1、薄膜制備與表面分析Thin Film Synthesis and Surface Analysis,武漢科技大學(xué) 材料與冶金學(xué)院 金屬材料工程系,概論 表面及表面科學(xué),固體的表面、或者說界面， 在人們的社會實(shí)踐中起著極為重要的作用。 表面科學(xué)的研究，對整個(gè)科學(xué)技術(shù)的發(fā)展具有重要的意義。 表面科學(xué)包括表面物理、表面化學(xué)、表面電子學(xué)、表面生物學(xué)等。,概論 表面及表面科學(xué),固體表面：物體與真空或氣體的界面。 固體表面可以指從單一的第一個(gè)原子層到幾個(gè)原子層厚度的表面層，甚至深達(dá)幾個(gè)微米的表面層。 在熱力學(xué)平衡的條件下，固體表面的化學(xué)組成、微觀結(jié)構(gòu)、原子振動狀態(tài)等均會與固體內(nèi)部產(chǎn)生一定的差異。,概論 表

2、面及表面科學(xué),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.,概論 表面分析技術(shù),表面分析技術(shù)是人們?yōu)榱双@取表面的物理、化學(xué)等方面的信息而采用的一些實(shí)驗(yàn)方法和手段。,概論 表面分析技術(shù),一般

3、地說，它是利用一種探測束如電子束、 離子束、光子束、中性粒子束等，有時(shí)還加上電場、磁場、熱等的作用，來探測材料的形貌、化學(xué)組成、原子結(jié)構(gòu)、原子狀態(tài)、電子狀態(tài)等方面的信息。,概論 表面分析技術(shù),概論 表面分析技術(shù),概論 表面分析技術(shù),概論 表面分析技術(shù),概論 表面分析技術(shù),部分表面分析設(shè)備的分析范圍,概論 表面分析技術(shù),概論 真空技術(shù)原理,為了使被研究的樣品不被周圍氣氛所污染，獲取“原子清潔”的表面，表面分析過程往往是在真空或超高真空中進(jìn)行的。目前，人們所廣泛使用的很多表面分析設(shè)備都具有真空系統(tǒng)。 薄膜制備設(shè)備往往涉及真空系統(tǒng)。,概論 真空技術(shù)原理,真空單位 Atmospheres (atm):

4、 Scale relative to our atmospheric pressure as 1 atm Pascal (Pa): SI unit equal to N/m2 mBar: Equal to 1x10-8 Pa. Torr or mmHg: Most commonly used pressure unit, based on mercury vacuum gauges.,概論 真空技術(shù)原理,真空的劃分,Atmospheric: 760 Torr Low Vacuum: 1 to 1x10-3 Torr Medium Vacuum: 1x10-3 to 1x10-5 Torr Hi

5、gh Vacuum (HV): 1x10-6 to 1x10-8 Torr Ultra-High Vacuum (UHV): 1x10-9 Torr,概論 真空技術(shù)原理,真空的意義,Monolayer Coverage Time For an ideal gas, the time needed for monolayer coverage is given by: tML 1019/ ZA where ZA is impingement rate.,概論 真空技術(shù)原理,真空的意義,Impingement Rate (Flux) For an ideal gas, the impingemen

6、t rate is given by: ZA = v / 4 where, - the number density of gas molecules v - the mean velocity,概論 真空技術(shù)原理,概論 真空技術(shù)原理,真空的獲得,Ultimate Pressure Low Vacuum (Rough) Pumps Rotary Vane Pumps Sorption Pumps High Vacuum Pumps Diffusion Pumps Turbo Molecular Pumps Ultra-High Vacuum Turbo Molecular Pumps Ion

7、Pumps Titanium Sublimation Pumps,Oil / Oil-Free Oil Rotary Vane Pumps Diffusion Pumps Turbo Molecular Pumps Oil-Free Turbo Molecular Pumps Ion Pumps Titanium Sublimation Pumps,概論 真空技術(shù)原理,真空的獲得,Gas enters the inlet port and is trapped between the rotor vanes and the pump body. The eccentrically mounte

8、d rotor 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 torr Robust, inexpensive Oil lubricated,概論 真空技術(shù)原理,真空的獲得,Liquid nitrogen cooled molecular sieve with large surface area A

9、tm to 10-3 Torr (two units working alternately) Quickly becomes saturated Must be baked at 200 C to remove adsorbed gases Simple, inexpensive, oil-free,概論 真空技術(shù)原理,真空的獲得,Momentum transfer to gas molecules through collision with directed jet of oil molecules Require cooling water, backing pump 10-3 to

10、10-7 Torr (to 10-9 Torr with LN2 cooling),Advantages Robust High pumping speed for relatively low cost. No vibration or noise. Disadvantages Oil as a pumping medium, high risk of back-streaming oil, cold traps required Potential for serious vacuum problems,概論 真空技術(shù)原理,真空的獲得,Molecules mechanically pump

11、ed by collision with angled high speed turbine 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 Torr Oil/grease/electromagnetic bearings Most common HV/UHV pum

12、p.,概論 真空技術(shù)原理,真空的獲得,Advantages Correctly operated 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.,概論 真空技術(shù)原理,真空的獲得,High voltage between anod

13、e and cathode (5 kV) Electrons are captured in anode 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 at

14、oms act as getter for reactive gases. 10-4 Torr to 10-11 Torr,概論 真空技術(shù)原理,真空的獲得,Advantages Clean, oil-free. No moving parts, no vibrations, quiet. Low power consumption and relatively long operating lives Disadvantage Do not pump noble gases well. Requires “regeneration” of Ti every 4-6 years.,概論 真空技術(shù)

15、原理,真空的獲得,Heated Ti filament evaporates Ti film onto cooled surface. Ti getters reactive gases by reaction. Operate at 10-8-10-11 Torr Inexpensive, reliable Periodic operation - not primary pumping mechanism,概論 真空技術(shù)原理,真空的獲得,Materials Considerations,Outgassing rates Producing “virtual” leaks Mechanica

16、l stability Temperature stability,Conductivity Chemical inertness Weldability,概論 真空技術(shù)原理,真空的獲得,Oxygen free high-purity copper (OFHC) Be-Cu alloy Tantalum, Molybdenum, Tungsten Teflon (gassy) MACOR (machinable glass composite) Alumina Quartz, pyrex (gassy) mu-metal magnetic shielding (Co, Ni, Fe) Moly

17、bdenum disulfide (lubricant),Compatible Materials,概論 真空技術(shù)原理,Materials to be Avoided (high vapor pressures) Zn, Cd: especially be careful of fasteners, bolts Brass Certain solders Any type of grease or oils,真空的獲得,Common Vacuum Problems Improper cleaning or handling techniques Using incompatible mater

18、ials Leaks Virtual leaks,概論 真空技術(shù)原理,真空的獲得,概論 真空技術(shù)原理,真空的獲得,概論 真空技術(shù)原理,真空的獲得,Pump Down Typically follows a well-defined sequence according to the types of pumps on the vacuum system For UHV systems, typically requires a few hours to reach a medium vacuum after a vent to air,Bake Out Heat the chamber to

19、temperatures between 100oC and 200oC for 1 - 2 days. Rapidly remove adsorbed gases from the chamber walls at high temperatures in order to lower the outgassing rates at room temperature. Generally it takes another day to cool and recover base pressure.,概論 真空技術(shù)原理,真空的測量,Heat filament with a constant c

20、urrent. Measure filament temperature with thermocouple. Gas molecules collide with and cool the filament. Voltage increases to keep filament at constant current. Atm to 10-4 Torr Fast, simple, inexpensive.,Thermocouple Gauge,概論 真空技術(shù)原理,真空的測量,Two identical heated filaments; one sealed at HV, one expos

21、ed to system. Current flows through Wheatstone bridge circuit. Pressure difference indicated by meter (non-linear). Atm to 10-4 torr. Simple, reliable, inexpensive.,Pirani Gauge,概論 真空技術(shù)原理,真空的測量,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 coll