Spectroscopy An introduction MENA3100,OBK, 24.01.18 Spectroscopy - PowerPoint PPT Presentation

Spectroscopy An introduction MENA3100,OBK, 24.01.18

Spectroscopy spectroscopy, n. The art of using the spectroscope; that branch of science which involves the use of the spectroscope. In mod. use, the investigation of spectra by any of various instruments. spectrum, n. 3 a. The coloured band into which a beam of light is decomposed by means of a prism or diffraction grating. Also, a dark band containing bright lines produced similarly; such a (coloured or dark) band, or the pattern of lines in it, as characteristic of the light source; hence, the pattern of absorption or emission of light or other electromagnetic radiation over any range of wavelengths exhibited by a body or substance. 3b. The entire range of wavelengths (or 3c. An actual or notional arrangement frequencies) of electromagnetic radiation, of the component parts of any from the longest radio waves to the phenomenon according to frequency, shortest gamma rays of which the range energy, mass, or the like. Cf. mass of visible light is only a small part; any spectrum n., power n. 1 one part of this larger range.

Spectro scopy vs. spectro metry -scopy, comb. form a formative element < Greek - σκοπία observation ( < σκοπε ῖ ν to examine, look at: see -y suffix 3 ), used to form ns. denoting: (a) (formerly) divination by inspection of something ( ooscopy , ornithoscopy ); (b) scientific examination by means of some instrument ( stethoscopy , telescopy ); (c) medical examination of some part of the body ( gastroscopy , peritoneoscopy ). -metry, comb. form A terminal element of nouns with the general sense ‘action, process, or art of measuring (something specified by the initial element)’.

Must disperse the colours

Refractive index is a function of colour

Diffraction from a grating (gitter)

Interference

Electromagnetic radiation X-rays most interesting for us Diffraction from crystal lattices

Electrons Wave-particel duality Louis de Broglie The wave nature of electrons

Charged particles can be manipulated by magnets

The detector may discriminate between energies

Why spectroscopy? We typically want information about Composition Energy of chemical bonds, bandgap …

(For us) it may be useful to separate into Absorpsjon and emission spectroscopy

Absorpsjon spectroscopy From the sun Fraunhofer lines (Helium: Pierre-Jules-César Janssen, 1868, 587.49 nanometers)

Interactions X-rays: Electrons Electrons: Electric field (electrons and protons) Neutrons: Atomic nucleus (almost true)

Most relevant absorpsion for us: Electron energy loss spectroscopy (EELS)

Quantitative vs. qualitative analysis

Exitation: Can give absorpsjon De-exitation (relaxation): Can give us interesting signals Heat Electromagnetic radiation Electron "beams"

Exitation by: De-exitation by: Ultraviolet light Light Fluorescence Phosphorescence X-rays X-rays Electrons Electrons X-rays Electrons

Read Spectroscopy with incident x-rays and with incident electrons By Johan Taftø

X-ray induced Transfer its energy to an electron If it leaves the sample we get a photoelectron The energy is E p = h n – E B 1 – W X-ray photoelectron spectroscopy (XPS)

X-ray induced X-ray absorpsjon as function of wavelength/energy X-ray absorpsjon spectroscopy (XAS)

Electron induced Electron energy loss spectroscopy (EELS) Ineleastic scattering

X-ray emission Energy dispersive spectroscopy (EDS) Wavelength dispersive spectroscopy

Auger electron emission