Substrate Bias Voltage Tailoring the Interfacial Chemistry of a-SiC_x:H: A Surprising Improvement in Adhesion of a-C:H Thin Films Deposited on Ferrous Alloys Controlled by Oxygen

Abstract

Hydrogenated amorphous carbon thin films (a-C:H) have attracted much attention because of their surprising properties, including ultralow friction coefficients in specific conditions. Adhesion of a-C:H films on ferrous alloys is poor due to chemical and physical aspects, avoiding a widespread application of such a film. One possibility to overcome this drawback is depositing an interlayeran intermediate thin filmbetween the carbon-based coating and the substrate to improve chemical interaction and adhesion. Based on this, interlayers play a key role on a-C:H thin-film adhesion through a better chemical network structure at the outermost layer of the a-SiC x :H interlayer, i.e., the a-C:H/a-SiC x :H interface. However, despite the latest important advances on the subject, the coating adhesion continues being a cumbersome problem since it depends on multifactorial causes. Thus, the purpose of this paper is to report a standard protocol leading to surprising good results based on the control of the interfacial chemical bonding by properly biasing the substrate (between 500 and 800 V) during the a-SiC x :H interlayer deposition at an appropriate low temperature, by using hexamethyldisiloxane as precursor. The interlayers and the outermost interfaces were analyzed by a comprehensive set of techniques, including X-ray photoelectron spectroscopy, glow discharge optical emission spectroscopy, and Fourier transform infrared spectroscopy. Nanoscratch tests, complemented by scanning electron microscopy and energy-dispersive X-ray spectroscopy, were used to evaluate the critical load for delamination to certify and quantify the adhesion improvement. This study was important to identify the chemical local bonding of the elements at the interface and its local environment, including the in-depth chemical composition profile of the coating. An important effect is that the oxygen content decreases on increasing substrate bias voltage, improving the adhesion of the film. This is due to the fact that energetic ion hitting the growing interlayer breaks Si–O and C–O bonds, augmenting the content of Si–C and C–C bonds at the outermost interface of the a-SiC x :H interlayer and enhancing the a-C:H coating adhesion. Moreover, the combination of high bias voltage (800 V) and low temperature (150 °C) during the a-SiC x :H interlayer deposition allows good adhesion of a-C:H thin films due to sputtering of light elements like oxygen. Therefore, an appropriated bias and temperature combination can open new pathways in a-C:H thin-film deposition at low temperatures. These results are particularly interesting for temperature-sensible metal alloys, where well-adhered a-C:H thin films are mandatory for tribological applications.

Low resistivity amorphous carbon-based thin films employed as anti-reflective coatings on copper

“…Despite the tremendous progress of anti-reflective coatings of well-aligned one-dimensional nanostructures, such as carbon nanotubes, or 2D velvet-like carbon [8], a much simpler solution using amorphous carbon films (a-C) has also been shown to reduce reflection from the near UV to IR broadband spectrum [9][10][11]. Such a solution has the advantage that it is straightforward to implement in industrial thin film deposition [12][13][14].…”

Adhesion of Amorphous Carbon Nanofilms on Ferrous Alloy Substrates Using a Nanoscale Silicon Interlayer: Implications for Solid-State Lubrication

“…9,10 Previous works pointed out that the interfaces are the most favorable regions for delamination of thin films. 10,20,22 Figure 3a illustrates the analyzed regions (identified at an approximate depth of 0−450 nm) of the E −1 sample, as a typical analysis approach performed for all the samples. The collected electrons were photoemitted from the a-C film surface and subsurface, the outermost interface (a-C film/Si interlayer), the Si interlayer, and, finally, the innermost interface (Si interlayer/ferrous alloy substrate).…”

“…The chemical structure of Si-containing interlayers is generally connected to the adhesion behavior at the innermost (steel/interlayer) and the outermost (interlayer/a-C) interfaces of the interlayer. 20 When a high content of oxygencontaining molecules is in the deposition chamber atmosphere, dangling bonds at these interfaces are promptly filled with oxygen, leading to the low adhesion of the films. 21 The decrease in the content of undesirable molecules and residual gases, such as water vapor and oxygen, in the deposition chamber is proposed as one of the key factors reducing the oxygen in the structure of the deposited interlayer.…”

Nano‐Twisted Double Helix Carbon Debris Improves the Wear Resistance of Ultra‐Thick Diamond‐Like Carbon Coatings

“…Recently, many efforts have been devoted to produce high quality ultra‐thick DLC coatings, such as developing new technologies, designing interface, applying plasma treatments and so on. [ 12–14 ] For example, Wang et al [ 12 ] prepared an ultra‐thick DLC coating with a thickness of about 50 μm by hollow cathode plasma‐enhanced chemical vapor deposition method. The deposited ultra‐thick DLC coating has good tribological performance with a friction coefficient less than 0.2 in air condition.…”

“…The deposited ultra‐thick DLC coating has good tribological performance with a friction coefficient less than 0.2 in air condition. Figueroa et al [ 13 ] designed a Silicon (Si) containing interlayer and achieved a high adhesion force of the DLC coating on ferrous alloys by applying high‐bias voltage (800 V) and low temperature (150 °C). Oka and Yatsuzuka used a carbon ion implantation treatment after sputter cleaning to achieve the adhesion force of DLC coating of more than 70 MPa.…”