Scanning Probe Techniques for Characterization of Vertically Aligned Carbon Nanotubes

This chapter presents the results of experimental studies of the electrical, mechanical and geometric parameters of vertically aligned carbon nanotubes (VA CNTs) using scanning probe microscopy (SPM). This chapter also presents the features and difficulties of characterization of VA CNTs in different scanning modes of the SPM. Advanced techniques for VA CNT characterization (the height, Young’s modulus, resistivity, adhesion and piezoelectric response) taking into account the features of the SPM modes are described. The proposed techniques allow to overcome the difficulties associated with the vertical orientation and high aspect ratio of nanotubes in determining the electrical and mechanical parameters of the VA CNTs by standard methods. The results can be used in the development of diagnostic methods as well as in nanoelectronics and nanosystem devices based on vertically aligned carbon nanotubes (memory elements, adhesive structures, nanoelectromechanical switches, emission structures, etc.)

Distributed Sensory System of Surface Cracks Monitoring Based on Electrical Impedance Tomography

In this paper, we propose a method of distributed sensory systems designing for monitoring of surface cracks in highly loaded constructions based on electrical impedance tomography. A thin conductive film with contacts on the perimeter applied on the monitored surface is used as a crack sensor. Registration and monitoring of surface cracks using the developed modified method of electrical impedance tomography (EIT) are carried out. The proposed method differs from the traditional EIT method as it has considerably lower computational complexity with sufficient resolving power. This makes it possible to use the proposed EIT method for continuous rapid monitoring of surface cracks during the operation of a controlled construction in real-time mode. The main stages of the proposed modified EIT method, a block diagram of the crack image reconstruction algorithm and a method for processing the crack images, which provide the possibility for adjusting the sensitivity of the monitoring system, are considered. The main modules of the monitoring system software are described. Analysis of the imitative modeling results of the cracks registering processes as a function of size, shape, and the arrangement of cracks, the number of boundary contacts of the distributed sensor, the step of the grid, and the parameters of a digital filter are considered. Comparative analysis of the developed and standard EIT methods for surface cracks monitoring in constructive elements was performed

A Quasi-Two-Dimensional Physics-Based Model of HEMTs without Smoothing Functions for Joining Linear and Saturation Regions of I-V Characteristics

A quasi-two-dimensional physics-based model of HEMT transistor without using any smoothing functions for joining the linear and saturation regions of current-voltage (I-V) characteristics was developed. Considering the intervalley transitions of electrons and the presence of holes in the channel of transistor, we calculated the nonuniform spatial distributions of the electrical field, electron temperature, and electron mobility within the channel. The model is in a good agreement with experimental data over the linear and saturation regions of operation. The model provides precise simulating of HEMT transistors and can be utilized as a tool for analysis and prediction of influence of the material parameters on device and circuit characteristics

The modeling design integral the electrostatic microelectromechanical switch of capacitive type

This article presents the optimization and static modeling of the design an integral microelectromechanical switch of capacitive type based on a parametric 3D model using finite element analysis software complex ANSYS. The values of the pull-down voltage and switching time are determined. The obtained results give a good theoretical help in the development of various high-performance electrostatic microelectromechanical switches

System of Surface Defect Monitoring Based on a Distributed Crack Sensor

In this paper, we propose a method for monitoring surface defects like cracks in highly loaded structures. This method is based on the ability of surface cracks to open under the influence of external loads, thus causing the appearance of stresses and tears in the sensitive element—thin films that were deposited on the surface of the test object. We developed a system for monitoring surface defects based on a distributed crack sensor, the functional scheme of the sensor and its design, the structural scheme and algorithm of the system operation, and its model as a VHDL (VHSIC (Very high speed integrated circuits) Hardware Description Language)-description

Piezoelectric Response of Multi-Walled Carbon Nanotubes

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