Nanomechanics and Multi-physics of Nanoscale Thin Films

Sandeep Kumar, Ph.D.
Assistant Professor, Mechanical Engineering Department
University of California Riverside

Thin  films  are  used  prevalently  in  micro-electronics,  data  storage,  sensors  and  actuators,  energy  conversion  and  micro-electro-mechanical systems,  where  they  experience  deformation  during  device fabrication  and  operation.  Design,  performance  and  reliability  of  these  devices  depend  on  our understanding  of  the  mechanics  and  physics  of  thin  films.  However,  when  film  thickness  is  below  a critical  length  scale,  not  only  single domain  (mechanical,  electrical,  thermal)  behavior  is  different  from the bulk, also strongly coupled.

To understand the mechanics and multi-physics of nanoscale thin films, we developed a nanofabricated experimental  setup  with  high-resolution  in-situ  microscopy,  so  the  deformation  mechanisms  can  be seen  while  the  properties  are  measured.    In  the  first  part  of  this  talk,  we  will  discuss  the length-scale effects  on  fracture  and  fatigue  properties  of  thin  films  while  correlating  the  quantitative  data  to underlying  deformation  mechanisms.  We  found  that  at  nanoscale  material  tend  to  become  “Flaw Tolerant” similar to naturally occurring biomaterials (a small crack in human bone will not result in brittle fracture).

In the second part of the talk, we will discuss a novel multi-physics study, where we utilized the current in-situ  TEM  experimental  setup  to  quantify  the  coupling  between  mechanical,  thermal  and  electrical  domains.  We  utilized  the  3ω method  for  freestanding  thin  films  to  measure  thermal  and  electrical  properties while simultaneously applying mechanical strain to the thin film. We found strong mechanical strain dependence for thermal and electrical properties in case of 100 nm aluminum thin films, which will be explained in terms of grain rotation as a dominant deformation mechanism.

Sandeep Kumar received the B.Tech. degree in mechanical engineering from the Regional Engineering College,  Kurukshetra,  India,  and  the  M.S.(research)  degree  from  the  Indian  Institute  of  Technology, Delhi, India. He completed his Ph.D. degree at Pennsylvania State University, University Park under the guidance  of  Prof.  Aman  Haque.  His  doctoral  research  explored  in  situ  TEM  (transmission  electron microscope) studies on mechanical properties and deformation mechanisms in nanoscale thin films and multilayer  hard  coatings.  His  current  research  interests  include  thermo-electro-mechanical  coupling  in thin films at nanoscale, performance issues with Li-ion battery electrodes and high temperature material characterization.  His  publishing  credits  include  thirteen  peer  reviewed  journal  papers,  three  peer reviewed conference papers and nine technical conference presentations.