Low-energy N2 Research Articles

Dynamic annealing assisted near-surface structural and bond stabilization in high-temperature low-energy N2+ implanted diamond.

Nitrogen-rich ultra-thin (1-2nm thick) layers in diamond produced by high-temperature nitrogen ion (N2+) implantation at low N2+ energies studied by in situ x-ray photoelectron spectroscopy are reported. Nitrogen bonding at the subsurface region and its thermal stability, as well as structural defects in polycrystalline diamond (PCD) implanted with 200, 500, and 800eV N2+ at room temperature (RT) and 600 °C at an ion dose of 4.5 × 1014 ions/cm2, are investigated. Implantation at RT leads to nitrogen bonding at interstitial and substitutional sites in the diamond lattice, which is associated with the C-N/C=N bond, lower intensity of the C≡N (nitrile-like) component associated with nitrogen bonding with carbon defects, and quaternary nitrogen. The relative composition of these chemical states varies with implantation energy, temperature, and post-implantation annealing temperature. Upon annealing the RT implanted layers above 500-600 °C, the interstitial nitrogen converts to substitutional nitrogen. This process competes with nitrogen desorption. The thermal stability of nitrogen increases with implantation energy. Implantation at 600 °C at 800eV resulted in a significantly lower concentration of nitrile-like bonds and a lower density of structural defects compared to RT implantation at the same energy. These effects are associated with dynamic annealing, which becomes more significant at higher implantation energies. Upon high-temperature implantation, nitrogen mostly populates directly substitutional sites. Nitrogen implantation at low energy and high temperature may be a viable way to nitride diamond surfaces with reduced density of defects where nitrogen is selectively bonded to substitutional sites. Finally, a comparison between nitrogen implantation into PCD and Diamond (100) [Di(100)] surfaces is presented.

Subsurface nitrogen bonding, thermal stability, and retention of 200 eV N2+ implanted polycrystalline diamond studied by in situ X-ray photoelectron spectroscopy

The properties of ultra-shallow nitrogen layers (<1 nm thick) in diamonds produced by very low energy (200 eV) N2+ implantation in polycrystalline diamond films at different doses (1.25×1014, 3.50×1014, 7.85×1014, 1.30×1015 and 9×1015 ions·cm−2), followed by thermal annealing, are investigated by in situ X-ray photoelectron spectroscopy. Spectral analyses of C(1s) and N(1s) peaks reveal that a chemical effect occurs depending on nitrogen local concentration and annealing temperature. Nitrogen exists in a predominant CN/C–N bonding configuration, followed by minor contributions of C≡N and quaternary-N configurations. Annealing (300–1000 °C) imparts complex effects that depend on local nitrogen concentration and bonding. The onset of nitrogen thermal desorption increases with ion dose: 300 °C for 1.25×1014 and 3.50×1014, 400 °C for 7.85×1014, and ∼650 °C for 1.30×1015 and 9×1015 ions·cm−2. Upon annealing to 1000 °C, the remaining nitrogen concentration in the diamond subsurface region increases with ion dose. The CN/C–N configuration was more thermally stable than the C≡N, while the quaternary-N is constant with annealing temperature. The nitrogen ion retention probability increased for 1.25×1014 and 3.50×1014 and decreased for the higher doses due to recombination-assisted desorption. This study may have important implications for stabilizing near-surface NV- centers for quantum sensing applications.

Comparative X-ray photoelectron spectroscopy analysis of nitrogen atoms implanted in graphite and diamond

Introduction: Insertion of N atoms at a nanoscale subsurface depth in single-crystal diamond (SCD) may enable new generations of quantum electronics devices. In this sense, it is critical to understand the interaction between implanted N atoms and C atoms in the diamond lattice.Methods: The investigation of the interaction of N atoms with SCD at the atomic scale using X-ray photoelectron spectroscopy (XPS) analysis involves in situ bombardment of the SCD surface with relatively low-energy (5,000 eV) N2 ions. In situ XPS analyses of SCD and highly oriented pyrolytic graphite (HOPG) before and after N-atom implantation are compared with published XPS analyses of C-N materials (e.g., g-CN, N in poly/single-crystal diamond).Results: The analyses revealed three N 1s peaks at 398–399 eV (N1), 399–400.5 eV (N2), and 401–403 eV (N3), with the N1 and N2 peaks assigned to C-N bonds and an N3 peak inaccurately assigned, in prior publications, to N-bonded contaminants (e.g., O, NH). In situ cleaning of the SCD and HOPG surfaces prior to N-atom implantation was performed to eliminate all atmospheric contaminants. This cleaning process revealed that the N3 peak is associated with N-C-bonded atoms and not the C-O/NH linkage, as previously suggested. Ex situ high resolution transmission electron microscopy (HRTEM) studies of N-implanted SCD show a defect-structured subsurface region.Discussion: An important side effect of the relatively low-energy N implantation in SCD is the formation of a 5–8 nm electrically conductive surface layer, an effect that may open the pathways for future research in diamond-based micro- and nano-electronics.

Воздействие плазмы N-=SUB=-2-=/SUB=- на монослои дисульфида молибдена

Based on ab initio DFT simulation results, the main processes of the interaction of thermal N atoms with MoS2 monolayers are revealed, potential mechanisms of defect formation by low-energy ions N2+ are described, and the ion threshold energy required to sulfur removal is estimated.

Photoelectrochemical water splitting with 600 keV N2+ ion irradiated BiVO4 and BiVO4/Au photoanodes

Low energy N2+ ion beam with 600 keV energy has been used to irradiate BiVO4 and Au nanoparticles loaded BiVO4 (BiVO4/Au) thin films deposited over fluorine doped tin oxide substrates via spray pyrolysis technique. Ion irradiation results in tailoring the optical, electrical, and morphological properties of the thin films and thence also responsible for changes in electrochemical properties. The scanning electron microscope images reveal the evolution of Au nanoparticles after irradiation at 2 × 1015 fluence to a nanourchins type of morphology. In consequence of morphological changes, the signature of surface plasmon resonance peak exhibited by Au nanoparticles in BiVO4/Au shows improvement. An increase of approximately 92% in photocurrent density in comparison to pristine BiVO4 has been found after irradiation in BiVO4/Au photoanode at 2 × 1015 ions/cm2 fluence. Moreover, irradiation also aids in improving photoelectrochemical response of BiVO4 photoanodes without Au nanoparticles. The enhancement can be attributed to the notable changes in onset potential, charge separation, charge transfer resistance and optical properties.

Revealing the Nitridation Effects on GaN Surface by First-Principles Calculation and X-Ray/Ultraviolet Photoemission Spectroscopy

In this paper, we report a systematic study of the nitridation effects on GaN surface by first-principles calculations and X-ray/ultraviolet photoemission spectroscopy (XPS/UPS). According to the calculated electronic structures, two surface bands (i.e., the upper band and the lower band) can be seen within the bandgap for the typical surface configurations that may occur in the experimental condition as a result of surface reconstruction. By the deployment of sufficient nitridation, the energy positions of the lower band are modified toward the valence band by ~1 eV, resulting in the overlapping of the lower surface band with the valence band. Meanwhile, the upper surface band is also modified toward the valence band, but by a smaller amount. The modification to the positions of the surface bands is furthermore manifested by XPS/UPS spectra characterization performed on GaN sample that underwent surface treatment with low-energy remote N2 plasma. The theoretical and experimental results insightfully proclaim the nitridation effects on material properties at atomic level, and support a surface-state ionization model for the GaN band-edge (3.4 eV) emission in metal-AlGaN/GaN Schottky-on-heterojunction diode under forward bias.

Kinetic modelling of NH3 production in N2–H2 non-equilibrium atmospheric-pressure plasma catalysis

Detailed plasma kinetics modelling is presented of a low electron energy N2–H2 atmospheric-pressure discharge for ammonia synthesis. The model considers both electron and vibrational kinetics, including excited N2(X, ν) and H2(X, ν) species, and surface reactions such as those occurring by the Eley–Rideal and Langmuir–Hinshelwood mechanisms and dissociative adsorption of molecules. The predictions of the model are compared to the measured NH3 concentration produced in a packed-bed dielectric barrier discharge reactor as a function of process parameters such as input gas composition and applied voltage. Unlike typical low-pressure plasma processes, under the plasma conditions considered here (reduced electric field E/N in the range 30–50 Td, electron density of the order 108 cm−3), the influence of ions is not significant. Instead, the reactions between radicals and vibrationally-excited molecules are more important. The active species in surface reactions, such as surface-adsorbed atomic nitrogen N(s) or hydrogen H(s), are found to be predominantly generated through the dissociative adsorption of molecules, in contrast to previously proposed mechanisms for plasma catalysis under low-pressure, high-E/N conditions. It is found that NH radicals play an important role at the early stages of the NH3-generation process, NH in turn is produced from N and H2(ν). Electron kinetics is shown to play a critical role in the molecular dissociation and vibrational excitation reactions that produce these precursors. It is further found that surface-adsorbed atomic hydrogen H(s) takes a leading role in the formation of NH3, which is another significant difference from the mechanisms in conventional thermo-chemical processes and low-pressure plasmas. The applied voltage, the gas temperature, the N2:H2 ratio in the input gas mixture and the reactivity of the surface material are all found to influence the ammonia production. The calculated results reproduce the observed trends in the dependence of NH3 production on the N2/H2 ratio in the input gas mixture and the applied voltage.

Phosphorous Diffusion in N2+-Implanted Germanium during Flash Lamp Annealing: Influence of Nitrogen on Ge Substrate Damage and Capping Layer Engineering

In this work we present a systematic study on post-implantation phosphorous diffusion control in Ge by co-implanted nitrogen in combination with various surface capping layers (Al2O3, SiO2 and Si3N4). Phosphorous has been implanted at low energy (11 keV) and high dose (1015 cm−2) in p-Ge (100) already implanted or not with low energy (10 keV−5 × 1014 cm−2) N2+. Flash Lamp Annealing (FLA) at 800–850°C for 20 ms in inert ambient has been used as post-implantation annealing scheme. In the absence of nitrogen, significant substrate damage and capping layer deterioration prevents a reliable comparison among the three capping materials. The presence of nitrogen in the Ge substrate, effectively suppresses the damage observed after the FLA. In this case, P diffusion is additionally retarded in the presence of Al2O3 as compared to SiO2 and Si3N4. The experimental results constitute a direct evidence of the action of the three capping layers as sinks for Ge vacancies with different interface recombination velocities. On the contrary, the nitrogen diffusion data suggest that interface recombination velocities of Ge interstitials are almost independent of the capping layer choice.

ORR Properties for Model Pt-Shell Layers Prepared on Nitrogen-Beam Irradiated Pt25Ni75(111) Substrate

Introduction Pt–M (M = Fe, Co, Ni, Cu, Pd, etc.) alloy and Pt/M core–shell nanoparticles have been intensively studied as oxygen reduction reaction (ORR) catalysts for polymer electrolyte fuel cells (PEFCs). As for the core–shell catalysts, the core elements easily dissolve in the electrolyte under the PEFCs operating conditions, leading to degradation of the catalytic activity. To control dissolution behavior of the core elements, Kuttiyiel et al. proposed the structure of Pt–shell/nitride–core nanostructures and demonstrated that nitride core is effective not only for enhancing ORR activity but also for improving durability [1]. For developing the practical Pt–M catalysts, it is significant to clarify a role of the nitrogen atoms located at the core–shell interface. In this study, we fabricate model catalyst structures that composed of Pt(111) epitaxial layers on low–energy N2–beam irradiated Pt25Ni75(111) substrate surfaces by using molecular beam epitaxy (MBE) and discuss the ORR activity and the durability. Experimental Model catalyst sample surfaces are fabricated as follows. First, Pt25Ni75(111) single crystal substrate was cleaned by Ar+ sputtering and annealing at 1173 K in ultra–high vacuum (UHV). Next, neutralized N2–beam (≤ 100eV) was irradiated onto the cleaned Pt25Ni75(111) at room temperature by using low–energy neutralized nitrogen ion beam gun. Then, 3ML–thick–Pt was deposited on the N2–beam irradiated Pt25Ni75(111) substrate by an electron–beam evaporation method at room temperature, followed by annealing at 673 K for 10 minutes in UHV to flatten the topmost surfaces. The resulting surface structure was verified by scanning tunneling microscopy (STM). The sample thus fabricated was transferred to electrochemical evaluation systems set in a N2–purged glove box without air exposure [2]. CV and LSV measurements were conducted in N2–purged and O2–saturated 0.1 M HClO4, respectively, and ORR activity was evaluated from j k values at 0.9 V vs. RHE by using Koutecky–Levich equation. The electrochemical stability of the sample was investigated by applying potential cycles between 0.6 V (3s) and 1.0 V (3s) in O2–saturated 0.1 M HClO4. Results and Discussion UHV–STM images of the as–prepared 3ML–Pt/Pt25Ni75(111) and 3ML–Pt/100eV–N2–beam irradiated Pt25Ni75(111) (3ML–Pt/N2–beam–Pt25Ni75(111)) surfaces are shown in Fig. 1(a). The line profiles of white arrows are depicted below the corresponding STM images. The STM images clearly show that atomically flat surfaces can be obtained through the UHV–process, irrespective of the 100eV–N2–beam irradiation. Furthermore, the both surfaces exhibited moiré–like height modulations (line profiles) that derived from lattice mismatches between the topmost Pt–shell layers and corresponding substrates. The results suggest that compressive surface strain should be induced for both the shell layers. Corresponding CV curves of the 3ML–Pt/Pt25Ni75(111) (blue), 3ML–Pt/N2–beam–Pt25Ni75(111) (red) and Pt(111) (black–dashed) are summarized in Fig. 1(b). Compared with the clean Pt(111), the total Hupd charges for the 3ML–thick–Pt surfaces considerably decreased and the onset of Oads positively shifted. Such CV features are common for highly–active Pt skin–type surfaces [2, 3]. Furthermore, the oxidation of the Pt shell layers for the latter N2–beam irradiated sample is suppressed in comparison to the former. ORR activities evaluated before and after 1000 potential cycles loading are summarized in Fig. 1(c). As for the initial activity enhancement factor, the 3ML–Pt/Pt25Ni75(111) andthe N2–beam irradiated one reveals ×15 and ×8 vs. Pt(111), respectively. The results suggest that the nitrogen atoms located at the Pt–shell/Pt25Ni75(111) interface should release the surface strain of the Pt–shell layers, leading to decrease in pristine ORR activity. In contrast, N2–beam irradiated sample is relatively stable against the potential cycle loading, indicating that the interface nitrogen atoms dominate not only activity but also durability of the Pt– shell/nitride–core type catalysts. At the PRiME 2016, I will discuss ORR activity and durability for various–thick Pt shells prepared on N2–beam–Pt25Ni75(111). Acknowledgement This study was supported by new energy and industrial technology development organization (NEDO) of Japan.

Incorporation of low energy activated nitrogen onto HOPG surface: Chemical states and thermal stability studies by in-situ XPS and Raman spectroscopy

In this paper we report the chemical states analysis of activated nitrogen incorporated highly oriented pyrolytic graphite (HOPG) surface under well-controlled conditions. Nitrogen incorporation is carried out by two different processes: an indirect RF nitrogen plasma and low energy (1keV) N2+ implantation. Bonding configuration, concentration and thermal stability of the incorporated nitrogen species by aforesaid processes are systematically compared by in-situ X-ray photoelectron spectroscopy (XPS). Relatively large concentration of nitrogen is incorporated onto RF nitride HOPG surface (16.2 at.%), compared to N2+ implanted HOPG surface (7.7 at.%). The evolution of N 1s components (N1, N2, N3) with annealing temperature is comprehensively discussed, which indicates that the formation and reorganization of local chemical bonding states are determined by the process of nitridation and not by the prior chemical conditioning (i.e., amorphization or hydrogenation) of the HOPG surface. A combined XPS and Raman spectroscopy studies revealed that N2+ implantation process resulted in a high level of defects to the HOPG surface, which cannot be annealed-out by heat treatment up to 1000°C. On the other hand, the RF nitrogen plasma process did not produce a high level of surface defects, while incorporating nearly the same amount of stable nitrogen species.

Catalyst free self-assembled growth of InN nanorings on stepped Si (5 5 3) surface

A novel technique for synthesis of high crystalline quality self-assembled InN nanorings, by nitriding the bulk deposited In/Si (553)-1×4 system using low energy N2+ ions at 520°C, has been demonstrated. Scanning electron microscopy images reveal the formation of ring shaped InN structures with average size ∼500nm. Anisotropic strain relaxation via self assembly could be the driving force for the formation of these InN rings on reconstructed Si (553) surface. High resolution X-ray diffraction analysis indicates high crystalline quality of these wurtzite InN nanostructures with c-plane. A strong downward band bending was observed in X-ray photoelectron spectroscopy valence band spectra which signify the large electron accumulation in the InN nanostructures.

Potassium and ion beam induced electron accumulation in InN

“We present angle resolved photoemission study of quantized electron accumulation subbands obtained from both clean and potassium deposited InN(0001¯) surfaces. Shifting of the quantized accumulation states toward higher binding energies upon low energy N2+ ion bombardment or a small amount of potassium adsorption is explained by the modification of the In-adlayer induced surface states. N2+ ion bombardment leads to a higher density of donor-type surface states by creating nitrogen vacancies near the surface. On the other hand, a small amount of K adsorbates initially donate their free electron to InN and result in more pronounced downward band bending. Eventually, further K adsorption leads to passivation of surface states and reduction of the surface electron accumulation. With the increase of the electron density, enhanced many-body interactions of electrons within the electron accumulation layer are observed.”

Simultaneous reduction and N-doping of graphene oxides by low-energy N2+ ion sputtering

An easy and catalyst-free method was used to obtain N-doped reduced graphene oxides (N-RGO) through low-energy N2+ ion sputtering of graphene oxides (GO). The simultaneous reduction and N-doping of GO during the sputtering were systematically investigated by X-ray photoelectron spectroscopy (XPS), near-edge X-ray absorption fine structure and Raman spectroscopy. The N-doping and reduction levels, which are determined by the N/C and O/C atomic ratios from the quantitative XPS analysis, respectively, can be easily controlled by varying the N2+ ion sputtering time. In addition, three different N species, namely, nitrile-like N, graphitic N and pyridinic N, can be distinguished in N-RGO.

Mechanical properties and thermal stability of SiBCN films prepared by ion beam assisted sputter deposition

The high hardness, exceptional high temperature stability, and oxidation resistance of bulk Si–B–C–N ceramics have led to the expectation that these materials will be good candidates for superior coating materials in high-temperature applications. In this study, SiBCN films were prepared using ion beam assisted sputter (IBAS) deposition, and the mechanical properties and thermal stabilities of the films at 600, 700, and 800°C in air were investigated. In particular, the effects of the ion beam assist on the properties of the SiBCN films were examined. The SiBCN films were deposited on Si plates by sputtering a target composed of Si+BN+C using a 2-keV Ar+ ion beam. A low-energy N2+ and Ar+ mixed ion beam irradiated the samples during the sputter deposition. The Si content in the SiBCN films was controlled by changing the Si/(BN+C) ratio of the target. BCN films were also deposited for comparison. The composition and chemical bonding structure of the prepared films were investigated by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. We found that c-BN bonds were formed in the ion-assisted BCN film. The oxide layer thickness on the SiBCN films after thermal annealing decreased due to the IBAS deposition and an increase in the Si content. Ion-assisted SiBCN films annealed at 800°C showed the highest hardness of 20GPa.

Surface characterization of self-assembled N–Cu nanostructures

We report on the process of low energy N2+ implantation and annealing of a Cu(001) surface. Through AES we study the N diffusion process as a function of the substrate temperature. With STM and LEIS we characterize the surface morphology and the electronic structure is analyzed with ARUPS. Under annealing (500<T<700K) N migrates to the surface and reacts forming a CuxN compound that decomposes at temperatures above 700K. LEIS measurements show that N locates on the four-fold hollow sites of the Cu(001) surface in a c(2×2) arrangement. Finally, a gap along the [001] azimuthal direction is determined by ARUPS. DFT calculations provide support to our conclusions.

Molecular Dynamic Simulation for the NV-N Center Formation by Means of N&lt;sub&gt;2&lt;/sub&gt; Beam Implantation into a Diamond

We have searched for an optimum condition to form a specific defect center called NY-N (nitrogen-vacancy-nitrogen) in a diamond, which is of interest, because of the possibility of a NOT system in a quantum computer. It is composed of one NV center made of a substitutional nitrogen (N) coupled with an adjacent vacancy (V) and an associated N atom. The second N is located at a mean distance (RN-N) of ~ 2 nm. Considering the cohesive potentials we performed an empirical molecular dynamic simulation for the low-energy N2 beam implantation into a diamond. The identification of a NV center was performed by a crystallographic analysis called the pixel-mapping (PM) method based on crystallography. We found that impact energy Eo could be decisive for the mean distance RN.N, while temperature T was decisive for the formation ofNY centers. The optimum set of conditions to form an NV-N center is a compromising choice of (Eo, T). The formation probability of the NY center exceeded 20 % when using (Eo, T) = (200 (eV/atom), 1000 K), however, the mean value was below 1.5 nm. A 1ittle higher energy than 200 (eV/atom) will be necessary for ideal NV-N centers.

The Straggling of Dissociation Distance in Molecular Beam Implantation

A specific crystalline defect in diamond may work as a NOT gate in a quantum computer. It is called NV-N center that is composed of two substitutional nitrogen atoms that are separated by c.a. 1.5 nm and one of them is adjacent to a vacancy. In order to find an optimal condition to produce it using a low-energy (100 ∼ 500 eV/atom) N2 beam implantation, we performed an empirical molecular dynamic simulation. By a high-temperatures implantation at 900∼1000 K, the formation probability of such desired NV-N centers was 5 ∼ 10%, which is comparable with a measured data.

Characterization of Nitrogen-Doped Carbon Nanotubes by Atomic Force Microscopy, X-ray Photoelectron Spectroscopy and X-ray Absorption Near Edge Spectroscopy

In this work, we perform a comparative study on single-walled carbon nanotubes (CNT) before and after low energy nitrogen ion bombardment (70 eV and 25 x 10-6 A/cm2) at room temperature. The morphology and the mechanical properties were studied by Atomic Force Microscopy (AFM). The bonding configuration of the N-doped CNTs was established by X-ray Photoelectron Spectroscopy (XPS) and X-ray Absorption Near Edge Spectroscopy (XANES). Single-walled carbon nanotubes were prepared using non-intrusive methods and deposited onto silicon substrates. For the spectroscopic studies, samples with a high concentration of CNTs were analyzed. XPS reveals different chemical states for carbon related to the incorporation of nitrogen. XANES confirms the hexagonal structure of the CNTs, resembling the bonding structure of hexagonal carbon nitrides. AFM images confirm that the CNTs were not destroyed after low energy N2+. The morphology of the original nanotubes maintains after nitrogen ion bombardment except for the incorporation of some pearl-shaped decoration, probably due to the adsorption of some contaminants or to deposition of re-sputtered material. Whereas CNTs improve their adherence to the substrate, this extra granularity on the CNT is easily removed even with the AFM tip. In conclusion, spectroscopic measurements and mechanical properties made clear information on the changes produced on CNT after nitrogen incorporation.

Controllable modification of self-assembled monolayer surface by using N2 neutral beam process

A novel technique of low-energy N2 neutral beam (NB) (&amp;lt;10 eV) irradiation was investigated as a means of controlling the surface nitridation of self-assembled monolayers (SAMs). This low-energy process without UV photons was able to nitride the surfaces of terphenyl SAMs. Furthermore, by varying the on/off period for irradiation, a pulse-time modulated NB process could be used to control the atomic ratio of nitrogen in terphenyl molecules. Time-of-flight secondary ion mass spectra revealed that one H in the terphenyl group was substituted by a NH2 group because of irradiation by the N2 beam. The data suggested that the low-energy NB technique caused less damage to modified surfaces than the conventional plasma process did. Therefore, we believe that it is a potential damage-free process for modifying the surfaces of soft organic materials and films.

The formation of V–Al–N thin films by reactive ion beam mixing of V/Al interfaces

The reactive ion beam mixing (IBM) of V/Al interfaces by low-energy N2+ ions at room temperature leads to the formation of V–Al–N ternary nitride thin films. The kinetics, growth mechanisms, composition and electronic structure of those films have been studied using X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, Factor Analysis and Monte Carlo TRIDYN simulations. The comparison of experimental results with those obtained from TRIDYN simulations suggests that the chemical reaction with the nitrogen partial pressure and processes driven by residual defects are the rate-controlling mechanisms during the reactive IBM of V/Al interfaces. The kinetics of mixing is characterized by two stages. During the first stage (≤4×1016 ions/cm2), the formation of vanadium nitride is observed. In the second stage, vanadium nitride is transformed into a V–Al–N ternary nitride due to Al incorporation in the near surface region. Moreover, the V/Al ratio can be varied in a broad range, whereas the nitrogen concentration slightly decreases with increasing the aluminium content of the film.