Research Interests

Postdoc/grad student positions are available in my group. The ideal candidate will have hands on experience with TEM and strong background in electronic materials/devices.  Send me your CV highlighting these experiences

 

Mechanics & Microscopy of Materials & Devices

 Our broader research interest is in the fundamentals of mechanics and physics of materials at multiple length-scales. Specifically, we study the effects of defects in electronic and engineering materials using high resolution microscopy. Recent interests encompass ionizing radiation effects on electronic devices, role of interfaces in wide bandgap devices, defect-electron interactions in nuclear, structural and battery electrode materials; multi-scale defects-property in nuclear graphite and developing experimental testbeds for in-situ (mainly TEM) studies. Our expertise is in mechanical (tension, bending, fracture, fatigue and creep) testing at the 1-100 nm length-scale. We also perform thermal conductivity (using the 3-omega technique and Raman) and electrical (diode/transistor) characterization from nanoscale to die-level specimens.

 

Overview

At the fundamental level, we are interested in determining how externally applied mechanical, electrical, thermal etc. stimuli interact with the defects and interfaces. The scientific questions are two-folds.

Firstly, how do size, defects and microstructure influence the multi-physics coupling? This allows us to explain the mechanical, electrical and thermal properties as function of the size and microstructure. This theme leads to fundamental understanding of the size-microstructure-property relationship as well as failure physics.

Secondly (and more importantly), can we control the microstructure with multi-physics coupling? This theme leads to fundamental understanding of the synthesis-microstructure relationship. The ulterior motive is to replace conventional thermal processing with multi-physics to achieve unprecedented microstructural control (such as room temperature annealing of metals or graphitization of carbon)

With focus on size dependent multi-physics phenomena, we study a wide variety of materials and systems for the coupling in the mechanical, thermal and electrical domains. This is performed on metals, semiconductors, ceramics, amorphous to graphitized carbon, irradiated nuclear materials to name a few.

 

Radiation Effects on Electronic Devices

We are working on single event effects and total ionization dose effects on the performance and reliability of electronic devices, such as GaN HEMTs and Ga2O3 diodes. The study involves both proton and heavy ion, gamma and more recently – neutron irradiation. Our focus is on how the mechanical domain influences the nucleation of damages. Mechanical stress localization (not to be confused with the average stress) can make devices vulnerable, particularly when coincided with the electrical field localizations. This hypothesis is expected to work better than single domain (just electrical domain) philosophy of device vulnerability. The mechanical domain is characterized by Raman and TEM. We see remarkable correlation between stress localization and damage nucleation in a variety of devices. The goal is to predict the spatial and temporal evolution of damage – and not just measure its path near failure conditions.

 

Analytical Microscopy

Microscopy has traditionally been a post-mortem tool. We design and fabricate multi-physics test-beds that work with electron, probe or plain optical microscopes. ‘Seeing and measuring’ in real-time allow us to link microstructure with property directly. Shown right is a MEMS chip with heaters, electrodes, actuators and sensors. The small footprint makes it compatible with virtually all forms of microscopy. Most of our experiments are performed inside a TEM.

 

Multi-Physics of Electronic Devices & Materials

At the device  (such as AlGaN/GaN high electron mobility transistors) level, we are interested in determining how they fail. They experience the harshest possible mechanical, electrical, thermal stressors and host a wide range of degradation mechanisms. To pinpoint the failure physics, we operate these transistors inside the TEM.  These in-situ experiments allow us to see the defect nucleation, semiconductor-metal inter-diffusion, cracking etc. failure mechanisms as we load the transistors with the stressors.

At the materials level, we apply similar approaches. Using our custom designed and fabricated MEMS devices under TEM/Raman/Infrared microscopes, we measure mechanical, electrical and thermal properties of electronic materials (from monolayer to thin films). The goal is to understand how does the <25 nm length-scale lead to unprecedented coupling among these domains.

 

Active Control of Microstructure

Whether it is a two (MoS2) or three (steel) dimensional material, the ultimate goal is the ability to control the microstructure (and hence the properties). For example, can we make amorphous material crystalline, or control the grain size/defect density?

We are working on non-traditional methods for active microstructural control. An example is metal annealing at near-room temperature. Another example is graphitization of carbon at near-room temperature. The ulterior motive is to develop energy saving materials (from electronic to structural) processing for desired microstructure & properties.

 

Mechanics and Physics of Materials

Our interests and capabilities extend to other materials, systems and configurations. Examples are structural, high temperature, radiation effects, energetics to name a few.

Nuclear Materials

Our interest in radiation effects on materials make nuclear materials a natural choice for research. We are working on (a) nuclear graphite and (b) cladding materials such as FeCrAl. The goal is to study effects of neutron, heavy and light ion as well as mitigation of the damage.

Other Topics of Interest

The flexibility offered by nanofabrication based experimental setup development and the diversity of questions promoted by collaborators enable us to work on interesting topics from thermal transport to bio-materials (shown in the image).