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Stanislaus S Wong

Publications and source records attributed to Stanislaus S Wong.

At least 19 recordsLinked to original sources
PubMed2006

Imperfect surface order and functionalization in vertical carbon nanotube arrays probed by near edge X-ray absorption fine structure spectroscopy (NEXAFS).

Probing surface order as well as the degree of structural modification in carbon nanotube systems is of fundamental importance for incorporation of these materials into practical functional devices. The current study pertains to the analysis of the surface order of vertically-aligned single-walled and multi-walled carbon nanotube arrays of varying length and composition by means of near-edge X-ray fine structure spectroscopy (NEXAFS). Both NEXAFS and scanning electron microscopy (SEM) studies concluded that the nanotubes in these samples were oriented vertically to the plane of the surface. However, NEXAFS polarization analysis provided a more quantitative and nuanced description of the surface structure, indicative of far less localized surface order, an observation partially attributed to misalignment and bending of the tubes. Moreover, it was demonstrated by NEXAFS that the surface order of the arrays was imperfect and relatively independent of the height of the nanotube arrays. In addition, we have shown that NEXAFS can be used to correlate the extent of chemical functionalization and oxygenation with disruption of the electronic and physical structure of nanotubes embedded in array motifs.

Carbon↗
PubMed2006

Size- and shape-dependent transformation of nanosized titanate into analogous anatase titania nanostructures.

A size- and shape-dependent morphological transformation was demonstrated during the hydrothermal soft chemical transformation, in neutral solution, of titanate nanostructures into their anatase titania counterparts. Specifically, lepidocrocite hydrogen titanate nanotubes with diameters of approximately 10 nm were transformed into anatase nanoparticles with an average size of 12 nm. Lepidocrocite hydrogen titanate nanowires with relatively small diameters (average diameter range of < or = 200 nm) were converted into single-crystalline anatase nanowires with relatively smooth surfaces. Larger diameter (>200 nm) titanate wires were transformed into analogous anatase submicron wire motifs, resembling clusters of adjoining anatase nanocrystals with perfectly parallel, oriented fringes. Our results indicate that as-synthesized TiO2 nanostructures possessed higher photocatalytic activity than the commercial titania precursors from whence they were derived.

Materials Testing↗
PubMed2006

Synthesis and growth mechanism of titanate and titania one-dimensional nanostructures self-assembled into hollow micrometer-scale spherical aggregates.

Three-dimensional, dendritic micrometer-scale spheres of alkali metal hydrogen titanate 1D nanostructures (i.e., nanowires and nanotubes) have been generated using a modified hydrothermal technique in the presence of hydrogen peroxide and an alkali metal hydroxide solution. Sea-urchin-like assemblies of these 1D nanostructures have been transformed into their hydrogen titanate analogues (lepidocrocite HxTi2-x/4squarex/4O4 (x approximately 0.7, square: vacancy)) by neutralization as well as into their corresponding anatase TiO2 nanostructured counterparts through a moderate high-temperature annealing dehydration process without destroying the 3D hierarchical structural motif. The as-prepared hollow spheres of titanate and titania 1D nanostructures have overall diameters, ranging from 0.8 to 1.2 microm, while the interior of these aggregates are vacuous with a diameter range of 100 to 200 nm. The constituent, component titanate and TiO2 1D nanostructures have a diameter range of 7+/-2 nm and lengths of up to several hundred nanometers. A proposed two-stage growth mechanism of these hollow micrometer-scale spheres was supported by time-dependent scanning electron microscopy, atomic force microscopy, and inductively coupled plasma atomic emission spectrometry data. We have also demonstrated that these assemblies are active photocatalysts for the degradation of synthetic Procion Red dye under UV light illumination.

Journal Article↗
PubMed2006

Near-edge X-ray absorption fine structure spectroscopy as a tool for investigating nanomaterials.

We have demonstrated near-edge X-ray absorption fine structure (NEXAFS) spectroscopy as a particularly useful and effective technique for simultaneously probing the surface chemistry, surface molecular orientation, degree of order, and electronic structure of carbon nanotubes and related nanomaterials. Specifically, we employ NEXAFS in the study of single-walled carbon nanotube and multi-walled carbon nanotube powders, films, and arrays, as well as of boron nitride nanotubes. We have focused on the advantages of NEXAFS as an exciting, complementary tool to conventional microscopy and spectroscopy for providing chemical and structural information about nanoscale samples.

Crystallography↗
PubMed2005

Synthesis of classes of ternary metal oxide nanostructures.

Nanoscale structures, such as nanoparticles, nanorods, nanowires, nanocubes, and nanotubes, have attracted extensive synthetic attention as a result of their novel size-dependent properties. Ideally, the net result of nanoscale synthesis is the production of structures that achieve monodispersity, stability, and crystallinity with a predictable morphology. Many of the synthetic methods used to attain these goals have been based on principles derived from semiconductor technology, solid state chemistry, and molecular inorganic cluster chemistry. We describe a number of advances that have been made in the reproducible synthesis of various ternary oxide nanomaterials, including alkaline earth metal titanates, alkali metal titanates, bismuth ferrites, ABO(4)-type oxides, as well as miscellaneous classes of ternary metal oxides.

Journal Article↗
PubMed2005

Near-edge X-ray absorption fine structure investigations of order in carbon nanotube-based systems.

Probing order in nanotube systems is of fundamental importance in devising applications of these tubes in field emission applications as well as for components of composite materials. We use near-edge X-ray absorption fine structure (NEXAFS) spectroscopy to qualitatively and quantitatively study the degree of order and alignment in a wide range of carbon nanotube-based systems, including single-walled carbon nanotube (SWNT) powder, SWNT films, and aligned multiwalled carbon nanotubes. The results are compared to analogous data obtained from a highly ordered pyrolytic graphite (HOPG) sample.

Journal Article↗
PubMed2005

Routes towards separating metallic and semiconducting nanotubes.

Separation of single-walled carbon nanotubes (SWNTs), according to their electronic characteristics, is essential to the development of molecular electronics, including field-effect transistors. Recent efforts by many groups have used non-covalent and covalent sidewall chemistry to probe differential reactivity in metallic and semiconducting nanotubes. These chemically based methods may more easily effect the bulk separation of tubes, as compared with physical techniques associated with (i) alternating current dielectrophoresis as well as (ii) the current-induced oxidation of metallic nanotubes, that have recently been reported as alternative methods of achieving chiral separations of nanotubes. Exploration of these types of reactions is critical for the development of interesting chemical and physical properties at the interface between molecules and materials as well as for establishing protocols for the selective functionalization of nanotubes.

Crystallization↗
PubMed2004

General, room-temperature method for the synthesis of isolated as well as arrays of single-crystalline ABO4-type nanorods.

Single-crystalline BaWO(4) and BaCrO(4) nanorods of reproducible shape and of varying sizes have been controllably prepared using a simple, room-temperature approach, based on the use of porous alumina template membranes. Aligned BaWO(4) and BaCrO(4) nanorod arrays can be obtained by dissolving the template. Our facile technique, which is analogous to biomineralization, offers a promising and generalized methodology to prepare other types of free-standing ABO(4) nanorods and their corresponding nanorod arrays. Extensive characterization of these samples has been performed using scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray spectroscopy (EDS), selected area electron diffraction (SAED), Raman spectroscopy, FT-infrared spectroscopy (FT-IR), and X-ray diffraction (XRD).

Journal Article↗
PubMed2004

Surface chemistry and structure of purified, ozonized, multiwalled carbon nanotubes probed by NEXAFS and vibrational spectroscopies.

Understanding of oxidative processes such as solution-phase ozonolysis in multiwalled carbon nanotubes (MWNTs) is of fundamental importance in devising applications of these tubes as components in composite materials, as well as for development of cutting and filling protocols. We present here an evaluation of various spectroscopic tools to study the structure and composition of functionalized nanotubes. We demonstrate near-edge X-ray absorption fine structure (NEXAFS) spectroscopy as a particularly useful and effective technique for studying the surface chemistry of carbon nanotubes.

Journal Article↗
PubMed2004

Selective metallic tube reactivity in the solution-phase osmylation of single-walled carbon nanotubes.

Single-walled carbon nanotubes have been reacted with osmium tetroxide (OsO(4)) in solution in the presence of O(2) and UV irradiation at 254 nm. We observe one main structural motif, namely thickly coated nanotube structures, densely covered with OsO(2), consisting of multiple bundles of derivatized tubes. In a few instances, bridging uncoated tubes, connecting these thickly coated structures, incorporate a number of smaller nanotube bundles, projecting out from the larger functionalized aggregates of tubes. It is believed that OsO(2) (a) initially forms on the nanotubes by the preferential covalent sidewall functionalization of metallic nanotubes and (b) subsequently self-aggregates. The formation of an intermediate charge-transfer complex is likely the basis for the observed selectivity and reactivity of metallic tubes. Extensive characterization of these osmylated adducts has been performed using a variety of electron microscopy and optical spectroscopy techniques.

Journal Article↗
PubMed2003

Large-scale synthesis of single-crystalline perovskite nanostructures.

Single-crystalline perovskite nanostructures with reproducible shape have been prepared using a simple, readily scaleable solid-state reaction in the presence of NaCl and a nonionic surfactant. Pristine BaTiO3 nanowires have diameters ranging from 50 to 80 nm with an aspect ratio larger than 25. Single-crystalline SrTiO3 nanocubes with a mean edge length of 80 nm have been produced using a similar procedure.

Journal Article↗
PubMed2003

In situ quantum dot growth on multiwalled carbon nanotubes.

The generation of nanoscale interconnects and supramolecular, hierarchical assemblies enables the development of a number of novel nanoscale applications. A rational approach toward engineering a robust system is through chemical recognition. Here, we show the in situ mineralization of crystalline CdTe quantum dots on the surfaces of oxidized multiwalled carbon nanotubes (MWNTs). We coordinate metallic precursors of quantum dots directly onto nanotubes and then proceed with in situ growth. The resulting network of molecular-scale "fused" nanotube-nanocrystal heterojunctions demonstrates a controlled synthetic route to the synthesis of complex nanoscale heterostructures. Extensive characterization of these heterostructures has been performed using scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, UV-visible spectroscopy, and X-ray diffraction (XRD).

Journal Article↗
PubMed2003

Rational chemical strategies for carbon nanotube functionalization.

Whereas the chemistry of fullerenes is well-established, the chemistry of single-walled carbon nanotubes (SWNTs) is a relatively unexplored field of research. Investigations into the bonding of moieties onto SWNTs are important because they provide fundamental structural insight into how nanoscale interactions occur. Hence, understanding SWNT chemistry becomes critical to rational, predictive manipulation of their properties. Among the strategies discussed include molecular metal complexation with SWNTs to control site-selective chemistry in these systems. In particular, work has been performed with Vaska's and Wilkinson's complexes to create functionalized adducts. Functionalization should offer a relatively simple means of tube solubilization and bundle exfoliation, and also allows for tubes to be utilized as recoverable catalyst supports. Solubilization of oxidized SWNTs has also been achieved through derivatization by using a functionalized organic crown ether. The resultant adduct yielded concentrations of dissolved nanotubes on the order of 1 g L(-1) in water and at elevated concentrations in a range of organic solvents, traditionally poor for SWNT manipulation. To further demonstrate chemical processability of SWNTs, we have subjected them to ozonolysis, followed by treatment with various independent reagents, to rationally generate a higher proportion of oxygenated functional groups on the nanotube surface. This protocol has been found to purify nanotubes. More importantly, the reaction sequence has been found to ozonize the sidewalls of these nanotubes. Finally, SWNTs have also been chemically modified with quantum dots and oxide nanocrystals. A composite heterostructure consisting of nanotubes joined to nanocrystals offers a unique opportunity to obtain desired physical, electronic, and chemical properties by adjusting synthetic conditions to tailor the size and structure of the individual sub-components, with implications for self-assembly.

Journal Article↗
PubMed2003

Hydrothermal synthesis of perovskite nanotubes.

A low-temperature hydrothermal reaction has been utilized to generate crystalline barium titanate and strontium titanate nanotubes, which have been characterized by means of X-ray diffraction and transmission electron microscopy, coupled with energy dispersive X-ray analysis.

Journal Article↗