IA EXAMS

• The Raman instrument consists of the following, main parts:

  • A laser light source
  • A system for focusing the laser on a specific point of the sample
  • A monochromator to analyze the scattered radiation
  • A detector to convert radiation into electric current
  • A recording system (computer)
• IR spectroscopy is commonly used to detect: organic compounds, like binders, plastic coating, etc.
• Some differencies between Raman and IR spectroscopy are:

  • Raman peaks are usually sharper that IR peaks
  • Raman spectrum extends down to very low wavenumbers (50-100 cm-1), while IR is limited to wavenumbers above 400-600 cm-1
  • Raman is a scattering spectroscopy, IR is an absorption spectrocopy.
• The physical event which is involved in the IR experiment it:

  The absorption of a photon, which causes a transition between two vibrational levels of the molecule.
• In the Fiber Optics Reflectance Spectrocopy (FORS), the reflectance is?


  The ratio between the intensity of the reflected light (I), and the intensity of the incident light (I0), i.e. R=I/I0
• Fluorescence is the phenomenon where?


  Some molecules absorb radiation at short wavelength (usually UV radiation) and re-emit radiation at longer wavelength (usually visible radiation)
• The XRF technique allows to identify:

  the elemental composition of a sample according to the emission of energies of the generated secondary X-rays
• X-ray fluorescence (XRF) is a technique used to determine the elemental composition of a sample
• During a SEM analysis, the possibility of detecting backscattered electrons allows to:

  determine the elemental composition of a certain volume portion of the sample, whose thickness depends on the energy of the primary beam and the chemical-physical nature of the sample.
• Azurite and malachite are two pigments that both contain Cu, O, C and H. X-ray powder diffraction (XRPD) allows to discriminate the two pigments based on their different structure.
• The XRPD of a glass produce broad and not resolved diffraction pattern,with no evident Bragg peaks, as consequence of the absence of long-range ordering of the material.
• Proton-induced X-ray Emission (PIXE) in raster scanning mode allows to perform 2D chemical imaging
• X-ray absorption spectroscopy (XAS) measured in the extended region of the absorption edge (EXAFS) of a specific element can be used for?

  Detecting the near neighbor atomic/configurational arrangement of the selected chemical element.

  Detecting the oxidation state of the selected chemical element
• In a Raman spectrum, the x axis reports usually the indication “Raman shift”,expressed in wavenumber units (cm-1). In the Raman experiment, the Raman shift is?


  Proportional to the energy difference between incident and anelastically

  scattered photon in the Raman experiment
• A common problem one meets performing Raman on Cultural Heritage objects is:

  Fluorescence (due to patinas, other degradation by-products, or the

  nature of the sample) can hide the Raman signals
• The “fingerprint region” in the IR spectrum is:

  A region at low wavenumber, below about 1200 cm-1 , characterized by

  many peaks, difficult to attribute to specific functional groups, but highly

  specific for a compound and useful for a search in database
• In Infrared spectroscopy, can you identify specific organic functional groups?

  Yes, because in IR you can obtain the atomic composition of your

  sample
• In the UV-VIS spectroscopy we probe:

  The electronic states of the molecules, and we get information about the “colour” in a physical meaning
• In Cultural Heritage investigations, FORS is widely applied to identify?

  Pigments and dyes, by comparison with a database of FORS spectra

  Binders and varnishes, identifying functional groups by their features in the FORS spectra
• Considering X-ray fluorescence spectroscopy (XRF), the emitted secondary x-rays are generated by:

  The emission of a core electron with the consequent formation of a hole.

  Once the hole is filled by an electron from the outer shells a secondary

  x-ray is emitted
• X-ray fluorescence spectroscopy allows to:

  determine the elemental composition and semi-quantitatively estimate

  their relative abundance.
• SEM-EDS allows to: obtain morphological and semi-quantitative/qualitative information on the elemental composition of the sample
• The detection of secondary electrons in a SEM analysis allows to highlight morphological details of the analyzed surface
• In a diffractogram (i.e., diffraction pattern) a single phase is characterized by he position of the peaks and their relative intensities
• It is possible to perform bulk imaging of metal objects (i.e. transmission

  radiography and tomography) by soft/hard X-ray and neutrons
• If I change the wavelength of the laser, in the Raman spectrum of the same material:

  The Raman shift of the peaks is always the same peak, but the intensity of the peaks can change.
• X-ray powder diffraction (XRPD) is an analytical technique based on:

  the constructive interference of the incident X-rays by the atomic planes with the subsequent generation of a diffraction pattern.
• The images obtained by collecting backscattered electrons are typically characterized by different brightness. In particular:

  elements with a high atomic number provide brighter images than elements with low atomic number
• Scanning electron microscopy coupled with energy dispersion spectrometry (SEM-EDS) point analysis in stationary mode allows to perform 2D imaging of chemical elements distribution.
• IR Spectroscopy: to characterize materials of a miniature

  • Advantage: Can provide information about the molecular composition of organic elements that may be present in the miniature.
  • Disadvantage: limited information on inorganic compounds.
• Raman spectroscopy: to characterize materials of a miniature:

  • Advantage: portable and non-invasive technique that provides information on molecular vibration, helping to identify pigments and other compounds that may be present.
  • Disadvantage: it is sensitive to fluorescence so the quality of the spectra will be damage.
• XRF Spectroscopy: to characterize material of a miniature:

  • Advantage: portable and non-invasive technique that helps to identify pigments and materials providing elemental composition
  • Disadvantage: it may not distinguish between pigments with same elements and may not capture information from the subsurface layers.
• IR spectroscopy: identify the elementary and molecular composition

  Description: IR radiation is directed onto the painted surface, the molecule in the paint absorbs specific wavelengths of IR light, causing molecular vibrations. The resulting spectrum provides information about the functional groups present in the pigments, binders, etc. Just works with organics.
• Raman spectroscopy: identify the elementary and molecular composition

  • Description: involves illuminating the painted surface with a laser light. The scattered light interacts with molecular vibrations, providing a spectrum that reveals information about the molecular composition of pigments and binders.
• XRD spectroscopy: identify the elementary and molecular composition

  • Description: involves directing X-rays at the painted surface and the resulting diffraction patter can be analyzed to identify the crystalline structure of the mineral pigments.
  • By analyzing the secondary X-rays the elemental composition of the pigments can be determined.
• UV-Vis spectroscopy: identify the elementary and molecular composition

  • Description: involves shining UV or Vis light on the surface and measure the absorbance or reflectance to identify pigments on their characteristic absorption bad.
• What is a Multi-spectral imaging?

  Imaging system that captures information in a limited number of bands/wavelengths, using a specific set of filters to isolate predefined wavelengths of interest.
• What is Hyper-spectral imaging?

  Imaging systems that captures data across a large number of continuous and narrow spectral bands, covering a wide range of the electromagnetic spectrum. This provides a detailed spectral signature for each pixel.
• What are some applications of Multi/Hyper spectral imaging?

  • Material identification
  • Authentication and forgery, detecting materials and techniques
  • Conservation and restoration, see alterations and degradation patterns
  • Mapping and documentation of the distribution of materials on surface
• What is a non-invasive technique?

  Methods that do not cause damage or alteration to the material or object under investigation. They typically involve measurements, imaging or analysis that are preformed without physically touching or extracting samples.