Au Monolayer Research Articles

Superhydrophobic Surface-Enhanced Raman Spectroscopy (SERS) Substrates for Sensitive Detection of Trace Nanoplastics in Water.

Nanoplastics, emerging as pervasive environmental pollutants, pose significant threats to ecosystems and human health due to their small size and potential toxicity. However, detecting trace levels of nanoplastics remains challenging because of limitations in the current analytical methods. Herein, we propose a method that combines superhydrophobic enrichment with SERS analysis for detecting trace nanoplastics in aqueous environments. Superhydrophobic SERS substrates were prepared by using a liquid-liquid self-assembly method. The superhydrophobicity facilitated analyte enrichment, and monolayer Au nanoparticles (AuNPs) enhanced the Raman signals. The detection limit for Raman probe crystal violet (CV) using this substrate reached nanomolar (10-9 M), with an RSD of 9.96% across a 40 × 40 μm2 area (441 spots), demonstrating excellent sensitivity and reproducibility. This method successfully detected polystyrene (PS) plastics ranging from 30 to 1000 nm in water with concentrations as low as 0.03 μg/mL. Additionally, nanoscale polyethylene terephthalate (PET) particles were detected in bottled water samples. This approach offers a promising platform for analyzing trace nanoplastics in environmental water samples and addresses the needs of environmental monitoring.

Hot Nanogap Networks-In-Triangular Nanoframes: A Strategy for Positioning Adsorbates Near Hot Spots.

This study reports the synthesis of plasmonic hot nanogap networks-in-triangular nanoframes (NITNFs), featuring narrow intraparticle nanogap networks embedded within triangular nanoframes. Starting from Au nanotriangles, Pt NITNFs are synthesized through a cascade reaction involving simultaneous Pt deposition and Au etching in a one-pot process. The Pt NITNFs are then transformed into plasmonically active Au NITNFs via Au coating. The near-field focusing capabilities of the Au NITNFs are tailored by fine-tuning the void area fraction down to 3.9%, resulting in the formation of narrow nanogaps of ≈1nm. This optimization enables the successful implementation of single-particle surface-enhanced Raman scattering (SERS) measurements. Then, monolayer Au NITNFs films on Al substrates are prepared, which enabled weakly adsorbing species to be positioned close to the hot spots of the NITNFs by anchoring them to the underlying Al substrates. As a representative sensing application, the SERS-based detection of gas-phase dimethyl methylphosphonate (DMMP) using a film of plasmonic NITNFs on an Al substrate exhibits outstanding performances, achieving a limit of detection of 5ppm and a detection time of 120 s.

Boron-induced transformation of ultrathin Au films into two-dimensional metallic nanostructures

The synthesis of large, freestanding, single-atom-thick two-dimensional (2D) metallic materials remains challenging due to the isotropic nature of metallic bonding. Here, we present a bottom-up approach for fabricating macroscopically large, nearly freestanding 2D gold (Au) monolayers, consisting of nanostructured patches. By forming Au monolayers on an Ir(111) substrate and embedding boron (B) atoms at the Au/Ir interface, we achieve suspended monoatomic Au sheets with hexagonal structures and triangular nanoscale patterns. Alternative patterns of periodic nanodots are observed in Au bilayers on the B/Ir(111) substrate. Using scanning tunneling microscopy, X-ray spectroscopies, and theoretical calculations, we reveal the role of buried B species in forming the nanostructured Au layers. Changes in the Au monolayer’s band structure upon substrate decoupling indicate a transition from 3D to 2D metal bonding. The resulting Au films exhibit remarkable thermal stability, making them practical for studying the catalytic activity of 2D gold.

Design of Bimetallic Boronene Structures Leveraging Neighboring Effects for Efficient Electrocatalytic CO2 Reduction Reaction

AbstractElectrocatalytic CO2 reduction (CO2RR) offers a promising avenue to address rising atmospheric CO2 levels by producing high‐value chemicals. However, the development of efficient, long‐lasting catalysts remains challenging. In this study, particle swarm optimization is employed to design a novel bimetallic boronene structure, thereby enhancing CO2RR activity through precise tuning of the metal‐substrate microenvironment. Through high‐throughput screening, seven CuMB4 (M = V, Zn, Nb, Ag, Cd, Ta, Au) monolayers are identified as promising CO2RR catalysts based on stability, conductivity, catalytic activity, and selectivity. These materials, characterized by hyper‐coordination and neighboring bimetallic effects, are proposed for synthesis via self‐assembled surface growth. Notably, CuZnB4 exhibited exceptional theoretical catalytic activity, characterized by remarkably low limiting potentials (UL) of −0.16 V for CH4 and −0.27 V for C2H4, as well as low kinetic barriers of 0.65 and 0.53 eV, respectively. The enhanced activity results from neighboring effects optimizing densely populated boron active sites and the ability to suppress hydrogen evolution reactions. Additionally, this study explored intrinsic properties influencing catalytic activity using volcano plots, descriptor analysis, and electron density evaluation. Unlike traditional catalysts prone to oxidation, CuMB4 varieties possess self‐activating properties, facilitating the conversion of *O/*OH to H2O and enhancing CO2 conversion. This research introduces robust CO2RR catalysts and provides insights into manipulating neighboring effects, thus guiding future catalyst design.

Tunable interfacial properties of monolayer GeSb2Te4 on metal surfaces

Abstract Atomically thin monolayer (ML) GeSb 2 Te 4 (GST) holds promising prospects in non-volatile memory applications because of its high non-homogeneous crystallization rate. In GST-based devices, the interaction between GST and metals is crucial, as it affects the electronic properties. Herein, based on first-principles calculations, we investigate the interaction and Schottky barrier height of contacts formed by the combination of ML GST with various metals. It is found that the interfaces of GST with Pt, Pd, Ir and W exhibit strong interaction, characterized by large binding energies ranging from 1.394 to 1.015 eV , and the interfaces between GST and Cu, Ag and Au display weak interaction. For the seven contacts, Ag and W form Ohmic contacts with ML GST, while Cu, Au, Pd, Ir, and Pt form n-type Schottky contacts, with Schottky barrier heights ranging from 0.029 to 0.353 eV . The strong Fermi level pinning at GST-metal interface is observed with a pinning factor of 0.378. Additionally, altering the interfacial distance and optimizing the layers of GST enable a transition from Ohmic contact to Schottky contact. These findings provide crucial guidance for the design and optimization of electronic devices based on phase change materials like GST.

Tunable Nanoislands Decorated Tapered Optical Fibers Reveal Concurrent Contributions in Through-Fiber SERS Detection.

Creating plasmonic nanoparticles on a tapered optical fiber (TF) tip enables a remote surface-enhanced Raman scattering (SERS) sensing probe, ideal for challenging sampling scenarios like biological tissues, site-specific cells, on-site environmental monitoring, and deep brain structures. However, nanoparticle patterns fabricated from current bottom-up methods are mostly random, making geometry control difficult. Uneven statistical distribution, clustering, and multilayer deposition introduce uncertainty in correlating device performance with morphology. Ultimately, this limits the design of the best-performance remote SERS sensing probe. Here we employ a tunable solid-state dewetting method to create densely packed monolayer Au nanoislands with varied geometric parameters in direct contact with the silica TF surface. These patterns exhibit analyzable nanoparticle sizes, densities, and uniform distribution across the entire taper surface, enabling a systematic investigation of particle size, density, and analyte effects on the SERS performance of the through-fiber detection system. The study is focused on the SERS response of a widely employed benchmark molecule, rhodamine 6G (R6G), and serotonin, a highly relevant neurotransmitter for the neuroscience field. The numerical simulations and limit of detection (LOD) experiments on R6G show that the increase of the total near-field enhancement volume promotes the SERS sensitivity of the probe. However, we observed a different behavior for serotonin linked to its interaction with the nanoparticle's surface. The obtained LOD is as low as 10-7 M, a value not achieved so far in a through-fiber detection scheme. Therefore, our work offers a strategy to design nanoparticle-based remote SERS sensing probes and provides new clues to discover and understand intricate plasmonic-driven chemical reactions.

Magnetism of Otherwise Nonmagnetic Elements: From Clusters to Monolayers.

Atomic clusters are known to exhibit properties different from their bulk phase. However, when assembled or supported on substrates, clusters often lose their uniqueness. For example, uranium and coinage metals (Cu, Ag, Au) are nonmagnetic in their bulk. Herein, we show that UX6 (X= Cu, Ag, Au) clusters, unlike their nonmagnetic bulk, are not only magnetic but also retain their magnetic character and structure when assembled into a two-dimensional (2D) material. The magnetic moment remains localized at the U site and is found to be 3μB in clusters and about 2μB in the 2D structure. In 2D UX4 (X = Cu, Ag, Au) monolayers, U atoms are found to be coupled antiferromagnetically through an indirect exchange coupling mediated by the coinage metal atoms. Furthermore, hydrogenation of these monolayers can induce a transition from the antiferromagnetic to the ferromagnetic phase. These results, based on density functional theory, have predictive capability and can motivate experiments.

Atomically dispersed Au single sites and nanoengineered structural defects enable a high electrocatalytic activity and durability for hydrogen evolution reaction and overall urea electrolysis

The development of exceptionally active and stable trifunctional electrocatalysts is essential to facilitate industrial applications of proton exchange membrane electrolyzers. Rare earth catalysts have a wide range of applications in alkaline solution oxidation, but limitations in their stability and activity prevent their further application. In this paper, Au doped CeO2 coated porous Aux/CeO2 (x = 1,2,3) was designed as a three-function electrocatalyst with excellent performance and stability. At 1 M KOH conditions, both the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER) reactions exhibit excess potentials of 159.6 and 320.8 mV at a current density of 10 mA cm-2. In addition, when incorporated into an Au2/CeO2 (0.05 mmol, HAuCl4·4H2O) microparticles, the catalyst exhibits the potential of 1.42 V(10 mA cm-2) containing 0.33 M urea in 1 M KOH. Remarkably, for hydrogen production driven by urea electrolysis, Au2/CeO2 demonstrated exceptional performance by requiring only a voltage input of 1.63 V. The reducing agent that forms the Au/CeO2 heterojunction modulates the electronic structure of the Au active site and optimizes the adsorption of the intermediate. In addition, the interaction of the Au monolayer with the CeO2 nanosphere effectively prevents excessive oxidation and dissolution of Au, and the porous hollow structure provides additional exposed active sites and facilitates mass transfer.

A DFT study of the proximity effect in the spin-orbit coupling in Au/graphene, Au/silicene, and Bi/silicene bilayers

The relativistic band structures of bilayers, built from graphene and silicene and monolayers of heavy atoms, Au and Bi, have been calculated within DFT. It is shown that when the orbital overlap is minor, like in the case of Au monolayer on graphene, a strong spin-orbit coupling in Au does not open a substantial gap in the Dirac cone. When, in contrast, the overlap of the wave functions is significant, like in the cases of Au and Bi adsorbed on silicene, the mixing of the bands (hybridization) destroys the cone structure and makes a separation of the bands by their origin or possession uncertain. In such cases, the spin-orbit splitting of the bands hardly could be attributed to a particular layer and corresponds to the band structure of the net layered system.

Twist-Angle Tuning of Electronic Structure in Two-Dimensional Dirac Nodal Line Semimetal Au2Ge on Au(111).

Topological semimetals have emerged as quantum materials including Dirac, Weyl, and nodal line semimetals, and so on. Dirac nodal line (DNL) semimetals possess topologically nontrivial bands crossing along a line or a loop and are considered precursor states for other types of semimetals. Here, we combine scanning tunneling microscopy/spectroscopy (STM/S) measurements and density functional theory (DFT) calculations to investigate a twist angle tuning of electronic structure in two-dimensional DNL semimetal Au2Ge. Theoretical calculations show that two bands of Au2Ge touch each other in Γ-M and Γ-K paths, forming a DNL. A significant transition of electronic structure occurs by tuning the twist angle from 30° to 24° between monolayer Au2Ge and Au(111), as confirmed by STS measurements and DFT calculations. The disappearing of DNL state is a direct consequence of symmetry breaking.

Impact of Thermal Annealing on the Interaction Between Monolayer MoS2 and Au

Herein, the impact of thermal annealing on the interaction between monolayer MoS2 and Au using Raman spectroscopy is investigated. It is found that MoS2 has two main modes of interactions with the underlying Au being either weakly coupled or strongly coupled. The regions strongly coupled to Au are hybridized to Au, minimally strained, and electron doped. The weakly coupled regions are found to be slightly hole doped with tensile strain of 1.0%. The overall areal coverage of the strongly coupled regions is not increased by thermal annealing, and the variability in the degree of hybridization increases at annealing temperatures above 100 °C. The data also show that monolayer MoS2 starts to decouple from Au around 100 °C, becoming fully decoupled above 200–250 °C, suggesting that monolayer MoS2 produced by Au‐assisted mechanical exfoliation may be more easily transferred off Au at elevated temperatures.

A first-principles investigation on the structural, stability and mechanical properties of novel Ag, Au and Cu-graphdiyne magnetic semiconducting monolayers

Most recently, silver-metalated graphdiyne (GDY) nanomembranes have been fabricated using the wet-chemistry approach, with highly efficient response for light-driven decomposition of antibiotics (ACS Appl. Nano Mater. 2023, 6, 7395). Inspired by this exciting advance, herein for the first time we theoretically explore the key physical properties of the single-layer M-(N)GDY (M=Cu, Ag, Au) monolayers. Spin-polarized density functional theory (DFT) results reveal that metalated GDY monolayers favor a high-spin ground state, presenting a magnetic moment of 3 µB/unitcell. The sheets are characterized as small band gap magnetic semiconductors, ranging between 0.112 and 0.960 eV, in which only one spin contributes to the band gap. Ab-initio molecular dynamics results confirm the remarkable thermal stability of the constructed graphdiyne nanomembranes at 1000 K. The dynamical stability and mechanical properties at the ground state are furthermore investigated using machine learning interatomic potentials. The ultimate tensile strengths of the metalated graphdiyne lattices are found to be decent, over 6 GPa close to the ground state, but a few folds lower than the native metal-free counterparts. The presented first-principles results confirm remarkable thermal, dynamical and mechanical stability, and appealing electronic characteristics of the metalated graphdiyne nanosheets, attractive to design advanced light-weight energy storage/conversion and spintronic nanosystems.

Realization of black phosphorus-like PbSe monolayer on Au(111) via epitaxial growth

Lead selenide (PbSe) has been attracted a lot attention in fundamental research and industrial applications due to its excellent infrared optical and thermoelectric properties, toward reaching the two-dimensional limit. Herein, we realize the black phosphorus-like PbSe (α-phase PbSe) monolayer on Au(111) via epitaxial growth, where a characteristic rectangular superlattice of 5 Å × 9 Å corresponding to 1 × 2 reconstruction with respect to the pristine of α-phase PbSe is observed by scanning tunneling microscopy. Corresponding density functional theory calculation confirmed the reconstruction and revealed the driven mechanism, the coupling between monolayer PbSe and Au(111) substrate. The metallic feature of differential conductance spectra as well as the transition of the density of states from semiconductor to metal further verified such coupling. As the unique anisotropic structure, our study provides a pathway towards the synthesis of BP-PbSe monolayer. In addition, it builds up an ideal platform for studying fundamental physics and also excellent prospects in PbSe-based device applications.

Size controlled, structural characterization and applications of glucopyranoside-based N-heterocyclic carbenes stabilized gold nanoparticles

N-heterocyclic carbenes (NHCs) have evidenced wonderful alternatives as surface ligands, while synthetic challenges have limited their application in chiral gold nanoparticles (AuNPs). To avoid using difficult-to-synthesize and light-sensitive NHC-Au(I) complex, we synthesized four glucopyranoside-based benzimidazolium bromide salts (1a–1d-Br) and their corresponding haloaurate(III) salts (2a–2d-AuCl4). Then, the first-generation sugar-substituted NHCs stabilized extra-small and ultra-stable chiral AuNPs (Au@NHCs-sugar NPs, 3a–3d-AuNPs) was synthesized though two mild, efficient, and operation-friendly one-pot chemical reduction methods. The obtained 3a–3d-AuNPs were characterized by UV–Vis, NMR, HR-TEM, TGA, CD, FT-IR, and XPS spectroscopy. The designed 3a–3d-AuNPs with core diameters ranging from 2.3 to 3.8 nm remained stable against glutathione for up to 24 h over a wide temperature range of 95 to −78 °C, and over 4 years in air. The absence of NCHN proton in 1H NMR and FT-IR of 3a–3d-AuNPs confirmed the formation of NHC-Au bond, and clearly showed that all acetyl groups, benzimidazolium heterocycle, and N-substituents maintained. XPS analyses revealed the presence of Au(0) and Au(I) in all Au@NHCs-sugar NPs. This result leads us to postulate that 3a–3d-AuNPs exhibit a monolayer of Au(I) surrounding an Au(0) core. These designed 3a–3d-AuNPs were studied for their self-assembly behavior, antibacterial activity against bacterium Xanthomonas citri susp. citri (Xcc), and catalytic activity towards the reduction of nitroarenes. All of them demonstrated strong antibacterial activity against Xcc with minimum inhibitory concentration value <0.03125 mg·mL−1.

Improved performance of electrochemical reduction of CO2 to HCOOH by Cu incorporation into the supported Au monolayer on tungsten carbide: A DFT study

Electrochemical reduction of CO2 into useful chemicals and fuels is a promising strategy to achieve carbon neutrality and storage of renewable electricity. But the realization of industrial application of this technology is hindered by the high energy consumption and low product selectivity. Using the first-principles methods, we explored the mechanism of electrochemical reduction of CO2 on Cu1Au8/WC(0001), in comparison with that on AuML/WC(0001) and CuML/WC(0001). The calculated results showed that incorporating of Cu into Au monolayer significantly enhanced the electrochemical adsorption of CO2, promoting the generation of HCOOH on the alloy surface. Electronic properties such as charge density differences (CDD), Bader charges and density of states (DOS) were investigated to reveal the intrinsic physical origin of the enhanced interaction between OCHO and the catalyst, which results in the improvement in the selectivity and reactivity of CO2 reduction to formic acid (HCOOH) on Cu1Au8/WC(0001). Cu1Au8/WC(0001) was confirmed to be a promising bifunctional catalyst for the efficient conversion of toxic CO to CO2 and selectively reduction of CO2 to useful value-added chemical HCOOH. This work provides a clue to design supported alloy catalysts with high product selectivity and catalytic activity for CO2RR.

STM Study of the Initial Stage of Gold Intercalation of Graphene on Ir(111).

In this paper, we present a study of the sub-monolayer gold intercalation of graphene on Ir(111) using scanning tunnelling microscopy (STM). We found that Au islands grow following different kinetics than growth on Ir(111) without graphene. Graphene appears to increase the mobility of Au atoms by shifting the growth kinetics of Au islands from dendritic to a more compact shape. Graphene on top of intercalated gold exhibits a moiré superstructure, with parameters significantly different from graphene on Au(111) but almost identical to graphene on Ir(111). The intercalated Au monolayer shows a quasi-herringbone reconstruction with similar structural parameters as on Au(111).

Seed-assisted electrodeposition of multilayer Au nanoparticles-assembled films for sensitive surface-enhanced Raman scattering detection

Surface-enhanced Raman scattering (SERS) spectroscopy can be used to realize sensitive rapid detection of molecules. Three-dimensional (3D) SERS substrates can provide more hotspots within the excitation laser beam when compared with the corresponding two-dimensional (2D) SERS substrates. Most of the methods for fabrication of 3D SERS substrates involve complex processes. Therefore, it is significant to develop a simple and effective method for fabrication of 3D SERS substrates. Here, a seed-assisted electrodeposition approach is developed for fabrication of a 3D SERS substrate composed of multilayer Au nanoparticles. Interestingly, it is demonstrated that a uniform film composed of multilayer Au nanoparticles that can serve as a 3D SERS substrate can be achieved directly by one-step electrodeposition on a conductive surface coated with monolayer Au seeds. It is found that a diffusion-controlled growth during electrodeposition narrows the nanoparticle size distribution and results monosized Au nanoparticles. The as-prepared multilayer Au nanoparticles-assembled film shows high SERS sensitivity and good spectral uniformity. For SERS detection of rhodamine 6G, a limit of detection as low as 3.4×10−12 M has been achieved. Moreover, good spectral uniformity (relative standard deviation ∼7.8%) and high substrate-to-substrate reproducibility (relative standard deviation ∼8.6%) have also been demonstrated. The as-prepared multilayer Au nanoparticles-assembled film is used to detect organic pollutants such as dye molecule crystal violet (CV) and methylene blue (MB). Calibration curves with a linear correlation between the logarithmic SERS intensity and logarithmic concentration of CV and MB have been obtained. Limit of detections for CV and MB are 1.2×10−8 M and 9.8×10−10 M, respectively. Therefore, the fabricated 3D SERS substrate has good application prospects in sensitive detection of organic molecules.

Large-Area Monolayer n-Type Molecular Semiconductors with Improved Thermal Stability and Charge Injection

We fabricated monolayer n-type two-dimensional crystalline semiconducting films with millimeter-sized areas and remarkable morphological uniformity using an antisolvent-confined spin-coating method. The antisolvent can cause a downstream Marangoni flow, which improves the film morphologies. The deposited crystalline monolayer films exhibit excellent thermal stabilities after annealing, which reveals the annealing-induced enhancement of crystallinity. The transistors based on the n-type monolayer crystalline films show linear output characteristics and superior electron mobilities. The improved charge injection between monolayer films and Au electrodes results from the energy level shift as the films decrease to the monolayer, which leads to a lower injection barrier. This work demonstrates a promising method for fabricating air-stable, low-cost, high-performance, and large-area organic electronics.

A theoretical study of the improved CO oxidation on WC supported Au monolayer by Cu doping

Metal monolayer supported on tungsten carbides have received considerable attention in the field of catalysis, while the adsorption properties of reactants need to be optimized to improve the catalytic activity further. Alloy monolayers on tungsten carbides can deliver different geometric and electronic characters from pure metal layers, owing to the change in local environments. Herein, using the first-principles calculations, the CO oxidation processes on the supported CuAu alloy monolayer on tungsten carbide are systematically investigated and compared with that on pure metal monolayers. It is found that introducing Cu dopant in Au monolayer will elevate the d-band center of the formed alloy monolayer and thus enhancing the adsorption of reactants around the Cu atom, which is caused by the charge redistribution. Especially, the unbalanced interaction strength between Cu-O and Au-O promotes the rotation and migration of oxygen atom to interact with the C atom of CO, which lowers the energy barriers for the formation and dissociation of OOCO intermediate. The oxidation of CO by an atomic O with the largest energy barrier of 0.27 eV along the Langmuir-Hinshelwood pathway is identified as the rate determining step, which is superior or comparable to the reported CO oxidation catalysts. The significance of alloy monolayer on tungsten carbides are further highlighted by comparing the adsorption energy and reaction barrier of rate-limiting step on the pure metal monolayers. This work is insightful for the rational design of highly efficient catalysts based on alloy systems.

Graphene-Au nanosphere composite arrays and their enhanced SERS performance

The effective regulation of the absorption properties of Au nanosphere arrays, as well as effective enhancement of its SERS performance, are of great significance for its applications in the field of optical sensing. In this paper, the polyol synthesis method was used to fabricate monolayer and bilayer periodic Au nanosphere arrays, onto which monolayer graphene was coated, and the optical properties of the obtained composite structures were investigated. The results showed that the coverage of graphene enhances the absorption peak intensities of the monolayer and bilayer Au nanoarrays by up to 32.92%, and the resonance peaks were red-shifted by up to 17 nm. The Raman signals of graphene-covered monolayer and bilayer Au nanosphere composite arrays are 180 and 280 times stronger than that of pristine graphene, due to the combination of chemical enhancement and electromagnetic enhancement. And the detection sensitivity of R6G molecules by graphene-bilayer Au nanosphere composite arrays is 10−6 M. In addition, the staggered stacking of bilayer Au nanosphere arrays can provide more plasmonic hotspots, resulting in higher Raman intensity of the substrate. These results will pave the way for the fabrication of highly efficient SERS substrates by providing various promising candidates.