All Publications

  • Imaging the electron charge density in monolayer MoS2 at the Ã…ngstrom scale. Nature communications Martis, J., Susarla, S., Rayabharam, A., Su, C., Paule, T., Pelz, P., Huff, C., Xu, X., Li, H. K., Jaikissoon, M., Chen, V., Pop, E., Saraswat, K., Zettl, A., Aluru, N. R., Ramesh, R., Ercius, P., Majumdar, A. 2023; 14 (1): 4363


    Four-dimensional scanning transmission electron microscopy (4D-STEM) has recently gained widespread attention for its ability to image atomic electric fields with sub-Ã…ngstrom spatial resolution. These electric field maps represent the integrated effect of the nucleus, core electrons and valence electrons, and separating their contributions is non-trivial. In this paper, we utilized simultaneously acquired 4D-STEM center of mass (CoM) images and annular dark field (ADF) images to determine the projected electron charge density in monolayer MoS2. We evaluate the contributions of both the core electrons and the valence electrons to the derived electron charge density; however, due to blurring by the probe shape, the valence electron contribution forms a nearly featureless background while most of the spatial modulation comes from the core electrons. Our findings highlight the importance of probe shape in interpreting charge densities derived from 4D-STEM and the need for smaller electron probes.

    View details for DOI 10.1038/s41467-023-39304-9

    View details for PubMedID 37474521

  • A semi-continuous process for co-production of CO2-free hydrogen and carbon nanotubes via methane pyrolysis CELL REPORTS PHYSICAL SCIENCE Sun, E., Zhai, S., Kim, D., Gigantino, M., Haribal, V., Dewey, O. S., Williams, S. M., Wan, G., Nelson, A., Marin-Quiros, S., Martis, J., Zhou, C., Oh, J., Randall, R., Kessler, M., Kong, D., Rojas, J., Tong, A., Xu, X., Huff, C., Pasquali, M., Gupta, R., Cargnello, M., Majumdar, A. 2023; 4 (4)
  • Photoabsorption Imaging at Nanometer Scales Using Secondary Electron Analysis. Nano letters Zhang, Z., Martis, J., Xu, X., Li, H., Xie, C., Takasuka, B., Lee, J., Roy, A. K., Majumdar, A. 2021


    Optical imaging with nanometer resolution offers fundamental insights into light-matter interactions. Traditional optical techniques are diffraction limited with a spatial resolution >100 nm. Optical super-resolution and cathodoluminescence techniques have higher spatial resolutions, but these approaches require the sample to fluoresce, which many materials lack. Here, we introduce photoabsorption microscopy using electron analysis, which involves spectrally specific photoabsorption that is locally probed using a scanning electron microscope, whereby a photoabsorption-induced surface photovoltage modulates the secondary electron emission. We demonstrate spectrally specific photoabsorption imaging with sub-20 nm spatial resolution using silicon, germanium, and gold nanoparticles. Theoretical analysis and Monte Carlo simulations are used to explain the basic trends of the photoabsorption-induced secondary electron signal. Based on our current experiments and this analysis, we expect that the spatial resolution can be further improved to a few nanometers, thereby offering a general approach for nanometer-scale optical spectroscopic imaging and material characterization.

    View details for DOI 10.1021/acs.nanolett.0c03993

    View details for PubMedID 33635654

  • High-Safety and High-Energy-Density Lithium Metal Batteries in a Novel Ionic-Liquid Electrolyte. Advanced materials (Deerfield Beach, Fla.) Sun, H., Zhu, G., Zhu, Y., Lin, M., Chen, H., Li, Y., Hung, W. H., Zhou, B., Wang, X., Bai, Y., Gu, M., Huang, C., Tai, H., Xu, X., Angell, M., Shyue, J., Dai, H. 2020: e2001741


    Rechargeable lithium metal batteries are next generation energy storage devices with high energy density, but face challenges in achieving high energy density, high safety, and long cycle life. Here, lithium metal batteries in a novel nonflammable ionic-liquid (IL) electrolyte composed of 1-ethyl-3-methylimidazolium (EMIm) cations and high-concentration bis(fluorosulfonyl)imide (FSI) anions, with sodium bis(trifluoromethanesulfonyl)imide (NaTFSI) as a key additive are reported. The Na ion participates in the formation of hybrid passivation interphases and contributes to dendrite-free Li deposition and reversible cathode electrochemistry. The electrolyte of low viscosity allows practically useful cathode mass loading up to 16 mg cm-2 . Li anodes paired with lithium cobalt oxide (LiCoO2 ) and lithium nickel cobalt manganese oxide (LiNi0.8 Co0.1 Mn0.1 O2 , NCM 811) cathodes exhibit 99.6-99.9% Coulombic efficiencies, high discharge voltages up to 4.4 V, high specific capacity and energy density up to 199 mAh g-1 and 765 Wh kg-1 respectively, with impressive cycling performances over up to 1200 cycles. Highly stable passivation interphases formed on both electrodes in the novel IL electrolyte are the key to highly reversible lithium metal batteries, especially for Li-NMC 811 full batteries.

    View details for DOI 10.1002/adma.202001741

    View details for PubMedID 32449260

  • A safe and non-flammable sodium metal battery based on an ionic liquid electrolyte. Nature communications Sun, H., Zhu, G., Xu, X., Liao, M., Li, Y., Angell, M., Gu, M., Zhu, Y., Hung, W. H., Li, J., Kuang, Y., Meng, Y., Lin, M., Peng, H., Dai, H. 2019; 10 (1): 3302


    Rechargeable sodium metal batteries with high energy density could be important to a wide range of energy applications in modern society. The pursuit of higher energy density should ideally come with high safety, a goal difficult for electrolytes based on organic solvents. Here we report a chloroaluminate ionic liquid electrolyte comprised of aluminium chloride/1-methyl-3-ethylimidazolium chloride/sodium chloride ionic liquid spiked with two important additives, ethylaluminum dichloride and 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide. This leads to the first chloroaluminate based ionic liquid electrolyte for rechargeable sodium metal battery. The obtained batteries reached voltages up to ~4V, high Coulombic efficiency up to 99.9%, and high energy and power density of ~420Whkg-1 and ~1766 W kg-1, respectively. The batteries retained over 90% of the original capacity after 700 cycles, suggesting an effective approach to sodium metal batteries with high energy/high power density, long cycle life and high safety.

    View details for DOI 10.1038/s41467-019-11102-2

    View details for PubMedID 31341162