RAMAN AND INFRAREDSPECTROSCOPIES
–PHOTOLUMINESCENCE
Mael [email protected]
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