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Graphene's unique physical and chemical properties have attracted substantial interest for various potential applications for electronics, spintronics, optoelectronics, and so on. Nanographene not only has the properties of graphene, but also has the special properties of edge state. Direct growth of nanographene on arbitrary substrate without catalyst has advantage of simplicity in device fabrications. In this paper, we review our recent progress on direct growth of nanographene on various substrates and using these nanographene as building blocks for electronic devices. The growth process is catalyst-free, scalable, and of low-temperature. Strain sensor, charge trapping memory (CTM) and resistance random access memory (RRAM) with excellent performances are demonstrated by tuning the size and density of as-grown nanographene on substrates.

Many types of tactile sensor have been proposed and developed, and they are becoming miniaturized and more precise at present state. Micro tactile sensors of high performance comparable to a human being are desired for robotic application, in which skilful and dexterous motion like a human being is necessary. Micromachining is one solution to realize a practical tactile sensor. In usual researches, capacitive, piezoelectric, and piezoresistive types are employed as the measurement principle of a micromachined sensor. In this paper, the MOSFET is applied and the drain current change of it when applied strain is employed as the measurement principle of tactile sensor. A fabricated sensor based on this principle detects strain with a good linearity. The result is compared with that of a conventional piezoresistive strain sensor, which shows the sensitivity of the developed MOSFET strain sensor has a good possibility compatible to conventional type sensors.

Industrialised nations have dedicated significant investments toward the development of civil infrastructure. To preserve this investment, attention must be given to proper maintenance. Structural Health Monitoring (SHM) has emerged as a tool to support this task. Networks of smart sensors, built upon wireless communication, have the potential to significantly improve SHM. Numerous platforms for smart sensors have been developed, most of which utilise proprietary hardware/software. The Berkeley Mote, utilised in this study, was the first open hardware/software platform to be developed. However, the Berkeley Mote was designed for generic applications and therefore the available sensors are not optimised for use in civil infrastructure applications. Acceleration and strain are among the most important physical quantities to judge the health of a structure. Although commercially available sensor boards have accelerometers, their applicability towards civil infrastructure is limited. This paper presents the development of new acceleration and strain sensor boards based on the Berkely-Mote platform and provides experimental verification of their performance within civil infrastructure applications.

In recent years, intensive researches have been stimulated to explore the promising prospect for carbon nanotubes (CNTs) in the fabrication of novel polymer sensor composites. In this study, the fabrication and properties of a flexible and stretchable composite elastomer fabricated from direct-spun carbon nanotube fiber (yarns) were presented, and the novel CNT fiber/polydimethylsiloxane (PDMS) elastic conductive composite shows the reversible two-stage conductivity owing to its unique structure of CNTs fabricated by the floating catalyst chemical vapor deposition (FCCVD). As the strain increased from 0% to 10% (Stage I), stretching the oriented CNT fiber/PDMS elastic conductive composite induces a constant decrease in the conductive pathways and contact areas between CNTs depending on the stretching distance. However, this composite elastomer will retain almost stable electrical resistance while being stretched by over 10% (Stage II). Furthermore, the composite shows very little variation in resistance under 187 stretching–releasing cycles up to a pre-strain level of 6%, indicating the outstanding stability and repeatability in performance as stretchable conductors. The microstructure, reversible two-stage conductive properties and mechanism were also discussed.

In this work, BC-PVA composite organohydrogels are prepared using polyvinyl alcohol (PVA) as matrix and bacterial cellulose (BC) nanofibers as reinforcement. BC-PVA@PPY conductive organohydrogels are obtained by depositing polypyrrole (PPY) on the BC-PVA organohydrogels via in situ polymerization of pyrrole. The mechanical properties of the organohydrogels are improved by the addition of BC nanofibers. The BC-PVA@PPY organohydrogels show good stability and repeatability in strain sensing. Due to their superior sensing performance, the BC-PVA@PPY organohydrogels can be used to monitor human activities (such as elbow movement and finger movement), indicating potential applications in wearable electronic devices.

A strain sensor based on the composites of poly (vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) filled by multi-walled carbon nanotube (MWNT) was prepared using a proposed fabrication process. Three kinds of MWNT loadings, i.e., 1.0wt.%, 2.0wt.% and 3.0wt.% were employed. Due to good dispersion state of MWNT in PVDF-HFP matrix, which was characterized by scanning electron microscope (SEM), this sensor was found to be of high sensitivity and stable performance. The sensor’s piezoresistivity varied in a weak nonlinear pattern, which was probably caused by the tunneling effect among neighboring MWNTs. The gauge factor of the sensor of 1.0wt.% MWNT loading was identified to be the highest, i.e., 33. This sensor gauge factor decreased gradually with the increase of addition amount of MWNT, which was 5 for the sensor of 3.0wt.% MWNT loading. This gauge factor was still higher than that of conventional metal-foil strain sensors. The electrical conductivity of PVDF-HFP/MWNT composites was also studied. It was found that with the increase of the addition amount of MWNT, the electrical conductivity of the PVDF-HFP/MWNT composites varied in a perfect percolation pattern with a very low percolation threshold, i.e., 0.77 vol.%, further indicating the very good dispersion of MWNT in the PVDF-HFP matrix.

Extensive numerical simulation and experimental measurements have been conducted to understand the piezoresistivity characteristics and the working mechanisms of highly sensitive strain sensors made from carbon nanotubes (CNTs) embedded polymer nanocomposites. When using two kinds of multi-walled carbon nanotubes (MWNTs), it was identified that the piezoresistivity characteristics of two sensors are different. When using comparatively straight MWNTs of a large diameter, named as MWNT-7, the fundamental working mechanism of this sensor is the tunneling resistance change among CNTs due to the distance change caused by applied strains. However, for another type of MWNTs, which is of a very small diameter and seriously curved shapes, and named as LMWNT-10, the main working mechanism of the sensor may be the piezoresistivity of MWNTs themselves due to deformation of MWNTs. Furthermore, for the sensors made from MWNT-7/epoxy, further numerical and experimental investigations have been carried out to explore the effects of processing parameters and material properties on sensor sensitivity. Both numerical and experimental results indicate that a higher tunneling resistance or higher ratio of the tunneling resistance to the total resistance of the sensor leads to a higher sensor sensitivity. Processing conditions and material properties play a role in determining the sensor sensitivity.