Electromechanical Photoemission and Field Emission Properties of Ultrananocystalline Diamond Films
Pérez Quintero, Kenneth J.
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Diamond materials have been the subject of intensive research for decades. Since the fabrication of diamond structures by chemical vapor deposition was demonstrated in the 1960’s, research and developments effor boomed. In 1994, ultrananocrystalline diamond(UNCD)films were developed in a microwave plasma assisted chemical vapor deposition!(MPCVD)!reactor!for!the!first!time!at!Argonne!National!Laboratory.!Later,!it! was demonstrated thatUNCD’s electrical conductivity properties could be tuned into semiRmetallic and evensuperconducting via the addition of dopants during synthesis. Particularly, the addition of nitrogen during MPCVD growth allowed growth of n"type electrically conductive UNCD films. In this work, we report the synthesis and characterization of NUNCD thin films for various applications. The first application is the development of a NUNCD hydrogen-terminated(NUNCD(H)) photocathode for photoinjector applications. Hydrogen-terminated materials display negative!electron affinity (NEA).In NEA materials, electrons from the conduction band can be emitted directly into the vacuum. Photocathodes displaying NEA are bright electron sources because they have high quantum efficiency (QE). The NUNCD(H) photocathode displayed a QE of ~10R3 at 254nm, which of interest to the photoinjector’s R&D community.The NUNCD(H) PC was also sensitive in the visible range at 405nm and 440nm. The experimental details and future directions are presented in this work. Secondly, a planar NUNCD field emission cathode (FEC) was developed and was tested in an RF electron injector. The emission from the NUNCD grain boundaries allowed the simple geometry of the FEC, avoiding lithography and transfer steps.The NUNCD FEC demonstrated peak!currents of 1 –80 mA at gradients of 45 –65MV/m.Thecurrent stability was tested over the course of an hour with excellent results.Raman spectroscopy and electron microscopy characterization done after testing demonstrated the FEC’s robustness. Finally, an NUNCD based nanoelectromechanical (NEM) switch was developed via an electron beam lithography / reaction ion etching (EBLRRIE) fabrication pathway. The fabrication pathway is demonstrated and the optimization of each fabrication step is presented. The!fabricated NUNCD NEM switch exhibited intrinsic compressive stress in the NUNCD nanowire source element. Previous research efforts suggest stress engineering can be achieved by reducing the pressure during the MPCVD growth or by increasing the thickness of the NUNCD layer. The results are discussed at length. The results presented in this work showcase the properties of NUNCD films and properties that have the potential for commercial applications.