iii sem class 1

8/8/2019 III Sem Class 1

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S.M. ShivaprasadICMS/CPMU, JNCASR


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In this talk:

Beauty is skin deep!X-ray Photoelectron SpectroscopyScanning Tunneling MicroscopySome of our work using these


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Dangling bonds

(2x1)

(1x1)


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atalysis and Chemical Reactions : Petroleum and Chemicals

orrosion and segregation: Oil, gas pipe lines, Buildings, vehicles, strucu

emiconductor Interfaces: Microelectronics and future devices

hermionic Emission: Desplay devices, TV tubes, PDP, LCD

aints and Coatings: Optical, wear & protection, electrical, magnetic

rittle Fracture: Turbo machines, bridges, machines

anostructures:All applications, smart drugs, genetic engg.,

rystal Growth: Semiconductors, Optical, Magnetic

ontaminants: Medicine, Food, semiconductors

terfaces: Solar cells, night vision, tooth and bone implants


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Surface Science and Nano-science

Semiconductor nanoparticles Self assembly by heteroepitaxy

Surface atoms - Reduced Co-ordination

Nanophase - Most are surface atoms !


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Density of states: Where electrons can stay !

3D 2D-sheet 1D- wire 0D-dot


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Band Gap

Valence Band

Conduction Band

Atom Molecule Solid

Size Band Gap

CdSe nanoparticles1- 10 nm size


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Confinement:Particle in a box

Discrete energy levelsQuantization

n=4

n=3

n=2

n=1

Surface to Volume Ratio

0

10

20

30

40

50

60

0 20 40 60 80 100 120

No of a toms/cluster

%o

fsurfaceatoms

Nano-phase atoms - All surface atoms !

Dangling bonds

Surface to volume ratio


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Study surfaces:

Need for Ultra high vacuum

Surface sensitive probes

Deg. of Vacuum (Pressure) Mean Free Path Time / ML(Torr) (m) (s)

Atmospheric 760 7 x 10-8 10-9

Low 1 5 x 10-5 10-6

Medium 10-3 5 x 10-2 10-3

High 10-6 50 1

UltraHigh 10-10 5 x 105 104


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Electrons as probes: Small size, charge and large scattering


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Base Pressure: 3x10-11 Torr11

XPS (Perkin Elmer: 1257) AES (Varian VT 112)

Techniques:1. Auger Electron Spectroscopy2. Low Energy Electron Diffraction3. X-ray Photoelectron Spectroscopy

4. Energy Loss Spectroscopy


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XPS, AES, UPS, EXAFS, LEED, LEEM, SHG, SIMS, PES, ELS,HREELS, ISS, LEIS, MEIS, SEXAFS, STM, AFM, MFM...


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Aspects of Heteroepitaxial Growth: Lattice Mismatch Ni/Ru(001) Surface Free Energy Pt/W(111) Dangling bond M/Si(111), (100)

Nanostructures: Controlled sizes, assembly

Hetero:

Epi:Taxy:

Different

Upon

Ordered

Aspects of Heteroepitaxial Growth


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Step Special Diffu. Binding Inter-diffu

Thermodynamicsvs.

Kinetics

1/ a = exp(-Ea/kT)Arrival

Re-evap.

Stranski-Krastanov(layers + island)

Wolmer Weber(island)

Frank van der Merwe(layer)

Growth Modes:

Heteroepitaxial Growth (Interface Formation):


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Is/Iso = (1-x) exp(-nl/ ) + x exp[-(n+1)l/ ] 0 x 1


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Dangling bonds

SurfacesIdeally terminated Si surface


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A new approach to the formation of compatiblesubstrates for GaN growth


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Advantages of Solid State Lightingtechnology

Highly efficient light sources Substantial reduction in electrical energy

consumption Substantial improvements in human visual

experience (True white light)

Cheaper and long lasting, no sudden break-downs Creation of III-V semiconductor technologies


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Solid State Lighting : Prospects and progress

E f fic ien cy o f W h i te

-2 0

0

2 0

4 0

6 0

8 0

1 0 0

1 2 0

1 9 8 5 1 9 9 0 1 9 9 5 2 0 0 0 2 0 0 5 2 0 1 0 2 0 1 5

Y ea

Lumensperwatt

Uses of LED:1. Mobile 40%2. Signs 23%3. Automotive 18%4. Others (biological) 12%5. Illumination 5%6. Signals 2%


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InGaN based Photovoltaics:Efficiency of > 70% - Achievable 50%


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Involves deposition of multi-layers:

Standard LED design


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Saphire (Al2O3) and GaNLattice Parameter Mismatch (13%)Thermal Expansion Mismatch (33%)

GaN on SiC and GaAs


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GaN buffer layers

Cree Demonstrates 131 Lumens per Watt White

LEDDURHAM, NC, JUNE 20, 2007 Cree, Inc. (Nasdaq:CREE), a market leader in LED solid-state lighting components, todayannounced LED efficacy test results that set a new benchmark for the LEDindustry. Cree reported results of 131 lumens per watt white LED efficacy,confirmed by the National Institute of Standards and Technology inGaithersburg, Maryland. Tests were performed using prototype white LEDswith Cree EZBright LED chips operating at 20 mA and a correlated colortemperature of 6027 K.

This is the highest level of efficacy that has been publicly reported for a whiteLED and raises the bar for the LED industry, said Scott Schwab, Cree generalmanager, LED chips. This result once again demonstrates Crees leadership inLED technology and provides a glimpse into the future as to why we believeLED-based lighting products could not only save energy, but also change theway people use light.

Technical advancements at the component level are critical to growing theemerging white LED lighting space. Crees results speak to the excitingdevelopments underway that will enable new white light applications and

subsequently facilitate market adoption, stated Fritz Morgan, chief technologyofficer for Color Kinetics, a leading innovator of LED lighting systems andtechnologies.

Lumens-per-watt is the standard used by the lighting industry to measure theconversion of electrical energy to light. As a reference, conventionalincandescent light bulbs are typically in the 10 to 20 lumens per watt range,while compact fluorescent lamps range from 50 to 60 lumens per watt.

High Defect Density > 1010 /cm3
http://en.wikipedia.org/wiki/Image:RBG-LED.jpghttp://en.wikipedia.org/wiki/Image:RBG-LED.jpg


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Outstanding limits:

Green emission (Indium incorporation) Si wafer technology adaptation (SiC epitaxial layer)

Defect density- types of defects (70 arc.sec assymetric XRD) Band dispersion and surface/interface modifications

Substrate Thermal Conductivity


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1. Problems in p-type doping (Si doping lattice expansion)

2. H-ions from ammonia detrimental

3. Substrate compatibility (lattice mismatch): Sapphire, SiC, AlN, Si

6. Substrate Thermal Conductivity:

4. Defect density (lateral epitaxial growth): Reduction of Schowbel barrier

5. Dislocation density: Effects on Quantum Efficiency and Life time

6. Layer Thickness Control : Layer uniformity

7. Thin metal contacts: Al, Ti and Au alloys: Schottky contacts

8. Interface sharpness and integrity: avoiding interfacial phases

Outstanding Issues in Growth of LED:30 lum/watt to 500 lum/watt (Theor. 763 lum/watt)


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Study surfaces:

Need for Ultra high vacuum

Surface sensitive probes

Deg. of Vacuum (Pressure) Mean Free Path Time / ML(Torr) (m) (s)

Atmospheric 760 7 x 10-8 10-9

Low 1 5 x 10-5 10-6

Medium 10-3 5 x 10-2 10-3

High 10-6 50 1

UltraHigh 10-10 5 x 105 104

NEED FOR ULTRA HIGH VACUUM


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NEED FOR ULTRA-HIGH VACUUM

From Kinetic Theory of Gases:

Molecular Flux:

Z = Nc/4V Hertz-Knudsen equation

N/V =Mol per unit vol, c is av. Speed of molecules

For a gas of Mol Wt M at temp T

c = (8RT / m) R=gas const.,

Since PV= nRT and N=nNA,

Z=nNAP (8RT /

m) or Z=NAP / (2

MRT)

For Pressure in Pa (Nm-2) and M (g mol-1)

Z= 2.635 x 1024

P / (MT) collisions m-2

s-1


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Calculating of effective pumping speedP1: pressure at the inlet of the pipe

S1: pumping speed at the inlet ofpipeC: conductance of the pipesP2: pressure at the inlet of the pump

S2: pumping speed at the inlet ofthe pumpContinuum of gas throughputQ = P1S1 = P2S2Q = C(P1-P2) C: conductance of the

pipeP2 = P1C/(S2 +C)S1 = S2 C/(S2 +C)If C >> S2 S1=S2If C = S2 S1=1/2S2


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Pumping Equation


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Obtaining UHV

Roughing UHV

Sorption Sputter IonTurbo_Rotary DiffusionDiaphragm Cryopump

Titanium Sublimation


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VACUUM PUMPING METHODS

Sliding VaneRotary Pump

MolecularDrag Pump

Turbomolecular

Pump

Fluid EntrainmentPump

VACUUM PUMPS(METHODS)

ReciprocatingDisplacement Pump

Gas TransferVacuum Pump

DragPump

EntrapmentVacuum Pump

Positive DisplacementVacuum Pump

KineticVacuum Pump

RotaryPump

DiaphragmPump

PistonPump

Liquid RingPump

RotaryPiston Pump

RotaryPlunger Pump

RootsPump

Multiple VaneRotary Pump

DryPump

AdsorptionPump

Cryopump

GetterPump

Getter IonPump

Sputter IonPump

EvaporationIon Pump

Bulk GetterPump

Cold TrapIon TransferPump

GaseousRing Pump

TurbinePump

Axial FlowPump

Radial FlowPump

EjectorPump

Liquid JetPump

Gas JetPump

Vapor JetPump

DiffusionPump

DiffusionEjector Pump

Self PurifyingDiffusion Pump

FractionatingDiffusion Pump

Condenser

SublimationPump


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Rotary Vane, Oil-Sealed Mechanical Pump

Pump Mechanism How the Pump Works
http://images.google.com/imgres?imgurl=http://www.poly-run.com/img/Single-Stage-Rotary-Vacuum-Pump-TW-2D-big.jpg&imgrefurl=http://www.poly-run.com/products/product-single-stage-rotary-vacuum-pump-tw-2d.html&h=360&w=360&sz=36&hl=en&start=1&um=1&tbnid=t6aU06XxJdeiUM:&tbnh=121&tbnw=121&prev=/images%3Fq%3Drotary%2Bvacuum%2Bpumps%26um%3D1%26hl%3Den%26rls%3Dcom.microsoft:*:IE-SearchBox%26rlz%3D1I7ADBF


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S i P


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Sorption Pump

VapourPressure
http://images.google.com/imgres?imgurl=http://www.mdc-vacuum.com/graphics/img3212.jpg&imgrefurl=http://www.mdc-vacuum.com/searchs/doc/VacuumPumps-Intro.htm&h=210&w=200&sz=15&hl=en&start=4&um=1&tbnid=10fw8xDzCgM8RM:&tbnh=106&tbnw=101&prev=/images%3Fq%3Dsorption%2Bvacuum%2Bpumps%26um%3D1%26hl%3Den%26rls%3Dcom.microsoft:*:IE-SearchBox%26rlz%3D1I7ADBF


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Oil Diffusion Pump


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LN2 reservoir with baffles

Gas Approximate VaporPressure (mbar)

Water (H2O)Argon (A)Carbon Dioxide (CO2)Carbon Monoxide (CO)Helium (He)Hydrogen (H2)

Oxygen (O2)Neon (Ne)Nitrogen (N2)Solvents

10-22

500

10 -7>760>760>760

350>760760


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DP Pumping Speed

10-10 10--3 10--1

Pu

mpingSp

eed( A

ir)

1 2 3 4

Inlet Pressure (Torr)

Critical Point

1. Compression Ratio Limit2. Constant Speed

3. Constant Q (Overload)

4. Mechanical Pump Effect


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Turbomolecular PumpROTOR BODY

HIGH PUMPING SPEED

HIGH COMPRESSION

EXHAUST

HIGH FREQ. MOTOR

INLET FLANGE

STATOR BLADES

BEARING

BEARING

Rotor - stator assembly


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Sputter Ion Pumps:
http://images.google.com/imgres?imgurl=http://www.canon-anelvatx.co.jp/english/products/pump/ionp.jpg&imgrefurl=http://www.canon-anelvatx.co.jp/english/products/pump/ionp.html&h=326&w=250&sz=8&hl=en&start=11&um=1&tbnid=H6DxGyAIedu2aM:&tbnh=118&tbnw=90&prev=/images%3Fq%3Dsorption%2Bvacuum%2Bpumps%26um%3D1%26hl%3Den%26rls%3Dcom.microsoft:*:IE-SearchBox%26rlz%3D1I7ADBF


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Cryo Pumps:
http://images.google.com/imgres?imgurl=http://www.oxford-instruments.com/wps/wcm/resources/image/468cacb04ed3207f/cryogenic-refrigerators.jpg&imgrefurl=http://www.oxford-instruments.com/wps/wcm/connect/Oxford%2BInstruments/Groups/Product%2BGroups/Cryogenic%2BRefrigerators/Cryogenic%2BVacuum%2BPumps&h=159&w=177&sz=8&hl=en&start=6&um=1&tbnid=p8rWTY7GyhE0UM:&tbnh=91&tbnw=101&prev=/images%3Fq%3Dcryo%2Bvacuum%2Bpumps%26um%3D1%26hl%3Den%26rls%3Dcom.microsoft:*:IE-SearchBox%26rlz%3D1I7ADBFhttp://images.google.com/imgres?imgurl=http://www.barber-nichols.com/images/vacuum_housing_pump2.jpg&imgrefurl=http://www.barber-nichols.com/products/cryogenic_products/vacuum_housing_cryogenic_pumps/default.asp&h=270&w=411&sz=47&hl=en&start=16&um=1&tbnid=bnpdvRVbdmFR_M:&tbnh=82&tbnw=125&prev=/images%3Fq%3Dcryo%2Bvacuum%2Bpumps%26um%3D1%26hl%3Den%26rls%3Dcom.microsoft:*:IE-SearchBox%26rlz%3D1I7ADBF


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Measuring UHV:

PenningIon Gauge

Bayer-Alpert Gauge (Nude)Spinning Rotor Gauge

Gauges


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GaugesGauge Operating Ranges

10-12 10-10 10-8 10-6 10-4 10-2 1 10+2

P (mbar)

Rough VacuumHigh VacuumUltra HighVacuumBourdon Gauge

Thermocouple Gauge

Cold Cathode Gauge

Capacitance Manometer

Hot Fil. Ion Gauge

Residual Gas Analyzer

Pirani Gauge

Spinning Rotor Gauge

McLeod Gauge

Th l G


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How the gauge works

Thermocouple Gauge

I i ti


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Ionization gauges
http://images.google.com/imgres?imgurl=http://www.volotek.com/assets/images/Gauge.jpg&imgrefurl=http://www.volotek.com/body_index.html&h=1200&w=1200&sz=245&hl=en&start=13&um=1&tbnid=_YI2KnOLN26OTM:&tbnh=150&tbnw=150&prev=/images%3Fq%3Dion%2Bvacuum%2Bgauge%26um%3D1%26hl%3Den%26rls%3Dcom.microsoft:*:IE-SearchBox%26rlz%3D1I7ADBF


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P bl th t t b L k
http://images.google.com/imgres?imgurl=http://www.lesker.com/newweb/Gauges/jpg/Dwg_Ion.jpg&imgrefurl=http://www.lesker.com/newweb/Gauges/gauges_technicalnotes_1.cfm&h=200&w=193&sz=9&hl=en&start=19&um=1&tbnid=XqSK1iuyjElyiM:&tbnh=104&tbnw=100&prev=/images%3Fq%3Dion%2Bvacuum%2Bgauge%2Bprinciple%26um%3D1%26hl%3Den%26rls%3Dcom.microsoft:*:IE-SearchBox%26rlz%3D1I7ADBFhttp://www.freepatentsonline.com/6515482-0-large.jpghttp://images.google.com/imgres?imgurl=http://images.pennnet.com/articles/sst/thm/th_0503sstgroverf2.jpg&imgrefurl=http://www.solid-state.com/display_article/222872/5/none/none/Feat/Choosing-the-right-ionization-gauge-for-high-vacuum-processe&h=212&w=300&sz=9&hl=en&start=23&um=1&tbnid=WbROTG-CBaN82M:&tbnh=82&tbnw=116&prev=/images%3Fq%3Dion%2Bvacuum%2Bgauge%26start%3D21%26ndsp%3D21%26um%3D1%26hl%3Den%26rls%3Dcom.microsoft:*:IE-SearchBox%26rlz%3D1I7ADBF%26sa%3DNhttp://images.google.com/imgres?imgurl=http://www.volotek.com/assets/images/Gauge.jpg&imgrefurl=http://www.volotek.com/body_index.html&h=1200&w=1200&sz=245&hl=en&start=13&um=1&tbnid=_YI2KnOLN26OTM:&tbnh=150&tbnw=150&prev=/images%3Fq%3Dion%2Bvacuum%2Bgauge%26um%3D1%26hl%3Den%26rls%3Dcom.microsoft:*:IE-SearchBox%26rlz%3D1I7ADBF


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Problems that appear to be Leaks

Outgassing

Leaks

Virtual

Real

Backstreaming

DiffusionPermeation

R id l G A l


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Residual Gas Analyzer

QUADRUPOLEHEAD

CONTROL UNIT


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How the RGA works

Y RGA SPECTRUM


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MASS NUMBER (A.M.U.)RELA

TIVEINT

ENSITY

NORMAL (UNBAKED)

SYSTEM

H2

H2O

N2,, COCO2

(A)

RGA SPECTRUM

MASS NUMBER (A.M.U.)RELA

TIVEIN

TENSI T

Y

SYSTEM WITH

AIR LEAK

H2

H2O

N2

CO2

(B)O2


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UHV Materials:

Degassing propertiesMachinability

BakabilityPermeabilityTransfer mechanisms (Bellows)


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THANK YOU

Eff ti P i S d


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Effective Pumping SpeedIf we attach a 500 L/s pump to a chamber with a 500 L/s conductance port, what is the effective pumping speed (EPS) from the chamber. Before calculating, let us set somelimits intuitively: A 500L/s pump is connected to the chamber by some magical 'infinite' conductance port, would the pump's pumping speed be affected?Answer - No. EPS is 500 L/sTwo 500L/s pumps are connected to the same chamber by separate, 'infinite' conductance ports, what is the EPS?Answer - EPS is 1000 L/sec.A 500L/s pump is connected to the chamber by a 500L/sec port, would the EPS be higher or lower than 500L/sec?Answer - Lower.This indicates that adding pumping speed and conductance in series lowers the overall pumping speed, while adding them in parallel increases the pumping speed. This soundsidentical to the series/parallel connections of electrical capacitances. Indeed, pumping speeds (PS) and conductances (C) are added to give effective pumping speed (EPS) usingexactly the same mathematic form as capacitances. To calculate series connection of chamber and pump noted above:1/EPS = 1/PS + 1/CSubstituting the numbers from our initial example, we find 1/EPS = 1/500 + 1/5001/EPS = 2/5001/EPS = 1/250EPS = 250 liter per sec That is, when the pumping speed and conductance are of equal value, the effective pumping speed is half the quotedpumping speed. Newcomers tovacuum technology, and even some old-timers, are surprised by this number.

Adding other components only worsens the problem. For example, what if we put an LN2 trap with 500L/sec conductance between the port and pump?1/EPS = 1/500 + 1/500 + 1/500

1/EPS = 3/5001/EPS = 1/167EPS = 167 liter per secClearly, using the quoted PS as the effective PS will cause serious errors in estimating base pressure and pump down time.

Now, we will take the ridiculous situation and connect a 2000L/sec pump to a chamber by a tube with 10L/sec conductance and calculate the EPS. 1/EPS = 1/2000 + 1/101/EPS = 201/20001/EPS = 1/9.95EPS =


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Assignment 1:

Plot the relationship between gas pressure (x-axis), time for surfacecontamination and mean free path lengths for He, H2, N2 and Ar,assuming ideal gas and sticking coefficient of 1.

iii sem class 1

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