ME Seminar: Four-dimensional Electron Imaging and Ultrafast Laser Spect12-07-2018

Speaker: Omar F. Mohammed

Title: Four-dimensional Electron Imaging and Ultrafast Laser Spectroscopy in Chemistry, Physics and Materials Science

Date/Time: July 19, 2018, 10:40 -11:30

Place: FENS 2019


Abstract: Light-generated charge-carrier collection in all optoelectronic devices is limited by the huge losses and ambiguous dynamics at surfaces and interfaces, which are ultrafast processes in nature that can only be visualized spatially and temporally by a one-of-a-kind scanning ultrafast electron microscopy (the sole technique capable of surface-selective visualization of light-triggered carrier dynamics at nanometer scale) along with ultrafast electronic and vibrational spectroscopies. In additional to our state-of-the-art femtosecond laser spectroscopic techniques, we have recently established and developed the second generation 4D S-UEM and demonstrate the ability to take time-resolved secondary electrons images (snapshots) of material surfaces with 650 fs and  4 nm temporal and spatial resolutions, respectively. These techniques have been used to explore the carrier dynamics of several photo-active materials commonly used in optoelectronic devices such as silicon, InGaN nanowires, p-n junctions, PbS quantum dots and CdTe single crystals [1-4]; ‘and we have clearly demonstrated in space and time how the surface morphology, surface passivation, thickness of the absorber layer, surface orientation, grains, surface defects and nanostructured features can significantly impact the overall dynamical processes on the surface of these absorber layers [5-6]. Finally, charge carrier dynamics at the interface of semiconductor quantum dots and perovskite single crystal and nanocrystals using femtosecond laser spectroscopy will be also presented and discussed.

Bio: Dr. Mohammed is the principal investigator of ultrafast laser spectroscopy and four-dimensional electron imaging laboratory and he is affiliated with Solar and Photovoltaics Engineering Research Center at KAUST, and at present, his research activities are focused on the development of highly efficient solar cells with the aid of cutting-edge nanotechnology, laser spectroscopy, and ultrafast electron imaging. Prior to joining KAUST in December 2012, Dr. Mohammed was a senior research associate in Professor Ahmed Zewail’s group at Caltech, USA. While there, Dr. Mohammed joined the research group of Professor Zewail and worked on the development of new laser spectroscopic and time-resolved electron imaging techniques. Prior to his arrival in Pasadena, California, Dr. Mohammed spent more than a decade in Germany, Switzerland and Japan, embarking on the development of new laser spectroscopic techniques for direct observation of many chemical, physical and biological processes in real time. The accomplishments of Dr. Mohammed have resulted in more than 120 articles, invited talks and conference proceedings; and a large number of these papers are published in very high impact scientific journals including Science, Nature Materials, Nano Letters, PNAS, JACS, Advanced Materials, Advanced Energy Materials, Angewandte Chemie, Chemical Communications, Advanced Functional Materials, Journal of Physical Chemistry Letters and Small.


2002-2006: Long-term fellowship (4 years), Max-Born Institute, Berlin, Germany

2006-2007: Post-doctoral Fellowship, University of Geneva, Switzerland

2007-2008: Post-doctoral Fellowship (JSPS fellowship) & Special post-doctoral researcher (RIKEN fellowship), RIKEN, Japan

2009-2010: Distinguished scholar award from Arab Fund for Economic and Social Development

2010-2011: The State Prize in Basic Sciences, Egypt



1- O. M. Bakr, O. F. Mohammed., Science 355, 1260 (2017).

2- A. O. El-Ballouli, E. Alarousu, M. Bernardi, S. M. Aly, A. P. Lagrow, O. M. Bakr, O. F. Mohammed., J. Am. Chem. Soc. 136, 6952 (2014).

3- R. Begum, M. R. Parida, A. L. Abdelhady, B. Murali, N. Alyami, G. H. Ahmed, M. N. Hedhili, O. M. Bakr, and O. F. Mohammed., J. Am. Chem. Soc. 139, 731 (2017).

4- O. F. Mohammed, D.-S. Yang, S. Pal, A. H. Zewail, J. Am. Chem. Soc. 133, 7708 (2011).

5- R. Bose, J. Sun, J. I. Khan, B. S. Shaheen, A. Adhikari, T. K. Ng, V. M. Burlakov, M. P. Parida, D. Priante, A. Goriely, B. S. Ooi, O. M. Bakr, O. F. Mohammed, Adv. Mater. 28, 5106 (2016).

6- R. Bose, A. Bera, M. R. Parida, A. Adhikari, B. S. Shaheen, E. Alarousu, J. Sun, T. Wu, O. M. Bakr, O. F. Mohammed, Nano Lett. 16, 4417 (2016).


Contact: Selmiye Alkan Gürsel