optical spectroscopy - lab practicals...5 . i. probing phonons by raman spectroscopy . raman active...
TRANSCRIPT
LAB PRACTICALS
Optical Spectroscopy User Summer School 2015
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ℎ𝜈𝜈𝑖𝑖𝑖𝑖 ≠ ℎ𝜈𝜈𝑜𝑜𝑜𝑜𝑜𝑜 PHOTOLUMINESCENCE RAMAN SCATTERING
ΔE ~ 1eV ΔE ~ (1-100)meV
LAB PRACTICALS – Optical spectroscopy of Al2O3
LAB PRACTICALS – Fiber-based setup
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Excitation laser
Sample
Objective
Dichroic beamsplitter
Band-pass filters
Laser line filter
Excitation fiber
Collection fiber
Spectrometer
Illuminator for visible inspection
LAB PRACTICALS – Optical spectroscopy of Al2O3
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I. Probing phonons by Raman spectroscopy
Two Al2O3 groups per unit cell
Phonon modes (1st order, Γ-point):
Γ = A2u + Eu + 2A1g + 5Eg + 2A2u + 4Eu + 3A2g + 2A1u
acoust. Raman IR silent
LAB PRACTICALS – Optical spectroscopy of Al2O3
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I. Probing phonons by Raman spectroscopy
Raman active modes: 7
2A1g + 5Eg = A1g + A1g + 5Eg
∥c ⊥c ⊥c
378 cm-1
Eg
418 cm-1 A1g
432 cm-1
Eg
451 cm-1
Eg
578 cm-1 Eg
751 cm-1 Eg
LAB PRACTICALS – Optical spectroscopy of Al2O3
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I. Probing phonons by Raman spectroscopy
Raman active modes: 7
2A1g + 5Eg = A1g + A1g + 5Eg
∥c ⊥c ⊥c
LAB PRACTICALS – Optical spectroscopy of Al2O3
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II. Excitation Spectroscopy: PL vs Raman spectroscopy
532nm excitation
PL Raman
LAB PRACTICALS – Optical spectroscopy of Al2O3
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II. Excitation Spectroscopy: PL vs Raman spectroscopy
Cr+
R1 (694nm)
R2 (693nm)
Ruby PL (and laser !!!)
R1 R2
gree
n
blue
Cr+ E4
E3 E2
E1
LAB PRACTICALS – Raman Scattering of Silicon
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400 600 800 1000 1200 1400
Inte
nsity
(arb
. uni
ts)
Frequency (cm-1)
Ist order peak
2nd order peak
Silicon
LAB PRACTICALS – Raman scattering on Graphene and Graphite
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Graphene: electronic bands dispersion Graphene: phonons dispersion
Two strongest Raman peaks: G peak: 1st order, E2g mode: q ≈ 0
2D peak: 2nd order: +q (-q), fully resonant
LAB PRACTICALS – Raman scattering on Graphene and Graphite
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Graphite
pristine SLG
defected SLG
Dependence of 2D peak on the number of graphene layers
L.M. Malard et al., Physics Reports 473, 51 (2009)
1580 cm-1 1650 cm-1
1360 cm-1
2700 cm-1
2450 cm-1
LAB PRACTICALS – Raman scattering on Graphene and Graphite
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Raman spectrum of graphene layers
LAB PRACTICALS – Raman scattering on Graphene and Graphite
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Double resonance 2D peak of graphene and BLG
LAB PRACTICALS – Raman scattering on Graphene and Graphite
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Band structure of graphite