a novel position detector based on nanotechnologies: the project
DESCRIPTION
A novel position detector based on nanotechnologies: the project. NanoChanT. M. Cuffiani. (Dipartimento di Fisica, Universita’ di Bologna). on behalf of the NanoChanT Collaboration. G.M. Dallavalle, L. Malferrari, A. Montanari, F. Odorici. (INFN, Sez. di Bologna). - PowerPoint PPT PresentationTRANSCRIPT
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)
M. Cuffiani IPRD04, Siena, 23-26 May 2004 2
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
M. Cuffiani IPRD04, Siena, 23-26 May 2004 3
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
M. Cuffiani IPRD04, Siena, 23-26 May 2004 5
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
M. Cuffiani IPRD04, Siena, 23-26 May 2004 6
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
M. Cuffiani IPRD04, Siena, 23-26 May 2004 7
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
M. Cuffiani IPRD04, Siena, 23-26 May 2004 8
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.
M. Cuffiani IPRD04, Siena, 23-26 May 2004 9
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
M. Cuffiani IPRD04, Siena, 23-26 May 2004 10
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)
M. Cuffiani IPRD04, Siena, 23-26 May 2004 11
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
M. Cuffiani IPRD04, Siena, 23-26 May 2004 12
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
M. Cuffiani IPRD04, Siena, 23-26 May 2004 13
Results: synthesis of CN (2)
TEM pictures of CN: well graphitized multi-wall CN (10-20 walls, spacing 0,34 nm)
Ni nanoparticles on top of CN
M. Cuffiani IPRD04, Siena, 23-26 May 2004 14
Results: synthesis of CN (3)
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
M. Cuffiani IPRD04, Siena, 23-26 May 2004 15
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
M. Cuffiani IPRD04, Siena, 23-26 May 2004 16
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