Field emission through diamond/Mo interfaces
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Myers, .d.Cuomo, J.J Hren
Departmentof MaterialsScience and Engineering North CarolinaState University,Raleigh, NC 27695, USA E-mail: [email protected]
Abstract The influence of interfacial nanostructure on electron emission from diamond coated Mo emitters is presented. Diamond coating is known to increase electron emissivity, but interfacial oxides and an amorphous layer change the magnitude. After annealing, emissivity was enhanced further and Mo 2C was formed at the interface, as well as a decrease in the oxides and amorphous layers. The shape of the FEM image changed but no individual emitting sites were observed. Possible mechanisms causing these changes are discussed. Introduction Recently there has been increased interest in vacuum microelectronic devices, especially for flat panel displays. To improve field emission properties, diamond field emitters are being developed and show promising results [1-4]. Diamond possesses many desirable properties, such as a wide band gap (5.4 eV), current stability, and negative electron affinity (NEA) on several faces after certain surface treatments [5]. Previous results indicate that high current emission at a low electric field is possible from diamond coated field emitters, but the reasons are not clear. Several studies explain the high emissivity as due to defects state in the gap[6], others due to conducting channels in the diamond [7] and high n-type doping [2 ].The high emissivity from diamond coatings can be explained by the low electron effective mass in diamond and by substitutional nitrogen doping, which produces a state located 1.7eV below the conduction band minimum [8]. Even if the diamond/vacuum surface exhibits NEA, the diamond/metal interface remains a barrier to the electron supply. A lower interfacial barrier could provide higher electron emissivity and more stable electron emission. However, it is well known that the electrical properties are sensitive to the electronic structure of interfaces. Research has been reported on metal/diamond interfaces. Carbide formation tends to show ohmic contact at the interface such as Moazed et al. [9 ] reported an ohmic contact on Mo/diamond interfaces after annealing. Tachibana et al.[ 10] and Gildebalt et al. [11 ] suggested a titanium carbide formed during annealing may alter the Schottky barrier to form an ohmic contact. S. Mikhailov et al.[12 ] reported the formation of Mo 2C carbide at a temperature as low as 400 'C on a Mo deposited CVD diamond. In this study, diamond coating and subsequent annealing effects on the interface between diamond and Mo are correlated with the electron emission properties. To clarify the mechanisms, I-V characteristics, FEM images, and electron energy distribution data were taken before and after annealing on the same emitters and the same interface was examined later by TEM.
339 Mat. Res. Soc. Symp. Proc. Vol. 448 ©1997 Materials Research Society
Experimental Procedure Mo emitters were fabricated by electrochemical etching. High pressure high temperature (HPHT) type Ib diamon
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