Low voltage electrodeposition of CNx films and study of the effect of the deposition voltage on bonding configurations

Carbon nitride (CN_x) films were deposited from acetonitrile at low voltage (150-450 V) through electrodeposition. The films were characterized by atomic force microscopy (AFM), Raman spectroscopy and Fourier transform infrared (FT-IR) spectroscopy. AFM investigations revealed that the grain size was ∼200 nm and roughness was ∼10 nm. The films were found to be continuous and close packed. IR spectra revealed existence of strong sp³, sp² type bonding and weak sp type carbon nitrogen bonds and these bonds were found to increase with voltage. The fraction of sp³-bonded species in the sample increased in low voltage range and after reaching maximum at 350 V, decreased for higher voltages. However, the concentration of sp² CN ring structures in the film increased with increasing voltage. Also, the peak width decreased at low voltages reaching a minimum and increased thereafter. It was observed that the voltage dependent increase in the concentration of polymeric type sp² CN (chain) structures was much more pronounced than that of graphitic type sp² CN (ring) structures. Raman spectra showed the presence of both the D and G bands. The shift in the G band indicated the presence of nitrogen in the film. The I_D/I_G ratio was found to increase with the incorporation of nitrogen. Auger electron spectroscopy (AES) showed a clear increase in the nitrogen content with increase in the voltage. The formation of the film could be explained on the basis of dissociation of electrolyte under applied voltage.     

Microstructure and tribological behavior of pulsed laser deposited a-CNx films

The a-CN_x films were deposited onto high-speed steel substrate by pulsed laser deposition at different nitrogen pressures. The tribological properties of the films in humid air and in vacuum were investigated using a ball-on-disk tribometer under various loads. The composition, microstructure and morphology of the films, wear tracks and paired balls were characterized by energy dispersive X-ray analysis (EDXA), X-ray photoelectron spectrum (XPS), Raman spectroscopy and scanning electron microscopy (SEM). With increasing the deposition pressure, the fraction of sp³ C bond reduces, the fraction of trapped nitrogen increases and the friction coefficient of the films declines both in humid air and vacuum. The friction coefficient of a-CN_x film decreases with increasing normal load. The tribological performances of the films in humid air are better than those of in vacuum. A transferred graphite-like tribo-layer is observed from a-CN_x film to the paired ball for both environments.     

基于Si-rich SiNx/N-rich SiNy多层膜结构电致发光特性研究

利用等离子体增强化学气相沉积法制备了富硅氮化硅/富氮氮化硅多层膜,并以此氮化硅基多层膜作为有源层构建电致发光器件,在室温下观察到了较强的电致可见发光.在此基础上,研究多层膜结构中作为势垒层的富氮氮化硅层对器件电致发光性质的影响,实验结果表明通过改变势垒层的Si/N组分,调制其势垒高度,器件的电致发光效率可得到显著地提高. 关键词： 电致发光 多层膜 氮化硅     

Structure and properties of (AlCrMnMoNiZrB0.1)Nx coatings prepared by reactive DC sputtering

The microstructure and properties of AlCrMnMoNiZrB_0.1 nitride films prepared by reactive direct current sputtering at various N₂-to-Ar flow ratios (R_N) were investigated. The films had an amorphous structure at low R_N and a face-centered cubic structure at a high R_N. As the R_N increased, the decrease in clusters and defects resulted in a dense columnar structure and low surface roughness. The peak hardness and modulus of the nitride films were 10.3 and 180 GPa, respectively. The enhanced hardness is ascribed to the increased metal-nitrogen bonding, solid solution strengthening of several metallic nitrides, and lattice strain. The nitride films deposited at R_N = 0.2, 0.5, and 0.8 had friction coefficients of 0.16, 0.12 and 0.15, respectively. Wear-out failure occurred within 400 s when R_N = 0 and 1.0. Adhesive wear was the dominant wear mechanism.     

Microstructure related photoluminescence in a-CNx films deposited by reactive rf magnetron sputtering

We investigated the photoluminescence (PL) properties of carbon nitride films (CN_x) deposited by rf magnetron sputtering and compared them to their microstructure depending on the target self-bias. While many of the data are compatible with ‘a-C:H like’ PL properties the observed variation of the PL efficiency η with respect to the target bias cannot be easily explained by the standard models. It is suggested that the observed variation of η is rather dominated by a change in microstructure which depends on the bombardment intensity during growth than by the concentration of non-radiative centres.     

Effects of hydrogen on photoluminescence properties of a-SiNx:H films prepared by VHF-PECVD

Luminescent hydrogenated amorphous silicon nitride films were prepared with different hydrogen flow rate in very high frequency plasma enhanced chemical vapor deposition system. Very bright orange-red light emissions can be clearly observed with the naked eye in a bright room for the films grown at the hydrogen flow rate of 30 sccm. The photoluminescence intensity of the film grown at the hydrogen flow rate of 30 sccm is found to be four times higher than that of the film without hydrogen dilution. However, with further increasing the hydrogen flow rate from 30 to 90 sccm, the photoluminescence intensity of the film rapidly decreases. Fourier-transform infrared absorption spectra indicate that the introduction of hydrogen concentration bonded to silicon and nitrogen is of a key role to enhance the photoluminescence intensity of the films. Based on the measurements of structural and bonding configurations, the improved photoluminescence intensity is attributed to the well hydrogen passivation of nonradiative defect states related to N and Si at proper hydrogen flow rate.     

Microstructure and properties of Nb/Ta multilayer films irradiated by a high current pulse electron beam

Nb/Ta multilayer films deposited on Ti6Al4V substrate with Nb and Ta monolayer thicknesses of 30 nm, 120 nm, and 240 nm were irradiated by a high current pulse electron beam (HCPEB) to prepare Nb-Ta alloyed layers. The microstructure and the composition of the outmost surface of melted alloyed layers were investigated using a transmission electron microscope (TEM) equipped with an X-ray energy dispersive spectrometer (EDS) attachment. The Ta content of the alloyed surface layer prepared from the monolayer of thickness 30 nm, 120 nm, and 240 nm was ～ 27.7 at.%, 6.37 at.%, and 0 at.%, respectively. It was found that the Ta content in the alloyed layer plays a dominant role in the microstructure of the films. The hardness and the wear rate of the alloyed layers decrease with the increasing content of Ta in the surface layer.     

AlNxOy thin films deposited by DC reactive magnetron sputtering

AlN_xO_y thin films were produced by DC reactive magnetron sputtering, using an atmosphere of argon and a reactive gas mixture of nitrogen and oxygen, for a wide range of partial pressures of reactive gas. During the deposition, the discharge current was kept constant and the discharge parameters were monitored. The deposition rate, chemical composition, morphology, structure and electrical resistivity of the coatings are strongly correlated with discharge parameters. Varying the reactive gas mixture partial pressure, the film properties change gradually from metallic-like films, for low reactive gas partial pressures, to stoichiometric amorphous Al₂O₃ insulator films, at high pressures. For intermediate reactive gas pressures, sub-stoichiometric AlN_xO_y films were obtained, with the electrical resistivity of the films increasing with the non-metallic/metallic ratio.     

High-frequency properties of discontinuous FeCoSi/native-oxide multilayer films

Discontinuous [FeCoSi (d)/native-oxide]₅₀ multilayer films were fabricated by DC magnetron sputtering without any post-deposition treatment. The films exhibit good soft magnetic properties with initial permeability μ_i larger than 100, the saturation magnetization 4πM_s and the in-plane uniaxial anisotropy field H_k increase as the magnetic FeCoSi layer thickness d is increased from 5.5 to 20.5 Å. As a consequence, the ferromagnetic resonance frequencies f_r of the films increase from 2.0 to 3.9 GHz. The combination of high f_r and large μ_i makes these films potential candidates for magnetic devices applied in the high-frequency range. The origin of the excellent high-frequency properties in discontinuous FeCoSi/native-oxide multilayer films is discussed.     

Structure, electrical and optical properties of TiNx films by atmospheric pressure chemical vapor deposition

Titanium nitride (TiN_x) films with various nitride compositions (x) were prepared on glass substrates by atmospheric pressure chemical vapor deposition using TiCl₄ and NH₃ as precursors. The structural, compositional, electrical and optical properties of the films were studied and the results were discussed with respect to nitride composition. The results showed a linear relationship between the lattice constant and the nitride composition. Resistivity of the films was minimized near x = 1. All the TiN_x films exhibited a transmission band with a peak value of about 15% in the visible region (400-700 nm). As the wavelength increased to transition point (λ_T-R), the reflectance of the obtained films presented a sharp increase and then reached a high value of about 50% near 2000 nm. Moreover, the red-shift of transmission band and the transition wavelength (λ_T-R) with increasing the nitride composition were also discussed.     

Microstructure and tribological properties of WS2/MoS2 multilayer films

In this paper, a novel method, namely, magnetron sputtering and low temperature ion sulfurizing combined technique was used to fabricate the solid lubrication WS₂/MoS₂ multilayer films. Scanning Electron Microscopy (SEM) was used to observe the surface and worn scar morphologies. X-ray diffraction (XRD) was utilized to analyze the phase structure. The nano-hardness and elastic modulus of WS₂/MoS₂ multilayer films were surveyed by the nano-indentation tester. The friction and wear test were conducted on a ball-on-disk wear tester under dry sliding condition. The results obtained showed that the WS₂/MoS₂ multilayer films exhibited a lower friction coefficient and better wear-resistance when compared with single WS₂ film and original 1045 steel.     

Structural and mechanical properties of compositionally gradient CrNx coatings prepared by arc ion plating

Compositionally gradient CrN_x coatings were fabricated using arc ion plating by gradually increasing N₂ flow rate during the deposition process. The effect of substrate bias, ranging from 0 to −250 V, on film microstructure and mechanical properties were systematically investigated with XRD, SEM, HRTEM, nanoindentation, adhesion and wear tests. The results show that substrate bias has an important influence on film microstructure and mechanical properties of gradient CrN_x coatings. The coatings mainly crystallized in the mixture of hexagonal Cr₂N, bcc Cr and fcc rock-salt CrN phases. N₂ flow rate change during deposition results in phase changes in order of Cr, Cr + Cr₂N, Cr₂N, Cr₂N + CrN, and CrN, respectively, along thickness direction. Phase fraction and preferred orientation in CrN_x coatings vary with substrate bias, exerting an effective influence on film hardness. With the increasing of bias, film microstructure evolves from an apparent columnar structure to a highly dense one. The maximum hardness of 39.1 GPa was obtained for the coatings deposited at a bias of −50 V with a friction coefficient of 0.55. It was also found that adhesion property and wear resistance of gradient CrN_x coatings were better than that of homogeneous CrN coatings.     

The influence of processing gas on the mechanical properties of sputtered B-C-N-H films

This work describes the microstructure and mechanical properties of B-C-N-H films synthesized by medium frequency magnetron sputtering from a boron target in a N₂ + CH₄ + Ar gas mixture. The increase in the CH₄ flow rate increases the carbonaceous compound species, causes the increase of the C atomic concentration and promotes the formation of sp³-hybridized carbon. The change of hardness with the CH₄ flow rate had a relationship with the residual stress. The coefficient of friction was reduced approximately from 0.8 to 0.18, and wear resistance was considerably improved by increasing the flow of CH₄ gas component from 0 to 40 sccm. The change of films’ hardness was discussed and attributed primarily to the internal defects and bonding characteristics, while the superior tribological properties of the films could be assigned to the formation of sp³-hybridized carbon and the C-H bonding.     

Enhancement of surface mechanical properties by using TiN[BCN/BN]n/c-BN multilayer system

The aim of this work is to improve the mechanical properties of AISI 4140 steel substrates by using a TiN[BCN/BN]_n/c-BN multilayer system as a protective coating. TiN[BCN/BN]_n/c-BN multilayered coatings via reactive r.f. magnetron sputtering technique were grown, systematically varying the length period (Λ) and the number of bilayers (n) because one bilayer (n = 1) represents two different layers (t_BCN + t_BN), thus the total thickness of the coating and all other growth parameters were maintained constant. The coatings were characterized by Fourier transform infrared spectroscopy showing bands associated with h-BN bonds and c-BN stretching vibrations centered at 1400 cm⁻¹ and 1100 cm⁻¹, respectively. Coating composition and multilayer modulation were studied via secondary ion mass spectroscopy. Atomic force microscopy analysis revealed a reduction in grain size and roughness when the bilayer number (n) increased and the bilayer period decreased. Finally, enhancement of mechanical properties was determined via nanoindentation measurements. The best behavior was obtained when the bilayer period (Λ) was 80 nm (n = 25), yielding the relative highest hardness (∼30 GPa) and elastic modulus (230 GPa). The values for the hardness and elastic modulus are 1.5 and 1.7 times greater than the coating with n = 1, respectively. The enhancement effects in multilayered coatings could be attributed to different mechanisms for layer formation with nanometric thickness due to the Hall-Petch effect; because this effect, originally used to explain increased hardness with decreasing grain size in bulk polycrystalline metals, has also been used to explain hardness enhancements in multilayered coatings taking into account the thickness reduction at individual single layers that make up the multilayered system. The Hall-Petch model based on dislocation motion within layered and across layer interfaces has been successfully applied to multilayered coatings to explain this hardness enhancement.     

Superconductivity and properties of FeTeOx films

Films of the parent compound FeTe can be made superconducting via the addition of interstitial oxygen. The process is reversible. We have characterized the new superconductors with a variety of experiments. X-ray diffraction shows that the superconductor has the same overall structure but a small lattice constant change compared to pure FeTe. X-ray absorption shows that superconducting FeTeO_x has a nominal valence of 3+. DFT calculations show the most likely position for interstitial oxygen and confirm that such oxygen incorporation does not produce a large change in structure.     

基于Si-rich SiNx/N-rich SiNy多层膜结构的量子点构筑及发光特性

利用等离子体增强化学气相沉积法制备Si-rich SiN_x/N-rich SiN_y多层膜,分别使用热退火和激光辐照技术对多层膜进行退火,以构筑三维限制、尺寸可控、有序的硅纳米晶.实验结果表明,经退火后,纳米硅晶粒在Si-rich SiN_x子层内形成,其尺寸可由Si-rich SiN_x子层厚度调控.实验还发现,激光辐照技术相比于热退火能更有效地改善多层膜的微结构,提高多层膜的晶化率,以激光技术诱导晶化的Si-rich SiN_x/N-rich SiN_y多层膜作为有源层构建电致发光器件,在室温下观察到了增强的电致可见发光,并且发光效率较退火前提高了40%以上. 关键词： 氮化硅 多层膜 限制结晶 纳米晶硅     

Structure evolution and mechanical properties enhancement of Al/AlN multilayer

A set of Al/AlN multilayers with various modulation periods were prepared using DC magnetron sputtering method. Low angle X-ray diffraction (LAXRD) was used to analyze the layered structure of multilayers. The phase structure of the films was investigated with grazing angle X-ray diffraction (GAXRD). LAXRD results indicate that well-defined multilayer modulation structures are formed for the relatively larger modulation periods. However, the loss of mutilayered structure is detected in the multilayer with low modulation period. A very wide amorphous peak is observed in multilayer with modulation period of 4 nm. The multilayers show obvious crystallization at larger modulation periods, however, the diffraction peaks are much wider than the Al single layer because of the interruption of the continuous columnar grain growth by alternating deposition processes. Nanoindentation experiments were performed to study the mechanical properties as a function of multilayer modulation period. It is found that the hardness of the multilayers is greater than the hardness calculated from rule of mixtures. With the modulation periods adjusted, the multilayers are even harder than its hard component (AlN). A maximum hardness of 24.9 GPa, about 1.9 times larger than its hard component (AlN) and 3.7 times larger than the hardness calculated from the rule of mixtures, is found at the multilayer with modulation period of 16 nm. The wear test results show that the multilayers possess lower and stable friction coefficient, and superior wear properties.     

SiOxNy thin films with variable refraction index: Microstructural, chemical and mechanical properties

In this work amorphous silicon oxynitride films with similar composition (ca. Si_0.40N_0.45O_0.10) were deposited by reactive magnetron sputtering from a pure Si target under different N₂-Ar mixtures. Rutherford backscattering (RBS) studies revealed that the coatings presented similar composition but different density. The mechanical properties evaluated by nanoindentation show also a dependence on the deposition conditions that does not correlate with a change in composition. An increase in nitrogen content in the gas phase results in a decrease of hardness and Young's modulus.The microstructural study by high resolution scanning electron microscopy (SEM-FEG) on non-metalized samples allowed the detection of a close porosity in the form of nano-voids (3-15 nm in size), particularly in the coatings prepared under pure N₂ gas. It has been shown how the presence of the close porosity allows tuning the refraction index of the films in a wide range of values without modifying significantly the chemical, thermal and mechanical stability of the film.     

掺杂BaTiO3/SrTiO3多层膜与太赫兹波相互作用

掺杂半导体中的载流子吸收在THz波段非常明显,其相互作用研究是研制THz通信中的关键器件之一的基础。采用氟化氪（KrF）脉冲准分子激光烧蚀沉积（PLD）技术,制备了Ni掺杂BaTiO3/SrTiO3多层膜。基于辐射频率为3.09 THz、脉冲功率为10 mW量级的THz 量子级联激光器(QCL)光源研究了太赫兹波在Ni掺杂BaTiO3/SrTiO3多层膜中的传输,发现损耗主要是Ni颗粒的非共振吸收导致。     

Microstructures and properties of plasma sprayed FeAl/CeO2/ZrO2 nano-composite coating

Commercial FeAl powders and ZrO₂ nano-particles as well as CeO₂ additive were reconstituted into a novel multi-compositional feedstock powders via spray drying. The resulting feedstock powders were used to deposit FeAl/CeO₂/ZrO₂ nano-composite coating by plasma spraying on 1Cr18Ni9Ti stainless steel. An X-ray diffractometer (XRD), a scanning electron microscope equipped with an energy dispersive spectrometer (SEM/EDS), and a field emission scanning electron microscope equipped with an energy dispersive spectrometer (FESEM/EDS) were employed to characterize the microstructure of the as-prepared feedstock powders and nano-composite coating. At the same time, the mechanical properties and friction and wear behavior of the nano-composite coating and pure FeAl coating were comparatively evaluated by using a Vickers microindentation tester and ball-on-disk sliding wear tribotester, respectively. And the wear mechanisms for the two types of coatings are discussed in terms of their microstructure and mechanical properties. Results indicate that the nano-composite coating has a much higher hardness and fracture toughness as well as drastically increased wear resistance than pure FeAl coating, which could be mainly attributed to the reinforcing effect of ZrO₂ nano-particles and partially attributed to the refining effect of CeO₂ in the nano-composite coating.