Plasma Synthesis of Silicon Quantum Dots

Dr. Lorenzo Mangolini
Mechanical Engineering
University of California, Riverside

This talk will highlight the advantages of a gas-phase, non-thermal plasma approach for the synthesis of silicon nanocrystals.  For the case of silicon, standard wet-chemistry techniques fail to produce small, crystalline silicon nanoparticles.  On the other hand, we will show that a gas-phase discharge can produce crystalline silicon  nanoparticles  with  sizes  below  5  nm.    For  that  size  range,  quantum confinement  effects  lead  to  an  opening  of  the optical  band  gap  and  to  the appearance of efficient fluorescence in the visible range.  For the plasma produced silicon quantum dots, we report that not only fluorescence in the visible is observed, but  that  world  record  fluorescence  efficiencies  are  measured  after  appropriate surface passivation.  Moreover, we will show that multiple plasmas can be used in series to nucleate, grow and functionalize the surface of the nanoparticles, with the final  goal  of  realizing  a  semiconductor  'ink',  which  is  of  great  interest  for  many applications, such as printable electronics.

Data from extensive material and process characterization will be presented, with the intent  of  showing  that  a  good  understanding  of  the  properties  of  silicon nanostructures  is  far  from  being  reached,  leaving  many  opportunities  to  perform scientifically relevant work in this area.  In particular, the potential applications of silicon nanostructures for photovoltaic applications will be discussed.

Lorenzo Mangolini received his Ph.D. and M.S. in Mechanical Engineering from the University of Minnesota, Minneapolis, and received his B.S. from the Polytechnic University  of  Milan,  Italy.  His  Ph.D.  work  focused  on  the  synthesis  and characterization  of  silicon  quantum  dots.  Upon  completion  of  his  Ph.D.,  Lorenzo joined the Chemical Engineering Department at the University of Minnesota as a Post-Doc, working on the fabrication of titania and zinc-oxide based photovoltaic devices. He  later  joined  Cima  Nanotech,  Inc.  as  a  Senior  Researcher,  working  on  the development  and  large-area  fabrication  of  transparent  conductive  coatings  for applications in the electronics industry. Lorenzo is currently an Assistant Professor in Mechanical Engineering in the Bourns College of Engineering at the University of California in Riverside.