Sub-millimeter Scale Research Articles

Formation of large-scale MoS2/Cu2O/ZnO heterostructure arrays by in situ photodeposition and application for ppb-level NO2 gas sensing

Photodeposition has been used extensively for nanomaterial growth on a substrate, but direct photodeposition of 2D transition metal dichalcogenides (TMDs) remains challenging. An alternative approach is to deposit 2D TMDs on a suitable nanomaterial template. In this work, large-scale MoS2/Cu2O/ZnO heterostructure arrays are formed by low-temperature in situ photodeposition and the nanocomposites are used for chemiresistive gas sensing at room temperature. Using 254 nm UV irradiation, Cu2O nanoclusters are photodeposited in solution on hydrothermally grown ZnO nanorod arrays and Cu2O/ZnO heterostructure arrays are first formed. MoS2 nanoparticles are subsequently photodeposited on Cu2O and MoS2/Cu2O/ZnO heterostructure arrays with good uniformity on a sub-millimeter scale are consequently produced. The ternary nanocomposite with a 45 min MoS2 photodeposition time shows the highest response of 890% toward 500 ppb NO2 under UV-activated sensing. An excellent linear sensitivity of 18.7 ppm–1 has been achieved and the estimated lowest detection limit is 1.3 ppb, exhibiting good potential for monitoring of environmental NO2 content. The outstanding performance is attributed to the combined chemical and electronic sensitization effects of the abundant heterojunctions in the nanocomposite. The present work reveals that facile in situ photodeposition is suitable for synthesis of large-scale MoS2/Cu2O/ZnO heterostructure arrays with remarkable gas sensing performance.

Perceptual echoes as travelling waves may arise from two discrete neuronal sources

Growing evidence suggests that travelling waves are functionally relevant for cognitive operations in the brain. Several electroencephalography (EEG) studies report on a perceptual alpha-echo, representing the brain response to a random visual flicker, propagating as a travelling wave across the cortical surface. In this study, we ask if the propagating activity of the alpha-echo is best explained by a set of discrete sources mixing at the sensor level rather than a cortical travelling wave. To this end, we presented participants with gratings modulated by random noise and simultaneously acquired the ongoing MEG. The perceptual alpha-echo was estimated using the temporal response function linking the visual input to the brain response. At the group level, we observed a spatial decay of the amplitude of the alpha-echo with respect to the sensor where the alpha-echo was the largest. Importantly, the propagation latencies consistently increased with the distance. Interestingly, the propagation of the alpha-echoes was predominantly centro-lateral, while EEG studies reported mainly posterior-frontal propagation. Moreover, the propagation speed of the alpha-echoes derived from the MEG data was around 10 m/s, which is higher compared to the 2 m/s reported in EEG studies. Using source modelling, we found an early component in the primary visual cortex and a phase-lagged late component in the parietal cortex, which may underlie the travelling alpha-echoes at the sensor level. We then simulated the alpha-echoes using realistic EEG and MEG forward models by placing two sources in the parietal and occipital cortices in accordance with our empirical findings. The two-source model could account for both the direction and speed of the observed alpha-echoes in the EEG and MEG data. Our results demonstrate that the propagation of the perceptual echoes observed in EEG and MEG data can be explained by two sources mixing at the scalp level equally well as by a cortical travelling wave. Importantly, these findings should not be directly extrapolated to intracortical recordings, where travelling waves gradually propagate at a sub-millimetre scale.

Van der Waals Epitaxy Growth of 2D Single-Element Room-Temperature Ferromagnet.

2D single-element materials, which are pure and intrinsically homogeneous on the nanometer scale, can cut the time-consuming material-optimization process and circumvent the impure phase, bringing about opportunities to explore new physics and applications. Herein, for the first time, the synthesis of ultrathin cobalt single-crystalline nanosheets with a sub-millimeter scale via van der Waals epitaxy is demonstrated. The thickness can be as low as ≈6nm. Theoretical calculations reveal their intrinsic ferromagnetic nature and epitaxial mechanism: that is, the synergistic effect between van der Waals interactions and surface energy minimization dominates the growth process. Cobalt nanosheets exhibit ultrahighblocking temperatures above 710 K and in-plane magnetic anisotropy. Electrical transport measurements further reveal that cobalt nanosheets have significant magnetoresistance (MR) effect, and can realize a unique coexistence of positive MR and negative MR under different magnetic field configurations, which can be attributed to the competition and cooperation effect among ferromagnetic interaction, orbital scattering, and electronic correlation. These results provide a valuable case for synthesizing 2D elementary metal crystals with pure phase and room-temperature ferromagnetism and pave the way for investigating new physics and related applications in spintronics.

Direct co-registration of [18F]FDG uptake and histopathology in surgically excised malignancies of the head and neck: a feasibility study.

Recent technical advancements in PET imaging have improved sensitivity and spatial resolution. Consequently, clinical nuclear medicine will be confronted with PET images on a previously unfamiliar resolution. To better understand [18F]FDG distribution at submillimetric scale, a direct correlation of radionuclide-imaging and histopathology is required. A total of five patients diagnosed with a malignancy of the head and neck were injected with a clinical activity of [18F]FDG before undergoing surgical resection. The resected specimen was imaged using a preclinical high-resolution PET/CT, followed by slicing of the specimen. Multiple slices were rescanned using a micro-PET/CT device, and one of the slices was snap-frozen for frozen sections. Frozen sections were placed on an autoradiographic film, followed by haematoxylin and eosin staining to prepare them for histopathological assessment. The results from both autoradiography and histopathology were co-registered using an iterative co-registration algorithm, and regions of interest were identified to study radiotracer uptake. The co-registration between the autoradiographs and their corresponding histopathology was successful in all specimens. The use of this novel methodology allowed direct comparison of autoradiography and histopathology and enabled the visualisation of uncharted heterogeneity in [18F]FDG uptake in both benign and malignant tissue. We here describe a novel methodology enabling the direct co-registration of [18F]FDG autoradiography with the gold standard of histopathology in human malignant tissue. The future use of the current methodology could further increase our understanding of the distribution of radionuclides in surgically excised malignancies and hence, improve the integration of pathology and molecular imaging in a multiscale perspective. ClinicalTrials.gov Identifier: NCT05068687.

Macroscopically ordered phase separation: A new strategy for improving the superconducting performance in Fe(Se, Te)

The phase separation commonly exists in Fe(Se, Te) and damages their superconducting performance. In this paper, we successfully tuned the phase separation in Fe(Se, Te) via adding FeF2 to the raw materials. A macroscopically ordered phase separation which exhibited submillimetre scale striations in width arranged along the c-axis was formed in the FeF2-added Fe(Se, Te), different from the commonly observed flower shape phase separation in FeF2-free Fe(Se, Te). Moreover, the two macroscopical separated phases were identified as FeSe0.6Te0.4 and FeSe0.4Te0.6. The regular phase separation morphology and the fixed phase composition enhanced the flux pinning behavior which induced the appearance of Δκ pinning and deferred the changing from point pinning to surface pinning with the raising temperature. As a result, Fe(Se, Te) with the macroscopically ordered phase separation overwhelms the common phase separation Fe(Se, Te) in Hc2, U0, and Jc. Notably, at 4.2 K, the critical current density Jc reaches 9.3 × 104 A/cm2 in self-field and 1.3 × 104 A/cm2 at 7 T which outclassed the reported values. Besides, the well-defined stoichiometry of the separated phase also lead to a higher Tc of 15.42 K with a narrower transition width of only 0.98 K. Overall, our work reveals the tuning of phase separation in Fe(Se, Te) in terms of phase morphology and stoichiometry, which is a new strategy for improving the superconducting performance in Fe(Se, Te).

Multiscale Analysis of Permeable and Impermeable Wall Models for Seawater Reverse Osmosis Desalination

In recent years, high permeability membranes (HPMs) have attracted wide attention in seawater reverse osmosis (SWRO) desalination. However, the limitation of hydrodynamics and mass transfer characteristics for conventional spiral wound modules defeats the advantage of HPMs. Feed spacer design is one of the effective ways to improve module performance by enhancing permeation flux and mitigating membrane fouling. Herein, we propose a multiscale modeling framework that integrates a three-dimensional multi-physics model with a permeable wall and an impermeable wall, respectively, at a sub-millimeter scale and a system-level model at a meter scale. Using the proposed solution framework, a thorough quantitative analysis at different scales is conducted and it indicates that the average errors of the friction coefficient and the Sherwood number using the impermeable wall model are less than 2% and 9%, respectively, for commercial SWRO membrane (water permeability 1 L m−2 h−1 bar−1) and HPMs (3 L m−2 h−1 bar−1, 5 L m−2 h−1 bar−1 and 10 L m−2 h−1 bar−1) systems, compared to the predictions using the permeable wall model. Using both the permeable and impermeable wall models, the system-level simulations, e.g., specific energy consumption, average permeation flux, and the maximum concentration polarization factor at the system inlet are basically the same (error < 2%), while the impermeable wall model has a significant advantage in computational efficiency. The multiscale framework coupling the impermeable wall model can be used to guide the efficient and accurate optimal spacer design and system design for HPMs using, e.g., a machine learning approach.

Evaluation of Geometric Data Registration of Small Objects from Non-Invasive Techniques: Applicability to the HBIM Field.

Reverse engineering and the creation of digital twins are advantageous for documenting, cataloging, and maintenance control tracking in the cultural heritage field. Digital copies of the objects into Building Information Models (BIM) add cultural interest to every artistic work. Low-cost 3D sensors, particularly structured-light scanners, have evolved towards multiple uses in the entertainment market but also as data acquisition and processing techniques for research purposes. Nowadays, with the development of structured-light data capture technologies, the geometry of objects can be recorded in high-resolution 3D datasets at a very low cost. On this basis, this research addresses a small artifact with geometric singularities that is representative of small museum objects. For this, the precision of two structured-light scanners is compared with that of the photogrammetric technique based on short-range image capture: a high-cost Artec Spider 3D scanner, and the low-cost Revopoint POP 3D scanner. Data capture accuracy is evaluated through a mathematical algorithm and point set segmentation to verify the spatial resolution. In addition, the precision of the 3D model is studied through a vector analysis in a BIM environment, an unprecedented analysis until now. The work evaluates the accuracy of the devices through algorithms and the study of point density at the submillimeter scale. Although the results of the 3D geometry may vary in a morphometric analysis depending on the device records, the results demonstrate similar accuracies in that submillimeter range. Photogrammetry achieved an accuracy of 0.70 mm versus the Artec Spider and 0.57 mm against the Revopoint POP 3D scanner.

Modification of the surface layer model and establishment of the surface layer thickness model of pure copper

The size effect of flow stress is one of the main factors affecting the deformation behavior of materials in microforming. The traditional surface layer model can well explain the phenomenon that the material flow stress decreases with the declining size of the specimen at sub-millimeter and micron scales, while it also exhibits some deficiencies inconsistent with reality. In order to more accurately describe the deformation behavior of materials at the microscale, the modified surface layer model was proposed based on the experimental results and plastic forming theory, in which the region where the flow stress was lower than that of the internal polycrystalline rather than just a single layer of grains in the surface region was taken as the surface layer. The calculation method of the thickness of the surface layer and the stress in each region was also presented. According to the stress distribution in each region, a surface-layer-thickness model based on grain size was proposed. With the results of micro upsetting experiments, the surface-layer-thickness model of T2 copper was fitted. It was validated that the modified-surface-layer model and surface-layer-thickness model can accurately predict the flow stress of the material at the microscale.

Modeling and Control of Conducting Polymer Actuator

Conducting polymer (CP) actuator has nonlinear dynamic characteristics during its charge process. In this study, we proposed an electromechanic model and an optimal controller for a type of ionic electroactive polymer (IEPA) actuator with submillimeter scale, which can produce large deformation under low actuation voltage. The electronic model is to describe the evolution of charge state in time domain. The mechanic model is to calculate the deformation of CP actuator under the actuation force and external force. Based on the electromechanic coupling model, a parameter identification method is proposed to estimate the nonlinear parameter of CP actuator. The experiments show that our electromechanic model successfully predicts the deformation of actuator under different input voltages with the identified parameters. In the last step, an optimal controller is designed to control the orientation of IEAP actuator, which achieves at a high control performance in our experiments. The success of the modeling and control lays the foundation work for the subsequent biomedical applications.

Bistable Reflection Assisted by Fano Resonance in DMDMW With Low-Threshold and Large Modulation Depth

Owing to an additional thinner planar waveguide with micron scale is attracted to the symmetrical metal cladding waveguide (SMCW) with sub-millimeter scale, the interference interaction between different Q-value guided modes would generate a Fano reflectivity curve. In our double metal-dielectric-metal waveguides (DMDMW) structure, a Kerr nonlinear medium is located in the guiding layer of the SMCW where the excited oscillating wave is enormously enhanced. Numerical calculations show that a minute variation of the incident light intensity will give rise to a change in the dielectric constant of the Kerr nonlinear medium and lead to positive feedback. A bistable reflection can be achieved with a low threshold and a large modulation depth because of the sharpness and the asymmetricity of the Fano reflectivity curve.

Supercomputing and machine learning-aided optimal design of high permeability seawater reverse osmosis membrane systems

Concentration polarization (CP) should limit the energy and cost reducing benefits of high permeability seawater reverse osmosis (SWRO) membranes operating at a water flux higher than normal one. Herein, we propose a multiscale optimization framework coupling membrane permeability, feed spacer design (sub-millimeter scale) and system design (meter scale) via computational fluid dynamics and system level modeling using advanced supercomputing in conjunction with machine learning. Simulation results suggest energy consumption could be reduced by 27.5% (to 1.66 kWh m−3) predominantly through the use of high permeability SWRO membranes (12.2%) and a two-stage design (14.5%). Without optimization, CP approaches 1.52 at the system inlet, whereas the optimized CP is limited to 1.20. This work elucidates the optimized permeability, module design, operating scheme and benefits of high permeability SWRO membranes in seawater desalination.

An Underactuated Adaptive Microspines Gripper for Rough Wall

Wall attachment has great potential in a broad range of applications such as robotic grasping, transfer printing, and asteroid sampling. Herein, a new type of underactuated bionic microspines gripper is proposed to attach to an irregular, rough wall. Experimental results revealed that the gripper, profiting from its flexible structure and underactuated linkage mechanism, is capable of adapting submillimeter scale roughness to centimeter scale geometry irregularity in both normal and tangential attachment. The rigid-flexible coupling simulation analysis validated that the rough adaptation was achieved by the passive deformation of the zigzag flexible structure, while the centimeter-scale irregularity adaptation come from the underactuated design. The attachment test of a spine confirmed that a 5 mm sliding distance of the spine tip on the fine brick wall promises a saturated tangential attachment force, which can guide the stiffness design of flexible structure and parameter selection of underactuated linkage. Furthermore, the developed microspines gripper was successfully demonstrated to grasp irregular rocks, tree trunks, and granite plates. This work presents a generally applicable and dexterous passive adaption design to achieve rough wall attachment for flat and curved objects, which promotes the understanding and application of wall attachment.

ESPRESS.0: Eustachian Tube-Inspired Tactile Sensor Exploiting Pneumatics for Range Extension and SenSitivity Tuning.

Optimising the sensitivity of a tactile sensor to a specific range of stimuli magnitude usually compromises the sensor's widespread usage. This paper presents a novel soft tactile sensor capable of dynamically tuning its stiffness for enhanced sensitivity across a range of applied forces, taking inspiration from the Eustachian tube in the mammalian ear. The sensor exploits an adjustable pneumatic back pressure to control the effective stiffness of its 20 mm diameter elastomer interface. An internally translocated fluid is coupled to the membrane and optically tracked to measure physical interactions at the interface. The sensor can be actuated by pneumatic pressure to dynamically adjust its stiffness. It is demonstrated to detect forces as small as 0.012 N, and to be sensitive to a difference of 0.006 N in the force range of 35 to 40 N. The sensor is demonstrated to be capable of detecting tactile cues on the surface of objects in the sub-millimetre scale. It is able to adapt its compliance to increase its ability for distinguishing between stimuli with similar stiffnesses (0.181 N/mm difference) over a large range (0.1 to 1.1 N/mm) from only a 0.6 mm deep palpation. The sensor is intended to interact comfortably with skin, and the feasibility of its use in palpating tissue in search of hard inclusions is demonstrated by locating and estimating the size of a synthetic hard node embedded 20 mm deep in a soft silicone sample. The results suggest that the sensor is a good candidate for tactile tasks involving unpredictable or unknown stimuli.

AUTONOMOUS SPERMATOZOON-LIKE MICROROBOT WITH CHEMICAL PROPULSION

Abstract Introduction Robotics, as one of today's fastest growing disciplines and in support of surgeons, can generate significant advantages for both doctors and patients, such as increased automation of routine procedures or the performance of previously impossible procedures. Microrobotics is the use of microscale robots to be introduced into the body. The aim of this study is to develop a prototype of an autonomous spermatozoon-like microrobot propelled by chemical reactions for navigation in lumens. Methods To study the propulsion of the microrobot, a simulation was carried out in COMSOL. The movement of the microrobot was simulated by applying alternating forces emulating chemical actuation with and without a passive flagellum, in a fluid environment. In addition, a macro-scale prototype was developed. Two motors were used for propulsion with attached propellers. Their speed and the development of the programmed functions for movement were monitored. The microrobot's movement, propulsion and flagellum effect were studied in water. Results The simulations showed that without the flagellum, a drifting movement was generated, stabilising with its presence, as well as adding an additional impulse. The prototype showed similar behaviour to that obtained in the simulations, moving in the desired way. Conclusions It has been shown that the presence of the flagellum, without actuation, generates an additional impulse to the one developed by the initial propulsion. The prototype has also shown the feasibility of the simulations, and the possibility of manufacturing a microrobot on a sub-millimetre scale.

Optimization of an Active Leveling Scheme for a Short-Range Gravity Experiment

At Cal Poly Humboldt, undergraduate researchers and faculty have constructed a torsion-pendulum experiment that seeks to measure gravitational interactions below test mass separations of 100 microns. The aim of this experiment is to look for deviations in the weak equivalence principle (WEP) and inverse-square law (ISL). The scale at which this experiment operates is within an untested range at the submillimeter scale. This apparatus’s torsion pendulum consists of equal masses with differing materials arranged as a composition dipole. The twist of this configuration is measured as an attractor mass oscillates in a parallel-plate arrangement nearby. The oscillation creates a time-dependent torque on the pendulum which can be studied for deviations in the WEP and ISL. At present, an active leveling scheme has been implemented to mediate the apparatus’s long-term tilt variations. This scheme has been optimized through the use of a power supply and proportional-integral-derivative (PID) loop that mitigates the variations in tilt by applying a voltage to a resistor attached to one of the apparatus legs. The applied voltage causes thermal expansion of the apparatus leg support structure, thus correcting and modulating the tilt of this experiment.

Terahertz Microjets as Realizations of Subwavelength Focusing in the Terahertz Spectrum

In this article, we recognize the growing interest to realize terahertz (THz) spectroscopy on the submillimetre scale and target its fundamental challenge—in the need for subwavelength focusing. The challenge is addressed here by way of the THz microjet. We show that THz microjets can be formed as intense focal spots with subwavelength sizes by focusing THz radiation through engineered dielectric spheres. The dielectric spheres are analyzed via the electromagnetic (Mie) theory and effective medium (Bruggeman) theory, and then implemented out of microcomposite material with the requisite (optimal) refractive indices and (minimal) extinction coefficients for the targeted 0.3–0.7-THz spectrum. Ultimately, the dielectric spheres are tested and found to realize THz microjets as intense focal spots with the desired subwavelength sizes.

Broadband one-dimensional range profiles characteristic of rough surface in terahertz band

<sec>The one-dimensional (1D) range profile is an important back scattering characteristic of objective, which reveals the longitudinal distribution of radar cross section (RCS) along the detection beam. Since the shape and posture can be reflected by the 1D range profile, it is of great significance in military to determine the target orientation, velocity and whether it is armed. In this paper, broadband terahertz 1D-range-profile measurement system is built based on the time-domain spectroscopy (TDS) system. It is in bistatic configuration (bistatic angle of 9°) and the signal-to-noise ratio (SNR) is 34.5 dB, with a gold mirror used as a reflector. Benefiting from the ultrashort terahertz pulse width (full pulse width of 0.52 ps), the bandwidth covers the frequency range from 0.1 THz to 2.5 THz (peaked at 0.9 THz), corresponding to the range resolution on a submillimeter scale.</sec><sec>Firstly, the 1D range profiles of several objects in different shapes are measured, including the step, cylinder, step cone and their combination, which indicates that the geometric profile of the target in the detection direction is adequate to identify the shape feature of the target and proves the reliability of the 1D range profile measuring system based on TDS. Secondly, aluminum plates with different surface roughness in a range of 0–25 μm are also characterized. The Kirchhoff approximation theory and small perturbation method (SPM) are introduced to illustrate the characteristics of broadband terahertz 1D range profile related to the surface roughness of target. It is found that the scattering characteristic of metal object in the terahertz range is sensitive to surface roughness. If the surface roughness of the object is larger, the peak intensity of the 1D range profile will be weaker and the echo signal pulse width becomes wider. The rule is also applicable for the cases with different incident angles. Furthermore, it is revealed that the time delay of the 1D range profile in the bistatic system is related to the rotation direction of the target, which is useful in estimating the posture of the target. In summary, the characteristics of 1D range profile for metal objects relating to shape, surface roughness and posture are studied. The conclusions have certain guiding significance for the target detection and recognition of terahertz radar.</sec>

Capillary-driven microfluidics: impacts of 3D manufacturing on bioanalytical devices.

Over decades, decentralized diagnostics continues to move towards rapid and cost-effective testing at the point-of-care (POC). Although microfluidics has become a key enabling technology for POC testing, the need for robust peripheral equipment has been a key limiting factor in reaching an ideal device. Manufacturing technologies are now reaching a level of maturity that allows the definition of 3D features down to the sub-millimeter scale. Employing three-dimensional (3D) features and surface chemistry allows the possibility to pre-program sophisticated control of the capillary flow avoiding bulky peripheral equipment. By designing a sequence of steps, like elution of reagents, washing, mixing, and sensing, capillary valves have become a powerful tool for POC applications. These valves use capillary force to stop and then release flows within pre-programmed capillary circuits without any moving part. Without their 3D structure, the feasibility of creating pre-programmed bioanalytical devices would be nearly impossible. Besides, the advent of smart materials and their variety of surface properties permitted the unprecedented ability to fabricate reliable flow control with a range of capillary driving forces. The classification of such capillary elements is presented in two functional steps - stop and actuation. This review includes the advances in 3D microfabrication, design, and surface chemistry for manufacturing bioanalytical devices. These developments are critically reviewed, focusing on the process and considering phenomena such as timing, reproducibility, unwanted diffusion, and cross-contaminations.

Development of micrometer-scaled aluminum-enriched phosphate glass beads with a silver activator for real-time profile measurement of a clinical carbon beam

Real-time monitoring of clinical carbon beams from a synchrotron accelerator was accomplished by using aluminum-enriched phosphate glass with a silver activator. Build-up effects are often observed in commercially available silver-containing phosphate glass that strongly limit the use of the glass in real-time dosimetry in clinical particle therapy fields. In this study, we modified the composition of silver-containing phosphate glass by adding an additional 0.2 mol% aluminum impurity to cause broadband radioluminescence under clinical carbon beam exposure. Convenient real-time radiation monitoring was accomplished on submillimeter scales by using aluminum-enriched silver-containing phosphate glass beads. Optical fiber dosimetry using the aluminum-enriched silver-containing phosphate glass was demonstrated, and stable radioluminescence was visualized for each bunch of 290 MeV u−1 from a synchrotron under different beam fluxes up to 3 × 109 particles/spill (clinical beam conditions).

A single-atom mechano-optical transducer for sensing sub-attonewton vector DC force

Mechano-optical transducers are devices that convert a force or displacement signal to an optical one, enabling ultrasensitive mechanical detection. Currently, ultraweak DC force sensors with high spatial resolution are in high demand for the search of possible exotic spin-dependent interactions beyond the standard model in sub-millimeter scale. Here, we demonstrate a mechano-optical transducer of a single trapped ion with the force sensitivity about 600 zN/Hz for the DC force. This method utilizes the Doppler shift of the time-resolved fluorescence to detect the ion's micromotion that is coupled to a vector force. By alternating the directions of the detection laser beams, the vector DC forces can be precisely measured. Such a mechano-optical transducer provides sub-attonewton sensitivity with the spatial resolution in single-atom level, enabling various uses for both scientific and industrial purposes.