Silicon Nanopillar Arrays Research Articles

Biomarker analysis from complex biofluids by an on-chip chemically modified light-controlled vertical nanopillar array device.

Nanostructured devices have proven useful in a broad range of applications, from diagnosing diseases to discovering and screening new drug molecules. We developed vertical silicon nanopillar (SiNP) arrays for on-chip multiplex capture of selected biomolecules using a light-induced release of the array's selectively captured biomarkers. This platform allows the rapid, reusable and quantitative capture and release of a selection of biomarkers, followed by their downstream analysis. Here we outline a standardized protocol for producing the SiNP-based capture-and-release device, which involves the detailed fabrication steps for single-zone nanopillar arrays, their morphological characterization and the chemical modification procedures applied for the anchoring of selective bioreceptors together with the light-controlled on-demand release of the chemical agent. In addition, we provide a detailed approach for the fabrication of a multizone-SiNP array, allowing the simultaneous capture and release of multiple biomarkers of interest. Finally, we demonstrate the entire process of selective and quantitative capture and release of biomolecules from biosamples by means of a commercial low-volume microplate reader system, using green fluorescent protein as a biomarker example. The entire protocol can be conducted within 45 h and requires knowledge in nanoscience, surface chemistry, device micro- and nanofabrication procedures, microfluidics and protein quantification techniques. These SiNP array devices have already demonstrated applications for highly selective and quantitative analysis of a wide range of biological and chemical species, including proteins, nucleic acids, small molecules and ionic species.

Preparation of Silicon Nanopillar Arrays Using Reactive Ion Etching with a Faraday Cage.

Faraday cages are extensively utilized in plasma-based etching and deposition processes to regulate ion behavior due to their shielding effect on electromagnetic fields. Herein, vertical silicon nanopillar arrays are fabricated through SF6 and O2 reactive ion etching. By incorporation of a Faraday cage in the plasma equipment, the impact of the Faraday cage on the morphology of the silicon nanopillars is analyzed; the Faraday cage blocks out the sputtered particles and eradicates the formation of silicon nanograss. Specifically, it regulates the value and dispersion of the etching rate by varying the mesh number and the distance from the grid wires to the sample surface. A "flattening belly" phenomenon of silicon nanopillars associated with the temperature is resolved using segmented multiple etching processes. This research contributes to an in-depth analysis of plasma etching using a Faraday cage as well as potential applications for silicon nanopillars.

Transdermal Minimally Invasive Optical Multiplex Detection of Protein Biomarkers by Nanopillars Array-Embedded Microneedles.

Biomarkers detection has become essential in medical diagnostics and early detection of life-threatening diseases. Modern-day medicine relies heavily on painful and invasive tests, with the extraction of large volumes of venous blood being the most common tool of biomarker detection. These tests are time-consuming, complex, expensive and require multiple sample manipulations and trained staff. The application of "intradermal" biosensors utilizing microneedles as minimally invasive sensing elements for capillary blood biomarkers detection has gained extensive interest in the past few years as a central point-of-care (POC) detection platform. Herein, we present a diagnosis paradigm based on vertically aligned nanopillar array-embedded microneedles sampling-and-detection elements for the direct optical detection and quantification of biomarkers in capillary blood. We present here a demonstration of the simple fabrication route for the creation of a multidetection-zone silicon nanopillar array, embedded in microneedle elements, followed by their area-selective chemical modification, toward the multiplex intradermal biomarkers detection. The utilization of the rapid and specific antibody-antigen binding, combined with the intrinsically large sensing area created by the nanopillar array, enables the simultaneous efficient ultrafast and highly sensitive intradermal capillary blood sampling and detection of protein biomarkers of clinical relevance, without requiring the extraction of blood samples for the ex vivo biomarkers analysis. Through preliminary in vitro and in vivo experiments, the direct intradermal in-skin blood extraction-free platform has demonstrated excellent sensitivity (low pM) and specificity for the accurate multiplex detection of protein biomarkers in capillary blood.

Influence of discontinuities on photonic waveguides.

Fabrication-induced imperfections in photonic wire waveguides, such as roughness, stitching errors, and discontinuities, degrade their performance and thereby lower the yield of large-scale systems. This degradation is primarily due to the high insertion losses induced by imperfections, which scale nonlinearly with the index contrast in wire waveguides. Here we investigate the influence of discontinuities in photonic waveguides and later show a platform that is robust to fabrication imperfections. Our platform is based on an array of silicon nano-pillars, arranged to form a sub-wavelength (SW) grating waveguide. We focus on investigating the robustness by considering an abrupt break in the waveguide, as an extreme case of discontinuity. We show that sub-wavelength silicon waveguides are robust against unwanted large discontinuities relative to the operating wavelength. We measure a transmission loss of <2.2 dB at 1550 n m, for a discontinuity of length 2.1 μ m, when compared to more than 7 d B of loss in conventional silicon wire waveguides for the same discontinuity. Our results show that this mode of protection is broadband, covering the entire telecommunication band (λ =1500-1600 nm). We believe that this investigation of the influence of discontinuities in photonic waveguides could be a step toward the realization of low-loss optical waveguides.

Direct Mapping of Cytomechanical Homeostasis Destruction in Osteoarthritis Based on Silicon Nanopillar Array (Adv. Healthcare Mater. 32/2023)

Direct Mapping of Cytomechanical Homeostasis Destruction in Osteoarthritis Based on Silicon Nanopillar Array (Adv. Healthcare Mater. 32/2023)

Enhanced near-infrared photodetection via whispering gallery modes in the wave-shaped sidewall silicon nanopillar arrays.

We demonstrate a near-infrared (NIR) photodiode (PD) by using a wave-shaped sidewall silicon nanopillars (WS-SiNPs) structure. The designed WS sidewall nanostructure increases the horizontal component of incident light and induces multiple whispering-gallery modes with low-quality factor, which increases the light absorption path. Thus, the WS-SiNP PD shows improved spectral responsivity and external quantum efficiency over straight sidewall silicon nanopillars and planar PDs in the NIR region. Especially, the peak responsivity of 0.648 A/W is achieved at a wavelength of 905 nm, which is used for light detection and ranging. Comparison with commercial photodiodes demonstrates the good optoelectrical characteristics of the fabricated device. The improved characteristics are validated by 3D finite differential time domain simulations. Based on these results, our device shows the potential for cost-effective Si-based optoelectronic devices to be utilized in future advanced applications.

Direct Mapping of Cytomechanical Homeostasis Destruction in Osteoarthritis Based on Silicon Nanopillar Array.

Osteoarthritis (OA) is the most prevalent joint degenerative disease characterized by chronic joint inflammation. The pathogenesis of OA has not been fully elucidated yet. Cartilage erosion is the most significant pathological feature in OA, which is considered the result of cytomechanical homeostasis destruction. The cytomechanical homeostasis is maintained by the dynamic interaction between cells and the extracellular matrix, which can be reflected by cell traction force (CTF). It is critical to assess the CTF to provide a deeper understanding of the cytomechanical homeostasis destruction and progression in OA. In this study, a silicon nanopillar array (Si-NP) with high spatial resolution and aspect ratio is fabricated to investigate the CTF in response to OA. It is discovered that the CTF is degraded in OA, which is attributed to the F-actin reorganization induced by the activation of RhoA/ROCK signaling pathway. Si-NP also shows promising potential as a mechanopharmacological assessment platform for OA drug screening and evaluation.

Observation of Capillary Condensation and Pattern Bending Phenomena in Si Nanopillars Using &lt;i&gt;In Situ&lt;/i&gt; TEM

Capillary condensation, a ubiquitous phenomenon involving the heterogeneous nucleation of liquid droplets, has significant implications in various industrial, biological, and atmospheric processes. Strong capillary forces induced by highly curved menisci of condensates can have potentially significant impact on the structural integrity and functionality of nanodevices. While the influence of surface properties on the nucleation and growth of water droplets has been extensively studied at microscale, our understanding of water condensation at the nanoscale remains limited due to experimental challenges in imaging liquids at nanometer scales. In this study, we employ in situ liquid phase TEM imaging and for the first time present real-time observations of water condensation dynamics on arrays of vertical silicon (Si) nanopillars. Experimental and simulation results show that nucleation of water droplets occurs at the edges of the nanopillars and substrate, followed by the growth of an interfacial layer resembling a corona around the nanopillars. Subsequently, the formation of bridges between adjacent growing coronas leads to the development of symmetric and asymmetric bridged nanopillar geometries. Importantly, we find that the formation of bridges can induce bending and collapse of the nanopillars, depending on their aspect ratios. Overall, this study provides valuable insights into the nanoscale dynamics of capillary condensation and paves the way for advanced engineering applications and optimization of various technological processes.

Biofouling potential of surface-enhanced Raman scattering-based seawater quality sensors by Ulva spp.

This study investigated the biofouling potential of surface-enhanced Raman scattering (SERS)-based sensor materials in the context of marine environments. Uncoated and monolithic commercial gold (Au) silicon nanopillar array SERS substrates, Au-coated carbon black nanoparticle (AuCB NP) substrates, uncoated and Au sputter-coated in-house SERS, and uncoated and Au sputter-coated glass controls were tested for biofouling potential using Ulva spp. as model biofouling organisms. The mean percentages of Ulva spp. zoospores that adhered per mm2 (×103) on the uncoated and coated Au silicon nanopillar array, AuCB NP, uncoated and Au sputter-coated in-house, and uncoated and Au sputter-coated glass substrates were 10.28%, 5.45%, 10.49%, 3.25%, 24.84%, 12.86% and 7.78%, respectively. Results indicated that surface properties such as hydrophobicity, roughness, Au sputter-coating and the presence of micro-refuges on nano- and microstructured substrates were critical to the biofouling formation.

Broadband Mechanically Tunable Metasurface Reflectivity Modulator in the Visible Spectrum.

Reflectivity modulation is a critical feature for applications in telecommunications, 3D imaging and printing, advanced laser machining, or portable displays. Tunable metasurfaces have recently emerged as a promising implementation for miniaturized and high-performance tunable optical components. Commonly, metasurface response tuning is achieved by electro-optical effects. In this work, we demonstrate reflectivity modulation based on a nanostructured, mechanically tunable, metasurface, consisting of an amorphous silicon nanopillar array and a suspended amorphous silicon membrane with integrated electrostatic actuators. With a membrane displacement of only 150 nm, we demonstrate reflectivity modulation by Mie resonance enhanced absorption in the pillar array, leading to a reflectivity contrast ratio of 1:3 over the spectral range from 400-530 nm. With fast, low-power electrostatic actuation and a broadband response in the visible spectrum, this mechanically tunable metasurface reflectivity modulator could enable high frame rate dynamic reflective displays.

Fabrication of ultrahigh aspect ratio Si nanopillar and nanocone arrays

High aspect ratio (HAR) structures have many promising applications such as biomedical detection, optical spectroscopy, and material characterization. Bottom-up self-assembly is a low-cost method to fabricate HAR structures, but it remains challenging to control the structure dimension, shape, density, and location. In this paper, an optimized top-down method using a combination of pseudo-Bosch etching and wet isotropic thinning/sharpening is presented to fabricate HAR silicon (Si) nanopillar and nanocone arrays. To achieve these structure profiles, electron beam lithography and reactive ion etching were carried out to fabricate silicon pillars having a nearly vertical sidewall, followed by thinning or sharpening by wet etching with a mixture of hydrofluoric (HF) acid and nitric acid (HNO3). For the dry etching step using the pseudo-Bosch process, the sidewall angle is largely dependent on the SF6/C4F8 gas flow ratio, and it was found that a vertical profile can be attained with a ratio of 22/38. For the wet etching process, a very large HNO3/HF volume ratio is shown to give smooth etching with a slow and controllable etching rate. The final structure profile also depends on the pattern density/array periodicity. When the array period is large, silicon nanopillar is thinned down, and its aspect ratio can reach 1:135 with a sub-100 nm apex. When the pillar array becomes very dense (periodicity much smaller than height), a very sharp nanocone structure is obtained after wet etching with an apex diameter under 20 nm.

Mechanism study of all-dielectric metamaterial wideband reflector based on quasi-canonical mode

All-dielectric metamaterial broadband reflectors have the advantages of low loss, high reflection efficiency, and compact structure. An in-depth understanding of the formation mechanism of their reflection bands is of great significance in optimizing metamaterial structure and performance, and in further designing novel photonic devices as well. In this work, two all-dielectric metamaterial broadband reflectors are constructed by using discrete silicon nanopillar array and silicon nanopillar array connected with a silicon sublayer. The quasi-normal modes of the metamaterial reflectors are solved. Combining the quasi-normal modes with the scattering matrix theory, we obtain the fitted reflection spectra of the metamaterial, and then reveal that the zero-frequency quasi-normal mode has a substantial influence on the accuracy of the fitting results. A dispersion relation analysis method is proposed to accurately solve the zero-frequency quasi-normal mode. Furthermore, the fitted resonance reflection spectrum and background reflection spectrum are obtained by using high-&lt;i&gt;Q&lt;/i&gt;-value quasi-normal mode and low-&lt;i&gt;Q&lt;/i&gt;-value quasi-normal mode, respectively. Our results show that the broadband reflection of the considered metamaterial reflectors should be attributed to the background reflection induced by the low-&lt;i&gt;Q&lt;/i&gt; quasi-normal modes. The research method proposed in this paper can also be used for discussing quasi bound states in the continuum, Mie resonances, and other resonance phenomena, which provides a new way for interpreting the spectral characteristics of metamaterials.

Simulation Study on Broadband Light Harvesting Properties of Aluminium Nanosphere and Silicon Nanopillar Arrays based Tandem Structure

Simulation Study on Broadband Light Harvesting Properties of Aluminium Nanosphere and Silicon Nanopillar Arrays based Tandem Structure

Metal-assisted chemically etched silicon nanopillars hosting telecom photon emitters

Silicon, a ubiquitous material in modern computing, is an emerging platform for realizing a source of indistinguishable single photons on demand. The integration of recently discovered single-photon emitters in silicon into photonic structures is advantageous to exploit their full potential for integrated photonic quantum technologies. Here, we show the integration of an ensemble of telecom photon emitters in a two-dimensional array of silicon nanopillars. We developed a top-down nanofabrication method, enabling the production of thousands of nanopillars per square millimeter with state-of-the-art photonic-circuit pitch, all the while being free of fabrication-related radiation damage defects. We found a waveguiding effect of the 1278 nm-G center emission along individual pillars accompanied by improved brightness compared to that of bulk silicon. These results unlock clear pathways to monolithically integrating single-photon emitters into a photonic platform at a scale that matches the required pitch of quantum photonic circuits.

Nanoscale geometry determines mechanical biocompatibility of vertically aligned nanofibers

Vertically aligned carbon nanofibers (VACNFs) are promising material candidates for neural biosensors due to their ability to detect neurotransmitters in physiological concentrations. However, the expected high rigidity of CNFs could induce mechanical mismatch with the brain tissue, eliciting formation of a glial scar around the electrode and thus loss of functionality. We have evaluated mechanical biocompatibility of VACNFs by growing nickel-catalyzed carbon nanofibers of different lengths and inter-fiber distances. Long nanofibers with large inter-fiber distance prevented maturation of focal adhesions, thus constraining cells from obtaining a highly spread morphology that is observed when astrocytes are being contacted with stiff materials commonly used in neural implants. A silicon nanopillar array with 500 nm inter-pillar distance was used to reveal that this inhibition of focal adhesion maturation occurs due to the surface nanoscale geometry, more precisely the inter-fiber distance. Live cell atomic force microscopy was used to confirm astrocytes being significantly softer on the long Ni-CNFs compared to other surfaces, including a soft gelatin hydrogel. We also observed hippocampal neurons to mature and form synaptic contacts when being cultured on both long and short carbon nanofibers, without having to use any adhesive proteins or a glial monoculture, indicating high cytocompatibility of the material also with neuronal population. In contrast, neurons cultured on a planar tetrahedral amorphous carbon sample showed immature neurites and indications of early-stage apoptosis. Our results demonstrate that mechanical biocompatibility of biomaterials is greatly affected by their nanoscale surface geometry, which provides means for controlling how the materials and their mechanical properties are perceived by the cells. Statement of significanceOur research article shows, how nanoscale surface geometry determines mechanical biocompatibility of apparently stiff materials. Specifically, astrocytes were prevented from obtaining highly spread morphology when their adhesion site maturation was inhibited, showing similar morphology on nominally stiff vertically aligned carbon fiber (VACNF) substrates as when being cultured on ultrasoft surfaces. Furthermore, hippocampal neurons matured well and formed synapses on these carbon nanofibers, indicating high biocompatibility of the materials. Interestingly, the same VACNF materials that were used in this study have earlier also been proven to be capable for electrophysiological recordings and sensing neurotransmitters at physiological concentrations with ultra-high sensitivity and selectivity, thus providing a platform for future neural probes or smart culturing surfaces with superior sensing performance and biocompatibility.

Broadband Low Reflection Surfaces With Silicon Nano-tube Square Arrays And Quantum Dot Layers

In this study, we take as a starting nanostructure which is already optimized in terms of the silicon nanopillar arrays’ structure pillar height, pillar diameter, and filling ratio such that the optical reflection from its surface is very low (weighted average reflection 3.75 percent). Full-field Finite Difference Time Domain method is used to simulate electric and magnetic fields and calculate the reflection from the modified nanostructured substrate surfaces in 400nm-1100nm spectral range. In this paper, we present the optimization of the structure in terms of the silicon nanotube structure cavity diameter, step coverage of the dielectric thin film. As a result, the weighted reflection is decreased to 3.35 percent. We also want to simulate the quantum dot solution layer deposited over the nanostructure. We modeled the quantum dots as Lorentz dielectric and decreased the optical reflection even lower level of 3.1 percent. Optimization recipe is clearly presented, and the developed method is not only useful for square arrays but also for regular arrays of nanopillars in general for photovoltaic devices.

Ultrasensitive and Broadband Optical Toroidal Modes in all‐Dielectric Nanostructures

AbstractDynamic toroidal dipole (TD) with its peculiar characteristic of broken space‐inversion and time‐reversal symmetries plays an important role in the fundamental physics of light–matter interaction. Here, TD metamaterials comprised of amorphous silicon nanopillar arrays embedded in spin‐on‐glass layer are experimentally demonstrated. Upon normal incidence of plane wave, the transverse toroidal moment and the associated anapole‐like state are excited in optical regime. The strong TD response stems from a complete head‐to‐tail configuration of the magnetic dipole moments within each individual nanopillar. Both the experimental and simulation results show that such TD mode sustains a large structural tolerance and can be spectrally tuned by elongating the cylindrical axis perpendicular to the light polarization, corresponding to a cross‐sectional variation from circular to elliptical shapes. The excited TD mode is found to exhibit ultrahigh refractive index sensitivity compared to other multipoles, resulting in a sensitivity of 459 nm (470 nm) per external refractive index change in the experiment (calculation). This approach provides a simple and straightforward path in realizing toroidal metamaterials and establishes a new flat‐optics platform for realizing active metadevices, sensors, and nonlinear nanophotonics.

Preventing the Capillary-Induced Collapse of Vertical Nanostructures.

Robust processes to fabricate densely packed high-aspect-ratio (HAR) vertical semiconductor nanostructures are important for applications in microelectronics, energy storage and conversion. One of the main challenges in manufacturing these nanostructures is pattern collapse, which is the damage induced by capillary forces from numerous solution-based processes used during their fabrication. Here, using an array of vertical silicon (Si) nanopillars as test structures, we demonstrate that pattern collapse can be greatly reduced by a solution-phase deposition method to coat the nanopillars with self-assembled monolayers (SAMs). As the main cause for pattern collapse is strong adhesion between the nanopillars, we systematically evaluated SAMs with different surface energy components and identified H-bonding between the surfaces to have the largest contribution to the adhesion. The advantage of the solution-phase deposition method is that it can be implemented before any drying step, which causes patterns to collapse. Moreover, after drying, these SAMs can be easily removed using a gentle air-plasma treatment right before the next fabrication step, leaving a clean nanopillar surface behind. Therefore, our approach provides a facile and effective method to prevent the drying-induced pattern collapse in micro- and nanofabrication processes.

Оптические свойства кремниевых нанопилларов со встроенным вертикальным p-n-переходом

Resonance reflection of light from the ordered arrays of silicon nanopillars (Si NP) was investigated. The height of Si NP was 450 nm. The effect of Si NP oxidation in concentrated nitric acid on the position of resonances in reflection spectra was studied. A weak influence of the additional polymeric coating on the characteristics of reflection from the structures was proven. It is established on the basis of the results of experimental investigation and direct numerical modeling by means of three-dimensional finite difference time domain algorithm (3D FDTD) that the dependence of the resonant wavelength for Si NP on the diameter of Si NP is a linear function with nonzero displacement depending on the pitch.

Optical properties of silicon nanopillars with a built-in vertical p-n-junction

Resonance reflection of light from the ordered arrays of silicon nanopillars (Si NP) was investigated. The height of Si NP was 450 nm. The effect of Si NP oxidation in concentrated nitric acid on the position of resonances in reflection spectra was studied. A weak influence of the additional polymeric coating on the characteristics of reflection from the structures was proven. It is established on the basis of the results of experimental investigation and direct numerical modeling by means of three-dimensional finite difference time domain algorithm (3D FDTD) that the dependence of the resonant wavelength for Si NP on the diameter of Si NP is a linear function with nonzero displacement depending on the pitch. Keywords: silicon nanopillars, structural colors, all-dielectric nanophotonics.