No abstract

PVD, CVD, and electrodeposited blanket Co films were studied using SEM, XRD, XPS, SIMS, open circuit wet etching in DHF, and linear sweep amperometry. All Co films exhibit (002) hexagonal close packed preferred orientation that is enhanced upon anneal, except for the PVD Co, whose texture is unchanged. Although as-deposited film resistivity varies significantly, post-anneal resistivity values for all films are similar (∼ 6-8 μ cm). As-deposited PVD Co and Co plated from an acidic sulfate chemistry are relatively pure, dissolve slowly in DHF, and show modest changes upon annealing. As-deposited CVD Co has high levels of impurities and correspondingly high DHF etch rates; annealing significantly reduces impurities and improves DHF etch resistance. Increased Co and reduced O at the surface is observed by XPS upon anneal for all films except for PVD Co. The role of Co oxidation in interconnect resistance and leakage behavior is assessed by employing different Co dielectric cap processes.

The authors report novel results toward optimizing the electrochemical performance of high vacuum deposited lithium-based all solid-state thin film microbatteries. This study investigated hermetic encapsulation, interfacial lithium formation processes, and the role of Li-blocking and Li-nucleating layers for improved Li-metal plating on copper anodes. Photoresist was found to be an effective temporary encapsulation material, where prior to cycling, well-encapsulated Li-metal full cells yielded a total resistance reduction of nearly two orders of magnitude (282 Ω cm2) and a total capacitance increase of roughly an order of magnitude (1.35 × 10−10 F/cm2) compared with nonencapsulated Li-metal full cells. To accelerate potential failure mechanisms, high stress applied currents were used during the electrochemical formation processes. Initial cycles caused high resistance voids to form at the lithium phosphorous oxy-nitride (LiPON)/copper interface of well-encapsulated half cells. Well-encapsulated full cells, in contrast, resulted in a very low resistance composite Li-Cu anode, with a void-free LiPON interface, two orders of magnitude lower resistance (0.43 Ω cm2) and three orders of magnitude higher capacitance (6.56 × 10−8 F/cm2) compared with the half cell. Cycling performance was investigated using both Li-blocking nickel-copper and Li-nucleating gold-copper metal bilayer anodes in 100-μm diameter half cells. Nickel-copper anodes facilitated higher discharge capacity (>9 μAh/cm2) at high charge rates (>12.7 mA/cm2) due to uniform Li-metal plating on blocking electrodes. Low charge rates (<0.7 mA/cm2) displayed low discharge capacity and immediate corrosion of the cell. Gold-copper anodes displayed the opposite effect, showing sustainable cycling, minimal cell corrosion, and a discharge capacity of >6 μAh/cm2 at lower charge rates (∼0.025 mA/cm2). The work expands on fundamentals in understanding the role of the metallic anode encapsulation, interface formation, and charge storage mechanisms with respect to sustainable cell impedance for applications such as solid-state lithium metal microbatteries and microelectrochemical resistance-modulated memory devices.

There is a growing interest in alcohol oxidation electrochemistry due to its role in renewable energy technologies. The goal of this work was to develop active non-precious metal electrocatalysts based on the Mo-V-(M)-O (M is Nb, Te) lattice. Selective gaseous alkane oxidation had been previously observed on these catalysts at elevated temperatures above 300°C. In this study, the activity of the catalysts at lower temperatures, 25−60°C, was investigated. Hydrothermal conditions were used to synthesize the Mo-V-(M)-O mixed oxides. Physical characterization of the catalysts were obtained by powder X-ray diffraction (XRD), scanning electron micrography (SEM) equipped with energy dispersive X-ray (EDX), transmission electron micrography (TEM), and X-ray photoelectron spectroscopy (XPS). The catalytic activity for the oxidation of cyclohexanol was studied electrochemically. Chronoamperometric studies were used to evaluate the long-term performance of the catalysts. The onset of alcohol oxidative current was observed between 0.2 and 0.6 V versus Ag/AgCl. Gas chromatography−mass spectrometry analysis was used to determine the nature of the oxidative products. The mild oxidation products, cyclohexanone and cyclohexene, were observed after oxidation at 60°C. The catalytic activity increased in the order Mo-V-O < Mo-V-Te-O < Mo-V-Te-Nb-O. Mo-V-(Te,Nb)-O based electrocatalysts efficiently catalyzed the oxidation of alcohols at low temperatures.