Nanoscale investigation of enhanced electron field emission for silver ion implanted/post-annealed ultrananocrystalline diamond films

Kalpataru Panda,I.-Nan Lin,Sundaravel Balakrishnan,Jeong Young Park,Jeong Jin Hyeok,Kamatchi Jothiramalingam Sankaran

doi:10.1038/s41598-017-16395-1

Abstract

Silver (Ag) ions are implanted in ultrananocrystalline diamond (UNCD) films to enhance the electron field emission (EFE) properties, resulting in low turn-on field of 8.5 V/μm with high EFE current density of 6.2 mA/cm2 (at an applied field of 20.5 V/μm). Detailed nanoscale investigation by atomic force microscopy based peak force-controlled tunneling atomic force microscopy (PF-TUNA) and ultra-high vacuum scanning tunneling microscopy (STM) based current imaging tunneling spectroscopy (CITS) reveal that the UNCD grain boundaries are the preferred electron emission sites. The two scanning probe microscopic results supplement each other well. However, the PF-TUNA measurement is found to be better for explaining the local electron emission behavior than the STM-based CITS technique. The formation of Ag nanoparticles induced abundant sp2 nanographitic phases along the grain boundaries facilitate the easy transport of electrons and is believed to be a prime factor in enhancing the conductivity/EFE properties of UNCD films. The nanoscale understanding on the origin of electron emission sites in Ag-ion implanted/annealed UNCD films using the scanning probe microscopic techniques will certainly help in developing high-brightness electron sources for flat-panel displays applications.

Highlights

Nowadays electron sources based on the field emission (FE) concept, namely “cold-cathodes”, are substituting the conventional thermionic electron sources
In contrast to standard Scanning tunneling microscopy (STM)-based current imaging tunneling spectroscopy (CITS) measurements that require the sample surfaces to be smooth at nanometer scale, tunneling atomic force microscopy (TUNA) can investigate surfaces with a root mean squared (RMS) roughness of several micrometers, which allows a wide picture of the overall morphology to be scanned
ultra-nanocrystalline diamond (UNCD) (Ag0) films via the Ag-ion implantation (Ag17D) and Ag-ion implantation/post-annealing (Ag17DA) processes are shown in the FESEM analysis in Fig. S1 of the supplementary information

Summary

Introduction

Nowadays electron sources based on the field emission (FE) concept, namely “cold-cathodes”, are substituting the conventional thermionic electron sources. Among the most extensively investigated nanostructured materials for cold cathode applications, carbon nanotubes[4,5,6,7], graphene8‒11and graphdiyne[12,13] have a prominent place, because of their superior FE properties These nanocarbon based electron field emission (EFE) materials face the challenge of insufficient lifetime stability[4,5,6,7,8,9,10,11,12,13]. In contrast to constant-current mode STM, physical tracking of the sample surface in TUNA means that the height data collected from the deflection of the cantilever avoids possible artifacts introduced by variations in the conductivity of the sample surface Another major advantage of TUNA is that it has a very high current sensitivity with a current measurement range up to 120 pA and a noise level of 50 fA. It should be noted that TUNA is not the same as conducting AFM where the tip is always in contact with the sample surface that can change the tip condition and may not always show the true electronic properties of the sample surface

Methods

Results

Conclusion