With the advent of the Internet of Everything (IoE) era, our civilization and future generations will employ an unimaginable complex array of electronics and sensors in daily life. Ferroelectric polymers represent a core group of materials supporting the fast development of IoE, and their functionality, straightforward processing and unmatched versatility make them prime candidates for integration in multifaceted devices. Since they are highly selective, highly responsive, highly scalable, self-powering and compatible with flexible and stretchable substrates, they can be easily integrated with various electronics into numerous stand-alone objects and even into skin as sensors for monitoring diverse mechanical, thermal and vital parameters. They can also be used in combination with other sensor materials for harvesting waste energy from mechanical and thermal sources, for data storage and for actuation. This article reviews the up-to-date accomplishments in the ferroelectric polymer field, with focus on materials involving polyvinylidene fluoride (PVDF), and also discussed both their current advancement and future growth in the development of sustainable systems.

Route towards sustainable smart sensors: ferroelectric polyvinylidene fluoride-based materials and their integration in flexible electronics

Highly flexible and sensitive strain sensors are essential components of wearable electronic devices. Herein, we present a novel graphene woven fabric (GWF)/polydimethylsiloxane (PDMS) composite as a highly flexible, sensitive strain sensor capable of detecting feeble human motions with an extremely high piezoresistive gauge factor of 223 at a strain of 3% and excellent durability. A wireless wearable musical instrument prototype made of the composite sensor demonstrates conversion of human motions to music of different instruments and sounds.

A highly sensitive graphene woven fabric strain sensor for wearable wireless musical instruments

Nanogenerators capable of converting energy from mechanical sources to electricity with high effective efficiency using low-cost, nonsemiconducting, organic nanomaterials are attractive for many applications, including energy harvesters. In this work, near-field electrospinning is used to direct-write poly(vinylidene fluoride) (PVDF) nanofibers with in situ mechanical stretch and electrical poling characteristics to produce piezoelectric properties. Under mechanical stretching, nanogenerators have shown repeatable and consistent electrical outputs with energy conversion efficiency an order of magnitude higher than those made of PVDF thin films. The early onset of the nonlinear domain wall motions behavior has been identified as one mechanism responsible for the apparent high piezoelectricity in nanofibers, rendering them potentially advantageous for sensing and actuation applications.

Direct-Write Piezoelectric Polymeric Nanogenerator with High Energy Conversion Efficiency

Two-dimensional crystals have emerged as a class of materials that may impact future electronic technologies. Experimentally identifying and characterizing new functional two-dimensional materials is challenging, but also potentially rewarding. Here, we fabricate field-effect transistors based on few-layer black phosphorus crystals with thickness down to a few nanometres. Reliable transistor performance is achieved at room temperature in samples thinner than 7.5 nm, with drain current modulation on the order of 10(5) and well-developed current saturation in the I-V characteristics. The charge-carrier mobility is found to be thickness-dependent, with the highest values up to ∼ 1,000 cm(2) V(-1) s(-1) obtained for a thickness of ∼ 10 nm. Our results demonstrate the potential of black phosphorus thin crystals as a new two-dimensional material for applications in nanoelectronic devices.

http://absimage.aps.org/image/MAR14/MWS_MAR14-2013-005031.pdf

Black Phosphorus Field-effect Transistors

A graphene field-effect transistor (gFET) was non-covalently functionalised with 1-pyrenebutyric acid N-hydroxysuccinimide ester and conjugated with anti-CD63 antibodies for the label-free detection of exosomes. Using a microfluidic channel, part of a graphene film was exposed to solution. The change in electrical properties of the exposed graphene created an additional minimum alongside the original Dirac point in the drain-source current (Ids) - back-gate voltage (Vg) curve. When phosphate buffered saline (PBS) was present in the channel, the additional minimum was present at a Vg lower than the original Dirac point and shifted with time when exosomes were introduced into the channel. This shift of the minimum from the PBS reference point reached saturation after 30 minutes and was observed for multiple exosome concentrations. Upon conjugation with an isotype control, sensor response to the highest concentration of exosomes was negligible in comparison to that with anti-CD63 antibody, indicating that the functionalised gFET can specifically detect exosomes at least down to 0.1 μg/mL and is sensitive to concentration. Such a gFET biosensor has not been used before for exosome sensing and could be an effective tool for the liquid-biopsy detection of exosomes as biomarkers for early-stage identification of diseases such as cancer.

/pdf/chemically-functionalised-graphene-fet-biosensor-for-the-1yz7y8uc8w.pdf

Chemically Functionalised Graphene FET Biosensor for the Label-free Sensing of Exosomes.

In this study, we investigated an energy harvesting effect of tensile stress using piezoelectric polymers and flexible electrodes. A chemical-vapor-deposition grown graphene film was transferred onto both sides of the PVDF and P(VDF-TrFE) films simultaneously by means of a conventional wet chemical method. Output voltage induced by sound waves was measured and analyzed when a mechanical tension was applied to the device. Another energy harvester was made with a metallic electrode, where Al and Ag were deposited by using an electron-beam evaporator. When acoustic vibrations (105 dB) were applied to the graphene/PVDF/graphene device, an induced voltage of 7.6 Vpp was measured with a tensile stress of 1.75 MPa, and this was increased up to 9.1 Vpp with a stress of 2.18 MPa for the metal/P(VDF-TrFE)/metal device. The 9 metal/PVDF/metal layers were stacked as an energy harvester, and tension was applied by using springs. Also, we fabricated a full-wave rectifying circuit to store the electrical energy in a 100 μF capacitor, and external vibration generated the electrical charges. As a result, the stored voltage at the capacitor, obtained from the harvester via a bridge diode rectifier, was saturated to ~7.04 V after 180 s charging time.

/pdf/energy-harvesting-efficiency-of-piezoelectric-polymer-film-2h1haywvf9.pdf

Energy harvesting efficiency of piezoelectric polymer film with graphene and metal electrodes

For device fabrication based on 2D materials such as graphene, hexagonal boron nitride (hBN) and transition metal dichalcogenides (TMDs), polymethyl methacrylate (PMMA) is conventionally used in the wet transfer and lithography processes. All these processes are sources of polymer residue, which degrade the intrinsic electrical and optical properties of devices. In this work, we report the effect of mechanical cleaning via contact mode atomic force microscopy (AFM) on the surface morphology and electrical behavior of chemical-vapor-deposition grown graphene. An AFM tip with large contact force was used to scan, and multiple scanning was performed to remove the residues of PMMA. Raman mapping was incorporated to confirm the cleaning effect using AFM. Transconductance properties associated with a field-effect-transistor device based on the cleaned graphene were analyzed. It was observed that charge-neutrality point was shifted towards zero gate voltage and the charge carrier mobility was increased. We claim that our technique provides a facile route to fabricate devices with less polymer residue and higher efficiency.

/pdf/influence-of-removing-pmma-residues-on-surface-of-cvd-3nh86aprd6.pdf

Influence of removing PMMA residues on surface of CVD graphene using a contact-mode atomic force microscope

Effect of grain boundaries on electrical properties of polycrystalline graphene

Nematic liquid crystal (LC) molecules adsorbed on two dimensional materials are aligned along the crystal directions of the hexagonal lattice. It was demonstrated that short electric pulses can reorient the aligned LC molecules in the preferred armchair direction of hexagonal boron nitride (h-BN). Several states with a variety of colors were obtained by changing the direction and strength of the electric pulses. The ab initio calculations based on density functional theory was carried out to determine the favorable adsorption configurations of the LC molecules on the h-BN surface. A non-volatile display, in which pixel resolution can be determined by grains of hexagonal surface, is proposed, which can offer a pathway towards dynamic high-quality pixels with low power consumption, and could define a new paradigm for all non-volatile display applications.

https://iopscience.iop.org/article/10.1088/2053-1583/aad85e/pdf

Sanghoon Park

Papers

Energy harvesting efficiency of piezoelectric polymer film with graphene and metal electrodes

Influence of removing PMMA residues on surface of CVD graphene using a contact-mode atomic force microscope

Effect of grain boundaries on electrical properties of polycrystalline graphene

Dynamics of liquid crystal on hexagonal lattice

Simple Photolithography Process for a Graphene-Based Device with Edge Contact