Nanoscale Accuracy Research Articles

On-Machine Calibration Method for In Situ Stereo Deflectometry System

Deflectometry is a promising method for the in situ measurement of specular surfaces. However, the accuracy of this method largely depends on the geometrical calibration, which suffers from a low convergence rate and local minima during the optimization. Off-machine calibration results in a change in geometry parameters due to the repeated disassembly of the measurement system and change of ambient temperature, which largely affects the measurement accuracy. This article presents a flexible on-machine calibration method with fewer intermediate parameters to accelerate the optimization for the in situ stereo deflectometry system. An inclined mirror with a fixed angle was mounted on the spindle of an ultraprecision machine tool and used as a reference plane reflecting the fringe displayed on the display screen. The reflected fringe captured by the cameras was encoded by an inclined mirror moving along the $C$ -axis and the $Z$ -axis of the machine tool. The preknowledge of the movement distance of the ultraprecision machine tool along the $Z$ -axis and rotation angle of the spindle with a nanoscale accuracy was used to largely reduce the number of intermediate variables involved in the optimization, thus improving the convergence speed of the global optimization method and calibration reliability. The experiment results show that this calibration method has higher calibration accuracy, measurement accuracy, and reliability compared to the conventional off-machine calibration method.

Quantifying accuracy and heterogeneity in single-molecule super-resolution microscopy

The resolution and accuracy of single-molecule localization microscopes (SMLMs) are routinely benchmarked using simulated data, calibration rulers, or comparisons to secondary imaging modalities. However, these methods cannot quantify the nanoscale accuracy of an arbitrary SMLM dataset. Here, we show that by computing localization stability under a well-chosen perturbation with accurate knowledge of the imaging system, we can robustly measure the confidence of individual localizations without ground-truth knowledge of the sample. We demonstrate that our method, termed Wasserstein-induced flux (WIF), measures the accuracy of various reconstruction algorithms directly on experimental 2D and 3D data of microtubules and amyloid fibrils. We further show that WIF confidences can be used to evaluate the mismatch between computational models and imaging data, enhance the accuracy and resolution of reconstructed structures, and discover hidden molecular heterogeneities. As a computational methodology, WIF is broadly applicable to any SMLM dataset, imaging system, and localization algorithm.

Phase modulation depth setting technique of a phase-generated-carrier under AOIM in fiber-optic interferometer with laser frequency modulation.

The phase modulation depth (PMD) in phase-generated-carrier demodulation is determined by the laser frequency modulation amplitude and working distance of a fiber-optic interferometer and must be set at a certain value. Active setting of the amplitude is unsuitable, especially for high-speed modulation, owing to variations in the laser source tuning coefficients. Existing calculation schemes for passive setting cannot work both owing to carrier phase delay (CPD) and the accompanied optical-intensity modulation (AOIM). Herein, a modified phase modulation depth calculation and setting technique is proposed. Double photoelectric detection and signal division are optimized to eliminate AOIM using a fiber delay chain and phase-locked amplifier module. Fast Fourier-transform and look-up table methods are used to calculate phase modulation depth without adding the carrier, which is unaffected by CPD. A fiber-optic Michelson interferometer is constructed to verify the feasibility of the proposed method. The experimental results show that AOIM can be eliminated; moreover, PMD can be calculated and set precisely. The displacement deviation is less than 1.03 nm. The resolution of measurement is considerably lesser than 1 nm and nanoscale accuracy is achieved in displacement measurement.

Automated Nanoscale Absolute Accuracy Alignment System for Transfer Printing.

The heterogeneous integration of micro- and nanoscale devices with on-chip circuits and waveguide platforms is a key enabling technology, with wide-ranging applications in areas including telecommunications, quantum information processing, and sensing. Pick and place integration with absolute positional accuracy at the nanoscale has been previously demonstrated for single proof-of-principle devices. However, to enable scaling of this technology for realization of multielement systems or high throughput manufacturing, the integration process must be compatible with automation while retaining nanoscale accuracy. In this work, an automated transfer printing process is realized by using a simple optical microscope, computer vision, and high accuracy translational stage system. Automatic alignment using a cross-correlation image processing method demonstrates absolute positional accuracy of transfer with an average offset of <40 nm (3σ < 390 nm) for serial device integration of both thin film silicon membranes and single nanowire devices. Parallel transfer of devices across a 2 × 2 mm2 area is demonstrated with an average offset of <30 nm (3σ < 705 nm). Rotational accuracy better than 45 mrad is achieved for all device variants. Devices can be selected and placed with high accuracy on a target substrate, both from lithographically defined positions on their native substrate or from a randomly distributed population. These demonstrations pave the way for future scalable manufacturing of heterogeneously integrated chip systems.

Modeling and prototype experiment of a monolithic 3-PUU parallel micromanipulator with nano-scale accuracy

This paper presents the design and experimental investigation of a piezo-driven monolithic compliant 3-PUU (1 prismatic joint (P-joint) and 2 universal joints (U-joints)) XYZ micro/nano manipulator with a high bandwidth frequency and a large workspace. The manipulator is manufactured using a 3D-printing technique, thus a monolithic structure is guaranteed. This feature allows the manipulator to work smoothly with high resolution, accuracy, and repeatability, and simultaneously, it avoids all the deficiencies of non-monolithic designs such as backlash, wear, and friction. Analytical and computational studies are conducted to investigate and confirm the performances of the manipulator. Additionally, an experimental study is performed to verify the analytical and computational results. The workspace is calculated using the three methods, and their relative errors along each axis are shown to validate the accuracy of the results. The tracking performances of the manipulator are validated in a feedback control strategy. Moreover, the proposed manipulator demonstrates the motion resolution of 23 nm, 24 nm, and 18 nm along X, Y, and Z axes, respectively. Finally, the experimental frequency test supports the computational results and confirms the manipulator’s high bandwidth frequency.

(Invited) Carbon Nanotube-Hybrid Nanoscale Devices

The controlled organization of individual molecules and nanostructures with nanoscale accuracy is key for the fabrication of the next generation optoelectronic devices and the investigation of events in biological and chemical assays. In this regard, we developed different platforms based on the in-solution assembly of classes of molecular materials (organic, inorganic, and biological with promising attributes) to single-walled carbon nanotubes (SWCNTs), employed as building blocks that allow for nanoscale studies to be performed in a variety of research fields.Through this approach, we assembled and investigated: molecular transport junctions,[1] metal nanowire devices using CNTs as vector templates,[2] static and dynamic organic-inorganic heterostructures consisting of Quantum Dot-CNT hybrids,[3,4] stimuli-responsive CNT-CdS/CNT-PbS devices[5] and DNA-CNT junctions,[6] protein-CNT nanohybrids,[7] and multiplexed biosensing devices based on aptamer- and protein-CNT heterostructures.[8,9] In this presentation, we will discuss relevant and recent examples among the aforementioned studies.[1] Journal of the American Chemical Society, 2016, 138, 2905-2908[2] Angewandte Chemie International Edition, 2019, DOI: 10.1002/anie.201902857[3] Small, 2017, 13, 1603042[4] Advanced Science, 2018, 5, 1800596[5] Submitted [6] Chemistry of Materials, 2019, 31, 1537-1542[7] Journal of the American Chemical Society, 2017, 139, 17834-17840[8] Nano Letters, 2018, 18, 4130-4135[9] Submitted

Optical nanomanipulation on solid substrates via optothermally-gated photon nudging

Constructing colloidal particles into functional nanostructures, materials, and devices is a promising yet challenging direction. Many optical techniques have been developed to trap, manipulate, assemble, and print colloidal particles from aqueous solutions into desired configurations on solid substrates. However, these techniques operated in liquid environments generally suffer from pattern collapses, Brownian motion, and challenges that come with reconfigurable assembly. Here, we develop an all-optical technique, termed optothermally-gated photon nudging (OPN), for the versatile manipulation and dynamic patterning of a variety of colloidal particles on a solid substrate at nanoscale accuracy. OPN takes advantage of a thin surfactant layer to optothermally modulate the particle-substrate interaction, which enables the manipulation of colloidal particles on solid substrates with optical scattering force. Along with in situ optical spectroscopy, our non-invasive and contactless nanomanipulation technique will find various applications in nanofabrication, nanophotonics, nanoelectronics, and colloidal sciences.

Correlating nano-scale surface replication accuracy and cavity temperature in micro-injection moulding using in-line process control and high-speed thermal imaging

Micro-injection moulding (μIM) stands out as preferable technology to enable the mass production of polymeric components with micro- and nano-structured surfaces. One of the major challenges of these processes is related to the quality assurance of the manufactured surfaces: the time needed to perform accurate 3D surface acquisitions is typically much longer than a single moulding cycle, thus making impossible to integrate in-line measurements in the process chain. In this work, the authors proposed a novel solution to this problem by defining a process monitoring strategy aiming at linking sensitive in-line monitored process variables with the replication quality. A nano-structured surface for antibacterial applications was manufactured on a metal insert by laser structuring and replicated using two different polymers, polyoxymethylene (POM) and polycarbonate (PC). The replication accuracy was determined using a laser scanning confocal microscope and its dependence on the variation of the main μIM parameters was studied using a Design of Experiments (DoE) experimental approach. During each process cycle, the temperature distribution of the polymer inside the cavity was measured using a high-speed infrared camera by means of a sapphire window mounted in the movable plate of the mould. The temperature measurements showed a high level of correlation with the replication performance of the μIM process, thus providing a fast and effective way to control the quality of the moulded surfaces in-line.

Nanoscale Resolution 3D Snapshot Particle Tracking by Multifocal Microscopy.

Accurate, precise, and rapid particle tracking in three dimensions remains a challenge; yet, its achievement will significantly enhance our understanding of living systems. We developed amultifocal microscopy (MFM) that allows snapshot acquisition of the imaging data, and an associated image processing approach, that together allow simultaneous 3D tracking of many fluorescent particles with nanoscale resolution. The 3D tracking was validated by measuring a known trajectory of a fluorescent bead with an axial accuracy of 19 nm through an image depth (axial range) of 3 μm and 4 nm precision of axial localization through an image depth of 4 μm. A second test obtained a uniform axial probability distribution and Brownian dynamics of beads diffusing in solution. We also validated the MFM approach by imaging fluorescent beads immobilized in gels and comparing the 3D localizations to their "ground truth" positions obtained from a confocal microscopy z-stack of finely spaced images. Finally, we applied our MFM and image processing approach to obtain 3D trajectories of insulin granules in pseudoislets of MIN6 cells to demonstrate its compatibility with complex biological systems. Our study demonstrates that multifocal microscopy allows rapid (video rate) and simultaneous 3D tracking of many "particles" with nanoscale accuracy and precision in a wide range of systems, including over spatial scales relevant to whole live cells.

Watching a Single Fluorophore Molecule Walk into a Plasmonic Hotspot

Plasmonic nanoantennas allow for enhancing the spontaneous emission, altering the emission polarization, and shaping the radiation pattern of quantum emitters. A critical challenge for the experimental realizations is positioning a single emitter into the hotspot of a plasmonic antenna with nanoscale accuracy. We demonstrate a dynamic light-matter interaction nanosystem enabled by the DNA origami technique. A single fluorophore molecule can autonomously and unidirectionally walk into the hotspot of a plasmonic nanoantenna along a designated origami track. Successive fluorescence intensity increase and lifetime reduction are in situ monitored using single-molecule fluorescence spectroscopy, while the fluorophore walker gradually approaches and eventually enters the plasmonic hotspot. Our scheme offers a dynamic platform, which can be used to develop functional materials, investigate intriguing light-matter interaction phenomena, and serve as prototype system for examining theoretical models.

Visualizing DNA folding and RNA in embryos at single-cell resolution.

Establishment of cell types during development requires precise interactions between genes and distal regulatory sequences. Our understanding of how these interactions look in three dimensions, vary across cell types in complex tissue, and relate to transcription remains limited. Here we describe optical reconstruction of chromatin architecture (ORCA), a method to trace the DNA path in single cells with nanoscale accuracy and genomic resolution reaching 2 kilobases. We applied ORCA to a Hox gene cluster in cryosectioned Drosophila embryos and labelled ~30 RNA species in parallel. We identified cell-type-specific physical borders between active and Polycomb-repressed DNA, and unexpected Polycomb-independent borders. Deletion of Polycomb-independent borders led to ectopic enhancer-promoter contacts, aberrant gene expression, and developmental defects. Together, these results illustrate an approach for high-resolution, single-cell DNA domain analysis in vivo, reveal domain structures that change with cell identity, and show that border elements contribute to formation of physical domains in Drosophila.

Standalone interferometry-based calibration of convex lens-induced confinement microscopy with nanoscale accuracy.

Strongly confined environments (confined dimensions between 1-100 nm) represent unique challenges and opportunities for understanding and manipulating molecular behavior due to the significant effects of electric double layers, high surface-area to volume ratios, and other phenomena at the nanoscale. Convex Lens-induced Confinement (CLiC) can be used to analyze the dynamics of individual molecules or particles confined in a planar slit geometry with continuously varying gap thickness. We describe an interferometry-based method for precise measurement of the slit pore geometry. Specifically, this approach permitted accurate characterization of separation distances as small as 5 nm, with 1 nm precision, without a priori knowledge or assumptions about the contact geometry, as well as a greatly simplified experimental setup that required only a lens, coverslip, and inverted microscope. The interferometry-based measurement of gap height offered a distinct advantage over conventional fluorescent dye-based methods; e.g., accurate interferometric height measurements were made at low gap heights regardless of solution conditions, while the concentration of fluorescent dye was significantly impacted by solution conditions such as ionic strength or pH. The accuracy of the interferometric measurements was demonstrated by comparing the experimentally measured concentration of a charged fluorescent dye as a function of gap thickness with dye concentration profiles calculated using Debye-Hückel theory. Accurate characterization of nanoscale gap thickness will enable researchers to study a variety of practical and biologically relevant systems within the CLiC geometry.

Integration of quantum dots with lithium niobate photonics

The integration of quantum emitters with integrated photonics enables complex quantum photonic circuits that are necessary for photonic implementation of quantum simulators, computers, and networks. Thin-film lithium niobate is an ideal material substrate for quantum photonics because it can tightly confine light in small waveguides and has a strong electro-optic effect that can switch and modulate single photons at low power and high speed. However, lithium niobate lacks efficient single-photon emitters, which are essential for scalable quantum photonic circuits. We demonstrate deterministic coupling of single-photon emitters with a lithium niobate photonic chip. The emitters are composed of InAs quantum dots embedded in an InP nanobeam, which we transfer to a lithium niobate waveguide with nanoscale accuracy using a pick-and-place approach. An adiabatic taper transfers single photons emitted into the nanobeam to the lithium niobate waveguide with high efficiency. We verify the single photon nature of the emission using photon correlation measurements performed with an on-chip beamsplitter. Our results demonstrate an important step toward fast, reconfigurable quantum photonic circuits for quantum information processing.

Microsphere-based interferometric optical probe

Fluorescent optical probes have rapidly transformed our understanding of complex biological systems by providing specific information on biological targets in the natural living state. However, their utility is often limited by insufficient brightness, photostability, and multiplexing capacity. Here, we report a conceptually new optical probe, termed ‘reflectophore’, which is based on the spectral interference from a dielectric microsphere. Reflectophores are orders-of-magnitudes brighter than conventional fluorophores and are free from photobleaching, enabling practically unlimited readout at high fidelity. They also offer high-degree multiplexing, encoded in their optical size, which can be readily decoded through interferometric detection with nanoscale accuracy, even in turbid biological media. Furthermore, we showcase their biological applications in cellular barcoding and microenvironmental sensing of a target protein and local electric field.

Hybrid integration of an evanescently coupled AlGaAs microdisk resonator with a silicon waveguide by nanoscale-accuracy transfer printing.

Hybrid integration of a III-V microdisk resonator on a silicon-on-insulator waveguide platform is demonstrated. Transfer printing with nanoscale accuracy is used to micro-assemble an evanescently coupled all-pass microdisk resonator with a targeted coupler gap of 100nm using pre-fabricated AlGaAs and silicon components. Transmission measurements show hybrid resonances with a loaded Q-factor of 7×103 and a cavity finesse of over 100.

(Invited) Electrochemical Micromachining Based on Confined Etching

Micromachining is becoming the cutting-edge of high-tech manufacturing because of the increasing industrial demand for supersmooth surfaces and functional three-dimensional micro/nano-structures in microelectromechanical systems, ultra-large scale integrated circuits, miniaturized total analysis systems, precision optics and so on. Taking advantage of no tool wear, no surface stress, environmental friendliness, simple operation, and low cost, electrochemical micromachining (ECM) has an irreplaceable role in micromachining. We present here our perseverant research in the last two decades on how to “confine” the ECM processes to occur at micrometer or even nanometer scale, that is, to ensure ECM with nanoscale accuracy. We have been developing the confined etchant layer technique (CELT) to fabricate three-dimensional micro- and nanostructures (3D-MNS) on different metals and semiconductor materials since 1992. In general, there are three procedures in CELT: (1) generating the etchant on the surface of the tool electrode by electrochemical or photoelectrochemical reactions; (2) confining the etchant in a depleted layer with a thickness of micro- or nanometer scale; (3) feeding the tool electrode to etch the workpiece. Scavengers, which can react with the etchant, are usually adopted to form a confined etchant layer. Through the subsequent homogeneous reaction between the scavenger and the photo or electrogenerated etchant in the electrolyte solution, the diffusion distance of the etchant is confined to micro- or nanometer scale, which ensures the nanoscale accuracy of electrochemical machining. However, because the thickness of the electrolyte solution between the tool electrode and the workpiece are usually at micro/nano-meter scale, it is a challenge to solve the problems of potential distribution and mass transfer in the ultra-thin layer electrolyte cell. In this presentation, we will introduce our recent work on the external physical field induced electrochemical reactions in which there is no need of 2-electrode or 3-electrode system in the conventional electrochemical system.

Electrical nucleation and detection of single 360° homochiral Néel domain walls measured using the anomalous Nernst effect

Using a thermoelectric measurement, we demonstrate the nucleation and detection of a single 360° homochiral Néel domain wall (DW), formed by an independently nucleated pair of 180° Néel DWs having the same helicity in a perpendicular magnetic anisotropy track. The DW formation is governed by strong interfacial Dzyaloshinskii-Moriya interaction (DMI) and detected at room temperature using the anomalous Nernst effect (ANE). A large DMI can be generated at an interface where the symmetry is broken between a material having a large spin-orbit coupling and a thin ferromagnetic layer. The ANE voltage, VANE∝∇T×M, is sensitive to the magnitude of the out-of-plane magnetization M through a confined in-plane temperature gradient ∇T and allows for the direct thermoelectrical detection of the DW position with nanoscale accuracy along the track. Here, we present evidence that independently nucleated pairs of 180° Néel DWs in microwire devices can be brought together by an applied magnetic field to form a 360° homochiral Néel DW. Subsequently, we show that a strong magnetic field needs to be applied in order to annihilate the 360° DW due to the strong interfacial DMI in our Pt/Co(0.6nm)/AlOx multilayers. In addition to enabling a high magnetic storage and data transfer rate with low power consumption in novel computational and storage devices, such DWs facilitate a reduction in bit size down to a few nanometers with metastability.

DNA Origami-Based Förster Resonance Energy-Transfer Nanoarrays and Their Application as Ratiometric Sensors.

DNA origami nanostructures provide a platform where dye molecules can be arranged with nanoscale accuracy allowing to assemble multiple fluorophores without dye-dye aggregation. Aiming to develop a bright and sensitive ratiometric sensor system, we systematically studied the optical properties of nanoarrays of dyes built on DNA origami platforms using a DNA template that provides a high versatility of label choice at minimum cost. The dyes are arranged at distances, at which they efficiently interact by Förster resonance energy transfer (FRET). To optimize array brightness, the FRET efficiencies between the donor fluorescein (FAM) and the acceptor cyanine 3 were determined for different sizes of the array and for different arrangements of the dye molecules within the array. By utilizing nanoarrays providing optimum FRET efficiency and brightness, we subsequently designed a ratiometric pH nanosensor using coumarin 343 as a pH-inert FRET donor and FAM as a pH-responsive acceptor. Our results indicate that the sensitivity of a ratiometric sensor can be improved simply by arranging the dyes into a well-defined array. The dyes used here can be easily replaced by other analyte-responsive dyes, demonstrating the huge potential of DNA nanotechnology for light harvesting, signal enhancement, and sensing schemes in life sciences.

Single point Linnik white-light spectral microscopic interferometer for surface measurement

According to the requirement for high precision surface measurement in complex situations, a single point Linnik type measuring system with long working distance is built based on white-light spectral interferometry. Five-step phase-shifting algorithm is used to extract accurate phase information in the measuring system. Several experiments are conducted to measure the absolute distance and film thickness, verifying the feasibility of the system. It has been achieved that the system can measure the surface form and film thickness with nanoscale accuracy.

Roll-to-Roll Nanoforming of Metals Using Laser-Induced Superplasticity.

This Letter describes a low-cost, scalable nanomanufacturing process that enables the continuous forming of thin metallic layers with nanoscale accuracy using roll-to-roll, laser-induced superplasticity (R2RLIS). R2RLIS uses a laser shock to induce the ultrahigh-strain-rate deformation of metallic films at room temperature into low-cost polymeric nanomolds, independently of the original grain size of the metal. This simple and inexpensive nanoforming method does not require access to cleanrooms and associated facilities, and can be easily implemented on conventional CO2 lasers, enabling laser systems commonly used for rapid prototyping or industrial cutting and engraving to fabricate uniform and three-dimensional crystalline metallic nanostructures over large areas. Tuning the laser power during the R2RLIS process enables the control of the aspect ratio and the mechanical and optical properties of the fabricated nanostructures. This roll-to-roll technique successfully fabricates mechanically strengthened gold plasmonic nanostructures with aspect ratios as high as 5 that exhibit high oxidation resistance and strong optical field enhancements. The CO2 laser used in R2RLIS can also integrate the fabricated nanostructures on transparent flexible substrates with robust interfacial contact. The ability to fabricate ultrasmooth metallic nanostructures using roll-to-roll manufacturing enables the large scale production, at a relatively low-cost, of flexible plasmonic devices toward emerging applications.