TEM investigation of TiNx-PACVD-coatings

The wear resistance of cermet cutting tools can be remarkably increased by TiN_x coatings. These layers are deposited at substrate temperatures of 723 K, 773 K and 973 K using a plasma-assisted chemical vapour deposition (PACVD) process. TEM investigations combined with EDXS analysis and electron diffraction gave information on structure and composition of the TiN_x layers and the interface range. X-ray structure investigations were performed additionally.The structure and the chlorine content of layers and interfaces change in dependence on the deposition temperature. All coatings show a columnar structure, but the fibre diameter increases with temperature. The fine-grained TiN_x layer deposited at 723 K has the highest chlorine content, a low-developed columnar structure and a 111 texture. The coatings deposited at 773 K and 973 K contain less chlorine impurities and have a 100 preferred orientation. The fibre structures at 723 K and 773 K can be resolved into single crystallites. By TEM investigations the fibres formed at 773 K are proved to be an accumulation of neighbouring and similarly oriented crystallites. Grain size determined by X-ray analysis and fibre diameter agree with each other. Grain sizes determined more exactly from TEM images are 6 nm at 723 K, 10 nm at 773 K and 30 nm at 973 K. In the interface region the thickness and the chlorine content of this zone decreases with increasing deposition temperature and simultaneously the layer adhesion increases.Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday     

Calibration standards for composition-depth profiles of non-stoichiometric titanium nitride coatings

Five different TiN_x coatings have been deposited on steel substrates by reactive magnetron sputtering. A quantitative analysis was carried out in two ways. The coatings were initially analysed by GDOS and after removing the coatings from the substrates and digesting the TiN_x powder, nitrogen was quantified by the Kjeldahl technique and titanium by AAS. A comparison of the results shows that AAS and Kjeldahl results correlate very well, whereas GDOS results deviate from these two methods systematically.     

TEM investigations on PECVD-titanium carbide layers

TiC_x-PECVD-layers were characterized by TEM. EDX analysis and electron diffraction. TiC_x-layers deposited using benzene showed a columnar structure, at which the column size decreases with rising excess carbon content. TiC_x-layers deposited using n-heptane presented a lamellar structure, at which the lamellar thickness diminishes with an increasing excess carbon content. In dependence on the layer thickness a periodic progress of the element contents was observed, at which a maximum for Ti and Cl correlates with a minimum for C. It was found that the incorporated chlorine is bonded to titanium. The lattice parameter depends on the chlorine content. Using TiCl₄/H₂/Ar-gas mixtures without any hydrocarbon, layers containing TiH₂ are formed.     

Effect of Active Fillers on Properties of Heat-Resistant Composites

The effect of active fillers such as titanium nitrides TiN _x , carbides TiC _x , and carbonitrides TiC _x N _y (0.5 < x or x + y ≤ 1.0) on properties of polymeric composites based on thermostable binders PAIS-104, SFP-012 AK-30, and ED-20 is studied.     

Depth scale calibration during sputter removal of multilayer systems by SNMS

Summary A key problem in sputter depth profile analysis is the conversion of bombardment time of primary ion dose into eroded depth. In particular during sputter removal of multilayer structures, both the total sputtering yieldY _tot and the particle density of the sample and, hence, the sputter erosion rate will in general vary between the different individual layers.The important role of this effect is demonstrated for Secondary Neutral Mass Spectrometry (SNMS) depth profile analysis of a model Ta-Si multilayer system where the observed ratio between individual Si- and Ta-layer removal times indicates an average film composition which is far off the TaSi₂-stoichiometry claimed by the manufacturer. The determination of absoluteY _tot as a function of sputter time from the recorded SNMS depth profile itself enables a non-linear calibration of the depth scale which yields a ratio ofd _Si/d _Ta = 2 between the individual Si and Ta layer thicknesses and, hence, confirms the true film stoichiometry.

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Kalibrierung der Tiefenskala beim Sputterabtrag von Vielschichtsystemen durch SNMS

     

Surface characterisation of TiCxN1 − x coatings processed by cathodic arc physical vapour deposition: XPS and XRD analysis

The properties of titanium carbonitride (TiCN) can be controlled by maintaining the C―N ratio within the coating to a certain level. An experimental study was carried out to vary the composition and properties of TiCN using cathodic arc physical vapour deposition (CAPVD). The substrate used was tungsten carbide (WC-6Co), which was prepared in-house through a powder metallurgy process. In order to form the TiC_xN_1 − x coatings, titanium (Ti) was used as the cathode, while methane (CH₄) and nitrogen (N₂) gases were used as sources for C and N, respectively. X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) were used to investigate the composition, chemical state, and bonding structure of the deposited coatings. The results show that the composition, intensity of elements, lattice parameter, and d-value of TiC_xN_1 − x coatings were successfully varied by controlling the CH₄ fraction (CH₄/N₂ ratio). With the increase in CH₄ fraction, the intensity of C and N within the TiC_xN_1 − x coatings increased and decreased, respectively. Consequently, the C―Ti and C―N bonds were increased and N―Ti bonds were decreased.     

Self-lubricating Ti–C–N nanocomposite coatings prepared by double magnetron sputtering

This paper is devoted to the development of Ti(C,N)-based nanocomposite protective coatings consisting of nanocrystals of a hard phase (TiN or TiC_xN_y) embedded in an amorphous carbon-based matrix (a-C or a-CN_x). The objective here is the achievement of a good compromise between the mechanical and tribological properties by the appropriate control of the hard/soft phase ratio and the microstructural characteristics of the film. To achieve this purpose, dual magnetron sputtering technique was employed following two different strategies. In the first one, we use Ti and graphite targets and Ar/N₂ gas mixtures, while in the second case, TiN and graphite targets are sputtered in an Ar atmosphere. By changing the sputtering power applied to each magnetron, different sets of samples are prepared for each route. The effect of the bias voltage applied to the substrate is also studied in some selected cases. The mechanical and tribological properties of the films are characterized and correlated with the microstructure, crystallinity and phase composition. The establishment of correlations enables the development of advanced coatings with tailored mechanical and tribological properties for desired applications.     

Contribution to the analytical characterization of coatings produced by thermal spraying

This paper reports on the use of Auger electron spectroscopy (AES)/ depth profile analysis for the investigation of plasma-sprayed coatings. Prior to spraying the St 37 substrates are heated to 300 °C or 500 °C for ceramic or metallic layers, respectively. Studies of the starting materials and of the interfaces are important if the adhesion mechanism is to be understood. Therefore the initial components—the unheated and heated substrates and the powder particles NiCrAl, Al₂O₃ and ZrO₂-7.25Y₂O₃—are analyzed. Depth profiles obtained from two coatings St 37/NiCrAl and St 37/Al₂O₃ show the influence of plasmaspraying on substrate surfaces and sprayed particles. Plasma-spraying mainly causes a decrease of superficial carbon contamination for both coating layers. In the case of St 37/NiCrAl incorporation of carbon in the sprayed layer is observed. The whole layer is almost completely oxidized except for some areas where substrate and particle material are present. It is assumed that these areas are identical with so-called adherence zones.Dedicated to Professor Günther Tölg on the occasion of his 60th birthday     

Composition of Ti-N films: EDX analysis during the sputtering process

Summary Energy dispersive X-ray (EDX) analysis was applied in-situ for measurements of composition, surface mass and deposition rate of Ti atoms during reactive sputtering. Electron beam excitation was used for the determination of composition and X-ray fluorescence (XRF) for the surface mass determination. Intensity measurements of the optical emission of Ti atoms agree well with the deposition rate of Ti atoms measured by XRF. The influences of nitrogen mass flow and negative bias substrate voltage on concentration and sputtering rate were investigated in homogeneous TiN_x films and TiN_x/TiN_y multilayers.     

Optimization of an electrochemical cell with an adsorption layer for NOx removal

The structure of a multilayer electrochemical cell with an adsorption layer was optimized by removing an yttria-stabilized zirconia cover layer. It was found that the NO_x removal properties of the electrochemical cell were dramatically enhanced through the optimization, especially under conditions of low voltage, intermediate temperature, and high O₂ concentration. The pronounced increase in activity and selectivity for NO_x decomposition after removing the ytrria-stabilized zirconia cover layer was attributed to the extensive release of selective reaction sites for NO_x species and a strong promotion for NO_x reduction from the interaction of the directly connected adsorption layer with both the Pt and catalytic layers. The optimized electrochemical cell may provide a promising solution for NO_x emission control.     

Effect of the procedure of chemostimulator application on the surface characteristics of V x O y /InP structures in the process of their thermooxidation

Evolution of morphology of surface and the composition of layer near the surface in the process of thermooxidation of V _x O _y /InP formed by soft and hard methods is shown. Dependence of morphology of film surface on the way of application of chemostimulator and the regime of thermooxidation is established. Both methods permit to obtain layers with the sufficiently smooth surface, but while using the hard method nanostuctured films are finally formed.     

Surface- and microanalytical characterization of ion-implanted Si-C-N layers

The development of production methods for carbonitridic hard coatings needs information on depth distributions of the layer components as well as on stoichiometries and binding states of the layer constituents. Si-C-N samples were produced by implanting ¹³C- and ¹⁵N-ions into c-Si <111>, and the implanted layers were investigated by means of NRA depth profiling. Afterwards several samples were characterized by surface analytical techniques, and XPS- and AES depth profiles were measured for typical samples. The measurements confirm the NRA depth profiles and stoichiometries. Furthermore, in all depth ranges C 1s- and N 1s binding energies are observed which are consistent with those of carbonitrides.     

Nitrogen depth distribution, interface and structure analysis of SiNx layers produced by low-energy ion implantation

Thin silicon nitride (SiN _x ) layers with the stoichiometric N/Si ratio of 1.33 in the maximum of the concentration depth distributions of nitrogen were produced by implanting 10 keV¹⁵N ₂ ⁺ in 100 silicon at room temperature under high vacuum conditions. The depth distribution of the implanted isotope was measured by resonance nuclear reaction analysis (NRA), whereas the layer structure of the implanted region and the geometrical thickness of the layers were characterised by high resolution transmission electron microscopy (TEM). SiN _x layers with a thickness of about 30 nm were determined by NRA. Channeling Rutherford backscattering spectrometry was used to determine the disorder in the silicon substrate. Sharp interfaces of a few nanometers between the highly disordered implanted region and the crystalline structure of the substrate thickness were observed by TEM. The high thermal stability of SiN _x layers with N/Si ratios from under to over stoichiometric could be shown by electron beam rapid thermal annealing (1100 °C for 15 s, ramping up and down 5 °C/s) and NRA.     

Nanometric resolution in glow discharge optical emission spectroscopy and Rutherford backscattering spectrometry depth profiling of metal (Cr,Al) nitride multilayers

In this work, we address the capability of glow discharge optical emission spectroscopy (GDOES) for fast and accurate depth profiling of multilayer nitride coatings down to the nanometer range. This is shown by resolving the particular case of CrN/AlN structures with individual thickness ranging from hundreds to few nanometers. In order to discriminate and identify artefacts in the GDOES depth profile due to the sputtering process, the layered structures were verified by Rutherford backscattering spectrometry (RBS) and scanning electron microscopy (SEM). The interfaces in the GDOES profiles for CrN/AlN structures are sharper than the ones measured for similar metal multilayers due to the lower sputtering rate of the nitrides. However, as a consequence of the crater shape, there is a linear degradation of the depth resolution with depth (approximately 40 nm/μm), saturating at a value of approximately half the thickness of the thinner layer. This limit is imposed by the simultaneous sputtering of consecutive layers. The ultimate GDOES depth resolution at the near surface region was estimated to be of 4–6 nm.     

Improving the oxidation resistance of AlCrN coatings by tailoring chromium out-diffusion

In this work, we have studied the improvement on the oxidation resistance of AlCrN-based coatings by adding a subsurface titanium nitride barrier layer. Since oxidation is interrelated with the inward diffusion of oxygen into the surface of Al_xCr_1−xN (x = 0.70) coatings and the outward diffusion of Cr to the surface, the oxidation behaviour of the aluminium-rich AlCrN coatings can be tuned by designing the coating in an appropriate layered structure. The buried depth of the embedded layer and the oxidation time were varied, and the changes in the AlCrN/TiN depth composition profiles and surface oxidation stoichiometry were analysed by means of Glow Discharge Optical Emission Spectroscopy (GDOES) and Cross Sectional SEM (X-SEM) maps. It was observed that when a TiN diffusion barrier of 300 nm was deposited near the top surface (500 nm from the surface) the inhibition of the inward diffusion of oxygen and formation of beneficial alumina surface layers was promoted and consequently an increase of the oxidation resistance is achieved. This is explained in terms of a limited surplus of chromium from the coating to the surface. This was corroborated after performing experiments using CrN as embedded barrier layer which resulted in a continuous surplus of chromium to the surface and the formation of Cr-rich oxides. GDOES, in combination with X-SEM elemental maps, was proved to be a fast and accurate technique to monitor composition in-depth changes during oxidation, providing unique information regarding the oxide structure formation.     

AES investigation of thermally sprayed Al2O3 coatings on steel

Summary The investigation of plasma sprayed steel/Al₂O₃ composites by means of Auger Electron Spectroscopy (AES) combined with depth profile analysis is described. Incomplete sprayed Al₂O₃ layers permit analysis of single sprayed particles and of surrounding uncovered steel substrate regions. More complete coatings are separated from the substrates, so that contact surfaces of substrates and Al₂O₃ layers can be analyzed. In order to determine the influence of preheating the substrates on the interface widths between steel substrate and Al₂O₃ coating and therefore on the adherence mechanism, both procedures are carried out for two preheating temperatures. It is shown that preheating hardly effects the interface widths beneath single sprayed particles but it causes laterally constant widths for complete layer fragments. Additionally, a comprehensive view about oxide layer thicknesses on the steel substrates before and after plasma spraying is offered.     

Comparative Analysis of a Solar Control Coating on Glass by AES, EPMA, SNMS and SIMS

 A solar control coating was analysed by different methods of surface analysis with respect to the layer sequence and the composition and thickness of each sublayer. The methods used for depth profiling were Auger electron spectroscopy, electron probe microanalysis, secondary neutral mass spectroscopy and secondary ion mass spectroscopy based on MCs⁺. The structure of the coating was unknown at first. All methods found a system of two metallic Ag layers, embedded between dielectric SnO_X layers. Additionally, thin Ni-Cr layers of 1–2 nm were detected on top of the Ag layers. Thus the detected layer sequence is SnO_X/Ni-Cr/Ag/SnO_X/Ni-Cr/Ag/SnO_X/glass. The Ni:Cr ratio in the nm-thin layers could be quantified by every method, the Cr fraction corresponding to less than one monolayer. We compare the capabilities and limitations of each method in routinely investigating this solar control coating. Importance was attached to an effective investigation. Nevertheless, by combining all methods, measuring artefacts could be uncovered and a comprehensive characterisation of the system was obtained.     

Analysis of layered AlxGa1 − xAs on gallium arsenide by electron microprobe and secondary-ion mass spectrometry

Two samples containing Al_xGa_{1 ? x}As layers (several micrometers thick) of different composition deposited on a gallium arsenide substrate were analyzed by two techniques. Electron microprobe analysis was used on a cross-section of the samples to measure layer thickness, to obtain qualitative information by means ov x-ray line scans, and to determine the composition of the layers accurately by energy-dispersive x-ray spectrometry. Depty profiles obtained by secondary-ion mass spectrometry were used to study depth resolution at large depth ranges. Results obtained by the two techniques are in excellent agreement and compare favourably with other published results concerning the same type of sample.     

Atom probe mass spectrometry

Round-robin characterization is reported on the sputter depth profiling of CrN/AlN multilayer thin-film coatings on nickel alloy by secondary ion mass spectrometry (SIMS) and glow-discharge optical emission spectrometry (GD-OES). It is demonstrated that a CAMECA SIMS 4550 Depth Profiler operated with 3 keV O₂⁺ primary ions provides the best depth resolution and sensitivity. The key factor is sample rotation, which suppresses the negative influence of the surface topography (initial and ion-induced) on the depth profile characteristics.