Particulate Standard Establishment for Absolute Quantification of Nanoparticles by LA-ICP-MS.

The development of nanotechnology has transformed many cutting-edge studies related to single-molecule analysis into nanoparticle (NP) detection with a single-NP sensitivity and ultrahigh resolution. While laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) has been successful in quantifying and tracking NPs, its quantitative calibration remains a major challenge due to the lack of suitable standards and the uncertain matrix effects. Herein, we frame a new approach to prepare quantitative standards via precise synthesis of NPs, nanoscale characterization, on-demand NP distribution, and deep learning-assisted NP counting. Gold NP standards were prepared to cover the mass range from sub-femtogram to picogram levels with sufficient accuracy and precision, thus establishing an unambiguous relationship between the sampled NP number in each ablation and the corresponding mass spectral signal. Our strategy facilitated for the first time the study of the factors affecting particulate sample capture and signal transductions in LA-ICP-MS analysis and culminated in the development of an LA-ICP-MS-based method for absolute NP quantification with single-NP sensitivity and single-cell quantification capability. The achievements would herald the emergence of new frontiers cut across a spectrum of toxicological and diagnostic issues related to NP quantification.

Superoscillation focusing with suppressed sidebands by destructive interference.

Optical superoscillation, a phenomenon that the local optical field can oscillate much faster than that allowed by its highest harmonic, can significantly overcome the Abbe diffraction limit. However, as the spot size is compressed below the superoscillation criteria of 0.38λ/NA, huge sidebands will inevitably appear around the central lobe with intensity hundreds of times higher than that of the central lobe. Here, we propose an approach to realize superoscillation by using destructive interference. The central lobe size can be compressed beyond the superoscillation criteria without formation of strong sidebands by destructive interference between focused fields. Such a super-resolution metalens can find its application in label-free far-field super-resolution microscopy.

Dielectric Walls/Layers Modulated 3D Periodically Structured SERS Chips: Design, Batch Fabrication, and Applications.

As an indispensable constituent of plasmonic materials/dielectrics for surface enhanced Raman scattering (SERS) effects, dielectrics play a key role in excitation and transmission of surface plasmons which however remain more elusive relative to plasmonic materials. Herein, different roles of vertical dielectric walls, and horizontal and vertical dielectric layers in SERS via 3D periodic plasmonic materials/dielectrics structures are studied. Surface plasmon polariton (SPP) interferences can be maximized within dielectric walls besieged by plasmonic layers at the wall thicknesses of integral multiple half-SPPplasmonic material-dielectric -wavelength which effectively excites localized surface plasmon resonance to improve SERS effects by one order of magnitude compared to roughness and/or nanogaps only. The introduction of extra Au nanoparticles on thin dielectric layers can further enhance SERS effects only slightly. Thus, the designed Au/SiO2 based SERS chips show an enhancement factor of 8.9 × 1010 , 265 times higher relative to the chips with far thinner SiO2 walls. As many as 1200 chips are batch fabricated for a 4 in wafer using cost-effective nanoimprint lithography which can detect trace Hg ions as low as 1 ppt. This study demonstrates a complete generalized platform from design to low-cost batch-fabrication to applications for novel high performance SERS chips of any plasmonic materials/dielectrics.

Artificial intelligence: A powerful paradigm for scientific research.

Artificial intelligence (AI) coupled with promising machine learning (ML) techniques well known from computer science is broadly affecting many aspects of various fields including science and technology, industry, and even our day-to-day life. The ML techniques have been developed to analyze high-throughput data with a view to obtaining useful insights, categorizing, predicting, and making evidence-based decisions in novel ways, which will promote the growth of novel applications and fuel the sustainable booming of AI. This paper undertakes a comprehensive survey on the development and application of AI in different aspects of fundamental sciences, including information science, mathematics, medical science, materials science, geoscience, life science, physics, and chemistry. The challenges that each discipline of science meets, and the potentials of AI techniques to handle these challenges, are discussed in detail. Moreover, we shed light on new research trends entailing the integration of AI into each scientific discipline. The aim of this paper is to provide a broad research guideline on fundamental sciences with potential infusion of AI, to help motivate researchers to deeply understand the state-of-the-art applications of AI-based fundamental sciences, and thereby to help promote the continuous development of these fundamental sciences.

Simultaneous achievement of superior response and full recovery of titanium dioxide/graphene hybrid FET sensors for NH3 through p- to n-mode switch.

The switch in the sensing mode for better identification of donor/acceptor gases with simultaneous enhancement of the sensing performance at a fixed working temperature particularly room temperature (RT) is quite challenging for gas sensors. Herein, TiO2/graphene hybrid field effect transistor (FET) sensors (TiO2/GFET) with varied hybrid areas are presented. Superior sensing and recovery performances for NH3 are achieved through sensing mode switch via gate biasing. 16.40% response and full recovery for 25 ppm NH3 are achieved for TiO2/GFET sensors with 100% titanium dioxide coverage (D100) at RT (27 °C) with 15-20% humidity upon switching sensing mode from p- to n via gate biasing. Full recovery is attributed to the Coulomb interaction between charged polar donor molecules and positively polarized surface which is enhanced by the switch from p- to n-mode. The humidity can enhance response up to -35.48% for 25 ppm NH3 with full recovery in n-mode for D100. D100 shows superior selectivity towards NH3 against both electron-acceptor NO2 and several other electron-donor analytes. The sensing behaviors for NH3 are well elucidated using energy band diagrams based on the experimental results. This study proposes a novel idea for performance improvement of FET based sensors with p- and n-type hybrid sensing materials through p (n)- to n (p)-mode switch assisted by gate biasing by incorporating suitable electron (hole) rich materials to compensate holes (electrons) in p (n)-type materials for electron donor (acceptor) gas detection.

A Generalized Methodology of Designing 3D SERS Probes with Superior Detection Limit and Uniformity by Maximizing Multiple Coupling Effects.

Accurate design of high-performance 3D surface-enhanced Raman scattering (SERS) probes is the desired target, which is possibly implemented with a prerequisite of quantifying formidable multiple coupling effects involved. Herein, by combining theory and experiments on 3D periodic Au/SiO2 nanogrid models, a generalized methodology of accurately designing high performance 3D SERS probes is developed. Structural symmetry, dimensions, Au roughness, and polarization are successfully correlated quantitatively to intrinsic localized electromagnetic field (EMF) enhancements by calculating surface plasmon polariton (SPP), localized surface plasmon resonance (LSPR), optical standing wave effects, and their couplings theoretically, which is experimentally verified. The hexagonal SERS probes optimized by this methodology realize over two orders of magnitudes (405 times) improvement of detection limit for Rhodamine 6G model molecules (2.17 × 10-11 m) compared to the unoptimized probes with the same number density of hot spots, an enhancement factor of 3.4 × 108, a uniformity of 5.52%, and are successfully applied to the detection of 5 × 10-11 m Hg ions in water. This unambiguously results from the Au roughness-independent extra 144% contribution of LSPR effects excited by SPP interference waves as secondary sources, which is very unusual to be beyond the conventional recognition.

Multichannel-Independent Information Encoding with Optical Metasurfaces.

Optical metasurfaces, as an emerging platform, have been shown to be capable of effectively manipulating the local properties (amplitude, phase, and polarization) of the reflected or transmitted light and have unique strengths in high-density optical storage, holography, display, etc. The reliability and flexibility of wavefront manipulation makes optical metasurfaces suitable for information encryption by increasing the possibility of encoding combinations of independent channels and the capacity of encryption, and thus the security level. Here, recent progress in metasurface-based information encoding is reviewed, in which the independent channels for information encoding are built with wavelength and/or polarization in one-dimensional/two-dimensional (1D/2D) modes. The way to increase information encoding capacity and security level is proposed, and the opportunities and challenges of information encoding with independent channels based on metasurfaces are discussed.

Nanogap-Engineerable Electromechanical System for Ultralow Power Memory.

Nanogap engineering of low-dimensional nanomaterials has received considerable interest in a variety of fields, ranging from molecular electronics to memories. Creating nanogaps at a certain position is of vital importance for the repeatable fabrication of the devices. Here, a rational design of nonvolatile memories based on sub-5 nm nanogaped single-walled carbon nanotubes (SWNTs) via the electromechanical motion is reported. The nanogaps are readily realized by electroburning in a partially suspended SWNT device with nanoscale region. The SWNT memory devices are applicable for both metallic and semiconducting SWNTs, resolving the challenge of separation of semiconducting SWNTs from metallic ones. Meanwhile, the memory devices exhibit excellent performance: ultralow writing energy (4.1 × 10-19 J bit-1), ON/OFF ratio of 105, stable switching ON operations, and over 30 h retention time in ambient conditions.

Polarization Encoded Color Image Embedded in a Dielectric Metasurface.

Optical metasurfaces have shown unprecedented capabilities in the local manipulation of the light's phase, intensity, and polarization profiles, and represent a new viable technology for applications such as high-density optical storage, holography and display. Here, a novel metasurface platform is demonstrated for simultaneously encoding color and intensity information into the wavelength-dependent polarization profile of a light beam. Unlike typical metasurface devices in which images are encoded by phase or amplitude modulation, the color image here is multiplexed into several sets of polarization profiles, each corresponding to a distinct color, which further allows polarization modulation-induced additive color mixing. This unique approach features the combination of wavelength selectivity and arbitrary polarization control down to a single subwavelength pixel level. The encoding approach for polarization and color may open a new avenue for novel, effective color display elements with fine control over both brightness and contrast, and may have significant impact for high-density data storage, information security, and anticounterfeiting.

A microfabricated 96-well wound-healing assay.

This article presents a microfabricated 96-well wound-healing assay enabling high-throughput measurement of cellular migration capabilities. Within each well, the middle area is the wound region, made of microfabricated gold surface with self-assembled PEG repellent for cell seeding. After the formation of a cellular confluent monolayer around the wound region, collagen solution was applied to form three-dimensional matrix to cover the PEG surface, initiating the wound-healing process. By interpreting the numbers of migrated cells into the wound regions as a function of specific stimuli with different concentrations, EC50 (half-maximal effective concentration) was obtained. Using H1299 as a model, values of EC50 were quantified as 8% and 160 ng/ml for fetal bovine serum and CXCL12, respectively. In addition, the values of EC50 were demonstrated not to be affected by variations in compositions of extracellular matrix and geometries of wounds, which can thus be regarded as an intrinsic marker. Furthermore, the migration capabilities of a second cell type (HeLa) were characterized by the developed wound-healing assay, producing EC50 of 2% when fetal bovine serum was used as the stimuli. These results validated the proposed high-throughput wound-healing assay, which may function as an enabling tool in studying cellular capabilities of migration and invasion. © 2017 International Society for Advancement of Cytometry.

Design and Calibration of a Novel Bio-Inspired Pixelated Polarized Light Compass.

Animals, such as Savannah sparrows and North American monarch butterflies, are able to obtain compass information from skylight polarization patterns to help them navigate effectively and robustly. Inspired by excellent navigation ability of animals, this paper proposes a novel image-based polarized light compass, which has the advantages of having a small size and being light weight. Firstly, the polarized light compass, which is composed of a Charge Coupled Device (CCD) camera, a pixelated polarizer array and a wide-angle lens, is introduced. Secondly, the measurement method of a skylight polarization pattern and the orientation method based on a single scattering Rayleigh model are presented. Thirdly, the error model of the sensor, mainly including the response error of CCD pixels and the installation error of the pixelated polarizer, is established. A calibration method based on iterative least squares estimation is proposed. In the outdoor environment, the skylight polarization pattern can be measured in real time by our sensor. The orientation accuracy of the sensor increases with the decrease of the solar elevation angle, and the standard deviation of orientation error is 0 . 15 ∘ at sunset. Results of outdoor experiments show that the proposed polarization navigation sensor can be used for outdoor autonomous navigation.

Fabrication of single-crystal silicon nanotubes with sub-10 nm walls using cryogenic inductively coupled plasma reactive ion etching.

Single-crystal silicon nanostructures have attracted much attention in recent years due in part to their unique optical properties. In this work, we demonstrate direct fabrication of single-crystal silicon nanotubes with sub-10 nm walls which show low reflectivity. The fabrication was based on a cryogenic inductively coupled plasma reactive ion etching process using high-resolution hydrogen silsesquioxane nanostructures as the hard mask. Two main etching parameters including substrate low-frequency power and SF6/O2 flow rate ratio were investigated to determine the etching mechanism in the process. With optimized etching parameters, high-aspect-ratio silicon nanotubes with smooth and vertical sub-10 nm walls were fabricated. Compared to commonly-used antireflection silicon nanopillars with the same feature size, the densely packed silicon nanotubes possessed a lower reflectivity, implying possible potential applications of silicon nanotubes in photovoltaics.

Visible-Frequency Dielectric Metasurfaces for Multiwavelength Achromatic and Highly Dispersive Holograms.

Dielectric metasurfaces built up with nanostructures of high refractive index represent a powerful platform for highly efficient flat optical devices due to their easy-tuning electromagnetic scattering properties and relatively high transmission efficiencies. Here we show visible-frequency silicon metasurfaces formed by three kinds of nanoblocks multiplexed in a subwavelength unit to constitute a metamolecule, which are capable of wavefront manipulation for red, green, and blue light simultaneously. Full phase control is achieved for each wavelength by independently changing the in-plane orientations of the corresponding nanoblocks to induce the required geometric phases. Achromatic and highly dispersive meta-holograms are fabricated to demonstrate the wavefront manipulation with high resolution. This technique could be viable for various practical holographic applications and flat achromatic devices.

Polarization-independent and high-efficiency dielectric metasurfaces for visible light.

Dielectric metasurfaces are capable of completely manipulating the phase, amplitude, and polarization of light with high spatial resolutions. The emerging design based on high-index and low-loss dielectrics has led to the realization of novel metasurfaces with high transmissions, but these devices usually operate at the limited bandwidth, and are sensitive to the incident polarization. Here, we report the realization of the polarization-independent and high-efficiency silicon metasurfaces spanning the visible wavelengths about 200 nm. The fabricated computer-generated meta-holograms exhibit a 90% diffraction efficiency, which are verified by gradient metasurfaces with measured efficiencies up to 93% at 670 nm, and exceeding 75% at the wavelengths from 600 to 800 nm for the two orthogonally polarized incidences. These dielectric metasurfaces effectively decouple the phase modulation from the polarization states and frequencies for visible light, which hold great potential for novel flat optical devices operating over a broad spectrum.

Study on evolving phases of accelerating generalized polygon beams.

Recently, accelerating beam is becoming a hotspot in optics research. In this paper, we studied the evolving phases of accelerating generalized polygon beams (AGPBs) and proposed a novel method to generate this beam family. An important discovery has been made about reconstructing AGPBs only by evolving low-frequency phases in high power region, which confirms the dominant role of phase terms in the AGPBs' evolution. We also succeeded controlling the size and quantity of AGPB's intensity peaks in an easy and direct manner by manipulating the evolving phases in low frequency. This result not only explains the self-healing property of AGPBs but also confirms that AGPBs can be a great candidate to function as an optical tweezer to trap and free microparticles and microcreatures for certain purpose.

Real-time phase measurement of optical vortices based on pixelated micropolarizer array.

The special spiral phase structure of an optical vortex leads to an intriguing study in modern singular optics. This paper proposes a real-time phase measurement method of vortex beam based on pixelated micropolarizer array (PMA). Four phase-shifting fringe images can be obtained from a single interference image, thus the vortex beam phase can be obtained in real-time. The proposed method can achieve full-field phase measurement of the vortex beam with the advantages of lower computation and vibration resistance. In the experiments, the typical phases of vortex with different topological charges are loaded on a spatial light modulator (SLM) to generate diffraction vortex beam, and the phase distribution of vortex beam is obtained in real-time, which confirm the robustness of this method. This method is of great significance in promoting the study of optical vortices.

Nano-fabricated pixelated micropolarizer array for visible imaging polarimetry.

Pixelated micropolarizer array (PMA) is a novel concept for real-time visible imaging polarimetry. A 320 × 240 aluminum PMA fabricated by electron beam lithography is described in this paper. The period, duty ratio, and depth of the grating are 140 nm, 0.5, and 100 nm, respectively. The units are standard square structures and the metal nanowires of the grating are collimating and uniformly thick. The extinction ratio of 75 and the maximum polarization transmittance of 78.8% demonstrate that the PMA is suitable for polarization imaging. When the PMA is applied to real-time polarization imaging, the degree of linear polarization image and the angle of linear polarization image are calculated from a single frame image. The polarized target object is highlighted from the unpolarized background, and the surface contour of the target object can be reflected by the polarization angle.

Growth of large-area 2D MoS2(1-x) Se2x semiconductor alloys.

Semiconducting MoS2(1-x) Se2x mono-layers where x = 0-0.40 are successfully grown over large areas. A random arrangement of the S and Se atoms and a tunable bandgap photoluminescence are observed. Atomically thin, 2D semiconductor alloys with tunable bandgaps have potential applications in nano- and opto-electronics. Field-effect transistors fabricated with the monolayers exhibit high on/off ratios of >10(5).

Uncooled infrared imaging device based on optimized optomechanical micro-cantilever array.

It is a major issue to improve the thermo-mechanical sensitivity of uncooled optomechanical focal plane arrays (FPAs) for infrared imaging. This work presents an optimized multi-fold interval metallized leg (IML) configuration to increase the thermo-mechanical sensitivity of an uncooled optomechanical bi-material micro-cantilever array. The inclination angle changes of the cantilever elements are measured in the IR imaging system using an optical readout with a knife-edge filtering operation in the spectrum plane. The multi-fold IML configuration consists of alternately connected unmetallized and metallized legs. With the optimized fold number, the thermo-mechanical sensitivity of a micro-cantilever array can be amplified to two times of one-fold IML for a 120 microm x 120 microm element with 1 microm thick SiNx/0.2 microm thick Au films. Room temperature objects are imaged with the fabricated FPA containing 160 x 160 elements and a 12-bit CCD. Further modeling analysis shows that the experimental results are well accordant with the theoretical calculation. An important practical feature of the implemented approach is its straightforward fabrication for a large FPA, without growing complexity and cost.

Uncooled IR imaging using optomechanical detectors.

In this study, we present an uncooled infrared imaging detector using knife-edge filter optical readout method. The tilt angle change of each cantilever in a focal plane array (FPA) can be simultaneously detected with a resolution of 10(-5) degrees. A deformation magnifying substrate-free microcantilever unit is specially designed. The multi-fold legs of microcantilever are interval metal coated to form a thermal deformation magnifying structure. Thermal and thermomechanical performance of this microcantilever unit are modeled and analyzed. An FPA with 100 x 100 pixels is fabricated and thermal images of human body are obtained by this detector.