Comparing Field Emission Stability of Lithography-free, Modified Multi-walled Carbon Nanotubes
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1204-K18-22
Comparing Field Emission Stability of Lithography-free, Modified Multi-Walled Carbon Nanotubes Archana Pandey, Abhishek Prasad, Jason Moscatello, and Yoke Khin Yap Department of Physics, Michigan Technological University, Houghton, MI 49931, U.S.A.
ABSTRACT Field emission from carbon nanotubes (CNTs) has been known for more than a decade but there is no commercialized product available in the market. Apparently, we need to improve our basics understanding on stable field emission from CNTs. Here we compared the field emission properties of as grown vertically-aligned multi-walled carbon nanotubes (MWCNTs) to two types of modified MWCNTs: 1) Conical bundles of opened-tip MWCNTs, and 2) Openedtip MWCNTs embedded in poly-methyl methacrylate (PMMA). We found that both types of modified MWCNTs have lower emission thresholds and better emission stability than the as grown samples. Among these modified samples, MCNTs embedded in PMMA has lower emission thresholds and better emission stability. We attributed these improvements to the filling of spacing between MWCNTs with PMMA that has higher dielectric constant than vacuum.
INTRODUCTION Tremendous efforts have been evidenced on the study of electron field emission from carbon nanotubes (CNTs). Although this property has been known for more than a decade [1], commercial field emission products based on CNTs is still not available. The possible reason for this situation is that the basic science for stable field emission still requires further investigation. Research efforts reported so far focused mainly on the low emission threshold fields (Eth) of various types of CNTs and the design of device configurations. However, long term emission stability, for example continuous emission test for more than 10 hours, has not been sufficiently discussed [2-8]. We have focused our efforts in understanding basic factors that contribute towards stable field emission from CNTs. We found that graphitic order of CNTs is one of the key factors for stable emission [9, 10]. In the present paper, we describe the methodology to increase the long term emission stability from multiwalled carbon nanotubes (MWCNTs) while keeping the emission threshold electric field low. We have found two simple and effective techniques for improving field emission stability of vertically-aligned MWCNTs without involving lithography processes: 1) self-assembled conical bundles of opened-tip VA-MWCNTs, 2) Opened-tip VA-MWCNTs embedded in poly-methyl methacrylate (PMMA). The opened-tip conical nanotube bundles were prepared by acid etching of the residual Ni catalysts at the tips of as grown VA-MWCNTs. The etched samples will self-assembled in to regular arrays of conical bundles. The PMMA embedded samples were prepared by dip-coating
of the as-grown VA-MWCNTs with PMMA followed by mechanical polishing to expose the tips of these VA-MWCNTs. All these samples were then compared for their current density versus applied electric field (J-E) properties, long-term emission stability for continuous emissi
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