Spectroscopy. An introduction MENA3100,OBK,

Transcription

1 Spectroscopy An introduction MENA3100,OBK,

2 Spectroscopy spectroscopy, n. spectrum, 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. 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 frequencies) of electromagnetic radiation, from the longest radio waves to the shortest gamma rays of which the range of visible light is only a small part; any one part of this larger range. 3c. An actual or notional arrangement of the component parts of any phenomenon according to frequency, energy, mass, or the like. Cf. mass spectrum n., power n. 1

3 Spectroscopy vs. spectrometry -scopy, comb. form a formative element < Greek -σκοπία observation ( < σκοπεῖν 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).

4 Must disperse the colours

5 Refractive index is a function of colour

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7 Diffraction from a grating (gitter)

8 Interference

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

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

12 Charged particles can be manipulated by magnets

13 The detector may discriminate between energies

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

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

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

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

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

19 Quantitative vs. qualitative analysis

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

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

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

23 X-ray induced Transfer its energy to an electron If it leaves the sample we get a photoelectron The energy is E p = hn E B1 W X-ray photoelectron spectroscopy (XPS)

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

25 Electron induced Electron energy loss spectroscopy (EELS) Ineleastic scattering

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

27 Auger electron emission