功能材料双语-电功能材料.ppt

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1、Chapter 3 Electrical Functional Materials,Definition: materials with special electrical properties or electromeric effect（电性效应）.,Semiconductor materials,Superconducting materials,Conductive materials,Electrical Functional Materials,classification of electrical functional materials,based on the condu

2、ctive mechanism：electron conduction material and ionic conduction material. electron conduction material: semiconductor, conductor and superconductor ：,conductivity S/m,insulator,semiconductor,conductor,superconductor：,the movement of an ion from one site to another through defects in the crystal la

3、ttice of a solid or aqueous solution, so the conductivity is smaller because the travelling speed of ion is slower than electron, the conductivity is no more than 102 S/m ，and usually smaller than 100 S/m,ionic conduction material,3.1 Conductor,（1）metal. the conductivity is 107108 S/m; sliver（6.63 1

4、07 S/m ）、copper（5.85 107 S/m ） aluminum （3.45 107 S/m ） （2）alloy. the conductivity is 105107 S/m; brass黄铜（1.60 107 S/m ）, nichrome镍铬合金 （9.30105S/m ） （3） inorganic nonmetallic. the conductivity is 105108 S/m. graphite石墨(2.5106 S/m).,crystal structure of graphite,applications of conductors,metals：cabl

5、e, electrical machine, radiation shielding, battery, switch, sensor, information transmission, contact material, etc， alloys: mainly used for resistance material and thermocouple material, for example platinum-rhodium platinum thermocouple（铂铑铂热电偶） inorganic nonmetallic：corrosion resistant conductors

6、 and conductive filler（导电填料）.,3.2 superconductor,Superconductivity was discovered on April8, 1911 by Dutch physicistHeike Kamerlingh Onnes, who was studying the resistance of solid mercury(汞) at cryogenic temperatures （冷冻温度）using the recently produced liquid helium（液氦）as a refrigerant. At the temper

7、ature of 4.2 K, he observed that the resistance abruptly disappeared. The precise date and circumstances of the discovery were only reconstructed a century later, when Onness notebook was found.,Definition of superconductors,Superconductivityis a phenomenon of exactly zeroelectrical resistanceand ex

8、pulsion ofmagnetic fieldsoccurring in certain materials whencooledbelow a characteristiccritical temperature.,Elementary properties of superconductors,exactly zero resistivity（绝对零电阻） Experimental evidence points to a current lifetime of at least 100,000 years.,Meissner effect（ 迈斯纳效应） the complete ej

9、ection ofmagnetic field linesfrom the interior of the superconductor as it transitions into the superconducting state,ejection ofmagnetic field lines,The occurrence of the Meissner effect indicates that superconductivity cannot be understood simply as the idealization of perfect conductivity in clas

10、sical physics.,The electrical resistivity of a metallic conductor decreases gradually as temperature is lowered. In ordinary conductors, such as copper or silver, this decrease is limited by impurities（杂质） and other defects（缺陷）. Even near absolute zero, a real sample of a normal conductor shows some

11、 resistance. In a superconductor, the resistance drops abruptly to zero when the material is cooled below its critical temperature.,critical temperatureTc，critical magnetic field Hc， critical current Jc（临界温度、临界磁场、临界电流密度）,the characteristics of superconductivity disappear when thetemperatureTcis high

12、er than thecritical temperatureTc; or higher than the critical magnetic field Hc, critical current Jc ,the regions separateed by Tc、Hc，Jc.,Josephson effect（约瑟夫森效应）,The Josephson effect is the phenomenon of supercurrenti.e. a current that flows indefinitely（无限期的） long without any voltage appliedacros

13、s a device known as a Josephson junction (JJ), which consists of two superconductors coupled by a weak link.,The weak link can consist of a thin insulating barrier (known as a superconductorinsulatorsuperconductor junction, or S-I-S), a short section of non-superconducting metal (S-N-S), or a physic

14、al constriction that weakens the superconductivity at the point of contact (S-s-S).,development of superconductor,77 K,By material: chemical elements alloys ceramics organic superconductors,Applications,Superconducting magnets(超导磁体) are some of the most powerful electromagnets(电磁铁) known. They are u

15、sed in Magnetic Resonance Imaging(MRI，磁共振成像) /nuclear magnetic resonance(NMR，核磁共振成像) machines, mass spectrometers(质谱仪), and the beam-steering magnets (光束转向磁体)used in particle accelerators(粒子加速器).,粒子加速器,内部温度：4万亿摄氏度 工作温度是-271.3，比外太空还冷,In the 1950s and 1960s, superconductors were used to build experime

16、ntal digital computers using cryotron switches（低温开关）. More recently, superconductors have been used to make digital circuits based on rapid single flux quantum （快速单量子通量）technology and RF （radio frequency，无线电频率）and microwave filters（微波过滤器） for mobile phone base stations.,Superconductors are used to b

17、uild Josephson junctions which are the building blocks of SQUIDs (superconducting quantum interference devices), the most sensitive magnetometers（磁力计） known. SQUIDs are used in scanning SQUID microscopes and magnetoencephalography（脑磁图）,high-performance smart grid（智能电网）, electric power transmission（电

18、力输送）, transformers（变压器）, power storage devices, electric motors（电动机） (e.g. for vehicle propulsion（汽车驱动）, as in maglev trains（磁悬浮列车）), magnetic levitation devices（磁悬浮装置）, fault current limiters,（故障电流限流器） and superconducting magnetic refrigeration（超导磁制冷）.,They can also be used for magnetic separation(

19、磁选), where weakly magnetic particles are extracted from a background of less or non-magnetic particles, as in the pigment industries.,核聚变堆用超导线圈,Superconducting submarine（超导潜水艇）,超导磁流体推进船,1992年1月27日，由日本船舶和海洋基金会建造的，第一艘采用超导磁流体推进器的轮船“大和”1号在日本神户下水试航。,maglev trains（磁悬浮列车）,近日，国家“十三五”重点研发计划现代轨道交通专项启动时速600公里高

20、速磁悬浮交通和时速200公里中速磁浮交通研发项目,superconducting electric power transmission,未来超导体汽车,寻找现实中的哈利路亚山室温超导体,3.3 semiconductor,has electrical conductivity between that of a conductor such as copper and that of an insulator such as glass（10-7104） Negative temperature coefficient（负的电阻温度系数）:thermal conductivityorelec

21、trical resistivity of a semiconductor lowers with increasing temperature, which is opposite to that of a metal.,semiconductor,useful properties: passing current more easily in one direction than the other; showing variableresistance(可变电阻); sensitivity to light or heat（对光/热敏感） So, electrical properti

22、es of a semiconductor material can be modified（修饰） by controlled addition of impurities（杂质）, or by the application of electrical fields or light.,basic concepts:,In solid-state physics, the electronic band structure (or simply band structure) of a solid describes those ranges of energy that an elect

23、ron within the solid may have and ranges of energy that it may not have (called band gaps or forbidden bands)带隙或禁带.,（1） Electronic band structure(band structure)电子能带结构,Physics of semiconductors（半导体物理学）,band gap, also called an energy gap （能隙）or bandgap（带隙）, is an energy range in a solid where no ele

24、ctron states can exist. generally refers to the energy difference (in electron volts) between the top of the valence band and the bottom of the conduction band in insulators and semiconductors.,(2) Band Gap（带隙）,(3) Forbidden Band（禁带 ） energy gap should be the energy difference between two different

25、energy band. for example conducting band and valence band. However, energy in between the two band is allowed. Forbidden band do not allow any energy resident in it,(4) Valence Band（价带） In solids, the valence band is the highest range of electron energies in which electrons are normally present at a

26、bsolute zero temperature. On a graph of the electronic band structure of a material, the valence band is located below the conduction band, separated from it in insulators and semiconductors by a band gap. the closest band beneath the band gap. In metals, the conduction band has no energy gap separa

27、ting it from the valence band.,(5) Empty band （空带）：no electron is filled,(7) Filled Band（满带）,(6) Conduction Band（导带 ） The closest band above the band gap,The valence electrons are bound to（限制在） individual atoms, as opposed to conduction electrons (found in conductors and semiconductors), which can m

28、ove freely within the atomic lattice of the material.,The totally filled orbitals（轨道） with highest range of electron energies form valence, the empty orbital with no electrons is called the conduction band.,1ev,The conductive mechanism of the semiconductor,Electrons can be excited across the energy

29、band gap (from filled band to empty gap ) of a semiconductor by various means, and leaving holes in the filled band，This process is known aselectronhole pair generation. The movement of electrons in the conduction band and holes in the filled band create current.,types of semiconductor materials,1.

30、Elements conductor,pure semiconductor, no defect, the concentration of impurity is less than10-9,adding controlled impurities to a semiconductor to modify the conductivity,the most commercially important of these elements are silicon （硅）and germanium（锗）. Silicon and germanium are used here effective

31、ly because they have 4 valence electrons in their outermost shell which gives them the ability to gain or lose electrons equally at the same time. A pure semiconductor, however, is not very useful, as it is neither a very good insulator nor a very good conductor.,Intrinsic semiconductor,Extrinsic se

32、miconductor(非本征半导体/杂质半导体),Adding impurity atoms （杂质原子）to a semiconducting material, known as “doping”,（掺杂） greatly increases the number of charge carriers within it.,larger electron concentration than hole concentration， electrons are the majority carriers,larger hole concentration than electron con

33、centration, holes are the majority carriers,N-type semiconductor（ electron doners ）电子施主 group VA（N、P、As、Sb、Bi）introduced into group A of the periodic table （C、Si、Ge、Sn）, creates an extra free electron p-type semiconductor（ holes, acceptors ）电子受主 group A（B、Al、Ga、In、Ta）all contain three valence electr

34、ons, when used to dope group A （C、Si、Ge、Sn），a vacant state ( an electron hole) is created, which can move around the lattice and functions as a charge carrier,Extrinsic semiconductor（非本征半导体）,energy band of semiconductor,n-type semiconductor: electron is in doner level施主能级 , the energy difference bet

35、ween doner level and bottom of conduction band （Ed）is much less than Eg（about three orders of magnitude）, so electron can be more easily excited to the conduction band than intrinsic excitation本征激发,for example: one over a billion of As doped Si，Eg is 1.610-19 J，Ed is 6.410-21 J. one over a billion o

36、f Sb doped Ge，Eg is 1.1510-19 J，Ed is1.610-21 J.,p-type semiconductor: hole is in accepted level受主能级, the energy difference between accepted level and top of conduction band （Ea）is much less than Eg, so electron in valence band can be more easily excited to the accepted band and leave an hole in val

37、ence band.,binary compound二元化合物 GaAs、CdS、SiC、GeS、AsSe3, etc By alloying multiple compounds, some semiconductor materials are tunable, e.g., in band gap or lattice constant晶格常数. The result is ternary三元, quaternary四元, or even quinary五元 compositions ternary compound三元化合物 AgGeTe2、AgAsSe2、CuCdSnTe4 , etc

38、,2. compounds,gallium arsenide (GaAs) has six times higher electron mobility than silicon, which allows faster operation; wider band gap, which allows operation of power devices at higher temperatures, and gives lower thermal noise to low power devices at room temperature; its direct band gap gives

39、it more favorable optoelectronic properties than the indirect band gap 间接带隙of silicon;,it can be alloyed to ternary and quaternary compositions, with adjustable band gap width, allowing light emission at chosen wavelengths, and allowing e.g. matching to wavelengths with lowest losses in optical fibe

40、rs; GaAs can be also grown in a semi-insulating半绝缘 form, which is suitable as a lattice-matching 晶格匹配insulating substrate for GaAs devices.,Conversely, silicon is robust强健的, cheap, and easy to process, whereas GaAs is brittle脆的 and expensive, and insulation layers can not be created by just growing

41、an oxide layer; GaAs is therefore used only where silicon is not sufficient.,binary solid solution： Bi-Sb ternary solid solution：Hg1-xCdxTe、GeAs1-xPx,Infrared detector material（红外探测材料）,High-speed response devices（高速响应器件）、 photo-communication（光通信）,3. solid solution,Use of semiconductors,A semiconductor diode(半导体二极管) (devices that allow current in only one direction) consists of p-type and n-type semiconductors placed in junction with one another. Currently, most semiconductor diodes use doped silicon or germanium.,LED,