Journal of large-scale research facilities, 2, A90 (2016) http://dx.doi.org/10.17815/jlsrf-2-86 Published: 16.11.2016 SPEEM: The photoemission microscope at the dedicated microfocus PGM beamline UE49-PGMa at BESSY II Helmholtz-Zentrum Berlin für Materialien und Energie * Instrument Scientists: - Dr. Florian Kronast, , Helmholtz-Zentrum Berlin für Materialien und Energie phone: +49 8062-14620, email: �orian.kronast@helmholtz-berlin.de - Dr. Sergio Valencia Molina, Helmholtz-Zentrum Berlin für Materialien und Energie phone: +49 8062-15619, email: sergio.valencia@helmholtz-berlin.de Abstract: The UE49-PGMa beamline hosts a photoemission electron microscope (PEEM) dedicated to spectromicroscopy and element-selective magnetic imaging on the nanometer scale. The instrument is an Elmitec PEEM III equipped with energy �lter and Helium cooled manipulator. Laser driven excita- tions can be studied using an attached Ti:Sa laser. A variety of customized sample holders is available for imaging in moderate magnetic / electric �eld, temperature control, or local laser excitations. With x-rays the instrument is capable of 30 nm spatial resolution. 1 Introduction Magnetic nanostructures are at the heart of modern data storage technology. Typical dimensions of magnetic bits are in the sub-100 nm region. In addition novel magnetoelectronics devices such as mag- netic random access memory junctions are operated on the sub-100 nm m scale. An understanding magnetic properties of such low-dimensional structures is only accessible to spectro-microscopy tools capable of appropriate lateral resolution. This goal is achieved by combining a photoemission micro- scope (SPEEM) with a dedicated microfocus PGM beamline (UE49 PGM). High photon �ux in com- bination with full polarization control makes this setup the ideal tool for space resolved and element selective investigation of nanostructures by means of chemical maps (X-ray absorption spectroscopy (XAS)) and magnetic imaging (X-ray magnetic circular dichroism (XMCO) and X-ray magnetic linear dichroism (XMLD)). *Cite article as: Helmholtz-Zentrum Berlin für Materialien und Energie. (2016). SPEEM: The photoemission micro- scope at the dedicated microfocus PGM beamline UE49-PGMa at BESSY II. Journal of large-scale research facilities, 2, A90. http://dx.doi.org/10.17815/jlsrf-2-86 1 http://jlsrf.org/ http://dx.doi.org/10.17815/jlsrf-2-86 http://dx.doi.org/10.17815/jlsrf-2-86 https://creativecommons.org/licenses/by/4.0/ Journal of large-scale research facilities, 2, A90 (2016) http://dx.doi.org/10.17815/jlsrf-2-86 Figure 1: Photograph of the SPEEM setup. 2 Instrument application The particular strength of this instrument is the element speci�city and quantitative magnetic contrast at high spatial resolution in combination with a variable sample environment. The instrument has been equipped with a LHe cryostat for sample temperatures down to 45 K. Special sample holders have been developed. Some of them combine temperature control in a range from 45 K to 600 K with the appli- cation of magnetic �elds of up to 75 mT and a voltage applied to the sample during imaging (Sandig et al., 2012). Customized power supplies and a dedicated software control allows for special features, such as lens tracking during application of magnetic or electric �eld, on-the-�y data recording, sub Kelvin temperature control and stabilization, or macro based data acquisition. A Ti:Sa laser system attached to the microscope can be used to study laser driven e�ects such as phase changes or magnetic switching. Di�raction limited laser spot sizes can be reached with a dedicated sample holder (Gierster, Pape, et al., 2015). Di�erent modes of operation are possible. Imaging of secondary electrons allows for XAS spectroscopy or magnetic imaging with XMCD or XMLD contrast. Due to an energy �lter also spatially resolved photo electron spectroscopy (XPS) and even angle resolved photo emission spectroscopy (micro ARPES) at kinetic energies of up to 1000 eV is possible. Even depth resolved XPS using the standing wave technique can be done (Gray et al., 2010; Kronast et al., 2008). At typical working conditions of the microscope the �eld of view is about 3 –10 µm and matches ideally with the x-ray spot size of 10x20 µm. The photon �ux provided by the 1200 l/mm grating allows electron count rates close to the space charging limit and is su�cient to optimize spatial resolution and collection e�ciency. Frame rates of 1-3 s at 5 µm �eld of view are possible. Some examples of typical applications are listed below: • Chemical maps by XAS and XPS (Fang et al., 2014; Moreno et al., 2010) • Magnetic domain imaging by XMCD and XMLD (Boeglin et al., 2009) • Phasetransitions / temperature dependent measurements (Ewerlin et al., 2013) • Field dependent measurements (Kronast et al., 2011) • Micro-spectroscopy on nanostructures, magnetic responses and interactions, probing of core shell structures (Kimling et al., 2011) • Magnetic transport and spin torque (Heyne et al., 2010) • Magnetic/magnetoelectric coupling in thin �lms and multifoerroics (Cheri� et al., 2010) 2 http://dx.doi.org/10.17815/jlsrf-2-86 https://creativecommons.org/licenses/by/4.0/ http://dx.doi.org/10.17815/jlsrf-2-86 Journal of large-scale research facilities, 2, A90 (2016) • Laser induced magnetic switching or phase changes (Gierster, Ünal, et al., 2015) • Time-resolved magnetization dynamics (fs-laser pump, X-ray probe) (Miguel et al., 2009) 3 Source The insertion device is the elliptical undulator UE49 with the following parameters: Type APPLE2 Location L108 Periode length 49 mm Periods/Pols 64 n Minimal Energy at 1,7 GeV 91.2 eV Minimal Gap 16 mm Polarisation linear variable 0° ... +90° elliptical, circular Table 1: Parameters of insertion device UE49. 4 Optical design The UE49-PGMa beamline is one of three branches at the UE49 insertion device, an Apple II-type un- dulator with full polarization control. For highest brilliance the UE49 is located in one of the low-beta sections of the BESSY II storage ring. A schematic layout of the UE49-PGMa beamline is shown in Figure 2. The beamline comprises �ve optical elements, four mirrors and one grating. The cylindrical mirror M1 and the toriodal mirror M3 serve as switching mirror units and distribute the beam to neigh- boring branches. M4 is an ellipsoidal refocussing mirror, optimized for high transmittance and small spot size. The x-ray spot on the sample is a de-magni�ed image of the exit slit. At an incidence angle of 74° and a slit opening of 200 µm the spot measures 20 µm in horizontal and 10 µm in vertical direction (FWHM). The beamline is equipped with a plane grating monochromator that covers an energy range from 80 to 1800 eV. With the �nest grating (1200 l/mm) a spectral resolution (E/∆E) of 10000 at 700 eV can be achieved. The photon �ux ranges from 1011 to 1013 ph/s/100 mA. A detailed �ux table for this grating is shown in Figure 3. Using di�erent gratings with a lower line density (600 l/mm and 300 l/mm) the photon �ux can be increased at the expense of spectral resolution. Main parameters of the UE49-PGMa beamline are summarized in Table 1 and Table 2. 3 http://dx.doi.org/10.17815/jlsrf-2-86 https://creativecommons.org/licenses/by/4.0/ Journal of large-scale research facilities, 2, A90 (2016) http://dx.doi.org/10.17815/jlsrf-2-86 Figure 2: Optical layout of beamline UE49-PGMa. Figure 3: Photon �ux measured with the 1200l/mm grating. 4 http://dx.doi.org/10.17815/jlsrf-2-86 https://creativecommons.org/licenses/by/4.0/ http://dx.doi.org/10.17815/jlsrf-2-86 Journal of large-scale research facilities, 2, A90 (2016) 5 Technical Data SPEEM Microscope Spatial resolution 25 nm Energy analyzer E < 0.3 eV Monochromator PGM Azimuthrotation Yes Temperatur control 45 - 600 K Electric and magnetic �eld max. 75 nT during imaging Beamline Monochromator PGM Energy range 80 to 1800 eV Energy resolution 10.000 at 700 eV Spot size on sample 10 x 20 µm Full polarization control Yes Fixed endstation Yes Preparationchamber Evaporation Fe, Co, Ni, Al... Ion sputtering Sample storage in vacuum up to 6 Pump Laser 800 nm wavelength 300 nJ max. pulse energy 80 fs pulse duration Repetition rate variable from single pulse to 2.5 MHz Table 2: Technical parameters for the SPEEM station and the UE49-PGMa beamline References Boeglin, C., Ersen, O., Pilard, M., Speisser, V., & Kronast, F. (2009). Temperature depen- dence of magnetic coupling in ultrathin NiO/Fe3O4(001) �lms. Phys. Rev. B, 80, 035409. http://dx.doi.org/10.1103/PhysRevB.80.035409 Cheri�, R. O., Ivanovskaya, V., Phillips, L. C., Zobelli, A., Infante, I. C., Jacquet, E., . . . Bibes, M. (2010). Electric-�eld control of magnetic order above room temperature. Phys. Rev. Lett., 105, 187203. http://dx.doi.org/10.1103/PhysRevLett.105.187203 Ewerlin, M., Demirbas, D., Brüssing, F., Petracic, O., Ünal, A. A., Valencia, S., . . . Zabel, H. (2013). Magnetic dipole and higher pole interaction on a square lattice. Phys. Rev. Lett., 110, 177209. http://dx.doi.org/10.1103/PhysRevLett.110.177209 Fang, H., Battaglia, C., Carraro, C., Nemsak, S., Ozdol, B., Kang, J. S., . . . Javey, A. (2014). Strong inter- layer coupling in van der Waals heterostructures built from single-layer chalcogenides. Proceedings of the National Academy of Sciences, 111(17), 6198-6202. http://dx.doi.org/10.1073/pnas.1405435111 Gierster, L., Pape, L., Ünal, A. A., & Kronast, F. (2015). A sample holder with integrated laser op- tics for an ELMITEC photoemission electron microscope. Review of Scienti�c Instruments, 86(2). http://dx.doi.org/10.1063/1.4907402 5 http://dx.doi.org/10.17815/jlsrf-2-86 http://dx.doi.org/10.1103/PhysRevB.80.035409 http://dx.doi.org/10.1103/PhysRevLett.105.187203 http://dx.doi.org/10.1103/PhysRevLett.110.177209 http://dx.doi.org/10.1073/pnas.1405435111 http://dx.doi.org/10.1063/1.4907402 https://creativecommons.org/licenses/by/4.0/ Journal of large-scale research facilities, 2, A90 (2016) http://dx.doi.org/10.17815/jlsrf-2-86 Gierster, L., Ünal, A., Pape, L., Radu, F., & Kronast, F. (2015). Laser induced magne- tization switching in a TbFeCo ferrimagnetic thin �lm: discerning the impact of dipolar �elds, laser heating and laser helicity by XPEEM. Ultramicroscopy, 159, Part 3, 508 - 512. http://dx.doi.org/10.1016/j.ultramic.2015.05.016 Gray, A. X., Kronast, F., Papp, C., Yang, S.-H., Cramm, S., Krug, I. P., . . . Fadley, C. S. (2010). Standing- wave excited soft x-ray photoemission microscopy: Application to co microdot magnetic arrays. Applied Physics Letters, 97(6). http://dx.doi.org/10.1063/1.3478215 Heyne, L., Rhensius, J., Ilgaz, D., Bisig, A., Rüdiger, U., Kläui, M., . . . Kronast, F. (2010). Direct deter- mination of large spin-torque nonadiabaticity in vortex core dynamics. Phys. Rev. Lett., 105, 187203. http://dx.doi.org/10.1103/PhysRevLett.105.187203 Kimling, J., Kronast, F., Martens, S., Böhnert, T., Martens, M., Herrero-Albillos, J., . . . Meier, G. (2011). Photoemission electron microscopy of three-dimensional magnetization con�gurations in core-shell nanostructures. Phys. Rev. B, 84, 174406. http://dx.doi.org/10.1103/PhysRevB.84.174406 Kronast, F., Friedenberger, N., Ollefs, K., Gliga, S., Tati-Bismaths, L., Thies, R., . . . Farle, M. (2011). Element-speci�c magnetic hysteresis of individual 18 nm Fe nanocubes. Nano Letters, 11(4), 1710- 1715. http://dx.doi.org/10.1021/nl200242c Kronast, F., Ovsyannikov, R., Kaiser, A., Wiemann, C., Yang, S.-H., Bürgler, D. E., . . . Fadley, C. S. (2008). Depth-resolved soft x-ray photoelectron emission microscopy in nanostructures via standing-wave excited photoemission. Applied Physics Letters, 93(24). http://dx.doi.org/10.1063/1.3046782 Miguel, J., Sánchez-Barriga, J., Bayer, D., Kurde, J., Heitkamp, B., Piantek, M., . . . Kuch, W. (2009). Time- resolved magnetization dynamics of cross-tie domain walls in permalloy microstructures. Journal of Physics: Condensed Matter, 21(49), 496001. Moreno, C., Munuera, C., Valencia, S., Kronast, F., Obradors, X., & Ocal, C. (2010). Reversible resistive switching and multilevel recording in La0.7Sr0.3MnO3 thin �lms for low cost nonvolatile memories. Nano Letters, 10(10), 3828-3835. http://dx.doi.org/10.1021/nl1008162 Sandig, O., Herrero-Albillos, J., Römer, F., Friedenberger, N., Kurde, J., Noll, T., . . . Kronast, F. (2012). Imaging magnetic responses of nanomagnets by XPEEM. Journal of Electron Spectroscopy and Related Phenomena, 185(10), 365 - 370. http://dx.doi.org/10.1016/j.elspec.2012.07.005 6 http://dx.doi.org/10.17815/jlsrf-2-86 http://dx.doi.org/10.1016/j.ultramic.2015.05.016 http://dx.doi.org/10.1063/1.3478215 http://dx.doi.org/10.1103/PhysRevLett.105.187203 http://dx.doi.org/10.1103/PhysRevB.84.174406 http://dx.doi.org/10.1021/nl200242c http://dx.doi.org/10.1063/1.3046782 http://dx.doi.org/10.1021/nl1008162 http://dx.doi.org/10.1016/j.elspec.2012.07.005 https://creativecommons.org/licenses/by/4.0/ Introduction Instrument application Source Optical design Technical Data