Sputtering Of Cr Research Articles

Characterizations of CrN/a-CN x nanolayered coatings deposited by DC reactive magnetron sputtering of Cr and graphite targets

CrN/a-CN x nanolayered coatings have been deposited by DC reactive magnetron sputtering of pure Cr and graphite targets. The total thickness is 1 μm and that of a-CN x layers is kept constant at 3.5 nm. The period (bilayer thickness) is in the range 8–16 nm. CrN and a-CN x layers are crystalline and amorphous respectively. The decrease of CrN layers’ thickness (decrease of period) in the stack leads to refinement of CrN microstructure associated with (200) preferred orientation. The hardness of nanolayered films is independent of the period’s thickness, while internal compressive stress, which remains between that of each elementary layer, follows an evolution close to that of the law of mixtures. The best tribological behaviours are reached for a periods’ thickness of 8 nm.

Fabrication and adhesion strength of Cu/Ni–Cr/polyimide films for flexible printed circuits

The adhesion strength of a Cu/Ni–Cr/polyimide flexible copper clad laminate (FCCL), was evaluated according to the thickness of the Ni–Cr (Ni:Cr = 95:5 ratio) seed layer using the 90° peel test. The changes in the morphology, chemical bonding and adhesion properties were characterized by SEM, AFM and XPS. The peel strength of the FCCL increased with increasing thickness of the Ni–Cr seed layer, due to the increase in the ion bombardment caused by the higher power used in the Ni–Cr sputtering process. This increase in the FCCL peel strength was attributed to the lower proportion of C–N bonds and higher proportion of C–O bonds in the polyimide surface. The adhesion strength between the metal and polyimide was mostly attributed to the chemical interaction between the metal layer and the functional groups of the polyimide.

The characterization of Cr secondary oxide phases in ZnO films studied by X-ray spectroscopy and photoemission spectroscopy

X-ray absorption near-edge structure (XANES), X-ray emission spectroscopy (XES), and X-ray photoemission spectroscopy (XPS) were used to characterize the Cr secondary oxide phases in ZnO films that had been prepared using a co-sputtering method. Analysis of the Cr L 3,2-edge XANES spectra reveals that the intensity of white-line features decreases subtly as the sputtering power increases, indicating that the occupation of Cr 3 d orbitals increases with Cr concentration in (Zn, Cr)O films. The O K-edge spectra show that the intensity of XANES features of (Zn, Cr)O films is lower than those of ZnO film, suggesting enhanced occupation of O 2 p-derived states through O 2 p–Cr 3 d hybridization. The XES and XPS spectra indicate that the line shapes in the valence band of (Zn, Cr)O films are quite different from those of ZnO and that the Cr 2O 3 phase dominates the spinel structure of (Zn, Cr)O films increasingly as the Cr sputtering power is increased. Over all results suggest that the non-ferromagnetic behavior of (Zn, Cr)O films can be attributed to the dominant presence of Cr 2O 3, whereas the bulk comprise phase segregations of Cr 2O 3 and/or ZnCr 2O 4, which results them the most stable TM-doped ZnO material against etching.

Time and energy resolved ion mass spectroscopy studies of the ion flux during high power pulsed magnetron sputtering of Cr in Ar and Ar/N 2 atmospheres

Mass spectroscopy was used to analyze the energy and composition of the ion flux during high power pulsed magnetron sputtering (HIPIMS/HPPMS) of a Cr target in an industrial deposition system. The ion energy distribution functions were recorded in the time-averaged and time-resolved mode for Ar +, Ar 2+, Cr +, Cr 2+, N 2 + and N + ions. In the metallic mode the dependence on pulse energy (equivalent of peak target current) was studied. In the case of reactive sputtering in an Ar/N 2 atmosphere, variations in ion flux composition were investigated for varying N 2-to-Ar flow ratio at constant pressure and HIPIMS power settings. The number of doubly charged Cr ions is found to increase linearly with increasing pulse energy. An intense flux of energetic N + ions was observed during deposition in the reactive mode. The time evolution of ion flux composition is analyzed in detail and related to the film growth process. The ionization of working gas mixture is hampered during the most energetic phase of discharge by a high flux of sputter-ejected species entering the plasma, causing both gas rarefaction and quenching of the electron energy distribution function. It is suggested that the properties (composition and energy) of the ion flux incident on the substrate can be intentionally adjusted not only by varying the pulse energy (discharge peak current), but also by taking advantage of the observed time variations in the composition of ion flux.

Structural and morphological evolution in magnetron co-sputtered (Zn, Cr)O films

In this study, x-ray diffraction, scanning electron microscopy, micro-Raman spectroscopy, x-ray absorption near-edge structure and particle-induced x-ray emission are used to characterize the microstructure of (Zn, Cr)O films prepared using a co-sputtering method. We found that the Cr ions did not substitute for the Zn sites but instead formed Cr nano-particles and secondary oxide phases (SOPs) of Cr2O3 and/or ZnCr2O4 in co-sputtered Zn1−xCrxO films with Cr content x ⩾ 0.1. Evidence is presented for the evolution of SOPs formed in (Zn, Cr)O films with increasing Cr sputtering power. Based on the inspection of the Cr and Zn contents in (Zn, Cr)O films, we conclude that the formation of the Cr2O3 phase is driven by a substantial increase in the atomic ratio of Cr/Zn, followed by the formation of a ZnCr2O4 phase promoted by a higher content of Cr than of Zn in film with increasing Cr sputtering power. It seems that a strong preference of Cr for octahedral rather than tetrahedral coordination with oxygen would trigger the formation of SOPs rather than the substitution of Cr into Zn sites and could be an obstacle for achieving a real Cr-substituted ZnO dilute magnetic oxide.

Magnetron sputtering of hard Cr–Al–N–O thin films

The design and synthesis of advanced wear resistant coatings combining metallic or covalent bonded hard materials and oxide phases in a novel metastable or nanocomposite thin film structure is an emerging new field of materials research. In this paper, the phase formation, microstructure evolution and correlation between the constitution, microstructure and growth conditions of magnetron-sputtered hard Cr–Al–N–O thin films are described. The deposition experiments were carried out with a Leybold Z 550 PVD machine following a combinatorial materials science based approach for the sputtering from a segmented target, composed of bulk ceramic CrAlN and Al 2O 3 pieces. In each experiment, six coatings of different composition, constitution and microstructure were obtained simultaneously by placing six substrate samples in individual positions relative to the target. Both non-reactive and reactive deposition processes (in a nitrogen/argon atmosphere) were applied. No substrate bias was used and the substrate temperature was kept constant below 200 °C. The constitution, microstructure and Vickers microhardness of the coatings is discussed in dependence of their chemical composition. While non-reactive deposition processes resulted in the growth of nanocrystalline thin films of moderate hardness but brittle character, the reactive deposition led to the growth of nanocrystalline coatings with high hardness (up to 2500 HV 0.05) and toughness.

Synthesis, Composition, and Electronic Structure of Cr−Si−N Thin Films Formed by Reactive Ion Beam Mixing of Cr/Si Interfaces

Cr−Si−N thin films have been synthesized by 3 keV N2+ reactive ion beam mixing (IBM) of Cr/Si interfaces. The kinetics of growth, composition, and electronic structure of the films formed have been analyzed using X-ray photoelectron spectroscopy, angle-resolved X-ray photoelectron spectroscopy (ARXPS), ultraviolet photoelectron spectroscopy, factor analysis, and Monte Carlo TRIDYN simulations. ARXPS results show that the composition of the films formed by reactive IBM is rather uniform in the near-surface region. The comparison of experimental results with those obtained from TRIDYN, which uses pure ballistic mechanisms, suggests that the processes driven by residual defects are the rate-controlling mechanisms during the reactive IBM of Cr/Si interfaces. The reactive IBM kinetic is characterized by two stages: below ∼3 × 1016 ions/cm2, a strong decrease of the Cr concentration along with a fast nitrogen incorporation is observed. This behavior can be explained mainly by Cr sputtering and nitrogen implantation. During this first stage, the formation of chromiun nitride and a small Si incorporation in the near-surface region are also observed, suggesting the formation of a CrNx/SiNx nanocomposite film. For ion doses above ∼3 × 1016 ions/cm2, the Cr/Si ratio can be varied in a broad range with nearly constant nitrogen concentration, as a consequence of sputtering, nitruration, and strong intermixing effects taking place simultaneously. Furthermore, during this second stage, chromium nitride is tranformed into a ternary (Cr−Si)N compound due to the strong Si incorporation in the near-surface region.

Morphology and conjugation of nanocrystals growing in Cr-O and V-O amorphous films during annealing

Methods of transmission electron microscopy and electron diffraction are used to determine the main morphological types of Cr 2 O 3 and V 2 O 3 nanocrystals as well as their evolution in the process of growth in crystallizing amorphous laser condensates during annealing. Films are deposited from laser erosion plasma by sputtering of Cr and V targets in an oxygen atmosphere. Annealing is carried out with an electron beam in the microscope column. Orientational relations are established for conjugation of crystals of various morphological types. The crystallization process in amorphous films with a thickness gradient is investigated. The impurity and size-impurity effects of amorphous state stabilization are revealed.

On the room-temperature ferromagnetism of Zn 1−xCr xO thin films deposited by reactive co-sputtering

We report on the preparation and detailed characterization of ferromagnetic (FM) Zn 1− x Cr x O thin films deposited on Si substrates using reactive co-sputtering of Cr and Zn in controlled oxygen atmosphere. X-ray diffraction (XRD) data showed wurtzite ZnO peaks in the FM films prepared with lower Cr sputter powers, whose position and intensities are influenced by Cr doping. However, samples prepared with higher Cr powers did not show ferromagnetism but displayed evidence of Cr 2O 3 and ZnCr 2O 4 phases with no zinc oxide (ZnO) phase. The magnetization is higher (saturation magnetization M s=18 emu/cm 3) for lower Cr concentrations and decreases for higher Cr doping. The samples were investigated extensively to understand the film composition, dopant distribution, homogeneity and potential origin of the observed ferromagnetism. Particle-induced X-ray emission (PIXE) studies were employed to determine the chemical composition as well as the Cr/Zn ratio in the films. Film uniformity and homogeneity, investigated using Rutherford backscattering spectrometry, showed a relatively uniform ZnO layer in the as-prepared samples but, in a sample annealed at 800 °C, showed some diffusion of Si from the substrate. X-ray photoelectron spectroscopy (XPS) studies indicated that Cr ions are in the oxidized state, but showed changes in the binding energy and Cr concentration when measured after removing 10 nm from the surface using Ar ion sputtering. Possible origins of the observed FM behavior are discussed based on the comprehensive characterization results.

Mechanical and physical properties of C and C–Cr sputter coatings measured at the nano-scale

X-ray photoelectron spectroscopy and nano-indentation were used to investigate the chemical/structural composition and the nano-scale mechanical/tribological properties of a group of sputtered C coatings doped with zero, low and high amounts of Cr. At zero and low Cr concentration, the coatings were composed of sp 2 and sp 3 hybridised C–C bonds and at high Cr concentration the coating reverted to a Cr:C ratio of 3:2, suggesting a Cr 3C 2 composition. The diffusion of adsorbed atmospheric O/H 2O from the surface of the coating into the bulk was reduced by the inclusion of Cr which implies a more dense surface structure. An increasing concentration of Cr produced a reduction of hardness, an increase of reduced modulus (with a high amount of Cr), an increase of wear rate and an increase of the (initial) coefficient of friction. A comparison was made between the nano-scale results in this work with those previously obtained from similar coatings, but using micro-hardness and macro-scale pin-on-disc techniques. In this comparison nano and micro-hardnesses followed similar trends, reducing with increasing Cr concentration; however, micro-hardness gave significantly higher absolute values and showed a greater difference between samples. Comparing wear rates for the two scales, trends were again similar at low load pin-on-disc measurements with wear rate increasing with increasing Cr concentration at, but no such agreement was found at higher load. The results for coefficient of friction were similar between the two scales of test.

Low cost thin film based piezoresistive MEMS tactile sensor

Most reported MEMS tactile sensors are fabricated by silicon micromachining process. Presently, the cost of the silicon-based MEMS fabrication is still relatively high, thus alternative process should be developed for low cost applications. In this work, we develop a low-cost non-silicon-based process for MEMS tactile sensor fabrication. The MEMS tactile sensor with a trampoline membrane structure has been fabricated by successive sputtering of Cr, Al, AlN, indium tin oxide (ITO), and Au layers through electroplated Ni micro-shadow masks over an 8 μm-thick photoresist sacrificial layer on a glass substrate. In addition, the sensitivity of the sensor has been optimized by controlling sputtering parameters including oxygen flow rate and film thickness of the ITO piezoresistive layer. The fabricated tactile sensor has been tested for displacement and force sensing by a Dektak surface profiler. The fabricated sensor is capable of small force sensing in μN ranges with good linear sensitivity of 0.2 mV/μN.

Examination of the pulsing phenomena in pulsed-closed field unbalanced magnetron sputtering (P-CFUBMS) of Cr–Al–N thin films

Pulsed DC magnetron sputtering was developed initially as a means of suppressing the arcing at the target during reactive sputtering. More recently, pulsing the magnetrons has also been shown to modify the intrinsic plasma parameters to bring higher ion energy and ion flux to the growing film at the substrate, which, in turn may have a strong influence on film structure and properties. This paper examines the effect of pulsing the unbalanced magnetrons in a two-cathode closed field configuration on the plasma properties, in particular, the ion energy distributions (IEDs) and ion flux, as determined using a Hiden electrostatic quadrupole plasma mass spectrometer (EQP). Chromium and aluminum targets were reactively sputtered in an Ar–N 2 atmosphere in this two-cathode pulsed-closed field unbalanced magnetron sputtering (P-CFUBMS) system. The pulsing parameters examined included: pulsed power (400 W to 1400 W), working pressure (0.13 Pa/1.0 mTorr to 0.53 Pa/4 mTorr), nitrogen to argon flow ratio, substrate to target distance (127 mm/5 in. and 203 mm/8 in.), duty cycle (40 kHz to 350 kHz frequency, 0.4 μs to 5 μs reverse time), operated under synchronized (voltage-time wave forms of the two magnetrons were in phase) and asynchronized (voltage-time wave forms of the two magnetrons were out of phase) conditions. The effect of the pulsing regimes on the ion energy and ion flux was determined for reactive sputtering of Cr–Al–N thin films. It was shown that pulsing both magnetrons in this P-CFUBMS configuration had a large effect on both the ion energies and ion fluxes generated within the plasma. The positive voltage overshoot and the positive pulse voltage developed on each target during the reverse voltage (positive) period increased the plasma potential and thereby increased the overall extended ion energy range. Three main ion energy regions in the IEDs were identified and related to different positive voltage values during the reverse pulse period. In addition, the extent of synchronization of the voltage waveforms of the two magnetrons also substantially influenced both the IEDs and the ion fluxes, while varying the pulsing frequencies and reverse times (duty cycle) in either synchronized or asynchronized modes also resulted in different ion energies and ion fluxes within the plasma. It was also found that the ion flux increased on increasing the EQP orifice to the chamber wall distance from 127 mm to 203 mm, and the ion energy range decreased as the working pressure increased from 0.13 Pa to 0.53 Pa. The ion energies and fluxes are shown to be strongly dependent on pulsing frequency, duty cycle and waveform.

Low-voltage high-resolution scanning electron microscope imaging of the uncoated and Cr-coated zeolite Beta

Fine surface features of the uncoated, as-synthesized zeolite Beta and the effect of Cr sputter coating on the appearance of these features were examined using high-resolution (lateral resolution ∼ 2.5 nm) field emission scanning electron microscopy (FE-SEM). The uncoated particles exhibited charging effects despite a reduced accelerating voltage (2 kV). Thus, only rapid scanning at “TV rates”, where an average of multiple frames is acquired, produced useful FE-SEM images. Pyramidal irregularities, resulting in the “saw teeth-like” surface features less than ∼20–30 nm in size, were observed on the uncoated particles. These images did not reveal any texture over flat areas of the surface. Deposition of thin Cr films with a nominal thickness of 1–2 nm reduced/eliminated sample charging so that a slow scanning speed could be used. The resulting images showed better topographic contrast than the images of the uncoated particles. The appearance of fine “teeth” was not affected by sputtering with thin 1–2 nm Cr films. However, the development of a grainy surface texture in the form of nodules smaller than ∼5 nm over flat areas of the surface, which appeared to grow in number density and size (to more than ∼5 nm) with the increasing nominal (up to 10 nm) Cr film thickness, could be observed. This is hypothesized to be the result of Cr particle formation. Sputtering used to deposit thin Cr films did not appear to damage crystal surfaces. Thus, thin (1–2 nm) Cr coatings improve image quality with little or no loss in surface texture resolution.

Mechanical behavior and oxidation resistance of Cr(Al)N coatings

Nanocrystalline chromium nitride and ternary chromium aluminium nitride thin films were deposited by reactive magnetron sputtering of Cr and Al targets in argon/nitrogen atmosphere varying the sputtering power and gas composition. The coatings were characterized in terms of crystal phase, chemical composition, microstructure, and mechanical properties by x-ray diffraction, x-ray photoelectron spectroscopy, including x-ray-induced Auger electron spectroscopy, transmission electron microscopy, selected-area electron diffraction, electron energy-loss spectroscopy, cross-sectional scanning electron microscopy, and ultramicrohardness tester. The incorporation of Al in the composition of the films produces an increase in the mechanical properties (hardness and reduced Young’s modulus) and an increased thermal resistance against oxidation in comparison to the pure CrN composition. The hardness behavior was attributed mainly to a reduction of the CrN crystallite size according to a Hall–Petch relationship. The oxidation resistance was evaluated after annealing both types of coatings in air up to 800°C. The oxygen content and the crystallite size appear almost unaltered in the CrAlN in contrast to the pure CrN films where the oxidation and grain growth is very noticeable at 800°C. This improvement in thermal stability in air is explained by the formation of a nanocomposite structure of small CrN crystals embedded in an amorphous aluminum oxide or oxinitride matrix that prevents the CrN phase from crystal growth and further oxidation.

Magnetron sputtering of Cr(Al)N coatings: Mechanical and tribological study

CrN coatings produced by magnetron sputtering are routinely deposited on tools and components for machining and forming applications. This paper reports on the effect of additions of aluminium (<15 at.%) on the mechanical and tribological properties of CrN coatings. Aluminium has been incorporated into CrN by co-sputtering of chromium and aluminium in a mixture of argon and nitrogen. Mechanical properties have been evaluated by ultramicroindentation techniques and scratch testing, while tribological tests have been carried out against ball bearing steel and titanium alloy balls by the pin-on-disc method. The thermal stability and oxidation resistance of the coatings have also been examined.A significant increase in hardness, reaching values up to 35 GPa, has been achieved for the CrAlN coatings when compared to CrN coatings. The improvement in tribological properties has also been remarkable, with a decrease in friction coefficient against bearing steel and also a non-adhesive wear mechanism against titanium alloy balls. In addition, the CrAlN coatings exhibited higher thermal stability than pure CrN coatings.

14.5% near-normal incidence reflectance of Cr/Sc x-ray multilayer mirrors for the water window.

Cr/Sc multilayer mirrors, synthesized by ion-assisted magnetron sputter deposition, are proved to have a high near-normal reflectivity of R = 14.5% at a grazing angle of 87.5 degrees measured at the wavelength lambda = 3.11 nm, which is an improvement of more than 31% compared with previously published results. Elastic recoil detection analyses show that the mirrors contained as much as 15 at. % of N and traces of C and O. Soft x-ray reflectivity simulations reveal interface widths of sigma = 0.34 nm and an exceptionally small layer thickness drift of approximately 1.6 x 10(-5) nm/multilayer period throughout the stack. Simulations show that a reflectivity of R = 25.6% is attainable if impurities and layer thickness drift can be eliminated. The abrupt interfaces are achieved with ion assistance with a low ion energy of 24 eV and high ion-to-metal flux ratios of 7.1 and 23.1 during Cr and Sc sputter deposition, respectively. In addition, a near-normal incidence reflectivity of 5.5% for the C VI emission line (lambda = 3.374 nm) from a laser plasma source was verified.

Analytical electron microscopy of interface layers between Ti(6% Al, 4% V) and a CrN cathodic arc coating

This paper reports on the applications of analytical electron microscopy to the study of cathodic arc deposited CrN coating on a Ti(6% Al, 4% V) substrate. Particular attention is given to analysis of the coating/substrate interface. Electron energy loss spectroscopy is used to show that the Cr sputter cleaning of the Ti(6% Al, 4% V) results in penetration of Cr into the substrate giving a bcc alloy layer whose composition varies from Ti(6% Al, 4% V) at the substrate interface to almost pure Cr at the coating interface. Subsequent deposition of CrN results in an initial deposition of sub-stoichiometric Cr2N followed by sub-stoichiometric CrN with a { 022} texture and a columnar structure. The degree of sub-stoichiometry of the nitrides depends on the substrate bias and the substrate orientation relative to the cathode.

Comparative evaluation of protective coatings and focused ion beam chemical vapor deposition processes

Dual-beam instruments incorporate both an electron column and an ion column into a single instrument, and therefore allow the chemical vapor deposition (CVD) process to be either ion- or electron-beam assisted. Damage has been observed in the surface layers of specimens in which ion-beam assisted CVD processes have been employed. Cross-section transmission electron microscopy (TEM) has been used to compare (100) Si substrates on which Pt metal lines have been grown by ion- and electron-beam assisted CVD processes. The micrographs show that a 30 keV Ga+ ion beam, a 5 keV ion beam, and a 3 keV electron beam imparts 50 nm, 13 nm, and 3 nm of damage to the Si substrate, respectively. In addition, Au–Pd and Cr sputter coatings were evaluated for the prevention of ion-beam induced surface damage. TEM cross-section specimens revealed that Cr sputter coatings &amp;gt; 30 nm in thickness are sufficient to protect the (100) Si surface from the 30 keV Ga+ ion beam while Au–Pd sputter coatings up to 70 nm in thickness may be discontinuous and, therefore, will not protect surface regions from ion beam damage.

Preparation of Cr 2 O 3 -Al 2 O 3 Solid Solutions by Reactive Magnetron Sputtering

(Al,Cr)2O3 layers were deposited on cemented carbide insert tips at a substrate temperature of 500 °C by means of reactive magnetron sputtering. An Al target was sputtered in RF mode and a Cr target in DC mode simultaneously in an oxygen/argon plasma. The influence of the Al and Cr sputter power and of the oxygen partial pressure on composition and structure of the (Al,Cr)2O3 layers as well as on the binding states of their components were investigated. Special attention was paid to the interpretation of the O ls and O-KLL fine structure and peak shifts. For the binary phases γ-Al2O3 and Cr2O3, a good agreement with literature values was observed in each case. In case of the ternary phases a continuous shift of the energetic position of the O1s peak, the O-KL23L23 transition and the modified Auger parameter α ′ of oxygen between the two binary phases γ-Al2O3 and Cr2O3 could be detected, indicating a wide range of solid solubility between Al2O3 and Cr2O3. As revealed by grazing incidence X-ray diffraction, the crystallinity of the ternary phases is less pronounced as compared to the binaries and increases with increasing oxygen flow rate.

Erosion and deposition during the sputter cleaning of substrates prior to the cathodic arc evaporation of transition metal nitride coatings

Reactive cathodic arc evaporation (CAE) is a physical vapour deposition technique employed to produce wear resistant coatings. The adhesion of the coating is improved if the substrate surface is sputter cleaned by running the arc in high vacuum with the substrate held at a rms bias of −1000 V prior to deposition of the coating. In this paper the erosion and deposition of material during the sputter cleaning process is examined using analytical electron microscopy on two different systems. Cr sputter cleaning of Ti results in the formation of a surface layer of thickness ∼20 nm at the surface. This layer is crystalline and has a graded composition with a high fraction of Cr at the vacuum surface and a high fraction of Ti at the substrate interface. There is also some penetration of Cr into the substrate. The material of the substrate is eroded at a rate ∼6 nm per Amp-h of cathode current. Ti sputter cleaning of an existing TiN coating, on the other hand, exhibits negligible erosion of the substrate but results in the deposition of a layer of α-Ti, the thickness of which is strongly dependent on the geometry of the system. The rapid variation of the thickness of the deposited Ti with the angle between the planes of the substrate and the cathode suggests that a plasma sheath does not form under these circumstances. A simple model of the ion trajectories is used to describe this variation of the Ti thickness. The presence of such a Ti layer has implications for the re-coating of tools with TiN. The variation of the thickness of the subsequent TiN layer on the substrate is much smaller.