Carbon Nanotube Electron Sources for Electron Microscopes
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Carbon Nanotube Electron Sources for Electron Microscopes Niels de Jonge1, Jim T. Oostveen1, Theo van Rooij1, Myriam Allioux1,*, Maya Doytcheva1, Monja Kaiser1, Kenneth B. K. Teo2, Rodrigo G. Lacerda2,** and William I. Milne2. 1
Philips Research, Prof. Holstlaan 4, 5656 AA Eindhoven, The Netherlands.
2
Department of Engineering, University of Cambridge, Trumpington Street,
Cambridge CB2 1PZ, United Kingdom. *Present address: ESPCI Paris, 10 Rue Vauquelin 75005 Paris, France. **Present address: Universidade Federal de Minas Gerais, Departamento de Física, Av. Antonio Carlos, 6627, 30123-970, Belo Horizonte, MG, Brazil. ABSTRACT High-quality electron sources can be made from individual multi-walled carbon nanotubes. A process was developed allowing the control over 1) the length of the fraction of the nanotube protruding from the support tip, 2) the contact length of the nanotube with the support tip, 3) the diameter of the nanotube. In addition, the cap of the nanotube was closed and the nanotube was cleaned thoroughly. The field emission model successfully describes the electron emission process of these electron sources and the work function is 5.1 eV. The emitters show a highly stable emission, as expected on account of the extremely stable structure of the carbon nanotube. INTRODUCTION Carbon nanotubes can be used as high-quality electron sources. The general idea is that carbon nanotubes have an advantage over field emitters from metals due to their large aspect ratio and extremely strong structure [1]. Several types of devices are under active consideration, for example, field emission displays [2], lighting elements [3], X-ray sources [4,5] and electron sources for electron microscopes [6]. Most groups perform measurements on emitters containing a multiple of carbon nanotubes in a film, matrix or in a bundle. Yet, for precise investigations of the relation between the structure of a carbon nanotube and its electron emitting behavior it is required to perform measurements on single carbon nanotubes. A second complication is that the nanotube has to be perfectly clean. This first section of this article describes a method
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to make high-quality electron sources from individual carbon nanotubes. The successive sections describe the precise investigation of the emission behavior and the emission stability. PREPARATION OF HIGH-QUALITY ELECTRON SOURCES FROM INDIVIDUAL CARBON NANOTUBES
Figure 1. Mounting procedure of a carbon nanotube electron source. (A) A carbon nanotube (CNT) protruding from a thin substrate containing many nanotubes is attached to a tungsten support tip. (B) The carbon nanotube is broken by Joule heating. (C) The open tube end is finally closed. Already in 1995 electron emitters were made consisting of single carbon nanotubes with the help of micromanipulators and an optical microscope [7]. This method was improved by employing nano-manipulators inside a scanning electron microscope (SEM) [8], thereby avoiding the (undesired) mounting of bundles of carbon nanotubes, or mult
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