Stephen O'Brien

City College of New York | CCNY · Department of Chemistry

The prospect of creating ferroelectric or high permittivity nanomaterials provides motivation for investigating complex transition metal oxides of the form Ba(Ti, MV)O3, where M = Nb or Ta. Solid state processing typically produces mixtures of crystalline phases, rarely beyond minimally doped Nb/Ta. Using a modified sol-gel method, we prepared sing...

Polyvinylidene difluoride trifluoroethylene (PVDF-TrFE) has received widespread application in flexible electronics and biomedical devices but is limited in its sensing modalities to piezoelectricity and pyroelectricity. The addition of optically or magnetically active nanoparticles could provide additional sensing modalities in the same element, w...

The application of nanomaterials made of rare earth elements within biomedical sciences continues to make significant progress. The rare earth elements, also called the lanthanides, play an essential role in modern life through materials and electronics. As we learn more about their utility, function, and underlying physics, we can contemplate exte...

Supramolecular self-assembly in biological systems holds promise to convert and amplify disease-specific signals to physical or mechanical signals that can direct cell fate. However, it remains challenging to design physiologically stable self-assembling systems that demonstrate tunable and predictable behavior. Here, the use of zwitterionic tetrap...

We report nanoscale Eu0.5Ba0.5TiO3, a multiferroic in the bulk and candidate in the search to quantify the electric dipole moment of the electron. Eu0.5Ba0.5TiO3, in the form of nanoparticles and other nanostructures is interesting for nanocomposite integration, biomedical imaging and fundamental research, based upon the prospect of polarizability,...

Supramolecular materials have gained substantial interest for a number biological and nonbiological applications. However, for optimum utilization of these dynamic self-assembled materials, it is important to visualize and understand their structures at the nanoscale, in solution and in real time. Previous approaches for imaging these structures ha...

Colloidal perovskite barium titanate (BaTiO3, or BT) nanoparticles (NPs), conventionally used for applications in electronics, can also be considered for their potential as nanocarriers for biomedical imaging and therapy. Biocompatible NPs containing high Z elements present options for extending resolution and sensitivity of computed tomography (CT...

BaMn3Ti4O14+δ (δ = 0.25, BMT-134), a recently discovered single-phase multiferroic complex oxide was doped with varying concentrations of Fe in order to assess the effect on magnetic and dielectric behavior. The novel compound BaMn3xFexTi4O14+δ (BMFT) was prepared via a sol-gel chemical solution processing method. Four substituted variations were s...

Barium titanate nanospheres (BTO-NPs) were deposited on carbon textile fibers, as a homogeneous coating (8 wt%; thickness 80–240 nm). The composite material/textile was thermally stable, porous, and water repellent. Its adsorption capacity against mustard gas surrogate vapors increased 17%, compared to those on separate carbon textiles and BTO-NPs,...

Nanotechnology offers a variety of pathways to novel and low cost device fabrication for a future that will undoubtedly contain literally billions of ubiquitous electronic devices. Nanocomposite metal–insulator–metal (MIM) capacitors are of interest due to the possibility of reducing the number of discrete components in printed circuit boards, and...

Nanocomposites are of great interest to electronic packaging, and the opportunities are readily comprehended. First is the ability to integrate materials cheaply, with better performance, miniaturization, and reliability for a wide range of applications, including embedded passives (capacitors, resistors), low-k materials, adhesives (electrically c...

Abstract Barium titanate nanoparticles (BTO-NPs) in the size range 8–12 nm, prepared by gel collection, are found to be a photoreactive detoxifier for Chemical Warfare Agent vapors, specifically, the sulfur mustard surrogate (2-chloroethyl ethyl sulfide). The relatively monodisperse, uniformly spherical BTO-NPs, initially dispersed in alcohol solve...

Barium titanate nanoparticles (BTO-NPs) in the size range 8–12 nm, prepared by gel collection, are found to be a photoreactive detoxifier for Chemical Warfare Agent vapors, specifically, the sulfur mustard surrogate (2-chloroethyl ethyl sulfide). The relatively monodisperse, uniformly spherical BTO-NPs, initially dispersed in alcohol solvents, form...

Lithium metal is a leading candidate for next-generation electrochemical energy storage and therefore a key material for the future sustainable energy economy. Lithium has a high specific energy, low toxicity, and relatively favorable abundance. The majority of lithium production originates from salt lakes and is based on long (>12 months) periods...

Frequency stable, high permittivity nanocomposite capacitors produced under mild processing conditions offer an attractive replacement to MLCCs derived from conventional ceramic firing. Here, 0-3 nanocomposites were prepared using gel-collection derived barium titanate nanocrystals, suspended in a poly (furfuryl alcohol) matrix, resulting in a stab...

Correction for ‘Interface structure, precursor rheology and dielectric properties of BaTiO 3 /PVDF–hfp nanocomposite films prepared from colloidal perovskite nanoparticles’ by Y. N. Hao et al. , RSC Adv. , 2017, 7 , 32886–32892.

Nanocomposite materials with uniform microstructure and high permittivity have attracted extensive interest in modern electronics. The compatibility between the filler phase and the polymer matrix is crucial in preparing high-performance composites. As an alternative to conventional surface modification treatment methodologies, hydroxylated colloid...

Inorganic materials synthesis techniques that can approach low temperature routes akin to chemical solution processing are attractive for their ability to prepare nanocrystalline oxides. These methods can offer thin film integration options more compatible with modern device platforms such as spray coated or printed devices (2D, 3D) and flexible el...

A new class of hollandite Ba–Mn–Ti oxide nanocrystals was synthesized. They are synthetic minerals exclusively composed of Ba, Ti, Mn, and O elements. The BaMn3Ti4O14.25 nanocrystals (designated BMT-134), a typical member of this newly discovered hollandite oxide group, possess a giant dielectric constant and multiferroic properties. In the present...

Organic-inorganic 0-3 nanocomposites, which combine the potentially high dielectric strength of the organic matrix and the high dielectric permittivity of the inorganic filler, are extensively studied as energy-storage dielectrics in high-performance capacitors. In this study, a gradated multilayer BaTiO3/poly(vinylidene fluoride) thin film structu...

We report the activation field and selective frequency-dependent ferroelectric behavior of BaMn3Ti4O14.25 (BMT-134) at room temperature. BMT-134, a recently discovered multiferroic complex oxide, exhibits antiferromagnetic and ferroelectric behavior and belongs to the hollandite crystal class. The microstructure can be manipulated through processin...

Colloidal perovskite oxide nanocrystals have attracted a great deal of interest owing to the ability to tune physical properties by virtue of the nanoscale, and generate thin film structures under mild chemical conditions, relying on self-assembly or heterogeneous mixing. This is particularly true for ferroelectric/dielectric perovskite oxide mater...

Supplementary Information for Hollandites as a new class of multiferroics

Solution processed NiSe2 nanorods were synthesized by a modified colloidal synthesis technique, by chemical reaction of TOPSe and nickel acetate at . The rods exist as an oleic acid ligand stabilized solution, with oleic acid acting as a capping group. Structural characterization by X-ray diffraction and transmission electron microscopy indicates t...

Discovery of new complex oxides that exhibit both magnetic and ferroelectric properties is of great interest for the design of functional magnetoelectrics, in which research is driven by the technologically exciting prospect of controlling charges by magnetic fields and spins by applied voltages, for sensors, 4-state logic, and spintronics. Motivat...

In this paper, based on recent research on BaTiO 3 (BT) nanoparticles, BT/P(VDF-HFP) nanocom-posites, frequency-dependent dielectric properties of such a material system with high energy density have been investigated as functions of the volume fraction of the nanoparticles at room temperature by several theoretical models. For single domain and si...

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Nanoparticle/polymer composite capacitors are a promising approach for fabricating high performance capacitors at low temperatures using printing techniques. In this work, the dependence of the operating voltage of nanoparticle/polymer composite capacitors on the electromigration parameter of the electrodes is investigated. The authors have previou...

Self-assembled films built from nanoparticles with a high dielectric constant are attractive as a foundation for new dielectric media with increased efficiency and range of operation, due to the ability to exploit nanofabrication techniques and emergent electrical properties originating from the nanoscale. However, because the building block is a d...

Transition metal ferrites such as CoFe2O4, possessing a large magnetostriction coefficient and high Curie temperature (T c > 600 K), are excellent candidates for creating magnetic order at the nanoscale and provide a pathway to the fabrication of uniform particle-matrix films with optimized potential for magnetoelectric coupling. Here, a series of...

Nanodielectric materials become one of the key materials to play an important role in sustainable and clean energy production, energy transformation, energy storage, and end usage in terms of energy storage capabilities due to the trade-off between dielectric constant, dielectric loss and voltage breakdown. Based on our recent research on BaTiO3 (B...

Nanoparticle polymer composite capacitors have been examined for some time as a route to high performance, printable capacitors. One approach to creating these compo-sites is to use a particle film together with vapor deposited polymers, which can yield high performance, but also forms a structurally asymmetric device. The performance of a nano-par...

Magnetic cobalt ferrite nanoparticles provide a pathway towards nanocomposites, due to the ability to fabricate particle-matrix thin films in the submicron range. In this work flexible particulate 0-3 type thin-films, composed of magnetic CoFe2O4 particles (8-18 nm) and ferroelectric poly(vinylidene fluoride-co-hexafluoropropene) (P(VDF-HFP)) polym...

With climbing worldwide oil prices and global warming, energy crisis poses a threat to living standards, economy, and even global environment. Nanodielectrics become one of the new materials activated to play a unique role in sustainable and clean energy production, energy transportation, energy storage, and end usage. Based on our recent research...

We present a novel approach to preparing bismuth acceptor doped barium titanate nanocrystal formulations that can be deposited in conjunction with polymers in order to prepare a thin film nanocomposite dielectric that exhibits desirable capacitor characteristics. Exploring the limits of dielectric function in nanocomposites is an important avenue o...

The intrinsic dielectric frequency dependent spectrum of single domain barium titanate (BaTiO3) at room temperature is investigated by considering the vibration of phonons and the conductivity of the tetragonal system in a wide frequency range up to THz. The proposed model combines Debye type of dissipation, soft mode theory, and the influence of c...

Recent studies of intrinsically n-type topological insulator (TI) Bi2Se3 demonstrated that doping with Cu introduces electrons into this system, and that in the narrow range of doping CuxBi2Se3 becomes a superconductor below Tc 5 K. It is presumed that Cu intercalates into Van der Waals gaps in the tetradymite structure of layered Bi2Se3, although...

The surface states of topological insulators are protected by time-reversal symmetry. Introducing magnetic impurities should break this symmetry and open a gap in the otherwise gapless surface states. Recent first-principle calculations predict that when topological insulators are doped with transition metal elements, such as Cr or Fe, a magnetical...

We report on the physical characteristics of horizonthally-grown Single-Walled Carbon Nanotubes (h-al-SWNT) arrays and their potential use as transparent and conducting alignment layer for liquid crystals display devices. Microscopy (SEM and AFM), spectroscopic (Raman) and electrical investigations demonstrate the strong anisotropy of h-al-SWNT arr...

Electrocatalysts consisting of polypyrrole (PPY) and Co deposited on carbon black (CB) at several compositions were prepared and tested for the oxygen reduction reaction (ORR) in a HClO4 buffer (pH=1) using a rotating ring-disk electrode (RRDE). It was determined that the most favorable catalyst composition (prior to calcination) had a CB:PPY weigh...

The surface states of topological insulators are robustly protected by time-reversal symmetry. Introducing magnetic impurities should open a gap in the otherwise gapless surface states. Recent first-principle calculations predict that when topological insulators are doped with transition metal elements, such as Cr or Fe, a magnetically ordered insu...

Understanding energy transfer mechanisms in graphene derivatives is strongly motivated by the unusually interesting electronic properties of graphene, which can provide a template for the creation of novel nanostructured derivatives. From a synthetic point of view, it is highly attractive to envision being able to synthesize pristine graphene from...

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Nanodielectrics is an emerging field with applications in capacitors, gate dielectrics, energy storage, alternatives to Li-ion batteries, and frequency modulation in communications devices. Self-assembly of high k dielectric nanoparticles is a highly attractive means to produce nanostructured films with improved performance—namely dielectric tunabi...

In this work, we characterize second-order Raman modes between 1650 and 2000 cm−1 of small-diameter single-wall carbon nanotubes (SWNTs). Raman spectra of single nanotubes are acquired by confocal Raman microscopy. Besides the frequently observed overtone M band and combination iTOLA modes, an additional mode involving combination of the radial bre...

Confocal Raman microscopy is used to record the Raman spectra of a metallic single-wall carbon nanotube (SWNT) exposed to ambient air under electrostatic gating. Significant and irreversible changes in the carbon−carbon stretching modes (G band) Raman spectrum of the tube are observed. The gate dependent frequency shift and line broadening of the G...

We have combined optical characterization with a magnetic actuation technique to measure the stiffness of single-walled carbon nanotubes of defined crystal structure. The measured stiffnesses correspond to an average Young's modulus of E = 0.97 +/- 0.16 TPa. For the structures investigated, no dependence on the nanotube chiral index was observed wi...

Confocal Raman microscopy was used to image and record the Raman spectra of individual single-wall carbon nanotubes (SWNTs) and single-layer graphene on silicon substrates at both room and low temperatures. The temperature-induced Raman spectral change of individual nanotubes is observed to be tube diameter dependent, with larger-diameter tubes typ...

We report a nanoparticle radius ratio dependent study of the formation of binary nanoparticle superlattices (BNSLs) of CdTe and CdSe quantum dots. While keeping all other parameters identical in the system, the effective nanoparticle radius ratio, gamma(eff), was tuned to allow the formation of five different BNSL structures, AlB(2), cub-NaZn(13),...

The formation process of CdSe-Au binary nanoparticle superlattices (BNSLs) was studied to elucidate the optimal conditions for self-assembly. Nanoparticle mixts. were prepd. under suitable and variable solvent evapn. conditions and the products analyzed by TEM. 1-Dodecanethiol is crit. for superlattice formation, prior to the onset of short-range n...

We have investigated the microwave properties of monodisperse, superparamagnetic g-Fe2O3 nanoparticle arrays using broadband ferromagnetic resonance. We identify a novel field for resonance relation in the films. Compared with ferromagnetic films of equal magnetization, resonance frequencies are suppressed for in-plane magnetization and enhanced fo...

We demonstrate the development and successful application of immunotargeted superparamagnetic iron oxide nanoparticles (ITSIONs), with in vivo magnetic resonance diagnostic and potential drug delivery capability for kidney disease. Further, the versatility of the conjugation chemistry presents an attractive route to the preparation of a range of bi...

Interactions in nanoparticle assemblies play an important role in modulating their interesting magnetic and optical properties. Controlling and fixing the distance between nanoparticles is therefore crucial to the development of next-generation nanodevices. Here, we show that the interparticle distance in two-dimensional assemblies can be quantitat...

We report binary nanoparticle superlattices obtained by self-assembly of two different semiconductor quantum dots. Such a system is a means to include two discretized, quantum-confined, and complimentary semiconductor units in close proximity, for purposes of band gap matching and/or energy transfer. From a range of possible structures predicted, w...

We present Mössbauer studies of hybrid iron-oxide nanoparticles obtained by the disproportionation of oleic acid stabilized wüstite (FexO) nanoparticles produced by selective oxidation of iron pentacarbonyl in high boiling temperature organic solvents. The results support X-ray diffraction and Transmission Electron Microscope studies of the presenc...

A review. Single-walled carbon nanotubes (SWNTs) have unique structural, mech., thermal and elec. properties, which make them attractive and important building blocks for nanotechnol. Oriented assembly of SWNTs presents a crucial prerequisite for both fundamental research at the individual SWNT level and nanotube-based device fabrication and applic...

A systematic study of the zeta (z)-potential distribution of surfactant-wrapped individual single-walled carbon nanotubes (SWNTs) dissolved in water is presented here. The surface charge on the SWNT micelles, as measured by the z-potential, has implications for the stability of the dispersions and for the electrophoretic and dielectrophoretic assem...

A beam-scanning confocal Raman microscope system capable of large-area imaging is developed for characterizing single-wall carbon nanotubes at the single tube level. Individual ultralong nanotubes grown on a large silicon substrate are systematically imaged by both confocal Raman microscopy and scanning electron microscopy. Raman spectra for more t...

Monodisperse ligand-capped cubic wüstite FexO nanocrystals were prepared by a novel thermal decomposition method of iron (II) acetate in the presence of oleic acid as the surfactant. Controlled size distributions of cubic nanoparticles possessing the rock salt crystal structure were isolated in the range 10–18 nm. The influence of molar ratio of su...

A versatile, convenient, and nontoxic solvothermal method for the synthesis of nanocrystalline iron, chromium, and manganese oxides is described. This method employs the reactions of metal acetylacetonate precursors and oxygen-containing solvents in a reaction to prepare metal oxide nanoparticles. Characterization of these nanocrystalline materials...

A novel solution method to control the diameter of ZnO nanorods is reported. Small diameter (2-3 nm) nanorods were synthesized from trihexylamine, and large diameter (50–80 nm) nanorods were synthesized by increasing the alkyl chain length to tridodecylamine. The defect (green) emission of the photoluminescence (PL) spectra of the nanorods var...

We investigated the optical properties of colloidal-synthesized ZnO spherical nanoparticles prepared from 1-octadecene (OD), a mixture of trioctylamine (TOA) and OD (1:10), and a mixture of trioctylphosphine oxide (TOPO) and OD (1:12). It is found that the green photoluminescence (PL) of samples from the mixture of TOA/OD and TOPO/OD is largely sup...

The adsorption dynamics of n-/isobutane on "closed"-end (as-prepared, c-CNTs) and open-end (vacuum-annealed) carbon nanotubes (o-CNTs) have been studied by molecular beam scattering adsorption probability measurements. Thermal desorption spectroscopy (TDS) and scanning electron microscopy have been used to characterize the CNTs. Evident from TDS da...

We report here a method to integrate discrete multicomponent assembly into molecular electronic devices. We first functionalize a molecule wired between the ends of a single-walled carbon nanotube so that it can be derivatized with a probe molecule. This probe then binds to a complementary biomolecule to form a noncovalent complex. Each step of che...

Nanoparticles of bulk antiferromagnets often exhibit ferromagnetic behavior due to uncompensated surface spins. The peak temperature in the zero-field-cooled magnetization of MnO—in contrast to other antiferromagnetic nanoparticles—has anomalous behavior, shifting to higher temperatures with decreasing nanoparticle size. We attribute this behavior...

Single-walled carbon nanotubes (SWNTs) have been precisely aligned and positioned in device architectures using ac dielectrophoresis by patterning floating metal posts or strips within the electrode gaps. These structures perturb the electric field, causing local enhancements in the field intensity, as seen in simulation, that guide the nanotubes a...

The AC dielectrophoretic assembly of single-walled carbon nanotubes (SWNTs) represents an attractive approach for the fabrication of SWNT devices. The dielectrophoresis approach relies on the deposition of water-soluble surfactant-wrapped individualized SWNTs in electrode gaps. We have tested a variety of different anionic, non-ionic, and cationic...

Combinations of up to 6 zone-edge and zone-center optical phonons are observed in the Raman spectra of individual single-walled carbon nanotubes (SWNTs). These multiphonon Raman modes exhibit distinct signatures of the one-dimensional nature of SWNTs and provide information on the phonon structure, exciton-phonon coupling, and excitonic transitions...

A new nonhydrolytic route for the preparation of well-crystallized size-tunable barium titanate (BaTiO3) nanocrystals capped with surface ligands is reported. Our approach involves: (i) synthesizing a “pseudo” bimetallic precursor, and (ii) combining the as-synthesized bimetallic precursor with a mixture of oleylamine with different surface coordin...

Quantitative determination of oxide nanoparticle composition and structure by X-ray photoelectron spectroscopy (XPS) has proven difficult for metal oxides because of three factors:  some oxide nanoparticles are prone to reduction in the XPS instrument under X-ray illumination in the ultrahigh vacuum (UHV) environment; the nanoparticle structure and...

Because subtle changes in phys. structure (chirality) can cause the electronic structure of carbon nanotubes to vary from metallic to semiconducting, the goal of fully controlled nanotube device fabrication has proved elusive. Using a mech. transfer technique in parallel with optical characterization, we have achieved the goal of placing 'the nanot...

The authors present a method for producing nanometer-scale gaps, based on metal evapn. through a suspended single-walled carbon nanotube acting as a shadow mask. 83% of the nanogap devices display current-voltage dependencies characteristic of direct electron tunneling. Fits to the current-voltage data yield gap widths in the 0.8-2.3 nm range for t...

The precise placement of single-walled carbon nanotubes (SWCNTs) in device architectures by ac dielectrophoresis involves the optimization of the electrode geometry, applied voltage and frequency, load resistance, and type of nanotube sample used. The authors have developed a toolkit to controllably integrate SWCNTs in device structures by the use...

By combining electron diffraction with Rayleigh scattering spectroscopy, we simultaneously determine the crystal structure and the optical transition energies of individual single-walled carbon nanotubes.

The physical displacement of individual single-walled carbon nanotubes is measured by Rayleigh light scattering. Each nanotube's Young's modulus is determined by an applied Lorentz force.

We find that nearly monodisperse copper oxide nanoparticles prepared via the thermal decomposition of a Cu(I) precursor exhibit exceptional activity toward CO oxidation in CO/O2/N2 mixtures. Greater than 99.5% conversion of CO to CO2 could be achieved at temperatures less than 250 degrees C for over 12 h. In addition, the phase diagram and pathway...

Advanced applications for high k dielec. and ferroelec. materials in the electronics industry continues to demand an understanding of the underlying physics in decreasing dimensions into the nanoscale. We report the synthesis, processing, and elec. characterization of thin (<100 nm thick) nanostructured thin films of barium titanate (BaTiO3) built...

We report a simple and efficient chemical vapor deposition (CVD) process that can grow oriented and long single-walled carbon nanotubes (SWNTs) using a cobalt ultrathin film ( approximately 1 nm) as the catalyst and ethanol as carbon feedstock. In the process, millimeter- to centimeter-long, oriented and high-quality SWNTs can grow horizontally on...

By combining electron diffraction with Rayleigh scattering spectroscopy, we determine the physical structure and optical transition energies of individual single-walled carbon nanotubes. This permits study of the energy-level structure as a function of nanotube chirality.