Improvement in the Analytical Capabilities of LA-ICP-MS for High Spatial Resolution U-Pb Dating of Zircon Using Mixed-Gas Plasma

In this work, a novel method for high spatial resolution U-Pb dating of zircon by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) at 10–16 μm spot diameter has been proposed. This was achieved by introducing 2% (v/v) water-ethanol vapours into ICP in combination with the shielded torch system to increase the sensitivity and suppress the isotopic fractionation effect. Precise and accurate concordant U-Pb ages for Plešovice, GJ-1, and 91500 zircons were obtained using the proposed method, and the results agreed well with the isotope dilution-thermal ionization mass spectrometry (ID-TIMS) and LA-ICP-MS within 2σ, except for the ages obtained using dry plasma at 10 μm spot diameter. Additionally, the effects of plasma condition (dry plasma or 2% (v/v) ethanol plasma) and spot size (10, 16, 24, or 32 μm) on precision (RSD), accuracy (RE), and uncertainty (2σ) of the 206Pb/238U ages have been studied. The results indicated that increasing the spot diameter and introducing 2% (v/v) water-ethanol vapours into ICP significantly improved the precision, accuracy, and uncertainty for small spot diameters (10 and 16 μm), while it exhibited little influence for intermediate spot diameters (24 and 32 μm). Furthermore, the effects of spot size and plasma condition on the precision, accuracy, and uncertainty strongly depended on the sensitivity of analytes.

Temporal characterization of laser-induced plasma of tungsten in air

In this manuscript, the time-resolved laser-induced breakdown spectroscopy (LIBS) on tungsten target in air and the coexistence of LTE among atoms and ions as well as the fulfillment of optically thin plasma condition are reported. The laser-induced plasma (LIP) of tungsten is generated by focusing the second harmonic of a Q-switched Nd:YAG laser of pulse width ~7 ns and repetition rate of 1 Hz on the tungsten target. The temporal evolution of LIP of tungsten is recorded at four different incident laser fluences of 60, 120, 180, and 270 J/cm2. The several atomic and singly ionized lines of tungsten are identified in LIP. For the estimation of plasma temperature via the Boltzmann plot, the transitions at 430.7, 449.4, 468.0, 484.3, 505.3, and 524.2 nm of Atomic transition of tungsten (WI) and that of the ionic transitions, First Ionic transition of Tungsten (WII) at 251.0, 272.9, and 357.2 nm are selected. The electron density is estimated using the Stark-broadened profile of WI line at 430.2 nm. The McWhirter criteria for the local thermodynamic equilibrium (LTE) condition is verified in present experimental conditions as well as the relaxation time and diffusion length are estimated to take into account the transient and inhomogeneous nature of the plasma. The optically thin plasma condition is studied by assessing the experimental intensity ratio of atomic lines and compared with that of the theoretical intensity ratio (branching ratio). The signal to noise ratio (SNR) is also obtained as a function of time with respect to laser pulse and incident laser fluence. All these observations indicate that the spectra should be recorded within the temporal window of 1–3.5 µs with respect to laser pulse where the plasma can be treated as optically thin as well as under LTE simultaneously along with the large SNR.

A Study on the Effect of Argon-Oxygen Plasma Treatment on Ultra-Thin Expanded PTFE Membrane

Polymer films are plasma treated to improve surface properties making them hydrophilic or hydrophobic. Expanded polytetrafluoroethylene (ePTFE) is used in a wide variety of applications but only a few report on plasma treated ePTFE. Within these very few studies on ePTFE, the use of ultra-thin membrane could hardly be found. The purpose of this study is to investigate the effect of plasma treatment (Argon-Oxygen) on the hydrophobicity of ultra-thin ePTFE membrane (4um thickness). This study used nine (9) experimental legs of ePTFE subjected to respective plasma power (150W, 315W and 600W) and exposure time (300s, 450s and 600s) for each leg. Contact angle was measured prior and after subjecting to plasma condition using contact angle meter. Energy pen was also used to verify its hydrophobicity. Scanning electron microscopy (SEM) with 10,000x magnification was used to check for any change in surface after exposing to each condition. The findings showed that the membrane surface changed after exposure to plasma. All legs became hydrophilic. 102◦ contact angle was measured from raw sample, but the samples exposed to plasma had contact angles ranging from max of 68◦ to min of 48◦. The results showed that the degree of surface change could be correlated to the plasma parameters applied. Furthermore, the highest radio frequency (RF) power applied resulted to contact angle in the range of 60◦ while the lowest RF power applied resulted to the lowest contact angle, in the range of 40◦, measured. On the other hand, no particular trend was observed based on exposure time. Based on the gathered results, the ultra-thin ePTFE, in order to maintain its hydrophobicity, must not be applied with argon-oxygen plasma treatment. However, if the ultra-thin ePTFE is to be made hydrophilic, argon-oxygen plasma treatment could be applied while adjusting the plasma parameters to meet the desired hydrophilicity level.