Gold Nanomesh Research Articles

Experimental characterization of quasi-2-dimension nanoporous gold ultra-thin film from nano to micro length scale

Quasi-2D nanoporous gold ultra-thin films have been elaborated and investigated by specific surface approaches. Three different microscopy techniques (Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), and Atomic Force Microscopy (AFM)) have been used for the characterizations. A careful statistical analysis of experimental images has been done, thanks to the development of a dedicated image analysis software. It reveals that the inhomogeneous gold nanomesh at low length scale becomes homogeneous at a length scale larger than the biggest pores size of about 2 μm, with a constant opacity reaching 35%. At such a scale, the ligaments present an average diameter of 20 nm and an average length of 70 nm. While TEM and SEM present similar results, AFM overestimates the geometric characteristics due to tip convolution effect. However, the topology of the nanomesh is not affected. This study also reveals pores with a much larger size in the quasi 2D nanoporous ultra-thin film than in its bulk counterpart for similar ligaments diameters, which could play an important role in its mechanical properties.

Wafer‐Scale Gold Nanomesh via Nanotransfer Printing toward a Cost‐Efficient Multiplex Sensing Platform

AbstractMultiplex sensing platforms via large‐scale and cost‐efficient fabrication processes for detecting biological and chemical substance are essential for many applications such as intelligent diagnosis, environmental monitoring, etc. For the past decades, the performance of those sensors has been significantly improved by the rapid development of nanofabrication technologies. However, facile processes with cost‐effectiveness and large‐scale throughput still present challenges. Nano‐transfer printing together with the imprinting process shows potential for the efficient fabrication of 100 nm structures. Herein, a wafer‐scale gold nanomesh (AuNM) structure on glass substrates with 100 nm scale features via nano‐imprinting and secondary transfer printing technology is reported. Furthermore, potential sensing applications are demonstrated towards biochemical substance detection by using AuNM structures as highly responsive substrates for achieving the surface enhanced Raman spectroscopy (SERS), and as working electrodes of electrochemical analysisfor the detection of metallic ions. In the SERS detection mode, different nucleotides can be detected down to 1 nm level and distinguished via theirunique fingerprint patterns. As for electrochemical analysis mode, Pb2+ ions can be detected out of other interfering components with concentration down to 30 nm. These multimodal sensing mechanisms provide complementary informationand pave the way for low‐cost and high‐performance sensing platforms.

Place & Play SERS: sample collection and preparation-free surface-enhanced Raman spectroscopy.

The ability to perform sensitive, real-time, in situ, multiplex chemical analysis is indispensable for diverse applications such as human health monitoring, food safety testing, forensic analysis, environmental sensing, and homeland security. Surface-enhanced Raman spectroscopy (SERS) is an effective tool to offer the ability by virtue of its high sensitivity and rapid label-free signal detection as well as the availability of portable Raman spectrometers. Unfortunately, the practical utility of SERS is limited because it generally requires sample collection and preparation, namely, collecting a sample from an object of interest and placing the sample on top of a SERS substrate to perform a SERS measurement. In fact, not all analytes can satisfy this requirement because the sample collection and preparation process may be undesirable, laborious, difficult, dangerous, costly, or time-consuming. Here we introduce "Place & Play SERS" based on an ultrathin, flexible, stretchable, adhesive, biointegratable gold-deposited polyvinyl alcohol (PVA) nanomesh substrate that enables placing the substrate on top of an object of interest and performing a SERS measurement of the object by epi-excitation without the need for touching, destroying, and sampling it. Specifically, we characterized the sensitivity of the gold/PVA nanomesh substrate in the Place & Play SERS measurement scheme and then used the scheme to conduct SERS measurements of both wet and dry objects under nearly real-world conditions. To show the practical utility of Place & Play SERS, we demonstrated two examples of its application: food safety testing and forensic analysis. Our results firmly verified the new measurement scheme of SERS and are expected to extend the potential of SERS by opening up untapped applications of sensitive, real-time, in situ multiplex chemical analysis.

Porous gold nanomesh films electrodeposited in toluene-based dynamic soft template

Two-dimensional (2D) metallic nanomaterials have received much attention as next-generation materials. The creation of the characteristic pores into 2D metallic materials is expected to improve performance in sensing, surface-enhanced Raman spectroscopy, electrocatalytic activity, and so on. Here, we report that gold electrodeposition in a toluene-based bicontinuous microemulsion (BME), called a dynamic soft template, provides porous gold nanomesh (PGNM) film. The selective toluene adsorption onto Au{111} surfaces induces anisotropic 2D growth of gold in the aqueous phase of BME, and an intertwined network of water and toluene nanochannels in BME resulted in the formation of abundant in-plane nanopores. Toluene adsorption during Au electrodeposition makes the {111}-oriented Au surfaces more lipophilic, i.e., a structural change in BME is induced to expose the organic phase solution selectively to the toluene-adsorbed {111} Au surfaces. This dynamic change in the BME solution structure during electrodeposition might enhance the anisotropic growth of gold (dynamic soft templating). Electrochemical behaviors of low-index planes of Au electrode supported the growth mechanism of PGNM film.

Highly Scalable, Wearable Surface‐Enhanced Raman Spectroscopy

AbstractThe last two decades have witnessed a dramatic growth of wearable sensor technology, mainly represented by flexible, stretchable, on‐skin electronic sensors that provide rich information of the wearer's health conditions and surroundings. A recent breakthrough in the field is the development of wearable chemical sensors based on surface‐enhanced Raman spectroscopy (SERS) that can detect molecular fingerprints universally, sensitively, and noninvasively. However, while their sensing properties are excellent, these sensors are not scalable for widespread use beyond small‐scale human health monitoring due to their cumbersome fabrication process and limited multifunctional sensing capabilities. Here, a highly scalable, wearable SERS sensor is demonstrated based on an easy‐to‐fabricate, low‐cost, ultrathin, flexible, stretchable, adhesive, and biointegratable gold nanomesh. It can be fabricated in any shape and worn on virtually any surface for label‐free, large‐scale, in situ sensing of diverse analytes from low to high concentrations (10–106 × 10−9 m). To show the practical utility of the wearable SERS sensor, the sensor is tested for the detection of sweat biomarkers, drugs of abuse, and microplastics. This wearable SERS sensor represents a significant step toward the generalizability and practicality of wearable sensing technology.

(Invited) Transparent and Flexible PEDOT:PSS/ITO/Ag/ITO Microelectrodes for Electrophysiology Recording

High-resolution microelectrodes made of transparent conducting materials are advantageous for electrophysiology recordings when used in combination with optogenetic stimulation or optical imaging. Existing transparent electrodes made of indium tin oxide (ITO), ultrathin metal, graphene, poly-(3, 4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT:PSS), gold nanomesh, or silver nanowire network present tradeoffs with optical transmittance, resistivity, mechanical flexibility, and biocompatibility. In this work, we designed and constructed a flexible, fully transparent microelectrode array using a PEDOT:PSS/ITO/Ag/ITO multilayer assembly. Nanometer-thick Ag provides high electrical conductivity while being transparent over a broad spectrum. ITO offers excellent transparency as well as chemical and biological stability to protect Ag from corrosion in the biological environments. PEDOT:PSS further reduces electrochemical impedance by increasing the active surface area with the same electrode size. The thickness of each layer of the multilayer assembly was optimized at a specific wavelength using admittance loci analysis to minimize the reflectance at the inhomogeneous material interfaces. As a proof of concept, an electrode array was designed to have two sub panels, each of which consisted of 16 microelectrodes on a 3x3 mm2 area, with various electrode diameters of 25 µm to 50 µm. The fabrication of such an array started from Parylene C deposition on a 3-inch silicon wafer. Photoresist (PR) was spun on the substrate and photolithographically patterned as a sacrificial mask. After that, ITO (20 nm), Ag (9.5 nm) and ITO (24 nm) thin films were sputtered consecutively in a radio-frequency (RF) magnetron sputtering system (Denton Explorer-14, Denton Vacuum, Inc), and then patterned using the liftoff process to form microelectrodes, interconnection wires, and contact pads. Next 2 μm Parylene C was deposited on the substrate as an insulating layer and selectively etched using oxygen plasma dry etching (RIE-1701 plasma system, Nordson March, Inc) to expose the recording sites and contact pads. After that, another PR mask was patterned to expose only the microelectrode sites followed by coating diluted 0.55% PEDOT:PSS. Finally, PR was rinsed off with acetone, IPA and DI water to remove unwanted PEDOT:PSS, leaving PEDOT:PSS only on top of the ITO-Ag-ITO microelectrodes.The optical, electrical, electrochemical, and mechanical properties of the PEDOT:PSS-ITO-Ag-ITO multilayer assembly was characterized using various experimental methods. In particular, a Filmetrics thin film analyzer was utilized to measure the transmittance of thin films in a wavelength range of 300 nm - 800 nm (F20-UVX, Filmetrics, Inc) and a four-point probe (SRM-232, Bridge Technology, Inc) analyzer was used to measure the sheet resistances of the samples. Compared to a single ITO film of the same thickness, the PEDOT:PSS/ITO/Ag/ITO assembly exhibits a combination of high broad-band transmission (>80%) and significantly improved conductivity. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) analyses demonstrated the significantly enhanced electrical impedance of the multilayer film by 91.85%. The electrochemical impedance of the films remained stable after 12 weeks of storage in room temperature air, with less than 12% change. Meanwhile, peel-off tests verified the excellent adhesion of the ITO-Ag-ITO assembly on the Parylene C substrate, and bending test results demonstrated the mechanical flexibility of the combined thin films over a large surface area. In addition, the noise performance of the transparent microelectrodes was analyzed under exposure to optical illumination of various wavelengths, confirming the negligible photon-induced artifacts suitable for electrophysiology recording in combination with optical imaging or stimulation. The optical transparency of the microelectrode array was further demonstrated under both the fluorescent and bright-field illumination conditions. Finally, the ability to use the transparent microelectrodes for recording neurophysiology and electrocardiography signals was demonstrated in vivo using rat models or in vitro using heart organoids.

Enhanced light-matter interactions in size tunable graphene-gold nanomesh

A hybrid graphene–gold nanomesh, realized through Au deposition on a patterned graphene nanomesh with a focused ion beam, is introduced and illustrated for enhanced light absorption in the visible spectrum. Numerical studies reveal that the hybrid nanomesh with dual resonances in the visible spectrum exhibit ~50% light absorption and enhancement factor as high as ~1 × 108. The simulations also show that the enhanced optical absorption is associated with the excitation of surface plasmons. This is confirmed through the localization of electric fields at the resonant wavelengths. Such a hybrid graphene–gold nanomesh exhibiting enhanced light-matter interactions paves the way toward plasmonics, surface-enhanced Raman scattering applications, etc.

Interconnected Heat-Press-Treated Gold Nanomesh Conductors for Wearable Sensors

We report the reduction in the wire resistance of gold nanomesh electrodes caused by interconnecting mesh electrodes. The porous-structured electrodes show high resistance because of the high junct...

27%‐Efficiency Four‐Terminal Perovskite/Silicon Tandem Solar Cells by Sandwiched Gold Nanomesh

AbstractMultijunction/tandem solar cells have naturally attracted great attention because they are not subject to the Shockley–Queisser limit. Perovskite solar cells are ideal candidates for the top cell in multijunction/tandem devices due to the high power conversion efficiency (PCE) and relatively low voltage loss. Herein, sandwiched gold nanomesh between MoO3 layers is designed as a transparent electrode. The large surface tension of MoO3 effectively improves wettability for gold, resulting in Frank–van der Merwe growth to produce an ultrathin gold nanomesh layer, which guarantees not only excellent conductivity but also great optical transparency, which is particularly important for a multijunction/tandem solar cell. The top MoO3 layer reduces the reflection at the gold layer to further increase light transmission. As a result, the semitransparent perovskite cell shows an 18.3% efficiency, the highest reported for this type of device. When the semitransparent perovskite device is mechanically stacked with a heterojunction silicon solar cell of 23.3% PCE, it yields a combined efficiency of 27.0%, higher than those of both the sub‐cells. This breakthrough in elevating the efficiency of semitransparent and multijunction/tandem devices can help to break the Shockley–Queisser limit.

Vapor dealloying of ultra-thin films: a promising concept for the fabrication of highly flexible transparent conductive metal nanomesh electrodes

The booming market of flexible electronic displays has urged the development of highly flexible transparent conductive electrodes (FTCE)1–3 with the ability to replace indium tin oxide (ITO) thin films routinely used as transparent conductive electrodes in photoelectronic devices. The high cost of indium and the poor mechanical stability of ITO under deformation are the main driving forces behind the development of this research area.4 The use of metal nanomeshes as FTCE is a promising concept with a real potential to substitute ITO in photoelectronic devices.5,6 However, the development of a low-cost fabrication approach allowing producing metal nanomesh electrodes with competitive prices and a high performance remains a real bottleneck for the photoelectronic industry. In this paper, we report on a robust approach very easy to implement allowing producing highly flexible metal nanomesh electrodes with high performance at a very low cost. This approach lies on a concept consisting in applying dealloying process to ultra-thin Au-Cu alloy thin films using acidic vapors instead of a liquid phase as routinely done in the literature. Using an appropriate procedure, the nanomeshes can be transferred to any planar or curved support where they can serve as a FTCE. As a proof of concept, we demonstrate that using this approach, one can easily fabricate gold nanomesh electrodes transferred onto polyethylene terephthalate (PET) film surface with 79% of transmittance and a sheet resistance as low as 44 Ω □−1 while maintaining exceptional stability under severe mechanical deformations.

Formation of Monolayer Polystyrene Array Template for Gold Nanomesh Structure

In this study, the preparation of monolayer array template was performed using 0.2 µm polystyrene (PS) nanospheres monodisperse micro particle deposited onto Indium Tin Oxide (ITO) coated glass substrate. The template was used to arrange the gold (Au) in nanomesh structure thus, enhance its homogeneity for having better sensitivity and repeatability in the plasmonic sensor application. PS nanosphere template was prepared by diluting 0.2 µm PS liquid with ethanol in the ratio of 1:3 and stirred with 400 rpm for 1 hours at 40 °C. Next, the PS solution was spin coated on ITO substrate at different speed variation starting from 200 rpm to 800 rpm in 3 minutes at room temperature. The template structure was then inspected with Field Emission-Scanning Electron Microscopy (FESEM). It was found that, the PS nanosphere template with 600 rpm speed shows the most orderly arrangement of PS array. Subsequently, the PS array template was used as a mask to deposit gold (Au) and performed via direct current (DC) sputtering method. Finally, the Au nanomesh structure was obtained using the lift ‒ off process of PS nanosphere template.

Bilayer Nanomesh Structures for Transparent Recording and Stimulating Microelectrodes

AbstractNanomeshed forms of metal have emerged as a promising biocompatible electrode material for future soft bioelectronics. However, metal/electrolyte interfaces are intrinsically capacitive, severely limiting their electrochemical performance, especially for scaled electrodes, which are essential for high‐resolution brain mapping. Here, an innovative bilayer nanomesh approach is demonstrated to address this limitation while preserving the nanomesh advantage. Electroplating low‐impedance coatings on a gold nanomesh template achieves an impedance < 30 kΩ at 1 kHz and a charge injection limit of 1 mC cm−2 for 80 × 80 µm2 microelectrodes, a 4.3× and 12.8× improvement over uncoated electrodes, respectively, while maintaining a transparency of ≈70% at 550 nm. Systematic characterization of transmittance, impedance, charge injection limits, cyclic charge injection, and light‐induced artifacts reveal an encouraging performance of the bilayer nanomesh microelectrodes. The bilayer nanomesh approach presented here is expected to enable next‐generation large‐scale transparent bioelectronics with broad utility in biology.

Breathable electronic skin

Electronics designed to stick to skin and transmit the body’s electric signals could improve the sensitivity of prosthetics or help doctors monitor patients’ vital signs. Unfortunately, conventional electrodes used for this purpose trap air and sweat against skin, causing irritation or inflammation when used for an extended period. Now, a team of researchers from the University of Tokyo, the Japan Science & Technology Agency, and Riken have developed a conductive gold nanomesh that is flexible and breathable while relaying electric signals (Nat. Nanotechnol. 2017, DOI: 10.1038/nnano.2017.125). To make the material, researchers led by Takao Someya at the University of Tokyo electrospun nanofibers of biocompatible polyvinyl alcohol (PVA) and interwove them to form a mesh. They then coated the top of the nanomesh with a layer of gold 70- to 100-nm thick. After applying this mesh to a person’s skin, researchers sprayed it with water to dissolve the PVA and form

Asymmetry in supramolecular assembly.

Photoresponsive organic nanowires connect to gold nanomesh and silicon electrodes

Showing particles their place: deterministic colloid immobilization by gold nanomeshes

The defined immobilization of colloidal particles on a non-close packed lattice on solid substrates is a challenging task in the field of directed colloidal self-assembly. In this contribution the controlled self-assembly of polystyrene beads into chemically modified nanomeshes with a high particle surface coverage is demonstrated. For this, solely electrostatic interaction forces were exploited by the use of topographically shallow gold nanomeshes. Employing orthogonal functionalization, an electrostatic contrast between the glass surface and the gold nanomesh was introduced on a sub-micron scale. This surface charge contrast promotes a highly site-selective trapping of the negatively charged polystyrene particles from the liquid phase. AFM force spectroscopy with a polystyrene colloidal probe was used to rationalize this electrostatic focusing effect. It provides quantitative access to the occurring interaction forces between the particle and substrate surface and clarifies the role of the pH during the immobilization process. Furthermore, the structure of the non-close packed colloidal monolayers can be finely tuned by varying the ionic strength and geometric parameters between colloidal particles and nanomesh. Therefore one is able to specifically and selectively adsorb one or several particles into one individual nanohole.

Ultrafast Phase Transition via Catastrophic Phonon Collapse Driven by Plasmonic Hot-Electron Injection

Ultrafast photoinduced phase transitions could revolutionize data-storage and telecommunications technologies by modulating signals in integrated nanocircuits at terahertz speeds. In quantum phase-changing materials (PCMs), microscopic charge, lattice, and orbital degrees of freedom interact cooperatively to modify macroscopic electrical and optical properties. Although these interactions are well documented for bulk single crystals and thin films, little is known about the ultrafast dynamics of nanostructured PCMs when interfaced to another class of materials as in this case to active plasmonic elements. Here, we demonstrate how a mesh of gold nanoparticles, acting as a plasmonic photocathode, induces an ultrafast phase transition in nanostructured vanadium dioxide (VO2) when illuminated by a spectrally resonant femtosecond laser pulse. Hot electrons created by optical excitation of the surface-plasmon resonance in the gold nanomesh are injected ballistically across the Au/VO2 interface to induce a subpicosecond phase transformation in VO2. Density functional calculations show that a critical density of injected electrons leads to a catastrophic collapse of the 6 THz phonon mode, which has been linked in different experiments to VO2 phase transition. The demonstration of subpicosecond phase transformations that are triggered by optically induced electron injection opens the possibility of designing hybrid nanostructures with unique nonequilibrium properties as a critical step for all-optical nanophotonic devices with optimizable switching thresholds.

Metallic nanomesh electrodes with controllable optical properties for organic solar cells

We have fabricated a metallic nanomesh using nanosphere lithography and metal evaporation. The metallic nanomesh has a precisely controlled nanostructure showing excellent uniformity with hexagonally arrayed periodic circular holes. A P3HT:PCBM organic solar cell, with the gold nanomesh electrode, demonstrates a high fill factor of 61% and a considerable power conversion efficiency of 3.12%. Electromagnetic simulation indicates that the optical properties of the metallic nanomesh can be optimized for organic photovoltaic devices by tuning the film thickness, hole diameter, and periodicity. These results show the promising potential of using a metallic nanomesh as the transparent electrode in organic solar cells.

Gold nanomesh induced surface plasmon for photocurrent enhancement in a polymer solar cell

In this study, a gold (Au) nanomesh layer was manufactured on an ITO-coated glass substrate at room temperature. The Au nanomesh was used to induce surface plasmon resonance (SPR) to enhance the photocurrent of a polymer solar cell. The Au nanomesh was manufactured by lift-off on closely packed PS nanospheres (diameter ∼50 nm; density ∼10 10/cm 2). The PS nanospheres were fabricated by modified block copolymer nano-patterning on ITO. A transmittance–reflection–absorbance spectrum was used to explore the induced surface plasmon. An extinction peak was observed at ∼580 nm indicate the possibility of Au nanomesh induced surface plasmon resonance. The short-circuit current density of the polymer solar cell was enhanced from 7.02 to 14.2 mA/cm 2 by the addition of Au nanomesh. Consequently, the power conversion efficiency enhanced from 1.9% to 3.2%. By the normalized input photon-to-current conversion efficiency (IPCE) measurement, enhanced photocurrent conversion efficiency at approximately 580 nm was observed that coincided with the extinction spectrum, indicating that the surface plasmon enhanced the photocurrent.