Linear Au Research Articles

Optical properties of ion track assisted Au nanochain like aggregates

The amorphous silica ( a-SiO 2) was irradiated with 6 MeV Si + ions with fluences of 1 × 10 11, 5 × 10 11 and 1 × 10 12 ions/cm 2 and etched with HF (hydro fluoric acid) for 6 min to produce ion tracks. The etched samples were coated with 12 nm thick gold films and were treated with rapid thermal processing (RTP) at 850 °C for 2 min in the nitrogen atmosphere. The RTP treated samples were etched with aqua-regia to remove the gold which has not diffused into the ion tracks. These samples were characterised with optical absorption and photoluminescence (PL) spectroscopy. The surface plasmon resonance (SPR) peak, which is characteristic of Au nano-aggregates was observed. SPR peaks at 2.17 and 2.28 eV are assigned to the dipolar and quadropolar resonance of linear chain of nanoclusters respectively and the resonance peak at 2.35 eV is attributed to non-linear aggregation of gold nanoparticles. The blue bands above ~ 3 eV are observed in PL which are close to the reported values for Au nanoclusters. Also the green PL band is observed around 2.6 eV and the green emission arises from the radiative recombination of sp-band electrons with d-band holes. The intensity of the green PL band is mainly due to the local electric field connected with the Au-particle plasmons oscillations. The mechanism behind the formation of linear Au nanochain is discussed.

Golden Metallopolymers with an Active T1 State via Coordination of Poly(4-vinyl)pyridine to Pentahalophenyl-Gold(I) Precursors

Brightly phosphorescent gold-based metallopolymers have been synthesized by reaction of nonluminescent reactants comprised of the commercially available polymer PVP = poly(4-vinylpyridine) and the Au(I) precursors [Au(C(6)X(5))THT] (X = F or Cl; THT = tetrahydrothiophene). The metallopolymer products exhibit remarkable photoluminescence properties including high solid-state quantum yield (up to 0.63 at RT) and coarse- and fine-tuning to multiple phosphorescence bands across the visible spectrum via luminescence thermochromism and site-selective excitation. The emissions are caused by intrachain and interchain aurophilic interactions between the linear Au(I) complexes in the metallopolymers. This investigation provides further manifestations of interesting chemistry and photophysics in N-heterocyclic coordination compounds of Au(I) by expansion from the small-molecule to the metallopolymer regime. The spectroscopic and material properties of the new class of metallopolymers are desirable for future studies that will utilize them as emitters for photonic applications such as polymer light-emitting diodes and sensors.

Charge-induced formation of linear Au clusters on thin MgO films: Scanning tunneling microscopy and density-functional theory study

Gold deposition onto ultrathin MgO films on Ag(001) results in the formation of linear Au clusters, as revealed from a combined scanning tunneling microscopy and density-functional theory study. The equilibrium structure of small Au clusters containing three to seven atoms is therefore different on thin film and bulk MgO(001) but also deviates from the shape of the respective gas-phase clusters. The peculiar one-dimensional growth regime of gold is stimulated by an electron transfer from the MgO/Ag interface to the deposited Au clusters, resulting in singly and doubly charged cluster anions. Only for larger atom numbers, the formation of compact two-dimensional clusters prevails on the MgO thin films.

Near-field imaging of optical antenna modes in the mid-infrared

Optical antennas can enhance the coupling between free-space propagating light and the localized excitation of nanoscopic light emitters or receivers, thus forming the basis of many nanophotonic applications. Their functionality relies on an understanding of the relationship between the geometric parameters and the resulting near-field antenna modes. Using scattering-type scanning near-field optical microscopy (s-SNOM) with interferometric homodyne detection, we investigate the resonances of linear Au wire antennas designed for the mid-IR by probing specific vector near-field components. A simple effective wavelength scaling is observed for single wires with lambda(eff) = lambda /(2.0+/- 0.2), specific to the geometric and material parameters used. The disruption of the coherent current oscillation by introducing a gap gives rise to an effective multipolar mode for the two near-field coupled segments. Using antenna theory and numerical electrodynamics simulations two distinct coupling regimes are considered that scale with gap width or reactive near-field decay length, respectively. The results emphasize the distinct antenna behavior at optical frequencies compared to impedance matched radio frequency (RF) antennas and provide experimental confirmation of theoretically predicted scaling laws at optical frequencies.

Extrapolation of Tikhonov and Lavrentiev regularization methods

We consider solution of linear ill-posed problem Au = f by Tikhonov method and by Lavrentiev method. For increasing the qualification and accuracy of these methods we use extrapolation, taking for the approximate solution linear combination of n ≥ 2 approximations of Tikhonov or Lavrentiev methods with different parameters and with proper coefficients. If the solution u* belongs to ℛ((A*A)n) and instead of f noisy data fδ with ||fδ − f|| ≥ δ are available, maximal guaranteed accuracy of Tikhonov and Lavrentiev approximations is O(δ2/3) and O(δ1/2), respectively, versus accuracy O(δ2n/(2n + 1)) and O(δn/(n + 1)) of corresponding extrapolated approximations. We propose several new rules for a posteriori choice of the regularization parameter, including modifications of the monotone error rule. Extensive numerical experiments show that in case u* ε ℛ(A*) the extrapolated Tikhonov approximation with a posteriori parameter choice (not using any smoothness information) is typically more accurate than Tikhonov approximation with optimal parameter.

Linearized Bregman iterations for compressed sensing

Finding a solution of a linear equation Au = f with various minimization properties arises from many applications. One such application is compressed sensing, where an efficient and robust-to-noise algorithm to find a minimal l 1 norm solution is needed. This means that the algorithm should be tailored for large scale and completely dense matrices A, while Au and A T u can be computed by fast transforms and the solution we seek is sparse. Recently, a simple and fast algorithm based on linearized Bregman iteration was proposed in [28, 32] for this purpose. This paper is to analyze the convergence of linearized Bregman iterations and the minimization properties of their limit. Based on our analysis here, we derive also a new algorithm that is proven to be convergent with a rate. Furthermore, the new algorithm is simple and fast in approximating a minimal l 1 norm solution of Au = f as shown by numerical simulations. Hence, it can be used as another choice of an efficient tool in compressed sensing.

QUANTUM CONDUCTANCE AND ELECTRONIC PROPERTIES OF LOWER DIAMONDOID MOLECULES AND DERIVATIVES

Diamondoids and their derivatives have found major applications as templates and as molecular building blocks in nanotechnology. An ab initio method we calculated the quantum conductance and the essential electronic properties of two lower diamondoids (adamantane and diamantane) and three of their important derivatives (amantadine, memantine and rimantadine). We also studies two artificial molecules that are built by substituting one hydrogen ion with one sodium ion in both adamantane and diamantane molecules. Most of our results are based on an infinite Au two-probe system constructed by ATK and VNL software, which comprise TRANSTA-C package. By changing various system structures and molecule orientations in linear Au and 2 × 2 Au probe systems, we found that although the conductance of adamantane and diamantane are very small, the derivatives of the lower diamondoids have considerable conductance at specific orientations and also showed interesting electronic properties. The quantum conductance of such molecules will change significantly by changing the orientations of the molecules, which approves that residues like nitrogen and sodium atoms have great effects on the conductance and electronic properties of single molecule. There are obvious peaks near Fermi energy in the transmission spectrums of artificial molecules, indicating the plateaus in I–V characteristics of such molecules.

Bonding analysis for NgAuOH (Ng = Kr, Xe)

AbstractNoble‐gas‐noble‐metal hydroxides NgAuOH (Ng = Kr, Xe) are investigated at the MP2 theoretical level. All species are found to be in Cs symmetry with an approximate linear NgAuO moiety. The noble‐gas‐noble‐metal bond lengths are comparable with covalent limits, and the corresponding binding energies have been computed to be 59.6 and 83.4 kJ/mol for KrAuOH and XeAuOH, respectively. Except the charge‐induced dipole contribution to the binding energies, the remainder could be ascribed to the higher‐order charge‐induction energies, dispersion energies, the contributions of multipole moments on AuOH and covalent effects. The title species are sufficiently chemical bound and are expected to be stable species theoretically. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008

On the Chemical Bonding of Gold in Auro-Boron Oxide Clusters AunBO- (n = 1−3)

During experiment on Au-B alloy clusters, an auro-boron oxide cluster Au2BO- was observed to be an intense peak dominating the Au-B mass spectra, along with weaker signals for AuBO- and Au3BO-. Well-resolved photoelectron spectra have been obtained for the three new oxide clusters, which exhibit an odd-even effect in electron affinities. Au2BO- is shown to be a closed shell molecule with a very high electron detachment energy, whereas AuBO and Au3BO neutrals are shown to be closed shell species with large HOMO-LUMO gaps, resulting in relatively low electron affinities. Density functional calculations were performed for both AunBO- (n = 1-3) and the corresponding HnBO- species to evaluate the analogy between bonding of gold and hydrogen in these clusters. The combination of experiment and theory allowed us to establish the structures and chemical bonding of these tertiary clusters. We find that the first gold atom does mimic hydrogen and interacts with the BO unit to produce a linear AuBO structure. This unit preserves its identity when interacting with additional gold atoms: a linear Au-[AuBO] complex is formed when adding one extra Au atom and two isomeric Au2-[AuBO] complexes are formed when adding two extra Au atoms. Since BO- is isoelectronic to CO, the AunBO- species can be alternatively viewed as Aun interacting with a BO- unit. The structures and chemical bonding in AunBO- are compared to those in the corresponding AunCO complexes.

Structural study of gold clusters

Density functional theory (DFT) calculations were carried out to study gold clusters of up to 55 atoms. Between the linear and zigzag monoatomic Au nanowires, the zigzag nanowires were found to be more stable. Furthermore, the linear Au nanowires of up to 2 nm are formed by slightly stretched Au dimers. These suggest that a substantial Peierls distortion exists in those structures. Planar geometries of Au clusters were found to be the global minima till the cluster size of 13. A quantitative correlation is provided between various properties of Au clusters and the structure and size. The relative stability of selected clusters was also estimated by the Sutton-Chen potential, and the result disagrees with that obtained from the DFT calculations. This suggests that a modification of the Sutton-Chen potential has to be made, such as obtaining new parameters, in order to use it to search the global minima for bigger Au clusters.

Cationic, linear Au(i) N-heterocyclic carbene complexes: synthesis, structure and anti-mitochondrial activity

Six linear, two-coordinate cationic Au(I) N-heterocyclic carbene complexes of the form [(R2Im)2Au]+ (R = Me 1, Me, Et 2, i-Pr 3, n-Bu 4, t-Bu 5 and Cy 6) have been prepared by the reaction of two equivalents of the appropriate dialkylimidazol-2-ylidene (R2Im) with (Me2S)AuCl in dmf. Single crystal structural studies for 1.PF6, 2.PF6), 3.Cl and 4-6.PF6 show that for all six complexes the gold(I) centres have quasi-linear C-Au-C coordination, with quasi-parallel pairs of aromatic imidazole planes, except in 5.PF6 where they are quasi-normal; in the latter, Au-C are 2.038(3), 2.033(3) A, cf. (e.g.) 2.027(2) A. Inter-cation Au...Au are close at 3.487(2), 3.525(2) A in 1PF6 and 2.PF6. The structural studies and low temperature NMR experiments provide no supportive evidence for the presence of pi back-bonding within this series of complexes. The lipophilicities of the six compounds, as estimated from the logarithm of the n-octanol-water partition coefficients (log P), varied across the series within the range -1.09 to 1.73. To investigate their potential as possible anti-mitochondrial anti-tumour agents, five of the compounds have been evaluated for their propensities to induce mitochondrial membrane permeabilization (MMP) in isolated rat liver mitochondria. At concentrations between 1-10 microM compounds 1.Br and 3-6.Cl induced dose-dependent, Ca2+-sensitive mitochondrial swelling at rates that increased with the lipophilicities of the complexes, with the most lipophilic compounds inducing the most rapid onset of swelling. The swelling was completely inhibited by cyclosporin A, the specific inhibitor of the mitochondrial permeability transition pore.

Assembly of Au colloids into linear and spherical aggregates and effect of ultrasound irradiation on structure

In this work, we aimed to tune the aggregation state of Au colloids by judicious regulation of their surface charges and by introduction of ultrasound irradiation. Au colloids were prepared by reduction of HAuCl4 with NaBH4 in the presence of 3-mercaptopropionic acid (MPA) as the stabilizing ligand. The Au colloids capped with MPA molecules possessing a single –SH terminal group, can form either linear or spherical Au colloid aggregates depending on the MPA ∶ Au ratio, solution pH and Au colloid concentration. Adjustment of these parameters provides a convenient means of regulating surface charge on the Au colloid surface and, thus, the state and degree of aggregation. The spherical aggregates appeared to be thermodynamically stable, and ultrasound irradiation could promote their formation. Intense ultrasound irradiation resulted in the formation of well-crystallized nanospheres whilst mild irradiation tended to produce a more amorphous product. This is the first observation of a sonication effect on the crystallization state in freely suspended Au colloids in aqueous solution.

Synthesis and structural characterisation of linear Au(I) N-heterocyclic carbene complexes: New analogues of the Au(I) phosphine drug Auranofin

The synthesis and characterisation of a series of neutral Au(I) N-heterocyclic carbene complexes [(NHC)AuX] (X = Cl and 2′,3′,4′,6′-tetra- O-acetyl-β- d-glucopyranosyl-1-thiolato) are reported. The chloro complexes were synthesised either by reaction of the appropriate 1,3-dialkylimidazol-2-ylidene with [(Me 2S)AuCl] or by transmetallation between the appropriate Ag(I)–NHC complex and [(Me 2S)AuCl]. The 2′,3′,4′,6′-tetra- O-acetyl-β- d-glucopyranosyl-1-thiolato complexes were prepared from the appropriate [(NHC)Au(I)Cl] complex and 2′,3′,4′,6′-tetra- O-acetyl-1-thio-β- d-glucopyranose under basic conditions. A cationic Au(I)–NHC triphenylphosphine adduct was also prepared. Structural studies (X-ray diffraction) of a number of the complexes show that in each case the gold atom is (quasi-) linearly two-coordinate, having C–Au–Cl, C–Au–S or C–Au–P coordination. In one case, a new phase of [(Cy 2Im)AuCl], the molecules pack pair-wise with a close Au⋯Au interaction (3.1566(6) Å). Preliminary studies show this complex is luminescent in the solid state.

Batch Preparation of Linear Au and Ag Nanoparticle Chains via Wet Chemistry

We present a simple, wet-chemical method for fabricating linear chains of Au and Ag nanoparticles by selectively etching alternating segments from striped metal nanowires. Nanowires composed of sacrificial Ni segments as well as Au and/or Ag segments were prepared by templated electrodeposition in the pores of alumina membranes. After removal from the membrane, wires were coated with SiO2, and selective etching revealed the nanoparticle chains. Extinction spectra are presented as a function of interparticle spacing.

Cyclic Trinuclear Gold(I) Compounds: Synthesis, Structures and Supramolecular Acid—Base π‐Stacks

AbstractFor Abstract see ChemInform Abstract in Full Text.

Some algorithms for computing Chebyshev normalized first-kind polynomials by roots

When numerically implementing the optimal binomial N -cycle Chebyshev iterative methods for solving the linear operator equations Au = f [1–13], the iterative sequence of approximations u k , k = 1, . . . , N , arises. In this case a transition operator is successively multiplied by operator factors of the form I − α k A , k ≤ N , where the parameters α k are inverse values to the roots of the Chebyshev first-kind polynomial of the degree N reduced to the segment [ m , M ], 0 < m < M , which comprises the spectrum of the operator A . For small values of ξ = m / M the norms of some of these operators are large. It is advisable to mix these operators with those which reduce the norm of the transition operator. An important problem is the stability of the iterative method u k +1 = u k – α k ( Au k – f ), k = 0,1, . . . , N –1. Its stability to round-off errors substantially depends on the sequence of parameters (permutation ϰ N ), because the transition operators I – α k Aξ for small values of ξ = m / M and some numbers k have a huge norm. In real computer-aided calculations this can lead to two undesirable effects: (1) a dramatic increase in || u k || for some 1 ≤ k < N, which can result in an emergency halt of the computer or a loss in significant digits in subsequent calculations, and (2) the corresponding increase in the errors at intermediate iterations. The algorithms for ordering parameters for the case N = 2 q 3 r have been studied in [1–6, 8, 9].

Electronic states of linear Au clusters supported on metal surfaces: why are they like those of a particle in a box?

Scanning tunneling spectroscopy and microscopy show that the empty states of linear Au clusters supported on a metal surface behave as if they are the states of an electron in an empty one-dimensional box. We show here that certain difficulties of this description are removed by a particle-in-a-cylinder model. This interpretation is supported by density functional calculations.

Luminescent gold(I) and silver(I) complexes of 2-(diphenylphosphino)-1-methylimidazole (dpim): characterization of a three-coordinate Au(I)-Ag(I) dimer with a short metal-metal separation.

The Au(I) and Ag(I) closed-shell metal dimers of 2-(diphenylphosphino)-1-methylimidazole, dpim, were investigated. dpim formed the discreet binuclear species [Ag2(dpim)2(CH3CN)2](2+) (1) when reacted with appropriate Ag(I) salts. Likewise, [Au2(dpim)2](2+) (3) and [AuAg(dpim)3](2+) (4) were produced via reactions with (tht)AuCl, tht is tetrahydrothiophene, and Ag(I). Compound 3 exhibits an intense blue luminescence (lambdamax=483 nm) in the solid state. However, upon initial formation of 3, a small impurity of Cl- was present giving rise to an orange emission (lambdamax=548 nm). Attempts to form [Au2(dpim)2]Cl2 yielded only (dpim)AuCl (2), which is not visibly emissive. The rare three-coordinate heterobimetallic complex [AuAg(dpim)3](2+) (4) exhibits intense luminescence in the solid-state resembling that of 3. The crystal structures of 1-4 were determined, revealing strong intramolecular aurophilic and argentophilic interactions in the dimeric compounds. Compound 1 has an Ag(I)-Ag(I) separation of 2.9932(9) A, while compound 3 has a Au(I)-Au(I) separation of 2.8174(10) A. Compound 4 represents the first example of a three-coordinate Au(I)-Ag(I) dimer and has a metal-metal separation of 2.8635(15) A. The linear Au(I) monomer, 2, has no intermolecular Au(I)-Au(I) interactions, with the closest separation greater than 6.8 A.

CYCLIC TRINUCLEAR GOLD(I) COMPOUNDS: SYNTHESIS, STRUCTURES AND SUPRAMOLECULAR ACID-BASE π-STACKS

Trinuclear 9-membered rings can be formed by gold(I) ions with exobidentate C,N or N,N monoanionic ligands. They are generally slightly irregular and puckered unless the metallocycle is imposed by intramolecular crystallographic symmetry. Gold-gold intramolecular interactions are always present and the complexes exhibit a roughly D3h symmetry. Crystal structures of these trinuclear complexes show individual complexes, dimers supramolecular columnar packing or more complex supramolecular aggregates. Dimers and supramolecular structures are held together by aurophilic intermolecular gold-gold interactions. Bulky substituents on the ligands can prevent intermolecular metal-metal interactions or the formation of supramolecular architectures. It is well established that the Au(I) center in many linear 2-coordinate Au(I) complexes displays electrophilic tendencies in reaction chemistry while also often accepting electron donors to expand the coordination. Trinuclear Au(I) pyrazolates, carbeniates and benzylimidazolates are well known and undergo electron loss through oxidative addition forming first Au(I,III) mixed valence species and ultimately (with the carbeniates, TR(carb), the benzylimidazolates, TR(bzim) and the chlorinated pyrazolate TR(Cl-pz) trinuclear Au(III) species. Surprisingly, these Au(I) carbeniates and benzylimidazolates also are excellent bases for the metals cations Tl(I) and Ag(I). The acidic, neutral [Hg(C6F4)3]3 interacts with TR(carb) and TR(bzim) as seen by X-ray solid state and solution NMR measurements. Recently it has been shown that the neutral pi acids C6F6 and TCNQ also form stacked pi-acid, pi-base solid state products with TR(carb) and TR(bzim). The TR(bzim) and TR(carb) products are luminescent as solids but C6F6 intercalation quenches the luminescence of the p-tol, ethoxy TR(carb), which is a dimer in the solid state. It is interesting that pi-acid, pi-base stacking can involve either a ABAB pattern or an ABBABBA pattern of the molecules, where B is base, TR(carb) or TR(bzim). The B units are aurophilically bonded to each other by two Au…Au linkages. DFT calculations demonstrate that the basicity of the BB dimer is increased relative to the molecular species.

The exact solution for solving a class nonlinear operator equations in the reproducing kernel space

In this paper, the author will introduce the Sobolev space W 1 2(Ω n) firstly and then give the reproducing properties of the space W 1 2(Ω n) . As these results of those, a class of the nonlinear operator equation ∑ n i=1 ∏ m i j=1 ( A ij u)= f is transformed to the n-dimensional linear operator equation Au= f. Finally, we also give the exact solution of this nonlinear operator equation.