Influence of metal contacts and charge inhomogeneity on transport properties of graphene near the neutrality point

There is an increasing amount of literature concerning electronic properties of graphene close to the neutrality point. Many experiments continue using the two-probe geometry or invasive contacts or do not control samples’ macroscopic homogeneity. We believe that it is helpful to point out some problems related to such measurements. By using experimental examples, we illustrate that the charge inhomogeneity induced by spurious chemical doping or metal contacts can lead to large systematic errors in assessing graphene’s transport properties and, in particular, its minimal conductivity. The problems are most severe in the case of two-probe measurements where the contact resistance is found to strongly vary as a function of gate voltage.     

Strong suppression of weak localization in graphene

Low-field magnetoresistance is ubiquitous in low-dimensional metallic systems with high resistivity and well understood as arising due to quantum interference on self-intersecting diffusive trajectories. We have found that in graphene this weak-localization magnetoresistance is strongly suppressed and, in some cases, completely absent. The unexpected observation is attributed to mesoscopic corrugations of graphene sheets which can cause a dephasing effect similar to that of a random magnetic field.     

Effect of Eu and Pb doping on the dosimetric properties of LiCAF

LiCaAlF₆ (LiCAF) crystals doped with two different ions (europium and lead) have been investigated as potential new dosimetric materials. The stability of thermally stimulated luminescence (TSL) glow peaks in LiCAF:Eu was evaluated by means of the initial rise technique. The decay times at room temperature of the traps related to the dosimetric glow peaks were found to range between 40 and 2 × 10⁴ years confirming the good dosimetric characteristics of this crystal. The glow curve of LiCAF:Pb is dominated by a peak at approximately 300 °C emitting in the UV region (³P_0,1–¹S₀ transition of Pb²⁺) superimposed to a very broad structure at lower temperature (20–200 °C) featuring recombination at an intrinsic defect centre. The anomalous behavior of the low temperature structure during thermal cleaning procedures prevented any reliable numerical analysis of the TSL glow peak at 300 °C.     

Products of carbon disulfide oxidation in ionized air

Products of plasmochemical reactions proceeding in gas mixtures containing toxic CS₂ impurity were studied. The mixtures were excited by 180-and 300-keV electron pulses of duration 3 ns and 48 μs, respectively.     

Elimination of styrene vapor from air by a pulsed electron beam

Styrene vapor contained in air in small amounts is decomposed when the air is subjected to a pulsed electron beam and non-self-maintained space discharge. The physical laws of the process and the final products of styrene vapor conversion are found. Experimental data make it possible to consistently describe the styrene vapor elimination from air exposed to a pulsed electron beam and relate the beam parameters to the properties of the gas flow being irradiated.     

Tunneling resonances in structures with a two-step barrier

Electron transport through an asymmetric heterostructure with a two-step barrier N⁺GaAs/N⁻GaAs/Al_0.4Ga_0.6As/Al_0.03Ga_0.97As/N⁻GaAs/N⁺GaAs was investigated. Features due to resonance tunneling both through a size-quantization level in a triangular quantum well, induced by an external electric field in the region of the bottom step of the barrier (Al_0.03Ga_0.97As layer), and through virtual levels in two quantum pseudowells of different width are observed in the tunneling current. The virtual levels form above the bottom step or above one of the spacers (N⁻GaAs layer) as a result of interference of electrons, in the first case on account of reflection from the Al_0.4Ga_0.6As barrier and a potential jump at the Al_0.03Ga_0.97As/N⁻GaAs interface and in the second case — from the Al_0.4Ga_0.6As barrier and the potential gradient at the N⁻GaAs/N⁺GaAs junction, reflection from which is likewise coherent. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 10, 814–819 (25 May 1998)     

Kinetic studies of the copper-catalyzed cross-coupling of 1-phenyltetrazole-5-thiol and iodobenzene

Kinetics of the copper-catalyzed cross-coupling of 1-phenyltetrazole-5-thiol and iodobenzene under thermal and dielectric heating has been studied; the kinetic parameters of the reaction have been calculated. Microwave irradiation has not influenced significantly the reaction molecular mechanism; the process acceleration can be due to macrokinetic effects.     

Mechanism of the interaction of dimethyl sulfoxide with N-methylmorpholine-N-oxide Monohydrate

The interaction of dimethyl sulfoxide with N-methylmorpholine-N-oxide (NMMO) monohydrate was studied by the NMR relaxation method. The mobility of DMSO molecules in the presence of NMMO monohydrate decreases due to the formation of a hydrogen bond between the water molecule of the monohydrate and a DMSO molecule. At the same time, the mobility of protons in the NMMO monohydrate increases due to a decrease in the strength of the water-NMMO hydrogen bond.     

The action of pulsed electron beams on carbon bisulfide impurity in air

The results are presented of experimental and theoretical studies of the action of nano-and micro-second electron beams on an atmospheric-pressure nitrogen-oxygen mixture with a CS₂ impurity. It is demon-strated that there are two modes of impurity conversion that depend on the beam parameters and differ in both the mechanism involved and the final products. The effect of the external electric field on the impurity conversion is studied experimentally. A computer model of the processes is developed, and an analysis of the experimentally observed effects is performed.