Professional Education


  • Doctor of Philosophy, Vanderbilt University (2016)
  • Bachelor of Engineering, Harbin Institute Of Technology (2011)

Stanford Advisors


All Publications


  • Anti-parity-time symmetry in diffusive systems SCIENCE Li, Y., Peng, Y., Han, L., Miri, M., Li, W., Xiao, M., Zhu, X., Zhao, J., Alu, A., Fan, S., Qiu, C. 2019; 364 (6436): 170-+
  • Thermal meta-device in analogue of zero-index photonics. Nature materials Li, Y., Zhu, K., Peng, Y., Li, W., Yang, T., Xu, H., Chen, H., Zhu, X., Fan, S., Qiu, C. 2018

    Abstract

    Inspired by the developments in photonic metamaterials, the concept of thermal metamaterials has promised new avenues for manipulating the flow of heat. In photonics, the existence of natural materials with both positive and negative permittivities has enabled the creation of metamaterials with a very wide range of effective parameters. In contrast, in conductive heat transfer, the available range of thermal conductivities in natural materials is far narrower, strongly restricting the effective parameters of thermal metamaterials and limiting possible applications in extreme environments. Here, we identify a rigorous correspondence between zero index in Maxwell's equations and infinite thermal conductivity in Fourier's law. We also propose a conductive system with an integrated convective element that creates an extreme effective thermal conductivity, and hence by correspondence a thermal analogue of photonic near-zero-index metamaterials, a class of metamaterials with crucial importance in controlling light. Synergizing the general properties of zero-index metamaterials and the specific diffusive nature of thermal conduction, we theoretically and experimentally demonstrate a thermal zero-index cloak. In contrast with conventional thermal cloaks, this meta-device can operate in a highly conductive background and the cloaked object preserves great sensitivity to external temperature changes. Our work demonstrates a thermal metamaterial which greatly enhances the capability for molding the flow of heat.

    View details for PubMedID 30510270

  • Photonic thermal management of coloured objects. Nature communications Li, W., Shi, Y., Chen, Z., Fan, S. 2018; 9 (1): 4240

    Abstract

    The colours of outdoor structures, such as automobiles, buildings and clothing, are typically chosen for functional or aesthetic reasons. With a chosen colour, however, one must control the radiative thermal load for heating or cooling purposes. Here we provide a comprehensive calculation of the tunable range of radiative thermal load for all colours. The range exceeds 680Wm-2 for all colours, and can be as high as 866Wm-2, resulting from effects of metamerism, infrared solar absorption and radiative cooling. We experimentally demonstrate that two photonic structures with the same pink colour can have their temperatures differ by 47.6°C under sunlight. These structures are over 20°C either cooler or hotter than a commercial paint with a comparable colour. Furthermore, the hotter pink structure is 10°C hotter than a commercial black paint. These results elucidate the fundamental potentials of photonic thermal management for coloured objects.

    View details for PubMedID 30315155

  • Nanophotonic control of thermal radiation for energy applications [Invited] OPTICS EXPRESS Li, W., Fan, S. 2018; 26 (12): 15995–6021
  • A Comprehensive Photonic Approach for Solar Cell Cooling ACS PHOTONICS Li, W., Shi, Y., Chen, K., Zhu, L., Fan, S. 2017; 4 (4): 774-782
  • Circularly polarized light detection with hot electrons in chiral plasmonic metamaterials NATURE COMMUNICATIONS Li, W., Coppens, Z. J., Besteiro, L. V., Wang, W., Govorov, A. O., Valentine, J. 2015; 6: 8379

    Abstract

    Circularly polarized light is utilized in various optical techniques and devices. However, using conventional optical systems to generate, analyse and detect circularly polarized light involves multiple optical elements, making it challenging to realize miniature and integrated devices. While a number of ultracompact optical elements for manipulating circularly polarized light have recently been demonstrated, the development of an efficient and highly selective circularly polarized light photodetector remains challenging. Here we report on an ultracompact circularly polarized light detector that combines large engineered chirality, realized using chiral plasmonic metamaterials, with hot electron injection. We demonstrate the detector's ability to distinguish between left and right hand circularly polarized light without the use of additional optical elements. Implementation of this photodetector could lead to enhanced security in fibre and free-space communication, as well as emission, imaging and sensing applications for circularly polarized light using a highly integrated photonic platform.

    View details for DOI 10.1038/ncomms9379

    View details for Web of Science ID 000363136100002

    View details for PubMedID 26391292

    View details for PubMedCentralID PMC4595755

  • Metamaterial Perfect Absorber Based Hot Electron Photodetection NANO LETTERS Li, W., Valentine, J. 2014; 14 (6): 3510–14

    Abstract

    While the nonradiative decay of surface plasmons was once thought to be only a parasitic process that limits the performance of plasmonic devices, it has recently been shown that it can be harnessed in the form of hot electrons for use in photocatalysis, photovoltaics, and photodetectors. Unfortunately, the quantum efficiency of hot electron devices remains low due to poor electron injection and in some cases low optical absorption. Here, we demonstrate how metamaterial perfect absorbers can be used to achieve near-unity optical absorption using ultrathin plasmonic nanostructures with thicknesses of 15 nm, smaller than the hot electron diffusion length. By integrating the metamaterial with a silicon substrate, we experimentally demonstrate a broadband and omnidirectional hot electron photodetector with a photoresponsivity that is among the highest yet reported. We also show how the spectral bandwidth and polarization-sensitivity can be manipulated through engineering the geometry of the metamaterial unit cell. These perfect absorber photodetectors could open a pathway for enhancing hot electron based photovoltaic, sensing, and photocatalysis systems.

    View details for DOI 10.1021/nl501090w

    View details for Web of Science ID 000337337100082

    View details for PubMedID 24837991

  • Probing and Controlling Photothermal Heat Generation in Plasmonic Nanostructures NANO LETTERS Coppens, Z. J., Li, W., Walker, D., Valentine, J. G. 2013; 13 (3): 1023–28

    Abstract

    In the emerging field of thermoplasmonics, Joule heating associated with optically resonant plasmonic structures is exploited to generate nanoscale thermal hotspots. In the present study, new methods for designing and thermally probing thermoplasmonic structures are reported. A general design rationale, based on Babinet's principle, is developed for understanding how the complementary version of ideal electromagnetic antennae can yield efficient nanoscale heat sources with maximized current density. Using this methodology, we show that the diabolo antenna is more suitable for heat generation compared with its more well-known complementary structure, the bow-tie antenna. We also demonstrate that highly localized and enhanced thermal hot spots can be realized by incorporating the diabolo antenna into a plasmonic lens. Using a newly developed thermal microscopy method based on the temperature-dependent photoluminescence lifetime of thin-film thermographic phosphors, we experimentally characterize the thermal response of various antenna and superstructure designs. Data from FDTD simulations and the experimental temperature measurements confirm the validity of the design rationale. The thermal microscopy technique, with its robust sensing method, could overcome some of the drawbacks of current micro/nanoscale temperature measurement schemes.

    View details for DOI 10.1021/nl304208s

    View details for Web of Science ID 000316243800025

    View details for PubMedID 23437919

  • Experimental demonstration of energy harvesting from the sky using the negative illumination effect of a semiconductor photodiode APPLIED PHYSICS LETTERS Ono, M., Santhanam, P., Li, W., Zhao, B., Fan, S. 2019; 114 (16)

    View details for DOI 10.1063/1.5089783

    View details for Web of Science ID 000466264600002

  • Simultaneously and Synergistically Harvest Energy from the Sun and Outer Space JOULE Chen, Z., Zhu, L., Li, W., Fan, S. 2019; 3 (1): 101–10
  • Thermal meta-device in analogue of zero-index photonics NATURE MATERIALS Li, Y., Zhu, K., Peng, Y., Li, W., Yang, T., Xu, H., Chen, H., Zhu, X., Fan, S., Qiu, C. 2019; 18 (1): 48-+
  • Anti-parity-time symmetry in diffusive systems. Science (New York, N.Y.) Li, Y., Peng, Y., Han, L., Miri, M., Li, W., Xiao, M., Zhu, X., Zhao, J., Alo, A., Fan, S., Qiu, C. 2019; 364 (6436): 170–73

    Abstract

    Various concepts related to parity-time symmetry, including anti-parity-time symmetry, have found broad applications in wave physics. Wave systems are fundamentally described by Hermitian operators, whereas their unusual properties are introduced by incorporation of gain and loss. We propose that the related physics need not be restricted to wave dynamics, and we consider systems described by diffusive dynamics. We study the heat transfer in two countermoving media and show that this system exhibits anti-parity-time symmetry. The spontaneous symmetry breaking results in a phase transition from motionless temperature profiles, despite the mechanical motion of the background, to moving temperature profiles. Our results extend the concepts of parity-time symmetry beyond wave physics and may offer opportunities to manipulate heat and mass transport.

    View details for PubMedID 30975886

  • Self-adaptive radiative cooling based on phase change materials OPTICS EXPRESS Ono, M., Chen, K., Li, W., Fan, S. 2018; 26 (18): A777–A787

    Abstract

    With the ability of harvesting the coldness of universe as a thermodynamic resource, radiative cooling technology is important for a broad range of applications such as passive building cooling, refrigeration, and renewable energy harvesting. However, all existing radiative cooling technologies utilize static structures, which lack the ability of self-adaptive tuning based on demand. Here we present the concept of self-adaptive radiative cooling based on phase change materials such as vanadium dioxide. We design a photonic structure that can adaptively turn 'on' and 'off' radiative cooling, depending the ambient temperature, without any extra energy input for switching. Our results here lead to new functionalities of radiative cooling and can potentially be used in a wide range of applications for the thermal managements of buildings, vehicles and textiles.

    View details for DOI 10.1364/OE.26.00A777

    View details for Web of Science ID 000443431400007

    View details for PubMedID 30184837

  • Spectrally Selective Nanocomposite Textile for Outdoor Personal Cooling. Advanced materials (Deerfield Beach, Fla.) Cai, L., Song, A. Y., Li, W., Hsu, P., Lin, D., Catrysse, P. B., Liu, Y., Peng, Y., Chen, J., Wang, H., Xu, J., Yang, A., Fan, S., Cui, Y. 2018: e1802152

    Abstract

    Outdoor heat stress poses a serious public health threat and curtails industrial labor supply and productivity, thus adversely impacting the wellness and economy of the entire society. With climate change, there will be more intense and frequent heat waves that further present a grand challenge for sustainability. However, an efficient and economical method that can provide localized outdoor cooling of the human body without intensive energy input is lacking. Here, a novel spectrally selective nanocomposite textile for radiative outdoor cooling using zinc oxide nanoparticle-embedded polyethylene is demonstrated. By reflecting more than 90% solar irradiance and selectively transmitting out human body thermal radiation, this textile can enable simulated skin to avoid overheating by 5-13 °C compared to normal textile like cotton under peak daylight condition. Owing to its superior passive cooling capability and compatibility with large-scale production, this radiative outdoor cooling textile is promising to widely benefit the sustainability of society in many aspects spanning from health to economy.

    View details for PubMedID 30015999

  • Optimization of Multilayer Optical Films with a Memetic Algorithm and Mixed Integer Programming ACS PHOTONICS Shi, Y., Li, W., Raman, A., Fan, S. 2018; 5 (3): 684–91
  • . Nature communications Zhang, C., Liu, Z., Chen, Z., Xie, Y., He, R., Tang, S., He, J., Li, W., Jia, T., Rebec, S. N., Ma, E. Y., Yan, H., Hashimoto, M., Lu, D., Mo, S., Hikita, Y., Moore, R. G., Hwang, H. Y., Lee, D., Shen, Z. 2017; 8: 14468-?

    Abstract

    The observation of replica bands in single-unit-cell FeSe on SrTiO3 (STO)(001) by angle-resolved photoemission spectroscopy (ARPES) has led to the conjecture that the coupling between FeSe electrons and the STO phonons are responsible for the enhancement of Tc over other FeSe-based superconductors. However the recent observation of a similar superconducting gap in single-unit-cell FeSe/STO(110) raised the question of whether a similar mechanism applies. Here we report the ARPES study of the electronic structure of FeSe/STO(110). Similar to the results in FeSe/STO(001), clear replica bands are observed. We also present a comparative study of STO(001) and STO(110) bare surfaces, and observe similar replica bands separated by approximately the same energy, indicating this coupling is a generic feature of the STO surfaces and interfaces. Our findings suggest that the large superconducting gaps observed in FeSe films grown on different STO surface terminations are likely enhanced by a common mechanism.

    View details for DOI 10.1038/ncomms14468

    View details for PubMedID 28186084

  • Passive Cooling of Solar Cells with a Comprehensive Photonic Approach Li, W., Shi, Y., Chen, K., Zhu, L., Fan, S., IEEE IEEE. 2017: 847–50
  • Harvesting the loss: surface plasmon-based hot electron photodetection NANOPHOTONICS Li, W., Valentine, J. G. 2017; 6 (1): 177–91
  • Interplay of structural and compositional effects on carrier recombination in mixed-halide perovskites RSC ADVANCES Talbert, E. M., Zarick, H. F., Orfield, N. J., Li, W., Erwin, W. R., DeBra, Z. R., Reid, K. R., McDonald, C. P., McBride, J. R., Valentine, J., Rosenthal, S. J., Bardhan, R. 2016; 6 (90): 86947–54

    View details for DOI 10.1039/c6ra16505b

    View details for Web of Science ID 000384232600022

  • Large-Scale All-Dielectric Metamaterial Perfect Reflectors ACS PHOTONICS Moitra, P., Slovick, B. A., Li, W., Kraychencko, I. I., Briggs, D. P., Krishnamurthy, S., Valentine, J. 2015; 2 (6): 692–98
  • Enhanced absorption in two-dimensional materials via Fano-resonant photonic crystals APPLIED PHYSICS LETTERS Wang, W., Klots, A., Yang, Y., Li, W., Kravchenko, I. I., Briggs, D. P., Bolotin, K. I., Valentine, J. 2015; 106 (18)

    View details for DOI 10.1063/1.4919760

    View details for Web of Science ID 000354259200004

  • Electron beam physical vapor deposition of thin ruby films for remote temperature sensing JOURNAL OF APPLIED PHYSICS Li, W., Coppens, Z. J., Walker, D., Valentine, J. G. 2013; 113 (16)

    View details for DOI 10.1063/1.4802628

    View details for Web of Science ID 000318550300022