Amorphous Silicon Nitride Matrix Research Articles

Low temperature in situ formation of cobalt in silicon nitride toward functional nitride nanocomposites.

This work highlights the first demonstration of a low-temperature in situ formation of Co nanocrystallites embedded within an amorphous silicon nitride matrix through careful control of the chemistry behind material design using perhydropolysilazane (PHPS) as a Si3N4 precursor further coordinated with CoCl2 and ammonia as a pyrolysis atmosphere. The Co nucleation was allowed to proceed at temperatures as low as 400 °C via thermal decomposition of Co2N pre-formed in situ by the reaction of CoCl2 with the Si centers of PHPS at the early stage of pyrolysis (220-350 °C).

Determination of the size dispersion of amorphous silicon quantum dots from a silicon nitride film containing silicon nanocrystals

In this work we will investigate the size distribution of the amorphous silicon quantum dots (Si-AQD) inside a silicon nitride film SiNx (x = 0.12). The studied film contains an ensemble of silicon nanocrystals (Si-nc) inside an amorphous silicon nitride matrix SiNy (y = 0.66). Since the nitrogen atoms number are less than the silicon atoms number in the amorphous matrix, we can suggest that silicon atoms can aggregate under amorphous quantum dots. In this context, we will first estimate the number of crystallized silicon atoms (c-Si). The number of amorphous silicon atoms (a-Si) can be deduced from the fraction of crystallized silicon atoms and leads to the determination of the number of nitrogen atoms.Results show that all the nitrogen atoms are localized in the Si-ncs cap shell. Thus, the amorphous quantum dots can be easily revealed from the scattering electron microscopy (SEM) image. The low yield of luminescence from amorphous quantum dots can explain the difference between both experimental and simulated photoluminescence (PL) from silicon nitride film containing Si-ncs.

Structural characterization determination of silicon nanocrystals embedded in amorphous silicon nitride matrix from the effect of the light scattering

In this work, we will study the elastic and inelastic light scattering by the silicon nanocrystals (Si-nc) embedded in amorphous silicon nitride matrix. Indeed, the photons are subjected to several modifications in terms of intensity, direction and wavelength when they interact with Si-ncs. The reflectance combined with photoluminescence (PL) and Raman spectroscopy are a very sensitive tool for probing the scattering light. Results show that the observed shift of the experimental PL peaks is attributed to the Raman scattering and the PL broadening peaks to the Rayleigh scattering. A novel method allowed the determination of both the core and the surface bond lengths of Si-nc was reported. The decrease of the Raman shift observed in structures containing Si-ncs is mainly due to the Si-nc curved surface, and it reflects the presence of silicon dangling bonds at the Si-nc interfaces.

Hybrid high power impulse and radio frequency magnetron sputtering system for TiCrSiN thin film depositions: Plasma characteristics and film properties

TiCrSiN thin films were successfully grown using a hybrid approach in which a high power impulse magnetron sputtering (HiPIMS) power was combined with a radio frequency (RF) power. Different Si contents were obtained by changing the RF power of Si target. The ion energy distribution functions (IEDFs) showed that the energy tails of all sputtered ions from the targets and sputtering gases shifted to a higher energy tails when the Si target power increased from 50 to 150 W. The peak power density of the TiCr target powered by HiPIMS and the corresponding Si content in the films increased from 1214 to 1350 W/cm2 and from 0.2 to 17.9 at.%, respectively, as the Si target power increased from 50 to 150 W. The Si atoms were in the form of amorphous Si3N4 phase. The Si content showed a major influence on the microstructure, adhesion and mechanical properties of TiCrSiN film. Although a nanocomposite microstructure was formed when the Si content was 17.9 at.%, lower hardness and acceptable adhesion property were obtained due to a microstructure consisting of small TiN nanograins embedded in a large amount of soft amorphous silicon nitride matrix. The hardness of TiCrSiN film reached a maximum hardness of 31.1 GPa at Si = 6.7 at.% due to the refined microstructure and grain boundary hardening effect.

Photoluminescence from silicon nanocrystals embedded in silicon nitride fabricated by low-pressure chemical vapor deposition followed by high-temperature annealing

The photoluminescence (PL) from silicon nanocrystals (Si-ncs) embedded in an amorphous silicon nitride matrix was examined both experimentally and through theoretical simulations. The film was prepared using low-pressure chemical vapor deposition with subsequent high-temperature annealing. The experimental parameters required for the PL modeling were determined using Raman spectroscopy. A novel method to estimate the nitrogen content, which allowed the determination of both the Urbach energy and the Tauc gap, was reported. The luminescence could be attributed to different origins, namely, Si-ncs, amorphous silicon nanodots, nitrogen and silicon defects, and amorphous matrix. A comparison between the experimental results and the modeling indicated that the existing models are unable to satisfactorily explain the observed PL.

Self-assembled nc-Si/a-SiNx: H quantum dots thin films: An alternative solid-state light emitting material

Nanocrystalline silicon quantum dots (QDs) of varying size from ~5.4 to 2.2nm embedded in amorphous silicon-nitride matrix (nc-Si-QDs/a-SiNx:H) were prepared via ICP-CVD (13.56MHz), using a mixture of silane (SiH4), ammonia (NH3) gases in H2-diluted plasma, by changing the low deposition pressure in a narrow range, 10–50mTorr at low substrate temperature (250°C). Strong visible photoluminescence (PL) tunable over a significantly wide range (1.67–3.02eV) has been observed. The origin of the PL is mostly attributed to band-to-band recombination due to the quantum confinement effect (QCE) in the nanocrystalline silicon QDs. A large amount of atomic hydrogen flux that originates due to the high degree dissociation of the gas molecules in high-density inductively coupled plasma (ICP) passivates well the nonradiative dangling bonds and helps in growing plenty of ultra-nanocrystallites that demonstrate intense visible photoluminescence. The red-shift of Raman peak and the corresponding line broadening have been associated to the confinement of optical phonons within the nc-Si QDs. The widening of band gap and tune-ability of visible photoluminescence over a notably wide range along with significantly high electrical conductivity of the material demonstrates enormous promise for its utilization in the fabrication of effective solid-state light emitting devices.

Tunable photoluminescence from nc-Si/a-SiNx:H quantum dot thin films prepared by ICP-CVD

Intense visible photoluminescence (PL) tunable within 1.66-2.47 eV, under UV 325 nm excitation, was obtained from nanocrystalline silicon quantum dots (∼5.72-1.67 nm in diameter) embedded in amorphous silicon-nitride matrix (nc-Si/a-SiN(x):H) prepared in RF-ICPCVD (13.56 MHz) at substrate temperatures between 400 to 150 °C. The dominant component of PL, having a narrow band width of ∼0.16-0.45 eV, originates from quasi-direct band-to-band recombination due to quantum confinement effect (QCE) in the nanocrystalline silicon quantum dots (nc-Si QDs) of appropriate size; however, the contribution of defects arose at lower substrate temperatures leading to asymmetric broadening. Intense atomic hydrogen flux in high-density inductively coupled plasmas (ICPs) provides a very high surface coverage, passivates well the nonradiative dangling bonds, and thereby favors the PL intensity. The average size of nc-Si QDs measured by HR-TEM appears consistent with similar estimates from Raman studies. The red shift of the Raman line and corresponding line broadening originates from the confinement of optical phonons within nc-Si QDs. Photoluminescence emerging from nc-Si/a-SiN(x):H quantum dots obtained from the low temperature and single-step plasma processing holds great promise for the fabrication of light-emitting devices and flexible flat panel displays.

Enhanced fracture toughness in carbon-nanotube-reinforced amorphous silicon nitride nanocomposite coatings

Multiwalled-carbon-nanotube (MWCNT)-reinforced silicon nitride coatings were grown to evaluate the toughness contribution of nanotubes in a ceramic coating. An MWCNT array was first grown using catalytic chemical vapor deposition of acetylene on a silicon substrate. This aligned MWCNT preform was then infiltrated with an amorphous silicon nitride matrix by low-pressure chemical vapor deposition of dichlorosilane (DCS) and ammonia (NH3). The fracture toughness of this material was determined by generating cracks using nanoindentation and then employing finite-element analysis to estimate the bridging toughness contribution of the MWCNTs. The MWCNT bridging toughness of the composites is determined to be ∼5.6MPam1/2, which is seven times higher than that of the matrix. The interfacial frictional stress is also estimated and ranges from 7 to 20MPa.

Ion beam induced dissolution and precipitation of in situ formed Si-nanostructures in a-SiNx:H matrix

We report here the response of in situ formed Si-nanostructures embedded in Si-rich hydrogenated amorphous silicon nitride matrix to 100MeV Ni8+ ions irradiation under normal incidence at room temperature. Prior to irradiation, Si-nanostructures are amorphous in nature having partial crystallinity. Irradiation with a fluence of 5×1012ions/cm2 leads to dissolution of Si-nanostructures. Nevertheless, irradiation with a relatively higher fluence of 1×1014ions/cm2 enhances the nucleation and leads to the formation of amorphous Si-nanostructures. The results are understood on the basis of intense electronic energy loss induced hydrogen desorption and consequent rearrangement of the amorphous network under thermal spike formalism of ion–material interaction.

Photoluminescence of As-Grown Silicon Nanocrystals Embedded in Silicon Nitride: Influence of Atomic Hydrogen Abundance

Silicon nanocrystals embedded in silicon nitride films were grown by direct plasma enhanced chemical vapor deposition at 300 degrees C, using mixtures of SiH2Cl2/NH3/H2/Ar. The films composition and chemical stability was tested by Fourier Transform Infrared Spectroscopy and Rutherford Backscattering Spectroscopy. The influence of hydrogen abundance during the deposition process on the photoluminescence of as-grown samples was studied as a function of the radiofrequency power and hydrogen dilution flow rate. In situ Optical Emission Spectroscopy allowed the diagnostic of the species in the plasma region and their general trends as a function of the radiofrequency power. The changes in the hydrogen content and silicon incorporation to the film as a function of the radiofrequency power were discussed in terms of silicon nanocrystals formation and growth in the silicon nitride matrix. The photoluminescence emission from the as-grown samples was found to red-shift with increasing hydrogen abundance. This observation is consistent with the increase in silicon content associated to nc-Si of larger size. On the other hand, the photoluminescence intensity was observed to decrease for very high radiofrequency powers and hydrogen dilutions. High Resolution Transmission Electron Microscopy confirmed the presence of silicon nanocrystals embedded in the amorphous silicon nitride matrix and allowed the correlation between the nanocrystals size and the photoluminescence emission energy using the quantum confinement model.

PHOTOLUMINESCENCE OF Si-RICH SiNx FILMS DEPOSITED BY LPCVD UNDER DIFFERENT CONDITIONS

The silicon-rich silicon-nitride thin films deposited by low pressure chemical vapor deposition at 800° C ~950° C , using dichlorosilane and ammonia as precursors, have the mosaic structure of crystallized silicon nanoclusters embedded in amorphous silicon nitride matrix, showing visible photoluminescence (PL) emission at room temperature with one to five separate peaks. The microstructures of the films change with the deposition temperatures and flux ratios of dichlorosilane to ammonia, which causes changes in the PL spectra of the films. In this paper, we report the experimental results and try to explain it with our gap states model.

Evolution with the annealing treatments of the photoluminescence mechanisms in a-SiNx:H alloys prepared by reactive evaporation

A wide range of amorphous hydrogenated silicon nitride thin films with an excess of silicon was prepared by evaporation of silicon under a flow of nitrogen and hydrogen ions. A strong visible photoluminescence at room temperature was observed for the as-deposited films as well as for films annealed up to 1100°C. The chemical composition and the structure of the films were investigated using x-ray photoelectron, thermal desorption, and Raman spectroscopies, infrared absorption measurements, grazing incidence x-ray diffraction experiments, and transmission electron microscopy. Two luminescence mechanisms were identified for the films depending on the annealing temperature. For annealing temperatures below 650°C, the films are made of amorphous silicon-rich phases mixed with nitrogen-rich phases. These inhomogeneities in the chemical composition, coupled with the evolution of the photoluminescence energies and intensities with the hydrogen content, suggest that the emission is due to the recombination process of the photogenerated carriers within the band-tail states. For temperatures higher than 800°C, a phase separation occurs and the films could be described as silicon nanoclusters embedded in an insulating amorphous silicon nitride matrix. The clusters are amorphous, and then crystallized when the annealing temperature is high enough. The correlation between the clusters sizes and the photoluminescence results suggests that the emission observed after annealing treatments at temperature higher than 900°C is due to the quantum confinement of the carriers inside the silicon clusters. By carefully choosing the preparation and the annealing conditions, it is possible to tune the photoluminescence energy in the visible range.

Effect of sputtering target power on microstructure and mechanical properties of nanocomposite nc-TiN/a-SiN x thin films

Nanocrystalline TiN has been imbedded in amorphous silicon nitride matrix to form a super hard nanocomposite thin film (nc-TiN/a-SiN x ) via magnetron sputtering. Adjusting Ti and Si 3N 4 target power ratio altered film composition, size, amount and distribution of the nc-TiN phase. At a Ti target power density of 5.5 W cm −2, the Ti to Si 3N 4 target power ratio should be greater than unity in order for nc-TiN to form, otherwise, Ti will dissolve in amorphous SiN x . The relationship between the film hardness and the crystallite size show Hall–Petch and anti-Hall–Petch relationship. A ‘scratch crack propagation resistance’ parameter, or CPR s= L c1( L c2− L c1), has been proposed to approximate thin film toughness from the critical load data easily obtained from a scratch adhesion test.

Thermal conversion of an iron nitride–silicon nitride precursor into a ferromagnetic nanocomposite

Iron nitride films, FeN, in a pure form and in the form of a nanocomposite in silicon nitride were prepared by reactive sputtering using iron or iron disilicide, respectively, as targets in a nitrogen plasma. Iron nitride decomposes into the elements by heating in vacuum to 800 °C. Intermediate phases such as Fe2N or Fe4N form at lower temperatures. The nanocomposites contain the iron phases as particles with an average size of ∼5 nm dispersed in the amorphous silicon nitride matrix. The magnetic properties of the nanocomposites were established. The precursor FeN–Si3N4 film is paramagnetic, while the Fe–Si3N4, obtained by heating in vacuum, is ferromagnetic and shows typical superparamagnetic behavior. These films are of interest as recording media with superior chemical and mechanical stability and may be encoded by localized heating.

Strong Visible Photoluminescence in Silicon Nitride thin Films Deposited at High Rates

AbstractAmorphous silicon nitrogen alloy (a-Si:Nx) thin films have been deposited using a novel hot filament chemical vapor deposition (HFCVD) technique. In this method, a hot tungsten filament is used to decompose ammonia to obtain highly reactive nitrogen precursor species which further react with disilane to form silicon nitride thin films. This allows for very high deposition rates ranging from 600 Å/min to 2500 Å/min at low substrate temperatures. These films deposited at high rates show strong photoluminescence (PL) at room temperature in the visible region when excited with the 457 nm line of Ar+ ion laser. Intrinsic defects introduced into the amorphous silicon nitride matrix due to the rapid deposition rates seem to give rise to the visible PL. The PL intensity is at least 8-10 times stronger than silicon nitride films deposited by conventional plasma enhanced CVD. PL peak position of this broad luminescence was varied in the visible region by changing the film stoichiometry (Si/N ratio). The PL peak energy also scales predictably with the refractive index and optical band gap of the films. These samples showed reversible PL fatigue and also have band edge tail states characteristic of amorphous materials.