Ⅰ. Vacuum Technology. 1. Introduction Vacuum empty in Greek Torricelli Vacuum 2 ) 760 mm. mbar 2 ) Enclosure. To pump. Thin Film Technology

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1 Ⅰ. Vacuum Technology. Introduction Vacuum empty in Greek 643 Torricelli Vacuum 76 mm Hg Enclosure F ma 76mmHg 76Torr atm (76cm) (3.6g / cm 3 ) (98.665cm/sec ).33 6 dynes/ cm.33bar.33 5 ascal( N / m ).4696 psi Torr 33.3 a. 333 To pump mbar

2 Atmosphere; composition 78.8 V % N.95 V % O.93 V % Ar.3 V % CO relative humidity 5% at 8.75 Torr of H O ressure 76 Torr Sea level -3 Torr 9 km ~ -, km ~ -3, km( 인공위성 ) ~ -6 milky way 참고 respiration 74 Torr Suction 3 Torr Octopus Torr

3 Vacuum range Low 5 < < - Torr Medium -3 < < 5 Torr Rotary pump High -6 < < -3 Torr Very high -9 < < -6 Torr CVD, RIE Ultrahigh - < < -9 Torr MBE, Surface analysis Extreme Utrahigh < - Torr 3

4 Vacuum Technology 참고문헌. A User s Guide to Vacuum Technology John F. O hanlon, nd Ed. John Wiley & Sons. Inc, Vacuum Technology Andrew Guthrie, Robert E. Krieger ublishing Company., Vacuum hysics and Technology in Methods of Experimental hysics, Eds. G.L. Weissler and R.W Carlson Academic ress,

5 Ⅱ. Gas roperties Gas Laws Boyle s law 66 V V ( N, T constant ) Charle s law 787 V T V T ( N, constant ) Law of Gay Lussac 8 Amonton s law V V ( + β t ) ( + β t ) T T ( N, V constant) 5

6 Dalton s law 8 nrt ( V constant ) n RT + + n + RT 3 + LL + + LL + i n RT i ( Ideal Gas law ) Avogadro s law 8 N, N N Graham s law : eg. 고무풍선, ( He/air ) 3 ( T, Vconstant ) 6.5 effusion effusion rate rate ( a) ( b) M M b a (, T constant ) 6

7 Distribution of Molecular Velocities -. N molecules at equilibrium at T -. magnitude C of the velocity vector c µ + υ + -. The fraction of molecules having simultaneously a velocity component between µ and µ + dµ, υ and υ + dυ, ω and ω + dω is 3 / ω ( µ + υ ω ) dn m m + 4π exp C N πkt kt dc -. fraction of molecules with a speed between c and c + dc 7

8 Velocity Distribution The distribution of particle velocities by Maxwell & Boltzmann f dn dν m 3 / N ν m / k T ( ν ) ν e π kt The most probable velocity ν p kt m / The average velocity ν 8k T πm /.8ν p The root mean square velocity rms 3k T m / ν. 5ν p 8

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10 Energy distribution dn N E E / kt de The most probable energy The average energy π ( k T ) E 3 / kt 3 E ave e k T

11 Mean free path λ π d n n : d gas density : molecular diameter For air at room temperature λ ( mm ) 6.6 : pascal Torr : 3 pascal mtorr :.3 λ m Torr article flux : particles per unit area and per unit time Γ nν 4 n k T π m /

12 Monolayer formation time t ml 4 : sticking coefficient Γ d m ν d A monolayer of air at room temperature ( d.37 nm, ν 467 m / s ) t ml.5 sec at 4 a

13 Viscosity Elementary gas transport phenomena The coefficient of absolute viscosity η is determined by momentum transfer Shear pressure F A x xz η du dy - Viscous force appears to be frictional: actually it is not - During molecular collision, molecue loses momentum by molecule 3

14 From kinetic theory η n mν λ 3 A more rigorous treatment n: gas density m: molecular mass ν : velocity λ : mean free path η.499 n mν λ.499 ( 4mk T ) π 3 / d / η ( m T ) d / Independent of n and 4

15 Thermal Conductivity H A K dt dy Application to pressure gauges: Thermo couple & irani gauges operates in the region in which the heat conduction to the wall is linearly dependent on pressure. heat flow heat conductivity is determined by energy transfer When the mean free path is smaller than the dimension of the chamber, K K 5 4 ( 9γ ) η Cν K mt d η C ν For simple kinetic theory: Considering vibrational and rotational energy of molecule: As does the viscosity,, γ C / C ν independent of pressure 5

16 Diffusion Flux the coefficient of diffusion: D dn Γ D, Γ D dx dn dx For self diffusion D 4 3 π n d / 3 kt π m T n n V kt 6

17 At low pressure (n, D ) This does not happen in real system due to the limited size of tube scattering At low pressure, Knudsen diffusion coefficient for a long capillary is D γυ 3 γ: radius of pipe υ: thermal velocity Diffusion front: Z o.3(dt) / 7

Chapter 10 Gases Characteristics of Gases Elements that exist as gases: Noble gases, O 2, N 2,H 2, F 2 and Cl 2. (For compounds see table 10.

Chapter 10 Gases Characteristics of Gases Elements that exist as gases: Noble gases, O 2, N 2,H 2, F 2 and Cl 2. (For compounds see table 10. Chapter 10 Gases 10.1 Characteristics of Gases Elements that exist as gases: Noble gases, O 2, N 2,H 2, F 2 and Cl 2. (For compounds see table 10.1) Unlike liquids and solids, gases expand to fill their