Transition Metal Nitride Films Research Articles

Energy dependence of non-Rutherford proton elastic scattering spectrum for hafnium nitride thin film

The energy dependence of the backscattering spectrum of non-Rutherford proton elastic scattering spectrum for a hafnium nitride (HfN) thin film was investigated. The purpose of the study is to demonstrate the feasibility of proton elastic scattering at 1.6MeV as a tool for compositional analysis of transition metal nitride films on a silicon substrate. A HfN thin film deposited on a silicon substrate was analyzed by a common Rutherford backscattering spectrometry (RBS) with an α beam at the energy of 1.98MeV, and also by a proton elastic scattering at the energies between 1.53MeV and 1.61MeV. The results of two measurements were compared, and a good agreement for nitrogen composition was obtained when the proton energy was higher than 1.59MeV. It was found that non-Rutherford proton elastic scattering can be used for the compositional analysis of HfN thin films with the thickness up to 230nm. In analyzing a thicker film, careful observation is necessary.

Influence of Al content on the phase formation, growth stress and mechanical properties of TiZrAlN coatings

Quaternary (Ti,Zr)1−xAlxN transition metal nitride films, with Al content x ranging from 0 to 0.37, were reactively sputter-deposited from individual metallic targets under Ar+N2 plasma discharges on Si substrates at Ts=270°C. The influence of Al addition on the crystal structure, phase formation, growth morphology and intrinsic stress development, electrical and mechanical properties was systematically investigated. Three distinct compositional regions were evidenced: i) for 0≤x≤0.07, films develop a columnar structure consisting of cubic TiZr(Al)N grains with (111) and (200) preferred orientation, large compressive stresses up to ~−4GPa and hardness increase from ~20 to ~24GPa, ii) for 0.09≤x≤0.16, Al incorporation favors the growth of nanocomposite films consisting of (200)-oriented cubic TiZr(Al)N nanocrystals surrounded by a highly-disordered matrix, accompanied by a decrease of compressive stress, whereas a maximum hardness H~27GPa and H/E ratio of 0.105 is reached at x~0.12 and x=0.14, respectively, and iii) x>0.16, XRD amorphous films are formed, with reduced mechanical properties. The structure–stress-properties relationship is discussed based on evolutionary growth regimes induced by incorporating a high-mobility metal in a refractory compound lattice.

Structure, electronic properties and electron energy loss spectra of transition metal nitride films

We present a thorough and critical study of the electronic properties of the mononitrides of the group IV–V–VI metals (TiN, ZrN, HfN, NbN, TaN, MoN, and WN) grown by Pulsed Laser Deposition (PLD). The microstructure and density of the films have been studied by X-Ray Diffraction (XRD) and Reflectivity (XRR), while their optical properties were investigated by spectral reflectivity at vertical incidence and in-situ reflection electron energy loss spectroscopy (R-EELS). We report the R-EELS spectra for all the binary TMN and we identify their features (metal-d plasmon and N-p+ metal-d loss) based on previous ab-initio band structure calculations. The spectral positions of p+d loss peak are rationally grouped according to the electron configuration (i.e. of the respective quantum numbers) of the constituent metal. The assigned and reported R-EELS spectra can be used as a reference database for the colloquial in-situ surface analysis performed in most laboratories.

Elastic Recoil Detection Analysis of FeN thin films

Thin films of transition metal nitrides are interesting materials due to their special features such as high hardness and chemical inertness. In our present work, we are reporting Elastic Recoil Detection Analysis of FeN/Si system using 100MeV Au beam. Recoils ions were detected using ΔE−E detector telescope. Diffraction pattern of pristine FeN thin films indicates amorphous nature of iron nitride thin film. MOKE results show irradiation can be used for controlling the magnetic properties such as coercivity.

Thermal stability of TiZrAlN films deposited by a reactive magnetron sputtering method

Quaternary TiZrAlN films are: • perspective for both oxidation and wear resistance applications and expectant substitution for TiN, (Ti,Al)N and (Ti,Zr)N hard films; • capable to possess by the unique properties due to possibility of nanocomposite structure formation during their synthesis. The aim of the present work is to study the thermal stability, under vacuum and air annealing, of quaternary transition metal nitride films, namely (Ti,Zr)1-xAlxN, with emphasis on the role of Al content on the structure and phase formation.

Factors determining the formation of nanostructures of transition metal boride and nitride films

The main factors responsible for the formation of columnar and layered nanostructures of transition metal boride and nitride films were determined by X-ray diffraction, electron microscopy, and secondary ion mass spectrometry. An expression was obtained for predicting the nanostructures of the deposited films from data on the supersaturation, elastic stresses, and ratios between free boundary energies. The nanocrystallite sizes in certain transition metal nitride and boride films were estimated.

Metallic seed layers for ion-beam assisted pulsed laser deposition of highly textured transition metal nitride films

Ion-beam assisted deposition (IBAD) is a promising technique for preparing highly textured templates on various substrates. A major requirement for the textured nucleation of materials with a rocksalt structure using the IBAD approach is an amorphous seed layer. Metallic Ta0.75Ni0.25 films were used as amorphous layers on Si/Si3N4 as well as on electropolished Hastelloy tapes for the ion-beam assisted pulsed laser deposition of transition metal nitrides. Highly biaxially textured TiN and NbN films have been grown on these layers even at room temperature in a reactive deposition process using an ion beam with an energy of 800 eV under an angle of 45° relative to the substrate normal. The cube texture was preserved to higher thicknesses using homoepitaxial growth. Finally, 10 nm thick Au films were used to study the surface texture quantitatively using x-ray diffraction showing in-plane orientations down to 8°. The results offer the possibility to realize a fully conductive buffer layer architecture for high-temperature superconductors based on the IBAD approach.

Ion-beam assisted pulsed laser deposition of textured transition-metal nitride films

AbstractIon-beam assisted deposition (IBAD) offers the possibility to prepare thin textured films on amorphous or non-textured substrates. It was shown within the last decade that the ion beam influences the nucleation in material with a rocksalt structure leading to a strong cube texture already within the first 10 nanometres. Among these materials, transition metal nitrides exhibit interesting physical properties as superconductivity, metallic behaviour or superior hardness. Therefore, a reactive IBAD process was applied for the preparation of highly textured transition metal nitride layers using pulsed laser deposition of pure metals in combination with a nitrogen-containing ion beam. The results on the in-plane textured growth of TiN are promising for the development of conducting buffer layer architectures for YBCO coated conductors based on the IBAD approach. Furthermore, this approach was used to prepare other highly textured transition metal nitride thin films like NbN and ZrN.

Low and increased solubility of silicon in metal nitrides: evidence by X-ray absorption near edge structure

Adding silicon to transition metal nitride (MN) films has been reported to significantly improve many of their mechanical properties including hardness, toughness, and oxidation resistance [1, 2]. As a result, the influence of microstructure on the mechanical properties of siliconcontaining metal nitrides has been a subject of intensive investigation for more than a decade [3]. Most microstructural studies of these materials report the formation of two-phase nanocomposite systems composed of nanocrystalline (nc) metal nitride grains embedded in an amorphous silicon nitride (a-Si:N) matrix [2]. This formation of nanocomposite microstructures has been explained by the lower free energy of the separate phases in comparison to that of ternary or quaternary nitride compounds. It has been argued that because the phase segregation rate is diffusion-controlled, temperatures above 500 C are needed in order to constraint any solubility of silicon into the metal nitride [4]. This claim has been supported, in most cases, using X-ray Diffraction (XRD) and transmission Electron Microscopy (TEM) techniques. These techniques are limited and cannot prove phase segregation has actually occurred during the deposition of the film or during sample preparation. However, recently, few studies have laid out the possibility of small amounts of Si dissolution into MN grains using X-ray absorption spectroscopy techniques [5, 6]. This work reports on the local structure and bonds of silicon in TiSiN and AlCrSiN investigated by X-ray diffraction (XRD) and X-ray absorption near edge structure (XANES). Samples were deposited using pulsed magnetron sputtering from Ti and Si targets and cathodic arc evaporation from customized AlCrSi targets, which contained 70 at.% of Al and a variable amount of Cr and Si, respectively. Both systems were deposited at 500 C. Mirror-polished squared cemented carbide inserts were used as substrates. The thickness of all the coating samples was within 3.5 ± 0.2 lm. A Siemens D500 diffractometer with a CuKa tube and the Q/2Q mode was used to perform XRD analysis and identify the phases formed. Chemical analysis was performed using Electron Dispersive Spectroscopy (EDS). XANES measurements of the Ti and Si K-edges were carried out at the KMC-1 beamline of the BESSY synchrotron facility with double crystal monochromator using a standard chamber equipped with a highresolution solid-state fluorescence detector. Si (111) monochromator crystals were used to provide photon energy selection at the Cr K-edge and Ti-Kedge while InSb (111) was used to collect the Si K-edge spectra. In Fig. 1a, x-ray diffraction patterns for TiSiN films revealed the formation of polycrystalline films containing the B1-TiN phase [7]. Increase in Si content resulted in a preferential growth change to (200) and a slight shift of the diffraction peaks to larger 2-theta. This shift suggests a small contraction of the NaCl type-TiN lattice with the J. L. Endrino Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones Cientificas, Cantoblanco, Madrid 28049, Spain

Impact and Indentation Resistance of Superhard AlCrN Thin Films

Binary transition metal nitride films have excellent tribological properties but these binary systems are still inadequate for high temperature applications due to their low oxidation temperature. Above 700°C, formation of porous oxides at the film surface deteriorates their mechanical properties rapidly by the. Especially impact and indentation resistance of these films deteriorate very quickly. In order to overcome these problems, Al based Al1-xCrxN films with X=0.29 and X=0.69 were synthesized by closed field unbalanced magnetron sputtering with vertical magnetron sources and their chemical composition, crystalline structure, morphology and mechanical properties including impact and indentation resistance were investigated. Synthesized Al1-xCrxN films formed solid solution showing FCC B1 type structure with strong (111) preferential orientation and films with X=0.29 showed a superhard hardness value of approximately 41GPa while films with X=0.69 did approximately 31GPa. While there was insignificant difference between Al1-xCrxN films with X=0.29 and X=0.69 in terms of Rockwell C indentation resistance, much improved impact resistance could be observed from the Al1-xCrxN films with X=0.29.

Surface kinetics and subplantation phenomena affecting the texture, morphology, stress, and growth evolution of titanium nitride films

We present a thorough study of the microstructure, texture, intrinsic stress, surface, and interface morphology of transition metal nitride (mainly TiN but also CrN) films grown on Si by reactive sputter deposition, with emphasis to the mechanisms of adatom migration on the surface and subplantation of energetic species. In order to study the effects of adatom mobility and the subplantation probability we vary the ion energy and growth temperature. For the experimental part of this work we used nondestructive, statistically reliable x-ray techniques (diffraction, reflectivity, scattering). The x-ray results are compared and correlated with supporting data of in situ spectroscopic ellipsometry as well as Monte Carlo simulations of the irradiation effects and surface diffusion of adatoms. We found that the texture and the surface and interface morphology are sensitive to the mechanism of dissipation of the impinging ions. If the energy is enough to overcome the subplantation threshold (∼50eV), then the films are highly compressed and exhibit ultrasmooth surfaces and rough interfaces. In this case, the texture of the films is not affected much by the ion energy, since the energy is dissipated in the bulk and contributes less to the surface mobility of adatoms. On the other hand, when the ion energy is below the subplantation threshold the texture of the films strongly depends on the ion energy and flux, the interfaces are atomically sharp and the surface morphology depends on the mobility and surface diffusion length of adatoms. However, in both cases these effects are dominant at the homogeneous growth. At the initial stages of nucleation and island growth the differences in the growth due to irradiation conditions are not pronounced and the thermodynamics of wetting of TiN on Si are prevailing factors.

Effect of substrate surface ion bombardment etching on reaction between chromium thin films and steel substrates

Thin coating films of transition metal carbides and nitrides are used because of their refractory characteristics and good mechanical properties . In this work we study the interaction between chromium thin films and steel substrates 100C6 type (AFNOR norms) containing approximately 1 wt.% of carbon. Chromium films are deposited at 200 °C by magnetron sputtering . In order to study the correlation between the pre-cleaning of substrates and the properties of coatings, two series of samples were prepared; the first is distinguished from the second by ion bombardment etching before chromium deposition. The study is carried out by X-ray diffraction, Auger electron spectroscopy , scanning electron microscopy and Vickers micro-hardness measurements. The changes observed in sample characteristics after heat treatments are associated with carbon and iron diffusion and with carbide formation. It is established that the micro-hardness of the first series is higher than that of the second series. This large difference is due to substrate etching, as induced by surface ion bombardment.

Effect of substrate surface ion bombardment etching on reaction between chromium thin films and steel substrates

Thin coating films of transition metal carbides and nitrides are used because of their refractory characteristics and good mechanical properties. In this work we study the interaction between chromium thin films and steel substrates 100C6 type (AFNOR norms) containing approximately 1 wt.% of carbon. Chromium films are deposited at 200 °C by magnetron sputtering. In order to study the correlation between the pre-cleaning of substrates and the properties of coatings, two series of samples were prepared; the first is distinguished from the second by ion bombardment etching before chromium deposition. The study is carried out by X-ray diffraction, Auger electron spectroscopy, scanning electron microscopy and Vickers micro-hardness measurements. The changes observed in sample characteristics after heat treatments are associated with carbon and iron diffusion and with carbide formation. It is established that the micro-hardness of the first series is higher than that of the second series. This large difference is due to substrate etching, as induced by surface ion bombardment.

Structural factors determining the nanomechanical performance of transition metal nitride films

ABSTRACTChromium nitride (CrN) and Titanium nitride (TiN) thin films were deposited employing unbalanced magnetron sputtering (UBMS) for various values of substrate bias voltage (Vb). The structural characterization of the films in terms of phase identification and the density determination was achieved utilizing X-Ray techniques (XRD and XRR respectively), while the internal stresses were calculated by the change of the substrate's curvature using Stoney's equation. The nanomecahnical properties of the films (hardness and elastic modulus) were investigated using the Nanoindentation (NI) technique in the Continuous Stiffness Measurement (CSM) configuration. According to the NI results the hardness of the films ranges between between 15–25 GPa while the elastic modulus between 180–250 GPa. The analysis revealed that the hardness of the films is maximum when their orientation is pure (either [111] or [100]), while it is minimized under mixed orientation regime. Furthermore, the hardness of the films increases as the internal compressive stresses and the mass density increase. The latter can be validated through the comparison of the results concerning the above films to reported results for TiN films prepared by balanced magnetron sputtering (BMS)

Microstructure and mechanical properties of Zr–Si–N films prepared by rf-reactive sputtering

ZrN and ZrSiN films were prepared in an rf sputtering apparatus that has a pair of targets facing each other (referred to as the facing target—type rf sputtering). Films were deposited on silicon wafers without bias application or substrate heating in order to examine only the effect of silicon addition to the transition metal nitride films. The contents of zirconium, nitrogen, and silicon of the films were determined with an electron probe microanalyzer. The transmission electron microscopy studies were carried out in addition to x-ray diffraction. For the high resolution transmission electron microscopy observation, the field emission type transmission electron microscope was used, which provides a point-to-point resolution of 0.1 nm. The samples were observed both parallel and perpendicular to the film surface, which were plane and cross sectional views, respectively. In order to investigate the relationship between the mechanical properties and microstructure of films, the hardness was measured by a nanoindentation system at room temperature. The load was selected to keep the impression depth below 60 nm (not more than 5% of film thickness) so that the influence from the substrate can be neglected. The hardness of the films increases with small Si additions reaching the maximum value of 35 GPa at around 3 at. % Si. The tendency to grow columnar grains was strongest around this composition, while grains became equiaxial above 5 at. % of Si. The films containing 12.8% Si, which showed the lowest hardness of 18 GPa, consist of nanocrystal grains. The presence of ZrN nanocrystals embedded in Si3N4 was not observed in the present study. The hardening mechanism due to the addition of small amounts of Si in ZrN can not be determined at this time. The grain size and residual stress can make minor contributions to the hardening. A possibility of solid solution hardening due to atomistic strain, such as nitrogen atoms at interstitial sites or other point defects is postulated and should be examined further.

Preparation of superconducting epitaxial thin films of transition metal nitrides on silicon wafers by molecular beam epitaxy

Epitaxial thin films of NbN and CrN on Si substrates were prepared by molecular beam epitaxy (MBE) and were characterized by X-ray diffraction, X-ray diffraction pole figure measurements, atomic force microscopy (AFM), and magnetic measurements. To our knowledge, CrN was grown epitaxially on Si substrates for the first time. Although lattice parameters of CrN and Si are significantly different, the epitaxial growth of CrN on Si(1 0 0) was explained by a good fitting of 4 unit cells of CrN to 3 unit cells of Si (misfit: 1.7%). NbN was found to grow epitaxially by using CrN as a buffer layer on Si(1 0 0), and this film was superconducting below 4.5 K. A CrN/NbN/CrN epitaxial sandwich structure was also prepared successfully, indicating that the NbN–CrN system is promising for superlattices of superconductor and insulator fabricated on Si substrate.

Epitaxial oxide thin films by pulsed laser deposition: Retrospect and prospect

Pulsed laser deposition (PLD) is a unique method to obtain epitaxial multi-component oxide films. Highly stoichiometric, nearly single crystal -like materials in the form of films can be made by PLD. Oxides which are synthesized at high oxygen pressure can be made into films at low oxygen partial pressure. Epitaxial thin films of high Tc cuprates, metallic, ferroelectric, ferromagnetic, dielectric oxides, superconductor-metal-superconductor Josephson junctions and oxide superlattices have been made by PLD. In this article, an ove rview of preparation, characterization and properties of epitaxial oxide films and their applications are presented. Future prospects of the method for fabricating epitaxial films of transition metal nitrides, chalcogenides, carbides and borides are discus sed.

Formation of niobium nitride by rapid thermal processing

The formation of group V transition metal nitride films by means of rapid thermal processing (RTP) has been investigated. Here we focus on the nitridation of niobium films of 200–500 nm thickness in the temperature range from 500 to 1100°C under laminar flow of molecular nitrogen or ammonia. The nitride phases formed were characterized by X-ray diffraction (XRD). Secondary neutral mass spectrometry (SNMS) and transmission electron microscopy (TEM) in combination with electron energy loss spectroscopy (EELS) were carried out on samples of selected experiments to provide more detailed information about the initial stages of nitride formation and the microstructure of the films. A classical formation sequence of nitride phases was observed with increasing nitrogen content in the order: α-Nb(N)→β-Nb 2N→γ-Nb 4N 3→δ′-NbN→Nb 5N 6. Furthermore, oxide enriched regions were discovered inside the metal films. These turned out to be formed mainly in the nitride sequence between the a-αNb(N) and β-Nb 2N-phases at the Nb/SiO 2 interface due to a reaction of the Nb with the SiO 2 layer of the silicon substrates on which the films had been deposited. The SiO 2 layer acts as diffusion barrier for nitrogen but also as source for oxygen, according to SNMS and TEM/EELS studies, resulting in the formation of Nb-oxides and/or oxynitrides at the Nb/SiO 2 interface.

Superconducting transition metal nitride films for THz SIS mixers

The development of sensitive THz SIS mixers requires a low-loss superconducting strip-line material with a transition temperature above 15 K. In this paper we examine the properties of (Nb,Ti)N, NbN, and (Nb,Zr)N thin films sputtered at ambient substrate temperature on glass wafers. The best properties are observed for the (Nb,Ti)N films, sputtered from an NbTi alloy target with 30 at.% Ti. A similar picture is observed for the epitaxial films deposited on the MgO wafers. We have also examined the homogeneity of the (Nb,Ti)N films versus film thickness and in plane since this factor is clearly important for the microwave behavior of the strip-line. We observe that (Nb,Ti)N films deposited on silicon, sapphire, and glass wafers have much worse homogeneity compared to the films deposited on the MgO wafers.

Formation of Transition Metal Nitrides by Rapid Thermal Processing (RTP)

Rapid thermal processing (RTP) was used to prepare group-5 transition metal (V, Nb, Ta) nitride films and to study the early stages of nitrogen incorporation in the metals and nitride formation. The RTP experiments were performed in the temperature range from 400 to 1000 °C in N2 and NH3 for 5 and 60 s, respectively. After RTP the films were characterized by X-ray diffraction (XRD). In the V–N system beside the known phases α-V(N) solid solution, β-V2N and δ-VN an intermediate phase denoted *-VNybetween α-V(N) and β-V2N was discovered which formed in the range from 600 to 800 °C in N2 and NH3. This phase may contain oxygen and, hence, may rather be considered as oxynitride. An analogous intermediate phase was also observed in the Nb–N and Ta–N systems. The SiO2 layer on the Si substrate on which the metal films were deposited acts as diffusion barrier for nitrogen, leading to a pile up of N in the metal film. In the nitridation of Ti/V multilayers in NH3 the indiffusion of N is faster than the interdiffusion and mixing of the metal at T ≤ 900 °C.