Showing papers in "Nano Letters in 2001"
TL;DR: In this paper, high monodisperse CdSe nanocrystals were prepared in a three-component hexadecylamine−trioctylphosphine oxide−tricylamine (HDA−TOPO−TOP) mixture, and the room-temperature quantum efficiency of the band edge luminescence was improved by surface passivation with inorganic (ZnS) or organic (alkylamines) shells.
Abstract: Highly monodisperse CdSe nanocrystals were prepared in a three-component hexadecylamine−trioctylphosphine oxide−trioctylphosphine (HDA−TOPO−TOP) mixture. This modification of the conventional organometallic synthesis of CdSe nanocrystals in TOPO−TOP provides much better control over growth dynamics, resulting in the absence of defocusing of the particle size distribution during growth. The room-temperature quantum efficiency of the band edge luminescence of CdSe nanocrystals can be improved to 40−60% by surface passivation with inorganic (ZnS) or organic (alkylamines) shells.
1,471 citations
TL;DR: Electron microscopy analysis of thin sections of the fungal cells indicated that the silver particles were formed below the cell wall surface, possibly due to reduction of the metal ions by enzymes present in the cell walls membrane.
Abstract: A novel biological method for the synthesis of silver nanoparticles using the fungus Verticillium is reported. Exposure of the fungal biomass to aqueous Ag+ ions resulted in the intracellular reduction of the metal ions and formation of silver nanoparticles of dimensions 25 ± 12 nm. Electron microscopy analysis of thin sections of the fungal cells indicated that the silver particles were formed below the cell wall surface, possibly due to reduction of the metal ions by enzymes present in the cell wall membrane. The metal ions were not toxic to the fungal cells and the cells continued to multiply after biosynthesis of the silver nanoparticles.
1,207 citations
IBM1
TL;DR: In this paper, the authors showed that n-type carbon nanotubes can be prepared not only by doping but also by simple annealing of SWNT-based p-FETs in a vacuum.
Abstract: Single wall carbon nanotubes (SWCNTs) have been used as the active channels of field effect transistors (FET). The next development step involves the integration of CNTFETs to form logic gates; the basic units of computers. For this we need to have both p- and n-type CNTFETs. However, without special treatment, the obtained CNTFETs are always p-type: the current carriers are holes and the devices are ON for negative gate bias. Here we show that n-type CNTFETs can be prepared not only by doping but also by a simple annealing of SWNT-based p-FETs in a vacuum. We use our ability to prepare both p- and n-type nanotube transistors to build the first nanotube-based logic gates: voltage inverters. Using spatially resolved doping we implemented this logic function on a single nanotube bundle.
1,196 citations
TL;DR: In this article, different kinds of safe, common, and low-cost compounds were proven to be good solvents/precursors for the synthesis of high quality CdSe nanocrystals.
Abstract: Different kinds of safe, common, and low-cost compounds were proven to be good solvents/precursors for the synthesis of high quality CdSe nanocrystals. The size, shape, and crystal structure of CdSe nanocrystals synthesized by these alternative routes can be varied in a controllable manner in a very broad size range, from about 1.5 nm to above 25 nm. Without any size sorting, the size distribution of the wurtzite nanocrystals in the size range smaller than about 15 nm can be readily controlled as narrow as with 5−10% relative standard deviation. The highest photoluminescence quantum efficiency of the nanocrystals was up to 20−30%. Cd(Ac)2 and fatty acids were found to be the most versatile cadmium precursor and solvent/ligand, respectively. The synthesis of high quality CdSe nanocrystals in the current systems is not feasible when the system contains any anions from a strong acid, either in the form of a cadmium precursor or as an added cadmium ligand. The experimental results indicate that the synthesis ...
988 citations
TL;DR: In this article, a simple colorimetric technique for the detection of small concentrations of aqueous heavy metal ions, including toxic metals such as lead, cadmium, and mercury, is described.
Abstract: A simple colorimetric technique for the detection of small concentrations of aqueous heavy metal ions, including toxic metals such as lead, cadmium, and mercury, is described. Functionalized gold n...
846 citations
TL;DR: In this article, the authors demonstrate high-quality, highly fluorescent, ZnSe colloidal nanocrystals (or quantum dots) that are doped with paramagnetic Mn2+ impurities.
Abstract: We demonstrate high-quality, highly fluorescent, ZnSe colloidal nanocrystals (or quantum dots) that are doped with paramagnetic Mn2+ impurities. We present luminescence, magnetic circular dichroism (MCD), and electron paramagnetic resonance (EPR) measurements to confirm that the Mn impurities are embedded inside the nanocrystal. Optical measurements show that by exciting the nanocrystal, efficient emission from Mn is obtained, with a quantum yield of 22% at 295 K and 75% below 50 K (relative to Stilbene 420). MCD spectra reveal an experimental Zeeman splitting in the first excited state that is large (28 meV at 2.5 T), depends on doping concentration, and saturates at modest fields. In the low field limit, the magnitude of the effective g factor is 430 times larger than in undoped nanocrystals. EPR experiments exhibit a six-line spectrum with a hyperfine splitting of 60.4 × 10-4 cm-1, consistent with Mn substituted at Zn sites in the cubic ZnSe lattice.
753 citations
TL;DR: In this paper, pyridine-like N structures are observed to be responsible for the metallic behavior and prominent features near the Fermi level, which could pave the way to real molecular heterojunction devices.
Abstract: Nitrogen-doped carbon nanotubes have been synthesized using pyrolysis and characterized by scanning tunneling spectroscopy and transmission electron microscopy. The doped nanotubes are all metallic and exhibit strong electron donor states near the Fermi level. Using tight-binding and ab initio calculations, we observe that pyridine-like N structures are responsible for the metallic behavior and the prominent features near the Fermi level. These electron rich structures are the first example of n-type nanotubes, which could pave the way to real molecular heterojunction devices.
716 citations
TL;DR: In this article, the band gaps of rod-like CdSe quantum dots with diameter varying from 3.0 to 6.5 nm and length from 7.5 to 40 nm were reported.
Abstract: We report the band gaps of rodlike CdSe quantum dots with diameter varying from 3.0 to 6.5 nm and length from 7.5 to 40 nm. A qualitative explanation for the dependence of band gap on width and length is presented.
577 citations
TL;DR: In this article, a tunable shape has been synthesized in THF, in the presence of hexadecylamine (HDA) or trioctylphosphineoxide (TOPO), in mild conditions and characterized by HREM and SQUID measurements.
Abstract: Nickel nanoparticles of tunable shape have been synthesized in THF, in the presence of hexadecylamine (HDA) or trioctylphosphineoxide (TOPO), in mild conditions and characterized by HREM and SQUID measurements. The formation of nanorods is promoted by a high amine content in the reaction medium. In contrast to what is observed for TOPO-protected nickel particles, the saturation magnetization of HDA-capped nanoparticles is comparable to that of bulk nickel, which demonstrates that the coordination of an amine ligand does not alter the magnetic properties of nickel.
488 citations
TL;DR: In this paper, specific binding of biotinilated bovine serum albumin (bBSA) and tetramethylrhodamine-labeled streptavidin (SAv−TMR) was observed by conjugating bBSA to CdSe−ZnS core−shell quantum dots (QDs) and observing enhanced TMR fluorescence caused by fluorescence resonance energy transfer (FRET) from the QD donors to the TMR acceptors.
Abstract: Specific binding of biotinilated bovine serum albumin (bBSA) and tetramethylrhodamine-labeled streptavidin (SAv−TMR) was observed by conjugating bBSA to CdSe−ZnS core−shell quantum dots (QDs) and observing enhanced TMR fluorescence caused by fluorescence resonance energy transfer (FRET) from the QD donors to the TMR acceptors. Because of the broad absorption spectrum of the QDs, efficient donor excitation could occur at a wavelength that was well resolved from the absorption spectrum of the acceptor, thereby minimizing direct acceptor excitation. Appreciable overlap of the donor emission and acceptor absorption spectra was achieved by size-tuning the QD emission spectrum into resonance with the acceptor absorption spectrum, and cross-talk between the donor and acceptor emission was minimized because of the narrow, symmetrically shaped QD emission spectrum. Evidence for an additional, nonspecific QD−TMR energy transfer mechanism that caused quenching of the QD emission without a corresponding TMR fluoresce...
484 citations
TL;DR: The rate of electron transfer at carbon electrodes depends on various factors such as the structure and morphology of the carbon material used in the electrodes as mentioned in this paper, and has been shown to be dependent on the number of electrodes used.
Abstract: The rate of electron transfer at carbon electrodes depends on various factors such as the structure and morphology of the carbon material used in the electrodes. With the advent of new carbon struc...
TL;DR: Electrophoretic isolation of 5 and 10 nm gold nanocrystals bearing discrete numbers of single-stranded DNA (1−5) is demonstrated and the potential use of these discrete conjugates in the fabrication of novel nanostructures is discussed.
Abstract: Colloidal nanocrystal/DNA conjugates hold the promise of becoming powerful probes for biological diagnostics as well as versatile building blocks for nanotechnology. To fully realize this potential, it is important to precisely control the number of oligonucleotides bound to the nanocrystal. Here we demonstrate electrophoretic isolation of 5 and 10 nm gold nanocrystals bearing discrete numbers of single-stranded DNA (1−5). The potential use of these discrete conjugates in the fabrication of novel nanostructures is discussed.
TL;DR: Stable hollow polyelectrolyte capsules were produced by means of the layer-by-layer assembling of poly(allylamine), PAH, and poly(styrenesulfonate), PSS, on melamine formaldehyde microcores followed by the core decomposition at low pH as mentioned in this paper.
Abstract: Stable hollow polyelectrolyte capsules were produced by means of the layer-by-layer assembling of poly(allylamine), PAH, and poly(styrenesulfonate), PSS, on melamine formaldehyde microcores followed by the core decomposition at low pH. These capsules are nonpermeable for urease in water and become permeable in a water/ethanol mixture. The capsules were loaded with urease in water/ethanol mixture and then resuspended in water. The urease molecules are kept in the capsule, whereas the small urea molecules rapidly diffuse through the capsule wall providing a substrate for the biocatalytic reaction.
TL;DR: Conjugates of bovine serum albumin and CdTe nanoparticles capped with l-cysteine have been synthesized via a one-pot glutaric dialdehyde cross-linking procedure and circular dichroism spectroscopy demonstrates that the tertiary structure of the protein remains largely intact after the conjugation.
Abstract: Conjugates of bovine serum albumin and CdTe nanoparticles capped with l-cysteine have been synthesized via a one-pot glutaric dialdehyde cross-linking procedure. Diads (1:1) with some amount of 2:1 albumin−nanoparticle assemblies preferably form in this reaction, as evidenced by gel electrophoresis. Circular dichroism spectroscopy demonstrates that the tertiary structure of the protein remains largely intact after the conjugation. Attachment of protein moieties result in a significant increase of CdTe emission, which is attributed to the resonance energy transfer from the tryptophan moieties of albumin to CdTe nanoparticles acting as receptors for the protein antennae.
TL;DR: Both PAMAM silver salts and nanocomposites displayed considerable antimicrobial activity without the loss of solubility and activity, even in the presence of sulfate or chloride ions.
Abstract: Silver complexes of poly(amidoamine) (PAMAM) dendrimers as well as different {silver−PAMAM} dendrimer nanocomposite solutions have been tested in vitro against Staphylococcus aureus, Pseudomonas aeruginosa, and Escherichia coli bacteria, using the standard agar overlay method. Both PAMAM silver salts and nanocomposites displayed considerable antimicrobial activity without the loss of solubility and activity, even in the presence of sulfate or chloride ions.
TL;DR: In this paper, a simple preparation method for single monodisperse CdS nanoparticles with controllable size and stability against oxidation is presented, where double-hydrophilic block copolymers consisting of a solvating poly(ethylene glycol) PEG block and a poly(polyethylene imine) PEI binding block have been used as effective stabilizers for the solution synthesis of high-quality CdC nanoparticles.
Abstract: A novel and simple preparation method for single monodisperse CdS nanoparticles with controllable size and stability against oxidation is presented. Double-hydrophilic block copolymers consisting of a solvating poly(ethylene glycol) PEG block and a poly(ethylene imine) PEI binding block have been used as effective stabilizers for the solution synthesis of high-quality CdS nanoparticles in water and methanol. Absorption, fluorescence spectroscopy, and transmission electron microscopy were employed for characterization, which revealed that the prepared CdS nanoparticles had a well-resolved cubic structure and were monodisperse in size. It was also found that the CdS nanoparticles were dispersed in solution as single entities and showed a very good resistance against oxidation for months, according to their polymer shell. The particle size was controllable in the range between 2 and 4 nm by adjusting the polymer concentration and choice of the solvent.
TL;DR: In this paper, the influence of synthesis conditions on the properties of nanocrystalline ZnS:Mn2+ is discussed, and different Mn2+ precursors and different ratios of the precursor concentrations [S2-]/[Zn2+) were used.
Abstract: The influence of the synthesis conditions on the properties of nanocrystalline ZnS:Mn2+ is discussed. Different Mn2+ precursors and different ratios of the precursor concentrations [S2-]/[Zn2+] were used. The type of Mn2+ precursor does not have an effect on the luminescence properties in the synthesis method described. On going from an excess of [Zn2+] to an excess of [S2-] during the synthesis, the particle diameter increases from 3.7 to 5.1 nm, which is reflected by a change in the luminescence properties. Photoluminescence measurements also showed the absence of the ZnS defect luminescence around 450 nm when an excess [S2-] is used during the synthesis. This effect is explained by the filling of sulfur vacancies. The ZnS luminescence is quenched with an activation energy of 62 meV, which is assigned to the detrapping of a bound hole from such a vacancy.
TL;DR: In this article, the authors describe a new method for manufg. a nanostructured porous layer of a semiconductor material on a conducting plastic substrate for use in an electrochem.
Abstract: The present paper describes a new method for manufg. a nanostructured porous layer of a semiconductor material on a conducting plastic substrate for use in an electrochem. or photoelectrochem. cell. The method involves the deposition of a layer of semiconductor particles on conducting plastic and the compression of the particle layer to form a mech. stable, elec. conducting, porous nanostructured film at room temp. Photoelectrochem. characteristics of the resulting nanostructured films are presented showing, for example, overall solar to elec. conversion efficiencies of up to 4.9% (0.1 sun). The potential use of the new manufg. method in future applications of nanostructured electrodes is discussed.
TL;DR: Alternative methods of controlling the direction of motion of microtubules on engineered kinesin tracks, how to load cargo covalently to microtubule, and how to exploit UV-induced release of caged ATP combined with enzymatic ATP degradation by hexokinase to turn the shuttles on and off sequentially are illustrated.
Abstract: Molecular shuttles have been built from motor proteins capable of moving cargo along engineered paths. We illustrate alternative methods of controlling the direction of motion of microtubules on en...
TL;DR: In this article, the authors reported the preparation of polystyrene and silica-coated Au nanorods (aspect ratio 13 with 16 nm short axis), which resulted in a modification of the optical properties.
Abstract: We report the preparation of polystyrene and silica-coated Au nanorods (aspect ratio 13 with 16 nm short axis). The coating resulted in a modification of the optical properties of the Au nanorods. Dissolution of the Au core from the polystyrene- and silica-coated Au nanorods using KCN enabled the formation of hollow polystyrene and silica nanotubes.
TL;DR: Palladium nanoparticles (2−3 nm in diameter) have been prepared within covalently functionalized poly(propylene imine) dendrimers, and the resulting composite materials are shown to be effective for Heck coupling reactions as discussed by the authors.
Abstract: Palladium nanoparticles (2−3 nm in diameter) have been prepared within covalently functionalized poly(propylene imine) (PPI) dendrimers, and the resulting composite materials are shown to be effective for Heck coupling reactions. Two novel concepts are demonstrated in this report. The first concept involves the incorporation of Pd0 nanoparticles into PPI dendrimers covalently functionalized with perfluorinated polyether chains on their periphery. The second concept involves the first example of a carbon−carbon coupling reaction catalyzed by a dendrimer-templated nanomaterial, specifically, the catalytic heterocoupling between nonactivated aryl halides and n-butylacrylate mediated by the dendrimer-encapsulated catalysts. These reactions were carried out in a homogeneous fluorous/organic reaction phase at elevated temperature, and the catalyst was recovered by cooling to room temperature and concomitant phase separation. The catalyst was found to be catalytically active at a reaction temperature of only 90 ...
TL;DR: In this paper, the nanowires were removed from their templates and functionalized with luminescent porphyrins, and the response to magnetic fields was quantified using video microscopy.
Abstract: Nickel nanowires prepared by electrochemical growth in alumina templates have been removed from their templates and functionalized with luminescent porphyrins. The nanowires response to magnetic fields was quantified using video microscopy. In viscous solvents, magnetic fields can be used to orient the nanowires; in mobile solvents, the nanowires form chains in a head-to-tail configuration when a small magnetic field is applied. The dynamics for chain formation have been quantitatively modeled. The results demonstrate a new approach for assembling nanowires.
TL;DR: In this article, the authors describe the first real space observation for the formation of a house of cards structure in polypropylene/clay nanocomposite melt under elongational flow by TEM analysis.
Abstract: This Letter describes the first real space observation for the formation of a house of cards structure in polypropylene/clay nanocomposite melt under elongational flow by TEM analysis. Both strong strain-induced hardening and rheopexy features are originated from the perpendicular alignment of the silicate layers to the stretching direction.
TL;DR: The phase transformation, coalescence, and twin structure of thermally annealed 6 nm FePt nanocrystals under high vacuum on an amorphous carbon surface have been investigated in this article.
Abstract: The phase transformation, coalescence, and twin structure of thermally annealed 6 nm FePt nanocrystals under high vacuum on an amorphous carbon surface have been investigated. A1-FePt phase to L10−...
TL;DR: In this paper, the biaxial flow-induced alignment of clay particles along the cell boundary was identified, which helps cells to withstand the stretching force from breaking the so thin cell wall and to improve the modulus of the foam.
Abstract: Via batch process in an autoclave, we conducted foam processing on polypropylene (PP)/clay nanocomposite (PPCN) by using supercritical CO2 as foaming agent under 10 MPa at 134.7 °C. Through transmission electron microscopy observation, the biaxial flow-induced alignment of clay particles along the cell boundary was identified. Such aligning behavior of clay particles helps cells to withstand the stretching force from breaking the so thin cell wall and to improve the modulus of the foam.
TL;DR: In this article, a nanosized α-nickel hydroxide with an interlayer spacing of 7.2 A has been synthesized with the aid of ultrasound radiation, which was found to possess good stability in KOH medium and the material might be interesting from the application point of view in secondary alkaline batteries.
Abstract: Nanosized α-nickel hydroxide with an interlayer spacing of 7.2 A has been synthesized with the aid of ultrasound radiation. This method was found to be a simple and convenient method to produce α-nickel hydroxide. The synthesized hydroxide was found to possess good stability in KOH medium and the material might be interesting from the application point of view in secondary alkaline batteries. The α-nickel hydroxide has been characterized by powder X-ray diffraction, transmission electron microscopy, DSC, thermogravimetric analysis, FT-IR spectroscopy, and elemental analysis.
TL;DR: In this paper, a nanostructured HAP and HAP−YSZ composites demonstrated excellent chemical and microstructural uniformity and mechanical properties, compared to conventional coarse-grained systems.
Abstract: Nanostructure processing was applied to derive hydroxyapatite and hydroxyapatite-zirconia bioceramics with ultrafine microstructures and significantly improved mechanical properties for orthopedic and dental implant applications. Despite its attractive bioactivity, hydroxyapatite (HAP) has been limited in applications due to the poor processability and mechanical strength of the conventional material. Through nanostructure processing, high-strength HAP has been obtained by pressure-assisted sintering. To further toughen the HAP matrix, nanocrystalline yttria-stabilized zirconia (YSZ) dispersoids have been introduced during HAP precipitation. The nanostructured HAP and HAP−YSZ composites demonstrated excellent chemical and microstructural uniformity and mechanical properties, compared to conventional coarse-grained systems.
TL;DR: In this paper, the behavior of water droplets confined in a carbon nanotube by means of parallel molecular dynamics simulations was studied by using a parallel simulation approach, and radial density profiles, radial hydrogen bond distributions, and contact angles for tube radii ranging from 125 to 375 A and for droplets containing up to 4632 water molecules were obtained.
Abstract: We study the behavior of water droplets confined in a carbon nanotube by means of parallel molecular dynamics simulations We report radial density profiles, radial hydrogen bond distributions, and contact angles for tube radii ranging from 125 to 375 A and for droplets containing up to 4632 water molecules Our results indicate nonwetting behavior of the pristine CNT at room temperatures
TL;DR: Carbon nitride spheres, with diameters ranging from 20 microns to as few as 30 nanometers, were prepared by template-directed solid-state or solution reaction of cyanuric chloride or fluoride with lithium nitride.
Abstract: Carbon nitride spheres, with diameters ranging from 20 microns to as few as 30 nanometers were prepared by template-directed solid-state or solution reaction of cyanuric chloride or fluoride with lithium nitride. The electron microscopy data on the hollow spheres suggest their multiwalled nanostructure, built by disorderly stacked C3N4 curved layers assembled from triazine rings and nitrogen bridges of pyramidal structure. The closed spherical shape of this form of carbon nitride suggests its use in lubricants, catalyst supports, gas storage, and drug delivery.
TL;DR: In this article, the optical absorption spectra of bimetallic gold and silver particles were measured and compared with various absorption profiles due to Au−Ag particles described in the literature.
Abstract: Bimetallic gold and silver particles, a core−shell type structure, have been prepared by a UV-photoactivation technique. The optical absorption spectra are recorded and compared with various absorption profiles due to Au−Ag particles described in the literature. Initially Au particles formed by UV irradiation, which act as the seed particles, catalyzed the reduction of added silver ion in the presence of UV light to yield bimetallic (Aucore−Agshell) particles. Preferential dissolution of Au particles by cyanide and TEM images of the particles corroborates the “core−shell” type configuration.