Silica Thin Films Research Articles

Optimization of dielectric films with dual ion beam sputtering deposition for high reflectivity mirrors

Abstract Dielectric thin films deposited by Ion beam sputtering deposition technique have superior properties of good adhesion and customized optical properties suits to many optical filters for electro-optical sensors. In the present work Tantalum Pentoxide (Tantala) and Silicon Dioxide (Silica) thin films are fabricated with dual ion beam sputtering deposition process. The process parameters are optimized to achieve better surface quality and optical constants. The effect of the assist ion beam on the film properties is evaluated. Multi-layer dielectric mirrors realized with 1000 ppm loss on optimization of single-layer Silica and Tantala films, which will be suitable for linear and Ring Laser Resonators. The films are characterized by ellipsometer, non-contact optical profiler, spectrophotometer, and cavity ring-down loss meter. The multi-layer mirrors were subjected to vacuum annealing and the effect of annealing on film reflectivity is evaluated. The work emphasizes the process requirements of Ion Beam Sputtering to realize high reflectivity and low loss mirrors of Tantala and Silica films from Ta2O5 and SiO2 target materials. It gives an insight into the process deficiencies in matching the theoretical design of multi-layer mirrors from the practical aspects of coatings.

Mass production technology and pore control of flexible mesoporous silica thin film

Mass production technology and pore control of flexible mesoporous silica thin film

Vertically oriented mesoporous silica film modified fluorine-doped tin oxide electrode for enhanced electrochemiluminescence detection of lidocaine in serum.

Owing to a nanochannel-based enrichment effect and anti-fouling ability, highly ordered and vertically oriented mesoporous silica thin film (VMSF) modified electrodes have demonstrated their great potential in direct and highly sensitive analysis of complex samples. In this work, a VMSF modified fluorine-doped tin oxide (FTO) electrode (VMSF/FTO) is fabricated for enhanced electrochemiluminescence (ECL) analysis of lidocaine in serum. VMSF with good integrity and mechanical stability can be rapidly and conveniently grown on FTO in a few seconds at room temperature using an electrochemically assisted self-assembly (EASA) method. Due to the strong electrostatic attraction between the cationic ECL probe and negatively charged nanochannel, the VMSF/FTO electrode shows significant enrichment of tris(2,2-bipyridine) ruthenium(ii) (Ru(bpy)32+), leading to ∼10 times enhancement of its ECL signal in comparison to the bare FTO electrode. Lidocaine, an anesthetic and antiarrhythmic drug, can act as the co-reactant of Ru(bpy)32+ and promote its ECL signal. Sensitive ECL detection of lidocaine is achieved by the sensor in a wide linear range from 10 nM to 50 μM with a low limit-of-detection (LOD) of 8 nM. Combined with the antifouling ability of VMSF, the VMSF/FTO electrode also realizes the accurate and rapid analysis of lidocaine in real serum samples.

Mesoporous silica thin films incorporated chitosan mixed matrix nanofiltration membranes for textile wastewater treatment

AbstractThe demand of nanofiltration (NF) membranes for practical and cost‐effective environmental treatment is exploding. Mixed matrix membranes (MMMs) have attracted tremendous interest on account of combining the benefits of polymer and inorganic fillers. In this study, mesoporous silica thin films with perpendicular nanochannels (SBA‐15(⊥)) incorporated in chitosan (CS) were fabricated for dye wastewater purification. Functional groups, such as amino or epoxy groups were introduced into SBA‐15(⊥) (SBA‐15(⊥)‐NH2, SBA‐15(⊥)‐Epo) for forming covalent bonds with chitosan matrix to improve their compatibility. The excellent performance in dye/salt fractionation in aqueous solution was demonstrated by SBA‐15(⊥)‐Epo/CS MMMs, which realized a cut off of 585 g/mol, 99.9% rejection of Congo red, while maintaining 85% permeation of NaCl. In addition, the separation mechanism of the resulting membrane was explored. The efficient NF performance of SBA‐15(⊥)‐Epo/CS membrane was attributed to its better compatibility between SBA‐15(⊥)‐Epo and chitosan matrix by virtue of the formation of covalent bonds thus to ensure the high dye rejection, and the vertically oriented nanochannels arrangement facilitated the molecule transportation. This work will inspire feasible synthesis of a new generation of MMMs membranes for dye wastewater purification.

Atomic and Electronic Structure of SiOx Films Obtained with Hydrogen Electron Cyclotron Resonance Plasma

The silicon oxide thin films obtained by thermal SiO2 treatment in hydrogen electron cyclotron resonance plasma at various exposure times are investigated. Using X-ray photoelectron spectroscopy, we have established that such treatment leads to a significant oxygen depletion of thermal SiO2, the more so the longer the treatment time. The atomic structure of the SiOx < 2 films obtained in this way is described by the random bonding model. The presence of oxygen vacancies in the plasma-treated films is confirmed by comparing the experimental valence band photoelectron spectra and those calculated from first principles, which allows the parameter x to be estimated. We show that thermal silicon oxide films treated in hydrogen plasma can be successfully used as a storage medium for a nonvolatile resistive memory cell.

Electrochemically Assisted Deposition of Nanoporous Silica Membranes on Gold Electrodes: Effect of 3‐Mercaptopropyl(trimethoxysilane) “Molecular Glue” on Film Formation, Permeability and Metal Underpotential Deposition

AbstractGold electrodes have been covered with vertically aligned mesoporous silica thin films by electro‐assisted self‐assembly. To ensure uniform surface coverage and good adhesion of the membrane to the gold surface, it was necessary to use a (3‐mercaptopropyl)trimethoxysilane (MPTMS) reagent to act as a “molecular glue” thanks to its thiol functionality, which is able to bind to the gold substrate and to its alkoxysilane moieties enabling condensation with the silica material. The MPTMS layer had, however, a significant effect on film permeability to redox species [Ru(NH3)63+ and ferrocenedimethanol (Fc(MeOH)2)]. MPTMS adsorption should be long enough to ensure proper adhesion of the film but not too long so as to avoid surface blocking or film defects; an optimal time window of 60–600 s soaking in 0.1 mM MPTMS in ethanol was evidenced. In addition, Cu underpotential deposition (UPD) experiments revealed that the silica membrane significantly affected the UPD process, suggesting some barrier effect of the porous membrane, but the interface Au/MPTMS/silica is not sharp and allowed metal UPD between the gold substrate and the silica thin film.

Aggregate-Free Deposition of Highly Organized Nanocomposite Silica Thin Films on Conductive Substrates By Electrochemically Induced Templated Sol-Gel Synthesis

The synthesis of ordered nanocomposite or nanoporous silica thin films by template-assisted sol-gel processes offers interesting applications in various fields including catalysis, sensors, membranes and energy. The electrochemically assisted self-assembly method allows the growth of highly ordered vertically aligned nanoporous silica thin films on conductive substrates. This orientation, optimized for high mass-transport capabilities, is difficult to obtain by classical approaches. The method involves submerging the conductive substrate in a pre-hydrolyzed precursor liquid followed by the application of a cathodic potential, thereby causing the electrogeneration of hydroxide ions. The pH increase in the diffusion layer near the electrode surface catalyzes the sol-gel formation and the result is a silica thin film that grows on the conductive substrate. The addition of cetyltrimethylammonium bromide (CTAB) micelle templates leads to the formation of a highly ordered nanostructure.A fundamental limitation of the method as reported in the literature is that the maximum layer thickness which can be obtained is rather limited due to the formation of aggregate by-products. In our contribution we show that diffusion layer thickness control is essential to obtain aggregate-free layers. Silica formation is catalyzed by OH- formed in the electrode’s diffusion layer, which quickly grows up to hundreds of microns under stationary conditions, thereby leading to composite thin films as well as precipitation of aggregates. By using a rotating disc electrode, the hydrodynamic layer is controlled, enabling aggregate-free film growth over a wide thickness range. Additionally, thin film coatings on high aspect ratio micropillar structures were demonstrated. Parameters such as precursor age, deposition temperature and deposition current were systematically investigated and the deposits were characterized using SEM, ellipsometry, TEM, FT-IR and an electrochemical redox probe. Using these techniques, we demonstrated the controlled growth of aggregate-free, uniform and nanostructured thin films with high mass-transport capabilities and thicknesses of 20 nm up to 15 µm, thereby significantly expanding the range of 50-150 nm as reported in literature. These results are explained using a single hydrodynamic layer model. Figure 1

Growing vertical aligned mesoporous silica thin film on nanoporous substrate for enhanced degradation, drug delivery and bioactivity

Mesoporous silica thin film has been widely used in various fields, particularly the medical implant coating for drug delivery. However, some drawbacks remain with the films produced by traditional method (evaporation-induced self-assembly, EISA), such as the poor permeability caused by their horizontal aligned mesochannels. In this study, the vertical aligned mesoporous silica thin film (VMSTF) is uniformly grown alongside the walls of titania nanotubes array via a biphase stratification growth method, resulting in a hierarchical two-layered nanotubular structure. Due to the exposure of opened mesopores, VMSTF exhibits more appealing performances, including rapid degradation, efficient small-molecular drug (dexamethasone) loading and release, enhanced early adhesion and osteogenic differentiation of MC3T3-E1 cells. This is the first time successfully depositing VMSTF on nanoporous substrate and our findings suggest that the VMSTF may be a promising candidate for bone implant surface coating to obtain bioactive performances.

Interface analysis of ultrathin SiO2 layers between c‐Si substrates and phosphorus‐doped poly‐Si by theoretical surface potential analysis using the injection‐dependent lifetime

AbstractPassivated contact structures are often representative of tunnel oxide passivated contact (TOPCon) and polycrystalline silicon on oxide (POLO) solar cells. These passivated contact technologies in silicon solar cells have experienced great strides in efficiency. However, characteristics analysis of poly‐Si/SiO2 applied to TOPCon and POLO solar cells as a carrier‐selective and passivated contact is still challenging because the silicon oxide film is very thin (&lt;1.5 nm), poly‐Si and silicon oxide properties change during thermal treatment for passivation effects, and dopant diffusion from poly‐Si layer to the silicon wafer occurs. In this study, the interfacial analysis was performed by applying an algorithm based on the extended Shockley–Read–Hall (SRH) theory to the P‐doped poly‐Si/SiO2/c‐Si structure. Quantitative parameters of the P‐doped poly‐Si/SiO2/c‐Si interface were extracted by fitting the measured and simulated lifetime curves with algorithms, such as Dit (interface trap density) and Qf (fixed charge), from which we were able to elucidate the passivation effect of the interface. The interface analysis method using this algorithm is meaningful in that it can quantify the passivation characteristics of TOPCon with very thin silicon oxide film. The interface characteristics were also analyzed using the injection‐dependent lifetime after thermal treatment of P‐doped poly‐Si/SiO2/c‐Si samples for passivation effect. After the 850°C thermal treatment, the following best passivation effects were verified, namely, ψs = 0.248 eV, Dit = 1.0 × 1011 cm−2·eV−1, Qf = 2.4 × 1012 cm−2, and J02 = 370 pA·cm−2. Through the analysis model using carrier lifetime theory, we investigated quantitatively the passivation properties of P‐doped poly‐Si/SiO2/c‐Si.

Reflectance of Silicon Photomultipliers at Vacuum Ultraviolet Wavelengths

Characterization of the vacuum ultraviolet (VUV) reflectance of silicon photomultipliers (SiPMs) is important for large-scale SiPM-based photodetector systems. We report the angular dependence of the specular reflectance in a vacuum of SiPMs manufactured by Fondazionc Bruno Kessler (FBK) and Hamamatsu Photonics K.K. (HPK) over wavelengths ranging from 120 nm to 280 nm. Refractive index and extinction coefficient of the thin silicon-dioxide film deposited on the surface of the FBK SiPMs are derived from reflectance data of a FBK silicon wafer with the same deposited oxide film as SiPMs. The diffuse reflectance of SiPMs is also measured at 193 nm. We use the VUV spectral dependence of the optical constants to predict the reflectance of the FBK silicon wafer and FBK SiPMs in liquid xenon.

Structural, thermal and surface properties of sticky hydrophobic silica films: Effect of hydrophilic and hydrophobic precursor compositions

The synthesis and study of silica thin films’ adhesive properties as a function of dimethyldimethoxysilane: tetraethoxysilane (DMDMS: TEOS (DT)) molar ratio and calcination temperature and its relationship with the silica polymer shape have been conducted. DT molar ratio was very influential on the silica thin film’s hydrophobic nature coated on the glass surface and indicated that the water droplets stuck to the silica-coated glass surface, not rolling down. The sticky property mainly originated from the non-uniformity of functional group composition and material surface roughness. The highest hydrophobic properties were obtained from the balanced composition of the DT molar ratio.

Cathodoluminescence Spectroscopic Stress Analysis for Silicon Oxide Film and Its Damage Evaluation.

We describe the stress analysis of silicon oxide (SiO2) thin film using cathodoluminescence (CL) spectroscopy and discuss its availability in this paper. To directly measure the CL spectra of the film under uniaxial tensile stresses, specially developed uniaxial tensile test equipment is used in a scanning electron microscope (SEM) equipped with a CL system. As tensile stress increases, the peak position and intensity proportionally increase. This indicates that CL spectroscopy is available as a stress measurement tool for SiO2 film. However, the electron beam (EB) irradiation time influences the intensity and full width at half maximum (FWHM), which implies that some damage originating from EB irradiation accumulates in the film. The analyses using Raman spectroscopy and transmission electron microscopy (TEM) demonstrate that EB irradiation for stress measurement with CL induces the formation of silicon (Si) nanocrystals into SiO2 film, indicating that CL stress analysis of the film is not nondestructive, but destructive inspection.

Determination of Thermal Conductivities for Thin-Film Materials in CMOS MEMS Process

The determination of thermal conductivities for complementary metal-oxide-semiconductor (CMOS) thin-film materials is very important as the operation and failure of integrated circuits (ICs) and CMOS microelectromechanical systems (MEMS) devices are most likely limited by thermal issues, that is, heat transfer. In this article, we present four micro thermal conductivity measurement (μTCM) devices for silicon oxide, polysilicon, and aluminum thin films using CMOS MEMS technology. To determine the thermal conductivities of those thin-film materials from the μTCM devices, a linear thermal resistance model was proposed and validated by the computational fluid dynamics (CFD) study, which showed an error of less than 5.5%. The thermal conductivities of thin-film materials were then measured over a temperature range of 210-362 K, while the measured results for silicon oxide, polysilicon, and aluminum at room temperature were 1.32, 21.22, and 70.2 W/mK, respectively. Those measured thermal conductivities were significantly smaller than the available bulk values. The discrepancies between the thin film and bulk materials are consistent with the reported data and trends, which reveals the importance of determining the thermal conductivities for thin-film materials in the CMOS MEMS process.

Passivation of n- and p-Type Silicon Surfaces With Spray-Coated Sol-Gel Silicon Oxide Thin Film

Thermally grown SiO2 is widely used for silicon surface passivation in solar cells and other applications due to excellent interfacial properties. SiO2 films with thickness in the range of 17 nm deposited by industrially viable spray-coating technique on both n- and p-type silicon are reported. Low values of interface state density of ${1.4}\times {10}^{{10}}$ cm $^{\boldsymbol -{2}}$ eV $^{\boldsymbol -{1}}$ on n-type and ${2.0}\times {10}^{{10}}$ cm $^{\boldsymbol -{2}}$ eV $^{\boldsymbol -{1}}$ on p-type were achieved. Fixed oxide charges in the range of 7.1– ${9.4}\times {10} ^{{11}}$ cm $^{\boldsymbol -{2}}$ and 3.9– ${6.5}\times {10} ^{{11}}$ cm $^{\boldsymbol -{2}}$ on n- and p-type, respectively, are obtained. Excellent passivation results in the effective surface recombination velocity of 0.97 cms $^{\boldsymbol -{1}}$ and 8.07 cms $^{\boldsymbol -{1}}$ at minority carrier concentration of $10^{{15}}$ cm $^{\boldsymbol -{3}}$ on n- and p-type Czochralski silicon, respectively, without the use of capping layer. SiO2 film exhibits dielectric breakdown field strength of 4.3 MVcm $^{\boldsymbol -{1}}$ and 5.6 MVcm $^{\boldsymbol -{1}}$ and leakage current density of ${2.2}\times 10 ^{\boldsymbol -{8}}$ Acm $^{\boldsymbol -{2}}$ and ${1.1}\times {10} ^{\boldsymbol -{8}}$ Acm $^{\boldsymbol -{2}}$ at 1 MVcm $^{\boldsymbol -{1}}$ on n- and p-type silicon, respectively. These values are superior to sol-gel-based SiO2 films reported previously and are comparable to or better than those reported for other methods for the growth or deposition of SiO2 on silicon. Amorphous nature of the film is validated by high-resolution transmission electron microscopy (TEM). The X-ray photoelectron spectroscopy (XPS) analysis shows nearly stoichiometric SiO x film.

Optical Properties of the SiOx (x &lt; 2) Thin Films Obtained by Hydrogen Plasma Processing of Thermal Silicon Dioxide

The optical properties and composition of thermal silicon oxide thin films processed in a hydrogen electron cyclotron resonance plasma have been studied by ellipsometry, quantum-chemical modeling, and photoluminescence spectroscopy. It has been found that the plasma processing of the films leads to their oxygen depletion and the formation of nonstoichiometric oxide SiOx < 2. The parameter x of the obtained SiOx films has been determined by comparing the experimental spectral dependence of the refractive index with the dependence obtained theoretically using the ab initio calculation. It is shown that an increase in the time of processing of thermal dioxide SiO2 in a hydrogen plasma leads to an increase in the refractive index of the film, as well as in the degree of its oxygen depletion. The dependence of the parameter x of the investigated films on the hydrogen plasma processing time is plotted.

Nanoindentation and nanoscratching analysis of high transparent F:SiOx thin films deposited by plasma polymerization

The mechanical behavior of the high transparent fluorine doped silicon oxide thin films was studied by nanoindentation and nanoscratching analysis. The films were deposited by plasma polymerization in a capacitively coupled RF plasma system using different mixture of Tetraethylorthosilicate-O2-CF4 in the plasma medium. It was found that, the addition of fluorine to the composition of the silicon oxide film, can decrease its optical absorption. Furthermore, it was shown that doping fluorine to SiOx film causes to decrease the hardness, H, elastic modulus, Er, as well as H/Er ratio (predicting the wear rate). But in F-SiOx films deposited in different oxygen flow rate, adding fluorine to the composition of the film increases H/Er ratio. Finally, all of the coated films, except the film deposited without the oxygen flow, could pass the harsh environmental durability test.

Preparation of mesoporous silica thin films at low temperature: a comparison of mild structure consolidation and template extraction procedures

Mesoporous thin films (MTFs) displaying high surface area and controlled porosity constitute interesting materials for a plethora of applications in optics and electronics. A critical aspect in MTF processing is template removal that usually consists in thermal treatment at 350 °C, which consolidates the oxide film but might change the pore features. In addition, the use of such high temperature must be avoided when organic functionalities are to be preserved, or in the case of film deposition on polymeric substrates. Here we present and compare five different methods to consolidate silica MTF (SMTF) in mild conditions, at a maximum processing temperature of 130 °C. Conditions, such as duration of the thermal treatment, vacuum conditions, exposure to acidic and alkaline media, were systematically explored and the resulting films were analyzed by optical microscopy, focused ion beam, scanning electron microscopy, ellipsometry, and infrared spectroscopy. The optimized conditions leading to accessible mesopores and a stable oxide structure that can be used as a mesoporous perm-selective electrode are discussed.

Bis(terpyridine) Iron(II) Functionalized Vertically-Oriented Nanostructured Silica Films: Toward Electrochromic Materials.

Recent and potential applications of electrochromic materials include smart windows, optoelectronic devices, and energy conversion. In this study, we have incorporated bis(terpyridine) iron (II) complexes into vertically-oriented silica thin films deposited on indium-tin oxide (ITO) and their electrochromic behavior has been investigated. If 2,2′:6′,2″-terpyridine is commonly used as a ligand for forming metallo-supramolecular assemblies, with the objective to get metal-terpyridine complexes with multiple stable redox states, their simple and reliable arrangement into linear structures enabling effective electronic communication is however more challenging. We propose to overcome this difficulty by generating such complexes within vertical nanochannels on electrode. Terpyridine ligands were firstly immobilized by combining a click chemistry azide/alkyne approach with an electrochemically-assisted self-assembly (EASA) method used to grow an oriented mesoporous silica membrane bearing azide groups which were further derivatized with 4′-ethynyl-terpyridine ligands. The resulting terpyridine-functionalized films were consecutively dipped in an aqueous solution of Fe(BF4)2 and then in a solution of terpyridine in acetonitrile to form the bis(terpyridine) iron (II) complexes in situ. The electrochromic properties of the films functionalized at various levels were examined by monitoring the changes in their UV/Vis spectra upon electrochemical oxidation at controlled potential of +1.2 V vs. Ag/AgCl. Due to facile charge delocalization during the Fe2+ to Fe3+ redox process, the bis(terpyridine) iron (II) functionalized silica films exhibited electrochromic properties by changing from violet to non-colored using TBABF4 in acetonitrile as an electrolyte. The bis(terpyridine) iron(II) film experienced reversible electrochromic switching by applying +0.5 V in a reverse reduction electrochemical process. The Fe(tpy)2-functionalized silica thin films displayed a good contrast ratio (ΔT%) of 47% and relatively high coloration efficiency (CE) of about 245 cm2/C with a response time of coloring and bleaching of a few seconds (< 4 s).

Structure of a Silica Thin Film on Oxidized Cu(111): Conservation of the Honeycomb Lattice and Role of the Interlayer

The metal–oxide interface has a crucial role in determining the growth of silica thin films. However, only a few metallic substrates have been explored so far. In previous studies, metal substrates...

Synthesis and thermal simulations of novel encapsulated CNT multifunctional thin-film based nanomaterial of SiO2-CNT and TiN-CNT by PVD and PECVD techniques for thermal applications

This research work focuses on synthesizing novel multi-layer thin-film 2D material which consists of CNTs as-synthesized thin film as the base material. These thin films could be used in various applications such as field emission materials, structural reinforcement, thermal dissipation, etc. Nearly vertically aligned carbon nanotubes (CNTs) were synthesized on a silicon substrate using Radio Frequency Plasma Enhanced Chemical Vapor Deposition (RF PECVD). In the current research, thin films of Titanium Nitride (TiN) and Silicon Dioxide (SiO2) is deposited on CNTs using Physical Vapor Deposition (PVD) technique. Transmission Electron Microscope (TEM) results indicate the presence of polycrystalline and amorphous features in TiN/CNT and SiO2/CNT composites. Energy Dispersive X-Ray Spectroscopy (EDS) in the TEM has been used to identify the deposited elements. Raman spectroscopy was used to determine the sp2, sp3 content and investigate the vibrational signature of molecules for the composites. The hardness of the composites was measured using nanoindentation. The hardness of TiN/CNT and SiO2/CNT calculated using values arising in compression testing of the films together is estimated to be 3.18 GPa and 2.80 GPa respectively. Thermal simulations to near synthesis material were carried out using Ansys software and found that a typical 80 °C temperature could be reduced to room temperature with the composite thin films. Simulations using software estimate the thermal heat flux for Si/CNT/TiN system is 1570 W/mm2 and the same for Si/CNT/SiO2 is 172.45 W/mm2.