Showing papers on "Silicon oxide published in 2018"

Efficient and Stable CsPbBr3 Quantum-Dot Powders Passivated and Encapsulated with a Mixed Silicon Nitride and Silicon Oxide Inorganic Polymer Matrix.

Abstract: Despite the excellent optical features of fully inorganic cesium lead halide (CsPbX3) perovskite quantum dots (PeQDs), their unstable nature has limited their use in various optoelectronic devices. To mitigate the instability issues of PeQDs, we demonstrate the roles of dual-silicon nitride and silicon oxide ligands of the polysilazane (PSZ) inorganic polymer to passivate the surface defects and form a barrier layer coated onto green CsPbBr3 QDs to maintain the high photoluminescence quantum yield (PLQY) and improve the environmental stability. The mixed SiNx/SiNxOy/SiOy passivated and encapsulated CsPbBr3/PSZ core/shell composite can be prepared by a simple hydrolysis reaction involving the addition of adding PSZ as a precursor and a slight amount of water into a colloidal CsPbBr3 QD solution. The degree of the moisture-induced hydrolysis reaction of PSZ can affect the compositional ratio of SiNx, SiNxOy, and SiOy liganded to the surfaces of the CsPbBr3 QDs to optimize the PLQY and the stability of CsPbB...

Ultrafine SiOx/C nanospheres and their pomegranate-like assemblies for high-performance lithium storage

Abstract: The application of silicon oxide (SiOx)-based anode materials in lithium-ion batteries is hampered by their low conductivity and large volume expansion To tackle both issues, ultrafine SiOx/C composite nanospheres with a uniform diameter of ∼40 nm were fabricated through a tri-component co-assembly approach The ultrafine SiOx/C nanospheres demonstrated a high specific capacity of 895 mA h g−1 after 200 cycles at 200 mA g−1 At a high current density of 1 A g−1, a capacity of 828 mA h g−1 could be achieved after 1000 cycles The ultrafine SiOx/C nanospheres were further assembled into pomegranate-like assemblies through spray drying The resultant pomegranate-like structure manifested a discharge capacity of 1024 mA h g−1 after 200 cycles at 500 mA g−1

Li4SiO4-Based Artificial Passivation Thin Film for Improving Interfacial Stability of Li Metal Anodes.

Abstract: An amorphous SiO2 (a-SiO2) thin film was developed as an artificial passivation layer to stabilize Li metal anodes during electrochemical reactions. The thin film was prepared using an electron cyclotron resonance–chemical vapor deposition apparatus. The obtained passivation layer has a hierarchical structure, which is composed of lithium silicide, lithiated silicon oxide, and a-SiO2. The thickness of the a-SiO2 passivation layer could be varied by changing the processing time, whereas that of the lithium silicide and lithiated silicon oxide layers was almost constant. During cycling, the surface of the a-SiO2 passivation layer is converted into lithium silicate (Li4SiO4), and the portion of Li4SiO4 depends on the thickness of a-SiO2. A minimum overpotential of 21.7 mV was observed at the Li metal electrode at a current density of 3 mA cm–2 with flat voltage profiles, when an a-SiO2 passivation layer of 92.5 nm was used. The Li metal with this optimized thin passivation layer also showed the lowest charge...

Sub-Monolayer Control of Mixed-Oxide Support Composition in Catalysts via Atomic Layer Deposition: Selective Hydrogenation of Cinnamaldehyde Promoted by (SiO2-ALD)-Pt/Al2O3

Abstract: Alumina-supported platinum catalysts have been modified with silicon oxide thin films grown using atomic layer deposition (ALD) in order to tune the acid–base and electronic properties of the oxide, and their performance has been tested for the hydrogenation of cinnamaldehyde. It was found that the silica layers greatly increase the stability of the platinum nanoparticles, preventing their sintering during high-temperature calcinations without affecting access to the metal surface in any significant way; the extent of CO adsorption, measured by infrared absorption spectroscopy was found to decrease by only one-third after 6 SiO2 ALD cycles. Additional Bronsted and Lewis acid sites were created upon the deposition of submonolayer coverages of silicon oxide, as probed via pyridine adsorption. The addition of the silicon oxide thin films reduced the overall activity of these catalysts but also increased their selectivity toward the production of the unsaturated alcohol. In addition, both turnover frequencies...

Method of post-deposition treatment for silicon oxide film

Abstract: A method of post-deposition treatment for silicon oxide film includes: providing in a reaction space a substrate having a recess pattern on which a silicon oxide film is deposited; supplying a reforming gas for reforming the silicon oxide film to the reaction space in the absence of a film-forming precursor, said reforming gas being composed primarily of He and/or H2; and irradiating the reforming gas with microwaves in the reaction space having a pressure of 200 Pa or less to generate a direct microwave plasma to which the substrate is exposed, thereby reforming the silicon oxide film.

A Lithium-Ion Battery using a 3 D-Array Nanostructured Graphene-Sulfur Cathode and a Silicon Oxide-Based Anode.

Abstract: An efficient lithium-ion battery was assembled by using an enhanced sulfur-based cathode and a silicon oxide-based anode and proposed as an innovative energy-storage system. The sulfur-carbon composite, which exploits graphene carbon with a 3 D array (3DG-S), was synthesized by a reduction step through a microwave-assisted solvothermal technique and was fully characterized in terms of structure and morphology, thereby revealing suitable features for lithium-cell application. Electrochemical tests of the 3DG-S electrode in a lithium half-cell indicated a capacity ranging from 1200 to 1000 mAh g-1 at currents of C/10 and 1 C, respectively. Remarkably, the Li-alloyed anode, namely, Liy SiOx -C prepared by the sol-gel method and lithiated by surface treatment, showed suitable performance in a lithium half-cell by using an electrolyte designed for lithium-sulfur batteries. The Liy SiOx -C/3DG-S battery was found to exhibit very promising properties with a capacity of approximately 460 mAh gS-1 delivered at an average voltage of approximately 1.5 V over 200 cycles, suggesting that the characterized materials would be suitable candidates for low-cost and high-energy-storage applications.

Hydrogen Evolution at the Buried Interface between Pt Thin Films and Silicon Oxide Nanomembranes

Abstract: This paper reports the performance of hydrogen evolution reaction (HER) electrocatalysts based on Pt thin film electrodes that are encapsulated by silicon oxide (SiOx) nanomembranes. This membrane-coated electrocatalyst (MCEC) architecture offers a promising approach to enhancing electrocatalyst stability while incorporating advanced catalytic functionalities such as poison resistance and tunable reaction selectivity. Herein, a room-temperature ultraviolet (UV) ozone synthesis process was used to systematically control the thickness of SiOx overlayers with nanoscale precision and evaluate their influence on the electrochemically active surface area (ECSA) and HER performance of the underlying Pt thin films. Through detailed characterization of the physical and electrochemical properties of the SiOx-encapsulated electrodes, it is shown that proton and H2 transport occur primarily through the SiOx coating such that the HER takes place at the buried Pt|SiOx interface. Increasing the thickness of the SiOx ove...

Silicon Oxide-Encapsulated Platinum Thin Films as Highly Active Electrocatalysts for Carbon Monoxide and Methanol Oxidation

Abstract: Direct alcohol fuel cells (DAFCs) have the potential to provide high power densities for transportation and portable applications. However, widespread use of DAFCs is greatly hindered by the lack of anode electrocatalysts that are inexpensive, stable, resistant to CO poisoning, and highly active toward alcohol oxidation. One promising approach to overcoming these challenges is to combine transition metal catalysts with oxide supports, such as SiO2, which are known to enhance alcohol oxidation by promoting CO oxidation at oxide|metal interfacial regions through the so-called bifunctional mechanism. Herein, we report on a membrane-coated electrocatalyst (MCEC) architecture for alcohol oxidation, in which a thin, permeable silicon oxide (SiOx) nanomembrane encapsulates a well-defined Pt thin film (SiOx|Pt). A key advantage of the MCEC design compared to oxide-supported nanoparticles is that the oxide encapsulation maximizes the density of oxide|metal interfacial sites between the SiOx and Pt catalyst. A seri...

Recombination Analysis of Phosphorus-Doped Nanostructured Silicon Oxide Passivating Electron Contacts for Silicon Solar Cells

Abstract: We analyze the recombination properties of passivating electron selective contacts based on nanostructured silicon oxide. Our contact design is based on an interfacial buffer oxide capped with a bilayer structure of phosphorus-doped silicon oxide and silicon which is annealed at 900 °C. We investigate in detail the effects of the initial dopant concentration in the bilayer and of the anneal dwell time on dopant in-diffusion, contact formation, and interface recombination. Our investigation addresses also the hydrogenation of interface defects and the effect of indium-tin-oxide (ITO) sputtering, allowing us to separate the interplay between enhanced field-effect passivation, Auger recombination, and interface recombination. After thermal annealing, the passivating electron selective contact presented here attains a saturation current density ( J 0) of 12.4 fA cm −2 for medium doping, which improves further upon hydrogenation to J 0 = 8.1 fA cm−2. For specific contact resistances <500 mΩ cm 2, however, higher doping concentrations are required. For those doping concentrations, the saturation current density is 13.9 fA cm−2 and increases by 10% upon sputter-deposition of an ITO layer on top of the electron selective stack.

Accommodating imperfectly aligned memory holes

Abstract: Methods of forming 3-d flash memory cells are described. The methods allow the cells to be produced despite a misalignment in at least two sections (top and bottom), each having multiple charge storage locations. The methods include selectively gas-phase etching dielectric from the bottom memory hole portion by delivering the etchants through the top memory hole. Two options for completing the methods include (1) forming a ledge spacer to allow reactive ion etching of the bottom polysilicon portion without damaging polysilicon or charge-trap/ONO layer on the ledge, and (2) placing sacrificial silicon oxide gapfill in the bottom memory hole, selectively forming protective conformal silicon nitride elsewhere, then removing the sacrificial silicon oxide gapfill before performing the reactive ion etching of the bottom polysilicon portion as before.

Insulator Materials for Interface Passivation of Cu(In,Ga)Se 2 Thin Films

Abstract: In this work, metal–insulator–semiconductor structures were fabricated in order to study different types of insulators, namely, aluminum oxide (Al2O3), silicon nitride, and silicon oxide (SiO x ) to be used as passivation layers in Cu(In,Ga)Se2 (CIGS) thin-film solar cells. The investigated stacks consisted of SLG/Mo/CIGS/insulator/Al. Raman scattering and photoluminescence measurements were done to verify the insulator deposition influence on the CIGS surface. In order to study the electrical properties of the CIGS–insulator interface, capacitance versus conductance and voltage ( C–G–V ) measurements were done to estimate the number and polarity of fixed insulator charges ( Qf ). The density of interface defects ( D it) was estimated from capacitance versus conductance and frequency ( C–G–f ) measurements. This study evidences that the deposition of the insulators at high temperatures (300 °C) and the use of a sputtering technique cause surface modification on the CIGS surface. We found that, by varying the SiO x deposition parameters, it is possible to have opposite charges inside the insulator, which would allow its use in different device architectures. The material with lower D it values was Al2O3 when deposited by sputtering.

Investigations of Si Thin Films as Anode of Lithium-Ion Batteries

Abstract: Amorphous silicon thin films having various thicknesses were investigated as a negative electrode material for lithium-ion batteries. Electrochemical characterization of the 20 nm thick thin silicon film revealed a very low first cycle Coulombic efficiency, which can be attributed to the silicon oxide layer formed on both the surface of the as-deposited Si thin film and the interface between the Si and the substrate. Among the investigated films, the 100 nm Si thin film demonstrated the best performance in terms of first cycle efficiency and cycle life. Observations from scanning electron microscopy demonstrated that the generation of cracks was inevitable in the cycled Si thin films, even as the thickness of the film was as little as 20 nm, which was not predicted by previous modeling work. However, the cycling performance of the 20 and 100 nm silicon thin films was not detrimentally affected by these cracks. The poor capacity retention of the 1 μm silicon thin film was attributed to the delamination.

Surface Chemistry Dependence of Mechanochemical Reaction of Adsorbed Molecules—An Experimental Study on Tribopolymerization of α-Pinene on Metal, Metal Oxide, and Carbon Surfaces

Abstract: Mechanochemical reactions between adsorbate molecules sheared at tribological interfaces can induce association of adsorbed molecules, forming oligomeric and polymeric products often called tribopolymers) This study revealed the role or effect of surface chemistry of the solid substrate in mechanochemical polymerization reactions As a model reactant, α-pinene was chosen because it was known to readily form tribopolymers at the sliding interface of stainless steel under vapor-phase lubrication conditions Eight different substrate materials were tested—palladium, nickel, copper, stainless steel, gold, silicon oxide, aluminum oxide, and diamond-like carbon (DLC) All metal substrates and DLC were initially covered with surface oxide species formed naturally in air or during the oxidative sample cleaning It was found that the tribopolymerization yield of α-pinene is much higher on the substrates that can chemisorb α-pinene, compared to the ones on which only physisorption occurs From the load dependence

Direct synthesis of graphene on silicon oxide by low temperature plasma enhanced chemical vapor deposition.

Abstract: Direct graphene growth on silicon with a native oxide using plasma enhanced chemical vapour deposition at low temperatures [550 °C–650 °C] is demonstrated for the first time. It is shown that the fine-tuning of a two-step synthesis with gas mixtures C2H2/H2 yields monolayer and few layer graphene films with a controllable domain size from 50 nm to more than 300 nm and the sheet resistance ranging from 8 kΩ sq−1 to less than 1.8 kΩ sq−1. Differences are understood in terms of the interaction of the plasma species – chiefly atomic H – with the deposited graphene and the native oxide layer. The proposed low temperature direct synthesis on an insulating substrate does not require any transfer processes and improves the compatibility with the current industrial processes.

In Situ Transmission Electron Microsopy of Oxide Shell-Induced Pore Formation in (De)lithiated Silicon Nanowires

Abstract: Silicon (Si) nanowires with a silicon oxide (SiOx) shell undergoing lithiation and delithiation were examined by in situ transmission electron microscopy (TEM). Large pores formed in the nanowires during the delithiation cycle. We found that the oxide shell constrains the expansion of the Si nanowires during lithitation and then induces pore formation in the nanowires. We propose that the SiOx shell prevents the vacancies that result from the loss of lithium from escaping the Si core, leading to pore nucleation and growth. It is also possible that the difference in mechanical properties of the expanding and contracting Si nanowire and SiOx shell contribute to the observed pore formation. This in situ study reaffirms the need to directly observe structural changes that occur during cycling in battery materials, especially when modified by coatings.

Environmental Electrometry with Luminescent Carbon Nanotubes

Abstract: We demonstrate that localized excitons in luminescent carbon nanotubes can be utilized to study electrostatic fluctuations in the nanotube environment with sensitivity down to the elementary charge. By monitoring the temporal evolution of the cryogenic photoluminescence from individual carbon nanotubes grown on silicon oxide and hexagonal boron nitride, we characterize the dynamics of charge trap defects for both dielectric supports. We find a one order of magnitude reduction in the photoluminescence spectral wandering for nanotubes on extended atomically flat terraces of hexagonal boron nitride. For nanotubes on hexagonal boron nitride with pronounced spectral fluctuations, our analysis suggests proximity to terrace ridges where charge fluctuators agglomerate to exhibit areal densities exceeding those of silicon oxide. Our results establish carbon nanotubes as sensitive probes of environmental charge fluctuations and highlight their potential for applications in electrometric nanodevices with all-optical...

Dielectric Properties and Ion Transport in Layered MoS2 Grown by Vapor-Phase Sulfurization for Potential Applications in Nanoelectronics

Abstract: Electronic and dielectric properties of vapor-phase grown MoS2 have been investigated in metal/MoS2/silicon capacitor structures by capacitance–voltage and conductance-voltage techniques. Analytical methods confirm the MoS2 layered structure, the presence of interfacial silicon oxide (SiOx) and the composition of the films. Electrical characteristics in combination with theoretical considerations quantify the concentration of electron states at the interface between Si and a 2.5–3 nm thick silicon oxide interlayer between Si and MoS2. Measurements under electric field stress indicate the existence of mobile ions in MoS2 that interact with interface states. On the basis of time-of-flight secondary ion mass spectrometry, we propose OH– ions as probable candidates responsible for the observations. The dielectric constant of the vapor-phase grown MoS2 extracted from CV measurements at 100 kHz is 2.6 to 2.9. The present study advances the understanding of defects and interface states in MoS2. It also indicates...

Effective passivation of silicon surfaces by ultrathin atomic-layer deposited niobium oxide

Abstract: This letter reports on effective surface passivation of n-type crystalline silicon by ultrathin niobium oxide (Nb2O5) films prepared by atomic layer deposition (ALD) and subjected to a forming gas anneal at 300 °C. A champion recombination parameter J0 of 20 fA/cm2 and a surface recombination velocity Seff of 4.8 cm/s have been achieved for ultrathin films of 1 nm. The surface pretreatment was found to have a strong impact on the passivation. Good passivation can be achieved on both HF-treated c-Si surfaces and c-Si surfaces with a wet-chemically grown interfacial silicon oxide layer. On HF-treated surfaces, a minimum film thickness of 3 nm is required to achieve a high level of surface passivation, whereas the use of a wet chemically-grown interfacial oxide enables excellent passivation even for Nb2O5 films of only 1 nm. This discrepancy in passivation between both surface types is attributed to differences in the formation and stoichiometry of interfacial silicon oxide, resulting in different levels of chemical passivation. On both surface types, the high level of passivation of ALD Nb2O5 is aided by field-effect passivation originating from a high fixed negative charge density of 1-2 × 1012 cm-3. Furthermore, it is demonstrated that the passivation level provided by 1 nm of Nb2O5 can be further enhanced through light-soaking. Finally, initial explorations show that a low contact resistivity can be obtained using Nb2O5-based contacts. Together, these properties make ALD Nb2O5 a highly interesting building block for high-efficiency c-Si solar cells.

Hydrogen passivation of silicon/silicon oxide interface by atomic layer deposited hafnium oxide and impact of silicon oxide underlayer

Abstract: HfO2 synthesized by atomic layer deposition (ALD) can be used as a passivation material for photodetectors. This paper shows a significant reduction of density of interface traps at the Si/SiO2 interface using ALD HfO2. This is explained by a chemical passivation effect due to presence of hydrogen from water used in the ALD process. Furthermore, ALD HfO2 layers appear negatively charged which generate an additional field effect passivation. The impact of the SiO2 underlayer is also discussed by comparing a chemical silicon oxide to a standard thermal silicon oxide. It is shown that chemical silicon oxide can act as a reservoir of hydrogen atoms which helps to reduce the density of defects close to the Si/SiO2 interface. This result demonstrates the importance of the surface preparation before the ALD of HfO2 in the passivation scheme. Finally, this work shows the correlation between negatively charged defects and Si–O–Hf bonds at the SiO2/HfO2 interface. A passivation stack composed of chemical oxide perm...

Silver oxide decomposition mediated direct bonding of silicon-based materials.

Abstract: Silicon-based materials are widely promising electronic components by the combination with metals in power electronics field. However, bonding metal and silicon-based materials generally requires specific surface modification due to their different chemical bonds. Here, we demonstrate a process for directly bonding metals to silicon-based materials that does not require surface treatment, based on the in situ decomposition of Ag2O paste, forming Ag nanoparticles (AgNPs). We demonstrate sound joints of Ag/silicon-based materials at 300–500 °C with the formation of a silicon oxide interlayer containing AgNPs. We propose that Ag in the interlayer attracted other Ag particles to the interface, playing a unique role in this direct bonding process. This process is suitable for various bonding applications in electronics, as well the fabrication of conducting paths for photovoltaic and other applications.