Paul G. Clem

Realizing optical magnetism from dielectric metamaterials.

We demonstrate, for the first time, an all-dielectric metamaterial resonator in the mid-wave infrared based on high-index tellurium cubic inclusions. Dielectric resonators are desirable compared to conventional metallo-dielectric metamaterials at optical frequencies as they are largely angular invariant, free of ohmic loss, and easily integrated into three-dimensional volumes. With these low-loss, isotropic elements, disruptive optical metamaterial designs, such as wide-angle lenses and cloaks, can be more easily realized.

Dielectric properties of random and 〈100〉 oriented SrTiO3 and (Ba,Sr)TiO3 thin films fabricated on 〈100〉 nickel tapes

Properties are presented for random and enhanced 〈100〉 orientation SrTiO3 and BaxSr1−xTiO3 (x=0.33, 0.50, and 0.67) films fabricated on base-metal 〈100〉 Ni tapes using a chemical solution deposition approach. Films were crystallized in a reducing atmosphere, which prevented Ni oxidation, but permitted growth of SrTiO3 and BaxSr1−xTiO3 films with dielectric loss tan δ between 0.003 and 0.015. For randomly oriented BaxSr1−xTiO3 (x=0, 0.33, 0.5, and 0.67) films, zero-field 100 kHz dielectric constants ranged from 250 to 420. Films with enhanced 〈100〉 orientation exhibited zero-field dielectric constants of 980 to 1500, three times higher than random films. Development of such high dielectric constants on Ni suggests a future method for inexpensive, high performance base-metal electrode capacitor fabrication. Properties are presented for random and enhanced 〈100〉 orientation SrTiO3 and BaxSr1−xTiO3 (x=0.33, 0.50, and 0.67) films fabricated on base-metal 〈100〉 Ni tapes using a chemical solution deposition approach. Films were crystallized in a reducing atmosphere, which prevented Ni oxidation, but permitted growth of SrTiO3 and BaxSr1−xTiO3 films with dielectric loss tan δ between 0.003 and 0.015. For randomly oriented BaxSr1−xTiO3 (x=0, 0.33, 0.5, and 0.67) films, zero-field 100 kHz dielectric constants ranged from 250 to 420. Films with enhanced 〈100〉 orientation exhibited zero-field dielectric constants of 980 to 1500, three times higher than random films. Development of such high dielectric constants on Ni suggests a future method for inexpensive, high performance base-metal electrode capacitor fabrication.

Optical magnetic mirrors without metals

The reflection of an optical wave from metal, arising from strong interactions between the optical electric field and the free carriers of the metal, is accompanied by a phase reversal of the reflected electric field. A far less common route to achieving high reflectivity exploits strong interactions between the material and the optical magnetic field to produce a “magnetic mirror” that does not reverse the phase of the reflected electric field. At optical frequencies, the magnetic properties required for strong interaction can be achieved only by using artificially tailored materials. Here, we experimentally demonstrate, for the first time to the best of our knowledge, the magnetic mirror behavior of a low-loss all-dielectric metasurface at infrared optical frequencies through direct measurements of the phase and amplitude of the reflected optical wave. The enhanced absorption and emission of transverse-electric dipoles placed close to magnetic mirrors can lead to exciting new advances in sensors, photodetectors, and light sources.

Self-assembled aerogel-like low dielectric constant films

A series of new spin-on nanoporous silica films with controlled porosity and dielectric constants were prepared by evaporation induced self-assembly (EISA) during spin-coating. Starting with a homogeneous solution of soluble silica and surfactant/swelling agent prepared in an alcohol/water solvent, preferential evaporation of alcohol during spin-coating results in the hierarchical self-assembly of surfactants plus swelling agent and soluble silica into a templated microemulsion system. Silicate polymerization followed by removal of surfactant and swelling agents via immediate calcination results in a highly porous silica film of the liquid crystalline assembly with controlled porosity ranging from 50% to 90% and dielectric constant ranging from 1.3 to 2.6. TEM and surface acoustic wave (SAW) techniques were used to characterize the microstructure of the films. The dielectric constant, Youngs modulus, and hardness of the final films are also discussed.

Effect of substrate composition on the piezoelectric response of reactively sputtered AlN thin films

Deposition parameters were found to have a marked effect on piezoelectric response of reactive radio frequency (RF) sputtered AlN thin films. The authors observed peizoelectric response values ranging from {minus}3.5 to +4.2 pm/V for 1 {micro}m thick AlN films deposited onto Ti/Ru electrode stacks. An investigation of the effects of deposition parameters, in particular the nature of the Ru/AlN interface, was conducted. The lag time between deposition of adjacent thin film layers appeared to have the greatest affect on the value of the piezoelectric response. This suggests that chemical reaction occurring on the Ru thin film surface is responsible for changing an important thin film property such as dipole orientation within the overlying AlN thin film.

All solution-chemistry approach for YBa2Cu3O7−δ-coated conductors

A need exists for low-cost coated-conductor fabrication methods for applications in magnet and electric-power technologies. We demonstrate high-critical current density (Jc) YBa2Cu3O7−δ (YBCO) films grown on Nb-doped SrTiO3 (Nb:STO) buffered Ni(100) tapes. All buffer and superconductor layers are deposited using solution chemistry. A 50 nm thick Nb:STO seed layer on Ni(100) acts as a template for the growth of subsequent thicker layers of Nb:STO. Nb doping improves the electrical conductivity and oxygen diffusion barrier properties of STO. YBCO grows heteroepitaxially directly on this buffer layer, resulting in a transport Jc(77 K)=1.3 MA/cm2.

Chemical solution deposition of -oriented SrTiO3 buffer layers on Ni substrates

Biaxially textured -oriented SrTiO 3 films were solution deposited on LaAlO 3 single crystals and -oriented polycrystalline Ni tapes. Solution variables including varying titanium alkoxide chain length, inclusion of chelating agents, and inclusion of donor dopant, were investigated for their effect on film orientation, morphology, and oxygen diffusivity. The best SrTiO 3 orientation on high lattice mismatch (11%) Ni substrates was achieved through use of a discontinuous nucleation seed layer, which provided nucleation sites for subsequent continuous SrTiO 3 films. Increased titanium alkoxide chain lengths appeared to suppress titanium hydrolysis reactions and improve film orientation. 1 3 C nuclear magnetic resonance showed that significant quantities of water were generated due to esterification reactions, which appeared to cause hydrolysis and subsequent orientation degradation in the absence of chelating agents such as acetylacetone.

Fast lithium-ion conducting thin-film electrolytes integrated directly on flexible substrates for high-power solid-state batteries.

By utilizing an equilibrium processing strategy that enables co-firing of oxides and base metals, a means to integrate the lithium-stable fast lithium-ion conductor lanthanum lithium tantalate directly with a thin copper foil current collector appropriate for a solid-state battery is presented. This resulting thin-film electrolyte possesses a room temperature lithium-ion conductivity of 1.5 × 10(-5) S cm(-1) , which has the potential to increase the power of a solid-state battery over current state of the art.

Thick sol-gel derived YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// films

YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// films have been prepared by spin-coating solutions of metal acetates dissolved in trifluoroacetic acid/methanol and trifluoroacetic acid/isopropanol/1,3 propanediol onto LaAlO/sub 3/[100] substrates. By using a rapid, low pO/sub 2/ pyrolysis process, high-quality diol films (0.25 /spl mu/m thick) with J/sub c/ values as high as 14 MA/cm/sup 2/ and 2 MA/cm/sup 2/ at 7 K and 77 K, respectively, were fabricated in one tenth the time, compared to conventional processing schemes. The effect of multicoating, in order to reach YBCO film thicknesses of 1.5 /spl mu/m, on the J/sub c/ was also studied.

Solution deposition planarization of long-length flexible substrates

Solution deposition planarization (SDP) is studied for preparing smooth flexible substrates in multimeter lengths. We demonstrate 0.5 nm rms surface roughness starting from unpolished metal tapes and a correlation of substrate roughness with the texture of subsequent ion-beam aligned films. Surface roughness reduction in SDP is modeled via film shrinkage during solution deposition and a residual roughness based on film thickness. Use of solution deposited a-Y2O3 to planarize substrates prior to ion-beam textured MgO growth shows an in-plane texture of MgO down to 4°. Utilizing these templates, we demonstrated superconducting YBa2Cu3Oy coated conductors with critical current densities of 2.8–4.0 MA/cm2 at 75 K.