Douglas L. Schulz

The first true inorganic fullerenes

Boron nitride and materials of composition MX2, where M is molybdenum or tungsten and X is sulphur or selenium, can form fullerene-like structures such as nested polyhedra or nanotubes. However, the analogy to the carbon fullerene family falls short because no small preferred structure akin to C60(ref. 5) has been found. We have discovered nano-octahedra of MoS2of discrete sizes in soots that we prepared by laser ablation of pressed MoS2targets. These nano-octahedra are much larger than C60structures, having edge lengths of about 4.0 and 5.0 nanometres, and may represent the first ‘inorganic fullerenes’.

Preparation and Characterization of LiMn2 O 4 Spinel Nanoparticles as Cathode Materials in Secondary Li Batteries

Nanoparticles of LiMn 2 O 4 spinels have been synthesized through a sol-gel method followed by annealing at various temperatures between 350 and 550°C. The particle sizes depend on annealing temperatures. At a low annealing temperature (350°C), the nanoparticles may have a size of 10 nm, estimated from transmission electron microscopy photographs. The annealing temperatures higher than 550°C give rise to particles larger than nanoscale. Some large porous Li 1.4 Mn 2 O 4 particles with 1 μm size were prepared for comparison through an emission process. The electrochemical tests indicate that those nanoparticles reduce capacities in the 4 V discharge region but improve rechargeability of the electrode materials. On the other hand, the nanoparticles significantly improve both capacities and cycling performance in the 3 V discharge region. The electrochemical properties of these materials are further investigated using cyclic voltammetry and ac impedance spectroscopy. The results reveal that the homogeneous-phase transition occurring in the 3 V region and at the first discharge plateau of the 4 V discharge region increases the difficulty of the Li + insertion/extraction process and affects rechargeability of the electrode materials. However, the nanoparticles and porous materials reduce charge-transfer resistances between the composite electrodes and electrolyte interface and increase the effectiveness of lithium intercalation into the active materials in comparison with those large but nonporous materials.

NANOPARTICLE PRECURSOR ROUTE TO LOW-TEMPERATURE SPRAY DEPOSITION OF CDTE THIN FILMS

In this letter we report a nanoparticle‐derived route to CdTe thin films. CdTe nanoparticles 39±8 A in diameter, prepared by an organometallic route, were characterized by x‐ray diffraction, UV‐Vis spectroscopy, transmission electron microscopy, and energy dispersive x‐ray spectroscopy. CdTe thin‐film deposition was realized by spraying a nanoparticle/butanol colloid onto SnO2‐coated glass substrates at variable susceptor temperatures. The resultant CdTe films were characterized by atomic force microscopy, x‐ray diffraction, and UV‐Vis spectroscopy. Smooth and dense CdTe thin films were obtained using growth temperatures ∼200 °C less than conventional spray pyrolysis. A growth temperature dependence upon CdTe grain size formation and crystallinity was observed by atomic force microscopy and x‐ray diffraction. UV‐Vis characterization revealed a transformation in the optical properties of the CdTe thin films as a function of growth temperature.

Cobalt ferrite nanoparticles: Achieving the superparamagnetic limit by chemical reduction

An unanticipated superparamagnetic response has been observed in cobalt ferrite materials after thermal treatment under inert atmosphere. Cobalt ferrite particles were prepared via normal micelle precipitation that typically yields CoxFe3−xO4 nanoparticles (x=0.6−1.0). While samples thermally treated under oxygen show majority spinel phase formation, annealing in nitrogen gas yields materials consisting of Co-Fe alloy, FeS, and CoFe2O4 spinel. After thermal treatment, thermomagnetic studies reveal composition-insensitive, but highly treatment-sensitive, saturation magnetization, coercivity, blocking temperature, and Verwey transition temperature dependence. Extremely high saturation magnetization (159 emu/g) with low coercivity (31 Oe) was observed for one of the treated compositions, which drastically deviates from prototypical cobalt ferrite with large magnetocrystalline anisotropy. We attribute such unique magnetic response to Co-Fe alloy coexisting with FeS and CoFe2O4 spinel where the diameter of the...

Work function and implications of doped poly(3,4-ethylenedioxythiophene)-co-poly(ethylene glycol)

We report work function and conductivity measurements of the block copolymer poly(3,4-ethylenedioxythiophene)-co-poly(ethylene glycol) (PEDOT-PEG) doped with perchlorate or para-toluenesulfonate anions. The electronic and chemical properties of doped PEDOT-PEG are discussed in the context of the hole injection for organic light emitting diodes. We show that different dopants can result in significant differences in conductivity with only small alterations to the work function.

A Review on Aerosol-Based Direct-Write and Its Applications for Microelectronics

Aerosol-based direct-write refers to the additive process of printing CAD/CAM features from an apparatus which creates a liquid or solid aerosol beam. Direct-write technologies are poised to become useful tools in the microelectronics industry for rapid prototyping of components such as interconnects, sensors, and thin film transistors (TFTs), with new applications for aerosol direct-write being rapidly conceived. This paper aims to review direct-write technologies, with an emphasis on aerosol-based systems. The different currently available state-of-the-art systems such as Aerosol Jet CAB-DW, MCS, and aerodynamic lenses are described. A review and analysis of the physics behind the fluid-particle interactions including Stokes and Saffman force, experimental observations, and how a full understanding of theory and experiments can lead to new technology are presented. Finally, the applications of aerosol direct-write for microelectronics are discussed.

Influences of Treatment Temperature and Water Content on Capacity and Rechargeability of V 2 O 5 Xerogel Films

V 2 O 5 xerogel films prepared with spray deposition have been investigated for their lithium battery applications. The influences of spray deposition and postannealing temperatures on the water content, structure, and electrochemical performance of the films have been studied. Water contents of the V 2 O 5 .nH 2 O films depend on the deposition and postannealing temperatures. One film sprayed at 150°C and annealed at 190°C exhibited a large discharge capacity and the longest cycling life. By contrast, the films sprayed or annealed at high temperatures (>250°C) showed poor electrochemical performance. The film deposited at a substrate temperature of 420°C demonstrated structural features and electrochemical behavior of orthorhombic V 2 O 5 . X-ray diffraction patterns of the films treated at different temperatures reveal that removal of too much water at high temperatures results in crystallization or a small interlayer spacing, which may restrict the diffusion of lithium ions inside V 2 O 5 .nH 2 O films. 51 V solid-state nuclear magnetic resonance spectra show that the films annealed at low temperatures (i.e., 120°C or room temperature) have broad peaks and significant downfield isotropic chemical shifts, suggesting that the interlayered water produces a distorted square-pyramidal ligand field that may favor lithium intercalation and electron transfer within the matrix of the films.

Next generation V2O5 cathode materials for Li rechargeable batteries

We report on investigations of vanadium oxide thin film cathodes prepared by three different synthesis techniques. Our experimental results on PLD-grown, textured V 2 O 5 crystalline films concur with reports in the literature that there is a voltage threshold above which, cycling appears to be completely reversible and below which, cycling appears to be irreversible. Crystalline films discharged beyond the threshold to 2.0 V exhibited an immediate and continuous fade in capacity as well as a nearly 90% decrease in XRD peak intensity and a similar decrease in Raman signal intensity in as few as ten cycles. PLD-grown amorphous films show capacity loss of < 2% over 200 cycles. Amorphous plasma-enhanced chemical vapor deposition (PECVD) films have capacities as high as 1.5 Li/V with excellent stability over 3000 cycles. Solution-grown nanoparticles (< 100 nm) of VO 2 were spray-deposited and sintered at relatively low temperatures to produce nanoporous films. Cycling properties along with structural investigations by XRD and Raman scattering will be presented.

Flattening a puckered cyclohexasilane ring by suppression of the pseudo-Jahn–Teller effect

We report the experimental and theoretical characterization of neutral Si(6)X(12) (X = Cl, Br) molecules that contain D(3d) distorted six-member silicon rings due to a pseudo-Jahn-Teller (PJT) effect. Calculations show that filling the intervenient molecular orbitals with electron pairs of adduct suppresses the PJT effect in Si(6)X(12), with the Si(6) ring becoming planar (D(6h)) upon complex formation. The stabilizing role of electrostatic and covalent interactions between positively charged silicon atoms and chlorine atoms of the subject [Si(6)Cl(14)](2-) dianionic complexes is discussed. The reaction of Si(6)Cl(12) with a Lewis base (e.g., Cl(-)) to give planar [Si(6)Cl(14)](2-) dianionic complexes presents an experimental proof that suppression of the PJT effect is an effective strategy in restoring high Si(6) ring symmetry. Additionally, the proposed pathway for the PJT suppression has been proved by the synthesis and characterization of novel compounds containing planar Si(6) ring, namely, [(n)Bu(4)N](2)[Si(6)Cl(12)I(2)], [(n)Bu(4)N](2)[Si(6)Br(14)], and [(n)Bu(4)N](2)[Si(6)Br(12)I(2)]. This work represents the first demonstration that PJT effect suppression is useful in the rational design of materials with novel properties.

Direct-Write Vapor Sensors on FR4 Plastic Substrates

Functioning chemiresistor vapor sensing devices on plastic substrates were prepared using low-temperature direct-Xwrite techniques. Interdigitated Ag electrodes were first deposited onto printed circuit boards using a mesoscale maskless materials deposition system (M3D). These Ag lines were 20-50 mum wide and 8-10 mum thick with good adhesion to the substrate and electrical conductivity of 4-12 muOmegamiddotcm. Deposition of chemoselective polymer/C black composite transducer layers on such lines gave sensors that responded to nerve gas stimulant (dimethylmethyl phosphonate) thereby demonstrating the efficacy of direct write for this application. A new approach to localized direct-write deposition, termed Enhanced M3D, allows the formation of sharply defined line edges and enables printing of conductors that operate at radio frequency with low signal loss. The direct-write approaches described here are amenable to future deposition on more interesting substrates and development of more sensitive transducers, orthogonal sensor arrays and an integrated power source/communication platform that might constitute the basis for radio-frequency identification (RFID) sensor tags