A critical analysis of recent advances in the synthesis and electrical characterization of nanofibers and nanotubes made of different conjugated polymers is presented. The applicability of various ...theoretical models is considered in order to explain results on transport in conducting polymer nanofibers and nanotubes. The relationship between these results and the one‐dimensional (1D) nature of the conjugated polymers is discussed in light of theories for tunneling in 1D conductors (e.g., Luttinger liquid, Wigner crystal). The prospects for nanoelectronic applications of polymer fibers and tubes as wires, nanoscale field‐effect transistors (nanoFETs), and in other applications are analyzed.
Conducting polymer nanowires and nanotubes hold promise for their applications in devices such as field‐ effect transistors (FETs, see Figure), as nanotips in field‐emission displays, and as sensors. This review analyzes recent advances in the synthesis and electrical characterization of nanotubes, and discusses their charge‐transport properties in light of theories for tunneling in one‐dimensional conductors.
Composite fibers based on chitosan coated with a conductive polymer polypyrrole (PPy) have been obtained. Their morphology was studied by scanning electron microscopy. The electrical conductivity of ...the fibers in the dry state and in a liquid culture medium simulating tissue fluid was evaluated. The values of resistivity ρ and conductivity σ of the studied fibers are determined depending on the number of PPy layers, the drawing ratio (orientation) of the fibers in a dry and liquid medium. It has been established that, with an increase in the spin draw from 0 to 100%, resistivity ρ of the fibers decreases (and conductivity σ increases) both in the dry state and in the liquid culture medium. In this case, the maximum drop in resistivity ρ of fibers upon immersion in a liquid culture medium was observed for unstretched fibers with two layers of PPy. It is shown that, after the initial fall of resistivity ρ, oriented chitosan fibers with one and two layers of PPy, resistivity ρ changes slightly in a liquid culture medium for 2 h. The studied oriented polymer fibers of chitosan coated with one and two layers of PPy are promising for use in the field of tissue engineering and regenerative medicine.
We have investigated the photoluminescence (PL) and photoconductivity of lead halide perovskite (CH
3
NH
3
PbBr
3
) films modified with different mixed cellulose esters (CEs). It was shown that the ...absorbance and PL spectra of CH
3
NH
3
PbBr
3
:CE films contain contributions of both the CH
3
NH
3
PbBr
3
and CE with the dominant contribution to the PL from perovskite component. The dependences of the integral PL intensities of the CH
3
NH
3
PbBr
3
:CE films on the optical excitation power turned out to be sublinear. This indicates that exciton recombination, as well as recombination via impurity levels, occurs in CH
3
NH
3
PbBr
3
:CE films at high excitation power levels. The conductivity of CH
3
NH
3
PbBr
3
:CE films at 300 K increases up to ~90 times when illuminated by a solar simulator, and this effect is environmentally stable due to the formation of hydrogen bonds between CE and the lead halide perovskite CH
3
NH
3
PbBr
3
. It is expected that appropriate selection of CE and optimization of CE inclusion will improve the optoelectronic properties and stability of composite films based on lead halide perovskite-CE composites.
Synaptic materials and devices that mimic biological synapses are essential components for neuromorphic computational operations. Polymer, perovskite, and composite (organic–inorganic) optoelectronic ...synaptic devices for neuromorphic operations based on memristor structures are considered as electronic analogues of synapses in electronic networks. Advances in optoelectronics have shown that electrical voltage and light can be components of synaptic devices. Such optoelectronic synaptic devices can simulate several key biological synaptic functions such as short-term plasticity, long-term plasticity, time-dependent spike plasticity, and spike rating. Synapses can be simulated using memristor devices and materials with resistive switching of the resistance under the action of an electric field and light. The results of studies of the effect of resistive switching in polymer and organometallic perovskite composite (organic-inorganic) memristor materials and devices based on them are described. The inclusion of graphene and graphene-oxide particles into the matrices of polymers and organometallic perovskites leads to switching and memory effects in such memristor materials and devices, which opens up the possibility of their use as optoelectronic synaptic devices in neuromorphic operations.
Linear dichroism and birefringence are detected in composite microfilaments consisting of polypropylene with carbon nanofibers in the terahertz spectral range. The magnitude of linear dichroism is a ...nonmonotonic function of the frequency, reaches values about 60% at low frequencies of 0.2–0.8 THz, then changes sign, and reaches –50% at a frequency of 1.8 THz, at which the maximum of the absorption band is observed in the microstructures under study. Birefrengence (the difference between the effective refractive indices of the ordinary and extraordinary waves) also changes sign at a frequency of about 1.5 THz, which is apparently due to the manifestation of resonant absorption in the studied microstructures near 1.8 THz. The observed birefringence is due to carbon nanofibers that are incorporated into the polypropylene filaments and are aligned in a certain manner because of the high-temperature stretching of filaments.
We present the results of studies of low-frequency noise and impedance spectroscopy (IS) in operating planar structures based on films of organic-inorganic halide perovskite CH
3
NH
3
PbBr
3
with and ...without embedded graphene oxide (GO) flakes as active layers of field-effect transistors and memory chips. It is shown that 1/
f
flicker noise dominates at low frequencies, while white shot-noise resulting from dark current fluctuations is the limiting noise at high frequencies. It is demonstrated that at similar currents the current noise power spectral density,
S
I
, values are lower by factor ~ 4 for the film CH
3
NH
3
PbBr
3
:GO with respect to that for the film CH
3
NH
3
PbBr
3
without GO flakes, thus it is concluded that GO flakes act as a trap passivation. The IS results show that under identical conditions the Cole-Cole plots for both films are in good agreement with the equivalent circuit model and represents series resistance, recombination resistance and geometric capacitance, respectively, which arise due to charge accumulation, charge transfer resistance and/or additional interfacial electronic states. The decrease in the noise density by factor 4 in the perovskite films with GO flakes is attributed to the higher conductivity of these films as well as to more uniform distribution of carriers over the sample cross section. The obtained results provide the way to improve the performance of next generation of organic-inorganic perovskite optoelectronic devices.
In this paper, we develop a finite element model that allows calculating the current-voltage characteristic of a bipolar memristor based on Pt/HfO
2
/TiN hafnium oxide, which reflects both the high- ...and low-resistance states of the memristor. Maxwell’s equations for the stationary case served as the mathematical basis of the model. The model allows evaluating the relation between the properties of materials included in the structure of the memristor and its operating current.
The growth of grains in nano- and submicrocrystalline nickel produced via equal channel angular pressing is investigated under conditions of non-isothermal annealing using differential scanning ...calorimetry and transmission electron microscopy. Both types of the material exhibit abnormal grain growth that can be described in terms of the Johnson–Mehl–Avrami formalism.
Quality control of welds in multilayer polyethylene pipelines is considered; specifically, butt welds are produced by a hot tool. Besides monitoring of the welding parameters and mechanical testing ...of the welds, it is expedient to use nondestructive ultrasonic testing so as to detect defects such as cracks, solid inclusions, and pores. The use of ultrasonic testing in a chordal configuration to detect model defects of 1-mm diameter is presented as an example.
A series of experiments was performed at the P critical facility of the National Research Center Kurchatov Institute to study neutron characteristics of the VVER type water-uranium fuel compositions ...that contain fuel pins with uranium enriched up to 6.5% in
235
U and erbium oxide (Er
2
O
3
) absorbers. Computational analysis of experiments was carried out by means of the precision MCU-PD code and the best-estimate code TVS-M, which are used for the VVER fuel cycle design. This paper describes the computational models implemented in both of these codes and presents the results of calculations of the main critical parameters in comparison with the experimental data.
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