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1、薄膜制备与表面分析Thin Film Synthesis and Surface Analysis,Qing-Yu ZhangState Key Laboratory for Materials Modification by Laser,Ion and Electron Beams,概论 表面及表面科学,固体的表面、或者说界面，在人们的社会实践中起着极为重要的作用。表面科学的研究，对整个科学技术的发展具有重要的意义。表面科学包括表面物理、表面化学、表面电子学、表面生物学等。,概论 表面及表面科学,固体表面：物体与真空或气体的界面。固体表面可以指从单一的第一个原子层到几个原子层厚度的表面层，甚
2、至深达几个微米的表面层。在热力学平衡的条件下，固体表面的化学组成、微观结构、原子振动状态等均会与固体内部产生一定的差异。,概论 表面及表面科学,Since it requires energy to terminate the bonding,the surface is energetically less stable than the bulk.,This energy is known as the surface free energy.In the case of liquid interfaces,this energy is called surface tension.,概论
3、 表面分析技术,表面分析技术是人们为了获取表面的物理、化学等方面的信息而采用的一些实验方法和手段。,概论 表面分析技术,一般地说，它是利用一种探测束如电子束、离子束、光子束、中性粒子束等，有时还加上电场、磁场、热等的作用，来探测材料的形貌、化学组成、原子结构、原子状态、电子状态等方面的信息。,概论 表面分析技术,概论 表面分析技术,概论 表面分析技术,概论 表面分析技术,概论 表面分析技术,部分表面分析设备的分析范围,概论 表面分析技术,概论 真空技术原理,为了使被研究的样品不被周围气氛所污染，获取“原子清洁”的表面，表面分析过程往往是在真空或超高真空中进行的。目前，人们所广泛使用的很多表面分
4、析设备都具有真空系统。薄膜制备设备往往涉及真空系统。,概论 真空技术原理,真空单位Atmospheres(atm):Scale relative to our atmospheric pressure as 1 atmPascal(Pa):SI unit equal to N/m2mBar:Equal to 1x10-8 Pa.Torr or mmHg:Most commonly used pressure unit,based on mercury vacuum gauges.,概论 真空技术原理,真空的划分,Atmospheric:760 TorrLow Vacuum:1 to 1x10-
5、3 TorrMedium Vacuum:1x10-3 to 1x10-5 TorrHigh Vacuum(HV):1x10-6 to 1x10-8 TorrUltra-High Vacuum(UHV):1x10-9 Torr,概论 真空技术原理,真空的意义,Monolayer Coverage TimeFor an ideal gas,the time needed for monolayer coverage is given by:tML 1019/ZAwhere ZA is impingement rate.,概论 真空技术原理,真空的意义,Impingement Rate(Flux)F
6、or an ideal gas,the impingement rate is given by:ZA=v/4where,-the number density of gas molecules v-the mean velocity,概论 真空技术原理,概论 真空技术原理,真空的获得,Ultimate PressureLow Vacuum(Rough)PumpsRotary Vane PumpsSorption PumpsHigh Vacuum PumpsDiffusion PumpsTurbo Molecular PumpsUltra-High VacuumTurbo Molecular
7、PumpsIon PumpsTitanium Sublimation Pumps,Oil/Oil-FreeOilRotary Vane PumpsDiffusion PumpsTurbo Molecular PumpsOil-FreeTurbo Molecular PumpsIon PumpsTitanium Sublimation Pumps,概论 真空技术原理,真空的获得,Gas enters the inlet port and is trapped between the rotor vanes and the pump body.The eccentrically mounted r
8、otor compresses the gas and sweeps it toward the discharge port.When gas pressure exceeds atmospheric pressure,the exhaust valve opens and gas is expelled.Atmosphere to 10-3 torrRobust,inexpensiveOil lubricated,概论 真空技术原理,真空的获得,LN2 cooled molecular sieve with large surface areaAtm to 10-3 Torr(two un
9、its working alternately)Quickly becomes saturatedMust be baked at 200 C to remove adsorbed gasesSimple,inexpensive,oil-free,概论 真空技术原理,真空的获得,Momentum transfer to gas molecules through collision with directed jet of oil moleculesRequire cooling water,backing pump10-3 to 10-7 Torr(to 10-9 Torr with LN2
10、 cooling),AdvantagesRobustHigh pumping speed for relatively low cost.No vibration or noise.DisadvantagesOil as a pumping medium,high risk of back-streaming oil,cold traps requiredPotential for serious vacuum problems,概论 真空技术原理,真空的获得,Molecules mechanically pumped by collision with angled high speed t
11、urbine blades(rotor).Several rotor arranged in a series spinning at 30,000-60,000 rpm.Rotor tangential velocity is on the order of the average thermal velocity of molecules.Atmosphere to 10-10 TorrOil/grease/electromagnetic bearingsMost common HV/UHV pump.,概论 真空技术原理,真空的获得,AdvantagesCorrectly operate
12、d they do not back-stream oil into the vacuum system at any time.They can be started and stopped in a few minutes time.Disadvantage Turbo pump can be noisy and they induce vibration.Turbo pumps are expensive.,概论 真空技术原理,真空的获得,High voltage between anode and cathode(5 kV)Electrons are captured in anode
13、 and spiral due the to magnetic field(longer path-length).Gas molecules are ionized by collisions with electrons and are accelerated to cathode.Ions embedded in cathode material(titanium)and sputter titanium atoms from surface.Sputtered Ti atoms act as getter for reactive gases.10-4 Torr to 10-11 To
14、rr,概论 真空技术原理,真空的获得,AdvantagesClean,oil-free.No moving parts,no vibrations,quiet.Low power consumption and relatively long operating livesDisadvantage Do not pump noble gases well.Requires“regeneration”of Ti every 4-6 years.,概论 真空技术原理,真空的获得,Heated Ti filament evaporates Ti film onto cooled surface.Ti
15、 getters reactive gases by reaction.Operate at 10-8-10-11 TorrInexpensive,reliablePeriodic operation-not primary pumping mechanism,概论 真空技术原理,真空的获得,Materials Considerations,Outgassing rates Producing“virtual”leaks Mechanical stability Temperature stability,Conductivity Chemical inertness Weldability,
16、概论 真空技术原理,真空的获得,Oxygen free high-purity copper(OFHC)Be-Cu alloyTantalum,Molybdenum,Tungsten Teflon(gassy)MACOR(machinable glass composite)Alumina Quartz,pyrex(gassy)mu-metal magnetic shielding(Co,Ni,Fe)Molybdenum disulfide(lubricant),Compatible Materials,概论 真空技术原理,Materials to be Avoided(high vapor
17、pressures)Zn,Cd:especially be careful of fasteners,bolts Brass Certain soldersAny type of grease or oils,真空的获得,Common Vacuum ProblemsImproper cleaning or handling techniquesUsing incompatible materialsLeaksVirtual leaks,概论 真空技术原理,真空的获得,概论 真空技术原理,真空的获得,概论 真空技术原理,真空的获得,Pump DownTypically follows a wel
18、l-defined sequence according to the types of pumps on the vacuum systemFor UHV systems,typically requires a few hours to reach a medium vacuum after a vent to air,Bake OutHeat the chamber to temperatures between 100oC and 200oC for 1-2 days.Rapidly remove adsorbed gases from the chamber walls at hig
19、h temperatures in order to lower the outgassing rates at room temperature.Generally it takes another day to cool and recover base pressure.,概论 真空技术原理,真空的测量,Heat filament with a constant current.Measure filament temperature with thermocouple.Gas molecules collide with and cool the filament.Voltage in
20、creases to keep filament at constant current.Atm to 10-4 TorrFast,simple,inexpensive.,Thermocouple Gauge,概论 真空技术原理,真空的测量,Two identical heated filaments;one sealed at HV,one exposed to system.Current flows through Wheatstone bridge circuit.Pressure difference indicated by meter(non-linear).Atm to 10-
21、4 torr.Simple,reliable,inexpensive.,Pirani Gauge,概论 真空技术原理,真空的测量,Heated filament produces electrons via thermionic emission.Electrons are accelerated towards anode grid.Many electrons pass through the grid and create positive ions from collisions with gas molecules.Ions are accelerated to collector
22、wire.Measure the current between anode and collector.Operate at 10-4 to 10-11 TorrSensitive,high accuracy,widely used.,Ion Gauge(Bayard-Alpert),概论 真空技术原理,真空的测量,Quadrupole mass spectrometer-RGA(residual gas analyzer)10-4 to 10-14 torrTotal pressure mode integrates all ion intensitiesPartial pressure mode indicates residual vacuum compositionHighly accurate,preciseComplex,expensive.,Mass Spectrometer,概论 真空技术原理,真空的测量,Typical UHV mass spectrum of residual gases before bakeout.,
