Honors & Awards


  • Teaching Fellowship, Stanford University (Sept. 2019)
  • Centennial Teaching Assistant Award Winner, Stanford University (June, 2019)
  • Robert S. Hilbert Memorial Optical Design Competition Winner, Synopsys (Aug, 2018)
  • James F. Gibbons Outstanding Student Teaching Award in Electrical Engineering, Stanford University (June 18, 2017)
  • Departmental Fellowship, Department of Electrical Engineering, Stanford University (Sept. 2014)

Professional Education


  • Doctor of Philosophy, Stanford University, EE-PHD (2020)
  • MS, Bangladesh University of Engineering and Technology, Electrical and Electronic Engineering (2011)
  • BS, Bangladesh University of Engineering and Technology, Electrical and Electronic Engineering (2009)

Stanford Advisors


Current Research and Scholarly Interests


My research focuses on trapping and controlled manipulation of sub-micron sized particles. The work included modeling, fabrication and testing of chips that employ optical forces and/or dielectrophoretic forces to trap and transport nanoparticles. Our goal is to develop lab-on-a-chip systems for biomedical and chemical applications.

Projects


  • Plasmonic trapping and manipulation of nanoparticles, Stanford University (9/1/2014 - Present)

    Design, fabrication and testing of C-shaped plasmonic structures for trapping and manipulation of dielectric and metallic nanoparticles.

    Location

    Stanford, CA

    Collaborators

  • Dielectrophoretic trapping, Stanford University (August 1, 2015 - Present)

    Selective trapping and manipulation of dielectric particles using dielectrophoresis

    Location

    Stanford, CA

    Collaborators

  • Adjoint optimization, Stanford University (March 1, 2016 - December 1, 2016)

    Application of discrete and continuous adjoint optimization techniques in practical engineering problems

    Location

    Stanford, CA

    Collaborators

  • Microfluidic system design for droplet generation, Stanford University (June 1, 2017 - Present)

    We are developing a microfluidic system that can generate droplets with diameters of a few micron.

    Location

    Stanford, CA

    Collaborators

  • On chip system for small volume biochemistry, Stanford University (June 1, 2017 - Present)

    A lab-on-a-chip microfluidic system capable of trapping and manipulating particles will be developed to perform small scale chemical reactions for bio applications.

    Location

    Stanford, CA

    Collaborators

Lab Affiliations


2021-22 Courses


All Publications


  • Optoelectronic tweezers with a non-uniform background field APPLIED PHYSICS LETTERS Zaman, M., Padhy, P., Cheng, Y., Galambos, L., Hesselink, L. 2020; 117 (17)

    View details for DOI 10.1063/5.0020446

    View details for Web of Science ID 000588490800002

  • Solenoidal optical forces from a plasmonic Archimedean spiral PHYSICAL REVIEW A Zaman, M., Padhy, P., Hesselink, L. 2019; 100 (1)
  • Fokker-Planck analysis of optical near-field traps. Scientific reports Zaman, M. A., Padhy, P., Hesselink, L. 2019; 9 (1): 9557

    Abstract

    The motion of a nanoparticle in the vicinity of a near-field optical trap is modeled using the Fokker-Planck equation. A plasmonic C-shaped engraving on a gold film is considered as the optical trap. The time evolution of the position probability density of the nanoparticle is calculated to analyze the trapping dynamics. A spatially varying diffusion tensor is used in the formulation to take into account the hydrodynamic interactions. The steady-state position distribution obtained from the Fokker-Planck equation is compared with experimental results and found to be in good agreement. Computational cost of the proposed method is compared with the conventionally used Langevin equation based approach. The proposed method is found to be computationally efficient (requiring 35 times less computation time) and scalable to more complex lab-on-a-chip systems.

    View details for DOI 10.1038/s41598-019-45609-x

    View details for PubMedID 31266994

  • Near-field optical trapping in a non-conservative force field. Scientific reports Zaman, M. A., Padhy, P., Hesselink, L. 2019; 9 (1): 649

    Abstract

    The force-field generated by a near-field optical trap is analyzed. A C-shaped engraving on a gold film is considered as the trap. By separating out the conservative component and the solenoidal component of the force-field using Helmholtz-Hodge decomposition, it was found that the force is non-conservative. Conventional method of calculating the optical potential from the force-field is shown to be inaccurate when the trapping force is not purely conservative. An alternative method is presented to accurately estimate the potential. The positional statistics of a trapped nanoparticle in this non-conservative field is calculated. A model is proposed that relates the position distribution to the conservative component of the force. The model is found to be consistent with numerical and experimental results. In order to show the generality of the approach, the same analysis is repeated for a plasmonic trap consisting of a gold nanopillar. Similar consistency is observed for this structure as well.

    View details for PubMedID 30679539

  • Near-field optical trapping in a non-conservative force field SCIENTIFIC REPORTS Zaman, M., Padhy, P., Hesselink, L. 2019; 9
  • Solenoidal optical forces from a plasmonic Archimedean spiral. Physical review. A Zaman, M. A., Padhy, P. n., Hesselink, L. n. 2019; 100 (1)

    Abstract

    The optical forces generated by a right-handed plasmonic Archimedean spiral (PAS) have been mapped and analyzed. By changing the handedness of the circularly polarized excitation, the structure can switch from a trapping force profile to a rotating force profile. The Helmholtz-Hodge decomposition method has been used to separate the solenoidal component and the conservative component of the force and quantify their relative magnitude. It is shown that the for right-hand circularly polarized excitation, the PAS creates a significant amount of solenoidal forces. Using the decomposed force components, an intuitive explanation of the motion of micro- and nanoparticles in the force field is presented. Vector field topology is used to visualize the force components. The analysis is found to be consistent with numerical and experimental results. Due to the intuitive nature of the analysis, it can be used in the initial design process of complex laboratory-on-a-chip systems where a rigorous analysis is computationally expensive.

    View details for DOI 10.1103/physreva.100.013857

    View details for PubMedID 33981919

    View details for PubMedCentralID PMC8112602

  • Extracting the potential-well of a near-field optical trap using the Helmholtz-Hodge decomposition APPLIED PHYSICS LETTERS Zaman, M., Padhy, P., Hansen, P. C., Hesselink, L. 2018; 112 (9)

    View details for DOI 10.1063/1.5016810

    View details for Web of Science ID 000427022500003

  • Capturing range of a near-field optical trap PHYSICAL REVIEW A Zaman, M., Padhy, P., Hesselink, L. 2017; 96 (4)
  • Dielectrophoresis-assisted plasmonic trapping of dielectric nanoparticles PHYSICAL REVIEW A Zaman, M. A., Padhy, P., Hansen, P. C., Hesselink, L. 2017; 95 (2)
  • Dynamically controlled dielectrophoresis using resonant tuning. Electrophoresis Padhy, P., Zaman, M. A., Jensen, M. A., Hesselink, L. 2021

    Abstract

    Electrically polarizable micro and nanoparticles and droplets can be trapped using the gradient electric field of electrodes. But the spatial profile of the resultant dielectrophoretic force is fixed once the electrode structure is defined. To change the force profile, entire complex lab-on-a-chip systems must be re-fabricated with modified electrode structures. To overcome this problem, we propose an approach for the dynamic control of the spatial profile of the dielectrophoretic force by interfacing the trap electrodes with a resistor and an inductor to form a resonant RLC circuit. Using a dielectrophoretically trapped water droplet suspended in silicone oil, we show that the resonator amplitude, detuning and linewidth can be continuously varied by changing the supply voltage, supply frequency and the circuit resistance to obtain the desired trap depth, range, and stiffness. We show that by proper tuning of the resonator the trap range can be extended without increasing the supply voltage, thus preventing sensitive samples from exposure to high electric fields at the stable trapping position. Such unprecedented dynamic control of dielectrophoretic forces opens avenues for the tunable active manipulation of sensitive biological and biochemical specimen in droplet microfluidic devices used for single cell and biochemical reactionanalysis. This article is protected by copyright. All rights reserved.

    View details for DOI 10.1002/elps.202000328

    View details for PubMedID 33599974

  • Photonic radiative cooler optimization using Taguchi's method INTERNATIONAL JOURNAL OF THERMAL SCIENCES Zaman, M. 2019; 144: 21–26
  • Design of a high numerical aperture achromatic objective lens for endomicroscopy OPTICAL ENGINEERING Zaman, M., Buyukalp, Y. 2019; 58 (7)
  • In-plane near-field optical barrier on a chip OPTICS LETTERS Padhy, P., Zaman, M., Hesselink, L. 2019; 44 (8): 2061–64

    Abstract

    Nanoparticles trapped on resonant near-field structures engraved on a metallic substrate experience forces due to the engravings, as well as the image-like interaction with the substrate. In the case of normally incident optical excitation, the force due to the substrate is solely perpendicular to its surface. Numerical simulations are presented to demonstrate that under the combined influence of the aforementioned forces, a plasmonic nanoparticle can be repelled from the engraving along the substrate, while attracting it towards the substrate along its normal. This behavior can be achieved over a range of excitation wavelengths of the short wavelength mode of the coupled particle-substrate-trap system. To the best of our knowledge, this is the first illustration of an in-plane near-field optical barrier on a chip. The barrier is stable against resistive heating of the nanoparticle, as well as the induced non-isothermal flow. The wavelength-dependent switch between the proposed in-plane potential barrier and the stable potential well can pave the way for the gated transport of single nanoparticles, while holding them bound to the chip.

    View details for DOI 10.1364/OL.44.002061

    View details for Web of Science ID 000464601900046

    View details for PubMedID 30985811

  • A semi-analytical model of a near-field optical trapping potential well JOURNAL OF APPLIED PHYSICS Zaman, M., Padhy, P., Hesselink, L. 2017; 122 (16)

    View details for DOI 10.1063/1.5000269

    View details for Web of Science ID 000414225500001

  • 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

    Abstract

    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

  • 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

  • Optimization of multilayer antireflection coating for photovoltaic applications OPTICS AND LASER TECHNOLOGY Sikder, U., Zaman, M. A. 2016; 79: 88-94
  • Application of Taguchi's method to optimize fiber Raman amplifier OPTICAL ENGINEERING Zaman, M. A. 2016; 55 (4)
  • Effect of Substrate in Optical Trapping of Metallic Nanoparticle on Nano Apertures and Engravings Padhy, P., Hansen, P., Ryan, J., Zaman, M., Huang, T. W., Hesselink, L., IEEE IEEE. 2016
  • Bouc-Wen hysteresis model identification using Modified Firefly Algorithm JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS Zaman, M. A., Sikder, U. 2015; 395: 229-233