Oxidation Of Si Research Articles

Demonstration of non-negligible oxygen exchange in the thermal oxidation of silicon carbide

Oxygen incorporation mechanism with various temperatures during the thermal oxidation of 4H–SiC in dry O2 has been investigated by the isotopic tracing technique. The results suggest that the oxygen exchange is the main incorporation mechanisms of oxygen for SiC oxidation. The temperature and locations of oxygen exchange are different from those in Si oxidation. In SiC thermal oxidation, oxygen exchange occurs even for extremely low oxidation rate at low temperature, and it is not confined to the surface region but throughout the oxide layer. The rate of oxygen exchange increases as temperature increases. This is the direct evidence that oxygen exchange in SiC oxidation cannot be negligible. By analysing the results of X-ray photoelectron spectroscopy and capacitance-voltage measurements, it is found that such significant oxygen exchange is not caused by a large number of defects. Moreover, based on the fitting of refractive index and extinction coefficient, the number of defects in the oxide layer decreases with the increase of temperature, which indicates that oxygen exchange contributes to reducing defects in the oxide layer during high-temperature oxidation and low-temperature post-oxidation annealing.

Concentrations, transport characteristics, and health risks of PM2.5-bound trace elements over a national park in central India

Fine particulate matter (PM2.5) mass and its chemical constituents were measured over Van Vihar National Park (VVNP) in Bhopal, central India. Fine PM collected over two years onto Teflon filters using a Mini-Vol® sampler were analyzed for trace elements using an Energy Dispersive X-ray fluorescence (ED-XRF) spectrometer. The temporal behaviour, dry deposition fluxes and transport pathways of elements, in addition to their health risks were examined in this study. S, K, Si, Al, Ca, and Fe accounted for most of the PM2.5-bound trace elements (~88% on average). Pronounced seasonality was observed for major elements (S, K, and Cl) and reconstructed soil (estimated as the sum of oxides of crustal elements, i.e., Si, Al, Ca, Fe, and Ti), with winter and post-monsoon season highs, potentially due to source strengths and favourable metrology during these seasons. The synoptic meteorology during these seasons favoured the fetch of particles from highly polluted regions such as the Indo-Gangetic Plain. The estimated average dry depositional flux of each element in this study was comparable to those measured/estimated for each of these species over other urban areas. The sum of the dry deposition flux for crustal elements (1301.9 ± 880.7 μg m−2 d−1) was in agreement with global dust cycle models. Air-parcel trajectory cluster analysis revealed that S, K, and Cl were influenced by biomass and coal burning in predominantly in central, and northwestern India, while reconstructed soil was influenced by air masses from the Arabian and Thar deserts. Finally, human exposure risk assessment to carcinogens (As, Cr, Cd, Pb and Ni) and non-carcinogens (Cu, Zn, Mn, V, Hg, Se and Al) revealed that no significant risk was posed by these elements. The assessment in this study was a screening for severe adverse effects, rather than a speciated health assessment. Thus, over the study region, monitoring, health risk assessment and mitigation measures, where needed, must be enhanced to ensure that trace elements induced health effects continue to be within safe levels.

Effect of Convection on Chirality of Spatiotemporal Patterns Observed in the Reduction of Hydrogen Peroxide

Background The spatiotemporal patterns have been reported in many electrochemical systems. Most of the patterns disappear when the reactions stop. This is because they originate from the spatial distribution of the local current and potential during the reactions. However, it is possible to inscribe the patterns into materials by utilizing the pattern formation in the material processing. This process enables to fabricate materials with unique shapes reflecting the pattern profile and is expected to be a new method for the production of such highly sophisticated materials. As one of the materials formed in this process, we have focused on the helical nanopore formed in the Platinum-assisted chemical etching of Si induced by the oxidation of Si and the reduction of H2O2. In this phenomenon, the helical pores are spontaneously formed by immersing the Si substrate modified with Pt nanoparticles into the etchant. We reported that the formation of helical pores originates from a spatiotemporal pattern emerging in the reduction reaction of H2O2 on the Pt particle. Our recent paper on helical nanopore formation in the etching of silicon implies that it is possible to fabricate chiral materials by utilizing the spatiotemporal pattern. In order to utilize the chiral material formed by the spatiotemporal pattern formation in the field of chiral chemistry, it is an inevitable task to control the chirality of the material. Because it is determined by the chirality of the pattern, we have to understand the effect of spatial symmetry breaking on the chirality of the spatiotemporal pattern. In this report, we focus on convection as the chiral condition introduced to the system and investigate its effect on the chirality of the spatiotemporal pattern. Among the several spatiotemporal patterns, we focus on the rotating waves (RW), where active and inactive sites rotate on the ring electrode because it is considered that this pattern emerges during the helical pore formation.Experimental In order to investigate the effect of the convection on the RW, we simulate the formation of the RW during the electrochemical reduction of H2O2 on the Platinum ring electrode based on the model constructed by Fukushima. In this model, we deal with the local electrode potential (E) and the local concentration of H2O2 (c) on the electrode surface as the variables. The differential equations governing E and c ware obtained by considering the equivalent circuit and the consumption and diffusion of H2O2, respectively. Since RWs have two different modes, which are the right-handed rotating wave (R-RW) and the left-handed rotating wave (L-RW), either may appear preferentially in the system where convection is considered. We conducted the simulation several times in a certain condition with random perturbation, and examined the percentage of R-RW in all RWs formed (R-RW%). In this simulation we always introduced the right-handed convection.Result and discussion The R-RW% changed depending on the velocity of the convection (v). When the convection was strong and v was 10 m/s, the R-RW was 0%, meaning that only the L-RW was formed. It should be emphasized that the RWs in the opposite direction to that of the convection, i.e. upstream RWs were formed in this condition. In contrast, when convection was mild and v was 0.1~1 m/s, the direction of the preferential RW was different from that of the RW formed when v was 10 m/s. In other words, the RW whose direction was the same as that of the convection (the downstream RW) was preferentially formed under mild convection. These results suggest that the formation of downstream RWs under mild convection is governed by the nonlinear dynamics. The observation of the change in the distribution of c and E showed that E in some area of the electrode got out of the potential region, where a negative differential resistance (NDR) appeared in the current-potential curve, at the initial stage of the RW formation. As a result, the double concavities emerged in the distribution of c. Therefore, we concluded that the competition of the effects of the convection on the double concavities and the whole concavity caused the change of the preferential RW with v.

(Invited) Atomic-Scale Investigations on the Wet Etching of Group IV Semiconductors in Acidic H2O2 Solution: The Case Ge Versus Si-Ge

Over the decades, Si-based complementary metal–oxide semiconductor (CMOS) technology has challenged the semiconductor industry in improving device performance while maintaining the scaling requirements. However, the use of the group IV semiconductor as a channel material is reaching its ultimate limit due to physical complications, such as gate leakage, parasitic resistance/capacitance and size channel effects [1]. Some workaround solutions have implemented trigate structures, while novel gate-all-around (GAA) nanowire or nanosheet devices are also explored.[2] One of the core challenges for these devices is the highly selective removal of sacrificial SiGe epitaxial layers to release active parts of the device.[3] This aspect is further complicated by the introduction of Ge as an alternative channel material of higher mobility.[4]Wet-chemical processing remains an essential step for new nanodevice fabrication. With channel widths of only a few tens of atomic layers, etching control up to the atomic-layer-scale is necessary. To achieve such a level of precision, basic insights in semiconductor/electrolyte interactions are indispensable. Unlike for Si, the surface chemistry of Ge in wet-chemical solutions has remained relatively unexplored. One of the factors impeding in-depth surface analysis is the high reactivity of Ge in air. For this reason, the use of an integrated surface preparation apparatus in a surface analytical tool is crucial to rule out controversial effects of atmospheric oxygen and water.In this work we discuss the wet-chemical etching of Ge (100) in acidic H2O2 solutions. Kinetic studies were performed using inductively coupled plasma mass spectrometry (ICP-MS). Under reaction limited conditions, we showed that surface chloride chemistry has a profound impact on the dissolution kinetics and the anisotropy of wet etching, while proton effects were found to be less important. These results served as a starting point for the comparison of Ge versus SiGe. We provide an atomic scale investigation on the influence of the Si bulk concentration versus the kinetics of etching. The results are complimented by synchrotron X-ray photoemission spectroscopy (SXPS) measurements. We highlight the use of an integrated surface preparation chamber directly connected to SXPS apparatus to obtain fundamental insights into the surface chemistry of these technologically relevant group IV semiconductors. The results suggest that, while the release of Ge atoms from surface sites is favorable, the Si oxide chemistry determines the etching kinetics of SiGe. Basic etching schemes help to explain the formation of a (quasi) self-limiting oxide on SiGe. Energy dependent surface composition analysis provided insight into the nature of the oxide layer that showed depletion of Ge components at the outer surface due to pull out effects.[6]In summary, this research provides a new outlook for various applications such as biomedicine [7], photodetectors [8] and for light absorbing and harvesting of solar energy [9]. In addition, it serves as an eye-opener for the potential of semiconductor surface chemical studies using an UHV-integrated chemical cell connected to XPS to study etching systems.[1] R. Pillarisetty, Nature 479 (2011), p. 324-328.[2] J. Ryckaert et al., IEDM San Francisco, CA, USA, pp. 29.4.1-29.4.4 (2019)[3] K. Wostyn, F. Sebaai, J. Rip, H. Mertens, L. Witters, R. Loo, A. Y. Hikavyy, A. Milenin, N. Horiguchi, N. Collaert, A. Thean, P. Mertens, S. De Gendt and F. Holsteyns, ECS Trans., 69, 147 (2015).[4] M. Kobayashi, G. Thareja, M. Ishibashi, Y. Sun, P. Griffin, J. McVittie, P. Pianetta, K. Saraswat, Y. Nishi: J. Appl. Phys. 106, p. 104117-7 (2009).[5] G. H. A. Abrenica, M. V. Lebedev, G. Okorn, D. H. van Dorp and M. Fingerle, Appl. Phys. Lett., 113, 062104 (2018)[6] Graniel Harne A. Abrenica, Mikhail V. Lebedev, Mathias Fingerle, Sophia Arnauts, Nazaninsadat Bazzazian, Wolfram Calvet, Clement Porret, Hugo Bender, Thomas Mayer, Stefan de Gendt and Dennis H. van Dorp, J. Mater. Chem. C, 2020, 8, 10060 (2020)[7] H. Geng, J. Dai, J. Li, Z. Di and X. Liu, Sci. Rep. 6, 37474 (2016)[8] J. Michel, J. Liu and L. C. Kimerling, Nat. Photonics 4, 527534 (2010)[9] S. L. Shinde, T. D. Dao, S. Ishii, L-W. Nien, K. K. Nanda and T. Nagao, ACS Photonics 4, 1722-1729 (2017)

(Invited) Layer Transfer Technology for Stacked Multi-Channel Semiconductor-on-Insulator Platform

Continuous scaling of device dimension pushed Si channel to its physical limit, alternative high mobility channels such as (Si)Ge and (In)GaAs have been considered to replace Si to further enhance CMOS performance. In the meantime, ultrathin body (UTB) semiconductor-on-insulator is compulsory structure for improved gate control and immunity against short channel effects in the ultimately scaled high performance and low power dissipation CMOS. To realize stacked multi- channel semiconductor-on-insulator platform on current mainstream Si wafers, layer transfer technology [1-3] utilizing direct bonding and selective etching was developed to integrate (Si)Ge or (In)GaAs channels on Si, showing great potential for ultimate device structures with heterogeneous integration.Figure 1(a) is the process flow for integrating InGaAs channel onto SiGe-on-insulator (SGOI) structure utilizing layer transfer technology [4]. It started with bottom SGOI pMOSFET fabrication. The SGOI structure was realized by 2-step Ge condensation technique, resulting in Ge content of 70%. After high k metal gate process, self-aligned Ni-SiGe alloy was formed as S/D metal. Subsequently, SiO2 interlayer was deposited by CVD, followed by CMP planarization. Then, InGaAs grown on InP was directly bonded onto SiO2 and InP substrates were selectively etched away. Finally, the top InGaAsOI nMOSFET fabrication and metal interconnection completed the CMOS fabrication. Fig. 1(b) shows the cross-sectional TEM images of fabricated InGaAs/SiGe channel stacked CMOS. Well aligned top and bottom devices are seen without any distinct defects.Figures 2 is a schematic flow for fabricating Ge/Si double channel-on-insulator structure by low temperature hetero-layer bonding technology (LT-HBT). The technology starts with the preparation of donor wafers (Fig. 2(a)) for the top Ge channel layer and host wafers (Fig. 2(b)) for the bottom Si channel layer. For donor wafers, a 200-nm-thick Ge was epitaxially grown on SOI wafer by reduced pressure CVD. After CMP planarization, ALD SiO2 is deposited onto Ge. For host wafers, implantation and dopant activation were carried out, followed by chemical treatment for Si oxidation. After surface activation by room temperature chemical treatment (Fig. 2(c)), the direct wafer bonding of both SiO2 surface was performed at 200 °C in a press machine (Fig. 2(d)). Then, the Si substrate of the donor wafer was removed with deep RIE. At this time, the BOX layer of the donor wafer serves as an etch-stop layer. Subsequently, the BOX layer and thin Si layer of the donor wafer were removed selectively in HF and TMAH solution, respectively (Fig. 2(f)). To precise control the top Ge channel thickness, a series of low damage etching process was adapted to thin down Ge (Fig. 2(g)). The realized double channel structure is fully isolated with an insulating insertion layer,[5] which is very promising for realizing novel complementary FET (CFET) with minimum process steps. The cross-sectional TEM image of Ge/Si stacked channel of CFET after high k metal gate process is demonstrated in Fig. 2(h). Even more multiple stacks can be realized by using LT-HBT. A vertically stacked three-layer structure with 2 bottom Si layers and 1 top Ge layers is also demonstrated using SOI-based donor wafers in Fig. 3, indicating the highly integrated density channel structure is possible. The feasibility of layer transfer technology has been proved for multi-channel structure with high mobility channels for N2 node and beyond. Acknowledgement This work was supported by JST Japan-Taiwan Collaborative Research Program, Grant Number JPMJKB1902, Japan and the Ministry of Science and Technology under Grant Number MOST-109-2628-E-492-001-MY3, 109-2923-E-492-001-MY3, 107-2221-E-492-016-MY3.

Sol-Gel Synthesis And Characterization Of New Inorganic Pigments Containing Oxides of Iron, Aluminum, Strontium and Silicate

A series of inorganic pigments containing iron, aluminum, strontium, and silicate were prepared by the sol-gel method using compounds with different structures and morphologies as starting materials. The synthesis of the compounds was carried out using the modified citrate method. All powders were placed in a muffle furnace and calcined in air at 1100°C for 6 hours. Powder samples containing Fe, Sr, Al and Si oxides were obtained. The structure and chemical composition of the synthesized five inorganic pigments were investigated comparatively by Fourier transform infrared spectroscopy (FTIR), UV-visible spectroscopy (UV-vis), X-ray diffraction (XRD), scanning electron microscopy (SEM), and Energy Distribution X-ray Analysis (EDX).

Behavior of magnesium impurity during carbochlorination of magnesium-bearing titanium slag in chloride media

Abstract In this study, the phase composition, morphology, and element distribution of Mg impurities in a low-grade titanium slag and in its chlorinated residue after carbochlorination were identified using XRD, SEM-EDS, and MLA. Most Mg impurities existed as anosovite, rutile, titanaugite, and Ti silicate phases before the carbochlorination process. The thermodynamic analysis revealed that the chlorination tendencies of Mg, Ti, Ca, Fe, and Mn oxides in the original titanium slag was much higher than those of Si and Al oxides in the temperature range of 700–850 °C. In addition, the binary phase diagram analysis indicates that the magnesium chloride (MgCl2) byproduct formed Na2MgCl4 eutectic salts in the NaCl-based salt bath. The carbochlorination experiments of the Mg-bearing titanium slag show that the chlorination ratio of magnesium oxide was above 93% under the suitable industrial conditions used for the extraction of titanium from Mg-bearing titanium slag. In addition, the formation of Na2MgCl4 eutectic salts after carbochlorination was confirmed, indicating that the negative effect of MgCl2 on the chlorination process was effectively eliminated. The Mg impurities in the chlorinated residue existed as titanaugite, quartz, chlorite, and rutile phases. Furthermore, we found that the carbochlorination of Mg-bearing titanium slag in chloride media effectively improved the comprehensive utilization efficiency of the Mg-bearing titanium slag. We believe that the proposed carbochlorination mechanism of the Mg-bearing titanium slag will provide thorough understanding and useful guidance on the practical industrial application of Mg-bearing titanium slag.

Polydopamine-mediated synthesis of Si@carbon@graphene aerogels for enhanced lithium storage with long cycle life

The application of Si as the anode materials for lithium-ion batteries (LIBs) is still severely hindered by the rapid capacity decay due to the structural damage caused by large volume change (> 300%) during cycling. Herein, a three-dimensional (3D) aerogel anode of Si@carbon@graphene (SCG) is rationally constructed via a polydopamine-assisted strategy. Polydopamine is coated on Si nanoparticles to serve as an interface linker to initiate the assembly of Si and graphene oxide, which plays a crucial role in the successful fabrication of SCG aerogels. After annealing the polydopamine is converted into N-doped carbon (N-carbon) coatings to protect Si materials. The dual protection from N-carbon and graphene aerogels synergistically improves the structural stability and electronic conductivity of Si, thereby leading to the significantly improved lithium storage properties. Electrochemical tests show that the SCG with optimized graphene content delivers a high capacity (712 mAh/g at 100 mA/g) and robust cycling stability (402 mAh/g at 1 A/g after 1500 cycles). Furthermore, the full cell using SCG aerogels as anode exhibits a reversible capacity of 187.6 mAh/g after 80 cycles at 0.1 A/g. This work provides a plausible strategy for developing Si anode in LIBs.

Quantitative analysis of factors increasing coercive field of iron powder cores – Influence of inclusions

The quantitative contribution of inclusions to coercive field in iron powder cores with different amounts of Si oxide inclusions was separated from that of other microstructural factors and analyzed. Coercive field decreased by 2.8 A m−1 with a 0.01 mass% decrease in the amount of Si in oxide. Si oxide inclusions also affected the recovery and recrystallization of the α-Fe phase, and the contribution of crystal grain boundaries and the contribution of dislocations decreased with a decrease in the amount of Si in oxide. The contribution of inclusions was compared with Kersten's calculation model based on changes of the domain wall area and Neel's calculation model based on changes of the number of magnetic poles, and the observed value was closer to the results of Kersten's calculation model. This suggests that the contribution of magnetic poles generated around an inclusion is small and the change of the domain wall area around the inclusion makes a larger contribution to coercive field.

Investigate on the Mechanism of HfO2/Si0.7Ge0.3 Interface Passivation Based on Low-Temperature Ozone Oxidation and Si-Cap Methods.

The interface passivation of the HfO2/Si0.7Ge0.3 stack is systematically investigated based on low-temperature ozone oxidation and Si-cap methods. Compared with the Al2O3/Si0.7Ge0.3 stack, the dispersive feature and interface state density (Dit) of the HfO2/Si0.7Ge0.3 stack MOS (Metal-Oxide-Semiconductor) capacitor under ozone direct oxidation (pre-O sample) increases obviously. This is because the tiny amounts of GeOx in the formed interlayer (IL) oxide layer are more likely to diffuse into HfO2 and cause the HfO2/Si0.7Ge0.3 interface to deteriorate. Moreover, a post-HfO2-deposition (post-O) ozone indirect oxidation is proposed for the HfO2/Si0.7Ge0.3 stack; it is found that compared with pre-O sample, the Dit of the post-O sample decreases by about 50% due to less GeOx available in the IL layer. This is because the amount of oxygen atoms reaching the interface of HfO2/Si0.7Ge0.3 decreases and the thickness of IL in the post-O sample also decreases. To further reduce the Dit of the HfO2/Si0.7Ge0.3 interface, a Si-cap passivation with the optimal thickness of 1 nm is developed and an excellent HfO2/Si0.7Ge0.3 interface with Dit of 1.53 × 1011 eV−1cm−2 @ E−Ev = 0.36 eV is attained. After detailed analysis of the chemical structure of the HfO2/IL/Si-cap/Si0.7Ge0.3 using X-ray photoelectron spectroscopy (XPS), it is confirmed that the excellent HfO2/Si0.7Ge0.3 interface is realized by preventing the formation of Hf-silicate/Hf-germanate and Si oxide originating from the reaction between HfO2 and Si0.7Ge0.3 substrate.

Enhanced photoelectrochemical performance of Si/TiO2 with a high atomic density SiO2 buffer layer

Nanostructured Si is a promising material for photoelectrochemical water splitting, but it has the problem of being well oxidized in water. Depositing a TiO2 layer on the Si surface is an effective way to protect it from oxidation and increase light absorption. However, the lattice mismatch between Si and TiO2 acts as a defect that causes an efficiency reduction. To improve the interface and electrical properties of TiO2/Si, nitric acid oxidation of Si (NAOS) is used to form a high-density SiO2 layer and analyze the effect of photoelectrochemical properties. Due to the lattice mismatch, the TiO2/Si sample (−3.12 mA/cm2) decreases about 1.8 times when using SiO2. In TiO2/SiO2/Si samples (-5.70 mA/cm2) further decrease after post-oxidation annealing (POA) (−7.70 mA/cm2). As a result, it can be seen that by fabricating an ultra-thin high-density SiO2 layer, the lattice mismatch at the TiO2/Si interface is reduced and the photocurrent density is improved.

Preparation of eco-friendly one-part geopolymers from gold mine tailings by alkaline hydrothermal activation

Environmental and economic issues caused by several tailings storages have attracted worldwide attention; therefore, these urgently need to be solved cost-effectively. In this study, gold mine tailings rich in Si and Al oxides were activated by an alkaline hydrothermal method for use as precursors to produce a one-part geopolymer. The results indicated that the crystalline mineral phases in tailings were partially or completely decomposed by alkaline hydrothermal activation. However, this decomposition depended heavily on the alkali content, temperature, and time. The decomposed tailings were converted to the amorphous sodium aluminosilicate reactant, thereby making tailings a reactive starting material. Subsequently, the one-part geopolymer was prepared from the activated tailings and slag by just adding water without adding any extra alkaline activator. By adding 60 wt% of slag, the one-part geopolymer with an optimum compressive strength value of 33.5 MPa at 28 days was obtained. This was much higher than that of the control sample containing raw tailings without any pretreatment. The high strength could have been because of the amorphous sodium aluminosilicate formed in the activated tailings that could dissolve in water to create alkaline conditions, which could effectively activate the pozzolanic activity of the slag. The main geopolymerization product was the glassy calcium-sodium aluminosilicate hydrate (C(N)-A-S-H) gel, which acted as a binder to closely connect the residual solid particles and form a hardened geopolymer material.

Reduced mixture model and elastic response of chemically swollen solids: Application to Si oxidation and lithiation

This paper presents a mixture model for coupled chemo-mechanical response of the general class of fluid-solid systems undergoing chemical reaction and large deformations. It further investigates our earlier works on the mathematical modeling of chemo-mechanical coupling and material evolution across advancing fronts of reactive fluids. A detailed analysis of the stress response of the chemically evolving solid is carried out, taking into account the changes in the reference unstressed configurations of the unreacted and reacted solid. This yields a systematic way to determine the material parameters required for the material constitutive models. The formulation for the fluid constituent is simplified for the case of slow diffusion, which yields a reduced system of governing equations wherein coercivity of the continuum system is inherited by the discrete system. The resulting nonlinear model lends itself to consistent linearization and is implemented in a finite element method. The nonlinear system of coupled equations is solved monolithically using the Newton-Raphson algorithm and quadratic convergence is attained. The method is applied to investigate the bending-dominated response of a silicon wafer during thermal oxidation, and to the problem of cross-section evolution during lithiation of a silicon nanowire.

High temperature characteristics and phase compositions of Cu/Mn multilayers with the different average thickness prepared by electrodeposition

Four different Cu/Mn multilayers are prepared on ferritic stainless steel 430 by direct current deposition, and the electrodeposition behavior of Cu and Mn is studied by chronopotentiometry and cyclic voltammetry. After oxidation at 750 °C for 500 h, the discontinuous Si oxides are formed in the vicinity of substrate/Cr2O3 oxide interface, Cu diffuses outward faster than Mn in CuMn compound oxides, and oxide compositions of designed samples are discussed based on the Cu-Mn-O phase diagram. The Cu-Mn compound oxide coatings do not effectively block outward diffusion of Fe, but effectively block Cr. The ASR value of the sample with the ratio of Cu/Mn about 1 is the lowest among all the samples, though its thickness of oxide layer (~15 µm) is in the middle of all samples. Besides Cr2O3 and SiO2, the formation of Mn3O4 and Fe2O3 oxides with low conductivity lead to the high ASR.

Enhanced friction and shock sensitivities of hexachlorodisilane hydrolyzed deposit mixed with KOH

In this work, the effects of potassium hydroxide (KOH) on friction and shock sensitivity of the hexachlorodisialne hydrolysis products were studied. A wide range of KOH content, from 0.02 to 21.5 wt%, in the mixture of KOH and HCDS hydrolyzed deposit was prepared by mixing the deposit with aqueous KOH solution and dried in glovebox. The lowest impact energy (LIE) and lowest friction force (LFF) were determined by BAM fall-hammer and friction test apparatus, respectively. It was found that both shock and friction sensitivities increased with an increase in the KOH content in the HCDS hydrolyzed deposit. In particular, the LIE and LFF decrease from 6 J to 326 N of the original deposit to less than 0.125 J and 7 N for deposit with 0.03 and 0.3 wt% KOH. Differential scanning calorimetry studies showed that a new exothermic peak was observed between 80 °C and 150 °C which is also accompanied by evolution of hydrogen. It is proposed that, the presence of KOH results in the formation of Si–Si–OK groups leading to the weakening of the neighboring Si–Si bonds. Any mechanical impact or friction will lead to the cleavage of the unstable Si–Si bonds and subsequently initiate a fast chain oxidation of adjacent Si–Si and Si–OH bonds to form more Si–O–Si groups, releasing H2 gas and heat. Recommendations were given for handling and disposing of these explosive deposits.

Precise fabrication of uniform sub-10-nm-diameter cylindrical silicon nanopillars via oxidation control

Silicon (Si) nanopillar (NP)-based gate-all-around metal–oxide–semiconductor field-effect transistors (MOSFETs) are considered the primary components of next-generation integrated circuits according to the International Roadmap of Devices and Systems. In order to replace fin-structured MOSFETs with a several-nanometer technology node that is currently used, a precise fabrication method for uniform Si NPs with a sub-10-nm diameter and cylindrical shape is required. This study demonstrates that a double-oxidation process is capable of solving this problem for the first time. In particular, it includes the first oxidation at 900°C with deep self-limiting oxidation for shape control and variance decrease and second oxidation at 1000°C with a controllable oxidation rate for precise diameter control, with wet etching between two oxidations. Although Si oxidation is orientation dependent, the traverse cross-section of Si NPs is experimentally confirmed to keep a circle shape during oxidation and is theoretically attributed to the edge effect.

Effect of Aluminium coating on the Ferro-Silica-Magnesium alloys’ hardness and corrosion rate

This paper studied the effect of Aluminium coating on the Fe-Si-Mg alloys surface to its hardness and corrosion rate. The Fe-Si-Mg-Al was formed from Fe-Si-Mg Powder Alloy, which was coated by Aluminium (Al) with the composition of (0; 2.2; 6.0; 10.2) wt%. The mechanical alloying was applied to conduct a wet mixing with the ball mill in a shaker mill for two hours. The powder was then dried and compress under eight tons of pressure for three minutes. The sample was then sintered in a tabular furnace with a temperature of 1000C for two hours and 5C/minutes of heating rate. Furthermore, the natural cooling rate was applied to reach room temperature. The sample was examined in an XRD to analyze the phase and tested under a SEM-EDX to evaluate the morphological structure as well as its dispersion. The results showed that the hardness rise as the increment of Al. It is because of the oxidation of Fe, Si, and Al, which formed Fe2O3, SiO2, and Al2O3 filled out the gap. The development of Al decreased the corrosion rate. Al with the composition of (6.0 wt%) was the lowest corrosion -3 rate which the value of 1.013x10 mmpy.

Phase Composition of Al-Si Coating from the Initial State to the Hot-Stamped Condition.

The chemical and phase composition of the coating and the coating/substrate interface of an Al-Si-coated 22MnB5 hot stamped steel was investigated by means of SEM-EDS, XRD, micro-XRD and electron diffraction. Moreover, the surface profile was analyzed by XPS and roughness measurements. The XPS measurements showed that the thickness of the Si and Al oxide layers increased from 14 to 76 nm after die-quenching, and that the surface roughness increased as well as a result of volume changes caused by phase transformations. In addition to the FeAl(Si) and Fe2Al5 phases and the interdiffusion layer forming complex structures in the coating, electron diffraction confirmed the presence of an Fe2Al5 phase, and also revealed very thin layers of Fe3(Al,Si)C, Fe2(Al,Si)5 and Al-bearing rod-shaped particles in the immediate vicinity of the steel interface. Moreover, the scattered nonuniform layer of the Fe2Al8Si phase was identified in the outermost layer of the coating. Despite numerous studies devoted to researching the phase composition of the Al-Si coating applied to hot stamped steel, electron diffraction revealed very thin layers and particles on the coating/substrate interface and outermost layer, which have not been analyzed in detail.

First-principles study of strain effect on oxygen vacancy in silicon oxide

The strain dependence of stability and diffusion barrier height of the O vacancy in Si oxide is examined using the first-principles calculation. It is found that the stability and the diffusion barrier height increase as the oxide is compressed. The analysis shows that the diffusion barrier height is determined by the Si–Si distance of the O vacancy. Based on these results, the dielectric breakdown of the gate Si oxide film in the three-dimensional structure metal-oxide-semiconductor field-effect transistor is also considered. It is suggested that the interfacial O-vacancy density increases because the interfacial oxide is subjected to compressive strain. On the other hand, the surface O-vacancy density decreases and the surface O-vacancy diffusion is promoted because the surface oxide is subjected to tensile strain. The reliability of the oxide film might be thus affected by the strain.

Formation of amorphous precipitates in a corroded over-aged Al-Mg-Si alloy

Coarse intermetallics and fine precipitates play an important role in the corrosion of Al alloys. So far, there is no systematic experimental investigation about the corrosion of nano-precipitates. In the present work, the morphology and chemical composition of the corroded MgSi nano-precipitates in an Al-Mg-Si alloy with different aging times have been studied by transmission electron microscopy. Coarsened βʹ precipitates occurring in the over-aged state were found to be corroded through dissolution of Mg and oxidation of the remnant Si during twin-jet electropolishing. They finally transformed to amorphous SiO2 precipitates, showing an almost unetched interface with the Al matrix. The proportion of amorphous precipitates increased with prolonging aging time, as larger precipitates were preferentially corroded. This newly discovered crystalline-to-amorphous phase transformation depletes acid electrolyte but shows no damage. Such an intragranular corrosion behavior partly accounts for why over-aged Al-Mg-Si alloys are less susceptible to pitting and intergranular corrosion.