Fluorine containing amorphous carbon films (CFx, 0.16≤x≤0.35) have been synthesized by reactive high power impulse magnetron sputtering (HiPIMS) in an Ar/CF4 atmosphere. The fluorine content of the ...films was controlled by varying the CF4 partial pressure from 0mPa to 110mPa at a constant deposition pressure of 400mPa and a substrate temperature of 110°C. The films were characterized regarding their composition, chemical bonding and microstructure as well as mechanical properties by applying elastic recoil detection analysis, X-ray photoelectron spectroscopy, Raman spectroscopy, transmission electron microscopy, and nanoindentation. First-principles calculations were carried out to predict and explain F-containing carbon thin film synthesis and properties. By geometry optimizations and cohesive energy calculations the relative stability of precursor species including C2, F2 and radicals, resulting from dissociation of CF4, were established. Furthermore, structural defects, arising from the incorporation of F atoms in a graphene-like network, were evaluated. All as-deposited CFx films are amorphous. Results from X-ray photoelectron spectroscopy and Raman spectroscopy indicate a graphitic nature of CFx films with x≤0.23 and a polymeric structure for films with x≥0.26. Nanoindentation reveals hardnesses between ~1GPa and ~16GPa and an elastic recovery of up to 98%.
► We successfully synthesized CFx (0.16≤x≤0.35) thin solid films by using HiPIMS. ► All as-deposited CFx films were found to exhibit an amorphous microstructure. ► CFx films with x≤0.23 showed a graphitic nature. ► A polymeric structure for CFx films with x?≥0.26 was found. ► DFT calculations showed plasma species and defects relevant for the film formation.
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•The XPS charge referencing method that relies on Ar 2p peak of implanted Ar is evaluated.•Broad systematic study covers wide range of thin film sample materials of metals, nitrides, ...carbides, and borides.•Ar 2p3/2 peak shifts by as much as 5.1 eV depending on the sample, which disqualifies this charge referencing method.•Ar 2p peak position correlates to the number of valence electrons available for screening.•An additional Ar 2p doublet is observed assigned to Ar-N and Ar-C complexes stabilized by van der Waals forces.
Correct binding energy (BE) spectra referencing of insulating samples remains the major challenge in modern XPS analyses. Ar 2p signal of implanted Ar is sometimes used for this purpose. The method relies upon the assumption that chemically inert species such as noble gas atoms would be ideally suited as other factors affecting core level peak positions (such as chemical bonding) can be excluded. Here, we present a systematic study on the Ar 2p referencing method applied to a wide range of thin film sample materials of metals, nitrides, carbides, and borides. All specimens exhibit a well-defined Fermi edge, which serves as an independent internal reference for Ar 2p spectra of in-situ implanted Ar. Ar 2p3/2 binding energy is shown to vary by as much as 5.1 eV between samples. This is more than typical chemical shifts of interest, which obviously disqualifies Ar 2p referencing. The BE of the Ar 2p peaks shows a strong correlation to the number of valence electrons available for screening, implying that the polarization energy has a major role for the observed large spread of Ar 2p3/2 BE values. In several cases of single-phase films, an additional Ar 2p doublet is observed with the Ar 2p3/2 BE referenced to the vacuum level higher than the gas phase value of 248.6 eV, which is tentatively assigned to the formation of Ar-N and Ar-C complexes stabilized by Van der Waals forces. Ar implantation into two-phase samples, exemplified here by phase-segregated NiCrC/a-C:H and nanocomposite c-TiN/SiNx thin films, leads to complex Ar 2p spectra, which further demonstrates unreliability of the referencing method. The firm conclusion of the study is that the Ar 2p3/2 peak from implanted Ar is not a remedy for the charge referencing problem.
We demonstrate, for the first time, the growth of metastable single-phase NaCl-structure high-AlN-content Ti1−xAlxN alloys (x ≤ 0.64) which simultaneously possess high hardness and low residual ...stress. The films are grown using a hybrid approach combining high-power pulsed magnetron (HPPMS/HIPIMS) and dc magnetron sputtering of opposing metal targets. With HIPIMS applied to the Al target, Aln+ ion irradiation (dominated by Aln+) of the growing film results in alloys 0.55 ≤ x ≤ 0.60 which exhibit hardness H ∼ 30 GPa and low stress σ = 0.2–0.7 GPa, tensile. In sharp contrast, films with corresponding AlN concentrations grown with HIPIMS applied to the Ti target, giving rise to Tin+ ion irradiation (with a significant Ti2+ component), are two-phase – cubic (Ti,Al)N and hexagonal AlN – with low hardness, H = 18–19 GPa, and high compressive stress ranging up to 2.7 GPa. Annealing alloys grown with HIPIMS applied to the Al target results in age hardening due to spinodal decomposition; the hardness of Ti0.41Al0.59N increases from 30 to 33 GPa following a 900 °C anneal.
► High-AlN-content Ti1−xAlxN alloys with high hardness and low stress are grown. ► Hybrid HIPIMS/DCMS configuration with elemental metal targets is used. ► Different growth pathways are obtained depending upon which target is ran in HIPIMS. ► Destructive role of Ti2+ ions for film properties is demonstrated. ► Al-HIPIMS/Ti-DCMS alloys have high kinetic solid-solubility limit, xmax = 0.64.
We present an overview of the photoelectron spectroscopy studies of thin films of the commercially important, electrically conducting polymer blend poly(3,4-ethylenedioxythiophene) oxidized with ...poly(4-styrenesulfonate), PEDOT–PSS. The issues discussed include the study of thermal effects, the influence of hydrochloric acid on the chemical and electronic structures of the films, phase segregation, as well as the energy level alignment at interfaces employing a PEDOT–PSS layer. All of these issues are important in applications of PEDOT–PSS as a hole-injecting electrode in polymer-based, light-emitting devices. Among the most important results are the identification of the three chemically different species in pristine PEDOT–PSS, namely poly(4-styrenesulfonic acid), poly(sodium 4-styrenesulfonate) and poly(3,4-ethylenedioxythiophene), the conversion of the sodium salt into free poly(styrenesulfonic acid) upon HCl treatment, and the decomposition of the free sulfonic acid component (presumably through loss of SO
3H) induced by annealing. It is also shown that phase segregation occurs in the PEDOT–PSS system, resulting in a predominance of PSS in the surface region. This issue has been studied using different approaches, including X-ray photoelectron spectroscopy studies of the sulfur S(2p) and oxygen O(1s) core levels, ultraviolet photoelectron spectroscopy of the valence band region combined with reference measurements and quantum chemical calculations, as well as variable photon energy investigations of sulfur S(2p) core levels. It is demonstrated that, in the context of the energy level alignment at the polymer–metal interfaces, PEDOT–PSS shows metallic-like behavior. Due to the latter, the insertion of a thin PEDOT–PSS layer between the hole-injecting electrode ITO and a polymer layer of poly(bis-(2-dimethyloctylsilyl)-1,4-phenylenevinylene) leads to the lowering of the barrier for hole injection, independent of the work function of the underlying ITO. PEDOT–PSS is also used to show the alignment of the electrochemical potential across metal–polymer–metal structures.
Amorphous nitrides are explored for their homogeneous structure and potential use as wear-resistant coatings, beyond their much studied nano- and microcrystalline counterparts. (TiB2)1-xSixN thin ...films were deposited on Si(001) substrates by a hybrid technique of high power impulse magnetron sputtering (HIPIMS) combined with dc magnetron sputtering (DCMS) using TiB2 and Si targets in a N2/Ar atmosphere. By varying the sputtering dc power to the Si target from 200 to 2000W while keeping the average power to the TiB2-target, operated in HIPIMS mode, constant at 4000W, the Si content in the films increased gradually from x=0.01 to x=0.43. The influence of the Si content on the microstructure, phase constituents, and mechanical properties was systematically investigated. The results show that the microstructure of as-deposited (TiB2)1-xSixN films changes from nanocrystalline with 2–4nm TiN grains for x=0.01 to fully electron diffraction amorphous for x=0.22. With increasing Si content, the hardness of the films increases from 8.5GPa with x=0.01 to 17.2GPa with x=0.43.
•Amorphous (TiB2)1−xSixN thin films were deposited by HIPIMS/DCMS.•Si contents x≥0.22 yield fully electron-diffraction amorphous films.•Hardness increases from 8.5GPa with x=0.01 to 17.2GPa with x=0.43.•Electron-diffraction amorphous films are dense and without porosities.
Highly adherent carbon nitride (CNx) films were deposited using a novel pretreatment with two high power impulse magnetron sputtering (HIPIMS) power supplies in a master-slave configuration: one to ...establish the discharge and one to produce a pulsed substrate bias. During the pretreatment, SKF3 (AISI 52100) steel substrates were pulse-biased in the environment of a HIPIMS Cr plasma in order to sputter clean the surface and to implant Cr metal ions. Subsequently, CNx films were prepared at room temperature by DC unbalanced magnetron sputtering from a high purity graphite target in a N2/Ar discharge at 3mTorr. All processing was done in an industrial CemeCon CC800 system. A series of depositions were obtained with samples at different bias voltages (DC and pulsed) in the range of 0-800V. Scanning transmission microscopy (STEM) and high resolution transmission electron microscopy (HRTEM) show the formation of an interface comprising a polycrystalline Cr layer of 100nm and an amorphous transition layer of 5nm. The adhesion of CNx films evaluated by the Daimler-Benz Rockwell-C reach strength quality HF1, and the scratch tests gives critical loads of 84N. Adhesion results are correlated to the formation of an optimal interfacial mixing layer of Cr and steel.
•XPS binding energies (BEs) of group IVb-VIb transition metal carbides (TMCs) are reported.•TMCs are grown under the same conditions and analyzed in the same instrument.•Core level spectra free from ...Ar+-etch artefacts are presented.•For each row in the periodic table C 1s BE increases from left to right.•C 1s BE decreases linearly with increasing carbide/metal melting point ratio.
We report x-ray photoelectron spectroscopy (XPS) core level binding energies (BE’s) for the widely-applicable groups IVb-VIb transition metal carbides (TMCs) TiC, VC, CrC, ZrC, NbC, MoC, HfC, TaC, and WC. Thin film samples are grown in the same deposition system, by dc magnetron co-sputtering from graphite and respective elemental metal targets in Ar atmosphere. To remove surface contaminations resulting from exposure to air during sample transfer from the growth chamber into the XPS system, layers are either (i) Ar+ ion-etched or (ii) UHV-annealed in situ prior to XPS analyses. High resolution XPS spectra reveal that even gentle etching affects the shape of core level signals, as well as BE values, which are systematically offset by 0.2–0.5 eV towards lower BE. These destructive effects of Ar+ ion etch become more pronounced with increasing the metal atom mass due to an increasing carbon-to-metal sputter yield ratio. Systematic analysis reveals that for each row in the periodic table (3d, 4d, and 5d) C 1s BE increases from left to right indicative of a decreased charge transfer from TM to C atoms, hence bond weakening. Moreover, C 1s BE decreases linearly with increasing carbide/metal melting point ratio. Spectra reported here, acquired from a consistent set of samples in the same instrument, should serve as a reference for true deconvolution of complex XPS cases, including multinary carbides, nitrides, and carbonitrides.
The influence of the Ti–Si cathode grain size on cathodic arc processes and resulting Ti–Si–N coating synthesis has been studied. 63mm Ti–Si cathodes containing 20–25at.% Si with four dedicated grain ...size of ~8μm, ~20μm, ~110μm, and ~600μm were fabricated via spark plasma sintering or hot isostatic pressing. They were evaporated in 2Pa nitrogen atmosphere in an industrial-scale arc deposition system and the Ti–Si–N coatings were grown at 50A, 70A, and 90A arc currents. The composition and microstructure of the virgin and worn cathode surfaces as well as the resulting coatings were characterized using optical and electron microscopy, X-ray diffraction, elastic recoil detection analysis, X-ray photoelectron spectroscopy, and nanoindentation. The results show that the existence of multiple phases with different work function values directly influences the cathode spot ignition behavior and also the arc movement and appearance. Specifically, there is a preferential erosion of the Ti5Si3-phase grains. By increasing the grain size of the virgin cathode, the preferential erosion is enhanced, such that the cathode surface morphology roughens substantially after 600Ah arc discharging. The deposition rate of the Ti–Si–N coating is increased with decreasing grain size of the evaporated Ti–Si cathodes. The droplet number density and the droplet shape of the coatings are influenced by the arc movement, which is also shown to depend on the cathode grain size.
•A decrease of the average roughness of the worn cathode surface by two orders of magnitude•A smoother and more continuous arc movement•Smaller macroparticles (droplets) in the coatings•A higher deposition rate of Ti–Si–N coatings
The reactive high power impulse magnetron sputtering processes of carbon in argon/tetrafluoromethane (CF4) and argon/octafluorocyclobutane (c-C4F8) have been characterized. Amorphous carbon fluoride ...(CFx) films were synthesized at deposition pressure and substrate temperature of 400mPa and 110°C, respectively. The CFx film composition was controlled in the range of 0.15<x<0.35 by varying the partial pressure of the F-containing gases from 0mPa to 110mPa. The reactive plasma was studied employing time averaged positive ion mass spectrometry and the resulting thin films were characterized regarding their composition, chemical bonding and microstructure as well as mechanical properties by elastic recoil detection analysis, X-ray photoelectron spectroscopy, transmission electron microscopy, nanoindentation, and water droplet contact angle measurements, respectively. The experimental results were compared to results obtained by first-principles calculations based on density functional theory. The modeling of the most abundant precursor fragment from the dissociation of CF4 and C4F8 provided their relative stability, abundance, and reactivity, thus permitting to evaluate the role of each precursor during film growth. Positive ion mass spectrometry of both fluorine plasmas shows an abundance of CF+, C+, CF2+, and CF3+ (in this order) as corroborated by first-principles calculations. Only CF3+ exceeded the Ar+ signal in a CF4 plasma. Two deposition regimes are found depending on the partial pressure of the fluorine-containing reactive gas, where films with fluorine contents below 24at.% exhibit a graphitic nature, whereas a polymeric structure applies to films with fluorine contents exceeding 27at.%. Moreover, abundant precursors in the plasma are correlated to the mechanical response of the different CFx thin films. The decreasing hardness with increasing fluorine content can be attributed to the abundance of CF3+ precursor species, weakening the carbon matrix.
•The growth of CFx films by reactive HiPIMS was demonstrated in CF4/Ar and C4F8/Ar.•Fluxes of abundant ion species in the plasma agree with our ab initio calculations.•Thin film properties depend on abundant precursor species in the plasma.•HiPIMS in C4F8 is beneficial regarding the controllability of the film properties.•HiPIMS in CF4 is an accessible tool for the functionalization of film surfaces.
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