratio (RR) of 1.9 ×106; and (iii) negative differential resistance with a peak-to-valley ratio (PVR) of 7.1 ×105. Our findings reveal a route towards the development of high-performance graphene spintronics technology using an electrodes edge engineering strategy.

Modeling of electrotransport properties of Li-intercalated graphene film

In this work, within the framework of density functional theory combined with the method of nonequilibrium Green’s functions the density of states, transmission spectrum, current-voltage characteristics, and differential conductivity of Li-intercalated graphene (LiC6) have been determined. It is shown that in the energy range of -1.3÷-1.05 eV the quasiparticle transport through the nanostructure is disable. The features of IV- and dI/dV-characteristics of LiC6 in the form of decreasing of resistance in the range of -0.4÷0.4 V were revealed, and in the interval of 0.4÷1.4 V formation of negative differential resistance area, related to scattering of quasiparticles. It is established, that LiC6 nanodevice has 12÷13 ballistic channels and has the maximum amount of conductance 12÷13G0 , where Go is the conductance quantum.

Conductance Quantization Behavior in Pt/SiN/TaN RRAM Device for Multilevel Cell

In this work, we fabricated a Pt/SiN/TaN memristor device and characterized its resistive switching by controlling the compliance current and switching polarity. The chemical and material properties of SiN and TaN were investigated by X-ray photoelectron spectroscopy. Compared with the case of a high compliance current (5 mA), the resistive switching was more gradual in the set and reset processes when a low compliance current (1 mA) was applied by DC sweep and pulse train. In particular, low-power resistive switching was demonstrated in the first reset process, and was achieved by employing the negative differential resistance effect. Furthermore, conductance quantization was observed in the reset process upon decreasing the DC sweep speed. These results have the potential for multilevel cell (MLC) operation. Additionally, the conduction mechanism of the memristor device was investigated by I-V fitting.