A PRACTICAL GUIDE TO SCANNING PROBE MICROSCOPY Authors (first edition) : Rebecca Howland and Lisa Benatar Project Editor and Booklet Designer: Christy Symanski Copy Editor: Linda Emerson Technical Illustrator: Janet Okagaki Revisions editor (March 2000): Jezz Leckenby Production Coordinator and Cover Designer: Clarence Wong Copyright Notice Copyright © 1993-2000 by ThermoMicroscopes. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means (electronic or mechanical, including photocopying) for any purpose, without written permission from ThermoMicroscopes. Trademarks AutoProbe, Aurora, CP-Research, Explorer, Explorer LifeSciences, Explorer PolymerSystem, M5, Piezolever, Ultralever, Microlever, dLever, ScanMaster, MicroCell, Materials Analysis Package, MAP, MapPlot, ProScan, PSI, Park Scientific Instruments and TopoMetrix Corporation are trademarks of ThermoMicroscopes. All others are trademarks of their respective owners. Contents i CONTENTS ................................................................................ I INTRODUCTION....................................................................................... V CHAPTER 1 SPM TECHNIQUES ...............................................................1 1.1 Scanning Tunneling Microscopy.............................................................. 2 1.2 Atomic Force Microscopy........................................................................ 5 1.2.1 Contact AFM ................................................................................... 7 1.2.2 Non-contact AFM .......................................................................... 10 1.2.3 Intermittent-contact AFM .............................................................. 13 1.3 Magnetic Force Microscopy................................................................... 13 1.4 Lateral Force Microscopy.............................................................................. 15 1.5 Other SPM Techniques........................................................................... 17 1.5.1 Force Modulation Microscopy....................................................... 17 1.5.2 Phase Detection Microscopy ......................................................... 18 1.5.3 Electrostatic Force Microscopy ..................................................... 20 1.5.4 Scanning Capacitance Microscopy................................................ 21 1.5.5 Scanning Thermal Microscopy...................................................... 21 1.5.6 Near-field Scanning Optical Microscopy ...................................... 22 1.5.7 Nanolithography ............................................................................ 22 1.6 SPMs as Surface Analysis Tools............................................................ 26 1.6.1 Scanning Tunneling Spectroscopy................................................. 26 1.6.2 Force vs. Distance Curves.............................................................. 27 1.7 SPM Environments................................................................................. 30 1.7.1 Ultra-high Vacuum ........................................................................ 30 1.7.2 Ambient.......................................................................................... 31 1.7.3 Liquid............................................................................................. 31 1.7.4 Electrochemical.............................................................................. 32 1.8 Further Reading ...................................................................................... 32 ii Contents CHAPTER 2 THE SCANNER ...................................................................35 2.1 Scanner Design and Operation ............................................................... 36 2.2 Scanner Nonlinearities............................................................................ 39 2.2.1 Intrinsic Nonlinearity..................................................................... 39 2.2.2 Hysteresis....................................................................................... 40 2.2.3 Creep.............................................................................................. 42 2.2.4 Aging.............................................................................................. 44 2.2.5 Cross Coupling............................................................................... 46 2.3 Software Correction................................................................................ 48 2.4 Hardware Correction .............................................................................. 49 2.4.1 Optical Techniques ........................................................................ 51 2.4.2 Capacitive Techniques................................................................... 51 2.4.3 Strain-gauge Techniques................................................................ 51 2.5 Tests for Scanner Linearity .................................................................... 52 2.5.1 Intrinsic Nonlinearity..................................................................... 52 2.5.2 Hysteresis....................................................................................... 53 2.5.3 Creep.............................................................................................. 53 2.5.4 Aging.............................................................................................. 55 2.5.5 Cross Coupling............................................................................... 56 2.5.6 Step Profile: Hysteresis, Creep, and Cross Coupling in Z............ 56 2.6 Further Reading ...................................................................................... 57 CHAPTER 3 SPM PROBES ...................................................................58 3.1 Introduction ............................................................................................ 58 3.2 Cantilevers.............................................................................................. 58 3.2.1 Properties of Cantilevers................................................................ 59 3.3 Tip Shape and Resolution....................................................................... 60 3.4 How to Select a Probe ............................................................................ 65 3.5 Probe Handling....................................................................................... 69 3.6 Further Reading ...................................................................................... 69 Contents iii CHAPTER 4 IMAGE ARTIFACTS ..............................................................70 4.1 Tip Convolution...................................................................................... 70 4.2 Convolution with Other Physics............................................................. 73 4.3 Feedback Artifacts.................................................................................. 73 4.4 Image Processing Capabilities................................................................ 74 4.5 Test for Artifacts..................................................................................... 75 4.6 Further Reading ...................................................................................... 75 CHAPTER 5 KEY FEATURES OF SPMS...................................................76 5.1 User Interface ......................................................................................... 76 5.2 Optical Microscope ................................................................................ 76 5.3 Probe Handling....................................................................................... 78 5.4 System Accessibility............................................................................... 78 Notes:..................................................................................................................... 1 iv Contents Introduction v INTRODUCTION In the early 1980's scanning probe microscopes (SPMs) dazzled the world with the first real-space images of the surface of silicon. Now, SPMs are used in a wide variety of disciplines, including fundamental surface science, routine surface roughness analysis, and spectacular three-dimensional imaging—from atoms of silicon to micron-sized protrusions on the surface of a living cell. The scanning probe microscope is an imaging tool with a vast dynamic range, spanning the realms of optical and electron microscopes. It's also a profiler with unprecedented 3-D resolution. In some cases, scanning probe microscopes can measure physical properties such as surface conductivity, static charge distribution, localized friction, magnetic fields, and elastic moduli. As a result, applications of SPMs are very diverse. This booklet was written to help you learn about SPMs, a process that should begin with a thorough understanding of the basics. Issues covered in this booklet range from fundamental physics of SPMs to their practical capabilities and instrumentation. Examples of applications are included throughout the text, and several application-specific articles are listed at the end of each chapter. ThermoMicroscopes was founded in 1998 with the merging of Park Scientific Instruments and TopoMetrix Corporation. Since the founding of these companies at the end of the 1980s, we have maintained strong ties to the academic community and a corporate philosophy that combines technology leadership