Work Function Characterization of Potassium-Intercalated, Boron Nitride Doped Graphitic Petals

Patrick T Mccarthy,Timothy S Fisher,Dmitry Zemlyanov,Rajib Paul,Ronald G Reifenberger

doi:10.3389/fmech.2017.00006

Patrick T Mccarthy, Timothy S Fisher + Show 3 more

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https://doi.org/10.3389/fmech.2017.00006

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Abstract

This paper reports on characterization techniques for electron emission from potassium-intercalated boron nitride modified graphitic petals. Carbon-based materials offer potentially good performance in electron emission applications owing to high thermal stability and a wide range of nanostructures that increase emission current via field enhancement. Furthermore, potassium adsorption and intercalation of carbon-based nanoscale emitters decreases work functions from approximately 4.6 eV to as low as 2.0 eV. In this study, boron nitride modifications of graphitic petals were performed. Hexagonal boron nitride is a planar structure akin to graphene and has demonstrated useful chemical and electrical properties when embedded in graphitic layers. Photoemission induced by simulated solar excitation was employed to characterize the emitter electron energy distributions, and changes in the electron emission characteristics with respect to temperature identified annealing temperature limits. After several heating cycles, a single stable emission peak with work function of 2.8 eV was present for the intercalated graphitic petal sample up to 1000 K. Up to 600 K, the potassium-intercalated boron nitride modified sample exhibited improved retention of potassium in the form of multiple emission peaks (1.8 eV, 2.5 eV, and 3.3 eV) resulting in a large net electron emission relative to the unmodified graphitic sample. However, upon further heating to 1000 K, the unmodified graphitic petal sample demonstrated better stability and higher emission current than the boron nitride modified sample. Both samples deintercalated above 1000 K.

Highlights

Carbon nanomaterials exhibit many excellent thermal, optical, and mechanical properties including but not limited to high thermal stability and high optical absorption, making them good candidates for thermionic and photoemission processes (Avouris et al, 2008; Yang et al, 2008; Castro Neto et al, 2009; Westover et al, 2010; Duyvuri et al, 2012)
Data resulting from the first heating cycle are not discussed in detail here as significant variation in Photoemission electron energy distributions (PEEDs) occurred owing to oxidized surface product bake off from the samples
Assisted photoemission from graphitic petals (GPs) and boron nitride modified GPs intercalated with potassium was studied in the present work as a method of identifying sample work functions

Summary

Introduction

Carbon nanomaterials exhibit many excellent thermal, optical, and mechanical properties including but not limited to high thermal stability and high optical absorption, making them good candidates for thermionic and photoemission processes (Avouris et al, 2008; Yang et al, 2008; Castro Neto et al, 2009; Westover et al, 2010; Duyvuri et al, 2012). Research in the field of electron emission often focuses on reducing the energy barrier in a material that an electron must overcome for emission, referred to as the work function. Obraztsov has performed extensive research in both classical and non-classical field emission of nanostructured carbon materials demonstrating reduced turn-on voltages of field emission and reduced work functions relative to carbon structures with macro or micro scale features (Obraztsov et al, 2000, 2002, 2003). Previous work has demonstrated that carbon nanofibers, nanotubes, and nanowalls intercalated with potassium exhibit significantly reduced work functions and are relatively stable near room temperature in vacuum (Robinson et al, 2005; McMullen, 2010; Westover et al, 2010; Vander Laan, 2011)

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