3D wiring

FIGURE 2 A representative photograph of a gold sample after dissolution of the latex. The highly ordered, lace-hke gold structure is an analogue of a 3D wire-mesh photonic crystal scaled down to the sub-micrometer region. SOURCE Adapted from Velev et al. (1999). Reprinted with permission from Nature. 

Sievenpiper, D. F., M. E. Sickmiller, and E. Yablonovitch. 1996. 3D wire mesh photonic crystals. Physical Review Letters 76(14) 2480-2483. 

The capped sticks model can be seen as a variation of the wire frame model, where the structure is represented by thicker cylindrical bonds (figure 2-123b). The atoms are shi unk to the diameter of the cylinder and ai e used only for smoothing or closing the ends of the tubes. With its thicker bonds, the capped sticks model conveys an improved 3D impression of a molecule when compared with the wire frame model. 

In order to represent 3D molecular models it is necessary to supply structure files with 3D information (e.g., pdb, xyz, df, mol, etc.. If structures from a structure editor are used directly, the files do not normally include 3D data. Indusion of such data can be achieved only via 3D structure generators, force-field calculations, etc. 3D structures can then be represented in various display modes, e.g., wire frame, balls and sticks, space-filling (see Section 2.11). Proteins are visualized by various representations of helices, / -strains, or tertiary structures. An additional feature is the ability to color the atoms according to subunits, temperature, or chain types. During all such operations the molecule can be interactively moved, rotated, or zoomed by the user. 

Chemical and electrochemical techniques have been applied for the dimensionally controlled fabrication of a wide variety of materials, such as metals, semiconductors, and conductive polymers, within glass, oxide, and polymer matrices (e.g., [135-137]). Topologically complex structures like zeolites have been used also as 3D matrices [138, 139]. Quantum dots/wires of metals and semiconductors can be grown electrochemically in matrices bound on an electrode surface or being modified electrodes themselves. In these processes, the chemical stability of the template in the working environment, its electronic properties, the uniformity and minimal diameter of the pores, and the pore density are critical factors. Typical templates used in electrochemical synthesis are as follows ... 

Fig. 1 Schematic drawing to show the concept of system dimensionality (a) bulk semiconductors, 3D (b) thin film, layer structure, quantum well, 2D (c) linear chain structure, quantum wire, ID (d) cluster, colloid, nanocrystal, quantum dot, OD. In the bottom, it is shown the corresponding density of states [A( )] versus energy (E) diagram (for ideal cases).

A better picture, which we keep as a mental reservation when confronted with the conventional drawings, is the contour diagram. A better sense of the n overlap from two p orbitals is given in Fig. 1.24, where we see more clearly from the contours on the left that in the bonding combination there is an enhanced electron population between the nuclei, but that it is no longer directly on a line between the nuclei. The wire-mesh diagrams illustrate the shapes of the n and n orbitals with some sense of their 3D character. 

Though quantum dots are typically thought of as OD nanostructures, quantum confinement effects are also exhibited in ID nanowires and nanorods. Buhro and coworkers have studied the effect on both size and shape on quantum confinement (Yu, H. Li, J. Loomis, R. A. Wang, L.-W. Buhro, W. E. Nature Mater. 2003, 2, 517). Their work provides empirical data to back up the theoretical order of increasing quantum confinement effects dots (3D confinement) > rods > wires (2D confinement) > wells (ID confinement). For an example of an interesting nanostructure comprised of both a nanorod and nanodot, see Mokari, T Sztrum, C. G. Salant, A. Rabani, E. Banin, U. Nature Mater. 2005,4, 855. 

Charge carriers in semiconductors can be confined in one spatial dimension (ID), two spatial dimensions (2D), or three spatial dimensions (3D). These regimes are termed quantum films, quantum wires, and quantum dots as illustrated in Fig. 9.1. Quantum films are commonly referred to as single quantum wells, multiple quantum wells or superlattices, depending on the specific number, thickness, and configuration of the thin films. These structures are produced by molecular beam epitaxy (MBE) and metalorganic chemical vapor deposition (MOCVD) [2j. The three-dimensional quantum dots are usually produced through the synthesis of small colloidal particles. 

As was mentioned earlier, CHQ nanotube arrays can be utilized in promising templates for nanosynthesis. Redox reaction of the nanotube in the presence of silver nitrate leads to the formation of silver nanowire arrays in the pores (pore size of 8 X 8 A ) of the CHQ nanotube. The wires exist as uniformly oriented 3D arrays of ultrahigh density. The driving force for the formation of these nanowires is the free energy gain due to the reduction-oxidation process [154,155]. It was experimentally observed that the resulting nanowire is comprised of four dumbbells, each of which contains two silver atoms, superimposed on one another, and crisscrossed in their length. 

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