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As the power consumption and heat generation of electronic devices continue to increase, higher demands are being placed on thermal management materials for heat dissipation. Graphene has been widely used as a thermally conductive filler to improve the thermal conductivity of polymers. However, the poor dispersibility of graphene nanoplates in polymers dramatically limits their practical use in thermal management. A promising strategy to increase the thermal conductivity of polymer composites is to construct interconnected three-dimensional graphene networks. This review summarizes the recent advances in the construction and applications of three-dimensional graphene-based polymer composites and ways to improve their thermal conductivity. The current challenges and prospects for the preparation and applications of these materials are considered.

The contact problem for thermoelectric materials with functionally graded properties is considered. The material properties, such as the electric conductivity, the thermal conductivity, the shear modulus, and the thermal expansion coefficient, vary in an exponential function. Using the Fourier transform technique, the electro-thermoelastic problems are transformed into three sets of singular integral equations which are solved numerically in terms of the unknown normal electric current density, the normal energy flux, and the contact pressure. Meanwhile, the complex homogeneous solutions of the displacement fields caused by the gradient parameters are simplified with the help of Euler’s formula. After addressing the non-linearity excited by thermoelectric effects, the particular solutions of the displacement fields can be assessed. The effects of various combinations of material gradient parameters and thermoelectric loads on the contact behaviors of thermoelectric materials are presented. The results give a deep insight into the contact damage mechanism of functionally graded thermoelectric materials (FGTEMs).

Interfacial thermal resistance (ITR) is a critical property for the performance of nanostructured devices where phonon mean free paths are larger than the characteristic length scales. The affordable, accurate and reliable prediction of ITR is essential for material selection in thermal management. In this work, the state-of-the-art machine learning methods were employed to realize this. Descriptor selection was conducted to build robust models and provide guidelines on determining the most important characteristics for targets. Firstly, decision tree (DT) was adopted to calculate the descriptor importances. And descriptor subsets with topX highest importances were chosen (topX-DT, X = 20, 15, 10, 5) to build models. To verify the transferability of the descriptors picked by decision tree, models based on kernel ridge regression, Gaussian process regression and K-nearest neighbors were also evaluated. Afterwards, univariate selection (UV) was utilized to sort descriptors. Finally, the top5 common descriptors selected by DT and UV were used to build concise models. The performance of these refined models is comparable to models using all descriptors, which indicates the high accuracy and reliability of these selection methods. Our strategy results in concise machine learning models for a fast prediction of ITR for thermal management applications.

The preparation of inorganic coatings on polymer surfaces to improve their performance is a frequently used method. However, the cracking and falling off of the coatings caused by different thermal...

Thermally conductive yet electrically insulating two-dimensional boron nitride nanosheets (BNNSs) have been an ideal choice for the enhanced fillers for improving thermal properties of polymer-based composites. As a nanofiller with an ultrahigh aspect ratio, BNNSs result in conspicuous stacking along the planar direction in the preparation of composites, which results in strong anisotropy of heat transfer and suppresses out-plane thermal dissipation. Thus, it is necessary to facilitate the out-plane heat transfer by building a favorable microstructure. Focusing on the structural design of the nanofiller itself here, we have fabricated a novel three-dimensional nanofiller with improved out-plane connections. Carbon nanotubes (CNTs) have been grown in situ on the surface of BNNSs using chemical vapor deposition. Utilizing these sandwich-like nanostructure BNNSs/CNTs as fillers in the composites, we have assembled diverse sorts of composites, such as flexible films, scleroid 3D mats, painted ink, and viscous grease. Simultaneously, their thermal and insulating properties have been evaluated. A nearly 330% enhancement of out-plane thermal conductivity from the control sample filled with pristine BNNS is achieved, and the composite also exhibits good electrical resistivity of above 7.5 × 10

Flexible, compressible and conductive aerogels were fabricated by incorporating polyaniline (PANI) into bacterial cellulose/chitosan (BC/CH) composites through facile freeze-drying technique. The PANI/BC/CH aerogel fabricated with the BC:CH weight ratio of 1:1 displayed the highest resistance response and showed extremely high sensitivity (1.41 kPa−1), low pressure detection (32 Pa), wide range of pressure deformation and extraordinary stability as a piezoresistive sensor. Polydimethylsiloxane (PDMS) was embedded into PANI/BC/CH aerogels to form PANI/BC/CH PDMS composites that displayed good stability under large mechanical deformation. Furthermore, applications of PANI/BC/CH aerogels and PANI/BC/CH/PDMS composites in piezoresistive sensors for wearable devices were also reported, which could detect human motions, ranging from joint movement to speech recognition, thus suggesting feasibility in health monitoring systems.

Dielectric composites with high thermal conductivity and mechanical strength have great potential in microelectronic packaging. However, conventional composites with excellent thermal conductivity generally possess high electrical conductivity which raises short-circuit problems and unsatisfactory mechanical properties which limits their applications. In this work, dielectric composites with superior thermal and mechanical performance are obtained by fabricating a new type of fillers with three-dimensional (3D) nanostructure. Specially speaking, carbon nanotubes (CNTs) are grown on the surface of boron nitride nanosheets (BNNS) by chemical vapor deposition (CVD), and then utilized as fillers in epoxy resin (BNNS/CNT/Epoxy). The thermal, mechanical and dielectric properties of as-prepared composites are investigated in details. It is shown that the cross-plane thermal conductivity enhancement of the novel composite is as high as 615% compared with the pure epoxy, higher than that of BNNS/Epoxy (380%). Meanwhile, the BNNS/CNT/Epoxy remains a high electrical resistivity of more than 1 Mohm·cm, which is important to avoid short-circuit in electronics. The tensile strength of the composite increases nearly 4 times with the increase of CVD time. These experimental results indicate that the fabricated BNNS/CNT has great potential for reinforcement of composites with wide applications.

Flexible graphene-based paper is promising for wide applications due to its outstanding electrical and thermal conductivities. Graphene flakes with large size are usually known as the key factor for improved paper performance. However, we find that a combination of flakes with large and small sizes is more favorable for both electrical and thermal conductivities than pure large flakes. In this work, flexible paper with enhanced electrical and thermal properties was fabricated by mixing graphene flakes with various size distributions. Large-size graphene (LSG) flakes play the role of a backbone structure, whereas small-size graphene (SSG) flakes fill the voids in the paper without disturbing the high orientation. The physical properties of the as-prepared graphene papers with contents of SSG varying from 0 to 100% have been investigated. It is found that the electrical and thermal conductivities of the paper with 25 wt% SSG are both around 140% higher than that of pure LSG paper. Our results indicate that the lightweight and flexible graphene-based paper has great potential for lateral heat dissipation applications requiring heat movement in a particular direction.

Due to high aspect ratio, excellent thermal conductivity, and electrical insulation, boron nitride exhibits a great potential in the field of electronic packaging. However, its longitudinal thermal conductivity is far poor than horizontal thermal conductivity, which limits its application in a wider field. Herein, a three-dimensional (3D) network structure is constructed by coating boron nitride nanosheets/carbon nanotubes on foam skeleton derived from the commercial polyurethane (PU) (3D BNNS/CNTs). The in-situ grown CNTs on the surface of BNNS produce an interconnected network structure. The resultant 3D skeleton coupled with cross-linked BNNS/CNTs endows it with excellent thermal and mechanical properties. After curing with epoxy resin, the optimized 3D BNNS/CNTs15 %/Epoxy composite obtains a high thermal conductivity of 1.49 W m−1 K−1 at a low loading of 20 wt%, which achieves a thermal conductivity enhancement of 1046 % compared to neat epoxy resin. Meanwhile, the synthesized 3D BNNS/CNTs15 %/Epoxy composite maintains a high electrical resistivity above 1010 Ω m, high elastic modulus of 1.0 GPa and tensile stress of 35 MPa. Thus, this strategy may offer a new insight for constructing advanced packaging materials with excellent thermal and mechanical performances for electronic device.

Molybdenum disulfide (MoS2) has attracted a great deal of attention to its unique properties in recent years. In this work, a scalable and green method was developed for the production of high-quality MoS2 nanosheets using shear-assisted supercritical CO2 exfoliation. Our experiments indicate that high temperature, pressure, and shearing speed are favorable to the exfoliation of MoS2. It is found that over 95% of the exfoliated MoS2 nanosheets are less than 10 layers, among which about 50% are 1–4 layers. Raman spectra and XRD patterns reveal that few-layer MoS2 nanosheets with high planar crystal structure are successfully prepared. Moreover, the produced MoS2 has a better stability in N-methyl-pyrrolidone (NMP) than the bulk MoS2. The concentration of the exfoliated MoS2 in NMP after sedimentation for 7 days is as high as 0.97 mg/ml.

A green shear-assisted rapid depressurization process was developed to produce highly-dispersed palygorskite (Pal) nanorods with abundant silica hydroxyl (Si-OH) groups by using supercritical CO2 (ScCO2) treatment. The disentangled Pal (DPal) nanorods prepared by ScCO2 were obtained with small particle sizes and high dispersity, and confirmed by electron microscopy and particle size analysis. Higher zeta potential and smaller contact angle were achieved for DPal due to the efficient exposure of Si-OH groups, consistent with the better rheological property as well as the higher adsorption of methylene blue (88%) and rhodamine B (86%). The nano viscosity reducer synthesized by DPal achieved a high viscosity reduction rate of 95% with Liaohe heavy oil, attributed to the higher degree of modification due to the increased Si-OH groups and the stronger aggregation effect on wax crystal caused by the nano viscosity reducer. The disentangled and modified Pal demonstrated great potential in dye adsorption and heavy oil viscosity reduction applications.

The scalable production of large quantities of defect-free graphene nanosheets (GNs) with low cost and excellent properties is essential for practical applications. Despite the highly intense research of this area, the mass production of graphene nanosheets with high solubility remains a key challenge. In the present work, we propose a scalable exfoliation process for hydrophilic GNs by ball-milling-assisted supercritical CO2 exfoliation in the presence of poly(vinylpyrrolidone) via the synergetic effect of chemical peeling and mechanical shear forces. The exfoliation difficulty has been reduced due to the intercalation effects of supercritical CO2 molecules. With the ball-milling assistance, the modifier has been introduced onto the edge or/and surface of the GNs. The process results in hydrophilic GNs with little damage to the in-plane structure. The GNs can be dispersed in various solvents with a concentration of up to 0.854 mg/mL (water) and remain stable for several months.

Hexagonal boron nitride nanosheets (BNNS) have been widely investigated as promising fillers for thermal composites because of their high thermal conductivity and electrical insulation, which avoid the short circuit risk effectively when applied in electronics. However, the poor dispersibility and weak interaction with matrix have hindered the further improvement of BNNS based thermal composites. Here, we propose a simple and green amino acid-assisted ball milling exfoliation process for highly hydrophilic glycine (NH2-CH2-COOH)-functionalized BNNS (BNNS-Gly) to improve their dispersion and reduce the thermal interface resistance between fillers and matrix. Three different types of thermal management materials have been prepared by dispersing BNNS-Gly into water, epoxy resin, and cellulose respectively, and their thermal properties have been investigated. As a result, the BNNS-Gly water nanofluid exhibits a 110% increment in thermal conductivity at 1.6 vol% loading compared with pure water. For BNNS-Gly/Epoxy composite, an enhancement of 109% of thermal conductivity compared with pure BNNS/Epoxy is achieved. According to the calculation of the Maxwell-Garnett effective medium theory (EMT) model, the thermal interface resistance between BNNS-Gly and epoxy is reduced by 62%. Besides, the thermal conductivity of BNNS-Gly/cellulose nanofiber (CNF) film reaches up to 16.2 W/mK at 70 wt% loading, which is 1.8-fold of that for BNNS/CNF. In summary, BNNS-Gly fabricated by this work show great advantages in thermal properties compared with widely-used pure BNNS based composites for improved dispersibility and enhanced interaction with matrix.

Facile construction of high-energy Li-ion batteries (LIBs) anode materials with robust heterostructure remains great challenges, especially for the fine integration of active materials with conductive carbon. Here, vertically aligned mixed-phase CoO/Co3O4 nanosheets anchored on wrinkled graphene (CoO/Co3O4/Gra) are controllably synthesized with the assistance of water-removable NaCl-templates through facile freeze-drying and calcination processes. In-depth investigations disclose that the wrinkled graphene induces the bonding with nucleating precursors, and the nanosheets vertically grow along the crystal planes of multilevel-NaCl. The as-formed mesoporous nanosheets-on-network structure endows the hybrids with efficient exposure of mixed-phase CoO/Co3O4 active sites and rapid charge-transfer channels. And the multiple composites can integrate the advantages of their long complements and fully exert their synergistic effects to solve the problems of the single metal oxide electrode. Furthermore, the electrochemical performance of hierarchically mesoporous architecture is beyond that of the single individual structure on account of the sufficient electrode/electrolyte interfaces, rapid Li+ diffusion and electron conduction, and stable structural integrity upon cycling. Accordingly, the capacitive kinetic of Li-storage behaviors is greatly enhanced by these synergistic effects. Serving as a LIBs anode material, the mesoporous CoO/Co3O4/Gra-4 hybrid yields superior reversible capacity (1390 mAh g−1 at 0.1 A g−1), high rate performance (1130 mAh g−1 at 0.2 A g−1), and impressive cycling stability (811 mAh g−1 after 500 cycles at 1 A g−1). This work may inspire the design of high-performance electrodes with advanced 3D hierarchical structures.

Composite material of NiO/CNTs consisting of two-dimensional porous NiO nanosheets threaded by carbon nanotubes was prepared by thermal treatment of Ni(OH) 2 /CNTs obtained from an in-situ hydro-thermal method. The introduction of CNTs during the synthesis processes can effectively prevented the aggregations of NiO nanosheets, and form interpenetrated composite structure. Therefore, porous NiO nanoflakes are threaded by CNTs, leading to the formation of the lightweight composite with different NiO loadings. The as-prepared NiO/CNTs composite is highly porous, effective for microwave absorption. The minimum reflection loss reaches −25.4 dB when the NiO loading is 85 wt% with thickness of 2.0 mm at 10 GHz. This composite material is expected to be a promising candidate as microwave absorbing materials.

Hollow carbon nanospheres (HCNs) with tunable sizes have been successfully prepared by the calcination of hollow copolymer nanospheres. Our findings indicate that compared to the counterpart solid carbon particle, HCNs all achieve substantially enhanced microwave absorption, suggesting that hollow structure plays an important role during microwave absorption. Moreover, further investigation on the effect of different HCNs sizes upon microwave absorption has been conducted. It is found that HCNs with an outer diameter of ∼70 nm and inner diameter of ∼30 nm exhibit the champion EM absorption performance, a minimum reflection loss (RL) of −50.8 dB at 13.5 GHz with a thickness of 1.9 mm, along with the corresponding bandwidth of RL less than −10 dB (90% absorption) covering 4.8 GHz. Notably, such excellent microwave absorption performance, probably as a result of well-matched impedance together with multiple reflection induced by the distinctive hollow structure, demonstrates HCNs to be one of the most competitive carbon-based absorbers to date. More importantly, this study provides an effective strategy to tune the microwave performance via tailoring the sizes of HCNs.

The formation of bis-hexahapto bonds between graphitic surfaces can electronically interconnect the surfaces of carbon materials containing the polybenzenoid ring system and increase the conductivity without introducing a strong perturbation to the in-plane electronic structure. In this paper, we report the use of organometallic chemistry to interconnect the surfaces of small scale graphene nanoplatelets by using a variety of metals and photochemically activated organometallic reagents.

A novel adsorbent based on zeolitic imidazolate framework-67 (ZIF-67, a sort of metal-organic framework) modified bacterial cellulose/chitosan (BC/CH) composite aerogel was prepared through a facile method combining physical mixture, in situ synthesis, and lyophilization. The water stability of CH aerogel was improved by incorporating BC nanofibers instead of using environmentally unfriendly chemical crosslinking agent. The loading rate of ZIF-67 was as high as 46.1% and the BET specific surface area of ZIF-67/BC/CH aerogel reached to 268.7 m2 g−1, which was much larger than that of BC/CH aerogel (8.4 m2 g−1). The as-prepared ZIF-67/BC/CH aerogel was employed to remove heavy metal ions and organic dye in aqueous solution. The adsorption capacities of the composite aerogel for Cu2+ and Cr6+ were 200.6 mg g−1 and 152.1 mg g−1, respectively. Moreover, the adsorption mechanism was investigated by X-ray photoelectron spectroscopy (XPS). Besides, the aerogel also showed almost 100% of removal rate toward active red X-3B through one time of adsorption. Consequently, the ZIF-67/BC/CH aerogel, as a novel and high efficient adsorbent, has a good application potential for wastewater treatment.

Flexible graphite nanoplatelets (GNPs)–copper nanowires (Cu NWs) composites of a sandwich-like structure were prepared by a simple filtration method. Cu NWs were sandwiched between GNPs films (G/NWs/G). The sandwiched structure results in conductivity up to 3.18 × 105 S m−1, higher than the reported graphene based papers and bulk graphite. The performance of the sandwiched papers is further improved to 8.65 × 105 S m−1 through mechanical pressing. Compared to the pure Cu NWs film, the sandwiched composite is oxidation resistant and stable in air, thus promising as candidates for high performance flexible electronics.

Single-walled carbon nanotube (SWNT) thin films provide a unique platform for the development of electronic and photonic devices because they combine the advantages of the outstanding physical properties of individual SWNTs with the capabilities of large area thin film manufacturing and patterning technologies. Flexible SWNT thin film based field-effect transistors, sensors, detectors, photovoltaic cells, and light emitting diodes have been already demonstrated, and SWNT thin film transparent, conductive coatings for large area displays and smart windows are under development. While chirally pure SWNTs are not yet commercially available, the marketing of semiconducting (SC) and metallic (MT) SWNTs has facilitated progress toward applications by making available materials of consistent electronic structure. Nevertheless the electrical transport properties of networks of separated SWNTs are inferior to those of individual SWNTs. In particular, for semiconducting SWNTs, which are the subject of this Account, the electrical transport drastically differs from the behavior of traditional semiconductors: for example, the bandgap of germanium (E = 0.66 eV) roughly matches that of individual SC-SWNTs of diameter 1.5 nm, but in the range 300-100 K, the intrinsic carrier concentration in Ge decreases by more than 10 orders of magnitude while the conductivity of a typical SC-SWNT network decreases by less than a factor of 4. Clearly this weak modulation of the conductivity hinders the application of SC-SWNT films as field effect transistors and photodetectors, and it is the purpose of this Account to analyze the mechanism of the electrical transport leading to the unusually weak temperature dependence of the electrical conductivity of such networks. Extrinsic factors such as the contribution of residual amounts of MT-SWNTs arising from incomplete separation and doping of SWNTs are evaluated. However, the observed temperature dependence of the conductivity indicates the presence of midgap electronic states in the semiconducting SWNTs, which provide a source of low-energy excitations, which can contribute to hopping conductance along the nanotubes following fluctuation induced tunneling across the internanotube junctions, which together dominate the low temperature transport and limit the resistivity of the films. At high temperatures, the intrinsic carriers thermally activated across the bandgap as in a traditional semiconductor became available for band transport. The midgap states pin the Fermi level to the middle of the bandgap, and their origin is ascribed to defects in the SWNT walls. The presence of such midgap states has been reported in connection with scanning tunneling spectroscopy experiments, Coulomb blockade observations in low temperature electrical measurements, selective electrochemical deposition imaging, tip-enhanced Raman spectroscopy, high resolution photocurrent spectroscopy, and the modeling of the electronic density of states associated with various defects. Midgap states are present in conventional semiconductors, but what is unusual in the present context is the extent of their contribution to the electrical transport in networks of semiconducting SWNTs. In this Account, we sharpen the focus on the midgap states in SC-SWNTs, their effect on the electronic properties of SC-SWNT networks, and the importance of these effects on efforts to develop electronic and photonic applications of SC-SWNTs.

We spectroscopically analyze the effect of e-beam deposition of lanthanide metals on the electronic structure and conductivities of films of semiconducting (SC) single-walled carbon nanotubes (SWNTs) in high vacuum. We employ near-infrared and Raman spectroscopy to interpret the changes in the electronic structure of SWNTs on exposure to small amounts of the lanthanides (Ln = Sm, Eu, Gd, Dy, Ho, Yb), based on the behavior of the reference metals (M = Li, Cr) which are taken to exemplify ionic and covalent bonding, respectively. The analysis shows that while the lanthanides are more electropositive than the transition metals, in most cases they exhibit similar conductivity behavior which we interpret in terms of the formation of covalent bis-hexahapto bonds [(η(6)-SWNT)M(η(6)-SWNT), where M = La, Nd, Gd, Dy, Ho]. However, only M = Eu, Sm, Yb show the continually increasing conductivity characteristic of Li, and this supports our contention that these metals provide the first examples of mixed covalent-ionic bis-hexahapto bonds [(η(6)-SWNT)M(η(6)-SWNT), where M = Sm, Eu, Yb].

Boron nitride nanosheets (BNNS) hold the similar two-dimensional structure as graphene and unique properties complementary to graphene, which makes it attractive in application ranging from electronics to energy storage. The exfoliation of boron nitride (BN) still remains challenge and hinders the applications of BNNS. In this work, the preparation of BNNS has been realized by a shear-assisted supercritical CO2 exfoliation process, during which supercritical CO2 intercalates and diffuses between boron nitride layers, and then the exfoliation of BN layers is obtained in the rapid depressurization process by overcoming the van der Waals forces. Our results indicate that the bulk boron nitride has been successfully exfoliated into thin nanosheets with an average 6 layers. It is found that the produced BNNS is well-dispersed in isopropyl alcohol (IPA) with a higher extinction coefficient compared with the bulk BN. Moreover, the BNNS/epoxy composite used as thermal interface materials has been prepared. The introduction of BNNS results in a 313% enhancement in thermal conductivity. Our results demonstrate that BNNS produced by supercritical CO2 exfoliation show great potential applications for heat dissipation of high efficiency electronics.

With the advent of many different forms of graphene (in addition to the long standing interest in fullerenes and carbon nanotubes), the characterization of carbon materials and their degree of conjugation is a particularly important topic in carbon science. We report the application of absorption spectroscopy and conductivity measurements to graphene derivatives and related carbon materials. Reduced graphene oxide (RGO) has been widely studied as a promising material for graphene applications because of its processability, and the same considerations apply to graphene functionalized with octadecylamine (ODA). This study utilizes a direct chemical modification of GO with ODA in the presence of dicyclohexylcarbodiimide to partially regenerate the graphene π-conjugation while producing a material (ODA-G) with excellent solubility in organic solvents. We show that the ODA-G exhibits optical absorptions, which are much stronger than those of GO, and comparable to liquid phase exfoliated graphene and reduced graphene oxide; the optical analysis is unified by the development of an analytical relationship between solid state absorption coefficients and solution state extinction coefficients, which allows the direct comparison of the electronic absorption spectroscopy of films and solutions of carbon materials. We further benchmark the regeneration of the graphenic structure in ODA-G with electrical conductivity measurements.

In this Perspective, we present an overview of recent fundamental studies on the nature of the interaction between individual metal atoms and metal clusters and the conjugated surfaces of graphene and carbon nanotube with a particular focus on the electronic structure and chemical bonding at the metal–graphene interface. We discuss the relevance of organometallic complexes of graphitic materials to the development of a fundamental understanding of these interactions and their application in atomtronics as atomic interconnects, high mobility organometallic transistor devices, high-frequency electronic devices, organometallic catalysis (hydrogen fuel generation by photocatalytic water splitting, fuel cells, hydrogenation), spintronics, memory devices, and the next generation energy devices. We touch on chemical vapor deposition (CVD) graphene grown on metals, the reactivity of its surface, and its use as a template for asymmetric graphene functionalization chemistry (ultrathin Janus discs). We highlight som...

Graphite nanoplatelets (GNPs) were reacted with transition metal (M) carbonyls followed by annealing and compaction to remove the CO ligands and form bis-hexahapto bonds between the GNP surfaces. The M-GNP films (M = Cr, W, Mo) were characterized with Raman spectroscopy and conductivity measurements. It was observed that interconnection of the graphitic faces of GNPs by bis-hexahapto metal coordination resulted in a decrease of electrical conductivity. The complexes offer promise as catalysts and in the fabrication of new 3-D electronic materials.

We report the preparation of organometallic side-wall complexes of single-walled carbon nanotubes (SWNTs) under conditions, which allow the study of both mono- and bis-hexahapto SWNT coordination compounds [(η6-SWNT)Cr(CO)3, (η6-SWNT)Cr(η6-C6H6), (η6-SWNT)2Cr]. The results are interpreted in terms of exohedral and endohedral binding of chromium to the SWNT sidewalls and ligand competition reactions suggest that endohedral binding provides a very stable and kinetically inert mode of organometallic bonding. We demonstrate that the electrical conductivity of SWNT thin films are significantly enhanced by side-wall bonding to Group 6 transition metals (M = Cr, Mo, and W), which serve to reduce the inter-carbon nanotube junction electrical resistance by the formation of SWNT interconnects [(η6-SWNT)2M].

A high-sensitivity mechano-luminescent sensor was fabricated on the basis of piezoelectric/electroluminescent composites. The working principle of this mechano-luminescent sensor was elucidated by analyzing the relationship between the piezoelectric-induced charges and the electroluminescent effects. When a stress is applied on the piezoelectric layer, electrical charges will be induced at both the top and bottom sides of the piezoelectric layer. The induced electrical charges will lead to a light output from the electroluminescent layer, thus producing a mechano-luminescence effect. By increasing the vibration strength or frequency applied, the mechano-luminescence output can be obviously enhanced. Mechano-luminescence sensors have potential in smart stress-to-light devices, such as foot-stress-distribution-diagnosis systems and dynamic-load-monitors for bridge hanging cables.

The in-plane alignment of graphite nanoplatelets (GNPs) in thin thermal interface material (TIM) layers suppresses the though-plane heat transport thus limiting the performance of GNPs in the geometry normally required for thermal management applications. Here we report a disruption of the GNP in-plane alignment by addition of spherical microparticles. The degree of GNP alignment was monitored by measurement of the anisotropy of electrical conductivity which is extremely sensitive to the orientation of high aspect ratio filler particles. Scanning Electron Microscopy images of TIM layer cross-sections confirmed the suppression of the in-plane alignment. The hybrid filler formulations reported herein resulted in a synergistic enhancement of the through-plane thermal conductivity of GNP/Al2O3 and GNP/Al filled TIM layers confirming that the control of GNP alignment is an important parameter in the development of highly efficient GNP and graphene-based TIMs.

The formation of covalent bonds to single-walled carbon nanotube (SWNT) or graphene surfaces usually leads to a decrease in the electrical conductivity and mobility as a result of the structural rehybridization of the functionalized carbon atoms from sp(2) to sp(3). In the present study, we explore the effect of metal deposition on semiconducting (SC-) and metallic (MT-) SWNT thin films in the vicinity of the percolation threshold and we are able to clearly delineate the effects of weak physisorption, ionic chemisorption with charge transfer, and covalent hexahapto (η(6)) chemisorption on these percolating networks. The results support the idea that for those metals capable of forming bis-hexahapto-bonds, the generation of covalent (η(6)-SWNT)M(η(6)-SWNT) interconnects provides a conducting pathway in the SWNT films and establishes the transition metal bis-hexahapto organometallic bond as an electronically conjugating linkage between graphene surfaces.

We report the response of the electrical conductivity of semiconducting single-walled carbon nanotube (SWNT) thin films on exposure to metal vapors of the early lanthanides under high vacuum conditions. We attribute the strongly enhanced conductivities observed on deposition of samarium and europium to charge transfer from the metals to the SWNT backbone, thereby leading to the first examples of mixed covalent-ionic bis-hexahapto bonds [(η(6)-SWNT)M(η(6)-SWNT), where M = Sm, Eu].

Thermal interface materials (TIMs) are crucial components of high density electronics and the high thermal conductivity of graphite makes this material an attractive candidate for such applications. We report an investigation of the in-plane and through-plane electrical and thermal conductivities of thin thermal interface layers of graphite nanoplatelet (GNP) based composites. The in-plane electrical conductivity exceeds its through-plane counterpart by three orders of magnitude, whereas the ratio of the thermal conductivities is about 5. Scanning electron microscopy reveals that the anisotropy in the transport properties is due to the in-plane alignment of the GNPs which occurs during the formation of the thermal interface layer. Because the alignment in the thermal interface layer suppresses the through-plane component of the thermal conductivity, the anisotropy strongly degrades the performance of GNP-based composites in the geometry required for typical thermal management applications and must be taken into account in the development of GNP-based TIMs.

Chemically modified single-walled carbon nanotubes (SWNTs) with varying degrees of functionalization were utilized for the fabrication of SWNT thin film catalyst support layers (CSLs) in polymer electrolyte membrane fuel cells (PEMFCs), which were suitable for benchmarking against the US DOE 2017 targets. Use of the optimum level of SWNT -COOH functionality allowed the construction of a prototype SWNT-based PEMFC with total Pt loading of 0.06 mg(Pt)/cm²--well below the value of 0.125 mg(Pt)/cm² set as the US DOE 2017 technical target for total Pt group metals (PGM) loading. This prototype PEMFC also approaches the technical target for the total Pt content per kW of power (0.125 g(PGM)/kW) at cell potential 0.65 V: a value of 0.15 g(Pt)/kW was achieved at 80°C/22 psig testing conditions, which was further reduced to 0.12 g(Pt)/kW at 35 psig back pressure.

We demonstrate the ability of first row transition metals to form electrically conducting interconnects between semiconducting single-walled carbon nanotubes (SWNTs) by constructive rehybridization between sidewall benzene rings as a result of the formation of bis-hexahapto-metal-bonds [(η6-SWNT)M(η6-SWNT)], which bridge adjacent SWNTs. Metal deposition on SWNT films enhances the conductivity by three distinct mechanisms: physisorption of gold leads to the formation of a non-interacting gold film and a monotonic conductivity increase; ionic chemisorption of lithium strongly increases the conductivity due to charge transfer to the SWNTs; covalent chemisorption of first row transition metals leads to an abrupt change in conductivity due to formation of (η6-SWNT)M(η6-SWNT) interconnects.

Clear magneto-light output is obtained from a fabricated three-phase composite of magnetostrictive, piezoelectric, and electroluminescent materials. Electrical charges, attributable to the magnetoelectric effect, are induced when a magnetic field is applied to the magnetostrictive/piezoelectric layers. These induced electrical charges result in a light signal emanating from the electroluminescent layer, thereby accomplishing a magneto-light effect. Increasing the strength of the applied ac magnetic field or the number of series-connected piezoelectric layers produces an enhanced magneto-light output. The magneto-light composite has potential applications in magnetic resonance imaging, optical monitoring of magnetic fields, magnetic/light sensing, and transducer technologies.