Resonant Laser Ablation of Metals Detected by Atomic Emission in a Microwave Plasma and by Inductively Coupled Plasma Mass Spectrometry

Abstract

It has been shown that an increase in sensitivity and selectivity of detection of an analyte can be achieved by tuning the ablation laser wavelength to match that of a resonant gas-phase transition of that analyte. This has been termed resonant laser ablation (RLA). For a pulsed tunable nanosecond laser, the data presented here illustrate the resonant enhancement effect in pure copper and aluminum samples, chromium oxide thin films, and for trace molybdenum in stainless steel samples, and indicate two main characteristics of the RLA phenomenon. The first is that there is an increase in the number of atoms ablated from the surface. The second is that the bandwidth of the wavelength dependence of the ablation is on the order of 1 nm. The effect was found to be virtually identical whether the atoms were detected by use of a microwave-induced plasma with atomic emission detection, by an inductively coupled plasma with mass spectrometric detection, or by observation of the number of laser pulses required to penetrate through thin films. The data indicate that a distinct ablation laser wavelength dependence exists, probably initiated via resonant radiation trapping, and accompanied by collisional broadening. Desorption contributions through radiation trapping are substantiated by changes in crater morphology as a function of wavelength and by the relatively broad linewidth of the ablation laser wavelength scans, compared to gas-phase excitation spectra. Also, other experiments with thin films demonstrate the existence of a distinct laser-material interaction and suggest that a combination of desorption induced by electronic transition (DIET) with resonant radiation trapping could assist in the enhancement of desorption yields. These results were obtained by a detailed inspection of the effect of the wavelength of the ablation laser over a narrow range of energy densities that lie between the threshold of laser-induced desorption of species and the usual analytical ablation regime. Normal ablation employs high-power lasers in an attempt to create a vapor plume without selective vaporization, and with a stoichiometry that accurately represents the stoichiometry of species in the solid sample. RLA, as a method of selective vaporization, appears to provide an opportunity to exploit selective vaporization in new ways.

A Review of Near‐Field Laser Ablation for High‐Resolution Nanoscale Surface Analysis

“…Laser ablation is a well-known sample introduction technique for surface microanalysis (23), but the resolution of LA has traditionally been limited by the diameter of the incident laser beam. For example, in recent work performed by us (24)(25)(26), the ablation laser spot size was on the order of 100-200 mm. Significantly smaller sample volumes can be liberated from the surface of interest by use of an apertured or apertureless probe with nanoscale dimensions.…”

A prospective microwave plasma source for in situ spaceflight applications

“…Previous estimates for Saha ionization, carried out by Niu & Houk on a commercial plasma at atmospheric pressure, 31 assumes a plasma at LTE where T ¼ T i ¼ T e ¼ T gas ¼ 7500 K. However, Chen & Han assessed the Saha equation for a non-LTE plasma, 37 and found that T e is the appropriate temperature to use as an input for the non-LTE Saha equation, as electron collisions are the dominant mechanism of ionization. Therefore, we use the framework of the Saha equation established by Niu & Houk, 31 (eqn (8) and (9)) with values of T e converted to K (1 eV ¼ 11 600 K) input as the plasma temperature.…”

“…In the commercial realm, plasmas are routinely applied as robust and reproducible sources for optical emission spectra, 5,6 as well as ionized organic compounds and monoatomic ions for mass spectrometry. [7][8][9][10][11][12][13][14] Commercial inductively coupled plasmas (ICPs) operate at high power output (>1 kW) and ionize desolvated solutions or ablated geologic material. Recent advances in plasma technology demonstrate that low power plasma sources, operating at ambient or reduced pressure, perform direct desorption and ionization of molecular compounds or geologic materials in their native state, although the potential to atomize large particles remains poorly constrained.…”

Carbon Paste Electrode Hexadecyltrimethylammonium Bromide Modified Natural Zeolite for Chromium(vi) Detection

“…Analysis of Cr(VI) in environmental samples is routinely carried out using analytical techniques, such as spectrophotometry [5], inductively coupled plasmaatomic emission spectrometry [6], atomic absorption spectrometry [7], high pressure liquid chromatography [8], X-ray fluorescence [9], and mass spectrometry [10]. However, these techniques always need extensive labor and analytical resources, which prohibit their use for rapid detection and field deployment [11].…”