10 March Conductance/Microscopes/MFC s. Flow Characteristics can be reduced to a function of pipe diameter and pressure. Las Positas College

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Benjamin Barnard Greer
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1 10 March 2003!More Isolation Applications!Conductance in!mitered Elbows!Radiused Elbows!MFC s and Gas Sources!Vacuum Microscopes Flow Characteristics can be reduced to a function of pipe diameter and pressure Viscous flow PD > 0.18 Torr-inches Transition flow Molecular flow PD <.004 Torr-inches 1

Conductance of a straight tube of circular crosssection (again, Air at Room Temperature) C = 4 3000 PD + 80D L 3 Diameter, D [inches] Pressure, P [Torr]

2 Conductance of a straight tube of circular crosssection (again, Air at Room Temperature) C = PD + 80D L 3 Diameter, D [inches] Pressure, P [Torr] Length, L [inches] EMPLOY PROPER UNITS!! DCS Exhaust,! Valve gunks up after 2 months.! Difficult to Service! Protected Ring Gate valve with purge. Vacuum Systems 2

3 Solution: Protected Ring Gate valve Vacuum Systems! 1500 mm Gate valve with integral bakeout covers.! For UHV Service at a Japanese Research Facility 3

4 Vacuum Systems! 1x10-9 T! High Radiation! All metal seals everywhere! Bake to only 150 C because of aluminum Vacuum systems Brazed 5 kw water cooled Photon Stop that technician forgot to hook up to cooling water. Air Guard saved the day. 4

5 Vacuum Systems! Butterfly for Stanford Gravity Probe B! Operate reliably at - 60C in orbit.! Buna N o- ring. Radiused Tubing is preferred in Forelines 5

6 Is it Molecular Flow?! Very Important Consideration! Knudsen Number: Mean Free Path to Feature length! A Dimensionless Parameter! Torr-Inches are functionally dimensionless!! Use Equations to decide Example: DN80 (3 ) tubing! What is the pressure in a 3 ID pipe when the mean free path is the same as the diameter?! Eq. 7 P=5x10-3 /(2.54*3)= 6.5x10-4 Torr! What is the type of flow at this pressure! Eq 14 D*P= 6.5x10-4 (2.54*3)= [Transition, but just barely] 6

7 Flow Regimes in 3 Tubing! Eq. 15! P = 0.004/(3*2.54) = 5.3x10-4 Torr! Eq 14! P = 0.18/(3*2.54) = 2.3x10-2 Torr! Transiton flow exists between these pressure regimes Comparing Eq 19 and 21 at 5.3x10-4 Torr! Assume L= 1! Eq. 21 (Molecular Flow)! C m =80D 3 /L = 2160 l/s! Eq. 19 (Viscous Flow)! C m =3000PD 4 /L = 2.0*D 4 = 128 l/s! Eq. 20 (Transition Flow)! C m = = 2322 l/s (+6%) 7

8 Comparing Eq 19 and 21 at 2.3x10-2 Torr! Again Assume L= 1! Eq. 21 (Molecular Flow)! C m =80D 3 /L = 2160 l/s (unchanged)! Eq. 19 (Viscous Flow)! C m =3000PD 4 /L = 2.0*D 4 = 5589 l/s! Eq. 20 (Transition Flow)! C m = = 7749 l/s Summary! Between 5.3x10-4 and 2.3x10-2 Torr, the conductance of a 1 section of 3 piping rises From 2300 to 7700 l/s! a factor of 3.3x 8

What is the difference between throughput and conductance (speed)?! Q=SP where P is the pressure! During steady state, throughput is constant in a system!

9 What is the difference between throughput and conductance (speed)?! Q=SP where P is the pressure! During steady state, throughput is constant in a system! Contuctance of components (and pumps) can change with pressure! Knowing the difference between throughput and speed is very important to vacuum technologists Pump Speed (S) 9

10 Pump Throughput (Q) Conductance of a 90 degree Mitered Elbow Use Equation 21 with an increase in L of L + =1.5D 10

11 90 Degree Mitered Elbow Example! 4 ID TMP Elbow with 5 inch A dimension (face-to-tube centerline)! L=10, L + =6, L total = 16! 80D 3 /L= 80*64/16= 320 l/s! Avoid mitered and radiused elbows in molecular flow systems if possible Viscous Conductance in Mitered Elbows of Arbitrary bend d L eff θ L/ D = 15= D L = 15 D= 15 2" = 30" + Angle (degrees) L/D Example: For tube diameter of 2", and bend angle of 45 degrees, then the effective length increment is

Viscous Conductance in 90 radiused tubes 6 r/ D = = 3 2 L = 3D= 6" + r d r/d L/D 1 20 1.

12 Viscous Conductance in 90 radiused tubes 6 r/ D = = 3 2 L = 3D= 6" + r d r/d L/D Example: For tube diameter of 2", at a bend radius of 6 the effective length increment is 6. Commercial Tubing for Foreline (Courtesy A&N) Example: 1.5 OD, 1.25 ID, r=a=2.25, r/d=1.8, L/D=13. For Mitered equivalent, L/D=60. 12

Mass Flow Controllers! An upstream control valve.! Used to bring source process gases into a vacuum System.! Extensively employed in Semiconductor Processing.

13 Mass Flow Controllers! An upstream control valve.! Used to bring source process gases into a vacuum System.! Extensively employed in Semiconductor Processing.! Interfaces to a host include Serial, DeviceNet.! Calibrated to a specific gas, uses specific heat of gas to discern flowrate Mass Flow Controllers! Electrical Input:! Setpoint (target flow in sccm)! Electrical Output:! Actual Flow (updated at ~500 ms)! Plumbing: 13

14 The Gas cabinet of a process tool may employ up to 8 of these, one for each gas Requirements MFCs must! Have very low particle shedding (upstream valve)! Be very reliable! Be typically enclosed in a special gas cabinet with exceptional personnel safety controls. 14

15 Vacuum Microscopes for Materials Studies Scattering experiments are the basis of our understanding of the basic structure of Matter. We use probes (beams of photons, electrons, neutrons and ions) to measure the scattering characteristics of materials, and deduce information about atomic structure, crystal structure and bonding. How does surface analysis work Detectors Probe beam material under analysis 15

16 Applications of Materials Research Properties of Solid State Physics Semiconductor Physics Disk Drive Technology Adhesion, Friction, Wear resistance Strength of Materials Environmental Remediation Nuclear Weapons Management Homeland Security Vacuum Technology in Materials Research Long mean-free-path for probe and emergent Ion beams Contamination Reduction Reduction of scattered Photons 16

17 Electrons: one of a family of useful particles Very small, negatively charged particles. The energy of electrons is typically expressed in electron-volts (the kinetic energy impated to an electron, initially at rest by a potential of 1 volt) 1 ev = joules 1keV = 1000 ev, 1MeV = 1000 kev Einstens Gift : E=Mc 2 Particle electron proton neutron alpha Symbol e or e- p n α or 4 He ++ Mass Energy (MeV)

18 Energy, Frequency and Wavelength c = λν c = speed of light ( m / s) λ = wavelength (meters) ν = frequency (Hertz) E = hν = hc λ E = energy (ev) h = Planc' s constant ( ev ) Another Relationship between Wavelength and Energy E = 12.4 kev λ Å Å = m 18

19 Consider Waves on the Ocean amplitude wavelength Frequency 19

20 Amplitude Waves in Phase Add Algebraically A A 2A 20

21 Waves out of Phase Cancel A A Zero amplitude Why do Stars twinkle? Inelastic Scattering Atomic Resonance Photons Wavelength and Frequency Electromagnetic Spectrum Matter LBL X-Ray Data Book 21

! Visible Light wavelength 0.7-0.4 Microns or ~5 ev! 192 Beam paths of 16 x16 tubing!

22 Photon Scattering! Photons of certain energies scatter when they strike certain types of gas molecules.! Visible Light wavelength Microns or ~5 ev! 192 Beam paths of 16 x16 tubing! $5 worth of PG&E focused for picoseconds on a small hydrogen target. Vacuum Systems! Scattering at Hanford LIGO 5x10-10 Torr The chamber is the heater bakeout element at 10,000 Amps! 22

23 Photons act like particle and waves Fluorescence Outer shell electrons change state and emit photons Energy is conserved 23

24 Electron Binding Energies Fluorescence and the photoelectric Effect 24

25 Available free at this website Contents: Electron Binding Energies X-Ray Energy Emission Energies Fluorescence Yields for K and L Shells Principal Auger Electron Energies Subshell Photoionization Cross-Sections Mass Absorption Coefficients Atomic Scattering Factors Energy Levels of Few Electron Ions Periodic Table of X-Ray Properties When the Emergence and Probe beams are the same " Auger Electron Spectroscopy (AES) " electron in / electron out " Rutherford Backscattering (RBS) " Ions in / ions out: " fluorescence spectroscopy (XRF) " Photons (X-rays) in / Photons out 25

26 When the Emergent and Probe Beams are not the same! Electron Microprobe Analysis (EMA)! electron in / x-ray out! Secondary Ion Mass Spectrometry (SIMS)! Probe Ion in / target ion out! photoelectron spectroscopy (XPS)! X-rays in / electrons out: X-ray Rutherfords first scattering experiment Rutherford scattering is a classical example of this type of analysis. In this technique, alpha particles (He ++ ) are used as the probe. Scattering of these particles by the nucleus of the atoms in the material under study provides information from which the nature and size of atoms are deduced. 26

What s going on electrons nucleus (protons & neutrons) + positive alpha particles + + In 1908 Rutherford was awarded the Nobel Prize - for chemistry Radium decays to release energetic protons

27 What s going on electrons nucleus (protons & neutrons) + positive alpha particles + + In 1908 Rutherford was awarded the Nobel Prize - for chemistry Radium decays to release energetic protons (alpha particles. The detector was a phosphorus screen. Some protons backscattered nearly 180 degrees when aimed at gold foil 400 atoms thick. The size of the nucleus was accurately estimated. 27

28 Rutherford Scattering Analysis chamber probe beam: source detector emerging radiation: electrons photons ions sample electrons photons ions Vacuum system What can we learn!we can deduce a significant amount of useful information from the emerging beam:!intensity - tells the amount of scattering and therfore the number of atoms, density.!energy- tells us the identity (composition) of the material.!beam trajectory - provides the material structure 28

29 Density, Composition, and Structure probe beam ø intensity (density) energy (composition) geometry(structure) Energy Loss During Scattering! Incident probe particles either scatter elastically (no energy loss) or cause an electronic transition in a target of the sample. The amount of energy lost by the probe particle is characteristic of the electronic structure of the sample.! Generally, an energy-dispersive detector is used to measure the energy of the emerging beam; this energy is typically expressed in electron-volts (EV). 29

30 X-Ray Diffraction λ = 2d sin(θ ) θ provides structural information: arrangement of atoms Secondary Ion Mass Spectroscopy probe ions mass spectrometer sample detector 30

31 Electron Microprobe Analysis Interaction volume probe beam emerging radiation K Beta Radiation Signature nucleus K β K L M 31

32 K Alpha Radiation Signature nucleus K α K L M Elemental Analysis using elemental energy dispersion signatures Cu k α Ni k α Intensity Cu k β Ni k β Energy, kev 32

33 For Further Reading! QED, the strange theory of light and matter, by Richard Feynman! No equations! comprehensive.! The classic oral PhD thesis question: Why is the Sky Blue? 33

Particles and Waves Final Revision Exam Questions Part 1

Particles and Waves Final Revision Exam Questions Part 1 Cover image: cutaway diagram of CERN, CERN Version 2013 P&W: Exam Questions Part 1 Version 2013 Contents Section 1: The Standard Model 1 Section