Formation of Monolayer Films by the Spontaneous Assembly of Organic Thiols from Solution Onto Gold.
About: This article is published in ChemInform.The article was published on 1989-04-11. It has received 327 citations till now. The article focuses on the topics: Monolayer.
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TL;DR: A link between interfacial bonding character and thermal conductance at the atomic level is experimentally demonstrated, which will enable future quantification of other interfacial phenomena and will be a critical tool to stimulate and validate new theories describing the mechanisms of interfacial heat transport.
Abstract: Interfaces often dictate heat flow in micro- and nanostructured systems. However, despite the growing importance of thermal management in micro- and nanoscale devices, a unified understanding of the atomic-scale structural features contributing to interfacial heat transport does not exist. Herein, we experimentally demonstrate a link between interfacial bonding character and thermal conductance at the atomic level. Our experimental system consists of a gold film transfer-printed to a self-assembled monolayer (SAM) with systematically varied termination chemistries. Using a combination of ultrafast pump-probe techniques (time-domain thermoreflectance, TDTR, and picosecond acoustics) and laser spallation experiments, we independently measure and correlate changes in bonding strength and heat flow at the gold-SAM interface. For example, we experimentally demonstrate that varying the density of covalent bonds within this single bonding layer modulates both interfacial stiffness and interfacial thermal conductance. We believe that this experimental system will enable future quantification of other interfacial phenomena and will be a critical tool to stimulate and validate new theories describing the mechanisms of interfacial heat transport. Ultimately, these findings will impact applications, including thermoelectric energy harvesting, microelectronics cooling, and spatial targeting for hyperthermal therapeutics.
570 citations
TL;DR: The use of the immobilization and manipulation of combinatorial mixtures of DNA on a support to solve a NP-complete problem, and considers a small example of the satisfiability problem (SAT), in which the values of a set of boolean variables satisfying certain logical constraints are determined.
Abstract: DNA computing was proposed1 as a means of solving a class of intractable computational problems in which the computing time can grow exponentially with problem size (the ‘NP-complete’ or non-deterministic polynomial time complete problems). The principle of the technique has been demonstrated experimentally for a simple example of the hamiltonian path problem2 (in this case, finding an airline flight path between several cities, such that each city is visited only once3). DNA computational approaches to the solution of other problems have also been investigated4,5,6,7,8,9. One technique10,11,12,13 involves the immobilization and manipulation of combinatorial mixtures of DNA on a support. A set of DNA molecules encoding all candidate solutions to the computational problem of interest is synthesized and attached to the surface. Successive cycles of hybridization operations and exonuclease digestion are used to identify and eliminate those members of the set that are not solutions. Upon completion of all the multi-step cycles, the solution to the computational problem is identified using a polymerase chain reaction to amplify the remaining molecules, which are then hybridized to an addressed array. The advantages of this approach are its scalability and potential to be automated (the use of solid-phase formats simplifies the complex repetitive chemical processes, as has been demonstrated in DNA and protein synthesis14). Here we report the use of this method to solve a NP-complete problem. We consider a small example of the satisfiability problem (SAT)2, in which the values of a set of boolean variables satisfying certain logical constraints are determined.
505 citations
TL;DR: The purely elastic response of these ultrathin membranes, coupled with exceptional robustness and resilience at high temperatures should make them excellent candidates for a wide range of sensor applications.
Abstract: Nanoparticle superlattices are hybrid materials composed of close-packed inorganic particles separated by short organic spacers. Most work so far has concentrated on the unique electronic, optical and magnetic behaviour of these systems. Here, we demonstrate that they also possess remarkable mechanical properties. We focus on two-dimensional arrays of close-packed nanoparticles and show that they can be stretched across micrometre-size holes. The resulting free-standing monolayer membranes extend over hundreds of particle diameters without crosslinking of the ligands or further embedding in polymer. To characterize the membranes we measured elastic properties with force microscopy and determined the array structure using transmission electron microscopy. For dodecanethiol-ligated 6-nm-diameter gold nanocrystal monolayers, we find a Young's modulus of the order of several GPa. This remarkable strength is coupled with high flexibility, enabling the membranes to bend easily while draping over edges. The arrays remain intact and able to withstand tensile stresses up to temperatures around 370 K. The purely elastic response of these ultrathin membranes, coupled with exceptional robustness and resilience at high temperatures should make them excellent candidates for a wide range of sensor applications.
419 citations
TL;DR: In this paper, the authors reported the synthesis of a tough α-Si3N4 solid solution with this kind of microstructure, which is 40% harder than β-Si 3N4 and is equally strong and tough.
Abstract: Silicon nitride (Si3N4) is a light, hard and strong engineering ceramic1,2. It can withstand harsh environments and support heavy loads at temperatures beyond those at which metals and polymers fail. It can also be manufactured reliably at a reasonable cost and in large quantities. There are two forms of silicon nitride3: α-Si3N4 and β-Si3N4. The former is harder, but only the latter is currently used in engineering applications, because only this form can be given a microstructure resembling a whisker-reinforced composite1,2,4, which gives it the necessary toughness and strength. Here we report the synthesis of a tough α-Si3N4 solid solution with this kind of microstructure. This material is 40% harder than β-Si3N4 and is equally strong and tough. Its hardness (22 GPa) is exceeded only by boron carbide and diamond (which are both brittle). These properties mean that this form of α-Si3N4 should be preferred over β-Si3N4 for all engineering applications, and it should open up new potential areas in which the ceramic can be applied.
385 citations
TL;DR: The key steps of each analytical procedure, namely DNA-probe immobilisation, hybridisation, labelling and electrochemical investigation of the surface, are discussed in detail with separate sections devoted to label-free and newly emerging magnetic assays.
379 citations
Cites background from "Formation of Monolayer Films by the..."
...The assumed reaction between a thiolate compound and a gold substrate is RSH+ Au ↔ RS-Au+ e− + H+ Although dense monolayers assemble in less then 1 h, well ordered monolayers can take days to form (Bain et al., 1989)....
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References
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TL;DR: In this paper, the authors used contact angles and optical ellipsometry to study the kinetics of adsorption of monolayer films and to examine the experimental conditions necessary for the formation of high-quality films.
Abstract: : Long-chain alkanethiols, HS(CH2)nX, adsorb from solution onto gold surfaces and form ordered, oriented monolayer films. The properties of the interfaces between the films and liquids are largely independent of chain length when n > 10; in particular, wetting is not directly influenced by the proximity of the underlying gold substrate. The specific interaction of gold with sulfur and other soft nucleophiles and its low reactivity toward most hard acids and bases make it possible to vary the structure of the terminal group, X, widely and thus permit the introduction of a great range of functional groups into a surface. Studies of wettability of these monolayers, and of their composition using X-ray photoelectron spectroscopy (XPS), indicate that the monolayers are oriented with the tail group, X, exposed at the monolayer-air or monolayer- liquid interface. The adsorption of simple n-alkanethiols generates hydrophobic surfaces whose free energy (19 mJ/sq. m) is the lowest of any hydrocarbon surface studied to date. Measurement of contact angles is a useful tool for studying the structure and chemistry of the outermost few angstroms of a surface. This work used contact angles and optical ellipsometry to study the kinetics of adsorption of monolayer films and to examine the experimental conditions necessary for the formation of high-quality films.
3,193 citations