Carbon Nanotube Field Research Articles

SU-GG-J-44: Carbon Nanotube Field Emission Technology Enables Novel Imaging and Irradiation System Development for Cancer Research and Clinical Application

Purpose:Carbon nanotubefield emission is an emerging nanotechnology for novel x‐ray imaging and radiation delivery systems development for cancer research and clinical application. In this presentation we will give a general review of the nanotechnology and its applications in the development of novel devices including CT imaging,tomosynthesis, and cancer research radiation delivery systems. Method and Materials:Carbon nanotubefield emission is a based on the unique properties of a nanomaterial called carbon nanotubes(CNT).CNT is the newest carbon allotrope discovered in 1991 and it is comprised of either a single graphene shell, called the single‐wall carbon nanotube, or multiple concentric graphene shells termed a multi‐wall carbon nanotube. The signature feature is a very large aspect ratio (ratio of diameter to length) that is typically is on the order 103. The high aspect ratio makes CNTs a practical and excellent field emitter that can produce high current density with intrinsically small divergence and extremely high temporal resolution. More importantly, its unprecedented flexibility in cathode design has launched new creativity in imaging and therapy system development. Results: We will show examples of our research development on CNTfield emission based imaging and irradiation systems that include 4D micro‐RT, stationary tomosynthesis, multi‐pixel electron microbeam cellular irradiator under real time microscope observation, and multi‐pixel x‐ray micro‐CT‐RT image‐guided and intensity‐modulated radiation for small animal tumor models. The technical challenges of the CNTfield emissiontechnology will also be discussed. Conclusion:Carbon nanotubefield emissiontechnology has shown great promise in developing novel imaging and radiation systems that can potentially advance cancer research and improve the quality and efficiency of cancer diagnosis and treatment.

Carbon nanotube transistors – chemical functionalization and device characterization

AbstractThis review presents an overview of the recent progress made in the field of carbon nanotube (CNT)‐based field‐effect transistors (FETs). Starting from the simplest device architectures, various methods reported for fabricating CNT‐FETs are presented. The main focus is laid on the use of chemical functionalization strategies both at a tube and at a device level to improve the performance of the devices. In addition to solid dielectric gate insulators, the use of liquids or solid polymer electrolytes as effective electrochemical gating media is outlined. Following this, device parameters of the various CNT‐FETs are compared and discussed. Finally, the utility of scanning photocurrent microscopy as an efficient characterization tool to estimate electronic band‐profiles of CNT‐FETs is highlighted. The review concludes with future perspectives in this rapidly emerging field. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Carbon nanotubes and porphyrins: an exciting combination for optoelectronic devices

Hybrids between carbon nanotubes and porphyrins, either covalently or non-covalently linked, have been the target of numerous groups with the aim of studying their properties and searching for potential applications. The state of the art in the field of carbon nanotubes and porphyrins is reviewed here.

Electrical detection of hepatitis C virus RNA on single wall carbon nanotube-field effect transistors

We report the unambiguous detection of a sequence of Hepatitis C Virus (HCV) at concentrations down to the fractional pM range using Single Wall Carbon Nanotube (SWNT) Field Effect Transistor (FET) devices functionalized with Peptide Nucleic Acid (PNA).

Elimination of current non-uniformity in carbon nanotube field emitters

Activation of abnormal emitting sites in Carbon Nano Tube (CNT) field emitters and their elimination is reported. CVD grown, patterned CNT was used as cathode for field emission studies. We encountered the problem of current non-uniformity in CNT cathode. This non-uniformity was attributed to abnormally active emitting sites during voltage ramp-up. The sudden increase in current resulted in region of positive slope in F–N curve, which can’t be explained by conventional F–N theory. Also the grown CNTs can be a mixture of metallic and semi conducting nature, which may cause deviation from the conventional F–N theory. We could eliminate abnormally active sites by electric field treatment, thereby increasing current uniformity and stability. The work is underway to understand the deviation in FN curve at high fields.

A Field Effect Transistor Fabricated with Metallic Single‐Walled Carbon Nanotubes

We report novel transport properties of the individual single‐walled carbon nanotube (SWNT) field effect transistors (FETs) decorated with the protein (streptavidin)‐coated nanoparticles. Upon adsorption of the protein‐coated nanoparticles at the metal‐nanotube contact, the metallic SWNT devices abruptly exhibit a p‐type semiconducting behavior. In the case of semiconducting SWNT devices, the adsorptions of protein‐coated nanoparticles make the gating more effective, resulting in a far suppressed off‐state leakage current as well as an enhanced on‐state p‐channel current. Through the ab initio electronic structure calculations, it is suggested that such an apparent metal‐semiconductor transition may be due to the intervening charged species in the contact area, originated from the surface of the proteins. Noting the separation of the semiconducting nanotubes from metallic ones would be a formidable task; we suggest that the device concept here could be another breakthrough for the nanotube‐based electronic devices, in which the nanotubes are not necessarily semi‐conducting.

Richard E. Smalley (6 June 1943–28 October 2005)

AbstractThe international scientific community suffered a great loss with the death of Richard Errett (Rick) Smalley at age 62 following a 6‐year battle against cancer. Throughout his career, Rick had a profound influence through his pioneering research in chemistry and nanoscience, his mentorship of young scientists, and his advocacy for the role of science in solving major societal problems.As a postdoctoral fellow working with Donald Levy and Lennard Wharton at the University of Chicago, Rick spearheaded the invention of supersonic jet spectroscopy. This powerful method cools gas phase molecules nearly to absolute zero, enormously simplifying many complex and otherwise uninterpretable spectra. Thirty years later, supersonic jet spectroscopy remains a vital tool in chemical physics.Rick Smalley came to Rice University in Houston, Texas in 1976 to accept his first and only faculty appointment. He and his students quickly built an advanced apparatus for supersonic jet spectroscopy and made important contributions to molecular physics. Rick then invented a device to laser‐vaporize high melting materials into small molecular clusters. By spectroscopically probing these novel species, he pioneered another new field: the study of small metal and semiconductor clusters. Rick, Harry Kroto and Robert Curl were investigating carbon clusters in 1985 when they made their famous discovery of the fullerenes, for which they shared the 1996 Nobel Prize in Chemistry. To date, tens of thousands of scientific papers have been published on fullerenes.In the early 1990's, Rick Smalley turned his attention to the new field of carbon nanotubes. His group made many landmark discoveries and invented nanotube growth methods that supplied samples for researchers around the world. Most recently, Rick expanded his horizons to seek solutions to the immense problem of global energy needs. He helped shape national and international research priorities, including the U.S. National Nanotechnology Initiative. Rick was a visionary and passionate believer in the power of science and technology to solve great problems. He advised students: “Be a scientist and save the world.”Rick Smalley had great personal charm and charisma. He loved to teach and inspire his students, some of whom described him as “Moses‐like”. He was fearless not only in abandoning the comforts of a successful research program to leap into promising but uncertain new fields, but also in battling his fatal disease while working intensely until the very end of his life. He was devoted to and is survived by his wife Deborah and two sons, Chad and Preston.Rick Smalley's untimely death is a loss not only to his family, friends, students, colleagues, and collaborators, but to the worldwide communities that he led and served. He will be deeply missed and long remembered. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Network Single-Walled Carbon Nanotube-Field Effect Transistors (SWNT-FETs) with Increased Schottky Contact Area for Highly Sensitive Biosensor Applications

Highly sensitive single-walled carbon nanotube-field effect transistor (SWNT-FET) devices, which detect protein adsorptions and specific protein-protein interactions at 1 pM concentrations, have been achieved. The detection limit has been improved 104-fold compared to the devices fabricated by photolithography. The substantially increased sensitivity is mainly due to the increased Schottky contact area which accommodates relatively more numbers of proteins even at very low concentration. The augmented number of proteins adsorbed on a device induces instant modulation of the work function of metal contact electrodes, which eventually changes the conductance of the device. Such devices have been attained by addressing metal electrodes on network-type SWNTs using a shadow mask on a tilted angle sample stage. The shadow mask allows metals to penetrate underneath the mask efficiently, therefore forming a thin and wide Schottky contact area on SWNT channels.

Uniform carbon-nanotube emitter for field-emission displays

— The synthesis of carbon-nanotube (CNT) field emitters for FEDs by thermal chemical vapor deposition (CVD) and their structural and emission characterization are described. Multi-walled nanotubes (MWNTs) were grown on patterned metal-base electrodes by thermal CVD, and the grown CNTs formed a network structured layer covering the surfaces of the metal electrode uniformly, which realized uniform distribution of electron emission. A technique for growing narrow MWNTs was also developed in order to reduce the driving voltage. The diameter of MWNT depends on the growth temperature, and it has changed from 40 nm at the low temperature (675°C) to 10–15 nm at the high temperature (900–1000°C). Moreover, narrower MWNTs were grown by using the metal-base electrode covered with a thin alumina layer and a metal catalyst layer. Double-walled nanotubes (DWNTs) were also observed among narrow MWNTs. The emission from the narrow CNTs showed a low turn-on electric field of 1.5 V/μm at the as-grown layer.

SIMULATION OF HIGH CURRENT FIELD EMISSION FROM VERTICALLY WELL-ALIGNED METALLIC CARBON NANOTUBES

We have studied the intense electron beams emitted from multiple metallic, vertical and well-aligned Carbon Nanotube (CNT) field emitters. A two-dimensional (2D) particle-in-cell simulation code MAGIC2D is used to obtain the I–V characteristics near to the apex of the emitters' surface for a given applied electric field and field enhancement factor over a wide range of parameters. The effects of electron space charge and electric field shielding from neighboring emitters are compared in low current and high current regimes. It is found that the electron space charge is dominant in high current regime, where the Fowler–Nordheim (FN) law becomes the 2D Child–Langmuir (CL) law. The emitter spacing, number of emitters, and emitter's uniformity are also particularly studied, and they are more critical in low current regime. Smooth transition from the FN law to CL law is demonstrated.

International patenting activity in the field of carbon nanotubes

Abstract Carbon nanotubes (CNT) are unique nanostructures with remarkable electronic and mechanical properties and could be used, for example, in nanometre-sized electronics or to strengthen polymer materials. Today, both SWNT and MWNT are being used as key components in the production of high-strength composites, and advanced sensors, electronic and optical devices, catalysts, batteries and fuel cells. Patenting activity in this sub-field of nanotechnology registered a spurt during the last 12 years––implying a breakthrough bringing about a technological paradigm shift in the field of fullerene since carbon nanotubes are fullerene-related structures. CNT is, thus, one of the key technologies likely to revolutionize information technology, materials and medicine and the present study aim to examine technological developments in this field based on international patenting activity during the period of 1991–2003.

Fabrication of carbon nanotube array and its field emission property

A fabrication process for carbon nanotubes (CNTs) field emitter array is reported. This process consists of formation of protrusions on a silicon substrate, selective deposition of catalyst film on tips of the protrusions and direct growth of the CNTs on the tips of the protrusions by plasma-enhanced chemical vapor deposition. In this process, number of the CNTs grown on each tip of the protrusion can be controlled by the size of the protrusion. The CNT field emitter arrays gave better field emission property than a continuous CNT film. A threshold voltage required to obtain 1 μA/cm2 of field emission current from the CNT field emitter array was about 300 V lower than that from the continuous CNT film. This improvement is presumably due to reduction of screening effect, which prevents the field from concentrating on the tip of the CNT emitters.

Synthesis and manipulation of carbon nanotubes

This paper reviews recent results in the field of carbon nanotube (CNT) research obtainedat our institute at EPFL. We show in particular that CNTs can be synthesizedby the catalytic vapour deposition (CVD) technique with high efficiency andpurity. Furthermore, we present recent examples of advances in the large-scaleproduction of CNTs as well as in the chemical and mechanical manipulation ofCNTs. The chemical manipulation involves covalent and non-covalent sidewallfunctionalization of single-wall CNTs and preparation of inorganic coatings on CVD-grownnanotubes for the realization of fibres and CNT-reinforced composites. Mechanicalmanipulation aims at the application of CNTs as tips for scanning probe microscopy.

Field emission characteristics of self-assembled carbon nanotubes on the gold surface

A method was studied to fabricate carbon nanotube (CNT) field emitters through self-assembly of thiol-modified CNTs onto a gold-coated substrate. By adsorption through simple immersion of the gold-coated substrate into thiol-modified CNT solution overnight, deposition of CNTs was accomplished. It was found that CNTs were deposited on the substrate as random aggregates of CNT bundles. The population density of CNTs on the gold-coated substrate was varied by controlled CNT concentration in ethanol. The I–V measurement of the self-assembled CNTs shows relatively good field emission characteristics with a low turn-on field (2.5 V/μm) and a high current density (40 μA/cm2 at 3 V/μm). In addition, more-populated CNTs on the substrate produce a higher current density. Therefore, the technique of self-assembly of CNTs on a selected area is expected to be a reliable way to prepare large-size panels with easy process and low cost. These advantages recommend further investigation of the self-assembly of CNTs.

Low-temperature magnetoresistance of individual single-walled carbon nanotubes: A numerical study

The low-temperature magnetoresistance induced by an axial magnetic field in individual single-walled carbon nanotubes (SWNTs) is studied numerically based on Boltzmann transport equation and \ensuremath{\pi} electronic energy dispersion relations for individual SWNTs as well as taking one-dimensional weak localization (WL) into account. It is shown that the Altshuler-Aronov-Spivak effect related to WL is much weaker in individual SWNTs than in individual multiwalled carbon nanotubes, whereas the Aharonov-Bohm (AB) effect related to tubular energy band structure is stronger in individual SWNTs when the conducting electrons occupy lower energy levels, but this effect weakens rapidly as conducting electron energy increases. This suggests that only the AB effect can be observed remarkably in the states of the conducting electrons with lower energy.

11.3: Invited Paper: Lighting Elements of Carbon Nanotube Field Emission Display

AbstractEach year the Society awards the Display of the Year Award to several display devices that exhibit leading edge technology or innovative solutions to an information display need. The following paper provides a summary of a Display of the Year award recipient from 1999 and 2000 SID conferences. The display described Carbon‐nanotube(CNT) Field Emission Display(FED) has produced the first commercial product as a lighting element, which is a 1‐pixel 20mm‐diameter cylindrical device intended to replace existing externally similar thermionic (CRT‐type) lighting elements used in outdoor displays and other high‐brightness applications.An excellent performance of carbon‐nanotubes as field‐emitters was demonstrated using a high‐voltage FED elements at SID in 1998 where a light‐source tube for outdoor large size display and diode type flat panel were presented with the screen printed nanotube cathode.After that, an x‐y addressable high‐luminance FED panel was introduced at IDRC in 1999. The experimental panel was performed ca.7×105 cd/m2 green light at 6kV, ca.1mA/cm2 dc‐driving condition.The results show the excellent performance of carbon nanotube FED as flat panel displays which are applicable to large size TV devices. This panel will be not only suitable for future TV display but also light‐sources for field sequential color LCDs.The CNT FED lighting‐element module is exciting not only because it is the first commercial implementation of CNT technology, but because it could pave the way for new generations of FED products.

Magnetic susceptibility of multilayered carbon nanotubes

A theoretical study of the magnetic susceptibility of multilayered carbon nanotubes in fields both parallel, H ∥, and perpendicular, H ⊥, to the tube axis has been carried out disregarding electron-electron interaction. The temperature dependences of the magnetic susceptibility obtained exhibit a nontrivial form for H ∥, which is related to the quasi-one-dimensionality of such a system as the nanotube. The dependences of the magnetic susceptibility on chemical potential χ(μ) have also been derived. At low temperatures, χ(μ) has sharp peaks in fields H ∥, which is connected with the presence of $${1 \mathord{\left/ {\vphantom {1 {\sqrt E }}} \right. \kern-\nulldelimiterspace} {\sqrt E }}$$ singularities in the density of states of nanotubes. The effect of interlayer coupling on magnetic susceptibility of small-radius tubes has been investigated numerically.