[en] The nanocrystallites of NiFe_2O_4 have been successfully synthesized by gas phase condensation using the dc thermal plasma arc method (NF-1) and by the chemical co-precipitation method (NF-2). The field emission studies were carried out on as-synthesized NF-1 and compared with NF-2 nanoparticles. The emission characteristic shows that NF-1 particles have a low turn-on field of 2.3 V μm"−"1 as compared to NF-2 particles, which have a turn-on field of 3.5 V μm"−"1. The Fowler–Nordheim plots obtained from the current–voltage characteristics show overall linear behavior as expected from the quantum mechanical tunneling phenomenon. Our results show that both nanoparticles exhibit good emission stability as an emitter without severe deviations from the initial set value. The highly faceted surfaces, along with high crystallinity of NF-1 nanoparticles, is responsible for improved field emission properties than that of NF-2 prepared by the chemical co-precipitation method. (paper)

[en] In this paper we report our results on nanosecond laser based surface micro (μ)-structuring of Tantalum (Ta) samples and their field emission behavior. Surface micro-structuring has been carried out using a typical laser fluence of 0.9 J cm⁻² and varying number of incident laser pulses in the range of 3000 to 9000. Laser treated samples have been characterized in terms of surface morphology, chemical phase and field emission behavior. Nanosecond laser irradiation resulted in formation of self assembled surface μ-protrusions in the laser treated region. Peak height of the generated μ-protrusions and average roughness of the laser treated region increased with increasing number of irradiating laser pulses. Laser treated specimens have shown enhanced field emission in comparison to pristine Ta specimen. Specimens μ-structured using 3000, 6000 and 9000 laser pulses per spot have shown field emission with turn on field (E_on) of 6.6 V⁻¹ μm⁻¹, 4.8 V ⁻¹ μm⁻¹ and 3.7 V ⁻¹ μm⁻¹, respectively. Also, maximum emission current density delivered by these laser modified specimens was found to increase with increasing number of laser pulses. Although, Ta specimen μ-structured with 9000 laser pulses has shown highest emission current density, emission current stability of this sample was poorer in comparison to specimens modified using 3000 and 6000 laser pulses. (paper)

[en] Carbon nanofibers (CNFs) and carbon nanotubes (CNTs) are grown on inconel substrates under two different experimental conditions using atmospheric pressure glow discharge radio-frequency (RF) PECVD process. A specially designed hollow cathode is used for this plasma generation. The growth is carried out at 610 and 660 °C substrate temperatures on inconel substrates. Our results show that CNFs and CNTs could be synthesized at 610 and 660 °C respectively irrespective of pre-treatment methods in either set. HRTEM results indicate that a temperature-induced transformation of CNFs into CNTs occur when the growth temperature is raised from 610 to 660 °C. With the help of characterization results and a schematic model, it is shown how an increase in hydrogen diffusion (∼44% increase) plays a pivotal role in this transformation by providing a sink for hydrogen atoms. Field emission results show that most defective CNFs contribute to the maximum emission current density. This better field emission behavior is explained on the basis that the outer surfaces of CNFs are more defective due to the presence of the open edges of the graphene planes, which results in better field emission from the outer surfaces of the CNFs. (paper)