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Mesoporous graphitic carbon nitride was used as both a nanoreactor and a reactant for the synthesis of ternary metal nitride nanoparticles. By infiltration of a mixture of two metal precursors into mesoporous carbon nitride, the pores act first as a nanoconfinement, generating amorphous mixed oxide nanoparticles. During heating and decomposition, the carbon nitride second acts as reactant or, more precisely, as a nitrogen source, which converts the preformed mixed oxide nanoparticles into the corresponding nitride (reactive templating). Using this approach, ternary metal nitride particles with diameters smaller 10 nm composed of aluminum gallium nitride (Al-Ga-N) and titanium vanadium nitride (Ti-V-N) were synthesized. Due to the confinement effect of the carbon nitride matrix, the composition of the resulting metal nitride can be easily adjusted by changing the concentration of the preceding precursor solution. Thus, ternary metal nitride nanoparticles with continuously adjustable metal composition can be produced.
ACS Nano 2008 Dec 23
PMID:Synthesis of ternary metal nitride nanoparticles using mesoporous carbon nitride as reactive template. 1920 83

We used polyethyleneglycol (PEG) as a modulator to manipulate pore and cell sizes in the porous anodic alumina (PAA) fabrication. It is shown for the first time that continuous manipulation of the pore size of PAA can be realized. Combined with the coexistent cell-size controlling effect, the morphology and properties of this important nanoscale template and separation membrane can be precisely regulated. The pore size modulation mechanism is proposed on the basis of the morphological and electrochemical results. The presence of PEG in the electrolyte results in a more compacted structure of the barrier layer alumina (BLA), although the barrier layer thickness does not change considerably. In addition, the additive can obviously restrain the chemical dissolution of alumina and shape smaller pores. These two effects combined with the increased viscosity of the electrolyte slow down the ion transportation and diminish the anodization current. Thus, the burning-down phenomena of the aluminum substrates can be avoided at relatively high voltage anodization, and an interpore distance up to 610 nm can be achieved.
ACS Nano 2008 May
PMID:Porous anodic alumina with continuously manipulated pore/cell size. 1920 93

This paper presents a systematic investigation on the controlled synthesis of wurtzite aluminum nitride (AlN) one-dimensional (1D) nanostructures in a chemical vapor deposition (CVD) system using Al and NH(3) as starting materials. By controlling reaction temperature and NH(3) flow, nanostructures with manifold morphologies including nanoneedles, branched nanoneedles, short nanorods, slim nanorods, and nanofences were synthesized with high yield and selectivity. The correlation between experiment parameters and product morphologies was interpreted by a surface diffusion based model. Moreover, electrical properties of a single nanoneedle were studied for the first time, in which typical semiconductor characteristics were observed. Silicon was speculated to incorporate into the AlN nanoneedle from silicon substrates during the synthesis, which served as an n-type donor and was responsible for the observed electrical behavior.
ACS Nano 2008 Jan
PMID:[0001] oriented aluminum nitride one-dimensional nanostructures: synthesis, structure evolution, and electrical properties. 1920 57

This paper describes a simple technique for fabricating uniform arrays of metal and metal oxide nanotubes with controlled heights and diameters. The technique involves depositing material onto an anodized aluminum oxide (AAO) membrane template using a collimated electron beam evaporation source. The evaporating material enters the porous openings of the AAO membrane and deposits onto the walls of the pores. The membrane is tilted with respect to the column of evaporating material, so the shadows cast by the openings of the pores onto the inside walls of the pores define the geometry of the tubes. Rotation of the membrane during evaporation ensures uniform deposition inside the pores. After evaporation, dissolution of the AAO in base easily removes the template to yield an array of nanotubes connected by a thin backing of the same metal or metal oxide. The diameter of the pores dictates the diameter of the tubes, and the incident angle of evaporation determines the height of the tubes. Tubes up to approximately 1.5 mum in height and 20-200 nm in diameter were fabricated. This method is adaptable to any material that can be vapor-deposited, including indium-tin oxide (ITO), a conductive, transparent material that is useful for many opto-electronic applications. An array of gold nanotubes produced by this technique served as a substrate for surface-enhanced Raman spectroscopy: the Raman signal (per molecule) from a monolayer of benzenethiolate was a factor of approximately 5 x 10(5) greater than that obtained using bulk liquid benzenethiol.
ACS Nano 2008 Apr
PMID:Fabrication of arrays of metal and metal oxide nanotubes by shadow evaporation. 1920 13

The self-ordering of nanoporous anodic aluminum oxide (AAO) in the course of the hard anodization (HA) of aluminum in sulfuric acid (H2SO4) solutions at anodization voltages ranging from 27 to 80 V was investigated. Direct H2SO4-HA yielded AAOs with hexagonal pore arrays having interpore distances D(int) ranging from 72 to 145 nm. However, the AAOs were mechanically unstable and cracks formed along the cell boundaries. Therefore, we modified the anodization procedure previously employed for oxalic acid HA (H2C2O4-HA) to suppress the development of cracks and to fabricate mechanically robust AAO films with D(int) values ranging from 78 to 114 nm. Image analyses based on scanning electron micrographs revealed that at a given anodization voltage the self-ordering of nanopores as well as D(int) depend on the current density (i.e., the electric field strength at the bottoms of the pores). Moreover, periodic oscillations of the pore diameter formed at anodization voltages in the range from 27 to 32 V, which are reminiscent of structures originating from the spontaneous growth of periodic fluctuations, such as topologies resulting from Rayleigh instabilities.
ACS Nano 2008 Feb
PMID:Self-ordered anodic aluminum oxide formed by H2SO4 hard anodization. 1920 31

Step-like porous gold nanowires of different shapes and diameters have been prepared by sequentially depositing alloy segments composed of different gold/silver ratios and de-alloying the silver component. For example, step-cone and nano-barbell porous gold nanowires were generated by a membrane-templated sequential deposition of gold-silver alloy segments from plating solutions of respectively decreasing or alternating gold/silver composition ratios. Alloy segments of different gold/silver ratios, prepared by using different plating potentials, also lead to multistep nanowires. In addition to step-like nanowires, we describe the preparation of cone- and bone-shaped porous nanowires from alloy nanowires of longitudinally changing compositions, generated via deposition from a flowing plating solution of a continuously changing composition. Such customization of the porous gold nanostructure is attributed to the chemical removal of silver and the different extents of gold reordering from alloy segments of different compositions. The latter leads to porous gold segments of smaller diameters from silver-rich alloy segments. The new "nanomachining" concept is versatile and could be extended to nanowires of diverse shapes with a variety of properties, generating an attractive assortment of nano-hardware.
ACS Nano 2007 Dec
PMID:Shape-tailored porous gold nanowires: from nano barbells to nano step-cones. 1920 60

The synthesis of carbon nanostructures, with interesting morphologies, has created a revolution in nanotechnology; carbon nanotube is a case in point, but other nanoscale morphologies of graphitic carbon could provide compelling uses. In particular short structures, including very short nanotubes, have proven impossible to be grown by existing techniques due to the difficulty in controlling and terminating growth during initial stages. Here we present architectures engineered from graphitic carbon, having up to 10(5) times smaller length/diameter (L/D) ratios compared to conventional nanotubes, revealing unique morphologies of nanocups, nanorings, and large area connected nanocup arrays. Such highly engineered hollow nanostructures were fabricated using precisely controlled short nanopores inside anodic aluminum oxide templates. The nanocups were effectively used to hold and contain other nanomaterials, for example, metal nanoparticles, leading to the formation of multicomponent hybrid nanostructures with unusual morphologies. The results reported here open up possibilities to integrate new morphologies of graphitic carbon in nanotechnology applications.
ACS Nano 2009 May 26
PMID:Engineering low-aspect ratio carbon nanostructures: nanocups, nanorings, and nanocontainers. 1940 23

Free-standing nanorod arrays of a thermally cross-linked semiconducting triphenylamine were fabricated on conductive ITO/glass substrates via an anodic aluminum oxide (AAO) template-assisted approach. By using a solution wetting method combined with a subsequent thermal imprinting step to fill the nanoporous structure of the template with a cross-linkable triphenylamine derivative, a polymeric replication of the AAO was obtained after thermal curing and selective removal of the template. To obtain well-aligned and free-standing nanorod arrays, aggregation and collapse of the nanorods were prevented by optimizing their aspect ratio and applying a freeze-drying technique to remove the aqueous medium after the etching step. Because of their electrochemical properties and their resistance against organic solvents after curing, these high density nanorod arrays have potential application in organic photovoltaics.
ACS Nano 2009 Jun 23
PMID:Template-assisted fabrication of free-standing nanorod arrays of a hole-conducting cross-linked triphenylamine derivative: toward ordered bulk-heterojunction solar cells. 1945 42

By varying the carbon nanotube (CNT) content in poly(N-vinylcarbazole) (PVK) composite thin films, the electrical conductance behavior of an indium-tin oxide/PVK-CNT/aluminum (ITO/PVK-CNT/Al) sandwich structure can be tuned in a controlled manner. Distinctly different electrical conductance behaviors, such as (i) insulator behavior, (ii) bistable electrical conductance switching effects (write-once read-many-times (WORM) memory effect and rewritable memory effect), and (iii) conductor behavior, are discernible from the current density-voltage characteristics of the composite films. The turn-on voltage of the two bistable conductance switching devices decreases and the ON/OFF state current ratio of the WORM device increases with the increase in CNT content of the composite film. Both the WORM and rewritable devices are stable under a constant voltage stress or a continuous pulse voltage stress, with an ON/OFF state current ratio in excess of 10(3). The conductance switching effects of the composite films have been attributed to electron trapping in the CNTs of the electron-donating/hole-transporting PVK matrix.
ACS Nano 2009 Jul 28
PMID:Electrical Conductance Tuning and Bistable Switching in Poly(N-vinylcarbazole)-Carbon Nanotube Composite Films. 1948 30

A phospho-directed nanoreactor with multiple functions is reported. Alumina-functionalized macroporous ordered silica foams (Al-MOSF) have been developed with large pore size, high pore volume (1.6 cm(3)/g), and a surface area of 186 m(2)/g rich in coordination unsaturated Al species, which can be used as phospho-directed nanoreactors for integrated in situ digestion and in situ phosphoisolation. By directly adding Al-MOSF to the conventional in-solution digestion system, both enzymes and proteins are quickly enriched in the macropores of the reactor to achieve a fast proteolysis without increasing the enzyme/protein concentration or using a preimmobilization process, thus the digestion time and the cost can be greatly reduced. Meanwhile, due to the chemo-affinity between alumina and phosphor groups, the Al-MOSF reactor can in situ isolate specific products of the enzymatic reaction (i.e., phosphopeptides) and release the nonspecific peptides to the solution. This strategy is simple, efficient, and successfully applied in the detection of phosphoproteins in real samples.
ACS Nano 2009 Nov 24
PMID:A phospho-directed macroporous alumina-silica nanoreactor with multi-functions. 1984 78


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