Wang Zh.M. One-Dimensional Nanostructures

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234 B.-K. Kim et al.

SWNT-based sensors bearing the appropriate functional groups have been in-

vestigated as potential sites for chemical or biological analyte recognition [27a.,4].

Pd nanoparticles [25], polyethyleneimine (PEI)-starch functionalization [47], and

naﬁon [48] have been suggested as suitable surfaces for H

and CO

sensors, as

well as for humidity and NH

sensors, respectively. In addition, SWNT-FETs func-

tionalized with antibodies or receptor molecules have been shown to exhibit strong

propensities for the selective detection of biological molecules such as proteins and

other small molecules [8].

In this section, we investigate the effect of metal cluster decoration on the elec-

trical transport properties and sensing characteristics of SWNT-FETs. It has been

demonstrated that the use of metal cluster coatings on nanoscale structures can de-

plete or populate carriers locally, thereby making the device either sensitized or

ineffective with respect to molecular adsorption [24, 59]. Here, we apply this con-

cept to p-type SWNT-FETs, and investigate the effects of different metal clusters

on the electrical transport and chemical sensing properties of carbon nanotubes.

First, the electrical transfer characteristics of the bare SWNT-FETs were mea-

sured, and then Al nanoparticle layers (approx. 5

A in thickness) were thermally

evaporated onto the devices at high vacuum. The gas sensing experiments were

conducted in a vacuum chamber, with Ar, NO

,NH

, and H

gases supplied with

precise ﬂow control.

Figure 9.15 shows the current–gate voltage characteristics (I–V

)oftheSWNT-

FETs before (black) and after (gray) metal cluster decoration. As shown in

Fig. 9.15a, the device exhibited clear p-type semiconducting behavior, with com-

plete depletion of the current around V

= 1V. However, the SWNT-FET was

Fig. 9.15 The transfer characteristics (I–V

) of SWNT-FETs before (black) and after (gray) metal

cluster decoration with (a) Pd and (b) Al nanoparticles. The current was measured at V

= 1, 0,

and −1V. In panel (a), the current was symmetric with respect to V

before and after decoration

with the Pd nanoparticles, so we only show the current measured at positive bias. In panel (b),

the current became highly asymmetric with respect to V

after the SWNT-FET was coated with

Al nanoparticles. The insets in (a) and (b) show AFM images of the metal-decorated carbon nan-

otubes. Reused with permission from Byoung-Kye Kim, Noejung Park, Pil Sun Na, Hye-Mi So,

Ju-Jin Kim, Hyojin Kim, Ki-Jeong Kong, Hyunju Chang, Beyong-Hwan Ryu, Youngmin Choi and

9 Designing the Carbon Nanotube Field Effect Transistor 235

found to lose much of its gate dependency after the nanotube was coated with Pd

nanoparticles. It is believed that the electrical conduction occurs through the nan-

otube, rather than through the Pd ﬁlm. Indeed, if the Pd ﬁlm did provide continuous

paths for electron conduction, then the magnitude of the current should be much

larger than that of the on-state p-channel current through the nanotube. Note that the

current shown in the gray curve in Fig. 9.15a is approximately 1.1µA irrespective

of the gate voltage. The AFM image in the inset in Fig. 9.15a also shows that the

Pd particles are unlikely to form continuous paths between the source and drain

electrodes. Instead, the loss of gate-dependency is ascribed to screening induced

by the Pd nanoparticles. By carrying out electrostatic calculations, we determined

that the metal nanoparticle monolayers (typically 5 nm in diameter, with a 3 nm

interparticle separation) are effective at screening the gate ﬁeld. Thus, Pd-decorated

SWNTs can be described as p-type degenerate semiconductors, and contain carriers

that are present even at positive gate voltages as a result of screening by the metal

particles. Note that Pd is a high work function metal, and thus the adsorption of Pd

particles onto the carbon nanotubes is expected to induce the formation of hole car-

riers. Figure9.15b shows the evolution of the electrical transfer characteristics of an

SWNT-FET coated with Al nanoparticles. Unlike the case in which Pd nanoparticle

coatings were used, a gate effect is observed for the Al-decorated SWNT-FETs. The

decreased conductance after Al decoration is consistent with the results discussed

in the previous section. The marked difference between this behavior and that of

the Pd-decorated SWNT-FETs may be either due to the difference between the

adhesion properties of Al and Pd, or to the difference between the work functions

of Pd and Al particles. As shown in the inset images in Fig. 9.15, Al deposited on

the nanotube tends to form large discrete particles, whereas the Pd nanoparticles

form much ﬁner particles with smaller interparticle spacings [57, 58]. Therefore,

the gate ﬁeld screening is likely to be greater following Pd decoration. Although the

Pd-coated devices exhibit ohmic transport behavior before and after nanoparticle

decoration, Al decoration results in the formation of a Schottky barrier, as discussed

later.

The sensitivity of the metal cluster-decorated SWNT-FETs to gas exposure was

also investigated.

Figure 9.16 shows the electrical transfer characteristics and gas sensing proper-

ties of the Al-decorated nanotubes. As shown in Fig. 9.16a, there is a signiﬁcant

decrease in the current immediately after Al decoration of the SWNT-FET (black

empty squares), which eventually partially recovers (gray ﬁlled circles and empty

dots). We also note that rightward shifts in the threshold voltage accompany the re-

covery in the current. Moreover, the observed decrease in the I

–V

slope can be

explained as a decrease in the work function of the electrode, whereas the shift in

the threshold voltage is due to an increase in carrier density [8]. Note that as ox-

idation proceeds, the work function of the Al surface increases to levels normally

associated with gold particles [41a.]. Thus, the partial recovery of the I

–V

slope

and the rightward shift in the threshold voltage (as shown in Fig. 9.18a) are largely

due to oxidation of the Al nanoparticle surfaces. Remarkably, many SWNT-FETs

exhibit diode-like, highly asymmetric behavior following Al decoration, as shown

236 B.-K. Kim et al.

Fig. 9.16 (a) I–V

characteristics of an Al-decorated SWNT-FET in ambient air conditions. Bias

voltage V

= 1V. The image inset shows the I–V

results for the bare (black) and Al-decorated

(gray) devices. (b) Gas sensing with bare (black) and Al-decorated (gray) SWNT-FETs. The back

gate voltage V

was maintained at −10V, whereas the source to drain bias was ﬁxed at 1 V. Reused

with permission from Byoung-Kye Kim, Noejung Park, Pil Sun Na, Hye-Mi So, Ju-Jin Kim,

Hyojin Kim, Ki-Jeong Kong, Hyunju Chang, Beyong-Hwan Ryu, Youngmin Choi and Jeong-O

in the inset in Fig. 9.16a. Such asymmetric I

–V

curves and the observed decrease

in the I

value are thought to be due to modiﬁcations of the contact barrier by the

Al nanoparticles in the metal–SWNT contact regions. It is likely that the adsorbed

Al particles increase the Schottky barrier in either the source or drain electrode,

thus inducing asymmetric I

–V

patterns. A few devices exhibited symmetric I–V

curves, which may result from the formation of Al particle layers on both electrodes.

Upon gas exposure, most of the Al-decorated SWNT-FETs were found to exhibit

greatly enhanced sensitivities in the range of 300–1,000%. Figure9.16b shows the

gas sensitivity of the bare (black) and Al-decorated (gray) SWNT-FETs. Before Al-

decoration, the sensitivity of the SWNT-FET is around 50%. However, this value is

signiﬁcantly enhanced (>1,000%) by Al decoration. This enhancement in sensitiv-

ity can be explained with one of two possible mechanisms. First, nanoscale Schottky

barriers are formed by the Al nanoparticle decorations at either the metal–SWNT

contact regions or on the nanotube itself. The formation of nano-Schottky barriers

will modulate the width of the conduction channel, such that the nano-Schottky bar-

rier itself will be modulated by molecular adsorption. The adsorption of NH

(or

) decreases (increases) the work function of the metal surface [27(a)], resulting

in a concomitant increase (decrease) in the Schottky barrier to hole transport. It was

observed that when the devices contained metallic nanotubes, the sensitivity im-

provement was not appreciable after decoration with Al nanoparticles. We note that

in these metallic devices the work function change as a result of metal electrode or

metal particle decoration is not expected to lead to modiﬁcation of the Schottky bar-

rier. Second, we cannot completely rule out the effects of modulation of the carrier

density in the nanotube body. Aluminum nanoparticles in the vicinity of the carbon

nanotube may increase the chemical reactivity toward the gas molecules [24,59].

9 Designing the Carbon Nanotube Field Effect Transistor 237

To clarify the origin of the sensitivity enhancement, we performed the following

experiment. First, we patterned nanotube devices so that only their source and drain

electrodes are exposed for metal cluster deposition. In the second type of device,

the AZ5214 photoresist and image reverse technique was used to deposit clusters

only on nanotubes. The electrical properties and sensor characteristics of both types

of devices were measured after careful lift-off. Figure9.17a and b show the sens-

ing characteristics of the contact-decorated and channel-decorated SWNT-FETs,

respectively. In both cases, a decrease in the conductance was observed after Al

cluster decoration. Figure 9.17a shows the sensing characteristics of the SWNT-FET

with contact electrodes that were decorated with Al clusters. The inset in Fig. 9.17a

shows an optical microscopy image of the device with its channel covered with

AZ5214. As shown in this ﬁgure, the sensitivity of the device, which was around

10% before contact decoration (the original device contained metallic nanotubes, so

the on/off ratio of the transistor was only 2), has improved to about 50%. In the case

of the channel-decorated SWNT-FET, almost no change or inferior sensitivity was

observed following Al decoration, as shown in Fig. 9.17b. Therefore, we conclude

that the observed sensitivity enhancement is mostly due to the modulation of the

contact barrier by the Al cluster decoration. This conclusion is conﬁrmed by the ob-

servation that the largest sensitivity enhancement was achieved with the SWNT-FET

that exhibited highly asymmetric I–V characteristics after Al decoration.

In summary, we investigated the effect of metal nanoparticle decoration on the

gas sensing capabilities of nanotube-based sensors. After coating the carbon nan-

otube with Al nanoparticles, the device was found to exhibit Schottky behavior,

i.e., the current passing through the nanotube was found to decrease. However,

the sensitivity to both NO

and NH

was found to be greatly enhanced by the Al

nanoparticle decoration. We suggest that metal-particle decoration could be used to

Fig. 9.17 (a) Gas sensing with bare (black) and contact-decorated (gray) SWNT-FETs. Bias volt-

ageV

= 1V. The inset shows an optical microscopy image of the device with its contact electrodes

open for Al decoration. (b) Gas sensing with bare (black) and channel-decorated (gray) SWNT-

FETs. Reused with permission from Byoung-Kye Kim, Noejung Park, Pil Sun Na, Hye-Mi So,

Ju-Jin Kim, Hyojin Kim, Ki-Jeong Kong, Hyunju Chang, Beyong-Hwan Ryu, Youngmin Choi and

238 B.-K. Kim et al.

tailor the transfer characteristics of nanoscale devices or to tune the sensitivity of

nanotube-based chemical and biological nanosensors.

9.3.4 Contact Engineering with Protein Nanoparticles

In this section we show that by modifying the contact barrier, metallic or semicon-

ducting carbon nanotubes can be transformed into ﬁeld effect transistors. By plac-

ing protein-coated nanoparticles in the metal–nanotube contact area, we achieved

p-type transport behavior in the device irrespective of whether the nanotube was

metallic or semiconducting.

Laser ablation grown tubes were spun over prefabricated alignment markers from

dichloroethane solution, and atomic force microscopy (AFM) was used to locate in-

dividual SWNTs. Electrical leads consisting of 5 nm Ti/30 nm Au were patterned

on top of the individual nanotubes by using e-beam lithography, and the electrical

characteristics of these devices were recorded as a reference. The devices were then

allowed to react overnight with a diluted solution of streptavidin-coated polystyrene

nanoparticles (∼120nm diameter) or a solution of streptavidin-coated 10 nm diam-

eter Au particles. Deionized water (pH 5.0) or 10 mM PBS (phosphate buffered

saline, pH 7.4) was used to dilute the protein-coated nanoparticles. After the reac-

tions with the protein-coated nanoparticles solution, the samples were washed with

clean buffer or DI water, and blown dry with dry N

gas. The electrical transport

properties of the samples reacted with the protein-coated nanoparticles were mea-

sured, and the sample morphologies were characterized with AFM.

Figure 9.18a shows the typical I–V

characteristics of the nanotube devices before

(black) and after (red) the adsorption of the protein-coated nanoparticles. Before the

reaction with the protein-coated nanoparticles, the devices exhibited p-type gate

effects with a mobility of

= 263cm

/Vs, where it was assumed that the gate

capacitance is given by C ≈2π

εε

L/ln(h/r) ∼ 6.08×10

−17

F, where L equals the

tube length (2µm for this sample), r is the radius of the nanotube, and h is the di-

electric layer thickness. The tube diameter was measured with AFM and found to

be around 1 nm, and the dielectric SiO

layer thickness was 200 nm. As shown in

Fig. 9.18a, this device has a rather poor on/off ratio (∼6) and a large subthresh-

old swing (>5V/decade) before the adsorption of the protein-coated nanoparticles.

Here, the subthreshold swing S is deﬁned as S =(dlogI/dV

)

−1

. After reaction

with the streptavidin-coated nanoparticles, the device exhibits a highly enhanced

p-type gate response. It is noteworthy that the channel closes completely at around

= 0.5V, whereas there was substantial current up to V

= 5V before the reac-

tion with the streptavidin-coated nanoparticles. The on/off ratio was increased to

and S (subthreshold swing) was decreased to 0.15 V/decade by the reaction

with the protein-coated nanoparticles. Considering that S is usually near 2V/decade

for this thickness of SiO

gate dielectric layer (∼200nm), this value for S is re-

markably small. If we assume that the self capacitance of each single tube does

not change, the enhancement of the mobility due to the reaction is ∼1900cm

/Vs.

9 Designing the Carbon Nanotube Field Effect Transistor 239

Fig. 9.18 Transport characteristics of semiconducting nanotube FETs with streptavidin-coated

polystyrene nanoparticles adsorbed (a) in the metal nanotube contact area, and (b) near the nan-

otube body far from the contact. The black lines in panels (a) and (b) are the I–V

curves before

protein adsorption, and the gray lines are those after protein adsorption. The insets in (a) and

(b) show AFM images of the devices after reaction with streptavidin-coated nanoparticles. Reused

with permission from Pil Sun Na, Noejung Park, Jinhee Kim, Hyojin Kim, Ki-Jeong Kong, Hyunju

Chang and Jeong-O Lee, A Field Effect Transistor Fabricated with Metallic Single-Walled Carbon

Taylor & Francis Ltd.

The inset in Fig.9.20a shows an AFM image of the device after the reaction with

the streptavidin-coated nanoparticles. As indicated by the circle, large clusters of

streptavidin-coated polystyrene nanoparticles were adsorbed only at the contact area

between the metal electrodes and the SWNT. When the protein-coated nanoparticles

were situated on the nanotube body in areas far from the contact region, there was

no apparent change in the conductance (Fig. 9.18b).

For metallic tubes, a more marked change occurs after the reaction with the

streptavidin-coated nanoparticles. Figure 9.19a shows the changes in the gate de-

pendent conductance after the sample had reacted with streptavidin-coated 10 nm

Au nanoparticles. Before the reaction, the sample exhibited typical metallic be-

havior (black curve), i.e., the conductance does not vary with variation of the gate

voltage from −5 to 5 V. After the sample had reacted with the streptavidin-coated

10 nm Au particles, the conductance increases for V

< 1V, and decreases abruptly

to zero for V

> 1V, i.e. there is a FET-like gate response from the metallic nan-

otube. The on/off ratio, mobility, and S of the device become 10

,215cm

/Vs, and

0.8 V/decade, respectively. It is also noteworthy that the conductance of this de-

vice saturates immediately after the p-channel current turns on, unlike the behavior

of Si-MOSFETs and typical SWNT-FETs. We believe this result conﬁrms that the

nanotube in our device is indeed metallic. The inset in Fig. 9.19a shows the AFM

images of the device before (left) and after (right) the reaction with the streptavidin-

coated 10 nm Au particles. A large cluster of streptavidin-coated Au particles is

marked with a black dotted circle in the inset on the right.

240 B.-K. Kim et al.

Fig. 9.19 (a, b) Transport characteristics of the two metallic nanotube devices decorated with

streptavidin-coated 10 nm Au particles. The black and gray curves in panels (a) and (b) are the

I–V

curves before and after protein adsorption, respectively. In panels (a) and (b), the left and right

insets show AFM images of the device before and after protein adsorption, respectively. Reused

with permission from Pil Sun Na, Noejung Park, Jinhee Kim, Hyojin Kim, Ki-Jeong Kong, Hyunju

Chang and Jeong-O Lee, A Field Effect Transistor Fabricated with Metallic Single-Walled Carbon

Taylor & Francis Ltd.

Figure 9.19b shows the measurements for another SWNT device with its contact

area loaded with streptavidin-coated 10 nm Au particles. As is shown in the inset, a

few streptavidin-coated Au particles are observed nearby the nanotube body. How-

ever, most of them are present in the metal–SWNT contact region (dotted black

circle). A sharp transition from almost metallic behavior to p-type semiconduct-

ing behavior is also observed in this device. If we assume a tube length of 2.8µm

and a diameter of 1.5 nm, the estimated mobility of this device is ∼3300cm

/Vs.

Again, the conductance saturates after the p-channel current commences. The de-

vices decorated with streptavidin-coated polystyrene nanoparticles exhibited similar

transitions (data not shown) to those with streptavidin-Au particles.

In previous studies, changes in the Schottky barrier at the metal–nanotube contact

have been discussed in relation to the conversions between p-type and n-type behav-

iors and between ambipolar and unipolar behaviors [12,33]. Adsorbed proteins are

known to affect the work functions of metal electrodes [8]. However, all previous

observations should be attributed to the Schottky barrier between the semiconduct-

ing nanotube and the metal electrodes. The conversion observed in this study from

metallic behavior to semiconducting behavior and the sharp increase in the gate re-

sponse have not previously been reported. Since streptavidin is known to have dif-

ferent charge states depending on the pH of the solution [54b.], its charge state is ex-

pected to depend on the gate bias in our device structure. When streptavidin-coated

nanoparticles were used in this experiment, about 5,000 protein molecules were im-

mobilized on each polystyrene nanoparticle, and the proteins are likely to adsorb in

close vicinity to the metal–nanotube contact. Figure 9.20 shows a schematic diagram

9 Designing the Carbon Nanotube Field Effect Transistor 241

Fig. 9.20 Schematic illustrations of (a) the dependence of the charge states of the protein-coated

nanoparticles on the gate bias, and (b) the resulting changes in the I–V

curves. In panel (b),the

dark and gray lines are the I–V

curves before and after protein adsorption, respectively. Reused

with permission from Pil Sun Na, Noejung Park, Jinhee Kim, Hyojin Kim, Ki-Jeong Kong, Hyunju

Chang and Jeong-O Lee, A Field Effect Transistor Fabricated with Metallic Single-Walled Carbon

Taylor & Francis Ltd.

Fig. 9.21 Atomic geometries optimized in ab initio calculations for (5,5) nanotubes in contact with

(a) the bare Au (111) surface and (b) oxygen and (c) rubidium adsorbates on the metal surface.

In the lower panels, the local potentials across the contact with respect to the Fermi level are

shown, as indicated by the arrow in panel (a). Reused with permission from Pil Sun Na, Noejung

Park, Jinhee Kim, Hyojin Kim, Ki-Jeong Kong, Hyunju Chang and Jeong-O Lee, A Field Effect

Transistor Fabricated with Metallic Single-Walled Carbon Nanotubes, Fullerenes, Nanotubes and

of the effects of the gate voltage on the electron transport and charge states of the

proteins.

The common observation of a large contact resistance has been attributed to the

presence of a tunneling barrier between the metal and the nanotube [11, 53]. We

suspect that after the reaction with protein-coated nanoparticles the metal–nanotube

242 B.-K. Kim et al.

contact might be contaminated with the terminal groups of the protein. Depending

on the gate bias, the protein could be charged either negatively or positively, which

affects the tunneling barrier at the metal–nanotube contact because of the contam-

inating terminal groups. We now show with ab initio electronic structure calcula-

tions [28, 29] that the tunneling barrier at the metal–nanotube contact is sensitive

to the presence of charged species near the metal–nanotube contact. Figure 9.21a

shows the optimized atomic geometry of a metallic (5,5) nanotube in contact with a

bare gold (111) surface. In Figs. 9.21b and c, there are oxygen and rubidium atoms

respectively adsorbed within the contact region. Owing to the electron transfer be-

tween the adsorbates and the metal surface, the oxygen adsorbates form a negatively

charged layer, whereas the rubidium atoms form a positively charged layer after do-

nating electrons to the metal. In the lower panels of Fig.9.21, the local potentials in

the Kohn–Sham equation are plotted across the contact, as indicated by the arrow in

Fig. 9.21a, with respect to the Fermi level. Note that oxygen adsorption, and conse-

quently, the presence of negatively charged particles, increases the tunneling barrier,

whereas the presence of rubidium adsorbates reduces the potential barrier. Because

of the large Au–Rb bond length (∼3.4

A), the distance from the Au (111) surface

to the carbon nanotube is increased, and thus the vacuum barrier becomes thicker.

However, we postulate that in our experiment the charge states of the contaminating

terminal groups at the metal–nanotube contact vary depending on the gate bias, with

only negligible changes in their chemical structures.

In conclusion, we fabricated carbon nanotube ﬁeld effect transistors and dec-

orated the metal–nanotube contact region with protein-coated nanoparticles. Re-

markably, the gate response was found to be sensitive to protein adsorption even for

metallic carbon nanotubes. Upon the adsorption of protein-coated nanoparticles at

the metal–nanotube contact, the devices fabricated with metallic SWNTs exhibit p-

type transport behavior. In the case of semiconducting SWNT devices, the adsorp-

tion of protein-coated nanoparticles makes the gating more effective, resulting in

greatly enhanced device performance, such as higher on/off ratios and decreased S.

This enhancement is due to the sensitivity of the contact barrier to the charge states

of the proteins, which can be controlled by varying the gate bias. This switching

mechanism could be generalized in the nanoelectronics, relieving a signiﬁcant ef-

fort to separate semiconducting nanotubes from the aggregate.

9.4 Conclusion

We have investigated the importance of the contact in SWNT-FETs to their electri-

cal transfer properties by using electronic structure calculations and experimental

electrical transfer measurements. By varying the work function of the metal elec-

trode in contact with the nanotube, it is possible to fabricate n-type transistors and

Schottky diodes with single-walled carbon nanotubes. Metal decoration and SAM

techniques were used to vary the Schottky barrier height. Contact decoration with Al

was shown to be an effective method of increasing the sensitivity of nanotube-based

9 Designing the Carbon Nanotube Field Effect Transistor 243

sensors. It was found that variation of the polarity of the SAM molecule can sig-

niﬁcantly affect the Schottky barrier height. Thus care must be taken with sensors

that use Schottky barrier height change as the transducing mechanism. Although

the effects of the contact are signiﬁcant for carbon nanotubes, the effects of channel

doping by oxygen and other species are also non-negligible.

Finally, we have shown that by substituting materials that can be charged by the

gate bias voltage at the metal–nanotube contact, it is possible to create transistors

even with metallic nanotubes. The charge state of the substituted particle can change

the height of the metal–nanotube tunneling barrier, resulting in a switch that can be

turned on and off by varying the gate voltage.

In summary, we have shown that nanotube devices with desirable properties can

be fabricated by using delicate control of the properties of the contact barrier. How-

ever, if large scale production of such designed nanotube devices is to be achieved,

methods with more precise control are required.

Acknowledgments This work was supported by MOST and grants from the KOSEF through the

Center for Nanotubes and Nanostructured Composites (CNNC), and KRISS-University Program

and Core Technology Development Project by ITEP, Korea

References

1. Antonov RD, Johnson AT (1999) Subband population in a single-wall carbon nanotube

diode. Phys Rev Lett 83:3274–3276

2. Appenzeller J, Knoch J, Derycke V, Martel R, Wind S, Avouris Ph (2002) Field-modulated

carrier transport in carbon nanotube transistors. Phys Rev Lett 89:126801–126804

3. Bachtold A, Hadley P, Nakanishi T, Dekker C (2001) Logic circuits with carbon nanotube

transistors. Science 294:1317–1320

4. (a)Besteman K, Lee J, Wiertz FGM, Heering HA, Dekker C (2003) Enzyme-coated car-

bon nanotubes as single-molecule biosensor. Nano lett 3:727–730; (b) Star A, Gabriel J-CP,

Bradley K, Gr

uner G (2003) Electronic detection of speciﬁc protein binding using nanotube

fet devices. Nano Lett 3:459–463

5. Bockrath M, Cobden DH, Lu J, Rinzler AG, Smalley RE, Balents L, McEuen PL (1999)

Luttinger-liquid behaviour in carbon nanotubes. Nature 397:598–601

6. Bockrath M, Cobden DH, McEuen PL, Chopra NG, Zettl A, Thess A, Smalley RE (1997)

Single-electron transport in ropes of carbon nanotubes. Science 275:1922–1925

7. Campbell IH, Rubin S, Zawodzinski TA, Kress JD, Martin RL, Smith DL, Barashkov NN,

Ferraris JP (1996) Controlling Schottky energy barriers in organic electronic devices using

self-assembled monolayers. Phys Rev B 54:R14321–R14324

8. Chen RJ, Choi HC, Bangsaruntip S, Yenilmez E, Tang X, Wang Q, Chang YL, Dai H (2004)

An investigation of the mechanisms of electronic sensing of protein adsorption on carbon

nanotube devices. J Am Chem Soc 126:1563–1568

9. Collins PG, Bradley K, Ishigami M, Zettl A (2000) Extreme oxygen sensitivity of electronic

properties of carbon nanotubes. Science 287:1801–1804

10. de Boer B, Hadipour A, Mandoc MM, van Woudenbergh T, Blom PWM (2005) Tuning of

metal work functions with self-assembled monolayers. Adv Mater 17:621–625

11. Delaney P, Ventra MD (1999) Comment on “Contact resistance of carbon nanotubes”. Appl

Phys Lett 75:4028–4029