CrN Thin Films Research Articles

Evolution of structural and optical properties of Ag implanted CrN thin films with annealing temperature

This study reports on the changes of the structural and optical properties occurring in CrN thin films upon Ag ion implantation. The films were grown by reactive sputtering on top of Si (100) wafers at a temperature of around 150 °C. Subsequently, the films were implanted with Ag ion fluences in the range of 0.5 × 1016 ions/cm2 ‒ 2 × 1016 ions/cm2 with energy of 200 keV. The structural and morphological changes, promoted by in-vacuum annealing of the as-implanted thin films at 200 °C, 400 °C and 700 °C, resulted in different optical responses of the CrN:Ag films due to the formation of Ag nanoparticles. The nanoparticles were inhomogenously distributed through the layer, which is related to the implantation distribution of silver in CrN. Apart from this, Ag nanoparticles with a size of 20–25 nm were formed at the surface of the layer. These structural properties are responsible for the formation of a broad optical absorption peak. This peak is located at ∼420 nm and can be associated with the plasmon resonance of Ag particles embedded in the CrN matrix.

Effects of indenter angle on micro‐scale fracture toughness measurement by pillar splitting

AbstractWe present improvements to a recently developed pillar splitting technique that can be used to characterize the fracture toughness of materials at the micrometer scale. Micro‐pillars with different aspect ratios were milled from bulk Si (100) and TiN and CrN thin films, and pillar splitting tests were carried out using four different triangular pyramidal indenters with centerline‐to‐face angles varying from 35.3° to 65.3°. Cohesive zone finite element modeling (CZ‐FEM) was used to evaluate the effect of different material parameters and indenter geometries on the splitting behavior. Pillar splitting experiments revealed a linear relationship between the splitting load and the indenter angle, while CZ‐FEM simulations provided the dimensionless coefficients needed to estimate the fracture toughness from the splitting load. The results provide novel insights into the fracture toughness of materials at small‐scales using the pillar spitting technique and provide a simple and reliable way to measure fracture toughness over a broad range of material properties.

Clustering of gold particles in Au implanted CrN thin films: The effect on the SPR peak position

We report on the formation of gold particles in 280nm thin polycrystalline CrN layers caused by Au+ ion implantation. The CrN layers were deposited at 150°C by d.c. reactive sputtering on Si(100) wafers and then implanted at room temperature with 150keV Au+ ions to fluences of 2×1016cm−2 to 4.1×1016cm−2. The implanted layers were analysed by the means of Rutherford backscattering spectrometry, X-ray diffraction, atomic force microscopy and spectroscopic ellipsometry measurements. The results revealed that the Au atoms are situated in the near-surface region of the implanted CrN layers. At the fluence of 2×1016cm−2 the formation of Au particles of ∼200nm in diameter has been observed. With increasing Au ion fluence the particles coalesce into clusters with dimensions of ∼1.7μm. The synthesized particles show a strong absorption peak associated with the excitation of surface plasmon resonances (SPR). The position of the SPR peak shifted in the range of 426.8–690.5nm when the Au+ ion fluence was varied from 2×1016cm−2 to 4.1×1016cm−2. A correlation of the shift in the peak wavelength caused by the change in the particles size and clustering has been revealed, suggesting that the interaction between Au particles dominate the surface plasmon resonance effect.

Stress Study on CrN Thin Films with Different Thicknesses on Stainless Steel

The reliability of a substrate curvature-based stress measurement method for CrN thin films on substrate with fluctuant surface was discussed. The stress error led by the ignorance of substrate thermal deformation was studied. Results showed that this error could be as large as several hundred MPa under general deposition conditions. Stress in the CrN thin films with different thicknesses ranging from 110 to 330 nm on stainless steel was studied by this method, in comparison with conventional results on silicon wafer. The thin films’ morphology and structure were investigated and related to the film stress. A significant result of the comparison is that stress evolution in the thin films on steel obviously differs from that on silicon wafer, not only because the two substrates have different coefficients of thermal expansion, which provokes thermal stress, but also the considerable discrepancy in the thin films’ grain coarsening rate and structure that induce different intrinsic stresses.

The improved corrosion resistance of sputtered CrN thin films with Cr-ion bombardment layer by layer

The sputtered CrN coatings, which were bombarded by the energetic Cr-ion via filtered arc ion plating layer by layer, were prepared to improve the corrosion resistance of the coated samples. By controlling the times of Cr ion bombardment, the influence of the Cr ion bombarding of the sputtered CrN were investigated from the aspect of the microstructure and corrosion behavior. The results indicated that the CrN film showed a suppressed effect on the coarse columnar structure and a more compact structure with lower porosity by introducing the Cr-ion bombardment. Potentiodynamic polarization curves showed that the CrN coated samples had an obvious improved corrosion resistance after the energetic Cr ion bombardment. With the bombarding times of Cr ion increasing from four to ten, the corrosion resistance of CrN coated samples showed a further improvement with corrosion potential increased about 100 mV and the corrosion current density decreased more than one order of magnitude when compared with the non-bombarded CrN coating.

The Effect of Base Pressure on Crystal Structure and Microstructure of CrN Thin Film Deposited by Reactive Magnetron Sputtering

The CrN thin films were deposited using reactive magnetron sputtering by varying base pressure to investigate the crystal structure, microstructure and composition of thin film. In this work, the films properties were characterized by XRD, FE-SEM and EDX techniques. The crystal structures were obtained the cubic of CrN with the crystal size between 23.23 – 28.25 nm and lattice parameters a = b = c = 4.142 - 4.160 Å. The XRD results indicated that the growth of preferred orientation was changed from (200) to (111) plane with increased the base pressure. The surface morphology of CrN thin films did not affected from base pressure. The thickness of CrN thin films which obtained from cross section analysis was decreased from 1788 to 1745 nm by varying the base pressure. The columnar pattern acccompany with the dense structure were investigated from the cross-section analysis. The Cr composition was substantly decreased whereas theN2 composition were increased which observed from EDX technique.

Thickness Dependent Structural and Electrical Properties of Magnetron Sputtered Nanostructured CrN Thin Films

In the present work, we have investigated the structural and electrical properties of CrN thin films for a thickness t in the 30-220 nm range, grown on Si (100) substrates. The CrN/Si (100) films exhibits a structural transition from hexagonal phase (β-Cr2N) to cubic phase (CrN) with the increasing in film thickness, the change in structural transition is attributed to the decrease of film-substrate interfacial strain. From electrical resistivity measurements, the thickness of 150 nm CrN/Si (100) film shown the metal-semiconductor phase transition at around 250 K with energy band gap (Eg) 81 meV in semiconducting region, whereas the thickness of 30, 110 and 220 nm CrN/Si(100) films were shown only semiconducting behaviour for whole temperature range of 50-400 K. On the other hand, a clear grain size was increased in CrN/Si films with increasing thickness and its influence on transport properties was also seen. The possibility of phase transition and occurrence of semiconducting behaviour in the CrN films were analysed.

CrN thin films prepared by reactive DC magnetron sputtering for symmetric supercapacitors

CrN thin films deposited on Si substrates show promising applications as electrode materials for high performance supercapacitors.

The Adhesion of CrN Thin Films Deposited on Modified 42CrMo4 Steel

Here, the effect of adhesion of CrN hard coatings on modified 42CrMo4 steel substrate is presented. Modifications of the substrate are shot peening, nitriding, shot peening, and nitriding joined process. In the shot peening process, two variable process parameters were used: exposure time (t) and air pressure (p). The nitriding process was conducted in the following parameters: nitriding potential Np = 4.86, nitriding time tn = 3 h, and temperature process T = 530°C. Modified substrates were characterized by surface hardness HV5 and hardness profiles on the cross section of samples and by surface roughness parameters. On such prepared substrates, the CrN coating was deposited. The adhesion of CrN coating on modified substrates was defined by the scratch test. Chemical and phase composition of the films was determined using EDS method and X-ray diffraction, respectively. The surface hardness of deposited films was also defined. The substrate of 42CrMo4 steel without mechanical and heat treatment coated by hard CrN film was used as a reference.

CrN thin films with ultra-low magnetoresistance prepared via solution processing for large-area applications

CrN thin films are versatile in lots of applications. To develop a facile processing method for large-area CrN thin films with low-cost is unquestionable to improve the technical advances in CrN applications. In this work, CrN thin films are prepared by chemical solution deposition processing for large-area applications. The electrical transport properties are investigated, showing semiconductor-like properties. Magnetoresistance at low temperatures under high magnetic fields is observed in the CrN thin films, showing ultra-low magnetoresistance under 14T of −0.14% and −0.10% at 4.2 and 2 K, respectively.

Nanostructure and Microstructure Evolution of D.C. Reactive Magnetron Sputtered CrN Thin Films

The CrN thin films were deposited on silicon (100) substrate using reactive magnetron sputtering technique. The films were characterized by XRD, FE-SEM, EDS and nanoindentation techniques to examine the effect of deposition time on crystal structure, compositions, microstructure and hardness. The crystal structure, microstructure, element composition and hardness. The higher crystallinity through longer deposition time were investigated. The grain aggregration with columnar structure were obtained from FE-SEM. The Cr and N contents were not direct relationship with deposition time. The CrN coated sample performed hardness varied between 9 - 16 GPa.

Adhesion analysis for chromium nitride thin films deposited by reactive magnetron sputtering

The thin film industry is continuously growing due to the wide range of applications that require the fabrication of advanced components such as sensors, biological implants, micro-electromechanical devices, optical coatings and so on. The selection regarding the deposition materials, as well as the deposition technology influences the properties of the material and determines the suitability of devices for certain real-world applications. This paper is focused on the adhesion force for several chromium nitride thin films obtained by reactive magnetron sputtering. All chromium nitride thin films were deposited on a silicon substrate, the discharge current and the argon flow being kept constant. The main purpose of the paper is to determine the influence of deposition parameters on the adhesion force. Therefore some of the deposition parameters were varied in order to study their effect on the adhesion force. Experimentally, the values of the adhesion force were determined in multiple points for each sample using the spectroscopy in point mode of the atomic force microscope. The obtained values were used to estimate the surface energy of the CrN thin films based on two existing mathematical models for the adhesion force when considering the contact between two bodies.

Thermal conductivity and mechanical properties of AlN-based thin films

While many research activities concentrate on mechanical properties and thermal stabilities of protective thin films, only little is known about their thermal properties being essential for the thermal management in various industrial applications. Based on the 3ω-method, we show the influence of Al and Cr on the temperature dependent thermal conductivity of single-phase cubic structured TiN and single-phase wurtzite structured AlN thin films, respectively, and compare them with the results obtained for CrN thin films. The dc sputtered AlN thin films revealed a highly c-axis oriented growth for deposition temperatures of 250 to 700 °C. Their thermal conductivity was found to increase strongly with the film thickness, indicating progressing crystallization of the interface near amorphous regions during the sputtering process. For the 940 nm AlN film, we found a lower boundary for the thermal conductivity of 55.3 W m-1 K-1. By the substitution of only 10 at. % Al with Cr, κ significantly reduces to ∼5.0 W m-1 K-1, although the single-phase wurtzite structure is maintained. The single-phase face centered cubic TiN and Ti0.36Al0.64N thin films exhibit κ values of 3.1 W m-1 K-1 and 2.5 W m-1 K-1, respectively, at room temperature. Hence, also here, the substitutional alloying reduces the thermal conductivity, although at a significantly lower level. Single-phase face centered cubic CrN thin films show κ values of 3.6 W m-1 K-1. For all nitride based thin films investigated, the thermal conductivity slightly increases with increasing temperature between 200 and 330 K. This rather unusual behavior is based on the high defect density (especially point defects) within the thin films prepared by physical vapor deposition.

A study of the oxidation behavior of CrN and CrZrN ceramic thin films prepared in a magnetron sputtering system

CrN and CrZrN ceramic thin films were produced by a planar type reactive sputtering system on glass and stainless steel substrates. We investigated oxidation resistance of CrN and CrZrN ceramic thin films with different Zr contents. The structure of the films at different thermal-annealing temperatures was investigated by X-ray diffraction (XRD), atomic force microscopy (AFM) and scanning electron microscopy (SEM). The mechanical properties of the films at different thermal-annealing temperatures were measured by nano-indentation. The results of this study showed that the addition of few amount of Zr (0.4at%), can improve thermal stability of CrZrN ceramic thin film and increase the oxidation temperature of the film from 600°C to 800°C. The relatively good oxidation resistance (800°C) and high hardness of the film with the lowest Zr content, indicates that this film is a good candidate for high temperature applications.

CrN thin films deposited by HiPIMS in DOMS mode

Abstract It is well known that increasing the energy of the bombardment species, whether by using a bias or an additional ion source in direct current magnetron sputtering (DCMS) or by optimizing the deposition conditions in mid-frequency bipolar magnetron sputtering, enables us to tailor the properties of the CrN thin films. In the last fifteen years, several magnetron sputtering deposition methods have been developed which have aimed to produce highly ionized fluxes of sputtered material, thus enabling increased control over the energy and impinging angle distributions of the bombarding species. In this study, CrN thin films were deposited by deep oscillation magnetron sputtering (DOMS), a variant of High-power Impulse Magnetron Sputtering (HiPIMS), in order to study the effect of the additional control of the energetic ion bombardment on the film properties. The structural properties of the CrN films (lattice parameter and preferred orientation) showed that an intense energetic bombardment is always present in the DOMS deposition irrespective of the deposition conditions. This energetic bombardment was attributed to energetic N neutrals which are reflected at the target surface upon impingement of N2+ ions. A change from a columnar growth mode to a featureless one was observed with an increasing peak power at both 0.3 and 0.7 Pa. At the same time, the hardness of the films increased from 21–22 GPa to 28–29 GPa. This transformation was attributed to the increasing fraction of ionized sputtered species with increasing peak power. The columnar growth is interrupted by preventing the shadowing effect, i.e., due to the higher ionization fraction at higher pressure and/or peak power, rather than by overcoming the shadowing effect by using more energetic bombardment.

Thermal Contact Conductance Analysis of Nitride and Carbonitride Thin Film Coatings for Thermal Interface Material Application

In order to reduce and maintain the bond line thickness between substrate and LED package, solid thin film with good thermal conductivity is suggested as thermal interface material and the proposed film thickness is about less than 1 µ. The surface parameter such as roughness and hardness is a key factor which alters the contact conductance between the two matt surfaces. Consequently, filtered vacuum cathodic arc deposited nitride thin films (CrN, TiN, AlTiN, and TiCN) on copper substrate were tested for thermal interface material applications in electronic packaging. The thermal contact conductance of the prepared thin films was evaluated using surface properties such as microhardness and surface roughness. The results were verified with the theoretical model. The measured microhardness and surface roughness of CrN thin film are 17 GPa (low) and 0.768 µm (high), respectively. The measured thermal contact conductance of all thin films showed linear properties for applied pressure and very close to the values of theoretical model. High value in thermal contact conductance of about 256 W/m2 K was noticed with CrN thin film at 1100 kPa. The percentage of deviation for our measured contact conductance value from the theoretical model value was decreasing for the increased contact pressure and observed low value (7 pct) for CrN thin film at 1100 kPa. The thermal conductivity of all thin films was also calculated from the conductance model and observed high value (19.34 W/mK) with CrN thin film.

Measuring Plasticity in Confined Cu Thin Films at Different Geometries

We report quantitative measurement of plasticity in confined Cu thin films with a new micro-pillar testing protocol. Polycrystalline Cu and CrN thin films were sequentially sputter deposited onto Si (100) substrates, forming thin film assemblies in which polycrystalline Cu thin films of various thicknesses were confined between non-deforming Si and CrN. Cylindrical micro-pillars of CrN/Cu/Si were fabricated through scripted focused Ga+ ion beam milling, with the interfaces either normal to the axial direction or at a 45° inclination. The CrN/Cu/Si micro-pillars were compression loaded in the axial direction with a flat diamond punch on an instrumented nanoindenter. The axial compression loading caused extensive plasticity within the thin Cu interlayers with the interfaces in both the normal and inclined orientations, but with distinctly different responses. We show that significant plastic flow occurs within the confined Cu thin films in both normal compression and shear loading. The flow stress of the confined Cu films is dependent on the Cu layer thickness and the deformation geometry. The presently described micro-pillar testing protocol offers quantitative evaluation of the plastic response of thin metal films under different deformation geometries. The present results offer new experimental examples of scale-dependent plasticity in thin metal films, and new experimental test cases for non-local plasticity theories.

Irradiation induced formation of VN in CrN thin films

Reactively sputtered CrN layer, deposited on Si(100) wafer, was implanted at room temperature with 80-keV V+ ions to the fluence of 2×1017ions/cm2. After implantation the sample was annealed in a vacuum, for 2h at 700°C. The microstructure and chemical composition of CrN films was investigated using Rutherford backscattering spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction and cross-sectional transmission electron microscopy (conventional and high-resolution), together with fast Fourier transformation analyses. It was found that vanadium atoms are distributed in the sub-surface region of CrN layer, with the maximum concentration at ∼20nm. After annealing the formation of VN nanoparticles was observed. The nanoparticles are spherical shaped with a size of 8–20nm in diameter.

Microstructure-controlled depth gradients of mechanical properties in thin nanocrystalline films: Towards structure-property gradient functionalization

Although the influence of the grain size on the mechanical properties of polycrystalline materials is well understood, the occurrence of depth-gradients of grain size, microstructure, and residual stresses in nanocrystalline thin films and their effect on the functional properties is a phenomenon which has not yet been studied in detail. Hence in this work, single-layered polycrystalline and mosaic epitaxial as well as multilayered CrN thin films were characterized by a combination of averaging as well as depth-resolved experimental techniques, such as cross-sectional X-ray nanodiffraction and small-angle cross-sectional nanoindentation. The results reveal the fundamental relationship between gradients of grain size, microstructure, and stresses, controlled by the film growth conditions, and gradients of hardness and elastic modulus. The effect of the compressive stress and structural defects associated with high particle energy on the mechanical properties of nanocrystalline thin films was found to be dominant over the grain size and crystallographic texture. These findings open the way to functionalize structure-property gradients in nanocrystalline thin films through microstructural design as demonstrated for multilayered CrN films.

Epitaxial CrN thin films with high thermoelectric figure of merit.

A large enhancement of the thermoelectric figure of merit is reported in single-crystalline films of CrN. The mechanism of the reduction of the lattice thermal conductivity in cubic CrN is similar to the resonant bonding in IV-VI compounds. Therefore, useful ideas from classic thermo-electrics can be applied to tune functionalities in transition metal nitrides and oxides.