E.Vittone Experimental Physics Dept. Torino University, INFN-INFM b

1. E.VittoneExperimental Physics Dept. Torino University, INFN-INFMb LIGHT DETECTION WITH SPECTRAL ANALYSIS AT THE LEGNARO NUCLEAR MICROPROBE: APPLICATIONS IN MATERIAL AND EARTH SCIENCES

2. ALCHIMIA Analysis of Light and Charge Induced by Ion Micro beAms • IBICC and IL characterisation of semiconductor and insulator materials and devices • IL / PIXE applications in Art, Archeology, Earth (Planetary) Sciences • Coordinator: Prof. C.Manfredotti (University of Torino ) • Collaborations: Physics Dept., Univ. of Padova (P.Rossi), • Natural History Museum, Univ. of Florence (G.Pratesi) • The experimental activity was carried out at the microbeam line of the National Laboratory of the Italian Institute for Nuclear Science in Legnaro.

3. Legnaro microbeam line IL

4. Legnaro microbeam chamber Sample Holder

5. Inside the microbeam chamber PIXE IL STIM Beam SELT

6. Inside the microbeam chamber

7. Inside the microbeam chamber Proton Beam Light Guide Parabolloidal Mirror Sample

8. IL apparatus Bellows Variable slits Photomultiplier Chamber Mirrors

9. Scheme of IL apparatus 1200 l/mm blazed at 500 nm, spectral range 300-900 nm HAMAMATSU R376 fused silica window (spectral range 160-850 nm). Monochromator F=0.3 m, aperture = F/4.2

10. The IL apparatus installed at LNL is a modified version of MONO-CL produced by Oxford Instruments for high resolution cathodoluminescence . Light collection : retractable (up to 75 mm) module with a parabolloidal aluminium mirror (LCE:80%), waveguide, quartz lens. Operation: monochromatic/panchromatic mode Monochromator: focal length=0.3 m, aperture = f/4.2; plane grating:1200 l/mm blazed at 500 nm, spectral range 300-900 nm Linear dispersion of the grating: 2 nm/mm; maximum resolution: 0.05 nm. Photomultiplier: HAMAMATSU R376 with fused silica window (wavelength range 160-850 nm).

11. Spectral Efficiency

12. The IL apparatus installed at LNL Acquisition: IL Spectroscopy: Oxford Instruments Photo Amplifier system (PA3) for power supplies, signal amplification and stepper motor drive electronics for the monochromator. IL imaging: amplification electronic chain (based on the AMPTEK 250 charge sensitive preamplifier and AMPTEK 275 hybrid differential OP-amp) which is integrated into the existing microprobe data acquisition system. The IL system can be easily moved from the ion microbeam analysis chamber and installed into a SEM (StereoScan 420, LEICA) for high-resolution cathodoluminescence (CL) imaging and spectroscopy.

13. Synergetic1 combination of PIXE and IL High ion microbeam current measurements Cubic boron nitride Libyan Desert Glass Diamond Tips Synergetic combination of IBICC and IL low ion microbeam current measurements (less than 0.1 fA) Diamond 1K.G.Malmqvist, M.Elfman, G.Remond, C.Yang, , Nucl. Instr. and Meth. in Phys. Res. B, 109/110 (1996), 227-233

14. Application of IL technique: three examples cBN Diamond Lybian Desert Glass (LDG)

15. Cubic boron nitride (cBN) Properties: cBN has physical and chemical properties isomorphic to those of diamond: extreme hardness, wide optical gap (6 eV), chemical inertness, high electrical resistivity and high thermal conductivity. Can be doped both p and n type and shows high thermal stability at high temperature and a lower solubility on ferrous material than diamond. Applications: hard coating and semiconductor layers in high temperature electronic devices . Sample details: amber c-BN powders for grinding application obtained from graphitic BN (h-BN) by means of high pressure and high temperature techniques and using Ca3N2+LiF+NH4F as catalyst.

16. cBN CL EPMA CL SEM

17. 100 mm IL IL SEIM PIXE IL

18. IL: two main bands centred at 420 nm and 600 nm CL: A broad band around 420 nm. PIXE Ca: due to the precursor (Ca3N2) used during the synthesis. Na, Si and Al are the main impurities of the originary h-BN. S: is due to the tar in the carbon tube; traces of sulphate remain on the sink surface after the various chemical treatments for c-BN separation. EPMA: only N and S Interpretation: We can then postulate that the luminescence is generated in the bulk of the material (the penetration range of protons is about 24 mm and the penetration of 20 keV electrons is of the order of some micrometers) and is probably related to Ca which acts as activator.

19. Libyan Desert Glass (LDG) is a natural glass composed of nearly pure silica (98 wt %). Discovered in 1932 by P.Clayton and L.Spencer in the Great Sand See in the Western Desert of Egypt, one of Earth’s most remote and inhospitable regions.

20. The formation of this glass, because of its unusual composition has for long been considered as mysterious. Probably it is the result of a meteorite impact in the Sahara sands, which ejected melted sand thrown into space and then shattered like broken glass upon re-impact. “It seemed easier to assume that it had simply fallen from the sky” (Spencer 1937).

22. A pectoral with the Sun god represented by both the scarab and the falcon which are fused as one. Above the scarab is the bark of the Moon with the eye of Horus representing the Moon. Composed of gold, lapis lazuli, calcite, turquoise, andglass. It was found on the mummy of Tutankhamun. LDG raw material was employed to carve the central motif (V.de Michele,Sahara,10(1998),107

23. LDG IL map centered at 400 nm

24. IL: • Matrix: Intense blue luminescence • PIXE • Matrix: Al, Ti, Fe, ;“Black region”: none • Interpretation: • The granular structure is composed of pure silica (lechatelierite protonucleus) enclosed in impure silica matrix. • Origin:quartz grains of the precursor rock (sand or sandstone) vitrified at very high temperature as suggested by a direct comparison with a local fulgurite and a substrate rock (Nubian Sandstone)1. • It corroborates the interpretetion of the LDG as the result of a meteorite impact in the Sahara sands, which ejected melted sand thrown into space and then shattered like broken glass upon re-impact. • 1Piacenza B: Proceedings of the “Silica ‘96” Meeting, Bologna 1997.

25. Diamond • RD-42 collaboration aimed to develop diamond detectors for high energy physics experiments. • IBICCcharacterisation of CVD diamond detectors (since 1994) at the Ruder Boskovich Institute of Zagreb and at LNL. • IBICC/ILcharacterisation in panchromatic mode (since 1997) at LNL. • Main results: • The polycristalline nature of CVD diamond strongly influences the transport properties of detectors. • The homogeneity of the charge collection response has to be taken into account for the fabrication of detectors for tracking applications.

26. Band A decay in sample CM1 Proton damage in diamond Sample: CM1 High irradiation dose produce damage. In diamond it is possible to observe an intensity decrease of band A and 615 nm peak. Also there is a 510 nm H3 centre creation. Sample: R117

27. IBIL response of detector grade diamond Sample: Nruv Sample: CM1 Sample: Nluc Sample: CM3

28. Diamond ESR measurements for paramagnetic nitrogen concentration were performed. In table, gray cells are referred to samples with not good detection performances. It seems that high nitrogen concentration create a broad band peak at 600-630 nm and that this peak could be taken as an index of bad detection performance. The A-band peak is due to a N-N centres. It is a broad band peak (about 0.5 eV) centred at 433 nm. High proton doses should create a N-V-N centre (peak at 510 nm in IBIL spectrum) due to the damaging of A-band centres.

29. Dark IBICC Spectra LIGHT IL spectrum

31. IL C.Manfredotti, F.Fizzotti, P.Polesello, E.Vittone, F.Wang, Phys. Stat. Sol. (a) 154, (1996) 327

32. IBICC Columnar structure; illumination improves the homogeneity of the lateral IBICC map. IL: Only “blue A-Band”; luminescent regions corresponds to regions where illumination is more effective on IBICC maps. Electroluminescence (EL): The EL spectrum is similar to the IL spectrum. The recombination is monomolecular and is due to a radiative recombination from the valence (or conduction) band to a deep recombination level located at about 3 eV1. 1C.Manfredotti et al. Phys. Stat. Sol. (a) 154, (1996) 327 .

33. INTERPRETATION • The same deep recombination level, located at 3 eV from the valence band, is responsible for free carrier trapping, and hence for the creation of space charge regions, and for luminescence. • Light emission is then more intense in regions where a high density of such traps occurs and hence where a strong polarisation field is present. • Illumination with blue light (effective only using photon energies higher than 2.5 eV) empties this trapping centre, removes the space charge and improves the charge collection efficiency.

34. Conclusions • Even considering IL a ”semi-quantitative" IBA technique, the analytical combination of PIXE or IBICC and IL is useful to study structural and opto-electronic properties of materials and devices. • The IL apparatus at the LNL allows the chromatic analysis of luminescence to be performed with high photon collection efficiency. This feature is necessary to perform coupled IBICC/IL measurements in wide band gap semiconductors as diamond. • The more commonly used PIXE/IL coupling is suitable to individuate structures in the bulk of c-BN grains and lechatelierite protonuclei in Libyan desert glass which are not clearly visible using other "traditional" nuclear microbeam techniques.