Nanocrystalline Gold Research Articles

Static and dynamic atom displacements in nanocrystalline powders from diffraction analysis at finite temperature

Static and dynamic atom displacements in nanocrystalline powders from diffraction analysis at finite temperature

Plane Stress Fracture Toughness Testing of Freestanding Ultra-Thin Nanocrystalline Gold Films on Water Surface.

Fracture toughness, which is the resistance of a material to crack propagation, is a critical material property for ensuring the mechanical reliability of damage-tolerant design. Recently, damage-tolerant design is introduced to flexible electronics by adopting micro-cracked ultra-thin nanocrystalline (NC) gold films as stretchable electrodes in a plane stress state. However, experimental investigation of the plane stress fracture toughness of those films remains challenging due to the intrinsic fragility from their sub-100nm thicknesses. Here, a quantitative method for systematically evaluating the plane stress fracture toughness of freestanding ultra-thin NC gold film on water surface platform is presented. After effectively fabricating single-edge-notched-tension samples with femtosecond laser, mode I stress intensity factors are measured in the plane stress state on water surface. Moreover, investigation regarding the effect of notch length, notch sharpness, and notch tip plasticity validates this method based on linear elastic fracture mechanics theory. As a demonstration, the thickness-dependent plane stress fracture toughness of ultra-thin NC gold films is qualitatively unveiled. It is revealed that the thickness confinement effect on grain boundary sliding induces a transition in fracture behavior. This method is expected to further clarify the fracture-related properties of various ultra-thin films for next-generation electronics.

Novel Label-Free Nanocrystalline Gold Interdigitated Microelectrode Immunosensor for the Rapid and Ultrasensitive Detection of SARS-CoV-2.

Waves of COVID-19 outbreaks have dragged down the global economy and endangered human life. There is an urgent need for timeliness and sensitive SARS-CoV-2 detection techniques to complement the existing PCR assay. Herein, the controllable growth of gold crystalline grains was achieved by applying the reverse current during pulse electrochemical deposition (PED) interval. The proposed method validates the effects of pulse reverse current (PRC) on the atomic arrangement, crystal structures, orientations, and film characteristics in Au PED. The gap between the gold grains on the surface of the nanocrystalline gold interdigitated microelectrodes (NG-IDME) fabricated by the PED+PRC process matches the size of the antiviral antibody. Immunosensors are prepared by binding a large number of antiviral antibodies on the surface of NG-IDME. The NG-IDME immunosensor has a high specific capture ability for SARS-CoV-2 nucleocapsid protein (SARS-CoV-2/N-Pro) and completes ultrasensitive and quantification of SARS-CoV-2/N-Pro in humans and pets within 5 min (the LOQ as low as 75 fg/mL). The specificity, accuracy, stability, and actual blind sample tests show that the NG-IDME immunosensor is suitable for the detection of SARS-CoV-2 in humans and animals. This approach assists in monitoring the transmission of SARS-CoV-2-infected animals to humans.

Molecular dynamics study of the tensile properties of gold nanocrystalline films irradiated by gallium Ions

Molecular dynamics study of the tensile properties of gold nanocrystalline films irradiated by gallium Ions

In situ diffraction monitoring of nanocrystals structure evolving during catalytic reaction at their surface

With decreasing size of crystals the number of their surface atoms becomes comparable to the number of bulk atoms and their powder diffraction pattern becomes sensitive to a changing surface structure. On the example of nanocrystalline gold supported on also nanocrystalline {text{CeO}}_2 we show evolution of (a) the background pattern due to chemisorption phenomena, (b) peak positions due to adsorption on nonstoichiometric {text{CeO}}_{2-x} particles, (c) Au peaks intensity. The results of the measurements, complemented with mass spectrometry gas analysis, point to (1) a multiply twinned structure of gold, (2) high mobility of Au atoms enabling transport phenomena of Au atoms to the surface of ceria while varying the amount of Au in the crystalline form, and (3) reversible {text{CeO}}_2 peaks position shifts on exposure to He–X–He where X is O2, H2, CO or CO oxidation reaction mixture, suggesting solely internal alternations of the {text{CeO}}_2 crystal structure. We found no evidence of ceria lattice oxygen being consumed/supplied at any stage of the process. The work shows possibility of structurally interpreting different contributions to the multi-phase powder diffraction pattern during a complex physico-chemical process, including effects of physi-, chemisorption and surface evolution. It shows a way to structurally interpret heterogeneous catalytic reactions even if no bulk phase transition is involved.

Electrochemical Biosensor for the Determination of Specific Antibodies against SARS-CoV-2 Spike Protein

In this article, we report the development of an electrochemical biosensor for the determination of the SARS-CoV-2 spike protein (rS). A gold disc electrode was electrochemically modified to form the nanocrystalline gold structure on the surface. Then, it was further altered by a self-assembling monolayer based on a mixture of two alkane thiols: 11-mercaptoundecanoic acid (11-MUA) and 6-mercapto-1-hexanol (6-MCOH) (SAMmix). After activating carboxyl groups using a N-(3-dimethylaminopropyl)-N'-ethyl-carbodiimide hydrochloride and N-hydroxysuccinimide mixture, the rS protein was covalently immobilized on the top of the SAMmix. This electrode was used to design an electrochemical sensor suitable for determining antibodies against the SARS-CoV-2 rS protein (anti-rS). We assessed the association between the immobilized rS protein and the anti-rS antibody present in the blood serum of a SARS-CoV-2 infected person using three electrochemical methods: cyclic voltammetry, differential pulse voltammetry, and potential pulsed amperometry. The results demonstrated that differential pulse voltammetry and potential pulsed amperometry measurements displayed similar sensitivity. In contrast, the measurements performed by cyclic voltammetry suggest that this method is the most sensitive out of the three methods applied in this research.

Accuracy Limits of Pair Distribution Function Analysis in Structural Characterization of Nanocrystalline Powders by X-ray Diffraction

We report the minimum errors of structural parameters, namely lattice parameter, crystallite size, and atomic displacement parameters, expected from Pair Distribution Function (PDF) analysis of nanocrystalline gold powders for the first time by a self-consistent computational methodology. Although PDF analysis has been increasingly used to characterize nanocrystalline powders by X-rays, the current literature includes no established error bounds to be expected from the resulting structural parameters. For accurate interpretation of X-ray diffraction data, these error bounds must be determined, and the obtained structural parameters must be cleared from them. Our novel methodology includes: 1) simulation of ideal powder diffraction experiments with the use of the Debye scattering equation, 2) pair distribution function analysis of the diffraction data with the Diffpy-CMI analysis software, and 3) determination of the errors from PDF analysis of the simulated diffraction data by comparing them with real-space analysis of spherical gold nanocrystals that are 30 nm size and smaller. Our results show that except for the lattice parameters and even with an ideal crystalline powder sample and ideal diffraction data, the extracted structural parameters from PDF analysis diverge from their true values for the studied nanopowder. These deviations are dependent on the average size of the nanocrystals and the energy of the X-rays selected for the diffraction experiments, where lower X-ray energies and small-sized nanocrystalline powders lead to greater errors.

Hard nanocrystalline gold materials prepared via high-pressure phase transformation

Hard nanocrystalline gold materials prepared via high-pressure phase transformation

Solid-state dewetting of thin Au films on oxidized surface of biomedical TiAlV alloy

Solid-state dewetting of thin Au films on oxidized surface of biomedical TiAlV alloy

Deformation and ductile fracture of nanocrystalline gold ultrathin nanoribbon: Width effect

AbstractMolecular dynamics simulations are used to investigate the mechanical properties of finite‐width nanocrystalline gold nanoribbons with a thickness of one grain size under tensile strain. We find strong variations in the Young's modulus and flow stress especially for the sample with narrow width. With statistical analysis, Young's modulus has a trend of increase with the decrease of width. Flow stress does not follow this trend. Ductile fracture is observed at large strain in these nanocrystalline nanoribbons, but the fracture strain and mechanism are different from those of thick films as observed in existing experiments. For small widths below 80 nm, fracture is a necking effect, while for larger widths, shear bands and formation of nanovoids due to stress concentration are the main mechanism. Voids are mainly distributed in special GBs that are parallel to the direction of the maximum principal stress of the plastic deformation tensor. We find there is a width regime (about 80–130 nm) for the ultrathin nanoribbon gold, which have good ductility and large fracture strain.

Nanoscale 3D Electroforming by Template Pyrolysis

A novel approach is demonstrated that extends the resolution of 3D electroforming. Photoresist templates with complex 3D geometries are generated using two‐photon lithography are shrunken by a factor of ≈5 through pyrolysis. A key discovery is that pyrolysis at 500 °C, instead of the higher temperatures normally used for pyrolysis, still shrinks the template by a significant amount but keeps the template nonconductive. This shrunken template is used for electroforming, or template‐assisted electrodeposition, and then etched away to reveal complex 3D structures of pure metal (>99 at%) with linewidths below 200 nm. The versatility of the technique is demonstrated by fabricating octet truss nanolattices from either nanocrystalline gold or microcrystalline copper. In situ micromechanical tests are used as an analytical technique to reveal that these lattices have yield strengths of 325 and 190 MPa for the gold and copper, therefore verifying the fidelity of the architecture.

Effect of voids on nanocrystalline gold ultrathin film

Effect of voids on nanocrystalline gold ultrathin film

Ion irradiation induced phase transformation in gold nanocrystalline films

Gold is a noble metal typically stable as a solid in a face-centered cubic (FCC) structure under ambient conditions; however, under particular circumstances aberrant allotropes have been synthesized. In this work, we document the phase transformation of 25 nm thick nanocrystalline (NC) free-standing gold thin-film via in situ ion irradiation studied using atomic-resolution transmission electron microscopy (TEM). Utilizing precession electron diffraction (PED) techniques, crystallographic orientation and the radiation-induced relative strains were measured and furthermore used to determine that a combination of surface and radiation-induced strains lead to an FCC to hexagonal close packed (HCP) crystallographic phase transformation upon a 10 dpa radiation dose of Au4+ ions. Contrary to previous studies, HCP phase in nanostructures of gold was stabilized and did not transform back to FCC due to a combination of size effects and defects imparted by damage cascades.

The Effect of Strain Rate on the Deformation Processes of NC Gold with Small Grain Size

The strength of nanocrystalline (NC) metal has been found to be sensitive to strain rate. Here, by molecular dynamics simulation, we explore the strain rate effects on apparent Young’s modulus, flow stress and grain growth of NC gold with small size. The simulation results indicate that the apparent Young’s modulus of NC gold decreases with the decrease of strain rate, especially for strain rates above 1 ns−1. The rearrangement of atoms near grain boundaries is a response to the decrease of apparent Young’s modulus. Indeed, the flow stress is also sensitive to the strain rate and decreases following the strain rate’s decrease. This can be found from the change of strain rate sensitivity and activation volume with the strain rate. Temperature has little effect on the activation volume of NC gold with small grain size, but has an obvious effect on that of relatively large grain size (such as 18 nm) under low strain rate (0.01 ns−1). Finally, grain growth in the deformation process is found to be sensitive to strain rate and the critical size for grain growth increases following the decrease of strain rate.

Defect annihilation in heavy ion irradiated polycrystalline gold

Defect annihilation in heavy ion irradiated polycrystalline gold

Mapping Electrochemical Heterogeneity at Gold Surfaces: A Second Harmonic Imaging Study.

Designing efficient catalysts requires correlating surface structure and local chemical composition with reactivity on length scales from nanometers to tens of microns. While much work has been done on this structure/function correlation on single crystals, comparatively little has been done for catalysts of relevance in applications. Such materials are typically highly heterogeneous and thus require methods that allow mapping of the structure/function relationship during electrochemical conversion. Here, we use optical second harmonic imaging combined with cyclic voltammetry to map the surface of gold nanocrystalline and polycrystalline electrodes during electrooxidation and to quantify the spatial extent of surface reconstruction during potential cycling. The wide-field configuration of our microscope allows for real-time imaging of an area ∼100 μm in diameter with submicron resolution. By analyzing the voltage dependence of each pixel, we uncover the heterogeneity of the second harmonic signal and quantify the fraction of domains where it follows a positive quadratic dependence with increasing bias. There, the second harmonic intensity is mainly ascribed to electronic polarization contributions at the metal/electrolyte interface. Additionally, we locate areas where the second harmonic signal follows a negative quadratic dependence with increasing bias, which also show the largest changes during successive cyclic voltammetry sweeps as determined by an additional correlation coefficient analysis. We assign these areas to domains of higher roughness that are prone to potential-induced surface restructuring and where anion adsorption occurs at lower potentials than expected based on the cyclic voltammetry.

Nanocrystalline gold with small size: inverse Hall–Petch between mixed regime and super-soft regime

ABSTRACT Molecular dynamics simulations were used to study the atomic mechanisms of deformation of nanocrystalline gold with 2.65–18 nm in grain size to explore the inverse Hall–Petch effect. Based on the mechanical responses, particularly the flow stress and the elastic-to-plastic transition, one can delineate three regimes: mixed (10–18 nm, dislocation activities and grain boundary sliding), inverse Hall-Petch (5–10 nm, grain boundary sliding), and super-soft (below 5 nm). As the grain size decreases, more grain boundaries present in the nanocrystalline solids, which block dislocation activities and facilitate grain boundary sliding. The transition from dislocation activities to grain boundary sliding leads to strengthening-then-softening due to grain size reduction, shown by the flow stress. It was further found that, samples with large grain exhibit pronounced yield, with the stress overshoot decrease as the grain size decreases. Samples with grain sizes smaller than 5 nm exhibit elastic-perfect plastic deformation without any stress overshoot, leading to the super-soft regime. Our simulations show that, during deformation, smaller grains rotate more and grow in size, while larger grains rotate less and shrink in size.

Nanocatalytic activity of clean-surfaced, faceted nanocrystalline gold enhances remyelination in animal models of multiple sclerosis

Development of pharmacotherapies that promote remyelination is a high priority for multiple sclerosis (MS), due to their potential for neuroprotection and restoration of function through repair of demyelinated lesions. A novel preparation of clean-surfaced, faceted gold nanocrystals demonstrated robust remyelinating activity in response to demyelinating agents in both chronic cuprizone and acute lysolecithin rodent animal models. Furthermore, oral delivery of gold nanocrystals improved motor functions of cuprizone-treated mice in both open field and kinematic gait studies. Gold nanocrystal treatment of oligodendrocyte precursor cells in culture resulted in oligodendrocyte maturation and expression of myelin differentiation markers. Additional in vitro data demonstrated that these gold nanocrystals act via a novel energy metabolism pathway involving the enhancement of key indicators of aerobic glycolysis. In response to gold nanocrystals, co-cultured central nervous system cells exhibited elevated levels of the redox coenzyme nicotine adenine dinucleotide (NAD+), elevated total intracellular ATP levels, and elevated extracellular lactate levels, along with upregulation of myelin-synthesis related genes, collectively resulting in functional myelin generation. Based on these preclinical studies, clean-surfaced, faceted gold nanocrystals represent a novel remyelinating therapeutic for multiple sclerosis.

Strain rate effects on tensile and compression behavior of nano-crystalline nanoporous gold: A molecular dynamic study

Strain rate effects on tensile and compression behavior of nano-crystalline nanoporous gold: A molecular dynamic study

Divergent influence of {1 1 1} vs. {1 0 0} crystal planes and Yb3+ dopant on CO oxidation paths in mixed nano-sized oxide Au/Ce1−xYbxO2−x/2 (x = 0 or 0.1) systems

In this paper, the fundamental information on interactions in systems concerning nanocrystalline gold disperses on the shaped (octahedron-like or cube-like) Ce1−xYbxO2−x/2 (x = 0 or 0.1) support has been discussed.