Immense development has been taken place not only to increase the bulk production, repeatability and yield of carbon nanotubes (CNTs) in last 25 years but preference is also given to acknowledge the basic concepts of nucleation and growth methods. Vertically aligned carbon nanotubes (VAC-NTs) are forest of CNTs accommodated perpendicular on a substrate. Their exceptional chemical and physical properties along with sequential arrangement and dense structure make them suitable in various fields. The effect of different type of selected substrate, carbon precursor, catalyst and their physical and chemical status, reaction conditions and many other key parameters have been thoroughly studied and analysed. The aim of this paper is to specify the trend and summarize the effect of key parameters instead of only presenting all the experiments reported till date. The identified trends will be compared with the recent observations on the growth of different types of patterned VACNTs. In this review article, we have presented a comprehensive analysis of different techniques to precisely determine the role of different parameters responsible for the growth of patterned vertical aligned carbon nanotubes. We have covered various techniques proposed in the span of more than two decades to fabricate the different structures and configurations of carbon nanotubes on different types of substrates. Apart from a detailed discussion of each technique along with their specific process and implementation, we have also provided a critical analysis of the associated constraints, benefits and shortcomings. To sum it all for easy reference for researchers, we have tabulated all the techniques based on certain main key factors. This review article comprises of an exhaustive discussion and a handy reference for researchers who are new in the field of synthesis of CNTs or who wants to get abreast with the techniques of determining the growth of VACNTs arrays.

Microcantilever beams are the most widely used mechanical elements in the design and fabrication of MEMS/NEMS-based sensors and actuators. In this work, we have proposed a new microcantilever beam design based on a stepped trapezoidal-shaped microcantilever. Single-, double-, triple- and quadruple-stepped trapezoidal-shaped microcantilever beams along with conventional rectangular-shaped microcantilever beams were analysed experimentally, numerically and analytically. The microcantilever beams were fabricated from silicon dioxide material using wet bulk micromachining in 25 wt% TMAH. The length, width and thickness of the microcantilever beams were fixed at 200, 40 and 0.96 µm, respectively. A laser vibrometer was utilized to measure the resonance frequency and Q-factor of the microcantilever beams in vacuum as well as in ambient conditions. Furthermore, finite element analysis software, ANSYS, was employed to numerically analyse the resonance frequency, maximum deflection and torsional end rotation of all the microcantilever beam designs. The analytical and numerical resonance frequencies are found to be in good agreement with the experimental resonance frequencies. In the stepped trapezoidal-shaped microcantilever beams with an increasing number of steps, the Q-factor, maximum deflection and torsional end rotation were improved, whereas the resonance frequency was slightly reduced. Nevertheless, the resonance frequency is higher than the basic rectangular-shaped microcantilever beam. The observed quality factor, maximum deflection and torsional end rotation for a quadruple-stepped trapezoidal-shaped microcantilever are 38%, 41% and 52%, respectively, which are higher than those of conventional rectangular-shaped microcantilever beams. Furthermore, for an applied concentrated mass of 1 picogram on the cantilever surface, a greater shift in frequency is obtained for all the stepped trapezoidal-shaped microcantilever beam designs compared to the conventional rectangular microcantilever beam.

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