Field emission enhancement ofamorphous carbon nitride films bythe addition ofargontothereactive gasofnitrogen

Carbon-based films suchasamorphous carbon (a-C), nanocrystalline diamond, diamond-like carbon havebeenproved tobeabetter electron field emitter withamuchhigher site density and lowerthreshold field. Inparticular, theaddition ofnitrogen willimprove thefield emission properties ofthese carbon-based films because nitrogen isthebest n-type dopant withits atomic sizesimilar tothatofcarbon andisshallow donorbelowtheconduction bandina-C[t]. Therefore, amorphous carbon nitride (a-CN,) film isconsidered asuperior field emission material toa-C.Recently wehavereported someresults about field emission froma-CNx films deposited inthepureN2[2]. Herewewill discuss theeffect oftheaddition ofArtoreactive gasofN2onthe field emission properties ofa-CNx fiLms. Thesamples ofa-CNx films wereprepared onSi(001) substrate byRFmagnetron sputtering method under thebasepressure of5X104Pa.TheCN-film samples aredeposited for30minat powersupply 150W without anysubstrate biasvoltage andtemperature. During deposition, Aris added tothereactive gasofN2while theflowratio ofN2andArisincreased frompureN2to1:1 andupto1:5atafixed reactive gaspressure. Theelectron field emission ofas-deposited a-CNx films wasmeasured inaparallel plate configuration withanode-to-sample spacing of100pm 107 2.(using glass fiber spacers) ata 10 Pavacuum.Thea-CNxfilm of0.5cminsizeisused asthe cathode. While increased bias voltage isapplied between theelectrodes, thecurrent flowing tothe ITOanodeismeasured using anAmperemeter. Besides, thechemical bonding ofa-CNxfilms is analyzed using Photoluminescence (PL)spectra, laser confocal Ramanspectroscopy (Renishaw Inc.) andX-ray photoelectron spectroscopy (XPS) (VGESCALABMK II) using MgKaradiation. Thesurface roughness ofthefilms ischaracterized byatomic force microscope (AFM). Figure. 1showsPLspectra ofa-CNxfilms atdifferent flowrates ofN2andAr.Itcanbeseen clearly that twoemission peaks appear ataround 1.85 and2.3eV, whichshould arise fromthe recombination ofoptically excited carriers inXandx*states ofsp2-bonded cluster, similar to a-C:Hfilms [3]. Whentheaddition ofArisenhanced, theintensity oftwoPLpeaks also increases markedly, signifying theenhancement ofsp2-bonded cluster contents inthea-CN. films. Figure.2 and3showtheXPSNIsandRamanspectra atdifferent flowrates ofN2andAr,respectively.