Highly Controllable Surface Plasmon Resonance Property by Heights of Ordered Nanoparticle Arrays Fabricated via a Nonlithographic Route

Ordered nanostructures arrays fabricated by anodic aluminum oxide (AAO) template-directed methods for energy conversion

Clean and efficient energy conversion systems can overcome the depletion of the fossil fuel and meet the increasing demand of the energy. Ordered nanostructures arrays convert energy more efficiently than their disordered counterparts, by virtue of their structural merits. Among various fabrication methods of these ordered nanostructures arrays, anodic aluminum oxide (AAO) template-directed fabrication have drawn increasing attention due to its low cost, high throughput, flexibility and high structural controllability. This article reviews the application of ordered nanostructures arrays fabricated by AAO template-directed methods in mechanical energy, solar energy, electrical energy and chemical energy conversions in four sections. In each section, the corresponding advantages of these ordered nanostructures arrays in the energy conversion system are analysed, and the limitation of the to-date research is evaluated. Finally, the future directions of the ordered nanostructures arrays fabricated by AAO template-directed methods (the promising method to explore new growth mechanisms of AAO, green fabrication based on reusable AAO templates, new potential energy conversion application) are discussed.

New insight into SPR modulating by two-dimensional correlation spectroscopy: the case for an Ag/ITO system

The localized surface plasmon resonance (LSPR) of Ag/indium tin oxide (ITO)@polystyrene (PS) in the visible-NIR region was dependent on the tuning of the carrier density caused by adjusting the thickness of the ITO layer. The two-dimensional correlation spectroscopy (2D-COS) results of the dependence of each component in the UV-vis-NIR spectrum on the carrier density response enabled the successful exploration of the carrier transport process.

An efficient nanopatterning strategy for controllably fabricating ultra-small gaps as a highly sensitive surface-enhanced Raman scattering platform

The realization of large-scale and high-density gaps with sizes as small as possible is crucial for designing ultra-sensitive surface-enhanced Raman scattering (SERS) substrates. As known, the ultrathin alumina mask (UTAM) surface nanopatterning technique allows the fabrication of periodic nanoparticle (NP) arrays with 5 nm gaps among the NPs, however, it still faces a significant challenge in realizing the reliable distribution of nanogaps over a large area, because of the unavoidable collapse of the UTAM pore wall during the traditional one-step homothermal pore-widening process. Herein, an efficient two-step poikilothermal pore-widening process was developed to precisely control the pore wall etching of a UTAM, enabling effectively avoiding the fragmentation of the UTAM and finally obtaining a large-scale UTAM with a pore wall thickness of about 5 nm. As a result, large-scale NP arrays with high-density sub-5 nm and even smaller gaps between the neighboring NPs have been realized through applying the as-prepared UTAM as the nanopatterning template. These NP arrays with sub-5 nm gaps show ultrahigh SERS sensitivity (signal enhancement improved by an order of magnitude compared with NP arrays with 5 nm gaps) and good reproducibility, which demonstrates the practical feasibility of this promising two-step pore-widening UTAM technique for the fabrication of high-performance active SERS substrates with large-scale ultra-small nanogaps.

Spindle-like porous N-doped TiO2 encapsulated (Ca,Y)F2:Yb3+,Tm3+ as the efficient photocatalyst near-infrared range

In this study, a novel photocatalyst composed of N-doped TiO₂ (N-TiO₂) and (Ca, Y)F₂:Yb³⁺, Tm³⁺ was prepared by simple dealloying followed by a hydrothermal method. The composite exhibits a homogeneous nanoporous structure consisting of large quantities of the spindle-like N-doped TiO₂ nanorods, on which the (Ca, Y)F₂:Yb³⁺, Tm³⁺ particles with a diameter of around 5 nm are uniformly dispersed. In addition, morphology and property of the N-TiO₂ can be controlled by adjusting the dealloying period. Results show that a short immersion time leads to a small size, large surface area and low band gap. As a result, the N-TiO₂/(Ca, Y)F₂:Yb³⁺, Tm³⁺ composite after dealloying for 48 h (TiO₂-48-C) exhibits higher degradation rates (65.6% for 10 h irradiation by 980 nm NIR) than others after dealloying for 60 h (TiO₂-60-C) and 72 h (TiO₂-72-C), indicating its excellent potential for practical applications.

NiFeP nanoflakes composite with CoP on carbon cloth as flexible and durable electrocatalyst for efficient overall water splitting

High-performance and earth-abundant NiFeP is an excellent bifunctional catalyst for water splitting in acidic and alkaline environments, and NiFeP nanoflakes on CoP layer composite with a conductive carbon cloth (CC) substrate as the trunk-leaf flexible structure (NiFeP/CoP/CC) is prepared by direct high-temperature phosphorization. Overpotentials of only 96.38 and 78.80 mV are required in hydrogen evolution reaction in 1 M KOH and 0.5 M H₂SO₄, respectively, to generate an electrocatalytic current density of 10 mA cm^-2. A small Tafel slope of 70.67 and 63.21 mV per decade are also observed from NiFeP/CoP/CC revealing a Volmer-Heyrovsky mechanism in both media. The electrocatalyst also delivers excellent oxygen evolution reaction performance in the alkaline environment and long-term electrochemical durability for at least 24 h in electrolytes over a wide pH range. A device is assembled with two identical flexible ultrathin NiFeP/CoP/CC as both the anode and cathode in 1 M KOH driven by a set of 1.6 V solar cells. During 32 h of electrolysis, the results show that the current of our electrodes maintains 80% performance at a constant voltage of 1.7 V for 32 h, and the NiFeP/CoP/CC anodes and cathodes have large potential in industrial alkaline water splitting.

Isolated Effects of Surface Ligand Density on the Catalytic Activity and Selectivity of Palladium Nanoparticles

Alkanethiolate-capped palladium nanoparticles (PdNPs) have previously been synthesized by using a modified Brust-Schiffrin synthesis (using alkanethiosulfate instead of alkanethiol), in which the nanoparticle core size is established during alkanethiosulfate ligand passivation of the nanoparticle nucleation-growth initiated by borohydride reduction. Because of the dependence of core size on the amount of ligand present, surface ligand density decreases with increasing core size. Herein we present a method in which the core size is established independent of ligand addition, allowing the formation of PdNPs with similar core sizes yet different surface ligand densities. In this method, the core size is established during the temporary passivation of growing nanoparticles by borohydride and tetra-N-octylammonium bromide (TOAB), allowing nucleation to reach completion. Various molar equivalents of alkyl thiosulfate are then added, prompting the replacement of borohydride and TOAB and the formation of alkanethiolate-capped PdNPs. The resulting PdNPs were characterized by using ¹H NMR, transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and inductively coupled plasma atomic emission spectroscopy (ICP-AES). The overall enhanced catalytic activity of hydrogenation/isomerization of alkenes and dienes was observed for PdNPs with a lower ligand density, proving the isolated effect of surface ligand density from other variations such as core size and shape. Surface ligand density is also shown to influence the hydrogenation/isomerization product selectivity of the catalytic reactions by regulating the formation of certain Pd-substrate intermediates and the kinetic diffusion of surface hydrogen/substrates.

Rapidly fabricating a large area nanotip microstructure for high-sensitivity SERS applications

Here, we propose a novel nanotip microstructure which can be easily fabricated through a simply Reactive Ion Etching (RIE) process combined with anodic aluminum oxide (AAO) membranes. When combined with Ag coating and annealing on the surface of micro-sized nanotip arrays, the as-formed Ag-nanoparticles (Ag-NPs)/Si-nanotip hybrid structure exhibited a significantly high enhancement factor and highly sensitive surface enhanced Raman scattering (SERS) for rhodamine 6G molecules. The nanotip microstructure showed a sharp curvature with an apex diameter which significantly affected the SERS results. The Ag-NPs/Si-nanotip hybrid structure verified a very prominent "hot spot" effect that exists around the nanotip structures, which contributed mainly to an enhanced SERS signal with an enhancement factor (EF) of 1.6 × 10⁶. Moreover, the Ag-NPs/Si-nanotip hybrid structure demonstrated superior sensitivity, with obvious featured Raman peaks even when the concentration was as low as 10^-10 M. Our work demonstrated a feasible way to prepare a novel nanotip microstructure with a highly localized surface plasmon resonance response which could be feasibly applied for highly sensitive and reproducible SERS applications.

The optimization of optical modes in Ni-BiVO4 nanoarrays for boosting photoelectrochemical water splitting

The full utilization of incident light is vitally important for boosting the photoelectrochemical activity of photoelectrodes. Herein, we introduce Ni-BiVO₄ nanoarrays for mediating the photoelectrochemical water splitting by optimizing the optical modes. Highly ordered Ni-BiVO₄ nanoarrays were fabricated using a nanoimprinted AAO templating technique. By controlling the thickness of BiVO₄, we efficiently regulate the photoelectrochemical activity, and the photocurrent was up to 0.91 mA cm^-2 at 1.4 V versus Ag/AgCl under 100 mW cm^-2 in the visible light, which is 3.25 times that of a flat Ni-BiVO₄ electrode with the same deposition cycles of BiVO₄. The optimal efficiency of a Ni-BiVO₄ nanoarrray-based photoelectrode can be attributed to the optimal morphology, which has the lowest reflection, the strongest scattering and the induced strongest absorption for the incident light among the nanoarrays samples with different thickness of BiVO₄. This work demonstrates the importance of the optimization of optical modes in the nanoarray photoelectrode in order to boost photoelectrochemical activity.

Reversibly tuning the surface state of Ag via the assistance of photocatalysis in Ag/BiOCl

Silver (Ag) nanoparticles can be spontaneously oxidized and present in different oxidized surface phases. The impact of oxidation induced photo absorption property and related photocatalytic activity are still unclear in Ag-decorated semiconductor photocatalysts. Herein, Ag-decorated BiOCl with the metallic Ag⁰ to oxidized Ag⁺ were employed to investigate the effect of surface state of Ag on relative photocatalyst properties. A redshift of localized surface plasmon resonance was observed as the Ag⁰ oxidized to Ag⁺ and a reversible manipulation was realized in UV light-driven photocatalysis. It is found that the Ag⁰/BiOCl presents higher photocatalytic activity than Ag⁺/BiOCl, but this difference is gradually decreasing under UV light irradiation compared with visible light irradiation. A controlled experiment suggests that the reduction of Ag⁺ under UV light reduced the difference between Ag⁰/BiOCl and Ag⁺/BiOCl. The possible mechanism for electron transport and the conversion between Ag⁺ and Ag⁰ via the assistance of the photoelectric effect from BiOCl has been elucidated. This photocatalytic reaction assisted reversible tuning the surface state of Ag/BiOCl will open up the possibility of rationally designing Ag-decorated semiconductors for light harvesting.

Enriching analyte molecules on tips of superhydrophobic gold nanocones for trace detection with SALDI-MS

The sensitivity of surface-assisted laser desorption/ionization (SALDI) mass spectrometry (MS) analysis depends on the efficiency of desorption and ionization of analyte molecules, which is usually limited by the low utilization efficiency of laser energy. Herein we demonstrate an efficient method to increase energy utilization efficiency for improving the efficiency of desorption and ionization of analyte molecules in SALDI-MS analysis. To increase the utilization efficiency of energy, a superhydrophobic gold film covered silicon nanocone array is fabricated and used as SALDI substrate. The nanocone array increases the absorption up to 99.65% at the wavelength of 355 nm, which is applied for SALDI-MS detection. The superhydrophobicity promotes the analyte molecules concentrated on the tips of nanocones where photon energy is confined, therefore, more energy can be provided for desorption and ionization of analytes. The energy efficiency is increased by using this substrate. The sensitivity of SALDI-MS analysis is greatly improved. For example, 100 amol/μL of rhodamine 6G, 100 fmol/μL of polyethyleneglycol, 100 ymol/μL of glutathione and 100 ymol/μL arginine still can be analyzed. The lake water containing malachite green was used as the real sample. The regression equation (Log I = 0.39 Log C + 6.58, R² = 0.9811) was obtained when the concentration of analyte was in the range from 10^-4 mol/L to 10^-8 mol/L. Therefore, the calculated LOD and LOQ are 1.35 × 10^-14 mol/L and 1.35 × 10^-7 mol/L, respectively. In addition, the lower relative standard deviation (0.7%, n = 10), proper recovery (113% and 91%), and low matrix effect (-1.1% and -1.1%) all demonstrate the great potential of the designed substrate in practical analysis.

Gap-mode excitation, manipulation, and refractive-index sensing application by gold nanocube arrays

The challenges in fabricating two-dimensional metallic nanostructures over large areas, which normally involve expensive and time-consuming nanofabrication techniques, have severely limited the exploration of the related applications based on plasmon-induced effects. Here, we cost-efficiently prepared large-area Au nanocube arrays (NCAs) using only the electrostatic forces between colloidal Au nanocubes and polyelectrolyte layers. This method provides a flexible way for obtaining controlled Au NCAs with various fill fractions and single-cube sizes. When the Au NCAs were arranged to be coupled with a continuous Au film, the plasmonic gap mode could be excited and manipulated, leading to significant and tunable light absorbance from the visible to the near-infrared parts of the spectrum. Besides, the as-prepared Au NCAs were used to construct a prototype refractive-index (RI) sensor, which exhibited excellent stability and sensitivity over 560 nm per RI unit.

The Generalized Analytical Expression for the Resonance Frequencies of Plasmonic Nanoresonators Composed of Folded Rectangular Geometries

A robust generalized analytical expression for resonance frequencies of plasmonic nanoresonators, which consists of folded rectangular structures, is proposed based on a circuit route. The formulation is rigorously derived from the lumped circuit analogue of the plasmon resonance in a rectangular metallic nanorod. Induced by the nonhomogeneous charge distributions in the plasmonic resonators of rectangular end-caps, the electromagnetic forces drive the harmonic oscillations of free electrons in the plasmonic nanoresonators, generating intrinsically nonlinear shape-dependent LC resonance responses. Even for the plasmonic nanoresonators with much larger structure sizes than the skin depths, the significant frequency deviations due to the phase-retardation behavior can still be adequately described by the generalized expression. Moreover, for a large range of plasmonic nanoresonators with various folded rectangular geometries, sizes and materials, the generalized analytical expression gives the underlining physics and provides accurate predictions, which are perfectly verified by a series of numerical simulations. Our studies not only offer quantitative insights of nearly any plasmonic nanoresonators based on folded rectangular geometries, but also reveal potential applications to design complex plasmonic systems, such as periodic arrays with embedded rectangular nanoresonators.

Surface strategies for catalytic CO2 reduction: from two-dimensional materials to nanoclusters to single atoms

This work constructively reviewed and predicted the surface strategies for catalytic CO₂ reduction with 2D material, nanocluster and single-atom catalysts

Buckling polystyrene beads with light

Colloidal transformation based on simple physicochemical processes has produced a wide variety of functional structures for different applications. But the lack of local selectivity of conventional transformation methods makes the fabrication of nanodevices with desired optical properties challenging. Here, we use a laser beam to transform spherical polystyrene (PS) beads into bull's eye-shaped nanopatterns or concentric nanorings, depending on the time of irradiation. The final morphologies are dependent on the size of the PS beads and the dielectric nature of the substrates. The simulated near field features show that it is the selective hollowing of PS beads that results in collapsing and buckling of the shells. This understanding provides a new route towards unconventional colloidal nanostructures and defect engineering in 2D photonic crystals that can be locally and selectively controlled by light.

Template-Guided Programmable Janus Heteronanostructure Arrays for Efficient Plasmonic Photocatalysis

Janus heteronanostructures (HNs), as an important class of anisotropic nanomaterials, could facilitate synergistic coupling of diverse functions inherited by their comprised nanocomponents. Nowadays, synthesizing deterministically targeted Janus HNs remains a challenge. Here, a general yet scalable technique is utilized to fabricate an array of programmable Janus HNs based on anodic aluminum oxide binary-pore templates. By designing and employing an overetching process to partially expose four-edges of one set of nanocomponents in a binary-pore template, selective deposition and interfacing of the other set of nanocomponents is successfully achieved along the exposed four-edges to form a densely packed array of Janus HNs on a large scale. In combination with an upgraded two-step anodization, the synthesis provides high degrees of freedom for both nanocomponents of the Janus HNs, including morphologies, compositions, dimensions, and interfacial junctions. Arrays of TiO₂-Au and TiO₂/Pt NPs-Au Janus HNs are designed, fabricated, and demonstrated about 2.2 times photocurrent density and 4.6 times H₂ evolution rate of that obtained from their TiO₂ counterparts. The enhancement was mainly determined as a result of localized surface plasmon resonance induced direct hot electron injection and strong plasmon resonance energy transfer near the interfaces of TiO₂ nanotubes and Au nanorods. This study may represent a promising step forward to pursue customized Janus HNs, leading to novel physicochemical effects and device applications.

Sandwiched ZnO@Au@CdS nanorod arrays with enhanced visible-light-driven photocatalytical performance

The development of high-performance photocatalysts is central to efforts focused on taking advantage of solar energy to overcome environmental and energy crises. Integrating different functional materials artfully into nanostructures can deliver more efficient photocatalytic activity. Here, sandwiched ZnO@Au@CdS nanorod films were synthesized via successive ZnO nanorod electrodeposition, Au sputtering and CdS electrodeposition. The as-synthesized composites were characterized by UV-vis spectrophotometer, x-ray diffractometer, scanning and transmission electron microscopy. Their photocatalytic activity was assessed by degrading Rhodamine B solution under visible light irradiation. ZnO@Au@CdS exhibited better photocatalytic performance than ZnO@CdS throughout the visible light region, and the corresponding enhancement factor of Au nanoparticles was measured as a function of CdS loading amount, and it could reach 190% with CdS deposition for 1 min. The normalized rate constant could reach 0.387 h^-1 for ZnO@Au@CdS-1min, which was equivalent to or better than results in reference photocatalysts. The enhancement mechanism of Au nanoparticles was estimated by comparing the monochromatic photocatalytic action spectra with the absorption spectrum of ZnO@Au@CdS, and it was mainly determined by incident photon energy. With selective excitation of Au nanoparticles by incident photons, the excited hot electrons in Au NPs are transferred to the conduction band of ZnO to boost photocatalytic reaction. With selective excitation of CdS, the enhanced interband absorption of CdS and relay station effect of Au nanoparticles should be responsible for the enhanced photocatalytic performance. Our work not only opens the door to the design of efficient supported photocatalysts, but also helps to understand the enhancement mechanism of LSPR effect on the photoelectric conversion of semiconductors.

Dependence of plasmon coupling on curved interfaces

The optical properties of coupled plasmon systems can be tuned by individual material and geometry, gap distance, and surrounding dielectric. This paper reports a dramatic effect of a curved interface in the nanoparticles dimer on the optical responses. Compared with gold nanorod (AuNR) monomer, AuNR dimers with different assembly types (such as end-to-end and side-by-side) can manipulate the longitudinal surface plasmon resonance (SPR_L) to red/blueshift. The electromagnetic field of the dimer is further enhanced in the interactive region. Under the incident polarization along the gap, a new resonance mode will be excited when AuNR dimers touch each other, and the SPR mode turns to blueshift from redshift due to the formation of the conductive coupling. It can be assumed that when one of the interactive surfaces is curved, an additional plasmon resonance can be stimulated under the polarization of incident light along the gap. The particular phenomenon can be explained by the plasmon hybridization theory. Silver nanocubes dimers (with sharp or smooth corners and edges) also possess the same property. Supported by finite-difference time-domain solutions, the coupled plasmon resonance mode represents high sensitivity to structural geometry.

Fabrication of plasmonic cavity arrays for SERS analysis

The plasmonic cavity arrays are ideal substrates for surface enhanced Raman scattering analysis because they can provide hot spots with large volume for analyte molecules. The large area increases the probability to make more analyte molecules on hot spots and leads to a high reproducibility. Therefore, to develop a simple method for creating cavity arrays is important. Herein, we demonstrate how to fabricate a V and W shape cavity arrays by a simple method based on self-assembly. Briefly, the V and W shape cavity arrays are respectively fabricated by taking KOH etching on a nanohole and a nanoring array patterned silicon (Si) slides. The nanohole array is generated by taking a reactive ion etching on a Si slide assembled with monolayer of polystyrene (PS) spheres. The nanoring array is generated by taking a reactive ion etching on a Si slide covered with a monolayer of octadecyltrichlorosilane before self-assembling PS spheres. Both plasmonic V and W cavity arrays can provide large hot area, which increases the probability for analyte molecules to deposit on the hot spots. Taking 4-Mercaptopyridine as analyte probe, the enhancement factor can reach 2.99 × 10⁵ and 9.97 × 10⁵ for plasmonic V cavity and W cavity array, respectively. The relative standard deviations of the plasmonic V and W cavity arrays are 6.5% and 10.2% respectively according to the spectra collected on 20 random spots.

Effective approach to strengthen plasmon resonance localized on top surfaces of Ag nanoparticles and application in surface-enhanced Raman spectroscopy

The spatial distribution of localized surface plasmon resonance (LSPR) plays a key role in many plasmonic applications. Based on the thermal stability of alumina templates, this work reports a novel approach to manipulate the distribution of LSPR and exhibits its significance for an important plasmonic application, the surface-enhanced Raman spectroscopy (SERS). A suitable thermal annealing sharpens the edges in top surfaces (far from the substrates) of Ag nanoparticles, which significantly strengthens the distal mode (DM) with the LSPR excited on the top surfaces. Because the top surface is the major place to adsorb probe molecules, this manipulation greatly improves the detection sensitivity of SERS. Our research provides a new way to improve the sensitivity of SERS, which also indicates that great care has to be taken on special LSPR mode which is largely responsible for a certain plasmonic application (e.g., the DM for SERS although it is not the major mode).

A unique patterned diamond stamp for a periodically hierarchical nanoarray structure

A diamond stamp with a hierarchical pattern was designed for the direct preparation of a periodic nanoarray structure, which was prepared by the reactive ion etching technique with a hierarchical ultrathin alumina membrane (HUTAM) as a mask. The optimal etching conditions for fabricating the diamond stamp were discussed in order to realize a vertical nanopore structure, avoiding structural damage from lateral etching. By using this diamond stamp, a polymer film with the desired hierarchical nanorod array structure can be obtained easily via the simple stamping process, which greatly simplifies the processing procedure. More importantly, the stamp is reusable because of its super-hardness, which ensures the reproducibility of the nanorod array pattern. Another merit is that the smooth surface of the etched diamond can avoid the use of a release agent. Our results prove that this hard stamp can be used for quick preparation of an elaborate periodic nanoarray structure. This study is significant in that it solves the problems of high cost and easy damage of stamps in nanoimprint lithography, and it might inspire more sophisticated applications of such an ordered structure in nanoplasmonics, biochemical sensing and nanophotonic devices.

Highly-Ordered 3D Vertical Resistive Switching Memory Arrays with Ultralow Power Consumption and Ultrahigh Density

Resistive switching random access memories (RRAM) have attracted great scientific and industrial attention for next generation data storage because of their advantages of nonvolatile properties, high density, low power consumption, fast writing/erasing speed, good endurance, and simple and small operation system. Here, by using a template-assisted technique, we demonstrate a three-dimensional highly ordered vertical RRAM device array with density as high as that of the nanopores of the template (10(8)-10(9) cm(-2)), which can also be fabricated in large area. The high crystallinity of the materials, the large contact area and the intimate semiconductor/electrode interface (3 nm interfacial layer) make the ultralow voltage operation (millivolt magnitude) and ultralow power consumption (picowatt) possible. Our procedure for fabrication of the nanodevice arrays in large area can be used for producing many other different materials and such three-dimensional electronic device arrays with the capability to adjust the device densities can be extended to other applications of the next generation nanodevice technology.

Facile Transferring of Wafer-Scale Ultrathin Alumina Membranes onto Substrates for Nanostructure Patterning

Ordered nanostructure arrays have attracted intensive attention because of their various applications. However, it is still a great challenge to achieve ordered nanostructure patterning over a large area (such as wafer-scale) by a technique that allows high throughput, large pattern area and low equipment costs. Here, through a unique design of the fabrication and transferring processes, we achieve a facile transferring of wafer-scale ultrathin alumina membranes (UTAMs) onto substrates without any twisting, folding, cracking and contamination. The most important in our method is fixing the UTAM onto the wafer-scale substrate before removing the backside Al and alumina barrier layer. It is also demonstrated that the thickness and surface smoothing of UTAMs play crucial roles in this transferring process. By using these perfectly transferred UTAMs as masks, various nanostructure patterning including nanoparticle, nanopore (nanomesh) and nanowire arrays are fabricated on wafer-scale substrates with tunable and uniform dimension. Because there are no requirements for UTAMs, substrates and materials to be deposited, the method presented here shall provide a cost-effective platform for the fabrication of ordered nanostructures on large substrates for various applications in nanotechnology.