Superdiffusive Thermal Transport in Polymer-Grafted Nanoparticle Melts.

In contrast to normal diffusion processes, thermal conduction in one-dimensional systems is anomalous. The thermal conductivity is found to vary with the length as κ∼L^{α}(α>0), but there is a long-standing debate on the value α. Here, we present a canonical example of this behavior in polymer-grafted spherical nanoparticle (GNP) melts at fixed grafting density and nanoparticle radius.

Enhanced thermal conductivity in copolymerized polyimide.

From flexible electronics and multifunctional textiles to artificial tissues, polymers penetrate nearly every aspect of modern technology. High thermal conductivity of polymers is often required in their applications, where heat dissipation is crucial to maintain product reliability and functionality. However, the intrinsic thermal conductivity of bulk polymers is largely hindered by the randomly coiled and entangled chain conformation.

Coupling Electronic and Phonon Thermal Transport in Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) Nanofibers.

The thermal transport of Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) nanofiber is contributed by the electronic component of thermal conduction and the phonon component of thermal conduction. The relationship between the electrical conductivity and thermal conductivity of these conducting polymers is of great interest in thermoelectric energy conversation. In this work, we characterized the axial electrical conductivities and thermal conductivities of the single PEDOT:PSS nanofibers and found that the Lorenz number is larger than Sommerfeld value at 300 K.

Thermal Conductivity of VO Nanowires at Metal-Insulator Transition Temperature.

Vanadium dioxide (VO) nanowires endowed with a dramatic metal-insulator transition have attracted enormous attention. Here, the thermal conductance of VO nanowires with different sizes, measured using the thermal bridge method, is reported. A size-dependent thermal conductivity was observed where the thicker nanowire showed a higher thermal conductivity.

Thermal manipulation and thermal rectification in π-stacked organic nanowires.

Thermal manipulation in nanowires (NWs) is of great significance for NW-based applications in the area of heat management and energy harvesting. Here, we experimentally demonstrate thermal conductivity manipulation and thermal rectification in π-stacked metallophthalocyanine (MPcs) NWs. By electron beam (E-beam) irradiation with a controllable dose, the thermal conductance of MPcs NWs can be continuously tuned to the desired values.

Surface contacts strongly influence the elasticity and thermal conductivity of silica nanoparticle fibers.

Granular materials are often encountered in science and engineering disciplines, in which controlling the particle contacts is one of the critical issues for the design, engineering, and utilization of their desired properties. The achievable rapid fabrication of nanoparticles with tunable physical and chemical properties facilitates tailoring the macroscopic properties of particle assemblies through contacts at the nanoscale. Models have been developed to predict the mechanical properties of macroscopic granular materials; however, their predicted power in the case of nanoparticle assemblies is still uncertain.

Thermal conductivity of one-dimensional organic nanowires: effect of mass difference phonon scattering.

We report the thermal conductivity of π-stacked metallophthalocyanine nanowires using the thermal bridge method. In the temperature range of 20-300 K, the thermal conductivity of copper phthalocyanine nanowires (CuPc NWs) and iron phthalocyanine nanowires (FePc NWs) increases with temperature and reaches a peak value at around T = 40 K, then decreases at a higher temperature following T behavior. For three FePc NWs, the peak values are 7.

Epitaxial nucleation and lateral growth of high-crystalline black phosphorus films on silicon.

Black phosphorus (BP) is a promising two-dimensional layered semiconductor material for next-generation electronics and optoelectronics, with a thickness-dependent tunable direct bandgap and high carrier mobility. Though great research advantages have been achieved on BP, lateral synthesis of high quality BP films still remains a great challenge. Here, we report the direct growth of large-scale crystalline BP films on insulating silicon substrates by a gas-phase growth strategy with an epitaxial nucleation design and a further lateral growth control.

Thermal conductivity of VO nanowires and their contact thermal conductance.

Vanadium pentoxide (V2O5)-based composites show outstanding performances as cathode materials in lithium-ion batteries. However, their inferior thermal conductivity restricts the heat dissipation through the cathode electrode. In this study, we measured the thermal conductivity of V2O5 nanowires using the thermal bridge method and found that their thermal conductivity is 3.

Conformal hexagonal-boron nitride dielectric interface for tungsten diselenide devices with improved mobility and thermal dissipation.

Relatively low mobility and thermal conductance create challenges for application of tungsten diselenide (WSe) in high performance devices. Dielectric interface is of extremely importance for improving carrier transport and heat spreading in a semiconductor device. Here, by near-equilibrium plasma-enhanced chemical vapour deposition, we realize catalyst-free growth of poly-crystalline two-dimensional hexagonal-boron nitride (2D-BN) with domains around 20~ 200 nm directly on SiO/Si, quartz, sapphire, silicon or SiO/Si with three-dimensional patterns at 300 °C.

A Paper-Like Inorganic Thermal Interface Material Composed of Hierarchically Structured Graphene/Silicon Carbide Nanorods.

With the increasing integration of devices in electronics fabrication, there are growing demands for thermal interface materials (TIMs) with high through-plane thermal conductivity for efficiently solving thermal management issues. Graphene-based papers consisting of a layer-by-layer stacked architecture have been commercially used as lateral heat spreaders; however, they lack in-depth studies on their TIM applications due to the low through-plane thermal conductivity (<6 W m K). In this study, a graphene hybrid paper (GHP) was fabricated by the intercalation of silicon source and the in situ growth of SiC nanorods between graphene sheets based on the carbothermal reduction reaction.

Tailoring the Thermal and Mechanical Properties of Graphene Film by Structural Engineering.

Due to substantial phonon scattering induced by various structural defects, the in-plane thermal conductivity (K) of graphene films (GFs) is still inferior to the commercial pyrolytic graphite sheet (PGS). Here, the problem is solved by engineering the structures of GFs in the aspects of grain size, film alignment, and thickness, and interlayer binding energy. The maximum K of GFs reaches to 3200 W m K and outperforms PGS by 60%.

Elastic Modulus and Thermal Conductivity of Thiolene/TiO Nanocomposites.

Metal oxide based polymer nanocomposites find diverse applications as functional materials, and in particular thiol-ene/TiO nanocomposites are promising candidates for dental restorative materials. The important mechanical and thermal properties of the nanocomposites, however, are still not well understood. In this study, the elastic modulus and thermal conductivity of thiol-ene/TiO nanocomposite thin films with varying weight fractions of TiO nanoparticles are investigated by using Brillouin light scattering spectroscopy and 3ω measurements, respectively.

Measuring the thermal conductivity and interfacial thermal resistance of suspended MoS using electron beam self-heating technique.

Establishment of a new technique or extension of an existing technique for thermal and thermoelectric measurements to a more challenging system is an important task to explore the thermal and thermoelectric properties of various materials and systems. The bottleneck lies in the challenges in measuring the thermal contact resistance. In this work, we applied electron beam self-heating technique to derive the intrinsic thermal conductivity of suspended Molybdenum Disulfide (MoS) ribbons and the thermal contact resistance, with which the interfacial thermal resistance between few-layer MoS and Pt electrodes was calculated.

Thermal Conductivity of Polymers and Their Nanocomposites.

Polymers are usually considered as thermal insulators, and their applications are limited by their low thermal conductivity. However, recent studies have shown that certain polymers have surprisingly high thermal conductivity, some of which are comparable to that in poor metals or even silicon. Here, the experimental achievements and theoretical progress of thermal transport in polymers and their nanocomposites are outlined.

Thermal conductivity of suspended few-layer MoS.

Modifying phonon thermal conductivity in nanomaterials is important not only for fundamental research but also for practical applications. However, the experiments on tailoring thermal conductivity in nanoscale, especially in two-dimensional materials, are rare due to technical challenges. In this work, we demonstrate the in situ thermal conduction measurement of MoS and find that its thermal conductivity can be continuously tuned to a required value from crystalline to amorphous limits.

Direct growth of nanographene at low temperature from carbon black for highly sensitive temperature detectors.

Graphene has attracted tremendous research interest owing to its widespread potential applications. However, these applications are partially hampered by the lack of a general method to produce high-quality graphene at low cost. Here, to the best of our knowledge, we use low-cost solid carbon allotropes as the precursor in plasma-enhanced chemical vapor deposition (PECVD) for the first time, and find that the hydrogen plasma and reaction temperature play a crucial role in the process.

Phonon thermal conduction in novel 2D materials.

Recently, there has been increasing interest in phonon thermal transport in low-dimensional materials, due to the crucial importance of dissipating and managing heat in micro- and nano-electronic devices. Significant progress has been achieved for one-dimensional (1D) systems, both theoretically and experimentally. However, the study of heat conduction in two-dimensional (2D) systems is still in its infancy due to the limited availability of 2D materials and the technical challenges of fabricating suspended samples that are suitable for thermal measurements.

Superior thermal conductivity in suspended bilayer hexagonal boron nitride.

We reported the basal-plane thermal conductivity in exfoliated bilayer hexagonal boron nitride h-BN that was measured using suspended prepatterned microstructures. The h-BN sample suitable for thermal measurements was fabricated by dry-transfer method, whose sample quality, due to less polymer residues on surfaces, is believed to be superior to that of PMMA-mediated samples. The measured room temperature thermal conductivity is around 484 Wm(-1)K(-1)(+141 Wm(-1)K(-1)/ -24 Wm(-1)K(-1)) which exceeds that in bulk h-BN, providing experimental observation of the thickness-dependent thermal conductivity in suspended few-layer h-BN.

Large thermoelectricity via variable range hopping in chemical vapor deposition grown single-layer MoS2.

Ultrathin layers of semiconducting molybdenum disulfide (MoS2) offer significant prospects in future electronic and optoelectronic applications. Although an increasing number of experiments bring light into the electronic transport properties of these crystals, their thermoelectric properties are much less known. In particular, thermoelectricity in chemical vapor deposition grown MoS2, which is more practical for wafer-scale applications, still remains unexplored.

Length-dependent thermal conductivity in suspended single-layer graphene.

Graphene exhibits extraordinary electronic and mechanical properties, and extremely high thermal conductivity. Being a very stable atomically thick membrane that can be suspended between two leads, graphene provides a perfect test platform for studying thermal conductivity in two-dimensional systems, which is of primary importance for phonon transport in low-dimensional materials. Here we report experimental measurements and non-equilibrium molecular dynamics simulations of thermal conduction in suspended single-layer graphene as a function of both temperature and sample length.

Electrochemical delamination of CVD-grown graphene film: toward the recyclable use of copper catalyst.

The separation of chemical vapor deposited (CVD) graphene from the metallic catalyst it is grown on, followed by a subsequent transfer to a dielectric substrate, is currently the adopted method for device fabrication. Most transfer techniques use a chemical etching method to dissolve the metal catalysts, thus imposing high material cost in large-scale fabrication. Here, we demonstrate a highly efficient, nondestructive electrochemical route for the delamination of CVD graphene film from metal surfaces.

Graphene for controlled and accelerated osteogenic differentiation of human mesenchymal stem cells.

Current tissue engineering approaches combine different scaffold materials with living cells to provide biological substitutes that can repair and eventually improve tissue functions. Both natural and synthetic materials have been fabricated for transplantation of stem cells and their specific differentiation into muscles, bones, and cartilages. One of the key objectives for bone regeneration therapy to be successful is to direct stem cells' proliferation and to accelerate their differentiation in a controlled manner through the use of growth factors and osteogenic inducers.

Toward high throughput interconvertible graphane-to-graphene growth and patterning.

We report a new route to prepare high quality, monolayer graphene by the dehydrogenation of graphane-like film grown by plasma-enhanced chemical vapor deposition. Large-area monolayer graphane-like film is first produced by remote-discharged radio frequency plasma beam deposition at 650 °C on Cu/Ti-coated SiO(2)-Si. The advantages of the plasma deposition include very short deposition time (<5 min) and a lower growth temperature of 650 °C compared to the current thermal chemical vapor deposition approach (1000 °C).