Nanocavity

Formation of nanometer-sized cavities could also enhance the mechanical properties of sohd materials to a certain extent [14-16]. For instance. Si atomic vacancy could trap oxygen atom to reduce its diffusivity [17]. He implantation induces 1-nm-sized bubbles that enhance the hardness of Ni layers by 

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Elosua, C., Bariain, C., Matias, I.R., Arregui, F.J., Luquin, A., Vergara, E. and Laguna, M. (2008) Indicator immobilization on Fahry-Perot nanocavities towards development of fiber optic sensors. Sensor and actuators B, 130, 158-163. 

The second procedure is different from the previous one in several aspects. First, the metallic substrate employed is Au, which does not show a remarkable dissolution under the experimental conditions chosen, so that no faradaic processes are involved at either the substrate or the tip. Second, the tip is polarized negatively with respect to the surface. Third, the potential bias between the tip and the substrate must be extremely small (e.g., -2 mV) otherwise, no nanocavity formation is observed. Fourth, the potential of the substrate must be in a region where reconstruction of the Au(lll) surface occurs. Thus, when the bias potential is stepped from a significant positive value (typically, 200 mV) to a small negative value and kept there for a period of several seconds, individual pits of about 40 nm result, with a depth of two to four atomic layers. According to the authors, this nanostructuring procedure is initiated by an important electronic (but not mechanical) contact between tip and substrate. As a consequence of this interaction, and stimulated by an enhanced local reconstruction of the surface, some Au atoms are mobilized from the Au surface to the tip, where they are adhered. When the tip is pulled out of the surface, a pit with a mound beside it is left on the surface. The formation of the connecting neck between the tip and surface is similar to the TILMD technique described above but with a different hnal result a hole instead of a cluster on the surface (Chi et al., 2000). 

Hazra P, Chakrabarty D, Chakraborty A, Sarkar N (2004) Intramolecular charge transfer and solvation dynamics of Nile red in the nanocavity of cyclodextrins. Chem Phys Lett 388(1-3) 150-157... 

Akahane Y., Asano T., Song B.S. and Noda S., High-Q photonic nanocavity in a two-dimensional photonic crystal, Nature 2003 425 944-947. 

Kojima, M., Nakajoh, M., Matsubara, C. and Hashimoto, S. (2002). Photooxygenation of aromatic alkenes in zeolite nanocavities. J. Chem, Soc. Perkin Trans. 2, 1894-1901... 

In this form sPS can absorb reversibly certain analytes, whose size and shape well fit the nanocavities establishing specific host guest interactions, when exposed to vapor or liquid environment where these compounds are present even in traces. 

Fig. 12.10 (a) SEM image of the circular Bragg nanocavity designed to support the m 0 mode in the 300 nm wide central pillar, (b) The evolution of the emitted spectrum from the device shown in Fig. 12.9a as a function of the pump intensity. Inset L L curve, indicating a lasing threshold of Pth 900 pW. (c) Calculated modal intensity profile of the nanocavity, (d) IR image of the emitted beam profile... 

Figure 12.10c shows a contour plot of the nanolaser index profile superimposed on a cross-section of the modal field intensity profile in the center of the active medium. As shown in the figure, the modal profile of the nanocavity is confined almost completely in the 300-nm wide central pillar with a modal volume of 0.213 (1/n)3 (0.024 pm3) only 1.75 times the theoretically possible limit of a cubic half... 

Scheuer, J. Green,W. M. J. DeRose, G. Yariv, A., Lasing from a circular Bragg nanocavity with an ultra small modal volume, Appl. Phys. Lett. 2005, 86, 251101... 

Schmidt, B. Almeida, V. Manolatou, C. Preble, S. Lipson, M., Nanocavity in a silicon waveguide for ultrasensitive nanoparticle detection, Appl. Phys. Lett. 2004, 85, 4854 4856... 

Painter O., Srinivasan, K., O Brien, J.D., Scherer, A., and Dapkus, P.D., 2001, Tailoring of the resonant mode properties of optical nanocavities in two-dimensional photonic crystal slab waveguides, J. Opt A Pure Appl. Opt. 3 S161-S170. 

Relatively straightforward is the definition of nanoscopic voids. Nanopores and nanocavities are elongated voids or voids of any shape, and nanomaterials can incorporate especially nanopores in an ordered or disordered way. The former is of crucial importance for many of the hybrid materials discussed in the book (e.g., in Chapters 16 or 18). Nanochannel is also frequently used instead of nanopore, often in biological or biochemical contexts. Besides nanoporous, the term mesoporous is often found in hybrid materials research. Interestingly, the IUPAC has defined the terms mesoporous (pores with diameters between 2 and 50 nm), microporous (pores with diameters <2 nm) and macroporous (pores with diameters >50 nm), yet has not given a definition of nanoporous in the IUPAC Recommendations on the Nomenclature of Structural and Compositional Characteristics of Ordered Microporous and... 

The features of the electrode used in this gas-phase electrocatalytic reduction of C02 are close to those used in PEM fuel cells [37, 40, 41] (e.g. a carbon cloth/Pt or Fe on carbon black/Nafion assembled electrode, GDE). The electrocatalysts are Pt or Fe nanoparticles supported on nanocarbon (doped carbon nanotubes), which is then deposited on a conductive carbon cloth to allow the electrical contact and the diffusion of gas phase C02 to the electrocatalyst. The metal nanoparticles are at the contact of Nation, through which protons diffuse. On the metal nanoparticles, the gas-phase C02 reacts with the electrons and protons to be reduced to longer-chain hydrocarbons and alcohols, the relative distributions of which depend on the reaction temperature and type of metal nanoparticles. Isopropanol forms selectively from the electrocatalytic reduction of C02 using a gas diffusion electrode based on an Fe/N carbon nanotube (Fe/N-CNT) [14, 39, 40]. Not only the nature of carbon is relevant, but also the presence of nanocavities, which could favor the consecutive conversion of intermediates with formation of C-C bonds. 

Finally, it is increasingly clear that molecules confined in the zeolitic nanocavities see their electronic properties modified. It has been shown for instance (19) that the dipole moment of acetonitrile increases significantly upon its introduction in the side pockets of MOR compared to the linear channels of the same zeolite. The guest molecule is made more basic and is easily protonated in such a confined environment. Zeolites also act as solid solvents and the anionic framework acts as the conjugate base of the proton thereby stabilizing some charged intermediates along concerted catalytic pathways. 

Liu Y, Bishop J, Willians L, Blair S, Herron J (2004) Biosensing based upon molecular confinement in metallic nanocavity arrays. Nanotechnology 15 1368-1374... 

Fig. 8 Experimental scheme of a spectral transmission experiment of a photonic crystal Bragg reflector micro-cavity fabricated out of refilled holes in silicon. The central refilled hole acts on a nanocavity. AuNPs are immobilized in and around the central nanocavity...

Key words Whispering gallery modes, nanostructure, microcrystal, nanocavity, polarization... 

K. Ariga, D. Sakai, T. Ogata, J. Kikuchi, Molecular Recognition by Wall-Assembling-Type Nanocavity in Aqueous Media , J. Nanosci. Nanotech., 2,41 (2002). 

Shape The radiative emission from molecules confined within metallic nanocavities and on the surface of nanoparticles is of great relevance to biotechnology. In 1986, it has been suggested that fluorescence enhancement and reduced observation volumes could be obtained from small metal apertures (85). Nanocavities of different shapes could induce different surface plasmon (SP) fields. More recently, some studies has been done for different shapes, such as circular (86-90), elliptical (91), coaxial (92), or rectangular (93, 94) metallic nanocavity(95). In 2003, single-molecule detection from a nanocavity was demonstrated (86). However, it might be difficult to position the biospecies in the nanocavities. 

Mahdavi, F., Liu, Y., Blair, S., (2007). Modeling Fluorescence Enhancement from Metallic Nanocavities. Plasmonics 2 129-141. 

Manna, L., De Vittorio, M., Cingolani, R., and Arakawa, Y. (2008). Two-Dimensional photonic crystal resist membrane nanocavity embedding colloidal dot-in-a-rod nanocrystals. Nano Lett, 8,1 260-264. 

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