Gang Wan

All Publications

• Atomic-Scale Moiré and Electronic Structure Analysis of Twisted Epitaxial MoS2-Au-MoS2 Heterostructures. Nano letters Cui, Y., Xu, K., Ren, P., Yuan, L., Czaja, P., Barnum, A., Sarkar, P., Altman, A., Bustillo, K., Kundu, S., Ramdas, A., Wang, X., Wan, G., Wang, Y., Wang, J., Song, C., Lim, C., Zheng, Q., Yao, H., Heinz, T., Hwang, H. Y., Majumdar, A., Dionne, J. A., Ophus, C., da Jornada, F. H., Sinclair, R., Cui, Y. 2026

  Abstract

  Twisted epitaxy enables precise orientation control of nanostructures confined within van der Waals (vdW) gaps. Here, we investigate the moiré and electronic structure of a representative twisted epitaxial system, where Au nanodiscs are grown inside twisted bilayer MoS2 with a 6° interlayer twist, inducing a 3° symmetrical misalignment of Au relative to each MoS2 layer (MoS2-Au-MoS2). Using multislice electron ptychography (MEP), we resolve the three-dimensional "moiré-of-moirés" structure of MoS2-Au-MoS2 with atomic resolution. Electron energy loss spectroscopy (EELS) shows that MoS2 encapsulation significantly reduces the plasmon energy of Au nanodiscs compared with their unencapsulated counterparts. Furthermore, first-principles calculations reveal that Au insertion alters the electronic band alignment near the Fermi level of bilayer MoS2. Our results introduce a twisted MoS2-Au-MoS2 heterostructure as a structurally and electronically rich material system and establish twisted epitaxy as a new strategy for moiré engineering and the synthesis of 2D-confined materials with tunable optoelectronic properties.

  View details for DOI 10.1021/acs.nanolett.5c04205

  View details for PubMedID 41705938

• A Humidity-Tolerant Photocatalyst for Methane Removal. Environmental science & technology Kessler, M. I., Randall, R., Wan, G., Xu, K., Zhang, Y., Dionne, J. A., Jackson, R. B., Majumdar, A. 2026

  Abstract

  To mitigate the climate impacts of methane, there has been substantial interest in the complete oxidation of methane to carbon dioxide by using photocatalysis at ambient temperatures. However, previous studies have primarily examined methane concentrations well above those found at most emission sources and have overlooked the role of realistic humidity. This work reports methane oxidation rates at 25 °C for oxide-based photocatalysts for methane concentrations ranging from 2 to 5000 ppm. Even under dry conditions with less than 2% relative humidity, residual water attracted to the hydrophilic surfaces of these photocatalysts severely inhibits methane oxidation. Thinning this water layer boosts methane oxidation rates by up to 1 order of magnitude. Furthermore, surface modification of titanium dioxide with a hydrophobic fluorosilane coating (1H,1H,2H,2H-perfluorooctyltriethoxysilane) enables room temperature photocatalytic removal of dilute methane even under conditions with up to 80% relative humidity. These findings and engineering solutions offer guidance for the development of light-driven approaches for scalable methane removal.

  View details for DOI 10.1021/acs.est.5c16764

  View details for PubMedID 41665929

• Hydrogenation of Oxides in Nonaqueous Battery Electrolytes and Beyond ACS ENERGY LETTERS Wan, G., Borodin, O., Norby, T., Pollard, T. P., Schroeder, M. A., Chen, C., Majumdar, A., Xu, K. 2025

  View details for DOI 10.1021/acsenergylett.5c01542

  View details for Web of Science ID 001539489700001

• Thickness-dependent polaron crossover in tellurene. Science advances Zhang, K., Fu, C., Kelly, S., Liang, L., Kang, S. H., Jiang, J., Zhang, R., Wang, Y., Wan, G., Siriviboon, P., Yoon, M., Ye, P. D., Wu, W., Li, M., Huang, S. 2025; 11 (2): eads4763

  Abstract

  Polarons, quasiparticles from electron-phonon coupling, are crucial for material properties including high-temperature superconductivity and colossal magnetoresistance. However, scarce studies have investigated polaron formation in low-dimensional materials with phonon polarity and electronic structure transitions. In this work, we studied polarons of tellurene, composed of chiral Te chains. The frequency and linewidth of the A1 phonon, which becomes increasingly polar for thinner tellurene, change abruptly for thickness below 10 nanometers, where field-effect mobility drops rapidly. These phonon and transport signatures, combined with phonon polarity and band structure, suggest a crossover from large polarons in bulk tellurium to small polarons in few-layer tellurene. Effective field theory considering phonon renormalization in the small-polaron regime semiquantitatively reproduces the phonon hardening and broadening effects. This polaron crossover stems from the quasi-one-dimensional nature of tellurene, where modulation of interchain distance reduces dielectric screening and promotes electron-phonon coupling. Our work provides valuable insights into the influence of polarons on phononic, electronic, and structural properties in low-dimensional materials.

  View details for DOI 10.1126/sciadv.ads4763

  View details for PubMedID 39772675

  View details for PubMedCentralID PMC11708887

• Solvent-mediated oxide hydrogenation in layered cathodes. Science (New York, N.Y.) Wan, G., Pollard, T. P., Ma, L., Schroeder, M. A., Chen, C. C., Zhu, Z., Zhang, Z., Sun, C. J., Cai, J., Thaman, H. L., Vailionis, A., Li, H., Kelly, S., Feng, Z., Franklin, J., Harvey, S. P., Zhang, Y., Du, Y., Chen, Z., Tassone, C. J., Steinrück, H. G., Xu, K., Borodin, O., Toney, M. F. 2024; 385 (6714): 1230-1236

  Abstract

  Self-discharge and chemically induced mechanical effects degrade calendar and cycle life in intercalation-based electrochromic and electrochemical energy storage devices. In rechargeable lithium-ion batteries, self-discharge in cathodes causes voltage and capacity loss over time. The prevailing self-discharge model centers on the diffusion of lithium ions from the electrolyte into the cathode. We demonstrate an alternative pathway, where hydrogenation of layered transition metal oxide cathodes induces self-discharge through hydrogen transfer from carbonate solvents to delithiated oxides. In self-discharged cathodes, we further observe opposing proton and lithium ion concentration gradients, which contribute to chemical and structural heterogeneities within delithiated cathodes, accelerating degradation. Hydrogenation occurring in delithiated cathodes may affect the chemo-mechanical coupling of layered cathodes as well as the calendar life of lithium-ion batteries.

  View details for DOI 10.1126/science.adg4687

  View details for PubMedID 39265020

• Intercalation of Hydrogen in Perovskite Oxide for Pseudocapacitive Energy Storage CHEMISTRY OF MATERIALS Lin, M., Lu, M., Chou, H., Wan, G., Chen, C. 2023; 35 (24): 10487-10494

  View details for DOI 10.1021/acs.chemmater.3c01985

  View details for Web of Science ID 001136395800001

• Intermittent Defect Fluctuations in Oxide Heterostructures. Advanced materials (Deerfield Beach, Fla.) Zhang, Q., Wan, G., Starchenko, V., Hu, G., Dufresne, E. M., Zhou, H., Jeen, H., Almazan, I. C., Dong, Y., Liu, H., Sandy, A. R., Sterbinsky, G. E., Lee, H. N., Ganesh, P., Fong, D. D. 2023; 35 (42): e2305383

  Abstract

  The heterogeneous nature, local presence, and dynamic evolution of defects typically govern the ionic and electronic properties of a wide variety of functional materials. While the last 50 years have seen considerable efforts into development of new methods to identify the nature of defects in complex materials, such as the perovskite oxides, very little is known about defect dynamics and their influence on the functionality of a material. Here, the discovery of the intermittent behavior of point defects (oxygen vacancies) in oxide heterostructures employing X-ray photon correlation spectroscopy is reported. Local fluctuations between two ordered phases in strained SrCoOx with different degrees of stability of the oxygen vacancies are observed. Ab-initio-informed phase-field modeling reveals that fluctuations between the competing ordered phases are modulated by the oxygen ion/vacancy interaction energy and epitaxial strain. The results demonstrate how defect dynamics, evidenced by measurement and modeling of their temporal fluctuations, give rise to stochastic properties that now can be fully characterized using coherent X-rays, coupled for the first time to multiscale modeling in functional complex oxide heterostructures. The study and its findings open new avenues for engineering the dynamical response of functional materials used in neuromorphic and electrochemical applications.

  View details for DOI 10.1002/adma.202305383

  View details for PubMedID 37578079

• Dynamic and reversible transformations of subnanometre-sized palladium on ceria for efficient methane removal NATURE CATALYSIS Jiang, D., Wan, G., Halldin Stenlid, J., Garcia-Vargas, C. E., Zhang, J., Sun, C., Li, J., Abild-Pedersen, F., Tassone, C. J., Wang, Y. 2023

  View details for DOI 10.1038/s41929-023-00983-8

  View details for Web of Science ID 001033754800001

• Phase Transition Dynamics in a Complex Oxide Heterostructure PHYSICAL REVIEW LETTERS Zhang, Q., Hu, G., Starchenko, V., Wan, G., Dufresne, E. M., Dong, Y., Liu, H., Zhou, H., Jeen, H., Saritas, K., Krogel, J. T., Reboredo, F. A., Lee, H., Sandy, A. R., Almazan, I., Ganesh, P., Fong, D. D. 2022; 129 (23): 235701

  Abstract

  Understanding the behavior of defects in the complex oxides is key to controlling myriad ionic and electronic properties in these multifunctional materials. The observation of defect dynamics, however, requires a unique probe-one sensitive to the configuration of defects as well as its time evolution. Here, we present measurements of oxygen vacancy ordering in epitaxial thin films of SrCoO_{x} and the brownmillerite-perovskite phase transition employing x-ray photon correlation spectroscopy. These and associated synchrotron measurements and theory calculations reveal the close interaction between the kinetics and the dynamics of the phase transition, showing how spatial and temporal fluctuations of heterointerface evolve during the transformation process. The energetics of the transition are correlated with the behavior of oxygen vacancies, and the dimensionality of the transformation is shown to depend strongly on whether the phase is undergoing oxidation or reduction. The experimental and theoretical methods described here are broadly applicable to in situ measurements of dynamic phase behavior and demonstrate how coherence may be employed for novel studies of the complex oxides as enabled by the arrival of fourth-generation hard x-ray coherent light sources.

  View details for DOI 10.1103/PhysRevLett.129.235701

  View details for Web of Science ID 000921040200015

  View details for PubMedID 36563221

• Amorphization mechanism of SrIrO3 electrocatalyst: How oxygen redox initiates ionic diffusion and structural reorganization. Science advances Wan, G., Freeland, J. W., Kloppenburg, J., Petretto, G., Nelson, J. N., Kuo, D. Y., Sun, C. J., Wen, J., Diulus, J. T., Herman, G. S., Dong, Y., Kou, R., Sun, J., Chen, S., Shen, K. M., Schlom, D. G., Rignanese, G. M., Hautier, G., Fong, D. D., Feng, Z., Zhou, H., Suntivich, J. 2021; 7 (2)

  Abstract

  The use of renewable electricity to prepare materials and fuels from abundant molecules offers a tantalizing opportunity to address concerns over energy and materials sustainability. The oxygen evolution reaction (OER) is integral to nearly all material and fuel electrosyntheses. However, very little is known about the structural evolution of the OER electrocatalyst, especially the amorphous layer that forms from the crystalline structure. Here, we investigate the interfacial transformation of the SrIrO3 OER electrocatalyst. The SrIrO3 amorphization is initiated by the lattice oxygen redox, a step that allows Sr2+ to diffuse and O2- to reorganize the SrIrO3 structure. This activation turns SrIrO3 into a highly disordered Ir octahedral network with Ir square-planar motif. The final Sr y IrO x exhibits a greater degree of disorder than IrO x made from other processing methods. Our results demonstrate that the structural reorganization facilitated by coupled ionic diffusions is essential to the disordered structure of the SrIrO3 electrocatalyst.

  View details for DOI 10.1126/sciadv.abc7323

  View details for PubMedID 33523986

  View details for PubMedCentralID PMC7793586