Metal coated, fs-laser fabricated silicon spikes as electron emitters for cold cathode applications
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Metal coated, fs-laser fabricated silicon spikes as electron emitters for cold cathode applications. Emmanuel Spanakis,1,3,4 Marios Barberoglou,1,2 Panagiotis Tzanetakis,1,2 and Costas Fotakis1,2 1 Foundation for Research & Technology – Hellas, Institute of Electronic Structure and Laser, Heraklion GR-71110, Greece. 2 Department of Physics, University of Crete, Vassilika Vouton, GR-711 10, Heraklion, Greece. 3 Department of Materials Science and Technology, University of Crete, Ampelokoipi GR-710 03, Heraklion, Greece 4 Department of Sciences, Technological Educational Institute of Crete, GR-710 04, Heraklion, Greece. ABSTRACT We have studied the effect of thin metal coatings on the electron emission characteristics of self-assembled silicon microstructures with nearly identical sharp features. We have employed a common template of spikes produced by fs-laser self-driven structuring of Si on which several different metals have been deposited. We find that, in the pristine state and in vacuum conditions achievable in device applications, all metal coatings do not result in marked change of either the minimum electric field necessary for emission or the maximum obtainable current density. In contrast, the durability of the emitters depends strongly on the metal used and is always enhanced with respect to bare Si. Furthermore, no signs of degradation were found within the 3-day time scale of our experiments with gold and chromium. On the contrary, these two metal coatings resulted in emission characteristics improving with time in typical operation conditions. INTRODUCTION In the last few years a considerable amount of research effort is being devoted in the development of efficient and durable tip-array cold electron emission cathodes for flat panel cathodoluminescent displays (or FEDs) [1]. Of the oldest materials used were refractory metals [2] and metal oxides [3,4]. Formation of good emitters on silicon is also pursued as these could be readily integrated to current Si-based microelectronics fabrication schemes for deep miniaturization in other applications [5]. In this work we try to evaluate the overall cold-electron emission performance of high aspect ratio self-assembled silicon spikes coated with several different metallic films. In our approach geometry is the same in all cases thus eliminating a potential contribution to the experimental results. The silicon spikes are formed by ultra-fast laser ablation of its surface [6,7]. We take advantage of the unique morphology of these spikes to use them as low threshold field templates. The metals we have employed for the coatings span a range of work functions from 2.9 eV (Gd) to 5.4 eV (Au). Tungsten and Molybdenum were chosen because they are commonly utilized as single tip cathodes in electron guns. Chrome and Titanium were also chosen as metallic alternatives, with similar work function, to n-type silicon. EXPERIMENT A single 2 x 1 cm2 wide area template with spikes has been fabricated by microstructuring Si under femtosecond (fs) laser irradiatio
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