Joy Tharian

Measurement of thermal conductivity of individual multiwalled carbon nanotubes by the 3-ω method

The thermal conductivity of individual multiwalled carbon nanotubes (outer diameter of ∼45nm) was obtained by employing the 3-ω method. To this end, the third-harmonic amplitude as a response to the applied alternate current at fundamental frequency (ω) is expressed in terms of thermal conductivity. A microfabricated device composed of a pair of metal electrodes 1μm apart is used to place a single nanotube across the designated metal electrodes by utilizing the principle of dielectrophoresis. The multiwalled carbon nanotube was modeled as a one-dimensional diffusive energy transporter and its thermal conductivity was measured to be 650–830W∕mK at room temperature.

Batch fabrication of carbon nanotube bearings

Relative displacements between the atomically smooth, nested shells in multiwalled carbon nanotubes (MWNTs) can be used as a robust nanoscale motion enabling mechanism. Here, we report on a novel method suited for structuring large arrays of MWNTs into such nanobearings in a parallel fashion. By creating MWNT nanostructures with nearly identical electrical circuit resistance and heat transport conditions, uniform Joule heating across the array is used to simultaneously engineer the shell geometry via electric breakdown. The biasing approach used optimizes process metrics such as yield and cycle-time. We also present the parallel and piecewise shell engineering at different segments of a single nanotube to construct multiple, but independent, high density bearings. We anticipate this method for constructing electromechanical building blocks to be a fundamental unit process for manufacturing future nanoelectromechanical systems (NEMS) with sophisticated architectures and to drive several nanoscale transduction applications such as GHz-oscillators, shuttles, memories, syringes and actuators.

Plastic deformation modes of gallium arsenide in nanoindentation and nanoscratching

The mechanical deformation by nanoindentation and scratching of gallium arsenide has been investigated using cross-sectional transmission electron microscopy. Twinning was found to be the main deformation process occurring during indentation while only slip bands and perfect dislocations are observed during scratching. This behavior is explained, in the authors’ experiments, with the strain rate in scratching being hundred times greater than in indentation. Hence, the low indentation velocity allows twins to be nucleated and propagated from surface inhomogeneities, whereas in scratching, the deformation occurs first in front of the indenter and the scratching speed allows only perfect α dislocation to propagate.

Microstructural investigation of lead‐free BGAs soldered with tin‐lead solder

Purpose – The goal of this work is to evaluate the feasibility of soldering tin‐silver‐copper balled BGAs using tin‐lead‐based solder and to investigate the influence of different production parameters on the microstructure of the solder joint.Design/methodology/approach – The soldering of the BGAs was done with various temperature profiles and two conveyor speeds under a nitrogen atmosphere in a full convection oven. One specimen from each temperature/time combination was cross‐sectioned. The cross sections were analysed with optical microscopy, scanning electron microscopy with energy dispersive X‐ray spectroscopy (SEM/EDS) at 30 kV and focused ion beam microscopy (FIB).Findings – The cross sections show a metallurgical bond between the solder and the tin‐silver‐copper balls of the BGA, even at a peak reflow temperature of 210°C. However, the balls alloy only partially with the solder, as the liquidus of tin‐silver‐copper balls is 217°C. As soon as the peak temperature exceeds the liquidus of the ball, ...

Degradation- and Failure Mode Analysis of III-V Nitride Devices

In this work, different failure modes and degradation mechanisms of AlInGaN LEDs were studied under different stress conditions. Another aim of this work was to develop a classification criteria of the LEDs based on initial RBL characteristics and enable the manufacturers ensure better reliability standards.

Site Controlled Nanotube Shell Etching for Interlayer Motion Based NEMS

We present a new method for local control of shell engineering in multiwalled carbon nanotubes (MWNTs) using the Joule-heating induced electric breakdown technique. By modulating the heat dissipation along a nanotube, we can confine its thinning and shell breakdown to occur within localized regions of peak temperatures. The modulation is achieved by using suitably nanomachined heat sinks with different degrees of thermal coupling at different parts of a current-carrying nanotube. Being compatible with CMOS unit processes, this method is expected to be a powerful tool to create batch fabricated nanobearings with sophisticated architectures for use in nanoelectromechanical systems (NEMS).