Murali Murugesan

Functionalization mediates heat transport in graphene nanoflakes.

The high thermal conductivity of graphene and few-layer graphene undergoes severe degradations through contact with the substrate. Here we show experimentally that the thermal management of a micro heater is substantially improved by introducing alternative heat-escaping channels into a graphene-based film bonded to functionalized graphene oxide through amino-silane molecules. Using a resistance temperature probe for in situ monitoring we demonstrate that the hotspot temperature was lowered by ∼28 °C for a chip operating at 1,300 W cm−2. Thermal resistance probed by pulsed photothermal reflectance measurements demonstrated an improved thermal coupling due to functionalization on the graphene–graphene oxide interface. Three functionalization molecules manifest distinct interfacial thermal transport behaviour, corroborating our atomistic calculations in unveiling the role of molecular chain length and functional groups. Molecular dynamics simulations reveal that the functionalization constrains the cross-plane phonon scattering, which in turn enhances in-plane heat conduction of the bonded graphene film by recovering the long flexural phonon lifetime.

A carbon fiber solder matrix composite for thermal management of microelectronic devices

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.

Reliability investigation of nano-enhanced thermal conductive adhesives

This paper deals with silver (Ag) coated silicon carbide nanoparticles (SiC@Ag NPs) for thermal conductive interconnect and die attach applications. The development of thermal interface materials with high thermal conductivity and excellent reliability has already been identified by the microsystems industry as one of the major bottlenecks hindering further integration at packaging level. In this paper, a new nano-enhanced high thermal conductive adhesive (TCA) has been developed and characterized. The composition is based on a high temperature conductive epoxy matrix and micro-sized Ag flakes. Efficient heat transfer is achieved through adding SiC@Ag NPs into the material. This special nanoparticle could increase thermal conductivity of the entire system (compared to no addition of nanoparticles) while having little effect on the electrical performance. To achieve these special double-layer nanoparticles, a new method was developed to do the silver plating. Transmission Electron Micro-scope (TEM) results indicate that a consistent silver layer was deposited homogeneously on the surface of SiC. Thermal conductivity test was performed after the SiC@Ag NPs were added into TCA. The results show that no obvious changes of thermal conductivity were observed when the ratio of nanoparticles increased from 0 to 1%, and the value is about 4.0w/(m*K). However, a significant improvement of thermal conductivity (8.3 w/(m*K)) was observed when the weight percentage of nano-particles reached to 3%. This increment was 100% higher than the case without nanoparticles. Further, electrical properties and reliability characterization were also studied in this work. The bulk resistivity results showed that adding a small amount of nanoparticles had little effect on the electrical performance of the entire system. The effects of addition of nanoparticles on the viscosity of the TCA were also measured.

Detecting single molecules inside a carbon nanotube to control molecular sequences using inertia trapping phenomenon

Here we show the detection of single gas molecules inside a carbon nanotube based on the change in resonance frequency and amplitude associated with the inertia trapping phenomenon. As its direct implication, a method for controlling the sequence of small molecule is then proposed to realize the concept of manoeuvring of matter atom by atom in one dimension. The detection as well as the implication is demonstrated numerically with the molecular dynamics method. It is theoretically assessed that it is possible for a physical model to be fabricated in the very near future.

Understanding noninvasive charge transfer doping of graphene: a comparative study

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.

Molecular dynamics simulation of inertial trapping-induced atomic scale mass transport inside single walled carbon nanotubes

The forced transverse vibration of a single-walled carbon nanotube (SWNT) embedded with atomic-size particles was investigated using molecular dynamic simulations. The particles inside the cylindrical cantilever can be trapped near the antinodes or at the vicinity of the SWNT tip. The trapping phenomenon is highly sensitive to the external driving frequencies such that even very small changes in driving frequency can have a strong influence on the probability of the location of the particle inside the SWNT. The trapping effect could potentially be employed to realize the atomic scale control of particle position inside an SWNT via the finite adjustment of the external driving frequency. It may also be suggested that the trapping phenomenon could be utilized to develop high-sensitive mass detectors based on a SWNT resonator.