Amorphous Silica Matrix Research Articles

Massive sulfides of Mount Jourdanne along the super-slow spreading Southwest Indian Ridge and their genesis

Modern massive sulfide deposits are known to occur in diverse tectonic settings and it is generally expected that hydrothermal deposits of similar geological settings shall have more or less similar mineralogical and geochemical signatures. However, the Mount Jourdanne sulfide deposits along the super-slow spreading Southwest Indian Ridge deviate from this common concept. These sulfide precipitates are Zn-rich (up to 35wt.%) and are characterized by high concentrations of Pb (≤3.5wt.%), As (≤1.1wt.%), Ag (≤0.12wt.%), Au (≤11ppm), Sb (≤967ppm), and Cd (≤0.2wt.%) which are unusual for a modern sediment-free mid-oceanic ridge system. Therefore, we have reinvestigated the sulfide samples collected during the INDOYO cruise in 1998, in order to explain their unusual mineralogy and geochemical composition. The sulfide samples are polymetallic and are classified as: a) chimneys, b) mounds, and c) hydrothermal breccias. The chimneys are small tube-like symmetrical bodies (30–40cm high; ~10cm diameter) and consist mainly of sphalerite and less chalcopyrite, set in a matrix of late amorphous silica. The inner wall shows a late-stage colloform sphalerite containing co-precipitates of galena and/or Pb–As sulfosalts. In contrast, the mound samples are dominated either by Fe-sulfides (pyrite) or by a mixture of pyrite and chalcopyrite with less sphalerite, pyrrhotite, amorphous silica and barite. Both, the chimney and mound samples, are characterized by layering and mineral zonation. The hydrothermal breccias are highly altered and mineralogically heterogeneous. They consist of silicified basaltic material that are impregnated with sulfides and contain cm-sized chimney fragments within a matrix of low-temperature minerals such as sphalerite and pyrite. The latter fragments mainly consist of chalcopyrite with isocubanite lamellae. In addition, these breccias contain late-stage realgar, boulangerite, galena, Pb–As sulfosalts and barite that are mostly confined to vugs or fractures. At least five mineralogical associations are distinguished that indicate different thermal episodes ranging from black smoker mineralization conditions to cessation of the hydrothermal activity. Based on the mineralogical associations and established literature in this regard, it is inferred that the mineralization at Mt. Jourdanne occurred mainly in three temperature domains. Above 300°C, the chalcopyrite (with isocubanite)–pyrrhotite association formed whereas the sphalerite dominated assemblage with much less chalcopyrite and pyrite formed around and below 300°C. The late-stage mineralization (below 200°C) contains colloform sphalerite, galena, Pb–As sulfosalts, realgar and barite. The unusual mineralogy and trace element chemistry for this modern VHMS deposit could be explained assuming hydrothermal leaching of some felsic differentiates underneath the basaltic cover and subsequent zone refining processes.

Interactions of three soil bacteria species with phyllosilicate surfaces in hybrid silica gels

To simulate iron consumption in soils, iron leaching from silicate minerals due to three heterotrophic bacterial strains and a chemical treatment was studied using hybrid silica gel (HSG) doped with two phyllosilicates, nontronite (NAu-2) or low-iron-content montmorillonite (SWy-2). HSG methodology, a novel way of separating bacteria cells from a colloidal mineral source, consisted in embedding colloidal mineral particles into an amorphous porous silica matrix using a classical sol-gel procedure. Pantoae agglomerans PA1 and Rahnella aquatilis RA1 were isolated from silicate-rich soils, that is, beech and wheat rhizospheres (Vosges, France); Burkholderia sp. G5 was selected from acidic and nutrient-poor podzol soils (Vosges, France). Fe release from clay minerals and production of bacterial metabolites, that is, low molecular weight organic acids (LMWOA) and siderophores, were monitored. Two LMWOA profiles were observed with major gluconate production (>9000μM) for Burkholderia sp. G5 and moderate production of lactate, acetate, propionate, formate, oxalate, citrate, and succinate (<300μM) for R.aquatilis RA1 and P.agglomerans PA1. HSG demonstrated its usefulness in revealing clay mineral-microorganisms interactions. The effect of bacterial exsudates was clearly separated from physical contact effect.

Development of Carbon- and Ceramic-Based Composites through Liquid Routes and Their Mechanical Properties

Carbon- and silicon carbide (SiC)-based materials, especially in the form of composites, have attracted more attention from reactor technologists than have other ceramics because they better fulfill the prime requirements of reactor materials, such as high-temperature stability and low susceptibility to irradiation and nonbrittle fracture. These composites are fabricated through different routes and may vary in their properties. Therefore, sufficient data need to be generated on the microstructure and mechanical properties of these composites. In the studies reported here, carbon- and SiC-based fibrous ceramic composites were prepared using a liquid-infiltration sol-gel technique with carbon fibers as reinforcement and hybrid sol and pitch as matrix precursors. To some compositions, SiC nanoparticles were added. The composites were heated to 1000°C and 1500°C. The sol-gel route results in an amorphous mixed oxycarbide, silica, and carbon matrix, which on heat treatment at 1500°C is converted to a semicrystalline SiC matrix composite. Scanning electron microscope examination of carbon fiber/carbon and carbon fiber/SiC composites showed good wetting of fibers by matrix resin, forming good bonding at the interface. The carbon fiber/SiC composites with SiC nanoparticles as additional reinforcement showed higher density as well as a 34% increase in flexural strength compared with those without nanoparticles. The addition of just 1 wt% of SiC nanoparticles decreased oxidation by 4 wt%.

Plasma-Induced Erosion on Ceramic Wall Structures in Hall-Effect Thrusters

A 60 wt% boron nitride (BN)–40 wt% silica () hot-pressed composite, denoted as M26, was used as the insulating chamber wall for a xenon plasma Hall-effect thruster operated for approximately 2000 h at power levels between 1.5 and 5 kW. The chamber wall showed a range of erosion microstructures. In the heavily eroded regions, striations in the surface topology were evident with surface protrusions in the generic shape of conical tips consisting of stratified BN and silica phases. Microcracking along the long axis of the BN basal plane was prevalent. Through a two-dimensional finite element model, the microcracking has been determined to occur because of the anisotropic thermal expansion of BN in the amorphous silica matrix. Exfoliation accompanied the microcracking in BN and resulted in the preferential loss of BN as compared with silica in these heavily eroded regions.

Nickel-based nanocrystals dispersed on SBA-16 gels: Synthesis and structural characterization

Porous monoliths of nanocomposites containing Ni (5wt.%) and FeNi (5wt.%) nanoparticles dispersed on an SBA-16 type matrix were prepared following a templated-gelation method based on the sol–gel process. The nanocomposites were characterized by energy dispersive X-ray spectroscopy, N2 physisorption at 77K, X-ray diffraction and transmission and scanning electron microscopy. In particular, N2 physisorption and transmission electron microscopy analysis show that the ordered mesoporous structure and the high surface area of all the samples are preserved after calcination in air at 500°C and also after reduction in H2 flux at 800°C, indicating a very high thermal stability of the samples. As a result of the effective dispersion of the nanophase within the porous texture, nanocomposites containing Ni nanocrystals with an average size of 6nm homogeneously dispersed within the pores of the amorphous silica matrix were obtained.

Chemical, Morphological and Electrical Properties of Porous Silicon Prepared by Photelectrochemical Etching

In this work, the nanocrystalline porous silicon (PS) films is prepared by photoelectrochemical etching of n-type silicon wafer with different currents density (20, 35 and 50 mA/cm 2 ) and etching time 15 min on the formation nano-sized pore array with a dimension of around few hundreds nanometric. The films were characterized by the measurement of FTIR spectroscopy and atomic force microscopy properties.Chemical fictionalization during the photoelectrochemical etching show on surface chemical composition of PS. The etching possesses inhomogeneous microstructures that contain a-Si clusters (Si3–Si–H) dispersed in amorphous silica matrix and (O-SiO, C-SiO). It is observed from the FTIR analyses that the Si dangling bonds of the as-prepared PS layer have large amount of Hydrogen to form weak (Si–H) bonds. The atomic force microscopy investigation shows the rough silicon surface; with increasing etching process (current density) porous structure nucleates which leads to an increase in the width (diameter) of surface pits. Consequently, the surface roughness also increases. The electrical properties of prepared PS; namely current density-voltage characteristics under dark, show that the pass current through the PS layer decreased by increasing the current density and etching time, due to increase the resistivity of PS layer. The PS layer shows a rectifying behaviour with different rectification ratio. C-V measurements demonstrate that the behaviour of the resulting junction is more like to Schottky junction. This study makes it clear that the charge carries depletion process occur in PS layer. Moreover, the charge carries decrease and width of depletion layer increase by increasing the current density. Keyword: porous silicon; nanostructure; etching; FTIIR; AFM; electrical properties.

Facile synthesis of nickel nanoparticles supported on carbon and silica matrix via a novel silica sol–gel process

In this work, we introduce a modified novel silica sol–gel process to synthesize hexagonal close-packed (hcp) and face-centered cubic (fcc) nickel (Ni) nanoparticles supported on amorphous carbon and silica matrix. The supporting of amorphous carbon and silica can prevent the Ni nanoparticles from aggregating and being oxided which would result in the loss of their magnetism and dispersibility. The phase structure of the Ni nanoparticles which were obtained from the gels pyrolyzed from 250 to 350 °C is hcp structure, whereas that of the Ni nanoparticles pyrolyzed at 750 °C is fcc structure. The grain sizes of the hcp Ni nanoparticles calcined at 250 °C range from 5 to 20 nm in diameter, and that of the fcc Ni nanoparticles calcined at 750 °C range in 7–35 nm. The studies of magnetic properties of the hcp and fcc Ni nanoparticles show that both have quite different magnetic behaviors.

Microwave absorption of ε-Fe2O3 precipitated from sputter deposited Fe–Si–O amorphous thin film by thermal annealing

Granular magnetic thin films were prepared by thermal annealing of rf-sputter-deposited Fe–Si–O amorphous films. The particle size of the precipitated Fe2O3 was controlled to obtain a pure ε-phase by adjusting the target chemical composition to an atomic ratio SiO2/Fe2O3=2 and annealing for 1 to 3h at 900°C. For a film annealed for 100min, an almost symmetrical ferromagnetic resonance signal was observed, with no evidence of residual ferric ions in the amorphous silica matrix.

Study on the formation of MCr2O4/SiO2 nanocomposites from hybrid gels PVA–TEOS–metal nitrates

Nanocomposites of MCr2O4/SiO2 type, for M=Zn, Mg, Ni, have been synthesized using a modified sol–gel method. In the first step, hybrid gels TEOS:PVA:H2O:M(NO3)2:Cr(NO3)3 have been prepared and dried at 80°C. These gels have been characterized by thermal analysis (TG–DTA) and FT-IR spectroscopy. Both technique have evidenced that around 110°C a redox reaction takes place between PVA and the mixture of metal nitrates with oxidation of poly(vinyl alcohol), PVA, to carboxylates that coordinate to M(II) and Cr(III) cations. Thus a homogenous mixture of carboxylates formed in the pores of silica gel. By thermal decomposition of these gels at 400°C the thermal decomposition of the carboxylates takes place leading to a homogenous mixture of oxides (MO and Cr2O3+x) that interacts during the calcinations at higher temperatures with formation of MCr2O4 embedded in silica matrix for M=Zn, Ni. For M=Mg the thermal decomposition of the corresponding carboxylates leads to an intermediary phase (MgCrO4) which further decomposes to MgCr2O4 at higher temperature. Thus Cr2O3 crystallizes well and is stabilised by the silica matrix, resulting in a lower reactivity. Due to this behaviour Cr2O3 is present as secondary crystalline phase in silica matrix beside MgCr2O4, as evidenced by XRD analysis. The obtained chromites nanoparticles with diameter up to 30nm at 1000°C, were homogenously distributed in the amorphous silica matrix, as evidenced by TEM and SEM microscopy.

Preparation of CuFe2O4/SiO2 nanocomposite starting from Cu(II)–Fe(III) carboxylates embedded in hybrid silica gels

Nanocomposites of the type 30 % CuFe2O4/70 % SiO2 were synthesized using the modified sol–gel method starting from tetraethylorthosilicate, metal nitrates (Fe(NO3)3·9H2O, Cu(NO3)2·3H2O) and the diol: 1,3-propane diol. The obtained hybrid gel, which contains within the pores, the metal nitrates and diol, was thermally treated at 140 °C, when the redox reaction between metal nitrates and 1,3-propane diol takes place forming Cu(II)–Fe(III) carboxylate compounds of malonate type. The thermal decomposition of the carboxylates within the gels pores, at ~300 °C, leads to simple or mixed metal oxides, uniformly distributed within the amorphous silica matrix. The spinel system CuFe2O4/SiO2 was obtained starting with 700 °C. The evolution of the spinel phase with the annealing temperature was investigated and resulted that at 1,000 °C, the matrix crystallizes into cristobalite and quartz. The formation of bulk CuFe2O4, starting from the same type of Cu(II)–Fe(III) carboxylate compounds was also investigated. A comparison between the thermal evolution of bulk CuFe2O4 and CuFe2O4/SiO2 starting from Cu(II)–Fe(III) carboxylate compounds was made. The magnetic behavior of the ferrite nanocrystallites depending on the annealing temperature was also investigated.

Gas-phase Synthesis of Silver Nanoparticles for Plasmonic Biosensors

ABSTRACTSilver (Ag) nanoparticles dispersed in an amorphous silica (SiO2) matrix or coated by a SiO2 layer were synthesized by flame spray pyrolysis (FSP). The coated nanoparticles were produced by using a modified enclosed FSP setup, in which the SiO2 precursor was injected through a ring above the FSP nozzle at various burner-ring-distances (BRDs), after the core Ag nanoparticles had been formed. The produced nanoparticles were characterized by XRD, BET, TEM and UV/vis analysis. The Ag particle size was possible to be controlled by tuning the FSP parameters. For the SiO2 coated nanoparticles, larger Ag core sizes were obtained for higher BRDs. All the produced nanoparticles exhibited the characteristic plasmon resonance frequency of Ag nanoparticles.

Synthesis of ordered mesoporous CoFe2O4-containing silica by self-assembly process

Magnetic CoFe2O4-containing silica with an ordered mesoporous structure was prepared by the self-assembly associated with triblock copolymer, tetraethyl orthosilicate, ferric nitrate and cobalt nitrate. Ammonia water was added to adjust the pH value for collecting the mixture, and then the products were obtained at various temperatures in air. The final products were investigated by transmission electron microscopy, scanning electron microscopy, X-ray diffraction, nitrogen adsorption–desorption isotherm, and vibrating sample magnetometer measurements. As a result, the as-prepared magnetically hybrid porous silica possesses ordered 2-D hexagonal (p6mm) mesoporosity with uniform pore-size distribution and high surface areas (up to 283m2/g at 1000°C). A pure CoFe2O4 with a high degree of crystallization was formed in the amorphous silica matrix at 1000°C. In addition, this self-assembly method can be applied to prepare other composites with highly ordered mesostructures. Such nanocomposites with hydrophilic and magnetic framework showed a good dispersibility in water and an easy separation procedure.

Ni0.5Zn0.5Fe2O4 nanoparticles dispersed in a SiO2 matrix synthesized by sol–gel processing

Abstract (Ni 0.5 Zn 0.5 Fe 2 O 4 )x/(SiO 2 )(100 − x) (x = 5, 20 and 50 wt.%) nanocomposites are synthesized by a sol–gel method using tetraethylorthosilicate (TEOS) and metallic nitrates as precursors, and by further annealing the powders for 1 h at 1273 K. X-ray diffraction (XRD), transmission electron microscopy (TEM), room temperature vibrating sample magnetometry (VSM) and SQUID measurements are employed for structural, morphological and magnetic sample characterization. For all the concentrations analyzed, the powder nanocomposites actually consist of spinel NiZn ferrite nanoparticles, dispersed in an amorphous silica matrix. TEM studies reveal different particle size distributions and particle morphologies for the three ferrite contents. The 20 wt.%-NiZn ferrite samples consist of nearly spherical nanoparticles, of about 8 nm, mainly superparamagnetic, well-dispersed in the amorphous silica matrix, while the 5 wt.%-NiZn ferrite samples exhibit a bimodal particle size distribution (5 and 30 nm) of single-domain nanoparticles embedded in the silica. In the 50 wt.%-NiZn ferrite samples, two particle families are observed: small round superparamagnetic nanoparticles of about 8 nm embedded in the amorphous silica matrix and large, non-spherical, ferrimagnetic ones, forming agglomerates outside the matrix. In all the synthesized samples, thickness fringes are observed inside some of the ferrite nanoparticles in dark field images. This contrast is explained using the theory of electron diffraction in a weak beam dark field (WBDF) condition and considering spherical ferrite nanoparticles. A large range of tailored magnetic properties varying the fraction, dispersion and mean size of the ferrimagnetic NiZn ferrite particles is obtained. Room temperature saturation magnetization values are found in the range 3.0–30.4 Am 2 /kg for the different concentration samples. Coercivity values, between 1.9 and 7.6 mT, are more than 50% higher than those measured in powders of pure stoichiometric NiZn ferrite nanoparticles and somewhat higher than those reported for similar NiZn ferrite/SiO 2 nanocomposites also synthesized by sol–gel processes. A correlation between the nanocomposite microstructure and the observed magnetic properties is established.

Influence of silane content on the optical properties of sol gel derived spin coated silica thin films

Sol gel technique in combination with spin coating method was utilized for the synthesis of silica thin films. Tetraethyl orthosilicate (TEOS) alkoxide silane precursor was used for one step synthesis of silica sol with 0.1M HCL as catalyst. Casting solution of silica sol was spin coated on glass substrate. The X-ray diffraction pattern revealed that the sample possesses amorphous silica matrix. Thin films were characterized by Fourier transform infrared spectroscopy (FTIR) and UV-Visible spectroscopy techniques to compare the effect of TEOS concentration. The optical properties of the silica thin films revealed that thin films have 90-95% transmittance in the visible range.

Luminescence Properties of Eu- and Mg-Codoped Sol-Gel SiO2 Glasses

A series of SiO2 nanostructures codoped with Eu3+; Mg2+ ions were obtained by a sol-gel method. The gels synthesized by the hydrolysis of Si(OC2H5)4, Eu(NO3)3·6H2O, and Mg(NO3)2 were heated in air at 600°C for 2 hours. Firstly, the total amount of Eu3+ ions was varied from 0 to 2.0 mol% to investigate the effect of self-damping, while in the second case, the Eu3+ ions were kept constant in the experiment at 0.5 mol% total doping and Mg2+ ions varied. The samples were characterized by X-ray diffraction, TEM, EDS, and UV lamp-excited luminescence spectroscopy. The Eu3+ ions were homogeneously dispersed in the silica and interacting with the small (1–5 nm) amorphous silica matrix. Strong red emissions located at 614 nm and 590 nm for doped and codoped SiO2 were observed from the UV light excitation at room temperature. The composition of around 1.25 mol% Eu3+ gave highest emission intensity. SiO2; Mg2+ ions portray strongly enhanced emissions due to energy transfer from Mg2+ to Eu3+, which is due to radiative recombination. An increase in luminescence intensity was observed as the Mg2+-to-Eu3+ ratio increased for the range investigated. The results show Eu3+ ion is located inside or at the surface of disordered SiO2 nanoparticles.

Preface: Phys. Status Solidi C 6/2012

AbstractThis proceedings issue is a selective collection of papers presented at Symposium B “Amorphous Nanostructured Materials” which was conducted during the E‐MRS Fall Meeting 2011, Warsaw, Poland. The symposium program covered various aspects of amorphous materials science and technology, including the preparation of materials and structures, the characterization and study of their properties (structural, optical, electrical, magnetic), the performance of devices. The objective of the symposium was to put together leading scientists working in the field and to update the research achievements in the area.Among the most substantial issues, discussions at the symposium highlighted the importance of structures and materials that combine amorphous and crystalline phases or that allow phase transitions between such phases. These structures have new physical properties and open the way to new potential applications in the fields of information and energy, in particular for information storage, light emission, and solar cells. Great emphasis was put on silicon‐based materials and structures, either from low temperature (amorphous, polymorphous, microcrystalline silicon) or high temperature processes (silicon nanoparticles and nanocrystals). Recent progress has been achieved in understanding the doping and defect properties of amorphous silicon, as well as the behavior of heterostructures comprising thin amorphous silicon films. Light emission properties of silicon nanoclusters and silicon‐based materials like rare‐earth implanted amorphous silicon dioxide and silicon oxicarbide layers were also underlined. A carrier multiplication effect in silicon nanocrystals embedded in an amorphous silicon oxide matrix was reported, implying the relaxation of photogenerated hot carriers not only at photon absorption sites but also through energy transfer into neighboring nanocrystals with creation of additional electron–hole pairs. Utilization of this effect should improve the efficiency of silicon‐based solar cells. Future trends in materials physics include the study of silicon–germanium nanocrystals and the use for hybrid silicon–organic electronics. In particular, silicon nanocrystals could be used in conjunction with organic semiconductors for hybrid bulk heterojunction solar cells. Studies of other nanostructured silicon‐based devices such as silicon heterojunction and silicon nanowires solar cells were also presented.Considerable attention was paid to the fabrication and properties of metallic nanostructures. In particular, a new method was reported allowing production of amorphous metal nanoparticles that, contrary to their crystalline counterparts, do not coagulate when approaching each other. This unusual property permitted fabrication of thin films consisting of closely packed but still individual nanoparticles. When made of magnetic materials, the characteristics of such films were shown to be determined by magnetic exchange interaction between the particles combined with particle self‐organization. As a result, the blocking temperature of the films was found to be close to room temperature, which is a property being important in magnetic storage application.Related to the above‐mentioned subjects, the issue content is organized as follows. First four articles are devoted to different aspects of light emission from silicon‐based materials (silicon oxicarbide, silicon and metal oxide clusters). The second group of three articles deals with correlation between structure and electrical properties of the materials based on amorphous silicon. Next, four articles consider technology and structure formation mechanisms of amorphous silicon. The following three articles touch upon the problem of silicon‐based solar cells. The last group of four articles deals with fabrication and properties of promising amorphous chalcogenides, metals, metal oxides, and carbon materials.All contributing authors are greatly acknowledged for their input to this issue.The symposium was sponsored by INCATTECH LLC (the company is located in St. Petersburg, Russia, www.incattech.com).

Tuning the properties of Ge-quantum dots superlattices in amorphous silica matrix through deposition conditions

In this work, we investigate the structural properties of Ge quantum dot lattices in amorphous silica matrix, prepared by low-temperature magnetron sputtering deposition of (Ge+SiO2)/SiO2 multilayers. The dependence of quantum dot shape, size, separation, and arrangement type on the Ge-rich (Ge + SiO2) layer thickness is studied. We show that the quantum dots are elongated along the growth direction, perpendicular to the multilayer surface. The size of the quantum dots and their separation along the growth direction can be tuned by changing the Ge-rich layer thickness. The average value of the quantum dots size along the lateral (in-plane) direction along with their lateral separation is not affected by the thickness of the Ge-rich layer. However, the thickness of the Ge-rich layer significantly affects the quantum dot ordering. In addition, we investigate the dependence of the multilayer average atomic composition and also the quantum dot crystalline quality on the deposition parameters.

New Synthesis and Magnetic Properties of NiFe2O4/SiO2 and Co0.5Zn0.5Fe2O4/SiO2 Nanocomposites Using Tetraglycolatosilane as Precursor

AbstractIn this work the new synthesis and magnetic properties of NiFe2O4/SiO2 and Co0.5Zn0.5Fe2O4/SiO2 nanocomposites using a water‐soluble silica precursor, tetraglycolatosilane (THEOS), by the sol‐gel method were reported. Nanocomposite were obtained by the thermal decomposition of the organic part at different annealing temperatures varying from 400 to 900 °C. Studies carried out using XRD, FT‐IR, TEM, STA (TG‐DTG‐DTA) and VSM techniques. XRD patterns show that NiFe2O4 and Co0.5Zn0.5Fe2O4 have been formed in an amorphous silica matrix at annealing temperatures above 600 and 400 °C, respectively. It is found that when the annealing temperature is up to 900 °C NiFe2O4/SiO2 and Co0.5Zn0.5Fe2O4/SiO2 samples show almost superparamagnetic behavior with a magnetization 4.66 emu/g and ferromagnetic behavior with a magnetization 10.11 emu/g, respectively. The magnetization and coercivity values of nanocomposites using THEOS were considerably less than previous reports using TEOS. THEOS as a silica matrix network provides an ideal nucleation environment to disperse ferrite nanoparticles and thus to confine them to aggregate and coarsen. By using THEOS over the currently used TEOS and TMOS, organic solvents are not needed due to the entire solubility of THEOS in water. Synthesized nanocomposites with adjustable particle sizes and controllable magnetic properties make the applicability of ferrites even more versatile.

Photoluminescence and structural properties of silicon nanostructures grown by layer-by-layer deposition

In this study, silicon nanostructures were synthesized by layer-by-layer (LBL) method using the radio-frequency plasma enhanced chemical vapor deposition (rf PECVD) technique. The influence of the substrate temperature on the morphological, structural and photoluminescence properties of these nanostructures were investigated using field emission scanning electron microscope (FESEM), high resolution transmission electron microscope (HRTEM), Micro-Raman scattering spectroscopy, X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and photoluminescence (PL) spectroscopy. The results revealed that the LBL deposition resulted in the formation of aggregates of nanocrystalline Si (nc-Si) grains with very small crystallites of a size of less than 3nm embedded in a mixed phase of hydrogenated amorphous silicon and amorphous silicon oxide matrix. The nc-Si grains produced wide PL in the range of 1.2–2.8eV at room temperature. The PL was seen to be strongly dependent on the presence of the silicon oxide phase in the grain boundary and the crystalline volume fraction of the nc-Si grains.

Silicon Filaments in Silicon Oxide for Next‐Generation Photovoltaics

Nanometer wide silicon filaments embedded in an amorphous silicon oxide matrix are grown at low temperatures over a large area. The optical and electrical properties of these mixed-phase nanomaterials can be tuned independently, allowing for advanced light management in high efficiency thin-film silicon solar cells and for band-gap tuning via quantum confinement in third-generation photovoltaics.