Research ArticleAPPLIED PHYSICS

Integrated quantitative PIXE analysis and EDX spectroscopy using a laser-driven particle source

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Science Advances  15 Jan 2021:
Vol. 7, no. 3, eabc8660
DOI: 10.1126/sciadv.abc8660
  • Fig. 1 Conceptual schemes of the experimental setups.

    (A) Schematic illustration for the LD-EDX setup. (B) Schematic illustration for the LD-PIXE setup. (C) Scanning electron microscope (SEM) cross-sectional view of the irradiated sample. (D) Detail of a recorded charge-coupled device (CCD) image for x-ray detection. Single-pixel events are indicated. (E) Top view scheme of the LD-PIXE setup. (F) Proton energy spectrum recorded with time-of-flight (ToF) spectrometer. No absolute calibration is provided on the vertical axis. The continuous black line is the average spectrum. The purple area represents the statistical uncertainty (i.e., ±SD), provided as the superposition of two separated contributions: the uncertainty on the signal for any energy value and the uncertainty on the maximum proton energy. (G) Absolute frequency distribution for the maximum proton energy recorded with ToF measurements. The vertical line represents the mean value, while the purple band width is two times the SD. Photo credit: Francesco Mirani, Politecnico di Milano.

  • Fig. 2 Laser-driven electron EDX/PIXE results.

    (A) Recorded spectrum with the LD-EDX setup. The red points are the average over the shots of x-ray intensity at each photon energy, while the length of the error bars is two times the SD. The blue line is the fitted spectrum. The filled blue curves are the Gaussian fits for the peaks. (B) Summary of the recorded x-ray line positions and intensity ratios of the Cr and Cu peaks. The first row reports the expected x-ray energies from literature. The second row is related to the x-ray spectrum used to calibrate the CCD (see Materials and Methods), while the last two rows list the peak positions in the spectra, expressed as the centroid of the fitting Gaussian. (C) Recorded spectrum with the LD-PIXE setup. The filled red curves are the Gaussian fits for the peaks. (D) Results of the LD-PIXE stratigraphic analysis. The red and yellow lines are retrieved from the yield ratio obtained from the LD-PIXE measurement. The red line is the thickness retrieved assuming a 100% Cr film. The yellow line is the thickness obtained assuming a 93% Cr and 7% O film. The blue line is the thickness obtained assuming the yield ratio from the LD-EDX measurement and a 93% Cr and 7% O film. The color-filled regions represent the statistical uncertainties.

  • Fig. 3 Finite element method (FEM) and Monte Carlo simulations of LD-EDX/PIXE.

    (A and B) Snapshots of the LD-EDX and LD-PIXE Monte Carlo simulations. (C) Slices of the magnetic field intensity distribution in the LD-PIXE setup obtained with FEM analysis. In the first panel, the position of the S1 and S2 slices is marked, while the TOP slice is taken parallel to the top view and passes through the center of the magnet. (D and E) LD-EDX and LD-PIXE Monte Carlo simulation outputs for electrons with initial temperature of 0.67 MeV as primary particles. The filled red areas are the energy spectra of the electrons incident on the sample surface. The filled blue curves are the x-ray differential yields. The inset graphs are the simulated x-ray spectra associated with electrons in LD-EDX and LD-PIXE setups, respectively. (F and G) Comparison between the simulated peaks and fits from experimental data for LD-EDX and LD-PIXE. The inset graphs compare the experimental and simulated x-ray yield ratios for LD-EDX and LD-PIXE. a.u., arbitrary units. Photo credit: Francesco Mirani, Politecnico di Milano.

  • Fig. 4 LD-EDX spectrum for the CCD energy calibration.

    Copper spectrum obtained with the LD-EDX setup used to calibrate the x-ray CCD. The inset graph is the pixel value distribution of the local background around the single-pixel events.

  • Fig. 5 Uncertainty evaluation for the LD-PIXE measurement.

    (A) Frequency distribution of the thickness resulting from the Monte Carlo simulation for the error calculation. The inset image shows the related uncertainty for the thickness measurement. (B) Heatmap scattered data. The extracted intensity ratio is reported on the x axis, while the resulting thickness is on the y axis. The color scale is related to the number of occurrences. The red points are obtained by fixing the proton spectrum as the average one. The green points are obtained by fixing the intensity ratio as the average value.

  • Fig. 6 Linear fit of the electron temperature as a function of the ratio between the copper x-ray yields due to electrons in LD-EDX and LD-PIXE.

    The blue points are the Monte Carlo simulated data. The black line is the linear fit. The red point is the copper x-ray yield ratio evaluated with the linear fit in correspondence of the electron temperature resulting from the analytical procedure presented in Materials and Methods.

Supplementary Materials

  • Supplementary Materials

    Integrated quantitative PIXE analysis and EDX spectroscopy using a laser-driven particle source

    F. Mirani, A. Maffini, F. Casamichiela, A. Pazzaglia, A. Formenti, D. Dellasega, V. Russo, D. Vavassori, D. Bortot, M. Huault, G. Zeraouli, V. Ospina, S. Malko, J. I. Apiñaniz, J. A. Pérez-Hernández, D. De Luis, G. Gatti, L. Volpe, A. Pola, M. Passoni

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    • S1 Magnetron sputtering parameters for the deposition of the Cr film.

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