Dr. Kai Xiao
Functional Nanomaterials Synthesis, Properties, and Devices

Dr. Xiao is a distinguished staff scientist in the Functional Hybrid Nanomaterials Group (Group leader, David B Geohegan) at Center for Nanophase Materials Sciences, ORNL and a joint faculty at the Bredesen Center and Department of Computer Science and Electrical Engineering, University of Tennessee at Knoxville. He obtained his Ph.D. degree in Physic Chemistry in 2004 from Institute of Chemistry, Chinese Academy of Sciences. Then he worked as a postdoc associate at CNMS and became a staff scientist in 2008. He has published about 190 papers, several patents, and 7 book chapters.

Professional and Synergistic Activities:

Focus issue, Symposium and Workshop Organizer,

  • The Focus Section: Heterogeneity in Beyond Graphene 2D Materials in JMR, Vol 35, issue 11, 2020. (Co-editor with Zakaria Balushi and Sefaattin Tongay)
  • Emerging 2D Non-Graphene Materials in XXVII International Materials Research Congress (IMRC2018). Co-organized with Deji Akinwande (University of Texas at Austin), and Talat Rahman (University of Central Florida)
  • Synthesis and Collective Phenomena in 2D and Layered Materials workshop in 2017 Joint Nanoscience and Neutron Scattering User Meeting, 2017. (Co-organized with David Mandrus and Travis Williams)

Editorial and Conference Board, Review and Service:

  • Steering committee member of 17th International Conference on Laser Ablation (COLA), 2024.
  • Co-chair of the 70th AVS 2D Materials Technical Group (2DMTG) Executive Council (EC), Tampa, FL, 2024
  • Sectary of the 69th AVS 2D Materials Technical Group (2DMTG) Executive Council (EC), 2023.
  • The committee member of the ‘2D Materials Focus Topic’ Program Committee for the AVS 65th International Symposium & Exhibition (2018)
  • International Advisory Committee of the International Conference on Computational Mathematics in Nanoelectronics and Astrophysics (CMNA 2018), India
  • International Advisory Committee Member for the Centre for Advanced Electronics at Indian Institute of Technology (IIT) Indore (2020)
Journal Editorial Board:
Scientific Report; AIMS Materials Science
Proposal Reviewer:

NSF Reviewer Panels on Organic Electronics, Materials Engineering and Processing (MEP) Program and Photonic Devices, Electronics, Photonics and Magnetic Devices (EPMD) program; DOE-BES; The European Research Council (ERC);  The Netherlands Dutch Research Council (NWO); ORNL seeds and LDRD; User proposal reviewer for the Molecular Foundry at Laurence Berkeley National laboratory and Stanford Synchrotron Radiation Lightsource (SSRL); the Czech Science Foundation and Israel Science Foundation.

 Journal Reviewer:

Nature, Nature Nano; Nature Materials; Nature Chem; Nature Comm.; Light: Science & Applications; NPG Asia Materials; Scientific Report; J. Am. Chem. Soc.; Nano Letters, J. Phys. Chem. B; Chem. Mater.; ACS Nano; Langmuir; Angew. Chem. Int. Ed.; Adv. Mater.; Adv. Func. Mater.; Adv. Energy Mater.; Small; ChemSusChem; PCCP; Chem. Eur. J; Appl. Phys. Lett.; Phys Rev Lett; Phys Rev B; Phys Rev Mater; Nanoscale; J. Mater. Chem.; Polymer Chemistry; Polymer Reviews; J. Appl. Polymer Sci.; 2D Materials; Materials Today

Honors and Awards:
  • The Nano Research Young Innovators (NR45) Awards in two-dimensional materials, 2021
  • UT-Battelle Outstanding Scholarly Output Award, 2020
  • CNMS Distinguished Scientific Paper Award, 2017
  • CNMS Distinguished Scientific Paper Award, 2014
Research Projects:
  1. DOE-BES Scientific User Facilities Division, Center for Nanophase Materials Sciences
  2. PI, DOE-BES Materials Science and Engineering Division, 2021-present, “Growth Mechanisms and Controlled Synthesis of Nanomaterials.”
  3. Co-PI, DOE-BES Materials Science and Engineering Division, 2015-2021, “Growth Mechanisms and Controlled Synthesis of Nanomaterials.”
  4. Co-PI, DOE NSRC-QIS, 2018-2021, “Thin Film Platform for Rapid Prototyping of Novel Materials with Entangled States for QIS”
  5. PI, ORNL-LDRD, 2013-2015, “Synthesis and Characterization of Novel Two-Dimensional Mesoscale Organic Nanomembranes”
  6. Co-PI, DOE-EERE, “Novel photon management for thin-film photovoltaics”
  7. Co-PI, ORNL-LDRD, “Rational design of deuterated conjugated polymers with controlled spin-polarized electron transport”

Research highlights

Autonomous material synthesis by pulsed laser deposition

Autonomous synthesis by an automated PLD platform, in situ diagnostics, and AI-ML revealed the optimal growth regime and demonstrated 10x faster than traditional PLD synthesis. The self-driving experiment grew ultrathin films of WSe2 using real-time laser reflectivity monitoring and in situ Raman spectroscopy as feedback. Gaussian process (GP) regression and Bayesian optimization were used to predict the Raman “score” and search the synthesis parameter space for optimal conditions. This study demonstrates a novel AI-ML guided synthesis approach that enables the accelerated discovery and autonomous optimization of the materials that can be synthesized by PLD. 

S. B. Harris, A. Biswas, S. J. Yun, C. M. Rouleau, A. A. Puretzky, R. K. Vasudevan, D. B. Geohegan, and K. Xiao, Small Methods 2301763 (2024). DOI: 10.1002/smtd.202301763

Isotopes anomalously affect the optical band gap in 2D materials

By growing lateral heterostructures of monolayer MoS2 with different Mo isotopes, researchers observed intrinsic isotope effect on photoluminescence, revealing how phonons couple strongly with excitons to anomalously shift the optical band gap in 2D materials compared to conventional semiconductors. This study provides fundamental insights into understanding the effect of exciton-phonon scattering on the optoelectronic properties of atomically thin 2D materials. It also opens new opportunities for tailoring their electronic and optical functionalities through isotope engineering, particularly for 2D optoelectronic devices such as transistors, photovoltaics, and photodetectors.

Y. Yu, V. Turkowski, J. A. Hachtel, A. A. Puretzky, A. V. Ievlev, N. U. Din, S. B. Harris, V. Iyer, C. M. Rouleau, T. S. Rahman, D. B. Geohegan, K. Xiao, Anomalous isotope effect on the optical bandgap in a monolayer transition metal dichalcogenide semiconductor, Science Advances 10(8), eadj0758 (2024). DOI: 10.1126/sciadv.adj0758.

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Growth of 2D Pentagonal PdSe2 Crystals with High Mobility

A chemical vapor deposition method was developed to successfully synthesize layered crystals of PdSe2, a pentagonal 2D materials, with exceptional optical and electrical properties approaching that of exfoliated crystals.

Stretching 2D crystals into the third dimension by conformal growth on curved surface

We revealed how atomically-thin 2D crystals can stretch as they grow over curved surfaces and how the incorporated strain changes their growth habits and optoelectronic properties.

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Driving defects to transform phases within 2D semiconducting PdSe2 yields seamless contacts

The mechanism for the defect-driven plasma-induced phase transformation of 2D PdSe2 into the crystalline non layered Pd17Se15 phase were revealed.

Neutrons Provide Insights into Increased Performance for Hybrid Perovskite Solar Cells

Neutron interactions revealed the orthorhombic structure of the hybrid perovskite stabilized by the strong hydrogen bonds between the nitrogen substitution of the methylammonium cations and the bromides on the corner-linked PbBr6 octahedra.

B. Yang, et al, Real-Time Observation of Order-Disorder Transformation of Organic Cations Induced Phase Transition and Anomalous Photoluminescence in Hybrid Perovskites, Advanced Materials, 30(22), 1705801(2018).

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