Residual stresses in titanium nitride thin films deposited by direct current and pulsed direct current unbalanced magnetron sputtering

This work presents a study on the effect of deposition parameters on the residual stresses developed in titanium nitride (TiN) thin films deposited onto cemented carbide (WC-Co) substrates. Depositions were conducted by reactive unbalanced magnetron sputtering of a single titanium target. Six different conditions were selected, varying parameters such as bias (0, − 50 or − 100 V), power applied to the target (direct current or pulsed direct current) and, in the cases where substrate bias was zero, substrate condition (ground or floating). Pulsed power was applied at a frequency of 50 kHz and with a reverse pulse time of 1 μs. Residual stresses were evaluated through X-ray diffraction, using the sin²ψ method. Results confirmed the effect of substrate bias on the residual stresses of thin films. Additionally, it was possible to observe that by pulsing the power to the target, residual stress varies as a consequence of the increased ion energy.     

DC substrate bias effects on the physical properties of hydrogenated amorphous carbon films grown by plasma-assisted chemical vapour deposition

Hydrogenated amorphous carbon (a-C:H) films have been grown from argon/methane gas mixtures by electron cyclotron resonance chemical vapour deposition (ECR-CVD) on silicon substrates. The effects of the application of a DC substrate bias on the structural, morphological and mechanical properties of the films have been explored by multiple analysis techniques such as infrared and micro-Raman spectroscopy, atomic force microscopy, nanoindentation and pin-on-disk wear testing. In general, within the range of applied substrate bias (i.e. from −300 up to +100 V) we have observed a strong correlation between all measured properties of the a-C:H films and the ion energy. This work shows that the properties can differ greatly and indicates a threshold energy in the order of 90 eV. For the production of hard, low-friction coatings energies above this value are required.     

Deposition of B4C/BCN/c-BN multilayered thin films by r.f. magnetron sputtering

Thin films of cubic boron nitride (c-BN) and B₄C/BCN/c-BN multilayers, were deposited by r.f. (13.56 MHz) multi-target magnetron sputtering from high-purity (99.99%) h-BN and a (99.5%) B₄C targets, in an Ar (90%)/N₂ (10%) gas mixture. Films were deposited onto silicon substrates with (100) orientations at 300 °C, with r.f. power density near 7 W/cm². In order to obtain the highest fraction of the c-BN phase, an r.f. substrate bias voltage between − 100 and − 300 V was applied during the initial nucleation process and − 50 to − 100 V during the film growth. Additionally, B₄C and BCN films were deposited and analyzed individually. For their deposition, we varied the bias voltage of the B₄C films between − 50 and − 250 V, and for the BCN coatings, the nitrogen gas flow from 3% to 12%. A 300-nm-thick TiN buffer layer was first deposited to improve the adhesion of all samples. X-ray diffraction patterns revealed the presence of c-BN (111) and h-BN phases. FTIR spectroscopy measurements indicate the presence of a peak at 780 cm^− 1 referred to as “out-of-plane” h-BN vibration mode; another peak at 1100 cm^− 1 corresponds to the c-BN TO mode and the “in-plane” vibration mode of the h-BN at 1400 cm^− 1. BN films deposited at 300 °C at a pressure of 4.0 Pa and under − 150 V of nucleation r.f. bias, applied for 35 min, presented the highest c-BN fraction, near 85%. By using 32 layers, it was possible to deposit a 4.6-μm-thick c-BN film with adequate mechanical properties and good adhesion to the substrate.     

Deposition of TiB2 onto X40 CrMoV 5-1-1 steel substrates by DC magnetron sputtering

Titanium diboride (TiB₂) films are being investigated due to their promising uses not only in electronic devices but also for mechanical purposes. Its excellent corrosion resistance and chemical stability, as well as high hardness and wear resistance, makes TiB₂ particularly suitable for aluminium processing (e.g. extrusion, die-casting and machining). In the present work, TiB₂ coatings were produced by non-reactive DC magnetron sputtering from a TiB₂ target on a tool steel substrate (AISI H13 premium/EN X40 CrMoV 5-1-1). Substrates similar to those frequently found on the aluminium injection industry were produced by vacuum quenching and tempering. The deposition parameters, namely the target/substrate distance, discharge current and substrate bias, were varied in order to obtain crystalline and well-structured films, suiting the substrate composition and microstructure. The coatings were characterized by X-ray diffraction (XRD) and scanning electron microscopy/EDS.A deposition rate of 23 nm/min was obtained for 0.85 A cathode current intensity and 70 mm substrate–magnetron distance. For positively biased substrates, all films are dense, without a columnar structure and show a (0 0 1) texture. For negatively biased substrates, there are less surface heating effects due to a much lower electron current through the substrate, and an ordered structure appears only at −150 V.     

Characterizations of CrN/a-CNx 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.     

Titanium oxide thin films synthesis by pulsed – DC magnetron sputtering

Titanium oxide thin films (1–4 μm) were deposited on the porous Hastelloy-X substrates using the pulsed – DC magnetron sputtering technique and characterized by X–ray diffraction (XRD) and scanning electron microscopy (SEM) methods. Firstly, the films were deposited at different distances between the magnetron and the substrate, as magnetron current and pressure in the deposition chamber were constant. The distance between the magnetron and the substrate was changed from 3 cm to 7 cm, and the deposition rate varied between 10.1 nm/min to 6.0 nm/min. Secondly, pressure influence for the deposition rate was investigated. The deposition rate decreased nearly 15% with the decrease of oxygen pressure from 1.3 to 6.0 Pa. Finally, the influence of the bias (applied to the substrate for the increase of deposition rate) on thin films phase and microstructure was investigated.The experimental results showed that formation of pure titanium oxide thin films was observed in all experimental cases. Only crystallite sizes and orientation were changed. The results showed that there is a possibility to change porosity and uniformity of the growing film by changing oxygen partial pressure during deposition or bias application to the substrate. The existence of columnar boundaries and nanocrystalline structure in the films was observed.     

Electrical-driven disaggregation of the two-dimensional assembly of colloidal polymer particles under pulse DC charging

Two-dimensional structures of polymer (polystyrene) colloidal particles were formed on a substrate by electrophoretic deposition in an aqueous suspension. The prepared suspension is stable for a few days; therefore, it was not necessary to place an additional mixing during the deposition process. The particle aggregation/disaggregation formation was observed on the metal surface in order to study the effect of pulse direct current (DC) charging in comparison with conventional DC charging. At the charging frequency of 80 Hz, it was observed that pulse DC charging with a maximum applied voltage of 3.3 V/cm (50% duty cycle) clearly reduced the degree of aggregation of particles having diameters of 50 and 300 nm comparing to those of DC charging. Pulse charging at high frequency is thus found to be more effective in preventing particle aggregation during electrophoretic deposition than conventional DC charging.     

Effects of nitrogen ion implantation and implantation energy on surface properties and adhesion strength of TiN films deposited on aluminum by magnetron sputtering

The performance of tribological coatings depends greatly on the adhesion strength between the coatings and substrates. In this work, we investigated the influence of the ion implantation energy of nitrogen on the adhesion and surface properties of TiN deposited on aluminum substrate. Aluminum samples were implanted with 15 keV, 30 keV and 40 keV nitrogen ions before TiN films were deposited using magnetron sputtering in a custom-designed multi-functional ion implanter. The adhesion properties of the implanted TiN films were assessed using nano-scratch tests and were observed to vary with the nitrogen ion implantation energy. Our frictional test results show that an appropriate ion implantation energy and dose can improve the frictional behavior of TiN films deposited on aluminum.     

AgTaO3 and AgNbO3 thin films by pulsed laser deposition

Silver tantalate AgTaO₃ (ATO) and silver niobate AgNbO₃ (ANO) films have been grown on to the LaAlO₃ (001) and sapphire Al₂O₃ (0112, r-cut) single crystals by pulsed laser deposition technique from stoichiometric ATO and ANO targets. X-ray diffraction study revealed epitaxial quality of ATO and ANO films on the LaAlO₃ (001) whereas on the sapphire r-cut substrate they are preferential (110) and (001) oriented. To characterize microwave films properties in the range from 1 to 40 GHz, coplanar line interdigital capacitors were fabricated by photolithography and lift-off technique. ANO film capacitors show superior properties: frequency dispersion was as low as 13%, voltage tunability (40 V, 200 kV/cm) was about 4.6% at 20 GHz, loss tangent ∼0.106 at 20 GHz, K-factor = tunability / tanδ from 49% @ 10 GHz to 33% at 40 GHz.     

Room temperature deposition of IZTO transparent anode films for organic light-emitting diodes

This study was to investigate anodic electrode IZTO films deposited by pulsed DC magnetron sputter at room temperature with various oxygen partial pressures onto glass substrate and to analyze the structural, electrical, and optical properties, as well as the relationship between the chemical binding state of the surface and the characteristics of IZTO films. In addition, the prepared IZTO films were used to fabricate the organic light emitting diodes (OLEDs) as an anode layer to study the device performances. The IZTO film deposited at optimal oxygen partial pressure of 2.0% in sputtering process showed the best properties, such as a low electrical resistivity and high optical transmittance of <5.1 × 10^?4 Ω cm and >80% in the visible wavelength of 400–800 nm, respectively. The OLED characteristics with the optimum condition showed good brightness and the lowest turn-on voltage of >10,000 cd/m² and 4.67 V. These results indicate that IZTO films can be a promising candidate as an alternative TCO electrode material for flexible and OLED devices.     

Efficient tri-wavelength actively Q-switched Yb:GAGG laser

An efficient acousto-optic Q-switched Yb-doped Gd₃Al_xGa_5−xO₁₂ (GAGG) (x = 0.5) laser is demonstrated. Under the absorbed pump power of 7.4 W, the maximum average output power of 1.4 W is obtained at the pulse repletion rate of 1 kHz , with the slope efficiency as high as 32%. The pulse width of 40 ns is achieved with the pulse energy and peak power of 1.4 mJ and 35 kW, respectively. What’ more, the output spectrum shows itself tri-wavelength in either CW or Q-switching mode. To our knowledge, this is the first time for realizing simultaneous tri-wavelength Yb:GAGG laser actively Q-switched operation.     

Effect of the target bias voltage during off-pulse period on the impulse magnetron sputtering

With a high-power impulse magnetron sputtering (HiPIMS) apparatus, it has been studied how the target bias voltage during the off-pulse period affects the stability of the generated plasma. We have prepared an electrical pulse power source which can control the target voltage during the pulse off period, in addition to the pulse voltage, repetition frequency and a duty ratio of the pulse. Time-resolved current-voltage characteristic was monitored by an oscilloscope, and plasma generation behavior was elucidated. With titanium target and at Ar gas pressures of 0.6–5 Pa, pulse-off bias voltage was changed between −300 and +100 V, and the I-V characteristics were recorded. On increasing the negative bias voltage, the time at which the target current began to rise was gradually delayed. And at a certain voltage, the delay suddenly disappeared. This voltage was found to be the sustain voltage of the dc discharge in the same condition. Applying positive bias voltage resulted in a much longer delay. These results suggest that the minimal discharge during the pulse-off period helps the initiation of high-density plasma, while the bias voltage which can not maintain the plasma contrarily hampers it.     

Bioactivity of calcium phosphate coatings prepared by electrodeposition in a modified simulated body fluid

The purpose of this study was to investigate bioactivity of calcium phosphate coatings prepared by electrodeposition in a modified simulated body fluid (SBF). Calcium phosphates were electrodeposited on commercially pure titanium substrates in the modified SBF at 60 °C for 1 h maintaining the cathodic potentials of − 1.5 V, − 2 V, and − 2.5 V (vs. SCE). Subsequently, the calcium phosphate coatings were transformed into apatites during immersion in the SBF at 36.5 °C for 5 days. The apatites consisted of needle-shaped crystallites distributed irregularly with different grain sizes. As the coatings were electrodeposited at higher cathodic potential, the crystallite of the apatites got denser and the grain sizes of the apatites became bigger during subsequent immersion in the SBF. However, as the coatings were electrodeposited at higher cathodic potential, the coatings were transformed into apatites with lower crystallinity and the Ca/P atomic ratio of the apatites got higher than 1.67, that of stoichiometric hydroxyapatite, after subsequent immersion in the SBF. In addition, CO₃²⁻ ions contained in the modified SBF were incorporated in the calcium phosphate coating during electrodeposition and had an influence on transforming the calcium phosphate into bonelike apatite during subsequent immersion in the SBF showing that CO₃²⁻ incorporated in the apatites disturbed crystallization of the apatites. These results revealed that the coating electrodeposited at − 2.0 V (vs. SCE) in the modified SBF containing CO₃²⁻ ions was the most bioactive showing transformation into carbonate apatite similar to bone apatite.     

Chacterization of titanium silicon nitride films deposited by PVD

In recent years, nitride coatings have found widespread applications for tool and other hard surfaces. In this work, the (Ti,Si)N system was investigated and some of its properties characterised. For this, (Ti,Si)N films with thicknesses ranging from 1 to 3.3 μm and different contents of Ti and Si were deposited onto silicon wafers and polished high-speed steel substrates by r.f. reactive magnetron sputtering technique. The atomic composition of the samples were measured by Rutherford Backscattering Spectrometry (RBS). Ti_1−xSi_xN samples with 0≤x≤0.37 were produced. With regard to the structural properties, two cubic crystallographic structures were found, with lattice parameters of about a=4.29 Å and 4.18 Å. The grain size, evaluated by Fourier analysis of X-ray peaks, ranged from 5 nm to 34 nm. Comparing the adhesion results, the Ti_0.70Si_0.30N and Ti_0.83Si_0.17N sample presented the best results in adhesion with a critical load for total failure around 115 N and 105 N, respectively.     

Correlation between anionic substitution and structural properties in AlCr(OxN1−x) coatings deposited by lateral rotating cathode arc PVD

The influence of oxygen content on the properties of cathodic arc-deposited AlCr(O_xN_1?x) coatings has been studied. All samples were prepared in a nitrogen-rich mixture of N₂ and O₂ at 550 °C using lateral rotating arc cathodes (LARC) technology together with a pulsed bias voltage. The obtained coatings were characterized by various techniques including XRD, EPMA, TEM, pin-on-disk wear tests and nanoindentation. The results obtained allow to classify the coatings into three groups with respect to their microstructure, mechanical properties and oxygen content, x. For the first group of samples with x ≤ 0.6, single-phase films of (Al,Cr)O_xN_1-x with fcc lattice were obtained, with well-developed columnar structure and a hardness of 30 to 33 GPa. In the second group, a diffuse columnar structure was observed while the fcc lattice was still present despite the large proportion of oxygen, 0.6 < x ≤ 0.97, and the observed hardness decreased to 25 GPa. No amorphous phase was detected in this group as confirmed by TEM. The simulation of XRD patterns of nitride lattices with oxygen incorporation allowed to suggest the formation of cation vacancies in the structure of the investigated oxynitride coatings. The third group is formed by coatings with x > 0.97, where a well-crystalline α-(Al,Cr)₂O₃ corundum phase was observed and the hardness increased again to 28 GPa. Our results indicate that the second group of coatings is metastable and after heat treatment transforms to a composite of cubic oxynitride and corundum oxide. Both friction and wear of samples from the entire investigated compositional range were studied at room temperature and 600 °C. The low wear rates observed for the oxynitride coatings underline their potential for use in turning and milling applications.     

Comparison of microstructure and mechanical properties of chromium nitride-based coatings deposited by high power impulse magnetron sputtering and by the combined steered cathodic arc/unbalanced magnetron technique

Sliding, abrasive, and impact wear tests were performed on chromium nitride (CrN)-based coatings deposited on mirror-polished M2 high speed steel substrates by the novel high power impulse magnetron sputtering (HIPIMS) utilising high peak cathode powers densities of 3000 W cm⁻². The coatings were compared to single layer CrN and multilayer superlattice CrN/NbN coatings deposited by the arc bond sputtering (ABS) technique designed to improve the coating substrate adhesion by a combined steered cathodic arc/unbalanced magnetron (UBM) sputtering process. The substrates were metal ion etched using non-reactive HIPIMS or steered cathodic arc at a substrate bias voltage of −1200 V. Subsequently a 2- to 3-μm thick CrN or CrN/NbN coating was deposited by reactive HIPIMS or UBM. No bias was used during the HIPIMS deposition, while the bias during UBM growth was in the range 75-100 V. The ion saturation current measured by a flat electrostatic probe reached values of 50 mA cm⁻² peak for HIPIMS and 1 mA cm⁻² continuous during UBM deposition. The microstructure of the HIPIMS coatings observed by transmission electron microscopy was fully dense in contrast to the voided columnar structure observed in conventional UBM sputtered CrN and CrN/NbN. The sliding wear coefficients of the HIPIMS CrN films of 2.3×10⁻¹⁶ m³ N⁻¹ m⁻¹ were lower by a factor of 4 and the roughness of the wear track was significantly reduced compared to the UBM-deposited CrN. The abrasive wear coefficient of the HIPIMS coating was 2.2×10⁻¹³ m³ N⁻¹ m⁻¹ representing an improvement by a factor of 3 over UBM deposited CrN and a wear resistance comparable to that of the superlattice CrN/NbN. The adhesion of the HIPIMS deposited CrN was comparable to state-of-the-art ABS technology.     

Tuning exchange bias in epitaxial Ni/MgO/TiN heterostructures integrated on Si(1 0 0)

Epitaxial Ni thin films are integrated with tunneling barrier MgO on Si(1 0 0) substrate. During pulsed laser deposition, early island-like structure transformed into uniform thin film with increasing number of laser pulses. This led to transitions in exchange bias from positive to negative and back to positive, which is ascribed to morphology associated residual strain. The Ni island structure has a coercive field as high as 3 times of that of the continuous film. The current work holds a tremendous promise in the realization of magnetic devices integrated with the Si-platform.     

New natively textured surface Al-doped ZnO-TCOs for thin film solar cells via magnetron sputtering

Natively textured surface aluminum doped zinc oxide (ZnO:Al) thin films were directly deposited via pulsed direct current (DC) reactive magnetron sputtering on glass substrates. During the reactive sputtering process, the oxygen gas flow rate was varied from 8.5 sccm to 11.0 sccm. The influences of oxygen flow rate on the structural, electrical and optical properties of naturally textured ZnO:Al TCO thin films with milky surface were investigated in detail. Gradual oxygen growth (GOG) technique was developed in the reactive sputtering process for textured ZnO:Al thin films. The light-scattering ability and optical transmittance of the natively textured ZnO:Al TCO thin films can be improved through gradual oxygen growth method while maintaining a low sheet resistance. Typical natively textured ZnO:Al TCO thin film with crater-like surface exhibits low sheet resistance (R_s ～ 4 Ω), high transmittance (T_a > 85%) in visible optical region and high haze value (12.1%).     

Electromagnetic shielding effectiveness of aluminum alloy–fly ash composites

The cenosphere and precipitator fly ash particulates were used to produce two kinds of aluminum matrix composites with the density of 1.4–1.6 g cm⁻³ and 2.2–2.4 g cm⁻³ separately. The electromagnetic interference shielding effectiveness (EMSE) properties of the composites were measured in the frequency range of 30.0 kHz–1.5 GHz. The results indicated the EMSE properties of the two types of composites were nearly the same. By using the fly ash particles, the shielding effectiveness properties of the matrix aluminum have been improved in the frequency ranges 30.0 kHz–600.0 MHz and the increment varied with increasing frequency. The EMSE properties of 2024Al are in the range −36.1 ± 0.2 to −46.3 ± 0.3 dB while the composites are in the range −40.0 ± 0.8 to −102.5 ± 0.1 dB in the frequency range 1.0–600.0 MHz. At higher frequency, the EMSE properties of the composites are similar to that of the matrix. The tensile strength of the matrix aluminum has been decreased by addition of the fly ash particulate and the tensile strength of the composites were 110.2 MPa and 180.6 MPa separately. The fractography showed that one composite fractured brittly and the other fractured in a microductile manner.     

Structural and optical properties of In doped Se–Te phase-change thin films: A material for optical data storage

Se_75−xTe₂₅In_x (x = 0, 3, 6, & 9) bulk glasses were obtained by melt quench technique. Thin films of thickness 400 nm were prepared by thermal evaporation technique at a base pressure of 10⁻⁶ Torr onto well cleaned glass substrate. a-Se_75−xTe₂₅In_x thin films were annealed at different temperatures for 2 h. As prepared and annealed films were characterized by X-ray diffraction and UV–Vis spectroscopy. The X-ray diffraction results show that the as-prepared films are of amorphous nature while it shows some poly-crystalline structure in amorphous phases after annealing. The optical absorption spectra of these films were measured in the wavelength range 400–1100 nm in order to derive the extinction and absorption coefficient of these films. It was found that the mechanism of optical absorption follows the rule of allowed non-direct transition. The optical band gap of as prepared and annealed films as a function of photon energy has been studied. The optical band gap is found to decrease with increase in annealing temperature in the present glassy system. It happens due to crystallization of amorphous films. The decrease in optical band gap due to annealing is an interesting behavior for a material to be used in optical storage. The optical band gap has been observed to decrease with the increase of In content in Se–Te glassy system.