UV-VIS AND RAMAN SPECTROSCOPY:

PRINCIPLE AND APPLICATIONS IN NANOTECHNOLOGY

PRESENTED BY:MANALI SOMANI (2015TTF2390)SNEHA NAWAGE (2015TTF2395)

ANUBHAV SHUKLA (2015TTF

PRESENTED TO:PROF. MANGALA JOSHI

▪ The study of molecular structure and dynamics through the absorption, emission and scattering of light

What is Spectroscopy?

Principle of Spectroscopy

• The principle is based on is the measurement of the spectrum of sample

containing atom/molecule

• Spectrum is a graph of intensity of absorbed or emitted radiation by

sample verses frequency or wavelength

• Spectrophotometer is an instrument design to measure the spectrum of a

compound.

RAMAN SPECTROSCOPY

Consider the collision between a photon and a molecule

ν0

νs

Raman Effect

▪ Scattering can be:– Elastic- Scattered photon have the same energy and

frequency as the incident photons; it is called as Rayleigh scattering

– Inelastic- A small fraction of light [approx. 1 in 107] is scattered at optical frequencies different than the frequency of incident photons. This process of scattering is termed the Raman effect

▪ Stokes Raman Scattering: Emitted photon is of lower frequency than incident photon

▪ Anti-stokes Raman Scattering: Emitted photon is of higher frequency than incident photon

Interaction between electric field of incident photon and molecule

▪ Light, with incident frequency ‘n0’, has an oscillating electric field (E) :

E = E0 cos (2pn0t)

▪ Induces molecular electric dipole (µ):

µ = E = E0 sin (2pn0t)

▪ Proportional to molecular polarizability ()

→Ease with which the electron cloud around a molecule can be distorted

▪ In molecular vibrations, the normal coordinate Q varies periodically with the vibrational frequency ‘nvib’

Q = Qo cos (2pnvibt)

where Qo is the magnitude of the given normal vibration

E

▪  = α αo +  (δα/δQ)0 Q = αo +  (δα/δQ)0 Qo cos (2pnvibt)

where (αo) is the equilibrium value of ( ), and α (δα/δQ)0 is the change in polarizability with external vibration.

▪ Resultant dipole

▪ Raman scattering occurs only when the molecule is ‘polarizable’

change in polarizability,

▪ Routine energy range: 200 - 4000 cm–1

Rayleigh scattering

µ = [α0E0 cos(2πνt)] + ½ (δα/δQ)0 E0[cos(2π(ν- νvib)t) - cos(2π(ν+ νvib)t)]

Raman scattering

Anti-Stokes Raman ScatteringStokes Raman Scattering

▪ Which modes will have a change in polarizability?

asymmetric stretch

Vibrational spectroscopy spectrum rules

symmetric stretch bend

• Gross selection rule in IR spectroscopy:vibration must lead to an oscillating dipole

4000 2000 0

Infrared spectrum of CO2

• Gross selection rule in Raman spectroscopy:vibration must lead to a change in polarizability

Vibrational spectroscopy spectrum rules

4000 2000 0

Only the symmetric stretch is observed. What happened to the other two vibrations?

Vibrational spectroscopy spectrum rules

Raman spectrum of CO2

Symmetric stretch

Q

ddQ> 0

Bend

Q

ddQ= 0

Asymmetric stretch

ddQ = 0

Q

Types of Raman Spectroscopy▪ Coherent Anti-Stokes Raman Spectroscopy (CARS)

▪ Resonance Raman (RR) Spectroscopy

▪ Surface-Enhanced Raman Spectroscopy (SERS)

▪ Surface-Enhanced Resonance Raman Spectroscopy (SERRS)

Information from Raman SpectroscopycharacteristicRaman frequencieschanges infrequency ofRaman peak

polarisation ofRaman peak

width of Ramanpeak

intensity ofRaman peak

composition ofmaterial

stress/strainstate

crystal symmetry andorientationquality ofcrystal

amount ofmaterial

e.g. Si 10 cm-1 shift per % strain

e.g. thickness oftransparent coating

e.g. MoS2, MoO3

e.g. orientation of CVDdiamond grains

e.g. amount of plasticdeformation

Identification of single atomic layers of graphene

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

Graphite

Graphene

Carbon NanotubeTypical Raman spectra for SWCNT

Raman spectra of the CNTs after different times of nitrogen plasma treatment

Comparison of Raman spectra of SWCNTs, DWCNTs, and MWCNTs

Effect of high-pressure on octahedra tilts: LaAlO3

P. Bouvier & J. Kreisel, J. Phys.: Condens. Matter (2002), Vol. 14, pp. 3981

‘Tilted’ perovskites (ABX3) 

Raman imaging in nano-technologyContacts on a Si wafer

Do the contacts induce strain ?

Raman (strain) image

Strain underneath & at corner of contacts

Potential effect on dopants …

Change in band position

Strain !

UV-VIS SPECTROSCOPY

Introduction

23

UV visible spectroscopy is also known as electronic spectroscopy in which, the amount

of light absorbed at each wavelength of UV and visible regions of electromagnetic

spectrum is measured.

This absorption of electromagnetic radiations by the molecules leads to molecular

excitations.

Principle of UV-VIS Spectrometry

Ultraviolet light and visible light cause an electronic Transition of electron from one filled orbital to another of higher Energy unfilled orbital.

These transition occur between the electronic energy levels. As molecule absorbs energy , an electron is promoted from occupied orbital to an unoccupied orbital of greater potential energy. Generally the most probable transition is from (HOMO) to (LUMO).

Continued… Ultraviolet absorption spectra arise from transition of

electron within a molecule from a lower level to a higher level.

A molecule absorb ultraviolet radiation of frequency (𝜗), the electron in that molecule undergo transition from lower to higher energy level.

The energy can be calculated by the equation, E=h 𝜗

25

E -E = h𝜗₁ ₒ

Etotal=Eelectronic+Evibrational+Erotational

The energies decreases in the following order:

Electronic >Vibrational > Rotational

Continued…

Types of Transitions

In U.V spectroscopy molecule undergo electronic transition involving σ, π and n electrons.

Four types of electronic transition are possible.

σ ⇾ σ* transition

n ⇾ σ* transition

n ⇾ π* transition

π ⇾ π* transition

Transition’s Characteristics

~ 400–700 nm

~ 150-250 nm

~ 200 – 400 nm

~ 115 nm

When a sample is exposed to light energy that matches the energy difference between a electronic transition within the molecule, the light energy would be absorbed by the molecule and the electrons would be promoted to the higher energy orbital.

A spectrometer records the degree of absorption by a sample at different wavelengths and the resulting plot of absorbance (A) versus wavelength (λ) is known as a spectrum.

The significant features: λmax (wavelength at which there is a maximum absorption) Emax (The intensity of maximum absorption)

The Absorption Spectrum

Continued…

UV-Vis Spectrum of Silver Nanoparticles

UV-visible spectrum of Silver Nanoparticles showing maximum absorption at 420 nm.

λmax

Emax

Lambert’s Law▪ When a monochromatic radiation is passed through a solution, the decrease in the intensity

of radiation with thickness of the solution is directly proportional to the intensity of the incident light.

▪ Let I be the intensity of incident radiation.x be the thickness of the solution.

Then IdxdI KI

dxdI

Lambert’s Law

Where, , A is AbsorbanceAII

0log

(ε is Absorption coefficient)A = ε ℓ

Beer’s Law• When a monochromatic radiation is passed through a solution, the decrease in the

intensity of radiation with thickness of the solution is directly proportional to the intensity of the incident light as well as concentration of the solution.

• Let I be the intensity of incident radiation.x be the thickness of the solution. C be the concentration of the solution.

Then

ICdxdI .

Beer’s Law

E is Molar extinction coefficient

0IIT

T is transmittanceA = ε C ℓ

Applications of UV-Vis spectroscopy

Detection of functional groups

Detection of extent of conjugation

Identification of an unknown compound

Determination of configurations of geometrical isomers

Determination of the purity of a substance

Stability of Nanoparticle

The optical properties of silver nanoparticles change when particle agglomerate

When nanoparticle aggregate, the plasmon resonance will be red-shifted to a longer wavelength

The peak will broaden or a secondary peak will form at longer wavelengths

Identification of Size & ShapeMagnitude, peak wavelength and

spectral bandwidth of the SPR of nanoparticles are dependent on particle size, shape and material composition

Different shape have characteristic peak in spectra like triangular shaped particles appear red, pentagon appear green, and blue particles are spherical.

Determination of Concentration

With increase in the concentration of silver nanoparticle the SPR peak show bathochromic shift ie. shift towards red.

Concentration of silver nanoparticle solutions can be calculated using the Beer-Lambert’s law as it correlates the optical density with concentration

In situ Nanoparticle Assesment

Use in determinate the changes that occur during the synthesis of the nano particle in the in situ process

Increase in no. of nano particle show Hypsochromic shift

References▪ Yoon D., Moon H. and Cheong H. Variations in the Raman Spectrum as a Function of the

Number of Graphene Layers. Journal of the Korean Physical Society (2009), Vol. 55 (3), pp. 1299-1303

▪ Ahmed Jamal G. R., Mominuzzaman S. M. Different Techniques for Chirality Assignment of Single Wall Carbon Nanotubes. Journal of Nanoscience and Nanoengineering (2015), Vol. 1 (2), pp. 74-83.

▪ Hooijdonk E. V., Bittencourt C., Snyders R.,Colomer J-F. Functionalization of vertically aligned carbon nanotubes. Beilstein J. Nanotechnol. (2013), Vol. 4, pp. 129–152.

▪ Bouvier P., Kreisel J. Pressure-induced phase transition in LaAlO3. J. Phys.: Condens. Matter (2002), Vol. 14, pp. 3981–3991

▪ Joshi M, Bhattacharyya A, Wazid A S, Characterization techniques for nanotechnology application in textile, Indian Journal of Fibre & Textile Research (2008), Vol. 33, pp. 304-317.

▪ Zook J M, Long S E, Cleveland D, Geronimo C A, MacCuspie R I, Measuring silver nanoparticle dissolution in complex biological and environmental matrices using UV–visible absorbance, Anal Bioanal Chem, (2011), Vol. 98, 1993-2002.

THANK YOU!