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SUMMARY:Bulk Photovoltaic effects and strain-related photo-effects in non-
 centrosymmetric materials
DTSTART:20171106T131500
DTEND:20171106T141500
DTSTAMP:20260921T085008Z
UID:99c74334f2d04c488a06a51e32c93af701a9e29d55e7e3622ae97b5d
CATEGORIES:Conferences - Seminars
DESCRIPTION:Prof. Marin Alexe\, University of Warwick\, UK\nTwo years afte
 r the invention of modern prototype solar cells\, it was found that a ferr
 oelectric material\, BaTiO3\, exhibits a photovoltaic effect distinct from
  that of p-n junctions\, later called the bulk photovoltaic (BPV) effect. 
 Under uniform illumination\, a homogeneous ferroelectric material gives ri
 se to a current under zero bias\, i.e. short-circuit current (ISC)\, that 
 depends on the polarization state of the incident light\, and produces an 
 anomalously large photo-voltage well exceeding the bandgap energy. The mic
 roscopic origins of this effect are still under debate. It supposed to ori
 ginate from the asymmetric distribution of photoexcited non-equilibrium ca
 rriers in k-space\, caused by absence of centrosymmetry in the material. I
 n the recent past\, the entire field of photo-ferroelectrics has been revi
 talized by the reports of photovoltaic effect in BiFeO3 (BFO)\, which is a
  ferroelectric/multiferroic material with one of the lowest band gap and s
 ignificant semiconducting properties.\n\nThe present talk will firstly pre
 sent the basics of the bulk photovoltaic effect and address the electronic
  origin of the anomalous BPV in BiFeO3. We will show that the existence of
  the abnormal PVE in BFO is directly correlated to the presence of photoel
 ectric active sub-band gap levels and moreover\, the PV effect can be larg
 ely tuned by modifying the occupancy (pumping) of these levels.\n\nWe will
  also show light-induced reversible switching of ferroelectric polarizatio
 n at room temperature in the same BiFeO3 thin films by the mediation of th
 e tip-enhanced photovoltaic effect. The enhanced short-circuit photocurren
 t density at an AFM tip contact area generates a local electric field well
  exceeding the coercive field\, enabling full optical control of ferroelec
 tric polarization. Finally\, we will discuss a new photovoltaic effect whi
 ch turns the BPV effect into a universal effect allowed in all semiconduct
 ors by mediation of the flexoelectric effect.\n\nYang\, M.\, Bhatnagar\, A
 . & Alexe\, M. Electronic Origin and Tailoring of Photovoltaic Effect in B
 iFeO3 Single Crystals. Adv. Electron. Mater. 1\, 1500139 (2015). Alexe\, M
 . & Hesse\, D. Tip-enhanced photovoltaic effects in bismuth ferrite. Natur
 e Communications 2\, 256 (2011). Yang\, M.\, Kim\, D.J\, & Alexe\, M.\, Fl
 exo-photovoltaic effect\, Science (submitted).\nYang\, M.\, Bhatnagar\, A.
  & Alexe\, M. Electronic Origin and Tailoring of Photovoltaic Effect in Bi
 FeO3 Single Crystals. Adv. Electron. Mater. 1\, 1500139 (2015).\nAlexe\, M
 . & Hesse\, D. Tip-enhanced photovoltaic effects in bismuth ferrite. Natur
 e Communications 2\, 256 (2011).\nYang\, M.\, Kim\, D.J\, & Alexe\, M.\, F
 lexo-photovoltaic effect\, Science (submitted).\n\nBio: Marin Alexe studie
 d Physics at the University of Bucharest and obtained his PhD in 1995 from
  the institute of atomic physics in Bucharest. He subsequently joined the 
 Max Planck Institute of Microstructure Physics as a postdoctoral fellow wh
 ere he got promoted to a senior scientist (permanent position). In 2012\, 
 he moved to Sung Kyun Kwan University in Korea where he was appointed as a
 n adjunct professor before he moved back to Europe in 2013 where he works 
 since as a chair of the functional material laboratory at the University o
 f Warwick\, UK. Professor Marin Alexe's research interests include nanosci
 ence and nanotechology\, ferroelectric nanostructures\, ultra-thin films\,
  as well as physics and engineering of complex oxide thin films.\n 
LOCATION:MXF 1 https://plan.epfl.ch/?room==MXF%201
STATUS:CONFIRMED
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