Carmen C. Garcia

Nanometric range depth-resolved analysis of coated-steels using laser-induced breakdown spectrometry with a 308 nm collimated beam

The spatial profile from an XeCl excimer laser was modified using a simple two-lenses telescope to generate a flat energy-profile beam that impinged a layered sample (a Zn-coated steel) without beam conditioning. The irradiance obtained (about 107 W cm–2) was high enough to vaporize the target, to cause plasma formation and to allow atomic emission spectrometry with acceptable signal-to-noise ratio. Modification in beam energy distribution resulted in flat ablated profiles and improved depth-resolution up to the few nm pulse–1 range was attained. The net intensity areas were transformed into normalized values leading to plots in excellent agreement with those provided by commercial depth-resolved analysis instruments.

Laser ablation inductively coupled plasma mass spectrometry—current shortcomings, practical suggestions for improving performance, and experiments to guide future development

Experimental parameters and processes important in laser ablation such as the wavelength, fluence and pulse width of the laser, the form of the ablation cell, the cell gas, the particle transport and atomization in the ICP have an impact on the analytical performance of laser ablation inductively coupled mass spectrometry. The paper discusses the influence of the aforementioned parameters and processes on LA-ICP-MS and presents proposals to map out strategies for optimum LA-ICP-MS analyses. Additionally, experiments are identified which still need to be done for better understanding of the relevant processes and further improvement of the analytical performance of the technique.

Non-matrix matched calibration of major and minor concentrations of Zn and Cu in brass, aluminium and silicate glass using NIR femtosecond laser ablation inductively coupled plasma mass spectrometry

The feasibility of using near-infrared (NIR) femtosecond laser ablation (fs-LA) inductively coupled plasma mass spectrometry (ICP-MS) for the analysis of solid samples with non-matrix matched standard reference materials was studied. Major and minor concentrations of Zn and Cu (433 μg g−1–0.95 g g−1) were measured in three sets of metallic and dielectric standards (brass, aluminium, silicate glass) using He as the ablation cell gas and, with admixed Ar, for aerosol transportation from the cell into an Ar-ICP-MS instrument. Not surprisingly for ICP-MS detection, the experimental Zn/Cu ion ratios were found to be dependent on the sampler cone position in the plasma. However, at a fixed sampler position the experimental Zn/Cu ratios of the brass and Al samples were found to be proportional to the certified ratios independent of the laser fluence applied (range: 2–42 J cm−2). In contrast, the Zn/Cu ratio of an optical transparent glass sample (NIST 610) was found to be strongly fluence dependent. However, with increasing fluence the measured ratio asymptotically approached the experimentally expected ratio taking into account the results obtained from the brass and aluminium measurements.

Angle-Resolved Laser-Induced Breakdown Spectrometry for Depth Profiling of Coated Materials

The combination of angle-resolved laser ablation with the use of a collimated beam is presented as a new approach to increase the depth-resolved capabilities of laser-induced breakdown spectrometry (LIBS). The effect of beam conditioning and the reduction of the effective sampling depth due to the angular dependence of laser ablation allow ablation rates lower than 2 nm/pulse for coated materials (Sn-coated steels and Cr-coated samples). Spectral information is obtained on a single-laser-shot basis. The effect of incidence angle has been examined from differentiated emission profiles, demonstrating the beneficial effect of working at incidence different from normal. A compromise between depth resolution and emission signal must be found at large angles due to the lower irradiance resulting from the increase in beam size at the interface for large angles of incidence. A comparison of the proposed approach with the analysis provided by a commercial glow-discharge device [glow discharge optical emission spectroscopy (GD-OES)] demonstrated quite satisfactory results.

Comparative analysis of layered materials using laser-induced plasma spectrometry and laser-ionization time-of-flight mass spectrometry ☆

Abstract Laser-induced plasma spectrometry (LIPS) and laser ionization time-of-flight mass spectrometry (LI-TOFMS) have been evaluated for the in-depth analysis of layered materials. LI-TOFMS shares with LIPS important advantages in terms of speed of analysis and negligible sample handling. However, additional features such as real multielemental capabilities and the absence of background contribution must be added to the former. In order to have a useful estimation of the potential of each technique, an in-depth characterized Zn-coated steel has been analyzed. Without complete optimization of the system, the averaged ablation rate has been measured to be in the range 20–30 nm/pulse without beam conditioning or optical modifications.

Nanometric in-depth characterization of P diffusion and TiO2 anti-reflective coatings in solar cells by laser ionization time-of-flight mass spectrometry

Laser ionization time-of-flight mass spectrometry has been used and demonstrated as a useful technique to obtain in-depth distribution profiles in solar cells. The in-depth distribution of P (a critical feature as it affects the location of the p–n junction) and measurement of the TiO2 anti-reflective coatings have been successfully demonstrated. In the latter application, a sampling depth of 0.3 nm pulse−1 was achieved. The method has been proved to be fast, it does not require sample handling or preparation, and it is free of charge effects that affect the ion beam techniques.

Ion extraction effects on the in-depth analysis of layered samples by time-of-flight mass spectrometry of laser-induced plasmas

The nature of the incoming ion beam is known to affect the sampling efficiency in orthogonal extraction time-of-flight mass spectrometry (OE-TOFMS). In the present work, laser ablation of a layered material (a Zn-coated steel) was performed under identical excitation conditions, and the generated ions were analyzed by OE-TOFMS. Using the same extraction parameters, a clear element-dependent shift in the flight times was observed. The shift only occurred at the interface of the layered sample. An explanation based on the different ablation rates and effective extraction field in the laser plume is presented.