Stanford Advisors

Current Research and Scholarly Interests

Currently, I am working on an on-chip platform to simultaneously trap and manipulate micron scale beads and droplets with an intention to implement chemical reactions on a chip at ultrasmall volumes.

All Publications

  • On the substrate contribution to the back action trapping of plasmonic nanoparticles on resonant near-field traps in plasmonic films OPTICS EXPRESS Padhy, P., Zaman, M., Hansen, P., Hesselink, L. 2017; 25 (21): 26198–214


    Nanoparticles trapped on resonant near-field apertures/engravings carved in plasmonic films experience optical forces due to the steep intensity gradient field of the aperture/engraving as well as the image like interaction with the substrate. For non-resonant nanoparticles the contribution of the substrate interaction to the trapping force in the vicinity of the trap (aperture/engraving) mode is negligible. But, in the case of plasmonic nanoparticles, the contribution of the substrate interaction to the low frequency stable trapping mode of the coupled particle-trap system increases as their resonance is tuned to the trap resonance. The strength of the substrate interaction depends on the height of the nanoparticle above the substrate. As a result, a difference in back action mechanism arises for nanoparticle displacements perpendicular to the substrate and along it. For nanoparticle displacements perpendicular to the substrate, the self induced back action component of the trap force arises due to changing interaction with the substrate as well as the trap. On the other hand, for displacements along the substrate, it arises solely due to the changing interaction with the trap. This additional contribution of the substrate leads to more pronounced back action. Numerical simulation results are presented to illustrate these effects using a bowtie engraving as the near-field trap and a nanorod as the trapped plasmonic nanoparticle. The substrate's role may be important in manipulation of plasmonic nanoparticles between successive traps of on-chip optical conveyor belts, because they have to traverse over regions of bare substrate while being handed off between these traps.

    View details for DOI 10.1364/OE.25.026198

    View details for Web of Science ID 000413103300123

    View details for PubMedID 29041280

  • Dielectrophoresis-assisted plasmonic trapping of dielectric nanoparticles PHYSICAL REVIEW A Zaman, M. A., Padhy, P., Hansen, P. C., Hesselink, L. 2017; 95 (2)
  • Adjoint method for estimating Jiles-Atherton hysteresis model parameters JOURNAL OF APPLIED PHYSICS Zaman, M. A., Hansen, P. C., Neustock, L. T., Padhy, P., Hesselink, L. 2016; 120 (9)

    View details for DOI 10.1063/1.4962153

    View details for Web of Science ID 000383978100014

  • Metal wire waveguide based all plasmonic refractive index sensor for terahertz frequencies SENSORS AND ACTUATORS B-CHEMICAL Padhy, P., Sahu, P. K., Jha, R. 2016; 225: 115-120