Ultrathin amorphous carbon films synthesized by filtered cathodic vacuum arc used as protective overcoats of heat-assisted magnetic recording heads

J Matlak,K Komvopoulos

doi:10.1038/s41598-018-27528-5

J Matlak, K Komvopoulos

Open Access

https://doi.org/10.1038/s41598-018-27528-5

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Journal: Scientific Reports	Publication Date: Jun 25, 2018
Citations: 19	License type: open-access

Affiliation: University of California, Berkeley

Abstract

Despite numerous investigations of amorphous carbon (a-C) films, a comprehensive study of the feasibility and optimization of sub-5-nm-thick a-C films deposited onto the write pole of heat-assisted magnetic recording (HAMR) heads is lacking. The main objective of this study was to identify the role of pulse substrate bias voltage and C+ ion incidence angle on the structure and thickness of 1–4-nm-thick a-C films deposited by a rather new thin-film deposition method, known as filtered cathodic vacuum arc (FCVA). The cross-sectional structure of a-C films synthesized under various FCVA conditions was examined by high-resolution transmission electron microscopy (HRTEM), scanning transmission electron microscopy (STEM), and electron energy loss spectroscopy (EELS). It was found that film growth under process conditions of low-to-intermediate substrate bias voltage (in the range of −25 to −100 V), low ion incidence angle (10°), very short deposition time (6 s), and fixed other deposition parameters (65% duty cycle of substrate pulse biasing and 1.48 × 1019 ions/m2·s ion flux) yields a-C films of thickness ≤4 nm characterized by a significant content (~50–60 at%) of tetrahedral (sp3) carbon atom hybridization. A threshold where sp3 hybridization is greatly reduced due to limited film growth was determined from the HRTEM/STEM and EELS measurements. The results of this study demonstrate the viability of FCVA to produce extremely thin and uniform protective a-C films with relatively high sp3 contents for HAMR heads.

Highlights

Ultrathin, amorphous carbon (a-C) films are extensively used as protective overcoats of magnetic recording media, because they demonstrate exceptional mechanical properties and structural stability[1]
A comparison of the high-resolution transmission electron microscopy (HRTEM) images shown in the right column of Fig. 1 indicates a decrease in film thickness with increasing ion incidence angle, consistent with the results of a previous filtered cathodic vacuum arc (FCVA) study of relatively thicker a-C films[27]
The multilayered a-C film structure revealed by HRTEM and scanning transmission electron microscopy (STEM)/energy loss spectroscopy (EELS) results can be interpreted in the context of the subplantation model[28]

Summary

Introduction

Amorphous carbon (a-C) films are extensively used as protective overcoats of magnetic recording media, because they demonstrate exceptional mechanical properties and structural stability[1]. FCVA is the only demonstrated and scalable low-temperature technique for synthesizing continuous and ultrathin a-C films with excellent nanomechanical/tribological properties, including high hardness and wear resistance[4]. Such films can withstand large temperature fluctuations while maintaining their structural stability[19,20], mainly because of the dominance of sp[3] hybridization. A significant fraction of sp[3] carbon atom hybridization is critical for preventing rapid structural destabilization and graphitization of the film due to laser heating during the write process of a HAMR head. Previous studies of ultrathin a-C films synthesized by the FCVA method have shown the formation of a multilayered film structure comprising an interface (intermixing) layer, a buffer layer with gradually increasing sp[3] fraction, a bulk layer of constant and high sp[3] content, and a surface layer with sp[3] hybridization sharply decreasing toward the film surface[22]

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