Laser-Formed Sensors with Electrically Conductive MWCNT Networks for Gesture Recognition Applications.

Currently, an urgent need in the field of wearable electronics is the development of flexible sensors that can be attached to the human body to monitor various physiological indicators and movements. In this work, we propose a method for forming an electrically conductive network of multi-walled carbon nanotubes (MWCNT) in a matrix of silicone elastomer to make stretchable sensors sensitive to mechanical strain. The electrical conductivity and sensitivity characteristics of the sensor were improved by using laser exposure, through the effect of forming strong carbon nanotube (CNT) networks. The initial electrical resistance of the sensors obtained using laser technology was ~3 kOhm (in the absence of deformation) at a low concentration of nanotubes of 3 wt% in composition. For comparison, in a similar manufacturing process, but without laser exposure, the active material had significantly higher values of electrical resistance, which was ~19 kOhm in this case. The laser-fabricated sensors have a high tensile sensitivity (gauge factor ~10), linearity of >0.97, a low hysteresis of 2.4%, tensile strength of 963 kPa, and a fast strain response of 1 ms. The low Young's modulus values of ~47 kPa and the high electrical and sensitivity characteristics of the sensors made it possible to fabricate a smart gesture recognition sensor system based on them, with a recognition accuracy of ~94%. Data reading and visualization were performed using the developed electronic unit based on the ATXMEGA8E5-AU microcontroller and software. The obtained results open great prospects for the application of flexible CNT sensors in intelligent wearable devices (IWDs) for medical and industrial applications.

Hybrid Carbon Nanotubes-Graphene Nanostructures: Modeling, Formation, Characterization.

A technology for the formation and bonding with a substrate of hybrid carbon nanostructures from single-walled carbon nanotubes (SWCNT) and reduced graphene oxide (rGO) by laser radiation is proposed. Molecular dynamics modeling by the real-time time-dependent density functional tight-binding (TD-DFTB) method made it possible to reveal the mechanism of field emission centers formation in carbon nanostructures layers. Laser radiation stimulates the formation of graphene-nanotube covalent contacts and also induces a dipole moment of hybrid nanostructures, which ensures their orientation along the force lines of the radiation field. The main mechanical and emission characteristics of the formed hybrid nanostructures were determined. By Raman spectroscopy, the effect of laser radiation energy on the defectiveness of all types of layers formed from nanostructures was determined. Laser exposure increased the hardness of all samples more than twice. Maximum hardness was obtained for hybrid nanostructure with a buffer layer (bl) of rGO and the main layer of SWCNT-rGO(bl)-SWCNT and was 54.4 GPa. In addition, the adhesion of rGO to the substrate and electron transport between the substrate and rGO(bl)-SWCNT increased. The rGO(bl)-SWCNT cathode with an area of ~1 mm2 showed a field emission current density of 562 mA/cm2 and stability for 9 h at a current of 1 mA. The developed technology for the formation of hybrid nanostructures can be used both to create high-performance and stable field emission cathodes and in other applications where nanomaterials coating with good adhesion, strength, and electrical conductivity is required.

Flexible Strain-Sensitive Silicone-CNT Sensor for Human Motion Detection.

This article describes the manufacturing technology of biocompatible flexible strain-sensitive sensor based on Ecoflex silicone and multi-walled carbon nanotubes (MWCNT). The sensor demonstrates resistive behavior. Structural, electrical, and mechanical characteristics are compared. It is shown that laser radiation significantly reduces the resistance of the material. Through laser radiation, electrically conductive networks of MWCNT are formed in a silicone matrix. The developed sensor demonstrates highly sensitive characteristics: gauge factor at 100% elongation -4.9, gauge factor at 90° bending -0.9%/deg, stretchability up to 725%, tensile strength 0.7 MPa, modulus of elasticity at 100% 46 kPa, and the temperature coefficient of resistance in the range of 30-40 °C is -2 × 10-3. There is a linear sensor response (with 1 ms response time) with a low hysteresis of ≤3%. An electronic unit for reading and processing sensor signals based on the ATXMEGA8E5-AU microcontroller has been developed. The unit was set to operate the sensor in the range of electrical resistance 5-150 kOhm. The Bluetooth module made it possible to transfer the received data to a personal computer. Currently, in the field of wearable technologies and health monitoring, a vital need is the development of flexible sensors attached to the human body to track various indicators. By integrating the sensor with the joints of the human hand, effective movement sensing has been demonstrated.

Electrically Conductive Networks from Hybrids of Carbon Nanotubes and Graphene Created by Laser Radiation.

A technology for the formation of electrically conductive nanostructures from single-walled carbon nanotubes (SWCNT), multi-walled carbon nanotubes (MWCNT), and their hybrids with reduced graphene oxide (rGO) on Si substrate has been developed. Under the action of single pulses of laser irradiation, nanowelding of SWCNT and MWCNT nanotubes with graphene sheets was obtained. Dependences of electromagnetic wave absorption by films of short and long nanotubes with subnanometer and nanometer diameters on wavelength are calculated. It was determined from dependences that absorption maxima of various types of nanotubes are in the wavelength region of about 266 nm. It was found that contact between nanotube and graphene was formed in time up to 400 fs. Formation of networks of SWCNT/MWCNT and their hybrids with rGO at threshold energy densities of 0.3/0.5 J/cm2 is shown. With an increase in energy density above the threshold value, formation of amorphous carbon nanoinclusions on the surface of nanotubes was demonstrated. For all films, except the MWCNT film, an increase in defectiveness after laser irradiation was obtained, which is associated with appearance of C-C bonds with neighboring nanotubes or graphene sheets. CNTs played the role of bridges connecting graphene sheets. Laser-synthesized hybrid nanostructures demonstrated the highest hardness compared to pure nanotubes. Maximum hardness (52.7 GPa) was obtained for MWCNT/rGO topology. Regularity of an increase in electrical conductivity of nanostructures after laser irradiation has been established for films made of all nanomaterials. Hybrid structures of nanotubes and graphene sheets have the highest electrical conductivity compared to networks of pure nanotubes. Maximum electrical conductivity was obtained for MWCNT/rGO hybrid structure (~22.6 kS/m). Networks of nanotubes and CNT/rGO hybrids can be used to form strong electrically conductive interconnections in nanoelectronics, as well as to create components for flexible electronics and bioelectronics, including intelligent wearable devices (IWDs).