NTEGRA spectra:Cutting edge of molecular sciences

Raman spectroscopy at the nanometer scaleNTEGRA spectra key featuresApplications

The Nature’s treasures had been hidden for ages…

Discover it with NTEGRA spectra!

Presentation overview

Raman spectroscopy: some theory

What is Raman spectroscopy?

Micro-Raman advantages and limitations

Enhanced Raman scattering, TERS, and nanometer scale Raman spectroscopy

What is Raman scattering?

Ground state

Virtual state

Reyleighscatteringω=ωo

Raman scatteringω=ωo ± Ω

Frequencies of the incident and scattered photons are different due to the energy loss caused by molecular

vibration.

Excited vibration states

Raman spectroscopyRaman shift (KR, in cm-1) can be

calculated as

KR = 107(λlaser-1 – λRam

-1) (λlaser and λRam taken in nm)

Example of Raman spectrum (Si doted with Ge)

Raman spectrum is characteristic for the molecule

type. It means that all molecules of given type placed in given circumstances always have similar Raman spectrum.

Thus Raman spectroscopy is a tool for molecule identification.

Data measured by I.Dushkin ,NTMDT Staff.

Where is Raman spectroscopy among other methods?

As a tool for characterization of chemical composition Raman spectroscopy is very close to IR-spectroscopy. These

are complementary techniques. For example, symmetric stretch of CO2 molecule is not visible in IR-spectrum but it is

visible in Raman spectrum.

Comprehensive libraries of IR and Raman spectra had been collected for almost all known substances in most states and

different environments for many decades of 20th century.

Micro-Raman: Spectroscopy and imaging

Micro-Raman imaging

Tightly focused laser beam

Sample on glass

Raman photon to be detected

Step one: Raman spectrum collecting from the specimen placed on the inverted microscope platform. Then Raman line of interest should be selected.

Step two: point-by-point scanning of the specimen with simultaneous collecting previously selected

Raman photons. The system reconstructs a map of the chosen molecule type distribution on the

specimen.

Step three (optional): mapping another Raman line.

Raman imaging

Example of micro-Raman images. Ge dots on the surface of Si. Left image obtained at characteristic line of Ge (412 cm-1), the right one obtained at main Si line (520 cm-1). Note that dark areas on the right image correspond to bright areas on the left one (arrows), as the Si signal cannot reach from beneath the Ge particles.

Data measured by I.Dushkin ,NTMDT Staff.

Two main limitations of micro-Raman

1. Researcher is enforced to deal with very weak signals

2. Spatial resolution is limited by far-field optics diffraction (the best spot size is about 200nm)

Enhanced Raman scattering

TERS – Tip Enhanced Raman Scattering

SERS – Surface Enhanced Raman Scattering

TIR – Total Internal Reflection

Abbreviation glossary:

Electromagnetic field enhancement

(a) Calculated field distribution [|Elocal (r, ω)) |2] near a silver tip located above a glass

substrate and irradiated by an on-axis focused HG10 laser mode. The contour lines scale by

a factor of 2. (From Rendell, Scalapino(1981), Hartschuh et al. (2004))

Under some circumstances silver tip becomes a very bright light source and

the light intensity locally is much bigger than the incident one.

Theoretically in some cases field intensity can be enhanced by a factor

of 106!

Tip enhanced Raman set up

Tightly focused laser beam

Au or Ag coated glass

Sample

Au or Ag coated AFM tip

Zone of strong field enhancement

To the enhanced Raman signal detection system

Au or Ag coated tip placed 1-2 nm higher the sample surface (in semi-contact mode) provides strong Raman signal enhancement (today – by several orders of magnitude). Au or Ag glass coating serves for additional plasmon resonance enhancement. As the Raman signal from beneath the tip is much larger than neighboring far-field signals the whole system resolution is limited only by the zone of field enhancement which in turn depends on the tip shape and size. Point-by-point scanning gives full object image. Otherwise point localized spectroscopy is possible.

20 sec/point

Single molecule identification

Gain time of 0.2 sec/point is enough to detect single molecule of 5’-hexachlorofluorescein modified oligonucleotides (upper scan, white circle). To identificate it by point-localized spectroscopy a bit more time is required (bottom scan and spectrum, emission maximum at 556 nm, that is characteristic for HCF dye).

Data courtesy Dr. Kudryashov, TII, Tokyo, Japan

For more details on SERS see recent articles

Near-field Raman spectroscopy using a sharp metal tip. Journal of Microscopy, (2003), Vol. 210, pp. 234–240. Achim Hartschuh, N. Anderson, & LukasNovotny

Tip-enhanced optical spectroscopy (TEX Paper; Article submitted to RoyalSociety, 2004) Achim Hartschuh, Michael R. Beversluis, Alexandre Bouhelierand Lukas Novotny

High-Resolution Near-Field Raman Microscopy of Single-Walled CarbonNanotubes. PHYSICAL REVIEW LETTERS (2003) V.90, N.9. AchimHartschuh, Erik J. Sa´nchez, X. Sunney Xie, and Lukas Novotny

Near-field Raman scattering enhanced by a metallized tip. Chemical PhysicsLetters 335 (2001) 369-374. Norihiko Hayazawa et al.

Nanoscale chemical analysis by tip-enhanced Raman spectroscopy. Chemicalphysics letters 318 (2000) 131-136. Raoul M. Stockle et al.

Setup key features

NTEGRA spectra –

the instrument for scientific break-through

Spectrometer

Illumination system

Solutions for TERS

NTEGRA-Spectra optical scheme

AFM, SNOM, STM Head

SpectrometerSpectrometer of NTEGRA

spectra is a perfectly designed module providing spectra with

accuracy of 0.03 cm-1.

Very important feature is that most spectrometer parts are motorized thus available

for distant tuning and adjustment from the system

software.

Laser confocal and Raman scattering signals are obtained

by two independent registration ports. It provide

two images gained simultaneously.

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Si(3)

O2

N2

Si(4)

Si(1) Si(2)

Raman shift, cm-1

Intensity, a.u.

Raman spectrum of silicon wafer. Si(4) peak is clear detectable. The first and second orders of silicon Raman spectrum are in deep saturation.

Excitation laser wavelength 488 nm, power 5mW, Confocal mode, pinhole 100 μm. Accumulation 1 min;Data measured by K.Mochalov ,NTMDT Staff.

High sensitivity for RAMAN spectra detection

How to choose a laserAs a whole Raman signal intensity is very low. About 1 photon of 107 incident ones is scattered by Raman effect.

I ~ 1/λ4

Raman signal intensity depends inversely on forth power of incident light wavelength. Laser with shorter wavelength gives stronger Raman signal. On the other hand it can be destructive

for some samples e.g. biological ones. Far-red light sources give very weak signal but it is fluorescence free and can penetrate

much deeper into the sample.

Thus it may be very helpful to change the light source during the experiment.

Choose it by a button click!

Setup assembling. Two lasers

(crimson arrows) with their power modules (blue

arrows) are to be connected. Then

they will be available from the system software. Up to three lasers can be installed.

Basement symmetry is important for long-term stability

Universal NTEGRA basement is highly symmetric.

Another essential point is material the basement is made

of. It is titanium that is perfectly balanced with piezoceramic in terms of

thermal expansion.

All these design solutions have been developed to

enhance the system long-term work stability.

Objective lens is rigidly integrated into SPM

providing exclusively high mechanical rigidity and stable performance of the

system.

Inverted microscope

objective lens is integrated into

the SPM central base unit

Thus high quality in long-term experiments is

possible.

More solutions for TERS

High precision movement in Z direction (RMS≤5nm) makes it possible to perform TERS on filmsSpecial optical parts (TIR objectives, special polarizer

etc.) greatly increase the effectiveness of laser light conversion into surface plasmons thus increasing the TERS intensitySoftware tunable pinhole provides optimal choice

between resolution and sensitivityTransparent objects can be studied with inverted microscope

Global software makes different devices to be NTEGRA

Spectrometer adjustment and

tuning

Global software

Spectra obtaining and analysis

Laser choice and

adjustment

SPM adjustment and tuning

SPM imaging and/or tip positioning for TERS

Another component(s) of Probe NanoLaboratory

Applications:

Real experiments prove the performance

Quantum dots – perfect spatial resolution

Quantum dots are nanometer scale aggregates of atoms with unique optical properties. On the left image two CdSe quantum dots separated by 610nm are perfectly resolved on laser confocalimage (luminescence at 575nm, note perfect resolution on the line profile). Right scan represents AFM image of these quantum dots.

610nm

Data measured by I.Dushkin ,NTMDT Staff.

Cantilever tip enhancement of the Raman signalIn

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Raman shift, cm-1

Raman spectrum of SWNT (bulk

specimen)

Tip-on mode

1595

TERS spectra of a single nanotube

2697

Tip-out mode

Raman spectra of single-w a l l S i C n a n o t u b e s .

Upper one is the spectrum obtained form the high concentration specimen of the SWNTs (divided by 15 ) . Two co lou r - l i ne spectra are that obtained from a low-concentration SWNT specimen. Note great tip enhancement of t h e R a m a n s i g n a l .

λex= 488nm, Pex~200μW, tint=5sec.

Data measured by K.Mochalov ,NTMDT Staff.

TERS imaging and AFM – simultaneously!

AFM image

Raman signal map1

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1 2

40 nm 1.8 nm

Single NanoTube (CSi SWNT) image as obtained in AFM and by Raman signal mapping.

TERS imaging provide the line from SWNT as narrow as 40 nm.

AFM line profile shows the height of 1 . 8 n m . T h a t means it is really a single nanotube.

Data measured by K.Mochalov ,NTMDT Staff.

Single molecule spectroscopy

Single microtubules labeled with fluorescein can be visualized (left image, excitation 488 nm, arrow point the microtubule). Point localized fluorescence spectroscopy was performed to obtain the spectrum (right) that corresponds well with the fluorescein emission spectrum on the inlet (peak maximum at 520 nm).

Data courtesy Dr. Kudryashov, TII, Tokyo, Japan

30 x 30 x 10 um

Data courtesy Dr. Kudryashov, TII, Tokyo, Japan

3D confocal image of Si by RAMAN at 520 cm-1

500 nm

1593 cm-1

173 cm-1

RBM

G-band

3x5 µm Raman image at G-band peak 1593 cm-1, 100 ms/point Raman spectrum, 10 sec accumulation

Excitation : 488 nm, 0.5mW. Objective lens 100X, NA=0.95

2D Raman Image of Carbon 2D Raman Image of Carbon NanotubesNanotubes on Micaon Mica

Data courtesy Dr. Kudryashov, TII, Tokyo, Japan

AFM 5x5 um image

Single Wall Carbon Single Wall Carbon NanotubesNanotubes Raman and AFM Raman and AFM imagesimages

RBM173 cm-1

G-band1593 cm-1

D-band1351 cm-1

Amorphouscarbon

1593 cm-1

1351 cm-1

173 cm-1

RAMAN

IMAGES

RAMAN

SPECTRA

Data courtesy Dr. Kudryashov, TII, Tokyo, Japan

E-mail: spm@ntmdt.ru

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