Sub-micrometer Resolution Research Articles

Additive Manufacturing of Nanostructures That Are Delicate, Complex, and Smaller than Ever.

Additive manufacturing with two-photon polymerization (TPP) has opened new opportunities for the rapid fabrication of 3D structures with sub-micrometer resolution, but there are still many fabrication constraints associated with this technique. This study details a postprocessing method utilizing oxygen-plasma etching to increase the capabilities of TPP. Underutilized precision in the typical fabrication process allows this subtractive technique to dramatically reduce the minimum achievable feature size. Moreover, since the postprocessing occurs in a dry environment, high aspect ratio features that cannot survive the typical fabrication route can also be achieved. Finally, it is shown that the technique also provides a pathway to realize structures that otherwise are too delicate to be fabricated with TPP, as it enables to introduce temporary support material that can be removed with the plasma. As such, the proposed approach grants access to a massively expanded design domain, providing new capabilities that are long sought in many fields, including optics, biology, robotics, and solid mechanics.

Nanoscale X-ray imaging of ageing in automotive lithium ion battery cells

Due to an increasing number of electric vehicles, battery pack endurance over the cell lifetime is an important issue of public interest, because it determines to a large degree the value of the vehicle. The exact state of health of a battery is still a major challenge for analysis, especially since the individual ageing factors are not well understood and depend on the cell chemistry and design. In this analysis, X-ray computer tomographic (CT) images of new and aged battery electrodes are compared to determine structural changes over lifetime. The X-ray CT images with sub-micrometer resolution show the internal pore structure of the electrodes and allow the identification of the morphology of the materials. Organic residues and depositions responsible for reduced porosity in aged anodes are quantified and visualized. Furthermore, particle cracking and current collector corrosion is detected on the cathode side. All these are ageing effects, which might influence the cell capacity and impedance. A quantitative analysis of the lithium distribution completes the interpretation of the ageing study confirming that the degradation can be attributed to the loss of cyclable lithium which is bound in the particle surface layer of the anode.

First demonstration of antimatter wave interferometry.

Interference of matter waves is at the heart of quantum physics and has been observed for a wide range of particles from electrons to complex molecules. Here, we demonstrate matter wave interference of single positrons using a period-magnifying Talbot-Lau interferometer based on material diffraction gratings. The system produced high-contrast periodic fringes, which were detected by means of nuclear emulsions capable of determining the impact point of each individual positron with submicrometric resolution. The measured energy dependence of fringe contrast in the range of 8 to 16 keV proves the quantum-mechanical origin of the periodic pattern and excludes classical projective effects, providing the first observation to date of antimatter wave interference. Future applications of this interferometric technique include the measurement of the gravitational acceleration of neutral antimatter systems exploiting the inertial sensing capabilities of Talbot-Lau interference.

Visualization of Inhomogeneuous Reactivity on Battery Material Using Scanning Electrochemical Cell Microscopy

To understand the metal oxide coating effect on battery performance, the following two techniques are required: 1) constructing a flat thin-film electrode surface to realize a well-defined interface and 2) analyzing the electrode/electrolyte interface reaction with nanoscale resolution. We previously studied flat LiCoO2 thin-film electrodes using in situ surface-sensitive X-ray absorption spectroscopy (XAS) and reported that Co reduction at the LiCoO2 surface resulting from electrolyte contact caused the initial degradation. We also showed that the ZrO2 layer successfully prevented physical contact between LiCoO2 and the electrolyte. And it confirmed that a thicker ZrO2 layer (above 2 nm) increased the diffusion resistance of the lithium ions in the ZrO2 layer. However, since XAS lacks in-plane resolution and provides only averaged information, it is impossible to analyze the ZrO2 morphology in detail. Recently, Taguchi et al. investigated a thin Li-Zr-layer (ca. 2 nm) on a LiCoO2 composite electrode by transmission electron microscopy (TEM). They suggested that this thin layer could improve the durability. However, it is difficult to analyze the electrochemical properties using TEM. To evaluate the intrinsic mechanism of the metal oxide coating effect, it is necessary to develop a novel in-situ method that can analyze the surface morphology with high spatial resolution and simultaneously determine the local electrochemical properties. Scanning electrochemical microscopy (SECM) is a powerful technique for linking the surface morphology of a sample to its electrochemical properties. For the battery materials, the SECM feedback mode is effective in monitoring solid electrolyte interphase formation. To directly and quantitatively investigate spatially resolved ionic processes, mercury-capped platinum ultramicroelectrodes were developed and employed for Li+ imaging based on Li stripping. However, it is difficult to visualize the Li+ flux in battery materials at the sub-micrometer scale by SECM. Scanning electrochemical cell microscopy (SECCM), which uses a nanopipette as a probe and forms a local electrochemical cell, is effective in characterizing surface reactivity. We recently applied SECCM for visualization of electrochemical activities on a lithium-ion battery cathode material at sub-micrometer resolution. The SECCM was applied to collect or provide Li in specified area confined by the nanopipette. Further, it collection visualized the electrochemical properties by scanning the nanopipette as an image. There are some strong advantages in SECCM for battery material research such as its high spatial resolution, small capacitive current, and isolated electrochemical cell. In this report, we applied SECCM to characterize a ZrO2-coated LiCoO2 thin-film electrode prepared by pulsed laser deposition. Local cyclic voltammetry (CV) and galvanostatic charge/discharge were performed to characterize the cycle durability and rate performance of ZrO2-coated LiCoO2 thin-film electrodes and to reveal the relationship between the ZrO2 morphology and thickness.

Optical Measurements of Three-Dimensional Microscopic Temperature Distributions Around Gold Nanorods Excited by Localized Surface Plasmon Resonance

The measurement and control of the temperature in microscopic systems, which are increasingly required in diverse applications, are fundamentally important. Yet, the measurement of the three-dimensional (3D) temperature distribution in microscopic systems has not been demonstrated. Here, we propose and experimentally demonstrate the measurement of the 3D temperature distribution by exploiting the temperature dependency of the refractive index (RI). Measurement of the RI distribution of water makes it possible to quantitatively obtain its 3D temperature distribution above a glass substrate coated with gold nanorods with sub-micrometer resolution, in a temperature range of 100C and with a sensitivity of 2.88C. The 3D temperature distributions that are obtained enable various thermodynamic properties including the maximum temperature, heat flux, and thermal conductivity to be extracted and analyzed quantitatively.

Sub-micrometer resolution liquid level sensor based on a hollow core fiber structure.

Liquid level measurement in lab on a chip (LOC) devices is a challenging task due to the demand for a sensor with ultra-high resolution but miniature in nature. In this Letter, we report a simple, compact in size, yet highly sensitive liquid level sensor based on a hollow core fiber (HCF) structure. The sensor is fabricated by fusion splicing a short section of HCF between two singlemode fibers (SMFs). Sensor samples with different lengths of HCF have been studied; it is found that the sensor with a HCF length of ∼4.73 mm shows the best sensitivity of ∼0.014 dB/μm, corresponding to a liquid level resolution of ∼0.7 μm, which is over five times higher than that of the previous reported fiber optic sensors to date. In addition, experimental results have demonstrated that the proposed sensor shows good repeatability of measurement and a very low cross sensitivity to changes in the refractive index of the surrounding medium.

Theoretical and experimental studies of electrostatic focusing for electrohydrodynamic jet printing

Electrohydrodynamic jet (e-jet) printing technology has the capability of sub-micrometer resolution with large-range viscous inks, but is incompatible with nonplanar and insulating substrates. Here, we develop a theoretical model for an electrostatic lens that is incorporated into an e-jet system to shape the electric field inside the printhead. The electrostatic lens can generate electrostatic focusing to drive a Taylor cone for the generation of jetting, without a voltage being applied between the printhead and the substrate, which avoids the influence of standoff height on the nonplanar substrate and the charge repulsion from polarization of the insulating substrate. The theoretical model, in combination with finite element simulation, is established to reasonably calculate each design parameter of the electrostatic lens-integrated printhead. Further, the e-jet printhead is successfully utilized to direct-write conductive lines with high-viscosity solutions and drop-on-demand print complex pattern with low-viscosity solutions on both insulating and curvilinear substrates. It leads to high-resolution e-jet printing on the arbitrary substrate in a direct, precise and low-voltage manner. The electrostatic lens-integrated printhead thoroughly breaks the restrictions of printing on insulating and nonplanar substrates and significantly broadens its applications.

Interface Solid-State Reactions in La0.8Sr0.2MnO3/Ce0.8Sm0.2O2 and La0.8Sr0.2MnO3/BaCe0.9Y0.1O3 Disclosed by X-ray Microspectroscopy

The stability of the electrode/electrolyte interface is a critical issue in solid-oxide cells working at high temperatures, affecting their durability. In this paper, we investigate the solid-state chemical mechanisms that occur at the interface between two electrolytes (Ce0.8Sm0.2O2, SDC, and BaCe0.9Y0.1O3, BCY) and a cathode material (La0.8Sr0.2MnO3, LSM) after prolonged thermal treatments. Following our previous work on the subject, we used X-ray microspectroscopy, a technique that probes the interface with submicrometric resolution combining microanalytical information with the chemical and structural information coming from space-resolved X-ray absorption spectroscopy. In LSM/BCY, the concentration profiles show striking reactive phenomena at the interface with a variety of micrometer-sized secondary phases: in particular, X-ray absorption spectra reveal at least three different chemical states for manganese (from +3 to +6). Also in LSM/SDC, a couple previously reported as chemically stable, we found...

Combined microfluidics–confocal Raman microscopy platform for studying enhanced oil recovery mechanisms

AbstractTo study the mechanism of enhanced oil recovery, it is important to characterize the three‐dimensional spatial distribution of various chemical species, especially water and oil, and their evolution during the course of water flooding. For example, visualizing the (selective) removal of oil from clay or silica substrates by low salinity water can yield important insights. Here, we present a platform that uses a microfluidic device (to represent water flooding at the pore scale) in combination with confocal Raman microscopy. Distributions of oil, water, and minerals are resolved at submicrometer resolution upon flooding water with changing composition. Using glass and gibbsite to mimic sandstone and clay, and water containing divalent cations (Ca2+), we find that oil containing a fatty acid preferentially adsorbs on the gibbsite. Removal of the divalent cations leads to release of the oil droplet. This finding is consistent with the multiple ion exchange mechanism and underlines that the presence of clay is important for low salinity enhanced oil recovery. We expect that our platform will pave the road towards systematic screening of water flood compositions in more complex systems.

Probing the Microstructure of Methylammonium Lead Iodide Perovskite Solar Cells

The microstructure of absorber layers is pivotally important for all thin‐film solar technologies. Using electron backscattered diffraction (EBSD), the crystal orientation in methylammonium lead iodide thin films with submicrometer resolution is reported. For the vast majority of (110) oriented grains, the c‐axis of the perovskite unit cell is oriented in‐plane. Although some adjacent grains exhibit the same in‐plane horizontal orientation of the c‐axis, no universal horizontal orientation of the c‐axis within the sample plane exists. The (110) crystal orientation correlates with an in‐plane orientation of the ferroelectric polarization as investigated by vertical and lateral piezoresponse force microscopy (PFM). The individual grains with different crystal orientations that exhibit different ferroelectric patterns and surface potentials are identified. The strong correlation between crystal orientation and ferroelectric polarization allows conclusions to be drawn about the microstructure from PFM measurements and, likewise, the ferroelectric polarization to be derived from crystallographic observations by EBSD.

Zone plates for angle-resolved photoelectron spectroscopy providing sub-micrometre resolution in the extreme ultraviolet regime.

This article reports on the fabrication and testing of dedicated Fresnel zone plates for use at the nano-ARPES branch of the I05-ARPES beamline of Diamond Light Source to perform angle-resolved photoelectron spectroscopy with sub-micrometre resolution in real space. The aim of the design was to provide high photon flux combined with sub-micrometre spot sizes. The focusing lenses were tested with respect to efficiency and spatial resolution in the extreme ultraviolet between 50 eV and 90 eV. The experimentally determined diffraction efficiencies of the zone plates are as high as 8.6% at 80 eV, and a real-space resolution of 0.4 µm was demonstrated. Using the zone-plate-based setup, monolayer flakes of the two-dimensional semiconductor WS2 were investigated. This work demonstrates that the local electronic structure can be obtained from an area of a few micrometres across a two-dimensional heterostructure.

Third harmonic generation imaging and analysis of the effect of low gravity on the lacuno-canalicular network of mouse bone.

The lacuno-canalicular network (LCN) hosting the osteocytes in bone tissue represents a biological signature of the mechanotransduction activity in response to external biomechanical loading. Using third-harmonic generation (THG) microscopy with sub-micrometer resolution, we investigate the impact of microgravity on the 3D LCN structure in mice following space flight. A specific analytical procedure to extract the LCN characteristics from THG images is described for ex vivo studies of bone sections. The analysis conducted in different anatomical quadrants of femoral cortical bone didn’t reveal any statistical differences between the control, habitat control and flight groups, suggesting that the LCN connectivity is not affected by one month space flight. However, significant variations are systematically observed within each sample. We show that our current lack of understanding of the extent of the LCN heterogeneity at the organ level hinders the interpretation of such investigations based on a limited number of samples and we discuss the implications for future biomedical studies.

Noninvasive Investigation of Phloem Structure by 3D Synchrotron X-Ray Microtomography.

X-ray microtomography (μCT) is a three-dimensional imaging technique, which has, over the past decade, established itself as a go-to method for nondestructive visualization of plant tissue with submicrometer resolution. μCT is closely related to medical computed tomography, in that a measurement consists of acquiring a series of radiographs from different directions around the sample. Especially with synchrotron X-ray sources, these radiographs exhibit significant phase contrast. This greatly enhances soft tissue contrast, making it well suited for plant imaging. Tomographic reconstruction techniques are then employed to convert the stack of radiographs into a 3D volumetric image. Compared with the laboratory X-ray tube-based systems, synchrotron tomography beamlines also offer high throughput, with tens of samples scanned over the course of a typical 24-h beam time.Synchrotrons are typically operated as user facilities, with a staff member assisting users in aligning the beamline and all instrumentation-related matters. From the user's point of view, success of a synchrotron μCT experiment is often dependent on secure sample mounting, choice of appropriate beam parameters, and post-processing the data, i.e., extracting scientifically meaningful results from the 3D image. In this chapter, we review the issues to consider in preparation of a μCT experiment from the point of view of a phloem researcher, emphasizing those aspects which are directly under the user's control rather than technical specifics, which vary from one beamline to another.

In-process measurement for cure depth control of nano stereolithography using evanescent light

One-shot layer-by-layer microstereolithography using evanescent light is regarded as one of the potential methods to achieve a spatial process resolution of submicrometer, meeting a demand for the next-generation nano/micro 3D manufacturing. However, there is a critical problem that curing phenomena by evanescent light is too sensitive to detailed exposure condition such as temperature of photosensitive resin, dynamic diffusion of free radicals, dissolved oxygen, and so on. To solve this critical problem, we developed an in-process evaluation method for potential cured thickness by evanescent light and experimentally succeeded in cure depth control with a layer thickness of submicrometer during its curing process.

Imaging and quantitative analysis of insecticide in mosquito net fibers using Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS).

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) analysis was used to qualitatively and quantitatively assess the distribution of permethrin insecticide on the surfaces and interiors of Olyset long-lasting insecticidal net (LLIN) fibers. Total insecticide content in LLINs has been established using many analytical methods. However, it is important to quantify the bioavailable portion residing on the fiber surfaces for incorporated LLINs. ToF-SIMS is a very surface sensitive technique and can directly image the spatial distribution of permethrin insecticide on the surface of Olyset fibers. Surface permethrin appeared as patchy deposits which were easily removed by acetone and reappeared after several days as interior permethrin migrated (bloomed) from the fiber interior. After a wash/incubation cycle, permethrin deposits were more diffuse and less concentrated than those on the as-received fibers. ToF-SIMS is particularly sensitive to detect the Cl- ion, which is the characteristic ion of permethrin. Ion implantation and quantification of dopants using SIMS is well established in the semiconductor industry. In this study, quantitative depth profiling was carried out using 35Cl- ion implantation to correlate secondary ion yield with permethrin concentration, yielding a limit of detection of 0.051 wt% for permethrin. In some cases, surface concentration differed greatly from the fiber interior (>1 μm below the surface). Two- and three-dimensional mapping of Cl at sub-micrometer resolution showed permethrin to be dissolved throughout the fiber, with about 2 vol% residing in disperse, high-concentration domains. This suggests that these fibers fall into the class of monolithic sustained-release devices. It is expected that ToF-SIMS can be a valuable tool to provide insight into the insecticide release behavior of other LLIN products, both current and future.

Lanthanide‐Based Thermometers: At the Cutting‐Edge of Luminescence Thermometry

AbstractPresent technological demands in disparate areas, such as microfluidics and nanofluidics, microelectronics and nanoelectronics, photonics and biomedicine, among others, have reached to a development such that conventional contact thermal probes are not accomplished anymore to perform accurate measurements with submicrometric spatial resolution. The development of novel noncontact thermal probes is, then, mandatory, contributing to an expansionary epoch of luminescence thermometry. Luminescence thermometry based on trivalent lanthanide ions has become very popular since 2010 due to the unique versatility, stability, and narrow emission band profiles of the ions that cover the entire electromagnetic spectrum with relatively high emission quantum yields. Here, a perspective overview on the field is given from the beginnings in the 1950s until the most recent cutting‐edge examples. The current movement toward usage of the technique as a new tool for thermal imaging, early tumor detection, and as a tool for unveiling the properties of the thermometers themselves or of their local neighborhoods is also summarized.

Polarization induced contrast X-ray fluorescence at submicrometer resolution reveals nanometer apatite crystal orientations across entire tooth sections

For biomedical research, successful imaging of calcified microstructures often relies on absorption differences between features, or on employing dies with selective affinity to areas of interest. When texture is concerned, e.g. for crystal orientation studies, polarization induced contrast is of particular interest. This requires sufficient interaction of the incoming radiation with the volume of interest in the sample to produce orientation-based contrast. Here we demonstrate polarization induced contrast at the calcium K-edge using submicron sized monochromatic synchrotron X-ray beams. We exploit the orientation dependent subtle absorption differences of hydroxyl-apatite crystals in teeth, with respect to the polarization field of the beam. Interaction occurs with the fully mineralized samples, such that differences in density do not contribute to the contrast. Our results show how polarization induced contrast X-ray fluorescence mapping at specific energies of the calcium K-edge reveals the micrometer and submicrometer crystal arrangements in human tooth tissues. This facilitates combining both high spatial resolution and large fields of view, achieved in relatively short acquisition times in reflection geometry. In enamel we observe the varying crystal orientations of the micron sized prisms exposed on our prepared surface. We easily reproduce crystal orientation maps, typically observed in polished thin sections. We even reveal maps of submicrometer mineralization fronts in spherulites in intertubular dentine. This Ca K-edge polarization sensitive method (XRF-PIC) does not require thin samples for transmission nor extensive sample preparation. It can be used on both fresh, moist samples as well as fossilized samples where the information of interests lies in the crystal orientations and where the crystalline domains extend several micrometers beneath the exposed surface.

Quantitative phase imaging of fiber Bragg gratings in multicore fibers.

Fiber Bragg gratings (FBGs) and multi-core fibers (MCFs) have independently demonstrated high levels of performance in numerous diverse applications. When integrated together, the devices can offer enhanced performance as well as open more applications. In all of these cases, the refractive index (RI) characterization of the FBGs is crucial in monitoring and validating the fabricated devices. To accomplish this, quantitative phase imaging (QPI) is a promising RI characterization candidate satisfying all of the requirements: noninvasive measurement, quantitative characterization, sub-micrometer resolution, no a priori knowledge, and 3D reconstruction. In this paper, we propose a new QPI method for characterization of the RI distribution of multiple FBGs in a single MCF. We have identified the key challenges associated with this approach: the pixel integration effect, aliasing effect, numerical aperture requirement, and characteristic functions recovery. We have further identified approaches for overcoming each of these challenges that have previously impeded this direction of research. The proposed method is supported by simulations of 2D and 3D gratings.

Predicting drug delivery efficiency into tumor tissues through molecular simulation of transport in complex vascular networks

Efficient delivery of anticancer drugs into tumor tissues at maximally effective and minimally toxic concentrations is vital for therapeutic success. At present, no method exists that can predict the spatial and temporal distribution of drugs into a target tissue after administration of a specific dose. This prevents accurate estimation of optimal dosage regimens for cancer therapy. Here we present a new method that predicts quantitatively the time-dependent spatial distribution of drugs in tumor tissues at sub-micrometer resolution. This is achieved by modeling the diffusive flow of individual drug molecules through the three-dimensional network of blood-vessels that vascularize the tumor, and into surrounding tissues, using molecular mechanics techniques. By evaluating delivery into tumors supplied by a series of blood-vessel networks with varying degrees of complexity, we show that the optimal dose depends critically on the precise vascular structure. Finally, we apply our method to calculate the optimal dosage of the cancer drug doxil into a section of a mouse ovarian tumor, and demonstrate the enhanced delivery of liposomally administered doxorubicin when compared to free doxorubicin. Comparison with experimental data and a multiple-compartment model show that the model accurately recapitulates known pharmacokinetics and drug-load predictions. In addition, it provides, for the first time, a detailed picture of the spatial dependence of drug uptake into tissues surrounding tumor vasculatures. This approach is fundamentally different to current continuum models, and reveals that the target tumor vascular topology is as important for therapeutic success as the transport properties of the drug delivery platform itself. This sets the stage for revisiting drug dosage calculations.

Development of a Miniaturized and Selective Impedance Sensor for Real-Time Slime Monitoring in Pipes and Tanks

A novel impedance sensor for monitoring the thickness of undesired micrometric deposits on the surfaces of water pipes and tanks is presented. Coplanar 10 μm-spaced gold microelectrodes were fouled in controlled laboratory conditions and the influence of slime on impedance response was measured. Two different sets of experiments were conducted to form slime on the electrodes surface, addressing biofilm growth and calcium carbonate precipitation, respectively. Following the formation, the thickness of the slime was characterized by Atomic Force Microscopy. Experimental tests highlighted that the impedance response is linear with to the thickness of the slime in both cases, in a 2 μm to 10 μm range. Interestingly, the slope of the response (i.e. of the ionic resistance change vs. thickness) is opposite: a decrease in the case of biofilm (-0.6 Ω/μm where the conductivity of the extracellular matrix becomes dominant) and an increase (+1.4 Ω/μm) in the case of inorganic deposits. In conclusion, this simple and robust sensor provides an accurate and selective determination of slime, while fouling and cleaning up cycles have demonstrated the possibility of regeneration. The final goal for the microsensor, once coupled to an electronic system for data processing and transmission, is the installation along the inner surface of pipes and tanks for real-time remote monitoring of long-term formation of slime with sub-micrometric thickness resolution.