Experimental Innovations in Surface Science

John T. Yates Jr.

Experimental Innovationsin Surface ScienceA Guide to Practical Laboratory Methodsand Instruments

Second Edition

123

John T. Yates Jr.Department of ChemistryUniversity of VirginiaCharlottesville, VAUSA

ISBN 978-3-319-17667-3 ISBN 978-3-319-17668-0 (eBook)DOI 10.1007/978-3-319-17668-0

Library of Congress Control Number: 2015941351

Springer Cham Heidelberg New York Dordrecht London© Springer International Publishing Switzerland 1998, 2015This work is subject to copyright. All rights are reserved by the Publisher, whether the whole or partof the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations,recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmissionor information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilarmethodology now known or hereafter developed.The use of general descriptive names, registered names, trademarks, service marks, etc. in thispublication does not imply, even in the absence of a specific statement, that such names are exempt fromthe relevant protective laws and regulations and therefore free for general use.The publisher, the authors and the editors are safe to assume that the advice and information in thisbook are believed to be true and accurate at the date of publication. Neither the publisher nor theauthors or the editors give a warranty, express or implied, with respect to the material contained herein orfor any errors or omissions that may have been made.

Printed on acid-free paper

Springer International Publishing AG Switzerland is part of Springer Science+Business Media(www.springer.com)

Preface to the Second Edition

A number of new experimental innovations have been added in over 50 newchapters. I thank each of the innovators for their contributions which areacknowledged in the text. I very much appreciated the graphical work of Dr. AnaStevanovic who skillfully converted hand drawings to computer graphics. I alsodeeply appreciate the assistance of Dr. Zhen Zhang in assembling the new andformer material to produce a well-organized second edition. And finally, I wish tothank Dr. Winfried Heichler and his son Jan Heichler for important high-resolutionoptical scanning of the first edition, allowing its fusion with new material in thesecond edition. I also thank the Department of Chemistry at the University ofVirginia for financial support of the graphics effort. And finally, as in the firstedition, I thank my loving and caring wife, Kerin Yates, for her continued supportand constructive criticism of the new book.

Virginia John T. Yates Jr.

v

Preface to the First Edition

The modern era of surface science, developed in the last 30 years, features hundredsof new physical and chemical measurement methods such as low-energy electrondiffraction and Auger electron spectroscopy, which form a vital foundation for thefield. These measurement methods constitute the basis for a number of books usedby beginning students as their introduction to experimental research.

This book is not about this particular experimental core of the field. Instead, it isabout those practical laboratory methods used throughout the field, but seldomcommunicated coherently in writing and drawings to beginning students. Thesepractical methods of design, construction, and measurement also form their ownfoundation for making possible significant research. They constitute a gold mine ofclever ideas and “tricks of the trade” about how to use basic materials and com-ponents effectively for research and measurement in surface science.Approximately 250 practical methods are described in the book in enough detailthat one could design a new experimental device from the book alone.

This book will be useful to beginning research workers in surface science as wellas to those who work with similar methods in fields such as semiconductor tech-nology, materials science, and physical electronics.

The contents of the book have been selected from unpublished informationsupplied by more than 100 workers in the field as well as from the literature, datingback to the mid-1960s. I have attempted to communicate the core ideas frompublished and unpublished accounts of research in easy-to-comprehend pictorialform, believing that pictures are the most effective mode for communication ofinformation of this type. Thus, the reader can learn much just by looking at thepictures. The text associated with each drawing gives more details. In many cases,the text and its citations indicate the originators and subsequent contributors to theinnovation, but in other cases the origin of the key ideas is unknown, makingaccurate historical citations impossible.

There are some topics that have not been addressed in the book, primarilybecause they are currently highly specialized and fast-moving activities that are bestlearned by advanced research students who have previously mastered some of thetopics covered in this book. Untreated topics include many details of the scanning

vii

tunneling microscope (STM), complex molecular beam techniques, and complexlaser-based measurements.

Updated information on United States and international suppliers of materialsand components used in surface science research is featured at the end of the book.Here the reader will find a guide to product sources as well as addresses and othercommunications information for all companies mentioned in the text footnotes aswell as many other company listings. I thank Dr. Jun Yoshinobu and Dr. JoachimAhner for help with these compilations.

I very much appreciate the involvement of many friends and colleagues whohave contributed to this book by sending me accounts of their innovative methods.This includes many of my own students and postdoctoral who have developedsome of the experimental methods described here. I also thank the publishers of theJournal of Vacuum Science and Technology for permission to use many publishedcontributions dating back to 1964. These were organized for me by ProfessorMichael Bozack and Mr. Kenneth W. Bryant at Auburn University, to whom I amgreatly indebted, and were invaluable in writing a portion of this book. I thank Dr.Fred Dylla and Mrs. Maria Taylor for their encouragement during work with AIPand with Springer-Verlag as the book progressed. Mrs. Marge Augenstein and Mrs.Mary Beth Merenick supplied accurate assistance in organizing the collection andverification of information for the book at the University of Pittsburgh, and inchecking the accuracy of the citations. Ms. Hana Novak took my hand-drawnmechanical drawings and skillfully converted them to computer graphics. The bookwould not have been produced without the financial assistance of the Alexandervon Humboldt Stiftung, which made possible my stay in the Department of Physics,Philipps University, Marburg, Germany. I am indebted also to the University ofPittsburgh for a coincident sabbatical leave to write the book. I wish to thank mymany German friends for their hospitality, particularly Dr. Heinz J. Jaensch andProfessor Dieter Fick for their friendship during my seven months in Marburg.I also thank my parents, Mr. and Mrs. J. Thomas Yates, Sr., for their hospitality inHagerstown, Maryland, during the completion of the book. And finally, and mostimportantly, I thank my wife, Kerin, for all of her support. Without her under-standing and constructive criticism, writing and illustrating the book would havebeen impossible.

March 1997 John T. Yates, Jr.R.K. Mellon Professor

Department of Chemistryand Department of Physics and Astronomy

Director, Surface Science CenterUniversity of Pittsburgh

viii Preface to the First Edition

Contents

Part I Vacuum System Technology

1 Motion in Vacuum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31.1 Crystal Manipulator with Six Degrees

of Motional Freedom. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31.2 Rotation in Ultrahigh Vacuum . . . . . . . . . . . . . . . . . . . . . . 61.3 Crystal Positioning Using Capacitance . . . . . . . . . . . . . . . . . 111.4 UHV Rotary Manipulator with Arcsec Resolution . . . . . . . . . 131.5 Solenoid Driven Linear Motion Device . . . . . . . . . . . . . . . . 151.6 An Inexpensive Linear Motion Device. . . . . . . . . . . . . . . . . 151.7 Translating Auger Spectrometer . . . . . . . . . . . . . . . . . . . . . 161.8 Simple Multiple Motion Manipulator . . . . . . . . . . . . . . . . . . 181.9 Simple Device for Small Rotations in Ultrahigh

Vacuum—Grating Application . . . . . . . . . . . . . . . . . . . . . . 181.10 Turntable Rotation in Ultrahigh Vacuum . . . . . . . . . . . . . . . 201.11 Small Motions in UHV Systems Using Shape Memory

Effect Alloys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201.12 Rotary Shutter Device Driven by Magnetic Eddy Current . . . 221.13 High-Speed Ultrahigh Vacuum Motor . . . . . . . . . . . . . . . . . 241.14 High-Speed Rotary Feedthrough for UHV Operation . . . . . . . 251.15 Self-lubricating Bearings in UHV . . . . . . . . . . . . . . . . . . . . 261.16 Lubrication for Heavy Sliding Loads

in Ultrahigh Vacuum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 271.17 Simple UHV Bearing for High-Speed Shafts . . . . . . . . . . . . 291.18 Flange-Mounted UHV Variable Aperture . . . . . . . . . . . . . . . 301.19 Linear Motion Platform (LMP) . . . . . . . . . . . . . . . . . . . . . . 311.20 Vacuum Trolley Transport System . . . . . . . . . . . . . . . . . . . 331.21 Thermally Compensated STM with Repeatable

Sample Positioning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

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2 Sample Transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 392.1 Sample Transfer from High Pressure to Ultrahigh

Vacuum. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 392.2 Novel Sample Transfer from UHV Chamber

to External Cell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 452.3 UHV Sample Transfer Device with Low-Temperature

Capability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 452.4 Internal Cup High-Pressure Cell . . . . . . . . . . . . . . . . . . . . . 492.5 High-Pressure Transfer Cell . . . . . . . . . . . . . . . . . . . . . . . . 502.6 Sample Transfer with Disconnect-I . . . . . . . . . . . . . . . . . . . 52

2.6.1 Transfer in Standard UHV Systems. . . . . . . . . . . . . . 522.6.2 Transfer in STM Systems . . . . . . . . . . . . . . . . . . . . 54

2.7 Sample Transfer with Disconnect-II. . . . . . . . . . . . . . . . . . . 542.8 Vibration-Free Translatable Device . . . . . . . . . . . . . . . . . . . 552.9 Mirror Port for Enhanced Sample Transfer . . . . . . . . . . . . . . 562.10 UHV Access Port . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

3 Electrical Connections. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613.1 Tungsten Ribbon—Attachment to Power Leads . . . . . . . . . . 613.2 Wrap Connection—Tungsten to Tungsten . . . . . . . . . . . . . . 623.3 Cold-Formed Wire Connector . . . . . . . . . . . . . . . . . . . . . . . 643.4 Ultrahigh Resistance Vacuum Feedthroughs . . . . . . . . . . . . . 643.5 Sliding Metal Electrical Contact . . . . . . . . . . . . . . . . . . . . . 663.6 Low-Profile Electrical Lead Clamp . . . . . . . . . . . . . . . . . . . 67References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68

4 Pumping and Trapping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 694.1 Water Aspirator/Sorption Pump Combination for Efficient

UHV System Evacuation . . . . . . . . . . . . . . . . . . . . . . . . . . 694.2 Ballast Pumping—Vibration Free . . . . . . . . . . . . . . . . . . . . 714.3 The Use of Appendage Titanium Sublimation Pumps

for Pumping Low Gas Loads in Ultrahigh Vacuum . . . . . . . . 724.4 Pressure-Equalizing Device in Complex Systems . . . . . . . . . 724.5 Diode Ion Pump Performance in He Pumping. . . . . . . . . . . . 754.6 Vacuum Applications of Metal Foams . . . . . . . . . . . . . . . . . 754.7 Cleaning of Ion Pumps by Chemical Etching . . . . . . . . . . . . 784.8 An Efficient Liquid Nitrogen Trap . . . . . . . . . . . . . . . . . . . 79References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80

5 Bakeout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 835.1 Bakeout of Metal Ultrahigh Vacuum Systems. . . . . . . . . . . . 83References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85

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6 Behavior of UHV Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 876.1 Wall Passivation in Stainless Steel Ultrahigh

Vacuum Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 876.2 Minimizing Wall Reactions in Ultrahigh Vacuum

Systems—Gas Dosers . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91

7 Mechanical Action on Samples . . . . . . . . . . . . . . . . . . . . . . . . . . 937.1 Simple UHV Crystal Cleaver . . . . . . . . . . . . . . . . . . . . . . . 937.2 Piezoelectric Fatigue Apparatus for UHV Operation . . . . . . . 95References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97

8 Gasket Seals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 998.1 Gasket Seals for Ultrahigh Vacuum Systems . . . . . . . . . . . . 998.2 Cryogenic Gasket Seals . . . . . . . . . . . . . . . . . . . . . . . . . . . 1018.3 Copper Gasket Removal Devices . . . . . . . . . . . . . . . . . . . . 1028.4 Unconventional Compression Seals for Ultrahigh Vacuum . . . 103References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105

9 Leak Repairs and Detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1079.1 Coaxial Pumped He Leak Detection Probe . . . . . . . . . . . . . . 1079.2 Temporary Leak Sealing of Welded Bellows . . . . . . . . . . . . 1089.3 Atmospheric Permeation—Viton O-Ring . . . . . . . . . . . . . . . 108References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110

10 Specialized UHV Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11310.1 Aluminum Ultrahigh Vacuum System . . . . . . . . . . . . . . . . . 11310.2 Surface Electrochemistry Apparatus. . . . . . . . . . . . . . . . . . . 114References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116

Part II Mechanical Fabrication Techniques

11 Grids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11911.1 Hemispherical Grids—Formation and Piercing . . . . . . . . . . . 11911.2 Making Flat Mesh Grids of Large Size . . . . . . . . . . . . . . . . 12011.3 Grid Fabrication Techniques—Conical Grid . . . . . . . . . . . . . 121References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122

12 Conductive Coatings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12312.1 Deposition of Electrically Conductive SnO2 Films. . . . . . . . . 123References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125

Contents xi

13 Phosphor Screens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12713.1 Sedimentation Method for Depositing Phosphor Screens . . . . 12713.2 Dusting Method for Coating Phosphor Screens . . . . . . . . . . . 129References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131

14 Thermionic Emitters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13314.1 Thoriated Thermionic Emitters . . . . . . . . . . . . . . . . . . . . . . 13314.2 Lanthanum Hexaboride Thermionic Emitters—Deposition

on Metals. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13514.3 Directly Heated Lanthanum Hexaboride

Thermionic Emitters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13714.4 Thermionic Emitter Mounting. . . . . . . . . . . . . . . . . . . . . . . 13914.5 Indirectly Heated Cathodes for High-Temperature

Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14114.6 Filament Power Supply Tester . . . . . . . . . . . . . . . . . . . . . . 14114.7 Bayard-Alpert Ionization Gauge with Corrections

for External Radiation and External Electron Flux Effects . . . 14214.8 Replacing Filaments in Glass Bayard-Alpert Gauges . . . . . . . 145References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146

15 Shielding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14915.1 Magnetic Shielding in Ultrahigh Vacuum. . . . . . . . . . . . . . . 14915.2 Electrical Isolation of UHV Components . . . . . . . . . . . . . . . 151References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152

16 Single Crystal Fabrication/Orientation . . . . . . . . . . . . . . . . . . . . . 15516.1 Making Small Au Single Crystals from Au Wire for STM

and Other Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15516.2 Single Crystal Orientation, Grinding, and Polishing . . . . . . . . 15616.3 A Simple Goniometer for Cutting Single Crystals . . . . . . . . . 15916.4 Ion Beam Polishing of Crystals

to Subnanometer Roughness . . . . . . . . . . . . . . . . . . . . . . . . 16016.5 Crystal Optical Alignment . . . . . . . . . . . . . . . . . . . . . . . . . 16116.6 Measurement of the Angles of Incidence

in a LEED Experiment . . . . . . . . . . . . . . . . . . . . . . . . . . . 16216.7 Measurement of Angle of Incidence of an Electron Beam

on a Single Crystal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165

17 Tip Fabrication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16717.1 Fabrication of Metal Tips Using Zone Electropolishing . . . . . 16717.2 Etching STM Tips Reproducibly . . . . . . . . . . . . . . . . . . . . . 16817.3 STM Tip Flasher . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170

xii Contents

17.4 Reverse Bias Method for Sharp Tip Etching. . . . . . . . . . . . . 17017.5 Sharpening Single Crystal Metal Tips

by Ion Bombardment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174

18 Spot-Welding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17518.1 Spot-Welding Difficult Junctions. . . . . . . . . . . . . . . . . . . . . 175References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177

19 Mechanical Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17919.1 Stretching Thin Metal Foils to a Wrinkle-Free Condition . . . . 17919.2 Making Micron-Size Holes for Supersonic Nozzles . . . . . . . . 180

19.2.1 Method I—Fig. 19.2a . . . . . . . . . . . . . . . . . . . . . . . 18019.2.2 Method II—Fig. 19.2b. . . . . . . . . . . . . . . . . . . . . . . 182

19.3 Straightening and Braiding Wires . . . . . . . . . . . . . . . . . . . . 183References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183

Part III Measurement Methods

20 Electrons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18720.1 Electron Gun Design and Behavior . . . . . . . . . . . . . . . . . . . 18720.2 Low-Energy Electron Gun for Broad-Beam Irradiation. . . . . . 18920.3 Low-Energy Electron Gun for Broad-Beam

Irradiation—Cylindrical Symmetry . . . . . . . . . . . . . . . . . . . 19020.4 Electron Energy Analyzers . . . . . . . . . . . . . . . . . . . . . . . . . 19120.5 Electron Spectrometer Calibration Using Graphite . . . . . . . . . 19620.6 Measurement of Electron Beam Angular Divergence . . . . . . . 19820.7 Measuring Anisotropy of Electrical Conductivity

of a Single Crystal—Four Point Probe . . . . . . . . . . . . . . . . . 20020.8 Spot Photometer for LEED Intensity Measurements. . . . . . . . 20120.9 Modified Faraday Cup for Electron Current Measurement . . . 20220.10 HREELS-Discrimination Between Single

and Multiple Electron Scattering Events. . . . . . . . . . . . . . . . 20520.11 Rejuvenation of Cu/Be Electron Multipliers . . . . . . . . . . . . . 20520.12 Geiger-Müller Counter for Inverse Photoemission . . . . . . . . . 206References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208

21 Ions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21121.1 Ion Sputter Gun with Low Gas Emission . . . . . . . . . . . . . . . 21121.2 Alternate Ion Bombardment Sources . . . . . . . . . . . . . . . . . . 21321.3 Ion Gun Based on Bayard-Alpert Gauge . . . . . . . . . . . . . . . 21421.4 Sputter Ion Gun—Cold Cathode . . . . . . . . . . . . . . . . . . . . . 21621.5 Broad Ion Sources—Improved Stability with Oxygen . . . . . . 218

Contents xiii

21.6 Focusing of Low-Energy Ions by Magnetic Field . . . . . . . . . 22021.7 Low Energy Ion Gun—Construction and Performance . . . . . . 22021.8 Measuring Ion Beam Dimensions . . . . . . . . . . . . . . . . . . . . 22321.9 Beam Position Monitor—Charged Particles . . . . . . . . . . . . . 22421.10 Pulse-Counting LEED/ESDIAD Analyzer—Using

MicroChannel Plate Detection. . . . . . . . . . . . . . . . . . . . . . . 22521.11 Time-of-Flight Measurements for Ions Generated

in ESDIAD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22721.12 Ion Detection with Kinetic Energy and Mass Resolution

Using a Hemispherical Energy Analyzer . . . . . . . . . . . . . . . 22921.13 Time-of-Flight Detection for Laser-Ionized Neutrals . . . . . . . 231References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232

22 Photons (UV) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23522.1 Hollow Cathode Resonance Lamp for He(II)

(40.8 eV) Photoemission . . . . . . . . . . . . . . . . . . . . . . . . . . 23522.2 He(I) and He(II) Ultraviolet Resonance Source . . . . . . . . . . . 23622.3 Photochemistry on Surfaces Using an Ultraviolet Lamp . . . . . 23822.4 Use of Polarized Ultraviolet Light for Photochemistry . . . . . . 24022.5 Photoreduction of Ag on Doped TiO2—Making

Enhanced Photoactivity Visible . . . . . . . . . . . . . . . . . . . . . . 24222.6 Reducing Radiation Damage in Raman Spectroscopy

of Solids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24322.7 Lyman-α Lamp Calibration Using a Chemical

Actinometer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24522.8 Pulsed Vacuum UV Light Source . . . . . . . . . . . . . . . . . . . . 24722.9 Grazing Incidence X-Ray Photoemission Spectroscopy

(GIXPS): Enhanced Surface Sensitivity . . . . . . . . . . . . . . . . 247References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250

23 Kinetics of Adsorption/Adsorbate Coverages . . . . . . . . . . . . . . . . 25323.1 Absolute Adsorption Uptake Measurements

from a Calibrated Effusive Molecular Beam . . . . . . . . . . . . . 25323.2 Measurement of Absolute Sticking Coefficient

at Desorption Temperature . . . . . . . . . . . . . . . . . . . . . . . . . 255References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257

24 Mass Spectrometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25924.1 Shielded Quadrupole Mass Spectrometers—Temperature-

Programmed Desorption. . . . . . . . . . . . . . . . . . . . . . . . . . . 25924.2 Enhanced Signal-to-Noise in Quadrupole

Mass Spectrometers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26224.3 Elimination of Spurious Electron Emission

from a Quadrupole Mass Spectrometer . . . . . . . . . . . . . . . . 265

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24.4 Ta Mass Spectrometer Filament . . . . . . . . . . . . . . . . . . . . . 26524.5 Modulated QMS Ion Source for Enhanced Sensitivity . . . . . . 26724.6 Line-of-Sight Mass Spectrometry for Thermal Desorption . . . 26924.7 Mass Spectrometer Calibration

by Molecular Decomposition . . . . . . . . . . . . . . . . . . . . . . . 270References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272

25 Temperature-Programmed Desorption/Reaction . . . . . . . . . . . . . . 27325.1 Thermal Desorption—Angular Resolved . . . . . . . . . . . . . . . 27325.2 Magic-Angle Thermal Desorption Mass Spectroscopy . . . . . . 27525.3 High-Temperature Thermal Desorption Spectroscopy. . . . . . . 27725.4 Automated Temperature Programmed Desorption

(TPD) Apparatus. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27825.5 Scanning Kinetic Spectroscopy—A Survey Method

for Investigation of Surface Reaction Processes. . . . . . . . . . . 28025.6 Temperature-Programmed Reaction Spectroscopy (TPRS) . . . 282References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284

26 Gas Chromatography—Enhanced Sensitivity . . . . . . . . . . . . . . . . 28726.1 Gas Chromatography—Sensitivity Enhancement . . . . . . . . . . 287Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 288

27 Work Function, Tunneling Spectroscopy and Ellipsometry . . . . . . 28927.1 Work Function Changes Using Retarding Diode Method . . . . 28927.2 Work Function Measurements Using an Electron Gun . . . . . . 29127.3 Work Function and Electron Reflection Coefficient

Measurements with the Shelton Diode . . . . . . . . . . . . . . . . . 29327.4 Improved Piezoelectric Drive Kelvin Probe . . . . . . . . . . . . . 29527.5 Improved Electromagnetic Drive Kelvin Probe . . . . . . . . . . . 29727.6 Kelvin Probe—High Temperature Flow Reactor . . . . . . . . . . 29927.7 Scanning Tunneling Spectroscopy (STS)—Compensation

for Density of States of the Tip. . . . . . . . . . . . . . . . . . . . . . 30027.8 Ellipsometry as a Tool for Studying Adsorption . . . . . . . . . . 302References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 303

28 Radioactive Adsorbates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30528.1 Radiotracer Techniques for Surface Studies . . . . . . . . . . . . . 305References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 307

29 Thin Film Deposition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30929.1 Thin Film Deposition to Absolute Surface Coverages . . . . . . 30929.2 Gold Evaporation Source . . . . . . . . . . . . . . . . . . . . . . . . . . 31229.3 Ionization Gauge Measurement of Film Evaporation Rate . . . 314

Contents xv

29.4 Reusable Quartz Crystals for FilmThickness Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . 314

29.5 Hybrid Thin Film Deposition Processes—Stableand Metastable Films. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 317

29.6 Sputter-Coating Inner Walls of Tubes . . . . . . . . . . . . . . . . . 317References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 319

30 Infrared Spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32130.1 Infrared Reflection Absorption Spectrometer. . . . . . . . . . . . . 32130.2 IRAS Measurements at High Pressure . . . . . . . . . . . . . . . . . 32330.3 Internal Reflection IR Spectroscopy—Silicon . . . . . . . . . . . . 32430.4 Internal Reflection IR Spectroscopy—Gallium Arsenide. . . . . 32730.5 Infrared Spectroscopy—Continuous Pumping

of Detector Dewar. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32830.6 Rapid IR Spectrometer Purge After Cell Transfer—Using

Rubber Sleeves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 329References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 331

31 Calorimetric Heats of Adsorption—Single Crystals. . . . . . . . . . . . 33331.1 Measurement of the Calorimetric Heat of Adsorption

on Ultrathin Metal Single Crystals. . . . . . . . . . . . . . . . . . . . 33331.2 Improved Adsorption Calorimeter for Single Crystals

at 100–350 K . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 334References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 336

32 Surface Debye Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33732.1 Measuring the Surface Debye Temperature

of a Single Crystal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 337References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 339

33 Friction and Fracture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34133.1 UHV Tribometer for Measuring the Coefficient

of Friction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34133.2 Pin-on-Disk Measurement—UHV . . . . . . . . . . . . . . . . . . . . 34333.3 UHV Fracture Stage for Surface Analysis After Fracture . . . . 343References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 345

Part IV Thermal Control

34 Heating Samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34934.1 Electronic Temperature Programmer—Metal Crystals . . . . . . 34934.2 Temperature Programming of Metal

and Semiconductor Crystals . . . . . . . . . . . . . . . . . . . . . . . . 351

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34.3 Mounting Nonweldable Crystals for Resistive Heatingand Cooling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 354

34.4 Strain-Free Single Crystal Mounting Azimuthal Motion . . . . . 35534.5 Heating Silicon Crystals and Temperature Measurements . . . . 35634.6 Avoiding Extraneous Electrical Effects Owing

to Heating Crystals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35934.7 Electron Bombardment Crystal Heating . . . . . . . . . . . . . . . . 36134.8 Indirect Sample Heating. . . . . . . . . . . . . . . . . . . . . . . . . . . 36334.9 Indirect Heating of Compound Semiconductors. . . . . . . . . . . 36534.10 Heating Design—Insulator Crystals . . . . . . . . . . . . . . . . . . . 36634.11 Cement Mounting—Semiconductor Crystals . . . . . . . . . . . . . 36834.12 Low-Stress Mount for Fragile Semiconductor Crystals . . . . . . 36934.13 Radiation Heating of Crystals Through Glass Windows . . . . . 37134.14 Pyrolytic Graphite Heating Element for UHV . . . . . . . . . . . . 37234.15 Heater—Paint-on Type . . . . . . . . . . . . . . . . . . . . . . . . . . . 37434.16 Mounting High-Temperature Tungsten Filaments . . . . . . . . . 37534.17 Rotatable Single Crystal. . . . . . . . . . . . . . . . . . . . . . . . . . . 37534.18 Radiation-Heated Evaporator . . . . . . . . . . . . . . . . . . . . . . . 378References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 378

35 Cooling Samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38135.1 6 K—Cryogenic Crystal Holder . . . . . . . . . . . . . . . . . . . . . 38135.2 Cooling Crystals by Contact with a Thermal Reservoir . . . . . 38335.3 Cooling Samples on Manipulators—Thermal

Conductivity Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38335.4 Vacuum-Jacketed Cryogenic Manipulator Rod . . . . . . . . . . . 38635.5 Manipulator Component with Cryogenic

Azimuthal Rotation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38835.6 Cooling Using Direct Contact . . . . . . . . . . . . . . . . . . . . . . . 38935.7 Cooling Reservoir—Horizontal Manipulator . . . . . . . . . . . . . 39035.8 Cryogenic Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . 39235.9 Sample Cooling Using Thermal Braid . . . . . . . . . . . . . . . . . 39235.10 Flexible Cooling Reservoir . . . . . . . . . . . . . . . . . . . . . . . . . 39435.11 Enhanced Cooling Using Liquid Nitrogen . . . . . . . . . . . . . . 39435.12 Level Alarm-Liquid Nitrogen . . . . . . . . . . . . . . . . . . . . . . . 39635.13 Liquid Nitrogen Reservoir—Non-leaking . . . . . . . . . . . . . . . 39835.14 Cryogenic Cooling to Below 4 K—Photon Stimulated

Desorption of Adsorbed He . . . . . . . . . . . . . . . . . . . . . . . . 39935.15 Static Temperature Control by Mixing Gas Streams. . . . . . . . 40135.16 Gas Thermal Switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 401References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 404

Contents xvii

36 Temperature Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40536.1 Tungsten-Rhenium Thermocouples—Calibration

Over a Wide Temperature Range . . . . . . . . . . . . . . . . . . . . 40536.2 Measuring Temperatures of Hot Filaments . . . . . . . . . . . . . . 40736.3 Pyrometric Measurement of Temperatures . . . . . . . . . . . . . . 40936.4 Pyrometer Measurements Through Windows Coated

Inadvertently with Variable-Thickness Thin Films . . . . . . . . . 41136.5 Calibration Point for Optical Pyrometer Used for Silicon . . . . 41336.6 Control of Silicon Temperature Using Resistivity . . . . . . . . . 415References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 417

Part V Delivery of Adsorbates to Surfaces

37 Gases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42137.1 Design and Performance of Microcapillary Array

Beam Doser . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42137.2 Gas Handling System for Array Beam Doser . . . . . . . . . . . . 42337.3 Calibration and Use of Array Beam Doser . . . . . . . . . . . . . . 42537.4 Sticking Coefficient and Surface Reactivity . . . . . . . . . . . . . 42637.5 Beam Doser Shutoff—Condensable Gases . . . . . . . . . . . . . . 42837.6 Neutral Beam Intensity Measurement Using a Stagnation

Detector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42937.7 Low Deadspace Aperture Valve for Repetitive

Gas Dosing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43037.8 Gas Flow Regulation—Squeeze Valve . . . . . . . . . . . . . . . . . 43337.9 Retractable Beam Doser with Convenient On-Off Control . . . 434References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 435

38 Evaporation Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43738.1 Degassing Evaporation Sources. . . . . . . . . . . . . . . . . . . . . . 43738.2 Metal Evaporation Sources for Downward Evaporation . . . . . 43938.3 Ultralow Coverage Metal Evaporation . . . . . . . . . . . . . . . . . 44038.4 Congruent Evaporation of Multicomponent Materials. . . . . . . 44238.5 Evaporator for Eutectic-Forming Metals . . . . . . . . . . . . . . . . 44438.6 Simple Lithium Metal Evaporation Source . . . . . . . . . . . . . . 44438.7 Aluminum Evaporation Sources—Long Lived . . . . . . . . . . . 44638.8 Cr Evaporator Sources of Compact Design. . . . . . . . . . . . . . 44838.9 Electron Beam Evaporator for Refractory Materials . . . . . . . . 44938.10 Small Electron Beam Evaporator for Refractory Metals . . . . . 45138.11 Electron Beam Evaporator . . . . . . . . . . . . . . . . . . . . . . . . . 45338.12 Break-Seal Ampoule Doser . . . . . . . . . . . . . . . . . . . . . . . . 45538.13 Cadmium Sulfide Evaporation Source . . . . . . . . . . . . . . . . . 45638.14 Arsenic Atom Source . . . . . . . . . . . . . . . . . . . . . . . . . . . . 456

xviii Contents

38.15 Portable Microevaporator for Depositing Low Coveragesof Single Atoms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 459

38.16 Nanoscale Templating of Close-PackedC60 Nanostructures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 460

38.17 Quantitative Molecular Beam Dosing of SlightlyVolatile Organics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 460

38.18 Organic Doser . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46438.19 Vapor Deposition of Organic Thin Films . . . . . . . . . . . . . . . 46438.20 Evaporator for Organic Film Deposition. . . . . . . . . . . . . . . . 465References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 468

39 Ions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47139.1 Solid State Cesium Ion Gun Source. . . . . . . . . . . . . . . . . . . 47139.2 Alkaline Earth Metal Ion Sources . . . . . . . . . . . . . . . . . . . . 473References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 475

40 Active Gases and Species . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47740.1 High Flux Atomic Hydrogen Sources—Thermal . . . . . . . . . . 47740.2 Atomic Hydrogen Beam Source—Radio

Frequency Driven . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48040.3 Atomic Fluorine Source . . . . . . . . . . . . . . . . . . . . . . . . . . . 48140.4 Alkali Metal Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48340.5 Thermal Source of Methyl Free Radicals . . . . . . . . . . . . . . . 48540.6 Production, Storage, and Use of Ozone . . . . . . . . . . . . . . . . 48640.7 Ozone Generator and Molecular Beam Doser Source. . . . . . . 48840.8 Detection of Ozone or Atomic Oxygen by Oxidation

of Silver Films . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49040.9 Purity of Ir and Pt Hot Filament Sources

for Atomic Oxygen Production . . . . . . . . . . . . . . . . . . . . . . 49140.10 Pure Hydrogen Peroxide Doser for Ultrahigh Vacuum . . . . . . 493References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 494

41 Electrochemical Sources and Devices . . . . . . . . . . . . . . . . . . . . . . 49741.1 Electrochemical Sulfur Source . . . . . . . . . . . . . . . . . . . . . . 49741.2 Electrochemical Halogen Sources . . . . . . . . . . . . . . . . . . . . 49841.3 Electrochemical I2 Doser . . . . . . . . . . . . . . . . . . . . . . . . . . 50141.4 Electrochemical Device Working in UHV . . . . . . . . . . . . . . 502References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 504

42 Gas Purification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50542.1 Gas Purification for Experiments at High Pressures . . . . . . . . 50542.2 Production and Purity Measurement

for Extremely Pure He. . . . . . . . . . . . . . . . . . . . . . . . . . . . 50742.3 Purification of Gases by Cryogenic or Gettering Methods . . . 509

Contents xix

42.4 Gas Purification by Permeation Through Metals . . . . . . . . . . 51142.5 O2 Source—Solid State . . . . . . . . . . . . . . . . . . . . . . . . . . . 51342.6 Reusable Sample Holder for Hydrogen

Permeation Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 513References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 514

43 Liquid Handling in UHV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51743.1 Adding Liquid to Atomically Clean Surfaces . . . . . . . . . . . . 517Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 518

Part VI UHV Windows

44 Spectroscopic Windows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52144.1 Mounting Infrared Windows on UHV Systems . . . . . . . . . . . 52144.2 Windows for Vacuum UV Transmission into Ultrahigh

Vacuum Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52444.3 Construction of Be Windows for Ultrahigh Vacuum Use . . . . 52644.4 Bakeable Aluminum Ultrahigh Vacuum Window . . . . . . . . . 52844.5 Metal Thin Foil Windows—Welding . . . . . . . . . . . . . . . . . . 52944.6 Preparation of Large-Area Si Single Crystal Windows . . . . . . 52944.7 Strain-Free Optical Window Mounting. . . . . . . . . . . . . . . . . 532References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 533

45 Observation Windows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53545.1 Shielded Observation Window . . . . . . . . . . . . . . . . . . . . . . 53545.2 Heated Internal Window for Prevention

of Film Deposition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53645.3 UHV Glass Window Seal—Low Optical Distortion. . . . . . . . 53745.4 Zero-Length Window Assembly . . . . . . . . . . . . . . . . . . . . . 539References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 540

Part VII Surface Preparation Methods

46 Cleaning Metal and Semiconductor Crystals—Examples . . . . . . . 54346.1 Surface Segregation and the Cleaning

of Metal Single Crystals. . . . . . . . . . . . . . . . . . . . . . . . . . . 54346.2 Chemical Method to Measure and Remove Carbon

from Pd . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54646.3 Surface Cleaning Procedures—Silicon . . . . . . . . . . . . . . . . . 54846.4 Preparation of Atomically Clean Tungsten Single Crystals . . . 551References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 551

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Part VIII High-Area Solids

47 Infrared Cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55547.1 Infrared Cell for Adsorption Studies

on Supported Catalysts . . . . . . . . . . . . . . . . . . . . . . . . . . . 55547.2 Wide-Temperature-Range IR Cell for High-Area Solids . . . . . 55747.3 Measurements of Diffusion Through Powders

Using Transmission Infrared Spectroscopy . . . . . . . . . . . . . . 56047.4 Using Transmission Infrared Spectroscopy to Witness

Diffusion into Core-Shell Structures . . . . . . . . . . . . . . . . . . 56247.5 Diffusion in Powders as Measured by Transmission

IR Spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56247.6 Transmission IR Spectroscopy Through Opaque Materials . . . 564References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 567

48 Adsorption/Desorption—Thermal . . . . . . . . . . . . . . . . . . . . . . . . 56948.1 Adsorption and Desorption from High-Area Solids . . . . . . . . 56948.2 Thermal Desorption from High Area Materials . . . . . . . . . . . 57148.3 Microcalorimetric Studies of Adsorption Heat on Powders . . . 57448.4 Chemical Vapor Synthesis of Oxide Nanoparticles . . . . . . . . 576References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 577

Part IX Safety

49 Protecting the Vacuum System . . . . . . . . . . . . . . . . . . . . . . . . . . 58149.1 Delay Circuit for Turbopumping Protection

Against Vacuum Loss from Power Interruptions . . . . . . . . . . 58149.2 Fast-Closing Beam Valve for UHV Chamber Protection . . . . 58349.3 Safety System for Oil Diffusion-Pumped UHV Systems. . . . . 58449.4 Folding Linear Magnetic Translator . . . . . . . . . . . . . . . . . . . 586References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 587

50 Protecting Personnel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58950.1 Electrical Shocks in the Laboratory . . . . . . . . . . . . . . . . . . . 58950.2 Accidental Electrical Charging from Ionization Gauge . . . . . . 590Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 592

Appendix A. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 593

Appendix B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 597

Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 643

Contents xxi