R.A. Zuhr

Fabrication and characterization of amorphous lithium electrolyte thin films and rechargeable thin-film batteries

Amorphous oxide and oxynitride lithium electrolyte thin films were synthesized by r.f. magnetron sputtering of lithium silicates and lithium phosphates in Ar, Ar + O2, Ar + N2, or N2. The composition, structure, and electrical properties of the films were characterized using ion and electron beam, X-ray, optical, photoelectron, and a.c. impedance techniques. For the lithium phosphosilicate films, lithium ion conductivities as high as 1.4 × 10−6 S/cm at 25 °C were observed, but none of these films selected for extended testing were stable in contact with lithium. On the other hand, a new thin-film lithium phosphorus oxynitride electrolyte, synthesized by sputtering Li3PO4 in pure N2, was found to have a conductivity of 2 × 10-6 S/cm at 25 °C and excellent long-term stability in contact with lithium. Thin-films cells consisting of a 1 μm thick amorphous V2O5 cathode, a 1 μm thick oxynitride electrolyte film, and a 5 μm thick lithium anode were cycled between 3.7 and 1.5 V using discharge rates of up to 100 μA/cm2 and charge rates of up to 20 μA/cm2. The open-circuit voltage of 3.6 to 3.7 V of fully-charged cells remained virtually unchanged after months of storage.

Electrical properties of amorphous lithium electrolyte thin films

The impedance of xLi2O·ySiO2·zP2O5 thin films deposited by RF-magnetron sputtering was analyzed using two models in which the frequency dependence of the bulk response was represented by: (1) a Cole-Cole dielectric function and (2) a constant phase angle element. Increases in the conductivity with Li2O concentration and with addition of SiO2 to Li2O-P2O5 compositions are attributed to an increase in Li+ mobility caused by changes in the film structure. A new amorphous oxynitride electrolyte, Li3.3PO3.9N0.17, prepared by sputtering Li3PO4 in N2, has a conductivity at 25°C of 2×10−6S/cm and is stable in conta with lithium.

Picosecond nonlinear optical response of a Cu:silica nanocluster composite

We describe the picosecond nonlinear optical response of a metal-dielectric composite made by implanting Cu ions in fused silica. The implanted Cu ions aggregate during implantation to form nanometer-diameter clusters in a dense, thin (~150 nm) layer just beneath the surface of the substrate. The third-order susceptibility X((3)) has an electronic component with a magnitude of the order of 10(-8) esu and is enhanced for laser wavelengths near the surface plasmon resonance of the copper colloids.

Physical and optical properties of Cu nanoclusters fabricated by ion implantation in fused silica

Cu clusters of nanometer dimensions were created by implantation of Cu ions into pure fused silica substrates at energies of 160 keV. The sizes and size distributions of the Cu clusters were measured by transmission electron microscopy, and were found to be determined by the ion‐beam current during implantation. Optical‐absorption spectra of these materials show the size‐dependent surface plasmon resonance characteristic of noble‐metal clusters. There are also significant size‐dependent effects in both the nonlinear index of refraction and two‐photon absorption coefficients. The distinctive variations in linear and nonlinear optical properties with Cu nanocluster sizes and size distributions affords potentially interesting possibilities for using these materials in nonlinear optical devices.

Nonlinear optical properties of metal-quantum-dot composites synthesized by ion implantation

Abstract Over a decade ago, it was demonstrated that composites comprising metal clusters embedded in dielectric hosts could be synthesized by ion implantation. The optical properties of these metal-cluster composites are dominated by two phenomena which alter the susceptibilities from those of bulk metals: One is a classical field enhancement effect, dielectric confinement, which leads to the characteristic surface plasmon resonance of the metal clusters seen in absorption spectra. The other effect is quantum confinement of the conduction-band electrons which enhances the nonlinear susceptibility of the metal clusters for diameters smaller than about 10 nm and makes them behave as quantum dots with electronic properties which approximate those of independent electrons confined in a spherical potential well. This paper reviews our studies of the nonlinear optical behavior of quantum-dot composites synthesized by ion implantation. We also consider the potential of these quantum-dot composites as materials for nonlinear waveguide devices.

Nanocrystalline Li{sub x}Mn{sub 2{minus}y}O{sub 4} cathodes for solid-state thin-film rechargeable lithium batteries

Thin-film cathodes of lithium manganese oxide, 0.3-3 μm thick, were deposited by rf magnetron sputtering of a LiMn 2 O 4 ceramic target onto unheated substrates. The resulting films were dense, ∼4.2 g/cm 3 , with a ∼50 A nanocrystalline spinel structure. The film composition was typically Li x Mn 2-y O 4 with y ∼ 0.3 and 1.2 < x < 2.2. When cycled in a thin-film rechargeable lithium battery, specific cathode capacities of 145 ± 23 and ∼270 mAh/g were realized for discharge from 4.5 V to either 2.5 or 1.5 V, respectively. The discharge and charge current densities were limited by the resistivity of lithium transport into and through the cathode. After thousands of cycles at 25°C, there was a small increase in cell resistance. After several hundred cycles at 100°C, the discharge curves developed a stable knee at ∼4 V characteristic of crystalline LiMn 2 O 4 cathodes. The polarization of the discharge/charge cycles were interpreted in terms of free energy of mixing curves.

ENCAPSULATED SEMICONDUCTOR NANOCRYSTALS FORMED IN INSULATORS BY ION BEAM SYNTHESIS

Abstract Both elemental and compound semiconductor nanocrystals have been formed in insulators by ion beam synthesis. Si nanocrystals in SiO2 give rise to strong optical absorption and intense photoluminescence (PL). The dose dependence of optical absorption provides evidence for size dependent changes in the Si nanocrystal bandgap due to quantum confinement, but the PL results suggest that surface or defect states play an important role in PL. CdS and CdSe nanocrystals have been formed in SiO2 and in Al2O3. Their structure, size, and optical properties are discussed.

Controlling the size, structure and orientation of semiconductor nanocrystals using metastable phase recrystallization

Materials engineering at the nanometre scale should provide smaller technological devices than are currently available,. In particular, research on semiconductor nanostructures with size-dependent optical and electronic properties is motivated by potential applications which include quantum-dot lasers and high-speed nonlinear optical switches,. Here we describe an approach for controlling the size, orientation and lattice structure of semiconductor nanocrystals embedded in a transparent matrix. We form nanocrystalline precipitates by implanting ions of the semiconductor into a single-crystal alumina substrate and applying thermal annealing. Control over the microstructure of the nanocrystals is achieved using substrate amorphization and recrystallization. In essence, the substrate microstructure is manipulated using ion beams to induce changes in impurity solubility, crystal symmetry and cation bonding, which exert a profound influence on the microstructure of the embedded precipitates—a concept familiar in metallurgy. This approach can be extended to exercise control over virtually any type of precipitate (such as metals, insulators or magnetic clusters) as well as epitaxial thin films.

Lithium Manganese Nickel Oxides Li x ( Mn y Ni1 − y ) 2 − x O 2 I. Synthesis and Characterization of Thin Films and Bulk Phases

The series Li x (Mn y Ni 1-y ) 2-x O 2 for x ≤ 1.33 and 0.38 ≤ y ≤ 0.50 shows a very close relationship to its parent series Li x Ni 2-x O 2 . The refine lattice parameters for at least 0.93 ≤ x ≤ 1.26 are a linear function of the concentration ratio Li/(Mn + Ni) which in turn is proportional to the averaged valence state of the transition metals. Li x (Mn y Ni 1-y ) 2-x O 2 is able to reversibly coprecipitate/reinsert Li 2 O and release/absorb O 2 . This self-regulation mechanism seems to always adjust the number of cations to an undisturbed oxygen sublattice according to the rule cations/anions = 1, which holds true at least for temperatures up to 800°C and oxygen partial pressures above 10 -5 atm. Samples prepared in air and under O 2 did not show nucleation of Li 2 O, not even for x > 1.0. The series Li x (Mn y Ni 1-y ) 2-x O 2 where 0.38 ≤ y ≤ 0.50 crystallizes in a rhombohedral unit cell (space group R3m) for x 1.25. The similarity between Li x Ni 2-x O 2 and Li x (Mn y Ni 1-y ) 2-x O 2 strongly suggests a rhombohedral → cubic transition at x 0.6 for the latter series. Derived from the linear dependence of the X-ray density on the stoichiometric parameter x, an equation was found with which the lithium concentration of Li x (Mn y Ni 1-y ) 2-x O 2 thin film phases over the entire range 0 ≤ x ≤ 1.33 can be determined accurately without extensive ion-beam analysis. XPS measurements on a film with the bulk stoichiometry Li 1.10 Mn 0.39 Ni 0.51 O 2 gave evidence for Mn 4+ and Mn 3+ , but no indication was found for nickel valence states other than Ni 2+ In order to meet the above-given stoichiometry, the averaged nickel valence state had to increase with film depth

Non-linear optical properties of nanometer dimension AgCu particles in silica formed by sequential ion implantation

Abstract Nanometer dimension metal colloids were formed in silica by sequential implantation of Ag and Cu ions. The Ag and Cu were implanted with Ag to Cu ratios of 9:3, 6:6 and 3:9 and total nominal dose 12 × 10 16 ions/cm 2 . The linear optical response was measured from 200 to 900 nm. The non-linear optical properties were measured using the Z-scan technique at a wavelength of 570 nm. The linear and non-linear optical properties were found to be dependent upon the Ag to Cu ratio.