C1s Core Level Research Articles

Identification of chemical species on plasma-treated polytetrafluoroethylene surface by ab-initio calculations of core-energy-level shift in X-ray photoelectron spectra

X-ray photoelectron spectroscopy (XPS) measurements and ab-initio calculations of the XPS chemical shift were performed to identify chemical species on plasma-treated polytetrafluoroethylene (PTFE) surfaces. The obtained C1s-XPS and O1s-XPS spectra confirmed the generation of oxygen-containing functional groups on plasma-treated PTFE surfaces. We investigated the effect of the substitution of F atoms in a CF2– chain by H atoms on the C1s core level binding energy in PTFE; our calculations showed that the C1s core level binding energy is linearly dependent on the number of substituted F atoms. This finding enables us to infer the number of substituted F atoms from the experimentally observed C1s-XPS spectra. We deconvoluted the experimentally observed C1s-XPS spectra of the plasma-treated PTFE surfaces using the calculated binding energies of various functional groups. It is impossible to reproduce the C1s-XPS spectra using the C1s core level binding energies of functional groups in the CF2– chain. However, they can be well reproduced by adding the calculated binding energies of the functional groups in the CH2– chain, indicating the substitution of the F atoms by the H atoms by plasma treatment. Furthermore, the time-of-flight secondary ion mass spectrometry confirmed the existence of H atoms on the plasma-treated PTFE surfaces.

Pressureless manufacturing of high purity Ti3AlC2 MAX phase material: Synthesis and characterisation

The reported study involves the synthesis of high purity layered ternary carbide Ti3AlC2 MAX phase material by mixing the TiH2, Al and TiC powders in a planetary ball mill followed by two step pressureless sintering in flowing Argon (Ar) atmosphere. XRD and Raman analysis confirms the presence of Ti3AlC2 phase without impurities of Al2O3 and TiC. The morphology studies using SEM confirms the lamellar structure of Ti3AlC2 and EDS measurements shows atomic percentage of Ti, Al and C are in compliance with the XRD phase analysis. X-ray Photoelectron spectroscopy investigations confirm the Ti–C bond. Core level XPS data of Al2p peak show a negative shift indicating electrostatic bonding of Al in Ti3AlC2. Ti2p and C1s core level spectra show the bonding of Mn+1Xn i.e TiC bond. TG-DSC results revealed approximately 7% increase in weight. Ti3AlC2 phase follows an endothermic pattern and does not undergo decomposition upto 1400 °C in vacuum environment. From XRD analysis at different temperatures, it was seen that Al2O3 and TiCx peaks started to form along with Ti3AlC2 at 1000 °C because of selective oxidation of Al into Al2O3. Thus, this study provides a beneficial approach to synthesis of high-purity Ti3AlC2 materials and understanding the thermal behaviour of Ti3AlC2 for high temperature applications.

In English

The hexagon-shape graphene nanoflakes (GNFs) limited by zigzag edges only (with doubly and triply coordinated atoms) have unique increased reactivity. Despite the high systems symmetry (D6h) the Carbon atoms in GNFs occupy non-equivalent positions. Can such physical and chemical characteristics of GNFs, which depend of the atom position in the cluster, definition? This characteristic together with the simplicity of its calculation makes it possible to predict the properties of nanoflakes obtained from GNFs by introducing single and multiatomic vacancies into them or by replacing Carbon atoms with electron withdrawing and electron donating atoms. This characteristic includes the C1s core-level binding energy shifts, the maxima of which characterize the C atoms of a certain type. The proposed work is devoted to quantum chemical calculations of the electronic density of states (DOS) of pristine hexagon-shape GNF C96 (multiplicity, M=5), their saturated counterpart –polycyclic aromatic hydrocarbon(PAH) C96H24 (M=1) and their derivatives with one and two single vacancies in the ground electronic state (GES). All calculations were performed using the density functional theory (DFT) method with the involvement of the valence-split basis set 6-31G (d,p). Systems with open shells were considered using the UB3LYP exchange-correlation functional. The obtained spectra were fitted using Gaussian curve fitting program to determine the binding energy for each peak. The Gaussian function distribution of the theoretically calculated C1s core-level binding energy shifts of GNFs testified the presence of six peaks, each of which refers to a certain type of Carbon atoms. The C1s peak with the highest binding energy (-285.57 eV) is caused by contributions from the doubly coordinated edge cyclic chain (ECC) Carbon atoms. The C1s orbitals of the central hexagon (CHex) atoms and the first cyclic chain (FCC) atoms form delocalized molecular orbitals (MOs) in different parts of the cluster. The analogous spectrum of PAH C96H24 is slightly shifted to the region of lower binding energies and contains only two well-defined peaks. The peak with a higher binding energy (-284.36 eV) is generated by the 1s states of the CHex atoms and the atoms of the FCC, which are bounded to the CHex atoms. The electronic DOS difference in C1s core-level spectra of GNF C96 (M=5) and their saturated counterpart PAH C96H24 is established due to the presence of two weakly bounded π-systems in GNF and common conjugated system in PAH. The electronic DOS of defect-containing cluster C96-1(1) (M=3) (one CHex atom has been removed from the C96nanoflake) is generated by the C1s core-level atoms of the second cyclic chain (SCC), which are located at the different distances from the center of the nanoflake. The peak of the lowest intensity (-284.63 eV) appears in the spectrum as a reflection of the appearance of doubly coordinated Carbon atoms surrounding the single vacancy in the C96-1(1) nanoflake. The analysis of the electronic DOS of the C1s core-level spectrum of the C96-2(1) nanoflakeis shown, that doubly coordinated Carbon atoms, concentrated around two single vacancies, are essentially non-equivalent. If the MO with the lowest binding energy is localized on two of them – the MO with the highest binding energy is localized on the third atoms (one around each single vacancy). The electronic C1s core-level DOS spectrum of defect-containing molecular systems with one C96-1(1)H24 and two C96‑2(1)H24 single vacancies are similar to the analogous spectrum of PAH C96H24. In the first of them – one additional maximum appears due to C1s atoms surrounding the single vacancy. In the second – there are two additional maxima, each of which is generated by C1s core-level atoms adjacent to individual vacancies.

Operando photoelectron spectroscopy analysis of graphene field-effect transistors

In this study, operando photoelectron spectroscopy was used to characterize the performance of graphene field-effect transistors under working conditions. By sweeping the back-gate voltages, the carrier concentration of the graphene channel on the 150 nm Si3N4/Si substrate was tuned. From the C1s core level spectra acquired under the application of different gate voltages, the binding energy shifts caused by electric-field effects were obtained and analyzed. Together with the C1s peak shape information and the photoluminescence spectrum of the Si3N4/Si substrate, the presence of local potential across the x-ray beam spot associated with defects and gate leakage current in amorphous Si3N4 was identified. The presence of defects in Si3N4/Si substrate could not only screen the partial electric field generated by the back gate but also serve as long-range scattering centers to the carriers, thus affecting charge transport in the graphene channel. Our findings will help further investigate the dielectric/graphene interface properties and accelerate the utilization of graphene in real device applications.

The effect of structural disorder on the hydrogen loading into the graphene/nickel interface

Hybrid materials composed by porous Ni foams coated by graphene appear appealing architectures to be applied in the field of hydrogen storage, where, due to the high surface-to-volume ratio of both components, are expected to be much more performant than their flat counterparts. In order to explore this possibility, in this study we have grown single layer graphene on nickel foams by chemical vapour deposition in ultra-high vacuum and have investigated the interaction with H atoms as a function of the temperature. By using high resolution C1s core level spectroscopy we found that nearly half of the graphene layer interacts with the support almost as strongly as with the flat ordered Ni substrate, whereas the other half is nearly free standing. Such dual electronic and structural coupling drives the hydrogenation of the graphene/foam interface. By using thermal programmed desorption combined with x-ray photoelectron spectroscopy we found that in the weakly interacting graphene regions, even at very low temperatures, H atoms easily intercalate below graphene, and enter in the bulk of the foam, from where they start to desorb around 180 K. This behaviour mimics what happens when dosing H atoms on the bare Ni foam. On the contrary, H intercalation below the strongly interacting graphene regions occurs only for temperatures around and above 200 K. The thermal desorption curves demonstrated that the presence of the graphene layer does not reduce the effectiveness of H loading in the bulk of the foam. On the other hand, it does not even increase significantly the stored amount with respect to the uncoated support, but contributes to stabilizing the stored hydrogen. Although the fundamental aspects of graphene/foam hydrogenation were here investigated in a regime far below the saturation of the bulk absorption, these measurements can be the starting point for further investigations aimed at establishing the ultimate storage capability of these hybrid nanostructured tanks.

XPS, UV–Vis, XRD, and PL spectroscopies for studying nickel nanoparticle positioning effect on nanocomposite film properties

AbstractThis work studies the impact of positioning nickel nanoparticles (Ni‐NPs) on the surface of doped (P84‐PEO) nanocomposite films by using an ultra‐uniform magnetic field as a model for positioning magnetic NPs inside a polymeric matrix. This process is used to achieve desired and adjustable optoelectronic properties and to obtain new optical and electrical characteristics. P84‐PEO copolymer doped with Ni‐NPs exposed to a 450 mT magnetic field during the preparation give rise to a momentous increase in surface roughness, surface reactivity, and modified optical parameters, besides forming Ni oxides on the surface. Based on X‐ray photoelectron spectroscopy experiments, substantial extra shifts occurred in the binding energies of photo‐excited electrons from the O1s and C1s core levels. Additionally, the deconvoluted O1s spectra displays an additional photoelectron peak at 530.0 eV, most likely attributed to oxidized Ni‐NPs at the surface. Moreover, optical and structural properties were studied using UV–Vis and PL spectroscopy and X‐ray diffraction.

Li-ion solvation in TFSI and FSI -based ionic liquid electrolytes probed by X-ray photoelectron spectroscopy

For Li-ion batteries, the Li-ion solvation in liquid electrolytes is a crucial parameter affecting directly the electrochemical cycling performance. X-ray photoelectron spectroscopy (XPS) can play an essential role for investigating the cation and anion electronic structure and monitoring the Li-ion solvation into various solvent and salt environments. In this contribution, we demonstrate the capability of conventional laboratory XPS using Al Kα X-ray source to determine the anions solvation shell of Li+ cation within the low vapour pressure and vacuum compatible ionic liquid electrolytes. 1M of LiTFSI and 1M of LiFSI salts dissolved in (EMIM+-FSI-) and (EMIM+-TFSI-) ionic liquids respectively are investigated by acquiring the F1s, N1s, C1s, S2p and Li1s core levels. The binding energy difference between the N1s component originating from the EMIM+ cation and the N1s component originating from TFSI- or FSIanions solvating the Li+ confirms that both TFSI- and FSIcontribute simultaneously to the Li+ solvation. Additionally, the stability of the TFSI and FSI -based ionic liquid electrolytes is carefully discussed for long X-ray exposure times.

C–Si bonded two-dimensional hole gas diamond MOSFET with normally-off operation and wide temperature range stability

A C–Si bonded SiO2/diamond interface is formed under a SiO2 mask during the selective diamond growth at a high temperature in a H2 atmosphere including methane (5%). A few monolayers with C–Si bonding at the SiO2/diamond surface are confirmed through X-ray photoelectron spectroscopy at the C1s and Si2p core levels from 290 eV to 271 eV and 107 eV–95 eV, respectively. In addition, secondary ion mass spectroscopy results suggest that the C–Si bonds, and not C–H bonds, are majority at the interface and are mainly responsible for the field effect transistor (FET) operation. Two-dimensional hole gas C–Si diamond metal–oxide–semiconductor FET (MOSFETs) are fabricated using the C–Si diamond sub-surface as a p-channel. The MOSFETs in which the actual length from the source to the drain (LSD) is 12 μm–6 μm show appreciable field-effect mobility (e.g. 140 cm2V−1s−1 at LSD = 12 μm and 300 K) and normally-off operation. The wide temperature characteristics of the C–Si MOSFETs are confirmed and the device shows high stability, and a high on/off ratio of 106 is maintained at 673 K. The C–Si bonding at the SiO2/diamond interface provide a lower interface state density which makes the MOSFET show high drain current density and field-effect mobility with normally-off operation.

Near ambient pressure X-ray photoelectron spectroscopy monitoring of the surface immobilization cascade on a porous silicon-gold nanoparticle FET biosensor

Porous silicon (PSi) offers extremely attractive optical, electronic and biofunctional properties for the development of biosensors. In the present work, we have studied the step by step sandwich biofunctionalization cascade of a PSi platform by near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) and, in parallel, we have developed a three electrode PSi device sensitive to changes in surface conductance. Prior to the NAP-XPS characterization, the organosilanization with glycidyloxy-propyl-trimethoxy-silane, the bioconjugation, and the gold nanoparticle (AuNP) sensitization layer were monitored by spectroscopic ellipsometry. The NAP-XPS analysis revealed outstanding results: a) the NAP-XPS chamber allows detecting the pristine PSi with negligible adventitious carbon contamination, b) the single oxygen bonded carbon component of the Glycidyl group dominates the C1s core level after organosilanization, c) the good progress of the biofunctionalization/recognition is confirmed by the increase of the silica to silicon component ratio in the Si2p core level and, d) the N1s core level describes identical features from the presence of aminoacid sequences in the capture/detection steps. A FET sensing of a prostate specific antigen (PSA) marker was performed through conjugation with AuNPs. For a given concentration of PSA (and AuNPs) the conductance increased with the increase of the gate voltage. For a given gate voltage, the conductance was observed to increase for increasing concentration of PSA. This allowed proposing a calibration line for the biosensor, which is valid from a clinically relevant range of 0.1 ng/mL.

Influence of surface crystal-orientation on transfer doping of V2O5/H-terminated diamond

Surface transfer doping of hydrogen-terminated diamond induced by high work function V2O5 oxide was investigated on samples with (100) and (111) surface crystal-orientations. An enhancement of sheet hole density and a decrease in sheet resistance were obtained in the case of (111) diamond as compared to (100). In particular, a sheet resistance as low as 1.8 kΩ/◻ and a sheet hole concentration of 1.1 × 1014 cm−2 were obtained by Hall effect measurements for V2O5/H-(111) oriented diamonds, the latter being about twice as high as the one obtained for V2O5/H-(100) oriented diamonds. This was confirmed by capacitance-voltage measurements on metal/V2O5/H-diamond diodes fabricated on the investigated samples, also resulting in the determination of the depth profiles of hole accumulation layers at the diamond surface. X-ray photoelectron spectroscopy measurements of the C1s core level shift were used to determine the differences in surface band bending, leading to a different hole accumulation layer formation efficiency at the V2O5/H-diamond interface. An upward band bending of 0.7 eV and 0.3 eV in response to the surface transfer doping induced by a 10 Å thick V2O5 layer was measured for (111) and (100) diamond surfaces, respectively. This is a further confirmation that V2O5 is more effective in surface transfer doping for H-(111) oriented diamond. The obtained results are very promising in view of the development of high-power metal oxide field effect transistors based on the H-diamond surface.

Core electron binding energies of adsorbates on Cu(111) from first-principles calculations.

Core-level X-ray Photoelectron Spectroscopy (XPS) is often used to study the surfaces of heterogeneous copper-based catalysts, but the interpretation of measured spectra, in particular the assignment of peaks to adsorbed species, can be extremely challenging. In this study we present a computational scheme which combines the use of slab models of the surface for geometry optimization with cluster models for core electron binding energy calculation. We demonstrate that by following this modelling strategy first principles calculations can be used to guide the analysis of experimental core level spectra of complex surfaces relevant to heterogeneous catalysis. The all-electron ΔSCF method is used for the binding energy calculations. Specifically, we calculate core-level binding energy shifts for a series of adsorbates on Cu(111) and show that the resulting C1s and O1s binding energy shifts for adsorbed CO, CO2, C2H4, HCOO, CH3O, H2O, OH, and a surface oxide on Cu(111) are in good overall agreement with the experimental literature.

Boosting surface charge-transfer doping efficiency and robustness of diamond with WO3 and ReO3

An advanced charge-transfer yield is demonstrated by employing single monolayers of transition-metal oxides—tungsten trioxide (WO3) and rhenium trioxide (ReO3)—deposited on the hydrogenated diamond surface, resulting in improved p-type sheet conductivity and thermal stability. Surface conductivities, as determined by Hall effect measurements as a function of temperature for WO3, yield a record sheet hole carrier concentration value of up to 2.52 × 1014 cm−2 at room temperature for only a few monolayers of coverage. Transfer doping with ReO3 exhibits a consistent narrow sheet carrier concentration value of around 3 × 1013 cm−2, exhibiting a thermal stability of up to 450 °C. This enhanced conductivity and temperature robustness exceed those reported for previously exposed surface electron acceptor materials used so far on a diamond surface. X-ray photoelectron spectroscopy measurements of the C1s core level shift as a function of WO3 and ReO3 layer thicknesses are used to determine the respective increase in surface band bending of the accumulation layers, leading to a different sub-surface two-dimensional hole gas formation efficiency in both cases. This substantial difference in charge-exchange efficiency is unexpected since both surface acceptors have very close work functions. Consequently, these results lead us to consider additional factors influencing the transfer doping mechanism. Transfer doping with WO3 reveals the highest yet reported transfer doping efficiency per minimal surface acceptor coverage. This improved surface conductivity performance and thermal stability will promote the realization of 2D diamond-based electronic devices facing process fabrication challenges.

Partial reduction of graphene oxide upon intercalation into exfoliated manganese thiophosphate

We have prepared novel nanohybrid Li2xMn1−xPS3/GO films consisting of graphene oxide (GO) and exfoliated MnPS3 nanosheets via an easy mixing protocol at room temperature. These films were investigated by SEM and AFM, as well as XRD, Raman and XPS spectroscopies, obtaining information about the nature of the interaction between MnPS3 and GO. In particular, the dark colour of the nanocomposite film and, more to the point, the analysis of (i) the C1s core level XPS spectra, (ii) the interlayer spacing obtained by XRD measurements and (iii) the increment in the intensity ratio ID/IG of the two bands typical of the carbon region of GO Raman spectra, suggest that a partial reduction of GO can be obtained right upon intercalation into Li2xMn1−xPS3.

The low threshold voltage n-type silicon transistors based on a polymer/silica nanocomposite gate dielectric: The effect of annealing temperatures on their operation

In this work, povidone/silica nanocomposite dielectric layers were deposited on the n-type Si (100) substrates for application in n-type silicon field-effect transistors (FET). Thermogravimetric analysis (TGA) indicated that strong chemical interactions between polymer and silica nanoparticles were created. In order to examine the effect of annealing temperatures on chemical interactions and nanostructure properties, annealing process was done at 423–513K. Atomic force microscopy (AFM) images show the very smooth surfaces with very low surface roughness (0.038–0.088nm). The Si2p and C1s core level photoemission spectra were deconvoluted to the chemical environments of Si and C atoms respectively. The obtained results of deconvoluted X-ray photoelectron spectroscopy (XPS) spectra revealed a high percentage of silanol hydrogen bonds in the sample which was not annealed. These bonds were inversed to stronger covalence bonds (siloxan bonds) at annealing temperature of 423K. By further addition of temperature, siloxan bonds were shifted to lower binding energy of about 1eV and their intensity were abated at annealing temperature of 513K. The electrical characteristics were extracted from current-Voltage (I-V) and capacitance-voltage (C-V) measurements in metal-insulator-semiconductor (MIS) structure. The all n-type Si transistors showed very low threshold voltages (−0.24 to 1V). The formation of the strongest cross-linking at nanostructure of dielectric film annealed at 423K caused resulted in an un-trapped path for the transport of charge carriers yielding the lowest threshold voltage (0.08V) and the highest electron mobility (45.01cm2/Vs) for its FET. By increasing the annealing temperature (473 and 513K) on the nanocomposite dielectric films, the values of the average surface roughness, the capacitance and the FET threshold voltage increased and the value of FET electron field-effect mobility decreased.

Thermally induced modification of the graphene oxide film on the tantalum surface

The interface chemical reactions, the deoxygenation and the overall thermal stability of the ex situ deposited graphene oxide (GO) thick film on the polycrystalline tantalum surface were studied by means of x-ray photoelectron spectroscopy (XPS) at room temperature and after annealing up to 600°С. The evolution of the Ta4f, C1s and O1s XPS core level spectra from the Ta/GO structure under study upon the increase of the annealing temperature was investigated with the reference to the uncovered Ta substrate surface. In the Ta/GO structure the Ta relative atomic concentration was about 1% at room temperature due to the low porosity of the GO layer while the thermal desorption of the overlayer at the elevated temperatures was accompanied by an increase of the Ta concentration up to 47% at 500°С. The C atoms relative concentration started decreasing after the annealing at 250°С accompanying the thermal desorption of the GO overlayer. The formation of the TaC compound starting from the 250°С annealing temperatures was determined. The relative oxygen concentration in the GO thick film was decreased upon increasing the annealing temperature accompanying both the thermal desorption of the GO material and the thermal reduction of the GO film.

High resolution core level spectroscopy of hydrogen-terminated (1 0 0) diamond

Synchrotron-based photoelectron spectroscopy experiments are presented that address a long standing inconsistency in the treatment of the C1s core level of hydrogen terminated (1 0 0) diamond. Through a comparison of surface and bulk sensitive measurements we show that there is a surface related core level component to lower binding energy of the bulk diamond component; this component has a chemical shift of eV which has been attributed to carbon atoms which are part of the hydrogen termination. Additionally, our results indicate that the asymmetry of the hydrogen terminated (1 0 0) diamond C1s core level is an intrinsic aspect of the bulk diamond peak which we have attributed to sub-surface carbon layers.

Doping mechanism of MoO3in 4,4′-Bis(N-carbazolyl)-1,1′-biphenyl: A photoelectron spectroscopic study

The doping mechanism of molybdenum oxide (MoO3) in the hole transport material 4,4′-Bis(N-carbazolyl)-1,1′-biphenyl (CBP) is explored extensively using photoelectron spectroscopy. Doping limit and doping efficiency are investigated in dependence on the MoO3 content. In addition, shape changes in Mo3d and C1s core level spectra of doped layers are compared to the respective emissions of the pristine materials. Using density functional theory (DFT) calculations, the additional feature in the C1s emission can be assigned to CBP+ cations and in the Mo3d emission a Mo5+ species can be identified. Therefore, charge transfer can not only be deduced indirectly from the movement of the Fermi level within the CBP energy gap, but also directly in the formation of cations of the matrix and anionic dopant species. Finally, the dopant morphology in dependence on the MoO3 content is derived indirectly from XPS measurements and is correlated to the observed doping efficiency. Because MoO3 precipitates form in the CBP matrix as evident from TEM measurements, the bilayer interface band alignment is analyzed by stepwise evaporation of CBP onto a MoO3 layer. The results of the interface experiment show that the CBP:MoO3 doping behavior can be well understood with the internal interface charge transfer doping model.

Oxidation of Planar and Plasmonic Ag Surfaces by Exposure to O2/Ar Plasma for Organic Optoelectronic Applications

ABSTRACTHere, we expose planar and plasmonic Ag surfaces to a low-power O2/Ar plasma to form an ultrathin surface oxide layer. We study the chemical state and morphology of the plasma-treated Ag surfaces using X-ray photoelectron spectroscopy, scanning electron microscopy, and dark-field microscopy. We observe the formation of an ultrathin layer (< 10 nm) composed of both AgOx and Ag2CO3 for a plasma exposure time of 1 s by investigating shifts in the Ag3d, O1s, and C1s core level binding energies. For an exposure time of 1 s, the surface structure of the planar and plasmonic Ag surfaces remains unchanged. For exposure times of 5 - 30 s, the planar Ag surfaces become porous and exhibit increased surface roughness. We demonstrate that the plasma-treated planar and plasmonic Ag surfaces lead to improvements in the excited-state population of a polymer:fullerene coating through ultrafast pump-probe reflectometry.

Unravelling the roles of surface chemical composition and geometry for the graphene–metal interaction through C1s core-level spectroscopy

Here we show that by using a combined experimental and theoretical approach it is possible to separate the contributions to the interaction strength between epitaxial graphene and transition metal surfaces arising from the geometrical and chemical properties of the supporting surfaces. This has been achieved by performing photoelectron measurements and numerical simulations of the C1s core level spectral distribution for a large number of graphene–metal systems, which have been obtained by systematic intercalation of different metals (Co, Rh, Ir and Ru) at the graphene–Ir(111) and graphene–Ru(0001) interfaces. We demonstrate that the chemical species of the substrate’s topmost layer plays a major role in determining the coupling between graphene and its substrate. Moreover, we show that both the experimental and the theoretical C1s spectral centres of mass are in linear relationship with the d-band centre of the transition metal substrate, which is considered a reliable descriptor of the graphene–substrate interaction strength. Our results provide a simple method to determine and tailor the properties of graphene–metal contacts.

Optimisation of tribological performance of sputtering Zr/ZrC coatings

An intelligent approach, which uses adaptive network based fuzzy inference systems (ANFIS) based on experimental designs, is used to characterise the tribological behaviour of undoped and Zr doped diamond-like carbon (DLC) films that are deposited using magnetron sputtering. An orthogonal array experiment is used and the effect of the deposition parameters on the films is determined. The films are analysed using X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Friction and wear tests are performed, using a pin-on-disk tribometer. This study identifies a group of highly developed hillock-like textures and lower wear volume loss is evident in the undoped and Zr doped films. The C1s core level XPS spectra show that the undoped and Zr doped films formed have a relative content of sp3 and sp2 hybrids. It is found that a value that is close to the estimated value, 0·5±0·05, of sp3/sp2 ratio results in better tribological properties in the undoped and Zr doped DLC films. These predicted values and the experimental results, for which an ANFIS predicts the tribological behaviour of the DLC films, are similar. The experimental results demonstrate that the tribological properties of DLC multilayer films are accurately predicted by an ANFIS. The results obtained for the ANFIS model are also compared to those for an ANN model and a Fuzzy system and it is shown that an ANFIS gives more reliable modelling of these sputtering processes and is more accurate and flexible than ANN and Fuzzy system models, which verifies the reliability and feasibility of this approach.