Carbon Nanotube Antenna in the sub Terahertz Range

By M.SREEKANTH REDDY

M.Tech ECE 1ST YEARREG.NO:14304012

DEPARTMENT OF ELECTRONICS ENGINEERING PONDICHERRY UNIVERSITY

CONTENTS

History of carbon nanotube Why carbon nanotube Properties CNT synthesizing CNT Antenna Conclusion

History of carbon nanotube

In the early 1950s, Radushkevich and Lukyanovich3 published a report on hollow carbon fibers that are 50 nm in diameter.

the demand by the space and aerospace industry for stronger, lightweight materials with improved mechanical properties has led to substantial progress in the production and characterization of carbon filaments and hollow carbon fibers.

Carbon nanotubes (CNTs) are now well into their teenage years.

In 1991 the true first invention was finally made

Why carbon nanotube

Carbon nanotubes (CNTs) are allotropes of carbon. These cylindrical carbon molecules have interesting properties that make them potentially useful in many applications in nanotechnology, electronics, optics and other fields of materials science, as well as potential uses in architectural fields. They exhibit extraordinary strength and unique electrical properties, and are efficient conductors of heat. Their final usage, however, may be limited by their potential toxicity.

Strength

Electrical

Thermal

Defects

One-Dimensional Transport

Properties

Strength Carbon nanotubes have the strongest tensile strength of any

material known. It also has the highest modulus of elasticity.

Electrical

If the nanotube structure is armchair then the electrical properties are metallic

If the nanotube structure is chiral then the electrical properties can be either semiconducting with a very small band gap, otherwise the nanotube is a moderate semiconductor

In theory, metallic nanotubes can carry an electrical current density of 4×109 A/cm2 which is more than 1,000 times greater than metals such as copper

All nanotubes are expected to be very good thermal conductors along the tube, but good insulators laterally to the tube axis.

It is predicted that carbon nanotubes will be able to transmit up to 6000 watts per meter per Kelvin at room temperature; compare this to copper, a metal well-known for its good thermal conductivity, which transmits 385 watts per meter per K.

The temperature stability of carbon nanotubes is estimated to be up to 2800oC in vacuum and about 750oC in air.

Thermal

Defects

Defects can occur in the form of atomic vacancies. High levels of such defects can lower the tensile strength by up to 85%.

Because of the very small structure of CNTs, the tensile strength of the tube is dependent on its weakest segment in a similar manner to a chain, where the strength of the weakest link becomes the maximum strength of the chain.

One-Dimensional Transport

Due to their nanoscale dimensions, electron transport in carbon nanotubes will take place through quantum effects and will only propagate along the axis of the tube. Because of this special transport property, carbon nanotubes are frequently referred to as “one-dimensional.”

Single-Wall Nanotube (SWNT)

Graphite sheet seamlessly wrapped to form a cylinder typically 1 nm in diameter

Armchair Zig-Zag

Multi-Walled Nanotubes (MWNT)

Multiple rolled layers of graphene sheets More resistant to chemical changes than SWNTs

CNT Synthesizing

Arc Discharge

Laser Ablation

Chemical Vapor Deposition (CVD)

Ball Milling

Arc Discharge

A direct current creates a high temperature discharge between two electrodes

Atmosphere is composed of inert gas at a low pressure

Originally used to make C60 fullerenes

Cobalt is a popular catalyst

Typical yield is 30-90%

Arc Discharge

• Simple procedure• High quality product• Inexpensive

Disadvantages• Requires further purification• Tubes tend to be short with• random sizes

Advantages

Laser Ablation

Discovered in 1995 at Rice University

Vaporizes graphite at 1200 ⁰C Helium or argon gas A hot vapor plume forms and

expands and cools rapidly Carbon molecules condense to

form large clusters Similar to arc discharge Yield of up to 70%

Laser Ablation

Advantages• Good diameter control

• Few defects

• Pure product

Disadvantages• Expensive because of lasers and high powered

equipment

Chemical Vapor Deposition

Carbon is in the gas phase

Energy source transfers energy

to carbon molecule

Common Carbon Gases

• Methane

• Carbon monoxide

• Acetylene

Chemical Vapor Deposition After energy transfer, the

carbon molecule binds to the

substrate

Temperature between 650 –

900 ⁰C

Yield is usually about 30%

One of the most common

methods of carbon nanotube

synthesis

Chemical Vapor Deposition

Advantages• Easy to increase scale to industrial

production

• Large length

• Simple to perform

• Pure product

Disadvantages

• Defects are common

Ball Milling

Powder graphite is placed in

a stainless steel container

Argon gas is used

Process occurs at room

temperature

Powder is then annealed

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