are the most popular methods. Electrically conductive nanomaterials, such as carbon black, [11] planar graphene, [12] carbon nanotube (CNT), [13] carbon nanofiber (CNF), [14] gold nanowires, [15] conductive polymer, [16] silver nanowires, [17] and silver flakes, [18] have been widely studied for the piezoresistive sensing applications both in stand-alone form and by dispersing into flexible polymers. Several review papers have summarized the state of the art of current research on highly flexible nanocomposites. [19][20][21] When used in standalone form, such as CNT bucky papers, these nanoparticles can provide superior electrical conductivity, but are lacking in flexibility. [22] The more practical approach is to disperse nanoparticles within a flexible polymer, such as PDMS, [23,24] polyimide, [25] and polyurethane. [26] It has been reported that a small amount of CNTs or CNFs dispersed in polymer can significantly enhance the electrical conductivity by orders. Among those, CNF is two orders of magnitude cheaper than its counterparts CNT and graphene. [14] Multiple key parameters, including electrical conductivity, sensitivity, sensing range, durability, and manufacturing cost and complexity, can impact on the performance of nanocomposite sensors. Advanced manufacturing technologies, such as etching and photolithography, have been employed to create critical microstructures in nanocomposites, resulting in novel pressure and strain sensors, though the manufacturing cost and scalability are often criticized. [24,27] Recently, graphene/ PDMS nanocomposites have shown good sensitivity with gauge factor of 61.3 and detectability of up to 20% tensile strain, but manufacturing requires freezing at −50 °C and heat treatment at 750 °C. [28] In terms of sensor performance, obtaining an optimum combination of sensitivity and sensing range is challenging. High gauge factors in the order of 1000 were obtained using a woven mesh configuration of graphene/polymer but this material only achieved up to 6% strain. [29] A graphene film was made in an easy single step process, and showed gauge factor of 1000 but its failure strain was only at 2% strain. [30] In general, highly flexible nanocomposites result in the trade-off of piezoresistive sensitivity. For example, Qin et al. reported that flexible nanocomposites using reduced graphene oxide and polyimide had the maximum stretching and compression sensing capability up to 50% strain with low gauge factors of 0.712 and 1, respectively. [25] Majority of the works on sensor A polydimethylsiloxane (PDMS)/carbon nanofiber (CNF) nanocomposite with piezoresistive sensing function is presented. Excellent electrical conductivity is achieved by dispersing the CNFs into PDMS. A facile, low cost, and scalable fabrication procedure allows the sensors to be made in different shapes. The piezoresistive sensors show repeatable response up to 30% tensile strain. In addition, the characterization of sensing mechanism using an in situ mechanical testing system within a scanning electron microscope...

In this work, we induce on-chip static strain into the transition metal dichalcogenide (TMDC) MoS2 with e-beam evaporated stressed thin film multilayers. These thin film stressors are analogous to SiNx based stressors utilized in CMOS technology. We choose optically transparent thin film stressors to allow us to probe the strain transferred into the MoS2 with Raman spectroscopy. We combine thickness dependent analyses from Raman peak shifts in MoS2 and atomistic simulations to understand the strain transferred throughout each layer. This collaboration between experimental and theoretical efforts allows us to conclude that strain is transferred from the stressor into the top few layers of MoS2 and the bottom layer is always partially fixed to the substrate. This proof of concept suggests that commonly used industrial strain engineering techniques may be easily implemented with 2D materials, as long as the c-axis strain transfer is considered.

This article presents the fabrication and characterization of poly dimethylsiloxane/carbon nanofiber (CNF)-based nanocomposites. Although silica and carbon nanoparticles have been traditionally used to reinforce mechanical properties in PDMS matrix nanocomposites, this article focuses on understanding their impacts on electrical and thermal properties. By adjusting both the silica and CNF concentrations, 12 different nanocomposite formulations were studied, and the thermal and electrical properties of these materials were experimentally characterized. The developed nanocomposites were prepared using a solvent-assisted method providing uniform dispersion of the CNFs in the polymer matrix. Scanning electron microscopy was employed to determine the dispersion of the CNFs at different length scales. The thermal properties, such as thermal stability and thermal diffusivity, of the developed nanocomposites were studied using thermogravimetirc and laser flash techniques. Furthermore, the electrical volume conductivity of each type of nanocomposite was tested using the four-probe method to eliminate the effects of contact electrical resistance during measurement. Experimental results showed that both CNFs and silica were able to impact on the overall properties of the synthesized PDMS/CNF nanocomposites. The developed nanocomposites have the potential to be applied to the development of new load sensors in the future. ARTICLE HISTORY

Transition metal dichalcogenides (TMDs) offer superior properties over conventional materials in many areas such as in electronic devices. In recent years, TMDs have been shown to display a phase switching mechanism under the application of external mechanical strain, making them exciting candidates for phase change transistors. Molybdenum ditelluride (MoTe2) is one such material that has been engineered as a strain-based phase change transistor. In this work, we explore various aspects of the mechanical properties of this material by a suite of computational and experimental approaches. Firstly, we present parameterization of an interatomic potential for modeling monolayer as well as multilayered MoTe2 films. For generating the empirical potential parameter set, we fit results from Density Functional Theory calculations using a random search algorithm called particle swarm optimization. The potential closely predicts structural properties, elastic constants, and vibrational frequencies of MoTe2 indicating a reliable fit. Our simulated mechanical response matches earlier larger scale experimental nanoindentation results with excellent prediction of fracture points. Simulation of uniaxial tensile deformation by Molecular Dynamics shows the complete non-linear stress-strain response up to failure. Mechanical behavior, including failure properties, exhibits directional anisotropy due to the variation of bond alignments with crystal orientation. Furthermore, we show the deterioration of mechanical properties with increasing temperature. Finally, we present computational and experimental evidence of an extended c-axis strain transfer length in MoTe2 compared to TMDs with smaller chalcogen atoms.

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