SiOx Structure Research Articles

Formation of a Controllable Diffusion Barrier Layer on the Surface of Polydimethylsiloxane Films by Infrared Laser Irradiation.

Developing a diffusion barrier layer on material interfaces has potential applications in various fields such as in packaging materials, pharmaceuticals, chemical filtration, microelectronics, and medical devices. Although numerous physical and chemical methods have been proposed to generate the diffusion barrier layer, the complexity of fabrication techniques and the high manufacturing costs limit their practical utility. Here, we propose an innovative approach to fabricate the diffusion barrier layer by irradiating poly(dimethylsiloxane) (PDMS) with a mid-infrared (λ = 10.6 μm) CO2 laser. This process directly creates a diffusion barrier layer on the PDMS surface by forming a heavily cross-linked network in the polymer matrix. The optimal irradiation conditions were investigated by modulating the defocusing distance, laser power, and number of scanning passes. The barrier thickness can reach up to 70 μm as observed by the scanning electron microscope (SEM). The attenuated total reflectance (ATR), electron dispersive X-ray (EDX), and X-ray photoelectron spectroscopy (XPS) analyses collectively confirmed the formation of the SiOx structure on the modified surface based on the decreased methyl group signal and the increased oxygen/silicon ratio. The diffusion test with the model drugs (rhodamine B and donepezil) demonstrated that the modified surface exhibits effective diffusion barrier properties and the rate of drug diffusion through the modified barrier layer can be controlled by the optimization of the irradiation parameters. This novel approach provides the possibility to develop a controllable diffusion barrier layer in a biocompatible polymer with prospective applications in the fields of pharmaceuticals, packing materials, and medical devices.

Swelling-Controlled Double-Layered SiOx/Mg2SiO4/SiOx Composite with Enhanced Initial Coulombic Efficiency for Lithium-Ion Battery.

Si-based anode materials are considered as potential materials for high-energy lithium-ion batteries (LIBs) with the advantages of high specific capacities and low operating voltages. However, significant initial capacity loss and large volume variations during cycles are the primary restrictions for the practical application of Si-based anodes. Herein, we propose an affordable and scalable synthesis of double-layered SiOx/Mg2SiO4/SiOx composites through the magnesiothermic reduction of micro-sized SiO with Mg metal powder at 750 °C for 2 h. The distinctive morphology and microstructure of the double-layered SiOx/Mg2SiO4/SiOx composite are beneficial as they remarkably improve the reversibility in the first cycle and completely suppress the volume variations during cycling. In our material design, the outermost layer with a highly porous SiOx structure provides abundant active sites by securing a pathway for efficient access to electrons and electrolytes. The inner layer of Mg2SiO4 can constrain the large volume expansion to increase the initial Coulombic efficiency (ICE). Owing to these promising structural features, the composite prepared with a 2:1 molar ratio of SiO to Mg exhibited initial charge and discharge capacities of 1826 and 1381 mA h g-1, respectively, with an ICE of 75.6%. Moreover, it showed a stable cycle performance, maintaining high capacity retention of up to >86.0% even after 300 cycles. The proposed approach provides practical insight into the mass production of advanced anode materials for high-energy LIBs.

Cubic SiC nanowire synthesis by DC arc discharge under ambient air conditions

Silicon carbide (SiC) is a widely used material characterized by unique physical and chemical properties. In the paper, cubic silicon carbide nanowires are synthesized via the non-vacuum DC (direct current) arc discharge method. DC arc is generated between the graphite rod and the graphite crucible under ambient air conditions without any vacuum or applying special defenses to the used atmosphere equipment. According to experimental data, the percentage of silicon carbide of the total product in interval from 70 A to 100 A increases from 3.9% up to 26.7% (mass), and in interval from 130 A to 200 A of arc discharge current decreases from 26.1% down to 19.9% (mass). The silicon carbide wires are characterized by the typical core-shell SiC–SiOx structure. It is possible to control the phase composition and increase the yield of SiC by changing the arc discharge current amplitude. The optimal synthesis parameters using the DC source with the maximum current of 200 A are a current of 200 A, synthesis time of 12 s and a silicon fraction in the initial mixture not more than 25% (mass) to completely process the initial silicon into its carbide.

Nanosized Potential Fluctuations in SiOx Synthesized by Plasma-Enhanced Chemical Vapor Deposition

This work was devoted to studying the atomic structure and electron spectrum of a-SiOx : H films created on silicon and glass substrates by means of plasma-enhanced chemical vapor deposition (PECVD). Depending on the conditions of oxygen supply into the reactor, the stoichiometric parameter x of the films was varied from 0.57 to 2. The structure of the films and the specific features of their electron structure were characterized depending on the parameter x with a complex of structural and optical methods and ab initio quantum-chemical simulation for the model SiOx structure. The studied SiOx : H films were established to consist predominantly of silicon suboxides SiOy, SiO2 clusters, and amorphous silicon. Based on the spatial fluctuations of their chemical composition, the model of bandgap width and potential fluctuations was proposed for SiOx electrons and holes. The obtained data would provide the charge transport in a-SiOx : H films with more precise modeling important for the creation of nonvolatile random-access memory (RAM) elements and memristors on their basis.

Optical Properties of Nonstoichiometric Silicon Oxide SiOx (x < 2)

The optical properties of amorphous nonstoichiometric silicon oxide (SiOx) films of variable composition (x = 0.62–1.92) formed by plasma-enhanced chemical vapor deposition are studied in the spectral range of 1.12–4.96 eV. Spectral ellipsometry showed that the refractive index dispersion character allows one to assign the formed SiOx films to silicon-like films, dielectrics, or intermediate-conductivity-type films depending on the content of oxygen in the gas phase during synthesis. A model of the SiOx structure for ab initio calculations is proposed and describes well the experimental optical spectra. Ab initio calculations of the dependences of the SiOx refractive index and band gap on stoichiometry parameter x are performed.

Maskless atmospheric pressure PECVD of SiOx films on both planar and nonplanar surfaces using a flexible atmospheric microplasma generation device

AbstractThis paper presents the use of a simple‐arranged, low‐cost, and flexible atmospheric pressure microplasma generation device (μPGD) with controlled gas discharge to achieve maskless atmospheric plasma‐enhanced chemical vapor deposition (PECVD) of SiOx films on both planar and nonplanar surfaces. The μPGD is mainly composed of a copper–polyimide–copper sandwich structure with predefined microfluidic channels. Uniform microplasmas of different shapes and dimensions were generated in the open air. SiOx films were masklessly deposited with well‐defined edges and good feature transfer fidelity. The SEM, EDS, XPS, and FTIR spectra of the deposited film confirm the SiOx structure. These results indicate that μPGD is able to achieve maskless PECVD of SiOx films in the open air, especially micropatterning on nonplanar surfaces.

Selectorless Oxide-based Resistive Switching Memory with Nonuniform Dielectric for Low Power Crossbar Array Applications

Resistive random access memory (RRAM) using various binary metal oxide structures have attracted attentions since the current nonvolatile memory (NVM) has been approaching the scaling limit. RRAMs has excellent scalability, high speed and low power operation ability which is desired for current hardware needs i.e. high density storage memory and in-memory computing architecture. Meanwhile, selector devices are essential to suppress the sneak path issue, which causes reading errors and hinders the implementation of RRAM in high-density cross-bar array configuration. However, additional selector device as commonly proposed one selector-one resistor (1S-1R) design, rises the process complexity and cost (Fig. (a)). In this work, non-uniform dielectric selectorless memristor devices have been demonstrated by utilizing the nonlinear (NL) resistive switching (RS) characteristics with gap design method for RRAM array applications. The device characteristics with current transport mechanisms, and effective trap level below conduction band in stacks have also been investigated. Interestingly, a seasoning effect determination with nonlinearity improvement is also demonstrated in a bilayer stacking architecture. Specifically, the low-k layer quality can be examined by 1st RESET process electrically after electroforming process in non-uniform dielectric constant layers structure, which provides an intrinsically design of layered functionality with mechanism insight deeply. The RRAM devices with various side lengths of 400 nm have been fabricated. The starting substrates were heavily-doped N+ Si wafers. Titanium nitride (TiN) of 200 nm was deposited as bottom electrode. Then, 7 nm of SiOx and followed by 7 nm of HfOx were deposited as resistive switching dielectric layers for realizing the bilayer selectorless structures by radio frequency (RF) sputtering. The graphite oxide was formed after HfOx deposition as reported in our previous work. Platinum of 165 nm was then deposited as top electrodes, as followed by lift-off method for RRAM devices (Fig. (b)). The HfOx (11 nm) single layer devices, SiOx (10 nm) single layer, and HfOx (4 nm)/SiOx (9 nm) bilayer devices are used as references. An Agilent B1500 and Lakeshore probe station were used for electrical characterization of the RRAM devices. To consider the selectorless RRAM stability, Fig. (c) shows the examination process for low-k layer quality determination by analyzing forming and 1st RESET processes in detail (HfOx (4 nm)/ SiOx (9 nm) structure as example). The I-V characteristics with high electroforming voltage and leaky post-forming resistance did not perform the nonlinearity selectorless characteristics as compared to the I-V characteristics with low electroforming voltage and resistive post-forming resistance one, which indicated that overshoot damage by forming process can determine the nonlinearity and selectorless device reliability. Note, although the low forming voltage devices have resistive post-forming resistance, the 1st RESET process at higher voltage side shows a nonlinearity increasing region (read at -0.5V). Transport in this voltage range is found to fit well to the Fowler-Nordheim (F-N) tunneling formula (Red region in Figure and zoom-in plot of Fig. (d) inset) with scientifically accepted accuracy (R2 =99%), which shown that less overshoot damage in lower forming voltage may induce Fowler–Nordheim (F-N) tunneling, as compared to which with higher forming voltage devices (Ohmic behavior in LRS, data not shown here). The results also confirm that the seasoning effect determination with NL improvement by robust low-k layer quality and less forming process damage can improve the nonlinearity and selectorless device reliability. In this study, build-in NL characteristics have been realized for the non-uniform dielectric selectorless memristors without an diode/selector. The seasoning effect determination with nonlinearity NL is examined the low-k layer quality by 1st RESET process after electroforming process, which provides an intrinsically design of layered functionality with mechanism insights deeply. Benchmark our results shown that the achievement of high performance and excellent reliability of built-in nonlinearity in 1R-only selectorless RRAM (NL > 120, memory window > 100, sub-µs switching speed, and NL retention) for the future bilayer selectorless RRAM low-power memory array configurations (Fig. (e)). The non-uniform dielectric memristor are promising for high-density, low-power, selectorless RRAM array applications. The highly NL characteristics observed in non-uniform dielectric bilayer devices are desirable in suppressing sneak path currents in crossbar arrays. Figure 1

Наноразмерные флуктуации потенциала в SiO-=SUB=-x-=/SUB=-, синтезированном плазмохимическим осаждением

The atomic structure and electron spectrum of a-SiOx:H films deposited on silicon and glass substrates by the plasma enhanced chemical vapor deposition method are considered in this paper. The film stoichiometric parameter «x» varied in the range from 0.57 to 2 depending on the oxygen supply to the reactor conditions. The film structures and the electronic structure peculiarities characterization, depending on the parameter «x» value, were carried out using a set of structural and optical techniques, as well as the ab initio quantum-chemical simulation for the model SiOx structure. It was established that the studied SiOx:H films mainly consist of silicon suboxide SiOy with SiO2 and amorphous Si clusters. Based on the spatial chemical composition fluctuations, the electron and hole potential fluctuations model for SiOx is proposed. The obtained results will allow a more accurate charge transport modeling in a-SiOx:H films, which is important for creating nonvolatile memory and memristor elements on the base of SiOx.

Conductivity and Surface Passivation Properties of Boron‐Doped Poly‐Silicon Passivated Contacts for c‐Si Solar Cells

Passivating the contacts of crystalline silicon (c‐Si) solar cells with a poly‐crystalline silicon (poly Si) layer on top of a thin silicon oxide (SiOx) film are currently of growing interest to reduce recombination at the interface between the metal electrode and the c‐Si substrate. This study focuses on the development of boron‐doped poly‐Si/SiOx structure to obtain a hole selective passivated contact with a reduced recombination current density and a high photo‐voltage potential. The poly‐Si layer is obtained by depositing a hydrogen‐rich amorphous silicon layer by plasma enhanced chemical vapor deposition (PECVD) exposed then to an annealing step. Using the PECVD route enables to single side deposit the poly Si layer, however, a blistering of the layer appears due to its high hydrogen content, which leads to the degradation of the poly‐Si layer after annealing. In this study, the deposition temperature and gas flow ratio used during PECVD step are optimized to obtain blister‐free poly‐Si layer. The stability of the surface passivation properties over time is shown to depend on the blister density. The surface passivation properties are further improved thanks to a post process hydrogenation step. As a result, a mean implied photo‐voltage value of 714 mV is obtained.

Surface modification of silicon oxycarbide films produced by remote hydrogen microwave plasma chemical vapour deposition from tetramethyldisiloxane precursor

The motivation for this contribution is the search for thin-film silicon oxycarbide (SiOC) materials suitable for modern electronics with good chemical/thermal stability, good barrier properties and conformal coverage, which can be deposited on rigid and flexible substrates, and whose surface can be organically functionalized. Two types of thin SiOC films of very different nature, such as polymer-like and ceramic-like, were fabricated by means of remote hydrogen microwave plasma chemical vapour deposition (RP-CVD) from 1,1,3,3–tetramethyldisiloxane (TMDSO). The RP-CVD coatings deposited on a silicon substrate were then modified by treatment with a direct radiofrequency (RF) plasma process induced in a mixture of argon and water vapour (Ar/H2O), which resulted in the surface activation through the formation of highly reactive silanol groups (SiOH). In this process a silicon oxide layer (SiOx) was also formed, and its growth was examined by FTIR, XPS and ellipsometry. The growth of the SiOx structure reduces the film thickness of silicon oxycarbide. Activation of the film surface is completed in <10 s. In the next modification step, the RP-CVD films were silanized by immobilizing (3-aminopropyl)triethoxysilane (APTES). Attachment of APTES molecules to the activated surface of SiOC films was observed with the development of an additional layer of SiOx on the surface. The silanization with APTES vapour under nitrogen allowed the formation of 10 nm-thick condensate. The AFM microscopic examination showed that the deposited APTES layers are homogeneous without aggregates specific for conventional silanization from the solution. The final modification of RP-CVD films was achieved by functionalization with an organic fluorescent probe, which involves the covalent attachment of pyrene to amino group of APTES using hydroxyimide ester linkage (PyNHS). The results of the present study proved that the chemical functionalization of thin silicon oxycarbide films was achieved.

Synthesis and structure evolution of phenolic resin/silicone hybrid composites with improved thermal stability

Phenolic resin/silicone hybrid composites (MPR) were prepared by a facile and low-cost method. FTIR results show that polycondensation of siloxane occurs in the presence of catalyst and water in the system, and siloxane oligomer was formed. During the curing process, the transesterification reaction between siloxane oligomer and phenolic resin (PR) makes silicon incorporated into PR. The TGA results indicate that introducing Si–O structure into PR can effectively improve the thermal stability of the resin. Compared with cured neat PR, temperatures at 5 and 10% mass loss of cured MPR can be improved by 43 and 36 °C. Its char yield at 800 °C was increased by about 9.1%. Cured MPR has been characterized by FTIR, XPS, XRD and Raman spectra to discuss the chemical state changes of silicon during pyrolysis process, as well as the effect of silicon on the char yield. On the one hand, the formation of Si–O–C structure can reduce the number of phenyl hydroxyl groups, which contributes to the reduced weight loss. On the other hand, the results indicate that Si–Ox structure was formed from the oxidation of Si–CH3 and hydrolysis of Si–O–C structures. According to Raman analyses, introducing silicone into the system cannot help to promote the formation of a more ordered structure. Additionally, the mechanical properties of cured MPR have also been improved.

Short-Range Order and Charge Transport in SiOx: Experiment and Numerical Simulation

The structure of nonstoichiometric silicon oxide (SiOx) has been studied by the methods of highresolution X-ray photoelectron spectroscopy and fundamental optical-absorption spectroscopy. The conductivity of SiOx (x = 1.4 and 1.6) films has been measured in a wide range of electric fields and temperatures. Experimental data are described in terms of the proposed SiOx structure model based on the concept of fluctuating chemical composition leading to nanoscale fluctuations in the electric potential. The maximum amplitude of potential fluctuations amounts to 2.6 eV for electrons and 3.8 eV for holes. In the framework of this model, the observed conductivity of SiOx is described by the Shklovskii–Efros theory of percolation in inhomogeneous media. The characteristic spatial scale of potential fluctuations in SiOx films is about 3 nm. The electron-percolation energy in SiO1.4 and SiO1.6 films is estimated to be 0.5 and 0.8 eV, respectively.

Polarized luminescence of nc-Si–SiOx nanostructures on silicon substrates with patterned surface

Polarization characteristics and spectra of photoluminescence (PL) of nc-Si–SiOx structures formed on the patterned and plane c-Si substrates are studied. The interference lithography with vacuum chalcogenide photoresist and anisotropic wet etching are used to form a periodic relief (diffraction grating) on the surface of the substrates. The studied nc-Si–SiOx structures were produced by oblique-angle deposition of Si monoxide in vacuum and the subsequent high-temperature annealing. The linear polarization memory (PM) effect in PL of studied structure on plane substrate is manifested only after the treatment of the structures in HF and is explained by the presence of elongated Si nanoparticles in the SiOx nanocolumns. But the PL output from the nc-Si–SiOx structure on the patterned substrate depends on how this radiation is polarized with respect to the grating grooves and is much less dependent on the polarization of the exciting light. The measured reflection spectra of nc-Si–SiOx structure on the patterned c-Si substrate confirmed the influence of pattern on the extraction of polarized PL.

A hybrid Si@FeSiy/SiOx anode structure for high performance lithium-ion batteries via ammonia-assisted one-pot synthesis

A hybrid micron/submicron-sized Si@FeSiy/SiOx structure is developed by ball-milling of Si and Fe powders via ammonia-assisted one-pot synthesis. It shows superior electrochemical performance as an anode material for lithium-ion batteries.

Synthesis and Solid-State Pyrolysis Behavior of POSS Containing Organometallic Polymer with Dicobalt Hexacarbonyl in the Side Chain

POSS containing organometallic polymer (P2-Co) with dicobalt hexacarbonyl in the side chain was synthesized for solid-state pyrolysis to produce magnetic nanoparticles. For comparison, its analogue (P1-Co) without POSS groups was also prepared. After pyrolysis, the nanospheres obtained from P2-Co with POSS groups, had a Co@C–SiOx structure with small and uniform size (~15 nm), and its diameter almost remained unchanged when the pyrolysis temperature increased, showing excellent sinter-resistant properties. However, the nanoparticles obtained from P1-Co sintered seriously at high temperature, and its size was enlarged from 45 to 160 nm, when the pyrolysis temperature increased from 700 to 850 °C. Meanwhile, the obtained nanoparticles all showed good magnetic properties, with the saturation magnetization in the range of 24.0–58.5 emu g−1, making them promising candidates for the actual applications.

Performance and characteristics of double layer porous silicon oxide resistance random access memory

A bilayer resistive switching memory device with an inserted porous silicon oxide layer is investigated in this letter. Compared with single Zr:SiOx layer structure, Zr:SiOx/porous SiOx structure outperforms from various aspects, including low operating voltages, tighter distributions of set voltage, higher stability of both low resistance state and high resistance state, and satisfactory endurance characteristics. Electric field simulation by comsolTM Multiphysics is applied, which corroborates that intensive electric field around the pore in porous SiOx layer guides the conduction of electrons. The constraint of conduction path leads to better stabilization and prominent performance of bilayer resistive switching devices.

Large-scale potential fluctuations caused by SiO x compositional inhomogeneity

The short-range order in amorphous SiOx (0 ≤ x ≤ 2) films has been studied by high-resolution X-ray photoelectron spectroscopy. Both the random bonding and random mixture models do not describe experimental photoelectron spectra of SiOx (x ≤ 2). An intermediate model of the SiOx structure has been proposed. The measured photoelectron spectra of the SiOx (x ≤ 2) valence band indicate the presence of the silicon phase and silicon oxide.

Room-Temperature Nanoimprinting Using Ladder Hydrogen Silsesquioxane

Ladder hydrogen silsesquioxane (HSQ) has been proposed as a replication material to be used in nanoimprinting processes at room temperature. We replicated ladder-HSQ patterns by nanoimprinting at room temperature that were as accurate as replicated caged-HSQ patterns. Caged HSQ is the standard replication material currently used in nanoimprinting at room temperature. Caged-HSQ-imprinted patterns completely disappeared when annealed at 300 °C. However, ladder-HSQ-imprinted patterns retained almost the same rectangular profile as they had before annealing, even after being subject to high-temperature annealing at 1000 °C. Fourier transform infrared spectroscopy showed that high-temperature annealing transformed the HSQ into a SiOx structure. This vitrification of HSQ resin improved its dry-etching durability, with the dry-etching rate when subject to CHF3 reactive-ion etching decreasing from 32 to 27 nm/min, which is close to the value of 26 nm/min for thermally grown SiO2 and a quartz substrate.

Comparison of SiO x structure in RF sputtered samples

The nano-structure of rf magnetron sputtered SiOx films is addressed. More specifically, it was examined whether boundary effects created by the confinement of the material into a thin film induces the formation of a layered structure parallel to the surface during annealing. Different films of SiOx (0 < x < 2) were deposited by an RF magnetron reactive sputtering technique by controlling the relative O2/Ar gas flow during sputter deposition. The graded samples used in this study were 10 nm (x = 2 at the interface to 0 at the surface) and 20 nm (x = 1 to 0), respectively. Samples were annealed in situ from room temperature to 570 °C. Infrared analysis (IR) and X-ray Photoelectron Spectroscopy (XPS) were used to analyze and compare the samples. IR spectra before and after annealing were compared with each other. XPS spectra were drawn during annealing to monitor the changes in the SiOx structure. The sputtered SiOx showed a tendency to decompose into Si and SiO2 during the annealing process. The reaction is characterized by an initial increase in the reaction rate when the temperature was raised, followed by a decrease in the reaction rate toward equilibrium. Two possible models can describe the process. The layer consists of a mixture of all possible sub-oxides with different activation energies for each sub-oxide or the O can segregate from the Si rich region toward an oxygen rich region, where the accumulation of the oxygen forms a diffusion barrier against further diffusion of the oxygen atoms at that specific temperature. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Effect of thermal heat treatment on oxygen-deficiency-associated defect centers: Relation to 1.8 eV photoluminescence bands in silica glass

Our previous studies have reported the existence of a 1.8 eV photoluminescence (PL) band [full width at half-maximum (FWHM) of 0.2–0.4 eV, decay time τ of ∼200 ns, PL excitation peak of 2.1 eV] in silica glass exposed to visible light. Oxygen-deficiency-associated defect centers [Si clusters or SiOx (x&amp;lt;2) structure] were thought to be the origin of this PL band. In this article, we describe the thermal heat treatment characteristics of the 1.8 eV PL band in silica glass (excited by visible light). In the low-temperature region (∼600 °C), we observed a decrease in the intensity of this PL band. On the other hand, the 2.1 eV PL band (FWHM of ∼0.32 eV, τ unknown) was observed for the case of annealing at a temperature around 1050 °C. We propose that the high probability SiOx (x&amp;lt;2) structure rather than the Si clusters plays a predominant role in the generation of the 1.8 eV PL band, and that crystalline Si nanoparticles are probably the origin of the 2.1 eV PL band.