M. K. Samani

Rapid fabrication of a novel Sn–Ge alloy: structure–property relationship and its enhanced lithium storage properties

A rapid solidification and high throughput melt spinning process is developed for the fabrication of new Sn–Ge alloys as anodes for high capacity lithium-ion batteries. Compared to pure micron-sized Sn and Ge, the alloy possesses enhanced lithium storage properties. High, reversible and stable capacities of over 1000 mA h g−1 are maintained over 60 cycles at 0.1 C. A good rate capability of 500 mA h g−1 at 5 C is also achieved, making it very attractive for very fast charge/discharge applications. More remarkably, it has a tap density of 2.05 g cm−3 and thus high volumetric capacities of 2050 mA h cm−3 at 0.1 C and 1025 mA h cm−3 at 5 C. The electrode was investigated via ex situ XRD, EXAFS and TEM at various cut-off voltages during the first cycle and after the first cycle to establish the structure–property relationship. The Sn–Ge alloy is observed to undergo a transformation from the crystalline Sn–Ge alloy into phase separated nanocrystalline Sn in an amorphous Ge matrix. The excellent lithium storage properties exhibited by Sn–Ge are attributed to the synergistic effect between the phases and the phase transformation occurred.

Thermal Conductivity of CrAlN and TiAlN Coatings Deposited by Lateral Rotating Cathode Arc

CrAlN and TiAlN coatings were deposited on stainless steel substrates by a lateral rotating cathode arc technique. The composition and structure of the as-deposited coatings were analyzed by energy dispersive analysis of X-rays (EDX) and X-ray diffraction (XRD). Thermal conductivity of these coatings is measured using pulsed photothermal reflectance (PPR) technique at room temperature. The measured thermal conductivity of pure TiN coating is around 11.9 W/mK. With increasing Al content, thermal conductivity of the TiAlN coatings decreased significantly and a minimum value of about 4.63 W/mK was obtained at the Al/Ti atomic ratio around 0.72. With the increase of Al content, thermal conductivity of CrAlN coatings decreased slightly but consistently. The variation of thermal conductivity in these coatings is explained in term of phonon scattering on grain boundaries and local strain centers caused by lattice distortion. In comparison with TiAlN, thermal conductivity of CrAlN coatings was evidently lower, which could be partially responsible for their better performance in high speed machining applications as observed in our previous work.

Molecular dynamic simulation of diamond/silicon interfacial thermal conductance.

Non-equilibrium molecular dynamic simulation was employed to investigate the interfacial thermal conductance between diamond and silicon substrate. The interfacial thermal conductance was computed based on Fouriers law. The simulation was done at different temperature ranges and results show that the interfacial thermal conductance between diamond-silicon is proportional to temperature and increases with temperature even above Debye temperature of silicon. Enhancement of thermal boundary conductance with temperature is attributed to inelastic phonon-phonon scattering at the interface. The system size dependence of interfacial thermal conductance was also examined. We found that thermal transport is a function of the system size when the size of system is smaller than the phonon mean free path and increases with the size of structure. We also simulated the effect of interface defect on phonon scattering and subsequently thermal conductance. The results also show that interface defect enhances acoustic pho...

Carbon based multi-functional materials towards 3D system integration. Application to thermal and interconnect management

In order to meet the demands of increasing package density and miniaturization of devices without compromising performance, the most challenging issues to tackle are thermal and interconnect management. In this paper, we will first understand the interfacial transport between Si and Carbon for better system integration and discuss how novel carbon films can be used for thermal extraction. Second, we will show how carbon nanotubes can be used as interconnects using a flip chip approach as well as potential radio frequency applications.

Study on thermal boundary conductance between diamond and amorphous carbon

Thermal boundary conductance at the interface of diamond-amorphous carbon has been calculated using non-equilibrium molecular dynamic simulation. In particular, we describe the effect of solid stiffness, which associated with sp3 hybridization ratio of amorphous carbon, on thermal boundary conductance. The result shows that by increasing the sp3 hybridization ratio of amorphous carbon, thermal boundary conductance between diamond and amorphous carbon increases.