ABSTRACT- structures, and devices. This paper gives a

ABSTRACT- The nanotechnology is a system
of innovative methods to control and manipulate matter at near atomic scale to
produce new materials, structures, and devices. This paper gives a review on
the growth, structural properties and practical applications of carbon nanofibers
as compared with those of conventional carbon fibers. Carbon nanofibers could
be produced via the catalytic chemical vapour deposition (CVD) as well as the
combination of electro spinningof organic polymer and thermaltreatment.
Nanotechnology offers the potential for tremendous improvement and advances in
the development of commercial products that may benefit society, such as
integrated sensors, semiconductors, medical imaging, drug delivery systems,
structural materials, sunscreens, cosmetics, and coatings. Nanotechnology is
one of the most enabling technologies across the world. By 2020, the global
market for nanotechnology-related products is predicted to reach $3 trillion
and employ 2 million workers in the United States alone 1.

Keywords-Nano sensor, Polymeric composites,
carbon fiber, Nanotube, Graphene, Nanotechnology, Nanomaterial’s, chemical
sensors, Radio frequency identification sensor.

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INTRODUCTION:

The Nano-objects are nanomaterial’s that have at least one
dimension less than 100 nanometre. Nanoparticles are a specific class or subset
of these Nano-objects, having three dimensions that are less than 100 nanometres3,
7, 9, 10. The Nanoparticles exhibit unique properties because of their Nano
scale dimensions. In recent years,
nanotechnology has emerged out as the backbone of contemporary devices based on
the sensors. It has opened up new dimension for the Nano devices in numerous
fields. Since this technique is unique, better and efficient than previous ones
in many aspects like the exceptional characteristics of Nano composites and
materials 15, 16, 31.Carbon nanofibers are linear, no
continuousfilaments that are different from continuous, several micrometre
diameter carbon fibres. The commercially available carbon nanofibers around the
world is calculated as 500 t/y. Carbon nanofibers exhibit high specific area,
flexibility, and super strength due to their Nano sized diameter that allow
them to be used in the electrode materials of energy storage devices,
hybrid-type filler in carbon fiber reinforced plastics and bone tissue scaffold
8. It is envisaged that carbon nanofibers will be key materials of green
science and technology through close collaborations with carbon fibres and
carbon nanotubes 11, 14, 15.

The design
of maintenance-free and passive wireless sensors like, gas sensor or fire
sensor is already being thoroughly tested. The other emerging fields are radio
frequency identification (RFID) sensors or biological sensors. It is observed
that various properties like chemical, mechanical and electrical are already
being studied and many such fields are already being explored. This level of
expertise is achieved till today from the first intervention of carbon
nanotubes by the scientist S. Iijima in the decade of 1990’s. The
investigations have predicted a very important factor about CNTs that their
activation power is much smaller than other conventional devices and it comes
out about 10000 times smaller than actual requirements of micro electro-mechanical
systems (MEMS) conventionally used. The CNTs are that’s why truly considered as
sensing elements of next generation 151. The CNT (Carbon Nanotube) has been
discovered by Sumio Iijima in 1991 184 and since then various  devices such as atomic force microscopy probe
tip 168, Nano actuator 169, nanotweezer 17,  Nano oscillator 18 and many more have been
made based on this structure. These accomplishments are obtained due to the
unique characteristics of the CNT such as big Young’s modulus, high stiffness,
small size, light weight, high aspect ratio 12, 13 and interesting
electrical properties 16, 20.

Let’s
consider the case of a CNT based prototype RFID sensor. It is observed that
this type of sensor exhibit unique features based on that it is roughly
categorised as maintenance free sensor. In this setup, this objective is
obtained if the sensor antenna measurements are used in a controlled way and
the simulation are obtained. Such a CNT Bucky paper can be easily characterized
by taking into consideration the sensitivity and dielectric behaviour of the
sensor. Another emerging application of CNT can be its ability to sense the
harmful gases like NH3 19, 21, and 22. The CNT’s ability as sensors to
measure sensitivity towards NH3 is experimentally verified and its applicability
is already tabulated in different studies. In the feasibility study of a CNT
based combinational materials, its depositions along with the inkjet printing
is already being realised. This approach is helpful in achieving the various
typical applications of CNT based sensors. This innovative approach is again
one of the emerging application domains of CNT’s in the various field of
internet communication technologies and integrated electronics environments 27,
28, 36. This is observed that there is a demand of the moment of a
sophisticated architecture which may be so innovative that it can be easily be
adopted in various research and development areas.There are many interesting
applications of the CNT like one in a resonator based sensors. These sensors
can be used in many sensing  applications
such as gas level sensing, metal deposition monitors, chemical reactor
monitors, mass detectors and biomedical sensors 32, 33. All these
applications follow general frequency phenomenon that is changes in mass causes
a shift in natural frequency and the resulted frequency shift can be used to
detect or predict either presence or concentration of the attached mass23,
24. The other properties of CNTs like extremely high stiffness and light
weight make CNT as an excellent platform to make a high frequency resonance
based sensor. This is predicted that the natural frequency of 10 GHz-1.5 THz
can be achieved by a CNT based cantilever or bridge beam 29. This value is among
the greatest value reported in the present Nano-mechanical resonators.  In the case of resonator based sensors, the
higher frequencies provide more sensitive sensors. The research has shown that Nano
tubes are considered to be a continuum models, such as shell or beam, with no
vacancy defect 30, 34, and 35. The studies are going on the resonator
frequency, based on quantity and the place of the vacancy defects 183. The
method and devices (SuFETs) for design of the bioelectronics sensors has been
proposed. The circuits consist of the superconducting material which is organic
generally and is used for fabricating solid-state field-effect transistor
(SuFET). This is further connected to a nerve fiber by a simple nanotube
contact. There may be a traditional low-ohmic contact also. There are many
application areas of organic and chemical gas sensors which are very promising.
These include the design and fabrication of devices built using carbon
nanotubes (CNT)-based FETs. The above approach of designing is best as an
application of SuFETT. Already observations has revealed that the range of
picked up signals varies from 0.6 nA to 10 A with frequencies from 20 to 2000
Hz.

1.
Similarity and Difference between Carbon Fibers and Carbon Nanofibers:

Since carbon nanofibers could be considered as the 1-D form
of carbon, their structure and properties are closely related to those of other
forms of carbon, especially to crystalline three-dimensional graphite,
turbostratic carbons and to their constituent 2-D layers. Therefore, several
forms of conventional carbon materials should be mentioned in terms of their
similarities and differences relative to a carbon nanofiber. Especially, a
direct comparison should be made between fibrous carbon materials, because the carbon
fiber acts as a bridge between carbon nanofibers and conventional bulky carbon materials
27, 28. In this section, the structures of carbon fibers as well as VGCFs
are described with a strong emphasis on the similarities and differences of
these 1-D carbon materials 39.

 

2. Basic
Theory and Concepts regarding Nanomaterial’s:

Carbon fibers represent an important class of graphite
related materials that are closely related to carbon nanofibers, with regard to
structure and properties. Carbon fibers have been studied scientifically since
the late 1950s and fabricated industrially since 1963. They are now becoming a
technologically and commercially important material in the aerospace,
construction, sports, electronic device and automobile industries.

 

Fig. 1: The
mechanical properties of various kinds of carbon and graphite fibers 40.

 

The global carbon fiber market has now grown to about 12 500
t/y of product, after 40 years of continuous R work 2. Carbon fibers
are defined as a filamentary form of carbon with an aspect ratio
(length/diameter) greater than 100. Probably, the earliest documented carbon
fibers are the bamboo char filaments made by Edison for use in the firstincandescent
light bulb in 1880. With time, carbon fibers were replaced by the more robust
tungsten filaments in light bulb applications, and consequently carbon fiber
R vanished at that early time. But in the late 1950s, carbon fibers once
again became important because of the aggressive demand from aerospace
technology for the fabrication of lightweight, strong composite materials, in
which carbon fibers are used as a reinforcement agent in conjunction with
plastics, metals, ceramics, and bulk carbons.

The
specific strength (strength/weight) and specific modulus (stiffness/weight) of
carbon fiber-reinforced composites demonstrate their importance as engineering
materials, due to the high performance of their carbon fiber constituents.
Since the temperature and pressure necessary to prepare a carbon fiber from the
liquid phase is at the triple point (T = 4100 K, p = 123 kbar), it would be
almost impossible to prepare carbon fibers from the melt under industrial
processing conditions. Carbon fibers are therefore prepared from organic precursors.
This preparation is generally done in three steps, including stabilization of a
precursor fiber in air (at ? 300 ?C), carbonization at ? 1100 ?C, and
subsequent graphitization (> 2500 ?C). Fibers undergoing only the first two
steps are commonly called carbon fibers, while fibers undergoing all three
steps are called graphite fibers. Carbon fibers are generally used for their
high strength, while graphite fibers are used for their high modulus 41, 42.

 

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