Fabrication and electronic properties of gold nanoparticle superlattices

Well-defined planar 1D chains and 2D superlattices of gold (Au) nanoparticles in the 1.5~9.7 nm range were successfully fabricated by a self-assembly technique. When the nanoscale ridge-and-valley structured carbon substrates were dipped in toluene solution of 3.4-nm Au nanoparticles followed by a natural dry, a planar array of 1D chains of Au nanoparticles were formed at the valleys of carbon substrates. On the other hand, the 1.5~9.7-nm Au nanoparticles protected by alkanethiols or 2,6-bis(1'-n-thioalkyl)benzimidazol-2-yl)pyridine easily formed hexagonal 2D superlattices on the flat carbon substrates, the inter-particle spacing being tuned by the ligand length and so on. It was found that for 2D superlattices consisting of large particles of ~5 nm the electron behavior was dominated by the Coulomb blockade effect at low temperature while the I–V response was ohmic at room temperature.     

【撤稿】Au纳米颗粒二维超晶格结构的稳定性

We synthesized 5.5 nm Au nanocrystals coated by dodecanethiol (C₁₂SH₂₆) by reverse micelle method. The Au nanocrystals are multiply twinned particles (MTP), which are mainly characterized by decahedral and icosahedral structures. The 2D hexagonal network self-organizationa of Au nanocrystals are realized on both amorphous carbon (AC) and highly oriented pyrolitic graphite (HOPG) surfaces. The stability of 2D superlattices of Au nanocrystals in vacuum has been systematically surveyed, and it is found that large single triangular nanocrystals have been formed after 75 days due to the coalescence among the neighboring nanoparticles and the rearrangement of the atomics. When the Au nanocrystals in 2D organizations are annealed in air (573 K, 15 min), higher ordered 2D self-assemblies are stable, whereas worm-like coalesced nanoparticles form in those less ordered organizations. This demonstrates that the thermal stability of 2D self-assemblies is determined by the level of nanocrystals ordering.     

Self-assembly of small gold nanoparticles through interligand interaction

Stable and monodisperse Au nanoparticles smaller than 2 nm are easily prepared by the reduction of HAuCl(4) x 4H(2)O in DMF/H(2)O in the presence of a series of bidentate ligands, 2,6-bis(1'-(n-thioalkyl)benzimidazol-2-yl)pyridine (TC(n)BIP, n = 3, 6, 8, 10, 12). The TC(n)BIP ligands afford stronger coordination ability than alkanethiols due to their bidentate nature. These small nanoparticles form hexagonal close-packed (hcp) two-dimensional (2D) superlattices with tunable interparticle spacings (from 1.2 to 2.5 nm), produced by changing the length of the ligand at both the hydrophobic amorphous carbon and the air-water interface. Long-range-ordered hcp 2D superlattices were fabricated through the cleavage and construction of interligand pi-pi interactions formed via an annealing process at the air-water interface.     

Interparticle spacing control in the superlattices of carboxylic acid-capped gold nanoparticles by hydrogen-bonding mediation

We have demonstrated that carboxylic acid-capped gold nanoparticles were self-assembled to form two-dimensional (2D) and/or three-dimensional (3D) superlattices at an air/water interface in the presence of a bifunctional hydrogen-bonding mediator such as 4-pyridinecarboxylic acid (PyC) or trans-3-(3-pyridyl)acrylic acid (PyA). Transmission electron microscopy revealed a hexagonal close-packed arrangement of nanoparticles in the superlattice with an extension of interparticle spacing. In the 2D superlattices, larger particles produced a higher-quality assembly having long-range translational ordering. Attenuated total reflectance IR (ATR-IR) spectroscopy revealed the presence of hydrogen bonds between the mediator used and the capping agents of carboxylic acid on nanoparticle surfaces. Since the experimentally obtained interparticle separation distance agreed approximately with that obtained by the geometrical model calculations, we conclude that the hydrogen-bonding mediation controlled the interparticle spacing or structure by monomolecular incorporation between adjacent nanoparticles in the superlattices.     

Highly ordered superlattices from polydisperse Ag nanoparticles: a comparative study of fractionation and self-correction

We have examined two different routes to construct highly ordered two- or three-dimensional (2D or 3D) superlattice structures from hydrophilic polydisperse mercaptosuccinic acid (MSA)-modified Ag nanoparticles of the average size of 2.5 nm. First, polydisperse particles were fractionized by the polyacrylamide gel electrophoresis (PAGE) method. Due to the size-dependent migration under the electric field, the particles were isolated into a series of gel bands and each band contained particles with significantly narrow size distribution. Subsequent to phase transfer into chloroform by cationic surfactant, long-range 2D superlattices were simultaneously formed on the substrate upon evaporation of chloroform. Second, 3D superlattices were directly grown at an air-water interface from the polydisperse bulk dispersion by diffusion of HCl vapor without any pretreatment for the size narrowing. The influence of diffusion rate of HCl was also studied. The achievement of 3D superlattices via this route was ascribed as a long-time self-correction process. Furthermore, it was revealed that the superlattice structures obtained by the above two procedures exhibited distinct features though the starting material was the same MSA-Ag nanoparticles. The surface distance of core between component particles, the orientation of particles inside the superlattice, and the process of superlattice formation were comprehensively studied. We confirmed that each growth process depended on a corresponding self-assembly mechanism.     

氨基功能化有序介孔Si02薄膜组装Au纳米粒子复合材料的可调色散性质

以聚环氧乙烷-聚环氧丙烷-聚环氧乙烷(P123)为模板剂,采用共溶胶的蒸发诱导自组装方法制备了氨基功能化介孔SO2薄膜,然后利用氯金酸(HAUCl4)与介孔SiO2薄膜孔道内壁的氨基之间的中和反应组装Au纳米粒子,制备得到Au/SiO2纳米复合材料.用TEM,XRD和UV-Vis光谱对材料进行了测试.结果表明,无水乙醇...     

Influence of Capping Ligands on the Self—organization of Gold Nanoparticles into Superlattices from CTAB Reverse Micelles

Gold nanoparticles with size 3-10nm (diameter) were prepared by the reduction of HAuCl4 in a CTAB/octane 1-butanol/H2O reverse micelle system using NaBH4 as the reducing agent.The as-formed gold nanoparticle colloid was characterized by UV/vis absorption spectrum and transmission electron microscopy(TEM).Various capping ligands,such as alkylthiols with different chain length and shape,trioctylphosphine(TOP),and pyridine are used to passivate the gold nanoparticles for the purpose of self-organization into superstructures.It is shown that the ligands have a great influence on the selforganization of gold nanoparticles into superlattices,and dodecanethiol C12H25SH is confirmed to be the best ligand for the self-organization.Self-organization of C12H25SH-capped gold nanoparticles into 1D,2D and 3D supperlattices has been observed on the carbon-coated copper grid by TEM without using any selective precipitation process.     

Controllable synthesis and catalysis application of hierarchical PS/Au core-shell nanocomposites

Polystyrene (PS)/gold (Au) core-shell nanocomposites with tunable size, high stability, and excellent catalytic activity have been synthesized by a facile method that combines the ionic self-assembly with the in situ reduction. The composition and stoichiometry, as well as its morphology and optical properties of these nanocomposites have been examined and verified by various characterization techniques. The size and the coverage of gold nanoparticles (NPs) can be simply tailored by changing the amount of 3-aminopropyltrimethoxysilane (APTES), the functionalization time, the protonation time, and the amount of chloroauric acid (HAuCl₄). The continuous red shifts of the localized surface plasmon resonance absorption of the Au NPs on the PS spheres are observed. Importantly, the obtained Au NPs with controllable and uniform size on the surfaces of amino-functionalized PS spheres exhibit excellent size-dependent catalytic properties for the reduction of 4-nitrophenol (4-NP) by NaBH₄.     

Organic mediator-induced structural transformation in superlattices of monolayer-protected gold nanoparticles

N-acetylglutathione (NAG)-protected gold nanoparticles self-assemble into three-dimensional (3D) face-centered cubic (fcc)-type superlattices at an air/water interface under highly acidic conditions. To prepare the well-defined superlattices, 1month's incubation is at least necessary since the size growth of the as-prepared nanoparticles is essential. Addition of 4-pyridinecarboxyic acid (PyC), a bifunctional hydrogen-bonding mediator, promotes the formation of the superlattices, which are created for about 2weeks' storage. Interestingly, PyC-induced nanoparticle superlattices are in a body-centered tetragonal (bct) structure. The fcc-to-bct phase transformation would be due to stronger interaction between NAG and PyC than that between NAG molecules on the gold nanoparticle surfaces.     

Gold-Titanium(IV) Oxide Plasmonic Photocatalysts Prepared by a Colloid-Photodeposition Method: Correlation Between Physical Properties and Photocatalytic Activities

Colloidal gold (Au) nanoparticles were prepared and successfully loaded on titanium(IV) oxide (TiO(2)) without change in the original particle size using a method of colloid photodeposition operated in the presence of a hole scavenger (CPH). The prepared Au nanoparticles supported on TiO(2) showed strong photoabsorption at around 550 nm due to surface plasmon resonance (SPR) of Au and exhibited a photocatalytic activity in mineralization of formic acid in aqueous suspensions under irradiation of visible light (>ca. 520 nm). A linear correlation between photocatalytic activity and the amount of Au loaded, that is, the number of Au nanoparticles, was observed, indicating that the activity of Au/TiO(2) plasmonic photocatalysts can be controlled simply by the amount of Au loading using the CPH method and that the external surface area of Au nanoparticles is a decisive factor in mineralization of formic acid under visible light irradiation. Very high reaction rates were obtained in samples with 5 wt % Au or more, although the rate tended to be saturated. The CPH method can be widely applied for loading of Au nanoparticles on various TiO(2) supports without change in the original size independent of the TiO(2) phase. The rate of CO(2) formation also increased linearly with increase in the external surface area of Au. Interestingly, the TiO(2) supports showed different slopes of the plots. The slope is important for selection of TiO(2) as a material supporting colloidal Au nanoparticles.     

Binary Assembly of Au Nanoparticles with Controllable Two‐dimensional Architecture Directed by Phosphate Backbone Modified Oligonucleotide

A three complementary strand oligonucleotide system was employed to assemble two different‐sized, 15 and 25 nm, Au nanoparticles into binary two‐dimensional (2D) structures. First, two non‐complementary strands of phosphate backbone modified oligonucleotides (PM oligo‐DNA) were loaded on the surface of the 15 and 25 nm Au nanoparticles, respectively. Upon the addition of the third linker DNA, which was half complementary to each of the modified DNA, the Au nanoparticles would be assembled to binary 2D aggregates. The number of the 15 nm Au nanoparticles around a 25 nm Au naoparticle can be readily controlled by the length of the DNA helix used.     

Fivefold symmetry in superlattices of monolayer-protected gold nanoparticles

Three-dimensional (3D) superlattices of gold nanoparticles were prepared at an air/solution interface. The surface of the gold nanoparticles used is protected by N-acetylglutathione (NAG). Morphological studies revealed that the superlattices formed fivefold symmetric structures such as pentagonal rod, decahedron, and icosahedron, which were probably developed by multiple twinning. Moreover, high-resolution surface images of the superlattices in fivefold symmetry showed excellent ordered arrangements of nanoparticles with both close-packed and non-close-packed structures.     

Structural characterization of self-assembled multifunctional binary nanoparticle superlattices

Nanocrystals of different size and functionality (e.g., noble metals, semiconductors, oxides, magnetic alloys) can be induced to self-assemble into ordered binary superlattices (also known as opals or colloidal crystals), retaining the size tunable properties of their constituents. We have built a variety of binary superlattices from monodisperse PbS, PbSe, CoPt3, Fe2O3, Au, Ag, and Pd nanocrystals, mixing and matching these nanoscale building blocks to yield multifunctional nanocomposites (metamaterials). Superlattices with AB, AB2, AB3, AB4, AB5, AB6, and AB13 stoichiometry with cubic, hexagonal, tetragonal, and orthorhombic symmetries have been identified. Assemblies with the same stoichiometry can be produced in several polymorphous forms by tailoring the particle size and deposition conditions. We have identified arrays isostructural with NaCl, CuAu, AlB2, MgZn2, MgNi2, Cu3Au, Fe4C, CaCu5, CaB6, NaZn13, and cub-AB13 compounds emphasizing the parallels between nanoparticle assembly and atomic scale crystal growth and providing confidence that many more structures will follow. Recently, we have demonstrated that electrical charges on sterically stabilized nanoparticles in addition to such parameters as particle size ratio and their concentrations can provide the formation of a much broader pallet of binary nanoparticle superlattices as compared with the limited number of possible superlattices formed by hard noninteracting spheres. In this contribution, we demonstrate a large variety of different binary superlattices, provide their detailed structural characterization, and discuss the role of energetic and kinetic factors in the cocrystallization process. We found that Coulomb, van der Waals, charge-dipole, dipole-dipole, and other interactions can contribute equally to cocrystallization, allowing superlattice formation to be dependent on a number of tunable parameters. We present binary superlattices as a new class of materials with a potentially unlimited library of constituents over a wide range of tunable structures.     

Three-dimensional nanocrystal superlattices grown in nanoliter microfluidic plugs

We studied the self-assembly of inorganic nanocrystals (NCs) confined inside nanoliter droplets (plugs) into long-range ordered superlattices. We showed that a capillary microfluidic platform can be used for the optimization of growth conditions for NC superlattices and can provide insights into the kinetics of the NC assembly process. The utility of our approach was demonstrated by growing large (up to 200 μm) three-dimensional (3D) superlattices of various NCs, including Au, PbS, CdSe, and CoFe(2)O(4). We also showed that it is possible to grow 3D binary nanoparticle superlattices in the microfluidic plugs.     

以碳微球为核的金纳米壳球体的制备

通过水热合成法制备了单分散碳微球, 并以此单分散碳微球为核, 利用其表面修饰的银纳米粒子作为种子, 进一步还原制备了以碳微球为核、以金为壳的金纳米壳(Nanoshell)球体. 通过透射电子显微镜和紫外可见吸收光谱对其形态以及光谱性质进行了表征. 研究结果表明, 采用该种方法制备出来的碳微球具有良好的单分散性, 表面修饰简便快捷, 利用碳微球为核制备的金纳米壳球体尺寸可控, 在近红外范围内有强吸收. 实验结果证明该方法是制备金纳米壳球体的一种有效新方法.     

Sensitive determination of dopamine in the presence of uric acid and ascorbic acid using TiO2 nanotubes modified with Pd, Pt and Au nanoparticles

A simple modified TiO(2) nanotubes electrode was fabricated by electrodeposition of Pd, Pt and Au nanoparticles. The TiO(2) nanotubes electrode was prepared using the anodizing method, followed by modifying Pd nanoparticles onto the tubes surface, offering a uniform conductive surface for electrodeposition of Pt and Au. The performance of the modified electrode was characterized by cyclic voltammetry and differential pulse voltammetry methods. The Au/Pt/Pd/TiO(2) NTs modified electrode represented a high sensitivity towards individual detection of dopamine as well as simultaneous detection of dopamine and uric acid using 0.1 M phosphate buffer solution (pH 7.00) as the base solution. In both case, electro-oxidation peak currents of dopamine were linearly related to accumulated concentration over a wide concentration range of 5.0 × 10(-8) to 3.0 × 10(-5) M. However in the same range of dopamine concentration, the sensitivity had a significant loss at Pt/Pd/TiO(2) NTs electrode, suggesting the necessity for Au nanoparticles in modified electrode. The limit of the detection was determined as 3 × 10(-8) M for dopamine at signal-to-noise ratio equal to 3. Furthermore, the Au/Pt/Pd/TiO(2) NTs modified electrode was able to distinguish the oxidation response of dopamine, uric acid and ascorbic acid in mixture solution of different acidity. It was shown that the modified electrode possessed a very good reproducibility and long-term stability. The method was also successfully applied for determination of DA in human urine samples with satisfactory results.     

金纳米颗粒在等离子体共振光催化剂中的作用机理研究

金纳米颗粒在等离子体共振光催化剂中具有多种不同的作用机理。本文采用溶胶-凝胶法合成了氮/碳共掺杂超薄二氧化钛(D-TiO₂)包覆的SiO₂/Au/D-TiO₂三明治型及SiO₂/D-TiO₂核壳纳米结构材料,对金纳米颗粒在含有可见光响应型半导体的等离子体共振光催化剂光催化分解水制氢反应中的作用机理进行了探索。研究结果表明,在该等离子体共振光催化剂的光催化反应过程中,金纳米颗粒同时体现出肖特基效应和等离子体共振效应作用机理,且作用机理与光生载流子的多少以及金纳米颗粒的负载量有关。负载量较低时,金纳米颗粒的作用机理与光生载流子的多少有关。而在高负载量条件下,金纳米颗粒在可见光照射下主要表现出肖特基效应对光催化活性的影响。     

有序介孔碳CMK-3负载金纳米微粒复合材料的制备和表征

分别采用等体积浸渍-甲醛还原、等体积浸渍-氢气还原及溶胶负载法在介孔碳CMK-3上负载金纳米微粒;利用透射电镜和粉末X射线衍射仪对比分析了采用3种方法得到的复合材料的微结构和相组成;并测定了采用溶胶负载法得到的不同金含量的复合材料的热稳定性.结果表明,所制备的金纳米微粒的尺寸因制备方法不同而呈现明显差异;负载于复合材料中的金纳米微粒具有很好的热稳定性.     

Ag/Au Alloy LSPR Engineering by Co‐deposition of RF‐Sputtering and RF‐PECVD

Silver‐Gold alloy/diamond like carbon (Ag‐Au/DLC) nanocomposite films were prepared by co‐deposition of RF‐sputtering and RF‐PECVD on glass substrates by using acetylene gas and silver‐gold target. The deposition process was carried out at room temperature in one minute with the variable parameters of initial pressures and RF powers. X‐ray diffraction analysis demonstrated the formation of Ag/Au alloy nanoparticles with a face‐centered cubic (FCC) structure. Localized surface plasmon and optical properties of Ag‐Au alloy nanoparticles were studied by UV‐visible spectrophotometry which showed that increasing RF power and initial pressure cause a redshift in all samples. Moreover, the effect of RF power and initial pressure on the size and shape of nanoparticles were studied by 2D Atomic force microscopy images. Energy dispersive X‐ray spectroscopy revealed the formation of Ag‐Au/DLC nanoparticles and the percentages of C, Ag, Au and O in all samples. The applied method for Ag/Au alloy preparation is the one step and low‐cost method which makes the samples ready for sensing application.     

Tunable plasmonic response from alkanethiolate-stabilized gold nanoparticle superlattices: evidence of near-field coupling

We report on the self-assembly of large-area, highly ordered 2D superlattices of alkanethiolate-stabilized gold nanoparticles ( approximately 10.5 nm in core diameter) onto quartz substrates with varying lattice constants, which can be controlled by the alkyl chain lengths, ranging from C12 (1-dodecanethiolate), C14 (1-tetradecanethiolate), C16 (1-hexadecanethiolate), to C18 (1-octadecanethiolate). These 2D nanoparticle superlattices exhibit strong collective surface plasmon resonance that is tunable via the near-field coupling of adjacent nanoparticles. The approach presented here provides a unique and viable means of building artificial "plasmonic crystals" with precisely designed optical properties, which can be useful for the emerging fields of plasmonics, such as subwavelength integrated optics.