No abstract

Controlling nanoparticles with atomic precision, somewhat like the way organic chemists control small molecules by organic chemistry principles, is highly desirable for nanoparticle chemists. Recent advances in the synthesis of gold nanoparticles have opened the possibility to precisely control the number of gold atoms in a particle. In this Perspective, we will discuss a size-focusing methodology that has been developed in the synthesis of a number of atomically monodisperse ultrasmall gold nanoparticles (also called nanoclusters). We focus our discussion on thiolate-stabilized Au nanoclusters (referred to as Au n (SR) m , where n and m are the respective number of metal atoms and ligands). The underlying principle of this size-focusing process is primarily related to the peculiar stability of certain sized Au n (SR) m nanoparticle, that is, "survival of the robustest", much like the natural law "survival of the fittest". We expect that this universal size-focusing method will ultimately allow for preparing a full series of size-discrete, atomically monodisperse nanoparticles that span the size regimes of both nonplasmonic nanoclusters and plasmonic nanocrystals. These well-defined nanoparticles will be of major importance for both fundamental science research and technological applications.

In the ever-expanding field of nanomaterials research, noble metal nanoparticles have received particular interest because of their fascinating properties and potential applications in catalysis, electronics, sensing, photonics, imaging, and biomedicine.[1] The shape-dependent properties of nanoparticles have stimulated research into noble metal nanoparticles of various shapes, such as nanorods or nanowires, nanocubes, nanoprisms, nano-octahedra and tetrahedra, nanoplates, and nanoflowers or nanostars. [1,2] Our interest focuses on star-or flower-shaped nanoparticles because their surface roughness and possible high-index facets could be utilized for surfacesensitive applications, such as catalysis and surface-enhanced Raman scattering (SERS). In fact, star-shaped gold nanoparticles are very efficient for SERS [2,3] and electrochemical applications [4] and also gyromagnetic imaging. [5] Similarly, Pt and Pd nanoflowers are excellent catalysts for the reduction of ferricyanide by thiosulfate, [6] methanol electro-oxidation, [7] and as electrocatalysts in polymer-electrolyte membrane fuel cells. [8,9] The superior catalytic activity of the flower-shaped nanoparticles stems from the exposure of certain high-index facets that are intrinsically more active towards specific reactions. For example, in the benzene hydrogenation reaction, Pt(100) produces only cyclohexane, whereas Pt(111) produces cyclohexane and cyclohexene.[10] Despite these superior properties, the synthesis of noble metal nanoflowers (or nanodendrites) with high degrees of structural anisotropy and having highly active facets on their surface is still a challenge, because nanoparticles tend to acquire shapes in which the surface is covered by low-index {100} and {111} facets favored by a lower surface energy.[11] Only a few reports are known for high-yield synthesis of noble metal nanoflowers with active facets, [2][3][4][5][6][7][8][9] 12] and these works are mainly based on a seeding growth approach. In particular, to develop wet chemistry approaches, a universal method for synthesizing nanoflowers of noble metals is therefore highly desirable.Herein, we report a universal approach for one-pot, highyield synthesis of nanoflowers of Au, Pd, and Pt using an amino acid based surfactant, sodium N-(4-n-dodecyloxybenzoyl)-l-isoleucinate (SDBIL; Supporting Information, Figure S1). High-resolution transmission electron microscopy (HRTEM) studies in conjunction with selected-area electrondiffraction (SAED) and X-ray diffraction (XRD) methods reveal that the nanoflowers have high-index facets (e.g., {220} and {311}) that could be utilized to attain enhanced catalytic activity.The Suzuki-Miyaura and the Heck coupling reactions are two important noble-metal-catalyzed processes for forming CÀC bonds to produce medicines, agrochemicals, and fragrances. [13,14] The Suzuki-Miyaura coupling reaction is generally catalyzed by Pd nanoparticles in high yields, [13] whereas Pt and Au nanoparticles were poor in catalyzing this reaction. However, by suitably controlling ...

We report our findings on the important role of bromide ions in the seeding growth process of Au nanorods. The seed-mediated process constitutes a well-developed method for synthesizing gold nanorods in high yield, which is facilitated by a micelle-forming surfactant, cetyltrimethylammonium bromide (CTA-Br). Despite the tremendous work in recent years, the growth mechanism of Au nanorods has not been fully understood. Contrary to the widely accepted mechanism of CTA(+) micelle-templated growth of Au nanorods, we have identified the critical role of bromide ions in the seeding growth of Au nanorods. We found that even when the micelle-forming agent (CTA(+)) concentration is below its critical micelle concentration (cmc), bromide ions added in the form of NaBr can successfully effect the growth of Au nanorods in good yield. By controlling the concentration of externally added bromide ions, the rod shape and dimensions of the resulting Au nanoparticles can be readily controlled in the presence of only a minimum amount of CTABr (as a steric stabilizer for nanorods). High-resolution TEM studies show that the as-formed nanorods are perfectly single crystalline, instead of penta-twinned ones, and are bound by {111} and {100} facets with a [110] direction as the elongation direction. A mechanism is proposed to account for the seeding growth of single crystalline Au nanorods. Overall, this work explicitly demonstrates that Br(-) indeed serves as an important shape-directing agent for gold nanorod formation in the seed-mediated process.

The use of gold nanoparticles coated with an organic monolayer of thiol for application in chemiresistive sensors was initiated in the late 1990s; since then, such types of sensors have been widely pursued due to their high sensitivities and reversible responses to volatile organic compounds (VOCs). However, a major issue for chemical sensors based on thiol-capped gold nanoparticles is their poor long-term stability as a result of slow degradation of the monothiol-to-gold bonds. We have devised a strategy to overcome this limitation by synthesizing a more robust system using Au nanoparticles capped by trithiol ligands. Compared to its monothiol counterpart, the new system is significantly more stable and also shows improved sensitivity towards different types of polar or non-polar VOCs. Thus, the trithiol-Au nanosensor shows great promise for use in real world applications.

In the ever-expanding field of nanomaterials research, noble metal nanoparticles have received particular interest because of their fascinating properties and potential applications in catalysis, electronics, sensing, photonics, imaging, and biomedicine.[1] The shape-dependent properties of nanoparticles have stimulated research into noble metal nanoparticles of various shapes, such as nanorods or nanowires, nanocubes, nanoprisms, nano-octahedra and tetrahedra, nanoplates, and nanoflowers or nanostars. [1,2] Our interest focuses on star-or flower-shaped nanoparticles because their surface roughness and possible high-index facets could be utilized for surfacesensitive applications, such as catalysis and surface-enhanced Raman scattering (SERS). In fact, star-shaped gold nanoparticles are very efficient for SERS [2,3] and electrochemical applications [4] and also gyromagnetic imaging. [5] Similarly, Pt and Pd nanoflowers are excellent catalysts for the reduction of ferricyanide by thiosulfate, [6] methanol electro-oxidation, [7] and as electrocatalysts in polymer-electrolyte membrane fuel cells. [8,9] The superior catalytic activity of the flower-shaped nanoparticles stems from the exposure of certain high-index facets that are intrinsically more active towards specific reactions. For example, in the benzene hydrogenation reaction, Pt(100) produces only cyclohexane, whereas Pt(111) produces cyclohexane and cyclohexene.[10] Despite these superior properties, the synthesis of noble metal nanoflowers (or nanodendrites) with high degrees of structural anisotropy and having highly active facets on their surface is still a challenge, because nanoparticles tend to acquire shapes in which the surface is covered by low-index {100} and {111} facets favored by a lower surface energy.[11] Only a few reports are known for high-yield synthesis of noble metal nanoflowers with active facets, [2][3][4][5][6][7][8][9] 12] and these works are mainly based on a seeding growth approach. In particular, to develop wet chemistry approaches, a universal method for synthesizing nanoflowers of noble metals is therefore highly desirable.Herein, we report a universal approach for one-pot, highyield synthesis of nanoflowers of Au, Pd, and Pt using an amino acid based surfactant, sodium N-(4-n-dodecyloxybenzoyl)-l-isoleucinate (SDBIL; Supporting Information, Figure S1). High-resolution transmission electron microscopy (HRTEM) studies in conjunction with selected-area electrondiffraction (SAED) and X-ray diffraction (XRD) methods reveal that the nanoflowers have high-index facets (e.g., {220} and {311}) that could be utilized to attain enhanced catalytic activity.The Suzuki-Miyaura and the Heck coupling reactions are two important noble-metal-catalyzed processes for forming CÀC bonds to produce medicines, agrochemicals, and fragrances. [13,14] The Suzuki-Miyaura coupling reaction is generally catalyzed by Pd nanoparticles in high yields, [13] whereas Pt and Au nanoparticles were poor in catalyzing this reaction. However, by suitably controlling ...

No abstract

As dimension shrinks in advanced technology nodes, the critical dimension (CD) plays a critical role and so does QTime. Front Opening Unified Pod (FOUP) door closure, delaying FOUP door opening, introducing N2 Purge and creating vacuum at optimum steps and for optimized duration has shown promising results in extending QTime and improving yield. Etch is often performed by reactive ion etching (RIE) process which generally has a physical and a chemical component to it. Etch residues, sometimes polymeric with metallic contaminants embedded inside, have to be removed in timely manner. If post etch residue (PER) is not removed soon enough, this gas/polymer then interacts with moisture inside the FOUP, leading to footing at the Nitride Stress layer and crystal growth on patterned wafers -thereby degrading yield. In this paper, we will discuss various approaches taken to improve the footing at bottom of contacts and increase the Queue Time (QTime) between Etch and Cleans processes.