Atomic and Molecular Beams: Production and Collimation

374 Pages·2013·6.044 MB·English

by  C B Lucas

Physics Lucas
Atomic and
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Molecular Beams
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Production and Collimation
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Atomic and molecular beams are employed in physics and chemistry oc
experiments and, to a lesser extent, in the biological sciences. These d

beams enable atoms to be studied under collision-free conditions and
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allow the study of their interaction with other atoms, charged particles,
radiation, and surfaces. Atomic and Molecular Beams: Production cn
and Collimation explores the latest techniques for producing a beam t
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from any substance as well as from the dissociation of hydrogen, oxygen, i
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nitrogen, and the halogens.

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The book not only provides the basic expressions essential to beam
design but also offers in-depth coverage of: a
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• Design of ovens and furnaces for atomic beam production
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• Creation of atomic beams that require higher evaporation
temperatures Cc
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• Theory of beam formation including the Clausing equation and
the transmission probability ll
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• Construction of collimating arrays in metals, plastics, glass, and r
other materials
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• Optimization of the design of atomic beam collimators tB
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While many review articles and books discuss the application of atomic e
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beams, few give technical details of their production. Focusing on
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practical application in the laboratory, the author critically reviews over
800 references to compare the atomic and molecular beam formation m
theories with actual experiments. Atomic and Molecular Beams:
Production and Collimation is a comprehensive source of material for
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experimentalists facing the design of any atomic or molecular beam and
theoreticians wishing to extend the theory.
The front cover photograph is reproduced with permission of the UCL Engineering Collection, 2012
K15926
ISBN: 978-1-4665-6103-8
90000
9 781466 561038
K15926_COVER.indd 1 11/6/13 3:06 PM

Atomic and
Molecular Beams
Production and Collimation

Atomic and
Molecular Beams
Production and Collimation
C B Lucas
Visiting Fellow
Department of Physical Sciences
The Open University
The front cover photograph is of a lamp originally belonging to Sir John Ambrose Fleming FRS, profes-
sor of Engineering at University College London. The carbon filament is attached with copper elec-
trodes within the evacuated envelope. In 1883 Professor Fleming explained that copper was deposited
on to the inside of the bulb except for a shadow of the filament produced opposite the connection at
the higher resistance. He therefore realised that atoms travel in straight lines. Hence the kinetic theory
of gases was verified experimentally and his observation has led to many applications of atomic and
molecular beams in fundamental research internationally. The photograph is reproduced with permis-
sion of the UCL Engineering Collection, 2012.
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Version Date: 20131122
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Contents
List of Figures ...........................................................................................................xi
List of Tables ..........................................................................................................xvii
Preface.....................................................................................................................xix
Acknowledgments ...................................................................................................xxi
Author ..................................................................................................................xxiii
Chapter 1 Introduction ..........................................................................................1
1.1 Atomic and Molecular Beam Basics .........................................1
1.2 A Review of Reviews ..............................................................11
Chapter 2 Kinetic Theory of Gases and Atomic Beam Terminology ................19
2.1 Introduction .............................................................................19
2.2 Kinetic Theory Expressions ....................................................19
2.3 Equations of Flow through an Orifice .....................................23
2.4 Determination of Atomic Diameter ........................................26
2.5 Atomic Beam Terminology .....................................................28
Chapter 3 Design of Ovens .................................................................................31
3.1 Introduction .............................................................................31
3.2 Heating Methods .....................................................................32
3.2.1 Indirect Electric Heating ............................................32
3.2.2 Passing a Current Directly through Oven ..................33
3.2.3 Electromagnetic Induction .........................................33
3.2.4 Indirect Heating by Electron Bombardment ..............34
3.2.5 Direct Heating by Electron Bombardment .................35
3.2.6 Heating by Photons ....................................................36
3.2.7 Other Methods ............................................................37
3.2.8 Discussion of Choice of Heating Method ..................37
3.3 Oven Design ............................................................................39
3.3.1 Oven Material .............................................................39
3.3.2 Oven Design Considerations ......................................41
3.3.3 Temperature Measurement .........................................43
3.3.4 Radiation Shields ........................................................43
3.4 Production of Circular Apertures and Slits .............................44
3.4.1 Introduction ................................................................44
3.4.2 Circular Apertures ......................................................44
3.4.3 Slits .............................................................................45
v
vi Contents
Chapter 4 Ovens for Evaporation of Alkali Metals and Their Salts ...................47
4.1 Introduction .............................................................................47
4.2 Ovens in Which a Reaction Takes Place .................................47
4.3 Conventional Ovens for Production of Beams of
Alkali Metals ...........................................................................53
4.4 Ovens for Alkali Halides .........................................................57
4.5 Evaporation from Ampoules ...................................................61
4.6 Recirculating Ovens ................................................................63
4.6.1 Introduction ................................................................63
4.6.2 Direct Return of Metal ...............................................63
4.6.3 Recycling by Capillary Action ...................................67
4.6.4 Recirculation by Ion Formation .................................70
4.6.5 Discussion of Recirculating Systems .........................72
Chapter 5 Ovens for Higher Temperatures .........................................................73
5.1 Introduction .............................................................................73
5.2 Beryllium, Magnesium, Calcium, Strontium and
Barium Beams .........................................................................73
5.3 Beams of Scandium and Yttrium ............................................80
5.4 Titanium and Zirconium Beams .............................................81
5.5 Beams of Vanadium and Compounds of Tantalum .................81
5.6 Chromium Beams ....................................................................82
5.7 Manganese Beams ...................................................................83
5.8 Iron, Cobalt and Nickel Beams ...............................................84
5.9 Beams of Copper, Silver and Gold ..........................................84
5.10 Zinc, Cadmium and Mercury Beams ......................................87
5.11 Beams of Boron, Aluminium, Gallium, Indium
and Thallium ...........................................................................90
5.12 Beams of Carbon, Silicon, Germanium, Tin and Lead ...........95
5.13 Beams of Phosphorus, Arsenic, Antimony and Bismuth ......100
5.14 Sulphur, Selenium, Tellurium and Polonium Beams ............101
5.15 Beams of the Lanthanides .....................................................102
5.16 Beams of the Actinides .........................................................104
5.17 Beam Sources for Refractory Materials ................................107
5.17.1 Introduction ..............................................................107
5.17.2 Beams from Wires ...................................................107
5.17.3 Beams from Rotating Cylinders ...............................109
5.17.4 Direct Electron-Beam Heating .................................110
Chapter 6 Production of Beams of Dissociated Atoms and Other Radicals ....111
6.1 Introduction ...........................................................................111
6.2 Production of Atomic Hydrogen by Thermal Dissociation ...111
6.2.1 Introduction ..............................................................111
Contents vii
6.2.2 Thermal Dissociation of Hydrogen on Tungsten
Filaments and Surfaces ............................................112
6.2.3 Thermal Dissociation of Hydrogen in Tungsten
and Other Furnaces ..................................................113
6.3 Discharge Sources for Atomic Hydrogen ..............................122
6.3.1 Introduction ..............................................................122
6.3.2 Wood’s Tubes ...........................................................123
6.3.3 Arc Sources ..............................................................128
6.3.4 Radiofrequency Discharges......................................130
6.3.5 Microwave Discharges .............................................140
6.4 Another Method for Producing a Beam of
Atomic Hydrogen ..................................................................151
6.5 Discussion of Atomic Hydrogen Production .........................151
6.6 Atomic Oxygen Beams ..........................................................152
6.7 Beams of Atomic Nitrogen ....................................................159
6.8 Sources of Halogen Beams ....................................................164
6.9 Beams of Other Radicals .......................................................169
6.10 Beams of Molecules of Gaseous Species ..............................171
Chapter 7 Gases ................................................................................................173
7.1 Introduction ...........................................................................173
7.2 Recirculation of Gases ...........................................................173
7.3 Atom Beam Levitation ..........................................................174
Chapter 8 Theory of Collimated Atomic Beam Formation ..............................177
8.1 Introduction ...........................................................................177
8.2 Clausing’s Treatment of Flow through a Tube.......................179
8.3 Solutions of Clausing Equation .............................................183
8.3.1 Introduction ..............................................................183
8.3.2 Early Solutions .........................................................185
8.3.3 Discussion of above Solutions ..................................189
8.3.4 Numerical Solutions .................................................190
8.3.5 Solutions at Higher Pressures ...................................191
8.4 Transmission Probability .......................................................193
8.4.1 Introduction ..............................................................193
8.4.2 Numerical and Empirical Calculations ....................194
8.4.3 Monte Carlo Calculations .........................................202
8.4.4 Other Aspects of Flow..............................................204
8.4.5 Allowing for Interatomic Collisions.........................205
8.5 Angular Distribution of Atomic Beam ..................................206
8.5.1 Introduction ..............................................................206
8.5.2 Collision-Free Theory ..............................................206
8.5.3 Density Distribution in a Tube .................................210
8.5.4 Effect of Interatomic Collisions ...............................211
8.5.5 Near-Field Effect ......................................................215
viii Contents
Chapter 9 Designing an Atomic Beam .............................................................217
9.1 Introduction ...........................................................................217
9.2 Expressions Needed to Predict Beam Properties ..................218
9.3 Optimising the Beam-Forming Impedance ..........................221
Chapter 10 Techniques of Multichannel Collimator Construction .....................225
10.1 Introduction ...........................................................................225
10.2 Metallic Foil Arrays ..............................................................226
10.3 Plastic Matrix Arrays ............................................................231
10.4 Arrays of Glass Capillaries ...................................................236
10.4.1 Introduction ..............................................................236
10.4.2 Capillary Drawing Techniques ................................237
10.4.3 Unfused Glass Arrays ..............................................238
10.4.4 Simple Fused Arrays ................................................238
10.4.5 Metal Core Arrays ....................................................240
10.4.6 Drawing of Fused Capillaries ..................................241
10.4.7 Drawing of Solid-Cored Capillaries ........................249
10.4.8 Other Methods of Producing Glass Arrays ..............254
10.4.9 Section Conclusion ...................................................255
10.5 Composite Metal Techniques ................................................256
10.6 Other Collimator Construction Techniques ..........................260
10.6.1 Introduction ..............................................................260
10.6.2 Stacks of Metal Wires and Tubes .............................260
10.6.3 Hole Boring Techniques ...........................................261
10.6.4 Aligned Bored Foils .................................................262
10.6.5 Wooden Collimators.................................................263
10.6.6 Dry Etching Techniques ...........................................265
10.6.7 Arrays in Silica, Silicon and Alumina .....................265
10.6.8 Possibilities for the Future ........................................269
10.7 Focussing Capillary Arrays ...................................................271
10.8 Chapter Conclusion ...............................................................274
Chapter 11 Comparison of Theory with Measurements .....................................275
11.1 Introduction ...........................................................................275
11.2 Beam Formed by Single Tubes ..............................................276
11.2.1 Introduction ..............................................................276
11.2.2 Measurements of Throughput ..................................276
11.2.3 Measurements of Axial Intensity .............................278
11.2.4 Measurements of Halfwidths ...................................279
11.3 Beams Formed by Plane Capillary Arrays............................285
11.3.1 Measurements of Throughput ..................................285
11.3.2 Measurements of Axial Intensity .............................288
11.3.3 Measurements of Halfwidths ...................................290