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When graphene is shrunk into ~10 nm scale graphene nanoribbons or nanomesh structures, it is expected that not only electrical properties but also thermal conductivity and thermoelectric property are significantly altered due to the quantum confinement effect and extrinsic phonon-edge scattering. Here, we fabricate large-area, sub-10 nm single- and bilayer graphene nanomeshes from block copolymer self-assembly and measure the thermal conductivity, thermoelectric and electrical transport properties to experimentally verify the effect of sub-10 nm quantum confinement, phonon-edge scattering and cross-plane coupling. Among the large variety of the samples, bilayer graphene nanomesh having 8 nm-neck width showed significantly low thermal conductivity down to ~78 W m −1 K −1 , which is the lowest thermal conductivity for suspended graphene nanostructures, and a high thermopower value of −520 μV K −1 , while it still shows the comparably high carrier mobility. Classical and quantum mechanical calculations successfully supported our nanomesh approach, which can achieve high thermoelectric properties based on the significantly reduced thermal conductivity and higher thermopower due to the confined geometry. [ABSTRACT FROM AUTHOR]

Accommodating localized strains and deformations imposed by human body movements is indispensable to reliable operation of wearable thermoelectric (TE) fabrics. Despite their inherent flexibility and conformability, TE fabrics can suffer from significantly compromised TE performance and mechanical reliability at large applied strains, owing to the limited stretchability of the constituting fibers/components. Here, we propose three-dimensional woven fabrics of high TE performance and exceptional mechanical reliability, encouraged simultaneously by passivation of TE fibers. Immersion-coating in carbon nanotube (CNT) ink effortlessly deposits TE sheath layers on polyurethane (PU) core fibers. PU passivation layers are encapsulated on the coated fibers not only to enhance the intrinsic fiber stretchability by enabling fiber reorientation of individual CNTs, but also to augment the TE properties by regulating heat transfer along PN legs. The passivated fibers are woven into three-dimensional fabrics that harvest heat in the out-of-plane direction with the highest normalized open-circuit voltage of 8.0 mV K−1 and normalized power per leg of 1.1 × 10−4 μW K−2 among the reported woven-type TE fabrics. The woven structure deformability and the passivation-induced fiber elasticity cooperatively achieve reliable fabric mechanical stability against bending and stretching up to 100% strain. Conforming seamlessly to the curved human forearm, the TE woven fabrics hold promises for efficient body heat harvesting to realize self-powered wearable electronics. [Display omitted] • High-performance three-dimensional thermoelectric fabrics of exceptional mechanical reliability against bending and stretching are demonstrated. • Immersion-coating offers a broadly applicable stretegy to facilely prepare thermoelectric fibers by depositing double-walled carbon nanotube (DWCNT) sheath layers on polymeric fibers. • Polyuerethane passivation of the DWCNT-coated fibers simultaneously improves their intrinsic stretchability by allowing for the individual DWCNTs to reorient themselves and enhances thermoelectric performance by regulating heat transfer along DWCNT sheath. • Plain-weaving the passivated fibers achieves the three-dimensional thermoelectric fabrics with the normalized open-circuit voltage of 8.0 mV K−1 and normalized power per leg of 1.1 × 10−4 μW K−2, and high stretchability of 100%, enabled by woven structure deformability and passiviation-induced fiber elasticity. [ABSTRACT FROM AUTHOR]

This study demonstrates atomic layer deposition (ALD) of an extremely thin Al 2 O 3 layer over n-type Bi 2 Te 2.7 Se 0.3 to alleviate the adverse effects of multiple boundaries on their thermoelectric performance. Multiple boundaries reduce thermal conductivity (κ), but generate electrons, deviating from the optimum carrier concentration. Only one Al 2 O 3 ALD cycle effectively suppresses Te volatilization at the grain boundaries, resulting in a decrease from 5.8 × 1019/cm3 to 3.6 × 1019/cm3 in the electron concentration. Concurrently, the one-cycle-Al 2 O 3 coating produces fine grains, thus inducing numerous boundaries, ultimately suppressing the lattice κ from 0.64 to 0.33 W/m·K. A further increase in the number of Al 2 O 3 cycles leads in a significant rise in the resistance, resulting in degradation of thermoelectric performance. Consequently, the ZT value is increased by 51 % as a result of Al 2 O 3 coating with a single ALD cycle. Our approach offers new insights into the simultaneous reduction of the κ and electron concentration in n-type Bi 2 Te 3 -based materials. • Boundary engineering strategy for thermoelectric materials. • Conformal and thin Al 2 O 3 layer over n-type Bi 2 Te 2.7 Se 0.3 thermoelectric materials. • Facile atomic layer deposition-based approach. • Suppression of Te volatilization at the grain boundaries. • Simultaneous reduction of lattice thermal conductivity and electron concentration. [ABSTRACT FROM AUTHOR]

Abstract The fluoride-based electrostrictive terpolymers are attractive in electromechanical applications. To obtain high electromechanical performance, the terpolymers are hybridized with various fillers such as carbon materials. However, the previous hybrid films have been fabricated with thickness of 20–100 μm due to poor dispersion of the fillers, indicating that these electrostrictive films require high driving voltages of more than 200 V. Herein, we have demonstrated the electrostrictive P(VDF-TrFE-CTFE) thin film hybridized with highly dispersed carbon blacks (CB). The CBs were chemically oxidized to improve the dispersion in the polymer matrix, thus leading to a successful fabrication of the oxidized CB/P(VDF-TrFE-CTFE) hybrid films with 8 μm thickness using solution casting method. The P(VDF-TrFE-CTFE) thin film with 2.75 wt% oxidized CB shows 1.6 fold increased dielectric constant and maximum polarization with low loss factor compared to the pure terpolymer. These enhancements of the 8 μm thick hybrid film enable to yield useful mechanical output at low driving voltages below 100 V. To evaluate the electromechanical performance of hybrid thin films, a unimorph cantilever was fabricated. With a low applied voltage of 90 V, the cantilever based on P(VDF-TrFE-CTFE) thin film with 2.75 wt% oxidized CB produces a displacement twice as high as that of the pure terpolymer. These results provide the first feasibility study of electrostrictive composites for practical applications, particularly human-related applications requiring a low driving voltage. [ABSTRACT FROM AUTHOR]

As commercial interest in flexible power-conversion devices increases, the demand is growing for high-performance alternatives to brittle inorganic thermoelectric materials. As an alternative, we propose a flexible single-walled carbon nanotube (SWCNT)–doped tellurium nanowire (TeNW) hybrid film and, for the first time, rationally engineer the work function of the SWCNTs to effectively filter charge carriers in an energy-dependent manner at the interfaces between the carbon and the inorganic semiconductor. The acid treatment used to control the SWCNT work function allows the interfacial barrier between the SWCNT and the TeNW to be raised and lowered. While the hybrid film with a large barrier of 0.82 eV has a low power factor due to poor carrier transfer, the power factor (3.40 μW m −1 K −2 ) in the film with a lower barrier of 0.23 eV is several times higher than that of either pure TeNW or hybrid film with 0.82 eV due to effective energy filtering effect. The transport characteristics of the hybrid film are explored to quantitatively elucidate the carrier filtering at the SWCNT–TeNW interfaces. These demonstrate the effectiveness of optimizing SWCNT work functions to improve the thermoelectric properties of SWCNT/TeNW hybrid films, thus indicating that this strategy can be applied to flexible/or wearable thermoelectrics. [ABSTRACT FROM AUTHOR]

Abstract: We fabricated a highly stretchable dielectric composite using ionic liquid-based single-walled carbon nanotube gel (IL-SWCNT) as a dielectric filler and polydimethylsiloxane (PDMS) as an elastomer matrix. Transmission electron microscopy images showed that the SWCNTs were highly exfoliated and dispersed in the polymer matrix due to the addition of the ionic liquid (IL). The dielectric constant at 100Hz of the IL-SWCNT/PDMS composite containing 1.6wt% SWCNTs was twice that of the SWCNT/PDMS composite without IL, and the dielectric loss was one fifth that of the SWCNT/PDMS composite. In addition, the elastic modulus of the IL-SWCNT/PDMS composite was significantly lower (0.36MPa at a strain of 20%) and the strain at break was higher (350%) compared to the corresponding values of the SWCNT/PDMS composites due to the plasticizer effects of the IL. These results provide the first feasibility study of the use of IL as both an exfoliation agent and a plasticizer in an effort to simultaneously improve the dielectric and mechanical properties of CNT-filled dielectric elastomers. [Copyright &y& Elsevier]

Abstract: The chemical functionalization and the resulting electrical properties of diamond thin-film transistors (TFTs) modified with organic monolayer films have been explored. Chemical processing steps were developed to produce amine-terminated surfaces in a manner compatible with pre-existing front-surface metal contacts and dielectric protecting layers. The electrical properties of the monolayer-modified TFTs fabricated using different procedures were investigated. Interchanging the order of the functionalization and contact deposition steps changes the devices transconductance by a factor of 100. Electrical measurements of thin-film transistor devices with three different molecular terminating groups show significant changes in threshold voltage that correspond with the expected charges of the functional groups. [Copyright &y& Elsevier]

As practical interest in wearable electronic devices and biomimetic transducers increases, the demand for elastomers with excellent dielectric behavior as well as good mechanical properties is growing. Herein, we propose a new concept of carbon black (CB)-embedded polydimethylsiloxane (PDMS) composites with high dielectric properties via a one-pot process. The dispersant-grafted CB 3wt% /PDMS composites show an enhanced dielectric constant of 1090 with low loss tangent as low as 0.45 at 100 Hz, which is 340- and 145-fold higher than those of the pure PDMS and dispersant-free CB 3wt% /PDMS, respectively. Experimental and simulation studies demonstrate that the dielectric properties of CB/PDMS composites depend on the CB dispersion in the PDMS matrix, which is influenced by the chain length of dispersant and the amount of residual dispersant. As a proof of concept, the capacitive pressure sensor based on CB/PDMS flat structure has been demonstrated, exhibiting 46-fold larger capacitance change than the pure PDMS based sensor. These results indicate that the sensor sensitivity can be significantly improved without additional micro-structuring and the large capacitance change enhances a tolerance to external noise sources. We believe that the elastomers with high dielectric properties show great potential for electronic applications including capacitive pressure sensors that should respond to various input pressures. [ABSTRACT FROM AUTHOR]