Nanosphere Lithography Technique Research Articles

Tunable Periodic Nanopillar Array for MAPbI3 Perovskite Photodetectors with Improved Light Absorption.

In the field of optoelectronic applications, the vigorous development of organic-inorganic hybrid perovskite materials, such as methylammonium lead triiodide (MAPbI3), has spurred continuous research on methods to enhance the photodetection performance. Periodic nanoarrays can effectively improve the light absorption of perovskite thin films. However, there are still challenges in fabricating tunable periodic patterned and large-area perovskite nanoarrays. In this study, we present a cost-effective and facile approach utilizing nanosphere lithography and dry etching techniques to create a large-area Si nanopillar array, which is employed for patterning MAPbI3 thin films. The scanning electron microscopy (SEM) and X-ray diffraction (XRD) results reveal that the introduction of nanopillar structures did not have a significant adverse effect on the crystallinity of the MAPbI3 thin film. Light absorption tests and optical simulations indicate that the nanopillar array enhances the light intensity within the perovskite films, leading to photodetectors with a responsivity of 11.2 A/W and a detectivity of 7.3 × 1010 Jones at 450 nm in wavelength. Compared with photodetectors without nanostructures, these photodetectors exhibit better visible light absorption. Finally, we demonstrate the application of these photodetector arrays in a prototype image sensor.

Nanosphere Lithography-Enabled Hybrid Ag-Cu Surface-Enhanced Raman Spectroscopy Substrates with Enhanced Absorption of Excitation Light.

We demonstrated a low-cost, highly sensitive hybrid Ag-Cu substrate with enhanced absorption for the excitation laser beam via the nanosphere lithography technique. The hybrid Ag-Cu surface-enhanced Raman spectroscopy (SERS) substrate consists of a Cu nanoarray covered with Ag nanoparticles. The geometry of the deposited Cu nanoarray is precisely determined through a self-assembly nanosphere etching process, resulting in optimized absorption for the excitation laser beam. Further Raman enhancement is achieved by incorporating plasmonic hotspots formed by dense Ag nanoparticles, grown by immersing the prepared Cu nanoarray in a silver nitrate solution. The structural design enables analytical enhancement factor of hybrid Ag-Cu SERS substrates of 1.13 × 105. The Ag-Cu SERS substrates exhibit a highly sensitive and reproducible SERS activity, with a low detection limit of 10-13 M for Rhodamine 6G detection and 10-9 M for 4,4'-Bipyridine. Our strategy could pave an effective and promising approach for SERS-based rapid detection in biosensors, environmental monitoring and food safety.

Modified Spin Textures in a 3D Magnetic Lattice

Modified Spin Textures Three dimensional magnetic nanostructures exhibit many new properties and phenomena due to the extra degree of freedom compared to two dimensional nanostructures. In article number 2200213, Vivian Ng and Ba Myint create a magnetic lattice by overlapping hour-glass structures arrays on a 2D antidot matrix through a self-aligned nanosphere lithography technique. The field reversal behaviour and magnetic properties of the 3D magnetic lattice are characterized by magnetic force microscopy and the spin-curvature display unique magnetic behaviour as a consequence of the interplay of magnetic coupling.

Fabrication of periodic, flexible and porous silicon microwire arrays with controlled diameter and spacing: Effects on optical properties

A new method of introducing nanopores with spongy morphology during fabrication of size and pitch controlled flexible silicon microwires (SiMWs) in wafer-scale is presented using nanosphere lithography technique in addition to metal catalyzed electroless etching technique by varying concentration of oxidant and introducing surfactant or co-solvents to the etching solution. For achieving a self-assembled monolayer closed-pack pattern of SiO2 microparticles in wafer-scale simple spin coating process was used. The effect of variation of the etchant, oxidant, and surfactant on the morphology and optical properties of SiMWs were studied. By simply controlling the diameter of SiO2 microparticles and concentration of H2O2 the size of the MWs as well as the introduction of pores could be controlled. The mechanism behind the formation of porous and flexible nature of the SiMWs is also demonstrated. Average reflectance was suppressed to below 8% in the broad spectral range of 400–800 nm for these SiMWs. The photoluminescence from the SiMWs showed a peak around 830 nm.

Combining Azimuthal and Polar Angle Resolved Shadow Mask Deposition and Nanosphere Lithography to Uncover Unique Nano-Crystals.

In this article, we present a systematic investigation on a multistep nanosphere lithography technique to uncover its potential in fabricating a wide range of two- and three-dimensional nanostructures. A tilted (polar angle) electron beam shower on a nanosphere mask results in an angled shadow mask deposition. The shape of the shadow also depends on the azimuthal angle of the mask sitting on top of the substrate. We performed angled shadow mask depositions with systematic variation of these two angular parameters, giving rise to complex nanostructures (down to 50 nm), repeated over a large area without defect. In this article, nanosphere lithography with two- and four-fold azimuthal symmetry was studied at constant tilt angles followed by variations in tilt without azimuthal rotation of the substrate. Finally, both angular parameters were simultaneously varied. The structure of shadow crystals was explained using Matlab simulation. This work stretches the horizons of nanosphere lithography, opening up new scopes in plasmonic and magnonic research.

Graphene Oxide-Coated Metal-Insulator-Metal SERS Substrates for Trace Melamine Detection.

Surface-enhanced Raman spectroscopy (SERS) has long been an ultrasensitive technique for trace molecule detection. However, the development of a sensitive, stable, and reproducible SERS substrate is still a challenge for practical applications. Here, we demonstrate a cost-effective, centimeter-sized, and highly reproducible SERS substrate using the nanosphere lithography technique. It consists of a hexagonally packed Ag metasurface on a SiO2/Au/Si substrate. A seconds-lasting etching process of a self-assembled nanosphere mask manipulates the geometry of the deposited Ag metasurface on the SiO2/Au/Si substrate, which attains the wavelength matching between the optical absorbance of the Ag/SiO2/Au/Si substrate and the excitation laser wavelength as well as the enhancement of Raman signals. By spin-coating a thin layer of graphene oxide on the substrate, a SERS performance with 1.1 × 105 analytical enhancement factor and a limit of detection of 10−9 M for melamine is achieved. Experimental results reveal that our proposed strategy could provide a promising platform for SERS-based rapid trace detection in food safety control and environmental monitoring.

Shape Modulation of Plasmonic Nanostructures by Unconventional Lithographic Technique.

Conventional nano-sphere lithography techniques have been extended to the fabrication of highly periodic arrays of sub-wavelength nanoholes in a thin metal film. By combining the dry etching processes of self-assembled monolayers of polystyrene colloids with metal physical deposition, the complete transition from increasing size triangular nanoprism to hexagonally distributed nanoholes array onto thin metal film has been gradually explored. The investigated nano-structured materials exhibit interesting plasmonic properties which can be precisely modulated in a desired optical spectral region. An interesting approach based on optical absorbance measurements has been adopted for rapid and non-invasive inspections of the nano-sphere monolayer after the ion etching process. By enabling an indirect and accurate evaluation of colloid dimensions in a large area, this approach allows the low-cost and reproducible fabrication of plasmonic materials with specifically modulated optical properties suitable for many application in biosensing devices or Raman enhanced effects.

Periodic Nanohole Arrays with Enhanced Lasing and Spontaneous Emissions for Low-Cost Plasmonic Devices

Periodic arrays of air nanoholes in thin metal films that support surface plasmon resonances can provide an alternative approach for boosting the light–matter interactions at the nanoscale. Nanohole arrays have garnered great interest in recent years for their use in biosensing, light emission enhancement, and spectroscopy. Here, we employ a simple technique to fabricate nanohole arrays and examine their photonic applications including enhanced lasing and spontaneous emission of novel nanomaterials. In contrast to the complicated and most commonly used electron-beam lithography technique, hexagonal arrays of nanoholes are fabricated by using a simple combination of shadowing nanosphere lithography technique and electron-beam deposition. Through spectral and temporal characterizations, it was shown that these arrays offer an enhancement in the lasing emission of an organic dye liquid gain medium with a quality factor above 150 as well as an accelerated decay rate for CdSe quantum dots. The simple fabrication of nanohole arrays together with their excellent optical responses can therefore offer a great potential in the industrialization of plasmonic devices for use in various realms of emerging technologies such as gas sensing, biomedical imaging, and ultrafast on-chip coherent light sources.

Enhanced photoluminescence of CsPbBr3-xIx nanocrystals via plasmonic Au nanoarrays.

Large scale ordered Au nanoarrays are fabricated by nanosphere lithography technique. The photoluminescence improvement of CsPbBr3-xIx nanocrystals by more than three times is realized in the CsPbBr3-xIx nanocrystal/Au nanoarray/Si structure. Time-resolved photoluminescence decay curves indicate that the lifetime is decreased by introducing the Au nanoarrays, which results in a increasing radiation recombination rate. The reflection spectra with two major valleys (the dip in the curve) located at ∼325 nm and 545 nm of Au nanoarray/Si structure, which illustrates two plasmonic resonance absorption peaks of the Au nanoarrays. The enhancement of photoluminescence is ascribed to a well match between the excitation/emission of CsPbBr3-xIx nanocrystals and localized surface plasmon/gap plasmon resonance absorption of the ordered Au nanoarrays, as also revealed from the finite-difference time-domain simulation analysis. Our work offers an effective strategy to improve the fluorescence of perovskite nanocrystals and provide the potential for further applications.

Light-Trapping SERS Substrate with Regular Bioinspired Arrays for Detecting Trace Dyes.

Recently, few studies have focused on the light-trapping surface-enhanced Raman scattering (SERS) substrate combined with Si micropyramids and Ag (or Au). However, the Si micropyramids possess no ordered period, which not only affects the repeatability of the SERS signal but also affects the theoretical exploration. Here, the ordered micropyramids with strong light-trapping capability were fabricated by utilizing unconventional nanosphere lithography and anisotropy wet etching technique. Then, the Ag nanobowls were assembled on the ordered micropyramids to form the SERS substrate with bioinspired compound-eyes structure by utilizing the liquid-solid interface self-assembly and transfer technique. Especially, the evidence for the contribution of antireflective Si micropyramids to Raman enhancement was first presented. For this bioinspired SERS substrate, the lowest concentration of R6G that can be detected is 10-13 M with the level of a single molecule, and the relative standard deviation (RSD) is 3.68%. Meanwhile, the quantitative analysis and qualitative analysis can be realized. Especially, simultaneous trace detection of four common dyes (R6G, CV, MG, and MB) in food can be realized, suggesting that this SERS substrate will have a good application prospect in the field of optical sensors.

Gold Nanoframe Array Electrode for Straightforward Detection of Hydrogen Peroxide

The nanostructuring of a sensing membrane is performed through colloidal nanosphere lithography (NSL) techniques with a tiny polystyrene nanobead template 100 nm in size. The solvent ratio adjustment has been proven to be effective in assisting the monolayer deposition of small templating particles with minimal defects. Two distinct structures, namely, a billowy gold nanostructure (BGN) where the nanobead template is left unetched and a gold nanoframe array (GNA) with a regular ring-like structure after template removal, are used for the extended-gate field-effect transistor (EGFET) electrodes. The GNA structure generates an electroactive surface area significantly (~20%) larger than its geometrical area as well as a greater surface roughness than the BGN. When integrated with the portable constant voltage–constant current (CVCC) FET circuitry for pH screening to determine the optimized measurement conditions for H2O2 sensing, the GNA sensing membrane also shows more improved Nernstian sensitivity at ~50 mV/pH than the BGN electrode. The more optimized sensitivity is then proven using the GNA in the detection of H2O2, the most common representative reactive oxygen species (ROS) involved in the environment, food, and neurodegenerative diseases, such as Parkinson´s and Alzheimer´s diseases. The GNA electrode has a sensitivity of 70.42 mV/log µM [H2O2] and a limit of detection (LoD) of 1.183 µM H2O2. The integrated ion sensing system employing unique, highly ordered gold array gate electrodes and a portable CVCC circuit system has shown a stable real-time output voltage signal, representing an alternative to bulky conventional FET devices for potential on-site H2O2 detection.

The Optical Properties of InGaN/GaN Nanorods Fabricated on (-201) β-Ga2O3 Substrate for Vertical Light Emitting Diodes

We fabricated InGaN/GaN nanorod light emitting diode (LED) on (-201) β-Ga2O3 substrate via the SiO2 nanosphere lithography and dry-etching techniques. The InGaN/GaN nanorod LED grown on β-Ga2O3 can effectively suppress quantum confined Stark effect (QCSE) compared to planar LED on account of the strain relaxation. With the enhancement of excitation power density, the photoluminescence (PL) peak shows a large blue-shift for the planar LED, while for the nanorod LED, the peak position shift is small. Furthermore, the simulations also show that the light extraction efficiency (LEE) of the nanorod LED is approximately seven times as high as that of the planar LED. Obviously, the InGaN/GaN/β-Ga2O3 nanorod LED is conducive to improving the optical performance relative to planar LED, and the present work may lay the groundwork for future development of the GaN-based vertical light emitting diodes (VLEDs) on β-Ga2O3 substrate.

Light management studies by using different surface texturing for thin c-Si solar cells

To realize the high-efficiency solar cell, surface texturing method is one of the well-liked and potential way for the last few decades. Though different research groups have adopted several types of nanostructured anti-reflective geometries for front surface texturing of solar cell but till today which type of dimension will be fruitful to get maximum efficiency of the cell is yet to be exposed. In this work, we are trying to give a comparative study of different types of nanostructure geometries like circle, ellipse, trapezoidal and triangle (or cone) made by same material silicon and try to investigate their potential to give minimum reflectance for better cultivation of electron–hole pair into the junction of the cell. Through this study, it was validated that the triangle or cone structures have the competence to satisfy maximum criteria like low reflectance, Omni-directionality with better harvesting of electron–hole pair into the junction of the solar cell without compromising its material and processing cost. Further these types of structures (cone or triangle) have the potentiality to enhance the efficiency (more than 27% compared to other structures) of solar cell with noticeable increment of short-circuit current of the device. Finally, we fabricated the optimized nanotriangle (or nanocone) geometry through nanosphere lithography technique to realize the structure in real world and found the same optical occurrence which was already explored in our simulation studies.

A nanomesh electrode for self-driven perovskite photodetectors with tunable asymmetric Schottky junctions.

Self-driven photodetectors are essential for many applications where it is unpractical to provide or replace power sources. Here, we report a new device architecture for self-driven photodetectors with tunable asymmetric Schottky junctions based on a nanomesh electrode. The vertical-channel nanomesh scaffold is composed of a hexagonally ordered nanoelectrode array fabricated via the nanosphere lithography technique. The top and bottom nanoelectrodes are separated by only 30 nm and the areal ratio of the two nanoelectrodes can be fine-tuned, which effectively modifies the geometric asymmetricity of the Schottky junctions in the photodetector devices. The self-driven photodetectors are fabricated by depositing the (FAPbI3)0.97(MAPbBr3)0.03 (MA = methylammonium, FA = formamidinium) perovskite films onto the nanomesh electrodes. Under the self-driven mode, the optimized device demonstrates a high detectivity of 1.05 × 1011 Jones and a large on/off ratio of 2.1 × 103. This nanomesh electrode is very versatile and can be employed to investigate the optoelectronic properties of various semiconducting materials.

Stepwise nanosphere lithography: an alternate way of fabricating nanostructures

This work demonstrates a new nanosphere lithography technique, termed stepwise nanosphere lithography, to create matrices of novel two- and three-dimensional nanostructures. Different sets of nanostructures are placed at desired locations through step-by-step deposition during thermal evaporation onto a substrate surface. Three deposition parameters: (1) number of deposition steps; (2) angle of deposition; and (3) nanosphere mask orientation angle were investigated. By changing these parameters, the ordering, shape, and size of nanostructures were modified accordingly. Two- and three-dimensional nanostructure matrices with different arrangements and symmetries were successfully simulated and fabricated experimentally through a combination of multiple stationary deposition stages with different parameters.

Performance Enhancement of a ZnO-based UV Photodetector Using Patterned Ag Nanoparticles

We studied the effect of a localized surface plasma resonance (LSPR) on ZnO-based ultraviolet photodetectors (UV-PDs) with periodic patterns of Ag nanoparticles (NPs), which had been formed by wrong a nanosphere lithography technique with a mask of polystyrene nanosphere arrays. The periodically patterned Ag NPs were positioned at the interface between the ZnO channel layer and the Si substrates, and the PD structures were constructed by forming two Al electrodes on the surface of the ZnO layer. Under λ = 365 nm UV light corresponding to the bandgap of ZnO, the photocurrent and the photoresponsivity of the ZnO UV-PDs with 100-nm-thick Ag NPs were about two times greater than those of PDs without NPs. The maximum responsivity was approximately 0.13 A/W near the 420- nm wavelength, which showed the maximum scattering efficiency. This enhanced performance of the ZnO-based UV-PDs resulting from an increase in the light absorption due to the LSPR of patterned Ag NPs.

Trilayer Nanomesh Films with Tunable Wettability as Highly Transparent, Flexible, and Recyclable Electrodes

AbstractMetallic mesh materials are promising candidates to replace traditional transparent conductive oxides such as indium tin oxide (ITO) that is restricted by the limited indium resource and its brittle nature. The challenge of metal based transparent conductive networks is to achieve high transmittance, low sheet resistance, and small perforation size simultaneously, all of which significantly relate to device performances in optoelectronics. In this work, trilayer dielectric/metal/dielectric (D/M/D) nanomesh electrodes are reported with precisely controlled perforation size, wire width, and uniform hole distribution employing the nanosphere lithography technique. TiO2/Au/TiO2 nanomesh films with small hole diameter (≤700 nm) and low thickness (≤50 nm) are shown to yield high transmittance (>90%), low sheet resistance (≤70 Ω sq−1), as well as outstanding flexural endurance and feasibility for large area patterning. Further, by tuning the surface wettability, these films are applied as easily recyclable flexible electrodes for electrochromic devices. The simple and cost‐effective fabrication of diverse D/M/D nanomesh transparent conductive films with tunable optoelectronic properties paves a way for the design and realization of specialized transparent electrodes in optoelectronics.

The Optical Properties of Dual-Wavelength InxGa1−xN/GaN Nanorods for Wide-Spectrum Light-Emitting Diodes

Abstract We fabricated the dual-wavelength InxGa1−xN/GaN nanorods for wide-spectrum light-emitting diodes (LEDs) by silica nanosphere lithography (SNL) technique. The emission properties of the dual-wavelength nanorods are characterized by micro-photoluminescence (micro-PL), cathodoluminescence (CL), and temperature-dependent PL (TDPL) measurements. Nanorod structure can effectively suppress quantum confined Stark effect (QCSE) compared with planar structure due to the strain relaxation. In addition, the internal quantum efficiency (IQE) of the green quantum well (QW) within nanorod structure increases, but the IQE of the blue QW clearly decreases because blue QW has severely suffered from the nonradiative recombination by surface damage. Furthermore, the IQEs of the green QW and the blue QW within the nanorod structure can be effectively improved by wet etching treatment, with an increase in factor by 1.3 when compared with unetched nanorod structure. Evidently, the dual-wavelength InxGa1−xN/GaN nanorods are beneficial to improve the optical performance compared with planar structure, presenting a potential to realize monolithic, high-efficiency, and cost-effective white LEDs.

Enhanced photoluminescence of MoS2–Au nanostructures: Nanotriangle and nanohole arrays

We investigated the photoluminescence (PL) characteristics of MoS2–Au hybrid nanostructures, fabricated by nanosphere lithography and wet-transfer techniques. Two kinds of Au nanostructures - such as nanotriangles (NTs) and nanoholes (NHs) - were fabricated for comparison. MoS2 monolayers on both NT and NH arrays exhibited enhanced PL intensity, compared with those on SiO2/Si substrates and flat Au thin films. Numerical simulations revealed clear distinction in the electric field intensity distributions in the NT and NH arrays at the PL excitation wavelength. Such difference could be attributed to the excitation of localized and propagating surface plasmon in the NT and NH arrays. This work helps us to understand how the plasmonic NT and NH arrays affect the physical properties of the MoS2 monolayers on them.

Size dependence of emission enhancement of Tris(8-hydroxyquinolinato) aluminum with plasmonic Al nanostructure

It is essential to understand which mechanism of localized surface plasmon (LSP) emission enhancement is to be utilized when combining plasmonic metal nanostructures with an emissive material to produce an optoelectronic device. Herein, we report on the size dependence and time-resolved dynamics of photoluminescence (PL) enhancement using three sizes of aluminum nanotriangles (Al NTs) on emission by tris(8-hydroxyquinolinato)aluminum (Alq3) for elucidating its enhancement mechanism. Al nanostructures were fabricated using a nanosphere lithography technique. Two-dimensionally aligned polystyrene (PSt) beads with different diameters were used as mask templates for obtaining the Al NTs. The absorption peaks red-shifted with increasing Al NT size, and hence, were attributed to the LSP resonance. From PL of Alq3 with and without Al NTs, 2–3 fold PL enhancements were observed among the samples with different Al NTs sizes. The significant shortening of the PL lifetime was observed only in Alq3/Al NTs using Ps500, indicating the effective coupling of LSP of Al NTs and the emission, which is also evidenced from the overlapping the PL peak and the LSP absorption. In contrast, the PL emission enhancement due to LSP coupling with the absorption process of Alq3 was dominant in Alq3/Al NTs using Ps200, suggested from the similarity of the PL decay curve with that of bare Alq3, and the excitation energy matching with LSP resonance. From these observation, we can distinguish the LSP coupling process (absorption or emission) from the presence or absence of lifetime enhancement in the time-resolved PL measurements, offering a guideline for designing the optical devices incorporating the metal nanostructures.