THE EMERGING FUTURE OF NANOTECHNOLOGY
PLASMONICS

Nazeer Rehman Mohammad & Taj Mohammad
Email: nazeer_485@rediffmail.com
Sri Sarathi Institute of Engineering and Technology
Nuzvid, Krishna District, A.P., India.
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ABSTRACT:

With the increasing quest for transporting large amounts of data at a fast speed along with miniaturization both electronics and photonics are facing limitations. Thus plasmonics is an upcoming technology that has the capacity of photonics and smallness of electronics which is to overcome the limitations of photonics and electronics. Before all plasmonic chips are developed plasmonics will probably be integrated with conventional silicon devices.Plasmonic wires will act as high band width free ways across the busiest areas of the chip. Plasmonics is useful in many areas for example it can useful in industry, optical, electronics, defense, medical systems. The emphasis is laid on basic definition of plasmonics, the need for idea of plasmonics, plasmonics as a researcher’s interest, some of the basic applications of plasmonics. Much focus is laid on the explanation of some of the applications which include Funneling of light, faster chips, Treatment of cancer and even invisibility.

PLASMONICS –Terminology:

Plasmonics refers to the investigation development and applications of enhanced electromagnetic properties of metallic nano structures. The term plasmonics is derived from the term PLASMONICS which are the quanta associated with longitudinal waves propagating in matter through the collective motion of large numbers of electrons.
	Plasma is a medium with equal concentration of positive and negative charges of which at least one charge type is mobile. In a solid the negative charges of the conduction electrons are balanced by an equal concentration of positive charge of ion cores.
	A plasma oscillation in a metal is a collective longitudinal excitation of the conduction electron gas against a background of fixed positive ions with plasma frequency.
	Surface plasmons are dense waves of electrons –bunches of electrons passing a point regularly – along the surface of a metal. Plasmons have the same frequencies and electromagnetic fields as light, but their sub-wavelength size means that they take up less space.
•	“Plasmonics thus is the technology of transmitting light like waves along       nanoscale wires”
•	“Plasmonics also called ‘LIGHT ON A WIRE’ would allow transmission of data at optical frequencies along the surface of tiny metallic wire”.

ROAD MAP TO PLASMONICS:

The Roadmap extends from 1980 to 2020 and represents the evolution of nanotechnology in three stages:
1.	The first stage, extending from 1980 to 2000, recognizes the emergence of a mature and largely consolidated nano tools sector and the existence of a nascent nano materials sector.
2.	The second stage, extending from 1990 to 2010, reflects the emergence of a mature and largely consolidated nano materials sector and the marketing of a growing number of nano tools and nano materials enabled products and processes.
3.	The third stage, extending from 2000 to 2020, foresees the use of nano tools and nano materials becoming widespread in many sectors, leading to the commercialization of new and improved products and processes enabled by the incorporation of nano devices and nano systems.Plasmonics belonging to this sector is going to make a faster tomorrow.

NEED FOR PLASMONICS:

Optical fibers now span the globe, guiding light signals that convey voluminous streams of voice communications and vast amount of data. This gargantuan capacity has led some researchers to prophesy that photonic devices –which channel and manipulate
Visible light and other electromagnetic waves—could someday replace electronic circuits in microprocessors and other computer chips.   
Photonic components such as fiber optic cables can carry a lot of data but are bulky compared to electronic circuits. Electronic components such as wires and transistors can be incredibly small, but carry less data. A problem holding back the progress of computing is that with mismatched capacities and sizes the two technologies are hard to combine in a circuit. Researchers can cobble them together, but a single technology that has the capacity of photonics and smallness of electronics with the best bridge of all.

	Researchers are pioneering such technology called plasmonics. It would allow transmission of data at optical frequencies along the surface of a tiny metallic wire, despite the fact that the data travels in the form of electron density distributions rather than photons.
            Another classic semiconductor issue that the researchers will have to address is ‘heat’. Chipmakers are constantly striving to ensure that their electronic chips don’t run too hot. Plasmonics also will generate some heat, but the exact amount is not yet known. Even if plasmonics runs as hot as electronics, if will still have the advantage of a higher data capacity in the same space.

PLASMONICS –- RESEARCHER’S INTEREST:

             Plasmon waves are of particular interest because these are at optical frequencies. The higher the frequency of the wave, the more the information we can transport .Optical frequencies are about 100,000 times greater than the frequency of today’s electronic microprocessors.
             The key is using a material with a low refractive index, ideally negative, such that the incoming electromagnetic energy is reflected parallel to the surface of the material and transmitted along its length as far as possible. There exists no natural material with a negative refractive index, so nanostructure materials must be used to fabricate effective plsmonic devices. For this reason, plasmonics is frequently associated with nanotechnology. 
            Plasmonics describes how ultra small metallic structures of various shapes capture and manipulate light and provides a practical design tool for nanoscale optical components. The fact that light interacts with nanostructures overcomes the belief held for more than a century that light waves couldn’t interact with anything smaller than their own wavelengths. 
            Research has shown that nanoscale objects can amplify and focus light in ways scientists never imagined. The ‘how’ of this involves plosmons-ripples of waves in the ocean of electrons flowing across the surface of metallic nanostructures. The type of Plasmon that exists on a surface use directly related to its geometric structure.
The potential of plasmonics right now is mainly limited by the fact that plasmons can typically travel only several millimeters before they extinct. Chips, meanwhile, are typically about a centimeter across, so plasmons can’t yet go the whole distance.

APPLICATIONS:
	
Plasmonics as a researcher’s interest has got a lot wonderful applications. Hence much of the emphasis is laid on the applications of plasmonics in near future. Many of these are yet to be made practical. But if these applications practically come true there’s going to be a technological revolution in future.
           
 When light of a specific frequency strikes a plasmon that oscillates at a compatible frequency the energy from light is harvested by the Plasmon, converted into electrical energy that propagates through the nanostructure and eventually converted back into light.

Plasmon printing:

Plasmon printing is a new approach to lithographic printing that takes advantage of the resonantly enhanced optical intensity in optical near field of metallic nano particles, and that could enable printing of deepsubwavelength feature using conventional photo resist and simple visible/UV light sources. In the field of chemical sensing, plasmonics offers the possibility of new technologies that will allow doctors, anti-terror squads and environmental experts to detect chemicals in quantities as small as a single molecule. The following diagram represents an example of nano lithography:

               
Schematic dip pen Lithography

Funneling light into tiny wires:

The Study of plasmonics is relatively new, but researchers have already developed prototype devices that demonstrate the promise of the technology.

Planar Wave Guide: 

Plasmons always flow along the boundary between a metal and a dielectric. For example light focused on a straight groove in a metal will generate plasmons that propagate in the thin plane at the metals surface. A Plasmon could travel as far as several centimeters in this planar waveguide – far enough to convey a signal from one part of a chip to another – but the relatively large wave would interfere with other signals in the nanoscale innards of a processor.

Planar Wave Guide
(Source: Scientific American: Nov2007)

Plasmon Slot Waveguide: 

Scientists have built much smaller plasmonic circuits by putting the dielectric at the core and surrounding it with metal. The Plasmon slot waveguide squeezes the optical signal, shrinking its wavelength by a factor of 10 or more. Researchers have constructed slot waveguides with width as small as 50nm –about the same size as the smallest electronic circuits. The plasmonic structure can carry much more data than an electronic wire, but it cannot transmit a signal farther than 100 microns.   

 

Plasmon Slot Wave Guide
(Source: Scientific American: Nov2007)

A Faster Chip: 

Slot wave guides could significantly boost the speed of the computer chips by rapidly tunneling large amount of data to the circuits that perform logical operations. In the rendering at the left, relatively large dielectric wave guides deliver optical signals to an array of plasmonic switches [dubbed “plasmonsters”]. This in turn 
distributes the signals to electronic transistors. The plasmonsters are composed of slot waveguides that measure 100nm across at their broadest points and only 20nm across at the intersections.

A faster Chip Model
(Source: Scientific American: Nov2007)

Just as Lithography is now used to imprint Circuit patterns on silicon chips, a similar process could mass produce miniscule plasmonic devices with arrays of narrow dielectric strips and gaps. These arrays would guide the waves of positive and negative charge on the metal surface; the alternating charge densities would be very much akin to the AC traveling along an ordinary wire. But because the frequency of an optical signal is so much higher than that of an electrical one—more than 400,000 GHz versus 60Hz – the plasmonic circuit would be able to carry much more data. Moreover, because electrical charge dose not travel from one end of a plasmonic circuit to another—the electrons bunch together and spread apart rather than streaming in a single direction – the device is not subject to resistance and capacitance effects that limit the data carrying capacity of IC’s with electrical inter connects.
Plasmonic circuits would be even faster and more useful if researchers could devise a “Plasmonster” switch – a 3 terminal plasmonic device with transistor like properties. Researchers have recently developed low power versions of such a switch. If scientists can produce Plasmonsters with better performance, the devices could serve as the core of an ultra fast signal processing system. 
	 
Cancer Treatment: 

NanoShells that consist of a thin layer of gold –typically about 10nm thick –deposited around the entire surface of a silica particle about 100nm across. Exposed to electro magnetic waves generates electron oscillations in the gold shell; because of the coupling interaction between the fields on the shell’s inner and outer surfaces, varying the size of particle and thickness of the gold layer changes the wavelength at which the particle resonantly absorbs energy.	

Palsmonic Nano Shell
(Source: Scientific American: Nov2007)

This phenomenon has turned nano shells in to a promising tool for cancer treatment. Researchers injected  plasmonic nano shells into the bloodstream of mice with cancerous tumors and found that the particles were non toxic, the nano shells tended to embedded themselves in the rodents cancerous tissues rather than healthy ones because more blood was circulated to the fast growing tumors.

Plasmonic Therapy for Cancer
(Source: Scientific American: Nov2007)

 Fortunately, human and animal tissues are transparent to radiation at certain IR wave lengths. When the researchers directed near – IR laser light through the mice’s skin and at the tumors, the resonant absorption of energy in the embedded nano shells raised the temperature of the cancerous tissues from about 37 C to about 45 C. The photo thermal heating kill the cancer cells while leaving the surrounding healthy tissue unharmed. In the mice treated with nano shells, all signs of cancer disappeared with in 10 days.

Plasmonic Therapy for Cancer
                            (Source: Scientific American: Nov2007)

Invisibility:
	
The most fascinating potential application of plasmonics would be the invention of an invisibility cloak. A tale of young scientist who discovers how to make his own body’s refractive index equal to that of air, rendering him invisible. Exciting a plasmonic structure with radiation that is close to the structure’s resonant frequency can make its refractive index equal to air’s , meaning that it would neither bend nor reflect light. 

How a Cloaking Device Might Word
(Source: Scientific American: Nov2007)

The structure would absorb light, but if it were laminated with a material that produces optical gain – amplifying the transmitted signal just as the resonator in a SPASER would – the increase in intensity would offset the absorption losses. The structure would become invisible, at least to radiation in a selected range of frequencies.
A true invisibility cloak however must be able to hide any thing with in the structure and work for all frequencies of visible light. The creation of such a device would be more difficult. Researchers have theorized that plasmonic materials could render objects invisible. In one proposal, the cloaking device would be a thick shell constructed of Meta materials, which exhibit unusual optical properties. This shell could bend electromagnetic radiation around its central cavity in which a space ship could be hidden. A space telescope pointed at the shell would see only the galaxy behind it.

CONCLUSION:
	The nanotechnology world is heralding a new order. The number of offers that are involved are many due to the multi disciplinary nature of technology, offering scope for many opportunities in the field.Plasmonics, the wonder of nanotechnology is an emerging subject of research presents a whole spectrum of new opportunities to build device components and systems for new architectures. Thus many applications of plasmonics which are to come true may conquer the future world. 
Thus nanocomputers will be self-assembling, using plasmonics (faster chips), rather than lithography that are used to create computer chips.
We have to reinvent the IC with molecular (plasmonical) rather than semiconductor components.
As a final bite, technology is going to create tools that will allow us to conquer disease, make a much faster world, and even an invisible man. The following chart indicates the graph of development in nanotechnology:

Technology Indication Sheet

REFERENCES:

1.	International Semantic, The International Technology Roadmap for Semiconductors.
2.	Scientific American journal – 2007 Edition
3.	Electronics for you magazine – 2007 Edition
4.	Electronics Today magazine--2007 Edition