Silica Research Articles

Inverse Vulcanization of Aziridines: Enhancing Polysulfides for Superior Mechanical Strength and Adhesive Performance

AbstractThis study introduces a novel approach to inverse vulcanization by utilizing a commercially available triaziridine crosslinker as an alternative to conventional olefin‐based crosslinkers. The model reactions reveal a self‐catalyzed ring‐opening of “unactivated” aziridine with elemental sulfur, forming oligosulfide‐functionalized diamines. The triaziridine‐derived polysulfides exhibit impressive mechanical properties, achieving a maximum stress of ~8.3 MPa and an elongation at break of ~107 %. The incorporation of silicon dioxide (20 wt %) enhances the composite's rigidity, yielding a Young's modulus of ~0.94 GPa. Furthermore, these polysulfides display excellent adhesion strength on various substrates, such as aluminum (~7.0 MPa), walnut (~9.6 MPa), and steel (~11.0 MPa), with substantial retention of adhesion strength (~3.3 MPa on steel) at −196 °C. The straightforward synthetic process, combined with the accessibility of the triaziridine crosslinker, emphasizes the potential for further innovations in sulfur polymer chemistry.

Inverse Vulcanization of Aziridines: Enhancing Polysulfides for Superior Mechanical Strength and Adhesive Performance.

This study introduces a novel approach to inverse vulcanization by utilizing a commercially available triaziridine crosslinker as an alternative to conventional olefin-based crosslinkers. The model reactions reveal a self-catalyzed ring-opening of "unactivated" aziridine with elemental sulfur, forming oligosulfide-functionalized diamines. The triaziridine-derived polysulfides exhibit impressive mechanical properties, achieving a maximum stress of ~8.3 MPa and an elongation at break of ~107 %. The incorporation of silicon dioxide (20 wt %) enhances the composite's rigidity, yielding a Young's modulus of ~0.94 GPa. Furthermore, these polysulfides display excellent adhesion strength on various substrates, such as aluminum (~7.0 MPa), walnut (~9.6 MPa), and steel (~11.0 MPa), with substantial retention of adhesion strength (~3.3 MPa on steel) at -196 °C. The straightforward synthetic process, combined with the accessibility of the triaziridine crosslinker, emphasizes the potential for further innovations in sulfur polymer chemistry.

Synthesis and Characterization of Na-P1 (GIS) Zeolite Using Rice Husk.

This work deals with the synthesis of Na-P1 (GIS) zeolite using rice husk as the starting material, instead of the more expensive chemicals currently used in the industry (i.e., Na aluminates and Na silicates). Rice husk is calcined at the temperature of 550 °C to obtain rice husk ash. Na-P1 is synthesized starting from rice husk ash, NaOH, and NaAlO2 by a protocol involving the mixing of a seed gel and a feedstock gel. Two synthesis runs are carried out at ambient pressure at the temperature of 110 °C by fixing the SiO2/Al2O3 ratio at 3.5 and 5.3, respectively. The synthesized products have been identified as well as the experiments developed by X-ray diffraction and scanning electron microscopy. Then, the most successful synthesized powders were also characterized by infrared spectroscopy, Raman spectroscopy, specific surface area (BET), and differential thermal analysis. The cell parameters are calculated using the Rietveld method. The combined Rietveld and reference intensity ratio methods allows us to exclude the presence of impurities and residual amorphous phase in the conducted experiments. Testing rice husk as a source of amorphous silica in the synthesis of Na-P1 represents both economic and environmental advantages. The high yields and the results of the experiment open the way for the transfer to an industrial production scale.

In-situ construction of dual-coated silicon/carbon composite anode for fast-charging Li-ion batteries

Silicon (Si) is regarded as a promising candidate anode for next-generation high-energy–density batteries due to its ultrahigh theoretical capacity of 4200 mAh g−1. However, silicon anodes face tremendous challenges during cycling, including huge volume expansion, highly unstable interfaces and inherently low conductivity. In this study, the dual-coated silicon/carbon composite anode (Si@SiOx@C) with high silicon content of 85 % is obtained by high-energy ball milling and combined with phenolic resin-assisted encapsulation. The amorphous SiOx layer (∼3 nm) facilitates the rapid Li+ transport and mitigates the volume expansion, while the hard carbon layer (∼3 nm) improves the electronic conductivity and helps to protect against silicon oxide layer erosion from electrolyte, synergistically contributing to the fast-charging performance. With the synergistic effect of dual coating, the Si@SiOx@C anode shows a high initial Coulombic efficiency of 91 % and maintains a high capacity of 1250 mAh g−1 even after 500 cycles at a high rate of 4 A/g. Moreover, the volume expansion of silicon anode during cycling is significantly reduced. This work provides a novel strategy for high silicon content anode in developing fast-charging batteries through dual-coating regulation.

Janus membrane with oriented fiber structure for boosted personal wet-thermal management

Personal wet-thermal management (PWTM) is not only highly desirable for human health and comfort, but also plays a notable role in the emerging smart wearable clothes and electronic devices as the levels of integration and multifunction are determined by it. In “human skin-wearable fibrous fabric-external environment” microclimate system, wearable fibrous fabric, as the “second skin” of human body, is the key to PWTM. In particular, excellent sweat/moisture transport capacity combined with passive radiative cooling, which concentrated on promoting sweat/moisture transport, solar radiation reflection and human body infrared radiation emission with zero-energy consumption, have attracted tremendous attentions. Nonetheless, improving sweat/moisture transport and radiative cooling performances, viz., boosting the synergistic management of wet-thermal to extend its applications remains a challenge. Herein, we report a facile PWTM strategy by fabricating hydrophobic/hydrophilic Janus membrane with oriented fibers decorated by silicon oxide nanoparticles via electrospinning. Taking advantages of the hydrophobic/hydrophilic asymmetric wettability and directional wicking of Janus fibrous membrane, sweat/moisture can be driven from skin to the external environment directionally. What’s more, the oriented fiber structure enhances both the solar reflectance (90.8%) and human body infrared radiation (HBIR) emittance (97.4%), which allows cooling down the temperature obviously. Compared with the traditional cotton fabric, the Janus fibrous membrane has excellent passive radiative cooling performance that a dramatic drop in temperature about 20°C can be achieved in outdoor environment. Such novel strategy provides a new and effective way to enhance the efficiency of PWTM.

Thermal conductivity of polar nitride perovskite LaWN3

ABX3-type nitride perovskites offer promising avenues for the future electronic industry, renowned for exceptional ferro- and piezo-electric properties with facile integration into prevalent nitride semiconductors. However, the paucity of in-depth investigations of thermal transport of nitride perovskites poses a substantial impediment to the practical implementation. Here, we experimentally investigate the thermal conductivity of orthorhombic polar LaWN3, synthesized by high-pressure high-temperature technique. The observed thermal conductivity exhibits drastic reduction with decreasing temperature, reminiscent of the behavior in amorphous silica. We postulate the anomalous glass-like thermal conductivity to a synergistic interplay of potential Ferron–phonon interactions, lattice disorders from octahedral distortions, and wave-like atomic tunneling. This study represents a pioneering exploration of thermal transport within nitride perovskites, paving the way for future advancements in nitride-based electronics.

Frazil ice changes winter biogeochemical processes in the Lena River

The ice-covered period of large Arctic rivers is shortening. To what extent will this affect biogeochemical processing of nutrients? Here we reveal, with silicon isotopes (δ30Si), a key winter pathway for nutrients under river ice. During colder winter phases in the Lena River catchment, conditions are met for frazil ice accumulation, which creates microzones. These are conducive to a lengthened reaction time for biogeochemical processes under ice. The heavier δ30Si values (3.5 ± 0.5 ‰) in river water reflect that 39 ± 11% of the Lena River discharge went through these microzones. Freezing-driven amorphous silica precipitation concomitant to increased ammonium concentration and changes in dissolved organic carbon aromaticity in Lena River water support microbially mediated processing of nutrients in the microzones. Upon warming, suppressing loci for winter intra-river nitrogen processing is likely to modify the balance between N2O production and consumption, a greenhouse gas with a large global warming potential.

Array of Graphene Solar Cells on 100 mm Silicon Wafers for Power Systems

High electrical conductivity and optical transparency make graphene a suitable candidate for photovoltaic-based power systems. In this study, we present the design and fabrication of an array of graphene-based Schottky junction solar cells. Using mainstream semiconductor manufacturing methods, we produced 96 solar cells from a single 100 mm diameter silicon wafer that was precoated with an oxide layer. The fabrication process involves removing the oxide layer over a select region, depositing metal contacts on both the oxide and bare silicon regions, and transferring large-area graphene onto the exposed silicon to create the photovoltaic interface. A single solar cell can provide up to 160 μA of short-circuit current and up to 0.42 V of open-circuit voltage. A series of solar cells are wired to recharge a 3 V battery intermittently, while the battery continuously powers a device. The solar cells and rechargeable battery together form a power system for any 3-volt low-power application.

Luminescence of copper-doped α-quartz crystal after oxygen treatment

Treatment of copper-doped natural α-quartz in oxygen atmosphere at 1200 °C leads to changes in luminescence properties. The luminescence center of AlO4−-Cu+ is modified. The intensity is low in the annealed sample and increases after X-ray irradiation at 293 K. Annealing of the irradiated sample leads to a strong peak of thermally stimulated luminescence (TSL) at ∼500 K. Its spectral composition is mainly due to the AlO4−-Cu+ center. Irradiation of the sample treated with oxygen at 77 K gives a new TSL peak at ∼180 K and a peak at 244 K existing in the untreated sample. Both peaks were attributed to Cuo centers released from different sites and recombined with a hole in AlO4 having additional oxygen. The introduction of copper ions into quartz removes alkali metal ions and eliminates the corresponding luminescence, but after treatment in oxygen, luminescence with similar parameters is restored at low temperatures. In this case, only the glow of the AlO4−-Cu+ center is observed in the recombination luminescence (TSL and afterglow). Therefore, modification of the AlO4−-Cu + center with oxygen imparts to this center properties similar to the complex center AlO4− (K, Na or Li ion) with monovalent aluminum ions, although the alkali ions are replaced by copper ions. The oxygen-treated sample exhibits an increased efficiency of energy transfer by excitons to the luminescence center, measured as excitation spectra in the region of fundamental absorption of silicon dioxide. The X-ray excitation of the self-trapped exciton luminescence does not depend on oxygen treatment. Also, the spectra of intrinsic optical reflection and Raman scattering do not change compared to the untreated sample. The obtained result is interpreted as a modification of the defect by high-temperature treatment in oxygen.

Molecular Dynamics Simulation of Bubble Formation in Confined Water in Si/SiO2 Nanochannels

Megasonic-based techniques are employed in the etching and cleaning processes in the semiconductor industry since they are gentler than other cleaning techniques and less apt to cause damage. In these processes, sound waves, at a frequency of 1 MHz or higher, are sent into etching or cleaning fluid, which could result in the formation of bubbles inside the fluid, revealing features and producing patterns. The formation and collapse of bubbles in nano-scale features is of interest in the semiconductor industry due to the potential effects on etching performance and surface roughness. Our understanding is still limited, however, because of the dimensions involved. Typically, the bubble size is too small, and the duration of bubble formation/collapse is too short, to allow easy study of the characteristics of bubble formation or collapse through experimental methods. Molecular dynamics (MD) simulation is a powerful tool to simulate such a phenomenon, which can facilitate understanding of bubble behavior in a confined space, and in the vicinity of the surface.In this work we use MD simulations to simulate bubble formation in confined water in silicone (Si) and silicon dioxide (SiO2) nanochannels. Our focus of study is to identify the mechanism type for bubble formation in these nanofeatures, and determine how the surface characteristics, including the wettability, influence bubble formation. Figures 1a and 1b show the simulation results of bubble formation in confined water in the Si and SiO2 nanochannels, respectively. Our results show that the bubble forms on the hydrophobic Si surface, indicating a heterogeneous bubble formation, while for the hydrophilic SiO2 surface, the bubble tends to form away from the surface and in the bulk of the liquid, indicating a homogeneous bubble formation. In a hybrid situation where both the hydrophobic Si and hydrophilic SiO2 surfaces are present (Figure 1c), heterogenous bubble formation is dominant and the bubble forms on the Si surface. Our work provides insights into the mechanism of bubble formation in the confined water in nanofeatures and how surface wettability affects it.

Strategic Cell Design for Long-Lasting Lithium-Ion Batteries with Sio/Graphite Anodes

Lithium-ion batteries (LIBs), first commercialized by Sony in the 1990s, have become the power source for numerous electronic devices and a key driver of the electric vehicle (EV) market growth. However, the development of next-generation batteries with an energy density exceeding 250 Wh/kg remains a critical challenge. High-energy-density batteries are essential to extend the driving range of EVs, improve the runtime of portable devices. Conventional graphite anodes are limited in their ability to meet the increasing demand for higher energy densities. As a result, silicon-based anodes, which offer 5-10 times higher specific capacity, have attracted significant interest. Silicon oxide (SiO), in particular, exhibits better cycling stability and reduced volumetric expansion (~100%) than pure silicon (~400%), though it faces challenges related to mechanical instability, low conductivity, and poor initial coulombic efficiency (ICE). To overcome these challenges, research on SiO/Graphite composite electrode has increased, combining graphite’s good conductivity and SiO’s high capacity to enhance energy density and cycle performance.Despite the great potential of SiO/graphite composite electrodes, problems such as capacity fading during long-term cycling still remain challenges. Various pre-lithiation strategies have been proposed to both compensate for irreversible lithium losses and improve cycling performance. Sacrificial cathodes are particularly attractive because they can be integrated into existing electrode fabrication processes, improving the electrochemical performance by mitigating excessive delithiation of the anode. However, over-lithiated sacrificial cathodes are prone to moisture sensitivity during fabrication and structural instability after delithiation, both of which negatively impact the battery's electrochemical performance. Additional processing steps, such as coating or composite material design, have been proposed to enhance the stability of sacrificial cathodes, but these approaches increase complexity and cost, hindering their practical application. Although various pre-lithiation strategies, including sacrificial cathodes, effectively enhance performance, they still face significant limitations when it comes to practical industrial applications.This study proposes a simple effective cell design strategy to significantly enhance the cycle performance of SiO/Graphite anode based full cells. It was observed that bi-modal (BM) cathodes, composed of a mixture of two types of NCM811 particles, exhibited greater overpotential at the end of discharge compared to uni-modal (UM) electrodes made entirely same type of NCM811 particles. The increased overpotential in bi-modal cathodes is attributed to the differences in reaction kinetics between the particles, leading to non-uniform reaction distributions within the electrode and resulting in greater overpotential during the later stages of discharge. This bi-modal cathode design lowers the anode’s end-of-discharge voltage, enabling better control of the delithiation swing range in SiO and improving the full cell's cycling stability.As a result, the SiO/Graphite-BM full cell retained 96% of its initial capacity after 150 cycles at a C-rate of C/3, while the SiO/Graphite-UM full cell dropped to 80% after 150 cycles, which is typically considered the end of battery life. Various electrochemical evaluations, including GITT and 3-electrode tests, confirmed that the observed performance differences were due to the overpotential variation in the cathode, which controlled the charge-discharge behavior of the anode and, in turn, influenced the cycle performance of the full cell. Furthermore, synchrotron operando XRD analysis and various post-mortem analyses revealed that the capacity fade was primarily attributed to the degradation of silicon within the anode. This approach offers a promising solution for enhancing the long-term stability and energy density of SiO/Graphite-based lithium-ion batteries.

(Invited) Silanes As Precursors and Inhibitors for Area-Selective Deposition

Silanes play a unique dual role in the field of area-selective deposition (ASD), serving as both precursors for common semiconductor-device films such as silicon dioxide, silicon oxycarbide (low-k) and silicon nitride, or as inhibitors of deposition processes via selective surface passivation. In this presentation we will review the evolution of silane precursors from simple thermal chemical vapor deposition (CVD) and epitaxial precursors such as tetraethoxysilane and silane, to the increasingly complex molecules used for plasma-enhanced CVD, atomic layer deposition, and ASD. Contemporary reported strategies for the use of silicon-containing molecules as ASD precursors and inhibitors will be assessed, and the inherent challenges of using similar chemistry for two contrasting purposes will be discussed. Specific topics that will be covered include the use of silanes to inhibit growth on both oxide and non-oxide surfaces, an inherently selective thermal process for growing mixed oxide films on dielectric layers, an inherently selective plasma-enhanced process for depositing silicon dioxide on dielectric layers, and an inherently selective plasma-enhanced process for growing silicon dioxide on metals.

(Invited) Applications of Oxygen Inserted Epitaxy

Silicon remains the semiconductor material of choice for most electronic applications of semiconductors and the silicon–silicon dioxide interface is one of the most studied interfaces. Over the past decade or more, epitaxial silicon-germanium (eSiGe) has found increasing applications in advanced logic, first for PMOS compressive source-drain (S/D) stressors, then as a channel material in high-k metal gate (HKMG) devices to help control the PMOS Vt, and more recently as a sacrificial layer to enable stacked nanosheets and even as a S/D liner to reduce phosphorus diffusion into the undoped nanosheets. Oxygen inserted (OI) silicon epitaxy was originally developed to complement and bridge the gap between silicon and silicon-germanium, and it has found applications ranging from improved figure of merit power devices to the most advanced nanosheet applications. In this paper we will provide an overview of OI silicon devices, their fundamental characterization and the electrical and physical benefits offered for a variety of semiconductor applications. Introduction Oxygen-inserted (OI) silicon had an unusual genesis for a semiconductor material, in that it was first explored using ab-initio quantum mechanical simulation. It was found that by carefully inserting a partial monolayer of oxygen during silicon epitaxy a stable layer could be manufactured where the individual oxygen atoms arranged themselves on a silicon-silicon bond, but that overall, the silicon retained its regular lattice, and the silicon-oxygen coordination was only one, as opposed to four in regular silicon dioxide. The idealized lattice configuration is shown in Fig. 1 (a). This configuration is technically thermodynamically metastable, but with a significant energetic barrier to formation of four-fold coordinated silicon dioxide, so that it can survive conventional semiconductor processing. Whereas a single oxygen atom is known to rapidly diffuse in silicon, there is a thermodynamic self-stabilization when the oxygen concentration has an aerial density of the order of 1E15cm-2, with an upper limit dependent both on the specific epitaxial recipe and the required defect density. If all available silicon bonds have attached oxygen, it is difficult to maintain high quality epitaxy. On the other hand, OI silicon has passed the most rigorous defect density requirements for advanced logic applications. Dopant engineering - simulation Oxygen is highly electronegative, and ab initio simulation shows that there is charge transfer in the silicon lattice in the near vicinity of the inserted oxygen as shown in Fig 1 (b). This leads to a change in the formation enthalpy for a single substitutional dopant atom or addition of a silicon point defect, vacancy or interstitial as shown in Fig 1 (c). The figure indicates that substitutional boron and phosphorus will have an energetic preference to be two or three silicon lattice atoms away from the inserted oxygen, whereas silicon point defects prefer to be coincident with the oxygen. As a result, the OI layers disrupt the diffusion of dopant-interstitial pairs, substantially reducing the dopant diffusion. Dopant engineering – experimental data OI silicon has been proven to create unique abrupt doping profiles for a variety of silicon and silicon germanium devices. In power devices, reducing the vertical and lateral diffusion below the OI silicon layer can be used to engineer significant improvement in critical figures of merit, such as the tradeoff between specific ON resistance (Rsp) and the breakdown voltage, and improved time constant (Ron∙ Coff) and reduced body current in RF power devices, while maintaining breakdown voltage. In advanced 3D applications, a 2nm thin liner of OI silicon has proven effective to create a diffusion barrier between highly doped epitaxial source/drain regions and undoped channels. By reducing dopant up-diffusion, thermally robust super-steep retrograde profiles can be created, which can be used to reduce local threshold voltage mismatch in both NMOS and PMOS devices by more than 50%. In gate-first HKMG planar CMOS applications, SiGe channel is used in the PMOS to facilitate Vt engineering. A thin OI silicon layer below the SiGe channel can be used to maintain a super-steep retrograde channel profile after HKMG formation and subsequent thermal processing. Interface interactions It has recently been discovered that OI silicon can also be used to engineer adjacent interfaces. For example, it has been shown by cryogenic measurements that OI silicon reduces surface roughness scattering of the silicon-dielectric interface. Also, OI silicon can reduce the interfacial dipole formed during HKMG processing, with benefits in reduced remote charge scattering and improved reliability.These and other examples of engineered silicon and silicon-germanium devices will be discussed in detail. Figure 1

Highly Efficient Si3N4/SiO2 Selective Etching Process with Non-Phosphoric Acid Solutions

Silicon nitride (Si3N4) and silicon dioxide (SiO2) are widely used as insulator or sacrificial film materials in the fabrication of semiconductor devices. In recent years, many 3D structured semiconductor devices such as NAND Flash and CFETs have been manufactured to increase the integration of semiconductor devices. In this case, a substrate with alternating layers of Si3N4 and SiO2 is used, and the device is fabricated by selectively etching the Si3N4 layer and depositing a dielectric or metal in its place. Therefore, the technology for selectively etching Si3N4 from Si3N4/SiO2 stacked substrates is very important. To selectively etch Si3N4, 85 wt% of phosphoric acid (H3PO4) is commonly used. However, H3PO4 has economic and environmental problems due to its high consumption during the etching process and non-recyclability. Additionally, the deformation problem of SiO2 layer after etching, particularly oxide regrowth, remains as a critical issue. The regrown oxide fills the gaps in the nano-patterned structure, hindering the mass transfer of the etchant and resulting in uneven etching. Therefore, to improve production yield and enhance the quality of the final device products, the development of an etchant and etching process that can replace H3PO4 is necessary.In this study, an etching process with high selectivity and good pattern geometry was developed using non-phosphoric acid-based etchants. It was also studied to improve the etching efficiency by adding various additives to the non-phosphoric acid based etching solution. The main etching solution was formulated based on nucleophilic chemicals. In addition, various additives, which are expected to improve selectivity by promoting the etching of Si3N4 and inhibiting the etching of SiO2, were added to the main etching solution to determine the effect of the additives on the etch rate. These additives, mainly surfactants (such as alkyl carboxylates, alkylamines, alkyl sulfonates, and alkylbenzene sulfonates) or antioxidants (cysteine, ascorbic acid, furan, pyrrole, imidazole, triazole, tetrazole, and piperazine, etc.), were combined in different configurations.The newly developed non-phosphoric acid etch process resulted in a significantly higher etch rate of Si3N4 compared to the conventional phosphoric acid etch process, and it also increased the Si3N4/SiO2 selectivity. When additives were introduced into the main etching solution, the maximum etch rate of Si3N4 was further enhanced while maintaining a low etch rate of SiO2, leading to an increase in the Si3N4/SiO2 selectivity. This enhancement is attributed to the formation of a passivation barrier on the SiO2 surface by the additive, which inhibits its reaction with the etchant. Through analysis of Si3N4/SiO2 multi-stack pattern structures etched, it was observed that oxide regrowth did not occur on the SiO2 layer after etching, even with much higher etch selectivity and Si3N4 etch rate. As a result, by utilizing a non-phosphoric acid etch solution along with appropriate additives, it was possible to enhance both the etch rate and selectivity while preventing oxide regrowth in the residual SiO2 layer. The application of this process is expected to facilitate the development of a high-throughput, low-cost, and eco-friendly semiconductor etching process compared to H3PO4-based processes.

Selective Etching of SiO2 over Si3N4 through Varying the Concentration of Fluorine Species

Silicon dioxide (SiO2) and silicon nitride (Si3N4) are widely used as an insulating layer to separate interconnection, due to the characteristic of their wide band gap. As the feature size of semiconductors has been continuously decreasing and their structures have become more complex recent years, SiO2 as an insulating layer is reaching its limit. One of the ways to overcome this limitation, next generation 3D structure semiconductors are developed. In order to manufacture these kinds of devices, a removal of SiO2 is required, however, as both SiO2 and Si3N4 layers are revealed, the highly selective SiO2 etching process over Si3N4 is needed. If the Si3N4 layers were etched during the SiO2 layer etching process, the Si3N4 layer could not be function as an insulating layer and an etch stop layer. As an etchant for the SiO2 layer, hydrofluoric acid (HF) and ammonium fluoride (NH4F) combining solution is mainly used. However, it is known that HF solution also causes the material loss of the Si3N4 layers. Therefore, the study of etching behaviors of SiO2 and Si3N4 in HF solution is needed. In HF solutions, main etching species of SiO2 and Si3N4 exists as fluorine species. The concentration of these fluorine species depends on various conditions, such as pH of the solution or the composition of HF and NH4F. Therefore, the dependence of SiO2 and Si3N4 etching rates on the conditions of HF solutions were investigated.To investigate the etching rates of SiO2 and Si3N4, the blanket SiO2 and Si3N4 wafer in which deposited on Si wafer by the low-pressured chemical vapor deposition method were used, respectively. A patterned SiO2/Si3N4 multi-stack structures were fabricated by plasma-enhanced chemical vapor deposition, to verify whether SiO2 was selectively etched over Si3N4 in HF solution. The HF solutions were prepared by adding various concentrations of HF to deionized water and NH4F was added in some cases. The pH of the HF solution was controlled by adding hydrochloric acid or ammonium hydroxide. The temperature maintained at 25 °C during the etching processes using a water bath. The blanket SiO2 and Si3N4 wafers were immersed in these solutions for 3 and 60 mins, respectively. The etching depth of the SiO2 and Si3N4 films was measured by spectroscopic ellipsometry. The morphology of patterned SiO2/Si3N4 multi-stack structures after etching process was observed using field-emission scanning electron microscopy (FE-SEM). The pH and the concentrations of each fluorine species of the prepared HF solutions were calculated based on the equilibrium constants, molar balance, and charge balance.To obtain the HF solution with the high SiO2 etching selectivity over Si3N4, blanket SiO2 and Si3N4 wafers were etched under various pH and initial concentrations of HF solution. As the pH of the HF solution was increased, at the same initial HF concentration, the SiO2/Si3N4 etching selectivity was increased. Meanwhile, the etching selectivity of SiO2 over Si3N4 was increased with the initial concentrations of HF increased, at a fixed pH of the solution. To investigate the reason for the dependencies of the SiO2 and Si3N4 etching rates on pH and initial concentrations of HF, the concentrations of each fluorine species were calculated. As a result, the etching mechanisms and the etching behaviors of SiO2 and Si3N4 in the HF solutions were suggested. Based on the etching kinetics of SiO2 and Si3N4, a patterned SiO2/Si3N4 multi-stack structure etching conditions were controlled to investigate the SiO2/Si3N4 selective etching ability of the HF solution. The cross-sectional FE-SEM images visually showed that high SiO2 etching selectivity compared to Si3N4 was achieved. As a result, highly selective SiO2 etching without loss of Si3N4 was obtained by adjusting only the concentrations of HF and NH4F, without any special additives through the suggested SiO2 and Si3N4 etching kinetics.

Composition of Quantum Dot Color Conversion Layer with ZnS Nanoparticle for Facile Ink Formulation and Uniform Inkjet Printing

Quantum dot (QD) is excellent material for next-generation displays because of their superior optical properties, such as high quantum efficiency, narrow full width at half maximum, high color purity, and photoluminescence quantum yield. QD demonstrated efficient absorption of blue light, coupled with high color-conversion efficiency, fabricated them suitable for use as color-conversion layers (CCLs). However, robustness in pixel patterning uniformity and a printing resolution should be further studied. Light emission via conversion through QD films or converter pixels still need to be improved because the blue light can directly transmit the QD layers, sometimes leading to insufficient energy to excite the QDs. Thus, many studies on QD CCLs have focused on improving the absorption and emission properties of QDs, formulating CCL resins with enhanced color conversion efficiency. Scattering can alter the optical path and incident angle of the emitted light to increase internal reflection so that light emission of the optical film can be enhanced for excitation of photons. Thus, light scattering particles, such as titanium dioxide (TiO2), silicon dioxide (SiO2), zinc oxide (ZnO), and zirconium oxide (ZrO2) were carefully tuned to achieve outstanding properties as QD CCLs, increasing color conversion efficiency.In this work, zinc sulfide (ZnS) light diffusers with hydrophobic properties and various size distribution were synthesized. ZnS and QD were mixed in acrylic resin, isobornyl acrylate, with proper composition of initiator and photocrosslinker. The recipe of mixing was considered for a fabrication of QD CCL ink with optimum viscosity, dispersion stability and uniformity, and printability. For the QD-CCL ink with relatively high viscosity, evaluation of jetting profile and pixel-patterning was conducted with commercial ink cartridge, Sapphire QE-256/30AAA (Fujifilm), combined with the custom-built inkjet printer and high-speed camera. With the scale up to 200ppi QD-CCL pattern, the color spectrum, printability, dispersion, optical properties (evaluation of color-emitting image), and surface uniformity were evaluated. Overall, this work will demonstrates the enhanced light converion behavior of QD-CCL layer fabricated by inkjet-printing process and provide a novel evaluation prorocol of uniformity for QD-CCL layer and color conversion device using blue micro-LED.

Radical Surface Chemistry: The Surprising Reactivity of Silica and Partially Oxidized Porous Silicon Surfaces

Silica and amorphous silicon oxides are generally considered to be inert substrates but have recently been shown to exhibit surprising catalytic activity as a base.1,2 While their weakly acidic nature has long been recognized, recent work has shown that during the formation of microdroplets contact electrification at the water/SiO2 interface is related to formation of radical species such as •OH and H•.3,4 Nano- and micro-structuring, asperities, and anisotropic charge distributions within the double layer may all play roles in the generation of electric fields that facilitate electrochemical processes such as the stripping of an electron from OH– generated by water autoionization that leads to •OH radical formation.5,6 Such radicals may participate in aqueous phase chemistry or produce surface bound radicals such as SiO• that act as active sites. We present evidence for such radical-mediated chemistry at amorphous silica and partially oxidized porous silicon surfaces. Examples include the formation of disulfide linkages from amino acids including cysteine, penicillamine, and glutathione that are mediated by a surface radical site on amorphous silica surfaces.7 Partially oxidized porous silicon is found to be a prodigious producer of H2O2 formed by the reactions of •OH radicals (or other reactive oxygen species) in solution. The reactive oxygen species formed couple synergistically with reduced pH to effectively kill salmonella. Experimental studies are supported by density functional theory (DFT) calculations, which are used to screen possible reactions based on their thermodynamics as well as to explore reaction pathways. 1Y. Li, T. F. Mehari, Z. Wei, Y. Liu, and R. G. Cooks, Angew. Chem., Int. Ed. Engl. 60, 2929 (2021). 2Y. Li, K.-H. Huang, N. Morato, and R. G. Cooks, Chem. Sci. 12, 9816 (2021). 3X. Chen, Y. Xia, Z. Zhang, L. Hua, X. Jia, F. Wang, and R. N. Zare, J. Am. Chem. Soc. 145, 21538 (2023). 4M. A. Mehrgardi, M. Mofidfar, and R. N. Zare, J. Am. Chem. Soc. 144, 7606 (2022). 5C. F. Chamberlayne and R. N. Zare, J. Chem. Phys. 152, 184702 (2020). 6H. Hao, I. Leven, and T. Head-Gordon, Nature Communications 13, 280 (2022). 7Y. Li, K. W. Kolasinski, and R. N. Zare, Proc. Natl. Acad. Sci. U. S. A. 120, e2304735120 (2023).

Ionic Conductivity of Anisotropically Sintered Apatite-Type Lanthanum Silicon Oxide

Apatite-type lanthanum silicon oxide (LSO) has attracted keen attention as one of the new solid electrolytes for its high oxygen ionic conductivity. LSO has a hexagonal apatite structure with oxygen sites coordinated along the c-axis direction and exhibits higher ionic conductivity in the c-axis direction than that of yttria stabilized zirconia, which has been put to practical use as a solid electrolyte. However, to fabricate a dense sintered body with LSO single phase, high sintering temperature of around 1700 ℃ is required due to its very small diffusivity of La and Si. From a practical standpoint, it is necessary to develop a process to lower the sintering temperatures and foster orientation along the c-axis direction to realize practice use of LSO as solid electrolytes.In this study, a powder coated with silicon oxide (SiO2) on the surface of lanthanum oxide (La2O3) powder was prepared for the purpose of completing the diffusion of La and Si at an early stage in sintering. This coated powder is noted as additive-free LSO. Further, a powder doped with tetrafluoroboric acid was also prepared for the purpose of lowering the sintering temperature by enhancing the diffusion of La and Si. This doped powder is noted as added LSO. Sintering behaviors of each powder, crystal phases and ionic conductivities of the obtained sintered bodies were measured.The experimental procedure is as follows. La2O3 powder and tetraethoxysilane (TEOS) were weighed to be La9.33Si6.00O26 and mixed in ethanol followed by dripping 10% ammonia water up to the pH of 10 in the mixed solution. Additive-free LSO was obtained by drying the mixed solution in an oven at 120 °C and then calcining at 400 °C. For the added LSO, the additive-free LSO was stirred in pure water in which a 42% tetrafluoroboric acid aqueous solution was added 10 wt.% to the additive-free LSO powder, and dried in an oven at 90 °C. Two types of prepared powders weighing 0.3 g were pelletized to a size of about 1 mm thick with a diameter of 10 mm by a uniaxial press of 10 MPa and an isostatic pressure of 100 MPa and sintered in a furnace. For the sintered bodies, sintered densities were measured, crystal phases were confirmed by X-ray diffraction (XRD), surface structures were observed by a scanning electron microscope (SEM), and the ionic conductivities were measured by an impedance analyzer.As a result, dense sintered bodies with a relative density exceeding 90 % were achieved by holding the pellet of additive-free LSO at 1700 °C and the added LSO at 1450 °C for 10 hours. From the XRD, it was confirmed that each sintered body consisted of LSO single-phase. The sintered body of the additive-free LSO exhibited high peak intensities associated with (100), which means the c-axis of LSO is oriented in the in-plane direction. SEM observation revealed that the sintered body of additive-free LSO is composed of many columnar grains grown in the in-plane direction. On the other hand, the sintered body of added LSO exhibited an equiaxed-grained structure. Further, by measuring the ionic conductivity of each sintered body in the in-plane and out-of-plane directions, it is revealed that the ionic conductivity of the additive-free LSO showed a higher ionic conductivity in the in-plane direction than in the out-of-plane direction, while the added LSO showed lower ionic conductivity regardless of along in-plane / out-of-plane directions.These results indicate that the difficult-to-sinter properties of LSOs is not only due to the low diffusivity of La and Si, as previously reported, but also preferential grain growth in the c-axis direction impinging on and blocking each other to lower shrinkage speed. Although the sintering temperature could be lowered by enhancing equiaxial grain growth by adding tetrafluoroboric acid, the ionic conductivity became lower, which is probably due to too many grains with a, b-axis orientation of poor ionic conductivity and grain boundaries between them. It could have better prospect to support high ionic conductivity and low sintering temperature at the same time that exploiting the preferential grain growth characteristics of LSO in the c-axis direction. Figure 1

Patterning of Sin and SiO2 Nanostructures for 3D Electronic Devices at Low Temperatures

Silicon oxide, SiO2, and silicon nitride, SiN, are widely used in memory and logic devices because of their dielectric properties, compatibility with silicon-based devices and etching selectivity. Advanced electronic devices are integrated increasingly in vertical direction, and critical etching challenges must be addressed to advance the technology roadmap. Among the enabling applications are vertical etching of SiO2 and SiN with high aspect ratio as well as lateral or isotropic etching of these films with high selectivity. Hydrofluoric acid gas has been used for over 30 years for isotropic etch of SiO2 (1, 2). The process has many similarities with wet etching using HF and requires the presence of water at the surface. Gas-phase etching of silicon nitride films has been demonstrated using moist HF vapor followed by heating of the wafer to remove ammonium fluorosilicate (NH4)2SiF6 or AFS as an intermediate reaction product (3). Recently, HF is used in high aspect ratio plasma etching of SiO2, SiN and multilayer stacks of these films at wafer temperatures below room temperatures (4). The elementary reactions bare resemblance with the vapor etch analogues. In this paper, we will present experimental results on plasma and vapor etching of SiO2 and SiN. The underlaying etching mechanisms will be explained using molecular dynamics and density functional theory.

Complementary Analysis on the SEI of Thin Film Siox Using X-Ray Photoemission Spectroscopy and X-Ray Reflectivity Methods

Silicon materials are expected as a high-capacity anode material for lithium-ion batteries. However, the life of the cell with such silicon materials tends to be short due to the pulverization of silicon associated with its large volume change, and electrolyte consumptions associated with the continuous growth of solid electrolyte interphase (SEI). Compared to pure silicon anodes, silicon oxide (SiOx) has been reported to mitigate such issues and extend the life of the battery1,2. In this study, we combined ex situ XPS (X-ray photoemission spectroscopy) and operando XRR (X-ray reflectivity) methods to investigate the phase transformations in the thin-film SiOx and the nature of SEI during the first lithiation/delithiation cycle to obtain the insights to improve the cycle performances.Using ex situ XPS, we examined the depth profile of the thin-film SiOx sample (Figure 1) at some representative potentials during the first cycle. This elucidated the evolution of chemical nature and thickness of the SEI, and simultaneously the irreversible phase changes in the SiOx. In recent years, the operando XRR method has been successfully applied to the pure silicon thin films3,4, revealing the nature (like thickness and electron density) of top and bottom SEI layers in early cycles. In this study, XRR was applied to thin-film SiOx for the first time. The insight from XPS and that from XRR were integrated for a comprehensive understanding on the evolution of the SEI layer and the SiOx electrode. A systematic comparison was made using the electrolytes with FEC and without FEC to better understand the importance of FEC. It was found out that the SEIs in both systems commonly show breathing behaviors, but the thickness of the SEI is almost always smaller in the FEC containing system. These findings can be a foundation for the high-performance batteries.1. Chen, T.; Wu, J.; Zhang, Q.; Su, X. Recent Advancement of SiOx Based Anodes for Lithium-Ion Batteries. J Power Sources 2017, 363, 126–144.2. Hsu, C.-H.; Chen, H.-Y.; Tsai, C.-J. Stoichiometry Dependence of Electrochemical Behavior of Silicon Oxide Thin Film for Lithium Ion Batteries. J Power Sources 2019, 438, 226943.3. Cao, C.; Steinrück, H.-G.; Shyam, B.; Stone, K. H.; Toney, M. F. In Situ Study of Silicon Electrode Lithiation with X-Ray Reflectivity. Nano Lett 2016, 16 (12), 7394–7401.4. Cao, C.; Steinrück, H.; Shyam, B.; Toney, M. F. The Atomic Scale Electrochemical Lithiation and Delithiation Process of Silicon. Adv Mater Interfaces 2017, 4 (22), 1700771. Figure 1