Towards carbon nanotube based molecular electronics [Elektronische Ressource] / Po-Wen Chiu

Sujets

• Physik

Informations

• Publié par: technische_universitat_munchen
• Publié le: 01 janvier 2003
• Nombre de lectures: 23
• Poids de l'ouvrage: 3 Mo

Extrait

Fakult at furÄ Physik
der
Technischen Universit at MuncÄ hen
Walter Schottky Institut
Towards Carbon Nanotube-based
Molecular Electronics
Po-Wen Chiu
Vollst andiger Abdruck der von der Fakult at furÄ Physik der Technischen
Universit at MuncÄ hen zur Erlangung des akademischen Grades eines
Doktors der Naturwissenschaften
genehmigten Dissertation.
Vorsitzender: Univ.-Prof. Dr. P. Vogl
PruferÄ der Dissertation: 1. Univ.-Prof. Dr. G. Abstreiter
2. Priv.-Doz. Dr. E. A. Schuberth
Die Dissertation wurde am 10. 06. 2003 bei der Technischen Universit at
MuncÄ hen eingereicht und durch die Fakult at furÄ Physik am 23. 07. 2003
angenommen.Contents
Symbols 1
Outline 3
1 Introduction 5
1.1 Carbon family and nanotubes . . . . . . . . . . . . . . . . . . . . 5
1.2 Electrical properties of nanotubes . . . . . . . . . . . . . . . . . . 8
1.2.1 Geometrical structure . . . . . . . . . . . . . . . . . . . . 8
1.2.2 Energy dispersion and density of states . . . . . . . . . . . 9
1.3 Nanoscale science and molecular electronics . . . . . . . . . . . . 14
2 Experimental techniques 19
2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
2.2 Device fabrication . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
2.2.1 Nanotube suspension . . . . . . . . . . . . . . . . . . . . . 20
2.2.2 Surface modification on Si chip . . . . . . . . . . . . . . . 20
2.2.3 Lithographical patterning . . . . . . . . . . . . . . . . . . 22
2.3 Electrical transport . . . . . . . . . . . . . . . . . . . . . . . . . . 26
2.4 Scanning force microscopy . . . . . . . . . . . . . . . . . . . . . . 28
3 Electrical transport in mesoscopic conductors 31
3.1 Classical conductivity . . . . . . . . . . . . . . . . . . . . . . . . . 31
3.2 Quantum conductance . . . . . . . . . . . . . . . . . . . . . . . . 32
3.3 Coulomb blockade effect . . . . . . . . . . . . . . . . . . . . . . . 33
3.3.1 Double junction structure . . . . . . . . . . . . . . . . . . 33
3.3.2 Single electron box . . . . . . . . . . . . . . . . . . . . . . 35
3.3.3 transistor . . . . . . . . . . . . . . . . . . . 36
4 Nanotube peapod transistors 41
4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
4.1.1 Band structure modulation by fullerenes . . . . . . . . . . 42
4.2 Purification and opening of nanotubes . . . . . . . . . . . . . . . 44
4.3 Insertion of metallofullerenes . . . . . . . . . . . . . . . . . . . . . 44
4.4 Imaging in a magnetic force microscope . . . . . . . . . . . . . . . 47
iii CONTENTS
4.5 Electrical Transport. . . . . . . . . . . . . . . . . . . . . . . . . . 48
4.5.1 In pristine nanotubes . . . . . . . . . . . . . . . . . . . . . 48
4.5.2 In large-diameter peapods . . . . . . . . . . . . . . . . . . 53
4.5.3 In small-diameter peapods . . . . . . . . . . . . . . . . . . 58
5 Interconnection of carbon nanotubes 65
5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
5.2 Chemical functionalization . . . . . . . . . . . . . . . . . . . . . . 66
5.3 Characterization of functionalized nanotubes . . . . . . . . . . . . 69
5.3.1 Atomic force microscopy . . . . . . . . . . . . . . . . . . . 69
5.3.2 X-ray photoelectron spectroscopy . . . . . . . . . . . . . . 72
5.3.3 Raman spectroscopy . . . . . . . . . . . . . . . . . . . . . 74
6 All-carbon nanotube transistors 81
6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
6.2 Device preparation . . . . . . . . . . . . . . . . . . . . . . . . . . 82
6.3 Electrical transport . . . . . . . . . . . . . . . . . . . . . . . . . . 82
6.3.1 T-junction with molecular linker . . . . . . . . . . . . . . . 82
6.3.2 without linker . . . . . . . . . . . . . 91
7 Summary and outlook 97
Appendix A 100
Bibliography 103
Curriculum Vitae 114
Publication list 116
Acknowledgements 119Symbols
p
a= 3a lattice constant of carbon nanotubes.c¡c
a nearest neighbor C¡C distance.c¡c
C chiral vector of carbon nanotubes.
C nanotube capacitance.t
de diameter.t
D diffusion constant.
ΔΦ Schottky barrier lowering.
E conduction band edge.C
E Fermi energy.F
E energy gap.g
E valence band edge.V
† dielectric constant of vacuum.0
† average dielectric constant of device.
g energy gain.
g transconductance.m
° strain along tube circumferential direction.
° energy overlap integral.0
~ reduced Planck’s constant.
k electronic wave vector.
k Fermi wave vector.F
k spring constant of cantilever.s
k vertices of hexagonal Brillouin zone of graphite.v
l mean free path.m
l phase coherence length.`
n electron density.e
Q quality factor of cantilever.
¾ electrical conductivity.
¾ elastic strain along tube axis.t
µ chiral angle of carbon nanotubes.
µ pyramidalization angle.p
` …-orbital misalignment angle.…
Φ Schottky barrier.b
Φ zero-bias Schottky barrier.b02 CONTENTS
„ hole mobility.h
” Poisson’s ratio.
” single-particle states per unit volume.s
¿ relaxation time.
T translational vector of carbon nanotubes.
v average velocity of electron.
v Fermi velocity.F
V output voltage from voltage adder.a
V carbon-gate voltage.cs
V drain-source vds
V back-gate voltage.gsOutline
In 1956 the NobelPrize wasawardedto Shockley, Bardeen and Brattainfor their
discovery of the transistor effect in 1947. The transistor is one of the most im-
portant inventions of the past century and often cited as the example of how
scientific research can lead to useful commercial products. The integration of
transistors in modern semiconductor electronics led to another revolution in hu-
man history. The Nobel Prize was again awarded to this great contribution in
2000. Half a century after the first transistor, the point-contact transistor, sci-
entists have demonstrated that semiconducting carbon nanotubes can also have
6transistor-like behavior. The transistor size has been shrunk by a factor of 10 .
This thesis outlines the process of making nanotube-based electronic devices, as
well as the study of their electrical transport. Particular emphasis is placed on
electrical transport and modification of electronic structure promoted via struc-
tural changes to the tube.
In chapter 1 we will present an introductory overview to carbon nanotubes
and their band structures. Several review papers [4, 96] are recommended for
detailed description in the electronic structure and consequent transport prop-
erties of carbon nanotubes. Chapter 2 will discuss the experimental methods
involved in device preparation and electrical studies. It is a challenge to exploit
thetransportpropertiesofspecificmoleculesbyapplyingselectivemetalcontacts
to them. This chapter, therefore, includes how we separate the tangled carbon
nanotubes isolating them in suspension and then selectively making contact on
desired nanotubes. The measurement setup for electrical transport is shown at
the end of this chapter.
Chapter 3 gives a brief description of the electrical transport in mesoscopic
conductors. Atappropriatetemperaturesthechargequantizationcanbeobserved
via single electron tunneling in junction/island/junction arrangement, which is
used for interpreting the transport behavior of carbon nanotubes at low temper-
atures.
Chapter 4 discusses very interesting hierarchal nanotube peapod structures,
i.e., metallofullerenes are peas and confined in the interior hollow of nanotubes.
The encapsulation of metallofullerenes is inspected by means of a high resolution
transmissionelectronmicroscope. Wewilldiscusstheroleofmetallofullerenesin-
sideananotubeandhowthisvariestheelectricalpropertiesofthehostnanotube
as a function of temperature.
34 CONTENTS
In conventional metal-oxide-semiconductor field-effect transistors (FETs), a
top gate is often used to control the conduction of the inversion layer underneath
the gate insulator. The carbon nanotube FETs in the published literature to
date are constructed either in back gate or in top gate configurations. This al-
lows the carbon nanotube FETs to be operated in macroscopic scale. In chapter
5, we will show a novel method of making carbon nanotube FETs operated in
real nanoscale. The conventional metal gate is replaced by an in-plane carbon
gate which is actually made by another carbon nanotube and insulated by the
single molecular linker to an active channel. To form these T-shape junctions,
chemical functionalization has been done to incorporate diaminal functionality
into carbon nanotubes. The presence of a molecular linker is evidenced by X-
rayphotoelectronspectroscopyandRamanspectroscopy. Howaone-dimensional
carbon nanotube gate works in modulating another one-dimensional carbon nan-
otube active channel will be discussed in chapter 6.Chapter 1
Introduction
1.1 Carbon family and nanotubes
Prior to the discovery of fullerenes, graphite and diamond were the only known
3crystalline forms of carbon. The diamond is sp -hybridized, forming a three-
dimensional (3D) network by binding the tetrahedral unit structures together,
2whereasthesp hybridizationingraphitelinkscarbonatomsinatwo-dimensional
(2D) layer of hexagons (Figure 1.1 (a) and (b)). In the latter case, the p orbitalsz
which are perpendi