(Normal Raman, SERS, TERS,…)

(Normal Raman, SERS, TERS,…)
라만분광학의 원리와 응용 (Normal Raman, SERS, TERS,…) 유 현 웅 나노측정센터

Use of the Raman spectrometer in gemmological laboratories: Review
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy Volume 80, Issue 2.4 carat single crystal diamond produced by chemical vapor deposition Filled emerald Cleaned emerald Yufei Meng, 2012

목 차 1. Raman 분광학의 역사 2. 산란 (Scattering) 과정 3. Raman 신호특성 4. Raman 응용
목 차 1. Raman 분광학의 역사 2. 산란 (Scattering) 과정 3. Raman 신호특성 4. Raman 응용 5. Raman 분광학의 진보

A New Type of Secondary Radiation C. V. Raman and K. S
A New Type of Secondary Radiation C. V. Raman and K. S. Krishnan, Nature, 121 (3048), 501, March 31, 1928 If we assume that the X-ray scattering of the 'unmodified' type observed by Prof. Compton corresponds to the normal or average state of the atoms and molecules, while the 'modified' scattering of altered wave-length corresponds to their fluctuations from that state, it would follow that we should expect also in the case of ordinary light two types of scattering, one determined by the normal optical properties of the atoms or molecules, and another representing the effect of their fluctuations from their normal state. It accordingly becomes necessary to test whether this is actually the case. The experiments we have made have confirmed this anticipation, and shown that in every case in which light is scattered by the molecules in dust-free liquids or gases, the diffuse radiation of the ordinary kind, having the same wave-length as the incident beam, is accompanied by a modified scattered radiation of degraded frequency. The new type of light scattering discovered by us naturally requires very powerful illumination for its observation. In our experiments, a beam of sunlight was converged successively by a telescope objective of 18 cm. aperture and 230 cm focal length, and by a second lens was placed the scattering material, which is either a liquid (carefully purified by repeated distillation in vacuo) or its dust-free vapour. To detect the presence of a modified scattered radiation, the method of complementary light-filters was used. A blue-violet filter, when coupled with a yellow-green filter and placed in the incident light, completely extinguished the track of the light through the liquid or vapour. The reappearance of the track when the yellow filter is transferred to a place between it and the observer's eye is proof of the existence of a modified scattered radiation. Spectroscopic confirmation is also available. Some sixty different common liquids have been examined in this way, and every one of them showed the effect in greater or less degree. That the effect is a true scattering, and secondly by its polarisation, which is in many cases quire strong and comparable with the polarisation of the ordinary scattering. The investigation is naturally much more difficult in the case of gases and vapours, owing to the excessive feebleness of the effect. Nevertheless, when the vapour is of sufficient density, for example with ether or amylene, the modified scattering is readily demonstrable. Nature, 121(1928) 501/Nobel Prize 1930 K.S. Krishnan, A. Sommerfeld and C.V. Raman

C.V. Raman in his laboratory
Raman’s Spectrograph with Photographic Plate and 1st Spectra Published in Indian Journal of Physics

Raman History Historical Raman use 1928 Raman discovered by C.V. Raman
Raman developed considerable popularity during the 1930’s By 1939 Raman had become a principle analysis technique 1945 more sensitive IR detectors had been developed IR becomes relatively inexpensive and uncomplicated IR gradually eclipses Raman as the vibrational technique of choice Significant developments made a dramatic impact on Raman 1965 Laser recognized as ideal light source 1986 CCD arrays available for Raman use Recent developments Rapid development in solid state and diode lasers Rapid development in optical filters (Notch, Edge) Raman currently reemerging as the technique of choice in some areas New generation of highly automated Raman instruments appearing today Serving as very productive investigative tools 1928년도에 라만 현상이 발견 되었고 1930년도에 라만이 개발되고 중요한 분석 툴로 사용되었다. 그러다 1940년 중반에 같은 바이브레이션 테크닉인 아이알이 발전하면서 비교적 싸고 사용이 쉬운 아이알 주로 사용되고 이러면서 라만이 뒤처지게 되었다.

Blue sky sunset

Scattering In addition to being absorbed and emitted by atoms and molecules, photons may also be scattered (approx. 1 in 107 in a transparent medium). This is not due to defects or dust but a molecular effect which provides another way to study energy levels. This scattering may be: Elastic and leave the molecule in the same state (Rayleigh Scattering) or Inelastic and leave the molecule in a different quantum state (Raman Scattering) Harmonic oscillator: n = √(k/μ) k: force constant μ : reduced mass C C m1m2 = C H Rayleigh Scattering m1+m2 Lord Rayleigh calculated that a dipole scatterer ≪ l scatters with an intensity: no. of scatterers polarizability 5 times more effective for 400nm than 600nm Hence the sky is blue! (and sunsets red) wavelength distance scatterer - observer

Raman Scattering selection rules
Scattering is not an oscillating dipole phenomenon! The presence of an electric field E induces a polarization in an atom/ molecule given by polarizability If the field is oscillating (e.g., photon) In atoms the polarizability is isotropic, and the atom acts like an antenna and reradiates at the incident frequency – Rayleigh Scattering only In molecules the polarizability may be anisotropic, and depends on the rotational and vibrational coordinates. This can also give rise to Raman Scattering. Gross Selection Rule: To be Raman active a molecule must have anisotropic polarizability [Less restrictive than the need for a dipole moment, symmetric molecules can be Raman active]

Types of interaction between radiation and matter
1. Reflection & scattering 2. Refraction & dispersion 3. Absorption & transition 4. Luminescence & emission Emission or chemiluminescence Refraction Sample Sample Reflection Scattering and photoluminescence A B Absorption along radiation beam Transmission C Sample Types of interaction between radiation and matter.

Absorbance vs Transmittance
Absorbance =Log (P0/P) = -Log (Transmittance) cf. Emission ~Intensity (P) Transmittance = P/P0

Absorption & Emission (Fluorescence,Phosphorescence; PhotoLuminescence)
Energy level diagram

Instrumental key features for Raman Measurements in Applications
- High spectral resolution Especially important in strain measurements (shifts much smaller than 1 cm-1) - High spatial resolution Motorized XY stages, Z motors and piezo-elements are essential in preparing maps or depth profiles. Autofocus capability can also be required. - Possibility to use different wavelength excitations Photoluminescence (PL), Resonant Raman (RR) measurements or to avoid fluorescence - Confocality Along with the excitation wavelength allows to control the probed volume (depth profiles!) - Possibility of the use plasma line as reference Necessary in strain measurements

Conceptual Raman Spectrometer
Excitation Laser Line Filter Presentation/ Collection Optics Sample Rayleigh and Raman Scattered light Rayleigh Rejection Filter Mechanism for Frequency Differentiation Detector IRayleigh = 106 x IRaman o o-Evib o-Evib Raman 400 800 1200 1600 2000 Raman shift (cm-1) Blocking Filter Rayleigh Notch filter, Edge filter

What do we need to make a Raman measurement ?
Rejection filter (A way of removing the scattered light that is not shifted( changed in colour). Sampling optics (A way of focussing the laser onto the sample and then collecting the Raman scatter.) Monochromatic Light source typically a laser Spectrometer and detector (often a single grating spectrometer and CCD detector.) Detector Grating Filter Laser Sample

Excitation Frequency/ Rayleigh Scattering
Raman Spectra : Sample excitation yields an entire Raman vibrational spectrum Anti-Stokes Raman Scattering Virtual Energy States Stokes Raman Scattering Rayleigh Scattering Excitation Energy 4 3 Vibrational Energy States 2 1 IR Absorbance Excitation Frequency/ Rayleigh Scattering 라만 스탁 스캐터링은 0.001%가 발생되고 여기서 스탁 스캐터링 90%, 안티 스탁 스캐터링이 10%. cm-1 3500 3500 Frequency of Vibrational Transitions

Raman vs IR 근본적인 차이점 v。-v v。 v v Raman scattering(stokes) IR spectrum
큰 에너지를 주고 빛의 파장이 얼마나 길어졌는지 혹은 짧아 졌는지 측정한다. 진동 준위 에너지 차 v에 해당하는 에너지를 가진 빛이입사한 후 그 파장의 빛의 세기가 얼마나 약해졌는지 측정한다.

Raman Spectroscopy: Absorption, Scattering, and Fluorescence
2nd Electronic Excited State 1st Electronic Excited State Excitation Energy, σ (cm–1) Electronic Ground State IR σ Resonance Raman Δσ=σemit–σ

Raman spectroscopy – choice of the Laser Excitation
Excitation Energy, σ (cm–1)

Infrared and Raman Spectroscopy Comparison
Absorption Senses dipole vibrations O-H, N-H, C=O Sample preparation necessary, short optical pathlength required Limited fiber-optic potential Non-aqueous samples End groups dominant in spectra Raman Emission of scattered laser light Senses polarizable vibrations C=C, Aromatics Little or no sample preparation, measure through transparent packaging Considerable fiber-optic potential Aqueous samples Molecular backbone more prominent Detects fundamental vibrations of diatomic homonuclear molecules Readily subtractable spectra

Raman complimentary to FT-IR
Use of Raman and FT-IR for structure elucidation Example: Trans-cinnamyl acetate C=O vs C=C peak차이- dipole moment (m) vs polarizability (a) FT-IR m? m? C=H C=C C=O C-O C=C C=C a? a? C-O Raman C=H C=O

Sensitivity Differences
Compounds for which Raman offers increased sensitivity Weak IR Absorbers often strong Raman emitters Symmetric bonds represented more (S-S, C-C, etc.) Molecular backbone emphasized more End groups de-emphasized Spectral range offers more information on inorganics

Access to Low Frequency Vibrations
Access to low frequencies is routine with Raman Generally limited only by Rayleigh rejection mechanism Filters allow access to 100 cm-1 or lower Often can be tuned to 50 cm-1 Atmospheric water vapor not a concern 217.78 150.67 48.75 81.56 Sulfur spectrum collected with 532 nm laser 244.61 300 250 200 150 100 50 Raman shift (cm-1)

Drawbacks of Raman Raman spectroscopy still has some drawbacks More expensive than IR IR most cost effective for routine sampling Fluorescence Serious obstacle to collecting Raman with some samples Potential of laser damage Some samples very sensitive to laser energy

Fluorescence Avoidance
Spectral correction after collection Several specialized baseline correction algorithms exist Not viable in cases where fluorescence saturates detector Confocal optics Can work well when the source of fluorescence is the substrate rather than the sample Excitation laser change Most reliable means of avoiding fluorescence Switch to an excitation frequency that does not stimulate fluorescence in the sample Typically this means switching to longer (NIR) wavelengths

Role of Laser Wavelength (Fluorescence Avoidance)
In general spectrum is invariant with excitation IRaman proportional to 1/4 If there is an absorptive transition close to a ex, the spectra will be quite variable with laser - some features will be enhanced (resonance Raman), others might disappear NIR or UV wavelengths have been used to avoid background fluorescence interference. Spatial resolution ~  ex, as a result of physical diffraction Dispersive Raman, 532 nm laser Dispersive Raman, 785 nm laser FT-Raman, 1064 nm laser 500 1000 1500 2000 2500 3000 3500

Intensity of Raman Emissions
Raman emission is excitation wavelength dependent Stronger emissions with shorter excitation wavelengths Raman emission proportional to (1/λ)4 Intensity of Raman Emissions relative to 1064 nm excitation at 780 nm at 633 nm at 532 nm at 473 nm Actual measurements further attenuated by wavelength dependent collection efficiency Theoretical emission gains often not fully realized

Confocal Raman Microscope (공초점 현미경)
detector pinhole beamsplitter Laser Confocal Microscopy: - much smaller background - 3-D information - slightly higher resolution objective sample focal plane

Accuracy of Raman Intensity
Raman spectra of the same sample collected under different conditions can be quite different in appearance 500 1000 1500 2000 2500 3000 Raman shift (cm-1) 785 nm laser 633 nm laser

White Light Correction
Intensity differences can be corrected for White light correction is an intensity normalization procedure Utilize a white light black body standard to develop a wavelength dependent scaling factor that can be applied to correct intensity NIST also has several standards available with emission characterized at specific excitation frequencies. Important when comparing to common reference spectra 785 nm laser 3000 2500 2000 1500 1000 500 Raman shift (cm-1) 785 nm laser white light corrected 3000 2500 2000 1500 1000 500 Raman shift (cm-1)

White Light Correction
Comparison of white light corrected spectra 500 1000 1500 2000 2500 3000 Raman shift (cm-1) 785 nm laser white light corrected 633 nm laser white light corrected

cm-1 vs wavelength (파수波數와 파장波長 관계)
레이저광원파장에 따른 벤젠분자스펙트럼위치

1 THz = 33 cm-1 The unit of spectroscopists, the wavenumber (cm-1):
1. 레이저광원 lex = 1064 nm = 9399 cm-1 (1/1064 nm = 1/1064E-7 cm) Breathing mode of benzene 9399 – 992 = 8407 cm-1 (= nm) Stretching mode of benzene 9399 – 3063 = 6336 cm-1 (= nm) cf. 400 cm-1 = 25,000 nm = 25 mm cm-1 = 2,500 nm = 2.5 mm 2. 레이저광원 lex = 633 nm = cm-1 (1/633 nm = 1/633E-7 cm) Breathing mode of benzene – 992 = cm-1 (= 674 nm) Stretching mode of benzene – 3063 = cm-1 (= 850 nm) homework lex = 532 nm? Breathing mode of benzene 562 nm Stretching mode of benzene 678 nm

Spectrometer issues associated with different excitations
Shorter wavelength excitation requires higher dispersion spectrometers and produce higher levels of stray light in the system. 1 nm is equivalent to: nm excitation nm excitation nm excitation nm excitation 300 400 500 600 700 800 900 1000 1200

The applications of Raman continue to expand…...
Since Raman spectra are derived from molecular vibrations, the technique can be applied to organic, inorganic, solid, liquid and solution samples. The highly specific information contained in Analytical Raman Spectra include molecular identification - composition, crystalline phase, and orientation….. And so on and may be applied to : Polymers Electrochemicals Forensic studies Thin films Mineralogy Pigments Biology Carbon compounds Semi-conductors On-line processes Quality control Industrial analysis Pharmaceuticals

Information from Raman Spectroscopy
characteristic Raman frequencies composition of material e.g. MoS2, MoO3 changes in frequency of Raman peak stress/strain state e.g. Si 10 cm-1 shift per % strain polarisation of Raman peak crystal symmetry & orientation e.g. orientation of CVD diamond grains e.g. amount of plastic deformation width of Raman peak quality of crystal intensity of Raman peak amount of material e.g. thickness of transparent coating

Topography shift of Si Raman line
Hardness and Stress Measurements of Thin Si Films Vickers indent in Si compressive 10 nm 0 nm Topography shift of Si Raman line 521 /cm 519 /cm tensile indenting force: 50 mN 2,7 µm diagonal, 210 nm depth

Nano-Size effects in Si nanowires by K. W. Adu et al. , Nano Lett
Raman shift (cm-1) Identification and characterization of nano-size effects

Phase Change Materials/Memories (PCM’s), e.g. GeTe
E. Gourvest, J. Kreisel, M. Armand, S. Maitrejean, A. Roule, S. Lhostis,C. Vallée, Appl. Phys. Lett. 95, (2009) Reflectivity at 670 nm (%) Raman Probing phase transition (a),(b) Probing transition region (a) Temperature (OC) Intensity (arb. Units) Raman shift (cm-1) Raman shift (cm-1)

SERS (Surface enhanced Raman spectroscopy): photon-plasmon interaction
Porous nanostructure with a sub-10 nm nanogap “SERS probe” “Nanogap” (a few nm) SERS: Surface plasmon or CT SERS-active structures: geometry-controlled nanostructures High sensitive SERS-active sites: well-defined & reproducible hot SERS nanostructures Analyte is localized at a junction between the nanoparticles (`hot spot‘)

Highly ordered 1D, 2D, and 3D SERS substrates
nanodisk string 2D-array Nanohole film a) 1D metal nanoparticle string, b) 1D metal nanodisk array, c) 2D close-packed nanoparticle array, d) 2D metal nanostructures templated by colloidal crystals, e) nanopore array decorated with metal nanoparticles, f) nanohole array in metal film Small 2008, 4, No. 10, 1576

TERS (Tip enhanced Raman scattering)
AFM with 100x 0.7 NA objective in upright configuration – for non-transparent samples 1 μm height letters are readable – thanks to 100x objective Apex of opaque Si tip looks transparent on the image This unique observation is due to high aperture (0.7 NA) of the imaging objective

(c) (a) Tip-Enhancement & Raman Resolution (a) (b) (c) (b)
Far-Field Raman ( without optical matching) Topography Raman 영상 : G-Band Overlay 영상 (c) (a) (b) Near-field Raman ( with optical matching, TERS ) Raman 영상 :G-Band Topography Overlay 영상 분해능 : 95nm Optical matching:< 80 nm (a) (c) (b)

Si-Si is a covalent bond, molecular backbone Silicon structures
Emerging 2 … Characterization of Silicon Morphology Si-Si is a covalent bond, molecular backbone Silicon structures Crystalline – Uniform bond angles & energies Very limited number of states – leads to sharp, narrow bands Amorphous – Variable bond angles & energies A distribution of possible states – leads to broad, diffuse bands

Measuring Silicon Crystallinity
Raman spectroscopy is ideal for this application Si-Si bonds are symmetrical and are strong Raman scatterers Raman is very sensitive to small changes in these bonds Raman is excellent to distinguish between amorphous and crystalline silicon Different peak locations and peak shapes Crystalline Silicon Band Amorphous Silicon Band 400 420 440 460 480 500 520 540 cm-1

Applications for Raman in Carbon Nanotechnology

Carbon NanoTube ? Graphene R. Smalley S. Iijima C60 : Fullerene
탄소로만 이루어져 있는 물질은 여러 가지가 있다. 대표적으로 연필심에서 볼 수 있는 흑연과 다이아몬드가 바로 그것이며, 요즘 나노 기술에서 관심의 대상이 되고 있는 플러린과 탄소나노튜브, Graphene도 다 탄소로만 이뤄진 물질이다. 같은 피를 나눈 가족이라도 생김새와 성격이 다른 것처럼, 이들은 모두 가족이나, 전기적 성질과 원자구조가 다르다. 먼저 플러린은 탄소 원자 60개가 모여 축구공 모양을 한 물질로 R. Smalley 등이 최초로 합성하여 노벨상을 받았다. 그 다음으로 맨 위에 보이는 탄소 원자가 2차원 벌집 구조를 형성하고 있는 층을 Graphene이라고 하며, 플러린이나 다이아몬드와 달리 금속성을 띤다. 이 Graphene 여러 층이 반더발스 결합을 이루며 위 아래로 적층된 것이 바로 연필심을 구성하고 있는 흑연이다. 이것 역시 금속성이다. 중간의 탄소나노튜브는 Graphene이 튜브 모양으로 말린 것으로서 1991년 S. Iijima가 최초로 발견하여 보고 하였다. 이 녀석은 플러린과 흑연의 중간 정도의 특이한 전기적 성질을 가진다. 말린 모양에 따라 어떤 경우는 금속성 어떤 경우는 반도체 성질을 가진다. 이것이 이 녀석을 연구하는 사람들에게는 참으로 큰 매력임과 동시에 이것을 이용하고자 하는 사람들의 골치를 썩히는 어떤 면에서 참 고약한 성질이다. 그래도 요놈 골치는 썩히지만 참 재능이 많고 매력적인 녀석이다. R. Smalley S. Iijima C60 : Fullerene Carbon nanotube Graphite(흑연) 52

Forms of Carbon Diamond sp3 bonded carbon Graphite sp2 bonded carbon
Sheet of aromatic rings Fullerenes Hollow carbon spheres Diamond-like Carbon (DLC) coatings Amorphous Carbon Properties similar to Diamond Sometimes hydrogenated Different forms sometimes called polymorphs More accurately allotropes Graphite – 이차 전지 재료로 많이 사용. 플러린 – 탄소 원자 60개로 구성된 공 모양의 분자로 된 물질. DLC – diamond 성질을 가지고 coating 물질로 주로 쓰인다. Allotropes – 동소체, 같은 원자로 구성되어 있지만 배열이 다른 것. 다른 배열을 가진 탄소 물질들이 있다.

Carbon Nanomaterials Graphene Single layers from Graphite structure
Graphene nanoribbons (GNR) roll up to form nanotubes SW-CNT MW-CNT Carbon nanowalls Walled graphene structures Single walled carbon nanotubes – SW-CNT Multi-walled carbon nanotubes – MW-CNT

How does Raman fit in? Spectra are well characterized by Raman
Amorphous Graphite Diamond Single-wall carbon nanotube G Band D Band RBM G’(2D) Band Note that the multiwall CNT spectra look similar to amorphous CNT and have no RBM. RBM = Radial Breathing Modes. RBM bands indicate the presence of SW (single walled) CNT.

Graphene characterization J. Phys. Chem. C 2011, 115, 22369
Optical and micro raman image plot of graphene islands on Cu foil Nature, 2012 Lee before oxidation after oxidation SEM AFM

CNT in cells Video Raman averaged spectra scan range of 50 µm x 50 µm
100 x 80 pixels (=8000 spectra) 90 ms/spectra averaged spectra scan range of 50 µm x 50 µm 150 x 150 pixels (=22500 spectra) 100 ms/spectra

“Point and Shoot” : Paint Chip Analysis
Basecoat Pigment Clearcoat

“Point and Shoot” - Trace Explosive Residue Analysis
TNT Specimen TNT PETN C-4 PETN: pentaerythritol tetra nitrate RDX: hexahydro-1,3,5-trinitro-1,3,5-s-triazine

Art and Archaeology – Paint and Pigment Identification
Pigment Characterization Art conservation Restoration Establishing authenticity FT-Raman - Colored pigments difficult to measure Sample heating Dispersive Raman – Better suited for pigment measurements Sample heating less of a problem Lower lasers powers used Higher sensitivity Smaller particle characterization Archaeology : 고고학, Authenticity : 진짜 판별

결 론 1. a versatile technique for the study of various materials
결 론 1. a versatile technique for the study of various materials 2. versatile for characterization and fundamental research 3. complimentary to other techniques (diffraction etc.)

감사합니다 참고자료 1. Thermo-Nicolet handouts 2. Horiba handouts
3. 라만분광법(하마구찌 히로오) 4. 연세대 분석대학원(팽기정)

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