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A dielectrophoretic device employing a planar array of microelectrodes is designed for controlled transport of individual microparticles. By exciting the electrodes in sequence, a moving dielectrophoretic force is created that can drag a particle across the electrodes in a straight line. The electrode shapes are designed to counter any lateral drift of the trapped particle during transport. This facilitates single particle transport by creating a narrow two-dimensional corridor for the moving dielectrophoretic force to operate on. The design and analysis processes are discussed in detail. Numerical simulations are performed to calculate the electromagnetic field distribution and the generated dielectrophoretic force near the electrodes. The Langevin equation is used for analyzing the trajectory of a microparticle under the influence of the external forces. The simulations show how the designed electrode geometry produces the necessary lateral confinement required for successful particle transport. Finally, experimental results are presented showing controlled bidirectional linear transport of single polystyrene beads of radius 10 and 5 μm for a distances 840 and 1100 μm, respectively. The capabilities of the proposed platform make it suitable for micro total analysis systems (μTAS) and lab-on-a-chip (LOC) applications.

A near-field optical trapping scheme using plasmonic C-shaped nano-engraving is presented. Utilizing the polarization sensitivity of the C-structure, a mechanism is proposed for dynamically controlling the electric field, the associated trapping force, and the plasmonic heating. Electromagnetic analysis and particle dynamics simulations are performed to verify the viability of the approach. The designed structure is fabricated and experimentally tested. Polarization control of the excitation light is achieved through the use of a half-wave plate. Experimental results are presented that show the functioning implementation of the dynamically adjustable plasmonic tweezers. The dynamic controllability can allow trapping to be maintained with lower field strengths, which reduces photo-thermal effects. Thus, the probability of thermal damage can be reduced when handling sensitive specimens.

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 resistor–inductor–capacitor (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 reaction analysis.

This article presents a general way to enable automatic generation of digitized laboratories (a sort of digital twin for laboratory experimental setups) from remote laboratories and their easy deployment and publication. To demonstrate its effectiveness, we use two existing tools to generate and publish two digitized laboratories online from two implementations of a Snell's law remote laboratory, although they could be applied to many other remote laboratories. The first of these tools is a communication protocol that was designed to manipulate laboratory equipment through the Internet. This protocol can be used to automatically loop through different possible laboratory states and store them. The second one is a web platform that allows uploading files, that contain data sets of the laboratory states, to publish the digitized laboratory as a web application that is generated automatically.

The plasmonic response of a nano C-aperture is analyzed using the Vector Field Topology (VFT) visualization technique. The electrical currents that are induced on the metal surfaces when the C-aperture is excited by light is calculated for various wavelengths. The topology of this two-dimensional current density vector is analyzed using VFT. The plasmonic resonance condition is found to coincide with a distinct shift in the topology which leads to increased current circulation. A physical explanation of the phenomenon is discussed. Numerical results are presented to justify the claims. The analyses suggest that VFT can be a powerful tool for studying the physical mechanics of nano-photonic structures.

Lab-on-a-chip (LOC) devices capable of manipulating micro/nano-sized samples have spurred advances in biotechnology and chemistry. Designing and analyzing new and more advanced LOCs require accurate modeling and simulation of sample/particle dynamics inside such devices. In this work, we present a generalized computational physics model to simulate particle/sample trajectories under the influence of dielectrophoretic or optical forces inside LOC devices. The model takes into account time varying applied forces, Brownian motion, fluid flow, collision mechanics, and hindered diffusion caused by hydrodynamic interactions. We develop a numerical solver incorporating the aforementioned physics and use it to simulate two example cases: first, an optical trapping experiment, and second, a dielectrophoretic cell sorter device. In both cases, the numerical results are found to be consistent with experimental observations, thus proving the generality of the model. The numerical solver can simulate time evolution of the positions and velocities of an arbitrarily large number of particles simultaneously. This allows us to characterize and optimize a wide range of LOCs. The developed numerical solver is made freely available through a GitHub repository so that researchers can use it to develop and simulate new designs.

Trapping and manipulation of micro and nanoparticles are essential functional elements of lab-on-a-chip and micro total analysis systems with applications ranging from single cell analysis, diagnostics, drug discovery, and chemical synthesis. Reliable optical trapping of subwavelength particles is difficult due to the diffraction limited gradient of the optical intensity. Near-field traps have emerged as excellent systems to overcome this bottleneck. Using a periodic arrangement of C-shaped apertures we demonstrate the on-chip manipulation of single sub-wavelength polystyrene beads. The wavelength and polarization sensitivity of these resonant nanostructures is exploited to expose the trapped bead to a time varying near-field force using wavelength and polarization multiplexing schemes. While optical trapping has the advantage of being contactless, dielectrophoresis provides higher forces due to the flexibility of applying larger voltages and field gradients. The RF/Microwave frequency regime where dielectrophoresis operates allows increased polarizability of certain samples due to contribution from orientational, molecular and atomic polarizations as well as particle’s electrical conductivity. Combining the above advantages of both the techniques we discuss photoinduced dielectrophoretic trapping and manipulation of nanoparticles. Using dielectrophoretic trapping we discuss the simultaneous manipulation of beads and droplets as a route for on chip chemical synthesis.

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.

The iLabs platform – a low cost, highly scalable way to provide online learning for remote and virtual laboratory experiments is introduced into a classroom setting for the first time. As the COVID-19 pandemic has disrupted conventional laboratory experiment-based teaching, the iLabs platform can be a potential solution to include remote and virtual experiments in the curricula. As a case study, the process and challenges of integrating an iLabs experiment into a course are discussed. The described process includes converting a physical experiment into an iLabs experiment and using it as a teaching tool in one course at Stanford University during the Autumn 2020-2021 quarter. Feedback collected from the students is discussed. Although performed on a small scale, the case study suggests that the platform has the potential to be a helpful teaching tool for science and technology classes. In addition to being a substitute for a physical laboratory during the pandemic, the platform can be included as a supplementary teaching tool complementing physical laboratory experiments after the pandemic as well and will aid remote education.

We propose using “iLabs,” which relies on the digitalization of an experiment and a virtual display with photographs, as a solution to overcome the lack of scalability of realistic online experimentation and facilitate educational conversations.

X-ray imaging by means of a grating-based Talbot-Lau interferometer has become an important tool for a wide variety of application areas such as security, medical and materials analysis. Imaging modalities include attenuation, differential phase contrast, and visibility contrast (or so-called dark field). We have developed a novel modeling approach based on ray tracing with commercially available software (Zemax OpticStudio) that yields image projections for all three modalities. The results compare favorably with experimental findings. Our polychromatic ray-based model accommodates realistic 3-D CAD objects with tailored materials properties and also allows for both surface and bulk scattering. As such, the model can simulate imaging of complicated objects as well as assist in a physical understanding of experimental projection details.

Ultraviolet decontamination of personal protective equipment, particularly masks, is important in situations where mask reuse is practiced. To assist in the development of UV-C decontamination chambers, we have constructed ray tracing models in Zemax OpticStudio v20.1 for two distinct geometries, namely, a rectangular cabinet and a cylindrical can. These models provide irradiance distributions that can be used for comparison with experiment, as well as to predict local irradiance variation over the surface of a mask. In this paper we describe the model details, including: (1) a mask object in CAD format; (2) our assumptions for modeling surface properties; (3) the use of polygon object detectors for local irradiance analysis; and (4) experimental results that compare favorably to the simulations.

A grating-based Talbot-Lau X-ray interferometer provides three imaging modalities, namely attenuation, differential phase contrast, and dark field. Of these, dark-field imaging is uniquely capable of detecting and characterizing micron-scale fine structure in an object via small-angle scattering that reduces fringe visibility. In Part 1 [Opt. Express 29, 40891 (2021)10.1364/OE.447794], we formulate a statistical optics model that predicts the change in visibility, or dark-field signal, as a function of the statistical properties of the scattering object as well as its location within the interferometer. In Part 2, we demonstrate use of this model by simulating an object comprising a random collection of scattering microspheres placed in an X-ray grating interferometer designed to operate at 28 keV. The statistical optics results are validated by numerical Fourier optics simulations.

A grating-based Talbot-Lau X-ray interferometer provides three imaging modalities, namely attenuation, differential phase contrast, and dark field. Of these, dark-field imaging is uniquely capable of detecting and characterizing micron-scale fine structure in an object via small-angle scattering that reduces fringe visibility. Several empirical studies have been published showing the utility of this imaging modality for a wide range of applications. There also exists a more limited set of theoretical papers, based primarily on wave-optics formulations. In this two-part paper we present a comprehensive statistical optics model of the dark-field effect. In Part 1, we develop the theoretical underpinnings of the model with an emphasis on a scattering object comprising a random collection of microspheres, and in Part 2 [Opt. Express 29, 40917 (2021)10.1364/OE.447798], we provide a variety of example simulation results.

We present a computer-aided design tool for ion optical devices using the adjoint variable method. Numerical methods have been essential for the development of ion optical devices such as electron microscopes and mass spectrometers. Yet, the detailed computational analysis and optimization of ion optical devices is still onerous, since the governing equations of charged particle optics cannot be solved in closed form. Here, we show how to employ the adjoint variable method on the finite-element method and Störmer-Verlet method for electrostatic charged particle devices. This method allows for a full sensitivity analysis of ion optical devices, providing a quantitative measure of the effects of design parameters to device performance, at near constant computational cost with respect to the number of parameters. To demonstrate this, we perform such a sensitivity analysis for different freeform N-element Einzel lens systems including designs with over 13,000 parameters. We further show the optimization of the spot size of such lenses using a gradient-based method in combination with the adjoint variable method. The computational efficiency of the method facilitates the optimization of shapes and applied voltages of all surfaces of the device.

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.

We present a device that can achieve controlled transport of colloidal microparticles using an array of micro-electrodes. By exciting the micro-electrodes in regular sequence with an AC voltage, a time-varying moving dielectrophoretic force-field is created. This force propels colloidal microparticles along the electrode array. Using this method, we demonstrate bidirectional transport of polystyrene micro-spheres. Electromagnetic simulation of the device is performed, and the dielectrophoretic force profile around the electrode array is mapped. We develop a Brownian dynamics model of the trajectory of a particle under the influence of the time-varying force-field. Numerical and experimental results showing controlled particle transport are presented. The numerical model is found to be in good agreement with experimental data. The developed numerical framework can be useful in designing and modeling lab-on-a-chip devices that employ external non-contact forces for micro-/nanoparticle manipulation.

Typical x-ray detectors have a fundamental trade-off between resolution and quantum efficiency (QE). High quantum efficiency x-ray detection requires a thick conversion medium, but decreases the resolution due to limited pixel aspect ratios for both direct and indirect x-ray detection. We present a method for x-ray detection, holographic x-ray detection, which uses photorefractive materials to create a high resolution and high efficiency detector. The x-ray image is recorded in the volume of the photorefractive material, bypassing the aspect ratio issue of typical x-ray detectors. Holographic x-ray detection operates in three stages: recording an x-ray hologram in a photorefractive crystal, reading the hologram with visible light, and then erasing the hologram using ultraviolet light. We have experimentally demonstrated holographic x-ray detection with a resolution of 208 lp/mm (80% QE at 40 keV), an order of magnitude resolution improvement over commercially available x-ray detectors while maintaining > 80% QE.

Lithium-ion batteries (LIBs) have profoundly advanced the development of electric vehicles (EVs). However, one of the remaining bottlenecks in their widespread deployment is the long charging time required for commercial LIBs. Today, there is a global push towards extreme fast charging (XFC) to reduce charging times to 10-15 minutes.1 But existing LIBs cannot achieve this goal without significantly reducing battery performance, mainly due to the loss of active Li. The lost Li either becomes “dead” from being electronically disconnected after plating on the anode or “inactive” because of the irreversible reaction of Li with the electrolyte to form a solid electrolyte interphase. Since lithium plating is identified as one of the major degradation mechanisms from XFC in LIBs,2 understanding its origin and characteristics is essential to developing designs to enable fast-charged batteries. Several studies have characterized Li plating using techniques such as cryo-electron microscopy, transmission electron microscopy, X-ray diffraction, and X-ray micro-computed tomography (CT) among others.3 While valuable, these characterization techniques have limitations4 in terms of their sample preparation, spatial resolution, and imaging contrast required to distinguish between materials of similar atomic number (Z). In addition, due to the complex electrochemical reaction mechanisms of Li metal plating, multiple methods for detecting Li metal and understanding the mechanistic details of Li plating are needed. Here, we are using simultaneous neutron and X-ray-based dual-mode micro-computed tomography, a non-destructive imaging modality, to investigate the characteristics of Li plating during XFC in LIBs. Since X-rays and neutrons are sensitive to the electron and nuclear density of the material, respectively, dual-mode X-ray and neutron CT allows the easy separation of the different anode components in a LIB such as Li, graphite, and pores. Higher energy X-rays are needed to get through the metallic components in batteries such as copper and aluminum. However, they do not have sufficient contrast to separate lithium from graphite. Thus, neutrons are used due to their high sensitivity to lighter elements such as lithium, especially 6Li, and carbon. We have performed multi-modal imaging experiments at the Neutron and X-ray Tomography (NeXT)5 system located on the BT-2 beamline at the National Institute of Standards and Technology Center for Neutron Research. We characterized pristine and cycled graphite anode strips containing plated lithium at different regions. For cycled anode strips, we disassembled the battery pouch cells and imaged the graphite anodes cycled under XFC conditions for 450 cycles at fully discharged condition. These strips were used to get sample sizes small enough to achieve the highest possible spatial resolution. The spatial resolution achieved by this technique was ~10-15 μm, thus providing sufficient resolution to pinpoint the location of Li plating within the thickness of the anode. For image processing, we employed bivariate histogram segmentation that uses information from both X-rays and neutrons to segment different anode components. With these dual-imaging datasets, we are now investigating whether a link exists between the spatial heterogeneity of Li metal plating and the local microstructure of the battery anode including porosity, tortuosity, and thickness. We want to investigate why and where Li plating occurs on the battery anode. Addressing these fundamental questions will inform improved battery designs, graphite anode architectures, and charging protocols that will reduce Li plating during XFC in LIBs. Ultimately, these improvements based on our research findings will help make charging an EV similar to filling up at a gas station. References: Liu, Y., Zhu, Y., & Cui, Y. (2019). Challenges and opportunities towards fast-charging battery materials. Nature Energy, 1. Tomaszewska, A., Chu, Z., Feng, X., O'Kane, S., Liu, X., Chen, J., ... & Li, Y. (2019). Lithium-ion battery fast charging: A review. eTransportation, 1, 100011. Liu, Qianqian, et al. "Understanding undesirable anode lithium plating issues in lithium-ion batteries." RSC advances91 (2016): 88683-88700. Li, Y., Li, Y., & Cui, Y. (2018). Catalyst: how cryo-EM shapes the development of next-generation batteries. Chem, 4(10), 2250-2252. LaManna, J. M., Hussey, D. S., Baltic, E., & Jacobson, D. L. (2017). Neutron and X-ray Tomography (NeXT) system for simultaneous, dual modality tomography. Review of Scientific Instruments, 88(11), 113702. Figure 1

We present evidence-based design principles for three different UV-C based decontamination systems for N95 filtering facepiece respirators (FFRs) within the context of the SARS-CoV-2 outbreak of 2019–2020. The approaches used here were created with consideration for the needs of low- and middle-income countries (LMICs) and other under-resourced facilities. As such, a particular emphasis is placed on providing cost-effective solutions that can be implemented in short order using generally available components and subsystems. We discuss three optical designs for decontamination chambers, describe experiments verifying design parameters, validate the efficacy of the decontamination for two commonly used N95 FFRs (3M, #1860 and Gerson #1730), and run mechanical and filtration tests that support FFR reuse for at least five decontamination cycles.

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.