Multiwalled carbon nanotube films as temperature nano-sensorsP. Ciambelli2,3 , A. Di Bartolomeo1, 3,, M. Sarno2,3, F. Giubileo1,4, C. Altavilla2,3, D. Sannino2,3, L. Iemmo1,S. Piano1, F. Bobba1, 3, A. M. Cucolo1, 3

1 Department of Physics "E.R. Caianiello", University of Salerno, via S. Allende, 84081 Baronissi (SA), Italy. 2 Department of Chemical and Food Engineering, University of Salerno, via Ponte Don Melillo, 84084 Fisciano (SA), Italy3 NANO_MATES, Research Centre for NANOMAterials and nanoTEchnology at University of Salerno, c/o Department of Physics "E.R. Caianiello", University of Salerno, 84081

Baronissi (SA), Italy 4 CNR-INFM Laboratorio Regionale SUPERMAT, via s. Allende, 84081 Baronissi (SA), Italy

CNT synthesis, film preparation and characterization

MWCNT film as temperature sensor

R(T) measurements

Multiwalled carbon nanotubes (MWNTs) Synthesis

MWNTs (length 100-200 µm, external diameter 10-25 nm, internal diameter 5-10

nm) were synthesized by ethylene catalytic chemical vapour deposition (CCVD) on

Co/Fe-Al2O3 catalyst. After HF treatment high purity multiwalled carbon

nanotubes (>97%) were obtained.

BuckyPaper free-standing film preparation

0.5 g of MWNTs were suspended in 100 g of H2O in presence of 0.1 mg of sodium

dodecyl sulfate, sonicated and then vacuum filtered through a membrane support.

After drying, a quite rigid paper was removed from the support.

SEM and Raman Spectroscopy characterisation

Films with bundle organization, of different thickness (300-500 µm) and density,

were produced.

A 4-probe method was used to measure the CNT film

resistance. Pt and Ge/Si sensors, close to the CNT film, were

added to monitor the temperature.

R(T) had usually a non-metallic (with negative dR/dT)

behaviour over a wide range of temperatures (4 to 420 K).

A transition from non-metallic to metallic behavior occurring

at a crossover temperature of few tens degrees around 0°C

was sometimes observed. A heterogeneous model (see Kaiser

A. B., Dusberg G., Roth S., Phys. Rev. B, 57, 3, 1998, 1814-

1821) involving regions of highly anisotropic metallic

conduction separated by tunneling barrier regions can explain

such mixed behavior by means of the competing mechanisms

of the metallic resistance rise and the barrier resistance

lowering for increasing temperature.

)]TT/(Texp[R)T/Texp(R)T(Rsctmm

++−=

The monotonic behaviour (either non-metallic or

metallic) suggests that multiwalled carbon nanotube

films can be used as miniaturized temperature sensors

with a temperature coefficient of resistance (TCR) of

the order of 10-3/°C, comparable with the ones for

other temperature sensors (with Pt, Si, Ge).

However, the nano-size of CNTs results in a very high

sensitivity to the environmental temperature change

and in an excellent time response, which is highly

desirable for local measurements in systems with very

rapid temperature variations and where the

perturbation introduced by the thermometer has to be

reduced as much as possible.

The CNT sensor shows a faster response than the Ge, Si and

PT ones. A long term stability (less than 1%) and a good

behavioural accordance with the measurements of traditional

thermistors have been observed in continuous, few days long,

operating cycles. An ideal sensor reaches the same

maximum/minimum resistance for the same

maximum/minimum temperature. This applies to our CNT

film for temperature swinging for several hours.

Nanotech 2008 – Boston June 1-5 2008

0 50 100 150 200 250 300

0,6

0,8

1,0

1,2

1,4

Temperature (K)

Resis

tan

ce

(O

hm

)

220 240 260 280 300 320 340 360 380 400 420 440

0,92

0,94

0,96

0,98

1,00

1,02

1,04

1,06

1,08

1,10

Resis

tance

(O

hm

)

Temperature (K)

T down T up

T down

T down T up

220 240 260 280 300 320 340 360 380 400 420

0,74

0,75

0,76

0,77

0,78

0,79

0,80

0,81

Re

sis

tance

(O

hm

)

Temperature (K)

Typical dimension of the bucky paper samples: 8 mm x 3 mm x 0,3 mm

As prepared MWNTs (TEM image)

CNT film (High magnification SEM image)

Raman spectra

University of SalernoCentre NANO_MATES

Transition from non-metallic

to metallic behaviour

Non-metallic behaviour Non-metallic behaviour

400 600 800 1000 1200 1400 1600 1800 2000

1,35

1,40

1,45

1,50

1,55

1,60

1,65

1,70

Tem

pera

ture

(K)

1/R

esis

tan

ce

CN

T

(1/O

hm

)

Time (s)

400 600 800 1000 1200 1400 1600 1800 2000

50

100

150

200

250

Ge Thermometer

1/R-CNT

0,0 0,5 1,0 1,5 2,0 2,5 3,0

0,7

0,8

0,9

1,0

1,1

1,2

Termometer

1/R-CNT

Te

mp

era

ture

(K)

Time (h)

0,0 0,5 1,0 1,5 2,0 2,5 3,0

0

5

10

15

20

25

30

35

1/R

esis

tan

ce

CN

T

(1/O

hm

)

Ge Thermometer

0 4 8 12 16 20 24

1,06

1,07

1,08

1,09

1,10

1,11

1,12

1,130 4 8 12 16 20 24

292

293

294

295

296

297

298

Tem

pe

ratu

re (K

)

Time (h)

Co

nd

ucta

nce (

1/O

hm

)

Pt Thermometer

Si Thermometer

Typical dimension of the bucky paper samples: 8 mm x 3 mm x 0,3 mm

220 240 260 280 300 320 340 360 380 400 420 440

0,92

0,94

0,96

0,98

1,00

1,02

1,04

1,06

1,08

1,10

Resis

tance

(O

hm

)

Temperature (K)

T down

T up

T down

T down

T up

CNT film (SEM image)

In addition, the working range for the CNT sensor is larger and its small size

implies a lower power consumption (< 1 µW).

Raman spectra confirm that the treatment

did not introduce defects into CNTs.