Nanopyramid Arrays Research Articles

Modified nanosphere lithography: application to the fabrication of ordered arrays of gold nanopyramids

In this work a modified approach to improve the capabilities of nanosphere lithography was performed to obtain ordered arrays of gold nanopyramids that can be used as Surface-Enhanced Raman Scattering (SERS) substrates. Specifically, shadow sphere lithography in combination with nanosphere lithography was used to fabricate metallic nanostructures of different sizes starting from the same mask of silica microspheres. An extensive study of the obtained samples with scanning electron microscopy, atomic force microscopy and Raman characterizations confirms that indeed this modification of the standard nanosphere lithography is an excellent candidate to produce ordered arrays of Au nanopyramids with good control on their geometric properties. Rhodamine 6G dye was used as a probe molecule to test our SERS substrates. These features can be used in turn to optimize the SERS substrates for several potential applications. Remarkably, it is shown that by this simple technique one can achieve enhancement factors and detection capabilities of dyes that are comparable with those obtained by using more sophisticated techniques as proposed recently in the literature.

Broadband light trapping in perovskite solar cells: Optimization and enhancement through exploiting multi-resonant Mie resonators

We present multi-resonant Mie resonators comprising dielectric nanopyramid arrays (DNPAs) for efficient broadband light trapping (LT) in perovskite solar cells (PSCs). Absorption in a 100 nm-thick active layer is significantly enhanced over a broad range of wavelengths through the simultaneous resonant excitation of electric and magnetic moments. Through optimization, a PSC integrated with a front-located DNPA LT structure having a base edge of 320 nm and a spacing of 180 nm at an aspect ratio of 1.5 yields a short-circuit current density (Jsc) of 18.13 mA/cm2, which is about 29 % higher than that of a planar PSC. Multipole resonance contributions and radiation patterns of DNPs are also investigated. The spectral overlap of the multipole resonances of the DNPAs can be easily tuned, thereby providing performance enhancements in diverse applications, such as nanoantennas, metasurfaces, photodiodes, and other solar cells.

Modulating Electronic Structure of Iridium Single-Atom Anchored on 3D Fe-Doped β-Ni(OH)2 Catalyst with Nanopyramid Array Structure for Enhanced Oxygen Evolution Reaction.

Developing high-performance electrocatalysts for oxygen evolution reaction (OER) is crucial in the pursuit of clean and sustainable hydrogen energy, yet still challenging. Herein, a spontaneous redox strategy is reported to achieve iridium single-atoms anchored on hierarchical nanosheet-based porous Fe doped β-Ni(OH)2 pyramid array electrodes (SAs Ir/Fe-β-Ni(OH)2), which exhibits high OER performance with a low overpotential of 175mV at 10mAcm-2 and a remarkable OER current density in alkaline electrolyte, surpassing Fe-β-Ni(OH)2/NF and IrO2 by 31 and 38 times at 1.43V versus RHE, respectively. OER catalytic mechanism demonstrates that the conversion of *OH→*O and the active lattice O content can be significantly improved due to the modulation effect of the Ir single atoms on the local electronic structure and the redox behavior of FeNi (oxy) hydroxide true active species. This work provides a promising insight into understanding the OER enhancement mechanism for Ir single-atoms modified FeNi-hydroxide systems.

Composite nanostructure comprising silver nanopyramids and silver nanoparticles for plasmon-enhanced fluorescence

In this study, a composite silver nanostructure is presented to serve as the platform for highly efficient plasmon-enhanced fluorescence (PEF). The composite nanostructure is realized by first employing nanosphere lithography (NPL) combined with reactive ion etching (RIE) technology to create a silver nanopyramid array, which is then further modified with silver nanoparticles. Utilizing DCJTB as the fluorophore, this composite nanostructure is found to outperform the use of either silver nanoparticles or silver nanopyramid array. Notably, it not only enhances the photoluminescence (PL) but also reduces the carrier lifetime. The influence of the particle size of silver nanoparticles and the height of the silver nanopyramids is also investigated. It is found that larger silver nanoparticles and higher silver nanopyramids lead to stronger local surface plasmon resonance (LSPR), thereby enhancing the PEF phenomenon. Compared with the performance of using bare glass substrate, the PL intensity of using the composite nanostructure is enhanced to 19.4 times and the carrier lifetime is shortened by 61%.

Quantitative analysis of microplastics in seawater based on SERS internal standard method.

Microplastics can enter the human body through the food chain and can cause cardiovascular or cerebrovascular diseases; thus, it is essential to detect microplastics sensitively and accurately. Traditional methods have some drawbacks, such as a low sensitivity and complicated experimental procedures, so it is difficult to detect microplastics less than 1 μm. While surface enhanced Raman scattering technology can compensate for these shortcomings, there are fewer reports on the quantitative detection of microplastics using SERS technology. In this study, SERS and an internal standard method were utilized to detect microplastics qualitatively and quantitatively. The electric field enhancement effect of common gold, silver, and copper substrates were simulated by the finite element method, and the influence rule of structural parameters on the enhancement factor was obtained to optimize structural parameters. Subsequently, a gold nanopyramid array substrate was prepared using the colloidal sphere template method. Finally, the prepared substrate was applied to detect polystyrene microplastics with a diameter of 500 nm, and the detection of limit is 1.8 × 10-4 mg mL-1 in the quantitative range of 2-2 × 10-4 mg mL-1, and the correlation coefficient of the linear regression equation is 0.9918. The experimental results showed that this proposal has a lower detection limit and a wider quantitative range and expands ideas for the qualitative and quantitative detection of microplastics in seawater.

Encapsulation of few-layered MoS2 on electrochemical-treated BiVO4 nanoarray photoanode: Simultaneously improved charge separation and hole extraction towards efficient photoelectrochemical water splitting

Bismuth vanadate (BiVO4) photoanode shows great potential for photoelectrochemical (PEC) water splitting but still suffers from the sluggish surface reaction kinetic and high charge loss. Further strengthening the intrinsic charge transport for the improvement of solar-to-hydrogen conversion becomes the top priority. Herein, an innovative highly-oriented E-BiVO4/MoS2 heterojunction photoanode is rationally designed and fabricated via directly encapsulating few-layered MoS2 nanosheets on electrochemical-treated BiVO4 (E-BiVO4) nanopyramid arrays. Systematic studies reveal that the electrochemical reduction process can create oxygen vacancies on BiVO4 lattice, thereby increasing the overall carrier concentration, and boosting the bulk and surface charge separation efficiencies. Meanwhile, the introduction of MoS2 as a heterojunction helps build the unidirectional charge transfer channels for further facilitated surface hole extraction and oxidation kinetics, synergistically devoting to the significantly enhanced PEC activity and photostability. As a result, the optimized E-BiVO4/MoS2 photoanode exhibits the highest photocurrent density of 2.11 mA/cm2 at 1.23VRHE and incident photon-to-electron conversion efficiency (IPCE) of 40.6 %, which are approximately 4.6 and 4.9 times higher than the pristine BiVO4. The present work demonstrates a feasible collaborative strategy to develop photoanodes with simultaneously improved charge separation and hole transport for efficient PEC water splitting application.

Absorption enhancement in GaAs based quantum dot solar cells using double-sided nanopyramid arrays.

Quantum dot solar cells (QDSCs) are regarded as one of the most efficient devices due to their intermediate band structures. A suitable light-trapping (LT) strategy matching the absorption spectrum is important to improve the photocurrent conversion efficiency of QDSCs. In this paper, we have proposed a design of the periodically patterned top and bottom dielectric nanopyramid arrays for highly efficient light trapping in GaAs-based QDSCs. The dielectric nanopyramid arrays significantly improve the light absorption of QDSCs in the longer wavelength between 0.8µm and 1.2µm. In addition, this LT structure ensures a completely flat window layer and back surface field layer while passivating these semiconductor surfaces. For the optimized double-sided structure, the short-circuit current generated by QDSC is 34.32m A/c m 2, where the photocurrent from the quantum dots (QDs) is 5.17m A/c m 2. Compared to the photocurrent of the QDSC without an LT structure, the photocurrent of the double-sided structure is increased by 84%. The QD photocurrent of the double-sided structure is increased by 570% compared to that of the QDSC without the LT structure.

Efficiency improvement in InP thin film solar cell using dielectric nanobars

In this paper, to significantly improve the conversion efficiency in a 1 μm InP thin film solar cell, array of perpendicular TiO 2 nanobars and backside grating are employed. TiO 2 nanobars are coated with a desired anti-reflector (AR) and partially embedded in the InP film to achieve strong light trapping. Optimizing the size of TiO 2 nanobars leads to an enhancement of 41.5% in the photocurrent current density, J ph , and 49.3% in power conversion efficiency, PCE, related to the conventional InP film. For boosting the long wavelength absorption, a back reflector (BR) structure including six SiO 2 layers with Si nanopyramid arrays is applied at the backside of the absorption film. Compared to the 1 μm InP thin film solar cell, the J ph and PCE are improved by 52.7% and about 59%, respectively. Finite-Difference-Time-Domain (FDTD) and Finite-Element-Method (FEM) are used to obtain the results.

Plasmonic Nanopyramid Array Enhancing Luminescence of MoS2 Investigated by Cathodoluminescence

AbstractTransition metal dichalcogenides (TMDs) like molybdenum disulfide (MoS2) have unique optical properties such as strong luminescence and a tunable bandgap. However, the small interaction distance due to the atomically thin nature of these materials is a limitation for applications. In this study, a significant enhancement of the A‐ and B‐exciton emission in MoS2 flakes through coupling with plasmonic Au nano‐pyramid arrays fabricated by a colloidal lithography technique is reported. This study experimentally maps local emission enhancement from the structure with a nanometer spatial resolution by cathodoluminescence (CL) technique. Strongly enhanced emission intensity within the MoS2‐Au pyramids is achieved due to the localized surface plasmon resonance confined in nano‐pyramids and its interaction with the periodicity‐based resonance of the array structure. The results provide an approach to significantly improve the luminescence intensity of MoS2 through optical interaction with the local plasmonic field, which is promising for applications in optoelectronic devices and nanophotonics.

Design of high quantum efficiency SPAD single-photon detector based on metasurface

This work discusses several metasurface structure types, their manufacturing processes, and the design and simulation of nanopyramid arrays, square slot arrays, and funnel arrays to improve absorption. In particular, a silicon-based continuous thin gold film-covered deep grooved thin metal structure was constructed and examined. It surpasses the silicon materials’ absorption thresholds, considerably expanding the NIR’s absorption range to 2000 nanometers. More information is provided regarding the impact of trench depth on cavity pattern and near-infrared absorption. Its preparation process is detailed, and its compatibility with SPAD single-photon detectors is confirmed. This information is likely to encourage the use of SPAD in domains such as near-infrared optical communication and other low-light detecting technologies.

Monolithic Nickel Catalyst Featured with High-Density Crystalline Steps for Stable Hydrogen Evolution at Large Current Density.

Producing hydrogen via electrochemical water splitting with minimum environmental harm can help resolve the energy crisis in a sustainable way. Here, this work fabricates the pure nickel nanopyramid arrays (NNAs) with dense high-index crystalline steps as the cata electrode via a screw dislocation-dominated growth kinetic for long-term durable and large current density hydrogen evolution reaction. Such a monolithic NNAs electrode offers an ultralow overpotential of 469mV at a current density of 5000mA cm-2 in 1.0m KOH electrolyte and shows a high stability up to 7000 h at a current density of 1000mA cm-2 , which outperforms the reported catas and even the commercial platinum cata for long-term services under high current densities. Its unique structure can substantially stabilize the high-density surface crystalline steps on the catalytic electrode, which significantly elevates the catalytic activity and durability of nickel in an alkaline medium. In a typical commercial hydrogen gas generator, the total energy conversion rate of NNAs reaches 84.5% of that of a commercial Pt/Ti cata during a 60-day test of hydrogen production. This work approach can provide insights into the development of industry-compatible long-term durable, and high-performance non-noble metal catas for various applications.

In-situ surface reconstruction of single-crystal (NiFe)3Se4 nano-pyramid arrays for efficient oxygen evolution

Transition metal-based selenides (TMSe) are considered as efficient pre-electrocatalysts towards oxygen evolution reaction (OER). However, the key factor in determining the surface reconstruction of TMSe under OER condition is not yet clear. Herein, we uncover that the crystallinity of TMSe will obviously impact the conversion degree from TMSe to transition metal oxyhydroxides (TMOOH) during OER. A novel single-crystal (NiFe)3Se4 nano-pyramid array grown on NiFe foam is fabricated by a facile one-step polyol process, which exhibits an excellent OER activity and stability, only requiring 170 mV to reach a current density of 10 mA cm−2 and can sustain for more than 300 h. In situ Raman spectrum studies reveals that the single-crystal (NiFe)3Se4 is partially oxidized on its surface during OER, generating a dense heterostructure of (NiFe)OOH/(NiFe)3Se4. Benefiting from the in situ formed heterointerface, the adsorption of OER intermediates on Ni active sites calculated by density functional theory (DFT) analysis is optimized, leading to the reduced energy barrier, which accounts for the enhanced intrinsic activity. This work not only reports a novel single-crystal (NiFe)3Se4 nano-pyramid array electrocatalyst with high-efficient OER performance, but also gains a deep insight into the role of the crystallinity of TMSe on the surface reconstruction during OER.

Gold Nanopyramid Arrays for Non-Invasive Surface-Enhanced Raman Spectroscopy-Based Gastric Cancer Detection via sEVs.

Gastric cancer (GC) is one of the most common and lethal types of cancer affecting over one million people, leading to 768,793 deaths globally in 2020 alone. The key for improving the survival rate lies in reliable screening and early diagnosis. Existing techniques including barium-meal gastric photofluorography and upper endoscopy can be costly and time-consuming and are thus impractical for population screening. We look instead for small extracellular vesicles (sEVs, currently also referred as exosomes) sized ⌀ 30–150 nm as a candidate. sEVs have attracted a significantly higher level of attention during the past decade or two because of their potentials in disease diagnoses and therapeutics. Here, we report that the composition information of the collective Raman-active bonds inside sEVs of human donors obtained by surface-enhanced Raman spectroscopy (SERS) holds the potential for non-invasive GC detection. SERS was triggered by the substrate of gold nanopyramid arrays we developed previously. A machine learning-based spectral feature analysis algorithm was developed for objectively distinguishing the cancer-derived sEVs from those of the non-cancer sub-population. sEVs from the tissue, blood, and saliva of GC patients and non-GC participants were collected (n = 15 each) and analyzed. The algorithm prediction accuracies were reportedly 90, 85, and 72%. “Leave-a-pair-of-samples out” validation was further performed to test the clinical potential. The area under the curve of each receiver operating characteristic curve was 0.96, 0.91, and 0.65 in tissue, blood, and saliva, respectively. In addition, by comparing the SERS fingerprints of individual vesicles, we provided a possible way of tracing the biogenesis pathways of patient-specific sEVs from tissue to blood to saliva. The methodology involved in this study is expected to be amenable for non-invasive detection of diseases other than GC.

Dual-phase nanoplasmonic sensing platform for monitoring blood protein adsorption and its coagulation in vitro

Protein adsorption onto solid surfaces is an immanent and spontaneous phenomenon that occurs in many fundamental biomedical applications. Recent research mainly focuses on collectively measuring the protein behaviors in confined localized nanosensing areas, whereas ignoring the ambient aqueous variation that directly affects protein behavior, such as the hydrogen bonding network in protein-water which serves as a crucial and mutually constrained environment. Herein, we develop a novel dual-phase plasmonic sensing platform with a gold nanopyramid array (GNPA), simultaneously monitoring protein binding at the nanosensing surface and the variation tendency of hydrogen bonding in aqueous solution. Two types of protein adsorption and their solution variation are explored: we first investigate bovine serum albumin (BSA) adsorption and its variation tendency of hydrogen bonding formation and fracture in water. Then we apply the sensing chip to monitor the fibrinogen adsorption and its real-time conversion to fibrin in an in vitro model of simulated blood coagulation, where the synchronous sensing signals of localized surface plasmon resonance (LSPR) and aqueous hydrogen bonding variations are acquired. It helps to reveal the connection between hydrogen bonding variations in protein-water solution and protein adsorption behaviors at the surface, a meaningful finding for comprehending the initiation of abnormal blood coagulation and the related thromboembolism disease. Moreover, the proposed dual-phase sensing strategy opens a new path for a wider variety of applications, ranging from monitoring microenvironmental changes inside the human body to detecting the water contamination or environmental pollutants.

Probing ND7/23 neuronal cells before and after differentiation with SERS using Sharp-tipped Au nanopyramid arrays

The development of local plasmonic nano sensors which are sensitive, whilst remaining non-invasive with high cell viability is challenging but of great interest for the investigation of cellular processes. With this aim, we developed an effective SERS active biointerface to monitor cell activity and discriminate between undifferentiated and differentiated neurons through principal component analysis. We propose a plasmonic tipped Au nanopyramids (Au NPs) array, which benefits from high aspect ratios and sharp tips that are excellent SERS sensors. To realise the structure, we developed a large-scale inexpensive fabrication route based on the assembly of charged nanospheres used as a mask by means of a colloidal lithography technique, to better space and shape the NPs. Here we show that Au NPs with tip curvatures of 10 nm and localized plasmon resonance at 785 nm can non-destructively probe ND7/23 neurons. We prove that these tips allow us to track ND7/23 neurons on the SERS substrate, detecting both the membrane constituents, proteins and lipids, and even intracellular DNA/RNA fragments.

Plasmon-enhanced near-infrared fluorescence detection of traumatic brain injury biomarker glial fibrillary acidic protein in blood plasma

An ultrasensitive plasmonic near-infrared fluorescent biosensor substrate has been developed for detection of glial fibrillary acidic protein (GFAP) biomarker in blood plasma, an important protein biomarker of traumatic brain injury (TBI). To minimize the interference from blood plasma sample matrix, a near-infrared fluorophore in the first biological transparency window is used in the biosensor. To amplify the fluorescence signals, a plasmonic gold nanopyramid array has been coupled to the fluorophore. Finite-difference time-domain simulation reveals that the excitation enhancement is primarily responsible for the fluorescence enhancement owing to the intense local electric field excited on the corners and edges. As a result, this biosensor exhibits a lower limit of detection of 0.6 pg/mL toward detection of GFAP in blood plasma.

Design Methodologies of InP nanopyramid array based low cost hybrid solar cells

In recent years, the use of organic materials have gained the interest for photovoltaic (PV) applications owing to its ability to yield maximum throughput, solution phase processes, thereby resulting in low cost power generation. To obtain the twin benefits of low cost and high efficiency, PV cell researchers are investigating the organic–inorganic (hybrid) based solar cells (SCs). Hybrid Solar cells (HSCs) combine organic and inorganic materials in order to make use of the relatively inexpensive manufacturing of organic photovoltaics (OPV) and gaining multiple benefits from the inorganic component, such as tunable optical properties, superior electronic properties and high power conversion efficiency (PCE). III-V based nanostructures showed exceptional light capturing and charge transport properties, and can be easily combined with organic materials to build HSCs. In this paper, we have investigated the optical and electrical properties of the PTB7:PC71BM/InP truncated nanopyramid (TNP) array based HSC. The investigated structure shows higher optical absorption and optical current density (Jsc) of ∼ 25.4 mA/cm2 when compared to their organic and inorganic counterparts. The photogeneration profile and electric field of the inorganic and HSC are simulated and compared. In addition, the electrical analysis of HSC shows PCE of 18.4% which outperforms their organic and inorganic counterparts.

Hexagonal arrays of plasmonic gold nanopyramids on flexible substrates for surface-enhanced Raman scattering

Surface-enhanced Raman spectroscopy (SERS) with pyramidal gold nanostructures increases the signal of Raman active analytes, since hotspots form at the edges and tip of a nanopyramid under illumination. 2D hexagonal arrays of pyramidal nanostructures with a quadratic base are fabricated through cost-effective nanosphere lithography and transferred onto elastomeric polydimethylsiloxane. By making use of the {111} crystal plane of a silicon (100) wafer, an inverted pyramidal array is etched, which serves as the complementary negative for the gold nanostructures. Either a continuous gold thin-film with protruding pyramids or separate isolated nanopyramids are produced. Three basic fabrication strategies are presented. The SERS enhancement is verified by Raman mapping of 4-mercaptobenzoic acid (4-MBA) molecules. Fabrication on a flexible substrate paves the way for future applications on curved surfaces or in situ tunable resonances.

Large-Area Periodic Organic–Inorganic Hybrid Perovskite Nanopyramid Arrays for High-Performance Photodetector and Image Sensor Applications

The rapid growth of organic–inorganic hybrid perovskite materials (such as methylammonium lead triiodide, MAPbI3) in photoelectric applications has prompted investigations of novel strategies to improve photodetection performance. Although a few surface nanofabrication methods have been applied to texture perovskite thin films to enhance light trapping, it remains challenging to pattern large-area periodic perovskite nanoarrays in a tunable and scalable manner. In this work, we report a facile and low-cost approach to fabricate large-area SiO2/Si nanopyramids arrays through nanosphere lithography. These nanopyramids arrays are used to pattern MAPbI3 thin films. We find that the introduction of nanopyramid arrays enhances the light intensity within the perovskite film, which is confirmed by light absorption tests and optical simulations. As a result, the photodetectors based on MAPbI3 with nanopyramid structures show excellent responsivity of 28.8 ± 1.0 A/W and detectivity of (3.5 ± 0.1) × 1011 Jones at 650 nm. The photoresponse of the photodetector to pulsed light is highly stable and reproducible, with rise and decay times of ∼0.7 and 1.1 ms, respectively. They also have a broader light sensitivity range from ultraviolet to infrared light, i.e., 340 nm to 1100 nm, compared to those without nanostructures. Finally, we demonstrate a prototype image sensor using these photodetector arrays.

Geometric optimization and performance enhancement of PEDOT: PSS/GaAs NP array based heterojunction solar cells

Polymer/semiconductor nanostructure array based solar cells (SCs) exhibit extremely low optical losses, excellent light-harvesting, improved carrier lifetime, increased defect tolerance etc. and can be a new pathway for low-cost high efficiency SCs. In order to fabricate efficient heterojunction SCs, it is extremely necessary to evaluate their optimal geometric configuration theoretically. In this article, using 3D-finite difference time domain (FDTD) method, we have optimized the geometric configuration of poly (3, 4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT: PSS) coated vertically aligned GaAs Nano pyramid (NP) array heterojunction SCs to obtain high average optical absorption and J sc of 92.2% and 41.1 mA/cm 2 , respectively. The optimized structure simulated in Lumerical Charge Solver DEVICE module, exhibit power conversion efficiency (PCE) of 15.9% despite low carrier mobility and lifetime of 1000 cm 2 v −1 s −1 and 2ns respectively. • Role of GaAs nanopyramids (NPs) in efficient light harvesting is studied. • Optimization of geometrical dimensions of the NPs is performed in terms of optical J sc . • Conformal coating of PEDOT:PSS results in absorption enhancement. • GaAs NPs/PEDOT PSS based solar cells exhibits PCE of ~13%.