High Resolution Krypton M4.5 X-ray Emission Spectra

High resolution M,,, (3d -+ 4p) x-ray emission spectra from a kwton plasma were measured using a recently developed grazing-incidence reflectiongrating monochromator/spectrometer with very high flux rates at extreme ultraviolet and soft x-ray wavelengths. The nominal resolving power of the instrument, E/AE, is about 300 in this energy range (-80 eV). Three dipole-allowed 3d -+ 4p emission lines were observed at 80.98 eV, 80.35 eV and 79.73 eV. A broad peak at about 82.3 eV, is tentatively assigned to transitions resulting from KI?', and effects of excitation energy on M, , , x-ray emission were observed. In this report, high resolution Mq 5 x-ray emission spectra from a krypton plasma produced in the discharge region of a Penning-type sputtering source [1,2] are presented. The discharge was excited by application of a high potential difference (1-2 kV) and magnetic field (1.2 kgauss) between two aluminum cathodes and a grounded anode. In the evacuated region between these cathodes, the krypton gas was leaked in continuously to an equilibrium pressure. At some distance (200 mm) from the discharge region, a thermocouple gauge measured a gas pressure of -15 mtorr. The diffuse discharge, extending over -5 mm in diameter, was placed behind the entrance slit of the monochromator. A recently-developed reflection grating spectrometer/monochromator, which provides extremely high throughput in the extreme ultraviolet (W) and soft x-ray (SXR) spectral regions [3] was used. Based upon measurements of the grating efficiency at the wavelengths reported here, the net throughput of the instrument is estimated to be 2 x steradians. This includes the efficiency of a channel electron multiplier overcoated with MgF2 to enhance the photon detection efficiency, which was positioned to intercept the radiation passing through the exit slit of the monochromator. sufficiently (')permanent address : PO Box 8046. Berkeley. CA 94707, U.S.A. Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19879110 C9-646 JOURNAL DE PHYSIQUE high count rates were provided to allow high resolution measurements of the spectral lines of krypton, i.e., at a nominal resolving power (E/AE) of approximately 300-500. Presented in Figure 1 is a wide scan of krypton plasma (along with aluminum) over the 100-200 A spectral region. This steppedscan spectrum was obtained in about 30 mins. The prominent Al(1V) and Al(II1) spectroscopic lines were observed. An accurate energy (or wavelength) calibration of the spectrum presented in Fig. 1 was obtained using A1 (IV) (2p6 -+ 2p5 3s) lines at 77.45 eV and 76.68 eV [1,4]. The spectral features in Fig. 1 agree with the low resolution electron excited krypton M4,5 x-ray emission spectra [5] from a supersonic jet of krypton gas. Fig. 1. Wide scan spectrum of krypton (+ aluminum) over the 100200 A spectral region from a Penning discharge tube. Prominent Al(1V) lines provided an accurate wavelength calibration. A detailed study of the 148-158 A spectral region was performed with higher resolution and better statistics, as shown in Figs. 2 and 3. The energies (wavelengths) of the prominent features in Figs. 2 and 3 are listed in Table 1. The detailed spectrum presented in Fig. 2 was obtained maintaining the source voltage at about 1.5 kV, which is below the binding energy of krypton-L electrons. The prominent features A, B and C are identified as dipole-allowed 3d + 4p emission lines. These assignments were confirmed by the observed 1:2:3 intensity ratio of peaks in the order of decreasing photon energy as predicted by a simple one-electron model and the energy differences as derived from the measured spin-orbit splitting of 3d levels [6] and 4p levels [7] in krypton. The broad peak D is tentatively assigned to transitions resulting from XCr2+ (3d,4s) which can be produced in the plasma either from initial singPe ionizations followed by. Coster-Kronig decay, or from direct double ionization. Previous work by Deslattes et al. [I] has shown that Penning sources produce multiple ionized species. The Kr-M4,5 x-ray spectrum, presented in Fig. 3, was obtained with potential difference in the Penning source maintained at 2.2 kV, which is sufficient to ionize L electrons in krypton (LI electronic binding energy is 1.9 keV). Comparing spectra presented in Fig. 2 with those in Fig. 3 (lower) obtained with the Table 1. The component wavelengths (energies) and assignments af major components in krypton plasma Peak Wavelength (A)/Energy (eV) ~ssignment A 155.5+0.1/79.73 Kr(3d5/zt4P3/z)