SiNx Matrix Research Articles

Evaluation under temperature cycling of the tribological properties of Ag-SiNx films for green tribological applications

Nowadays, one of the most important challenges in the tribology field is to avoid the excessive consumption of soft metals such as Ag at elevated temperatures through the re-design of the self-lubricant films, to achieve the long-term lubricant under the temperature-cycling environments, for widely used in real industrial applications. This paper took up this challenge to develop a novel green film, by composing nano-particles Ag into the amorphous SiNx matrix using magnetron sputtering system, for achieving the long-term lubricant under the room temperature (RT)-500 °C temperature-cycling conditions. Results showed that the film exhibited a dual-phase of face-centered cubic (fcc) Ag and amorphous SiNx. An excellent RT-500 °C wear-resistance performance was observed for the films with the Ag content of 1.3–9.4 at.%, whilst the film at 15.8 at.% Ag exhibited the best anti-frictional performance (COF 0.3–0.5 for RT-500 °C conditions) at the cost of wear rate. The self-lubricant tribology behaviors under the RT-500 °C cycling conditions were mainly attributed by the synergism of: (1) mechanical properties, (2) excellent high-temperature chemical stability of SiNx matrix, and (3) the lubricant nature of Ag and its elevated temperature diffusion behaviors.

Influence of deposition pressure on the microstructure and mechanical properties of CVD TiAlSiN coatings

Deposition pressure is one of the key factors affecting the quality of chemical vapor deposition (CVD) coatings. In this study, the influence of deposition pressure on the microstructure and mechanical properties of CVD TiAlSiN coatings was systematically studied for the first time. It is found that within the deposition pressure range from 400 to 2000 Pa, an increase in deposition pressure has a significant influence on the microstructure of the coating, but has a minimal effect on the properties. According to grazing incidence X-ray diffraction (GIXRD) measurement, as the pressure increases from 400 to 1000 Pa, the preferred face-centered cubic (fcc-) (200) orientation disappears. Full width at half-maximum (FWHM) of three coatings implies that the grain size of the coating decreases at first and then increases with the increasing deposition pressure. TEM results indicate that Ti0.09Al0.89Si0.02N coating is self-organized with a periodically alternating Al-rich (10–14 nm) and Ti-rich (2–5 nm) nanolamellae, while Ti0.22Al0.74Si0.04N and Ti0.10Al0.87Si0.03N coatings consist of nanocrystalline (Ti,Al)N embedded in amorphous SiNx matrix. There is basically no change for the hardness of three coatings, and all values are in the range of 28.6 ± 1.2 GPa. The present work provides an inspiration for depositing CVD TiAlSiN coating with a specific microstructure by controlling the deposition parameters.

GaN nanocrystals obtained by Ga and N implantations and thermal treatment under N2 into SiO2/Si and SiNx/Si wafers

The formation of GaN nanocrystals in SiO2/Si and SiNx/Si dielectric layers implanted with Ga + and N + ions, followed by annealing at 950 °C for 60–120 min in N2, has been studied by high resolution transmission electron microscopy (HRTEM), synchrotron radiation X-ray diffraction (XRD), X-ray absorption fine structure (XAFS) technique at the Ga K-edge, as well as by Rutherford Backscattering spectrometry (RBS), X-Ray photoelectron spectroscopy (XPS), Raman spectroscopy (RS) and Scanning electron microscopy (SEM). The effect of the dielectric matrix, of the gas annealing environment (N2) and of the annealing time at 950 °C have been investigated. GaN nanocrystals implanted near the surface are observed in SiO2/Si only. The hexagonal wurtzite crystalline structure was confirmed by HRTEM, XRD and Raman spectroscopy. However, the synthesis process is multiphasic as elemental Ga0 nanoparticles at larger depths and Ga2O3 rods (~200–300 nm) on the surface were formed in addition to implanted h-GaN, as shown by TEM, XAFS, SEM, XPS and Raman spectroscopy. Moreover, Ga atoms are always remaining on some vacant Si sites in the SiO2 matrix. The local environment around Ga is quite different in the SiNx matrix, as seen by XAFS. This difference can be explained by the gallium and nitrogen diffusions which are much faster in the case of the SiO2 matrix, as shown by RBS profiles. Results are discussed in close comparison with existing literature.

Evaluation of electron traps in SiNx by discharge current transient spectroscopy: verification of validity by comparing with conventional DLTS

Discharge current transient spectroscopy (DCTS) is a promising technique for detecting the trap level and density in dielectrics because it is based on a simple emission process. In order to confirm the validity of DCTS, we compare the results from the conventional deep-level transient spectroscopy (DLTS) technique for samples of CVD-grown silicon nitride (SiNx) films. Results indicated that a trap level, about 0.6 eV below the energy level of the conduction band edge in the SiNx thin films estimated by DCTS is in good agreement with that obtained from DLTS analysis, and it is found that the trap density increases with the decreasing N/Si ratio in the SiNx film. As a proposed estimation for energy level in defects, it will be originated from hydrogen-incorporated defects in the SiNx matrix. This study demonstrates that the DCTS method will be a useful electrical method for the evaluation of defects.

Rapid Thermal Process for Crystallization Silicon Nitride Films

ABSTRACTSynthesis and characterisation of silicon nanocrystals (Si NCs) materials are carried out. We investigated the morphological and structural Si NCs embedded in the silicon nitride (SiNx) matrix. The study has been carried out on thin films thermally annealed at high temperature by rapid thermal annealing after deposition at 380°C by plasma-enhanced chemical vapour deposition. Our study evidenced the existence of an Si NCs embedded on the SiNx matrix. This has been proven by Raman spectra and high-resolution transmission electron microscopy (HR-TEM). A sharp peak at a frequency of 515 cm−1 ascribed to the transverse optical (TO) mode becomes broader and makes a symmetric shoulder on the higher frequency side with an increase in the annealing temperature. HR-TEM analyses have demonstrated that Si NCs having a mean radius ranging between 3 and 5 nm. This confirms the a-SiN phase transition to the c-SiN phase by the formation of silicon NCs.

Phase separation within NiSiN coatings during reactive HiPIMS discharges: A new pathway to grow NixSi nanocrystals composites at low temperature

The precise control of the growth nanostructured thin films at low temperature is critical for the continued development of microelectronic enabled devices. In this study, nanocomposite Ni-Si-N thin films were deposited at low temperature by reactive high-power impulse magnetron sputtering. A composite Ni-Si target (15 at.% Si) in combination with a Ar/N2 plasma were used to deposit films onto Si(0 0 1) substrates, without any additional substrate heating or any post-annealing. The films microstructure changes from a polycrystalline to nanocomposite structure when the nitrogen content exceeds 16 at.%. X-ray diffraction and (scanning) transmission electron microscopy analyses reveal that the microstructure consists of nanocrystals, NixSi (x > 1) 7–8 nm in size, embedded in an amorphous SiNx matrix. It is proposed that this nanostructure is formed at low temperatures due to the repeated-nucleation of NixSi nanocrystals, the growth of which is restricted by the formation of the SiNx phase. X-ray photoelectron spectroscopy revealed the trace presence of a ternary solid solution mainly induced by the diffusion of Ni into the SiNx matrix. Four-probe electrical measurements reveal all the deposited films are electrically conducting.

Adhesive-deformation relationships and mechanical properties of nc-AlCrN/a-SiNx hard coatings deposited at different bias voltages

A series of Al-Cr-Si-N hard coatings were deposited on WC-Co substrates with a negative substrate bias voltage ranging from −50 to −200 V using cathodic arc evaporation system. A Rockwell-C adhesion test demonstrated that excellent adhesion was observed at lower bias voltages of −50 V and −80 V, while further increases in bias voltage up to −200 V led to severe delamination and worsening of the overall adhesion strength. X-ray diffraction and transmission electron microscopy analysis revealed a single phase cubic B1-structure identified as an AlCrN solid solution with a nanocomposite microstructure where cubic AlCrN nanocrystals were embedded in a thin continuous amorphous SiNx matrix. Coatings exhibited a 002-texture evolution that was more pronounced at higher bias voltages (≥−120 V). Stress-induced cracks were observed inside the coatings at high bias voltages (≥−150 V), which resulted in stress relaxation and a decline in the overall residual stresses.

Compositionally gradient PVD CrAlSiN films: structural examination and oxidation resistance

The thermal stability and the resistance against oxidation of quaternary compositionally gradient CrAlSiN coatings deposited on steel substrate are investigated by examining their structural, morphological and chemical features before and after oxidation tests, as well as by quantitative thermal analysis. The as-deposited samples exhibit a columnar structure, with each column consisting of nanocrystals as fine as 20 nm. The as-deposited coating is mainly composed of CrxAl1−xN solid solution nanocrystals, which are embedded in an amorphous SiNx matrix. When exposed to high-temperature dry air environment the coated samples exhibit remarkable stability as they remained intact up to 800°C. Over 800°C, elements from the substrate outdiffused and modified the chemical content of the film, but still remain oxidation-resistant up to 900°C.

Improving the wear and corrosion resistance of Ti–6Al–4V alloy by deposition of TiSiN nanocomposite coating with pulsed-DC PACVD

In this work, titanium silicon nitride (TiSiN) hard ceramic coatings were deposited on Ti-6Al-4V bio-alloy to improve its wear and corrosion resistance via pulsed-DC plasma-assisted chemical vapor deposition (PACVD) method. The results showed that TiSiN coatings are composed of TiN nano-crystallites embedded in the amorphous SiNx matrix. Increasing the Si content of coating from 0 to 25.1wt%, leads to a significant reduction of its thickness from 4 to 0.5µm due to the occurrence of the controlled surface reaction phenomena. Using SiCl4 as the Si precursor for the TiSiN coatings results in increasing the surface roughness from 20.8nm of the TiN coating up to 31.4nm for the TiSiN coating with 25.1wt% Si due to the strong etching effect of SiCl4. Si addition up to 17.2wt%, reduces the TiN grains size which considerably raises the hardness (about 1000HV0.01) and also wear resistance of TiSiN coating due to the formation of the SiNx amorphous matrix and its grain growth-prohibiting effect. The electrochemical tests in simulated body fluid (SBF) represented the higher corrosion resistance of TiSiN coatings in comparison with Ti-6Al-4V alloy. The higher corrosion resistance of TiSiN coating is related to its nano-composite structure and also the formation of silicon dioxide passive layer beside the titanium dioxide layer on the surface of this coating. The highest wear resistance and corrosion protective efficiency of 77% was achieved for the TiSiN coatings with 17.2wt% and 11.3wt% of Si, respectively.

Down-shifting Si-based layer for Si solar applications

SiNx and SiNx:Tb3+ thin layers were deposited by reactive magnetron co-sputtering with the objective of optimizing the light management in Si solar cells. Those Si-based layers are developed to be compatible with the Si-PV technology. An efficient energy transfer between SiNx matrix and terbium ions (Tb3+), enhancing this system absorption, has been demonstrated and optimized. The layer composition and microstructure as well as its optical properties have been analyzed with the aim of improving both its anti-reflective properties and its luminescence emission intensity. An optimized layer was obtained by co-sputtering of Si and Tb targets in a nitrogen rich atmosphere. The emission efficiency of the SiNx:Tb3+ layer is compared to the one of previously optimized SiOxNy:Tb3+ layer. Finally we show how SiNx:Tb3+ thin films may be integrated on top of Si solar cells and act simultaneously as a down-shifting layer and antireflective coating.

Microstructure and photoluminescence of sputtered silicon-rich-nitride on anodic aluminum oxide annealed at low temperature

Abstract Silicon nanocrystals (nc-Si) or nanoparticles (np-Si) embedded in a dielectric matrix have been studied extensively for potential application in Si-based optoelectronic devices or photovoltaics. Typically, nc-Si embedded in a SiNx matrix are conventionally fabricated by plasma-enhanced chemical vapor deposition, followed by high-temperature annealing at 1000 °C or more. In this work, we used magnetron sputtering to deposit silicon-rich-nitride (SRN) films on anodic aluminum oxide (AAO) substrates to achieve the formation of nc-Si embedded into the SiN x matrix after low-temperature annealing. Commercial AAO templates, with mean pore diameters of 100 nm and 200 nm, were used for SRN deposition and annealing at the relatively low temperature of 700 °C. The morphology, crystallization, bonding and photoluminescence (PL) behavior of the annealed SRN thin films on the AAO substrate were examined by GIXRD, HRSEM, and Raman, Fourier transform infrared and PL spectroscopy. Due to the spatially confined synthesis of the AAO templates, red-shifting of the PL peak was observed in the annealed SRN on the 200 nm AAO template, compared to that on the 100 nm one. The effects of pore diameter and their boundaries on the evolution of microstructure and PL behavior of the SRN on AAO template was investigated in detail.

A Monolithic Silicon Nanocrystal Photonic Transducer for a Real-time Biomarker Detection

We demonstrate the monolithic Si nanocrystal (NC) photonic transducer for a real-time protein detection. The monolithic photonic transducer was composed of the Si NC light-emitting diode (LED), Si NC photodetector (PD), and Si nitride (SiNx) optical waveguide that was optically self-aligned to the LED and PD. The Si NCs used as the fabrication of LED and PD were synthesized in the SiNx matrix. Antibodies were immobilized onto the surface of SiNx optical waveguide of the photonic transducer through self-assembled monolayers and surface aldehyde formation. Colloidal gold (Au) nanoparticles (NPs) were used to amplify the optical signal due to the strong surface plasmon resonance. The binding reaction of the Au NPs with the immobilized antibodies within the evanescent field at the transducer surface of the SiNx optical waveguide causes attenuated total reflection of the waveguided modes and thus reduction of the PD photocurrent. The detection limit of prostate-specific antigen (PSA) was around 1 ng/mL.

Electron transport through a metallic nanoparticle assembly embedded in SiO2 and SiNx by low energy ion implantation

AbstractOriginal substrates have been developed to offer a new approach to modulate and analyse simultaneously electro‐optical and transport properties through an assembly of metallic nanoparticles (NPs). Using low energy ion implantation, silver NPs have been synthesized at the vicinity of the free surface of a SiO2 or SiNx matrix. Varying the parameters of the process allows us to modify the density of NPs and their distance to the surface. While Ag NPs surface fraction in SiO2 cannot exceed 20%, it reaches 30% in SiNx. In the latter case, NPs with mean diameter is about 2.1 nm have an interdistance compatible with tunnel effect. We then developed devices that electrically address the embedded assembly of NPs for I‐V characterization. The transport measurements on these devices show that an exploitable conduction is possible within the Ag NPs assembly in SiNx. The Arrhenius‐type temperature dependence model was successfully applied demonstrating that electron transport follows a simple thermally activated behaviour with the occurrence of a strongly localized regime. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Ag doped silicon nitride nanocomposites for embedded plasmonics

The localized surface plasmon-polariton resonance (LSPR) of noble metal nanoparticles (NPs) is widely exploited for enhanced optical spectroscopies of molecules, nonlinear optics, photothermal therapy, photovoltaics, or more recently in plasmoelectronics and photocatalysis. The LSPR frequency depends not only of the noble metal NP material, shape, and size but also of its environment, i.e., of the embedding matrix. In this paper, Ag-NPs have been fabricated by low energy ion beam synthesis in silicon nitride (SiNx) matrices. By coupling the high refractive index of SiNx to the relevant choice of dielectric thickness in a SiNx/Si bilayer for an optimum antireflective effect, a very sharp plasmonic optical interference is obtained in mid-range of the visible spectrum (2.6 eV). The diffusion barrier property of the host SiNx matrix allows for the introduction of a high amount of Ag and the formation of a high density of Ag-NPs that nucleate during the implantation process. Under specific implantation conditions, in-plane self-organization effects are obtained in this matrix that could be the result of a metastable coarsening regime.

Different charging behaviors between electrons and holes in Si nanocrystals embedded in SiNx matrix by the influence of near-interface oxide traps**Project supported by the National Basic Research Program of China (Grant No. 2010CB934402) and the National Natural Science Foundation of China (Grant No. 11374153).

Si-rich silicon nitride films are prepared by plasma-enhanced chemical vapor deposition method, followed by thermal annealing to form the Si nanocrystals (Si-NCs) embedded in SiNx floating gate MOS structures. The capacitance–voltage (C–V), current–voltage (I–V), and admittance–voltage (G–V) measurements are used to investigate the charging characteristics. It is found that the maximum flat band voltage shift (ΔVFB) due to full charged holes (∼ 6.2 V) is much larger than that due to full charged electrons (∼ 1 V). The charging displacement current peaks of electrons and holes can be also observed by the I–V measurements, respectively. From the G–V measurements we find that the hole injection is influenced by the oxide hole traps which are located near the SiO2/Si-substrate interface. Combining the results of C–V and G–V measurements, we find that the hole charging of the Si-NCs occurs via a two-step tunneling mechanism. The evolution of G–V peak originated from oxide traps exhibits the process of hole injection into these defects and transferring to the Si-NCs.

Monte Carlo simulation of silicon nanocrystal formation in the presence of impurities in a SiNx matrix

In the present work, the formation of silicon nanocrystals in the case of the presence of impurities in a SiNx matrix was simulated by using the Monte Carlo (MC) technique. A new pattern describing the distribution of impurities in the simulation matrix was proposed to study using the MC method the formation of silicon nanocrystals. The MC simulation results indicate that the formed crystallites size decreases as the amount of impurities in the matrix increases. The influences of the process temperature and the crystallographic orientation number on the crystallization kinetics were analyzed. The crystallographic orientation number was found to have no significant influence on the obtained nanostructure, and the increase in the temperature values was found to promote the formation of larger silicon crystallites. A strong relationship between the grain boundary energy constant values and the content of impurities introduced in the simulation matrix was established. The proposed approach was applied to analyze an existing experimental dataset. The results revealed a good statistical agreement between the theoretical and experimental grain size distributions and nanostructures.

Mechanical and corrosion-resistant properties of Ti–Nb–Si–N nanocomposite films prepared by a double glow discharge plasma technique

Two quaternary Ti–Nb–Si–N nanocomposite films, with differing Nb contents, were deposited onto Ti–6Al–4V substrates using a double glow discharge plasma technique. The chemical composition and microstructure of the films were characterized by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The Ti–Nb–Si–N films exhibit a typical nanocomposite structure, in which nanocrystalline (Ti,Nb)N grains, ~8nm in diameter, were embedded in an amorphous SiNx matrix. The hardness and elastic modulus of the Ti–Nb–Si–N nanocomposite films were measured by nanoindentation. The electrochemical behavior of the Ti–Nb–Si–N nanocomposite films was investigated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) in a 3.5wt% NaCl solution. For comparative purposes, these measurements were also performed on TiN and Ti–Si–N films. The results show that the Ti–Nb–Si–N nanocomposite films exhibit both higher hardness and corrosion resistance than the TiN and TiSiN films, which could be attributed to their nanocomposite structure together with the incorporation of both Nb and Si into the TiN films.

Size-dependent coupling between localized surface plasmons and excitons in silicon nitride matrix

The size-dependent coupling between localized surface plasmons (LSPs) and excitons within a silicon nitride (SiN(x)) matrix is investigated. A strong correlation between the photoluminescence (PL) enhancement and this resonance coupling is observed. From the analysis of the relationship between the dipolar resonance peaks of Ag nanostructures with various sizes and those of PL enhancement, we ascribe the enhancement of PL from the SiN(x) matrix by the addition of Ag nanostructures mainly to the LSP resonance coupling.

Enhancement of orange-yellow electroluminescence extraction from SiNx light-emitting devices by silver nanostructures

A multilayer structure of ITO/SiNx/Ag/p/p(+)-Si/Au was fabricated to improve the extraction of the orange-yellow electroluminescence from SiNx-based light-emitting devices (LEDs), and an about 5 times enhancement of external quantum efficiency (EQE) was obtained. This improved light-extraction is mainly originated from the increase of root-mean-square roughness of ITO electrode and reflectivity at longer wavelength via the addition of elongated Ag nanostructures. For the structure with the dipolar resonance peak of Ag nanostructures far from the emission wavelength of SiNx matrix, the increased surface roughness of ITO electrode has a dominant effect on the improvement of the light-extraction. Moreover, the decrease of on-series resistance by the addition of Ag nanostructures due to its enhanced local electrical fields also has a benignant contribution to the improved EQE. Our work may provide a promising approach to improve the EQE of LEDs, which is not limited to SiNx matrix.

The coupling between localized surface plasmons and excitons via Purcell effect

The coupling between localized surface plasmons (LSPs) within silver nanostructures and excitons in a silicon-rich silicon nitride (SiNx) matrix has been demonstrated via the Purcell effect. A simple model is employed for the estimation of the Purcell factor as well as the average position of excitons within a luminescence matrix. The estimated average position of the excitons is located at approximately 40 nm beneath the top surface of the SiNx films. The approaches for further improving the optoelectrical properties of the luminescence matrix are anticipated based on the model we adopted. The optimization of the thickness of the luminescence matrix as well as the size and shape of metal nanostructures may be the alternative approaches. Besides, the application of multilayers with the luminescence matrix inserted between barrier layers (we defined it as confined structures here) may be also an available choice. Our work may provide a deep comprehension on the coupling between LSPs and excitons, which is not limited to a certain luminescence material but with unconfined structures.