a novel position detector based on nanotechnologies: the project

M. Cuffiani IPRD04, Siena, 23-26 May 2004 1

A novel position detector based on nanotechnologies:

the project

M. Cuffiani

M. C., G.P. Veronese (Dip. di Fisica, Universita’ di Bologna)

G.M. Dallavalle, L. Malferrari, A. Montanari, F. Odorici

(Dipartimento di Fisica, Universita’ di Bologna) on behalf of

the NanoChanT Collaboration

R. Angelucci, F. Corticelli, R. Rizzoli (IMM-CNR, Sez. di Bologna)

(INFN, Sez. di Bologna)


Can available nanotechnologies be fitted to improve the performances of particle detectors ?

For instance: space resolution of silicon microstrip detectors is limited by charge spreading in the active layer; it would be enhanced if thinner active layers could be used. However: detection efficiency and mechanical stiffness of the system must be preserved use n.t. to achieve the necessary stiffnesswhile keeping thin the sensitive silicon layer.

Introduction


The NanoChanT project

involvednanotechnologies:

- Nanochannels built in an insulator (alumina, Al2O3) template with regular and uniform pattern (overall area: 1 cm2)

- Nanoconductors (carbon nanotubes) grown inside the alumina template, to be used as charge collectors between the active medium and the R/O electronics.

Possible alternative: metal nanowires

- Bonding nanoconductors – Si layer

The purpose of the Nano Channel Template project is the fabrication of a position particle detector which allows a sub-micrometer space resolution

Thin Silicon

R/O electronics

Basic idea

Nanotube arrayNanotube array

M. Cuffiani IPRD04, Siena, 23-26 May 2004

Metallic strips: pitch 500 nm; length 10 mm; area 5·103 m2

R/O electronics: 50 x 100 m2; area 5·103 m2

Same area

Carbon nanotubes: diameter 40 nm; pitch 100 nm.

p+

n+ & metal pixels pitch 500 nm

metal pad

Thin CMOS electronics

Thin SiO2

Thin Si (5 m)

Alumina 50 m thick

The nanochannel active layer detector


Nanochannels in alumina

typical size and pitch of nanochannels are 40 nm and 100 nm; they depend on the parameters of the process:-voltage (40 V – 190 V)-acid type (oxalic, phosphoric)-acid concentration (0,3 molar) -temperature (5 oC)

Anodization of iperpure aluminum foils (1 cm2 area, 100 m thickness) in acid solutions, under controlled conditions produces an oxide (Al2O3, alumina) with self-organized and regular honeycomb structure.

Alumina has a good mechanical strength and is a good electrical insulator


Carbon nanotubes (CN)

.

tubes made of a single sheet of graphene (SingleWallNanoTube) or more sheets (MultiWallNanoTube)

The regular geometry gives CN excellent mechanical and electrical properties

CN diameters are in the range 1 - 500 nm; CN lengths can range from several m to mm


Electrical properties of CN

Depend on the curvature axis (chirality) of the graphene sheetLow resistivity (of the order 100-200 cm)

High current densities (up to 109 – 1010 A/cm2)

our goal: low resistance ohmic contacts CN-metal

.

Stability of resistence w.r.t. temperature and time

B.Q. Wei et al.,A.P.L. 79 (2001) 1172

Science 285 (1999) 1719Y. Zhang et al.,

nanotube

W leads

2,5 m


Results: nanochannels in aluminaregular nanopore array that extends over several mm; various pore diameters and pitches;layer thickness up to 100 m

SEM side view from the top-edge of the porous alumina sample.

SEM top view: pore size 40 nm, pitch 100 nm.


CN inside alumina

Alumina nanochannels are suitable to grow aligned CN, after the deposition of a catalyst (Ni, Co, Fe) at the bottom of each pore. So far, in the literature, CN successfully grown inside alumina templates having thickness a few (6) m. Not enough for our purposes.

(insulator)

(metal or semiconductor)

Carbon Nanotubes

Al2O3

A.F.M. 12 (2002) 1

W.B. Choi et al.,

our goal: grow CN in alumina templates 50 m thick


Results: deposition of catalyst

SEM cross-section (with back-scattered electrons): ~ 20m thick alumina layer. Pores: size 30nm, pitch 100nm.

Co wire lengths up to 5 m investigate the possibility to grow metal nanowires over the whole nanochannel length, as a possible alternative to CN.

Cobalt

Alumina

Aluminum

First step: electrodeposition of metal (Co) catalyst on pores bottom- Co based electrolyte- AC: 200 Hz, 16 V (rms)


Synthesis of CN

Reactor for the synthesis of CN via Chemical Vapor Deposition (CVD)

Thermal decomposition of hydrocarbons (CH4,

C2H2) at temp. 600 – 900

°C, followed by carbon diffusion in the catalyst particles and carbon precipitation to form CN


Results: synthesis of CN (1)

CN on SiO2: Ni nanoparticles as catalyst, C2H2 as carbon

precursor (p = 1 atm., T = 650 °C)

top view of Ni nanoparticles on the SiO2 substrate, before CN growth

“carpet” of oriented CN (20 m length, 50 nm diameter)

first results of the process: grow CN on flat substrates



TEM pictures of CN: well graphitized multi-wall CN (10-20 walls, spacing 0,34 nm)

Ni nanoparticles on top of CN



SEM cross-section image of CN (100 nm in diameter) grown in alumina. C2H2

as carbon gas; T = 650 °C

Cobalt on top of CN

Alumina

CN

CN in alumina: tuning of the processes is ongoing

Problem: large area (1 cm2) alumina samples tend to warp under thermal treatment. Possible solutions under test


Bonding CN – metal layer - Si

TiN (20 nm) Ti metallizat.

CN

Ni (2 nm)

anode

Formation of conductive TiC during CN growth

particle

(1) Field emission properties of CN to test the bonding between CN and metal

(2) Measure charge collection efficiency using particles

Si substrate

p+

n+

n Si diode


Summary

Alumina growth of ordered arrays of nanochannels

Carbon Nanotubes growth of well graphitized vertically aligned MWCN on flat substrates; grow CN inside nanochannels of 50 m length

Catalyst deposition of Co nanoparticles (possibly nanowires) on pore bottom ends

Bonding field-emission tests to check the bonding CN – Si diode.

ongoing

ongoing

a novel position detector based on nanotechnologies: the project

Documents

nm pitch

pitch of nanochannels

nm cn lengths

alumina template

nm length

carbon nanotubes cn

cn excellent mechanical

cm2 area