NIST Database for the Simulation of Electron Spectra For Surface Analysis (SESSA)* 1. What is it? 2. What can it do? 3. Summary Cedric Powell National Institute of Standards and Technology, Gaithersburg *https://www.nist.gov/srd/nist-standard-reference-database-100. 1
1. What is SESSA*? SESSA can be used to simulate AES and XPS spectra of multilayer films and of nanostructures such as islands, lines, spheres, and layered spheres on surfaces. Users can specify the compositions and dimensions of each material in the sample structure and the measurement configuration. SESSA contains needed physical data: differential inverse inelastic mean free paths, total inelastic mean free paths, differential elastic-scattering cross sections, total elastic-scattering cross sections, transport cross sections, photoionization cross sections, photoionization asymmetry parameters, electron-impact ionization cross sections, photoelectron lineshapes, Augerelectron lineshapes, fluorescence yields, and Auger-electron backscattering factors. SESSA can be operated through a graphical user interface (GUI) or through a command line interface (CLI). The GUI enables a user to enter needed information in an intuitive way (sample morphology, composition, dimensions, instrument configuration, excitation source, spectrometer energy range) while the CLI facilitates simulations for similar conditions (i.e., batch runs). *https://www.nist.gov/srd/nist-standard-reference-database-100 2
GUI for a Planar Sample (C/SiO 2 /Si) 3
GUI for a Planar Sample (C/SiO 2 /Si) 4
GUI for Periodic Array of Cu Islands or Lines on a Si Substrate 5
GUI for Periodic Array of Au-core/C-shell Nanoparticles on a Si Substrate 6
GUI for a Planar Sample (C/SiO 2 /Si): Peak Tab 7
GUI to Specify Excitation Source GUI for Spectrometer: Specify Energy Range 8
GUI for Instrument Settings 9
GUI for Simulation [Example: Planar Sample (C/SiO 2 /Si)] O 1s C 1s Si 2s Si 2p 10
2. Examples of SESSA Applications (a) Absolute Quantification of Surface Impurities on Layered Samples Schematic of Multilayer Mirrors Used for Extreme Ultraviolet Lithography (e.g., N, S, P, F, Cl, Br) XPS has been used to assess detect and quantify trace levels of surface impurities on mirrors arising from outgassing of resists We developed a procedure to quantify amounts of surface impurities rather than assuming sample to be homogeneous and using instrumental software N. S. Faradzhev, S. B. Hill, and C. J. Powell, Surf. Interface Anal. (in press); DOI: 10.1002/sia.6289 11
Intensity (counts x 10-5 ) Comparison of Measured XPS Spectrum for a Multilayer Mirror Sample (solid blue circles) and a Simulated Spectrum (solid red triangles) for 0.25 nm SiO 2 /0.25 nm CCl 0.01 /0.25 nm C/0.25 nm RuO 2 /3 nm Ru/4.3 nm Si/ 3 nm Mo/Si 7 6 5 4 3 2 1 B Simulated Spectrum Measured Spectrum Ru 3s O 1s Ru 3p C 1s Ru 3d 0 800 700 600 500 400 300 200 100 0 N. S. Faradzhev, S. B. Hill, and C. J. Powell, Surf. Interface Anal. (in press); 12 DOI: 10.1002/sia.6289
Intensity (counts x 10-5 ) Comparison of Measured XPS Spectrum for a Multilayer Mirror Sample (solid blue circles) and a Simulated Spectrum (solid red triangles) for 0.25 nm SiO 2 /0.25 nm CCl 0.01 /0.25 nm C/0.25 nm RuO 2 /3 nm Ru/4.3 nm Si/ 3 nm Mo/Si 0.8 Comparison of measured and simulated Cl 2p intensities gives a surface Cl coverage of 0.20 ML (± 21 %) 0.6 0.4 0.2 B Simulated Spectrum Measured Spectrum Mo 3d Cl 2p Si 2s Si 2p Ru 4s Ru 4p N. S. Faradzhev, S. B. Hill, and C. J. Powell, Surf. Interface Anal. (in press); 13 DOI: 10.1002/sia.6289 0.0 250 200 150 100 50 Binding Energy (ev) 0
(b) Comparison of Simulated Cu 2p Spectra from Cu/Au Nanoparticles Relative Intensity We used SESSA to determine the Au-shell thicknesses that gave a selected Cu 2p peak intensity for different Cu-core diameters 2.5 2.0 1.5 Elastic scattering on Spectrum 0.775 nm Au/10 58 nm Cu Spectrum 0.70 nm Au/5 56 nm Cu Spectrum 0.475 nm 54 Au/2 nm Cu Spectrum 0.255 nm 52A Au/1 nm Cu Spectrum 0.085 nm 60 Au/0.5 nm Cu Au Cu 1.0 0.5 0.0 450 500 550 Electron Energy (ev) C. J. Powell, M. Chudzicki, W. S. M. Werner, and W. Smekal, J. Vac. Sci. Technol. A 14 33, 05E113 (2015).
Relative Intensity We used SESSA to determine the Cu-shell thicknesses that gave a selected Cu 2p peak intensity for different Au-core diameters 2.5 2.0 1.5 Elastic scattering on Spectrum 0.073 nm Cu/10 58 nm Au Spectrum 0.068 nm 56 Cu/5 nm Au Spectrum 0.060 nm 54 Cu/2 nm Au Spectrum 0.050 nm 52A Cu/1 nm Au Spectrum 0.050 nm 60 Cu/0.5 nm Au Cu Au 1.0 0.5 0.0 450 500 550 Electron Energy (ev) C. J. Powell, M. Chudzicki, W. S. M. Werner, and W. Smekal, J. Vac. Sci. Technol. A 15 33, 05E113 (2015).
Relative Intensity We used SESSA to determine the Au-shell thicknesses that gave a selected Cu 2p peak intensity from Au-core/1 nm Cu-shell/Au-shell nanoparticles for different Au-core diameters 2.5 2.0 1.5 Elastic scattering on Spectrum 58 Spectrum 56 Spectrum 54 Spectrum 52A Spectrum 60 0.51 nm Au/1 nm Cu/10 nm Au 0.49 nm Au/1 nm Cu/5 nm Au 0.45 nm Au/1 nm Cu/2 nm Au 0.40 nm Au/1 nm Cu/1 nm Au 0.34 nm Au/1 nm Cu/0.5 nm Au Au Au 1.0 Cu 0.5 0.0 450 500 550 Electron Energy (ev) C. J. Powell, M. Chudzicki, W. S. M. Werner, and W. Smekal, J. Vac. Sci. Technol. A 16 33, 05E113 (2015).
Relative Intensity We used SESSA to determine the Au content of CuAu x nanoparticles that gave A selected Cu 2p intensity for different nanoparticle diameters 2.5 2.0 1.5 Elastic scattering on Spectrum 58 Spectrum 56 Spectrum 54 Spectrum 52A Spectrum 60 d = 10 nm, x = 2.70 d = 5 nm, x = 2.60 d = 2 nm, x = 2.10 d = 1 nm, x = 1.32 d = 0.5 nm, x = 0.55 CuAu x 1.0 0.5 0.0 450 500 550 Electron Energy (ev) C. J. Powell, M. Chudzicki, W. S. M. Werner, and W. Smekal, J. Vac. Sci. Technol. A 17 33, 05E113 (2015).
(c) Validation of the Shard Formula for Determining Shell Thicknesses of Core-Shell Nanoparticles. We determined shell thicknesses, T NP, from the Shard formula using peak intensities from SESSA simulations for (a) Au-core/C-shell, (b) C-core/Au-shell, (c) Al-core/Cu-shell, and (d) Cu-core/Al-shell NPs and compared these values with the corresponding true values, T, used in the simulations for different Au-core diameters, D. 1.2 Au-core/C-shell NPs 1.1 T NP /T 1.0 0.9 D (nm) 1 nm 2 nm 5 nm 10 nm 0.8 0 1 2 3 C-shell Thickness T (nm) C. J. Powell, W. S. M. Werner, H. Kalbe, A. G. Shard, and D. G. Castner (to be published). 18
T NP /T We determined shell thicknesses, T NP, from the Shard formula using peak intensities from SESSA simulations for (a) Au-core/C-shell, (b) C-core/Au-shell, (c) Al-core/Cu-shell, and (d) Cu-core/Al-shell NPs and compared these values with the corresponding true values, T, used in the simulations for different Au-core diameters, D. 1.2 1.1 C-core/Au-shell NPs D (nm) 1 nm 2 nm 5 nm 10 nm 1.0 0.9 0.8 0 1 2 3 Au-shell Thickness T (nm) C. J. Powell, W. S. M. Werner, H. Kalbe, A. G. Shard, and D. G. Castner (to be published). 19
T NP /T We determined shell thicknesses, T NP, from the Shard formula using peak intensities from SESSA simulations for (a) Au-core/C-shell, (b) C-core/Au-shell, (c) Al-core/Cu-shell, and (d) Cu-core/Al-shell NPs and compared these values with the corresponding true values, T, used in the simulations for different Au-core diameters, D. 1.2 1.1 Al-core/Cu-shell NPs D (nm) 1 nm 2 nm 5 nm 10 nm 1.0 0.9 0.8 0 1 2 3 Cu-shell Thickness T (nm) C. J. Powell, W. S. M. Werner, H. Kalbe, A. G. Shard, and D. G. Castner (to be published). 20
T NP /T We determined shell thicknesses, T NP, from the Shard formula using peak intensities from SESSA simulations for (a) Au-core/C-shell, (b) C-core/Au-shell, (c) Al-core/Cu-shell, and (d) Cu-core/Al-shell NPs and compared these values with the corresponding true values, T, used in the simulations for different Au-core diameters, D. 1.2 1.1 Cu-core/Al-shell NPs D (nm) 1 nm 2 nm 5 nm 10 nm 1.0 0.9 0.8 0 1 2 3 Al-shell Thickness T (nm) C. J. Powell, W. S. M. Werner, H. Kalbe, A. G. Shard, and D. G. Castner (to be published). 21
3. Summary SESSA* is a NIST database that contains extensive data for quantitative AES and XPS SESSA can be used to simulate AES and XPS spectra for multilayer thin films and of nanostructures such as islands, lines, spheres, and layered spheres on surfaces. Users can specify the compositions and dimensions of each material in the sample and the measurement configuration. 22 *https://www.nist.gov/srd/nist-standard-reference-database-100