Silicon Oxide Nanostructures Research Articles

Synthesis of Silicon and Germanium Oxide Nanostructures via Photonic Curing; a Facile Approach to Scale Up Fabrication.

Silicon and Germanium oxide (SiOx and GeOx) nanostructures are promising materials for energy storage applications due to their potentially high energy density, large lithiation capacity (~10X carbon), low toxicity, low cost, and high thermal stability. This work reports a unique approach to achieving controlled synthesis of SiOx and GeOx nanostructures via photonic curing. Unlike conventional methods like rapid thermal annealing, quenching during pulsed photonic curing occurs rapidly (sub-millisecond), allowing the trapping of metastable states to form unique phases and nanostructures. We explored the possible underlying mechanism of photonic curing by incorporating laws of photophysics, photochemistry, and simulated temperature profile of thin film. The results show that photonic curing of spray coated 0.1 M molarity Si and Ge Acetyl Acetate precursor solution, at total fluence 80 J cm-2 can yield GeOx and SiOx nanostructures. The as-synthesized nanostructures are ester functionalized due to photoinitiated chemical reactions in thin film during photonic curing. Results also showed that nanoparticle size changes from ~48 nm to ~11 nm if overall fluence is increased by increasing the number of pulses. These results are an important contribution towards large-scale synthesis of the Ge and Si oxide nanostructured materials which is necessary for next-generation energy storage devices.

Hydrogen sorption by nanostructures at low temperatures (Review article)

The features of hydrogen sorption by a wide range of nanostructures — fullerite C60, carbon nanotubes, graphene structures, nanodispersed carbon, including Pd-containing nanoclusters, ordered silicon-oxide-based nanostructures (the MCM-41 family) and silicon-oxide aerogel — have been reviewed. Special attention is given to the sorption characteristics of carbon nanostructures that have been exposed to various modifying treatments (oxidation, gamma-ray irradiation in gas atmosphere, action of pulsed high frequency gas discharge). Two mechanisms of physical low-temperature sorption of hydrogen have been revealed to predominate in such nanostructures in different temperature intervals. At the lowest temperatures (8–12 K), the sorption can actually proceed without thermal activation: it is realized through the tunnel motion of hydrogen molecules along the nanostructure surfaces. The periodic structure of the potential relief, allowed by the surface frame of carbon and silicon-oxide nanostructures, along the rather low interpit barriers are beneficial for the formation of low-dimensional (including quantum) hydrogen-molecule systems practically without thermally activated diffusion. In such nanostructures, the hydrogen diffusion coefficients are actually independent of temperature at 8–12 K. At higher temperatures (12–295 K), a thermally activated mechanism of hydrogen diffusion prevails. The periodic structure of fullerite C60 contains periodic interstitial cavities, separated by rather low potential barriers. Their sizes are sufficient to accommodate impurity hydrogen molecules and, thus, allow diffusion processes, which can also have a tunnel nature. It is shown that gamma-irradiation and high-frequency gas discharge processing increase markedly the quantity of hydrogen strongly bonded to carbon nanostructures.

Acute and chronic toxicity of amine-functionalized SiO2 nanostructures toward Daphnia magna

Silicon oxide (SiO2) nanostructures (SiO2NS) are increasingly being incorporated into an array of products, notably in the food, pharmaceutical, medical industries and in water treatment systems. Amorphous SiO2NS have low toxicity, however, due to their great versatility, superficial modifications can be made and these altered structures require toxicological investigation. In this study, SiO2NS were synthetized and amine-functionalized with the molecules (3-aminopropyl)triethoxysilane (APTMS) and 3-[2-(2-aminoethylamino)ethylamino]propyltrimethoxysilane (AEAEAPTMS), named SiO2NS@1 and SiO2NS@3, respectively. The bare SiO2NS, SiO2NS@1 and SiO2NS@3 samples were characterized and the influence of the culture medium used in the toxicological assays was also evaluated. The effect of amine functionalization of SiO2NS was investigated through acute and chronic toxicity assays with Daphnia magna. Modifications to ultrastructures of the intestine and eggs of these organisms were observed in TEM and SEM analysis. The toxicity was influenced by the surface modifications and a possible Trojan horse effect was highlighted, particularly in the case of chronic exposure. Exposure to all NSs promoted alterations in the microvilli and mitochondria of the D. magna intestine and some damage to egg cells was also observed. The results demonstrate the importance of carrying out a full characterization of these materials, since surface modifications can enhance their toxic potential.

Unraveling how nanoscale curvature drives formation of lysozyme protein monolayers on inorganic oxide surfaces

The development of nanostructured material interfaces is critical to various application areas spanning diverse fields such as medicine, energy, and sensing. One of the most promising areas involves nanomedicine and drug delivery and involves the formation of noncovalently adsorbed protein coatings on nanostructured surfaces such as inorganic nanoparticles. The coatings can form naturally as part of the so-called protein corona or be purposely incorporated as functional elements to evade immune recognition or to enable enzymatic function, for example. To date, most relevant studies have examined the underlying adsorption processes on planar surfaces while the effect of nanoscale curvature on protein adsorption is still being unraveled across many dimensions. Herein, we investigated the ionic strength-dependent adsorption of antibacterial lysozyme protein onto planar and nanostructured silicon oxide surfaces by employing the quartz crystal microbalance-dissipation and localized surface plasmon resonance sensing techniques. Our findings revealed that lysozyme undergoes greater adsorption-related denaturation and spreading on planar surfaces which led to multilayer formation, while nanoscale curvature effects suppress protein denaturation on nanostructured surfaces leading to monolayer formation. We discuss these findings within the context of protein-surface and protein-protein interactions and how subtle changes in adsorption pathways can drive the formation of distinct macromolecular assemblies. Looking forward, we also discuss how such measurement strategies can enable mechanistic insights into the formation of protein coatings on nanostructured surfaces with broad implications for nano-bio interface science.

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

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.

A Study of Nanoscale Profiling Modes of a Silicon Surface via Local Anodic Oxidation

The nanoscale profiling modes of an (100) n-type silicon substrate surface through the local anodic oxidation (LAO) are studied. The influence of relative humidity and pulse voltage at LAO on the geometric parameters of silicon oxide nanostructures (SONs) and shaped profile nanostructures (SPNs) formed within the liquid etching of SONs is elucidated. It is shown that an increase in LAO voltage pulse amplitude from 10 to 20 V causes a gain in the SON height from 0.6 ± 0.2 to 2.0 ± 0.3 nm at a relative humidity of 70 ± 1%. The results can be applied for the design of technological processes in the element-base fabrication of silicon nanoelectronics using scanning probe nanotechnology.

Optimization of Preparation Conditions to Control Structural Characteristics of Silicon Dioxide Nanostructures Prepared by Magnetron Plasma Sputtering

In this work, highly-pure silicon oxide nanostructures were prepared by a closed-field unbalanced magnetron plasma sputtering technique. These nanostructures were characterized by Fourier-transform infrared spectroscopy, UV-visible spectroscopy, x-ray diffraction, scanning electron microscopy, energy-dispersive x-ray spectroscopy and atomic force microscopy in order to determine the optimum preparation conditions. Minimum particle size of 20 nm was determined for the samples prepared at an inter-electrode distance of 4 cm, Ar:O2 gas mixing ratio of 70:30, total gas pressure of 0.08 torr, discharge voltage of 2.5 kV, discharge current of 35 mA, anode temperature of 27 ∘C (room temperature) and cathode temperature of about 40 ∘C. These conditions are optimized to control the structural characteristics of such nanostructures and hence to satisfy certain requirements and purposes in spectroscopic and photonic applications of SiO2 nanostructures.

Erratum to “Design Issues for Performance Enhancement in Nanostructured Silicon Oxide Biosensors: Modeling the Frequency Response” [Aug 16 3241-3248

Erratum to “Design Issues for Performance Enhancement in Nanostructured Silicon Oxide Biosensors: Modeling the Frequency Response” [Aug 16 3241-3248

Polymer Nanodot-Hybridized Alkyl Silicon Oxide Nanostructures for Organic Memory Transistors with Outstanding High-Temperature Operation Stability

Organic memory devices (OMDs) are becoming more important as a core component in flexible electronics era because of their huge potentials for ultrathin, lightweight and flexible plastic memory modules. In particular, transistor-type OMDs (TOMDs) have been gradually spotlighted due to their structural advantages possessing both memory and driving functions in single devices. Although a variety of TOMDs have been developed by introducing various materials, less attention has been paid to the stable operation at high temperatures. Here we demonstrate that the polymer nanodot-embedded alkyl silicon oxide (ASiO) hybrid materials, which are prepared by sol-gel and thermal cross-linking reactions between poly(4-vinylphenol) (PVP) and vinyltriethoxysilane, can deliver low-voltage (1~5 V) TOMDs with outstanding operation stability (>4700 cycles) at high temperatures (150 °C). The efficient low-voltage memory function is enabled by the embedded PVP nanodots with particular lattice nanostructures, while the high thermal stability is achieved by the cross-linked ASiO network structures.

Mixed titanium, silicon, and aluminum oxide nanostructures as novel adsorbent for removal of rhodamine 6G and methylene blue as cationic dyes from aqueous solution

Mixed oxide nanoparticles containing Ti, Si, and Al of 8–15 nm size range were synthesized using a combined sol-gel - hydrothermal method. Effects of composition on the structure, morphology, and optical properties of the nanoparticles were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), microRaman spectroscopy, and diffuse reflectance spectroscopy (DRS). Dye removal abilities of the nanoparticles from aqueous solutions were tested for different cationic dyes. While all the mixed oxide nanoparticles revealed high and fast adsorption of cationic dyes, the particles containing Ti and Si turned out to be the best. The adsorption kinetics and equilibrium adsorption behavior of the adsorbate - adsorbent systems could be well described by pseudo-second-order kinetics and Langmuir isotherm model, respectively. Estimated thermodynamic parameters revealed the adsorption process is spontaneous, driven mainly by the electrostatic force between the cationic dye molecules and negative charge at nanoparticle surface. Highest dye adsorption capacity (162.96 mg MB/g) of the mixed oxide nanostructures containing Ti and Si is associated to their high specific surface area, and the presence of surface Si-Oδ- groups, in addition to the hydroxyl groups of amorphous titania. Mixed oxide nanoparticles containing 75% Ti and 25% Si seen to be the most efficient adsorbents for removing cationic dye molecules from wastewater.

Design Issues for Performance Enhancement in Nanostructured Silicon Oxide Biosensors: Modeling the Frequency Response

Nanostructured silicon oxide impedance biosensors with ordered nanopores promise highly sensitive and selective label-free electrical detection of biomolecules through unique frequency-dependent sensitivity characteristics. Despite these promising experimental results, the fundamental mechanisms controlling the frequency-dependent phenomena and hence the design considerations have not been explored. In this paper, we consistently model the fluid and the solid regions of the sensors and discuss the design issues with respect to the pore dimensions for enhancing the sensitivity, selectivity, and repeatability toward detection of ultralow and moderate concentration of target biomolecules. The simulation results have been validated with experiments. The results indicate that the optimal design of nanoporous silicon oxide biosensors is different from the conventional idea of increasing the surface-to-volume ratio of such sensors. Instead, the design approach is nontrivial and the optimum pore dimensions are dependent on the target biomolecule charge, concentration, and distribution. It has been observed that a figure of merit is essential to design such sensors with improved commercial viability.

Passivating electron contact based on highly crystalline nanostructured silicon oxide layers for silicon solar cells

We present a novel passivating contact structure based on a nanostructured silicon-based layer. Traditional poly-Si junctions feature excellent junction characteristics but their optical absorption induces current losses when applied to the solar cell front side. Targeting enhanced transparency, the poly-Si layer is replaced with a mixed-phase silicon oxide/silicon layer. This mixed-phase layer consists of an amorphous SiOx matrix with incorporated Si filaments connecting one side of the layer to the other, and is referred to as nanocrystalline silicon oxide (nc-SiOx) layer. We investigate passivation quality, measured as saturation current density, and nanostructural changes, characterized by Raman spectroscopy and transmission electron microscopy, carefully studying the influence of annealing dwell temperature. Excellent surface passivation on n-type and also p-type wafers is shown. An optimum annealing temperature of 950°C is found, resulting in a saturation current density of 8.8fAcm−2 and 11.0fAcm−2 for n-type and p-type wafers, respectively. Even before forming gas annealing, emitter saturation current densities of 27.9 fA cm−2 (n+/n junction) and 32.0 fA cm−2 (n+/p junction) are reached. Efficient current extraction is presented with specific contact resistivities of 86mΩcm2 on n-type wafer and 19mΩcm2 on p-type wafers, respectively. High-resolution transmission electron microscopy reveals that the layer stack consists of intermixed SiOx and Si phases with the Si phases being partly crystalline already in the as-deposited state. Thermal annealing at temperatures ≥850°C further promotes crystallization of the Si-rich regions. The addition of the SiOx phase enhances the thermal stability of the contact and should allow to tune the refractive index and improve transparency, while still providing efficient electrical transport through the crystalline Si phase, which extends throughout almost the entire contact.

Synthesis of nanoscale silicon oxide oxidation state distributions: The transformation from hydrophilicity to hydrophobicity

Silicon oxide nanostructures which span the range from hydrophilic to hydrophobic have been synthesized. The surface chemistry of these silicon-based nanostructures was analyzed using a combination of X-ray photoelectron spectroscopy, reflectance infrared spectroscopy, scanning electron microscopy, and thermogravimetric analysis. The dominant oxidation state for the nanostructured oxides shifts from an average oxidation state of +III to a combination of +II and +III oxidation states. A correlation of the ability to adsorb water with variations in the surface Si:O ratios was observed showing a transition from hydrophilic to hydrophobic character.

Spectral shift of cresyl violet luminescence on charged silicon oxide nanostructures

Nanolithography by local oxidation of dodecyl‐terminated silicon using a scanning probe microscope is a practical method for the generation of silicon oxide nanostructures on a well‐defined substrate. We report on the functionalization of such structures by the selective binding of the cationic dye cresyl violet by electrostatic interactions. The bound dye molecules could be optically excited and showed a clear luminescence emission. Additionally to the fluorescence light from monomers, an additional blue‐shifted emission was found. This emission is an indication of the formation of charge‐transfer complexes between the cationic dye molecules and anions in the oxide nanostructures. AFM topography and fluorescence image of selectively cresyl violet modified silicon oxide nanostructures on alkyl‐terminated silicon surfaces.

Functional bisimide dyes bound via electrostatic interactions to oxide nanostructures generated by AFM lithography

Silicon oxide nanostructures have been functionalized by selective binding of a positively charged bisimide dye derivative. The structures were prepared by AFM nanolithography via local anodic oxidation (LAO) of dodecyl-terminated silicon and are negatively charged due to the production process. Therefore cationic spermine-functionalized perylene bisimide (sf-PBI) molecules can be bound to the structures by electrostatic interactions. The assembly of the sf-PBI units on the LAO nanostructures is verified by AFM height measurements and means of fluorescence microscopy. Emission spectra from the dye-functionalized oxide show that the molecules are able to form excimers. These excimers are characterized by a broad and featureless red-shifted emission band and an increased excited state life time. In contrast to the emission of sf-PBI films on uncharged silicon oxide, the excimer emission was found to decrease strongly low temperatures. This might be explained by a very tight binding due to the electrostatic attraction of the molecules to the LAO oxide.

Fabrication of arbitrarily shaped silicon and silicon oxide nanostructures using tip-based nanofabrication

The authors report fabrication of arbitrary shapes of silicon and silicon oxide nanostructures using tip-based nanofabrication (TBN). A heated atomic force microscope (AFM) tip deposits molten polymer on a substrate to form polymer nanostructures that serve as etch mask to fabricate silicon or silicon oxide nanostructures. The authors demonstrate how TBN can be combined with conventional wet etching as well as metal-assisted chemical etching, in order to fabricate these nanostructures. The size of the TBN-fabricated silicon nanostructures is around 200 nm. Silicon nanostructures fabricated using metal-assisted chemical etch can have very smooth sidewalls with, roughness as small as 2 nm. The authors show fabrication of arbitrary shapes of silicon and silicon oxide nanostructures including those with curved and circular shapes. Our results show that TBN using a heated AFM tip can function as an additive nanolithography technique with minimum contamination, and is compatible with existing nanofabrication methods.

An Investigation on the Effect of the Catalyst on Physical Properties of Silicon Oxide Nanostructures Prepared by CVD Technique

Here, nano and microstructures of silicon oxide layers grown on p-Si (111) wafer have synthesized by evaporating SnCl2.2H2O powder in a mixture of Ar and O2 gas flow using chemical vapor deposition (CVD) technique. The growth temperature and the vacuum pressure were 950 °C and 10-3 torr, respectively. Through this study, samples have characterized by SEM, XRD, EDS and PL methods. The grown sample while has a combination of porous and layered morphology, it has a polycrystalline nature including a mixture of SiO2-x (002) and SnO2 phases. The EDS elemental analysis confirmed the presence of Si, O and Sn atoms in the composition, which is consistent with the XRD data. The PL spectrum show a strong peak in violet region (424 nm) attributed to the crystal defects at the SiO2-x and SnO2 interfaces.

Preparation of nanostructured silicon oxide and silicon nitride films using nanotechnologies

The synthesis of silicon oxide and silicon nitride surface nanostructures is used as an example to demonstrate the possibility of using correlation relationships with inductive parametric constants for quantitatively assessing the reactivity of surface functional groups and predicting the conditions of surface reactions.

Selective surface modification of lithographic silicon oxide nanostructures by organofunctional silanes

This study investigates the controlled chemical functionalization of silicon oxide nanostructures prepared by AFM-anodization lithography of alkyl-terminated silicon. Different conditions for the growth of covalently bound mono-, multi- or submonolayers of distinctively functional silane molecules on nanostructures have been identified by AFM-height investigations. Routes for the preparation of methyl- or amino-terminated structures or silicon surfaces are presented and discussed. The formation of silane monolayers on nanoscopic silicon oxide nanostructures was found to be much more sensitive towards ambient humidity than, e.g., the silanization of larger OH-terminated silica surfaces. Amino-functionalized nanostructures have been successfully modified by the covalent binding of functional fluorescein dye molecules. Upon excitation, the dye-functionalized structures show only weak fluorescence, which may be an indication of a relatively low surface coverage of the dye molecules on length scale that is not accessible by standard AFM measurements.

Nanostructured Silicon Oxide Dual-Function Layer in Amorphous Silicon Based Solar Cells

ABSTRACTWe report the results of using n-type hydrogenated nanocrystalline silicon oxide alloy (nc-SiOx:H) in hydrogenated nanocrystalline silicon (nc-Si:H) and amorphous silicon germanium alloy (a-SiGe:H) single-junction solar cells. We used VHF glow discharge to deposit nc-SiOx:H layers on various substrates for material characterizations. We also used VHF glow discharge to deposit the intrinsic layer in nc-Si:H solar cells. RF glow discharge was used for the deposition of the doped layers and the intrinsic layer in a-SiGe:H solar cells. Various substrates such as stainless steel (SS), Ag coated SS, and ZnO/Ag coated SS were used for different cell structures. We found that by using nc-SiOx:H to replace the ZnO and the a-Si:H n-layer in nc-Si:H solar cells, the cell structure is greatly simplified, while the cell performances remain nearly identical to those made using the conventional n-i-p structure on standard ZnO/Ag BR’s. Solar cells with nc-SiOx:H as the n layer directly deposited on textured Ag show similar quantum efficiency (QE) as the n-i-p cells on ZnO/Ag BRs. In both cases, QE is higher than that in the n-i-p cells made directly on Ag coated SS. This effect is probably caused by the shift of surface plasmon-polariton resonance frequency due to the difference in index of refraction of ZnO, nc-SiOx:H, and Si.