C.K. Chiang

Polymeric electrolyte based on poly(ethylene imine) and lithium salts

The dissolution of lithium salts in linear poly(ethylene imine) was investigated because of its possible role as a solid electrolyte in lithium batteries. Lithium salts included in the study are LiF, LiCl, LiBr, LiI, LiSCN, LiClO4 and LiBF4. When cast from solution in a common solvent, a uniform mixture is obtained (expect for the case of LiF). Interaction of the salt and polymer can be characterized by observing a loss in crystallinity of the polymer and an increase in the glass transition temperature. At concentrations of salt below 10 mole %, the polymer can slowly recrystallize at room temperature but at higher concentrations, the mixture remains amorphous for an indefinite period of time. DC conductivity at room temperature is about .0000001 S/cm but increases to .001 S/cm at 150 C.

A Framework for Broadband Characterization of Individual Nanowires

A framework for broadband characterization of individual nanowires (NWs) is discussed in this letter. Specifically, on-wafer multiline thru-reflect-line (TRL) measurements, finite element modeling, and specially fabricated test structures with both extremely high and low impedances are jointly used to validate the feasibility of both measurements and modeling for characterizing small components. The test structures are designed as coplanar waveguide (CPW) devices with 100 nm and 250 nm diameter platinum (Pt) NWs. Though it is not possible to distinguish between the conductivity of the wire and contact resistances, we determine a range for conductivity and contact resistance over wide microwave bandwidth by minimizing the standard deviation between the measurements and full-wave modeling.

High frequency characterization of a Schottky contact to a GaN nanowire bundle

A two-port GaN nanowire (NW) device with one Schottky contact and one Ohmic contact was characterized up to 10 GHz using on-wafer microwave measurements. In addition to the measurement of the broadband response, two additional applications of microwave measurements are introduced: (1) the capability to distinguish a Schottky-type contact from an Ohmic contact based on the reflected broadband signals (S11 and S22) and (2) the measurement of a capacitance voltage (CV) curve for a Schottky contact to a bundle of a few NWs. The junction capacitance of the Schottky contact is determined at various bias voltages by fitting the broadband response with a microwave circuit model. The carrier concentration is estimated from the resulting CV curve to be 5.3×1018/cm3 and the Schottky barrier height is estimated to be 0.89 eV.

Impedance spectrum of a single grain boundary in yttrium stabilized zirconia

Abstract Impedance measurements are reported for a bicrystal and single crystals of yttrium-stabilized ZrO 2 (YSZ) over the range from 100 to 10 7 Hz, and for temperatures from 200 to 500°C in air. In addition to the impedances introduced by the conduction process within the grains and by charge transfer process at the electrodes, the grain-boundary introduced an additional impedance which was observed as an additional arc when the impedance was plotted in the complex plane. These data and an examination by both optical and scanning electron microscopy reveal the grain boundary to be a gap between the adjacent crystals, with occasional bridges of YSZ. These results illustrate the potential of impedance spectroscopy for studying intercrystalline interfaces in solid conductors.

Chemical modification of poly(ethylene imine) for polymeric electrolyte

Abstract Linear PEI has been chemically modified in an attempt to prevent formation of a crystalline complex without altering its ability to dissolve salts and conduct ions. Three main systems were investigated: (a) poly(N-acetylethylene imine), (b) partially quaternized PEI with ethyl or butyl groups, and (c) PEI cross-linked with diepoxyoctane. Dissolution of salt was followed by x-ray diffraction on the mixtures and changes in T g as determined by DSC. In all cases, the crystallinity was destroyed but conductivity of salt-containing polymer was not improved. However, lightly cross-linked PEI exhibits much improved mechanical properties and the incorporation of .05 mole NaI/mole of monomer yields a conductivity of 5×10 −5 S / cm at 100 °C.

Constricted diamagnetic hysteresis loops observed for the high Tc superconductors

Magnetic hysteresis loops, ac susceptibility, and resistivity measurements have been made on a Ba2 YCu3 O7−x‐type high‐ Tc superconductor. The shape of the hysteresis loops well below Tc are reminiscent of constricted hysteresis loops observed in certain ferromagnetic materials which are usually associated with magnetic aftereffects. Similar dynamic effects, with a time constant on the order of 10 s at 40 K, are shown to be present in the superconducting material. This dynamic magnetic viscosity effect is in addition to the flux creep observed for longer time periods.

Preparation and properties of polymeric solid electrolyte: Polyethylene oxide--sodium iodide complexes

Abstract The thermal and electrical properties of mixtures of polyethylene oxide and sodium iodide were measured for concentrations of salt up to 25 mole %. A maximum in dc conductivity is observed at low concentrations of NaI, a region in which no crystalline complex is formed as determined from DSC measurements.

Magnetic behavior of both superconducting thin films and their deposition targets

The superconducting properties of the bulk oxides La1.85Sr0.15CuO4−x and Ba2YCu3O7−y were investigated through their magnetic behavior by vibrating‐sample magnetometry and complex ac susceptibility, and by dc resistivity and microwave response. These oxides were then used as targets in the preparation of thin films using a laser‐ablation technique. The superconducting properties of the films were established through their microwave response. The M‐H loops at low temperatures clearly establish the type‐II behavior of the Ba‐Y‐Cu‐O materials. The real part of the ac susceptibility showed the superconducting transition. Simultaneously, the imaginary part of the ac susceptibility showed the existence of nonsuperconducting portions in the samples which have a low enough resistivity to carry a significant amount of current. The novel method of microwave response was used to detect the superconductivity for both the bulk oxides and the thin films.

Modeling and metrology of metallic nanowires with application to microwave interconnects

Broadband characterization of individual metallic nanowires for microwave interconnect applications is discussed. Circuit and method of moments (MoM) modeling are benchmarked using a set of coplanar waveguide (CPW) test devices with Au microwire (MW) interconnect and air gaps in the middle of the CPW. Comparison with measurements reveals significantly larger errors from circuit models though all dimensions are much smaller than wavelength. Similar CPW devices hosting 100 nm and 250 nm diameter Pt nanowires (NWs) are then investigated to determine the ranges of conductivity and contact resistance for each Pt NW. An algorithm that utilizes the transmission line theory and different nanowire lengths to determine the actual conductivity and contact resistance is proposed and validated.

The atomic fingerprint of YBa2Cu3O7−x-type high-temperature superconductors observed by field ion microscopy

Abstract The high-transition-temperature superconducting oxides YBa2Cu3O7−x, YbBa2Cu3O7−x, SmBa2Cu3-O7−x, GdBa2(Cu0.96Fe0.04)3O7−x, and GdBa2(Cu0.92Fe0.08)3O7−x (0