272 research outputs found
Self-assembled Au-nanoparticle/organic films and their application as vapor-sensing chemiresistors
Synthesis of CdS and CdSe nanocrystallites using a novel single-molecule precursors approach
The synthesis of CdS and CdSe nanocrystallites using the thermolysis of several dithioor
diselenocarbamato complexes of cadmium in trioctylphosphine oxide (TOPO) is reported.
The nanodispersed materials obtained show quantum size effects in their optical spectra
and exhibit near band-edge luminescence. The influence of experimental parameters on
the properties of the nanocrystallites is discussed. HRTEM images of these materials show
well-defined, crystalline nanosized particles. Standard size fractionation procedures can
be performed in order to narrow the size dispersion of the samples. The TOPO-capped CdS
and CdSe nanocrystallites and simple organic bridging ligands, such as 2,2¢-bipyrimidine,
are used as the starting materials for the preparation of novel nanocomposites. The optical
properties shown by these new nanocomposites are compared with those of the starting
nanodispersed materials
Evolution of the electronic structure with size in II-VI semiconductor nanocrystals
In order to provide a quantitatively accurate description of the band gap
variation with sizes in various II-VI semiconductor nanocrystals, we make use
of the recently reported tight-binding parametrization of the corresponding
bulk systems. Using the same tight-binding scheme and parameters, we calculate
the electronic structure of II-VI nanocrystals in real space with sizes ranging
between 5 and 80 {\AA} in diameter. A comparison with available experimental
results from the literature shows an excellent agreement over the entire range
of sizes.Comment: 17 pages, 4 figures, accepted in Phys. Rev.
Combinatorial approaches toward patterning nanocrystals
A scheme for generating complex, spatially separated patterns of multiple types of semiconducting and/or metallic nanocrystals is presented. The process is based on lithographic patterning of organic monolayers that contain a photolabile protection group and are covalently bound to SiO2 surfaces. The process results in spatially and chemically distinct interaction sites on a single substrate. Nanocrystal assembly occurs with a high selectivity on just one type of site. We report on the production of binary, tertiary, and quatemary patterns of nanocrystals. We highlight and discuss the differences between nanocrystal/substrate assembly and molecule/substrate assembly. Finally, we investigate the assembled structures using photoluminescence and absorption spectroscopy
Complex crystal structures formed by the self assembly of di-tethered nanospheres
We report the results from a computational study of the self-assembly of
amphiphilic di-tethered nanospheres using molecular simulation. As a function
of the interaction strength and directionality of the tether-tether
interactions, we predict the formation of four highly ordered phases not
previously reported for nanoparticle systems. We find a double diamond
structure comprised of a zincblende (binary diamond) arrangement of spherical
micelles with a complementary diamond network of nanoparticles (ZnS/D); a phase
of alternating spherical micelles in a NaCl structure with a complementary
simple cubic network of nanoparticles to form an overall crystal structure
identical to that of AlCu_2Mn (NaCl/SC); an alternating tetragonal ordered
cylinder phase with a tetragonal mesh of nanoparticles described by the [8,8,4]
Archimedean tiling (TC/T); and an alternating diamond phase in which both
diamond networks are formed by the tethers (AD) within a nanoparticle matrix.
We compare these structures with those observed in linear and star triblock
copolymer systems
Crystal Growth of Thiol-Stabilized Gold Nanoparticles by Heat-Induced Coalescence
A monolayer of dodecanethiol-stabilized gold nanoparticles changed into two-dimensional and three-dimensional self-organized structures by annealing at 323 K. Subsequent crystal growth of gold nanoparticles occurred. Thiol molecules, although chemisorbed, form relatively unstable bonds with the gold surface; a few thiols desorbed from the surface and oxidized to disulfides at 323 K, because the interaction energy between thiol macromolecules is larger than that between a thiol and a nanoparticle. The gold nanoparticles approached each other and grew into large single or twinned crystals because of the van der Waals attraction and the heat generated by the exothermic formation of disulfides
Fabrication of Massive Sheets of Single Layer Patterned Arrays Using Lipid Directed Reengineered Phi29 Motor Dodecamer
The bottom-up assembly of patterned arrays is an exciting and important area in current nanotechnology. Arrays can be engineered to serve as components in chips for a virtually inexhaustible list of applications ranging from disease diagnosis to ultra-high-density data storage. Phi29 motor dodecamer has been reported to form elegant multilayer tetragonal arrays. However, multilayer protein arrays are of limited use for nanotechnological applications which demand nanoreplica or coating technologies. The ability to produce a single layer array of biological structures with high replication fidelity represents a significant advance in the area of nanomimetics. In this paper, we report on the assembly of single layer sheets of reengineered phi29 motor dodecamer. A thin lipid monolayer was used to direct the assembly of massive sheets of single layer patterned arrays of the reengineered motor dodecamer. Uniform, clean and highly ordered arrays were constructed as shown by both transmission electron microscopy and atomic force microscopy imaging
Directed Self-Assembly: Expectations and Achievements
Nanotechnology has been a revolutionary thrust in recent years of development of science and technology for its broad appeal for employing a novel idea for relevant technological applications in particular and for mass-scale production and marketing as common man commodity in general. An interesting aspect of this emergent technology is that it involves scientific research community and relevant industries alike. Top–down and bottom–up approaches are two broad division of production of nanoscale materials in general. However, both the approaches have their own limits as far as large-scale production and cost involved are concerned. Therefore, novel new techniques are desired to be developed to optimize production and cost. Directed self-assembly seems to be a promising technique in this regard; which can work as a bridge between the top–down and bottom–up approaches. This article reviews how directed self-assembly as a technique has grown up and outlines its future prospects
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