Engineering Thin Films and Nanostructures with Ion Beams

Emile Knystautas, Emile Knystautas

• Publisher: CRC Press
• Year: 2018
• ISBN:
  9781351836753
• Edition: 1
• Topic: Tecnologia e ingegneria
• Subtopic: Nanotecnologia e MEMS

While ion-beam techniques have been used to create thin films in the semiconductor industry for several decades, these methods have been too costly for other surface treatment applications. However, as manufacturing devices become increasingly smaller, the use of a directed-energy ion beam is finding novel industrial applications that require the custom tailoring of new materials and devices, including magnetic storage devices, photonics, opto-electronics, and molecular transport. Engineering Thin Films and Nanostructures with Ion Beams offers a thorough narrative of the recent advances that make this technology relevant to current and future applications.Featuring internationally recognized researchers, the book compiles their expertise in a multidimensional source that:

• Highlights the mechanisms and visual evidence of the effects of single-ion impacts on metallic surfaces
  
• Considers how ion-beam techniques can help achieve higher disk-drive densities
  
• Introduces gas-cluster ion-beam technology and reviews its precedents
  
• Explains how ion beams are used to aggregate metals and semiconductors into nanoclusters with nonlinear optical properties
  
• Addresses current challenges in building equipment needed to produce nanostructures in an industrial setting
  
• Examines the combination of ion-beam techniques, particularly with physical vapor deposition
  
• Delineates the fabrication of nanopillars, nanoflowers, and interconnected nanochannels in three dimensions by using atomic shadowing techniques
  
• Illustrates the production of nanopores of varying dimensions in polymer films, alloys, and superconductors using ion-beam irradiation
  
• Shows how fingerprints can be made more reliable as forensic evidence by recoil-mixing them into the substrate using ion beamsFrom the basics of the ion-beam modification of materials to state-of-the-art applications, Engineering Th

Chapter 1

Introduction

Thin films can be produced in many forms and have properties that can differ significantly from their corresponding bulk form. They can be prepared by a host of techniques such as sputtering (single or multiple) layers on a substrate, creating buried waveguides by ion implantation in an optical material, or making complex nanostructures by ion irradiation during vapor deposition.

While ion-beam techniques have been a staple of the semiconductor industry for several decades, their application to other areas, for example metal surface treatment, have not been nearly as successful, generally because of cost considerations. Now, however, with the advent of devices of ever-smaller dimensions, the use of a directed-energy ion beam appears bound to find many novel industrial applications in the custom tailoring of new materials and devices. Such potential applications are too numerous to list here, and any attempt to make predictions at this point about which will pan out and which will not will likely turn out to have completely missed the mark a few years hence.

This book will hopefully provide newcomers to this exciting field with an introduction to its potential and also bring them up to speed on some of the current research in this area.

The first chapter deals with fundamental aspects and examines in detail the effects of a single ion impinging on a thin film. Using a unique “crossed beam” apparatus at Argonne National Laboratory consisting of a powerful transmission electron microscope that views a surface that is bombarded by hundreds of keV heavy ions, Steve Donnelly and his colleagues have studied the dynamics of crater and hole formation on metallic surfaces when individual ions impinge on a surface. Comparison with molecular dynamics simulations have given a satisfyingly complete picture of some of the basic mechanisms involved in the formation of craters and their (occasional) annealing by subsequent ion impacts. On the other hand, there are still other matters, such as the emission of nanoclusters, which require further study. Visual evidence of the effects of single-ion impacts is provided in the compact disc accompanying this volume, which contains some stunning video clips of the phenomena discussed. It is suggested that the reader watch these while reading the corresponding text. Rarely can one see sequential phenomena presented so vividly on a microscopic scale.

Magnetic recording is the topic of the following chapter by IBM Almaden’s John Baglin, who discusses the ever-increasing demand for higher and higher disk-drive densities and how ion-beam techniques can help to achieve them. After briefly discussing some fundamental results that show the relative roles of ionization and collision processes for various ion beams and energies, he shows how ion-beam mixing (as opposed to ion implantation) can be used in some applications even in an industrial environment, where one might normally expect such a technique to be prohibitively expensive. He points out that spatial resolution issues can also be resolved in the application of ion-beam processing to magnetic storage technology.

For many years one of the standard reference books on ion implantation was the treatise by Jim Hirvonen [“Ion Implantation,” J.K. Hirvonen, Ed., vol. 18 of “Treatise on Materials Science and Technology,” Academic Press, N.Y., 1980]. In the present volume, with two co-authors, he presents an updated review of ion implantation, ion-beam mixing and IBAD (ion-beam-assisted deposition), pointing out the strengths and weaknesses of each, as well as a realistic assessment of their applicability to a variety of research and manufacturing applications. In addition, the authors introduce a relatively new technique, GCIB (gas-cluster ion-beam technology) in whose development they played a major role. This powerful new tool has many similarities to the older techniques but also some characteristics that could not have been guessed by straightforward extension from the older ones. Many recent applications of GCIB technology are discussed, especially in the context of an industrial environment.

Peter Townsend’s monograph [P.D. Townsend, P.J. Chandler and L. Zhang, “Optical Effects of Ion Implantation,” Cambridge University Press, 1994] on the optical applications of ion implantation is now 10 years old, and he contributes herein (along with co-author P.J.T. Nunn) a chapter reviewing these. In addition to discussing the most recent developments in the field, as well as their relevance to industrial applications, he shares the results of many of his own innovative experiments on several aspects of this wide area.

One of the topics mentioned in Townsend and Nunn’s review, that of the non-linear properties of metallic nanoclusters in glasses, is further expanded by the Padova group led by Paolo Mazzoldi. Together with their Venetian colleagues (for centuries Venice has been known for its expertise in glass), they trace the history of the optical properties of metallic nanoclusters in glasses back to Faraday, who spoke of metallic inclusions as being responsible for the coloration of glasses. The most recent approach, as described in their chapter, shows how the use of binary alloy nanoclusters allows one to tune the optical properties of glasses by varying the relative composition of such alloys.

The next chapter, by Misra and Nastasi of Los Alamos National Laboratory, discusses an important aspect of thin-film preparation by ion bombardment that is all too often ignored in the literature: the stresses, both tensile and compressive, that can be generated by ion-beam methods, and the problems to which these can give rise (delamination for instance). They discuss the origins of such stresses at the atomic defect level and describe how varying ion-beam energy and dose can modify these to achieve the desired results.

While ion-beam techniques are now standard practice in the semiconductor industry, the demand for micro-devices of ever-smaller dimensions will require considerable refinement. An overview of current problems and their practical solution is provided in the chapter by Koji Matsuda and Masayasu Tanjyo, both with the Nissin Ion Equipment Co. Ltd. in Kyoto. Their discussion centers on the demands of production-line equipment in an industrial, rather than a pure R&D setting.

Daniel Gall’s chapter focuses on applying ion-beam techniques combined with physical vapor deposition to the eventual creation of complex nanostructures in transition metal nitrides. He provides examples of how nanopipes can be tailored and how atomic shadowing can create separated columns. Current and future work with deposition at shallow angles to the surface opens up the prospect of made-to-measure nanopillars, zigzag-shaped columns and helices, “nanoflowers,” and interconnected nanochannel arrays, to name just a few. Applications are anticipated in magnetic storage devices, photonics, opto-electronics and molecular transport, among others.

For many years, Bob Fleischer and his colleagues at GE–Schenectady have exploited a technique for producing nanometer-dimensioned pores in polymer films. Ion-beam irradiation is first used to loosen or break bonds in the polymer along the ion trajectory, then chemical etching preferentially removes atomic-scale material that is found along the ion tracks in the film. In Chapter 10, he recalls this work and updates it, discussing the mechanisms by which tracks are formed, and hence how the dimensions of the ensuing pores can be controlled. He also discusses track formation in other materials such as intermetallic compounds and oxide superconductors. Aside from the typical applications of these nanopores as filters, there are many others presented, ranging from the study of voltage pulses generated by viruses and sea-urchin sperm to improving the properties of superconductors by creating obstacles to the movement of magnetic flux lines.

The last chapter, by Jim Koch of the University of Connecticut, is a good example of the possibilities of innovation in this field. His work shows how fingerprints can be made permanent and hence more reliable as forensic evidence by recoil-mixing them into the substrate using ion beams. Not only does the record thus become permanent but the fingerprint (even if only a partial one) can then be subjected to very sensitive surface-analytical techniques that can identify not only its shape but also its chemical composition.

A Glossary is included at the end of the book for some terms that may not be familiar to all, given that the intended audience for this volume consists of those who are not already working in this particular field. The definitions provided are “practical” in nature and not intended to be rigorous, aiming rather to facilitate a fluid reading of the book without interruptions to consult references.

Finally, a compact disc that contains several video files to supplement the chapter on single-ion impacts (by Donnelly et al.) is included at the end of the book.

Chapter 2

Single Ion Induced Spike Effects on Thin Metal Films: Observation and Simulation

S.E. DONNELLY, R.C. BIRTCHER, AND K. NORDLUND

CONTENTS

Abstract

2.1 Introduction

2.2 Crater and Hole Formation

2.2.1 Ex Situ Studies of Crater Formation

2.2.2 In Situ Studies of Crater Formation

2.2.2.1 Gold

2.2.2.2 Silver

2.2.2.3 Lead

2.2.2.4 Indium

2.2.3 Crater Annihilation

2.2.4 In Situ Studies of Hole Formation

2.2.5 Craters and Holes — Discussion

2.2.4.1 Crater and Hole Annihilation — Discussion

2.3 Nanocluster Emission

2.3.1 Craters and Nanoparticles

2.3.2 Nanoparticle Collection

2.3.3 Radiation Effects on Nanoparticles

2.3.4 Nanoparticle Ejection Rates

2.3.5 Relationship of Nanoparticle Ejection to Cratering and Cascade Events

2.3.6 Nanoparticle Ejection Mechanisms

2.3.7 Ejected Nanoparticle Size Distribution

2.3.8 Shock Wave Model

2.3.9 Relationship of Nanoparticle Ejection to Sputtering

2.3.10 Synthesis

2.3.11 Summary of Nanoparticle Experiments

2.4 MD Molecular Dynamics Simulations of Crater Production

2.4.1 Monte Carlo Simulations versus Molecular Dynamics

2.4.2 Channeling Effects

2.4.3 MD Simulation Method

2.4.4 Formation of Ordinary Craters

2.4.4.1 Surface Damage Mechanisms

2.4.4.2 Basic Crater Formation Mechanism

2.4.5 Formation of Exotic Crater Structures

2.4.6 Analysis Based on MD

2.4.7 Observations of Nanocluster Ejection

2.5 Conclusions

Acknowledgments

References

ABSTRACT

The combination of in situ electron microscopy with molecular dynamics (MD) simulations gives important insights into the processes occurring during ion-beam engineering of thin films. This chapter compares and contrasts experimental observations and MD simulations of individual heavy-ion impacts on metal films. These impacts result in the formation of craters and other surface features on metals and the ejection of nano-particles. Images in the manuscript and video sequences on the accompanying CD-ROM illustrate the processes. The simulations of ion impacts match the experiment and give remarkable insight into the processes that give rise to the observed surface structures. Liquid flow and micro-explosions have been unequivocally identified in the MD work and provide an atomic-level understanding of the processes giving rise to cratering. An incomplete understanding exists of the emission of nanoclusters by ion impacts where the experimental size distribution of the emitted particles exhibits a power-law relationship, suggesting that this could be a shock-wave phenomenon. Although this is not, as yet, supported by the MD work, further simulations giving rise to improved statistics on nanocluster emission should enable a better comparison between experiment and simulation and thus serve to test this interpretation.

2.1 INTRODUCTION

Up to a certain energy density, the interaction of an energetic ion with a solid can be successfully described as a series of binary collisions involving the impinging ion and recoiling substrate atoms in what is generally described as a collision cascade. Monte Carlo simulation programs have been extremely successful in using this binary collision approach to estimate statistical parameters such as the distributions of implanted ions and of radiation damage (but neglecting any annealing processes that may take place). Under certain conditions of high energy-deposition density, this approach, however, is inappropriate. As first suggested by Brinkman [1,2], when the mean free path between displacing collisions approaches the interatomic spacing of the substrate, the interaction can no longer be regarded as one involving independent binary collisions and this description breaks down. In such cases, a small highly disturbed region is formed, in which the mean kinetic energy of the atoms may be up to several electronvolts per atom; this is known as an energy or displacement spike. At some time after the initial energy deposition (of order tens of picoseconds), the kinetic energy in the spike may be shared in a relatively continuous distribution by all the atoms within the spike region. Under some conditions this may give rise to an effective temperature within the spike zone significantly above that required for melting — this phase is generally referred to as a thermal spike or a heat spike.

These concepts of displacement and thermal spikes resulting from single ion impacts were first discussed in the scientific literature more than half a century ago; experimentally, however, until much more recently it has been difficult to obtain information about individual spike effects. This is because spikes are both small (typically a few nanometers in diameter) and of short duration (typically around 10 psec). To obtain information on spikes resulting from individual ions thus requires techniques with a high spatial resolution. As far as the time scale is concerned, no technique with adequate spatial resolution has a temporal resol...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Table of Contents
• Chapter 1 Introduction
• Chapter 2 Single Ion Induced Spike Effects on Thin Metal Films: Observation and Simulation
• Chapter 3 Ion Beam Effects in Magnetic Thin Films
• Chapter 4 Selected Topics in Ion Beam Surface Engineering
• Chapter 5 Optical Effects of Ion Implantation
• Chapter 6 Metal Alloy Nanoclusters by Ion Implantation in Silica
• Chapter 7 Intrinsic Residual Stress Evolution in Thin Films During Energetic Particle Bombardment
• Chapter 8 Industrial Aspects of Ion-Implantation Equipment and Ion Beam Generation
• Chapter 9 Nanostructured Transition-Metal Nitride Layers
• Chapter 10 Nuclear Tracks and Nanostructures
• Chapter 11 Forensic Applications of Ion-Beam Mixing and Surface Spectroscopy of Latent Fingerprints
• Glossary
• Index