Jun 19, 2006
Nanocomposites enable ultrathin metallic cantilevers
Scientists have long recognized that metals would make wonderful building blocks for a variety of electro-mechanical devices, since they are electrically conductive, optically reflective, mechanically tough and in some cases bioactive.
Until now, metal nano-electro-mechanical systems (NEMS) have not been achievable because thin metal films tend to be composed of many differently oriented crystals, or grains, with a wide size distribution. This leads to the films being hundreds - if not thousands - of times too rough for use in nanometre scale devices and to the virtually insurmountable problem of gross distortion during fabrication.
At Lawrence Berkeley National Laboratory and the University of Alberta, we have eliminated these issues by making a nanoscale composite consisting of an ultra-dense distribution of nanometre-sized hard crystalline molybdenum particles in an amorphous aluminium-rich matrix. The beauty of this microstructure is that the resultant thin films are nearly atomically smooth at any thickness; ten times harder and fifty percent stiffer than normal; almost stress-free; and still maintain metallic conductivity.
These unique properties have allowed us to use established nanofabrication methods to build a variety of NEMS cantilevers with dimensions previously unachievable using any material. At a thickness of 4 nanometres, metal nanocomposite cantilevers promise to offer exquisite force sensitivity that is literally thousands of times higher than that of conventional cantilevers fabricated from materials like silicon, nitrides or carbides.
The major applications of our structures are as ultra-sensitive AFM/SPM cantilevers and as static and resonating NEMS sensors. Metal-based devices fabricated at such a fine scale promise to be a groundbreaking technology, redefining detection limits in the nano-world. We are currently building fully functional on-chip NEMS using Al-Mo, as well as developing other alloy systems with specialized properties for sensing and probe-microscopy applications.
About the author
Dr Velimir Radmilovic is principal investigator, National Center for Electron Microscopy, Lawrence Berkeley National Laboratory, University of California at Berkeley, US, and Dr David Mitlin is assistant professor, Chemical and Materials Engineering, University of Alberta, Edmonton, Canada.