sem-cl presentation at icom 2015 - budva montenegro
TRANSCRIPT
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Cathodoluminescence in electron microscopy:from phosphor evaluation to single particle analysis
Philippe F. Smet, Lisa I.D.J. Martin, Jeroen Wattez, Filip Strubbe, Jonas J. Joos, Jonas Botterman, Katleen Korthout, Sofie Abé, Heleen Sijbom, Dirk Poelman
http://LumiLab.UGent.behttp://tiny.cc/amazingCL
[email protected]@pfsmet
ICOM 2015 – Budva/Montenegro – September 1 2015
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‘Cold light’: generation of light in a non-thermal way
• Photoluminescence (PL)• Cathodoluminescence (CL)• Electroluminescence (EL)• Chemoluminescence• Bioluminescence• Radioluminescence (RL)• Triboluminescence• Sonoluminescence• Thermoluminescence (TL) (?)
CL: a brief introduction
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Focused electron beam(1 to 30 keV)
Heat
Light (CL)
White x-rays
Characteristic x-rays
Auger e-
Secondary e-
Backscattered e-
Transmitted e-Diffracted e-
Sample
CL: a brief introduction
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CL: a brief introduction
Cathode ray tube (CRT)Field emission display (FED/SED)
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CL
CL: a brief introduction
4µm
4µm
25keV
SrS
Casino
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CL: Spatial resolution
STEM-CL
Zagonel et al, Nano Letters 2011(11) 568-573Nanometer scale spectral imaging of quantum emitters in nanowires
Halfgeleiders?
20nm
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EDX detector
Electron detectors
Spectrograph
CCD
SEM chamber
Optical fiber
Setup - 1. Add light collection and analysis to SEM-EDX
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Data collection method51200 spectra
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Phosphor (nm)
FWHM (nm)
400 nm
445 nm
(K) (ns)
SrSi2O2N2:Eu2+ 541 74 ++ + 0.62 450 905
Ba3Si6O12N2:Eu2+ 524 75 + - 0.39 435 1270
ZnGa2S4:Eu2+ 542 50 + ++ 0.14 242 135
SrGa2S4:Eu2+ 534 49 ++ ++ 0.71 460 450
Case 1: ZnGa2S4:Eu
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Case 1: ZnGa2S4:Eu
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ZnGa2S4:Eu (1%)
EuGa2S4
Case 1: ZnGa2S4:Eu
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Saturated green emission, but...• Severe thermal quenching• Short lifetime• Low quantum efficiency (<20%)
Origin of green luminescence?
Case 1: ZnGa2S4:Eu
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EDX: chemical compositionat the microscopic scale
Zn in green, Eu in red
J.J. Joos et al, Optical Materials Express 3 (2013) 1338
Case 1: ZnGa2S4:Eu
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Zn in green, Eu in red
Formation of EuGa2S4 percipitates
J.J. Joos et al, Optical Materials Express 3 (2013) 1338
Case 1: ZnGa2S4:Eu
CL mapping EDX mappingOptical behaviour Chemical composition
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Case 2: Sr0.25Ba0.75Si2O2N2:Eu
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Case 2: Sr0.25Ba0.75Si2O2N2:Eu
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Case 2: Sr0.25Ba0.75Si2O2N2:Eu
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Case 2: Sr0.25Ba0.75Si2O2N2:Eu
PL, 10K
PL, 295K
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Case 2: Sr0.25Ba0.75Si2O2N2:Eu
3 2
1
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Case 2: Sr0.25Ba0.75Si2O2N2:Eu
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Temperaturestage
EDX detector
Electron detectors
Spectrograph
CCD
SEM chamber
Optical fiber
Setup - 2. Add a temperature stage
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Case 3: Thermal quenching in SrGa2S4:EuSr
Si2O
2N2:E
u2+
Ba3S
i 6O12
N2:E
u2+
ZnGa
2S4:E
u2+
SrGa
2S4:E
u2+
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5µm
Total CL intensity
Peak emission wavelength
l(nm)FWHM
nm
Case 3: Thermal quenching in Sr0.9Eu0.1Ga2S4
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2.5µm
Total CL intensity (-20°C)
CL (100°C)/CL (-20°C)
60%
100%
80%
EDX Eu-L signal
Total CL intensity (100°C)
Case 3: Thermal quenching in Sr0.9Eu0.1Ga2S4
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Recording CL maps at different temperaturesAligning all maps by appropriate shifting/skewing
5µm
Temperature (K)
Local variations in Eu concentrationaffect global thermal quenching
Case 3: Thermal quenching in Sr0.9Eu0.1Ga2S4
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Case 4: Lifetimes in SEM-CL
D. den Engelsen et al., Ultramicroscopy 2015 http://dx.doi.org/10.1016/j.ultramic.2015.05.009
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Temperaturestage
EDX detector
Electron detectors
Spectrograph
ICCD
SEM chamber
Optical fiber
Beam blanker
Pulse generator
Setup - 3. Add a fast beam blanker
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Eu-rich
Ca-rich
t-mapping
Case 4: Luminescence lifetime in (Ca,Eu)2SiS4
D. Poelman and P.F. Smet, Physica B 439 (2014) 35-40
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3 points are sufficient to calculate t - saves time!
Case 4: Luminescence lifetime in (Ca,Eu)2SiS4
D. Poelman and P.F. Smet, Physica B 439 (2014) 35-40
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Eu-rich
Ca-rich
t-mapping
Case 4: Luminescence lifetime in (Ca,Eu)2SiS4
D. Poelman and P.F. Smet, Physica B 439 (2014) 35-40
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Temperaturestage
EDX detector
Electron detectors
Spectrograph
ICCD
SEM chamber
Optical fiber
Setup - 4. Collecting optics. Let’s integrate?
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Case 5: Single particle analysis – SrS:Eu
K. Korthout et al. / Optical Materials 33 (2011) 1128–1130
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Case 5: Single particle analysis – SrS:Eu
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Case 5: Single particle analysis – SrS:Eu
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Case 5: Single particle analysis – SrS:Eu
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Case 5: Single particle analysis – Ray tracing simulation
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Case 5: Single particle analysis - Ray tracing simulation
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Case 5: Single particle analysis - Ray tracing simulation
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Case 5: Single particle analysis
620nm
622nm
624nm
CL intensity
Emission barycenter
Reabsorption playsa role!
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Application notes
Type of materials• Impurity doped phosphors: + to ++• Quantum dots: -• Organic compounds: --
Spatial resolution• Depends on sample morphology• Thickness and composition• Accelerating voltage
Collection optics: integrating setup or fiber?• CL emission intensity• Need for BSE/EDX• Topic of interest
K2SiF6:Mn4+
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Case 6: Hybrid conversion layers (phosphor + quantum dots)
CdSe/CdS core-shell quantum dots
SrGa2S4:Eu phosphorOrganic binder
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Conclusions
• ‘Standard’ photoluminescence research at microscale
• Discriminates between bulk and local behaviour
• Interesting add-on in phosphor research
• Standalone for single-particle analysis
CL in electron microscopy
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Acknowledgments
Thank you for your attention!
http://LumiLab.UGent.behttp://tiny.cc/amazingCL
[email protected]@pfsmet