Introducing organic nanowire transistors

ISSN:1369 7021 © Elsevier Ltd 2008APRIL 2008 | VOLUME 11 | NUMBER 438

Introducing organic nanowire transistors

Historically, there have been more examples of one-dimensional

inorganic nanostructures1,2 for use in nanoscale devices than

their organic semiconductor nanowire counterparts3,4. Organic

semiconductors are advantageous in general because of their facile

and large-scale synthesis, solution processability, and molecular

and electronic tunability by molecular design5,6. One-dimensional

organic nanostructures, such as nanowires, nanotubes,

nanoribbons, and nanofibers prepared via self-assembly4 from

conjugated small molecules or conjugated polymers constitute

next-generation materials for a vast array of electronic

applications7,8. They are promising materials for a multitude of

applications including vapor sensors9,10, phototransistors11,12,

solar cells13, nanoscale lasers14, memory elements15,

miniaturization of devices16, and as the active semiconductor

elements for organic field-effect transistors (OFETs)17,18.

It is well known that the performance of organic semiconductors

is governed by how molecules or polymer chains assemble in the solid

state19,20. Because organic molecules in nanowires self-assemble into

highly organized single-crystalline nanostructures4, they are ideal for

fundamental studies. Moreover, nanowires are model systems for

elucidating transport mechanisms8,21, addressing the role of nanoscale

domains in microstructures21,22, structure-property relationships23, and

for understanding intrinsic transport phenomena24. Enabling nanowire

synthesis from novel, never-before-used organic semiconductors may

very well open up new areas in science with a host of applications in

nanosensors, photovoltaics, wearable devices, and highly sophisticated

integrated logic.

This review highlights some current examples of organic nanowire

transistors as they make their debut in the rapidly evolving area of

organic electronics. Because of the enormous development in this

Organic nanowires self-assembled from small-molecule semiconductors and conducting polymers have attracted an enormous amount of interest for use in organic field-effect transistors. This new class of materials offers solution processability, the potential for elucidating transport mechanisms and structure-property relationships, and the realization of high-performance transistors that rival the performance of amorphous Si. We discuss the self-assembly of one-dimensional, single-crystalline organic nanowires, show the structures of commonly employed organic semiconductors, and review some of the advances in this field.

Alejandro L. Briseno1*, Stefan C. B. Mannsfeld2, Samson A. Jenekhe1,3, Zhenan Bao2, and Younan Xia1*

1Department of Chemistry, University of Washington, Seattle, WA 98195, USA

2Department of Chemical Engineering, Stanford University, Stanford, CA 94305, USA

3Department of Chemical Engineering, University of Washington, Seattle, WA 98195, USA

*E-mail: [email protected], [email protected]

mt114p38_47.indd 038mt114p38_47.indd 038 07/03/2008 09:33:2907/03/2008 09:33:29

mailto:[email protected]

mailto:[email protected]

Introducing organic nanowire transistors REVIEW

APRIL 2008 | VOLUME 11 | NUMBER 4 39

area, it is impossible to survey all the interesting breakthroughs and

accomplishments from research groups around the world. There is no

question that research in this highly dynamic area will continue to

strongly develop and one can expect prospective contributions from

scientists in diverse areas.

Field-effect transistor operation and designOFETs are not only of technological interest25, but also as a

tool for determining charge transport parameters of organic

semiconductors26,27. An organic thin film transistor consists of the

following components: (i) an organic semiconductor; (ii) an insulating

dielectric layer; and (iii) three electrode terminals. Two of the

electrodes, the source and drain, are in contact with the semiconductor

film and are often deposited by thermal evaporation. The third

electrode, the gate, modulates the current flow across the source-

drain electrodes. Upon applying a gate voltage, a ‘channel’ of charges

is formed at the dielectric-semiconductor interface, thus facilitating a

flow of current between the source and drain electrodes. Fig. 1 shows a

‘top contact’ single nanowire field-effect transistor (FET).

The key parameters in characterizing an OFET are its field-effect

mobility, threshold voltage, and current on/off ratio26,27. The field-

effect mobility in the saturation regime can be calculated by the

equation, IDS = (W·C ·µ/2·L)(VG – VT)2, where L is the channel length,

W is the channel width, C is the capacitance per unit area of the

insulating layer, VT is the threshold voltage, VG is the gate voltage, and

µ is the field-effect mobility. In order to calculate the carrier mobility

reliably using this equation, it is important to determine whether the

relatively small dimensions of organic nanowires still satisfy the charge

sheet approximation28.

Theoretical calculations and experiments using organic

semiconductors show that the charge density of a semiconductor is

confined to the first few monolayers at the insulator-semiconductor

interface28–30. Moreover, it is presumed that the charges located

near the interface have the highest mobility. The charge-sheet

approximation requires that the charge density distribution in a

conducting channel be approximated as a sheet of charges that all

follow the same surface potential gradient on top of the dielectric

surface. This approximation usually holds true as long as the sheet of

charges is much thinner than the dielectric layer thickness. Depending

on the lateral dimensions of the nanowires and the chosen device

geometry, the validity of the charge-sheet approximation could be

questionable. For instance, in the case of hexathiapentacene (HTP)

nanowires31, the diameter ranges from 200 nm to about 1 µm and if

one assumes that there is a similar decline of vertical charge density at

the insulator-nanowire interface (~2 nm) at large gate voltages, then

the height of the corresponding charge sheet is still much smaller than

the gate dielectric layer thickness and the nanowire diameter (by a

factor of about 100–500). Therefore, the use of an individual organic

nanowire will follow the charge-sheet approximation and still represent

a good estimate for the charge density distribution at the dielectric

interface.

One-dimensional self-assembly via π–π interactionsThere is great interest in planar aromatic molecules that exhibit face-

to-face (π-stack) stacking since this packing theoretically results in

high mobilities in devices such as FETs32. This phenomenon is reported

to be the result of increased overlap between the electronic wave

functions of neighboring molecules in the stack32. The strong overlap

in electronic wave functions leads to an increase in bandwidth, and this

directly correlates to electrical conductivity in the coherent transport

regime33.

This type of stacking is more common with molecules that

possess a two-dimensional extended aromatic system and is rarely

observed for linear molecules such as oligoacenes. For the former

type of molecules in particular, self-assembly via strong π−π

interactions has been demonstrated to result in the formation of one-

dimensional nanostructures3,4. Some examples of one-dimensional

structures include nanofibers, nanowires, nanoribbons/nanobelts, and

microwires self-assembled from hexabenzocoronene derivatives34,

perylene tetracarboxylic diimide (PTCDI) derivatives35–39, pentacene

derivatives31,40–42, metal phthalocyanines11,43–46 and porphyrins47,

polythiophene polymers13,17,21,22,48–52, and several other organic

semiconductors53–57.

More recently it has been shown that if π-stacking can be achieved

in linear oligoacene derivatives, high carrier mobilities are obtained in

transistor devices42,58–61. Among the oligoacenes61,62, pentacene and

its derivatives61 have thus far exhibited the best reported performances

in thin-film devices. Despite these promising results, there are only a

few reports31,40–42 on one-dimensional nanostructures (e.g. nanowires)

synthesized from oligoacenes, let alone derivatives thereof63. A

possible explanation for this slow development is the relative scarcity

of oligoacene derivatives that stack face-to-face and also the lack of

investigation of current molecules that co-facially pack in the solid

state. Fortunately, intelligent molecular design and modern synthetic

methods have enabled chemists to increase the degree of anisotropy in

the intermolecular interactions, yielding new organic semiconductors

that exhibit face-to-face packing, and thus, more likely to self-assemble

into nanowires. Fig. 1 Schematic of an organic single nanowire FET.

mt114p38_47.indd 039mt114p38_47.indd 039 07/03/2008 09:33:4707/03/2008 09:33:47

REVIEW Introducing organic nanowire transistors

APRIL 2008 | VOLUME 11 | NUMBER 440

The molecules in one-dimensional nanostructures predominantly

self-assemble along the π−π stacking direction, which gives a high

charge-carrier mobility along the long axis of the nanostructure

as a result of the strong intermolecular coupling between the

packed molecules32,33. It is known that the tendency to form face-

to-face stacked structures can be enhanced by adding peripheral

substituents58–61,64,65, as well as with an increase of π-surface-to-

circumference ratios66. The face-to-face π-stacking motif is believed

to be more efficient for charge transport than most edge-to-face

‘herringbone-packing’ structures32,61. Fig. 2 shows examples of organic

semiconductors that form one-dimensional structures through strong

π-π interactions. These semiconductors have also been shown to

function successfully as one-dimensional organic crystalline transistors.

HTP is an example of a π-stacked small organic semiconductor

that adopts face-to-face packing in nanowires31. Fig. 3a shows HTP

molecules stacking face-to-face along the [100] crystallographic a-

axis with π-to-π distances of 3.54 Å64. In this example, π-stacking

is attributed to the chalcogen atoms located on the periphery of

pentacene’s backbone, which by steric hindrance prevent the edge-

to-face geometry that normally leads to the herringbone structure of

pentacene61. A distance of ~3.37 Å, which is smaller than twice the

van der Waals radius of the S atom (3.70 Å), is observed between the

central and outermost S atoms of a neighboring HTP molecule64. The

overlap of the molecular π-orbitals, crucial for the charge transport in

organic semiconductor materials, is significant only along the nanowire

direction (Fig. 3b). This type of stacking is also well known for PTCDI

Fig. 2 Known examples of (a) p-type, (b) n-type, and (c) polymer semiconductors that π-stack and function as one-dimensional organic single-crystalline FET s.

(b)(a)

(c)

mt114p38_47.indd 040mt114p38_47.indd 040 07/03/2008 09:33:4807/03/2008 09:33:48



derivatives35–39, and underscores the applicability of nanowires for

high-performance transistor devices.

Although the synthesis of one-dimensional organic structures

is becoming more prevalent, dimensionality control still remains a

challenge. With a few exceptions53, it is often more difficult to control

the length and width of one-dimensional structures when grown

directly on substrates41,56,57 versus those grown in solution3,21,31,35.

One way of reducing the dimensions of nanowires is by adding a

‘bad’, non-dissolving solvent to the solution mixture containing

the organic semiconductor31,35,38. This process forces the organic

molecules to precipitate out from solution38. Surfactants such

as cetyltrimethylammonium bromide (CTAB) are also known to

stabilize and control the dimensions of nanostructures via coulombic

attraction between cationic ammonium head groups and π-electrons

in aromatic molecules. Microemulsions, interfacial self-assembly, and

reprecipitation are also well known methods of producing narrow

distributions of nanostructures in solution9. Porous alumina templates

can also be used for the synthesis of one-dimensional crystalline

structures12,14.

Nanowires via solution depositionOne of the greatest challenges for organic thin-film transistors

is the achievement of ultimate control of both film morphology

and the degree of crystallinity67. Even the best performing organic

semiconductors inevitably contain molecular disorder and grain

boundaries, which effectively reduce the mobility of the material.

Organic single crystals, on the other hand, are known to have superior

performance68–72 as they are largely free of grain boundaries or

molecular disorder. However, their fragility and brittleness make them

very difficult to work with and reports of fabricating devices from

solution-borne single crystals are somewhat unusual.

Fig. 3 (a) Theoretically predicted growth morphology of a single-crystal HTP

nanowire. (b) Molecular packing of HTP along the a-axis of the unit cell.

The illustration shows the face-to-face π-stacking direction. (Reprinted with

permission from31. © 2007 American Chemical Society.)

Fig. 4 (a) Synthesis of HTP, (b) solution dispersion and transmission electron

micrograph of HTP nanowires, (c) electrical characteristics of a single-

crystal HTP nanowire, and (d) a scanning electron micrograph of a nanowire

transistor. (Reprinted with permission from31. © 2007 American Chemical

Society.)

(b)

(a) (a)

(b)

(c)

(d)

mt114p38_47.indd 041mt114p38_47.indd 041 07/03/2008 09:33:4907/03/2008 09:33:49



Solution deposition offers a cost-effective method for fabricating

large-area electronic components from organic materials73–75. While

solution-deposition techniques have been reported with some level

of success, there are still unresolved issues in controlling the crystal

packing and film-forming properties. Therefore, there is a growing

need to explore organic single-crystal nanostructures as solution-

processable materials. The idea is to employ high-performance organic

semiconductors that self-assemble into highly crystalline nanowires

either in solution or at the substrate-solution interface. So far, single-

crystal nanowire transistors have shown mobilities comparable to thin-

film transistors of the same material. In many cases, the single-crystal

nanowires have even shown mobilities larger than thin-films of the

same materials31,41,44,47,54,55.

Fig. 4 shows (a) the synthesis of HTP and (b) a dispersion of

nanowires in chloroform, as well as a high-performance nanowire

transistor exhibiting a mobility of 0.27 cm2/Vs31. The single-crystal

HTP nanowire transistor exhibits a mobility over six times greater than

that of vapor-deposited HTP thin-film transistors64. The higher mobility

of the nanowire transistors compared with vapor-deposited thin-film

transistors can be attributed to the high level of structural perfection

of the single-crystal HTP nanowires in addition to the fact that they

are essentially free of grain boundaries68–72. Furthermore, it is not

uncommon for mobility to be higher in single-crystals than in the thin-

film form of a semiconductor material31,41,44,47,54,55,58,76.

Nuckolls and coworkers recently described the synthesis, solution

self-assembly, and electrical properties of a hexabenzocoronene (HBC)

derivative (Fig. 5)34. A pick-and-place procedure using an elastomeric

stamp was used to pick individual ‘cables’ from tangled mats to

fabricate single nanowire transistors with mobilities as large as

0.02 cm2/Vs. The structure and packing of HBC molecules within the

nanowires were studied by transmission electron microscopy (TEM) and

it was determined that the molecules self-assemble in one-dimensional

stacks along the nanowire axis where charge transport should be

optimal.

Solution processability of bulk quantities of one-dimensional

wires has also been demonstrated with highly soluble, air-stable

oligoarenes56. Single oligoarene microwire transistors were tested with

hole mobilities on the order of ~10–2 cm2/Vs. Cho and coworkers

recently reported a record mobility of 1.42 cm2/Vs for a single-

crystalline triisopropylsilylethynyl pentacene microribbon41. To date,

this is the largest mobility of an individual one-dimensional organic

single crystal via solution processing (Fig. 6).

Nanowires via physical vapor transportGrowth of single-crystal organic nanowires via physical vapor transport

is an alternative way of producing high-performance materials for

use in FETs77. The main advantage is that one does not need to

handle the organic nanowires and this eliminates the possibility of

contamination (single-crystal nanowires can be directly grown onto

prefabricated source-drain electrodes)68. If care is not taken, solution

deposition of nanowires may incorporate debris and increase the

chance of contamination at the substrate-nanowire interface. However,

by growing nanowires directly onto substrates, contamination can

be greatly minimized. Some drawbacks to growing organic nanowires

via physical vapor transport, however, are low throughput of device

fabrication and, depending on the organic material being thermally

evaporated, it may not be possible to grow nanowires directly onto

plastic substrates unless low melting point (high vapor pressure)

materials are employed (e.g. anthracene, tetracene, etc.). Nevertheless,

some of the highest-mobility nanowire transistors have been

Fig. 5 (a) Schematic of an individual HBC nanowire transistor; (b) scanning electron micrograph of an HBC nanowire bridging the source-drain electrodes;

(c) transfer characteristics; and (d) output characteristics. (Reprinted with permission from34. © 2006 American Chemical Society.)

(b)(a)

(c) (d)

mt114p38_47.indd 042mt114p38_47.indd 042 07/03/2008 09:33:5107/03/2008 09:33:51



fabricated via physical vapor transport44,55. Both p- and n-type organic

semiconductor nanowires (i.e. CuPc, F16CuPc) have been grown and

single-nanowire transistors have yielded mobilities on the order of

10–1 cm2/Vs43,44. Sun et al.55 recently reported single-crystal microwire

transistors from perylo[1,12-b,c,d]thiophene (PET) with mobilities as

large as 0.8 cm2/Vs. Again, the one-dimensional single-crystal devices

yielded mobilities of more than one order of magnitude greater than

thermally evaporated thin-film transistors of the same material.

Although PET was synthesized over 30 years ago78, no reports on its

use in transistors had previously been reported. The PET molecules pack

face-to-face along the b-axis of the unit cell with interplanar distances

of 3.47 Å and S...S intermolecular contact distances of 3.51 Å.

Flexible nanowire transistorsA real-world challenge for flexible electronics and displays is the ability

to fabricate and process organic transistors in a facile and low-cost

manner, over large areas, and on mechanically flexible substrates.

Nanometer-thin rubrene single-crystals fabricated onto flexible

substrates with mobilities as large as 4.6 cm2/Vs have recently

been reported72. The flexible devices bend to a radius of less than

1 cm without any significant loss in performance. Large-area arrays

of patterned rubrene microcrystal transistors on flexible polyimide

substrates also show similar results68. CuPc single-crystal nanowires

also exhibit a high degree of mechanical flexibility43. This study was

carried out by mechanically bending a nanowire with a microprobe

to well over 180° without any fracturing of the nanowire. It did not,

however, report the effects of mechanical deformation on device

performance.

We have recently fabricated HTP nanowire transistors on

mechanically flexible substrates to evaluate their performance for

applications in flexible electronics31. Our approach to measuring the

Fig. 6 (a) Schematic of the molecular packing of TIPS-PENT molecules self-assembled into a single-crystalline ribbon. (b) Micrograph of a single TIPS-PENT

microribbon transistor (S= Source, D= Drain), (c) output characteristics, and (d) transfer characteristics. (Reprinted with permission from41. © 2007 Wiley-VCH.)

Fig. 7 (a) Transfer characteristics of an HTP nanowire network transistor

fabricated on a flexible substrate. (b) Photograph of an array of bottom-

contact network nanowire devices. Inset shows a typical device with the

single-crystal nanowires bridging the source-drain electrodes. (Reprinted with


(b)(a)

(c) (d)

(a)

(b)

mt114p38_47.indd 043mt114p38_47.indd 043 07/03/2008 09:33:5307/03/2008 09:33:53



devices on plastic substrates is similar to the one described in recent

reports68,72. In order to demonstrate the facile processability of the

solution-dispersible nanowires, we spray-coated the nanowires from a

chloroform/ethanol (1:1) solution directly onto prefabricated source-

drain electrodes on polyimide substrates. Fig. 7 shows the output and

transfer characteristics of an HTP nanowire network device on a flexible

substrate. A mobility of 0.032 cm2/Vs, a current on/off ratio of ~103,

and a threshold voltage of –8 V were obtained for the flexible device.

Single nanowire transistors on flexible substrates were also fabricated.

A mobility of 0.19 cm2/Vs and a current on/off ratio of >103 were

obtained. The study shows no change in mobility before, during, or

after an applied strain to the flexible device.

N-type nanowires and complementary logic Electron-transporting organic semiconductors and n-channel

OFETs27,79 are highly desirable as they will enable the fabrication of

complementary inverters35,76,80,81. Among n-type semiconductors,

the PTCDIs are the most widely studied because of their commercial

availability, low cost, chemical stability, and promising electronic and

optoelectronic applications36. In addition, PTCDIs have a propensity

to self-assemble into one-dimensional nanostructures through π−π

stacking35–39. Our group has demonstrated the use of PTCDI nanowires

as the n-channel semiconductor in organic FETs and as a building block

in high-performance complementary inverters (Fig. 8)35. Devices based

on a network of PTCDI nanowires show electron mobilities and current

on/off ratios on the order of ~10–2 cm2/Vs and 104, respectively.

Complementary inverters based on n-channel PTCDI nanowire

transistors and p-channel HTP nanowire OFETs achieve gains as high as

eight. These results demonstrate the first example of the use of one-

dimensional organic semiconductors in complementary inverters.

It has also been shown that single-crystal n-type F16CuPc nanowires

can be grown by physical vapor transport directly onto the surfaces of

SiO244. High-performance, air-stable n-channel transistors have been

subsequently fabricated by employing asymmetrical drain/source (Ag/

Au) electrodes44. Electron mobilities as large as 0.2 cm2/Vs and on/off

ratios of 6 × 104 have been measured from single-crystal nanowire

Fig. 9 (a) Output and (b) transfer characteristics of an individual F16CuPc

single-crystal nanowire transistor showing n-type characteristics. Insert shows

an individual nanowire with source and drain electrodes. (Reprinted with


Fig. 8 (a) A series of optical photographs showing the self-assembly of PTCDI nanowires over time. (b) Schematic of an inverter with p- and n-type nanowire

networks. (c) Digital photograph of a substrate containing 13 discrete nanowire inverters. (d) Static inverter transfer characteristics. (Reprinted with permission

from35. © 2007 American Chemical Society.)

(a)

(b)

(a)

(b) (c)

(d)

mt114p38_47.indd 044mt114p38_47.indd 044 07/03/2008 09:33:5607/03/2008 09:33:56



transistors (Fig. 9). The first n-channel, single-nanowire phototransistor

was also reported earlier this year11. The air-stable phototransistors

show remarkably fast and reversible switching and exhibit a strong

photodependence. This finding is expected to open up new areas in

low-cost, large-area opto-isolators, optical switches, and retro sensors.

Polymer nanowire transistors The charge transport properties in one-dimensional conducting

polymers have been intensely studied in recent years particularly

because of their impact on modern technology8. Self-assembled

nanowires of poly(3-hexylthophene) (P3HT) are of great interest

because the polymer semiconductor itself is known to self-organize

and yield a high field-effect mobility82. Furthermore, P3HT nanowires

are of fundamental interest because they can shed light on the

intrinsic transport properties of polymer semiconductors and serve as

a model system for elucidating transport mechanisms and for studying

structure-property relationships21–24,48.

The self-assembly and molecular packing of polymer chains within

P3HT nanowires was first reported in 199348. Nonregioregular P3HT

nanowires were precipitated from p-xylene and cyclohexanone. It was

also determined that P3HT chains pack face-to-face along the nanowire

axis (b-axis of unit cell). Based on this structural determination,

Merlo and Frisbie21,22 extended the work with regioregular P3HT and

fabricated single polymer nanowire transistors. This seminal work

demonstrated that probing the transport in discrete polymer nanowires

could provide a way of addressing the role of microstructure in thin

films. They also measured the conductance and turn-on voltage of both

single nanowires and nanowire networks as functions of the charge

density, temperature, and substrate surface energy. Fig. 10a shows

a model of the face-to-face molecular packing of P3HT chains along

the nanowire axis and in the direction of transport measurements. A

field-effect mobility of 0.02 cm2/Vs and on/off ratios of ~106 were

determined for the P3HT nanowires (Fig. 10b,c).

Fig. 11 shows one-dimensional single-crystal P3HT microwires

grown via self-assembly49. The P3HT crystals were grown on self-

assembled monolayers by using a self-seeded method from a dilute

chloroform solution. The key requirement in growing the polymer

crystals is a high solvent vapor pressure environment. The P3HT chains

self-organize via strong π−π interactions along the [010] direction

(b-axis). The single-crystal microwires were structurally and electrically

characterized and current-voltage measurements show unusual gate

modulation unlike those of standard OFETs.

Polymer nanowires via electrospinning Electrospinning has recently emerged as an alternative method of

preparing nanowires from conducting polymers for applications in

electronic devices83. Electrospinning is primarily used for high molecular

weight polymers because of the limitation on molecular weight and

suitable solvents. These requirements are ideal for employing high

molecular weight polymer semiconductors such as P3HT for FETs.

For instance, single electrospun polymer nanowire transistors have

been demonstrated by several groups50–52 with mobilities as high

as 0.03 cm2/Vs52. It has also been shown that blends of polymer

semiconductors can be electrospun through a coaxial two-capillary

spinneret50. These results demonstrate that electrospun nanofibers

of binary blends of polymer semiconductors (poly[2-methoxy-5-(2’-

ethyl-hexyloxy)-1,4-phenylene vinylene] or MEH-PPV with P3HT) have

tunable electronic properties that can be used in FETs. Future work in

the area of electrospinning will likely include the use of some recently

reported air-stable, high-performance polymer semiconductors17,84.

Fig. 10 (a) Packing orientation of P3HT polymer chains along a nanowire

axis. (b) Atomic force microscopy image showing an individual P3HT

nanowire across a source-drain electrode and (c) the corresponding transfer

characteristics. (Reprinted with permission from21. © 2004 American Chemical

Society.)

(a)

(b)

(c)

mt114p38_47.indd 045mt114p38_47.indd 045 07/03/2008 09:33:5807/03/2008 09:33:58



Another area in need of exploration is the structural characterization of

electrospun nanofibers to determine the molecular packing of polymer

chains within the nanowires. At this point, it is unclear if the molecular

packing of electrospun P3HT nanofibers is consistent with the packing

of P3HT nanofibers prepared via solution self-assembly21,48.

Summary and outlookOrganic nanowires are an important class of semiconductor materials

for use in OFETs. From small-molecule single-crystal nanowires

to crystalline polymer nanowires, these materials have proven

valuable for understanding structure-property relationships, intrinsic

transport properties, and are model systems for elucidating transport

mechanisms.

Although their use has brought about significant advances in the

area of organic electronics, there are still several challenges that must

be met before transistors can become practical devices. One of the

most difficult challenges is to pattern and align organic nanowires

either via physical vapor transport or solution processing. The

significance of patterning is to reduce and eliminate parasitic leakage

paths, which often result in large ‘off’ currents85–87. Although there

have been recent examples in patterning one-dimensional organic

structures (Fig. 12)45,53,68, these reports still do not show aligned

patterning. The goal for nanowire patterning is to control the azimuthal

Fig. 12 (a) CuPc single-crystal nanowires with different widths grown onto

SiO2 surfaces via physical vapor transport. (Reprinted with permission from45.

© 2006 Wiley-VCH.) (b) Arrays of F16CuPc 1-D single-crystals patterned onto

SiO2 via physical vapor transport. (Reprinted with permission from68. © 2006

NPG.) (c) Chlorotetracene nanowires patterned onto source-drain devices

via solution-processing. (Reprinted with permission from53. © 2006 American

Chemical Society.)

Fig. 11 (a) Optical micrograph of P3HT single-crystal microwires, (b) scanning electron micrograph with a close-up showing the well-defined facets, and (c) a

TEM micrograph with the corresponding electron diffraction pattern (d). (e) Molecular packing of P3HT chains in an orthorhombic unit cell, and (f) a schematic

representation of molecular packing of P3HT chains showing the π−π stacking. (Reprinted with permission from49. © 2006 Wiley-VCH.)

(a)

(b)

(d)

(c)

(e)

(f)

(b)(a)

(c)

mt114p38_47.indd 046mt114p38_47.indd 046 07/03/2008 09:33:5907/03/2008 09:33:59



orientation of the nanowires so that they all align in a single direction.

This is important for optimal charge transport when fabricating devices.

This idea has been demonstrated with inorganic nanowires via methods

that include microfluidics88 and transfer printing89.

Other challenges include the synthesis of new high-performance,

air-stable polymers and small molecules from both p- and n-type

semiconductors that pack face-to-face. The synthesis of ambipolar

organic semiconductors would allow the fabrication of integrated

circuits on a single organic nanowire. This feat would enable integrated

devices to be scaled down to the nanoscale.

Finally, some immediate challenges that can be addressed include

contact resistance issues, determining transport mechanisms in single-

crystal nanowires (this requires temperature-dependent studies), and

finding a way of making herringbone-packing semiconductors (i.e.

pentacene, rubrene, etc.) to self-assemble into nanowires without the

use of difficult-to-remove templates.

REFERENCES

1. Xia, Y., et al., Adv. Mater. (2003) 15, 353

2. Lieber, C. M., et al., MRS Bull. (2003) 28, 486

3. Schenning, A. P. H. J., and Meijer, E. W., Chem. Commun. (2005), 3245

4. Hoeben, F. J. M., et al., Chem. Rev. (2005) 105, 1491

5. Lloyd, M. T., et al., Materials Today (2007) 10, (11) 34

6. Shin, T. J., et al., Chem. Mater. (2007) 19, 5882

7. Meijer, E. W., and Schenning, A. P. H. J., Nature (2002) 419, 353

8. Aleshin, A. N., Adv. Mater. (2006) 18, 17

9. Huang, J., et al., J. Am. Chem. Soc. (2003) 125, 314

10. Hernandez, S. C., et. al., Electroanalysis (2007) 19, 2125

11. Tang, Q., et al., Adv. Mater. (2007) 19, 2624

12. O’Brien, G. A., et al., Adv. Mater. (2006) 18, 2379

13. Berson, S., et al., Adv. Funct. Mater. (2007) 17, 1377

14. O’Carroll, D., et al., Nat. Nanotechnol. (2007) 2, 180

15. Tseng, R. J., et al., Nano Lett. (2005) 5, 1077

16. Nguyen, T., et al., J. Am. Chem. Soc. (2004) 126, 5234

17. Ong, B. S., et al., Adv. Mater. (2005) 17, 1141

18. Wanekaya, A. K., et al., J. Phys. Chem. C (2007) 111, 5218

19. DeLongchamp, D. M., et al., Adv. Mater. (2005) 17, 2340

20. DeLongchamp, D. M., et al., Adv. Mater. (2007) 19, 833

21. Merlo, J. A., and Frisbie, C. D., J. Phys. Chem. B. (2004) 108, 19169

22. Merlo, J. A., and Frisbie, C. D., J. Polym. Sci. Part B: Polym. Phys. (2003) 41, 2674

23. Yang, H., et al., J. Polym. Sci. Part B: Polym. Phys. (2007) 45, 1303

24. Aleshin, A. N., et al., Phys. Rev. Lett. (2004) 93, 196601

25. Dimitrakopoulos, D., and Malenfant, P. R. L., Adv. Mater. (2002) 14, 99

26. Zaumseil, J., and Sirringhaus, H., Chem. Rev. (2007) 107, 1296

27. Newman, C. R., et al., Chem. Mater. (2004) 16, 4436

28. Tanase, C., et al., Phys. Status Solidi A (2004) 201, 1236

29. Alam, M., et al., IEEE Trans. Electron Devices (1997) 44, 1332

30. Horowitz, G., J. Mater. Res. (2004) 19, 1946

31. Briseno, A. L., et al., Nano Lett. (2007) 7, 668

32. Curtis, M. D., et al., J. Am. Chem. Soc. (2004) 126, 4318

33. Cornil, J., et al., Adv. Mater. (2001) 13, 1053

34. Xiao, S., et al., J. Am. Chem. Soc. (2006) 128, 10700

35. Briseno, A. L., et al., Nano Lett. (2007) 7, 2847

36. Würthner, F. Chem. Commun. (2004), 1564

37. Che, Y., et al., J. Am. Chem. Soc., (2007) 129, 7234

38. Datar, A., et al., J. Phys. Chem. B. (2006) 110, 12327

39. De Luca, G., et al., Adv. Funct. Mater. (2007) 17, 3791

40. Lee, W. H., et al., Appl. Phys. Lett. (2007) 90, 132106

41. Kim, D. H., et al., Adv. Mater. (2007) 19, 678

42. Li, Y., et al., Chem. Mater. (2007) 19, 418


44. Tang, Q., et al., J. Am. Chem. Soc. (2006) 128, 14634


46. Tong, W. Y., et al., J. Phys. Chem. B. (2006) 110, 17406

47. Minari, T., et al., Appl. Phys. Lett. (2007) 91, 123501

48. Ihn, K. J., et al., J. Polym. Sci. Part B: Polym. Phys. (1993) 31, 735

49. Kim, D. H., et al., Adv. Mater. (2006) 18, 719

50. Babel, A., et al., Macromolecules (2005) 38, 4705

51. Gonzalez, R., and Pinto, N. J., Synth. Met. (2005) 151, 275

52. Liu, H., et al., Appl. Phys. Lett. (2005) 87, 253106

53. Briseno, A. L., et al., J. Am. Chem. Soc. (2006) 128, 3880

54. Jiang, H., et al., Appl. Phys. Lett. (2007) 91, 123505

55. Sun, Y., et al., J. Am. Chem. Soc. (2007) 129, 1882

56. Zhou, Y., et al., J. Am. Chem. Soc. (2007) 129, 12386

57. Mas-Torrent, M., et al., J. Am. Chem. Soc. (2004) 126, 984

58. Moon, H., et al., J. Am. Chem. Soc. (2004) 126, 15322

59. Payne, M. M., et al., J. Am. Chem. Soc. (2005) 127, 4986

60. Miao, Q., et al., J. Am. Chem. Soc. (2006) 128, 1340

61. Anthony, J. E., Chem. Rev. (2006) 106, 5028

62. Bendikov, M., et al., Chem. Rev. (2004) 104, 4891

63. Al-Kaysi, R. O., et al., Macromolecules (2007) 40, 9040

64. Briseno, A. L., et al., J. Am. Chem. Soc. (2006) 128, 15576

65. Kobayashi, K., et al., Org. Lett. (2006) 8, 2385

66. Cho, D. M., et al., Org. Lett. (2005) 7, 1067

67. McCulloch, I., Nat. Mater. (2004) 4, 583

68. Briseno, A. L., et al., Nature (2006) 444, 913

69. Sundar, V. C., et al., Science (2004) 303, 1644

70. de Boer, R. W. I., et al., Phys. Status Solidi A (2004) 201, 1302

71. Gershenson, M. E., et al., Rev. Mod. Phys. (2006) 78, 973

72. Briseno, A. L., et al., Adv. Mater. (2006) 18, 2320

73. Sirringhaus, H., Adv. Mater. (2005) 17, 2411

74. Chabinyc, M. L., and Salleo, A., Chem. Mater. (2004) 16, 4509

75. Katz, H. E., et al., Acc. Chem. Res. (2001) 34, 359

76. Briseno, A. L., et al., Appl. Phys. Lett, (2006) 89, 222111

77. Kloc, C., et al., J. Cryst. Growth (1997) 182, 416

78. Rogovik, V. I., J. Org. Chem. (USSR) (1974) 10, 1084

79. Babel, A., and Jenekhe, S. A., J. Am. Chem. Soc. (2003) 125, 13656

80. Klauk, H., et al., Nature (2007) 445, 745

81. Crone, B., et al., Nature (2000) 403, 521

82. Sirringhaus, H., et al., Nature (1999) 401, 685

83. Li, D., and Xia, Y., Adv. Mater. (2004) 16, 1151

84. McCulloch, I., et al., Nat. Mater. (2006) 5, 328

85. De Vusser, S., et al., Appl. Phys. Lett. (2006) 88, 103501

86. Menard, E., et al., Chem. Rev. (2007) 107, 1117

87. Dickey, K. C., et al., Appl. Phys. Lett. (2007) 90, 244103

88. Duan, X., MRS Bull. (2007) 32, 134

89. Ahn, J. H., et al., Science (2006) 314, 1754

mt114p38_47.indd 047mt114p38_47.indd 047 07/03/2008 09:34:0407/03/2008 09:34:04

Documents

Introducing organic nanowire transistors