. Ritika

All Publications

• Catalysis in Extreme Field Environments: A Case Study of Strongly Ionized SiO2Nanoparticle Surfaces. Journal of the American Chemical Society Linker, T. M., Dagar, R., Feinberg, A., Sahel-Schackis, S., Nomura, K., Nakano, A., Shimojo, F., Vashishta, P., Bergmann, U., Kling, M. F., Summers, A. M. 2024

  Abstract

  High electric fields can significantly alter catalytic environments and the resultant chemical processes. Such fields arise naturally in biological systems but can also be artificially induced through localized nanoscale excitations. Recently, strong field excitation of dielectric nanoparticles has emerged as an avenue for studying catalysis in highly ionized environments, producing extreme electric fields. While the dynamics of laser-driven surface ion emission has been extensively explored, understanding the molecular dynamics leading to fragmentation has remained elusive. Here, we employ a multiscale approach performing nonadiabatic quantum molecular dynamics (NAQMD) simulations on hydrogenated silica surfaces in both bare and wetted environments under field conditions mimicking those of an ionized nanoparticle. Our findings indicate that hole localization drives fragmentation dynamics, leading to surface silanol dissociation within 50 fs and charge transfer-induced water splitting in wetted environments within 150 fs. Further insight into such ultrafast mechanisms is critical for the advancement of catalysis on the surface of charged nanosystems.

  View details for DOI 10.1021/jacs.4c08550

  View details for PubMedID 39327984

• Tracking surface charge dynamics on single nanoparticles. Science advances Dagar, R., Zhang, W., Rosenberger, P., Linker, T. M., Sousa-Castillo, A., Neuhaus, M., Mitra, S., Biswas, S., Feinberg, A., Summers, A. M., Nakano, A., Vashishta, P., Shimojo, F., Wu, J., Vera, C. C., Maier, S. A., Cortés, E., Bergues, B., Kling, M. F. 2024; 10 (32): eadp1890

  Abstract

  Surface charges play a fundamental role in physics and chemistry, in particular in shaping the catalytic properties of nanomaterials. However, tracking nanoscale surface charge dynamics remains challenging due to the involved length and time scales. Here, we demonstrate time-resolved access to the nanoscale charge dynamics on dielectric nanoparticles using reaction nanoscopy. We present a four-dimensional visualization of the spatiotemporal evolution of the charge density on individual SiO2 nanoparticles under strong-field irradiation with femtosecond-nanometer resolution. The initially localized surface charges exhibit a biexponential redistribution over time. Our findings reveal the influence of surface charges on surface molecular bonding through quantum dynamical simulations. We performed semi-classical simulations to uncover the roles of diffusion and charge loss in the surface charge redistribution process. Understanding nanoscale surface charge dynamics and its influence on chemical bonding on a single-nanoparticle level unlocks an increased ability to address global needs in renewable energy and advanced health care.

  View details for DOI 10.1126/sciadv.adp1890

  View details for PubMedID 39110806

  View details for PubMedCentralID PMC11305382

• Reaction nanoscopy of ion emission from sub-wavelength propanediol droplets. Nanophotonics (Berlin, Germany) Rosenberger, P., Dagar, R., Zhang, W., Majumdar, A., Neuhaus, M., Ihme, M., Bergues, B., Kling, M. F. 2023; 12 (10): 1823-1831

  Abstract

  Droplets provide unique opportunities for the investigation of laser-induced surface chemistry. Chemical reactions on the surface of charged droplets are ubiquitous in nature and can provide critical insight into more efficient processes for industrial chemical production. Here, we demonstrate the application of the reaction nanoscopy technique to strong-field ionized nanodroplets of propanediol (PDO). The technique's sensitivity to the near-field around the droplet allows for the in-situ characterization of the average droplet size and charge. The use of ultrashort laser pulses enables control of the amount of surface charge by the laser intensity. Moreover, we demonstrate the surface chemical sensitivity of reaction nanoscopy by comparing droplets of the isomers 1,2-PDO and 1,3-PDO in their ion emission and fragmentation channels. Referencing the ion yields to gas-phase data, we find an enhanced production of methyl cations from droplets of the 1,2-PDO isomer. Density functional theory simulations support that this enhancement is due to the alignment of 1,2-PDO molecules on the surface. The results pave the way towards spatio-temporal observations of charge dynamics and surface reactions on droplets.

  View details for DOI 10.1515/nanoph-2022-0714

  View details for PubMedID 39635141

  View details for PubMedCentralID PMC11501279

• Reaction nanoscopy of ion emission from sub-wavelength propanediol droplets NANOPHOTONICS Rosenberger, P., Dagar, R., Zhang, W., Majumdar, A., Neuhaus, M., Ihme, M., Bergues, B., Kling, M. F. 2023

  View details for DOI 10.1515/nanoph-2022-0714

  View details for Web of Science ID 000964452600001

• Imaging elliptically polarized infrared near-fields on nanoparticles by strong-field dissociation of functional surface groups. The European physical journal. D, Atomic, molecular, and optical physics Rosenberger, P., Dagar, R., Zhang, W., Sousa-Castillo, A., Neuhaus, M., Cortes, E., Maier, S. A., Costa-Vera, C., Kling, M. F., Bergues, B. 2022; 76 (6): 109

  Abstract

  We investigate the strong-field ion emission from the surface of isolated silica nanoparticles aerosolized from an alcoholic solution, and demonstrate the applicability of the recently reported near-field imaging at 720 nm [Rupp et al., Nat. Comm., 10(1):4655, 2019] to longer wavelength (2  μ m) and polarizations with arbitrary ellipticity. Based on the experimental observations, we discuss the validity of a previously introduced semi-classical model, which is based on near-field driven charge generation by a Monte-Carlo approach and classical propagation. We furthermore clarify the role of the solvent in the surface composition of the nanoparticles in the interaction region. We find that upon injection of the nanoparticles into the vacuum, the alcoholic solvent evaporates on millisecond time scales, and that the generated ions originate predominantly from covalent bonds with the silica surface rather than from physisorbed solvent molecules. These findings have important implications for the development of future theoretical models of the strong-field ion emission from silica nanoparticles, and the application of near-field imaging and reaction dynamics of functional groups on isolated nanoparticles.The online version contains supplementary material available at 10.1140/epjd/s10053-022-00430-6.

  View details for DOI 10.1140/epjd/s10053-022-00430-6

  View details for PubMedID 35782906

  View details for PubMedCentralID PMC9236975

• Imaging elliptically polarized infrared near-fields on nanoparticles by strong-field dissociation of functional surface groups EUROPEAN PHYSICAL JOURNAL D Rosenberger, P., Dagar, R., Zhang, W., Sousa-Castillo, A., Neuhaus, M., Cortes, E., Maier, S. A., Costa-Vera, C., Kling, M. F., Bergues, B. 2022; 76 (6)

  View details for DOI 10.1140/epjd/s10053-022-00430-6

  View details for Web of Science ID 000817283600001

• All-optical nanoscopic spatial control of molecular reaction yields on nanoparticles OPTICA Zhang, W., Dagar, R., Rosenberger, P., Sousa-Castillo, A., Neuhaus, M., Li, W., Khan, S. A., Alnaser, A. S., Cortes, E., Maier, S. A., Costa-Vera, C., Kling, M. F., Bergues, B. 2022; 9 (5): 551-560

  View details for DOI 10.1364/OPTICA.453915

  View details for Web of Science ID 000799613700015