Lasers – Raman spectrometry Vítězslav Otruba 2010prof. Otruba1 2010prof. Otruba2 2010prof. Otruba3 IR absorption Raman scattering Principles of the Raman effect 2010prof. Otruba4 SCATTERING of RADIATION the scattered photon has a different energy than the incident photon radiant two-photon transition between two stationary states of molecules whose vibration energies are E1 a E2, caused by interaction with the photon of incident radiation with frequency ν0 >( E2 - E1) / h, accompanied by radiation of scattered photon with energy hνR= hν0 ± ( E2 - E1 ), where hνvib = E2 - E1 The scattered photons carry information about the energetic spectrum of the scattering center as well as the spatial orientation of a particular chemical bond, (it is like molecular "business card"). However, without special measures, only a single photon of hundreds of millions to hundreds of billions of incident photons is scattered in this way.The Raman scattering cross-section is about 10 −30 cm2. Light scattering occurs in all directions around the scattering particle. 2010prof. Otruba5 Rayleigh (molecular) scattering 2010prof. Otruba6 Lord John Rayleigh rightly found that the intensity of the scattered radiation was directly proportional to the fourth power of the radiation frequency, or inversely proportional to the same power of its wavelength; light scattering occurs in all directions around the scattering particle and is even of three kinds: scalar scattering in which the intensity is uniform in all directions, scattering symmetrical and antisymmetric, the intensity of which varies in different directions, as well as the polarization of scattered radiation. At the same time, if a monochromatic light falls on a particle of frequency ν0, then the diffuse radiation has the same frequency ν0 ', but its intensity is much lower than the intensity of the incident radiation; in this case we say that the spectrum of scattered radiation consists of a single spectral line. All the experiments of Rayleigh's contemporaries confirmed this theory. Neither he nor any of his contemporaries could, however, suspect that there were at least ten types of light scattering, or that the blue sky was not caused by light scattering on individual molecules but by so-called atmospheric density fluctuations, ie random random clusters of molecules contained in an atmosphere that lasts an extremely short time, that is, only for the duration of the collision of at least three such molecules. 2010prof. Otruba7 Principle of Raman spectrometry 1 2010prof. Otruba8  The Raman scattering is based on the radiant two-photon transition between two stationary vibrational states of a molecule whose energies are E1 and E2, induced by interaction with the photon of incident radiation at the frequency  ν0> | E2-E1 | / h,  where h is Planck's constant, and is accompanied by the photon emission of scattered radiation at the frequency νR.This scattering effect can be simply imagined as the simultaneous absorption of the exciting photon by a molecule as the molecule moves to a virtual energy level and the emission of a secondary photon, subject to the condition of energy conservation: hνR = hν0 ± (E2 - E1) (1)  There are several possibilities of such a transition according to the position of the virtual energy level in relation to the actual states of the molecule (eg normal and resonant Raman effect). Principle of Raman spectrometry 2 2010prof. Otruba9 In the classical approximation, for a molecule interacting with radiation, the dipole moment p is induced in the molecule : where ν0 is the frequency of excitation radiation, νvib is the vibration frequency, E is the vector of the electric field intensity of the incident radiation, q are the internal coordinates of the molecule and α is the polarizability of the molecule (polarisability is the degree of "difficulty" with which a negative charge is deflected by electric field).The equation shows that the molecule emits radiation at an unchanged frequency( ν0 - Rayleigh scattering ) and radiation with frequencies( ν0 + νvib ) a ( ν0 – νvib ), which are collectively called Raman scattering, with the lower frequency ( ν0 – νvib) corresponding to Stokes scattering, while the higher frequency ( ν0 + νvib) belongs to anti-Stokes scattering. From the equation it is also evident that for the formation of the Raman lines is necessary that the vibratory motion cause change in polarizability, namely that: Non-resonance Raman spectra 2010prof. Otruba10 The magnitude of the frequency shift ωv does not depend on the frequency of the incident radiation.The probability of the Raman effect increases with the fourth power of the incident radiation frequency and is three orders of magnitude less than the Rayleigh scattering Raman spectrum 2010prof. Otruba11 Raman spectrum of substances present in the atmosphere 2010prof. Otruba12 Spectrum of Raman Lidar Raman resonance spectra 2010prof. Otruba13 Resonance Raman scattering occurs when the frequency of radiation incident on the scattering particle matches or approaches the frequency of the particle's quantum transition. Compared to the radiation intensity of non-resonant Raman scattering, the intensity can be increased by 3 to 6 orders. Resonance Raman scattering 2010prof. Otruba14  virtual level near the electron excited state  UV resonance Raman spectroscopy - nucleic acids, proteins  Visible range - coordination compounds, organic dyes, hemoproteins  NIR - "pre-resonance"? - low energy electron transitions  Excitation profiles - dependence of Raman spectra (selected bands) on excitation wavelength Raman resonance spectrometry 2010prof. Otruba15  Enhancement factor102–104  Practical aspects  For solutions - the question of choice of concentration and position of the excitation beam  Self-absorption  Fluorescence  Choice of beam geometry, focus  Concentration profile Instrumentation for Raman spectrometry 2010prof. Otruba16 Solid, respectively liquid sample is placed in front of the slot of the spectrometer.The sample is irradiated with a focused laser beam with an output power greater than 100mW, usually of an ion Ar (λ = 514.5 nm - green and 488 nm - blue) or a He-Ne laser (λ = 632.8 nm).The Nd:YAG laser with frequency multiplier and laser diodes is often used recently. The monochromator must have very low diffuse radiation (usually double).The detector is usually a photomultiplier, respectively. intensified CCD detector. Diagram dispersive Raman instruments 2010prof. Otruba17 2010prof. Otruba18 Technological advances in Raman spectroscopy in the past 20 years 1. FT Raman spectrometry + excitation in the NIR region - solves the problem with fluorescence + high accuracy of wavenumbers - lower scattering intensity - more difficult to detect Raman shift 2. Multichannel CCD detectors Raman shift + Significant improvement in signal to noise ratio (SNR) + Significant reduction in measurement time single channel multi channel (in both cases excitation 2010prof. Otruba19 3. Fiber optics (integrated probes) + use for process monitoring and control + significant increase of application potential + "remote" spectrometer integrated fiber probe containing the necessary filters (BP, BR) and focusing optics sample spectrometer laser 4. Holographic filters + significant reduction in spectrometer dimensions and cost + more radiation on the detector - an individual filter is required for each excitation wavelength Scheme compact Raman spectrometer detector wavelength analyzer collection optics computer sample laser radiation suppression filter 2010prof. Otruba20 Dispersion and non-dispersive spectrometers Dispersion multichannel Raman spectrometer Non-dispersive FT Raman spectrometer Raman spectrum Raman spectrum multichannel detector blue red sample sample Advantages Disadvantages sensitivity higher signal to noise ratio exc 200-800 nm (limited by CCD detector response) a compromise between resolution and range more fluorescence changing spectral resolution high frequency determination accuracy higher aperture always exc greater than 1064 nm usually without fluorescence worse signal to noise ratio often high excitation power of the laser 2010prof. Otruba21 Lasers for Raman spectroscopy dispersive Raman spectrometers (limited by silicon CCD detectors) non-dispersive FT Raman spectrometers Continuous (CW) lasers typical power second harmonic Ar+ air cooled water cooled second harmonic dye,Ti: sapphire continuously tunable 2010prof. Otruba22 Filtration of the excitation light Why? for suppressing unwanted spontaneous emission (eg. plasma lines in ion lasers, wide background from Nd:YAG and diode lasers) How? • interference filters • pre-monochromator like filter from laser flat mirror diffraction grating exit aperture Grating premonochromator for filtering plasma lines from the collimated beam from laser glass cube holographic grating exit aperture high pass holographic bandpass filter, up to 80% (Kaiser Optical System) 2010prof. Otruba23 A very effective suppression of the plasma lines of the ion laser 2010prof. Otruba24 Double monochromator Advantages: high resolution excellent background separation measurements near the excitation line Disadvantages: slow measurement (step by step) too large dispersion for multi-channel detection Double monochromator scheme (eg. Spex 1403) 70s to 80s 2010prof. Otruba25 Triple spectrometer 2010prof. Otruba26 from sample Triple spectrometer pre-monochromator (filter) spectrograph multichannel detector A diagram illustrating the operation of a triple spectrograph Advantages: excellent background separation 10-12 - 10-14 measurements near the excitation line versatility Disadvantages: low aperture (low light on detector) high price 2010prof. Otruba27 Holographic notch filters throughput relative to 514.5 nm relative to 514.5 nm opticaldensity angle to the normal bandwidth bandwidth bandwidth bandwidth edge width edge width edge width edge width Holographic Notch Filter (HNF) and Holographic Super Notch Filter (HSNF)Throughput Dependence of optical density HNF on the angle of rotation of the filter Angular Tuning of HNF Filter (Calcite Spectrum) 2010prof. Otruba28 Non-dispersive spectrometers FT Raman - a multiplex technique where many wavelengths are generated by an interferometer and which generates an interferogram recorded by one detector Figure of FT Raman spectrometer based on Michelson interferometer modulation - linear motion of the mirror, which generates the path difference a-b = 2x Interferogram (A) for cyclohexane excited at 1064 nm and Raman spectrum (C) resolution maximum mirror path 2010prof. Otruba29 propagation of light in optical fiber general scheme for the use of optical fibers fiber probe arrangement (n around 1) Two methods of connecting optical fibers to the spectrometer: A) direct connection without possibility of f spectrometer adaptation B) a conventional method allowing even placing the BR filter in a collimated beam Fiber probes 2010prof. Otruba30 High aperture holographic imaging spectrograph focal plane entrance aperture holographic transmission grating (fixed, replaceable) slit holographic notch filter Scheme of transmission holographic spectrograph (e.g. Kaiser 1.8i) Advantages large aperture (transition from f / 4 to f / 1.4 represents almost an order increase of signal on detector (4 / 1.4) 2 = 8.2) compactness (small size) high dispersion Disadvantage different gratings for different excitation wavelengths Nonlinear methods - SRS and ASRS 2010prof. Otruba31 SRS (Stimulated Raman Scattering) is a variant of the dual resonance (a) method in which the laser (frequency ωL) level 2 is virtual. If ωV is the frequency of the vibration transition, then ωL - ωV = ωS. If we insert an auxiliary beam into the cuvette with the frequency ωS, ie with the Stokes frequency of the Raman spectrum, the amplification at this frequency occurs. In the case of ASRS (Antistokes SRS) two virtual levels 2 and 4 are excited and ωL + ωV = ωAS. The methods are used to measure high resolution up to 0.01 cm-1. Tunable infrared (Raman) lasers are based also on this principle. Diagram of energy levels and transitions for a) stimulated Raman scattering, b) anti-Stokes stimulated Raman scattering Inverse Raman spectrometry (a) Using a laser dye to generate a continuum (b) Using a white light continuum produced by slffocusing of picosecond laser pulses in water (c) Illustratinon of the spectrum 2010prof. Otruba32 Raman spectroscopy 2010prof. Otruba33  Each line of the Raman spectrum is dependent on its properties:  on the number and mass of co-vibrating atoms of a molecule  on their spatial arrangement  on a molecular internal force field  Obviously, Raman spectra can be used analytically, especially in solving some differences in constitutions which are difficult to prove chemically Prof. Dr.Arnošt Okáč:Výklad k základním operacím v chemické analyse, JČMF 1948 Experimental advantages 2010prof. Otruba34  possibility of measurement in aqueous environment ➥ low intensity of Raman scattering for water ➥ the optical materials used are not sensitive to moisture  possibility of measurement in glass containers ➥ measurement in closed ampoules – e.g. under vacuum  easy to use glass fiber optics  minimum treatment requirements for solid samples  intense bands -C=C-, -N=N-, -S-S and other symmetric vibrations Application of Raman s. in geology 2010prof. Otruba35  phase identification and analysis: in some cases, RS is the simplest or even the only one method available to identify a mineral, especially when encased in another transparent, non-fluorescent mineral. It makes it easier to distinguish members of isomorphic series more easily than X-ray diffraction.  to identify gases in gas - liquid enclosures  study of structure (especially bond of OH groups), structure order  Phase transitions (temperature change of perovskite structure in the Earth mantle)  Determination of thermodynamic properties of minerals Other applications of RS in geology 2010prof. Otruba36  resonance Raman spectroscopy  Electronic Raman spectroscopy  hyper-Raman spectroscopy  coherent antistokesian Raman scattering (CARS) Geological materials - hematite 2010prof. Otruba37 Identification of drugs 2010prof. Otruba38 Identification of drugs 2010prof. Otruba39 Study of complexes 2010prof. Otruba40 Archeology - ceramics 2010prof. Otruba41 Analysis of compounds in the discharge lamp 2010prof. Otruba42 2010prof. Otruba43 Analysis of compounds in the discharge lamp Analysis of carbon materials 2010prof. Otruba44 diamond like carbon diamond DORISS system (depth of 3607 meters in Monterey Bay) 2010prof. Otruba45 2010prof. Otruba46 2010prof. Otruba47 Raman micro probe 2010prof. Otruba48 Analysis of cereal grains 2010prof. Otruba49 Paper surface mapping 2010prof. Otruba50 Spatial distribution of aerosol 2010prof. Otruba51 BDP - beclomethasone Detection of infected erythrocytes 2010prof. Otruba52 Confocal microscope 2010prof. Otruba53 Focused beams of laser light are scanned across the sample (Laser Scanning Microscopy, LSM) and light only from the desired focal plane is allowed to enter the detector. These microscopes provide excellent axial resolution, and very good signal to noise sampling, however this often comes with a sacrifice in temporal resolution due to the slow nature of scanning pixel-by-pixel across the image during capture. Some systems overcome this speed issue with either faster scanners. Scanning mirrors 2010prof. Otruba54 Sample optics movable mirror Confocal Raman microscope 2010prof. Otruba55 miror lens Raman microspectroscopy 2010prof. Otruba56 Raman nanospectroscopy 2010prof. Otruba57  Near field techniques  probe near surface („near field“)  Near-field spectroscopy  Near field microscopy  SNOM – scanning near-field optical microscopy  UV-vis, IR (IR-SNOM), Raman spectroscopy +TERS  photoluminescence, fluorescence  resolution better than 50 nm  spectroscopy of single molecule Application of SNOM 2010prof. Otruba58  Single Molecule DetectionJ.K.Trautmanet al. Nature 369,40, (1994)  Raman ScatteringC.L. Jahnckeet al. Appl. Phy. Lett. 67 (17), 2483 (1995)  Polarization and OrientationB. McDaniel et al. , Appl. Opt. 37, 84 (1998)  Magnetic-ImagingU. Hartman, J. Magn.& Magn. Mater. (1996)  Data StorageH.J. Mamin, IBM J. Res. Develop. (1995)  Biological Imaging. VanHulstet al. J. Struct. Bio., 119,222 (1997)  Quantum Dots, QuantumWires H.F. Hess et al. Science 264, 1740 (1994)  Lithography S. Madsen et al. J.App. Phy.82 (1) 49(1997).  Photonic Device Characterization S.K. Burrattoet al. App. Phy. Lett.65, 2654 (1994)  Semiconductor/ Defect Characterization LaRosaet al. Mater. Res. Soc. Symp. Proc. 406,189-194 (1996) Raman - SNOM 2010prof. Otruba59  probe distance - up to 10 nm  probe aperture  scanning modes  transmission (transparent samples only)  reflective - sharp probe - transmitter, receiver, both  scattering - transmitter, receiver, both Raman-SNOM 2010prof. Otruba60 probe distance –to 10 nm • probe aperture • scanning modes perpendicular or oblique laser excitation Phase separation AFM image of PMMA-SBR polymer blend, centrifugally (polymethymethacrylate - styrene-butadiene- rubber) applied to a glass substrate. Scan 20x20 µm, topographic 30 nm scale Raman image of PMMA-SBR polymer blend. PMMA surfaces are color coded in blue, SBR surfaces are displayed in red. views: 200x200 spectra 2010prof. Otruba61 Measurement of stress in material AFM measurement of indentation fromVickers hardness test Si. A 2.75 µm diagonal and 210 nm depth imprint was created by force 50 mN. Scan area: 10x10 µm. Raman display the same areas as in the adjacent figure. The image was calculated from the position of the parabolic approximation peak 2010prof. Otruba62 Measurement of stress in material _ phonons 2010prof. Otruba63  Fonon - quasi-particles of crystal lattice vibrations, vibrational quantum spreading through the crystal lattice. Phonons can be used to describe the propagation of sound waves in solids.The name phonon originated as an analogy to a photon.A photon is a particle of an electromagnetic field, a phonon is a quasi-particle of an undamped sound field in a solid. It ranks among the bosons. Mechanical stress in nanostructures 2010prof. Otruba64 Special techniques of RS 2010prof. Otruba65  resonance - RR  surface-enhanced - SERS  surface enhanced resonance - SERRS  photoacoustic– PARS (non-linear, pulsed)  hyperRaman (two photon pumping)  coherent anti-Stokes - CARS  coherent Stokes - CSRS RRS (Resonance Raman Scattering 2010prof. Otruba66  Excitation into the absorption band of the molecule, but there is a risk of photodegradation and interference with the fluorescence RRS 10-6 M porphyrin Nonlinear methods - CARS 2010prof. Otruba67 In the CARS ("four-frequency mixing") method, unlike ASRS, relaxation from the first virtual level 2 is forced by radiation from the second laser at ω2, which causes an increase in the population of level 3 and the antistokes transition is stimulated emission of coherent and directed radiation.The ωAS emission is based on a narrow cone. In dispersion samples (liquids), the wave vectors are summed in vector (c), so that no dispersion element is required to separate the detected radiation, unlike gases (b). Coherent Anti-Stokes Raman Scattering 2010prof. Otruba68  CARS can stimulate the production of a significantly larger amount of signal than spontaneous Raman microscopy. Like spontaneous Raman, CARS probes vibrational modes in molecules and does not require the introduction of exogenous dyes or markers, which is advantageous in imaging small molecules, such as metabolites, for which labeling may significantly affect their molecular properties.  CARS is a process that involves four photons that interact with the third order nonlinear susceptibility of the sample, which is a function of the vibrational frequencies .To understand a CARS event, consider two photons: a pump, of energy , and a Stokes, of lower energy . Consider also a molecule with a single resonance, represented by a third order susceptibility.A CARS event can be understood in two steps. Upon the illumination of the molecule with the pump and Stokes photons,the first step is initiated if the condition is met; that is, if the diference in energy between the pump and Stokes photons matches the energy of the excited vibrational state of the molecule, so that the molecule is excited. Once this happens, the second step is the result of the interaction of this excited state with a third photon,known as the probe, of energy .This photon gains the energy of excitation of the molecule, and an anti-Stokes photon is emitted with an energy that has a higher frequency than any of the incident photons. CARS instrumentation 2010prof. Otruba69 CARS requires first power tunable lasers that are technically and economically challenging. Unlike conventional Raman spectrometry, the radiant fluxes in CARS are very intense, so the signal detection requirements are minimal. E.g. when monitoring the benzene vibration transition at 992 cm-1 (totally symmetrical vibration of the benzene ring), excitation to virtual levels at 513 nm, P = 100 kW / 6μs, stimulation at 540 nm, P = 30 kW / 6μs, coherent radiation power from Interactive space 300W! Efficiency can be achieved up to 10%, for spontaneous Raman scattering it is 10-5 to 10-8%. Coherent anti-Stokes Raman scattering microscopy (CARS): 2010prof. Otruba70  F-CARS and ECARS microscopy with co- propagating incident beams, forward and backward signal collection, respectively  Obj., objective lens; F., filter; BC., beam combiner; L., lens; M., mirror CARS microscopy 2010prof. Otruba71 Broadband Coherent anti-Stokes Raman Microscope for Materials Research – CARS 2010prof. Otruba72 Fig. Shows the distribution of individual components in a mixture of polystyrene (PS) and polymethyl methacrylate (PMMA).The image is generated based on the relative ratio between peaks of 800 and 1000 cm-1. epi-CARS microscopy We used epi-CARS microscopy to image ex vivo mouse brain tissues. Epi-CARS microscopy suppresses the nonresonant background from the aqueous medium. Mosaic picture of an epi CARS mouse brain image. The brain tumor is on the left side and extends across the center line and distorts the symmetry of thebrain.The magnification was 20x. Image is displayed in pseudo-color. 2010prof. Otruba73 Surface Plasmon Resonance(SPR) 2010prof. Otruba74 Plasmonics Surface Enhanced Raman Spectroscopy SERS Tip Enhanced Raman Spectroscopy/Microscopy TERS Aplication of SPR 2010prof. Otruba75  sensitivity enhancement of spectroscopy techniques including fluorescence, Raman spectroscopy ... (surface enhanced Raman spectroscopy ~ 1014 – 1015x allows identification of a single molecule)  change of refractive index by adsorption of molecules on metal-dielectric interphase  shift of resonance due to adsorption of molecules on the interphase  noble metal nanoparticles exhibit strong UV-Vis absorption bands (not present in "macro")  measurement of thickness adsorbed layers, binding constants of ligands ... Basic nomenclature 2010prof. Otruba76  SERS – Surface Enhanced Raman Scattering. Raman scattering on molecules bound to the surface of a precious metal (gold, silver) can increase both scattered and incident radiation due to the resonance interaction of photons with the quanta of electron gas oscillations in the field of crystal lattice ions bound to the surface.  Plazmon – quasi-particles (quantum) of longitudinal electron gas oscillations in solids (in crystal lattice of metals, in non-metals, in plastics). In metals, for example, it is possible to excite plasma oscillations as a collective excitation of conductive electron gas against the background of crystal lattice cations. Reflected or transmitted electrons or photons interacting with plasmons exhibit energy losses equal to integral multiples of the plasmon's energy.The generation of plasmon (in most materials with an energy of 10 ÷ 20 eV) leads to energy losses, which are manifested in the form of so-called Ferrel radiation (discovered in 1960) in the UV or visual field.  Surface plasmons – plasmons occurring at the interface of vacuum or material with positive relative permittivity and environment with negative relative permittivity (usually metals or doped semiconductors).They interact strongly with photons to form another quasi-particle - the polariton. SERS 2010prof. Otruba77  Surface Enhanced Raman Scattering – the method brings a great improvement in MS by applying suitable metal molecules or nanoparticles (eg Ag) to the investigated surface.  The amplification of Raman signals is of the order of 104 - 106, in some systems it may be even higher.  The improved sensitivity of the method is related to the fact that molecules near Ag or Au nanoparticles exhibit surface plasmon resonance. However, this explanation is not the only one.  Surface plasmon is a quasi-particle. It is a collective excitation of free electrons on the conductor-insulator interface. Surface-enhanced Raman scattering, SERS The difference between the SERS spectrum of the 2- mercaptoethanol monomolecular layer on the surface of the roughened silver (a) and the spectrum of liquid 2mercaptoethanol (b). Due to the attractive surface forces that modify the structure of the electron sheath, the two spectra differ. (For clarity, the spectra are offset and displayed at different scales.) Source:Wikipedia. 2010prof. Otruba78 wave number shift Surface plasmons 2010prof. Otruba79 Surface Plasmon - polariton = coherent "collective" oscillations of electrons in the conductive band Its electromagnetic states are coupled to the metal / dielectric interface formed by charge in metal (e-) and elmag. field in both phases - resulted in associated oscillations e-density and elmag. field (= "Levels" of electron density oscillations ) - field intensity exponentially decreases with distance from the surface of the metal phase (=> localization in the interphase) propagates as a longitudinal wave at the interface The properties of the plasmon depend on- composition of interphases(ε, Ra) - refractive index of dielectrics (light guide, detection of chemical bonds, nanostructures) Mechanism of surface plasmon resonance(Surface Plasmon Resonance) 2010prof. Otruba80  The incident light λ (hν) excites the electron cloud oscillations of the conductive band with subsequent amplification of the elmg. field at the surface interface  ⇒ in light absorption resonance, λSPEC increases by several orders of magnitude (= surface plasmon resonance)  Metallic nanostructure acts as an antenna. surface plasmonmetal Nanoparticle plasmons 2010prof. Otruba81  Nanoparticle plasmon no longer exists localized energy levels (forming a band / cloud). Min. particle size:> 2 nm.  Interaction with light => excitation of e-cloud oscillations => polariton (el. Polarization)  Small nanoparticle interaction with light => dipole radiation (E-field) (a, b)  larger nanoparticles => quadrupole radiation (c) Surface Enhanced Raman Spectroscopy 2010prof. Otruba82  Conditions :  Max. enhancement (incident and scattered light (Raman) is amplified by plasmon resonance) for frequencies with minimal shift Δλ (both can not be very shifted in resonance => less gain)  Plasmon oscillations must be perpendicular to the surface  use of Au,Ag, Cu (NIR-Vis) nanostructures  „Hot-Spots“ (the signal is not representative to the surface)  combination of advantages  fluorescence - high light gain  Raman spectroscopy - structural information  Theory:  binding - charge transfer, formation of bonds  excitation of surface plasmon  ? SERS Spectroscopy 2010prof. Otruba83  giant enhancement of Raman signal  two mechanisms involved  electromagnetic-long range, depends on metalsubstrate properties (surface plasmonsare involved)–coinmetals –Au, Ag, Cu  chemical-local, molecular structure plays an important role (formation of surface complex) SERS - history 2010prof. Otruba84  An important milestone in the use of combination scattering was the discovery of surface-enhanced Raman scattering in 1977 by two groups of researchers independently of each other. Historically, the first SERS - Surface Enhanced Raman Scattering - of pyridine adsorbed onto the surface of electrochemically roughened silver was measured in 1974, but was not correctly interpreted.At the same time, both groups proposed two primary SERS theories, recognized to this day: electromagnetic, based on excitation of surface bound plasmon, while chemical theory is based on charge transfer complexes.  The most commonly used materials for SERS are gold and silver with a surface with irregularities at least one order of magnitude less than the wavelength of incident light.The resonant frequencies of these materials fall within the range of visible light and near infrared radiation.The amplification of the combination scattering for a flat substrate is in the range of 103 ÷ 106. SERS on nanostars 2010prof. Otruba85  Calculated enhance and cross-section values for a hypothetical nanostar with two- pronged.  Source: P. S. Kumar et al; Nanotechnology 19 (2008). Nanostars 2010prof. Otruba86 Image of a nano-star in a transmission scanning electron microscopeTEM -Transmission Electron Microscopy, creating an image of a thin object by passing energy electrons.The image formed by the passed electrons is then enlarged and focused by electron optics and converted to visible radiation on the screen, which is usually further recorded by a CCD camera.Another technique is SEM, in which the image is produced from reflected electrons. It is complemented by a single gold nanostar image using Atomic Force Microscope (AFM), an atomic force microscope.The machine scans the surface of the material using a tip suspended on a flexible swing arm.The tip is attracted by electrostatic and van derWaals forces. Movements of the arm above the surface are monitored by a laser.The microscope is so sensitive that it can track the electron orbitals of material molecules.The AFM microscope was invented in 1986 by G. Binnig, C. Quat and C. Gerber. (bottom left) and a phase portrait of a nano-star using electrostatic microscopy (bottom right, white areas show areas with charge accumulation at the sharp peaks of the star. Source: Nanotechweb). Individual nanostars 2010prof. Otruba87 Source: NIST Nanostars penetrate to the living cell 2010prof. Otruba88  The video shows the movement of individual nanostars bound to EGFR (Epidermal Growth Factor Receptor) protein molecules in a living human cell grown from a cervical cancer. Note the unbound nanoparticles moving rapidly across the field of view.The bound nanoparticles move slowly, towards the cell nucleus.  Source:Aaron et al.: Opt. Express 16/3 (2008). Tip Enhanced Raman Spectroscopy 2010prof. Otruba89 Section cut TER(S) (A = IRT/IR0) λ = 541 nm, dT-S = 4 nm From nanoparticle plasmon resonance (SE) to tip enhancement (TE) P. Hewageegana, M. I. Stockman: Plasmonics enhancing nanoantennas Infrared Physics & Technology 50 (2007) 177– 181 TERS instrumentation 2010prof. Otruba90 Source: He-Ne laser (632.8 nm) ~0.3 mW on sample Example of TERS application 2010prof. Otruba91 Monolayer of dye adsorbed on Au film, STM Ag-tip G. Picardi, K. Domke, D.Zhang, B. Ren, J. Steidtner B. Pettinger, Fritz-Haber-Institut der Max-Planck-Gesellschaft Instrumentation-integrated AFM + TERS 2010prof. Otruba92 Instrumentation - integrated AFM + TERS two optical ports 2010prof. Otruba93 Combination - AFM, Raman nanomapping 2010prof. Otruba94 Parallel images of silicon semiconductor AFM image –9 x 7 μm Image of Ramanovy intensity–520 cm-1, the same area Application 2010prof. Otruba95  according to the type of investigated material  anorganic  organic  geological  biological …  by instrumentation  dispersion vs. FT  macro x micro x nano  according to the data evaluation method  spectra libraries, „ puzzles solving ", chemometrics … Studied materials 2010prof. Otruba96  SAMPLES – solids, liquids, phase interfaces  examples  anorganic –corrosion layeres, surfaces of hard disc, silicon, amorphous carbon, diamonds  organic -supramolecular systems, contaminants in enviroment  polymers -photolabile materials  biological-in vitro, in vivo  geological -minerals, rocks  archaeological - from the Paleolithic to the Modern Age Field measurements 2010prof. Otruba97 Field measurements 2010prof. Otruba98 Hanheld Raman spectrometer – AHURA