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 interlayeran intermediate thin
filmbetween 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.
TiO 2 is one of the most investigated semiconducting materials and is used in a wide range of applications, e.g. in photocatalysis for water splitting, decomposition of pollutants and selfcleaning windows [1][2][3][4], in memory capacitors and transistors as the dielectric material [5], in lithium-ion batteries as anode material [6][7][8], in gas and humidity sensors [9,10], in antireflective coatings [11] and in paints, paper, food and personal care products as white pigment [12], etc. Crystalline TiO 2 in bulk form is typically found in two tetragonal structures, anatase and rutile phases, and in one orthorhombic structure, brookite phase [2,13]. However, in thin films, only anatase and rutile have been observed [14,15]. Among these phases, anatase possesses the highest photocatalytic activity in spite of its higher band gap (~3.2 eV versus ~3.0 eV for rutile) due to better carrier mobility [16,17], and the best properties for lithium-ion intercalation due to its special 3D crystal structure that contains many open channels for insertion/extraction of Li ions [7,8,18].
The surface behaviour of surface mechanical attrition treated (SMATed) and plasma-nitrided AISI 2205 and AISI 304L steels was investigated in the present study. The intersection of the mechanical twins formed the submicron-size rhombic blocks in the surface region of the SMATed AISI 304L steel. However, such microstructural feature was absent in the SMATed AISI 2205 steel. The improvement in the surface-hardness due to the SMAT was about 70-80% for AISI 2205, and more than 100% for AISI 304L steel. The nature of passive film formed on the AISI 2205 steel was different from the AISI 304L steel. Passive film formed on the SMATed AISI 304L steel was relatively more unstable than that of the AISI 2205 steel at an elevated electric-potential and in a plasma environment. The plasma-nitriding response was affected due to the different passivation behaviour of the SMATed, and non-SMATed steels.
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