Monday, December 12, 2011
In the time that you have been reading this article, about 10 000 000 000 000 000 neutrinos have passed through you without your noticing. Neutrons are tiny, yet with the power to confirm or overthrow a number of scientific theories. Neutrinos, meaning ‘little neutral ones’, are everywhere, all around us. These tiny elementary particles travel through space at close to the speed of light and have no charge. They were once thought to have no mass either, but scientists now suggest that they do have a mass; it is estimated to be less than a billionth of the mass of a hydrogen atom, but the research continues.
Neutrinos come in three types, according to the standard model of particle physics: the electron neutrino, muon neutrino, and tau neutrino, which have all been confirmed experimentally. A fourth, ‘sterile’ type has been proposed, which is immune to the weak force of the standard model. Were sterile neutrinos to be found, a new realm of physics beyond the standard model would open up.
Unlike most other particles, neutrinos are able to escape from dense regions such as the core of the sun or the milky way, and they can travel long distances from far-away galaxies without being absorbed, carrying information about these areas. In this sense, neutrinos are cosmic messengers, and neutrino astronomy is becoming increasingly important. So far, only two sources of extraterrestrial neutrinos have been observed: the sun and supernovae. On earth, both natural and artificial neutrino sources exist: radioactive materials from inside earth can undergo beta decay, producing geo-neutrinos. In addition, nuclear fission reactors produce neutrinos, and particle accelerators are being used as neutrino sources for research. Finally, when cosmic rays hit Earth’s atmosphere, atmospheric neutrinos are emitted as decay products of pions and muons.
Scientists now propose that cubic-metre antineutrino detectors could be used to non-intrusively monitor and safeguard nuclear reactors. Neutrino detectors would provide real-time information about the reactor core power and possibly even its isotopic composition. An array of about 500 such detectors worldwide would be able to calculate the power output of individual reactors, allowing the detection of clandestine nuclear weapons testing. Geo-neutrinos produced during natural radioactive dacay of uranium, thorium and potassium in earth’s crust may help answer the question of crust composition.
Neutrinos are very useful for studying astronomical and cosmological phenomena, and neutrino detectors are being built worldwide, deep underground to filter out the ‘noise’ of other particles.
Think of toy elephant, image of wood recedes;
Think of elements five*, thought of universe recedes
Think of universe, thought of elements recedes.
Thirumoolar, Eight Century A.D.
Note: *The five elements are water, land, sky, fire and air
மரத்தை மறைத்தது மாமத யானை
மரத்தின் மறைந்தது மாமத யானை
பரத்தை மறைத்தது பார்முதல் பூதம்
பரத்தின் மறைந்தது பார்முதல் பூதம்
திருமூலர், கி.பி.எட்டாம் நூற்றாண்டு
According to uncertainty principle,
the position and momentum of a particle
say electron cannot be determined simultaneously
to any desired degree of accuracy.
Heisenberg, Twentienth Century A.D
Sunday, August 28, 2011
Who is the father of Physics?
Technically Isaac Newton would be more likely to deserve the name father of physics. Albert Einstein would be more likely to be called the father of astrophysics-although physics and astrophysics are related. Physics is the science of matter and energy. Astrophysics is matter and energy as it relates to the universe. Since a father should be the first person who comes up with physics it could be thought as Thales of Miletus who was the first who came up with primordial matter.
Physics though it employs mathematical means to comprehend various concepts which are then subjected to tests or experiments also has a philosophical aspect about it. The ancient Greek philosopher Thales (6th century BC) is widely regarded as the father of physics. He is credited with being the first to study the heavens; some of his achievements include predicting a solar eclipse, construction of an almanac and his statement that all 'things' are formed of one primary element.
Some important philosopher physicists of the period include Aristotle, Democritus and Archimedes. The father of Modern Physics is considered to be the Italian physicist Galileo Galilei most famous for his assertion of the heliocentric view of the solar system. Some famous physicists of the modern period are Sir Isaac Newton, Johannes Kepler, Benjamin Franklin, Michael Faraday, Nikolai Tesla, Niels Bohr and Albert Einstein among others.
Thin film science now covers a wide span of disciplines such as solid-state physics, surface science, crystallography, crystal growth, optics, electronics, and materials science etc.,These investigations have led to numerous inventions in the form of active devices and passive components, piezo-electric devices, micro miniaturization of power supply, rectification and amplification, sensor elements, storage of solar energy and its conversion in other forms, magnetic memories, super conducting films, interference films, reflecting and anti reflecting coatings and many others. The present development trend is towards newer types of devices, monolithic and hybrid circuits, Field Effect Transistors (FET), Metal Oxide Semiconductor Transistors (MOSFET), sensors for different applications, switching devices, cryogenic applications, high-density memory systems for computers etc.,
Further because of compactness, better performance and reliability coupled with low cost of production and low package weight, thin film devices and components are performed over their counter parts.
COMPARISON TO THICK FILM
A casual comparison of film behavior and physical chemical characteristics revealed the sensitivity of film properties on the preparative conditions, film structures, and presence of defects and impurities and even on film thickness especially for ultra thin films. In fact various physical constants reveal to bulk material properties may not often be the same for corresponding films prepared from the bulk. However with increasing film thickness these tend to assume corresponding bulk values. A transition from the bulk to the thin film states may even cause a drastic change in its properties as illustrated by the behaviors of alkali metals and also noble metals. For example the highly conducting sodium, potassium, rubidium, gold and platinum having positive temperature coefficient of resistance in the bulk form show negative temperature coefficient of resistance when in thin film states thus behaving as semi conducting films. Bulk bismuth and antimony, which are metallic in nature, behave as semiconductors in the thin film states. Buckel and Hilsch observed that thin bismuth films unlike bulk showed super conducting behavior properties at low temperature. Highly disordered or amorphous films have electrical or magnetic properties, which may differ by several orders from that of the bulk single crystals. All films whether prepared by vacuum deposition or by other techniques are invariably associated with some growth defects or imperfections such as lattice defects stacking defects twinning, disorders in atomic arrangements, dislocation, grain boundaries, foreign atom inclusion et.., There is often a considerable deviation from that of the bulk behavior and sometimes new phenomenon are observed in thin film states.
Definition of thin film
What ever be the film thickness limit an ideal film can mathematically be defined as a homogeneous solid material contained between tow parallel planes and extended infinitely in two dimensions say x and y but restricted along the third direction z, which is perpendicular to the x-y plane. The dimension along z direction is known as the film thickness (d or t). Its magnitude vary from a limit d®0 to any arbitrary value say 10 mm but always remaining much less than those as long the two direction x and y.
THICKNESS OF THIN FILM
Thin films can be divided mainly into three types based on their thickness. The first one is the ultra thin film, which has a thickness of 50-100 Angstrom units. The second one is the thin or very thin film, which has a thickness of 100-1000 Angstrom units and the third one, is comparatively thicker one which has a thickness greater than 1000 Angstrom .
DEFECTS IN thin films
A real film however, deviates considerably from the ideal core since its two surfaces are never exactly parallel even when formed in the best experimental deposition condition and also the material contained between the two surfaces are rarely homogeneous, neither uniformly distributed nor of the same species. It is also a common experience that a film may also contain many imperfections, impurities, dislocations, grain boundaries and various other defects and may also be discontinuous. Further the top surface of a film often develops some topographical features and characteristic of the growth conditions and these features can no doubt be minimized but cannot altogether be avoided. The bottom surface of a film in contact with a substrate generally takes up the topographical features of the latter. Some of the factors, which determine the physical, chemical, optical, and other properties of the film, are the following: The rate of deposition, substrate temperature, environmental condition, residual gas pressure in the system, purity of the material to be deposited, inclusion of foreign material in the deposit, inhomogeneity of the film, structural and compositional variations of the film in localized or wider area etc., some of which have been actually observed. It is well known that the resistance of a freshly deposited metal film and in fact almost any other film when kept in vacuum changes irreversibly to a lower value with time. But on log ageing at room temperature or even a short annealing at a little higher temperature in vacuum its resistance attains a constant value, which is reversible with temperature. Vand reported that the resistance of a metal film when plotted against its temperature of deposition showed a maximum and minimum. But on heat treatment of the film tend to a more stable, no doubt, due to annealing of its defects stains etc. The film resistance then becomes more or less reversible with temperature
EVAPORATION SOURCES OR HEATING SOURCES
There are several types of practicing heating sources made from refractory metals such as tungsten, molybdenum, tantalum etc., These sources may be made from single or multi stranded filament to various shapes or from straight strips with or without any dimple at the center or in the form of a boat and some times having the shape of a cylindrical etc.,
METHODS OF THIN FILM PREPARATION
This method is used to deposit metals, alloys and also many other compounds. This involves the evaporation of the material in vacuum by thermal energy and allowing the vapour stream of the change to condense on the substrate so as to form a continuous and adherent deposit of desired thickness. Refractory metals like tungsten, molybdenum or tantalum are generally used in the form of a wire or strip having different shapes. The choice of a particular refractory metal as a heating source depends on the material to be evaporated so that the evaporant material does not react with the refractory metal at the high temperature of evaporation. How ever the formation of alloy in the source cannot be avoided. Hence coating of refractory oxides such as Al2O3, BeO or other suitable materials is often given over the filament or strips so as to present the direct contact between the molten charge and the refractory metal. In any case when a direct heating of the charge is made the filament or strip is pre-cleaned by passing a heavy current through it so as to make it whit hot or incandescent for a very short period so that all the surface impurities of the filament or the strip are removed by evaporation and this is called flash cleaning. Usually a shutter is placed in between the heating source and the substrate so that no vapour stream of the charge can reach substrate.The quality and characteristic of the deposit will depend on the rate of deposition, substrate temperature, ambient pressure and the uniformity of the film and the geometry of the evaporant source and its distance from substrate.
This method is generally adopted when a material has a tendency to decompose or dissociate during evaporation as in the case of some alloys, group of III- V compounds such as InSb, AlSb, etc., titanates, molybdates and even some oxide metals etc., Basically the process is similar to the thermal evaporation techniques with the difference that only a small amount of the charge in powder form is fed at a time to a white hot boat of tungsten, modybdenum or tantalum so that an instantaneous evaporation of the total charge takes place without leaving any residue. Because of the high temperature of the boat as well as the limited amount of the charge fed at a time to the boat there will be no time for constituents to build up by differential vapour pressure. Hence composition of the gaseous phase will be more or less the same as that of the charge and it is expected that on condensation the deposits will retain the composition of the evaporant.
This method of deposition is called flash evaporation since there is no accumulation of the charge on the heated boat before the arrival of the next charge the question of the enrichment of the residue by one constituent as in the normal process does not arise at all.The charge in powder form is fed from a reservoir or a hopper to a heated boat through a chute and the feeding rate can be made continuous or intermittent by using a vibrator or suitable cam arrangement. All other requirements for deposition are more or less similar to those of the normal evaporation process. For some oxides or titanates often a part of the molten charge is maintained over the heated boat, which is then constantly fed, by small amount of fresh charge depending on the rate of evaporation. By this method a constant composition thin film can be produced
ELECTRON BEAM METHOD
This is one of the best methods for the deposition of metals, alloys, refractory metal at a high rate and is now routinely used for the production of metal film resistors and others. In this technique an electron beam accelerated with a voltage of say 2-10V is focused on the surface of a charge which is normally kept inside a graphite crucible placed on water cooled copper block. Thus high-energy electron beam emitting from the cathode impinges on the charge, which is at the same potential as the anode is converted into intense heat energy, which melts the charge. By suitable focusing the electron beam and controlling its intensity it is possible to keep the top surface of the charge in a molten condition from which evaporation can take place. The temperature attained by the charge at the surface can be as high as 3000 C or more and hence refractory metals such as. tantalum, molybdenum, tungsten etc., can be melted and evaporated by this technique.
There are three types of electron beam guns. In the first type the work accelerated gun where electron gun where electron beam coming out of a loop type of a filament is accelerated directly towards the charge or through an appropriate shield thus concentrating the beam. In the second method there is a self-accelerated gun where electrons are emitted from hairpin type of filament and focused through a Wehnelt cylinder on the material. In the third type there is a bent beam electron gun where a beam of electron is bent by an appropriate magnetic field and then focused on the charge. It is also possible to have an oscillating electron beam to facilitate the melting of the charge. In all cases necessary precautions are taken so that evaporation is discontinuous before the charge is exhausted since the last residue may contain some of the impurities coming out of the container vessel such as graphite or other material. It may be mentioned here that because of the high temperature of working the electron beam gun assembly is water-cooled.
The ejection of atoms from the cathode surface by impinging of energetic positive ions of noble gases such as Helium, Argon, Neon, Krypton, Xenon at a reduced pressure under high DC voltage gives rise to sputtering phenomenon. It is now possible to make various resistive, semi conducting, super conducting and magnetic films by this method in a better way.
There are two types of sputtering. If the process does not involve any chemical reaction between bombarding gas ions and cathode then it is known as physical sputtering.If on the other hand some reaction s are involved then it is termed as reactive sputtering. Both these types of sputtering are carried out in a comparatively poor vacuum condition and are known as high pressure sputtering.The mechanism of the process involves a momentum transfer between impinging energetic ions or neutrals and the cathode surface atoms as a result of which a physical removal of atoms takes place. Various workers especially by Wehner have amply verified this momentum transfer theory of Stark Conclusions drawn are that the sputtering yield increase with the energy and the mass of the bombarding ions and also with the decrease of angle of incidence to the target. A minimum energy is required to start the sputtering process. Sputtered atoms have much higher energies than those of the thermally evaporated ones and the former are, however ejected along the crystallographic directions of the cathode metal lattices.
HETROJUNCTION THIN FILMS TECHNOLOGY
Based on the hetrojunction thin film technology, integrated circuits are fabricated. Integrated circuit technology is a branch of microelectronics. With this technology we can produce miniature electronic equipment in a large extent. Integrated circuits on a small single chip of silicon of size 5 to 50 mils (1 mil=25 m m) contain a large number of both active and passive elements with interconnections. In this small chip a single transistor can be accommodated in an area 1 mil by 1 mil which means that a chip may contain 50 components with inter connections. The process of fabrication of integrated circuits is similar to the process of fabrication of individual transistors or diodes.The basic structure of integrated circuits is as shown in figure, which consists of four distinct layers.The bottom layer is a p-type silicon of thickness 6 mils known as substrate upon which the whole integrated circuit is built.
The second layer is a thin (1 mil) N type silicon formed over the substrate. Active and passive components are built within this N type layer. These components are transistors, diodes, capacitors and resistors. These are made within the N type layer by diffusing a p-type and N-type impurities suitable in certain precisely defined regions. The selective diffusion of impurities over the second N-type layer over the precisely defined regions is possible with the help of third SiO2 layer, which is formed over the second layer. This layer prevents the diffusion of impurities over the second N-type layer. Therefore from the selected regions SiO2 is etched out by a process called photo lithography and impurities can be allowed to diffuse to these regions. Therefore the other regions are protected form impurity diffusions. The fourth layer is a metallic layer, which is added to make interconnections between various components that are fabricated.
ADVANTAGES OF THIN FILMS
Small in size
Low cost due to processing of large quantities
Low power requirements
Lesser weight due to miniature circuit
Higher reliability, because all components are fabricated simultaneously and no soldering joints
The maintenance of thin film based IC system is easier than the discrete system
Interconnection errors are non-existant
Temperature difference between parts of a circuit is small.
Saturday, March 12, 2011
நாம் ஏன் இப்படி
எப்போதும் துணிகளை மடித்துக்கொண்டு
எதையாவது சுத்தம் செய்துகொண்டு
எதையாவது அடைய முயற்சித்துக்கொண்டு
எப்போதும் நம்மை நிரூபித்துக்கொண்டு
ஒரு சிகரெட்டைப்போல எரிந்துகொண்டு
தேவையற்ற பொருட்களால் நம் தனிமையை நிரப்பிக்கொண்டு
யாரிடமாவது நம்மைப் பிணைக்க முயற்சித்துக்கொண்டு
ஒரு அபத்தமான சினிமாவின் முதல் காட்சியைப் பார்த்துக்கொண்டு
கடற்கரையில் கூட்டத்தோடு கூட்டமாய் நின்றுகொண்டு
நம் குழந்தைகளை சந்தேகித்துக்கொண்டு
நம் வீட்டிலேயே திருடிக்கொண்டு
மலிவான பொருட்கள் எங்கே கிடைக்கின்றன என்று
புகழுள்ள மனிதர்களை அனாவசியமாய்த் தெரிந்துகொண்டு
சதா எதேனும் ஒரு நோயைப்பற்றி பேசிக்கொண்டு
எப்போதும் பருவநிலையினைப் பற்றி புகார் செய்துகொண்டு
சிறிய வருமானத்திற்கான சிறிய கணக்குகள் எழுதிக்கொண்டு
அதிர்ஷ்டத்தின் வருகையை எதிர்நோக்கிக்கொண்டு
யாருடைய சாவுக்காவது காத்துக்கொண்டு
நமது தூக்குக் கயிற்றின் உறுதியைச் சோதித்துக்கொண்டு
முட்டாள்களின் கவிதையைப் படித்துக்கொண்டு
அடுத்த முதல்வர் யார் என்று யோசித்துக்கொண்டு
பௌர்ணமி தினங்களில் மனம் உடைந்து அழுதுகொண்டு
தவறான முடிவுகளுக்காக வருந்திக்கொண்டு
தவறிப்போன சந்தர்ப்பங்களுக்காக ஏங்கிக்கொண்டு
யாருடைய அன்புக்காகவாவது ஏங்கிக்கொண்டு
யாரையாவது இணங்கச் செய்துகொண்டு
கடன் கொடுப்பவர்களிடம் நட்பு பாராட்டிக்கொண்டு
சிறிய தவறுகளுக்கு பெரிய தண்டனைகள் கொடுத்துக்கொண்டு
பிறரது கடிதங்களைத் திருடிப் படித்துக்கொண்டு
தன் வழியே போகும் எறும்புகளை நசுக்கி அழித்துக்கொண்டு
கூண்டுகளில் பறவைகளை அடைத்து வைத்துக்கொண்டு
போலிக் கடவுள்களிடம் கண்ணீர் சிந்திக்கொண்டு
எதிர்காலத்தை அவ்வளவு உறுதியாய் திட்டமிட்டுக்கொண்டு
மற்றவர்களின் கடமைகளை நினைவூட்டிக்கொண்டு
நமது இயலாமையை மறைக்க யாரையாவது சவுக்கால்
பூனைகளுக்கு உணவுதர மறுத்துக்கொண்டு
யாரையாவது இறுகப் பற்றிக்கொண்டு
உடல் குறைபாடுகளைப் பற்றி சிந்தித்துக்கொண்டு
மலிவான வாசனைத் திரவியங்களைப் பயன்படுத்திக்கொண்டு
பொது அறிவை வளர்த்துக்கொண்டு
எதற்காவது பயன்படுமென்று எல்லாவற்றையும் பாதுகாத்துக்கொண்டு
எப்போதும் யாரையாவது கண்காணித்துக்கொண்டு
உடல் பயிற்சியினால் மரணத்தை வெல்ல முயற்சித்துக்கொண்டு
எளிய இரக்கங்களால் நம் மனிதத் தன்மையை நிரூபித்துக்கொண்டு
தங்க முலாம் பூசப்பட்ட போலி ஆபரணங்களை அணிந்துகொண்டு
அவமதிப்புகளைப் பொருட்படுத்தாமலிருக்க கற்றுக்கொண்டு
திறக்க மறுக்கும் கதவுகளைத் தட்டிக்கொண்டு
வேலைகளுக்குள் நம்மை நாமே மறைத்துக்கொண்டு
நம் பால்யத்தை நினைவுகூர்ந்துகொண்டு
ஒரு மூலையில் சுருண்டு படுத்துக்கொண்டு
வேறு வழியில்லை என்று எழுந்துகொண்டு
யாருக்காகவோ தியாகம் செய்துகொண்டு
எளிய உணர்ச்சிகளுக்காகப் பலியிட்டுக்கொண்டு
எப்போதோ நன்றாக இருந்தோம் என்று நினைத்துக்கொண்டு
எப்போதோ நன்றாக இருப்போம் என்று நினைத்துக்கொண்டு
சாதாரணமானவற்றை சிறந்ததென ஏற்றுக்கொண்டு
Wednesday, January 19, 2011
Open the file "Hosts" or "LMHosts" from C:\Windows\System32\Drivers\Etc. Then add the following line at the end of the file 127.0.0.1 http://www.xyz.com/ which means when someone tries to visit http://www.xyz.com/ from your website it gets blocked because the site is redirected to 127.0.0.1 which is the IP of your own computer. To know the IP of any website just go to DOS and type " ping http://www.xyz.com/ ".
To properly use HOSTS you must make sure ENABLE DSN is turned on : Control Panel --> Network --> Your TCP/IP adapter name --> TCP/IP Properties --> DNS Configuration tab --> Check enable DNS box --> Apply OK
The following is the order in which Windows tries resolving hostnames only if all fails do you get the error Page Not Found
P.S : Try this in your friends computer when he is not in the seat ;-) just open the Hosts file and type the URL which he frequently use and the IP of some other URL So that when he clicks the URL the browser redirects him to some other page.