Si-rich Oxide Layer Research Articles

Behavior of Fe-based alloys in a liquid lead-bismuth environment under simultaneous proton irradiation and corrosion

The performance and longevity of nuclear reactors are significantly influenced by the behavior of their structural materials, particularly under conditions of corrosion and irradiation. This study investigates the combined effects of corrosion and irradiation on three alloys: Fe-Ni-Cr-Al-Nb, Fe-Cr-Al-Y, and Fe-12Cr-2Si, exposed to a liquid Pb-4wt% Bi mixture at 675 °C for 4 h. 3 MeV proton irradiation was employed to understand the simultaneous effects of irradiation on the corrosion behavior of these alloys. When exposed to liquid lead-bismuth at 675 °C for 4 h, the Fe-Cr-Al-Y and Fe-12Cr-2Si alloys exhibited superior corrosion resistance compared to the Fe-Ni-Cr-Al-Nb alloy. Conversely, the Fe-Ni-Cr-Al-Nb alloy demonstrated significant Pb-Bi penetration, which was further accelerated by proton irradiation, resulting in increased penetration depth. This revealed that irradiation-induced damage can accelerate the corrosion rate of Fe-Ni-Cr-Al-Nb steel in lead-bismuth environments. Microstructural analysis using SEM/EDX, STEM, and diffraction patterns uncovered complex alloy interactions and potential chemical transformations in the irradiated Fe-Ni-Cr-Al-Nb alloy. This included the presence of lamellar or rod-like structures near Pb-Bi penetration sites and the selective retention of nickel by aluminum. In contrast, the Fe-12Cr-2Si alloy exhibited effective corrosion resistance attributed to a uniform distribution of elements and the formation of a protective Si-rich oxide layer. The Fe-Cr-Al-Y alloy developed distinct oxide layers, with chromium oxide predominating and a slight aluminum oxide layer, indicating the critical role of chromium oxide as a protective barrier.

Study on the effect of Si content on the compatibility of F/M steels with lead-bismuth eutectic using small punch testing

This study investigates the impact of silicon (Si) on the corrosion resistance and post-corrosion toughness of ferrite/martensitic (F/M) steels in a liquid lead-bismuth eutectic (LBE) environment. Corrosion tests were performed on HT-9 and EP-823 (1.17 wt.% Si) steels at 550 °C for 1000 h under oxygen-controlled conditions. The resulting oxide layer consisted of an outer magnetite layer, a spinel layer and an inner oxide zone (IOZ). A Si-rich oxide layer was identified within the spinel and IOZ layers of EP-823, which slowed the growth rate of the oxide layer, enhanced antioxidant performance, and inhibited dissolution corrosion by the LBE. Post-corrosion mechanical properties were evaluated using a small punch test. Results showed a significant reduction in HT-9’s toughness within 240 h of corrosion, while EP-823 exhibited increased brittleness after 500 h due to Si-promoted carbide and Laves phase precipitation, significantly reducing its toughness.

Effect of Silicon on Dynamic/Static Corrosion Resistance of T91 in Lead-Bismuth Eutectic at 550 °C.

The 9–12% Cr ferritic–martensitic heat-resistant steel is the main candidate structural material for the Lead-cooled Faster Reactor. The lower Gibbs free energy change of Si oxide can promote the formation of a stable oxide layer, which can improve the corrosion resistance of the material. Therefore, it is of great significance to study the effect of silicon (Si) on the corrosion resistance of T91 steel in lead–bismuth eutectic (LBE). The corrosion resistance of T91 steel with Si contents of 0.5 wt.%, 1.3 wt.%, and 2.0 wt.%, both in dynamic and static LBE at 550 °C, was investigated. The microstructure was analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM), while the oxide films were characterized by electron probe microanalysis (EPMA). Results show that the addition of Si is conducive to improving the corrosion resistance of T91 steel in LBE. T91 steel with high Si content has a thinner and more stable oxide film. The change of Si content can change the contact angle between the steel and LBE, and the contact angle is the largest when the Si content is 1.3 wt.%. The Si-rich oxide layer is usually located in the inner oxide layer, which promotes the formation of a Cr oxide layer located in the internal oxidation zone (IOZ). Si will not enter the precipitated phase, but only change the ferrite content. The oxidation model of T91 steel containing Si in LBE was also proposed.

Influence of Si addition on the corrosion behavior of 9 wt% Cr ferritic/martensitic steels exposed to oxygen-controlled molten Pb-Bi eutectic at 550 and 600 °C

Three 9 wt% Cr ferrite/martensite steels (two alloyed with Si) have been exposed to oxygen-controlled LBE at 550 and 600 °C, respectively. The passivating oxide scale consists of a spinel layer plus internal oxidation zone (IOZ). By adding Si, the thickness of spinel layer is decreased while the IOZ is enhanced. Moreover, a Si-rich oxide layer is observed underneath the spinel layer on Si-containing samples after 2000 h exposure at 600 °C. Besides, the less visible cracks/exfoliations on Si-containing samples indicate the positive role of Si addition on scale adherence. Data availabilityThe raw/processed data required to reproduce these findings cannot be shared at this time due to technical or time limitations.The datasets obtained during the current study are available from the corresponding author on reasonable request.

Effect of silicon on oxidation behavior of 9Cr-ODS steel at 650 °C

The effect of silicon content on the evolution of oxide layer and oxides in Si-containing 9Cr-ODS steel during 5, 20 and 50 h oxidation was studied. The experiment was carried out at 650 °C in air. XRD was used to analyze oxide phase at different oxidation times. The morphology and elemental composition of the oxides were investigated by SEM/EDS. With the silicon content increasing, the oxidation resistance of ODS steel was improved. The oxide layer of 0.5 wt%Si specimen was mainly composed of Fe2O3, and the Mn-rich and Cr-rich oxides were found at oxidation 50 h. The Si-rich oxide layer was gradually generated in the 4 wt%Si specimen with the increase of the oxidation times. Meanwhile, a discontinuous Mn-rich and Cr-rich oxide layer was found on the surface of 4 wt%Si specimen steel after 50 h of oxidation. The reason is that the diffusion of Fe3+ was prevented by Si-rich oxide layer. Moreover, the diffusion rate of Cr and Mn was increased by a large amount of Si-doped. Consequently, the addition of Si is beneficial to the oxidation resistance of ODS steel.

Improvement of the storage ability of Si-rich oxide layer in poly-Si based nonvolatile memory devices by implementation of taguchi method

The storage ability of silicon-rich silicon oxide (Si-rich SiOx) floating gates plays a critical role in poly-Si nonvolatile memory devices. In this study, the Taguchi method, a statistical means of experimental design which allows for the optimization of the storage characteristics with a dramatic reduction in the number of experiments by approximately 90%, is used. The memory window of the metal insulator semiconductor devices is used as a figure of merit to find out the optimal process parameters. Furthermore, the analysis of variance showed that the substrate temperature is the dominant factor affecting the memory characteristics of the SiOx storage layers. A significant improvement in the performance of poly-Si nonvolatile memory devices using the optimal Si-rich SiOx as a charge storage layer was observed. These devices show retention of the threshold voltage shift exceeding ∼98% after 104 s and ∼96% after 10 years extrapolation with programming/erasing voltages of −12 V/+11 V at a low duration of 1 μs. Therefore, the poly-Si based nonvolatile memory devices using Si-rich SiOx as a storage layer show a high potential for memory system applications.

Effect of combined additions of Si, Mn, Cr and Al to carbon steel on material transfer in a steel/TiN coated tool sliding contact

Material transferred from steel work materials onto the cutting tools largely affects tool life and machining performance. This material transfer is strongly influenced by the steel composition, and different alloying can have very different effects. Crossed cylinders sliding tests can be used to simulate the contact between the chip and the tool in machining. In this work such a test is used to evaluate material transfer and friction characteristics of a TiN coated tool sliding against five model steels. These model steels are especially designed to study the effects from specific combination of alloy elements, i.e. the steels, containing 0.55 mass% C and 1 mass% Si, are alloyed with one or more of 1 mass% Mn, Cr and Al. When using the steels alloyed without Al, Si-rich oxide layers are formed on the coating, resulting in a low friction coefficient. When using the steels alloyed with Al, almost pure Al–O layers are formed, resulting in a higher friction coefficient and rapid coating cracking. Essentially, the most easily oxidized alloy element is most strongly enriched in the oxide and decides the main mechanism of the material transfer and friction behavior.

Effect of SiO2 layers on electroluminescence from Si nanocrystal/SiO2 superlattices prepared using argon ion beam assisted sputtering

This study investigated the electroluminescence (EL) properties of Si-rich oxide (SRO)/SiO2 superlattices light emitting devices (LEDs). Each SiO2 layer of the superlattices was prepared by using argon ion beam assisted sputtering (IBAS). Transmission electron microscopy revealed that the treatment of Ar ion beams on the SiO2 layers did not affect the size or distribution of the Si nanocrystals in the SRO layers, but enhanced the thin-film quality of the SiO2 and formed a clear SiO2/SRO interface. The refractive index of SiO2 was increased by IBAS because of an increase in the density of SiO2. The EL efficiency was doubled for the IBAS device compared with that of a reference device. According to the retention property, the enhanced EL intensity of the IBAS device was ascribed to lower the charge loss rate through enhancing injection barrier of SiO2. The mechanism of the EL enhancement of the IBAS LED was discussed.

Silicon monoxide role in silicon nanocluster formation during Si-rich oxide layer annealing – Monte Carlo simulation

A kinetic Monte Carlo model of silicon nanocluster (Si-nc) formation during high temperature annealing of Si suboxide layers was suggested. The model takes into account, along with silicon and oxygen atom diffusion, the processes of silicon monoxide creation and dissociation. It was demonstrated that the presence of SiO in the system results in an increase of Si-nc critical nuclear size and can accelerate nanocluster growth. It was found that Si-ncs were formed only in the SiOx layer with x<1.8. Three stages of Si-nc aggregation were revealed: silicon cluster nucleation, coalescence of neighbor Si-ncs, and slow enlargement of separately located clusters. Annealing of the SiO2 film containing nonstoichiometric SiOx layers resulted in Si-nc or cavity formation depending on temperature. The type of the process was determined by ratio between SiO dissociation and evaporation rates.

Effects of annealing ambient on the photoluminescence properties of Si-rich oxide/SiO2 multilayer films containing Si-nanocrystals

In this study, Si-nanocrystals (Si-NCs) have been prepared by annealing Si-rich oxide (SRO)/SiO2 multilayer films in Ar and N2, and the effects of annealing ambient on the photoluminescence (PL) properties are studied. XPS results show that the chemical compositions for the SRO and SiO2 layers are SiO1.1 and SiO2, respectively. FTIR results show that phase separation between Si and SiO2 occurs after annealing treatment, and Si-NCs are obtained which have been proved by the TEM images. Large and high density Si-NCs are obtained in the Ar-annealed film, and high structural disorder exists at the interface of Si-NCs. Compared with the film annealed in N2, a 2.4 times PL enhancement is obtained for the Ar-annealed sample, and the PL peak shifts toward low energy. Two lifetime distribution bands are obtained by fitting the time-resolved PL spectra, and the proportion of slow PL decay component increases from 69.7 to 84.0 %. The PL intensity for the Ar-annealed film is further enhanced by hydrogen passivation, and the slow PL decay component is increased to 87.5 %. Analyses show that both interface states recombination and quantum confinement effect (QCE) related optical transition in the Si-NCs exist in the optical emission process, and intense PL can be obtained only when the QCE become dominant PL mechanism.

The evolution of photoluminescence from Si cluster to nanocrystal in Si-rich oxide/SiO2 multilayer films

The evolution of photoluminescence (PL) from Si cluster to nanocrystal in Si-rich oxide (SRO)/SiO2 multilayer films is reported. Two PL bands can be obtained when the SRO layer thickness is no larger than 2 nm, and the high energy PL band (blue band) is related to the interband transition of Si cluster caused by quantum confinement effect (QCE), while the low energy band (red band) is related to the interface recombination. Both Si clusters and nanocrystals exist in the film when the SRO layer is increased to 3 nm, and the intense PL in the red band suggests that Si nanocrystals becomes the main light-emitting centers. The blue band disappears when the SRO layer is increased to 4 nm, and the PL mechanisms of the red band are QCE and interface defects in Si nanocrystals.

Effects of annealing treatments on the photoluminescence decay properties of Si-rich oxide/SiO2 multilayer films

In this work, Si-rich oxide (SRO)/SiO2 multilayer films have been deposited and the photoluminescence (PL) decay properties of the films with different annealing temperatures are studied. The PL shifts toward low energy with increasing the annealing temperature, and intense PL at around 1.4eV is obtained after annealing at 1100°C. The PL decay curves can be well fitted by a multiexponential PL decay model, and the peak of the PL lifetime distribution band shifts toward longer time with increasing the annealing temperature. Two lifetime distribution bands are obtained after the formation of crystallized Si-QDs, and the proportion of slow component increases from 69.72% to 77.04% after hydrogen passivation. Analyses show that defect states recombination in the SRO layer is the main optical emission mechanism when the annealing temperature is lower than 900°C, and interband transition in the Si-QDs due to quantum confinement effect is the main PL mechanism when the film is annealing at 1100°C.

Three-dimensional imaging for precise structural control of Si quantum dot networks for all-Si solar cells

All-Si tandem solar cells based on Si quantum dots (QDs) are a promising approach to future high-performance, thin film solar cells using abundant, stable and non-toxic materials. An important prerequisite to achieve a high conversion efficiency in such cells is the ability to control the geometry of the Si QD network. This includes the ability to control both, the size and arrangement of Si QDs embedded in a higher bandgap matrix. Using plasmon tomography we show the size, shape and density of Si QDs, that form in Si rich oxide (SRO)/SiO2 multilayers upon annealing, can be controlled by varying the SRO stoichiometry. Smaller, more spherical QDs of higher densities are obtained at lower Si concentrations. In richer SRO layers ellipsoidal QDs tend to form. Using electronic structure calculations within the effective mass approximation we show that ellipsoidal QDs give rise to reduced inter-QD coupling in the layer. Efficient carrier transport via mini-bands is in this case more likely across the multilayers provided the SiO2 spacer layer is thin enough to allow coupling in the vertical direction.

Effects of silicon plasma ion implantation on electrochemical corrosion behavior of biodegradable Mg–Y–RE Alloy

Rapid degradation is the major obstacle hindering a wider use of magnesium based biomaterials. In this work, silicon, one of the essential elements in the bone tissues, is implanted into WE43 magnesium alloy to improve its corrosion behavior. X-ray photoelectron spectroscopy (XPS) reveals the formation of a gradient surface structure with a gradual transition from a Si-rich oxide layer to Si-rich layer. Electrochemical studies reveal that Si implantation offers a remarkable improvement in the corrosion resistance of WE43 Mg alloy in simulated body fluid (SBF).

Oxidation behavior of IN738LC in situ deposited with SiO2 during a burner rig test

A burner rig was utilized for in situ depositing SiO2 on IN738LC and simultaneously for testing its oxidation behavior. For the SiO2 deposition, a mixture of TEOS and methanol was steadily fed into the combustion chamber of the burner rig during processing. The exhaust flame temperature was set at 1374°C, and the oxide precursors in the exhaust gas were carried vertically toward the pin-type specimens of IN738LC infixed to a carousel, 10cm away from the exhaust gas nozzle. A thermal cycle consisting of a 54min run and subsequent a 6min pause was repeated four times, and a processed specimen was analyzed in terms of the deposition and oxidation of the substrate.All over the processed specimen was deposited with a Si-rich oxide layer. The surface morphology of the layer varied depending on the surface temperature: from broccoli-shaped grains of several micrometers in diameter at the location of the highest surface temperature of 1018°C to finely dispersed particles of ≤1μm at the cold (≤800°C) peripheral regions of the specimen. Underneath the deposited layer, oxide scales were formed to be ≥10μm in thickness, being identified as outer Cr-rich and inner Al-rich one. Al-rich oxide formed a continuous layer (~3μm) at the location of the highest surface temperature, which became particles broadly distributed near the surface on going to the cold peripheral regions. Meanwhile, Cr-rich oxide formed a continuous layer (3–5μm) at the cold regions, which became narrower and eventually disappeared at the hottest region. The changeover of the oxidation modes accorded with the behavior of the EDX intensity of Cr as a function of that of Al in the oxide scale; the Cr intensity decreased, while the Al intensity increased toward the hotter region. The EDX Si signal for the deposited layer increased with that of O with an increase in the surface temperature along the specimen, suggesting that the layer became denser at the location of higher surface temperatures. It was discussed that the deposited porous layer was densified during the process to a degree depending on the surface temperature of the specimen, which rendered the layer compacter at the location of higher surface temperatures. The oxygen diffusion through the compacter layer was suppressed more effectively, resulting in the preferred oxidation of Al over Cr in the alloy, namely better protection of the metal substrate in terms of the oxidation.

Nanosecond Field-Induced Quenching of the Luminescence from Er-Doped Silicon Nanocrystals

Er-doped Si-rich SiO2 gate oxide layers containing silicon nanocrystals are prepared by implantation of Si+ and Er+ into SiO2 thin films. The photoluminescence from both Si nanocrystals around 700-850 nm and Er3+ ions at 1.54 microm is strongly quenched by applying electric field in the Si-rich oxide layer. The quenching time and the recovery time of the photoluminescence from Si nanocrystals are less than 50 ns under pulsed field modulation. The quenching rate of the luminescence increases with increasing the density and reducing the size of the silicon nanocrystals. Our results indicate that the fast quenching process originates from the quantum confined Stark effect and enhanced exciton ionization by carrier tunneling between the silicon nanocrystals under the high electric field.

Effects of Si Content on the Oxidation Behavior of Fe–Si Alloys in Air

The oxidation behavior of Fe–Si alloys at 1073K in air was investigated. The oxidation kinetics described by the parabolic rate law of diffusion controlled oxidation and the oxidation rate decrease with the increasing Si content. Fe-Si alloys were oxidized for different times at 1073K to obtain the same scale thickness of approximately 30μm. Observations of scale cross-sections indicated the structure of oxide scale and elemental distribution in oxide scales strongly depends on Si content. The oxide scale on Fe-Si alloys with low Si content consisted of three layers with an outer Fe2O3, an intermediate Fe3O4 and an inner FeO and some voids were formed in Fe3O4 and FeO layers. The Si-rich oxide layer was formed at the scale/alloy interface of Fe-Si alloys with high Si content. Furthermore, the amount of internal oxidation zone increased with the increasing Si content. Observations of scale cross-sections indicated that the structure of oxide scale and elemental distribution in oxide scale strongly depend on Si content.

Energy selective contacts for hot carrier solar cells

Double barrier resonant tunnelling structures consisting of silicon quantum dots (QDs) in silicon dioxide ( SiO 2 ) matrix have been studied for Energy Selective Contacts for Hot Carrier solar cell. A single layer of silicon QDs has been fabricated by high temperature annealing of SiO 2 / Si-rich oxide (SRO)/ SiO 2 layers deposited by RF magnetron sputtering. Compositional analysis of SRO films obtained with different sputtering target has been accurately measured with Rutherford backscattering spectroscopy. Size-controlled growth of Si QDs has been studied with photoluminescence measurements which demonstrate that QD sizes can be controlled with SRO layer thickness. In addition, resonant tunnelling behaviour of SiO 2 / Si QD/ SiO 2 structures has been investigated.

Effects of Si-rich oxide layer stoichiometry on the structural and optical properties of SiQD/SiO2 multilayer films

The effects of the stoichiometry of the Si-rich oxide (SRO) layer,O/Si ratio, on the structural and optical properties ofSRO/SiO2 multilayer films were investigated in this work.SRO/SiO2 multilayer filmswith different O/Si ratios were grown by a co-sputtering technique, and Si quantum dots (QDs) were formed withpost-deposition annealing. By transmission electron microscopy (TEM) and glancing incidencex-ray diffraction (GIXRD), it was found that the Si QD size decreases with increases inO/Si ratio. The photoluminescence (PL) spectrum varies with theO/Si ratio in band position, shape and intensity. In addition, it wasobserved that the absorption edge blue-shifts with increases in theO/Si ratio. The change in the absorption edge is consistent with strengthening quantumconfinement effects in Si QDs, as indicated by TEM and GIXRD. The optical propertieswere also investigated by 2D photoluminescence excitation (2D-PLE) and lifetimemeasurements. The origin of emission and absorption is discussed based on the absorption,PL, 2D-PLE and decay time measurements.

Absorption and transport properties of Si rich oxide layers annealed at various temperatures

Thin films of SiOx (x = 1.15, d = 1 and 2 µm), deposited by thermal vacuum evaporation of SiO on n- and p-type crystalline Si or quartz substrates, and then furnace annealed at 250, 700 and 1000 °C, are studied. Optical and infrared transmission measurements prove phase separation upon annealing at 700 and 1000 °C and growth of amorphous Si nanoparticles upon annealing at 700 °C, whose optical band gap is ∼2.6 eV. High-resolution electron microscopy data confirm growth of Si nanocrystals with average size ∼5 nm in the films annealed at 1000 °C. Both kinds of transmission data were used to estimate the nanoparticle volume fraction and values of 0.2–0.25 and 0.25–0.30 for the films annealed at 700 and 1000 °C, respectively, are determined. Current–voltage characteristics (at fields >5 × 104 V cm−1) are measured on metal/SiOx/c-Si/metal structures to explore carrier transport mechanisms in all kinds of samples. They are nearly symmetric, which indicates that in all samples carrier transport via structures is dominated by the transport in the SiOx layers. It is concluded that current transport is space-charge-limited for the layers annealed at 250 °C. In the films further annealed at 700 °C containing amorphous nanoparticles, Poole–Frenkel transport mechanism is reported while tunnelling is assumed for the films annealed at 1000 °C.