Use of Multi-Walled Carbon Nanotubes for UV radiation detection

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1 Use of Multi-Walled Carbon Nanotubes for UV radiation detection Viviana Carillo 11th Topical Seminar on Innovative Particle and Radiation Detectors (IPRD08) 1-4 October 2008 Siena, Italy

2 A new nanostructured material: CARBON Since 15 years a new material is continuously increasing its importance so that people begin to consider it as the birth of a new era: The Post-Silicon ERA This material is CARBON in the form of NANOTUBES

3 What is CNT? A Carbon Nanotube is a single graphene sheet rolled up to form an empty cylinder. The electronic properties of one of these nano-objects depend on the chiral vector of the tube, representing the versus of the rolling in terms of the unit vectors of the hexagonal graphene lattice.

4 Carbon Nanotubes (CNTs) Molecular Nanowires (d ~ 1 nm, l ~ 1 µm) MWNTs SWNTs Single Graphene Sheets (d nm, L µm-range) N Semiconductor n-m /3 N Metal Coaxial graphene sheets (d nm, (dout 20AD, 100CVD nm) L µm-range Vias Nanocomposites Channel (FETs), Ballistic Conduction, Luminescence e-wave guides, SETs Semiconductor CNT contribute to the fotoresponsivity, while the metallic CNT are necessary in order to extract the charges

5 Development of radiation detectors based on carbon nanotubes

6 Patternization

7 Sapphire Comb-like electrodes Electrodes Microstrip Pt 100 µm Si3N4 Silicon Aluminium Sapphire Silicon Quartz GEOMETRY and SUBSTRATES

8 Radiation detector made of Multi-Walled Carbon Nanotubes 30 nm P t Si3N4 CNT 100 µm 500 µm Sapphire Au + Pt 250 nm Dark current 10 ps pulse shape Laser 355 nm 532 nm 1064 nm CNT 50 Ω Drain voltage Oscillograph Im p No ortan am si g t : n pli f i c al at i on World first A. Ambrosio et al: A prototype of a Carbon Nanotube microstrip radiation detector, Nuclear Instruments and Methods in Physics Research A 589 (2008)

9 Signals detected with the first carbon nanotube radiation detector

10 Signal comparison at different wawelenghts

11 Collected electrons / incident photons (E-06) Collected electrons / incident photons No signal amplification No CNT annealing.. as cast MWCNT

12 CNT absorbance (log10 1/T)

13 Photocurrent vs λ small area whole area 0.3 Absorbance Photon energy (ev) absorbance InorX 10 (As) 0.7 Photocurrent normalized to the number of photons Inor vs photon energy, obtained illuminating the whole surface of a MWCNT sample with filtered light ( ) as well as small part of the surface with laser spots (*). Continuous line indicates the absorbance spectrum of the same MWCNT sample. M. Passacantando et al: Photoconductivity in defective carbon nanotube sheets under ultraviolet visible near infrared radiation, APPLIED PHYSICS LETTERS 93,

14 The main problem Signal generated inside CNTs is collected by means of electrodes in a plane orthogonal to the nanotube axis. The charge must migrate by tunneling and has a great probability to be reabsorbed. The efficiency of such device is very low.

15 A different architecture under test Dark current Nanotubes growth on a silicon substrate may create a diode-like junction with surprising photoresponsivity properties. With this architecture the charge generated inside CNTs by radiation can be collected trough the silicon substrate without great attenuation.

16 The answer of detector to a pulsed red light

17 Measured photocurrent

18 Collected electrons / incident photons (E-06) Conversion efficiency Sapphire

19 Conclusion CNTs demonstrate important photoconductive properties; The maximum sensitivity is in the UV region; The first microstrip detector made of multi- walled carbon nanotubes grown on sapphire substrate have been realized.

20 Next Study of new architecture with CNTs grown on silicon substrate; Charge amplification inside the silicon substrate; Nanotubes coating.

21 INFN & University of L Aquila Bari Napoli Perugia Roma 2 Development of UV Single Photon Detector based on Carbon Nanotubes Funded by INFN for the three-year period