M. CuffianiIPRD04, Siena, May 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. CuffianiIPRD04, Siena, May 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 stiffness  while keeping thin the sensitive silicon layer. Introduction

M. CuffianiIPRD04, Siena, May The NanoChanT project involved  nanotechnologies: - Nanochannels built in an insulator (alumina, Al 2 O 3 ) template with regular and uniform pattern (overall area: 1 cm 2 ) - 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 array

Metallic strips: pitch 500 nm; length 10 mm; area 5·10 3  m 2 R/O electronics: 50 x 100  m 2 ; area 5·10 3  m 2 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. CuffianiIPRD04, Siena, May 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 o C) Anodization of iperpure aluminum foils (1 cm 2 area, 100  m thickness) in acid solutions, under controlled conditions produces an oxide (Al 2 O 3, alumina) with self-organized and regular honeycomb structure. Alumina has a good mechanical strength and is a good electrical insulator

M. CuffianiIPRD04, Siena, May 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 nm; CN lengths can range from several  m to mm

M. CuffianiIPRD04, Siena, May Electrical properties of CN Depend on the curvature axis (chirality) of the graphene sheet Low resistivity (of the order  cm) High current densities (up to 10 9 – A/cm 2 ) 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) 1719 Y. Zhang et al., nanotube W leads 2,5  m

M. CuffianiIPRD04, Siena, May Results: nanochannels in alumina regular 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. CuffianiIPRD04, Siena, May 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 Al 2 O 3 A.F.M. 12 (2002) 1 W.B. Choi et al., our goal: grow CN in alumina templates  50  m thick

M. CuffianiIPRD04, Siena, May Results: deposition of catalyst SEM cross-section (with back-scattered electrons): ~ 20  m 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. CuffianiIPRD04, Siena, May Synthesis of CN Reactor for the synthesis of CN via Chemical Vapor Deposition (CVD) Thermal decomposition of hydrocarbons (CH 4, C 2 H 2 ) at temp. 600 – 900 °C, followed by carbon diffusion in the catalyst particles and carbon precipitation to form CN

M. CuffianiIPRD04, Siena, May Results: synthesis of CN (1) CN on SiO 2 : Ni nanoparticles as catalyst, C 2 H 2 as carbon precursor (p = 1 atm., T = 650 °C) top view of Ni nanoparticles on the SiO 2 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. CuffianiIPRD04, Siena, May 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. CuffianiIPRD04, Siena, May Results: synthesis of CN (3) SEM cross-section image of CN (  100 nm in diameter) grown in alumina. C 2 H 2 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 cm 2 ) alumina samples tend to warp under thermal treatment. Possible solutions under test

M. CuffianiIPRD04, Siena, May 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. CuffianiIPRD04, Siena, May 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   