Ronald P. Reade

Laser deposition of biaxially textured yttria‐stabilized zirconia buffer layers on polycrystalline metallic alloys for high critical current Y‐Ba‐Cu‐O thin films

Pulsed laser deposition of yttria‐stabilized zirconia (YSZ) layers on polycrystalline metallic alloy substrates is used to produce an intermediate layer for YBa2Cu3O7−δ (YBCO) thin‐film growth. The desired (001) YSZ texture is obtained at 1.0 mTorr oxygen pressure and 70 °C. Significant improvement in (001) texturing is demonstrated by using an ion beam to assist growth. Argon‐ion‐assisted growth produces layers with alignment of the in‐plane crystal axes in addition to the (001)‐normal texture. Highly c‐axis‐oriented biaxially aligned YBCO thin films can be deposited on these layers, with Tc(R=0)=92 K and Jc (77 K, B=0 T)=6×105 A/cm2 and Jc (77 K, 0.4 T)=8×104 A/cm2. With further improvement of the YSZ texture, the YBCO current‐carrying capacity of films on polycrystalline metallic alloys may approach that of films on single‐crystal substrates.

Metal buffer layers and Y‐Ba‐Cu‐O thin films on Pt and stainless steel using pulsed laser deposition

A versatile pulsed laser deposition chamber was employed for fabricating metal buffer layers and superconducting YBaCuO thin films on metallic substrates. Ag buffer layers were found to improve the resistive transition behavior for superconducting films on Pt and stainless steel. As‐deposited YBaCuO films with Tc (R=0) at 84 K were produced on stainless steel using in situ laser‐deposited Ag buffer layers. The critical current density was measured to be approximately 103 A/cm2 at 67 K.

Electrochemical Studies of the LiFePO4 Thin Films Prepared with Pulsed Laser Deposition

Thin films of LiFePO 4 have been prepared on stainless steel substrates with pulsed laser deposition utilizing an Ar atmosphere. Raman spectral analysis revealed the presence of carbon in the films, even though the targets contained less than a few percent residual carbon. The Raman spectra also suggest the presence of iron oxide species on the surface of the film. Though the film morphology became rough with cycling and thicker films were cleaved; the films showed good stability on cycling. The 75-nm-thick film prepared with a carbon-containing target showed a reversible cycling of more than 90 mAh/g for 60 cycles. The use of the low-carbon (<1 wt %), green-colored target significantly lowered the carbon content of the LiFePO 4 film. The low-carbon films cycled stable at moderate current density but with lower capacities such as 80 and 51 mAh/g for the 75 and 335-nm films, respectively. Film capacity and crystallinity improved significantly when the pulsed-laser-deposited target-substrate distance was reduced to less than 5 cm. The 156-nm-thick film produced in this way showed a layered texture in surface morphology and delivered more than 120 mAh/g, keeping its particle morphology on cycling. The excellent capacity retention, despite low-carbon content, can be attributed in part to the enhanced conductivity derived from the excellent adherence between pulsed-laser-deposited film and the substrate.

Electrochemical Studies of Nanoncrystalline Mg2Si Thin Film Electrodes Prepared by Pulsed Laser Deposition

Electrochemically active thin films of Mg 2 Si in various film thicknesses of 30-380 nm have been prepared with the pulsed laser deposition technique. The thinnest film of 30 nm showed a highly stable cycling behavior at 0.1-1.0 V vs. Li, delivering capacity greater than 2000 mAh/g for more than 100 cycles. Though the film morphology became remarkably rougher with cycling, the films showed good stability. However, the first cycle irreversible capacity loss increased with film thickness. Therefore, lithium adsorption/desorption reaction forming Li-Si alloy at the Si-rich film surface is suggested as one of the sources of the large capacity of the 30 nm film. The superior capacity retention, when compared to porous electrodes of this alloy, may be attributed to a limited structural volume change in the two-dimensional film, shorter lithium diffusion path and enhanced conductivity from stainless steel substrate. The goals of this study are to promote the emerging need of thin film anodes for all solid-state microbatteries and clarify the capacity failure of powder intermetallic anodes for rechargeable lithium batteries.

Characterization of Y‐Ba‐Cu‐O thin films and yttria‐stabilized zirconia intermediate layers on metal alloys grown by pulsed laser deposition

The use of an intermediate layer is necessary for the growth of YBaCuO thin films on polycrystalline metallic alloys for tape conductor applications. A pulsed laser deposition process to grow controlled‐orientation yttria‐stabilized zirconia (YSZ) films as intermediate layers on Haynes Alloy No. 230 was developed and characterized. YBaCuO films deposited on these YSZ‐coated substrates are primarily c‐axis oriented and superconducting as deposited. The best YBaCuO films grow on (001) oriented YSZ intermediate layers and have Tc (R=0) = 86.0 K and Jc ∼ 3×103 A/cm2 at 77 K.

Cu2Sb Thin-Film Electrodes Prepared by Pulsed Laser Deposition for Lithium Batteries

Thin films of Cu2Sb, prepared on stainless steel and copper substrates with a pulsed laser deposition technique at room temperature, have been evaluated as electrodes in lithium cells. The electrodes operate by a lithium insertion/copper extrusion reaction mechanism, the reversibility of which is superior when copper substrates are used, particularly when electrochemical cycling is restricted to the voltage range 0.65-1.4 V vs. Li/Li+. The superior performance of Cu2Sb films on copper is attributed to the more active participation of the extruded copper in the functioning of the electrode. The continual and extensive extrusion of copper on cycling the cells leads to the isolation of Li3Sb particles and a consequent formation of Sb. Improved cycling stability of both types of electrodes was obtained when cells were cycled between 0.65 and 1.4 V. A low-capacity lithium-ion cell with Cu2Sb and LiNi0.8Co0.15Al0.05O2 electrodes, laminated from powders, shows excellent cycling stability over the voltage range 3.15 - 2.2 V, the potential difference corresponding to approximately 0.65-1.4 V for the Cu2Sb electrode vs. Li/Li+. Chemical self-discharge of lithiated Cu2Sb electrodes by reaction with the electrolyte was severe when cells were allowed to relax on open circuit after reaching a lower voltage limit of 0.1 V. The solid electrolyte interphase (SEI) layer formed on Cu2Sb electrodes after cells had been cycled between 1.4 and 0.65 V vs. Li/Li+ was characterized by Fourier-transform infrared spectroscopy; the SEI layer contributes to the large irreversible capacity loss on the initial cycle of these cells. The data contribute to a better understanding of the electrochemical behavior of intermetallic electrodes in rechargeable lithium batteries.

Y–Ba–Cu–O multilayer structures with amorphous dielectric layers for multichip modules using ion‐assisted pulsed‐laser deposition

Existing technology to construct high‐temperature superconductor (HTSC) multichip modules (MCM’s) incorporating several YBa2Cu3O7−δ (YBCO) thin films and thick dielectric layers are based on epitaxial growth of all layers from the template of a single‐crystal substrate. This work demonstrates an alternate method to fabricate these structures: the use of a biaxially aligned yttria‐stabilized zirconia (YSZ) intermediate layer deposited by ion‐assisted pulsed‐laser deposition. Using this technique, a YBCO thin film with Tc∼87 K and Jc∼3×105 A/cm2 was grown on a 5 μm amorphous SiO2 layer. In addition, YBCO/YSZ/SiO2/YSZ/YBCO/CeO2/YSZ and YBCO/YSZ/amorphous‐YSZ/YBCO/CeO2/YBCO multilayer structures were constructed.

Ion-beam nanotexturing of buffer layers for near-single-crystal thin-film deposition: Application to YBa2Cu3O7-δ superconducting films

A method of producing biaxially textured template layers for near-single-crystal-quality film growth on substrates that do not provide a template for oriented crystalline growth is described and compared to existing methods. This technique, ion-beam nanotexturing (ITEX), produces a biaxially textured layer by oblique ion irradiation of an amorphous film surface. Using in situ reflection high-energy electron diffraction and ex situ x-ray diffraction, an yttria-stabilized zirconia (YSZ) template layer fabricated by ITEX is shown to have the appropriate surface texture for YBa2Cu3O7-δ coated conductor fabrication. A YBa2Cu3O7-δ thin film deposited on an ITEX YSZ layer has a critical current of 2.5×105 A/cm2 (77 K, 1 μV/cm). ITEX produces texture rapidly and should be ideally suited for future low-cost manufacturing.

Angular magnetoresistance provides texture information on high- Tc conductors

Abstract Angular magnetoresistance measurements are performed by rotating a superconductor to an angle θ in a fixed magnetic field, while monitoring the resistance R . It is argued theoretically that for fields well above the lower critical field, H ⪢ H cl, the bulk resistivity of the conductor is independent of θ if the crystallites of which it is composed are randomly oriented. Non-random orientation (a key aspect of texture) is revealed, therefore, by variations of R with θ. Dips in R indicate that the field is parallel to the copper oxide planes in a significant fraction of the current-carrying crystallites. C -axis, a -axis, and other textured film conductors are used to illustrate the technique. The angular magnetoresistance is found to be an important supplement to conventional texture determinations by microscopy and X-ray diffraction.

Oblique ion texturing of yttria-stabilized zirconia: the {211} structure

Amorphous (Zr,Y)Ox films were synthesized by reactive magnetron sputtering and subsequently crystallized by oblique ion bombardment. Crystalline texture nucleated by the ion beam was replicated by solid-phase epitaxial growth throughout the formerly amorphous yttria-stabilized zirconia (YSZ) film. The resulting YSZ films have (211) orientation normal to the substrate with in-plane directions (111), parallel, and (110), transverse, to the azimuth of the ion beam. We hypothesize that the texture mechanism involves ion-induced film compression and shear. The results, taken together with prior work, show that oblique ion texturing of amorphous films is a general phenomenon that can be used to fabricate substrates with more than one type of crystallographic orientation.