Electron Emission Microscope Michael J. Eller February 12 th 2013
Concept primary ions Individual mass spectrum n. Individual mass spectrum 2 EEM lenses x n,y n.. x 2, y 2 x 1, y 1 Position sensitive detector Sample HV magnetic field Ions Secondary electrons start Individual mass spectrum 1 MCP stop ToF measurement X 1,Y 1 2 X 2,Y 2.. X n,y n
3 Design
Ø13.0 Ø6.0 Ø35.56 Ø50.0 Ø35.56 Ø6.0 Ø50.0 Detailed Design MCP/Phosphor Assembly L5 22.63 L2 L3 L4 Target J Secondary Ions 6 L1 31.13 Ø2.0 1.5 6.38 1.5 1.5 6.38 1.5 Ø7.0 5.0 5.0 4 All dimensions are in mm 6.0 Parameters of objective lens L1 Parameters of lenses L2.3.4.5
Electron Imaging Detector Fiber Optic Rods (10μm) Pair of MCPs (Photonis) Schneider Unifocal Lens 1:1 5 P43 Phosphor Screen (decay time ~100μs)
6 Camera Exposure Time
Electronic Scheme 7
Timing 8 Not to Scale
Mapping Impacts 9 50keV C 60 2+ -> 500 Line Per Inch Grid Coated by Cholesterol
Processed Image Image from 30keV C 60 +2 -> CsI 10
Spot Size Distribution 11
Center of Mass Image from 30keV C 60 +2 -> CsI 12
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Center of Mass Image from 30keV C 60 +2 -> CsI 14
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Resolution Define Effective Probing Area of Each Projectile Preform Line Scan 18
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Conclusions 1-2µm resolution achieved with EEM Co-localization of emitted ions Electron emission independent of number and type of SI emitted from homogeneous samples Mapping of any ion chosen is equivalent Electron emission specific to the class of sample investigated (Organic, Metal, Ionic Salt etc.) 22
Acknowledgments Texas A&M University: Dr. E. A. Schweikert Dr. Li-Jung Chen Aaron Clubb Dr. John Daniel DeBord Chao-Kai Liang Dr. Francisco Fernandez-Lima Dr. Veronica Pinnick Dr. Rajagopalachary Sidhartharaja Dr. Stanislav Verkhoturov Fan Yang IPN-Orsay Dr. Serge Della-Negra 23
Electron Emission
Electron Probability Distributions 26 S. V. Verkhoturov, M. J. Eller, R. D. Rickman, S. Della-Negra, E. A. Schweikert, Journal of Physical Chemistry C 2010, 114, 5637.
Measured Electron Yields Y exp np( n) n Y Analyte 15keVC + 60 30keV C +2 60 Glycine 3.2 3.9 Guanine 3.1 3.6 Si wafer 3.1 4.1 Al wafer 3.6 5.7 Au wafer 3.9 5.9 CsI on 400 mesh grid 5.6 7.8
Ion Selected Electron Distributions Is emission of electrons affected by type of emitted ion? 28
Ion Selected Electron Distributions Is emission of electrons affected by emission of multiple secondary ions? 29 S. V. Verkhoturov, M. J. Eller, R. D. Rickman, S. Della-Negra, E. A. Schweikert, Journal of Physical Chemistry C 2010, 114, 5637.
Flat Surfaces
Guanine Target Analyzed with C60 at 30keV 3 electron center of mass, 2 step collimation 200 and 25 pixels, all electron Radar Plot
Guanine Target Analyzed with C60 at 30keV Horizontal Line Scan of Radar Plot
Guanine Target Analyzed with C60 at 30keV Vertical Line Scan of Radar Plot
Electron Emission
35 Object Size Effect on Electron Emission
Comparison Projectile EEM Microprobe Microscope Species Analyzed Cs + NA 30nm 500nm Isotopes, small fragment ions (e.g. CN) Au + 3 NA 300nm NA Isotopes, small fragment ions, low yield molecular ions C + 60 1-2um 1um 4um Isotopes, small fragment ions, high yield molecular ions 36
500 mesh grid coated by cholesterol
3 electrons required to calculate a center of mass after 1 step collimation of at 200 pixels. Normalized to the number of center of masses calculated.
3 electrons required to calculate a center of mass after 2 step collimation at 200 and 100 pixels. Normalized to the number of center of masses calculated.
3 electrons required to calculate a center of mass after 2 step collimation at 200 and 50pixels. Normalized to the number of center of masses calculated. No binning.
3 electrons required to calculate a center of mass after 1 st collimation step at 200 pixels. Normalized to the number of center of masses calculated.
3 electrons required to calculate a center of mass after 2 nd collimation step at 25pixels. Normalized to the number of center of masses calculated.
3 electrons required to calculate a center of mass after combination of both collimations. Normalized to the number of center of masses calculated.
3 electrons required to calculate a center of mass after 2 step collimation at 200 and 25 pixels. Normalized to the number of center of masses calculated. No binning.