Field emission study from tantalum surfaces micro-structured with femtosecond pulsed laser irradiation
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Field emission study from tantalum surfaces micro-structured with femtosecond pulsed laser irradiation A. K. Singh1 · S. R. Suryawanshi2 · M. A. More2 · Sucharita Sinha3 Received: 5 April 2018 / Accepted: 20 July 2018 © Springer-Verlag GmbH Germany, part of Springer Nature 2018
Abstract This paper presents our results on surface micro-structuring of tantalum samples using femtosecond (fs) pulsed laser irradiation and its effect on field emission performance. Micro-structuring of Ta targets has been carried by varying laser fluence in the range 0.35–0.55 J/cm2 while keeping target scan speed constant at 25 µm/s. Laser-treated surfaces have shown the formation of high density micro-protrusions and an oxide phase mainly consisting of crystalline T a2O5. Our results showed substantial improvement in field emission performance of laser micro-structured surfaces in comparison to pristine Ta surface. Areal number density of micro-protrusions decreases from 8.8 × 105 to 3.5 × 105 protrusions/cm2 as incident laser fluence varied from 0.35 to 0.55 J/cm2. Ta sample micro-structured with 0.55 J/cm2 laser fluence has shown low turn on field (~ 4.0 ± 0.6 Vµm− 1) and high-field enhancement factor (4500 ± 500).
1 Introduction Field emitting cathodes offer several advantages over their thermionic counterparts. These advantages include high energy efficiency [1], compact size, high brightness [1], fast switching capability (up to few GHz) [2], low energy spread of the emitted electrons [3], low operating temperature, and long cathode lifetime [4]. Due to their aforementioned advantages, field emitting cathodes have been replacing the conventional thermionic emitting cathodes in many applications. Apart from replacing thermionic cathodes in the existing technologies, there are various applications which have become possible only due to invention of field-emitting cathodes. Some of the interesting applications of fieldemitting cathodes are space craft charging measurement and control [5], electron sources in free electron lasers [6], electron source in FESEM [7], X-ray tubes [8], microwave generation, and RF amplification [9, 10].
* A. K. Singh [email protected] 1
Laser and Plasma Technology Division, Bhabha Atomic Research Centre, Mumbai 400085, India
2
Department of Physics, Savitribai Phule Pune University, Pune, India
3
Laser and Plasma Surface Processing Section, Bhabha Atomic Research Centre, Mumbai 400085, India
Field emission cathodes can be either in the form of single tip or large area cathodes consisting of a large number of emitting sites. Although single tip field emitting cathodes can deliver electron beam with higher brightness in comparison to large-area field-emitting cathodes (LAFEC), they are restricted in terms of lower current carrying capacity. Therefore, in applications which require large current along with high current density, LAFEC are employed. Hence, the development of LAFEC with low turn on electric field and capable of delivering stable large emission current is of significance. Emis
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