Temperature Dependence Of Electron Density Research Articles

Temperature dependence of resistivity of carbon micro/nanostructures: Microscale spatial distribution with mixed metallic and semiconductive behaviors

The temperature coefficient of resistivity (θT) of carbon-based materials is a critical property that directly determines their electrical response upon thermal impulses. It could have metal- (positive) or semiconductor-like (negative) behavior, depending on the combined temperature dependence of electron density and electron scattering. Its distribution in space is very difficult to measure and is rarely studied. Here, for the first time, we report that carbon-based micro/nanoscale structures have a strong non-uniform spatial distribution of θT. This distribution is probed by measuring the transient electro-thermal response of the material under extremely localized step laser heating and scanning, which magnifies the local θT effect in the measured transient voltage evolution. For carbon microfibers (CMFs), after electrical current annealing, θT varies from negative to positive from the sample end to the center with a magnitude change of >130% over <1 mm. This θT sign change is confirmed by directly testing smaller segments from different regions of an annealed CMF. For micro-thick carbon nanotube bundles, θT is found to have a relative change of >125% within a length of ∼2 mm, uncovering strong metallic to semiconductive behavior change in space. Our θT scanning technique can be readily extended to nm-thick samples with μm scanning resolution to explore the distribution of θT and provide a deep insight into the local electron conduction.

Temperature dependence of electron density and electron–electron interactions in monolayer epitaxial graphene grown on SiC

We report carrier density measurements and electron–electron (e–e) interactions in monolayer epitaxial graphene grown on SiC. The temperature (T)-independent carrier density determined from the Shubnikov–de Haas (SdH) oscillations clearly demonstrates that the observed logarithmic temperature dependence of the Hall slope in our system must be due to e–e interactions. Since the electron density determined from conventional SdH measurements does not depend on e–e interactions based on Kohn’s theorem, SdH experiments appear to be more reliable compared with the classical Hall effect when one studies the T dependence of the carrier density in the low T regime. On the other hand, the logarithmic T dependence of the Hall slope δRxy/δB can be used to probe e–e interactions even when the conventional conductivity method is not applicable due to strong electron–phonon scattering.

The influence of physical-chemical characteristics of surface modified copper nanoparticles on E. coli cell population growth suppression and on electrostatic properties of their membranes

The biological activity of copper nanoparticles, able to suppress growth of E. coli cells population under contact interactions, was explored. Three types of samples with oxide layers of various sizes, thickness and composition were used in experiments. It was found out, that an increase in electron density on the external membrane of E. coli correlated with copper nanoparticles suppression capability and with lower activation energy of electron transfer on bacteria. The analysis of experimental data helps to correct conditions for obtaining nanoparticles with certain properties of their surface oxide layers. The character of temperature dependence of electron density reveals the electron type of conductivity in contact area of E. coli and nanoparticles. These results help to find approach to understanding the nature of toxic influence of copper nanoparticles on E. coli cells under contact interaction.

The effect of infrared radiation on quantum magnetotransport in n-InGaAs/GaAs with two strongly coupled quantum wells

Longitudinal ρxx(B) and Hall ρxy(B) magnetoresistances are measured as a function of transverse magnetic field in n-InGaAs/GaAs nanostructures with strongly coupled double quantum wells in the temperature range T = 0.05–60 K and magnetic fields B = 0–16 T before and after low-temperature infrared irradiation. The appearance of persistent photoconductivity causes the type of the temperature dependence of resistance to be changed: from insulator-like (dρ/dT < 0) for T ≤ 8 K to metallic-like (dρ/dT > 0) at higher temperatures. It is shown that this is related to the temperature dependence of electron density. The strong temperature dependence of electron mobility observed before the illumination practically disappears after infrared irradiation.

Interaction of deep-level traps with the lowest and upper conduction minima in InP

Deep-level electron traps in bulk, vapor-phase epitaxial (VPE) and liquid-phase epitaxial (LPE) undoped InP crystals are investigated by an extensive method of capacitance measurement. Eight different traps are found in bulk and VPE crystals, and on the other hand no traps are found in LPE crystals. Characteristics of three traps with emission activation energies of ΔEe=0.43, 0.59, and 0.63 eV are analyzed in detail. The absolute energy levels for these traps measured from the lowest Γ conduction minimum are ET=0.34, 0.20, and 0.24 eV, respectively. It is shown that the 0.43-eV trap is coupled to the Γ minimum and that the 0.59- and 0.63-eV traps are coupled to the upper L minima. The capture of Γ electrons by the 0.43-eV trap is found to exhibit a thermally activated capture cross section σ with a barrier energy of ΔEB=0.09 eV. On the contrary, the temperature dependence of capture of L electrons by the 0.59-eV trap is found to be dominated by the temperature dependence of electron density in the L minima and to exhibit a negligible ΔEB for σ. The intervalley energy separation ΔELΓ?0.39 eV is derived and found consistent with the observed emission and capture properties of both of the L-coupled traps. Reasonable agreements are obtained between the capture cross sections derived from capture and from emission experiments, for both the Γ-coupled and L-coupled traps, respectively.