Carbon nanotube dative junction assembly Dative (dipolar) bonds are a potentially valuable form of noncovalent interaction for use in diamondoid and macromolecular nanostructures. These interactions require a lone pair donor, such as the lone pair of nitrogen, and an acceptor, such as the empty sp2 orbital or boron. Boron and nitrogen are both good structural replacements for the C-H fragments found in hydrocarbons (nitrogen because it is isoelectronic with the C-H unit, boron because it can accommodate three covalent bonds to leave the last orbital empty). In this design, carbon nanotubes are functionalized with adamantane-based dative hinges that lock each fragment into place to form the extended network. (grey = carbon, white = hydrogen, blue = nitrogen, green = boron; left: van der Waals rendering. right: ball-and-stick rendering) These designs are the result of a collaboration with Dr. Ralph Merkle into the application of the dative bond in molecular building block approaches for molecular-based materials design.Carbon nanotube dative junction assembly
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Crimp junctions for perpendicular carbon nanotube scaffolding In this design, two rigid diamondoid rings are fused at a quasi-tetrahedral junction and sized, through the addition or subtraction of repeat subunits in each ring, to accommodate two carbon nanotubes of different diameters. The crimping of the nanotubes is a result of van der Waals packing of the rings, a feature that can be enhanced or removed by adjusting the ring size. (grey = carbon, white = hydrogen, blue = nitrogen, red = oxygen)
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Low-friction bearing assembly with two carbon allotropes In this design, two diamondoid rings replace small segments of a carbon nanotube, providing a lock for a third, larger ring. The larger ring includes a stitch-work of oxygens to create an electron-rich interior whose effective circular van der Waals packing just touches that of the nanotube framework.
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Rigid rod-based nanomechanical gear assembly Here, a five-fold rotation axis in a single rigid rod is coupled to four rings composed of 15 subunits each. A pagodanoid junction is included along this rigid rod to raise the five sections of the assembly to create an elevated gearing system. The image at left is a van der Waals representation. At right, only the oxygen and nitrogen atoms are shown (as spheres) to highlight the rod interior. (grey = carbon, white = hydrogen, blue = nitrogen, red = oxygen) All images are the result of molecular mechanics structure calculations using either Tinker (MM2 parameters) or NAMD (CHARMM). Images were made with VMD. VMD and NAMD are developed with NIH support by the Theoretical and Computational Biophysics group at the Beckman Institute, University of Illinois at Urbana-Champaign. Tinker is a product of the Ponder Lab in the Department of Biochemistry and Molecular Biophysics at the Washington University School of Medicine. E. Zelman and Apple Computer are thanked for their generous donation of resources.
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纳米团簇的制备
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Core/shell nanoparticles
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Gold Nano Anchors Put Nanowires in Their Place Scanning electron microscope image shows rows of horizontal zinc-oxide nanowires grown on a sapphire surface. The gold nanoparticles are visible on the ends of each row Illustration shows how crystalline zinc oxide nanowires (blue) push "seeds" of gold nanoparticles (red) forward as they grow Researchers at the National Institute of Standards and Technology (NIST) have demonstrated a technique for growing well-formed, single-crystal nanowires in place—and in a predictable orientation—on a commercially important substrate. The method uses nanoparticles of gold arranged in rows on a sapphire surface as starting points for growing horizontal semiconductor "wires" only 3 nanometers (nm) in diameter. Other methods produce semiconductor nanowires more than 10 nm in diameter. NIST chemists' work was highlighted in the Oct. 11 issue of Applied Physics Letters.* Part of the vision of nanotechnology is the possibility of building powerful, extraordinarily compact sensors and other devices out of atomic-scale components. So-called “nanowires”—long thin crystals of, e.g., a semiconductor— could not only link nanoelectronic devices like conventional wire but also function as devices themselves, tipped with photodetector or light-emitting elements, for example. An obvious stumbling block is the problem of working with components so small that only the most sophisticated measurement instruments can even track them. To date, the most successful nanowire alignment method involved growing large numbers of the rod-like crystals on a suitable base like blades of grass, shearing them off, mixing them in a solvent, and forcing them to align by either flow or surface confinement on the test substrate to orient most of the crystals in a specific horizontal direction. Further photolithography steps are required to ensure that nanowires are positioned correctly. In contrast, the NIST technique grows arrays of nanowires made of zinc oxide, a semiconductor widely used in optoelectronics, with precise alignments. The gold "anchors" are placed with a chemical etching step and the orientation of the wires—horizontal, vertical or at a 60 degree angle from the surface—is determined by tweaking the size of the gold particles.
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"Anatomy of a Nanoprobe"
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Professor Charles M. Lieber Group A schematic illustration of the chemical force microscopy setup used to stretch and break duplex DNA. The inset shows a cartoon representations between two complementary strands immobilized on the tip and sample surfaces. The DNA shown in the cartoon corresponds to the relaxed B-DNA conformation
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Magnetic Nanotubes Dr. Rafal E. Dunin-Borkowski, University of Cambridge Department of Materials Science & Metallurgy Gallery The nanotubes were fabricated in the University of Cambridge Engineering department by Yasuhiko Hayashi, who grew them using a Cobalt-Palladium catalyst. This alloy remains present in the ends of the nanotubes, and is magnetic. The nanotubes you see here have a 70-100nm diameter. Characterisation of the magnetic properties was carried out by Ed Simpson and Takeshi Kasama using Electron Holography, a TEM technique which records the phase of an electron wave. The phase, being affected by any magnetic field the electron passes through, therefore records any information on the magnetic properties on the sample under investigation. From this, the magnetic induction maps you see here can be generated. The colours represent the direction and intensity of the field, and the contours, the magnetic field lines. It is an entirely quantitative technique, so as well as these images of the field, the magnetic moment, for instance, can be deduced too.
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Magnetic field of an iron crystal inside a carbon nanotube This image won First Prize in the "Science Close-Up" category in the Daily Telegraph Visions of Science competition. The image shows a multi-walled carbon nanotube, approximately 190nm in diameter, containing a 35-nm-diameter iron crystal encapsulated inside it. Electron holography has been used to obtain a map of the magnetic field surrounding the iron particle, at a spatial resolution of approximately 5nm. The magnetic phase contours show that the particle contains a single magnetic domain. An external magnetic field could be applied to such particles to exert a torque on the surrounding nanotube.
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Crystal Kaleidoscope This is a false colour convergent beam electron diffraction pattern recorded at 150kV parallel to the three-fold axis of lanthanum aluminate. In addition to the mesh of reflections at the centre, the pattern also shows concentric circles of reflections in successive higher order Laue zones. Odd numbered zones have only a single branch of intensity that corresponds to scattering solely from the oxygen atoms in the structure.
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Magnetic Rock The image shows the magnetic microstructure in a natural, finely exsolved intergrowth of magnetite blocks in an ulvospinel matrix, which is influenced both by the shapes of the individual magnetite blocks and by magnetostatic interactions between them. Different colours correspond to different directions of magnetic induction in the sample
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Magnetic field lines in a bacterial cell The image shows the magnetic field lines in a single bacterial cell. The fine white lines are the magnetic field lines in the cell, which were measured using off-axis electron holography. Such bacteria live in sediments and bodies of water, and move parallel to geomagnetic field lines as a result of the torque exerted on their magnetosome chains by the earth's magnetic field.
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'Dancing' quantum dot Plan view bright field transmission electron micrograph of a germanium/silicon quantum dot in a silicon matrix. The quantum dot, grown by molecular beam epitaxy, is coherently strained due to Ge/Si crystal lattice mismatches giving rise to strain induced banding contours. The straight edge at the top left shows the Si 110 plane. Field of view is approximately 620nm wide. Acknowledgments: Diana Zhi, Paul Midgley, Rafal Dunin-Borkowski, Don W. Pashley, Bruce A. Joyce
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Yttrium barium copper oxide 'dragonflies' Internal structure of yttrium barium copper oxide (YBCO) ink, prepared by sol-gel methods. The superconducting YBCO ink is jet-printed onto the substrate. Cracking occurs when the stable YBCO ink dries too quickly, giving this 'dragonfly' effect. Image taken by optical microscopy. Diagonal length of image approximately 125 microns. Acknowledgments: Tarek Mouganie, Bartek A. Glowacki
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Design of the Month: Worm Drive Assembly This worm drive assembly designed by K. Eric Drexler, Josh Hall, Ninad Sathaye and Mark Sims includes 11 components totalling 25,374 atoms. The animations below have been created from simulation results using NanoEngineer-1 Alpha 7, taking just over 370 hours to complete on a Dell laptop running WindowsXP. It is the largest model ever simulated with NanoEngineer-1. More information about this model is coming soon.
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MarkIII(k) Planetary Gear Name: MarkIII(k) Designer: K. Eric Drexler Date: 2004 Number of components: 12 Number of atoms: 3,853 Width: 4.2 nm Height: 4.2 nm Depth: 4.2 nm Gear Ratio: 45:16 Speed Ratio: 2.8125:1 Output Torque: > 1x10–18 m-N Angular Speed > 10 GHz Power > 1 nW Power Density > 10 GW/cm2 Efficiency > 99.8% This is the MarkIII(k), a planetary gear created by K. Eric Drexler. A planetary gear couples an input shaft via a sun gear to an output shaft through a set of planet gears (attached to the output shaft by a planet carrier). The planet gears roll between the sun gear and a ring gear on the inner surface of a casing. The animation below was produced from a NanoEngineer-1 molecular dynamics simulation. A section of the casing atoms have been hidden to expose the internal gearing assembly. Planetary gears are attractive targets for molecular modeling because (with careful choice of planet numbers and sun- and ring-gear symmetries) the overall symmetry of the system virtually guarantees low energy barriers along the desired motion coordinate. They also pack considerable complexity into a small structure. Planetary gears are common mechanical systems used for speed reduction (= torque multiplication). Macroscale versions are found in automobile transmissions, electric screwdrivers, and Mars landers. The MarkIII(k) gear updates an early 1990s design by Drexler and Merkle, modified to reduce interactions between the sun gear and the bases of the planet gears. The original version was designed with very small moving parts in order to fit the computational constraints of the time. The planet gears are near the lower limits of diameter for functional gear components, and because of this, the "gear teeth" in this system are better thought of as smooth, low-amplitude corrugations in the gear surfaces The single covalent (sigma) bonds linking each of the nine planet gears to the carrier gear are easily seen in this POV-Ray image.
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Drexler-Merkle Differential Gear Name: Differential Gear Designers: K. Eric Drexler and Ralph Merkle Date: 1995 Number of components: 7 Number of atoms: 8,292 Width: 5.8 nm Height: 5.8 nm Depth: 5.8 nm This molecular differential gear was designed by K. Eric Drexler and Ralph Merkle sometime around 1995 while together at Xerox PARC. Here you can clearly see the casing and six components of the internal assembly as each is hidden in the cutaway view. This animation loop shows the results of a molecular dynamics simulation done with NanoEngineer-1. It is the first time the Drexler-Merkle differential gear has ever been simulated. While the individual frames of the animation loop were rendered using POV-Ray, NanoEngineer-1 generated the POV-Ray files automatically. The gearbox casing was hidden to expose the internal gearing mechanism. Notice that the front and back shafts rotate in opposite directions. If you'd like to see how this was done, click "How I Simulated the Drexler-Merkle Differential Gear". Dr. Drexler provides the following brief description of the differential gear: In this view the two cylindrical shafts and their facing bevel (conical) gears are shown, along with two of the four casing-mounted pinion gears that mesh with both shaft-gears. Acceptably smooth motion (despite the atomic granularity of the building blocks) is made possible by geometry and symmetries. For example, the shaft-gears have 14-fold symmetry, while the casing has 4-fold symmetry; if one pinion gear is exactly opposite a shaft-gear tooth, its 90-degree partners will be opposite shaft-gear grooves. Thus, energy fluctuations at the tooth-meshing frequency will cancel, leaving only higher-frequency, lower-amplitude fluctuations as barriers to rotation. The shafts rotate in the casing on standard sliding-interface bearings, using the same principle to achieve smooth motion. The lowest quality bearings are those between the pinion gears and the casing, which lack the regularity required for high smoothness. The structure is designed to be built chiefly of hydrogen (white), carbon (gray), silicon (black), nitrogen (blue), phosphorus (purple), oxygen (red), and sulphur (yellow). The larger size of second-row atoms helps in constructing tapered gears and reduces the number of atoms needed to construct the outer cylinder of the casing. Such structures are far beyond the state of the art of chemical synthesis today, but their design and modeling is becoming straightforward. - K. Eric Drexler
