10 The Age of Electronic Materials Stone Age-Bronze Age-Iron Age-what's next?Some individ- uals have called the present era the space age or the atomic age. However,space exploration and nuclear reactors,to mention only two major examples,have only little impact on our every- day lives.Instead,electrical and electronic devices (such as ra- dio,television,telephone,refrigerator,computers,electric light, CD players,electromotors,etc.)permeate our daily life to a large extent.Life without electronics would be nearly unthinkable in many parts of the world.The present era could,therefore,be called the age of electricity.However,electricity needs a medium in which to manifest itself and to be placed in service.For this reason,and because previous eras have been named after the ma- terial that had the largest impact on the lives of mankind,the present time may best be characterized by the name Electronic Materials Age. We are almost constantly in contact with electronic materials, such as conductors,insulators,semiconductors,(ferro)magnetic materials,optically transparent matter,and opaque substances. The useful properties of these materials are governed and are characterized by electrons.In fact,the terms electronic materials and electronic properties should be understood in the widest pos- sible sense,meaning to include all phenomena in which electrons participate in an active (dynamic)role.This is certainly the case for electrical,magnetic,optical,and even many thermal phe- nomena.In contrast to this,mechanical properties can be mainly interpreted by taking the interactions of atoms into account,as explained in previous chapters
10 Stone Age—Bronze Age—Iron Age—what’s next? Some individuals have called the present era the space age or the atomic age. However, space exploration and nuclear reactors, to mention only two major examples, have only little impact on our everyday lives. Instead, electrical and electronic devices (such as radio, television, telephone, refrigerator, computers, electric light, CD players, electromotors, etc.) permeate our daily life to a large extent. Life without electronics would be nearly unthinkable in many parts of the world. The present era could, therefore, be called the age of electricity. However, electricity needs a medium in which to manifest itself and to be placed in service. For this reason, and because previous eras have been named after the material that had the largest impact on the lives of mankind, the present time may best be characterized by the name Electronic Materials Age. We are almost constantly in contact with electronic materials, such as conductors, insulators, semiconductors, (ferro)magnetic materials, optically transparent matter, and opaque substances. The useful properties of these materials are governed and are characterized by electrons. In fact, the terms electronic materials and electronic properties should be understood in the widest possible sense, meaning to include all phenomena in which electrons participate in an active (dynamic) role. This is certainly the case for electrical, magnetic, optical, and even many thermal phenomena. In contrast to this, mechanical properties can be mainly interpreted by taking the interactions of atoms into account, as explained in previous chapters. The Age of Electronic Materials
174 10.The Age of Electronic Materials Electrical The first observations involving electrical phenomena in mate- Phenomena rials probably began when static electricity was discovered. (Lightning,of course,preceded these experiments,but this could not be controlled by man.)Around 600 B.C.,Thales of Miletus,a Greek philosopher,realized that a piece of amber,having been rubbed with a piece of cloth,attracted feathers and other light particles.Very appropriately,the word "electricity"was later coined by utilizing the Greek word electron,which means amber. It was apparently not before 2300 years later that man again be- came seriously interested in electrical phenomena.In 1729, Stephen Gray (a British Chemist)found that some substances conducted the "effluvium"of electricity whereas others did not. In 1733,C.F.Du Fay (a French scientist)postulated the existence of two types of electricity,which he termed glass (or vitreous) electricity and amber (or resinous)electricity,depending on which material was rubbed.Benjamin Franklin'later designated to them the plus and the minus sign,implying that one type of electricity would cancel the other.His ideas were based on his famous kite experiments in 1752 in which he demonstrated "the sameness of electrical matter with that of lightning."This clas- sification was expanded almost 100 years later to include five kinds of electricity,namely,frictional,galvanic (animal),voltaic, magnetic (by induction),and thermal. Magnetism Magnetism(or,more precisely,ferro-or ferrimagnetism),that is, the mutual attraction of two pieces of iron or iron ore,was like- wise already known to the antique world.The term "magnetism" is said to have been derived from a region in Turkey (or north- ern Greece?),called Magnesia,which had plenty of iron ore.Now, iron does not immediately attract another piece of iron.For this, at least one of the pieces has to be magnetized,that is,simply said, its internal "elementary magnets"need to be aligned in parallel. Magnetizing causes no problem in modern days.One merely places a piece of iron into a wire coil through which a direct cur- rent is passed for a short time.(This was discovered by the Dan- ish physicist Hans Christian Oersted at the beginning of the 19th century.)But how did the ancients do it?There may have been at least two or three possibilities.First,a bolt of lightning could have caused a magnetic field large enough to magnetize a piece of iron or iron ore.Once one magnet had been produced and iden- tified,more magnets could have been obtained by rubbing virgin pieces of iron with the first magnet.There could have been an- 11706-1790,American publisher,scientist,and diplomat
The first observations involving electrical phenomena in materials probably began when static electricity was discovered. (Lightning, of course, preceded these experiments, but this could not be controlled by man.) Around 600 B.C., Thales of Miletus, a Greek philosopher, realized that a piece of amber, having been rubbed with a piece of cloth, attracted feathers and other light particles. Very appropriately, the word “electricity” was later coined by utilizing the Greek word electron, which means amber. It was apparently not before 2300 years later that man again became seriously interested in electrical phenomena. In 1729, Stephen Gray (a British Chemist) found that some substances conducted the “effluvium” of electricity whereas others did not. In 1733, C.F. Du Fay (a French scientist) postulated the existence of two types of electricity, which he termed glass (or vitreous) electricity and amber (or resinous) electricity, depending on which material was rubbed. Benjamin Franklin1 later designated to them the plus and the minus sign, implying that one type of electricity would cancel the other. His ideas were based on his famous kite experiments in 1752 in which he demonstrated “the sameness of electrical matter with that of lightning.” This classification was expanded almost 100 years later to include five kinds of electricity, namely, frictional, galvanic (animal), voltaic, magnetic (by induction), and thermal. Magnetism (or, more precisely, ferro- or ferrimagnetism), that is, the mutual attraction of two pieces of iron or iron ore, was likewise already known to the antique world. The term “magnetism” is said to have been derived from a region in Turkey (or northern Greece?), called Magnesia, which had plenty of iron ore. Now, iron does not immediately attract another piece of iron. For this, at least one of the pieces has to be magnetized, that is, simply said, its internal “elementary magnets” need to be aligned in parallel. Magnetizing causes no problem in modern days. One merely places a piece of iron into a wire coil through which a direct current is passed for a short time. (This was discovered by the Danish physicist Hans Christian Oersted at the beginning of the 19th century.) But how did the ancients do it? There may have been at least two or three possibilities. First, a bolt of lightning could have caused a magnetic field large enough to magnetize a piece of iron or iron ore. Once one magnet had been produced and identified, more magnets could have been obtained by rubbing virgin pieces of iron with the first magnet. There could have been anElectrical Phenomena Magnetism 174 10 • The Age of Electronic Materials 11706–1790, American publisher, scientist, and diplomat
10.The Age of Electronic Materials 175 FiGURE 10.1.Depiction of an ancient Chinese compass called a sinan. (or Zhe'nan)Zhe point;nan south.The spoon-shaped device was carved out of a lodestone and rested on a polished bronze plate.The rounded bottom swiveled on the "earth plate"until the spoon handle pointed to the south. other possibility.It is known that if a piece of iron is repeatedly hit very hard,its"elementary magnets"will be "shaken loose"and will align in the direction of the earth's magnetic field(which is quite weak,i.e.,only about half a gauss).An iron hammer,for ex- ample,is north magnetic on its face of impact in the northern hemisphere.Could it have been that a piece of iron was used as a hammer and thus became a permanent magnet?A third possi- bility is that iron-or nickel-containing meteorites responded with an alignment of their"elementary magnets"in an electromagnetic field during their immersion into the earth's atmosphere. One of the major applications of magnetism was the compass which is said to have been invented independently in China (be- fore A.D.1100,possibly before 1040)and in Western Europe (about A.D.1187).Other sources emphasize that the Chinese,as early as A.D.80(or even earlier),had a device called a sinan, which consists of a piece of iron ore carved (by a jade cutter) into the shape of a ladle;see Figure 10.1.When placed on a pol- ished plate of bronze,called the "earth plate,"the spoon swiveled until the handle pointed to the south which was considered by the Chinese rulers to be the imperial direction toward which all seats had to face.The ladle resembles the Big Dipper (or great bear)whose pointer stars point to the Polaris or North Star.An- other device,the iron fish compass,described in A.D.1044 in a Chinese book was fabricated by allowing molten iron rods to so- lidify in the north-south direction that is,in the earth magnetic field which induces permanent magnetism in the metal(thermo remanence).The fish-shaped leaf was placed on water where it
other possibility. It is known that if a piece of iron is repeatedly hit very hard, its “elementary magnets” will be “shaken loose” and will align in the direction of the earth’s magnetic field (which is quite weak, i.e., only about half a gauss). An iron hammer, for example, is north magnetic on its face of impact in the northern hemisphere. Could it have been that a piece of iron was used as a hammer and thus became a permanent magnet? A third possibility is that iron- or nickel-containing meteorites responded with an alignment of their “elementary magnets” in an electromagnetic field during their immersion into the earth’s atmosphere. One of the major applications of magnetism was the compass which is said to have been invented independently in China (before A.D. 1100, possibly before 1040) and in Western Europe (about A.D. 1187). Other sources emphasize that the Chinese, as early as A.D. 80 (or even earlier), had a device called a sinan, which consists of a piece of iron ore carved (by a jade cutter) into the shape of a ladle; see Figure 10.1. When placed on a polished plate of bronze, called the “earth plate,” the spoon swiveled until the handle pointed to the south which was considered by the Chinese rulers to be the imperial direction toward which all seats had to face. The ladle resembles the Big Dipper (or great bear) whose pointer stars point to the Polaris or North Star. Another device, the iron fish compass, described in A.D. 1044 in a Chinese book was fabricated by allowing molten iron rods to solidify in the north-south direction that is, in the earth magnetic field which induces permanent magnetism in the metal (thermo remanence). The fish-shaped leaf was placed on water where it FIGURE 10.1. Depiction of an ancient Chinese compass called a sinan. (or Zhe nan) Zhe point; nan south. The spoon-shaped device was carved out of a lodestone and rested on a polished bronze plate. The rounded bottom swiveled on the “earth plate” until the spoon handle pointed to the south. 10 • The Age of Electronic Materials 175
176 10.The Age of Electronic Materials floated on the surface while the fish's head pointed to the south. A Chinese book printed in 1325 describes a wooden turtle,con- taining a loadstone and a needle as its tail,pointing to the south There are no reports that the Chinese used these devices for nav- igation probably because China was a land-based culture.They were probably used instead to align the edges of pyramids,etc., along the north-south axis or as described above. In the western world,on the other hand,the first mention of a compass was by an English Augustian monk(Alexander Neckam, 1157-1217)in his book entitled "De Naturis Rerum."There is also a document by an Arab writer who,in 1242,reports that a mag- netic needle floating on water on top of a wooden splinter points to the north star.The bishop of Acre,Jaques Vitry,wrote in 1218 that the compass is a necessary instrument for navigation on the seas.Around 1300 the south Italian mariners of Amalfi are said to have perfected to some degree the compass from a needle float- ing on water to a round box (called later a "bussola")in which a compass card with a wind rose,divided into 32 points,is attached to the rotating needle.During the 15th century it was realized that the compass needle does not point to true north but assumes an angle,called variation (or declination),with the meridian.Mag- netism is also mentioned in poetic works such as the Divine Com- edy by Dante (written between 1310 and 1314)or in La Bible by the French monk Guyot de Provins (written about 1206).Mag- netism was (and occasionally still is today)considered as a re- pellent against witchcraft and most anything,to heal madness and insomnia,and as an antidote against poison. The modern compass consists quite similarly to the bussola of a pivoted bar magnet whose tip,which points to the general di- rection of geographic north,is called the "north-seeking pole"or simply the north pole.The bowl is suspended in gimbals,that is, in rings,pivoted at right angles to each other so that the com- pass is always level.Around 1500,the term lodestone appears in the literature when referring to magnetized iron ore,that is,iron oxide,particularly when used in a compass.This word is derived from the old English word lode,which means to lead or to guide. Optical The study of optical phenomena likewise goes back to antiquity. Phenomena Interestingly enough,there used to be an intense debate whether in vision something moves from an object to the eye or whether something reaches out from the eye to an object.In other words, the discussions revolved around the question of whether vision is an active or a passive process.Specifically,Pythagoras,a Greek philosopher and mathematician (living during the 6th century
floated on the surface while the fish’s head pointed to the south. A Chinese book printed in 1325 describes a wooden turtle, containing a loadstone and a needle as its tail, pointing to the south. There are no reports that the Chinese used these devices for navigation probably because China was a land-based culture. They were probably used instead to align the edges of pyramids, etc., along the north-south axis or as described above. In the western world, on the other hand, the first mention of a compass was by an English Augustian monk (Alexander Neckam, 1157–1217) in his book entitled “De Naturis Rerum.” There is also a document by an Arab writer who, in 1242, reports that a magnetic needle floating on water on top of a wooden splinter points to the north star. The bishop of Acre, Jaques Vitry, wrote in 1218 that the compass is a necessary instrument for navigation on the seas. Around 1300 the south Italian mariners of Amalfi are said to have perfected to some degree the compass from a needle floating on water to a round box (called later a “bussola”) in which a compass card with a wind rose, divided into 32 points, is attached to the rotating needle. During the 15th century it was realized that the compass needle does not point to true north but assumes an angle, called variation (or declination), with the meridian. Magnetism is also mentioned in poetic works such as the Divine Comedy by Dante (written between 1310 and 1314) or in La Bible by the French monk Guyot de Provins (written about 1206). Magnetism was (and occasionally still is today) considered as a repellent against witchcraft and most anything, to heal madness and insomnia, and as an antidote against poison. The modern compass consists quite similarly to the bussola of a pivoted bar magnet whose tip, which points to the general direction of geographic north, is called the “north-seeking pole” or simply the north pole. The bowl is suspended in gimbals, that is, in rings, pivoted at right angles to each other so that the compass is always level. Around 1500, the term lodestone appears in the literature when referring to magnetized iron ore, that is, iron oxide, particularly when used in a compass. This word is derived from the old English word lode, which means to lead or to guide. The study of optical phenomena likewise goes back to antiquity. Interestingly enough, there used to be an intense debate whether in vision something moves from an object to the eye or whether something reaches out from the eye to an object. In other words, the discussions revolved around the question of whether vision is an active or a passive process. Specifically, Pythagoras, a Greek philosopher and mathematician (living during the 6th century Optical Phenomena 176 10 • The Age of Electronic Materials
10.The Age of Electronic Materials 177 B.c.),believed that light acts like feelers and travels from the eyes to an object and that the sensation of vision occurs when these rays touch that object.Euclid,a Greek mathematician,recognized at about 300 B.C.that light propagates in a straight line.Further, he related that the angle of reflection equals the angle of incidence when light is impinging the surface between two different media. Even though refraction was also known and observed in the an- tique world,it was not before 1821 when W.Snell,a Dutchman, formulated its mathematical relationship.(Refraction is the change in the direction of propagation when light passes the in- terface between two media having different optical densities.) Optical materials,particularly glasses,became of prime im- portance once the refractive power of transparent materials was discovered.This found applications in magnifying glasses and notably in telescopes.Plane and convex mirrors,as well as con- vex and concave lenses,were known to the Greeks and the Chi- nese.Their knowledge probably went back to a common source in Mesopotamia,India,or Egypt.There is written evidence that the telescope was invented independently many times before Galileo built his version in 1609.He observed with it the craters of the moon,the satellites of Jupiter,and the orbiting of Venus around the sun,thus shattering the Ptolemaic theory (A.D.150). As we shall describe in Chapter 15,glass was known to the Egyp- tians as early as 3500 B.C.,and crude lenses have been unearthed in Crete and Asia Minor that are believed to date from 2000 B.C. Modern optical devices include lasers,optical telecommunica- tion,optical data storage (compact disk),and possibly,in the near future,the optical computer. Thermal Heat was considered to be an invisible fluid,called caloric,until Phenomena late into the eighteenth century.It was believed that a hot piece of material contained more caloric than a cold one and that an object would become warmer by transferring caloric into it.In the mid-1800s,Mayer,Helmholtz,and Joule discovered inde- pendently that heat is simply a form of energy.They realized that when two bodies have different temperatures,thermal energy is transferred from the hotter to the colder one when the two are brought into contact. All taken,electrical,magnetic,optical,and thermal phenom- ena were considered to be unrelated to each other until the eigh- teenth century and were thought to be governed by their own in- dependent laws.Many brilliant scientists have corrected this view and enhanced our knowledge on this in the past two centuries. Among them were Oersted,Ampere,Volta,Ohm,Coulomb
B.C.), believed that light acts like feelers and travels from the eyes to an object and that the sensation of vision occurs when these rays touch that object. Euclid, a Greek mathematician, recognized at about 300 B.C. that light propagates in a straight line. Further, he related that the angle of reflection equals the angle of incidence when light is impinging the surface between two different media. Even though refraction was also known and observed in the antique world, it was not before 1821 when W. Snell, a Dutchman, formulated its mathematical relationship. (Refraction is the change in the direction of propagation when light passes the interface between two media having different optical densities.) Optical materials, particularly glasses, became of prime importance once the refractive power of transparent materials was discovered. This found applications in magnifying glasses and notably in telescopes. Plane and convex mirrors, as well as convex and concave lenses, were known to the Greeks and the Chinese. Their knowledge probably went back to a common source in Mesopotamia, India, or Egypt. There is written evidence that the telescope was invented independently many times before Galileo built his version in 1609. He observed with it the craters of the moon, the satellites of Jupiter, and the orbiting of Venus around the sun, thus shattering the Ptolemaic theory ( A.D.150). As we shall describe in Chapter 15, glass was known to the Egyptians as early as 3500 B.C., and crude lenses have been unearthed in Crete and Asia Minor that are believed to date from 2000 B.C. Modern optical devices include lasers, optical telecommunication, optical data storage (compact disk), and possibly, in the near future, the optical computer. Heat was considered to be an invisible fluid, called caloric, until late into the eighteenth century. It was believed that a hot piece of material contained more caloric than a cold one and that an object would become warmer by transferring caloric into it. In the mid-1800s, Mayer, Helmholtz, and Joule discovered independently that heat is simply a form of energy. They realized that when two bodies have different temperatures, thermal energy is transferred from the hotter to the colder one when the two are brought into contact. All taken, electrical, magnetic, optical, and thermal phenomena were considered to be unrelated to each other until the eighteenth century and were thought to be governed by their own independent laws. Many brilliant scientists have corrected this view and enhanced our knowledge on this in the past two centuries. Among them were Oersted, Ampère, Volta, Ohm, Coulomb, 10 • The Age of Electronic Materials 177 Thermal Phenomena
178 10.The Age of Electronic Materials Drude,Seebeck,Henry,Maxwell,Thomson,Helmholtz,and Joule.However,one "natural philosopher,"as he called himself, stood out.He was probably the greatest systematic experimen- tal genius the world has known.He believed that certain funda- mental laws of nature,such as the interrelationships between electrical,magnetic,and optical phenomena,must and can be found if only the proper experiments were conducted.His name was Michael Faraday,who lived from 1791 to 1867.He made most of his fundamental discoveries at the British Royal Insti- tution.His life and his accomplishments shall serve as an ex- ample of an individual who significantly advanced our under- standing of electronic materials during the nineteenth century. Michael Faraday,at the age of 14,became the apprentice to a bookbinder and bookseller who generously allowed him to read the books which he bound.Michael was particularly fascinated by the chapter on electricity which he found in the Encyclopedia Britannica.Inspired by this reading,he experimented in the back room of the book shop with simple,home-built electric devices, in particular with a machine that created electricity by friction. Soon Faraday visited lectures on natural sciences given by John Tatum(costing one shilling per evening,the sum of which was provided to him by his brother,a blacksmith).While attending them,Faraday took detailed lecture notes which he expanded af- terwards from memory.A few months later,Faraday was given several tickets to listen to Sir Humphrey Davy (a well-known chemist at that time who lectured at the Royal Institution).Fara- day again prepared meticulous notes and sent a copy of them to Davy asking him to be allowed to "enter into the service of sci- ence"as his assistant.This wish was eventually granted when Faraday was 21 years old.From then on Faraday helped Davy with his chemical research and his lecture experiments,and served him during his extended visit to Europe. In 1819,Oersted discovered (in connection with a classroom demonstration)that a wire conveying an electric current would deflect a close-by magnetic compass needle;Figure 10.2(a).(Elec- tric currents were commonly produced at that time by galvanic cells,that is,by a repetitive arrangement of copper and zinc plates that were immersed in diluted sulfuric acid.)This gave Faraday the idea to invert the experiment,that is,to hold the magnet fixed and let the current-carrying wire rotate around the magnet.The device which Faraday designed and eventually built was,in prin- ciple,the first electric motor,that is,the forebearer of all electric motors used today [Figure 10.2(b)].(Concomitantly,Oersted found that a current-carrying wire would move in a magnetic field.And
Drude, Seebeck, Henry, Maxwell, Thomson, Helmholtz, and Joule. However, one “natural philosopher,” as he called himself, stood out. He was probably the greatest systematic experimental genius the world has known. He believed that certain fundamental laws of nature, such as the interrelationships between electrical, magnetic, and optical phenomena, must and can be found if only the proper experiments were conducted. His name was Michael Faraday, who lived from 1791 to 1867. He made most of his fundamental discoveries at the British Royal Institution. His life and his accomplishments shall serve as an example of an individual who significantly advanced our understanding of electronic materials during the nineteenth century. Michael Faraday, at the age of 14, became the apprentice to a bookbinder and bookseller who generously allowed him to read the books which he bound. Michael was particularly fascinated by the chapter on electricity which he found in the Encyclopedia Britannica. Inspired by this reading, he experimented in the back room of the book shop with simple, home-built electric devices, in particular with a machine that created electricity by friction. Soon Faraday visited lectures on natural sciences given by John Tatum (costing one shilling per evening, the sum of which was provided to him by his brother, a blacksmith). While attending them, Faraday took detailed lecture notes which he expanded afterwards from memory. A few months later, Faraday was given several tickets to listen to Sir Humphrey Davy (a well-known chemist at that time who lectured at the Royal Institution). Faraday again prepared meticulous notes and sent a copy of them to Davy asking him to be allowed to “enter into the service of science” as his assistant. This wish was eventually granted when Faraday was 21 years old. From then on Faraday helped Davy with his chemical research and his lecture experiments, and served him during his extended visit to Europe. In 1819, Oersted discovered (in connection with a classroom demonstration) that a wire conveying an electric current would deflect a close-by magnetic compass needle; Figure 10.2(a). (Electric currents were commonly produced at that time by galvanic cells, that is, by a repetitive arrangement of copper and zinc plates that were immersed in diluted sulfuric acid.) This gave Faraday the idea to invert the experiment, that is, to hold the magnet fixed and let the current-carrying wire rotate around the magnet. The device which Faraday designed and eventually built was, in principle, the first electric motor, that is, the forebearer of all electric motors used today [Figure 10.2(b)]. (Concomitantly, Oersted found that a current-carrying wire would move in a magnetic field. And 178 10 • The Age of Electronic Materials
10.The Age of Electronic Materials 179 FIGURE 10.2.(a)Oersted's ex- periment in which a com- pass needle is deflected by a wire conveying an electrical current (a sophisticated ver- sion of this design served later as a galvanometer).(b) Schematic representation of Faraday's device in which a current-carrying wire rotates around a permanent mag- net.Note that the trough is filled with liquid mercury to (a (b) provide an electrical contact. Ampere discovered that two parallel wires through which currents flowed in the same directions attracted each other,whereas they were repelled when the currents flowed in opposite directions.) Faraday's second and probably greatest single discovery was born out of his conviction that,if electric currents would produce magnetism,the reverse must also occur.Experiments with sta- tionary magnets and wires failed.Today we realize that this must be the case;otherwise,a perpetual motion would be created.Fi- nally,in 1831,Faraday demonstrated electromagnetic induction in a series of fundamental experiments.The first of them involved an iron ring on which two separate coils were wound as shown in Figure 10.3(a).If the current in the primary circuit was opened and closed,a galvanometer connected to the secondary winding deflected momentarily each time (and in opposite directions,re- spectively).In a second experiment,Faraday moved a permanent magnet in and out of a wire coil to which a galvanometer was con- nected.He found deflections in opposite directions depending on which way the magnet was moved;Figure 10.3(b).Finally,a wire or coil that was moved within the field of a horseshoe magnet showed,likewise,deflections on a galvanometer,Figure 10.3(c). Based on these experiments,Faraday created the first dynamo ma- chine consisting of a copper disk which he rotated between the poles of a large permanent magnet.He tapped the induced cur- rent from the axis and the edge of that disk. The common element of these experiments was eventually rec- ognized to be that any change in magnetic flux induces a pulse of an electrical current in a loop-shaped piece of wire.Moreover,Fara-
Ampère discovered that two parallel wires through which currents flowed in the same directions attracted each other, whereas they were repelled when the currents flowed in opposite directions.) Faraday’s second and probably greatest single discovery was born out of his conviction that, if electric currents would produce magnetism, the reverse must also occur. Experiments with stationary magnets and wires failed. Today we realize that this must be the case; otherwise, a perpetual motion would be created. Finally, in 1831, Faraday demonstrated electromagnetic induction in a series of fundamental experiments. The first of them involved an iron ring on which two separate coils were wound as shown in Figure 10.3(a). If the current in the primary circuit was opened and closed, a galvanometer connected to the secondary winding deflected momentarily each time (and in opposite directions, respectively). In a second experiment, Faraday moved a permanent magnet in and out of a wire coil to which a galvanometer was connected. He found deflections in opposite directions depending on which way the magnet was moved; Figure 10.3(b). Finally, a wire or coil that was moved within the field of a horseshoe magnet showed, likewise, deflections on a galvanometer; Figure 10.3(c). Based on these experiments, Faraday created the first dynamo machine consisting of a copper disk which he rotated between the poles of a large permanent magnet. He tapped the induced current from the axis and the edge of that disk. The common element of these experiments was eventually recognized to be that any change in magnetic flux induces a pulse of an electrical current in a loop-shaped piece of wire. Moreover, Fara- 10 • The Age of Electronic Materials 179 FIGURE 10.2. (a) Oersted’s experiment in which a compass needle is deflected by a wire conveying an electrical current (a sophisticated version of this design served later as a galvanometer). (b) Schematic representation of Faraday’s device in which a current-carrying wire rotates around a permanent magnet. Note that the trough is filled with liquid mercury to (a) (b) provide an electrical contact. – – + + N S Hg
180 10.The Age of Electronic Materials (a) (b) (c) FIGURE 10.3.Schematic representations of Faraday's experiments in which he discovered induction.(a)Soft iron ring on which a primary and a secondary coil of insulated wire is wound.(b)Paper tube on which a wire coil is helically wound.(c)A wire is moved in and out of a magnetic field of a horseshoe magnet.The galvanometer shown is an instrument that measures electric current.It consists,for example, of a compass around which several layers of insulated wire are wound;compare to Figure 10.2(a). day introduced into physics the concept of magnetic and electric lines of force.This idea,which emphasized a field between mag- netic poles,was the major impetus for Maxwell to formulate his fundamental equations of electrodynamics. After having thus established a connection between magnetism and electricity,Faraday felt that a relationship between light and magnetism must likewise exist.However,this was harder to prove. He eventually succeeded,in 1844,when he showed that the plane of polarization of light was caused to rotate in a strong magnetic field when the light path was parallel to the direction of the mag- netic field;Figure 10.4.The direction of rotation was found to be the same as the direction of current flow in the wire of an elec- tromagnet.This rotation was initially discovered to occur in lead- containing glass (heavy flint glass),which he had created in un- related research about 20 years earlier.The Faraday effect is known today to take place in many liquids,solids,and gases. In addition,Faraday tried to,but was unsuccessful in finding a possible relationship between gravity and electricity,a task that was picked up again by Einstein nearly 100 years later.But even Einstein did not make any progress at this. Faraday also discovered two quantitative laws of electrolysis (i.e.,laws which describe the precipitation or liberation of chem- ical elements on electrodes that are immersed into an electrolyte and to which a voltage is applied).He found,in 1833,after an extended series of laborious experiments,that:
day introduced into physics the concept of magnetic and electric lines of force. This idea, which emphasized a field between magnetic poles, was the major impetus for Maxwell to formulate his fundamental equations of electrodynamics. After having thus established a connection between magnetism and electricity, Faraday felt that a relationship between light and magnetism must likewise exist. However, this was harder to prove. He eventually succeeded, in 1844, when he showed that the plane of polarization of light was caused to rotate in a strong magnetic field when the light path was parallel to the direction of the magnetic field; Figure 10.4. The direction of rotation was found to be the same as the direction of current flow in the wire of an electromagnet. This rotation was initially discovered to occur in leadcontaining glass (heavy flint glass), which he had created in unrelated research about 20 years earlier. The Faraday effect is known today to take place in many liquids, solids, and gases. In addition, Faraday tried to, but was unsuccessful in finding a possible relationship between gravity and electricity, a task that was picked up again by Einstein nearly 100 years later. But even Einstein did not make any progress at this. Faraday also discovered two quantitative laws of electrolysis (i.e., laws which describe the precipitation or liberation of chemical elements on electrodes that are immersed into an electrolyte and to which a voltage is applied). He found, in 1833, after an extended series of laborious experiments, that: 180 10 • The Age of Electronic Materials FIGURE 10.3. Schematic representations of Faraday’s experiments in which he discovered induction. (a) Soft iron ring on which a primary and a secondary coil of insulated wire is wound. (b) Paper tube on which a wire coil is helically wound. (c) A wire is moved in and out of a magnetic field of a horseshoe magnet. The galvanometer shown is an instrument that measures electric current. It consists, for example, of a compass around which several layers of insulated wire are wound; compare to Figure 10.2(a). (a) (b) (c) 0 N S 0 N S 0
10.The Age of Electronic Materials 181 Plane polarized Lead-glass cylinder light Polarizer Analyzer Magnetic field direction FIGURE 10.4.Schematic representation of the rotation of the plane of polarization of plane polarized light in lead glass,when applying a magnetic field(Faraday effect).In plane polarized light,the electric vector vibrates only in one direction,shown to be the paper plane in the left part of the figure.Polarizer and analyzer are identical devices which allow the light to pass in only one vibrational direction. 1.The amount of material precipitated at an electrode is pro- portional to the quantity of electricity (current multiplied by time)consumed;see Eq.(9.11). 2.The amount of material precipitated (or liberated)at an elec- trode by a unit amount of electricity is proportional to its equivalent mass;see Eq.(9.11).(The equivalent mass of a sub- stance is the atomic mass associated with a unit gain or loss of electrons.For example,during the electrolysis of a MgCl2 solution,one unit of electricity,that is,9.649 X 104 coulombs,2 or 6.02 x 1023 electrons,3 deposits 24.312/2 grams of Mg on the negative electrode and liberates 35.453 grams of chlorine gas at the positive electrode;see Appendix IV.) Furthermore,Faraday introduced the terms anode,cathode,an- ion,cation,and electrode. Not enough,Faraday also made contributions to chemistry (liq- uefaction of chlorine under pressure,isolation of benzene,etc.), and he performed "sponsored research"on stainless steel and on glass.His fundamental studies on nonconducting materials (called dielectrics)led to a specific form of recognition:The unit of capacity (that is,the ability to hold an electric charge)was eventually named one farad.(The capacitance is one farad when one coulomb of electricity changes the potential between the plates of a capacitor by one volt,see Chapter 11 and Appendix II.)Finally,the Faraday cage was named after him.(The Faraday 2Faraday constant. 3Avogadro constant
1. The amount of material precipitated at an electrode is proportional to the quantity of electricity (current multiplied by time) consumed; see Eq. (9.11). 2. The amount of material precipitated (or liberated) at an electrode by a unit amount of electricity is proportional to its equivalent mass; see Eq. (9.11). (The equivalent mass of a substance is the atomic mass associated with a unit gain or loss of electrons. For example, during the electrolysis of a MgCl2 solution, one unit of electricity, that is, 9.649 104 coulombs,2 or 6.02 1023 electrons,3 deposits 24.312/2 grams of Mg on the negative electrode and liberates 35.453 grams of chlorine gas at the positive electrode; see Appendix IV.) Furthermore, Faraday introduced the terms anode, cathode, anion, cation, and electrode. Not enough, Faraday also made contributions to chemistry (liquefaction of chlorine under pressure, isolation of benzene, etc.), and he performed “sponsored research” on stainless steel and on glass. His fundamental studies on nonconducting materials (called dielectrics) led to a specific form of recognition: The unit of capacity (that is, the ability to hold an electric charge) was eventually named one farad. (The capacitance is one farad when one coulomb of electricity changes the potential between the plates of a capacitor by one volt, see Chapter 11 and Appendix II.) Finally, the Faraday cage was named after him. (The Faraday 10 • The Age of Electronic Materials 181 FIGURE 10.4. Schematic representation of the rotation of the plane of polarization of plane polarized light in lead glass, when applying a magnetic field (Faraday effect). In plane polarized light, the electric vector vibrates only in one direction, shown to be the paper plane in the left part of the figure. Polarizer and analyzer are identical devices which allow the light to pass in only one vibrational direction. Polarizer Plane polarized light Lead-glass cylinder Magnetic field direction N S Analyzer 2Faraday constant. 3Avogadro constant
182 10.The Age of Electronic Materials cage is a box of metal screen that shields its interior from elec- tromagnetic radiation. Faraday's life was coined by a search for truth and unity.He showed that the above-mentioned five kinds of electricity in- volved the same principal mechanism.Later he demonstrated that many of the forces of nature are intimately interconnected as described above. Faraday was also a brilliant public speaker who went to great pains to express his ideas in a clear and simple language.In par- ticular,his lectures on Friday evenings in which he usually showed a number of experiments and his lectures to the youth at Christmas time were quite popular.Regardless of his accom- plishments and his fame,Faraday was modest and indifferent to money and honors such as knighthood or becoming the presi- dent of the British Royal Society(which he declined to accept). In summary,Michael Faraday was a true scientist and a role model whose impact on society can still be felt today. Nature of The following chapters are mainly concerned with the interactions Electrons of electrons with matter.Thus,a brief discussion of the nature of electrons is quite in order.We have already mentioned in Section 3.2 that electrons can be considered to be part of an atom which, in an elementary description,orbit the atomic core.Some of these electrons,particularly those in the outermost orbit (i.e.,the va- lence electrons),are often only loosely bound to their nuclei.There- fore,they disassociate with relative ease from their core and then combine to form a "sea"of electrons.These free electrons govern many of the electronic properties of materials,particularly in con- ductors.In other cases,such as in insulators,the electrons are bound somewhat stronger to their nuclei and thus,under the in- fluence of an alternating external electromagnetic force,may os- cillate about their core.This constitutes an electric dipole,as de- scribed in Section 3.2.We shall return to this concept when we discuss the electronic properties of dielectric materials. Now,to our knowledge,nobody has so far seen an electron, even by using the most sophisticated equipment.We experience merely the actions of electrons,for example,on a television screen or in an electron microscope.In each of these instances, the electrons seem to manifest themselves in quite a different way,that is,in the first case as a particle and in the latter case as an electron wave.Accordingly,we shall use the terms "wave" and "particle"as convenient means to describe the different as- pects of the properties of electrons.This is called the "duality" of the manifestations of electrons.A more complete description
cage is a box of metal screen that shields its interior from electromagnetic radiation.) Faraday’s life was coined by a search for truth and unity. He showed that the above-mentioned five kinds of electricity involved the same principal mechanism. Later he demonstrated that many of the forces of nature are intimately interconnected as described above. Faraday was also a brilliant public speaker who went to great pains to express his ideas in a clear and simple language. In particular, his lectures on Friday evenings in which he usually showed a number of experiments and his lectures to the youth at Christmas time were quite popular. Regardless of his accomplishments and his fame, Faraday was modest and indifferent to money and honors such as knighthood or becoming the president of the British Royal Society (which he declined to accept). In summary, Michael Faraday was a true scientist and a role model whose impact on society can still be felt today. The following chapters are mainly concerned with the interactions of electrons with matter. Thus, a brief discussion of the nature of electrons is quite in order. We have already mentioned in Section 3.2 that electrons can be considered to be part of an atom which, in an elementary description, orbit the atomic core. Some of these electrons, particularly those in the outermost orbit (i.e., the valence electrons), are often only loosely bound to their nuclei. Therefore, they disassociate with relative ease from their core and then combine to form a “sea” of electrons. These free electrons govern many of the electronic properties of materials, particularly in conductors. In other cases, such as in insulators, the electrons are bound somewhat stronger to their nuclei and thus, under the influence of an alternating external electromagnetic force, may oscillate about their core. This constitutes an electric dipole, as described in Section 3.2. We shall return to this concept when we discuss the electronic properties of dielectric materials. Now, to our knowledge, nobody has so far seen an electron, even by using the most sophisticated equipment. We experience merely the actions of electrons, for example, on a television screen or in an electron microscope. In each of these instances, the electrons seem to manifest themselves in quite a different way, that is, in the first case as a particle and in the latter case as an electron wave. Accordingly, we shall use the terms “wave” and “particle” as convenient means to describe the different aspects of the properties of electrons. This is called the “duality” of the manifestations of electrons. A more complete description 182 10 • The Age of Electronic Materials Nature of Electrons
