Carbon nanotube four-terminal devices for pressure sensing applications

Carbon nanotubes (CNTs) are of high interest for sensing applications, owing to their superior mechanical strength, high Young’s modulus and low density. In this work, we report on a facile approach for the fabrication of carbon nanotube devices using a four terminal configuration. Oriented carbon nanotube films were pulled out from a CNT forest wafer and then twisted into a yarn. Both the CNT film and yarn were arranged on elastomer membranes/diaphragms which were ar-ranged on a laser cut acrylic frame to form pressure sensors. The sensors were calibrated using a precisely controlled pressure system, showing a large change of the output voltage of approximately 50 mV at a constant supply current of 100µA and under a low applied pressure of 15 mbar. The results indicate the high potential of using CNT films and yarns for pressure sensing applications

Numerical investigation on the influence of defects on the buckling behavior of single-and multi-walled carbon nanotubes

The effect of defects on the buckling behavior of single- and multi-walled carbon nanotubes based on the finite element method was analyzed. For this purpose, two fundamental carbon nanotubes (armchair and zigzag) were constructed in their perfect forms. Then, the buckling behavior of carbon nanotubes was evaluated by comparing their critical loads obtained from the simulation and analytical calculations. In the second phase, three most likely atomic defects, i.e., impurities (doping with Si atoms), vacant sites (carbon vacancy) and introduced perturbations of the ideal geometry in different amounts to the perfect models were simulated. Finally, the buckling behavior of imperfect carbon nanotubes was numerically evaluated and compared with the behavior of the perfect ones. In addition, simple relations were developed from the obtained results for prediction of the buckling behavior of imperfect carbon nanotubes as a function of the amount of defects. The results reveal the fact that the existence of any type of defects in the structure of carbon nanotubes leads to a lower critical load and as a result, lower buckling properties. As an outlook, curved and composite single walled carbon nanotubes were exemplarily considered as a deviation from the perfect straight form. Investigating this effect yielded that the existence of any curvature or kink in the structure of nanotubes decreases their buckling strength. This study provides a realistic prediction of buckling properties of carbon nanotubes which is of high importance in nano-industry and the production of nano-composites and reinforced materials

A numerical evaluation of the influence of defects on the elastic modulus of single and multi-walled carbon nanotubes

Finite element models of single-walled and multi-walled carbon nanotubes in their perfect and fundamental forms (zigzag and armchair) were constructed. Then, after obtaining the mechanical properties of perfect carbon nanotubes, three types of imperfections, i.e., doping with Si atoms, carbon vacancy and perturbation of the ideal location of the carbon atom were introduced in different amounts to the perfect models to make them imperfect. Finally, the mechanical properties of the imperfect carbon nanotubes were numerically simulated and compared with those of perfect ones. Simple relations which predict the change of Young’s modulus as a function of the imperfection percentage were derived. The results show that the existence of any kind of imperfection in the perfect models leads to lower stiffness values. This study allows to realistically judge any simulation based on perfect structures and gives for the first time a good estimate to which extend the values based on perfect structures must be lowered in order to account for common imperfections to predict the mechanical properties of carbon nanotubes which are nowadays used in the production of advanced nanocomposites and reinforced materials