Abstract A new ultrahigh-resolution photoemission electron microscope called PEEM3 is being...
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Abstract A new ultrahigh-resolution photoemission electron microscope called PEEM3 is being developed at the Advanced Light Source. An electron mirror combined with a sophisticated magnetic beam separator is used to provide simultaneous correction of spherical and chromatic aberrations. PEEM3 electron mirror has four rotationally symmetric electrons and gives three free knobs to adjust the focal length, the chromatic and the spherical aberrations so that a wide aberration region can be covered for all the operation modes of objective lens. PEEM3 magnetic separator has double mirror symmetry configuration and images its entrance plane 1:1 in its exit plane. A further enormous advantage of the aberration correction is the increase of electron transmission. The goal of the PEEM3 project is to achieve the highest possible transmission of the system at resolutions comparable to our present PEEM2 system and to enable significantly higher resolution, albeit at the sacrifice of intensity. We have left open the possibility to add an energy filter at a later date, if it becomes necessary driven by scientific need to improve the resolution further. The instrument will be installed on an elliptically polarized undulator beamline and will be used for the study of complex materials at high spatial and spectral resolution. Advanced Light Source Experimental Systems Group An Aberration Corrected Photoemission Electron Microscope at the Advanced Light Source J.Feng 1 , A.A.MacDowell 1 , R. Duarte 1 , A.Doran 1 , E.Forest 2 , N. Kelez 1 , M.Marcus 1 , D.Munson 1 , H.A.Padmore 1 , K.Petermann 1 , S. Raoux 3 , D. Robin 1 , A. Scholl 1 , R. Schlueter 1 , P.Schmid 1 ,J. Stöhr 4 , W.Wan 1 , D.H. Wei 5 and Y. Wu 6 1)Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA2)High Energy Accelerator Research Organization, 1-1 Oho, Tsukuba, Ibaraki 305-0810, Japan 3)IBM, Almaden Research Center, 650 Harry Road, San Jose, CA 95120 USA 4)Stanford Synchrotron Radiation Laboratory, P.O.Box 20450, Stanford, CA 94309, USA 5) SRRC, No.1 R &D Rd. VI, Hsinchu 300, Taiwan 6)Department of Physics, Duke University, Durham, NC 27708, USA K-B m irror X-ray Im mersion lens Electric dodecapole Field lens Apertures Electron tetrode m irror Diagnostic C C D detector Deflector Transferlens M agnetic Beam separator Sam ple Electric-m agnetic dodecapole Projectorlens Interm ediate lens Deflector Projectorlens Im aging CCD detector O bjective lens Transferoptics Projector/D etector Electron M irror Projector/D etector Fig.1 C onceptofa X-ray photoem ission electron m icroscope using electron m irrorcorrectoratthe ALS PEEM3 microscope consists of objective lens, electric-magnetic dodecapole, magnetic beam separator, electron mirror, transfer and projector lens. Variable beam sizes on sample from 3micron to 50 micron are carried out by a pair of bendable K-B mirror. Additionally, a UV-lamps and a laser system will be mounted to the sample chamber. The critical components of PEEM3 are the electron mirror aberration corrector and aberration-free magnetic beam separator. 5 axis sam ple supportheatable- coolable10 -10 torr Table1. Specification ofPEEM 3 separator Fig.2 M echanical 3D m odel ofPEEM 3 layout In-vacuum vibration isolated opticaltable CCD Magnetic coil CCD M irror Separatorcooling w aterfeedthrough Electron path 5900m m Y -374m m Y -362m m X 71m m X Spherical Aberration -306m m Y -84m m X Chromatic aberration 259.6G auss Field 20KeV Bending electron energy 72.39A,-144.78A, 72.39A Currentin coils 90 0 Totalbend angle 22.5 0 ,45 0 M irror reflection 0 D ispersion at 45 degree 3m m ,3m m ,3m m W idth of groove 7m m Size ofgap 28cm Size of m agnet Fig.3 PE E M 3 endstation on the A LS 11.0.1 section floor.PEE M 3 m icroscope w illbe installed to a softX-ray EPU beam line.A bendable K -B m irror w ill provide 3 to 50 m icron spotsize on sam ple. PEEM 3 m icroscope PEEM 3 VLS m onchrom ator Sam ple transfer PEEM 2 –PEEM 3 com parison PEEM 2 PEEM 3 O ptics Electrostatic lens Electrostatic lens Electrostatic m irror M agnetic separator D iagnostic lastim age m ovable pinhole, alignm entPEEM C orrector O ctopole Electrom agnetic dodacapole R esolution 20nm 5nm Transm ission 5% >90% @ 50nm Beam line Bending 7.3.1.1 EPU 11.0.2 Relative 1 >1000 Flux density Fig.4 Spherical and chrom atic aberration region covered by PEE M 3 electrode m irrorand the values required to correctthe aberrations ofthe objective lens fordifferentobjectpotentials and w orking distance. Fig.5.C om parison ofresolution versus transm ission ofPEEM 2 and PEEM 3.The acceleration potential is 20kV and the w orking distance is 2m m. In our model to determine the resolution of PEEM3, the secondary electron distribution is used. We create a statistical ensemble of electrons with initial energy and angle spread and track the electron beam distribution weighted with the probability anywhere in the system. The resolution is defined as 68% in intensity of the point spread function. The diffraction effect is calculated for each energy electron and summed up incoherently to yield diffraction Airy pattern. Operating at 20kV and 2mm working distance, the point resolution for 100% transmission reaches 50nm with the mirror corrector, a significant reduction from that of 440nm without correction. The best resolution can be achieved is 5nm at 2% transmission. An elliptically polarized undulator (EPU) at the straight sector 11 of the ALS will be used to produced in-plan linear, perpendicular linear, left and right handed circularly polarized radiation with continuous change of ellipticity. A variable line space (VLS) plane grating monochromator beamline will provide soft x-ray in the spectral range from 100eV to 1500eV. The beam separator is of so-called double mirror symmetry for each quadrant of the magnet to cancel all the second-order geometric aberrations. The imaging property of the beam separator is equivalent to that of a telescopic four round lens. The object side focal plane of the first lens is transferred with unit magnification into the image side focal plane of the fourth lens. The specification of the separator is given in table 1. PEEM3 Concept PEEM3 Layout PEEM3 Performance PEEM3 Endstation
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Transcript of Abstract A new ultrahigh-resolution photoemission electron microscope called PEEM3 is being...
Abstract A new ultrahigh-resolution photoemission electron microscope called PEEM3 is being developed at the Advanced Light Source. An electron mirror combined with a sophisticated magnetic beam separator is used to provide simultaneous correction of spherical and chromatic aberrations. PEEM3 electron mirror has four rotationally symmetric electrons and gives three free knobs to adjust the focal length, the chromatic and the spherical aberrations so that a wide aberration region can be covered for all the operation modes of objective lens. PEEM3 magnetic separator has double mirror symmetry configuration and images its entrance plane 1:1 in its exit plane. A further enormous advantage of the aberration correction is the increase of electron transmission. The goal of the PEEM3 project is to achieve the highest possible transmission of the system at resolutions comparable to our present PEEM2 system and to enable significantly higher resolution, albeit at the sacrifice of intensity. We have left open the possibility to add an energy filter at a later date, if it becomes necessary driven by scientific need to improve the resolution further. The instrument will be installed on an elliptically polarized undulator beamline and will be used for the study of complex materials at high spatial and spectral resolution.
Advanced Light Source
Experimental Systems Group
An Aberration Corrected Photoemission Electron Microscope at the Advanced Light
Source J.Feng1, A.A.MacDowell1, R. Duarte1, A.Doran1, E.Forest2, N. Kelez1, M.Marcus1, D.Munson1, H.A.Padmore1, K.Petermann1, S. Raoux3, D. Robin1, A. Scholl1, R. Schlueter1, P.Schmid1,J. Stöhr4, W.Wan1, D.H. Wei5 and Y. Wu6
1)Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA2)High Energy Accelerator Research Organization, 1-1 Oho, Tsukuba, Ibaraki 305-0810, Japan 3)IBM, Almaden Research Center, 650 Harry Road, San Jose, CA 95120 USA 4)Stanford Synchrotron Radiation Laboratory, P.O.Box 20450, Stanford, CA 94309, USA 5) SRRC, No.1 R &D Rd. VI, Hsinchu 300, Taiwan 6)Department of Physics, Duke University, Durham, NC 27708, USA
K-Bmirror
X-ray
Immersion lens
Electric dodecapole
Field lens
Apertures
Electron tetrode mirror
Diagnostic CCD detector
Deflector
Transfer lens
Magnetic Beam separator
Sample
Electric-magnetic dodecapole
Projector lens
Intermediate lens
Deflector
Projector lens Imaging CCD detector
Objective lens Transfer optics Projector / Detector
Electron Mirror
Projector/Detector
Fig.1 Concept of a X-ray photoemission electron microscope using electron mirror corrector at the ALS
PEEM3 microscope consists of objective lens, electric-magnetic dodecapole, magnetic beam separator, electron mirror, transfer and projector lens. Variable beam sizes on sample from 3micron to 50 micron are carried out by a pair of bendable K-B mirror. Additionally, a UV-lamps and a laser system will be mounted to the sample chamber. The critical components of PEEM3 are the electron mirror aberration corrector and aberration-free magnetic beam separator.
5 axis sample support heatable-coolable 10-10 torr
Table1. Specification of PEEM3 separator
Fig.2 Mechanical 3D model of PEEM3 layout
In-vacuum vibration isolated
optical table
CCD
Magnetic coil
CCD
Mirror
Separator cooling water feedthrough
Electron path
5900mmY
-374mmY
-362mmX
71mmXSpherical Aberration
-306mmY
-84mmXChromatic aberration
259.6GaussField
20KeVBending electron energy
72.39A, -144.78A, 72.39A
Current in coils
900Total bend angle
22.50, 450Mirror reflection
0Dispersion at 45 degree
3mm, 3mm, 3mmWidth of groove
7mmSize of gap
28cmSize of magnet
Fig.3 PEEM3 endstation on the ALS 11.0.1 section floor. PEEM3 microscope will be installed to a soft X-ray EPU beamline. A bendable K-B mirror will provide 3 to 50 micron spot size on sample.
PEEM3 microscope
PEEM3 VLS monchromator
Sample transfer
PEEM2 –PEEM3 comparison
PEEM2 PEEM3Optics Electrostatic lens Electrostatic lens
Electrostatic mirrorMagnetic separator
Diagnostic last image movable pinhole, alignment PEEM
Corrector Octopole Electromagneticdodacapole
Resolution 20nm 5nm
Transmission 5% >90%@50nm
Beamline Bending 7.3.1.1 EPU 11.0.2
Relative 1 >1000Flux density
Fig. 4 Spherical and chromatic aberration region covered by PEEM3 electrode mirror and the values required to correct the aberrations of the objective lens for different object potentials and working distance.
Fig.5. Comparison of resolution versus transmission of PEEM2 andPEEM3. The acceleration potential is 20kV and the working distance is 2mm.
In our model to determine the resolution of PEEM3, the secondary electron distribution is used. We create a statistical ensemble of electrons with initial energy and angle spread and track the electron beam distribution weighted with the probability anywhere in the system. The resolution is defined as 68% in intensity of the point spread function. The diffraction effect is calculated for each energy electron and summed up incoherently to yield diffraction Airy pattern. Operating at 20kV and 2mm working distance, the point resolution for 100% transmission reaches 50nm with the mirror corrector, a significant reduction from that of 440nm without correction. The best resolution can be achieved is 5nm at 2% transmission.
An elliptically polarized undulator (EPU) at the straight sector 11 of the ALS will be used to produced in-plan linear, perpendicular linear, left and right handed circularly polarized radiation with continuous change of ellipticity. A variable line space (VLS) plane grating monochromator beamline will provide soft x-ray in the spectral range from 100eV to 1500eV.
The beam separator is of so-called double mirror symmetry for each quadrant of the magnet to cancel all the second-order geometric aberrations. The imaging property of the beam separator is equivalent to that of a telescopic four round lens. The object side focal plane of the first lens is transferred with unit magnification into the image side focal plane of the fourth lens. The specification of the separator is given in table 1.
PEEM3 Concept PEEM3 Layout
PEEM3 PerformancePEEM3 Endstation
