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This paper presents the improved thermal property of three-dimensional (3D) graphene network modified polydimethylsiloxane (PDMS) composites. It shows that with a 2 wt.% loading of graphene foams (GF), the thermal conductivity of GF/PDMS composite was successfully increased from 0.19 W/mK to 0.42 W/mK, which is 2.2 times higher than that of neat PDMS. However, if GF was transformed into graphene sheets (GS) by sonication, the thermal conductivity of GS/PDMS was decreased to 0.28 W/mK. The remarkable improvement of the thermal properties is attributed to the 3D interconnected graphene network in GF, which form continuous heat transfer networks. Furthermore, the finite element analysis was conducted to evaluate the effect of GFs in composites, where some parameters such as thickness and thermal conductivity were analyzed and discussed. Our results indicate that the continuous 3D GFs holds great potential as fillers to improve the thermal property of polymer materials.

Abstract: During the last decades, there has been growing interest in using therapeutic messager RNA (mRNA) together with drug delivery systems. Naked, unformulated mRNA is, however, unable to cross the cell membrane and is susceptible to degradation. Here we use graphene quantum dots (GQDs) functionalized with polyethyleneimine (PEI) as a novel mRNA delivery system. Our results show that these modified GQDs can be used to deliver intact and functional mRNA to Huh‐7 hepatocarcinoma cells at low doses and, that the GQDs are not toxic, although cellular toxicity is a problem for these first‐generation modified particles. Functionalized GQDs represent a potentially interesting delivery system that is easy to manufacture, stable and effective., Message delivered! A novel graphene quantum dots based mRNA drug delivery platform was prepared. The results show that these modified GQDs can deliver intact and functional mRNA to Huh‐7 hepatocarcinoma cells at low doses. The transfection efficiency for FGQDs/mRNA complexes was 25 % with a formulation concentration of 4000 ng mRNA/mL, but comparable transfection efficiencies could be achieved at much lower doses if the ratio between carrier and cargo was optimized. This work describes the first steps towards a potentially interesting preparation method for stable and effective mRNA delivery systems.

Graphene attracts great attention due to its excellent properties. However, the mechanical of assembled graphene-based film is usually inferior than its inherent mechanical properties. Herein, we construct a high-performance graphene-based film via vacuum filtration process by using graphene as matrix and hydroxylated Carbon Nanotube (CNT) as reinforcement agent. The synergistic interaction of hydrogen bonds between CNT and graphene Oxide (GO) and ionic bonds between Fe2+ on CNT and GO significantly improve the mechanical properties of free-standing and flexible rGO/CNT film. Scanning Electron Microscopic (SEM) imaging and stress transfer mechanism analysis show that the introduction of CNT can hinder the slippage of GO sheets and promote the stress transfer under the continuous loading. The obtained rGO/CNT film shows high toughness of 3 MJ/m3, which is 3.6 times higher than that of GO sheets. This facile and scalable strategy can pave the way for the fabrication of high-performance graphene-based film in various applications.

In recent years, laser-reduced graphene oxide (LRGO) has received widespread interest, however, the thermal properties of graphene films obtained by laser reduction of GO are rarely reported. In this paper, a pulsed laser was used to reduce the prepared GO films. The obtained LRGO films were characterized by scanning electron microscopy (SEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS). The thermal diffusivity of the LRGO was measured as 7.3 mm2/s, higher than that of GO measured as 5.9 mm2/s. The heating performance of LRGO was performed under different DC voltages and the results show that the temperature can reach up to 91 °C with a response time of 14 s under the voltage of 18 V. The excellent electrothermal performance of LRGO films indicate that the LRGO films are promising as heating elements for various application such as defoggers.

The current development of the electronics system requires capabilities beyond conventional heat transfer approaches. New solutions based on advanced materials are being developed to tackle the current challenges in the development of electronics systems and the nanoscale 2D materials such as graphene are at the centre of the effort to exploit the intrinsic properties of carbon nanomaterials. In this work, we introduce a new concept of graphene-coated copper nanoparticles (G-CuNPs) and explore their multifunctional potential applications in metallic based paste used in electronics. The nanoscale powder was found to present a core/shell structure with the copper particle at its core and a disordered multilayer graphene structure continuously coating its surface. The composition of the particles was analysed, and the presence of the coating was found to provide oxidation protection for the metallic core. Thermogravimetric analysis (TGA) showed an additional role of the G-CuNPs with a reduction effect without the use of an additional reducing agent. Furthermore, due to the combined effect of the size of the particles and the oxidation-free metallic core, Differential Scanning Calorimetry (DSC) analysis revealed a melting depression at temperatures as low as $155 ^{\circ}\mathrm{C}$. Finally, the mechanical properties of the nanocoating were investigated and the results showed an enhanced ductility at the surface of the particles due to the presence of the multi-layered graphene structure, which might be exploited for powder flow and lubrication effect.

A thin film Gold/Platinum/Titanium (Au/Pt/Ti) - based microheater with pectination construction and a four-point probe was fabricated on a silica substrate. A standard lithography process was used to transfer the circuit pattern onto the substrate, and then Au/Pt/Ti was deposited on the substrate by an evaporator. Standard calibration was carried out at various temperatures, which can be obtained the relationship between the temperature and the resistance of the microheater, the results show that the Au/Pt/Ti-based microheater has a good linear relationship between the temperature and the resistance, indicating the microheater can also be used as a temperature sensor. Furthermore, the effects of different input powers, the geometry, and the thickness of the thin-film metals of the microheater were investigated and discussed. Finally, a finite element model was set up to see the temperature distribution of the microheater after the electric potential is applied.

Purpose This study aims to develop a bimodal nano-silver paste with improved mechanical property and reliability. Silicon carbide (SiC) particles coated with Ag were introduced in nano-silver paste to improve bonding strength between SiC and Ag particles and enhance high-temperature stability of bimodal nano-silver paste. The effect of sintering parameters such as sintering temperature, sintering time and the proportion of SiC particles on mechanical property and reliability of sintered bimodal nano-silver structure were investigated. Design/methodology/approach Sandwich structures consist of dummy chips and copper substrates with nickel and silver coating bonded by nano-silver paste were designed for shear testing. Shear strength testing was conducted to study the influence of SiC particles proportions on the mechanical property of sintered nano-silver joints. The reliability of the bimodal nano-silver paste was evaluated experimentally by means of shear test for samples subjected to thermal aging test at 150°C and humidity and temperature testing at 85°C and 85 per cent RH, respectively. Findings Shear strength was enhanced obviously with the increase of sintering temperature and sintering time. The maximum shear strength was achieved for nano-silver paste sintered at 260°C for 10 min. There was a negative correlation between the proportion of SiC particles and shear strength. After thermal aging testing and humidity and temperature testing for 240 h, the shear strength decreased a little. High-temperature stability and high-hydrothermal stability were improved by the addition of SiC particles. Originality/value Submicron-scale SiC particles coated with Ag were used as alternative materials to replace part of nano-silver particles to prepare bimodal nano-silver paste due to its high thermal conductivity and excellent mechanical property.

Thermally conductive materials with electrically insulating properties have been extensively investigated for thermal management of electronic devices. The combined properties of high thermal conductivity, structural stability, corrosion resistance and electric resistivity make hexagonal boron nitride (h-BN) a promising candidate for this purpose. Theoretical studies have revealed that h-BN has a high in-plane thermal conductivity up to 400 - 800 W m−1 K−1 at room temperature. However, it is still a big challenge to achieve high thermally conductive h-BN thick films that are commercially feasible due to its poor mechanical properties. On the other hand, many polymers exhibit advantages for flexibility. Thus, combining the merits of polymer and the high thermal conductivity of h-BN particles is considered as a promising solution for this issue. In this work, orientated PVP/h-BN films were prepared by electrospinning and a subsequent mechanical pressing process. With the optimized h-BN loading, a PVP/h-BN composite film with up to 22 W m−1 K−1 and 0.485 W m−1 K−1 for in-plane and through-plane thermal conductivity can be achieved, respectively. We believe this work can help accelerate the development of h-BN for thermal management applications.

Vertically aligned carbon nanotube arrays (VACNTs) show a great potential for various applications, such as thermal interface materials (TIMs). Besides the thermally oxidized SiO2, atomic layer deposition (ALD) was also used to synthesize oxide buffer layers before the deposition of the catalyst, such as Al2O3, TiO2, and ZnO. The growth of VACNTs was found to be largely dependent on different oxide buffer layers, which generally prevented the diffusion of the catalyst into the substrate. Among them, the thickest and densest VACNTs could be achieved on Al2O3, and carbon nanotubes were mostly triple-walled. Besides, the deposition temperature was critical to the growth of VACNTs on Al2O3, and their growth rate obviously reduced above 650 °C, which might be related to the Ostwald ripening of the catalyst nanoparticles or subsurface diffusion of the catalyst. Furthermore, the VACNTs/graphene composite film was prepared as the thermal interface material. The VACNTs and graphene were proved to be the effective vertical and transverse heat transfer pathways in it, respectively.

With the ever increasing demand for improved thermal management solutions in modern electronic devices, carbon nanotubes (CNTs) have been suggested as a candidate material for thermal interface materials (TIMs). However, the interfacial resistance between CNTs and matching substrate is huge due to poor interaction at the interface. With the help of chemical functionalization, these materials can be exploited to their full potential in TIM applications. By utilizing the epoxy-silane-based monolayers, covalent anchoring can be obtained between the CNTs and target substrate in order to bridge the interface, where high resistances, otherwise, would arise. To adapt CNT arrays to the epoxy chemistry, the CNTs have subsequently been subjected to nitrogen plasma in order to activate them with amino groups. The thermal interfaces were measured, and the thermal resistance was found to be decreased by 5% in comparison with the reference samples.

Vertically aligned carbon nanotubes (VACNTs) were synthesized on different oxide buffer layers using chemical vapor deposition (CVD). The growth of the VACNTs was mainly determined by three factors: the Ostwald ripening of catalyst nanoparticles, subsurface diffusion of Fe, and their activation energy for nucleation and initial growth. The surface roughness of buffer layers largely influenced the diameter and density of catalyst nanoparticles after annealing, which apparently affected the lifetime of the nanoparticles and the thickness of the prepared VACNTs. In addition, the growth of the VACNTs was also affected by the deposition temperature, and the lifetime of the catalyst nanoparticles apparently decreased when the deposition temperature was greater than 600 °C due to their serious Ostwald ripening. Furthermore, in addition to the number of catalyst nanoparticles, the density of the VACNTs was also largely dependent on their activation energy for nucleation and initial growth.

Functional fillers, such as Ag, are commonly employed for effectively improving the thermal or electrical conductivity in polymer composites. However, a disadvantage of such a strategy is that the cost and performance cannot be balanced simultaneously. Therefore, the drive to find a material with both a cost efficient fabrication process and excellent performance attracts intense research interest. In this work, inspired by the core–shell structure, we developed a facile manufacturing method to prepare graphene‐encapsulated Cu nanoparticles (GCPs) through utilizing an improved chemical vapor deposition (CVD) system with a cold wall reactor. The obtained GCPs could retain their spherical shape and exhibited an outstanding thermal stability up to 179 °C. Owing to the superior thermal conductivity of graphene and excellent oxidation resistance of GCPs, the produced GCPs are practically used in a thermally conductive adhesive (TCA), which commonly consists of Ag as the functional filler. Measurement shows a substantial 74.6 % improvement by partial replacement of Ag with GCPs.

In order to meet the ever more demanding requirements of modern thermal management with the increasing high power density, an easy-fabricated laminated graphene film/indium/aluminum (GF/In/Al) composite was developed. The GF was fabricated through assemble graphene oxide (GO) sheets in a layer-by-layer structure and then subjected to graphitization process at high temperature as well as press forming process. The fabricated GF exhibits ultrahigh in-plane thermal conductivity together with good tensile strength. The GF/In/Al laminated composite was fabricated by hot-pressing indium coated GF and Al layers in vacuum environment. The indium layer was easily coated onto the GF due to its low melting point along with good flowing property. The thermal resistance measurements show that the indium bonding possess greater preponderance of reducing contact resistance than without bonding material and thermal conductive adhesive (TCA) bonding, because indium layer could fill the gap between GF and Al layers, and provide more stable connection. The results show that the obtained laminated composite could be potentially used in the thermal management of high power systems.

Thermally reduced graphene oxide/carbon nanotube (rGO/CNT) composite films were successfully prepared by a high-temperature annealing process. Their microstructure, thermal conductivity and mechanical properties were systematically studied at different annealing temperatures. As the annealing temperature increased, more oxygen-containing functional groups were removed from the composite film, and the percentage of graphene continuously increased. When the annealing temperature increased from 1100 to 1400 &deg, C, the thermal conductivity of the composite film also continuously increased from 673.9 to 1052.1 W m&minus, 1 K&minus, 1. Additionally, the Young&rsquo, s modulus was reduced by 63.6%, and the tensile strength was increased by 81.7%. In addition, the introduction of carbon nanotubes provided through-plane thermal conduction pathways for the composite films, which was beneficial for the improvement of their through-plane thermal conductivity. Furthermore, CNTs apparently improved the mechanical properties of rGO/CNT composite films. Compared with the rGO film, 1 wt% CNTs reduced the Young&rsquo, s modulus by 93.3% and increased the tensile strength of the rGO/CNT composite film by 60.3%, which could greatly improve its flexibility. Therefore, the rGO/CNT composite films show great potential for application as thermal interface materials (TIMs) due to their high in-plane thermal conductivity and good mechanical properties.

In many applications like sensors, displays, and defoggers, there is a need for transparent and efficient heater elements produced at low cost. For this reason, we evaluated the performance of graphene-based heaters with from one to five layers of graphene on flexible and transparent polyethylene terephthalate (PET) substrates in terms of their electrothermal properties like heating/cooling rates and steady-state temperatures as a function of the input power density. We found that the heating/cooling rates followed an exponential time dependence with a time constant of just below 6 s for monolayer heaters. From the relationship between the steady-state temperatures and the input power density, a convective heat-transfer coefficient of 60 W&middot, m&minus, 2&middot, &deg, C&minus, 1 was found, indicating a performance much better than that of many other types of heaters like metal thin-film-based heaters and carbon nanotube-based heaters.

High sinter density is desired in powder metallurgy components as the requirement for performance is increasing day‐by‐day. One of the promising ways to achieve improved densification during sintering is through the addition of nanopowder to the conventional micrometer sized metal powder. It is well known that the surface chemistry of the powder has a decisive effect on sintering and consequently the properties of the components produced. Extensive research has hence been conducted to elucidate the surface chemistry and its influence on sintering for powder used in conventional powder metallurgy. Nanopowder, owing to high surface to volume ratio, can contribute to the activation of sintering at lower temperatures and enhance the sinter density. In this context, the surface chemistry of the nanopowder is also expected to exhibit substantial influence on sintering. The present investigation is aimed at establishing a methodology to study the surface chemistry and oxide thickness of nanopowder. For this purpose, iron nanopowder of 3 different size fractions: 35 to 45, 40 to 60, and 60 to 80 nm with core‐shell structure were studied. Different approaches were adopted to evaluate the shell thickness of the iron nanoparticles. The methodology was developed and tried on low alloy steel nanopowder to measure oxide thickness. X‐ray photoelectron spectroscopy, thermogravimetry, and high‐resolution scanning electron microscopy techniques were used to study the nanopowder. Results from different core‐shell models for iron nanopowder were found to be consistent except in the case where depth profiling was taken into account. The results were in agreement with the values obtained from thermogavimetry‐surface area correlation.

In this work, we systematically investigate and compare noninvasive doping of chemical vapor deposition graphene with three molecule dopants through spectroscopy and electrical conductivity techniques. Thionyl chloride shows the smallest improvement in conductivity with poor temporal and thermal stability and nitric acid induces the biggest sheet resistance reduction with modified stability. Molybdenum trioxide doping stands out, after thermal annealing, with both causing a significant sheet-resistance reduction and having superior temporal and thermal stability. These properties make it ideal for applications in advanced electronics. Theoretical studies based on the van der Waals density functional method suggest that cluster formation of molybdenum trioxide underpins the significant reduction in sheet resistance, and the stability, that arises after thermal annealing. Our comparative study clarifies charge transfer doping of graphene and brings understanding of the weak-interaction nature of such non-destructive doping of graphene. Our work also shows that we can use weak chemisorption to tailor the electronic properties of graphene, for example, to improve conductivity. This ability open up possibilities for further use of graphene in electronic interconnects, field effect transistors and other systems.

The currently dominant thermoelectric (TE) materials used in low to medium temperature range contain Tellurium that is rare and mild-toxic. Silicon is earth abundant and environment friendly, but it is characterized by a poor TE efficiency with a low figure of merit, ZT . In this work, we report that ZT of amorphous silicon (a-Si) thin films can be enhanced by 7 orders of magnitude, reaching ∼0.64 ± 0.13 at room temperature, by means of arsenic ion implantation followed by low-temperature dopant activation. The dopant introduction employed represents a highly controllable doping technique used in standard silicon technology. It is found that the significant enhancement of ZT achieved is primarily due to a significant improvement of electrical conductivity by doping without crystallization so as to maintain the thermal conductivity and Seebeck coefficient at the level determined by the amorphous state of the silicon films. Our results open up a new route towards enabling a-Si as a prominent TE material for cost-efficient and environment-friendly TE applications at room temperature.

Herein, we demonstrate a unique supercapacitor composite electrode material that is originated from a sustainable cellulosic precursor via simultaneous one-step carbonization/reduction of cellulose/graphene oxide mats at 800 °C. The resulting freestanding material consists of mechanically stable carbon nanofibrous (CNF, fiber diameter 50–500 nm) scaffolds tightly intertwined with highly conductive reduced graphene oxide (rGO) sheets with a thickness of 1–3 nm. The material is mesoporous and has electrical conductivity of 49 S cm−1, attributed to the well-interconnected graphene layers. The electrochemical evaluation of the CNF/graphene composite electrodes in a supercapacitor device shows very promising volumetric values of capacitance, energy and power density (up to 46 F cm−3, 1.46 W h L−1 and 1.09 kW L−1, respectively). Moreover, the composite electrodes retain an impressive 97% of the initial capacitance over 4000 cycles. With these superior properties, the produced composite electrodes should be the “looked-for” components in compact supercapacitors used for increasingly popular portable electronics and hybrid vehicles.

Poor bonding strength between nanomaterials and cement composites inevitably lead to the failure of reinforcement. Herein, a novel functionalization method for the fabrication of functionalized graphene oxide (FGO), which is capable of forming highly reliable covalent bonds with cement hydration products, and therefore, suitable for use as an efficient reinforcing agent for cement composites, is discussed. The bonding strength between cement and aggregates was improved more than 21 times with the reinforcement of FGO. The fabricated FGO also demonstrated many important features, including high reliability in cement pastes, good dispersibility, and efficient structural refinement of cement hydration products. With the incorporation of FGO, cement mortar samples demonstrated up to 40 % increased early and ultimate strength. Such results make the fast demolding and manufacture of light constructions become highly possible, and show strong advantages on improving productivity, saving cost, and reducing CO2 emissions in practical applications.

The integration of metallic nanoparticlcs (NPs) in nanofluids was found to enhance the thermal properties of the mixture and affect the rheological properties of the base liquid. However, due to their size and electrochemical properties, the added metallic nanoparticlcs have a limited contribution to the thermal transport and their stability hinders further development of such an approach in thermal management. We investigated in this work the effect of the presence of graphene as a coating layer of on copper nanoparticles dispersed in water as a water-based graphene coated copper nanofluid. Electronics microscopy was deployed to investigate the presence and the number of layers of graphene around the metallic nanoparticles. The observed particles were found to have a spherical morphology with a full coating of several layers. The elemental characterization of the NPs showed the presence of graphitic structure confirming the nature of the coating. The thermal properties of the fluid were estimated versus loading fraction of graphene coated nanoparticles and temperature using a hot disk method. An increase of up to 17% was recorded at a concentration of 0.1 w.% at 45deg C. Dynamic Light Scattering and zeta potential were used to investigate the electrochemical properties of the produced nanoparticles. The particles were found to present weak surface charges corresponding to a zeta potential of 6mV that promoted the segregation of the NPs. The rheological properties of the resulted fluids were investigated using viscometer. The NFs were found to have a Newtonian behaviour.

Hexagonal Boron Nitride (h-BN) has been considered as a promising enhancement filler for thermal management due to its high thermal conductivity, structural stability, and super electrical resistivity. Numerus studies have reported using BN as an enhancement filler to achieve high thermally conductive polymer based thermal management materials. However, there are limited data regarding the influence of the flake size of BN sheets to the thermal management property of BN filled composites. In this work, three h-BN size geometries, including microscale h-BN powder, h-BN nanosheets, and a mixture of micro and nanoscale h-BN, were studied regarding its thermal transfer performance. The results show that h-BN nanosheets are able to achieve the highest in-plane thermal conductivity with loading from 0 – 5 wt% while for the through-plane thermal conductivity, all three geometries show similar thermal property when the filler loading less than 5 wt%. Through-plane thermal conductivity exhibits a sudden increase to 5.69 W m−1 K−1 at a loading of 5 wt%..

A novel nano-silver paste with characteristics of sintering at low temperature and operating at high temperature is one of the most promising interconnect materials in the semiconductor industry. This study focuses on the shear strength of sintered multi-scale silver paste synthesized by nano-silver particles, micro-silver particles and submicron silicon carbide particles coated with Ag (SCA). The silver paste was sintered at 250 °C without pressure. The shear strength reaches 9.22 MPa, with 64 wt.% nano-silver particles, 16.5 wt.% micro-silver particles and 1.5 wt.% SCA, respectively. With this, it shows great potential for high power electronics interconnect and cooing applications.

The experimental work presented here, for the first time using electrophoretic technique to fabricate graphene oxide (GO)-based resistive random access memory (RRAM). By using electrophoretic technique, nonvolatile RRAM devices with Aluminum (Al)/GO/Indium tin oxide (ITO) cross-bar sandwich-like structure were fabricated. The fabricated devices show typical bipolar resistant switching behavior with ON/OFF ratio more than 10, retention time more than 102 s, and transition voltage less than 1.7 V. The switching mechanism for the devices is ascribed to the formation and rupture of the conducting filament induced by the diffusion of oxygen ions. The results show that the electrophoretic technique holds great potential for film manufacturing for RRAM.

Bilayer graphene is attractive for digital device applications due to the appearance of a bandgap under application of an electrical displacement field. Controllable and fast synthesis of bilayer graphene on copper by chemical vapor deposition is considered a crucial process from the perspective of industrial applications. Here, a systematic investigation of the influence of process parameters on the growth of bilayer graphene by chemical vapor deposition in a low pressure cold wall reactor is presented. In this study, the initial process stages have been of particular interest. We have found that the influence of the hydrogen partial pressure on synthesis is completely the opposite from that found for traditional tubular quartz CVD in terms of its influence on the graphene growth rate. H2/CH4 ratio was also found to effectively influence the properties of the synthesized bilayer graphene in terms of its atomic structure, whether it be AB-stacked or misoriented. Different pre-treatments of the copper foil, in combination with different annealing processes, were used to investigate the nucleation process with the aim of improving the controllability of the synthesis process. Based on an analysis of the nucleation activity, adsorption-diffusion and gas-phase penetration were employed to illustrate the synthesis mechanism of bilayer graphene on copper foil. After optimization of the synthesis process, large areas, up to 90% of a copper foil, were covered by bilayer graphene within 15 minutes. The total process time is only 45 minutes, including temperature ramp-up and cool-down by using a low pressure cold wall CVD reactor.

Indium-based thermal interface materials are superior in thermal management applications of electronic packaging compared to their polymer-based counterparts. However, pure indium has rather low tensile strength resulting in poor reliability. To enhance the mechanical properties of such a material, a new composite consisting of electrospun randomly oriented continuous polyimide fibres and indium was fabricated. The composite has been characterised by tensile tests and in-situ transmission electron microscopy straining observations. It is shown that the composite's ultimate tensile strength at 20 degrees C is five times higher than that of pure indium, and the strength of the composite exceeds the summation of strengths of the individual components. Furthermore, contrary to most metallic matrix materials, the ultimate tensile strength of the composite decreases with the increased strain rate in a certain range. The chemical composition and tensile fracture of the novel composite have been analysed comprehensively by means of scanning transmission electron microscopy and scanning electron microscopy. A strengthening mechanism based on mutually reinforcing structures formed by the indium and surrounding fibres is also presented, underlining the effect of compressing at the fibre/indium interfaces by dislocation pileups and slip pinning.

This paper presents a novel nanocomposite thermal interface material (Nano-TIM) consisting of a silver coated polyimide network and the indium matrix. One of the potential applications of this Nano-TIM is for heat dissipation in integrated circuits and electronic packaging. The shear strength of the Nano-TIM was investigated with DAGE-4000PSY shear tester. The shear strength of Nano-TIM is 4.5 MPa, which is 15% higher than that of the pure indium thermal interface material. The microstructure of cross-section and fracture surface was studied using Scanning Electron Microscopy (SEM). SEM pictures show a uniform polymer fiber distribution and solid interface between silver coated fibers and indium matrix. The thermal fatigue resistance of the Nano-TIM was evaluated by monitoring the variation of thermal interface resistance during the thermal cycling test (-40 to 125 degrees C). The thermal interface resistance was measured with a commercial xenon flash instrument after 100, 200, 300, 400, 500, and 1000 temperature cydes. The results-of thermal cycling test show that Nano-TIM presented consistent reliability performance with pure indium. Furthermore, the tooling effect of Nano-TIM was demonstrated through measuring the power chip temperature in the die attached structure by using an Infrared Camera. In the test, the Nano-TIM shows a comparable cooling effect to pure indium TIM for die attach applications in electronics packaging.

Boron and phosphorus segregated at grain boundary are investigated by auger electron spectroscopy in high-strength interstitial free steels. The results show that the segregated concentration of phosphorus at grain boundaries reduces greatly with increasing the contents of boron in the high-strength interstitial free steels. The segregation concentration of phosphorus at grain boundary is about 14 at.-% for the boron-free high-strength steel. For the boron-bearing high-strength interstitial free steel, the segregation concentration of phosphorus at grain boundary is about 2–4 at.-%, and the boron concentration at grain boundary is about 5–14 at.-%. The fracture morphology of the steels indicates that almost all grains are intergranular fracture for the boron-free high-strength interstitial free steel. The intergranular fracture grains reduced greatly for the boron-bearing interstitial free steel. The number of low-angle grain boundaries increased with the increasing of boron in the high-strength i...

High density packaging in combination with increased transistor integration inevitably leads to challenging power densities in terms of thermal management. Here, a novel highly thermal conductive and lightweight graphene based thermal interface materials (GT) was developed for thermal management in power devices. Composed by vertically graphene structures, GTs provide a continuous high thermal conductivity phase along the path of thermal transport, which lead to outstanding thermal properties. The highest through-plane thermal conductivity GTs reaches to 1000 W/mK, which is orders of magnitude higher than conventional TIMs, and even outperforms the pure indium by over ten times. In addition, a thin layer of indium metal that coated on the surface of GTs can easily form alloys with many other metals at a relatively low reflow temperature. Therefore, GTs, as an excellent TIM, can provide complete physical contact between two surfaces with minimized the contact resistance. The measured total thermal resistance and effective thermal conductivity by using 300 $\sim 3.7 Kmm$ 2 $ \textit {/W and $\sim 90\mathrm {W} /$ mK, respectively. Such values are significantly higher than the randomly dispersed composites presented above, and show even better thermal performance than pure indium bonding. In addition, GTs has more advantages than pure indium bonding, including low weight (density $ \lt 2\mathrm {g} /cm$}^{3}),$

Copper is generally considered as an electronic packaging material due to its good electrical, thermal properties and relatively low cost. However, copper needs high processing temperature, which negatively affects the electronics reliability. In this paper, silver nanoparticles sintering is evaluated for the propose to decrease the processing temperature of copper. Different fractions of silver nanoparticles were mixed with 10 ×m Cu powder and sintered at temperatures of 250°C, 300°C, 400°C and 500°C, under low pressures 4MPa and 8MPa, and a high pressure of 100MPa for comparison. Densities from 45% to 94% of the density of bulk Cu have been achieved while the thermal and electrical conductivities have been evaluated and reached a value of around 270W/m.K and 1.41×106 S/m.

Tip-growing cells provide a useful model system for studying the underlying mechanisms of plant cell growth. The apical growth of root hairs is dependent on the microfilament skeleton, and auxin is an important regulator of root hair development. We functionally characterized actin bundling proteins AtFIM4 and AtFIM5, which were preferentially expressed in tip-growing cells such as pollen tubes and root hairs. The morphology and length of root hairs in atfim4/atfim5 double mutant line had obvious defects. In addition, we found the growth of root hairs of atfim4/atfim5 double mutant was insensitive to exogenous IAA (indole-3-acetic acid) treatment. So we consider that AtFIM4 and AtFIM5 act together to regulate the growth of root hair in an auxin-insensitive way.

A light-weight, robust and highly thermal conductive copper/graphene film laminated structure was developed as novel heat spreading materials for thermal management applications. The advantages of the copper/graphene film laminated structure lie in its ability to combine both good mechanical properties of metals and excellent thermal properties of graphene film. Graphene films (GFs) were fabricated via self-assembly of graphene oxide (GO) sheets and post-treated by high temperature graphitization and mechanical pressing. The resulted GFs show excellent flexibility and greatly improved tensile strength which is over 3 times higher than commercial PGS. The successful lamination between copper and GFs was realized by indium bonding. Thin indium layers can provide complete physical contact between copper and GFs, and thereby, minimize the contact resistance induced by surface roughness. The measured contact thermal resistance between copper and GFs bonded by indium is in the range of 2-5 Kmm2/W for a working temperature between 20 °C to 100°C. This value is orders magnitude lower than other bonding methods, including direct hot pressing of copper and GFs, tape bonding and thermal conductive adhesive (TCA) bonding. By tailoring the thickness of GFs, desirable laminated composites with optimized thermal conductivity can be obtained, which offers an efficient heat dissipation solution for power driven systems.

Thermal-crosstalk has become a prominent issue in modern electronic. Here, we present a new type of vertically-ordered Boron Nitride (voBN) thin films to address such limitation. voBN has a high anisotropic thermal conductivity with 16 times difference between through-plane and in-plane and can be deposited in room temperature. We studied the thermal properties with 3\omega method and verified with COMSOL Multiphysics simulations. Such characteristic would allow hotspot density to increase by 295%.

International audience; It is demonstrated that a graphene-based film (GBF) functionalized with silane molecules strongly enhances thermal performance. The resistance temperature detector results show that the inclusion of silane molecules doubles the heat spreading ability. Furthermore, molecular dynamics simulations show that the thermal conductivity (κ) of the GBF increased by 15%–56% with respect to the number density of molecules compared to that with the nonfunctionalized graphene substrate. This increase in κ is attributed to the enhanced in-plane heat conduction of the GBF, resulting from the simultaneous increase of the thermal resistance between the GBF and the functionalized substrate limiting cross-plane phonon scattering. Enhancement of the thermal performance by inserting silane-functionalized molecules is important for the development of next-generation electronic devices and proposed application of GBFs for thermal management.

In this work, flexible multifunctionalized carbon nanotube (CNT)-based hybrid nanowires are synthesized through surface modification processes. The good dispersability of the hybrid nanowire in polar solvents facilitates directly making fine patterns with a minimum width of 40 μm for applications of flexible and stretchable circuits (FSCs). The hybrid nanowire possesses a flexible and highly conductive structure which demonstrates stable electro-mechanical properties on polydimethylsiloxane (PDMS) substrates under large structural deformation. FSCs fabricated from the hybrid nanowires show a constant resistance of 0.096 Ω □-1 (equivalent of a resistivity 0.96 Ω μm) under repeated bending cycles. The FSCs also have a low and stable sheet resistance of 0.4 Ω □-1 for strains up to 30%, which is almost four orders of magnitude lower than that of pure CNT samples (1316 Ω □-1). Further improved stretchability and electro-mechanical properties (0.1 Ω □-1, at the strain of 100%) are achieved with a prestrain PDMS substrate. Repeated deformation tests demonstrate the high reliability of FSCs. The observed stable and reliable electro-mechanical performance of FSCs suggests the potential use of the material in wearable and portable electronics. Multifunctionalized hybrid nanowires based on carbon nanotubes are prepared through different surface modification processes. These hybrid nanowires exhibit both the high electrical conductivity of metal and excellent mechanical properties of carbon nanotubes together with good dispersability. Flexible and stretchable electrodes based on the hybrid nanowires demonstrate stable electro-mechanical properties under large structural deformations.

Robust methods for transferring vertically aligned carbon nanotube (CNT) bundles into through-silicon vias (TSVs) are needed since CNT growth is not compatible with complementary metal–oxide–semiconductor (CMOS) technology due to the temperature needed for growing high-quality CNTs (∼700°C). Previous methods are either too complicated or not robust enough, thereby offering too low yields. Here, a facile transfer method using tape at room temperature is proposed and experimentally demonstrated. Three different kinds of tape, viz. thermal release tape, Teflon tape, and Scotch tape, were applied as the medium for CNT transfer. The CNT bundle was adhered to the tape through a flip-chip bonder, and the influence of the bonding process on the transfer results was investigated. Two-inch wafer-scale transfer of CNT bundles was realized with yields up to 97% demonstrated. After transfer, the use of several different polymers was explored for filling the gap between the transferred CNT bundle and the sidewalls of the TSV openings to improve the filling performance. The current–voltage characteristic of the CNT TSVs indicated good electrical performance, and by measuring the via resistance as a function of via thickness, contact resistances could be eliminated and an intrinsic CNT resistivity of 1.80 mΩ cm found.

A facile chemistry route to prepare symmetric poly(L-lactide) (PLLA)-based dendritic L-lysine copolymer (PLLA-d), with a PLLA block as the core and lysine dendrons in the two ends to provide certain density of positive charges, through a divergent method is reported. The polymers were characterized by H-1 NMR, GPC and MALDI-TOF to confirm the well-defined chemical architecture. The study on crystallization behaviour demonstrated that the introduction of the lysine dendron favoured the formation of banded spherulites when compared with the PLLA polymer. The differential scanning calorimetry (DSC) results showed that the lysine dendron disrupted PLLA crystalline region and lowered the melting point and crystallinity of PLLA. The PLLA-d was fabricated into honeycomb films (H-PLLA-d) through the breath-figure method for water contact angle test and in vitro study, with flat PLLA, honeycomb PLLA, and flat PLLA-d films (PLLA, H-PLLA, and F-PLLA-d, respectively) as the controls. The water contact angle test indicated that the hydrophilicity of the PLLA-d film was strongly improved after the incorporation of the lysine dendron into PLLA. The incorporation of the lysine dendron increased the surface zeta potential and decreased the mechanical properties of PLLA. Mouse osteoblastic cell (MC3T3-E1) functions including cell attachment, adhesion, proliferation, and differentiation were investigated on PLLA, H-PLLA, F-PLLA-d and H-PLLA-d films. The results indicated that MC3T3-E1 cell functions were significantly enhanced on F-PLLA-d or H-PLLA films and especially H-PLLA-d ones. This study not only demonstrates a facile approach to fabricate a novel copolymer film (H-PLLA-d), which combines positive charges with honeycomb pores, but also provides a potential biomaterial for bone repair by improving osteoblastic cell functions.

A silver alloyed n-type bismuth telluride (Bi2Te3) thermoelectric (TE) bulk material with nano crystalline structure was studied and characterized in this paper. The Bi2Te3 nanopowders used in this study were first fabricated via a patented explosion based process. Then, the various concentrations of Ag nanoparticles (0-20 wt. %) were added into the Bi2Te3 nanopowders in order to increase the electrical conductivity. Combining the benefits of high electrical conductivity (1.51x10(5) S.m(-1)) and low thermal conductivity (0.441 W.m(-1).K-1), the dimensionless figure of merit (ZT value) of 1.48 for this n-type Bi2Te3 TE material is achieved at 300 K temperature.

In this work a Cu paste consisting in both micro and nanoparticles was produced. The copper paste was produced with different additive weight percentages of Ag coated SiC and sintered for 30min at 500°C under 6,5MPa in N 2 atmosphere. The thermal resistance and composition of the resulting joints was studied. XPS and EDX measurements show no significant oxidation of the Cu after sintering, which is attributed to the combination of reductive agents in the paste and the inert atmosphere. SEM images of cross sections show contacts with no voids between the SiC particles and the copper matrix. Thermal conductivity measurements with laser flash analysis (LFA) show that the additive increases the effective thermal conductivity to more than double of that of the pure copper paste at 2% additive weight percentage, but bigger amounts yield smaller improvements and presumably would eventually worsen it.

We demonstrate the thermal conductivity enhancement of the vertically aligned carbon nanotube (CNT) arrays (from ∼15.5 to 29.5 W/mK, ∼90% increase) by encapsulating outer boron nitride nanotube (BNNT, 0.97 nm-thick with ∼3–4 walls). The heat transfer enhancement mechanism of the coaxial C@BNNT was further revealed by molecular dynamics simulations. Because of their highly coherent lattice structures, the outer BNNT serves as additional heat conducting path without impairing the thermal conductance of inner CNT. This work provides deep insights into tailoring the heat transfer of arbitrary CNT arrays and will enable their broader applications as thermal interface material. MOE (Min. of Education, S’pore)

Heat management is one of the major challenges in modern electronic devices. The higher performance results in a production of greater amount of heat which needs to be efficiently dissipated so as to ensure the electronic devices operational during the period of lifetime. This paper discusses the application of micro- and nano-materials in thermal interface materials (TIM) used for heat management. Effects of type, size and geometry of different fillers were experimentally investigated. The results showed that it is recommended to utilize silver particles compared to copper ones to achieve higher heat dissipation. And the particles of smaller size may enhance the thermal conductivity of elaborated materials.

In this work, we have synthetized a reduced graphene oxide functionalized with silver nanoparticles (G/Ag) by a method developed in our previous study and incorporated it in a hydrogel based on polyvinyl alcohol (PVA) as gelator through a freezing/thawing method. The hydrogel has been tested to catalyze the reduction at room temperature of nitrile group of benzonitrile in water by using glucose as a natural and mild reducing agent.

With increased power density and continued miniaturization, effective thermal dissipation is of significant importance for operational lifetime and reliability of electronic system. Advanced thermal interface materials (TIMs) with excellent thermal performance need to be designed and developed. Here we report novel TIMs consisted of boron nitride (BN) nanofibers and pure indium (In) solder for heat dissipation applications. The BN nanofibers are fabricated by electrospinning process and nitridation treatment. After surface metallization by sputtering, the porous BN film is infiltrated with liquid indium by squeeze casting to form the final solid composites. The new composites show the in-plane and through-plane thermal conductivity respectively of 60 and 20 W/m K. The direction dependence thermal properties of the TIM are due to the anisotropic thermal performance of BN nanofibers in the composite. A low thermal contact resistance of 0.2 K mm2/W is also achieved at the interface between this new composite and copper substrate. These competent thermal properties demonstrate the great potential of the BN–In TIMs in thermal management for electronic system.

A carbon fiber based tin–silver–copper alloy matrix composite (CF-TIM) was developed via electrospinning of a mesophase pitch with polyimide and carbonization at 1000 °C, followed by sputter coating with titanium and gold, and alloy infiltration. The carbonized fibers, in film form, showed a thermal conductivity of ∼4 W m−1 K−1 and the CF-TIM showed an anisotropic thermal conductivity of 41 ± 2 W m−1 K−1 in-plane and 20 ± 3 W m−1 K−1 through-plane. The thermal contact resistance of the CF-TIM was estimated to be below 1 K mm2 W−1. The CF-TIM showed no reduction in effective through-plane thermal conductivity after 1000 temperature cycles, which indicates the potential use of CF-TIM in thermal management applications.

Graphene, the typical two-dimensional sp2 hybridized carbon allotrope, is widely used as a filler for improving the mechanical performance of polymers. However, its superhydrophobic surface makes it a big challenge to obtain stable graphene dispersions, especially in water-borne systems. On the contrary, graphene oxide (GO) shows excellent dispersibility in water, but strong oxidants and acids destroy its structure and degrade its mechanical properties. This largely limits its application in water-borne coatings. In this work, graphene from mechanical exfoliation was surface modified by p-aminophenol derived diazonium salt to achieve a homogenous dispersion. Moreover, the hydroxyl groups in p-aminophenol are able to combine with epoxy resins during the curing process to improve mechanical performance of the final coatings. The result shows that functionalized graphene shows a lower coefficient of friction and better abrasion resistance compared to GO.

Stacking of silicon chips with carbon nanotube (CNT)-based through-silicon vias (TSVs) is experimentally demonstrated. Polymer filling is used to improve the transfer quality of CNTs into pre-etched silicon holes. Special hexagonal CNTs are designed to achieve high aspect ratio (10:1) CNT vias. TSVs filled with closely packed CNTs show a highly linear dc $I$ – $V$ response. The proposed process works at room temperature, which makes it compatible with existing device fabrication flow.

PurposeThe composition and thickness of surface oxide of solder particles is extremely important to the quality of interconnect and reliability of packaged system. The purpose of this paper is to develop an observable measurement to research the issue.Design/methodology/approachAES (Auger electron spectroscopy), XPS (X‐ray photoelectron spectroscopy), TEM (transmission electron microscopy) and STEM (scanning transmission electron microscopy) were employed to examine the oxide layer on microscale solder powders. Conventional techniques and FIB (Focus Ion Beam) were employed for the TEM sample preparation. High angle annular dark field (HAADF) pattern was applied to distinguish the oxide layer and the solder matrix by the contrast of average atomic number. The results were confirmed by AES and XPS measurement.FindingsThe solder powders were exposed to air (70% relative humidity) at 150°C for 0, 120 and 240 h for the accelerated growth of oxide. The surface oxide thickness was 6 nm and 50 nm measured by TEM for 0 h and 120 h samples, respectively. It was found that the increase in surface oxide thickness of solder particles is proportional to the rooting of time. The elemental distribution along the oxide was quantified by line scanning using STEM and the atomic ratio of Sn to O in the oxide layer nearer to the outer, the middle, and the inner (adjacent to the solder matrix) was found to be 1:2, 2:3 and 1:1, respectively. The result was validated using XPS which gave Sn to O ratio of 1:2 at 5 nm depth of surface oxide.Originality/valueThis is the first time FIB technology has been used to prepare TEM specimens for solder particles and TEM pictures shown of their surface oxide layer. Though requiring more care in sample preparation, the measurements by TEM and STEM are believed to be more direct and precise.

Vertically-aligned multiwall carbon nanotubes were deposited on silicon substrate by low pressure chemical vapor deposition (LPCVD), which can be utilized as heat spreaders in high power electronic packaging due to their remarkable thermal conductivity. The infrared emissivity of the vertically aligned multiwall carbon nanotubes was then characterized based on the FLIR SC600 infrared imaging system. The average infrared emissivity of the multiwall carbon nanotubes sample was about 0.92, which agrees well with experimental results reported before. Scanning electron microscopy (SEM) images of the multiwall carbon nanotubes were further analyzed to explain its high emissivity, and the reason can be attributed to the homogeneous sparseness and aligned structure of the vertically aligned multiwall carbon nanotubes.