Experimental determination of cross sections for $K$-shell ionization by electron impact for C, O, Al, Si, and Ti

Cross sections for $K$-shell ionization by electron impact were determined from films of Al, Si, and Ti and their oxides deposited on carbon substrates, for incident energies between 2.5 and 25 keV. The spectral processing of the x-ray emission spectra took into account corrections due to the presence of a spontaneous oxide layer formed on the monoelemental films and to the supporting material. Carbon $K$-shell ionization cross sections were determined from the contribution of the substrate to the measured spectra, while for oxygen, data from the three oxide films were taken. The mass thickness of the coatings was characterized by x-ray reflectivity. The results obtained were compared with other experimental data sets, semiempirical approaches, and theoretical models.

Figure 1

Spectrum of Al film deposited on carbon substrate (gray line) and of carbon substrate itself (black line) measured at 3 keV, showing the presence of a spontaneous oxide layer grown on the sample surface.

Figure 2

Intensity of the carbon sum peak $I_{\mathrm{sum}}$ as function of the square of the C-$K\alpha$ peak intensity. Linear fit with nonzero (solid line) and null (dotted line) intercept.

Figure 3

X-ray emission spectrum from Si film, measured at 3 keV. Dots: experimental data; gray line: fit considering substrate and oxide layer effects; black line: fit considering only substrate effects.

Figure 4

Bremsstrahlung from the carbon bulk sample measured at 15 keV (dots) and simulated using the detector acceptance solid angle calculated in this work (line).

Figure 5

Ionization cross section for carbon as a function of electron energy $E_{\mathrm{o}}$. (a) Comparison between experimental determinations. (b) Experimental data obtained in this work compared with theoretical and semiempirical approximations. Circles: this work; open triangles: Ref. 21; solid triangles: Ref. 22; black thin solid line: Ref. 4; light gray thick solid line: Ref. 9; black thick solid line: Ref. 10; black dashed line: Ref. 23; black dotted line: Ref. 24; light gray dash dotted line: Ref. 25; black dash dotted line: Ref. 26; dark gray thick solid line: Ref. 27; and dark gray dash dotted line: Ref. 28.

Figure 6

Ionization cross section for oxygen as a function of electron energy $E_{\mathrm{o}}$. (a) Comparison between experimental determinations. (b) Experimental data obtained in this work compared with theoretical and semiempirical approximations. Circles: this work; squares: Ref. 17; gray open triangles: Ref. 20; black open triangles: Ref. 21; black thin solid line: Ref. 4; light gray thick solid line: Ref. 9; black thick solid line: Ref. 10; black dashed line: Ref. 23; black dotted line: Ref. 24; light gray dash dotted line: Ref. 25; dark gray thick solid line: Ref. 27; and dark gray dash dotted line: Ref. 28.

Figure 7

Ionization cross section for aluminum as a function of the electron energy $E_{\mathrm{o}}$. (a) Comparison between experimental determinations. (b) Experimental data obtained in this work compared with theoretical and semiempirical approximations. Circles indicate the results from the present work. Solid circles: Al film; open circles: Al${}_2$O${}_3$ film; triangles: Ref. 15; black thin solid line: Ref. 4; light gray solid line: Ref. 9; black thick solid line: Ref. 10; light gray dash dotted line: Ref. 25; dark gray solid line: Ref. 27; and dark gray dash dotted line: Ref. 28.

Figure 8

Ionization cross section for silicon as a function of the electron energy $E_{\mathrm{o}}$. (a) Comparison between experimental determinations. (b) Experimental data obtained in this work compared with theoretical and semiempirical approximations. Circles indicate the results from the present work. Solid circles: Si film; open circles: SiO${}_2$; triangles: Ref. 16; squares: Ref. 17; black thin solid line: Ref. 4; light gray solid line: Ref. 9; black thick solid line: Ref. 10; dark gray solid line: Ref. 27; and dash dotted line: Ref. 28.

Figure 9

$K$-shell ionization cross section for titanium as a function of the electron energy $E_{\mathrm{o}}$. (a) Comparison between experimental determinations. (b) Experimental data obtained in this work compared with theoretical and semiempirical approximations. Circles indicate the results from the present work. Solid circles: Ti; open circles: TiO${}_{2;}$ solid up triangles: Ref. 11; solid down triangles: Ref. 19; open up triangles: Ref. 18; black thin solid line: Ref. 4; light gray solid line: Ref. 9; black thick solid line: Ref. 10; dark gray solid line: Ref. 27; and dash dotted line: Ref. 28.