Amar Kumbhar

Lanthanum Nitride Endohedral Fullerenes La3N@C2n (43≤n≤55): Preferential Formation of La3N@C96

While the trimetallic nitrides of Sc, Y and the lanthanides between Gd and Lu preferentially template C(80) cages, M(3)N@C(80), and while those of Ce, Pr and Nd preferentially template the C(88) cage, M(3)N@C(88), we show herein that the largest metallic nitride cluster, La(3)N, preferentially leads to the formation of La(3)N@C(96) and to a lesser extent the La(3)N@C(88). This is the first time that La(3)N is successfully encapsulated inside fullerene cages. La(3)N@C(2n) metallofullerenes were synthesized by arcing packed graphite rods in a modified Krätschmer-Huffman arc reactor, extracted from the collected soot and identified by mass spectroscopy. They were isolated and purified by high performance liquid chromatography (HPLC). Different arcing conditions were studied to maximize fullerene production, and results showed that yields have a high La(2)O(3)/C dependence. Relatively high yields were obtained when a 1:5 ratio was used. Three main fractions, La(3)N@C(88), La(3)N@C(92), and La(3)N@C(96), were characterized by UV/Vis-NIR and cyclic voltammetry. Unlike other trimetallic nitride metallofullerenes of the same carbon cage size, La(3)N@C(88) exhibits a higher HOMO-LUMO gap and irreversible reduction and oxidation steps.

Simple cubic super crystals containing PbTe nanocubes and their core-shell building blocks.

We report a preparation of high-quality cubic PbTe nanocrystals and their assembly into both square-array, two-dimensional patterns and three-dimensional simple cubic super crystals. The influence of oleylamine in the nanocrystal synthesis and core-shell formation through an anion-exchange mechanism was also studied. The simple cubic super crystals together with two-dimensional assembly patterns containing PbTe nanocubes and their core-shell building blocks were examined using TEM, SEM, AFM, XRD, SAXS, and FTIR. Such super crystals consisting of cubic structural building blocks may allow engineering of more complex materials from which novel properties may emerge.

Characterization of the natural barriers of intergranular tunnel junctions: Cr2O3 surface layers on CrO2 nanoparticles

Cold-pressed powder compacts of CrO2 show large negative magnetoresistance (MR) due to intergranular tunneling. Powder compacts made from needle-shaped nanoparticles exhibit MR of about 28% at 5 K. Temperature dependence of the resistivity indicates that the Coulomb blockade intergranular tunneling is responsible for the conductance at low temperature. In this letter we report direct observation and characterization of the microstructure of the intergranular tunnel barriers, using transmission electron microscopy, x-ray diffraction (XRD), and x-ray photoelectron spectroscopy (XPS). A very thin native oxide layer with a thickness of 1–3 nm on the surface of CrO2 powders has been observed. The composition and crystal structure of this surface layer has been determined to be Cr2O3 by XPS and XRD. The dense and uniform Cr2O3 surface layers play an ideal role of tunnel barriers in the CrO2 powder compacts.

New M3N@C2n Endohedral Metallofullerene Families (M=Nd, Pr, Ce; n=40–53): Expanding the Preferential Templating of the C88 Cage and Approaching the C96 Cage

Three new families of trimetallic nitride template endohedral metallofullerenes (TNT EMFs), based on cerium, praseodymium, and neodymium clusters, were synthesized by vaporizing packed graphite rods in a conventional Krätschmer-Huffman arc reactor. Each of these families of metallofullerenes was identified and characterized by mass spectroscopy, HPLC, UV/Vis-NIR spectroscopy, and cyclic voltammetry. The mass spectra and HPLC chromatograms show that these larger metallic clusters are preferentially encapsulated by a C(88) cage. When the size of the cluster is increased, the C(96) cage is progressively favored over the predominant C(88) cage. It is also observed that the smaller cages (C(80)-C(86)) almost disappear on going from neodymium to cerium endohedral metallofullerenes. The UV/Vis-NIR spectra and cyclic voltammograms confirm the low HOMO-LUMO gap and reversible electrochemistry of these M(3)N@C(88) metallofullerenes.

Coreduction Colloidal Synthesis of III–V Nanocrystals: The Case of InP†

Colloidal Group 13–Group 15 semiconductor nanocrystals (III–V NCs) have been the subject of intensive studies during the last two decades because of rich phenomena associated with quantum confinement. However, studies of III–V NCs are restricted owing to synthetic difficulties. As a consequence of the attractive applications as luminescence probes for bioimaging and as photovoltaic devices, InP NCs have become the most extensively studied III–V system. The synthetic studies of InP NCs are therefore more advanced compared to other III–V systems. By adaptating Wells0 dehalosilylation reaction, some feasible synthetic methods for colloidal InP NCs have been established by several groups. These methods usually involve the reaction of an indium salt with tris(trimethylsilyl)phosphine, P(TMS)3, in a high-boiling-point solvent at high temperatures. At first, Micic et al. chose coordinating solvents (e.g., trioctylphosphine oxide (TOPO) and trioctylphosphine (TOP)) as the reaction medium for the synthesis. To obtain crystalline NCs, growth must be carried out over a long period of time (up to seven days). Even then, the assynthesized NCs showed a broad size distribution, and a further size-selective post-treatment was required to achieve monodispersity. Later, Battaglia and Peng further developed this synthesis by replacing the phosphorous-based coordinating solvent with a noncoordinating one, such as octadecene, and using fatty acids as capping ligands. This synthetic variation not only greatly shortened the reaction time to a few hours, but also generated monodisperse InP NCs without any size sorting. Recently, Xu et al. showed that InP NCs of similar quality could also be rapidly produced in some weak coordinating solvents such as fatty-acid esters. However, all of these methods are dependent on the use of expensive P(TMS)3 precursor as the phosphorus source. This results in a high cost, hampering scale-up of the synthesis. To decrease the cost of the synthesis, a few phosphorous compounds, such as In(tBu2P)3 and Na3P, as well as white phosphorus (P4) have been explored as alternative phosphorus sources. However, the replacement of P(TMS)3 by In(tBu2P)3 or Na3P leads to much less control over the particle size. Moreover, the use of these phosphorus sources brings about some new problems. For example, the synthesis of the organometallic precursor is complex and also highcost, and the preparation of Na3P requires a handling of hazardous and pyrophoric sodium metal and P4. [17] When using the simplest phosphorus source, that is, P4, the syntheses are usually conducted under hydrothermal or solvothermal conditions; the as-synthesized InP NCs are polydisperse and aggregated, giving rise to very low quality. Recently, our group reported that colloidal InP NCs could be prepared using a wet-chemical reduction approach in which P4 and LiBH(C2H5)3 (superhydride) were involved. [22] However, the as-prepared NCs showed a broad size distribution. Therefore, it is still a big challenge to explore an alternative economic phosphorus source for the synthesis of InP NCs of an acceptable quality. As phosphorus halides, such as PCl3, can be reduced to elemental phosphorus with extremely high activity, these compounds may be superior phosphorus sources to P4 for the synthesis of InP NCs. It is anticipated that chemical reaction between freshly reduced indium and phosphorus results in a more rapid nucleation burst, which favors the formation of higher-quality NCs. Herein, we report the first example of using PCl3 to synthesize high-quality InP NCs through a coreduction colloidal approach. The synthesis was carried out in octadecene in the presence of stearic acid as capping ligand; the reactions involve simultaneous reduction of In(OAc)3 and PCl3 with superhydride. The hot-injection method, which has been extensively adopted for the colloidal synthesis of monodisperse NCs, is however inapplicable to our system owing to the low boiling point of PCl3 (76 8C). We thus have to carry out the redox reactions at a low temperature (ca. 40 8C) to retain PCl3 in the starting solution, and then elevate the temperature for the NC growth. Figure 1 depicts an X-ray diffraction (XRD) pattern and a transmission electron microscopy (TEM) image of a typical sample grown at 250 8C for 4 h. All detectable diffraction peaks in Figure 1a can be indexed to those of the zinc blende structure InP (ICDD PDF Card No. 73-1983). The broad nature of these peaks indicates the extremely small size of the particles. Figure 1b shows that the InP NCs are dot-shaped and quasi-monodisperse. The average particle size is about (3.5 0.5) nm based on statistical sampling of this image. These results clearly demonstrate that the present synthetic method is effective to generate InP NCs of relatively high quality. The growth process of InP NCs was investigated by monitoring the UV/Vis absorption spectra of samples grown [*] Dr. Z. Liu, D. Xu, J. Zhang, Dr. Z. Sun, Prof. J. Fang Department of Chemistry State University of New York at Binghamton Binghamton, NY 13902 (USA) Fax: (+1)607-777-4478 E-mail: jfang@binghamton.edu

Fabrication and properties of magnetic particles with nanometer dimensions

Novel nanocrystalline inorganic materials ranging from metals to ternary metal oxides and fluorides have been synthesized in aqueous solutions with restricted environment of reverse micelles. This technique allowed also sequential synthesis leading to a core–shell type structure. Methods of synthesis of nanoparticles of magnetic metals Fe, Co and alloys FePtX and CoPtX coated with gold, metal ferrites MFe2O4 (M=Mn, Fe and Co) and antiferromagnetic fluoromanganites NaMnF3 and KMnF3 have been developed. The synthesized materials were characterized using X-ray diffractometry, TEM microscopy with EDAX analysis and SQUID magnetometry. Novel physical properties of these materials are discussed with emphasis given to the differences between course and fine-grained magnetic materials.

Nonaqueous Synthesis and Photoluminescence of ITO Nanoparticles

SnO(2) has successfully been doped into octahedral In(2)O(3) nanoparticles using a high-temperature nonaqueous reaction. The resultant ITO nanoparticles exhibit a particle/crystal decrease in size, sphericity in morphology, and enhancement in photoluminescence.

Sustainable Mesoporous Carbons as Storage and Controlled-Delivery Media for Functional Molecules

Here, we report the synthesis of surfactant-templated mesoporous carbons from lignin, which is a biomass-derived polymeric precursor, and their potential use as a controlled-release medium for functional molecules such as pharmaceuticals. To the best of our knowledge, this is the first report on the use of lignin for chemical-activation-free synthesis of functional mesoporous carbon. The synthesized carbons possess the pore widths within the range of 2.5-12.0 nm. In this series of mesoporous carbons, our best result demonstrates a Brunauer-Emmett-Teller (BET) surface area of 418 m(2)/g and a mesopore volume of 0.34 cm(3)/g, which is twice the micropore volume in this carbon. Because of the dominant mesoporosity, this engineered carbon demonstrates adsorption and controlled release of a representative pharmaceutical drug, captopril, in simulated gastric fluid. Large-scale utilization of these sustainable mesoporous carbons in applications involving adsorption, transport, and controlled release of functional molecules is desired for industrial processes that yield lignin as a coproduct.

Magnetic properties of cobalt and cobalt-platinum alloy nanoparticles synthesized via microemulsion technique

Metallic cobalt and cobalt-platinum alloys of various nanometer sizes have been synthesized via the microemulsion technique and their magnetic properties have been characterized. Preparation of cobalt and cobalt-platinum alloy nanoparticles was achieved by reducing aqueous metallic salts confined in the polar regions of the reverse micelle of cetyltrimethyl bromide (CTAB) with sodium borohydride. These particles are further coated with gold by reducing aqueous gold salts with borohydride. The dc susceptibility data of 15 nm gold coated Co, CoPt and CoPt/sub 3/ particles exhibit a blocking temperature of 4 K, 80 K and 106 K and coercivity of 20 Oe, 300 Oe, and 415 Oe at 10 K, respectively. Annealing these samples at 400/spl deg/C further enhanced their magnetic properties. The two cobalt-platinum alloys have been synthesized and characterized by x-ray powder diffraction and transmission electron microscopy.

Patterned functional carbon fibers from polyethylene

Carbon fibers having unique morphologies, from hollow circular to gear-shaped, are produced from a novel melt-processable precursor and method. The resulting carbon fiber exhibits microstructural and topological properties that are dependent on processing conditions, rendering them highly amenable to myriad applications.