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Staff information


Michel Sassi

Materials Scientist
Pacific Northwest National Laboratory
PO Box 999
MSIN: K8-96
Richland, WA 99352


Michel Sassi obtained his Ph.D. in France in 2010 from Aix-Marseille University. His research work focused on quantifying inter-molecular and molecule-substrate interactions of self-assembled 2D molecular films adsorbed on metallic substrates. From 2010 to 2014, Dr. Sassi joined the Nanochemistry Research Institute (NRI) at Curtin University (Perth, Western Australia, Australia) where his research focused on developing a fundamental understanding of the effects of radioactive decay in nuclear related materials and small (bio)molecules. This led him to develop a unique way of using first principles simulations to understand and predict the physical, chemical, and structural consequences of radionuclide transmutation following radioactive decay. In 2014, Dr. Sassi joined PNNL and has been providing expertise in the areas of interface chemistry, earth and nuclear materials science. Dr. Sassi is a versatile computational expert who has built his reputation by solving interdisciplinary problems in chemistry, physics, geochemistry, environmental, nuclear and materials science.

His research is centered on developing a fundamental understanding of the chemical and physical processes that drive the properties of diverse materials, and how these processes affect their interactions with the environment. In the geochemistry area, Dr. Sassi employs ab initio simulations to investigate the reactivity at the mineral-fluid interface encompassing molecular adsorption, surface configuration and defects, as well as determining the structure, relative thermodynamics, and phase transitions between different mineral phases. In nuclear materials related areas, his research focuses on understanding radiation induced defects, microstructure evolution, quantification of the effect of radioactive transmutation in condensed matter and in molecules, and chemical kinetics.

Research Interests

  • Develop a fundamental understanding of the physical and chemical processes involved in (nano)minerals and nuclear materials.
  • Chemical and structural consequences of radioactive decay in nuclear materials and molecules.
  • Radiation induced defects, microsctructure evolution.
  • Surface reactivity and ab initio thermodynamics of bulk phase materials.
  • Prediction of bulk material phases based on composition and transition pathways.
  • Simulation of X-ray spectra (XMCD, XANES, EXAFS) for material characterization and defect quantification.
  • Simulation of phonon, IR, Raman and Sum Frequency Generation (SFG) spectra for bulk and surface characterization.
  • Ab initio numerical simulations.
  • Chemical kinetics.

Education and Credentials

  • Ph.D., Physics and Materials Science, Aix-Marseille University, France (2010).
  • M.S., Physics, Aix-Marseille University, France (2007).
  • B.S., Physics, Aix-Marseille University, France (2005).

Affiliations and Professional Service

  • Member of American Chemical Society
  • Peer Reviewer for Chemistry of Materials (ACS), Environmental Science & Technology (ACS), The Journal of Physical Chemistry C (ACS), Scientific Reports (NPG), Applied Surface Science (Elsevier), Clays and Clay Minerals (Springer Nature), Minerals (MDPI), Materials (MDPI), Journal of Synchrotron Radiation (IUCr)

PNNL Publications


  • Matthews B.E., M. Sassi, C.M. Barr, C. Ophus, T.C. Kaspar, W. Jiang, and K. Hattar, et al. 2021. "Percolation of Ion-Irradiation-Induced Disorder in Complex Oxide Interfaces." Nano Letters 21, no. 12:5353-5359. PNNL-SA-161595. doi:10.1021/acs.nanolett.1c01651
  • Sassi M., A.M. Chaka, and K.M. Rosso. 2021. "Ab Initio Thermodynamics Reveals the Nanocomposite Structure of Ferrihydrite." Communications Chemistry 4, no. 1:134. PNNL-SA-164602. doi:10.1038/s42004-021-00562-7


  • Bilbrey J.A., C.M. Ortiz Marrero, M. Sassi, A.M. Ritzmann, N.J. Henson, and M. Schram. 2020. "Tracking the chemical evolution of iodine species using recurrent neural networks." ACS Omega 5, no. 9:4588-4594. PNNL-SA-148824. doi:10.1021/acsomega.9b04104
  • Henson N.J., M. Sassi, A.M. Ritzmann, S.E. Muller, and A.E. Johnson. 2020. Chemical Modeling of the Capture of Radioiodine Species. PNNL-30371. Richland, WA: Pacific Northwest National Laboratory. Chemical Modeling of the Capture of Radioiodine Species
  • Sassi M., A.M. Ritzmann, and N.J. Henson. 2020. "Consequences of 131I transmutation in gas phase radioiodine molecules and adsorbed on graphite surface." Journal of Physical Chemistry C 124, no. 39:21461-21466. PNNL-SA-153560. doi:10.1021/acs.jpcc.0c05928
  • Sassi M., E.D. Walter, O. Qafoku, K.M. Rosso, and Z. Wang. 2020. "Radiation-induced interfacial hydroxyl transformation on boehmite and gibbsite basal surfaces." Journal of Physical Chemistry C 124, no. 40:22185-22191. PNNL-SA-153541. doi:10.1021/acs.jpcc.0c06844
  • Sassi M., Z. Wang, E.D. Walter, X. Zhang, H. Zhang, X.S. Li, and A. Tuladhar, et al. 2020. "Surface Hydration and Hydroxyl Configurations of Gibbsite and Boehmite Nanoplates." Journal of Physical Chemistry C 124, no. 9:5275-5285. PNNL-SA-149815. doi:10.1021/acs.jpcc.0c00659
  • Simonnin P., M. Sassi, B. Gilbert, L. Charlet, and K.M. Rosso. 2020. "Phase Transition and Liquid-like Superionic Conduction in Ag2S." Journal of Physical Chemistry C 124, no. 18:10150-10158. PNNL-SA-152823. doi:10.1021/acs.jpcc.0c00260
  • Spurgeon S.R., T.C. Kaspar, V. Shutthanandan, J. Gigax, L. Shao, and M. Sassi. 2020. "Asymmetric Lattice Disorder Induced at Oxide Interfaces." Advanced Materials Interfaces 7, no. 8:Article No. 1901944. PNNL-SA-148989. doi:10.1002/admi.201901944
  • Walter E.D., K.C. Schwarz, S. Anil Kumar, Y. Chen, M. Sassi, Z. Wang, and K.M. Rosso. 2020. "Evolution of Radicals from the Photolysis of High Ionic Strength Alkaline Nitrite Solutions." Journal of Physical Chemistry A 124, no. 16:3019-3025. PNNL-SA-150363. doi:10.1021/acs.jpca.9b11438
  • Wang Z., E.D. Walter, M. Sassi, X. Zhang, H. Zhang, S. Li, and Y. Chen, et al. 2020. "The role of surface hydroxyls on the radiolysis of gibbsite and boehmite nanoplatelets." Journal of Hazardous Materials 398. PNNL-SA-150311. doi:10.1016/j.jhazmat.2020.122853


  • Andrade de Notini L., D. Latta, A. Neumann, C.I. Pearce, M. Sassi, A.T. N'Diaye, and K.M. Rosso, et al. 2019. "A Closer Look at Fe(II) Passivation of Goethite." ACS Earth and Space Chemistry 3, no. 12:2717-2725. PNNL-SA-144188. doi:10.1021/acsearthspacechem.9b00224
  • Bagus P.S., M. Sassi, and K.M. Rosso. 2019. "Cluster Embedding of Ionic Systems: Point Charges and Extended Ions." Journal of Chemical Physics 151, no. 4:044107. PNNL-SA-147745. doi:10.1063/1.5108728
  • Notini L., D. Latta, A. Neumann, C.I. Pearce, M. Sassi, A.T. N'Diaye, and K.M. Rosso, et al. 2019. "A Closer Look at Fe(II) Passivation of Goethite." ACS Earth and Space Chemistry 3, no. 12:2717-2725. PNNL-SA-150749. doi:10.1021/acsearthspacechem.9b00224
  • Sassi M., and K.M. Rosso. 2019. "Reply to "Comment on ‘Roles of Hydration and Magnetism on the Structure of Ferrihydrite from First Principles'"." ACS Earth and Space Chemistry 3, no. 8:1581-1583. PNNL-SA-147743. doi:10.1021/acsearthspacechem.9b00160
  • Sassi M., and K.M. Rosso. 2019. "Roles of Hydration and Magnetism on the Structure of Ferrihydrite from First Principles." ACS Earth and Space Chemistry 3, no. 1:70-78. PNNL-SA-142092. doi:10.1021/acsearthspacechem.8b00138
  • Sassi M., T.C. Kaspar, K.M. Rosso, and S.R. Spurgeon. 2019. "Effect of structure and composition on the electronic excitation induced amorphization of La2Ti2-xZrxO7 ceramics." Scientific Reports 9, no. 1:Article No. 8190. PNNL-SA-139722. doi:10.1038/s41598-019-44621-5
  • Spurgeon S.R., M. Sassi, C. Ophus, J. Stubbs, E.S. Ilton, and E.C. Buck. 2019. "Nanoscale Oxygen Defect Gradients in UO2+x surfaces." Proceedings of the National Academy of Sciences (PNAS) 116, no. 35:17181-17186. PNNL-SA-141717. doi:10.1073/pnas.1905056116


  • Bagus P.S., C.J. Nelin, M. Sassi, E.S. Ilton, and K.M. Rosso. 2018. "Consequences of Realistic Embedding for the L2,3 Edge XAS of a-Fe2O3." Physical Chemistry Chemical Physics 20, no. 6:4396-4403. PNNL-SA-131666. doi:10.1039/c7cp06926j
  • Notini L., D. Latta, A. Neumann, C.I. Pearce, M. Sassi, A.T. N'Diaye, and K.M. Rosso, et al. 2018. "The role of defects in Fe(II) - goethite electron transfer." Environmental Science & Technology 52, no. 5:2751-2759. PNNL-SA-131667. doi:10.1021/acs.est.7b05772
  • Okumura M., S.N. Kerisit, I. Bourg, L.N. Lammers, T. Ikeda, M. Sassi, and K.M. Rosso, et al. 2018. "Radiocesium interaction with clay minerals: Theory and simulation advances Post-Fukushima." Journal of Environmental Radioactivity 189. PNNL-SA-137174. doi:10.1016/j.jenvrad.2018.03.011
  • Stifler C., N. Kollin Wittig, M. Sassi, C. Sun, M.A. Marcus, H. Birkedal, and E. Beniash, et al. 2018. "X-ray Linear Dichroism in Apatite." Journal of the American Chemical Society 140, no. 37:11698-11704. PNNL-SA-131664. doi:10.1021/jacs.8b05547


  • Bagus P.S., C.J. Nelin, E.S. Ilton, M. Sassi, and K.M. Rosso. 2017. "Analysis of X-ray adsorption edges: L2,3 edge of FeCl4-." Journal of Chemical Physics 147, no. 22:Article No. 224306. PNNL-SA-131505. doi:10.1063/1.5006223
  • Okumura M., M. Sassi, K.M. Rosso, and M. Machida. 2017. "Origin of 6-fold Coordinated Aluminum at (010)-type Pyrophyllite Edges." AIP Advances 7, no. 5:055211. PNNL-SA-153406. doi:10.1063/1.4983213
  • Sassi M., C.I. Pearce, P.S. Bagus, E. Arenholz, and K.M. Rosso. 2017. "First-Principles Fe L2,3-Edge and O K-Edge XANES and XMCD Spectra for Iron Oxides." Journal of Physical Chemistry A 121, no. 40:7613-7618. PNNL-SA-131673. doi:10.1021/acs.jpca.7b08392
  • Sassi M., M. Okumura, M. Machida, and K.M. Rosso. 2017. "Transmutation effects on long-term Cs retention in phyllosilicate minerals from first principles." Physical Chemistry Chemical Physics 19, no. 39:27007-27014. PNNL-SA-131843. doi:10.1039/c7cp04496h


  • Sassi M., K.M. Rosso, M. Okumura, and M. Machida. 2016. "Radiation-Damage Resistance in Phyllosilicate Minerals from First Principles and Implications for Radiocesium and Strontium Retention in Soils." Clays and Clay Minerals 64, no. 2:108-114. PNNL-SA-113803. doi:10.1346/CCMN.2016.0640203


  • Bagus P.S., M. Sassi, and K.M. Rosso. 2015. "Intermediate Coupling For Core-Level Excited States: Consequences For X-Ray Absorption Spectroscopy." Journal of Electron Spectroscopy and Related Phenomena 200. PNNL-SA-108070. doi:10.1016/j.elspec.2015.04.021
  • Wen H., M. Sassi, Z. Luo, C. Adamo, D. Schlom, K.M. Rosso, and X. Zhang. 2015. "Capturing ultrafast photoinduced local structural distortions of BiFeO3." Scientific Reports 5. PNNL-SA-110895. doi:10.1038/srep15098

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