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Feb 2013

Volume 84, Issue 2, Articles (02xxxx)

Issue Cover Spotlight Figure

Rev. Sci. Instrum. 84, 021101 (2013); http://dx.doi.org/10.1063/1.4789314 (14 pages)

Alexey Goncharov

Typical permanent magnet electrostatic plasma lens, characteristically about 15 cm long and 10 cm inner diameter. The magnets are shown in black between grey spacers. A set of cylindrical ring electrodes are located within the magnetic field region, with field lines connecting ring electrode pairs symmetrically about the lens midplane.

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An exchangeable-tip scanning probe instrument for the analysis of combinatorial libraries of electrocatalysts

Eric D. Rus, Hongsen Wang, Anna E. Legard, Nicole L. Ritzert, Robert Bruce Van Dover, and Héctor D. Abruña

Rev. Sci. Instrum. 84, 024101 (2013); http://dx.doi.org/10.1063/1.4776199 (8 pages)

Online Publication Date: 7 February 2013

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A combined scanning differential electrochemical mass spectrometer (SDEMS)-scanning electrochemical microscope (SECM) apparatus is described. The SDEMS is used to detect and spatially resolve volatile electrochemically generated species at the surface of a substrate electrode. The SECM can electrochemically probe the reactivity of the surface and also offers a convenient means of leveling the sample. It is possible to switch between these two different scanning tips and techniques without moving the sample and while maintaining potential control of the substrate electrode. A procedure for calibration of the SDEMS tip-substrate separation, based upon the transit time of electrogenerated species from the substrate to the tip is also described. This instrument can be used in the characterization of combinatorial libraries of direct alcohol fuel cell anode catalysts. The apparatus was used to analyze the products of methanol oxidation at a Pt substrate, with the SDEMS detecting carbon dioxide and methyl formate, and a PtPb-modified Pt SECM tip used for the selective detection of formic acid. As an example system, the electrocatalytic methanol oxidation activity of a sputter-deposited binary PtRu composition spread in acidic media was analyzed using the SDEMS. These results are compared with those obtained from a pH-sensitive fluorescence assay.
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07.78.+s Electron, positron, and ion microscopes; electron diffractometers
81.15.Cd Deposition by sputtering
82.45.Fk Electrodes
88.30.G- Fuel cell systems
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
07.75.+h Mass spectrometers

Scanning droplet cell for high throughput electrochemical and photoelectrochemical measurements

John M. Gregoire, Chengxiang Xiang, Xiaonao Liu, Martin Marcin, and Jian Jin

Rev. Sci. Instrum. 84, 024102 (2013); http://dx.doi.org/10.1063/1.4790419 (6 pages)

Online Publication Date: 12 February 2013

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High throughput electrochemical techniques are widely applied in material discovery and optimization. For many applications, the most desirable electrochemical characterization requires a three-electrode cell under potentiostat control. In high throughput screening, a material library is explored by either employing an array of such cells, or rastering a single cell over the library. To attain this latter capability with unprecedented throughput, we have developed a highly integrated, compact scanning droplet cell that is optimized for rapid electrochemical and photoeletrochemical measurements. Using this cell, we screened a quaternary oxide library as (photo)electrocatalysts for the oxygen evolution (water splitting) reaction. High quality electrochemical measurements were carried out and key electrocatalytic properties were identified for each of 5456 samples with a throughput of 4 s per sample.
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82.80.-d Chemical analysis and related physical methods of analysis
82.45.Fk Electrodes

The influence of laterally inhomogeneous corrosion on electrical and optical calcium moisture barrier characterization

H. Klumbies, L. Müller-Meskamp, T. Mönch, S. Schubert, and K. Leo

Rev. Sci. Instrum. 84, 024103 (2013); http://dx.doi.org/10.1063/1.4791798 (8 pages)

Online Publication Date: 20 February 2013

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The reaction of calcium thin films with water – monitored optically or electrically – is widely used for evaluating ultrahigh barrier foils for the encapsulation of organic electronic devices. We studied the common optical and the electrical method and compared them with in situ atomic force microscope topography scans. All three methods were applied at the same sample in parallel in a typical test design containing a gas volume for water distribution next to the calcium layer of 60 and 1000 nm thickness, respectively. The common assumption for the interpretation of such measurement data is laterally homogeneous calcium consumption of the layer from top to bottom. In contrast, we observed a significant ratio of laterally inhomogeneous corrosion of the calcium on the micro-scale for both thicknesses. Some areas were strongly or completely corroded through the whole layer while others exhibited less or no corrosion. Furthermore, those corroded spots grew in lateral direction. As a consequence of lateral inhomogeneous calcium corrosion the electrical calcium measurement method underestimates the amount of calcium left; according to our results this does not affect the water vapor transmission rate (WVTR). Optical data evaluated by Lambert-Beer law underestimate the amount of calcium left as well and also underestimate the WVTR. If the data are evaluated, using a linear relationship between transmission and amount of calcium left, the both values are more precise. The scope of this study is to call attention to the existence of lateral inhomogeneity in calcium corrosion and its impact on the calcium permeation measurements. While more investigations would be needed to quantify the effect of this inhomogeneity on the electrical and optical method in general, the discussion sheds light on the way, calcium test data are influenced by lateral inhomogeneous calcium corrosion. Our observations highlight the need for careful interpretation of calcium test results, but also demonstrate its capabilities for precise ultrahigh barrier measurements.
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73.61.At Metal and metallic alloys
78.66.Bz Metals and metallic alloys
81.65.-b Surface treatments
68.37.Ps Atomic force microscopy (AFM)
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