Prita Pant

Probing thermal expansion of graphene and modal dispersion at low-temperature using graphene nanoelectromechanical systems resonators.

We use suspended graphene electromechanical resonators to study the variation of resonant frequency as a function of temperature. Measuring the change in frequency resulting from a change in tension, from 300 to 30 K, allows us to extract information about the thermal expansion of monolayer graphene as a function of temperature, which is critical for strain engineering applications. We find that thermal expansion of graphene is negative for all temperatures between 300 and 30 K. We also study the dispersion, the variation of resonant frequency with DC gate voltage, of the electromechanical modes and find considerable tunability of resonant frequency, desirable for applications like mass sensing and RF signal processing at room temperature. With a lowering of temperature, we find that the positively dispersing electromechanical modes evolve into negatively dispersing ones. We quantitatively explain this crossover and discuss optimal electromechanical properties that are desirable for temperature-compensated sensors.

Polymer nanocomposite nanomechanical cantilever sensors: material characterization, device development and application in explosive vapour detection

This paper reports an optimized and highly sensitive piezoresistive SU-8 nanocomposite microcantilever sensor and its application for detection of explosives in vapour phase. The optimization has been in improving its electrical, mechanical and transduction characteristics. We have achieved a better dispersion of carbon black (CB) in the SU-8/CB nanocomposite piezoresistor and arrived at an optimal range of 8-9 vol% CB concentration by performing a systematic mechanical and electrical characterization of polymer nanocomposites. Mechanical characterization of SU-8/CB nanocomposite thin films was performed using the nanoindentation technique with an appropriate substrate effect analysis. Piezoresistive microcantilevers having an optimum carbon black concentration were fabricated using a design aimed at surface stress measurements with reduced fabrication process complexity. The optimal range of 8-9 vol% CB concentration has resulted in an improved sensitivity, low device variability and low noise level. The resonant frequency and spring constant of the microcantilever were found to be 22 kHz and 0.4 N m(-1) respectively. The devices exhibited a surface stress sensitivity of 7.6 ppm (mN m(-1))(-1) and the noise characterization results support their suitability for biochemical sensing applications. This paper also reports the ability of the sensor in detecting TNT vapour concentration down to less than six parts per billion with a sensitivity of 1 mV/ppb.

“Organic CantiFET”: A Nanomechanical Polymer Cantilever Sensor With Integrated OFET

Nanomechanical cantilever based biochemical sensors translate molecular interactions into nanomechanical motions that can be measured by different transduction techniques. Improved sensitivity, reliability, and also cost effectiveness of such sensor platforms have been achieved by the use of polymer materials, along with the employment of smart and compatible transduction techniques. This paper explores an ultrasensitive nanomechanical cantilever sensor platform with a novel transduction technique by integrating a strain-sensitive organic field-effect transistor within a polymer nanomechanical cantilever. This sensor, named as “organic CantiFET,” has a surface stress sensitivity of 401 with a low-noise floor. This categorizes the organic CantiFET as an efficient biochemical sensor having a minimum detectable surface stress in the range of 0.18 mN/m.

Fabrication and characterization of novel polymer composite microcantilever sensors for explosive detection

In this paper, we report the development of a SU-8 based novel polymer composite microcantilever sensor designed for surface stress measurements. Nanoindentation study was carried out for measuring the Youngs modulus of the polymer composite. A low cost process, optimized for fabrication of composite SU8 microcantilevers with thickness as small as 3 µm is developed and characterized as part of this work. Further, this paper also demonstrates the application of this polymer composite cantilever for explosive detection with the appropriate surface coatings carried out on the polymer surface.

Deformation Twinning in Zirconium: Direct Experimental Observations and Polycrystal Plasticity Predictions

Deformation twinning was directly observed in three commercial zirconium alloy samples during split channel die plane-strain compression. One pair of samples had similar starting texture but different grain size distributions, while another pair had similar grain size distribution but different starting textures. Extension twinning was found to be more sensitive to the starting texture than to the grain size distribution. Also, regions of intense deformation near grain boundaries were observed. A hierarchical binary tree-based polycrystal plasticity model, implementing the Chin-Hosford-Mendorf twinning criterion, captured the experimentally observed twinning grains’ lattice orientation distribution, and the twin volume fraction evolution, provided the critical resolved shear stress for extension twinning,

Probing thermal expansion of graphene and modal dispersion at low-temperature using graphene NEMS resonators

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Loading and texture bias on the competitive slip activity for basal and prismatic slip systems in HCP alloys

τ0, was assumed much larger than any of the values reported in the literature, based on the viscoplastic self-consistent model. A comparison of the models suggests that