Bio


Shanyuan (Alex) Niu is a postdoctoral scholar at Stanford University working with Prof. Wendy Mao. Shanyuan obtained his Ph.D. in Materials Science from University of Southern California, under the supervision of Prof. Jayakanth Ravichandran. Shanyuan's general research interest lies in the big, fun interdisciplinary playground between materials science, physics, chemistry, and photonic and optoelectronic technologies. Shanyuan currently works on studying material under extreme conditions.

Honors & Awards


  • William F. Ballhaus, Jr. Prize for Excellence in Graduate Engineering Research, (2019)
  • PhD Achievement Award, University of Southern California (2019)
  • Grad School Banner Bearer, Student Speaker, USC Commencement & Viterbi Hooding (2019)
  • Best Dissertation Award in Materials Science, USC Viterbi (2019)
  • Link Foundation Energy Fellowship, Link Foundation (2017-2019)
  • Ovshinsky Travel Grant Award, APS DMP (2019)
  • Outstanding Self-Financed Students Abroad, CSC (2018)
  • Best Oral Presentation Award, MFD 13th Symposium (2018)
  • Distinguished Student Award, APS FIP (2018)
  • Travel Award for Excellence in Graduate Research, APS FGSA (2018)
  • Best Research Assistant Award, USC MFD (2017)
  • Best Poster Award, MFD 11th &12th Symposium (2015-2016)
  • Excellent Teaching Assistant, USC Viterbi (2015)

Professional Education


  • Master of Science, University of Southern California (2014)
  • Doctor of Philosophy, University of Southern California (2019)
  • Ph.D., University of Southern California, Materials Science
  • M.S., University of Southern California, Materials Science
  • B.S., Nanjing University, Materials Science & Engineering

Stanford Advisors


All Publications


  • Pressure-induced excimer formation and fluorescence enhancement of an anthracene derivative JOURNAL OF MATERIALS CHEMISTRY C Dai, Y., Liu, H., Geng, T., Ke, F., Niu, S., Wang, K., Qi, Y., Zou, B., Yang, B., Mao, W. L., Lin, Y. 2021; 9 (3): 934–38

    View details for DOI 10.1039/d0tc04677a

    View details for Web of Science ID 000612717600017

  • Preserving a robust CsPbI3 perovskite phase via pressure-directed octahedral tilt. Nature communications Ke, F. n., Wang, C. n., Jia, C. n., Wolf, N. R., Yan, J. n., Niu, S. n., Devereaux, T. P., Karunadasa, H. I., Mao, W. L., Lin, Y. n. 2021; 12 (1): 461

    Abstract

    Functional CsPbI3 perovskite phases are not stable at ambient conditions and spontaneously convert to a non-perovskite δ phase, limiting their applications as solar cell materials. We demonstrate the preservation of a black CsPbI3 perovskite structure to room temperature by subjecting the δ phase to pressures of 0.1 - 0.6 GPa followed by heating and rapid cooling. Synchrotron X-ray diffraction and Raman spectroscopy indicate that this perovskite phase is consistent with orthorhombic γ-CsPbI3. Once formed, γ-CsPbI3 could be then retained after releasing pressure to ambient conditions and shows substantial stability at 35% relative humidity. First-principles density functional theory calculations indicate that compression directs the out-of-phase and in-phase tilt between the [PbI6]4- octahedra which in turn tune the energy difference between δ- and γ-CsPbI3, leading to the preservation of γ-CsPbI3. Here, we present a high-pressure strategy for manipulating the (meta)stability of halide perovskites for the synthesis of desirable phases with enhanced materials functionality.

    View details for DOI 10.1038/s41467-020-20745-5

    View details for PubMedID 33469021

  • High frequency atomic tunneling yields ultralow and glass-like thermal conductivity in chalcogenide single crystals. Nature communications Sun, B. n., Niu, S. n., Hermann, R. P., Moon, J. n., Shulumba, N. n., Page, K. n., Zhao, B. n., Thind, A. S., Mahalingam, K. n., Milam-Guerrero, J. n., Haiges, R. n., Mecklenburg, M. n., Melot, B. C., Jho, Y. D., Howe, B. M., Mishra, R. n., Alatas, A. n., Winn, B. n., Manley, M. E., Ravichandran, J. n., Minnich, A. J. 2020; 11 (1): 6039

    Abstract

    Crystalline solids exhibiting glass-like thermal conductivity have attracted substantial attention both for fundamental interest and applications such as thermoelectrics. In most crystals, the competition of phonon scattering by anharmonic interactions and crystalline imperfections leads to a non-monotonic trend of thermal conductivity with temperature. Defect-free crystals that exhibit the glassy trend of low thermal conductivity with a monotonic increase with temperature are desirable because they are intrinsically thermally insulating while retaining useful properties of perfect crystals. However, this behavior is rare, and its microscopic origin remains unclear. Here, we report the observation of ultralow and glass-like thermal conductivity in a hexagonal perovskite chalcogenide single crystal, BaTiS3, despite its highly symmetric and simple primitive cell. Elastic and inelastic scattering measurements reveal the quantum mechanical origin of this unusual trend. A two-level atomic tunneling system exists in a shallow double-well potential of the Ti atom and is of sufficiently high frequency to scatter heat-carrying phonons up to room temperature. While atomic tunneling has been invoked to explain the low-temperature thermal conductivity of solids for decades, our study establishes the presence of sub-THz frequency tunneling systems even in high-quality, electrically insulating single crystals, leading to anomalous transport properties well above cryogenic temperatures.

    View details for DOI 10.1038/s41467-020-19872-w

    View details for PubMedID 33247101