Single-Wall Carbon Nanotubes Field Emission Properties: A Theoretical Study of the Effects of Cs
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AA8.6.1
Single-Wall Carbon Nanotubes Field Emission Properties: A Theoretical Study of the Effects of Cs Brahim Akdim1, Xiaofeng Duan2, Donald A. Shiffler3, and Ruth Pachter1* Air Force Research Laboratory, Materials & Manufacturing Directorate and 2Aeronautical Systems Center Major Shared Resource Center for High Performance Computing, WrightPatterson Air Force Base, OH; 3Air Force Research Laboratory, Directed Energy Directorate, Kirtland Air Force Base, NM. 1
ABSTRACT Carbon nanotubes-based materials appeal for explosive emission, in forming cathode plasma, of interest for high-power microwave tubes. Cs intercalation has demonstrated a significant reduction of the work function of carbon nanotubes, thus improving field emission properties. An understanding of the detailed adsorption effects is important because the current saturation is attributed, in part, to adsorption mechanisms. In this paper, we report a density functional theory study of the effects of Cs on field emission of single-wall carbon nanotubes (SWCNTs), as an example of an approach to be taken for a fundamental understanding of such properties. INTRODUCTION Carbon nanotubes could be utilized for energetic applications, for example, by oxidation of the iron nanoparticles embedded within SWCNTs, when exposed to a bright flash of white light [1], or by hydrogen sorption [2]. Carbon nanotubes also attracted considerable attention for field emission, due to emitting high currents (up to 1A/cm2) at low field (ca. 5V/µm) [3], including high current electron beams. Most recently, the use of explosive emission in forming cathode plasma has been noted [4], which is of interest for field emission cathodes in high-power microwave tubes [5]. Because current saturation was attributed primarily to adsorption [6], we have previously studied theoretically the current suppression upon oxygen adsorption [7,8]. On the other hand, intercalation of alkali metals, such as Cs intercalation, which affects the properties of carbon nanotubes [9], showed a significant reduction of the work function of SWCNTs [10,11]. An understanding of these governing effects is key for such nanodevices fabrication [12,13,14]. Indeed, although an improvement in the emission properties has been previously noted in a theoretical study of Cs intercalation, an extended system was investigated [15]. In this work, we summarize a preliminary study on the field emission properties upon Cs adsorption at the tips of SWCNTs, studying both capped and uncapped systems, and applying an electric field to mimic the experimental emission environment for different tip geometries. Theoretical studies of adsorption were also found to be useful for energetic applications [16]. *
Corresponding author: E-Mail: [email protected]
AA8.6.2
COMPUTATIONAL DETAILS The calculations were performed using an all-electron linear combination of atomic orbitals density functional theory (DFT) approach [17], shown to be adequate for modeling SWCNTs [18,19], using the double numerical polarized (DNP) basis set. Th
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