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The creation of sustainable power sources for wearable electronics and self-powered systems is a promising direction of modern electronics. At the moment, a search for functional materials with high values of piezoelectric coefficient and elasticity, as well as non-toxicity, is underway to generate such power sources. In this paper, nitrogen-doped carbon nanotubes (N-CNTs) are considered as a functional material for a piezoelectric nanogenerator capable of converting nanoscale deformations into electrical energy. The effect of defectiveness and of geometric and mechanical parameters of N-CNTs on the current generated during their deformation is studied. It was established that the piezoelectric response of N-CNTs increased nonlinearly with an increase in the Young's modulus and the aspect ratio of the length to diameter of the nanotube and, on the contrary, decreased with an increase in defectiveness not caused by the incorporation of nitrogen atoms. The advantages of using N-CNT to create energy-efficient piezoelectric nanogenerators are shown. [ABSTRACT FROM AUTHOR]

Recent studies have shown that nitrogen doping of carbon nanotubes (CNTs) can lead to the formation of piezoelectric properties in them, not characteristic of pure CNTs. In this work, nitrogen-doped CNTs were grown by plasma-enhanced chemical vapor deposition and the effect of the aspect ratio of the nanotube length to its diameter on its piezoelectric coefficient d 3 3 was shown. It was observed that as the aspect ratio of the nanotube increased from 7 to 21, the value of d 3 3 increased linearly from 7.3 to 10.7 pm/V. This dependence is presumably due to an increase in curvature-induced polarization because of an increase in the curvature and the number of bamboo-like "bridges" in the nanotube cavity formed as a result of the incorporation of pyrrole-like nitrogen into the nanotube structure. The obtained results can be used in the development of promising elements of nanopiezotronics (nanogenerators, memory elements, and strain sensors). [ABSTRACT FROM AUTHOR]

Aligned carbon nanotubes (CNTs) are among the most promising nanostructures in nanoelectronics. However, at the moment, CNTs have not received wide practical application for producing electronic devices, owing to the fact that electrical parameters of devices based on CNTs seriously deviate from those that were theoretically predicted. Previously, these phenomena were not associated with the properties of CNTs and were attributed to the parasitic effects of the environmental impact, and substrate- and interface-related influences. In this paper, using piezoresponse force microscopy, it is shown for the first time that aligned CNTs with a diameter of 52 ± 9 nm and a length of 1.5 ± 0.27 μm have an abnormally large piezoelectric strain coefficient with a value of 203 ± 18 pm V−1, which exceeds the values of typical piezoelectric nanomaterials. It has been established that piezoelectric properties of aligned CNTs lead to the presence of hysteresis in current–voltage characteristics when sawtooth voltage pulses are applied, and cause a significant decrease in conductivity when rectangular voltage pulses are applied. This effect opens up broad prospects for the use of aligned carbon nanotubes for producing nanopiezotronic devices and makes it possible to explain anomalous effects of resistive switching of the CNTs and electronic devices based on them. [ABSTRACT FROM AUTHOR]

The results of experimental studies of the dependence of the memristor effect of bundles of vertically aligned carbon nanotubes on the pressing force magnitude and the switching voltage are presented. The improvement of the memristor effect is shown with increasing pressing force and switching voltage. The dependence of the surface potential on the deformation of nanotubes located along the bundle cross section is shown. The obtained results can be used in the development of promising nanopiezotronics devices. [ABSTRACT FROM AUTHOR]

Recent studies reveal that carbon nanostructures show anomalous piezoelectric properties when the central symmetry of their structure is violated. Particular focus is given to carbon nanotubes (CNTs) with initial significant curvature of the graphene sheet surface, which leads to an asymmetric redistribution of the electron density. This paper presents the results of studies on the piezoelectric properties of aligned multi-walled CNTs. An original technique for evaluating the effective piezoelectric coefficient of CNTs is presented. For the first time, in this study, we investigate the influence of the growth temperature and thickness of the catalytic Ni layer on the value of the piezoelectric coefficient of CNTs. We establish the relationship between the effective piezoelectric coefficient of CNTs and their defectiveness and diameter, which determines the curvature of the graphene sheet surface. The calculated values of the effective piezoelectric coefficient of CNTs are shown to be between 0.019 and 0.413 C/m2, depending on the degree of their defectiveness and diameter. [ABSTRACT FROM AUTHOR]

The paper presents a theoretical model of the catalytic centers formation processes during annealing of multilayer nanosized metal films for carbon nanotubes growth. The approach to the description of the model is based on the mass transfer processes under the influence of mechanical thermoelastic stresses, which arise due to the difference in the thermal expansion coefficients of the substrate materials and nanosized metal layers. The thermal stress gradient resulting from annealing creates a drop in the chemical potential over the thickness of the film structure. This leads to the initiation of diffusion mass transfer between the inner and outer surfaces of the films. As a result, the outer surface begins to corrugate and fragment, creating separate islands, which serve as the basis for the catalytic centers formation. Experimental research on the formation of catalytic centers in the structure of Ni/Cr/Si was carried out. It is demonstrated that the proposed model allows to predict the geometric dimensions of the catalytic centers before growing carbon nanotubes. The results can be used to create micro- and nanoelectronics devices based on carbon nanotube arrays. [ABSTRACT FROM AUTHOR]

Recent studies in nanopiezotronics have indicated that strained graphene may exhibit abnormal flexoelectric and piezoelectric properties. Similar assumptions have been made with regard to the properties of carbon nanotubes (CNTs), however, this has not so far been confirmed. This paper presents the results of our experimental studies confirming the occurrence of a surface piezoelectric effect in multi-walled CNTs under a non-uniform strain. Using atomic force microscopy, we demonstrated the piezoelectric response of multi-walled CNTs under compression and bending. The current generated by deforming an individual CNT was shown to be −24 nA. The value of the surface potential at the top of the bundle of strained CNTs varied from 268 mV to −110 mV, depending on strain type and magnitude. We showed that the maximum values of the current and the surface potential can be achieved when longitudinal strain predominates in a CNT. However, increasing the bending strain of CNTs does not lead to a significant increase in current and surface potential, due to the mutual compensation of piezoelectric charges concentrated on the CNT side walls. The results of the study offer a number of opportunities and challenges for further fundamental research on the piezoelectric properties of carbon nanotubes as well as for the development of advanced CNT-based nanopiezotronic devices. [ABSTRACT FROM AUTHOR]