材料导论课件

1、材料导论PositionEHl光的传播X-radiationMicrowavesg-radiationUVIRRadio waves10-6 10-3 1 103 106 109 1012Wavelength(nm)可见光光波谱系微波无线电波h is Plancks constant 光子：光波：qiqrRefraction beamGlassVacuum (or air)Incident beamqiReflected beam11.2.1 反射入射反射折射Fresnels formula反射率金属的反射率 0.90.95反射发生在表层0.1m极少量被吸收非金属反射率低大部分被吸收或透射固体

2、对真空或空气的反射材料2对材料1的反射Incident lightSpecular reflectionDiffuse reflectionTrue surface topographyAverage surface入射光特征反射弥散散射实际表面平均表面实际表面的反射理想粗糙表面qiqrTransmitted beamIncident beamI0IT11.2.2 折射透射入射折光指数绝大多数材料 mr 1故与极化有关折射机理例题：将激光束引入折光指数为1.5的玻璃纤维，如何能使光线泄漏为最小？(a) 设玻璃纤维处于空气(n=1)中, 光线以60的角度进入, a = 90-60 = 30:So

3、lution60a = 30b有泄漏为避免发生透射，入射角必须小于90 - 62.7=27.3 。Maximum angle = 90 aab = 90(c) 如果纤维浸于水(n=1.333)中, 则:(1) 电子极化 生热11.2.4 吸收与透射吸收机理(2) 电子跃迁 显示颜色产生跃迁的条件：例题: 计算可见光谱中光子完全透射和完全吸收的临界带隙Solution这说明带隙大于 3.1 eV的非金属材料不能吸收光线，如果材料是纯的，则为无色透明。可见光最短波长 (min)约为0.4m, 则吸收可见光的最大带隙Eg(max)为：可见光最大波长(max)约为0.7m，发生吸收的最小带隙Eg(mi

4、n)为：如果带隙1.8 eV，则全部可见光被吸收，材料不透明如果带隙在1.8和3.1eV之间，则材料显示颜色跃迁后的几种可能DEDE1DE2DE1DE2光子光子光子声子吸收不仅与介质本质有关，也与路径长短有关b为吸收系数（单位mm-1），由材料本质所决定Incident light rayPore (n=1)Glass or ceramic (n1)Scattered light ray内部孔穴造成的散射入射光弥散反射特征反射弥散透射特征透射Diffuse reflectionSpecular reflectionDiffuse transmissionSpecular transmissio

5、n透明与半透明I0RIncident beamI0Transmitted beamI0(1-R)2e-bxReflected beamReflected beamI0R(1-R) e-bxI0 (1-R)Absorption反射光吸收反射光透射光入射光I0(1-R)e-bxEXAMPLE 设计一滤板，使能至少透过95% Zn的 Ka X光。以铝为材料，其吸收系数为1.08 104 m-1，忽略反射Solution由公式故铝板厚度应小于等于0.0047mmEXAMPLE 一材料的反射率为0.15，吸收系数为1 104 m-1. 设计一挡板使只有1%的光线透过.Solution11.3 光学性质的

6、应用E0Incoming electronE1 + E2 + E3 + E4 + E5 = E0E1E2E3E4E511.3.1 X-ray fluorescent analysis(X萤光分析）Ka l = 0.154nm DE = 1.29 10-15JKb l = 0.139nm DE = 0.15 10-15JLa l = 1.336nm DE = 1.43 10-15Jwhere K = 1s2 level L = 2s2p6 level M = 2s2p6d10 levelCopperKLM铜Characteristic peaksContinuous radiationHigh-

7、energy stimulusLaKbKalswlIntensity of emitted radiationLow-energy stimulusEnergyWavelengthShort wavelength limitFluorescence(萤光)reemission occurs for times much less than one secondPhosphorescence(磷光)for longer times11.3.2 LUMINESCENCE (发光)再发射时间较长再发射时间短于1秒PhotonStimulusValence bandNo Eg l very longe

8、e金属激励光子价带萤光材料StimulusPhotonConduction bandValence bandeeEg激励光子价带Trap EdEgStimulusConduction bandValence bandeee磷光材料激励光子价带松弛时间，材料常数撤除光源后的时间初始光强时间t光强例题：为电视机的蓝色选择一种材料蓝光波长为4.510-5cm，其光子能量为SOLUTION查表找到CaWO4，光子波长为4.3 10-5cm，松弛时间为4 10-6s，正好作为蓝光材料，但不能产生磷光。又找到ZnS的Eg为5.671 10-19J，可提供一个(5.671-4.422) 10-19 = 1.

9、249 10-19 J的中间带隙于是选ZnS为杂质材料，可以产生磷光。5.6714.422CaWO4ZnSEg-EdEgElectroluminescencelight-emitting diodes (LEDs)Isilver contactn-typep-type+电致发光电子 空穴hnIncident photonhn Eg11.3.3 光导性n-typep-typeVoltage producedeh+太阳能电池 Light Amplification by Stimulated Emission of Radiation. Coherent beamFlash lampRubyPow

10、er source11.3.4 激光电弧灯反射前晶体中部反射后基态Cr原子激发Cr原子(a)(b)(c)(d)(e)完全镀银部分镀银HolesExcited electronsValence bandPhoton emissionConduction bandEg(a)Valence bandConduction bandRecombined excited electron and hole(b)完全镀银部分镀银Valence bandConduction bandNew excited electronNew hole(c)Valence bandConduction band(d)Val

11、ence bandConduction band(e)Valence bandConduction band(f)InputSignalEncoderElectrical/Optical ConverterRepeaterOptical/Electrical ConverterDecoderOutputSignalFiber Optic Cable11.3.5 光导纤维输入信号电光转换 复制 光电转换 输出编码解码Digital encoding IntensityTime(a)IntensityTime(b)数字编码Coaxial design of commercial optical f

12、ibers CoreCladdingCoating同轴光缆IntensityIntensityIntensityTime Input pulse Time Input pulse Time Input pulse IntensityIntensityIntensityTime Output pulseTime Output pulseTime Output pulse(c)(b)(a)完Visible spectrum4 x 10-7m5 x 10-7m6 x 10-7m7 x 10-7mg-Raysx-RaysUltravioletVisibleInfraredMicrowaveRadio,

13、TVEnergy (eV)Frequency (Hz)Wavelength (m)10-1010010410210610810-410-610-810-210201022101010810610410181016101210141km 1 A1 nm1mm1mm1m10-1410-1210-1010-810-610-410-21001021040.4mm0.5mm0.6mm0.7mmVisible spectrum wavelength一些透明材料的折光指数 Material Average Index of RefractionCeramicsSilica glass 1.458Borosi

14、licate (Pyrex) glass 1.47Soda-lime glass 1.51Quartz (SiO2) 1.55Dense optical flint glass 1.65Spinel (MgAl2O4) 1.72Periclase (MgO) 1.74Corundum (Al2O3) 1.76PolymersPolytetrafluoroethylene 1.35Polymethyl methacrylate 1.49Polypropylene 1.49Polyethylene 1.51Polystyrene 1.600.2 0.3 0.4 0.5 0.6 0.7 0.8 1.

15、0 1.5 2.0 2.5 3.0ReflectedTransmitted visibleFraction of radiant energyWavelength (mm)1.0 0.8 0.6 0.4 0.2 0AbsorbedIncident wavePrimary reflected waveSecondary reflected wavel1/4 l入射主反射二级反射空气Substrate (n2n1)基材Air (n=1)Coating (n11)涂层反射的最小化电子极化能量吸收速度降低折射电子跃迁11.2.1 作用机理吸收后再释放E5E3E4E2E1EnergyDE = E4-E2 = hn42电子跃迁 频率为n42的入射光子DEPhotonemittedDEFermienergyEnergyFilled statesEmpty statesPhoton absorbed金属中的电子跃迁DEPhotonemittedExcitedfreeelectronDEEgPhotonabsorbedEnergyConduction bandValence bandBand gapHole非金属中的电子跃迁DEPhotonabsorbedEnergyConduction bandValence