QUANTUM DOTS:-

Introduction

Quantumdots are nano-meter-scale "boxes" for selectively holding or releasing electrons. Over the past 14 years they have been transformed from laboratory curiosities to the building blocks for a future computer industry. Quantum dots are small metal or semiconductor boxes that hold a well-defined number of electrons. The number of electrons in a dot may be adjusted by changing the dot's electrostatic environment. Dots have been made ranging from 30nm to 1 micron in size, and holding from zero to hundreds of electrons.

Brief History

During the1980's ideas concerning the Quantum Dot surfaced when researchers in the field of computing were trying to construct something close to "nano-scale" in the field of computing.

The Mechanism of Quantum Dot

By using an external light (e.g. Ultraviolet) on nano-crystals (e.g. made from semiconductor materials such as zinc sulphide, cadmium selenide, indium phosphide or lead sulphide), the nano-crystal will absorb the light and then, as a result of the crystal being stimulated by the absorbed light, it will re-emit the light, usually of a certain colour, depending on the size of the quantum dot.

It has been observed in experiments and shown theoretically that reducing the dimensions of a quantum dot raises the effective operating temperature of the electron confinement device. Present day quantum dots are large enough (approximately 1-10 microns long and wide) that they require cooling with liquid helium or, at least, liquid nitrogen, to cryogenic temperatures. However, for a practical technology with widespread applications based upon such quantum-effect devices, it will be necessary to achieve room temperature operation. This requirement implies that it is necessary to invent and manufacture molecular-scale quantum dots that are only approximately 1 to 10 nanometers in linear dimension. Such a quantum dot would probably be constructed as a single molecule i.e. a molecular quantum dot. Molecular quantum dots are one example of the next-generation technology known as Molecular-scale electronics.
Professor James Tour of the University of South Carolina and Professor Mark Reed of Rale University are collaborating on the chemical synthesis and testing of molecular wires. These operate by allowing electrons to move nearly ballistically along the length of a chain of ring-like chemical structures with conjugated pi-orbitals.
It has been suggested by Tour and by others, that it may be possible to insert chemical groups of lower conductance into such a molecular wire, creating paired barriers to electron migration through the chain. Such barriers might create a molecular quantum-effect device that would function in a fashion similar to solid-state resonance tunnelling devices that already have been fabricated, tested, and applied in prototype quantum-effect logic.
Work in the area of quantum-based devices for nano-scale metrology will be directed to fabricating an ultra-small SQUID (Superconducting Quantum Interference Device) for applications in single-particle detection. The fabrication of such a device will be a significant achievement, and should prove important in areas such as future nano-scale frequency standards, emerging quantum computers and single-particle sensor technologies and in the study of adatom-surface interactions.

Many researchers in nano-electronics are talking of a possible architecture for computer logic based on quantum dots. As mentioned previously, a quantum dot is a box that holds a discrete number of electrons. Adjusting electricfields in the neighbourhood of the dot, for example by applying a voltage to a nearby metal gate, can change this number. Of course, since quantum dots are fabricated in solids, not in vacuum, there are many electrons in them. However, almost all of these are tightly bound to atoms in the solid. The few electrons spoken of are extra ones beyond those that are tightly bound. These extra electrons could roam free in a solid were they are not confined in a quantum dot.

In nano-structures, the electrical properties can be markedly different from their macroscopic equivalents thereby revealing many novel effects. "Progress in the field has been hampered by two problems," said Arizona State University Chemistry Professor Devens Gust. "The first has been in making robust, reproducible electrical connections to both ends of molecules. After this has been achieved, the next problem is knowing how many molecules there actually are between the electrical contacts."

Applications

The uses or possible future uses of Quantum Dots can cover various applications with impressive futuristic results.

The following are just few examples:

1. Quantum computers.
2. Domestic and office lighting applications.
3. Medical Applications.
4. Television screens and monitors.
5. Silicon Photovoltaic cells

Conclusion

Generally speaking, atoms are quantum dots, however, adding a number of molecules together in small space, produce the quantum dots effects.
Addition or removal of an electron changes the properties of a quantum dot, resulting in a “benefit” in one way or another.

Quantum Dots and their applications are the next step in the field of nanotechnology, which in the future will bring applications in commercial and non-commercial fields. Quantum Dots may be still in the research stage at the present time, however, their applications and the benefits which they will bring along has already encouraged companies and governmental organisations to invest heavily in this field.


SUGGESTED TOPICS TO READ : STRING THEORY
                                                        :THEORY OF EVERYTHING
                                                         : NANO TECHNOLOGY

HEROS APPARATUS-NEWTONS THIRD LAW OF MOTION MODEL

HERO'S ENGINE

HERO'S ENGINE IS A SIMPLE MODEL TO EXPLAIN NEWTONS THIRD LAW OF MOTION.FOR THIS APPARATUS WE NEEDED A CUP, TWO PIECES OF STRAW OR PIPES(L SHAPED) /PIECE OF RE-FILLER OF PEN  .THEN JOIN THEM AS IN PICTURE.AND FILL THE CUP WITH WATER.

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READ ALSO :HOW TO MAKE A KALEIDOSCOPE
                       :HOW TO MAKE MOMENTUM CONSERVATION MODELS

SPACE TIME-...............

Space/Time and the theory of relativity: are they all related...

Special relativity is a theory of the structure of space time. It was introduced in Albert Einstein's 1905 paper "On the Electrodynamics of Moving Bodies"

And, because relativity calls for the curvature of space to be equal to the curvature of time, the researchers could calculate whether light was influenced in equal amounts by both, as it should be if general relativity holds true.

General Relativity: Einstein's earlier theory of time and space, special relativity, proposed that distance and time are not absolute. The ticking rate of a clock depends on the motion of the observer of that clock; likewise for the length of a "yardstick." Published in 1915, general relativity proposed that gravity, as well as motion, can affect the intervals of time and of space. The key idea of general relativity, called the equivalence principle, is that gravity pulling in one direction is completely equivalent to acceleration in the opposite direction. A car accelerating forwards feels just like sideways gravity pushing one back against his seat. An elevator accelerating upwards feels just like gravity pushing one downwards.

If gravity is equivalent to acceleration, and if motion affects measurements of time and space (as in special relativity), then it follows that gravity does so as well. In particular, the gravity of any mass, such as the sun, has the effect of warping the space and time surrounding it. For example, the angles of a triangle no longer add up to 180 degrees, and clocks tick more slowly the closer they are to a gravitational mass like the sun.

Many of the predictions of general relativity, such as the bending of starlight by gravity and a slight shift in the orbit of the planet Mercury, is quantitatively confirmed by experiment. Two of the strangest predictions, impossible ever to completely confirm, are the existence of black holes and the effect of gravity on the universe as a whole (cosmology).

SUGGESTED TOPICS TO READ MORE : STRING THEORY
                                                   QUANTUM DOTS

STUDY AID FOR PLUS TWO PHYSICS STUDENTS 2

 PART 2
1. RAINBOW
 2.OPTICAL TELESCOPE
 3. INTERFERENCE,DIFFRACTION,REFRACTION ETC 
 4. RIPPLE TANK EXPERIMENT
 5. YOUNGS EXPERIMENT
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HIGGS BOSON

The Higgs boson or Higgs particle is an elementary particle believed to exist in the Standard Model of physics. It may have finally been detected in July 2012, almost 50 years after being predicted, but it will take further testing to be certain. Its discovery, or confirmation of its existence, would be monumental because it would finally prove the existence of the Higgs field, the simplest and longest standing explanation of why some fundamental particles have mass when 'naive' theory says they should be massless, and - linked to this - why the weak force has a very short range while the electromagnetic force has an unlimited range. Its discovery would profoundly influence human understanding of the universe, validate the final unconfirmed part of the Standard Model, guide other theories and discoveries in particle physics, and – as with other fundamental discoveries of the past – potentially over time lead to developments in "new" physics, new technology, and enhancements to society.
This unanswered question in fundamental physics is of such importance that it led to a decades-long search for the Higgs boson and finally the construction of one of the most expensive and complex experimental facilities to date, the Large Hadron Collider
able to create and study Higgs bosons and related questions. On 4 July 2012, two separate experimental teams at the Large Hadron Collider announced that they had each independently confirmed the existence of a previously unknown boson of mass between 125 and 127 GeV/c² which physicists suspected eventually will be agreed to be a Higgs boson, and whose known behaviour (up to December 2012) closely matches a Standard Model Higgs boson.
The Higgs boson is named after Peter Higgs, who—along with Brout and Englert, and with Guralnik, Hagen, and Kibble ("GHK")—proposed the mechanism that suggested such a particle in 1964. Higgs was the only one who emphasised the existence of the particle and calculated some of its properties. Although Higgs' name has become ubiquitous in this theory, the resulting electroweak model (the final outcome) involved several researchers between about 1960 and 1972, who each independently developed different parts. In mainstream media the Higgs boson is often referred to as the "God particle," from a 1993 book on the topic; the sobriquet is strongly disliked by many physicists, who regard it as inappropriate sensationalism.
In the Standard Model, the Higgs particle is a boson with no spin, electric charge, or color charge. It is also very unstable, decaying into other particles almost immediately. The Higgs particle is a quantum excitation of one component of the four component Higgs field, a scalar field with two neutral and two electrically charged components, forming a complex doublet of the weak isospin SU(2) symmetry, and with U(1) weak hypercharge of +½ (or +1 depending on convention). The field has a "Mexican hat" shaped potential and takes on a nonzero strength everywhere (including otherwise empty space) which breaks the weak isospin symmetry in its vacuum state. When this happens, three of the four Higgs field components are "absorbed" by the originally massless SU(2) and U(1) gauge bosons (the "Higgs mechanism") to become the longitudinal components of the now-massive W and Z bosons. The fourth electrically neutral component separately couples to other particles known as fermions (via Yukawa couplings), causing these to acquire mass as well. The fourth component's quantum excitations manifest as the Higgs boson. Some versions of the theory predict more than one kind of Higgs fields and bosons. Alternative "Higgsless" models would be considered if the Higgs boson is not discovered.

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MAGMA 2013,IIT GUWAHATI,DEPT.OF PHYSICS..INTERNATIONAL CONFERENCE

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