Surface morphology of AlN films synthesized by pulsed laser deposition

Surface morphology of AlN films, synthesized on Si substrates by pulsed laser deposition, has been examined by recording atomic-force-microscopy (AFM) images. The influence of N₂ ambient pressure, ranging from 5 × 10⁻⁴ Pa to 10 Pa, is reflected well in the alteration of the surface roughness and size of crystallites of the AlN films. A tendency of a decrease in the surface roughness with increasing N₂ pressure was observed, which also correlates with the polycrystalline structure of the films. Deposition in vacuum resulted in the highest surface roughness due to the large size of crystallites emerging from the surface, while increasing the nitrogen pressure yielded smaller crystallites and a smoother film surface. The presented results could be useful for applications of pulsed laser deposited AlN in different optical and acoustic devices, where the crystalline quality of the AlN films and the surface is very important.     

Preparation of the hard CNx thin films using NO ambient gas by pulsed laser deposition

Pulsed laser deposition (PLD) technique has been widely used in thin film preparation because of its wonderful and excellent properties and amorphous carbon nitride (CN_x) thin films are recognized to have potential for applications like hard coating and electron field emission device. We have deposited CN_x thin films by KrF excimer laser – (λ= 248 nm) ablation of pure graphite target in pure NO gas ambient condition. In this paper, we have prepared the CN_x thin films at various ambient NO gas pressure of 1.3–26 Pa and laser fluence of 2– 5J cm^?2 on Si (100) substrate. We consider that the hardness of CN_x thin films improves due to the increase the nitrogen/carbon (N/C) ratio. The N/C ratio depended on the ambient NO gas pressure and laser fluence. We obtainedthe maximum N/C ratio of 1.0 at NO 3.3 Pa. The typical absorption of CN bonds such as sp² C–N, sp³ C–N, G band and D band were detected from the infrared absorption measurement by FTIR in the deposited CN_x thin films.     

Effect of an increase in the nitrogen content of the working gas on the microstructure of reactive sputtered TiN thin films

TiN films were deposited on (100)-Si substrates by RF-reactive sputtering. The effects of processing parameters and substrate orientation on the stoichiometry, resistivity and microstructure of reactively sputtered TiN thin films were investigated. The RF-power was fixed at 50 W, and the nitrogen content in the working gas was adjusted so that target nitridation occurred at a relatively low nitrogen content, 2.6% N₂, in a fixed total flow rate of gases of 46.25 standard cubic centimetres (sccm). The N₂ percentage was varied from 2.6% to 15.4%. The films were continuous and 200 nm thick. Films deposited with the substrate facing the target exhibited 111-texturing, while films on substrates lying in the same plane of the target surface had 100-texturing. Both X-rays photoelectron spectroscopy and high-resolution detailed scans of the Auger electron energy spectrum were used for the stoichiometry determination. On the 100-textured TiN films, the N/Ti ratio was 1.0 at low N₂ flow rates; the N/Ti ratio rapidly increased with N₂ flow rate, and then levelled off. The films had resistivities ranging from 85 to 1340 µ cm, and the functional dependence of both N/Ti and the resistivity values behaved similarly with increasing N₂. X-ray single-line profile analysis of the 200-reflection indicated that the average crystallite size decreased and the average strain increased with increasing nitrogen content in the working gas. The Si/TiN structures were heat treated in the temperature range from 300 to 600°C in a quartz tube under 1 atm (10⁵Pa) of flowing high purity Ar gas. Heat treatment at 300°C did not affect the TiN film integrity, while treatment at 400–600°C resulted in void-type defects.     

Properties of ZrNx films with x > 1 deposited by reactive radiofrequency magnetron sputtering

Thin ZrN_x films have been prepared by reactive radiofrequency magnetron sputtering varying the nitrogen partial pressure in the range 0-3.26 Pa. The films have been analyzed by X-ray photoelectron spectroscopy (XPS) and by optical characterization in the UV-Vis-IR range. The cross-section and surface morphology of the samples were examined by means of field emission gun-scanning electron microscopy. The effects of the nitrogen partial pressure on the ZrN_x films stoichiometry have been studied correlating the N 1s photoelectron peaks with different bounding states for the zirconium nitride. The XPS depth profile analysis has revealed the presence of metastable phases (ZrN₂, Zr₃N₄) that vanishes when lowering the nitrogen partial pressure. The optical analysis has permitted to distinguish two different behaviours of the deposited samples in the visible range: semi-transparent and absorbent. Drude-Lorentz model fitted the behaviour of absorbent films, while the O'Leary model was applied to the semi-transparent ones. The semi-transparent films had a band gap varying between 2.36 and 2.42 eV, typical values of N-rich zirconium nitride films. Morphological analysis showed a compact and dense columnar structure for all the samples. A simple growth model explains the presence of the different nitride phases considering implantation and re-sputtering effects.     

Correlations between optical properties, microstructure, and processing conditions of Aluminum nitride thin films fabricated by pulsed laser deposition

Aluminum nitride (AlN) films were deposited using pulsed laser deposition (PLD) onto sapphire (0001) substrates with varying processing conditions (temperature, pressure, and laser fluence). We have studied the dependence of optical properties, structural properties and their correlations for these AlN films. The optical transmission spectra of the produced films were measured, and a numerical procedure was applied to accurately determine the optical constants for films of non-uniform thickness. The microstructure and texture of the films were studied using various X-ray diffraction techniques. The real part of the refractive index was found to not vary significantly with processing parameters, but absorption was found to be strongly dependent on the deposition temperature and the nitrogen pressure in the deposition chamber. We report that low optical absorption, textured polycrystalline AlN films can be produced by PLD on sapphire substrates at both low and high laser fluence using a background nitrogen pressure of 6.0 × 10^− 2 Pa (4.5 × 10^− 4 Torr) of 99.9% purity.     

Characterization of gallium-nitrogen co-doped zinc oxide thin films prepared by RF diode sputtering

We investigated the possibility of achieving p-type zinc oxide (ZnO) by RF diode sputtering and gallium-nitrogen co-doping. ZnO:Ga:N thin films were prepared with a different N₂ content in Ar/N₂ working gas, ranging from 0 to 100%, and at a varying substrate temperature, from room temperature (RT) to 300 °C. A hole conduction with maximum carrier concentration of 2.6 × 10¹⁸ cm⁻³, mobility of 2 cm²/Vs and resistivity of 1.5 Ω cm resulted from deposition at RT with 100% N₂. It arose from N incorporation and formation of N_O acceptors. In the secondary ion mass spectrometry (SIMS) depth profiles of the co-doped films were observed NO/NO₂ negative ions. Average transmittance (including Corning glass substrate) across the visible spectrum varied (60 ÷ 66%) with increasing nitrogen content (50 ÷ 100% N₂). As the substrate temperature increased (RT - 300 °C), highly transparent (T ∼72-83%) and conductive (electron concentrations of 10¹⁷-10¹⁹ cm⁻³) n-type ZnO:Ga:N films were attained. Reduction of optical band gap (E_g) (∼3.13-3.08 eV) was observed for co-doped ZnO films. Atomic force microscopy (AFM) images revealed that the films grown at RT have roughness of approximately 5.3 nm while roughness of those grown at 300 °C is approximately 3.9 nm.     

Effect of background gas environment on oxygen incorporation in TiN films deposited using UHV reactive magnetron sputtering

The effect of the base pressure on the incorporation of oxygen into reactively magnetron-sputtered metal-nitride films has been investigated. A UHV sputtering system with a base pressure of less than 10⁻⁶ Pa was used to examine the relationship between a deliberately introduced background pressure of oxygen and a measured oxygen content in the sputter-deposited TiN films. The results showed that with an oxygen partial pressure of 10⁻⁴ Pa, the deposited TiN was found to include 10-20 at.% of oxygen when measured by the technique of X-ray photoelectron spectroscopy (XPS). When no oxygen was admitted into the system, no trace of oxygen could be detected in the deposited TiN films. The incorporation mechanism is discussed in terms of the coverage-dependent sticking probabilities of O₂ and N₂ on a Ti metal surface.     

Multi-phase structured silicon carbon nitride thin films prepared by hot-wire chemical vapour deposition

In this work, Silicon Carbon Nitride (Si-C-N) thin films were deposited by Hot Wire Chemical Vapour Deposition (HWCVD) technique from a gas mixture of silane (SiH₄), methane (CH₄) and nitrogen (N₂). Six sets of Si-C-N thin films were produced and studied. The component gas flow rate ratio (SiH₄:CH₄:N₂) was kept constant for all film samples. The total gas flow-rate (SiH₄ + CH₄ + N₂) was changed for each set of films resulting in different total gas pressure which represented the deposition pressure for each of these films ranging from 40 to 100 Pa. The effects of deposition pressure on the chemical bonding, elemental composition and optical properties of the Si-C-N were studied using Fourier transform infrared (FTIR) spectroscopy, Auger Electron Spectroscopy (AES) and optical transmission spectroscopy respectively. This work shows that the films are silicon rich and multi-phase in structure showing significant presence of hydrogenated amorphous silicon (a-Si:H) phase, amorphous silicon carbide (a-SiC), and amorphous silicon nitride (a-SiN) phases with Si-C being the most dominant. Below 85 Pa, carbon content is low, and the films are more a-Si:H like. At 85 Pa and above, the films become more Si-C like as carbon content is much higher and carbon incorporation influences the optical properties of the films. The properties clearly indicated that the films underwent a transition between two dominant phases and were dependent on pressure.     

AFM surface analysis of ZnO layers prepared by pulsed laser deposition at different oxygen pressures

Polycrystalline thin films of zinc oxide were deposited by pulsed laser deposition onto silicon substrates at different oxygen partial pressures in the range of 1-35 Pa. For ablation of the sintered zinc oxide target a pulsed Nd:YAG laser was used. Other processing parameters such as laser pulse energy, pulse repetition rate, substrate temperature and deposition pressure were identical. The effect of oxygen pressure on the structural properties of the films was systematically studied by using atomic force microscopy. The surface morphology, average roughness S_a, root mean square S_q, and mean size of grains on selected places with 2 × 2 μm² area of prepared samples were evaluated. Detailed structural analysis confirmed that partial oxygen pressure leads to the modification of surface morphology. Mean grain size in height and lateral direction decreases with raising oxygen pressure from 1 to 5 Pa while the further increase of oxygen pressure from 5 to 35 Pa results in grain size enlargement. The zinc oxide film formed at oxygen partial pressure 5 Pa shows smallest values of evaluated parameters (S_a = 0.6 nm, S_q = 0.7 nm and mean size of grains 50 nm).     

Structure and chemical bonds in reactively sputtered black Ti-C-N-O thin films

The evolution of the nanoscale structure and the chemical bonds formed in Ti-C-N-O films grown by reactive sputtering were studied as a function of the composition of the reactive atmosphere by increasing the partial pressure of an O₂ + N₂ gas mixture from 0 up to 0.4 Pa, while that of acetylene (carbon source) was constant. The amorphisation of the films observed by transmission electron microscopy was confirmed by micro-Raman spectroscopy, but it was not the only effect associated to the increase of the O₂ + N₂ partial pressure. The chemical environment of titanium and carbon, analysed by X-ray photoemission spectroscopy, also changes due to the higher affinity of Ti towards oxygen and nitrogen than to carbon. This gives rise to the appearance of amorphous carbon coexisting with poorly crystallized titanium oxynitride. The evolution of the films colour is explained on the basis of these structural changes.     

Structural and mechanical properties of multi-element (AlCrMoTaTiZr)Nx coatings by reactive magnetron sputtering

(AlCrMoTaTiZr)N_x high-entropy films were deposited on silicon wafer and cemented carbide substrates from a single alloy target by reactive RF magnetron sputtering under a mixed atmosphere of Ar and N₂. The effect of nitrogen flow ratio R_N on chemical composition, morphology, microstructure, and mechanical properties of the (AlCrMoTaTiZr)N_x films was investigated. Nitrogen-free alloy film had an amorphous structure, while nitride films with at least 37 at.% N exhibited a simple NaCl-type FCC (face-centered cubic) structure. Mixed structures occurred in films with lower nitrogen contents. Films with the FCC structure were thermally stable without phase decomposition at 1000 °C after 10 h. The (AlCrMoTaTiZr)N film deposited at R_N = 40% exhibited the highest hardness of 40.2 GPa which attains the superhard grade. The main strengthening mechanisms for this film were grain-size and solid-solution strengthening. A residual compressive stress of 1.04 GPa was small to account for the observed hardness. The nitride film was wear resistant, with a wear rate of 2.8 × 10^− 6 mm³/N m against a loaded 100Cr6 steel ball in the sliding wear test. These high-entropy films have potential in hard coating applications.     

Ion beam deposition of α-Ta films by nitrogen addition and improvement of diffusion barrier property

Ta thin films were deposited on Si (100) substrates by an ion beam deposition method at various substrate bias voltages under Ar + N₂ atmosphere with different pressure ratios of Ar and N₂. The effects of nitrogen pressure in the plasma gas and the substrate bias voltage on the surface morphology, crystalline microstructure, electrical resistivity and diffusion barrier property were investigated. It was found that the fraction of a metastable β-phase in the Ta film deposited at the substrate bias voltage of − 50 V films decreased by adding nitrogen gas, while the α-Ta phase became dominant. As a result, the Ta films deposited at the substrate bias voltage of − 50 V under Ar (9 Pa) + N₂ (3 Pa) atmosphere showed a dominant α-phase with good surface morphology, low resistivity, and superior thermal stability as a diffusion barrier.     

Synthesis-structure-property relations for Cr-B-N coatings sputter deposited reactively from a Cr-B target with 20 at% B

Cr-B-N films were synthesized by unbalanced magnetron sputtering from a sintered Cr-B target with 20 at% B in an Ar-N₂ discharge at varying N₂ partial pressures (p_N2) of up to 64% of the total pressure (p_Ar+p_N2=0.4 Pa). Coating composition and microstructure were investigated by X-ray diffraction, X-ray photoelectron spectroscopy and wavelength-dispersive electron-probe microanalysis and correlated with mechanical and tribological properties measured by microindentation and dry sliding ball-on-disk tests. For low nitrogen partial pressures (p_N2?22%), the XRD patterns are composed of broad overlapping peaks with low intensity. These films have hardness values of ∼15 GPa and indentation moduli of ∼150 GPa. Increasing p_N2 from 22% to 28% results in an increase of the N content from ∼38 to 50 at% where the films meet the quasi-binary CrN-BN composition. Thereby, an increase of the hardness from ∼15 to 32 GPa is obtained. A further increase in p_N2 up to 64% results in minor changes of the chemical composition, micro and bonding structure as well as mechanical properties. While in ball-on-disk testing early failure was observed for coatings grown at p_N2?22%, higher nitrogen contents in the discharge yielded friction coefficients of ∼0.43 independent of chemical composition, microstructure and mechanical properties.     

Mechanical properties optimization of tungsten nitride thin films grown by reactive sputtering and laser ablation

Transition metal nitrides coatings are used as protective coatings against wear and corrosion. Their mechanical properties can be tailored by tuning the nitrogen content during film synthesis. The relationship between thin film preparation conditions and mechanical properties for tungsten nitride films is not as well understood as other transition metal nitrides, like titanium nitride. We report the synthesis of tungsten nitride films grown by reactive sputtering and laser ablation in the ambient of N₂ or N₂/Ar mixture at various pressures on stainless steel substrates at 400  C. The composition of the films was determined by XPS. The optimal mechanical properties were found by nanoindentation based on the determination of the proper deposition conditions. As nitrogen pressure was increased during processing, the stoichiometry and hardness changed from W₉N to W₄N and 30.8-38.7 GPa, respectively, for films deposited by reactive sputtering, and from W₆N to W₂N and 19.5-27.7 GPa, respectively, for those deposited by laser ablation.     

Growth and surface characterization of magnetron sputtered zinc nitride thin films

Zinc nitride films were deposited on Si(100) substrates at room temperature using RF-magnetron sputtering in pure N₂ and in Ar + N₂ atmospheres. Two active phonon modes (270.81 and 569.80 cm^− 1) are observed in Raman spectra for films deposited in Ar + N₂ atmosphere. Atomic force microscopy showed that the average surface roughness of the films deposited in pure N₂ atmosphere (1.3-3.33 nm) was less than for those deposited in a mixed Ar + N₂ atmosphere (10.3-12.8 nm). Low temperature cathodoluminescence showed two emission bands centered at 2.05 eV and 3.32 eV for both types of films.     

Mechanical properties and thermal stability of nitrogen incorporated diamond-like carbon films

The nitrogen incorporated diamond-like carbon films were deposited on Si (100) substrates by arc ion plating (AIP) under different N₂ content in the gas mixture of Ar and N₂. The influence of N₂ content on the film microstructure and mechanical properties was studied by atomic force microscopy, transmission electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and nanoindentation. It was found that the hardness (H), elastic modulus (E), elastic recovery (R) and plastic resistance parameter (H/E) decrease with increasing the nitrogen content. The decrease of mechanical properties of DLC films resulted from nitrogen incorporation was associated with total sp³ carbon bond content and N-sp³C bond content. The structural modification as well as mechanical properties of the annealed nitrogen incorporated diamond-like carbon films was investigated as a function of annealing temperature. Raman spectra indicate that the I_D/I_G ratio starts to increase and G peak position shifts upward at the annealing temperature over 500 °C. The hardness and elastic modulus of thermally annealed nitrogen incorporated DLC films decreased slightly at lower annealing temperature and then significantly decreased at higher annealing temperature. The strong covalent bonding between C and N atoms is expected to be effective on their thermal stability enhancement.     

Microstructure and ferroelectric properties of epitaxial BaTiO3/SrRuO3/SrTiO3 (001) films grown by pulsed laser deposition under high oxygen pressure

BaTiO₃ films were epitaxially grown on SrTiO₃ (001) substrates buffered with SrRuO₃ films as bottom electrode by pulsed laser deposition under high oxygen pressure of 30 Pa. The quality of the BaTiO₃/SrRuO₃/SrTiO₃ multilayer films was analyzed by means of X-ray diffraction, atomic force microscopy and transmission electron microscopy. BaTiO₃ films were found to be highly c-axis-oriented tetragonal phase with c/a = 1.002. The dielectric constant first increased with increasing temperature, and showed a peak at the Curie temperature of about 356 K. The films had well-saturated hysteresis loops with a remnant polarization of 7.3 μC/cm² and a coercive field of 29.5 kV/cm at room temperature.     

Ultra-thin zinc oxide film on Mo(100)

Zinc oxide films on a single crystal Mo(100) substrate were fabricated by annealing the pre-deposited metal Zn films in 10^− 5-10^− 4 Pa O₂ ambience at 300-525 K, and were characterized by in situ Auger electron spectroscopy, electron energy loss spectroscopy, low energy electron diffraction and high-resolution electron energy loss spectroscopy. The results show that the atomic ratio of oxygen to zinc in zinc oxide film is significantly dependent on sample annealing temperature and O₂ pressure. A stoichiometric zinc oxide film has been obtained under ∼10^− 4 Pa O₂ at about 400 K. A redshift of Fuchs-Kliewer phonon energy correlated with surface oxygen deficiency is observed.     

Growth of highly oriented LiTaO3 thin film on Si with amorphous SiO2 buffer layer by pulsed laser deposition

High-quality single-phase, c-axis textured LiTaO₃ thin films have been deposited on Si(100) substrate with amorphous SiO₂ buffer layer for optic waveguide application by pulsed laser deposition under optimized conditions of 30 Pa oxygen pressure and 650 °C. The amorphous SiO₂ buffer layer with a thickness of 100 nm was coated on the Si(100) by thermal oxidation at 1000 °C. Li-enriched LiTaO₃ ceramic target was used during the deposition. In order to study the influence of oxygen pressure on the orientation, crystallinity and morphology, different oxygen pressures (10 Pa, 20 Pa, 30 Pa and 40 Pa) were used. X-ray diffraction (XRD) results showed that LiTaO₃ thin films exhibited highly c-axis orientation under 30 Pa. It was observed by scanning electron microscopy (SEM) that the as-grown film in the optimal conditions was characterized by a dense and homogeneous surface without cracks, and the average grain size was in the order of 25 nm.     

Pulsed laser deposition of cobalt ferrite in a reactive O2:N2 atmosphere: effect of the deposition pressure and temperature

Thin films of CoFe₂O₄ have been fabricated by pulsed laser ablation of a metallic CoFe₂ target at two different temperatures (200 and 400 °C) and in various O₂:N₂, 20:80 pressures [from 0.7 Pa (5×10^-3 Torr) up to 26.7 Pa (2×10^-1 Torr)]. Too low pressures resulted in an insufficient oxidation of the deposited material and an antiferromagnetic (Fe,Co)O phase is observed together with CoFe₂O₄. A minimum pressure of 6.7 Pa was found necessary to obtain pure CoFe₂O₄ films with magnetic properties close to the bulk. The higher the pressure and the temperature, the larger was the roughness of the films. The optimum deposition temperature and pressure to obtain flat (3 nm rms roughness) CoFe₂O₄ films were, respectively, 200 °C and 6.7 Pa.