Viviana Carillo 11th Topical Seminar on Innovative Particle and Radiation Detectors (IPRD08) 1 - 4 October 2008 Siena, Italy

Use of Multi-Walled Carbon Nanotubes for UV radiation detection

A new nanostructured material: A new nanostructured material: CARBONCARBON

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 ERAThe Post-Silicon ERAThis material is CARBONCARBON in the form of

NANOTUBESNANOTUBES

What is CNT?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.

Carbon Nanotubes (CNTs)Carbon Nanotubes (CNTs)Molecular Nanowires (d ~ 1 nm, l ~ 1 µm)

|n-m|/3 ∈ N

SWNTsSingle Graphene Sheets

(d ≈ 0.7 ÷ 3 nm, L ≈ µm-range)

∉ NSemiconductor

Ballistic Conduction,

e-wave guides, SETs

Metal

Channel (FETs),

Luminescence

MWNTs

Coaxial graphene sheets (d ≈ 2 ÷ 100 nm, (dout ≈ 20AD, 100CVD nm)

L ≈ µm-rangeVias

Nanocomposites

Semiconductor CNT contribute to the fotoresponsivity, while the metallic CNT are necessary in order to extract the charges

Development of radiation detectors based on carbon nanotubes

http://gint.na.infn.it/

Patternization

GEOMETRYand

SUBSTRATES

100 µm

PtSi3N4

Sapphire

Silicon

Sapphire

Silicon

Aluminium Quartz

Comb-like electrodes

Electrodes

Microstrip

Radiation detector made of Multi-Walled Carbon

Nanotubes

World first

100 µm

Pt

Si3N4

Au + Pt250 nm

Sapphire

500 µmLaser CNT

50 Ω

355 nm

532 nm

1064 nm Oscillograph

Drain voltage

Important: No signal

amplificationA. Ambrosio et al: “A prototype of a Carbon Nanotube microstrip radiation detector”, Nuclear Instruments

and Methods in Physics Research A 589 (2008) 398–403

Dark current

CNT

30 nm

10 ps pulse shape

Signals detected with the first carbon Signals detected with the first carbon nanotube radiation detectornanotube radiation detector

Signal comparison at different wawelenghts

Collected electrons / Collected electrons / incident photonsincident photons

No signal amplification

No CNT annealing…..

as cast MWCNTas cast MWCNT

Col

lect

ed e

lect

rons

/ in

cide

nt

phot

ons

(E-0

6)

CNT absorbanceCNT absorbance(log(log1010 1/T) 1/T)

Photocurrent vs Photocurrent vs λλ

1.0 1.5 2.0 2.5 3.0 3.5 4.00.4

0.8

1.2

1.6

2.0

2.4

small area whole area

Photon energy (eV)

I norX

10-2

1 (As)

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

Absorbance

absorbance

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, 051911 2008

The main problemThe 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 re-absorbed.

The efficiency of such device is very low.

A different architecture under test

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.

Dark current

The answer of detector to a pulsed red light

Measured photocurrentMeasured photocurrent

Col

lect

ed e

lect

rons

/ in

cide

nt p

hoto

ns

(E-0

6)

Conversion Conversion efficiencyefficiency

Sapphire

ConclusionConclusion

CNTs demonstrate important CNTs demonstrate important photoconductive properties;photoconductive properties;

The maximum sensitivity is in the UV The maximum sensitivity is in the UV

region;region;

The first microstrip detector made of multi-The first microstrip detector made of multi-walled carbon nanotubes grown on walled carbon nanotubes grown on sapphire substrate have been realized.sapphire substrate have been realized.

Next …Next … Study of new architecture with CNTs Study of new architecture with CNTs

grown on silicon substrate;grown on silicon substrate;

Charge amplification inside the silicon Charge amplification inside the silicon substrate;substrate;

Nanotubes coatingNanotubes coating

…… ……..

Development of UV Single Photon Development of UV Single Photon Detector based on Carbon NanotubesDetector based on Carbon Nanotubes

INFN&

University of

L’AquilaBari

NapoliPerugiaRoma 2

Funded by INFN for the 2009 – 2011 three-year period