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We observe the interaction of electromagnetic radiation with different properties of the matter. Each type of spectroscopy gives a different picture of the matter â†’the spectrum
The spectrum is the variation of the intensity of the radiation as a function of the frequency or wavelength Spectroscopy is a technique that uses the interaction of energy with a sample to perform an analysis. Photoelectron spectroscopy is based on Einstein's photoelectric effect. Photoelectron spectroscopy is based upon a single photon in/electron out process and from many viewpoints this underlying process is a much simpler phenomenon than the Auger process. The energy of a photon of all types of electromagnetic radiation is given by the Einstein relation:
E = h Î½
Photoelectron spectroscopy uses monochromatic sources of radiation. XPS the photon is absorbed by an atom in a molecule or solid, leading to ionization and the emission of a core (inner shell) electron. By contrast, in UPS the photon interacts with valence levels of the molecule or solid, leading to ionization by removal of one of these valence electrons. The kinetic energy distribution of the emitted photoelectrons (i.e. the number of emitted photoelectrons as a function of their kinetic energy) can be measured using any appropriate electron energy analyser and a photoelectron spectrum can thus be recorded. The process of photoionization can be considered in several ways: one way is to look at the overall process as follows:
A + hÎ½ â†’ A+ + e-
Conservation of energy then requires that:
E (A) + hÎ½ = E (A+ ) + E(e-)
Since the electron's energy is present solely as kinetic energy (KE) this can be rearranged to give the following expression for the KE of the photoelectron:
KE = hÎ½ - (E (A+ ) - E(A) )
The final term in brackets, representing the difference in energy between the ionized and neutral atoms is generally called the binding energy (BE) of the electron - this then leads to the following commonly quoted equation:
KE = hÎ½ - BE
Thus, photoelectron spectroscopy measures the relative energies of the ground and excited positive ion states that are obtained by removal of single electrons from the neutral molecule. There are several instruments that are used to perform a spectroscopic analysis. In simplest terms, spectroscopy requires an energy source (commonly a laser, but this could be an ion source or radiation source) and a device for measuring the change in the energy source after it has interacted with the sample (often a spectrophotometer or interferometer).
There are as many different types of spectroscopy as there are energy sources. Here are some examples:
Astronomical Spectroscopy: Energy from celestial objects is used to analyze their chemical composition, density, pressure, temperature, magnetic fields, velocity, and other characteristics. There are many energy types that may be used in astronomical spectroscopy.
Atomic Absorption Spectroscopy: Energy absorbed by the sample is used to assess its characteristics. Sometimes absorbed energy causes light to be released from the sample, which may be measured by a technique such as fluorescence spectroscopy.
Attenuated Total Reflectance Spectroscopy: This is the study of substances in thin films or on surfaces. The sample is penetrated by an energy beam one or more times and the reflected energy is analyzed. Attenuated total reflectance spectroscopy and the related technique called frustrated multiple internal reflection spectroscopies are used to analyze coatings and opaque liquids.
Electron Paramagnetic Spectroscopy: This is a microwave technique based on splitting electronic energy fields in a magnetic field. It is used to determine structures of samples containing unpaired electrons.
Electron Spectroscopy: There are several types of electron spectroscopy, all associated with measuring changes in electronic energy levels.
Fourier Transform Spectroscopy: This is a family of spectroscopic techniques in which the sample is irradiated by all relevant wavelengths simultaneously for a short period of time. The absorption spectrum is obtained by applying a mathematical analysis to the resulting energy pattern.
Gamma-ray Spectroscopy: Gamma radiation is the energy source in this type of spectroscopy, which includes activation analysis and Mossbauer spectroscopy.
Infrared Spectroscopy: The infrared absorption spectrum of a substance is sometimes called its molecular fingerprint. Although frequently used to identify materials, infrared spectroscopy also may be used to quantify the number of absorbing molecules.
Laser Spectroscopy: Absorption spectroscopy, fluorescence spectroscopy, Raman spectroscopy, and surface-enhanced Raman spectroscopy commonly use laser light as an energy source. Laser spectroscopes provide information about the interaction of coherent light with matter. Laser spectroscopy generally has high resolution and sensitivity.
Mass Spectrometry: A mass spectrometer source produces ions. Information about a sample may be obtained by analyzing the dispersion of ions when they interact with the sample, generally using the mass-to-charge ratio.
Multiplex or Frequency-Modulated Spectroscopy: In this type of spectroscopy, each optical wavelength that is recorded is encoded with an audio frequency containing the original wavelength information. A wavelength analyzer can then reconstruct the original spectrum.
Raman Spectroscopy: Raman scattering of light by molecules may be used to provide information on a sample's chemical composition and molecular structure.
X-ray Spectroscopy: This technique involves excitation of inner electrons of atoms, which may be seen as x-ray absorption. An x-ray fluorescence emission spectrum may be produced when an electron falls from a higher energy state into the vacancy created by the absorbed energy.
RESULT AND DISCUSSION:
300 BC -1800
300 BC - Euclid discussed the focus of a spherical mirror.
50 AD - Cleomedes discussed the refraction of light.
139 AD - Claudius Ptolemy made detailed tables on the reflection and refraction of light.
1010 - Althazen (965-1038) described the planar nature of reflection.
1304 - Theodoric of Freiberg explained the water-droplet origins of rainbows.
1500 - Leonardo Da Vinci (1452-1519) mentioned diffraction in his notebooks.
1608 - Hans Lippershey made one of the first telescopes. Shortly afterwards, Galileo Galilei (1564-1642) made a telescope and turned it to the heavens.
1609 - Zacarias Joannides made the first microscope.
1620 - Willebrord Snell van Royen (1591-1626) discovered the law of refraction.
1637 - Descartes derived the law of refraction theoretically.
1663 - Robert Boyle (1627-1691) first observed interference rings, now known as Newton's rings.
Chromatic decomposition of light had been known for a long time, if only through the rainbow. In the second half of the 17th century, Isaac Newton named "spectrum" the colored figure obtained by scattering sunlight through a prism. Beginning in 1666, Newton demonstrated the fixity of the colors thus formed, and synthesized white light by mixing these colors.
Chromatic decomposition of light had been known for a long time, if only through the rainbow. In the second half of the 17th century, Isaac Newton named "spectrum" the colored figure obtained by scattering sunlight through a prism. Beginning in 1666, Newton demonstrated the fixity of the colors' thus formed, and synthesized white light by mixing these colors'.
1669 - Bartholinus discovered the polarization of light by Iceland spar.
1678 - Romer determined the speed of light, by observing Jupiter's moons.
1690 - Christian Huygens (1629-1695) proposed a wave theory of light.
1728 - Bradley discovered the aberration of light.
1729 - Chester Moor-Hall (1704-1771) and John Dollond (1760-1761) made the first aberration-corrected lens.
1752 - T Melvill published first observation of a line spectrum.
1800 - W Herschel discovered the Infrared, by its heating effect.
Although the spectral nature of light is present in the rainbow, it was beyond the ability of early man to recognize its significance. It was not until 1666 that Newton showed that the white light from the sun could be dispersed into a continuous series of colors. Newton introduced the word "spectrum" to describe this phenomenon. His instrument employed a small aperture to define a beam of light, a lens to collimate it, a glass prism to disperse it, and a screen to display the resulting spectrum. This first spectroscope was nearly in modern form. Newton's analysis of light was the beginning of the science of spectroscopy. It gradually became clear that the sun's radiation has components outside the visible portion of the spectrum. W Herschel (1800) demonstrated that the sun's radiation extended into the infrared, and J.W. Ritter (1801) made similar observations in the ultraviolet. These studies were the precursors of radiometric and photographic measurements of light, respectively. Spectral lines and their quantitative measurement The achievements of Joseph Fraunhofer provided the quantitative basis for spectroscopy. Fraunhofer, born near Munich in 1787, extended Newton's discovery by observing that the sun's spectrum, when sufficiently dispersed, was crossed by a large number of fine dark lines (1814), now known as Fraunhofer lines. W.H. Wollaston had earlier observed a few of these lines (1802), but failed to attach any significance to them. These were the first spectral lines ever observed, and Fraunhofer employed the most prominent of them as the first standards for comparing spectral lines obtained using prisms of different glasses. Fraunhofer also studied spectra of the stars and planets, using a telescope objective to collect the light. This laid the foundation for the science of astrophysics. Fraunhofer also developed the diffraction grating, an array of slits, which disperses light in much the same way, as does a glass prism, but with important advantages. With a prism, the angle at which a spectral line is dispersed depends on the type of glass used. This makes it difficult to compare different spectral measurements, and absolute wavelength measurement is not possible. Gratings, which employ interference of light waves to produce diffraction, provide a means of directly measuring the wavelength of the diffracted beam. Earlier, T. Young had demonstrated that a light beam passing through a slit emerges in a pattern of bright and dark fringes. Fraunhofer extended these studies to the case of two, three and many closely spaced slits, and thus developed the transmission grating. With this, he was able to directly measure the wavelengths of spectral lines. Fraunhofer achievements are all the more impressive, considering that he died at the early age of 39.
Early 19th century
Spectroscopy was born in 1801, when the British scientist William Wollaston discovered the existence of dark lines in the solar spectrum.
1801 - J W Ritter and W H Wollaston discovered Ultraviolet, by its chemical effects.
1801 - Thomas Young presented the principle of the interference of light.
In 1802, William Hyde Wollaston fitted the entrance of his spectroscope with a fine slit to improve resolution and discovered the presence of fixed black lines within the solar spectrum. In 1814, Joseph von Fraunhofer invented the diffraction grating (transmission). After fitting it onto a theodolite, he resumed Wollaston's work and marked the relative positions of several hundreds of black lines. He was, however, unable to provide a satisfactory explanation for their presence.
1807 - Young presented the three color theory of vision.
1811 - Arago discovered rotary polarization by quartz.
1813 - Arago discovered the polarization of scattered light.
1815 - Fresnel rediscovered the interference of light.
1818 - Fresnel explained the polarization of light.
1826 - Balard discovered the photo-sensitivity of silver bromide.
1826 - Talbot and Herschel studied the changing colors of flames when sodium, potassium, lithium and strontium salts were introduced into the flame.
Thirteen years later, Joseph von Fraunhofer repeated Wollaston's work and hypothesized that the dark lines were caused by an absence of certain wavelengths of light. It was not until 1859, however, when German physicist Gustav Kirchhoff was able to successfully purify substances and conclusively show that each pure substance produces a unique light spectrum, that analytical spectroscopy was born. Kirchhoff went on to develop a technique for determining the chemical composition of matter using spectroscopic analysis that he, along with Robert Bunsen, used to determine the chemical makeup of the sun. Photoelectron spectroscopy is an extension of the photoelectric effect, first explained by Einstein in 1905, to atoms and molecules in all energy states. The technique involves the bombardment of a sample with radiation from a high-energy monochromatic source and the subsequent determination of the kinetic energies of the ejected electrons. The source energy, hÎ½, is related to the energy of the ejected electrons, (1/2)mev2, where me is the electron mass and v is the electron velocity.
Mid 19th century
In 1832, J F Herschel described the specific coloration given to flames by metal salts. This was the first spectrochemistry observation, from which major work on emission spectra originated. It was fast found that emission spectra include bright lines at set locations.
1835 - Schwerd developed a "wave" theory of the diffraction grating.
1837 - Knox discovered that the conductivity of selenium changes with illumination.
1840 - Joseph Max Petzval (1807-1891) made the first portrait camera lens.
1842 - Doppler discovered the effect named after him, that the wavelength of light changes with the speed of the source relative to the observer.
1845 - Michael Faraday (1791-1867) observed that a magnetic field could rotate the plane of polarization of light.
1850 - Foucault showed that light travels more slowly in water than in air, as predicted by wave theory.
M A Masson introduced in 1851 the apparatus shown above. This is the first spark emission spectrometer known. The set-up consists of a prism mounted on a Duboscq goniometer with a rather complete sparking source. Underneath the set-up are records of the position of iron and copper emission lines in the visible domain.
1856 - Ludwig Philipp van Seidel (1821-1896) derived the theory of third order aberration. In 1859, Gustav Robert Kirchhoff and Robert Bunsen demonstrated the reversibility of emission lines: "within the spectrum, an element absorbs the light at the exact location of the lines which it can emit". They stated the basic law of elementary spectrometry which states: "each element has specific properties as regards the light it emits".
They explained Fraunhofer black lines as being caused by the absorption of solar light by metal vapors present in the colder layers surrounding the sun. They even identified the element responsible for some of these black lines. This work paved the way for atomic spectrochemistry and announced the advent of modern physics.
1860 - Foucault observed the absorption of spectral lines in one flame by another.
1864 - James Clark Maxwell presented the electromagnetic theory of light.
1866 - William Huggins made the first spectroscopic study of a nova.
1868 - A J Angstrom published a compilation of all the visible lines in the solar spectrum.
1869 - Angstrom made the first reflection grating.
1873 - Abbey described the optical limit in imaging.
1873 - Maxwell presented his 'Treatise on Electricity and Magnetism'.
1877 - Gouy invented the first pneumatic nebuliser for introducing liquids into flames.
1882 - H A Rowland greatly improved diffraction gratings, introducing curved gratings.
1885 - J J Balmer found a formula for the Hydrogen series; J R Rydberg and W Ritz then found formulae for other simple spectra.
1891 - Gabriel Lippmann made the first color photographic plate.
1893 - V Schumann studied the 'vacuum' Ultraviolet.
1897 - J J Thomson discovered the electron.
1899 - Hertz developed the theory of dipole radiation, the basis of modern radio.
1900 - Max Planck discovered the quantum.
The end of the nineteenth and beginning of the twentieth century's was marked by significant efforts to quantify and explain the origin of spectral phenomena. Beginning with the simplest atom, hydrogen, scientists including Johann Balmer and Johannes Rydberg developed equations to explain the atom's frequency spectrum. It was not until Niels Bohr developed his famous model in 1913 that the energy levels of the hydrogen spectrum could accurately be calculated. However, Bohr's model failed miserably when applied to other elements that had more than one electron. It took the development of quantum mechanics by Werner Heisenberg and Erwin Schrodinger in 1925 to universally explain the spectra of most elements. From the discovery of unique atomic spectra developed modern spectroscopy. The three main varieties of spectroscopy in use today are absorption, emission, and scattering spectroscopy. Absorption spectroscopy, including Infrared and Ultraviolet spectroscopy, measures the wavelengths of light that a substance absorbs to give information about its structure. Emission spectroscopy, such as fluorescence and laser spectroscopy, measures the amount of light of a certain wavelength that a substance reflects. Lastly, scattering spectroscopy, to which Raman spectroscopy belongs, is similar to emission spectroscopy but detects and analyzes all of the wavelengths that a substance reflects upon excitation
In the early 1950's, certain identification of a new molecule by melting point/chemical analysis/derivative formation typically took 2-7 days, and could take much longer. Now, the same identification typically takes 15 minutes to one day, depending on complexity and availability of spectroscopic tools.
Since the early 1960's, many chemists use spectroscopy for quantitative analysis, i.e., to tell how much of a specific substance is in a mixture. When you look at a glass of colored soda into which ice has melted, you know at once that it is diluted relative to the original soda.
Early 20th century
1905 - Albert Einstein explained the photoelectric effect.
1905 - Einstein presented the special theory of relativity, in which the speed of light is independent of the motion of its source and constant in any inertial frame of reference.
1913 - Niels Bohr's theory of the atom, explains the Balmer, Rydberg and Ritz formulas of simple spectra.
1913 - Johannes Stark discovered the Stark effect, the splitting of spectral lines in an electric field.
1923 - Compton explained x-ray scattering.
1925-7 - Quantum theory of the atom, developed by many people including Wolfgang Pauli (exclusion principles), Werner Heisenberg (uncertainty principle), Erwin Schrödinger (wave equation), Louis de Broglie, Max Born (wave function as probability), Jordan, and Paul A M Dirac (relativistic wave equation).
1928 - Niels Bohr proposed the Complementarily Principle.
1930 - Gerlach and Schweitzer introduced the ratio method for intensities.
1936 - Thanheiser and Heyes used photocells to measure intensities.
1942-9 - Giulio Racah presented his formulation of the angular components of Schrödinger's equation.
~1945 - P M Duffieux and R K Luneberg introduced Fourier methods to optics.
1947 - Willis E Lamb discovered the Lamb shift.
1947 - Dennis Gabor developed holography.
1948 - Sin-itiro Tomonaga, Julian S Schwinger and Richard P Feynman developed quantum electrodynamics (QED).
1949 - D R Bates and Agnette Damgaard presented an approximate solution to the radial part of Schrödinger's equation.
1950 - A Kastler caused population inversion in excited atoms.
Late 20th century
1951 - E M Purcell and R V Pound first observed net induced emission.
1951-2 - C H Townes, Nikolai G Basov and Alexandra M Prokhorov first suggested the principle of the maser.
1953 - Zernike awarded the Nobel Prize for phase-contrast microscope
1954 - Alan Walsh invented the atomic absorption spectrometer (AAS)
1960 - T H Maiman demonstrated the first simple laser.
1965 - S J I L Greenfield invented 'high-power' ICP
1966 - Alfred Kastler awarded Nobel Prize for optical methods for studying atomic energy levels.
1967 - W Grimm invented his glow discharge source.
1968 - Grimm presented the first quantitative analysis with his new source.
1969 - V A Fassel and P W J M Boumans developed 'low-power' ICP.
1970 - J E Greene and J M Whelan reported the first depth profile with the Grimm glow discharge source.
1972 - C J Belle and J D Johnson reported the first quantitative depth profile with the Grimm source.
1972 - Boumans determined the main characteristics of the Grimm glow discharge.
1973 - Charlotte E Moore published extensive tables of atomic energy levels.
1975 - Roger Berneron demonstrated the wide capabilities of GD-OES for qualitative depth profiling.
1978 - Ritzl produced the first commercial GD-OES instrument using the Grimm source.
1985 - J Pons-Corbeau introduced the first algorithm for quantitative depth profiling in GD-OES.
1988 - M Chevrier and Richard Passetemps invented the first radio frequency powered Grimm source.
The era of modem spectroscopy began with the invention of the laser, which provides intense, collimated monochromatic radiation throughout optical spectral range. Historically, the laser was an extension of the maser, a microwave oscillator developed by N.G. Basov and A.M. Prokhorov in the USSR and C.H. Townes in the US (1954). In a brilliant intellectual breakthrough, in 1958 Townes and A.L. Schawlow proposed ex- tending the maser principle into the optical regime. They pointed out that an interferometer of the type developed by Fabry and Perot in 1900 would also function as an optical resonator. When atoms or molecules in a state of inversion (more atoms in the upper level of the atomic transition than in the lower one) are placed within the resonator, the emission should dramatically increase in intensity and decrease in line width. They called their device an optical maser, but the term laser (for light amplification using stimulated emission of radiation) soon caught on instead. The first working prototypes were built soon after. The ruby laser, a pulsed solid state laser emitting red light at a wavelength of 694 nm, was developed by T.H. Maiman in 1960, and the He-Ne laser, a continuous-wave gas laser emitting infrared light at 1.15 mm, was developed shortly afterwards by A. Javan. There rapidly followed a host of new laser sources: CO2 ( Î»=9-10 Å), Nd:YAG (Î»=1064 nm), argon and krypton ion lasers, which produce multiple visible wavelengths, and many others. The dye laser, developed by P.P. Sorokin, F.P. Schafer, B.B. Snavely and others in 1966, is of particular significance because it provides monochromatic radiation, which can be broadly tuned over the visible spectral range. Laser light, with its high intensity, narrow spectral line width and phase coherence, immediately stimulated new interest in atomic and molecular spectroscopy. Because the first lasers were fixed in frequency, the earliest work was done on the laser medium itself, and on spectral lines, which happened to coincide with the frequency of a laser source. Transitions under study were sometimes Stark- or Zeeman-tuned into resonance. Tunable lasers, the dye laser in particular, greatly extended the scope of possible measurements. Laser light opened the field of ultra-high resolution spectroscopy. Saturation spectroscopy, developed by Javan, Schawlow, W.E. Lamb, Jr. and others, provided sub-Doppler resolution of spectral lines of atomic and molecular vapors. Ordinarily, such lines are limited in resolution by thermal atomic motion ("Doppler broadening"). Intense, monochromatic laser light can selectively saturate an optical transition, producing extremely narrow Doppler- free resonances. Techniques for producing two-photon Doppler-free resonances were devised (V.P. Chebotayev). Atomic beams were also used to eliminate Doppler broadening and produce narrow spectral lines. Figure 1 illustrates the advances made over conventional spectroscopy measurements. parameters to be measured. By studying the shapes of these narrow lines, collisional processes could be studied. Further, by locking the laser frequency to a narrow spectral line, its wavelength (or frequency) could be accurately defined, making possible laser wave- length and frequency standards, and eventually laser atomic clocks (J. Hall, K. Evenson). Laser light also opened the possibility of conducting spectroscopy in the time domain. Coherent transient processes such as free induction decay and photon echoes, which had been observed earlier at radio frequencies, now began to be studied in the optical domain (S.G. Hartmann). In addition, the interaction of laser light with optically thick samples, in which coherent re-radiation can significantly modify the response of the sample, was studied for the first time. Effects observed included self-induced transparency (E. Hahn), in which a normally opaque sample becomes transparent to an intense light pulse, and Dicke superradiance (M.S. Feld), in which atoms are made to undergo emission proportional to the square of the number of radiators. Intense laser light has opened the field of nonlinear optics, the formalism of which was developed by N. Bloembergen. Frequency mixing processes such as second harmonic generation (P. Franken) were discovered and exploited to generate coherent light at new wavelengths deep in the ultra-violet and far infrared. Other nonlinear optical effects studied include the stimulated Raman effect (R. Hellworth), four-wave mixing and other stimulated processes induced by the high intensities of laser light (large number of photons per mode). Multiphoton absorption in atoms was used to ionize and detect trace quantities, and multiphoton absorption in molecules was used to produce large quantities of highly excited state species (V.S. Letokhov).
NEWS RESULT: New results in laser spectroscopy continue to advance the field. The development of atom traps by H. Dehmelt and W. Paul, combined with laser slowing of atomic beams due to photon recoil, called laser cooling, has led to techniques for highly localized confinement of isolated atoms, as well as dense collections of atoms and, recently, Bose-Einstein condensation. These species, arrested in space, can then be studied free of the usual external perturbations, providing spectroscopic data of extremely high resolution for fundamental studies and applications.
Nobel Prizes: There have been a relatively large number of Nobel Prizes awarded in spectroscopy. These Prizes exemplify both experimental and theoretical contributions to the growth of spectroscopic investigations as well as the development and discoveries related to spectroscopy. Although the following list of Nobel Prize winner is certainly not inclusive, it provides a starting point to learn more about the historical development of spectroscopy through the contributions of individual researchers.
Experimental Contributions to Spectroscopy
H.A. Lorentz and P. Zeeman (1902) discovery of the splitting of spectral lines in magnetic
J. Stark (1919) discovery of the splitting of spectral lines in electric fields
C.V. Raman (1930), the first to demonstrate spectral line shifts due to inelastic light scattering (Raman effect)
W.E. Lamb, Jr. (1955), who discovered the fine structure splitting in the first excited state of atomic hydrogen (this work was actually done with microwaves, but its origin and impact have been central to studies of atomic spectra)
R.S.Mulliken (1966) and G. Herzberg (1971), for their contributions to molecular spectroscopy
A.L. Schawlow (1981), for work in the field of laser spectroscopy
A. ZewailA.Zewail (1999), for studies of the transition states of chemical reactions using femtosecond spectroscopy
Theoretical Contributions to Spectroscopy
M. Planck (1918), who discovered the elemental quantum of action
N. Bohr (1922), the first to link the regularities of spectral lines to the quantum structure of atoms
P.A.M. Dirac and E. Schrodinger (1933), for their contributions to the quantum theory of atoms
W. Pauli (1945), who discovered the quantum exclusion principle
Inventions and Discoveries Related to Spectroscopy
A.A. Michelson (1907) invention of the interferometer, a hallmark in spectroscopic instrumentation
C.H. Townes , N.G. Basov and A.M. Prokhorov (1964) development of the maser, a source of coherent microwave radiation, which led to development of the laser and opened the field of modern spectroscopy
A. Kastler (1966) for the development of optical pumping of atoms
N. Bloembergen (1981) for his contributions to nonlinear optics
H.G. Dehmelt and W. Paul (1989) received this award for invention of the ion trap, an important tool in current spectroscopic research
APPLICATION OF SPECTROSCOPY:
Material science provides a varied and challenging range of samples for spectroscopic analysis which is ideally suited to the versatility offered by Renishaw's inVia Raman microscope. Typical materials include composites, polymers and catalyst reagents. Many of these samples can benefit from a second, complementary analysis technique, such as the pioneering structural and chemical analyser, a combination of scanning electron microscope (SEM) and microRaman capabilities For example, a recent case study involved the use of Renishaw Raman technology to investigate a crack in a steel component from a nuclear reactor.
A key issue in the rapidly evolving world of microelectronics is quality control during miniaturisation processes. One of the principal hurdles to overcome is strain-induced failure arising from lattice mismatch among different materials, different thermal expansion coefficients, sharp patterning, and device re- scaling. The ability of Raman microscopy to monitor stress, and other parameters such as surface/device temperature, make it an effective tool throughout the semiconductor device manufacturing process, starting with R&D through to the production line.
Conventional Raman spectroscopy is limited to a spatial resolution on the micron scale. By using novel techniques and materials, information can be gained from structures on a sub-micron or nanometre scale e.g. Raman may be used to classify the diameter of carbon nanotubes, given that the frequency of the radial breathing mode (RBM) is related to the tube diameter. Pioneering products such as the award winning Nanonics NSOM/AFM 100 Confocal/Renishaw Raman microscope system have demonstrated superior spatial resolution than is possible with the normal far-field diffraction limit.
Biological and biomedical
Raman spectroscopy has demonstrated the sensitivity to distinguish between cancerous, pre-cancerous and normal tissues, and its sensitivity to changes in cell metabolites and protein structures elevate it above competing spectroscopic techniques. Biological systems and materials provide unique challenges to Raman technology. Using Raman systems with Ultraviolet (UV) and Near Infrared (NIR) laser excitations allows the spectral region with the strongest fluorescence to be avoided. In addition to fluorescence, the majority of biological samples can be classified as weak Raman scatterers, with pigmented materials (such as vascular tissue) being strong absorbers of laser energy and thus more prone to laser damage. Renishaw has risen to these challenges by developing innovative techniques such as Streamline plus imaging to maximise the effectiveness of Raman in studying biological and biomedical materials.
In the field of forensic sciences, Raman spectroscopy is predominantly used for the unambiguous identification of unknown substances. Given that Raman is a non-destructive technique, it has the advantage of being able to identify trace amounts of substances without compromising the evidence in any way, even allowing identification to be performed through a glass or plastic container. The high sensitivity, confocal performance and imaging capabilities of the inVia Raman microscope are key requirements, where enforcement agencies require detailed information on materials to obtain a successful prosecution. Renishaw's Raman microscopes have gained international recognition for successfully completing difficult forensic investigations such as distinguishing active drug forms and cutting agents from illicit materials, and proving which ink was deposited first in 'crossed ink' document authentication cases.
Art and heritage applications
The mission for conservators and art historians has always been the sympathetic restoration of works of art and artefacts of historical interest. In the past, this has not always been possible, leading to the damage of countless irreplaceable items by inappropriate restoration work. By allowing conservators to understand the original materials (paints, pigments, lacquers etc) in addition to any degradation processes, Raman spectroscopy facilitates more sympathetic restoration. Crucially, Raman analysis is non destructive, and the use of remote fibre probes allows analysis to be performed on virtually any sample in-situ. Renishaw's expertise in this area was recognised in 2002 when the Sindonic Conservation Committee in agreement with Cardinal Poletto of the Turin diocese, selected their Raman instrumentation to provide analysis of the Holy shroud.
Raman spectroscopy fulfils a critical analytical role at many stages of the pharmaceutical product design and production process. Applications range from monitoring and controlling large scale manufacturing processes, to profiling the distribution of active pharmaceutical ingredients (API) and excipients at different stages in a formulation cycle. Raman offers unparalleled polymorph discrimination, is capable of studying aqueous and solid samples, and is particularly suited to combining with other analytical techniques given that it provides non-destructive analysis requiring little or no sample preparation.
Gemology, geology and mineralogy
In the field of gemology, the Raman and photoluminescence capabilities of Renishaw's inVia Raman systems are widely used to identify whether diamonds have been artificially treated at high temperature and pressure (known as HPHT treated or GE-POL diamonds) to change their colour and hence value. In addition to gemstone classification, Raman is utilised to identify inclusions, fillers, waxes and other treatments that have an impact on gem valuation. Geologists and mineralogists use Renishaw's structural and chemical analyser (SEM-SCA) to benefit from the imaging and analytical capabilities of scanning electron microscopes (SEMs) combined with the chemical and structural characterisation provided by Raman spectroscopy.