RAMAN AND INFRAREDSPECTROSCOPIES

–PHOTOLUMINESCENCE

Mael Guennoumael.guennou@list.lu

Materials Characterisation Day – 14/10/2016

M. Guennou – 14/10/16

GENERALITIES

Vibrational spectroscopy

Vibration frequencies are a unique fingerprint

for a given material, at given external conditions

A probe for…

… identifying materials (solids, liquids, gas)

… types of bonding (C-C � C=C) and their environment

… structural phase transitions

… investigating strain effects (thin films, nano-structures etc.)

… investigating coupling phenomena (spin-phonon, electron-phonon etc.)

etc.

https://commons.wikimedia.org/wiki/File:Thermally_Agitated_Molecule.gif – by GregL – CC-BY-SA

M. Guennou – 14/10/16

GENERALITIES

0 Frequency/energy (cm-1)

Abs

orba

nce

Anti-StokesStokes

Rayleigh

0 Frequency/energy (cm-1)

Inte

nsity

(ar

b. U

nits

)

Raman scattering vs. IR absorption process

M. Guennou – 14/10/16

GENERALITIES

A vibration that modulatesthe dipole moment (or polarization) is IR active.

A vibration that modulatesthe polarizability is Raman active.

Example: CO2 molecule

IR inactive IR active

Raman active Raman inactive

A given mode may be• Raman and IR active• Raman active only• IR active only• « Silent »

Raman and infrared activities of vibration modes

M. Guennou – 14/10/16

Bruker Vertex 70 FT-IR spectrometer + Hyperion 2000

INFRARED SPECTROSCOPY

Specifications:

Spectral range: 8000 to 350 cm-1

Standard resolution: 0.4 cm-1

Rapid scan: 15 spectra/s @8 cm-1 spectral resolution

2 detectors: DTGS detector

Liquid N2 cooled MCT detector

Samples: films, bulk, liquids

High resolution FT-IR Spectrometerwith a microscope system

Contact @LIST:Jérôme Bour

M. Guennou – 14/10/16

Reflection mode• 80° reflection• 13°-83° variable angle

Vertex 70 measurement modes

INFRARED SPECTROSCOPY

Attenuated Total Reflection (ATR) with Ge and Diamond crystals

Transmission mode

M. Guennou – 14/10/16

HYPERION 2000 microscope

INFRARED SPECTROSCOPY

Fully automated microscope for IR mapping and video viewing with integrated high resolution color LCD

Specifications:

Spectral range: 7000 to 600 cm-1

Adjustement accuracy: 50 x 75 mm2 manual and motorized stage accuracy better than ± 1 µm

Standard detector: Liquid N2 cooled MCT detector

Measurement modes: ATR-objective (Ge-crystal 30x30 µm), measurement area down to 5x5 µm,

Reflection mode with grazing angle objective

Transmission mode (spatial resolution ~ 100 µm)

M. Guennou – 14/10/16

Diene functionalisation of VTMOS-MA copolymer films

INFRARED SPECTROSCOPY

Process:• VTMOS-MA copolymer deposited on Al foils• Reaction with 5-MFA (gas or wet chemistry reaction)• Annealing

A. Manakhov, M. Moreno-Couranjou, P. Choquet, N. Boscher, J.-J. Pireaux, Surface & Coatings Technology 205 (2011) S466–S469

FTIR (ATR mode with Ge crystal) used to follow the process and compare efficiencies by tracking of:• C=O in cyclic anhydride at 1770 and 1850 cm-1

• C=O in carboxylic group at 1715 cm-1

• C=O in amide at 1660 cm-1

• C=O in imide at 1716 cm-1

• N-H stretching at 1560 cm-1

M. Guennou – 14/10/16

Photocatalytic activity of TiO 2 thin film

INFRARED SPECTROSCOPY

Process:TiO2 film deposited on Si substrate atatmospheric pressure

Monitoring of the photocatalytic activity by• Deposition of stearic acid on the film• Illumination under UV light (254 nm)• Measurement of characteristic peak

area

FTIR used in the transmission mode (transparent substrate)

2800 2850 2900 2950 3000

CH2 and CH

3 bands from stearic acid

Inte

nsity

(ar

b. u

nits

)

Wavenumber (cm-1)

As-deposited t = 0 min t = 66 min t = 122 min t = 200 min t = 334 min t = 1148 min t = 1385 min t = 1600 min

0 200 400 600 800 1000 1200 1400 1600 18000,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

Pea

k ar

ea (

cm-1)

Time (min)

τ = 185 min

S. Olivier, R. Maurau, N. Boscher, P. Choquet, J. Dutroncy, T. Sindzingre, T. Belmonte, OptiClean Project, 2012

M. Guennou – 14/10/16

Micro-Raman spectrometer

RAMAN SPECTROSCOPY

M. Guennou – 14/10/16

Specifications:• 5 excitation wavelengths: 325, 442, 532, 633, 785 nm• Spectral range:10/150 to 4000 cm-1• Resolution: 0.8 cm-1• Motorized XYZ stage, repeatability 100 nm• Confocal microscope, diffraction limited spatial resolution• « Streamline » mode for quick mapping

Environments:• Temperature: -196 ºC to 1500 ºC (soon He temperatures)• Electric field• Uniaxial strain• Coupling with an AFM (Bruker innova)

Practical considerations:• Virtually no sample preparation• Good Raman signature: transparent materials (oxides,

fluorides, diamond, SiC etc.)• Not so good Raman signature: disorder (chemical, structural,

…), metallic character, absorption/reflectivity in the visible range, bad crystalline quality…

RAMAN SPECTROSCOPYRenishaw inVia Raman spectrometer

M. Guennou – 14/10/16

Semiconductor-to-metal transition in VO 2

RAMAN SPECTROSCOPY

• Massive and abrupt drop in electrical resistance up to 4 orders of magnitude.

• Reflects Infrared radiation in the NIR (1800-2300 nm)

• Abrupt drop in thermal emissivity

S. Kumar et al., Phys. Status Solidi A 212, 1582 (2015)

Raman spectra @532 nm

M. Guennou – 14/10/16

Investigation of multilayer with multiple wavelengths

RAMAN SPECTROSCOPY

Thicknesses:55 nm35 nm20 nm40 nm

J. Kreisel, M. Weber, N. Dix, F. Sánchez, P. Thomas and J. Fontcuberta, Adv. Funct. Mater. 22, 5044 (2012)

Importance of the wavelength comes from:• different absorption at different wavelength• interaction with other excitations (electronic…)

Such interactions can be• desirable: signal enhancement by resonant Raman scattering• a plague: unwanted fluorescence etc.

Raman spectra of the different layersrevealed at different wavelengths.

M. Guennou – 14/10/16

Investigation of multilayer with multiple wavelengths

RAMAN SPECTROSCOPY

Analysis of strain/stress states of individual layers or components.

Rule of thumb:• Shift to the higher frequencies = compressive stress• Shift to the lower frequencies = tensile stress

• CeO2: compressive strain state ~ 0.5 GPa• BaTiO3: compressive strain state ~ 2.5 GPa• LaNiO3: mode degeneracy lifted due to in

plane stress.

J. Kreisel, M. Weber , N. Dix , F. Sánchez , P. Thomas and J. Fontcuberta, Adv. Funct. Mater. 22, 5044 (2012)

Thicknesses:55 nm35 nm20 nm40 nm

M. Guennou – 14/10/16

Nano-objects

RAMAN SPECTROSCOPY

Substrate: 0.5 mm

Thin film on a substrate0.4 nm < t < 100 nm and more

Is there a limiting thickness or size?

No general answer! It depens on:� Excitation wavelength� Sample absorption� Enhancement mechanisms

Nanoparticles in a matrix

• Very small sample volume → very low Raman intensity

• Very large substrate/matrix volume → very strong background signal

M. Guennou – 14/10/16

Nano-objects

RAMAN SPECTROSCOPY

A. C. Ferrari, et al., Phys. Rev. Lett. 97, 187401 (2006);

Graphene

Graphite

Graphene and carbon-based nano-objects

M. Guennou – 14/10/16

PHOTOLUMINESCENCE

Virtual level

Conduction band

Infrared

(absorption)

Raman

(scattering)

Photoluminescence

(emission)

Vibrational level

Defect level

M. Guennou – 14/10/16

Specifications:• Excitation wavelengths: 325, 442, (532, 633, 785) nm• Spectral range: 340-1200 nm• Motorized XYZ stage, repeatability 100 nm• Confocal microscope, diffraction limited spatial

resolution• « Streamline » mode for quick mapping

Environments:• Temperature: -196°C to 1500°C• Electric field

PHOTOLUMINESCENCERenishaw inVia spectrometer

M. Guennou – 14/10/16

PL vs. Raman signals

PHOTOLUMINESCENCE

Energy (eV)

Inte

nsi

ty(a

rb.

un

its)

Photoluminescence

Band-to-band

785 nm excitation 633 nm excitation 532 nm excitation

Raman peak Raman shift (cm-1)

GaAs single crystal

M. Guennou – 14/10/16

ZnO thin films

PHOTOLUMINESCENCE

Films of 100-150 nm deposited by Atomic layer deposition (ALD)

Energy (eV)

Nor

mal

ized

inte

nsity Shift of the intrinsic

photoluminescence peak

regarding the time of purge.

D. Spirito, PhD Thesis, LIST.

M. Guennou – 14/10/16

THE TEAM

Thank you for your attention

B. El AdibRaman spectroscopy

J. BourFT-IR spectroscopy

P. GrysanRaman spectroscopy

M. GuennouRaman / PL