optical spectroscopy - lab practicals...5 . i. probing phonons by raman spectroscopy . raman active...

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