Two-dimensional Ag Research Articles

Construction of a crystalline Ag(i) coordination polymer based on a new ligand generated from unusual in situ aza-Michael addition reaction

A two-dimensional (2D) Ag(I) coordination polymer [Ag(Htzsuc)]n (1, H2tzsuc = 2-(1H-1,2,4-triazol-1-yl)succinic acid) comprising a ligand not included in the original reaction mixture but instead generated through an unusual in situ aza-Michael addition reaction of 1H-1,2,4-triazole and fumaric acid during hydrothermal treatment was synthesised. Moreover, the thermal stability and luminescent properties of 1 were discussed.

Synthesis and Characterization of a Novel Luminescent Silver(I)-Chromium(III) Heterometallic Hybrid Material With a Tripodal Ligand N-(Carbamoylmethyl) Iminodiacetato Acid (H2ADA)

Using the tripodal N-(carbamoylmethyl)iminodiacetato acid (H2ADA) ligand and corresponding Ag(I) and Cr(III) salts, a novel two-dimensional (2D) heterometallic Ag(I)-Cr(III) coordination polymer [AgCr(ADA)2]n (1) has been isolated. H2ADA are deprotonated into ADA2−, which adopts a novel asymmetrical η1, η1, η1, η2, μ5-pentadentate coordination mode to bridge neighboring seven-coordinated Ag(I) and five-coordinated Cr(III) ions forming a 2D inorganic-organic hybrid framework containing 2D Ag-O-Cr inorganic connectivity. The solid-state fluorescence spectrum of 1 was also investigated exhibiting the maximum emission peak at 609 nm while no fluorescence emission band can be observed for the free ligand. 1 also represents a luminescent heterometallic hybrid framework with scarcely reported pentacoordinated deprotonated H2ADA ligands. Supplemental materials are available for this article. Go to the publisher's online edition of Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry to view the supplemental file.

Synergistic Modulation of Surface Interaction to Assemble Metal Nanoparticles into Two‐Dimensional Arrays with Tunable Plasmonic Properties

A simple strategy based on the synergistic modulation of inter-particle and substrate-particle interaction is applied for the large-scale fabrication of two-dimensional (2D) Au and Ag nanoparticle arrays. The surface charge of the substrate is used to redistribute the double layer electric charges on the particles and to modulate the inter-particle distance within the 2D nanoparticle arrays on the substrate. The resultant arrays, with a wide range of inter-particle distances, display tunable plasmonic properties. It can be foreseen that such 2D nanoparticle arrays possess potential applications as multiplexed colorimetric sensors, integrated devices and antennas. Herein, it is demonstrated that these arrays can be employed as wavelength-selective substrates for multiplexed acquisition of surface-enhanced Raman scattering (SERS) spectra. This simple one step process provides an attractive and low cost strategy to produce high quality and large area 2D ordered arrays with tunable properties.

Kinetically driven shape changes in early stages of two-dimensional island coarsening: Ag/Ag(111)

We present here a detailed analysis of the shapes of two-dimensional Ag islands of various sizes observed during the early stages of coarsening on the Ag(111) surface, using kinetic Monte Carlo (KMC) simulations, and show that selectivity is due to the formation of kinetically stable island shapes that survive longer than nonselected sizes, which decay into nearby selected sizes. The stable shapes have a closed-shell structure---one in which every atom on the periphery has at least three nearest neighbors. These findings further explain our earlier study in which we found that in the early stages coarsening proceeds as a sequence of selected island sizes resulting in peaks and valleys in the island size distribution [G. Nandipati, A. Kara, S. I. Shah, and T. S. Rahman, J. Phys.: Condens. Matter 23, 262001 (2011)]. This selectivity is dictated by the relative energetics of edge-atom diffusion and detachment and attachment processes and by the large activation barrier for kink detachment. Our simulations were carried out using a very large database of processes identified by each atom's unique local environment using the self-learning KMC scheme. The activation barriers were calculated using semiempirical interaction potentials based on the embedded-atom method.

Rational design of high performance surface plasmon resonance sensors based on two-dimensional metallic hole arrays

We have rationally designed two-dimensional Au and Ag hole arrays for high performing surface plasmon resonance (SPR) sensing. The figure-of-merit (FOM), which is defined as sensitivity/linewidth, is found to be highly geometry-dependent. For sensitivity, we find it is equal to the period of array when exciting low order surface plasmon modes at low incident angle. Therefore, increasing period improves sensitivity. On the other hand, narrow linewidth can be obtained from small hole size so that the radiative decay loss is minimized. By using a pair of orthogonally oriented polarizer and analyzer, the signal-to-noise ratio (SNR) can be greatly enhanced due to the elimination of the nonresonant reflection background. As a proof of our strategy, we have obtained FOM larger than 100/RIU and SNR higher than 110 from Au arrays. Our results show the importance of understanding the basic properties of surface plasmon polaritons in order to systematically optimize the performance of the plasmonic system for a given application.

Formation of Ag Nanoframes with Facilitation of Dithiols

Two-dimensional Ag nanoprisms readily formed Ag triangular nanoframes upon electron beam irradiation. Following meso-2, 3-dimercaptosuccinicacid (DMSA) ripening behavior, continuous electron beam exposure transformed a solid nanoplate into a core/void/shell morphology, which then evolved into a hollow nanoframe structure. TEM was used to observe the ripening and etching processes of Ag nanoprisms as a function of DMSA concentration and electron irradiation time. X-ray diffraction (XRD) and FT-IR analysis were conducted to characterize the Ag nanoprism structure and surface before and after treatment with DMSA. X-ray photoelectron spectroscopy (XPS) was used to determine surface chemical compositions and indicated DMSA was adsorbed on the Ag nanoprisms in the form of Ag(+)-S(-). Raman measurements provided evidence of a disulfide group on Ag nanoprisms. Similar organosulfur structures such as mercaptosuccinic acid and 2-mercaptoacetic acid were also studied with results suggesting that the two S-H groups of dithiol DMSA played the crucial role in nanoframe fabrication. Using the same strategy with DMSA, the nano-architecture can be extended to 2D nanodiscs yielding nanorings.

Two-dimensional dendritic Ag3PO4 nanostructures and their photocatalytic properties

Two-dimensional dendritic Ag(3)PO(4) nanostructures have been synthesized in high-yield by reacting Ag nanowires with H(2)O(2) and NaH(2)PO(4) in aqueous solution at room temperature, which exhibit much higher photocatalytic activities than irregular Ag(3)PO(4) nanocrystals and N-doped TiO(2) catalyst for the degradation of organic contaminants under visible light irradiation.

Effect of Cr position and metal deposition direction on two-dimensional Ag nanoparticle array structure during nanosphere lithography

Ag nanoparticles with 2-dimensional (2D) array structure were fabricated via nanosphere lithography. The influence of Cr interlayer position and metal deposition direction on the array structure was systematically studied. It was found that the structure of the 2D Ag nanoparticle array with Cr interlayer was better than that without interlayers. When the Cr interlayer was deposited on the PS mask, the tips of the acquired triangle nanoparticles were much sharper, and the area of the nanoparticle array was much larger than the other cases. Moreover, the achieved nanoparticle array has a better uniformity and compactness in structure, and higher binding ability to the substrate when Cr and Ag deposition direction was perpendicular to the surface of the substrate. Further absorption spectrum experiment proved the improvement of the structure and feature of the 2D Ag nanoparticle array. All these are very crucial for the future modification and fabrication of biochemical sensors with the 2D Ag nanoparticle array.

Static substrate deposition: Toward longer time scale deposition simulations

We report on the development of a new method for simulating the deposition of atoms onto surfaces, which allows for longer time scales and/or larger system sizes. The method involves simulating only the deposited material on a purely static substrate and corrects for the missing thermal fluctuations and energy exchange effects that surface atoms experience as a result of a static substrate. This method may be viewed as an intermediate approximation between the discrete kinetic Monte Carlo and the full molecular dynamics (MD) methods, because it retains the full trajectory dynamics for the deposited atoms. The method can achieve speed-up times of approximately two orders of magnitude for submonolayer depositions on large simulation substrates. We first apply the method to an ideal prototypical system involving the deposition of Pt material on Pt substrates with two-dimensional Ag monolayer substrate patterns, where we show that it produces nanostructures and small cluster diffusion behavior almost identical to that observed during full MD simulations. As an ideal second application of the method, we use it to deposit Pt and Au onto a reconstructed Au(111) surface representative of a herringbone reconstruction and comment on the findings. Finally, we comment on the limitations and possible future improvements.

Lateral and vertical manipulations of single atoms on the Ag(1 1 1) surface with the copper single-atom and trimer-apex tips

We study the lateral and vertical manipulations of single Ag and Cu atoms on the Ag(111) surface with the Cu single-atom and trimer-apex tips using molecular statics simulations. The reliability of the lateral manipulation with the Cu single-atom tip is investigated, and compared with that for the Ag tips. We find that overall the manipulation reliability (MR) increases with the decreasing tip height, and in a wide tip-height range the MR is better than those for both the Ag single-atom and trimer-apex tips. This is due to the stronger attractive force of the Cu tip and its better stability against the interactions with the Ag surface. With the Cu trimer-apex tip, the single Ag and Cu adatoms can be picked up from the flat Ag(111) surface, and moreover a reversible vertical manipulation of single Ag atoms on the stepped Ag(111) surface is possible, suggesting a method to modify two-dimensional Ag nanostructures on the Ag(111) surface with the Cu trimer-apex tip.

Atomically resolved nucleation and initial growth of a Ag three-dimensional island on Si(001) substrate

The initial growth of a Ag three-dimensional island on an atomically resolved Si(001) substrate was investigated in situ by scanning tunneling microscopy (STM) at room temperature. It took \ensuremath{\sim}20 min for the island to grow from nucleation to a final dimension of 25 nm \ifmmode\times\else\texttimes\fi{} 35 nm \ifmmode\times\else\texttimes\fi{} 22 monolayers (ML). Uniquely, the island growth occurred under no Ag deposition. The Ag atoms required for the growth were provided from the two-dimensional Ag layer and diffusing Ag atoms on the layer that was deposited before the observation. Thanks to this unique growth mechanism, it was allowed to observe the island growth under an isotropic supply of Ag atoms without the shadowing effect of metal deposition by a scanning probe. On the other hand, the STM measurement itself affected finite effects on the growth; attractive interaction between the probe and Ag atoms promoted nucleation of the island, and tunnel current injection may have increased the effective temperature of the system. Despite such a measurement effect, some growth processes that are characteristic of typical metal thin-film growth on silicon substrates were clearly visualized, such as anisotropic and nonmonotonic growth rates that were affected by atomic surface defects, and the growth mode transition from area oriented to height oriented due to an accumulation of stress arising from the lattice mismatch.

Synthesis, structural characterization and properties of Ag(i)-complexes based on double-armed 1,3,4-oxadiazole bridging ligands

Four semirigid symmetric double-armed oxadiazole bridging ligands L1–L4 were designed and synthesized in good yields by reactions of 2,5-bis(2-hydroxyphenyl)-1,3,4-oxadiazole and 2,5-bis(3-hydroxyphenyl)-1,3,4-oxadiazole with 3-(bromomethyl)benzonitrile and 4-(bromomethyl)benzonitrile, respectively. The coordination chemistry of these four ligands with various Ag(I) salts has been investigated. Eleven discrete, one- and two-dimensional polymeric Ag(I) complexes (1–11) were prepared by solution reactions and characterized by infrared spectroscopy, elemental analysis, and single-crystal X-ray diffraction. Compared to our reported ligands of this type, L1–L4 are more flexible. The ligand conformation and polyatomic anion templating effect play a key role in determining the final supramolecular structures. Compound 6 contains 3D intersecting channels with different interior microenvironments. It can absorb two different types of guest molecules (benzene and THF) independently or take them up simultaneously from a mixture of two kinds of guests. Furthermore, it can completely separate THF/furan and benzene/toluene guest substrates in liquid phase, respectively.

Effects of thermal evaporation and electron beam evaporation on two-dimensional patterned Ag nanostructure during nanosphere lithography

In the process of fabricating two-dimensional Ag nano-arrays via nanosphere lithography, different deposition methods present different lattice point shapes of Ag nanostructure. Nano-triangles are produced by thermal evaporation whereas nano-rings are obtained by electron beam evaporation although they are both of hexagonal lattice. It is indicated that the sizes, the surface nanocurvature, the thermal and the kinetic energies of the particles deposited are key factors controlling the formation of the shape of Ag lattice point.

Selective synthesis of hexagonal Ag nanoplates in a solution-phase chemical reduction process

Two-dimensional (2-D) Ag nanoplates have surface plasmon resonances which can be tuned from the visible to the near-IR by varying the size and morphology of the nanoplates. Due to their anisotropic structures and different surface energy distributions, Ag nanoplates—especially triangular ones—are kinetically stable and can transform into other nanostructures. Taking advantage of the synergetic effects of HNO3 and Cl− in the reduction solution, uniform Ag hexagonal nanoplates (HNPs) have been captured during the transformation of Ag triangular nanoplates (TNPs). The dimensions of the Ag HNPs can be controlled by changing the concentrations of reagents in the reaction or/and reduction solutions. Resonance absorption spectra of the obtained Ag HNPs indicated that their in-plane resonance peaks could be tuned from the visible to the near-IR region, showing their potential applications in medical diagnosis.

Angle resolved surface enhanced Raman scattering (SERS) on two-dimensional metallic arrays with different hole sizes

The angle resolved surface enhanced Raman scattering (SERS) on two-dimensional Ag hole arrays has been studied as a function of hole size. The Raman enhancement factor has been found to increase with increasing hole size. In particular, by correlating the Raman mappings with the dispersion relations, the enhancement has been attributed to fast surface plasmon polariton radiative decay rate and strong coupling efficiency. Our results indicate that it is possible to optimize the geometry of the arrays to obtain desirable SERS.

First-principles study of the mechanism of ethylene epoxidation over Ag–Cu particles

Silver–copper alloys have been proposed as catalysts for ethylene epoxidation due to their superior selectivity compared to pure silver, the predominant catalyst for this reaction. Under reaction conditions it has been previously shown that, rather than a two-dimensional (2D) Ag–Cu alloy, a thin copper oxide-like layer forms on top of silver, and several possible surface structures were identified (Phys. Rev. Lett., 2010, 104, 035503). By means of density-functional theory calculations, we study the mechanism of ethylene epoxidation catalyzed by the thin oxide-like surface structures. We identify different reaction pathways that will compete and/or synergetically interplay in the catalysis. In general, the reaction mechanism is structure-dependent and the reaction does not always proceed through the formation of (meta)stable intermediates, in contrast to clean Ag and the 2D alloy. Analyzing the competing reactions, we discuss how the addition of Cu improves the selectivity and stress the overall importance of accounting for the effect of ambient conditions.

Fabrication of uniform Ag/TiO2 nanotube array structures with enhanced photoelectrochemical performance

In the current work, pulse current deposition has been used to prepare evenly distributed and uniformly sized Ag nanoparticles on a TiO2 nanotube array photoelectrode. The Ag particle size and loading were controlled by the pulse deposition time. The Ag/TiO2 nanotube arrays were characterized by SEM, TEM, XRD, XPS and UV-vis diffuse reflection absorption. The resulting electrode contained intimately coupled, three-dimensional Ag/TiO2 structures with greatly improved photocurrent generation and charge transfer compared to a two-dimensional random Ag particle layer deposited directly on top of the nanotube array by the regular photoinduction method. A model mechanism is proposed to illustrate the uniform Ag nanoparticle deposition via the new deposition technique developed in the current work that promotes the uniform distribution of the Ag particles whilst minimizing their deposition at tube entrances, thus effectively preventing the pores from becoming clogged.

Density functional study of surface-supported planar magic Ag nanoclusters

Experimentally, self-organized Ag planar clusters have been observed on the periodic template found on the Pb quantum islands, which are grown on the Si(111) surface. These planar clusters register a remarkable abundance variation at some specific atomic numbers and possess enhanced stability. They are thus denoted as two-dimensional magic Ag nanoclusters (or nanopucks). In this work, detailed calculations based on ab initio density functional theory are made to illuminate how the size and shape effects related to electronic confinement influence the sequence of these two-dimensional Ag nanostructures. The simulation results demonstrate that the evolution of a sequence of planar magic Ag clusters is strongly correlated with their electronic structures. Meanwhile, the role of substrate in the formation of magic Ag clusters is also examined. The symmetry and size of the periodic pattern on the substrate have helped to build up the distinguishable geometric structures in experiment. Further analysis of the related electronic and geometrical properties of these clusters not only explains the occurrence and sequence of the magic numbers but also helps to elucidate the mechanism of their formation.

Polynuclear crystal growth in electrocrystallization of silver: Determining the nucleus size via the nucleation theorem

We employ the nucleation theorem for a model-independent determination of the size of the two-dimensional (2D) Ag nucleus with the aid of experimental data for nucleation-mediated electrochemical crystal growth. The growth is investigated of a screw dislocation-free Ag(100) single crystal face in aqueous solution of AgNO3 at 318 K. The data are for the stationary values of the overpotential during galvanostatic pulses with sufficiently high amplitudes to ensure polynuclear growth mechanism. It is found that the Gibbs-Thomson equation of the classical theory of 2D nucleation describes very well the experimentally obtained overpotential dependence of the size of the 2D Ag nucleus.

Nucleation in electrochemical growth of the Ag(100) crystal face: Determining the nucleus size via the nucleation theorem

We employ the nucleation theorem for a model-independent determination of the size of the two-dimensional (2D) Ag nucleus with the aid of experimental data for the nucleation-mediated electrochemical growth of the Ag(100) crystal face in aqueous solution of AgNO(3) at 318 K. These data are for the stationary rate of 2D nucleation, for the initial portion of the potentiostatic current transient pertaining to atomically smooth face, and for the galvanostatic current corresponding to stationary growth of the face. It turns out that the 2D nucleus is constituted of 17-64 Ag atoms when the overpotential is in the range of 12-22.4 mV. Upon expressing the overpotential in terms of supersaturation, it is found that the experimental data for the size of the 2D Ag nucleus are in conformity with existing simulation data for the size of the 2D nucleus on the (100) face of Kossel crystal (the simulation nucleus contains 1-30 atoms). It is found as well that the Gibbs-Thomson equation of the classical theory of 2D nucleation describes very well the supersaturation dependence of the size of both the Ag and the simulation nucleus.