Structural, Nanomechanical, and Field Emission Properties of Amorphous Carbon Films Having Embedded Nanocrystallites Deposited by Filtered Anodic Jet Carbon Arc Technique
This paper reports the effect of substrate bias on the structural, nanomechanical, and field emission properties of amorphous carbon films having embedded nanocrystallites (a-C:nc films) deposited by filtered anodic jet carbon arc technique. X-ray diffraction results exhibit predominantly an amorphous nature of the films. High-resolution transmission electron microscope images showed the amorphous nature of the films with nanocrystallites embedded in the amorphous matrix. Ultrafine nanograined microstructures with average grain size between 20 and 30？nm are observed throughout the film with a majority of the grains of single crystallites. A strong influence of substrate bias has been observed on the structural, nanomechanical, and field emission properties. Maximum nanohardness (H) of 58.3？GPa, elastic modulus (E) of 426.2？GPa, and H/E of 0.136 have been observed in a-C:nc films deposited at ？60？V substrate bias which showed 82.6% sp3 content. 1. Introduction Amorphous carbon films have been center of attention for a variety of applications due to their chemical inertness, high optical transparency in the visible and near infrared, good adhesion to different substrates, low surface roughness, and good electrical, mechanical, and field emission properties [1–10]. The a-C films have been deposited by various techniques such as filtered cathodic vacuum arc (FCVA) [11–15], pulsed laser deposition (PLD) [16], sputtering, and electron cyclotron resonance (ECR) [17]. Compared to other deposition techniques, FCVA process offers the unique opportunity of growing different forms of carbon ranging from diamond-like to graphite-like and various intermediate materials such as tetrahedral amorphous carbon (ta-C), hydrogen and nitrogen incorporated ta-C (ta-C: H, ta-C: N), nanoclusters, nanocomposites, and nanotubes. The properties of carbon films mainly depend on the process parameters such as substrate bias, system geometry, pressure, arc current, and arc voltage and the environmental conditions during the growth of the films. There are established theoretical [18] and experimental [19] methods for the formation of different carbon nanostructures such as nanotube and fullerene by arc discharge. Amaratunga et al. [19–21] reported the deposition of hard and highly elastic carbon films which consist of graphitic sp2 bonding using a graphite cathode with localized high pressure of helium or nitrogen at the arc spot. Depending upon whether the gas is injected through the cathode or anode, the technique will be termed as cathodic jet carbon arc (CJCA) or anodic jet carbon
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