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Microspectroscopy and spectromicroscopy with photoemission electron microscopy using a new kind of imaging energy filter
Surface Science 480 (2001) 196±202
www.elsevier.nl/locate/susc
Microspectroscopy and spectromicroscopy with photoemission electron microscopy using a new kind of imaging energy ®lter M. Merkel a,*, M. Escher a, J. Settemeyer a, D. Funnemann b, A. Oelsner c, nhense c Ch. Ziethen c, O. Schmidt c, M. Klais c, G. Scho a
FOCUS GmbH, Am Birkhecker Berg 20, D-65510 Hunstetten-Gorsroth, Germany b OMICRON GmbH, D-65232 Taunusstein, Germany c Johannes Gutenberg-Universitat, D-55099 Mainz, Germany
Abstract The use of an imaging retarding ®eld analyser attached to the FOCUS IS-PEEM is described. This kind of energy ®lter is a simple, powerful tool to obtain microspectra from areas of down to about 1 lm using (V)UV and X-ray excitation sources. First results of microspectroscopy measured by excitation with a laboratory as well as a synchrotron X-ray source are presented. Ó 2001 Elsevier Science B.V. All rights reserved. Keywords: Electron microscopy; Photoelectron spectroscopy
1. Introduction Photoemission electron microscopy (PEEM) is able to deliver laterally highly resolved images along with detailed spectroscopic information [1]. Studies of the chemical composition with XANES [2±4] and ESCA spectromicroscopy [2,5,6] show the potential of the technique using PEEM in combination with synchrotron sources. The use of a retarding ®eld analyser (RFA) combined with a PEEM optics is a rather new attempt to obtain microspectra and/or energy ®ltered images. In combination with laboratory sources for VUV and X-ray excitation, it accomplishes a simple method for the chemical analysis of sample surfaces. Additionally the energy ®ltering has the potential to * Corresponding author. Tel.: +49-6126-91400; fax: +496126-91473. E-mail address: [email protected] (M. Merkel).
enhance the lateral resolution of the microscope by reducing the in¯uence of chromatic aberrations. For this purpose, dispersive ®lters (e.g. of the hemispherical type) are already successfully used [2,5]. The RFA described in the following is a simple and easy to use alternative to such more sophisticated and expensive devices.
2. Experimental The schematic experimental set-up is shown in Fig. 1. The imaging energy ®lter (IEF), working as RFA, was used in combination with a standard FOCUS IS-PEEM. Using the built-in iris aperture of this microscope, small sample areas for spectroscopy can be selected, which is illustrated by the inset. The current (technical) limit of the ®eld of view is as low as 1 lm in diameter. This opens up the way to do UPS/XPS microspectroscopy from
0039-6028/01/$ - see front matter Ó 2001 Elsevier Science B.V. All rights reserved. PII: S 0 0 3 9 - 6 0 2 8 ( 0 1 ) 0 0 8 3 5 - 4
M. Merkel et al. / Surface Science 480 (2001) 196±202
197
Fig. 1. The experimental setup. The inset shows images of Pd stripes (5.9 lm periode) without and with the iris aperture closed to about 6 lm ®eld of view.
small sample areas only depending on the actual photon ¯ux. We used dierent photon sources for excitation, these are: (i) UV-lamp (hm P 4:9 eV), (ii) VUV discharge lamp (hm 16:8 eV (NeI), hm 21:2 eV (HeI)), (iii) monochromatized and focused AlKa1 radiation (hm 1486:7 eV), (iv) synchrotron source (BESSY I, SX700/III monochromator). For performance evaluation, we have studied microstructured Pd stripes on Si (3.8 and 5.9 lm period, thickness 100 nm, sputtered 30 min, 5 10 5 mbar argon), a GaAs (Te) wafer (similar preparation) and a ¯ashed tungsten (1 1 0) crystal. Energy resolution has been determined to be down to 0.5 eV using the UV lamp and about 1 eV using the laboratory X-ray source. The IEF consists of two basic parts. The ®rst section is designed as a retarding lens, which delivers the required deceleration and shaping of the electron rays to a telescopic beam. The second part is a double grid system close to the entrance of the image intensi®er. The complete unit makes up an
energy high pass for the electrons. The corresponding high pass image of the observed sample region shows no noticeable distortion as compared to the standard PEEM mode. Spectra are acquired by either changing the applied grid potential keeping the sample at a ®xed bias or alternatively by sweeping the sample potential retaining a preadjusted grid potential. The microscope is operated using a microprocessor controlled power supply (FOCUS intelliPEEM) which is able to be remotely controlled via a RS232 or CAN computer interface. The power supply oers convenient mode switching, taking advantage of a built-in memory buer for up to 10 complete parameter sets. This memory function allows the fast switching between imaging and spectra acquisition. The sweeping of the relevant potentials during data acquisition is accomplished by interfacing with a 16 bit DAC in the PC. The acquisition of spectra was done by direct electronic readout of the modi®ed image intensi®er (double MCP collector screen) using a RC-coupled
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M. Merkel et al. / Surface Science 480 (2001) 196±202
preampli®er/discriminator delivering TTL shaped counting pulses. 3. Results and discussion A typical result taken using the Hg lamp at the excitation energy of hm 4:9 eV (threshold photoemission) is presented in Fig. 2a. It clearly shows that in the bandpass image (iv) (calculated weighted dierence of images (ii) and (iii), which
are high pass images taken at dierent grid voltages) the contrast is well enhanced. The lateral resolution in image (i) was determined to be around 37 and 22 nm in image (iv). Due to the low excitation energy used, the energy spread and the corresponding chromatic aberration is small. Therefore the image quality enhancement is mainly determined by the very eective discrimination of areas with dierent work functions. This allows the detection of details in the bandpass image, which are not seen in the raw images or in
Fig. 2. (a) Spectromicroscopy of a Pd stripe structure (3.8 lm periode) on Si using a Hg-high pressure (HBO100) excitation source (hm P 4:9 eV). Sample bias: 7 V. Retarding voltages (i) 0 V, no retarding, (ii) and (iii) high pass image at 11 and 10 V, (iv) grey scale stretched dierence image of (iii) and (ii) ! bandpass image. (b) Microspectroscopy at the same sample. Two dierent spectra with ®eld of view of 15 lm and 1 lm and their 1st derivatives are shown. Sample bias: 5 V; achieved energy resolution: about 0.4±0.5 eV.
M. Merkel et al. / Surface Science 480 (2001) 196±202
199
Fig. 3. Spectromicroscopy of a characteristic feature on the Pd/Si sample using NeI-excitation (hm 16:8 eV, FOCUS HIS13, ®eld of view: 15 lm). (a) No energy discrimination, grid voltage 0 V. (b), (c) and (d) Energy discriminated images with band passes of 0±8 V, 10±25 V and 8±10 V.
the image with the grid set to sample potential (no energy discrimination) (a). Fig. 2b shows raw spectra with 15 lm and 1 lm ®eld of view and the corresponding derivatives. The sample was a Pd:Si lines and spaces structure, sample bias was 5 V, sample current 120 nA. The shape of the spectra changes with the ®eld of view, giving a width of the Ôwide ®eld peakÕ of 0.9 eV (fwhm) and a shift of the high energy limit of the spectra by 0.42 eV. Every image detail contributes to a spectrum with it's own characteristic spectral ®nger print. The large ®eld of view delivers a more integral spectrum. The discrimination of dierent spectral features originated by small lateral areas as part of the larger ®eld of view is enhanced. To get the lateral distribution of a certain spectral feature a band pass image obtained at that speci®c energy is taken. Using higher excitation energies in the UPS range (NeI-excitation, hm 16:8 eV), the image contrast is mainly determined by changes of the valence band density of states. A strong enhancement of such small deviations is shown in the bandpass images of Fig. 3. The ``stop sign'' like feature is nearly not seen in the raw image (Fig. 3a) and changes its contrast upon changing the related energy band for imaging (Fig. 3b±d). Fig. 4 shows
a comparison of UPS spectra measured at a Pd/Si micro structured sample, taken with an OMICRON ``EA125'' hemispherical electron energy analyser and the PEEM/IEF combination. The other two curves are the measured integral I E spectrum and its numerical derivative N E
Fig. 4. Comparison of IEF spectra of the Pd/Si sample using HeI-excitation (hm 21:2 eV, HIS13) with results taken on the same sample with a state of the art hemispherical electron energy analyzer (OMICRON EA125). Data courtesy J. Westermann (OMICRON).
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M. Merkel et al. / Surface Science 480 (2001) 196±202
dI E=dE. The results show qualitatively the same shape, neglecting the dierent energy transmission functions of the two spectrometers, that in¯uences the intensity distribution. From this comparison it is clear, that the PEEM/IEF combination is in spite of its limited spectral resolution (not better than DE 0:5 eV) a versatile alternative for a wide range of spectroscopic investigations, if microscopical lateral information is needed at the same time. We performed XPS microspectroscopy using two dierent XPS light sources: synchrotron radiation as well as a laboratory X-ray source. The results are compared in Figs. 5 and 6. At the beamline SX700/III (BESSY I/Berlin) an excitation energy of hm 100 eV was used (Fig. 5) with a photon ¯ux around 109 photons/s. The sample was a tungsten (1 1 0) single crystal, that was cleaned by oxygen treatment and annealing at 2000 K. The grid potential was set to a ®xed reference voltage. The observed ®eld of view was around 100 lm. Fig. 5a shows the raw data, 5b the derivative. The spin±orbit splitting (DE 2:2 eV) of the W-4f states is clearly resolved. In the laboratory a 300 W monochromatized AlKa source was used for excitation (OMICRON DAR 400 M X-ray source with XM500 monochromator). Step width was 0.1 eV, sampling time 4 s for every data point, and ®eld of view ca. 100 lm, all values typical for the laboratory XPS microspectra shown in this article. Owing to a long acquisition time, the raw data obtained with the laboratory source (Fig. 6a) have nearly the same SNR as those obtained at the synchrotron source (Fig. 5a). This is a major point, because beamtime at synchrotron sources for most experiments is only available for some weeks a year. Fig. 6b shows, that the spin orbit split 4f states of tungsten are clearly resolved (as with the synchrotron source), with a FWHM of the W 4f 7=2 line of 1.1 eV. Taking a wider spectral range with an energy resolution of about 1 eV, the spectra show the anticipated W 4d and 4p states (Fig. 6c). Fig. 7a shows a wide range energy scan of a GaAs(Te) wafer, whereas 7b and c give a more detailed insight into the spectral details of the Ga/ As 3p and 3d states. Spectra of this kind give an estimate for the electron ¯ux at dierent energies
Fig. 5. XPS microspectroscopy of a W(1 1 0) surface using synchrotron radiation (hm 100 eV, BESSY I, SX700/III): (a) raw data I E, (b) ®rst derivative N E dI=dE.
and the resulting acquisition times for the XPS imaging in future experiments. 4. Conclusion and outlook These ®rst and preliminary performance tests show, that the PEEM/IEF combination is applicable for laterally resolved XPS spectroscopy with excitation by laboratory X-ray sources. The combination of the IEF RFA with the FOCUS ISPEEM is able to deliver an energy resolution down to 0.5 eV with a smallest ®eld of view of 1 lm. The results are comparable qualitatively to that of well established dispersive electron energy
M. Merkel et al. / Surface Science 480 (2001) 196±202
201
Fig. 6. Laboratory XPS microspectroscopy of a W(1 1 0) surface using monochromatized AlKa (hm 1487 eV) excitation: (a) raw data I E, (b) ®rst derivative N E, (c) wide range spectrum showing the 4p, d and f states. The lower curve at (b) was strongly smoothed and vertically magni®ed to identify the Fermi edge region.
Fig. 7. Laboratory XPS microspectroscopy of a GaAs(Te) wafer using monochromatized AlKa (hm 1487 eV) excitation: (a) wide range spectrum showing both the Ga and As 2p states together with the corresponding LMM Auger peaks. Details (b) and (c) show the 2p, 3p and 3d excitations of gallium and arsine.
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M. Merkel et al. / Surface Science 480 (2001) 196±202
analysers. Chemical analysis of microscopic sample areas by laterally resolved XPS spectroscopy was possible both with synchrotron and laboratory X-ray sources, in both cases with a spectral resolution of about 1 eV. The demonstrated approach takes bene®t of the combination of a versatile energy high pass ®lter with the microscopical imaging performance of a state of the art PEEM. By that means we believe to meet a wider ®eld of applications for such instruments. Acknowledgements Part of the work was funded by BMBF, Germany, through grants FKz-No. 13N7864 and FKz-No. 05 SL8 UMA 0.
References [1] H. Ade (Ed.), Spectromicroscopy, J. Electron Spectrosc. Relat. Phenom. 84 (1997). Special issue. [2] B.P. Tonner, D. Dunham, T. Droubay, M. Pauli, J. Electron Spectrosc. Relat. Phenom. 84 (1997) 211. [3] Ch. Ziethen, O. Schmidt, G.H. Fecher, C.M. Schneider, G. Sch onhense, R. Fr omter, M. Seider, K. Grzelakowski, M. Merkel, D. Funnemann, W. Swiech, H. Gundlach, J. Kirschner, J. Electron Spectrosc. Relat. Phenom. 88±91 (1998) 983. [4] Ch. Ziethen, O. Schmidt, G.K.L. Marx, G. Sch onhense, R. Fr omter, J. Gilles, J. Kirschner, C.M. Schneider, O. Gr oning, J. Electron Spectrosc. Relat. Phenom. 107 (2000) 261. [5] E. Bauer, C. Koziol, G. Lilienkamp, T. Schmidt, J. Electron Spectrosc. Relat. Phenom. 84 (1997) 201. [6] O. Schmidt, Ch. Ziethen, G.H. Fecher, M. Merkel, M. Escher, D. Menke, U. Kleineberg, U. Heinzmann, G. Sch onhense, J. Electron Spectrosc. Relat. Phenom. 88±91 (1998) 1009.
www.elsevier.nl/locate/susc
Microspectroscopy and spectromicroscopy with photoemission electron microscopy using a new kind of imaging energy ®lter M. Merkel a,*, M. Escher a, J. Settemeyer a, D. Funnemann b, A. Oelsner c, nhense c Ch. Ziethen c, O. Schmidt c, M. Klais c, G. Scho a
FOCUS GmbH, Am Birkhecker Berg 20, D-65510 Hunstetten-Gorsroth, Germany b OMICRON GmbH, D-65232 Taunusstein, Germany c Johannes Gutenberg-Universitat, D-55099 Mainz, Germany
Abstract The use of an imaging retarding ®eld analyser attached to the FOCUS IS-PEEM is described. This kind of energy ®lter is a simple, powerful tool to obtain microspectra from areas of down to about 1 lm using (V)UV and X-ray excitation sources. First results of microspectroscopy measured by excitation with a laboratory as well as a synchrotron X-ray source are presented. Ó 2001 Elsevier Science B.V. All rights reserved. Keywords: Electron microscopy; Photoelectron spectroscopy
1. Introduction Photoemission electron microscopy (PEEM) is able to deliver laterally highly resolved images along with detailed spectroscopic information [1]. Studies of the chemical composition with XANES [2±4] and ESCA spectromicroscopy [2,5,6] show the potential of the technique using PEEM in combination with synchrotron sources. The use of a retarding ®eld analyser (RFA) combined with a PEEM optics is a rather new attempt to obtain microspectra and/or energy ®ltered images. In combination with laboratory sources for VUV and X-ray excitation, it accomplishes a simple method for the chemical analysis of sample surfaces. Additionally the energy ®ltering has the potential to * Corresponding author. Tel.: +49-6126-91400; fax: +496126-91473. E-mail address: [email protected] (M. Merkel).
enhance the lateral resolution of the microscope by reducing the in¯uence of chromatic aberrations. For this purpose, dispersive ®lters (e.g. of the hemispherical type) are already successfully used [2,5]. The RFA described in the following is a simple and easy to use alternative to such more sophisticated and expensive devices.
2. Experimental The schematic experimental set-up is shown in Fig. 1. The imaging energy ®lter (IEF), working as RFA, was used in combination with a standard FOCUS IS-PEEM. Using the built-in iris aperture of this microscope, small sample areas for spectroscopy can be selected, which is illustrated by the inset. The current (technical) limit of the ®eld of view is as low as 1 lm in diameter. This opens up the way to do UPS/XPS microspectroscopy from
0039-6028/01/$ - see front matter Ó 2001 Elsevier Science B.V. All rights reserved. PII: S 0 0 3 9 - 6 0 2 8 ( 0 1 ) 0 0 8 3 5 - 4
M. Merkel et al. / Surface Science 480 (2001) 196±202
197
Fig. 1. The experimental setup. The inset shows images of Pd stripes (5.9 lm periode) without and with the iris aperture closed to about 6 lm ®eld of view.
small sample areas only depending on the actual photon ¯ux. We used dierent photon sources for excitation, these are: (i) UV-lamp (hm P 4:9 eV), (ii) VUV discharge lamp (hm 16:8 eV (NeI), hm 21:2 eV (HeI)), (iii) monochromatized and focused AlKa1 radiation (hm 1486:7 eV), (iv) synchrotron source (BESSY I, SX700/III monochromator). For performance evaluation, we have studied microstructured Pd stripes on Si (3.8 and 5.9 lm period, thickness 100 nm, sputtered 30 min, 5 10 5 mbar argon), a GaAs (Te) wafer (similar preparation) and a ¯ashed tungsten (1 1 0) crystal. Energy resolution has been determined to be down to 0.5 eV using the UV lamp and about 1 eV using the laboratory X-ray source. The IEF consists of two basic parts. The ®rst section is designed as a retarding lens, which delivers the required deceleration and shaping of the electron rays to a telescopic beam. The second part is a double grid system close to the entrance of the image intensi®er. The complete unit makes up an
energy high pass for the electrons. The corresponding high pass image of the observed sample region shows no noticeable distortion as compared to the standard PEEM mode. Spectra are acquired by either changing the applied grid potential keeping the sample at a ®xed bias or alternatively by sweeping the sample potential retaining a preadjusted grid potential. The microscope is operated using a microprocessor controlled power supply (FOCUS intelliPEEM) which is able to be remotely controlled via a RS232 or CAN computer interface. The power supply oers convenient mode switching, taking advantage of a built-in memory buer for up to 10 complete parameter sets. This memory function allows the fast switching between imaging and spectra acquisition. The sweeping of the relevant potentials during data acquisition is accomplished by interfacing with a 16 bit DAC in the PC. The acquisition of spectra was done by direct electronic readout of the modi®ed image intensi®er (double MCP collector screen) using a RC-coupled
198
M. Merkel et al. / Surface Science 480 (2001) 196±202
preampli®er/discriminator delivering TTL shaped counting pulses. 3. Results and discussion A typical result taken using the Hg lamp at the excitation energy of hm 4:9 eV (threshold photoemission) is presented in Fig. 2a. It clearly shows that in the bandpass image (iv) (calculated weighted dierence of images (ii) and (iii), which
are high pass images taken at dierent grid voltages) the contrast is well enhanced. The lateral resolution in image (i) was determined to be around 37 and 22 nm in image (iv). Due to the low excitation energy used, the energy spread and the corresponding chromatic aberration is small. Therefore the image quality enhancement is mainly determined by the very eective discrimination of areas with dierent work functions. This allows the detection of details in the bandpass image, which are not seen in the raw images or in
Fig. 2. (a) Spectromicroscopy of a Pd stripe structure (3.8 lm periode) on Si using a Hg-high pressure (HBO100) excitation source (hm P 4:9 eV). Sample bias: 7 V. Retarding voltages (i) 0 V, no retarding, (ii) and (iii) high pass image at 11 and 10 V, (iv) grey scale stretched dierence image of (iii) and (ii) ! bandpass image. (b) Microspectroscopy at the same sample. Two dierent spectra with ®eld of view of 15 lm and 1 lm and their 1st derivatives are shown. Sample bias: 5 V; achieved energy resolution: about 0.4±0.5 eV.
M. Merkel et al. / Surface Science 480 (2001) 196±202
199
Fig. 3. Spectromicroscopy of a characteristic feature on the Pd/Si sample using NeI-excitation (hm 16:8 eV, FOCUS HIS13, ®eld of view: 15 lm). (a) No energy discrimination, grid voltage 0 V. (b), (c) and (d) Energy discriminated images with band passes of 0±8 V, 10±25 V and 8±10 V.
the image with the grid set to sample potential (no energy discrimination) (a). Fig. 2b shows raw spectra with 15 lm and 1 lm ®eld of view and the corresponding derivatives. The sample was a Pd:Si lines and spaces structure, sample bias was 5 V, sample current 120 nA. The shape of the spectra changes with the ®eld of view, giving a width of the Ôwide ®eld peakÕ of 0.9 eV (fwhm) and a shift of the high energy limit of the spectra by 0.42 eV. Every image detail contributes to a spectrum with it's own characteristic spectral ®nger print. The large ®eld of view delivers a more integral spectrum. The discrimination of dierent spectral features originated by small lateral areas as part of the larger ®eld of view is enhanced. To get the lateral distribution of a certain spectral feature a band pass image obtained at that speci®c energy is taken. Using higher excitation energies in the UPS range (NeI-excitation, hm 16:8 eV), the image contrast is mainly determined by changes of the valence band density of states. A strong enhancement of such small deviations is shown in the bandpass images of Fig. 3. The ``stop sign'' like feature is nearly not seen in the raw image (Fig. 3a) and changes its contrast upon changing the related energy band for imaging (Fig. 3b±d). Fig. 4 shows
a comparison of UPS spectra measured at a Pd/Si micro structured sample, taken with an OMICRON ``EA125'' hemispherical electron energy analyser and the PEEM/IEF combination. The other two curves are the measured integral I E spectrum and its numerical derivative N E
Fig. 4. Comparison of IEF spectra of the Pd/Si sample using HeI-excitation (hm 21:2 eV, HIS13) with results taken on the same sample with a state of the art hemispherical electron energy analyzer (OMICRON EA125). Data courtesy J. Westermann (OMICRON).
200
M. Merkel et al. / Surface Science 480 (2001) 196±202
dI E=dE. The results show qualitatively the same shape, neglecting the dierent energy transmission functions of the two spectrometers, that in¯uences the intensity distribution. From this comparison it is clear, that the PEEM/IEF combination is in spite of its limited spectral resolution (not better than DE 0:5 eV) a versatile alternative for a wide range of spectroscopic investigations, if microscopical lateral information is needed at the same time. We performed XPS microspectroscopy using two dierent XPS light sources: synchrotron radiation as well as a laboratory X-ray source. The results are compared in Figs. 5 and 6. At the beamline SX700/III (BESSY I/Berlin) an excitation energy of hm 100 eV was used (Fig. 5) with a photon ¯ux around 109 photons/s. The sample was a tungsten (1 1 0) single crystal, that was cleaned by oxygen treatment and annealing at 2000 K. The grid potential was set to a ®xed reference voltage. The observed ®eld of view was around 100 lm. Fig. 5a shows the raw data, 5b the derivative. The spin±orbit splitting (DE 2:2 eV) of the W-4f states is clearly resolved. In the laboratory a 300 W monochromatized AlKa source was used for excitation (OMICRON DAR 400 M X-ray source with XM500 monochromator). Step width was 0.1 eV, sampling time 4 s for every data point, and ®eld of view ca. 100 lm, all values typical for the laboratory XPS microspectra shown in this article. Owing to a long acquisition time, the raw data obtained with the laboratory source (Fig. 6a) have nearly the same SNR as those obtained at the synchrotron source (Fig. 5a). This is a major point, because beamtime at synchrotron sources for most experiments is only available for some weeks a year. Fig. 6b shows, that the spin orbit split 4f states of tungsten are clearly resolved (as with the synchrotron source), with a FWHM of the W 4f 7=2 line of 1.1 eV. Taking a wider spectral range with an energy resolution of about 1 eV, the spectra show the anticipated W 4d and 4p states (Fig. 6c). Fig. 7a shows a wide range energy scan of a GaAs(Te) wafer, whereas 7b and c give a more detailed insight into the spectral details of the Ga/ As 3p and 3d states. Spectra of this kind give an estimate for the electron ¯ux at dierent energies
Fig. 5. XPS microspectroscopy of a W(1 1 0) surface using synchrotron radiation (hm 100 eV, BESSY I, SX700/III): (a) raw data I E, (b) ®rst derivative N E dI=dE.
and the resulting acquisition times for the XPS imaging in future experiments. 4. Conclusion and outlook These ®rst and preliminary performance tests show, that the PEEM/IEF combination is applicable for laterally resolved XPS spectroscopy with excitation by laboratory X-ray sources. The combination of the IEF RFA with the FOCUS ISPEEM is able to deliver an energy resolution down to 0.5 eV with a smallest ®eld of view of 1 lm. The results are comparable qualitatively to that of well established dispersive electron energy
M. Merkel et al. / Surface Science 480 (2001) 196±202
201
Fig. 6. Laboratory XPS microspectroscopy of a W(1 1 0) surface using monochromatized AlKa (hm 1487 eV) excitation: (a) raw data I E, (b) ®rst derivative N E, (c) wide range spectrum showing the 4p, d and f states. The lower curve at (b) was strongly smoothed and vertically magni®ed to identify the Fermi edge region.
Fig. 7. Laboratory XPS microspectroscopy of a GaAs(Te) wafer using monochromatized AlKa (hm 1487 eV) excitation: (a) wide range spectrum showing both the Ga and As 2p states together with the corresponding LMM Auger peaks. Details (b) and (c) show the 2p, 3p and 3d excitations of gallium and arsine.
202
M. Merkel et al. / Surface Science 480 (2001) 196±202
analysers. Chemical analysis of microscopic sample areas by laterally resolved XPS spectroscopy was possible both with synchrotron and laboratory X-ray sources, in both cases with a spectral resolution of about 1 eV. The demonstrated approach takes bene®t of the combination of a versatile energy high pass ®lter with the microscopical imaging performance of a state of the art PEEM. By that means we believe to meet a wider ®eld of applications for such instruments. Acknowledgements Part of the work was funded by BMBF, Germany, through grants FKz-No. 13N7864 and FKz-No. 05 SL8 UMA 0.
References [1] H. Ade (Ed.), Spectromicroscopy, J. Electron Spectrosc. Relat. Phenom. 84 (1997). Special issue. [2] B.P. Tonner, D. Dunham, T. Droubay, M. Pauli, J. Electron Spectrosc. Relat. Phenom. 84 (1997) 211. [3] Ch. Ziethen, O. Schmidt, G.H. Fecher, C.M. Schneider, G. Sch onhense, R. Fr omter, M. Seider, K. Grzelakowski, M. Merkel, D. Funnemann, W. Swiech, H. Gundlach, J. Kirschner, J. Electron Spectrosc. Relat. Phenom. 88±91 (1998) 983. [4] Ch. Ziethen, O. Schmidt, G.K.L. Marx, G. Sch onhense, R. Fr omter, J. Gilles, J. Kirschner, C.M. Schneider, O. Gr oning, J. Electron Spectrosc. Relat. Phenom. 107 (2000) 261. [5] E. Bauer, C. Koziol, G. Lilienkamp, T. Schmidt, J. Electron Spectrosc. Relat. Phenom. 84 (1997) 201. [6] O. Schmidt, Ch. Ziethen, G.H. Fecher, M. Merkel, M. Escher, D. Menke, U. Kleineberg, U. Heinzmann, G. Sch onhense, J. Electron Spectrosc. Relat. Phenom. 88±91 (1998) 1009.