SiO2 Nanocomposite Thin Films Research Articles

Kinetics driving nanocomposite thin-film deposition in low-pressure misty plasma processes

Mist-assisted methods have recently attracted much attention for plasma deposition in high-quality (multi)functional thin films. However, very little is known on plasma interactions with misted colloidal solutions and their role in plasma process kinetics. Time-resolved optical diagnostics have been carried out to study the deposition of TiO2–SiO2 nanocomposite thin films in low-pressure oxygen-argon plasmas with organosilicon precursors and TiO2 suspensions. Each pulsed injection of the dispersion was followed by a pressure rise due to solvent evaporation. This caused a significant reduction in the electron temperature and density, which mitigated matrix precursor fragmentation and SiO2 deposition as TiO2 nanoparticles were supplied to the film. Comparing injections with and without nanoparticles, misty plasma effects were dominated by plasma droplets rather than plasma-nanoparticle interactions. Successive matrix-rich and nanoparticle-rich deposition steps were confirmed by in situ spectroscopic ellipsometry.

TiO2–SiO2 nanocomposite thin films deposited by direct liquid injection of colloidal solution in an O2/HMDSO low-pressure plasma

TiO2 nanoparticles (NPs), 3 nm in size, were injected inside a very-low-pressure O2 plasma reactor using a liquid injector and following an iterative injection sequence. Simultaneously, hexamethyldisiloxane (HMDSO) vapor precursor was added to create a SiO2 matrix and a TiO2–SiO2 nanocomposite (NC) thin film. Both the liquid injection and vapor precursor parameters were established to address the main challenges observed when creating NCs. In contrast to most aerosol-assisted plasma deposition processes, scanning/transmission electron microscopy (S/TEM) indicated isolated (i.e. non-agglomerated) NPs distributed in a rather uniform way in the matrix. The fraction of the TiO2 NPs inside the SiO2 matrix was estimated by SEM, spectroscopic ellipsometry (SE), and x-ray photoelectron spectroscopy. All techniques provided coherent values, with percentages between 12% and 19%. Despite the presence of TiO2 NPs, SE measurements confirmed that the plasma-deposited SiO2 matrix was dense with an optical quality similar to the one of thermal silica. Finally, the percentage of TiO2 NPs inside the SiO2 matrix and the effective refractive index of the NCs can be tuned through judicious control of the injection sequence.

Fabrication and optical properties of Au:SiO2 nanostructured thin films

We demonstrate synthesis and theoretical study of the optical properties of Au:SiO2 nanocomposite thin films. Localized surface plasmon resonance peak induced by Au NPs was clearly observed in optical spectra at wavelength range between 500 and 600 nm. Intensity and position of PL peak are demonstrated to depend on the Au NPs embedding depth.

CdS nanodroplets over silica microballs for efficient room-temperature LPG detection.

An efficient room-temperature sensor for liquified petroleum gas (LPG) is demonstrated by employing CdS:SiO2 nanocomposite thin films (CdS:SiO2 NCTFs) for the first time. CdS:SiO2 NCTFs exhibiting the morphology of CdS nanodroplets on micron-sized spherical balls of SiO2 were deposited using the pulsed laser deposition (PLD) method, followed by thermal annealing. The targets of chemically synthesized CdS nanoparticles and commercially procured SiO2 were used to deposit CdS:SiO2 NCTFs by swapping them at a frequency ratio of 2 : 8 laser pulses per second, which was selected to ensure nearly the same ratio of CdS to SiO2 in NCTFs and was confirmed by X-ray photoelectron spectroscopy. Sensor fabrication was carried out on bare CdS thin films and as-grown and annealed CdS:SiO2 NCTFs using an Ag paste over Pt interdigitated electrodes to measure the resistance of the films in air and in the presence of reducing gases, viz., LPG, H2, H2S, NO2 and CO2. The present sensor showed the highest response for LPG and the observed value was ∼71% for 1000 ppm at RT with the response time and recovery time of 91 s and 140 s, respectively. The response of the sensor was sustainable up to 75 °C and then decreased, which suggested its promising usage for low-temperature regions as well. A low detection limit of 20 ppm at RT for LPG was determined; however, a significant response was observed only at 50 ppm. The sensor retained ∼96% of its initial response even after 8 weeks and that too at 100 °C. The present LPG sensor is highly promising due to its high sensitivity, low detection limit, low response and recovery times, good reproducibility, RT operation and simple fabrication technique.

Target swapping in PLD: An efficient approach for CdS/SiO2 and CdS:Ag(1%)/SiO2 nanocomposite thin films with enhanced luminescent properties

A novel synthesis method for luminescent and by-products (like CdO) free CdS/SiO2 and CdS:Ag(1%)/SiO2 (i.e. 1%Ag doped CdS/SiO2) nanocomposite thin films at room temperature by pulsed laser deposition is reported. Targets of CdS, CdS:Ag(1%) and SiO2 are used to deposit CdS/SiO2 and CdS:Ag(1%)/SiO2 nanocomposite thin films by swapping them at a frequency ratio of 2:8 laser pulses/sec. X-ray photoelectron spectroscopy analysis ensures the ratio of CdS to SiO2 in nanocomposite as 21:79 which is nearly same as the ratio of incident pulses/sec (i.e. 2:8) on the two targets. Transmission electron micrographs visualize the formation of CdS/ CdS:Ag(1%) nanocrystals in nanocomposite systems after annealing at 500 °C. Highly intense and broad red emission is achieved from CdS/SiO2 and CdS:Ag(1%)/SiO2 nanocomposites. The efficiencies of emission from pristine CdS:SiO2 and CdS:Ag(1%)/SiO2 nanocomposites are found to be enhanced by approximately two times as compared to sole nanocrystalline CdS and CdS:Ag(1%) thin films respectively and further enhanced upto 7 times on annealing the nanocomposite systems at 500 °C.

PH dependent studies of chemical bath deposition grown ZnO-SiO2 core-shell thin films

ZnO-SiO2 core-shell thin films were synthesized using chemical-bath deposition at different pH. Optical studies were done to optimize the thin films to find suitable parameters for solar cell buffer layers. These studies were done by measuring the transmission at 500 nm, which is the peak of the solar spectrum. All the parameters were seen to be highly pH dependent. The transmittance for a sample synthesized with a pH of 10.8 reached 85%. The transmittance was found not to depend on the bandgap values, but it was found possibly to depend on the fewer defect states created at a particular pH, as shown by Urbach energy and scanning electron microscopy (SEM) surface structure. An appreciable transmittance was observed in the blue region of the spectrum which had been missing until now in commercial CdS-based buffer layers. The Fourier-transform infrared and the energy dispersive X-ray spectra confirmed that the films were composed of only ZnO and silica only: no impurities were found. The urbach energy values and the SEM image of sample S3 clearly indicate the creation of fewer of defects, leading to higher crystallintiy and higher transmittance. Therefore, this shortcoming can be resolved by the substituted buffer layer of ZnO:SiO2 nano-composite thin film, which can enhance the blue response of the photovoltaic cells.

Sol–gel preparation and corrosion properties of Zn–SiO2 nanocomposite thin film

In this study, a novel nanocomposite thin film of Zn–SiO2 is considered. The thin film is a viable alternative for higher abrasion-resistant coatings. DLS technique revealed that the nanoparticle size is to be below 10 nm, and FE-SEM showed particle size to be below 17 nm in the obtained coating. The coating was found to be highly adhesive with an amorphous structure and hardness value above 1000HV. Corrosion resistance studies using linear polarization technique revealed that this unique nanocomposite has a lower corrosion rate than hot-dip galvanized steel at higher positive potentials. A conclusive mechanism for corrosion and erosion improvement has been proposed.

Sol-gel synthesis of xTiO2(100 − x)SiO2 nanocomposite thin films: Structure, optical and antireflection properties

Sol-gel xTiO2(100−x)SiO2 nanocomposite thin films with x=0, 25, 50, 75 and 100mol % were dip-coated on glass and silicon substrates. The influence of the composition on structure, morphology and optical properties was studied by X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, scanning electronic microscopy, monochromatic ellipsometry at λ=632.8nm and ultraviolet–visible absorbance spectroscopy. The optical properties were discussed on the basis of the microstructure. After annealing at 500°C, results showed high pure materials, homogenous crack-free surfaces with good adherence and high optical qualities. The 100% TiO2 crystallizes in the anatase phase and exhibits nanograins of 6 to 10nm in size. However, all the other compositions are amorphous with comparable grains around 4nm in size. The averaged transmittance decreases with increasing the TiO2 content but remains higher than 90%. Whatever the composition, the coating thickness increases linearly as the withdrawal speed increases from 10 to 54mm/minute. The relationship between refractive index and composition was analyzed by fitting the experimental data to different theoretical models for the refractive index of mixed films. Results showed that depending on the withdrawal speed, the data can properly fit either the Drude or the linear models. Thus, the film thickness can be adjusted by the control of the withdrawal speed. However, the control of the composition allows easily the tuning of the refractive index from 1.48 to 2.18 at λ=632.8nm to achieve optimum anti-reflection characteristics. Different anti-reflection designs of both single and double layers were experimentally examined. Gains (assigned to the reduction of reflection losses) up to 54 and 63% were predicted with 75% TiO2 single-coating and SiO2/TiO2 double-coatings respectively.

Low-temperature synthesis of oriented CoPtCu–MgO and CoFePt–Ag–SiO<sub>2</sub> nanocomposite thin films by rf-magnetron sputtering

Nanocomposite thin films composed of oriented Co50Pt44Cu6 nanoparticles embedded in a MgO matrix has been synthesized by rf-magnetron co-sputtering onto NaCl(001) substrates kept at 620 K. As the sputtering power increases, (001) orientation is improved and atomic ordering is also promoted. However, superlattice reflections are quite weak and the ordered region is limited in local area of the nanoparticles, indicating low degree of order. Electron diffraction and elemental mapping revealed that additive Cu is alloyed with CoPt. We have also fabricated (Co26Fe20)Pt44–Ag10–SiO2 nanocomposite thin films at 675 K for comparison. Atomic ordering is promoted by Fe and Ag addition as well as higher substrate temperature; however, it was found that ternary element (Cu, Ag, Fe) addition into CoPt alloy is not so effective to promote atomic ordering. Origin of the slow ordering kinetics is discussed using thermodynamical parameters.

Structural, optical and photocatalytic properties of NiO–SiO2 nanocomposites prepared by sol–gel technique

NiO–SiO2 nanocomposite thin films were prepared by sol–gel technique. The formed films gels were calcined at 200, 400, 600, 800 and 1100°C for 4h leading to NiO–SiO2 nanocomposites. For these films, the X-ray diffraction, the Fourier transform infrared absorption and the field emission scanning electron microscopy were investigated. Our results show that the NiO(200) diffraction peak dominates in the preset work. NiO phase appeared in the XRD patterns for all samples. The newly prepared photocatalysts films have been evaluated by the determination of their photonic efficiencies for degradation of methylene. The results reveal that the photonic efficiency increases with increasing calcination temperature up to 600°C with the maximum photonic efficiency being 0.62%. In addition, porous structures were observed and improve the sensitivity of these nanocomposites for gas sensing.

Nonvolatile floating gate memory characteristics of Sb2Te–SiO2 nanocomposite thin films

Nonvolatile floating gate memory (NFGM) device composed of Sb2Te nanocrystals (NCs) as the charge-storage traps embedded in SiO2 matrix was prepared by the target-attachment sputtering method at various nitrogen (N2) incorporation conditions. Via post annealing at 450°C in ambient air, the sample prepared at the condition N2/Ar=0.1 exhibited a maximum memory window (ΔVFB) shift=4.4V and charge density=4.2×1012cm−2 under ±7V gate voltage sweep. N2 incorporation not only reduced the Sb2Te NC size to about 5nm, but also suppressed the oxygen defects and antimony oxides in the sample. Feasibility of the Sb2Te chalcogenide NCs to NFGM fabrication with the simplified process and relatively low annealing temperature is demonstrated.

A characterization on emission property of In2O3–SiO2 nanocomposite thin films

Nanocomposite thin films containing finely dispersed, crystalline In2O3 nanoparticles embedded in SiO2 matrix were fabricated by target-attachment sputtering method. Transmission electron microscopy observed single crystalline In2O3 nanoparticles uniformly embedded in SiO2 matrix of the samples with In2O3 content less than about 60vol.%. Photoluminescence spectra of the In2O3–SiO2 nanocomposite samples were found to comprise of the blue, green and red emissions. Analytical results indicated that the red and green emissions are correlated to the transitions from conduction band (CB) edge to the Ini••• and V‴In defect levels, respectively, while the blue emission is originated from the transition from CB edge to VO•• level or from VO• level to the valence band edge.

A comprehensive study of structural and magnetic properties of sputter deposited nickel–silica thin films

► Ni nanoparticles embedded in silica matrix have been synthesized by DC/RF sputtering. ► Magnetic properties of nickel nanoparticles have been found size dependent strongly. ► Ni nanoparticles are found to be superparamagnetic ≤6 nm. ► Coercivity decreases with increase in particle size and concentration. The present work reports the formation of Ni nanoparticles inside the SiO 2 matrix and deals with the influence of Ni concentration on structural and magnetic properties of Ni–SiO 2 nanocomposite thin films. The films with varying Ni concentration (20–55 at% measured by Rutherford back scattering spectroscopy) were deposited using DC/RF magnetron co-sputtering. TEM and XRD analysis reveal the formation of FCC Ni nanoparticles in all the samples. The particle size varies from 3 to 10 nm as a function of Ni concentration. The surface roughness of the films is also found to increase with increase in nickel concentration. Magnetic measurements show that the Ni nanoparticles behave as superparamagnets when their size is ≤6 nm, in spite of their large volume fractions. The results show that the magnetic properties of the nanoparticles can be controlled by their size and Ni concentration in the samples.

Influence of sol composition on natural superhydrophilicity of sol gel–derived TiO2–SiO2 nanocomposite thin films

TiO2–SiO2 nanocomposite thin films have been deposited via a sol-gel route. These films exhibit a natural and persistent superhydrophilicity, which allows considering new applications for easy to clean surfaces. Influence of the sol composition on the composite film morphology and thickness has been studied by atomic force microscopy, scanning electron microscopy, transmission electron microscopy, and ellipsometry measurements. The wettability of nanocomposite films has been studied and discussed in relation to morphology and thickness features. It is concluded that, while such features can influence the wettability of nanocomposite films, intrinsic effects arising from their TiO2–SiO2 composition probably play a predominant role.

Optical and photocatalytic properties of TiO2/Ag–SiO2 nanocomposite thin films

The TiO2/Agx–(SiO2)1−x nanocomposite thin films with a bilayer structure were prepared via a chemical solution approach combined with a sol–gel spin-coating processing. The TiO2/Ag0.15–(SiO2)0.85 thin film is about 200nm in thickness including a top anatase–TiO2 layer approximately 60nm, while the approximately spherical Ag nanoparticles with 10–30nm in diameter were embedded uniformly in the amorphous SiO2 matrix of the sublayer. The UV–Vis absorption peaks appeared in the wavelength of 420nm due to the surface plasmon resonance (SPR) of Ag particles. The SPR peaks manifest a red-shift with increasing Ag content from 6 to 15at.%, whereas blue-shift from 15 to 20at.%. The photocatalytic activity enhanced by increasing Ag content up to 15at.% but reduced by further increasing Ag content. It is found that the optimal Ag loading for achieving the highest photocatalytic activity is 15at.%.

Characterization of AgInSbTe-SiO2 Nanocomposite Thin Film for Hydrogen Gas Sensor Applications

ABSTRACTHydrogen (H2) sensing property of AgInSbTe (AIST)-SiO2 nanocomposite thin film prepared by target-attachment sputtering method was investigated in this work. The sample subjected to a 400°C-annealing for 90 sec exhibits a significant sensitivity (58.9 %) and short response time (75 sec) upon the exposure to an ambient containing 200 ppm H2 at 75°C. The gas sensing capability is ascribed to the presence of antimony oxides, e.g., Sb2O3 and Sb2O5, in nanocomposite layer which provide the charge carriers for sensing reactions. Moreover, the high specific-surface-area (SSA) feature of AIST nanocrystals in nanocomoposite layer provided numerous sites for reduction/oxidation reactions and thus a good H2 gas sensing property can be achieved.

Characteristics of AgInSbTe–SiO2 nanocomposite thin film applied to nonvolatile floating gate memory devices

Nanocomposite thin films containing AgInSbTe (AIST) particles embedded in anSiO2 matrix was prepared by sputtering deposition and its feasibility for nonvolatilefloating gate memory (NFGM) was investigated. The sample subjected to a400 °C annealing exhibited a distinct hysteresis memory window(ΔVFB) shift = 6.6 V andcharge density = 5.2 × 1012 cm − 2 after ± 8 V gate voltage sweep. Electrical measurement revealed the current transport is via the Schottkyemission in low applied field and the space-charge-limited conduction mechanism in high appliedfield in the samples, regardless of their thermal history. Transmission electron microscopy andx-ray photoelectron spectroscopy indicated that the metallicSb2Te nanocrystals (NCs) with diameters about 5–7 nm dispersed in a nanocomposite layer may serve as thediscrete charge-storage traps for nonvolatile memory. Analytical results illustrate the utilization of anAIST–SiO2 nanocomposite layer as the core structure of NFGM devices is able to simplify the devicestructure and fabrication process.

Phase Transition Kinetics and Recording Characteristics of Nanocomposite Layers Prepared by Sputtering Process Utilizing AgInSbTe–SiO2 Composite Target

AgInSbTe (AIST)–SiO2 nanocomposite thin films were successfully prepared by sputtering deposition utilizing an AIST–SiO2 composite target and their phase-transition behaviors were investigated. Transmission electron microscopy (TEM) revealed that the as-deposited composite layer contained nano-scale quaternary alloy particles about 5 nm in size randomly embedded in the SiO2 matrix. In situ reflectivity–temperature measurements showed that the AIST–SiO2 nanocomposite and pristine AIST layers exhibit similar abrupt reflectivity changes at about 200 °C. However, the presence of the SiO2 phase hindered particle growth in the nanocomposite layers which, in turn, caused a mild increase in the phase-transition temperatures. Johnson–Mehl–Avrami (JMA) analysis indicated that, regardless of the film thickness, the amorphous-to-crystalline transition in nanocomposite layers proceeds in a bulk-like manner. Dynamic tests revealed that modulations higher than 0.8, 0.6, and 0.5 were achieved when 11T, 4T, and 3T signals, respectively were, written in the one-layer AIST–SiO2 disk sample. The unique phase transition behavior of nanocomposite layers and signal property analysis of disk samples demonstrated that a nanocomposite layer can be a new alternative for write-once optical data storage.

A Pyrrole-Containing Surfactant as a Tecton for Nanocomposite SiO2 Films

A surfactant featuring a polymerizable pyrrole head group (dodecyl-dimethyl-(2-pyrrol-1-yl-ethyl)-ammonium bromide, DDPABr) was synthesized. The thermotropic behavior of the surfactant was investigated by differential scanning calorimetry (DSC) and X-ray scattering techniques, with small-angle X-ray scattering (SAXS) analysis revealing a highly ordered lamellar bilayer structure. After full characterization, DDPABr was used in the preparation of mesostructured SiO2 nanocomposite thin films via evaporation-induced self-assembly (EISA). Resulting thin SiO2-DDPABr films were studied by 1D and 2D small-angle X-ray scattering (SAXS) techniques, indicating a lamellar nanocomposite structure. Suitable theoretical SAXS models were applied to fit the experimental 1D SAXS data. The surfactant could be chemically polymerized within the lamellar domains.

Synthesis and characterization of sol-gel derived Mn2+ doped In2S3 nanocrystallites embedded in a silica matrix

Mn2+ doped In2S3–SiO2 nanocomposite thin films were synthesized by sol-gel technique. The films were annealed in air at different temperatures (473–623 K) and characterized by optical, microstructural and electron spin resonance (ESR) study. Optical transmittance study revealed the manifestation of quantum size effect while ESR indicated the presence of manganese in indium sulphide as dispersed dopant rather than manganese cluster.