Au Interface Research Articles

Semitransparent Cu2O Films Based on CuO Back Layer for Photoelectrochemical Water Splitting and Photovoltaic Applications.

Cuprous oxide (Cu2O) as an intrinsic p-type semiconductor is promising for solar energy conversion. The major challenge in fabricating Cu2O lies in achieving both high transparency and high performance in a tandem device. The Cu2O photocathodes often employ gold as the back contact layer. However, it is not an optimal choice in tandem device due to its poor transmission, scarcity, and electron-hole recombination at the interface of Au and Cu2O. Here, we presented a facile method that utilizes the earth-abundant material copper oxide (CuO) to fabricate highly transparent Cu2O devices. The maximum transmittance of the Cu2O film on CuO (FTO/CuO/Cu2O) increased from 42 % to 58 % compared with Cu2O film on Au (FTO/Au (3 nm)/Cu2O) in 550-800 nm. After coating atomic layer deposition (ALD) layers and hydrogen evolution reaction (HER) catalyst, the photocurrent density at 0 V (versus RHE) of the semitransparent Cu2O photocathode with CuO as the back layer for photoelectrochemical (PEC) water splitting reached -4.9 mA cm-2, which showed a 24.5 % improvement compared with FTO/Au/Cu2O photocathode. Moreover, expanding the CuO layer strategy to the field of solar cells enables Cu2O solar cells to achieve a PCE of 2.37 %.

Computational and Experimental Investigations of the Au and NiOOH Interface in the Oxygen Evolution Reaction

The transition to renewable energy sources is crucial for combating climate change, and hydrogen (H2) is a promising clean fuel. Electrolysis of water, specifically the oxygen evolution reaction (OER), is a key process for producing H2. Prior experimental results have shown that gold (Au) could improve the apparent activities of the OER electrocatalysts such as nickel hydroxide (Ni(OH)2) in alkaline electrolytes.1-3 However, the detailed interfacial atomic structure and mechanisms of the increased catalytic activity remain poorly understood.To understand the interfacial effect between Au and Ni(OH)2 in the OER process, our research uses the model system of Au nanoparticles (NPs) and nickel oxyhydroxide (NiOOH), which is the active phase of Ni(OH)2 layers in the OER, to investigate their interfacial interactions with both experimental and computational approaches. We hypothesize that the Au NPs on NiOOH enhances the OER activity by promoting electron transfer at the interface. Our studies involve computational analysis using Density Functional Theory (DFT) calculations to obtain the local density of states (LDOS), which can help us better visualize and compare the local electronic structure of NiOOH in the presence and in the absence of AuNPs. Two architectures of the Au and NiOOH interface will be investigated: Au NPs on a NiOOH film and NiOOH NPs on a Au film.Additionally, Bader analysis is employed to determine the Bader charge, offering a more detailed understanding of how electrons are distributed across the AuNPs/NiOOH interface. Furthermore, the catalytic efficacy of AuNPs on NiOOH is assessed through electrodepositions followed by cyclic voltammetry(CV) measurements. The experimental and computational results will be directly compared, and this research is expected to contribute to the insights of substrate and catalyst interactions for design of more efficient electrocatalysts.

Ohmic contacts to n-type SiC: Influence of Au and Ta intermediate layers

In this study, the optimization of metal-semiconductor contacts to reduce the contact resistance of ohmic contacts on n-type 4H-SiC. The commonly used Ni/Au metal scheme served as a reference. We introduced two novel metal schemes: (i) incorporating a thin interfacial Au layer (2 nm) into Ni/Au, resulting in Au/Ni/Au, and (ii) introducing a thin intermediate barrier layer of Ta (20 nm) into Ni/Au, resulting in Ni/Ta/Au. Rapid thermal annealing (RTA) is performed at different temperatures and durations and the electrical characteristics of the contacts are measured. X-ray diffraction analysis was employed to investigate the intermediate phases formed during annealing. In the Au/Ni/Au metal scheme, the presence of Au at the interface promoted the formation of additional phases of nickel-silicide (Ni3Si and Ni3Si2). Compared to the traditional Ni/Au scheme, the modified metal schemes led to lower surface roughness and reduced contact resistance. Specific contact resistivity values are calculated, 2.2 × 10−5 Ω-cm2 for Ni/Au, 1.37 × 10−5 Ω-cm2 for Au/Ni/Au, and 4.84 × 10−5 Ω-cm2 for Ni/Ta/Au. This research offers valuable insights for the selection of metal schemes in designing ohmic contacts on n-type SiC, with potential applications in various semiconductor device technologies.

Interfacial Auδ−–OV–Ti Structure Promoted C–H Bond Activation for Selective Oxidation of Fatty Alcohols to Fatty Acids

Interfacial Au^δ−–O_V–Ti Structure Promoted C–H Bond Activation for Selective Oxidation of Fatty Alcohols to Fatty Acids

Salt-Assisted, In Situ Current Nanowelding of an Interfacial Au Nanoparticle Film for a High-Performance Electrocatalyst.

Interfacial self-assembly is a well-established method for the preparation of a two-dimensional (2D) metal nanofilm from nanoscale building blocks. However, the as-prepared nanofilm exhibits limited conductivity because of the large contact resistance at the junctions among its building blocks. Here, we report a salt-assisted, in situ current nanowelding strategy to weld an interfacial Au nanoparticle (NP) film for downstream applications, such as high-performance electrocatalysts. Particularly, we found that salt-assisted interfacial assembly can reduce the size of the nanogaps among neighboring Au NPs and, in turn, greatly improve the conductivity of the resultant Au NP film. Consequently, the Au NP film can be readily welded using current, and the welding extent can be monitored in real-time by looking at the passing current. The welding finally produces a nanoporous Au film (NPGF) with a network nanostructure, high conductivity, and abundant active sites so that it delivers a large current density of 86.96 μA·cm-2 (1.81 times higher than that from the pristine Au NP film) and shows improved cycling stability for methanol electrooxidation. Thus, these results offer a low-cost, solution-processable approach for the fabrication of a large-area, interconnected nanofilm from nanoscale building blocks beyond Au NPs, which may find diverse downstream applications.

Cyclic Failure of a Cr–Au Bilayer on Polyimide: In Situ Transmission Electron Microscopy Observations of Interfacial Dislocation Mechanisms

This work presents in situ transmission electron microscopy observations of dislocation activities and associated fatigue properties in a cross‐sectional sample of a Cr–Au bilayer on a polyimide substrate under cyclic loading. Dislocation structures in the Au layer are observed to evolve into a geometrically necessary boundary parallel to the Cr–Au interface, which significantly impedes dislocation motion and plays a crucial role in enhancing the fatigue resistance of the studied sample. While a comparison to the damage in a conventional blanket film testing geometry reveals some differences in the accumulation of plastic flow, the findings can provide insights into the underlying mechanisms governing fatigue in nanostructured multilayer materials on polymer substrates.

Scanning Tunneling Microscopy Examination of Molecules with Fused Thiophene and Pyrrole Groups Adsorbed on the Electrified Au(111) Interface

Scanning Tunneling Microscopy Examination of Molecules with Fused Thiophene and Pyrrole Groups Adsorbed on the Electrified Au(111) Interface

NIR-Mediated Cu2O/Au Nanomotors for Synergistically Treating Hepatoma Carcinoma Cells.

We presented a NIR-driven Janus Cu2O/Au nanomotor. The nanomotor has a truncated octahedral structure. By asymmetric Au evaporation, the light response range of Cu2O nanomotor is extended to near-infrared range, and the speed of Cu2O/Au nanomotors under NIR is significantly increased. In promoting apoptosis of hepatocellular carcinoma, except the nanotoxicity of Cu2O itself, the Au layer enhances the photothermal properties, allowing Cu2O/Au nanomotors to induce apoptosis in hepatocellular carcinoma cells by heating them. On the other hand, a Schottky barrier formed at the interface of Cu2O and Au, preventing the recombination of electrons, which makes more electrons react with biomolecules to produce toxic ROS to kill hepatocellular cells. The killing rate of hepatocellular carcinoma cells reached 87 % by the combined effect of nanotoxicity inhibition of proliferation and photothermal & photodynamic therapy (PTT & PDT). Nanomotors in combination with multiple approaches are explored as a new treatment to tumor in this article.

Probing the interface of choline chloride-based deep eutectic solvent ethaline with gold surfaces: A molecular dynamics simulation study

Technologies involving a solvent|surface interface, such as nanotechnology, electrochemistry, and energy storage applications, are actively pursuing ecologically responsible and sustainable development practices. In response to this pressing need, deep eutectic solvents have emerged as a promising solution to bridge the gap between technological requirements and environmental concerns. In this work, we present the results of a molecular dynamics simulation study of the interface between a monocrystalline gold surface and the deep eutectic solvent ethaline, where a molar ratio of 1:2 choline chloride:ethylene glycol was used for ethaline. The simulations covered a range of temperatures from 313 K to 343 K and applied charge values ranging from 0 to ± 24 μC cm‒2. Several key interfacial properties were thoroughly analyzed, including among others, charge density profiles, radial distribution functions, hydrogen bond close contacts, and molecular orientation. Additionally, we examined how the differential capacitance varied upon the applied potential. Our findings reveal that, at neutral surfaces, all components of the solvent are present in the innermost layer, with ethylene glycol molecules being the most prevalent, followed by choline cations and a residual amount of chloride anions. For lower applied charges, this mixed composition at the boundary layer persists, despite the growing accumulation of ionic species with charges opposite to that of the electrode. As surface polarization increases, unique innermost boundary layers composed exclusively of one of the ionic species and the hydrogen bond donor molecules are observed, forming a multilayer structure, with subsequent layers enriched of paired counterions. Interestingly, even at higher applied charges, choline cations and ethylene glycol molecules tended to orient themselves in a parallel fashion toward the electrodes. Differential capacitance curves exhibited a camel-shaped behavior, suggesting a complex interplay of electrochemical processes at the DES|Au(100) interface. In summary, our study provides valuable insights into the interfacial properties of deep eutectic solvents on gold surfaces and their response to changes in temperature and potential, which are crucial for understanding and optimizing deep eutectic solvent-based electrochemical systems.

Aggregation‐Induced Emission (AIE) of Au(I)‐GSH Complexes is Activated by Optical Manipulation and Exhibits Surprising 780 nm Emission

AbstractAn optical manipulation method to activate the aggregation‐induced emission (AIE) of Au(I)‐glutathione (Au(I)‐GSH) complexes is presented. First, the well‐known AIE‐type Au(I)‐GSH complexes with a solid emission wavelength of 570 nm are synthesized. At the beginning of the focusing a 1064 nm continuous‐wave (CW) laser at the interface of Au(I)‐GSH complexes solution, its luminescence is hardly detectable. However, with the extension of the laser irradiation time, aggregate appears and rapidly grows, and strong luminescence is shown, indicating the activation of AIE of Au(I)‐GSH complexes through optical manipulation. Surprisingly, the emission peak is at 780 nm and no blue‐shift is observed with the emission intensity increases. The activated AIE emission wavelength by optical manipulation is longer than reported previously, which means that optical manipulation activates AIE in a unique manner. The switching on/off of the activation of AIE is arbitrarily controlled by changing the laser power. In this paper, the luminescence phenomenon and mechanism of AIE are discussed from the perspective of the movement limitation of Au(I)‐GSH complexes under optical manipulation. It is of significant importance for further insights into the luminescence of Au(I)‐GSH complexes and their future development.

K-O2 electrochemistry at the Au/DMSO interface probed by in situ spectroscopy and theoretical calculations.

The reaction mechanism underpinning the operation of K-O2 batteries, particularly the O2 reactions at the positive electrode, is still not completely understood. In this work, by combining in situ Raman spectroelectrochemistry and density functional theory calculations, we report on a fundamental study of K-O2 electrochemistry at a model interface of Au electrode/DMSO electrolyte. The key products and intermediates (O2-, KO2 and K2O2) are identified and their dependency on the electrode potential is revealed. At high potentials, the first reduction intermediate of O2-* radical anions (* denotes the adsorbed state) can desorb from the Au electrode surface and combine with K+ cations in the electrolyte producing KO2via a solution-mediated pathway. At low potentials, O2 can be directly reduced to on the Au electrode surface, which can be further reduced to at extremely low potentials. The fact that K2O2 has only been detected in the very high overpotential regime indicates a lack of KO2 disproportionation reaction both on the Au electrode surface and in the electrolyte solution. This work addresses the fundamental mechanism and origin of the high reversibility of the aprotic K-O2 batteries.

Density functional theory study of Au-fcc/Ge and Au-hcp/Ge interfaces.

In recent years, nanostructures with hexagonal polytypes of gold have been synthesised, opening new possibilities in nanoscience and nanotechnology. As bulk gold crystallizes in the fcc phase, surface effects can play an important role in stabilizing hexagonal gold nanostructures. Here, we investigate several heterostructures with Ge substrates, including the fcc and hcp phases of gold that have been observed experimentally. We determine and discuss their interfacial energies and optimized atomic arrangements, comparing the theory results with available experimental data. Our DFT calculations for the Au-fcc(011)/Ge(001) junction show how the presence of defects in the interface layer can help to stabilize the atomic pattern, consistent with microscopic images. Although the Au-hcp/Ge interface is characterized by a similar interface energy, it reveals large atomic displacements due to significant mismatch. Finally, analyzing the electronic properties, we demonstrate that Au/Ge systems have metallic character, but covalent-like bonding states between interfacial Ge and Au atoms are also present.

Second harmonic generation as a probe of structure and dynamics of ionic liquids at the electrode interface

Electrochemical second harmonic generation (ESHG) has been applied as a probe of the slow dynamics in the electric double layer (EDL) at the ionic liquid (IL)/Au interface. When the electrode potential was stepped, the SHG signal from the interface was relaxed on the time scale longer than tens of seconds, which is distinctively slower than the RC time constant of the cell. This ultraslow relaxation in ESHG was quantitatively analyzed and discussed for several ILs, revealing that the ultraslow relaxation itself is a common phenomenon for the EDL in the ILs studied but the asymmetry of the time constants to the potential-step directions depends on the IL ions, which is likely to reflect the structure ordering of the interfacial ionic layer in the EDL depending on both ILs and the potential. The EDL structure in equilibrium has also been investigated via SHG measurements with a potential scan at a sufficiently slow rate; the potential dependence of the SHG signal was found to deviate from a simple parabolic one, reflecting the camel-shaped static differential capacitance for the EDL in ILs.

Crystal Lattice Rearrangement Occurred at Au/Ag Bonded Interface in Atomic Diffusion Bonding in Vacuum

The crystal lattice rearrangement which occurs at the bonded interface of two films during atomic diffusion bonding processing in vacuum was examined using Au and Ag films. Results revealed that remarkable crystal lattice rearrangement occurs at the bonded interface of Au−Ag bonded films at room temperature. Grains formed continuously across the original interface over the entire thickness of the bonded films. Also, the (111) preferred grain orientation was effective at enhancing the crystal lattice rearrangement. The crystal lattice rearrangement did not accompany remarkable interdiffusion of Au and Ag at the interface, even though the crystal lattice formed continuously across the original interface. In addition to crystal lattice rearrangement, grain boundary diffusion plays an important role in bonding processes, enhancing the interdiffusion between Au and Ag films. Grain boundary diffusion is likely to be effective to fill the gaps in the boundaries of grains formed by crystal lattice rearrangement.

An atomistic study on the strain rate and temperature dependences of the plastic deformation Cu–Au core–shell nanowires: On the role of dislocations

Abstract Recently, Cu–Au core–shell nanowires have been extensively used as conductors, nanocatalysts, and aerospace instruments due to their excellent thermal and electrical conductivity. In experimental studies, various methods have been presented for producing, characterizing, and strengthening these structures. However, the mechanical behavior and plastic deformation mechanisms of these materials have not been investigated at the atomic scale. Consequently, in the present study, we carried out uniaxial tensile tests on Cu–Au nanowires at various tension rates and temperatures by means of the molecular dynamics approach. The Cu–Au interface was found to be the main site for nucleation of perfect dislocations, Shockley partials, and stacking faults due to the stress concentration and high potential energy arising from the atomic mismatch between shell and core layers. It was observed that an increase in the strain rate from 108 to 1,011 s−1 shortened the time required for the nucleation of dislocations, decreasing the dislocation density. This emphasizes that dislocation nucleation and slip mechanisms are time-dependent. Moreover, it was found that the interaction of Shockley partials can lead to the creation of lock dislocations, such as Hirth, Frank, and Stair-rod dislocations, imposing obstacles for the slip of other dislocations. However, as the tension temperature rose from 300 to 600 K, opposite-sign dislocations removed each other due to thermally activated mechanisms such as dislocation climb and dislocation recovery. Furthermore, the combination of Shockley partial dislocations decreased the stacking fault density, facilitating the plastic deformation of these structures. The yield strength and elastic modulus of the samples increased with the strain rate and substantially decreased as the temperature rose.

Microstructure, mechanical properties and fracture behavior of GH3535 alloy joints brazed with Au–18Ni filler metal

Vacuum brazing of GH3535 alloy was conducted using Au–18Ni (wt%) filler metal. The effect of brazing temperature on the microstructure and mechanical properties was investigated. Furthermore, the microstructural evolution and fracture mechanisms of brazed joints were discussed. The cross section of brazed joint could be divided into two distinctive reaction zones. The typical microstructure of the joint brazed at 1030 °C/10min was GH3535 substrate/Ni (s.s) + Mo-rich Ni (s.s) + Au-rich phase/Au (s.s) + FeNi3/Au-rich phase + Mo-rich Ni (s.s) + Ni (s.s) + GH3535 substrate. Raising the brazing temperature promoted the diffusion of elements, Ni (s.s) and Au (s.s) gradually increased, and the second phase particles consisting of FeNi3 gradually decreased. With the increase in brazing temperature, the shear strength of brazed joints first increased and then decreased. The maximum room shear strength of 420 MPa was obtained at 960 °C/25min and the high temperature shear strength of 153 MPa was obtained at 600 °C. Fracture analysis indicated that cracks initiated at the interface of Au (s.s) and then propagated along the zone of FeNi3 with dimple and tearing ridges patterns.

In-situ monitoring of plasmon-induced nanoscale photocatalytic activity from Au-decorated TiO2 microflowers

Noble-metal-decorated semiconductor photocatalysts have attracted noticeable attention due to their enhanced photocatalytic activity. Herein, we have synthesized the pure rutile phase of TiO2 nanorods, with microflower morphology, using a hydrothermal method and decorated them with Au to observe plasmon-induced enhanced photocatalytic efficiency. The optical bandgap engineering through Au-decorated TiO2 introduces midgap states that help with charge compensation during photodegradation studies. The surface plasmonic resonance peak of Au is observed together with the defect peak of TiO2, extending the absorption of the solar spectrum from the UV to the visible region. The quenching in photoluminescence intensity with increased Au thickness indicates the formation of a Schottky junction at the interface of Au and TiO2 that helps to reduce photogenerated charge carrier recombination. The softening of the E g Raman mode and photothermal effects originate from the nonradiative decay of localized surface plasmons through electron–phonon and phonon–phonon relaxation. The photocatalytic degradation of Rhodamine 6G is monitored by exposing the sample to UV and visible light sources under Raman spectroscopy. The Au decoration plays a crucial role in promoting charge separation, Schottky junction creation, photothermal effects, and UV to visible light absorption to enhance photocatalytic activity, which can be explained on the basis of the charge transfer mechanism. Our in-situ photodegradation study at the interface of noble metal and semiconducting materials will pave the way toward improving the understanding of plasmon-enhanced photocatalytic applications.

Two-Photon Photoemission Spectroscopy and Microscopy for Electronic and Plasmonic Characterizations of Molecularly Designed Organic Surfaces.

Functional surfaces decorated with organic molecules and/or nanoclusters (NCs) composed of several tens of atoms are promising for use in future photoelectronic substrates, whose functionalities are governed by molecular local electronic/plasmonic excitations at the interfaces. Here, we combine two-photon photoemission spectroscopy (2P-PES) and microscopy (2P-PEEM) to investigate the local excited-state dynamics at organic surfaces functionalized with NCs. The 2P-PES and 2P-PEEM for organic fullerene (C60) layers on graphite and Au substrates demonstrated photophysical characterization of electronic and plasmonic properties, including propagating surface plasmon polaritons (SPPs). The SPP propagation at the Au interface buried by overlayered C60 can be visualized by Agn NC deposition, which enhances plasmon-induced hot electrons, where the threshold number of Ag atoms (n ≥ 9) for the plasmonic response is revealed by the size dependence of 2P-PES for Agn NCs on C60 layers.

Selective Self-Assembly and Modification of Herringbone Reconstructions at a Solid-Liquid Interface of Au(111).

The precise control of molecular self-assembly on surfaces presents many opportunities for the creation of complex nanostructures. Within this endeavor, selective patterning by exploiting molecular interactions at the solid-liquid interface would be a beneficial capability. Using scanning tunneling microscopy at the 1,2,4-trichlorobenzene/Au(111) interface, we observed selective self-assembly of 1,3,5-tris(4-methoxyphenyl)benzene (TMPB) molecules in the face-centered cubic (FCC) regions of Au(111). Density functional theory calculations suggest higher adsorption energy of TMPB molecules at FCC regions, explaining the preference for self-assembly. The molecular coverage is found to increase with the concentration of the applied solution, eventually yielding a full monolayer. Moreover, the adsorption of TMPB molecules induces a concentration-dependent lifting of the herringbone reconstruction, observed as an increase in the area of the FCC regions at higher concentrations. Our results represent a simple and cost-effective selective nanoscale patterning method on Au(111), providing a possible avenue to guide the co-adsorption of other functional molecules.

Synergistic effect of acid-base and redox properties of nano Au/CeO2-cube on selective hydrogenation of nitrobenzene to aniline

Catalysts with 1 wt% gold doped on various morphologies of ceria (nano-cubes, nano-rods and nano-polyhedra), were prepared by the deposition precipitation method. The samples are characterized and used to catalyze the hydrogenation of nitrobenzene in ethanol. The highest nitrobenzene conversion (92%) and aniline selectivity (90%) are achieved from the catalyst supported by nano-cube CeO2 (1 wt% Au/CeO2-cube). The calcination temperatures of both the support and catalyst can influence the acid-base properties, the morphology and the valance of Au and Ce, which are key factors in the adsorption of nitrobenzene, the desorption of aniline and the formation of active H− species, respectively. We find that small-size Au nanoparticles (2.1 nm) with appropriate ratio of Au0 to Auδ+, acid/base sites with sufficient density and appropriate strength, and oxygen vacancy of ceria on the interface of Au and ceria are favorable to the formation of aniline on 1 wt% Au/CeO2-cube.