Nanostructured Silicon Nitride Research Articles

Coaxial Micro Ring Arrays Fabricated on Self‐Assembled Microtube Cavities for Resonant Light Modulation

AbstractComposite optical microcavities, as a versatile platform for light manipulation, have been theoretically revealed that the configuration of concentrically coupled resonant trajectories can significantly enhance the coupling strength, which is however challenging in experimental preparation. Here coaxial whispering gallery resonator chains were designed and fabricated with optically coupled modes split apart by more than the free spectral range (FSR) of the cavity itself. Because such three dimensional (3D) coupled optical systems are extremely difficult to obtain with traditional processing techniques an approach is developed to release and roll‐up pre‐strained, nanostructured silicon nitride membranes into microtubular optical cavities. Parallel nano‐ridges modified on the patterned membranes form into coaxial micro ring arrays after the membrane rolls up into a microtubular structure. Energetic degeneracy, as a consequence of mode splitting exceeding the FSR, leads to interference between bonding and antibonding modes with different mode identities (mode number), resulting in novel light modulation in the form of hybrid super wave modes, which display a distinct hopping behavior resembling linear stretch modes of an oscillator chain.

Polyetheretherketone fibers woven fabrics coated nanostructured silicon nitride and load EGCG as artificial ligaments for promoting ligament-bone integration

Design of an artificial ligament with osteogenic activity to promote ligament-bone integration for anterior cruciate ligament (ACL) reconstruction remains a huge challenge. In this work, polyetheretherketone fibers with nanostructured silicon nitride coating (PSN) and loading epigallocatechin gallate (EGCG) were woven into fabrics (PSN@EG) for artificial ligament application.The in vitro experiments confirmed that PSN@EG significantly upregulated M2 macrophage polarization that promoted secretory of anti-inflammatory cytokines while downregulated M1 macrophage polarization that inhibithed secretory of pro-inflammatory cytokines. Moreover, PSN@EG remarkably improved osteoblastic differentiation of rat bone marrow mesenchymal stem cells (BMSC) while suppressed osteoclastic differentiation of rat bone marrow-derived macrophages (BMM) in macrophage condition medium. The in vivo experiments revealed that PSN@EG promoted new bone formation for ligament-bone integration that inhibited fibrous encapsulation formation. It could be suggested that the synergistic effects of the optimized surface charactieristics (e.g., nano-micro topography), and sustained release of Si ions and EGCG caused the immunomodulatory of PSN@EG, which improved pro-osteogenic macrophage polarization that provided a favorable anti-inflammatory immune environment for enhancing osteogenesis while inhibiting osteoclastogenesis. In summary, PSN@EG with immunomodulatory significantly promoted osteoblastic differentiation while suppressed osteoclastic differentiation, thereby facilitating osteogenesis for ligament-bone integration. As a novel artificial ligament, PSN@EG has tremendous potential for ACL reconstruction.

Anti‐Corrosive and Zn‐Ion‐Regulating Composite Interlayer Enabling Long‐Life Zn Metal Anodes

AbstractThe Zn metal anode is considered one of the most promising anode choices for aqueous Zn‐based batteries. Nevertheless, dendrites and intricate side reactions have hindered its usage. Herein, an elastic and anti‐corrosive interlayer is introduced to address the problem. The idiosyncratic dielectric behavior of amorphous and nanostructured silicon nitride (Si3N4) is utilized to manipulate the ion kinetics, by uniformly dispersing its particles in polyacrylonitrile (PAN) to fabricate an interlayer attached to Zn metal (PSN‐Zn). PAN serves as an elastic constraint to inhibit drastic dendrite evolution and blocks H2O/O2 corrosion, and Si3N4 with a high dielectric constant can facilitate the ion kinetics and endow uniform Zn deposition. The electrochemical stability and deposition consistency of the Zn anodes are greatly improved, with an extended lifespan of over 800 h at 1 mA cm−2. Even under draconian deep‐discharging (DODZn = 60%) and high current density (10 mA cm−2), the PSN‐Zn anode can still operate stably for over 250 h. The effect of the dielectric property is systematically discussed and verified by experiments and theoretical simulations. Moreover, full cells with vanadium‐ and manganese‐based cathodes also deliver excellent performance, indicating the use of the multifunctional interlayer as an appealing approach for rechargeable aqueous zinc batteries.

Enhanced light absorption of ultrathin crystalline silicon solar cells via the design of front nanostructured silicon nitride

Enhanced light absorption of ultrathin crystalline silicon solar cells via the design of front nanostructured silicon nitride

A comparative study of nanostructured Silicon-Nitride electrical properties for potential application in RF-MEMS capacitive switches

The present paper aims to investigate the electrical properties of nanostructured SiNx with embedded (i) CNTs of random orientation, (ii) columnar bunches of vertically aligned CNTs and (iii) columnar Au nanorods. MIM capacitors were used to assess the effect of dielectric film structure on the electrical properties. The charge transport mechanism was assessed through current - voltage characteristics and the charge draining efficiency through the top electrode potential decay. In the case of random oriented CNTs, the transport mechanisms are Frenkel-Poole and field emission at low and high electric fields respectively. In the case of Au nanorods, the hopping and Frenkel-Poole mechanisms are detected at low and high electric fields respectively. Finally, for vertically aligned CNTs the current-voltage characteristic is found to follow ohm's law. The discharge rate through the bulk material is found to depend on nanofillers morphology.

Amorphous Silicon Nitride - an Anode Material for the Next Generation Li-Ion Batteries

Despite a decade of extensive research, silicon, as material for anodes of lithium ion batteries, still has not become a practical solution. Suffering from enormous expansion/contraction during lithiation/delithiation cycles, silicon undergoes rapid self-destruction resulting in battery failure. To counteract the degradation several options has been explored over the years. Those include downsizing of the material to nanoparticles, doping and coating with organic or inorganic shells. An alternative approach was proposed to mitigate the structural destruction of silicon, which is preparation of the alloyed materials. In the present work we demonstrate the use of nanostructured amorphous substoichiometric silicon nitride as such alternative anode material. We demonstrate that upon lithiation, silicon nitride forms lithiated subunits of silicon and ternary phase of lithium silicon nitride, which serves as a matrix material. Such phase separation leads to remarkable stability: the nanostructured thin films of SiNx allowed fabrication of electrodes exhibiting capacities above 1500 mAh/g for 2000 cycles. To achieve sufficient capacities for the practical applications, we demonstrate the application of this principle to particle-based composite electrodes, using SiNx nanoparticles fabricated through a CVD process. Such amorphous substoichiometric nanoparticles demonstrated reversible capacities above 1000 mAh/g and excellent cycling stability over several hundred cycles. We also demonstrate the effects of chemical composition on initial and long-term cycling stability of nanostructured silicon nitride.

Electron-beam radiation induced degradation of silicon nitride and its impact to semiconductor failure analysis by TEM

By in-situ transmission electron microscopy (TEM), we performed a detailed study on the electron-beam radiation damage to nanostructured silicon nitride thin-film process layers in a typical semiconductor NVM device. It was found that high-dose electron-beam radiation at 200 kV led to rapid degradation of silicon nitride process layers, i.e. thin-downing of nanostructured silicon nitride, inter-diffusion of O and N, the formation of bubble-like defects and segregation of N at neighbouring interfaces. Further detailed analysis revealed that radiation-induced modification in the microstructure and chemical composition of silicon nitride layers could be ascribed to the electron radiation induced knock-on damage and ionization damage. The radiation enhanced diffusion (RED) accounted for the continuous thin-down of the nitride process layer and the formation of bubble-like defects in thick nitride spacer process layers. The work well demonstrated the electron-beam sensitivity of nanostructured silicon nitride materials in the semiconductor devices, and thus may give useful information about electron-dose control during TEM failure analysis of the semiconductor devices containing nanostructured silicon nitride process layers.

Fabrication of nanostructured silicon nitride thin film gas sensors by reactive direct current magnetron sputtering

In this work, high-quality nanostructured silicon nitride films were prepared by reactive direct current magnetron sputtering technique. The properties of the prepared structures were determined by the ratios of gases (argon and nitrogen) in the discharge gas mixture. This parameter was effectively seen important to control the structural characteristics of the prepared nanostructures, especially surface roughness and particle size. The prepared nanostructures were successfully tested for gas-sensing applications and they exhibited reasonably high sensitivity for their resistance changes to gas concentration with increasing temperature (up to 96% at 350 °C). This work can be good attempt to use silicon nitride nanostructures in such important application.

Preparation of Nanostructured SixN1−x Thin Films by DC Reactive Magnetron Sputtering for Tribology Applications

In this work, nanostructured silicon nitride (SixN1−x) thin films were prepared by reactive magnetron sputtering using an Ar/N2 gas mixture of 1:1. The structures and fractional compositions of the prepared samples were determined by x-ray diffraction (XRD) and electron-dispersion x-ray diffraction (EDS) patterns as functions of inter-electrode distance. They showed that the prepared films were polycrystalline and the partial amount of silicon (x) is in the range 0.825–0.865 as the inter-electrode distance was in the range 2.5–7.5 cm. The particle sizes of the prepared nanostructures were determined by field-effect scanning electron microscopy (FE-SEM) to be about 38 nm. The measured Vickers microhardness of the prepared films showed relatively high values (570-750 kg.f/mm2) and decreased with decreasing film thickness, which is inversely proportional to the inter-electrode distance. These results encourage using these nanostructures for coating of wearable tools in industrial tribology applications.

Electrical properties of nanostructured SiN films for MEMS capacitive switches

The electrical properties of gold nanorods nanostructured silicon nitride films are comprehensively investigated with the aid of metal–insulator–metal capacitors and RF MEMS capacitive switches. Different nanorod diameters and densities were grown on the bottom electrode and with orientation normal to dielectric film surface. A simple physical model, which does not take the effect of electric field fringing into account, was developed to describe both the DC and low frequency electrical properties. It has been shown that the nanorods distribution and dimensions determine the electrical properties as well as the dielectric charging phenomena of the nanostructured films. Finally, in MEMS switches it has been shown that the nanorods presence does not affect the capacitance variance nor the RF characteristics of the device.

Nanostructured silicon nitride from wheat and rice husks

Nanoparticles, submicron-diameter tubes, and rods of Si3N4 were synthesized from the thermal treatment of wheat and rice husks at temperatures at and above 1300 °C in a nitrogen atmosphere. The whole pattern Rietveld analysis of the observed diffraction data from treatments at 1300 °C showed the formation of only hexagonal α-phase of Si3N4 with an R-factor of 1%, whereas samples treated at 1400 °C and above showed both α- and β-phases with an R-factor of 2%. Transmission electron microscopy showed the presence of tubes, rods, and nanoparticles of Si3N4. In a two-step process, where pure SiC was produced first from rice or wheat husk in an argon atmosphere and subsequently treated in a nitrogen atmosphere at 1450 °C, a nanostructured composite material having α- and β-phases of Si3N4 combined with cubic phase of SiC was formed. The thermodynamics of the formation of silicon nitride is discussed in terms of the solid state reaction between organic matter (silica content), which is inherently present in the wheat and rice husks, with the nitrogen from the furnace atmosphere. Nanostructures of silicon nitride formed by a single direct reaction or their composites with SiC formed in a two-step process of agricultural byproducts provide an uncomplicated sustainable synthesis route for silicon nitride used in mechanical, biotechnology, and electro-optic nanotechnology applications.

Effect of high energy milling on the formation and properties of sialon ceramics prepared from silicon nitride-aluminium nitride precursors

Abstract Nanostructured silicon nitride and aluminium nitride powder mixtures have been successfully produced by high-energy mechanical activation. Subsequent high sintering activity and β-sialon formation at low temperature resulted from activation milling at high acceleration. Densification of the samples prepared from the activated powders commenced at temperatures by about 200 °C lower, as compared with the samples prepared from the non-activated powder mixture. 27 Al MAS NMR spectra clearly showed the effect of mechanical activation on the structural changes and phase evolution of the sialon precursor during heat treatment. After pressureless sintering at 1600 °C for 60 min, β-sialon samples had a Young’s modulus of 281 GPa, microhardness of 12.8 GPa, fracture toughness of 4.6 MPa m 0.5 and flexural strength of 632±129 MPa. The unique structure and bi-modal grain size distribution that is retained after conventional sintering at 1600 °C opens up new possibilities for tailoring the microstructure and related properties of these materials.

Multiresolution atomistic simulations of dynamic fracture in nanostructured ceramics and glasses

Multimillion atom molecular-dynamics (MD) simulations are performed to investigate dynamic frac- ture in glasses and nanostructured ceramics. Using multiresolution algorithms, simulations are carried out for up to 70 ps on massively parallel computers. MD results in amorphous silica (a-SiO2) reveal the formation of nanoscale cavities ahead of the crack tip. With an increase in applied strain, these cavities grow and coalesce and their coalescence with the advancing crack causes fracture in the system. Recent AFM studies of glasses confirm this behavior. The MD value for the critical stress intensity factor of a-SiO2 is in good agreement with experiments. Molecular dynamics simulations are also performed for nanostructured silicon nitride (n-Si3N4). Structural correlations in n-Si3N4 reveal that interfacial regions between nanoparticles are amorphous. Under an external strain, nanoscale cavities nucleate and grow in interfacial regions while the crack meanders through these regions. The fracture toughness of n-Si3N4 is found to be six times larger than that of crystalline α-Si3N4. We also investigate the morphology of fracture surfaces. MD results reveal that fracture surfaces of n-Si3N4 are characterized by roughness exponents 0.58 below and 0.84 above a certain crossover length, which is of the order of the size of Si3N4 nanoparticles. Experiments on a variety of materials reveal this behavior. The final set of simulations deals with the interaction of water with a crack in strained silicon. These simulations couple MD with a quantum-mechanical (QM) method based on the density functional theory (DFT) so that chemical processes are included. For stress intensity factor K = 0. 4M Pa m 1/2 , we find that a decomposed water molecule becomes attached to dangling bonds at the crack or forms a Si-O-Si structure. At K = 0. 5M Pa m 1/2 , water molecules

Structure and Bond Properties of Compacted and Heat-Treated Silicon Nitride Particles

Particles of silicon nitride with dimensions < 15 nm are compacted into macroscopic solids (nanostructured silicon nitride solids, NANO-SSNS) and heat-treated under differing conditions. The structure and the bond nature of these silicon nitride solids are investigated by X-ray radial distribution functions, X-ray photoelectron spectra, X-ray diffraction patterns, and transmission electron microscopy observations. The particles do not grow after heat treatment at various temperatures between 25 and 1300 °C, and the volume fraction of the interface in NANO-SSNS is still large and the interfaces remain characteristics of the initial solid. The structure of the interfaces is a new type of short-range order structure differing from that inside the particles, i.e. the concentration of Si ions with coordination number < 4 is large. The bond structure of these materials is not the typical covalent bond. After heat treatments in the range 25 to 1300 °C, specimens retain the structure of the amorphous state.

Strong Polarity and Bond Characterization of Nanostructured Silicon Nitride Solids

ABSTRACTNanostructured silicon nitride solids (NANO–SSNS) were investigated by x–ray photoelectron spectroscopy (XPS), electron spin resonance (ESR) and dielectric measurements. It is found that the dielectric constant of NANO–SSNS depends strongly on the measuring frequency, f. When f&lt;100Hz, at room temperature it is forty times as much as that of conventional Si3N4. ESR measurements show that a large number of unbinding electrons exist in interfaces. This suggests that the NANO–SSNS possess strong polarity. The study on the bond properties indicates that a large number of unsaturated and dangling bonds exist in interfaces of NANO–SSNS.