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We present an experimental and theoretical study of the optical transmission of a thin metal screen perforated by two subwavelength slits, separated by many optical wavelengths. The total intensity of the far-field double-slit pattern is shown to be reduced or enhanced as a function of the wavelength of the incident light beam. This modulation is attributed to an interference phenomenon at each of the slits, instead of at the detector. The interference arises as a consequence of the excitation of surface plasmons propagating from one slit to the other. DOI: 10.1103/PhysRevLett.94.053901 PACS numbers: 42.79.Dj, 73.20.Mf, 78.66.Bz Recently, there has been a surge of interest in the phenomenon of light transmission through subwavelength apertures in metal plates. This followed the observation by Ebbesen et al. [1] that the transmission through a twodimensional hole array can be much larger than predicted by conventional diffraction theory [2]. This discovery has rekindled the interest in a similar but simpler problem, viz., the transmission of a one-dimensional array of subwavelength slits in a metal film, i.e., of a metal grating [1,[3][4][5][6][7][8][9][10][11][12][13][14][15][16]. In many cases the enhanced transmission of hole or slit arrays has been explained in terms of the excitation of (coupled) surface plasmons on the metal film [3][4][5][6], an explanation that has recently been challenged [16]. It has been shown that, for slit arrays, Fabry-Pérot-type waveguide resonances can also give rise to a considerably enhanced transmission [5,7,9,10,12].In the present Letter we study an even more fundamental system than the metallic grating, namely, a thin metal layer perforated by just two parallel subwavelength slits. In contrast to the systems that have recently attracted so much attention, our slits are separated by many optical wavelengths. Thus we study the light transmission of a setup that lies at the heart of wave physics, namely, that of Thomas Young. We do, however, not focus on the wellknown interference pattern named after him, but on the angle-integrated power transmission coefficient of the perforated screen, i.e., the transmission integrated over many interference orders. We show that this transmission coefficient is strongly modulated as a function of the wavelength of the incident light for the case that that light is TMpolarized, i.e., with the electric field aligned perpendicular to the slits. In contrast, there is no such modulation when the incident light is TE-polarized, or when the ''wrong'' metal is chosen. All our observations can be explained in terms of a model involving the coherent transport of electromagnetic energy between the slits by surface plasmons.Our samples consist of a 200 nm thick gold film, evaporated on top of a 0.5 mm thick fused quartz substrate with a 10 nm thick titanium adhesion layer between the gold and the glass. In such a sample a two-slit pattern is written using a focussed ion beam, each slit being 50 m long and 0:2 m wide. The slits are separated by a dis...

Nanoporous materials are often accessed by a supramolecular approach using soft matter templates. Porous silicates and organosilicates synthesized by wet chemistry processes have been intensively studied for the last 20 years. Due to the versatility of the sol-gel chemistry, thermally sensitive bonds, organic molecules [1] and polymers [2] can be introduced either at the pore surfaces or in the network, and pore size, distribution and organization can be controlled as well.[3] The combination of the most important properties of the inorganic and organic components, coupled with the control of the "empty space" has suggested many potential applications for these materials.[4] For example, several thin-film applications in emerging optical, electronic, biological and filtration technologies have been envisioned. [5,6] Until now, a major roadblock in the realization of technological applications for these materials seems to be their poor mechanical properties. Indeed, the incorporation of pores into brittle glasses often has a catastrophic effect on their mechanical and fracture properties. This behavior is even more pronounced when moving from silicate to organosilicate materials (ORMOSILS) due to a decrease in network atom connectivity, impacting potential applications for these materials. A case in point is the observation that the fracture energy value, G c , for dense methylsilsesquioxane (MSSQ) glass is typically less than 5 J.m -2 , as compared to 10 J.m -2 for SiO 2 . [7] The presence of methyl substituents, while useful to lower the dielectric constant, generate free volume and impart hydrophobicity, simultaneously reduces the density, modulus, hardness and fracture energy. [7][8][9][10] We have recently demonstrated that these organosilicates show a strong power relationship dependence between film density and mechanical properties (e.g. modulus and fracture resistance), resulting in a rapid decay of the latter with increase in porosity. [7] For MSSQ materials, unfortunate consequences of this are: a) at low level of porosity the modulus decreases extremely rapidly (e.g. 50 % reduction at 15 vol.% porosity), b) at higher porosities (> 30 %), the modulus vs density curves tend to converge, abrogating any anticipated benefits by starting from dense materials with higher modulii.[11] Without acceptable fracture resistance, porous organosilicate glasses would be of little utility in any of the applications cited above. This statement is especially applicable to microelectronics, where dense organosilicate materials containing varying amount of Si-Me substitutents (k = 2.7-3.0) are currently used as the insulating layers in 90 nm interconnect technology, [12,13] and porous analogs will be implemented in future electronic devices. [14,15] Escalating integration issues are anticipated for materials with increased porosity since many of the integration processes require good mechanical properties (e.g. chemical mechanical polishing, chip dicing, wire bonding, etc). [16,17] Mechanical instability and the associated...

The complex [MnII(R,R-mcp)(CF3SO3)2] is an efficient and practical catalyst for the epoxidation of electron-deficient olefins. This catalyst is capable of epoxidizing olefins with as little as 0.1 mol % catalyst in under 5 min using 1.2 equiv of peracetic acid as the terminal oxidant. A wide scope of substrates are epoxidized including terminal, tertiary, cis and trans internal, enones, and methacrylates with >85% isolated yields.

[reaction: see text] An organocatalytic route to narrowly dispersed poly(carbosiloxanes) of predictable molecular weight and end group fidelity is described. N-Heterocyclic carbenes (NHC) and 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) catalyze the ring opening of cyclic carbosiloxanes. The pK(b) of the catalyst is important in preventing adverse transetherification reactions and obtaining well-defined polymers. Mechanistic studies indicate that hydrogen bonding to TBD or the NHC activates alcohols or silanols for ring-opening reactions.

We explore the application of a high-temperature precursor delivery system for depositing high boiling point organosilicate precursors on plastics using atmospheric plasma. Dense silica coatings were deposited on stretched poly(methyl methacrylate), polycarbonate and silicon substrates from the high boiling temperature precursor, 1, 2-bis(triethoxysilyl)ethane, and from two widely used low boiling temperature precursors, tetraethoxysilane and tetramethylcyclotetrasiloxane. The coating deposition rate, molecular network structure, density, Young's modulus and adhesion to plastics exhibited a strong dependence on the precursor delivery temperature and rate, and the functionality and number of silicon atoms in the precursor molecules. The Young's modulus of the coatings ranged from 6 to 34 GPa, depending strongly on the coating density. The adhesion of the coatings to plastics was affected by both the chemical structure of the precursor and the extent of exposure of the plastic substrate to the plasma during the initial stage of deposition. The optimum combinations of Young's modulus and adhesion were achieved with the high boiling point precursor which produced coatings with high Young's modulus and good adhesion compared to commercial polysiloxane hard coatings on plastics.

Hyperconnected network architectures can endow nanomaterials with remarkable mechanical properties that are fundamentally controlled by designing connectivity into the intrinsic molecular structure. For hybrid organic–inorganic nanomaterials, here we show that by using 1,3,5 silyl benzene precursors, the connectivity of a silicon atom within the network extends beyond its chemical coordination number, resulting in a hyperconnected network with exceptional elastic stiffness, higher than that of fully dense silica. The exceptional intrinsic stiffness of these hyperconnected glass networks is demonstrated with molecular dynamics models and these model predictions are calibrated through the synthesis and characterization of an intrinsically porous hybrid glass processed from 1,3,5(triethoxysilyl)benzene. The proposed molecular design strategy applies to any materials system wherein the mechanical properties are controlled by the underlying network connectivity.

Most commercially available CO detectors are based upon metal oxides or electrochemical cell technologies. None of these approaches use the selective adsorption of CO gas on a molecular complex. Conversely, cobalt(III) corroles can bind small gaseous molecules allowing them for an application as sensing components for gas detectors. Here we describe the ability of cobalt corroles to selectively coordinate carbon monoxide vs. dinitrogen and dioxygen. The coordination properties were determined in the solid state and the adsorption characteristics were compared to those of the reference compound (To-PivPP)Fe(1,2-Me2Im), known for its remarkable CO binding properties. The adsorption data evidence that the selectivity, affinity and capacity of the cobalt(III) corroles for CO are larger than those of the porphyrin complex. However, from a chemical point of view, the selectivity of cobalt(III) corroles for CO vs. O2 is infinite since these derivatives do not bind O2 while (To-PivPP)Fe(1,2-Me2Im) does with an M value (PO2(1/2)/PCO(1/2)) equal to 51. In this manuscript we also show that the affinity of cobalt(III) corroles for CO is closely related to the Lewis acid character of the central cobalt(III) ion and therefore to the nature of the substituents at the periphery of the corrole macroring.