Silica Thin Films Research Articles

Design and Numerical Analysis of Ultra-Broadband Absorber with Chimney Type Structure

In this study, a novel ultra-broadband absorber is suggested and numerically analyzed to demonstrate that the suggested absorber can achieve an average absorbance of 98.6% in the visible to near-infrared wavelength range (496–2100 nm). The structure of the proposed new ultra-wideband absorber consists of four thin films of silicon dioxide (SiO2), iron (Fe), magnesium fluoride (MgF2), and chromium (Cr). We have examined the structure’s electromagnetic field intensity distribution at numerous selected optical wavelengths and the influence of various structural parameters on the absorption performance of the absorber to offer a physical mechanism underlying the ultra-broadband absorption effect. Furthermore, in the presence of high-performance absorption, the structure has the effect of stabilizing absorption at large angles of incidence and is polarization-independent at vertical angles of incidence. The study also assesses the solar absorption capability of this structure, indicating that the structure has potential applications in solar absorption, such as solar energy collection and conversion, solar power generation, and thermal emitters.

Tolerance of Silicon Oxide‐Coated Pt/C Catalyst Toward CO and H2S Contamination in Hydrogen for Proton Exchange Membrane Fuel Cells

Platinum on graphitized low surface area carbon (Pt/C) is coated with a silicon oxide thin film and is employed as anode catalyst to manipulate the tolerance of proton exchange membrane fuel cells toward carbon monoxide and hydrogen sulfide contamination. The SiO2 coating, prepared by successive hydrolysis of 3‐aminopropyl‐triethoxisilane and tetraethoxysilane, forms clusters in proximity to Pt in sizes comparable to the catalyst particles, leaving most of the carbon surfaces free. The performance with and without CO is investigated in situ at relative humidities (RH) of 100%, 70%, and 40%. When operated with neat hydrogen, SiO2‐Pt/C shows marginally better performance owing to an improved protonic conduction due to the water retaining hydrophilic SiO2. Upon operation with CO‐contaminated fuel, the SiO2‐Pt/C performs worse than that of Pt/C particularly at high RH. CO stripping measurements reveal an increase in CO oxidation potential for the SiO2‐Pt/C, suggesting an increased CO coverage and consequently higher anode overpotentials during operation with CO‐contaminated fuel. Upon operation with H2S in the fuel, the SiO2 coating extends the lifetime until the cell voltage broke down, which is attributed to the enhanced water retention due to SiO2 and the solubility of sulfuric species.

In Vitro Study of Zirconia Surface Modification for Dental Implants by Atomic Layer Deposition.

Zirconia is a promising material for dental implants; however, an appropriate surface modification procedure has not yet been identified. Atomic layer deposition (ALD) is a nanotechnology that deposits thin films of metal oxides or metals on materials. The aim of this study was to deposit thin films of titanium dioxide (TiO2), aluminum oxide (Al2O3), silicon dioxide (SiO2), and zinc oxide (ZnO) on zirconia disks (ZR-Ti, ZR-Al, ZR-Si, and ZR-Zn, respectively) using ALD and evaluate the cell proliferation abilities of mouse fibroblasts (L929) and mouse osteoblastic cells (MC3T3-E1) on each sample. Zirconia disks (ZR; diameter 10 mm) were fabricated using a computer-aided design/computer-aided manufacturing system. Following the ALD of TiO2, Al2O3, SiO2, or ZnO thin film, the thin-film thickness, elemental distribution, contact angle, adhesion strength, and elemental elution were determined. The L929 and MC3T3-E1 cell proliferation and morphologies on each sample were observed on days 1, 3, and 5 (L929) and days 1, 4, and 7 (MC3T3-E1). The ZR-Ti, ZR-Al, ZR-Si, and ZR-Zn thin-film thicknesses were 41.97, 42.36, 62.50, and 61.11 nm, respectively, and their average adhesion strengths were 163.5, 140.9, 157.3, and 161.6 mN, respectively. The contact angle on ZR-Si was significantly lower than that on all the other specimens. The eluted Zr, Ti, and Al amounts were below the detection limits, whereas the total Si and Zn elution amounts over two weeks were 0.019 and 0.695 ppm, respectively. For both L929 and MC3T3-E1, the cell numbers increased over time on ZR, ZR-Ti, ZR-Al, and ZR-Si. Particularly, cell proliferation in ZR-Ti exceeded that in the other samples. These results suggest that ALD application to zirconia, particularly for TiO2 deposition, could be a new surface modification procedure for zirconia dental implants.

Design of a Reconfigurable Ultra-Wideband Terahertz Polarization Rotator Based on Graphene Metamaterial

In this work, a reconfigurable ultra-wideband transmissive terahertz polarization rotator based on graphene metamaterial is proposed that can switch between two states of polarization rotation within a broad terahertz band by changing the Fermi level of graphene. The proposed reconfigurable polarization rotator is based on a two-dimensional periodic array of multilayer graphene metamaterial structure, which is composed of metal grating, graphene grating, silicon dioxide thin film, and a dielectric substrate. The graphene metamaterial can achieve high co-polarized transmission of a linearly polarized incident wave at the off-state of the graphene grating without applying the bias voltage. Once the specially designed bias voltage is applied to change the Fermi level of graphene, the polarization rotation angle of linearly polarized waves is switched to 45° by the graphene metamaterial at the on-state. The working frequency band with 45-degree linear polarized transmission remaining above 0.7 and the polarization conversion ratio (PCR) above 90% is from 0.35 to 1.75 THz, and the relative bandwidth reaches 133.3% of the central working frequency. Furthermore, even with oblique incidence at large angles, the proposed device retains high-efficiency conversion in a broad band. The proposed graphene metamaterial offers a novel approach for the design of a terahertz tunable polarization rotator and is expected to be applied in the applications of terahertz wireless communication, imaging, and sensing.

The non-innocent role of cobalt in manipulating the magnetic and electric properties of mesoporous silica thin films

SiO2 does not have magnetic elements; therefore, it behaves as a diamagnetic material with a possible paramagnetism due to oxygen vacancy defects. Incorporation of magnetic elements and pores into SiO2 films can add an additional functionality to its dielectric and insulating properties. Herein we report the incorporation of Co element into the mesoporous framework of SiO2 (Co–SiO2) thin films through chemical sol-gel based-spin coating processes. The thus obtained Co–SiO2 thin film exhibits transition in the magnetic properties, increase in the specific surface area and a decrease in the leakage current while maintaining better electric conductivity. For comparison, the bare mesoporous SiO2 (m-SiO2) films were prepared at identical conditions. Interestingly, a S-type shape on the isothermal magnetization measurements versus magnetic field (M vs. H) curves appeared at 5 K in case of the Co–SiO2 films, and a paramagnetic behavior was observed at 50 K and above. The temperature-dependent magnetization (M vs. T) measurements of the Co–SiO2 films also showed an increase of magnetization below 50 K. It is anticipated that Co substitutes Si although presence of the CoO and/or Co3O4 phases cannot be completely ruled out. These results support the idea that a ferromagnetic-like transition takes place in the Co-doped SiO2 films below 50 K due to Co doping. At the same time, a reduction in the leakage current density was determined in Co–SiO2, while maintaining better charge transfer in 1.0 M KOH for ion conducting devices.

Ultra-thin silver nanowires’ synthesis in pore-confined space of mesoporous silica thin film

In the present work, we report a synthesis procedure for the preparation of vertically aligned mesoporous silica thin films containing long, nanometer-scale thin silver nanowires inside pores. The inter-channel nanowires had a fine crystalline structure and a diameter of no more than 2 nm. Despite the diameter being the edge of the theoretical possibility of synthesis, the nanowires were stable enough to be observed by transmission electron microscope and could be clearly observed. For the synthesis, we applied the idea of silica nanoreactors, and the procedure consists of two steps: fabrication of an initial organically-functionalized silica thin film containing silver ions distributed regularly inside vertically aligned pores and following thermal decomposition resulting in the decomposition of the organic anchoring groups and the formation of metallic crystalline nanowires from released silver atoms. Both the final nanocomposite and the initial material were studied by means of transition electron microscopy and electrochemical techniques: linear scan and differential pulse anodic stripping voltammetry. The crystallinity of silver nanowires inside silica mesopores was proved by electron diffraction. The spatial confinement realized by silica nanochannels facilitated the stabilization of relatively small and ultra-thin nanowires and the formation of a hexagonal P63/mmc silver crystalline structure instead of the more common Fm3m cubic.

Effects of the Polymer Amount and pH on Proton Transport in Mesopores

AbstractProton exchange membranes (PEMs) have various applications, such as in electrolysis technology for hydrogen generation, vanadium flow batteries for energy storage, and fuel cells for energy conversion. To increase PEM performance and expand the range of PEM applications, the underlying transport mechanisms of PEMs need to be understood. Mesoporous silica thin films are versatile model materials for proton transport investigation and are prepared with a pore size of ≈12 nm and film thickness of ≈565 nm by evaporation‐induced self‐assembly, providing an ordered, mesoporous, rigid matrix that allows us to deduce the structure‐property relationship with respect to proton conductivity. Different amounts of sulfonic acid‐bearing groups are introduced into the mesopores using the grafting‐through polymerization of sulfopropylmethacrylate. The relationship between proton transport and the pH of the surrounding solution in poly‐sulfopropylmethacrylate‐functionalized mesopores is investigated using electrochemical impedance spectroscopy. The proton conductivity is found to depend on both the proton concentration in solution and the number of proton transporting groups inside the pore, indicating the major role of charge regulation and the confinement effect on proton transport.

Automated Multi‐ and Block‐Copolymer Writing in Mesoporous Films Using Visible‐Light PET‐RAFT and a Microscope (Small 16/2023)

Mesoporous Films An oxygen tolerant, DDMAT-initiated and visible-light induced photo electron/energy transfer-reversible addition-fragmentation chain-transfer (PET-RAFT) allows for direct polymer writing in a mesoporous silica thin film. Using a commercially available microscope, micrometer scale resolution of the placement of three different polymers as well as block-copolymer functionalization are achieved. This flexible approach makes rapid prototyping of polymer patterns in mesoporous silica thin film easily accessible. More details can be found in article number 2207762 by Annette Andrieu-Brunsen and co-workers.

Optical modeling of a radioisotope atmospheric chamber

Volatile radioisotopes represent a substantial health risk when released into the environment. To better understand the environmental fate of radioisotopes, the authors constructed a cylindrical steel-walled chamber to simulate the atmospheric processing of volatile radioactive gases. Optical modeling was performed for the properties of simulated sunlight in the chamber to better characterize atmospheric reaction studies. Optical simulations were performed using two wall materials (steel and thin-film silica) and validated against experimental measurements. This optical analysis methodology can be used to improve the fidelity of atmospheric models by accounting for optical inhomogeneities enabling a firmer grasp of radioisotopes’ environmental fate.Graphical abstract

Low‐temperature atmospheric pressure plasma conversion of polydimethylsiloxane and polysilazane precursor layers to oxide thin films

AbstractWe study the conversion of two polymeric silicon precursor compound layers (perhydropolysilazane and polydimethylsiloxane) on a silicon wafer and polyethylene terephthalate substrates to silicon oxide thin films using a pulsed atmospheric pressure plasma jet. Varying the scan velocity and the number of treatments results in various film compositions, as determined by X‐ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. The mechanism suggested for the conversion process includes the decomposition of the precursor triggered by plasma‐produced species, the oxidation of the surface, and finally, the diffusion of oxygen into the film, while gases produced during the precursor decomposition diffuse out of the film. The latter process is possibly facilitated by local plasma heating of the surface. The precursor conversion appears to depend sensitively on the balance between the different contributions to the conversion mechanism.

Quantitative Characterization of the Anisotropic Thermal Properties of Encapsulated Two-Dimensional MoS2 Nanofilms.

Two-dimensional (2D) semiconductors exhibit unique physical properties at the limit of a few atomic layers that are desirable for optoelectronic, spintronic, and electronic applications. Some of these materials require ambient encapsulation to preserve their properties from environmental degradation. While encapsulating 2D semiconductors is essential to device functionality, they also impact heat management due to the reduced thermal conductivity of the 2D material. There are limited experimental reports on in-plane thermal conductivity measurements in encapsulated 2D semiconductors. These measurements are particularly challenging in ultrathin films with a lower thermal conductivity than graphene since it may be difficult to separate the thermal effects of the sample from the encapsulating layers. To address this challenge, we integrated the frequency domain thermoreflectance (FDTR) and optothermal Raman spectroscopy (OTRS) techniques in the same experimental platform. First, we use the FDTR technique to characterize the cross-plane thermal conductivity and thermal boundary conductance. Next, we measure the in-plane thermal conductivity by model-based analysis of the OTRS measurements, using the cross-plane properties obtained from the FDTR measurements as input parameters. We provide experimental data for the first time on the thickness-dependent in-plane thermal conductivity of ultrathin MoS2 nanofilms encapsulated by alumina (Al2O3) and silica (SiO2) thin films. The measured thermal conductivity increased from 26.0 ± 10.0 W m-1 K-1 for monolayer MoS2 to 39.8 ± 10.8 W m-1 K-1 for the six-layer films. We also show that the thickness-dependent cross-plane thermal boundary conductance of the Al2O3/MoS2/SiO2 interface is limited by the low thermal conductance (18.5 MW m-2 K-1) of the MoS2/SiO2 interface, which has important implications on heat management in SiO2-supported and encased MoS2 devices. The measurement methods can be generalized to other 2D materials to study their anisotropic thermal properties.

Two-step GISAXS characterization of NiSi2 nanoplates and Ni nanocrystals embedded in a silicon wafer covered with a silica thin film

Here, an experimental grazing-incidence small-angle X-ray scattering (GISAXS) study of the nanostructure of a sample composed of a Si(001) wafer covered by a Ni-doped SiO2 thin film and thermally treated at high temperature is described. Previous studies indicated that this type of composite contains Ni nanocrystals mainly inside the thin film and NiSi2 nanoplates buried in the Si wafer. To achieve accurate determinations of low-resolution structural parameters of the nanoparticles derived from the experimental results (shape, volume and size), two GISAXS patterns were recorded. The first pattern was produced by the Si wafer covered by a nanoporous Ni-doped SiO2 thin film and the second pattern was recorded after removal of the SiO2 thin film by chemical etching. By using the procedure of best fitting of a modeled isotropic GISAXS intensity to a set of 1D GISAXS patterns recorded before thin-film removal, the average radius and radius dispersion of a size polydisperse set of spherical Ni nanocrystals were determined. The GISAXS pattern recorded after removal of the SiO2 thin film was almost completely due to the scattering intensity produced by oriented NiSi2 nanoplates located inside the Si wafer. By fitting a theoretical function for the X-ray scattering intensity produced by oriented nanoplates to a set of experimental 1D GISAXS patterns, the maximum diameters and average thickness of the hexagonal NiSi2 nanoplates were determined. The GISAXS intensity pattern produced by the sample after thin-film removal is essentially anisotropic (with only a weak isotropic contribution from Ni nanocrystals), thus allowing for precise quantitative determinations of the relevant sizes of the NiSi2 nanoplates.

Enhanced electrical stability of thin film transistors based on nanocrystalline silicon films

In this work, nanocrystalline silicon (nc-Si) films were achieved by using normally processing method of amorphous silica thin film transistors (a-Si TFTs), plasma enhanced chemical vapor deposition (PECVD). The effects of PECVD process parameters on the crystallization rate of nc-Si films were comprehensively studied and then an optimized nc-Si film has been achieved with a crystallinity of 50.87%. The electrical properties and stability of nc-Si TFTs are further investigated and compared with a-Si TFTs. The ΔV th of the nc-Si TFTs are 0.14 V and −3.32 V under positive bias-temperature-illumination stress (60 °C, 30 V, 6000 nit) and negative bias-temperature-illumination stress (60 °C, −30 V, 6000 nit) after 1 h, which are 1.96 V and −5.51 V for a-Si TFT, respectively. The result reveals better photo stability of nc-Si TFTs than a-Si TFTs which is attributed to fewer defect states in nc-Si films.

Internal wettability investigation of mesoporous silica materials by ellipsometric porosimetry

Silica-based mesoporous films have been widely applied in the fabrication of advanced functional materials, such as anti-reflective coatings, bio-, and chemical sensing devices, due to their unique properties, e.g., high surface area, controlled porosity, and the ease and tailorability of their synthesis. Precise knowledge of their pore architecture is crucial, highlighting the need for accurate characterization tools. In this sense, ellipsometric porosimetry represents a powerful and versatile characterization platform, providing access to reliable information about total porosity, pore size, pore size dispersity, mechanical properties (Young's modulus) and surface area of a great variety of mesoporous thin films.While the underlying framework of modeling capillary condensation via the Kelvin equation is well established, one descriptor, the internal wettability of mesoporous architectures remains a challenging variable for reliable material characterization. Wetting on the nanoscale cannot be observed via the traditional drop-shape method, while approximating internal wetting by the macroscopic property can be inaccurate as the two wetting behaviors do not necessarily correlate. Herein, we present a method based on vacuum ellipsometric porosimetry for the determination of the internal contact angle of functionalized mesoporous silica thin films. Tuning of the surface energy for a known mesoporous architecture by methyl-functionalization enabled us to relate differences in the pore filling for various adsorptives (water, methanol, toluene, cyclohexane) to their internal contact angles. Our study serves as a guide for generalized internal contact angle determination suitable for a wide range of organic adsorptives and mesoporous sorbent materials.

Reflectance investigation on dielectric reflectors using ethanol, methanol and isopropanol as solvents in the synthesis process

Dielectric reflectors are made up of a range of solvents in the wet chemical sol–gel based synthesis technique. The unexpected scarcity of solvents such as ethanol complicates matters, influencing the optical characteristics of the created multilayer structure. To eliminate the need for solvents, a new method for generating dielectric reflectors employing a variety of solvents must be created. We provide here an experimental inquiry on the synthesis and fabrication procedure of dielectric reflectors employing different solvents such as ethanol, methanol, and isopropanol that has not been reported previously to the best of our knowledge. The fabricated reflectors are characterized with AFM for roughness analysis and found 26, 5, and 1.2 nm for the solvent ethanol, methanol, and isopropanol respectively. Cross-sectional FE-SEM analysis supported the fabrication of titania and silica thin films with bright and dark colours on the dielectric reflectors. When ethanol was employed as the solvent, reflectance analysis using UV–vis spectroscopy approach showed 100 % reflectivity in the near-infrared region, and when methanol and isopropanol were used, improved reflectance as well as shift in the stop band were observed respectively.

Alkaline earth metal ion doping to enhance the light emission from Er3+:SnO2 nanocrystal Co-doped silica films.

Alkaline earth metal ions (Mg2+, Ca2+, Sr2+) have been introduced into Er3+:SnO2 nanocrystal co-doped silica thin films fabricated by a sol-gel method combined with a spin-coating technique. It is found that the incorporation of alkaline earth metal ions can enhance the light emission from Er3+ at the wavelength around 1540 nm and the strongest enhancement is observed in samples doped with 5 mol% Sr2+ ions. Based on X-ray diffraction, X-ray photoelectron spectroscopy and other spectroscopic measurements, the improved light emission can be attributed to more oxygen vacancies, better crystallinity and a stronger cross-relaxation process with the introduction of alkaline earth metal ions.

히터 위치에 따른 건식 스크러버 내 열-유동 특성에 관한 수치적 연구

The fourth Industrial Revolution will increase the demand for 3D NAND due to the development of technologies such as artificial intelligence and big data in the future. In the manufacturing process of 3D NAND, which stacks semiconductors in a stacked structure, the demand for gas for deposition and etching increases compared to 2D NAND. It is important to remove process gas with high efficiency because it causes global warming effects. To this end, the industry is introducing scrubber technology. In this study, the thermal fluid characteristics of a scrubber capable of decomposing and removing nitrous oxide (N₂O) used to deposit a silicon dioxide (SiO₂) thin film in a semiconductor process were analyzed according to the location of the heater. As a result of the analysis, the pressure and velocity distribution in the scrubber was high in the area of the fluid flowing into the heater, and in terms of heat transfer, the air temperature was found to be affected by the capacity of the heater and the flow rate of the flowing fluid.

Synthesis and characterization of novel multi-layer silica thin films with tailored mesostructure as anti-reflective coatings

Photovoltaic devices are highly in need of glass covers to protect solar cells against environmental damage, especially for outdoor performance. Antireflective coatings on these glass covers are essential upon which many studies on designing new coating are ongoing to exhibit both satisfactory optical properties and adequate mechanical stability. This study compares different types of three-layer mesoporous silica coatings with graded porosity fabricated by the evaporation-induced self-assembly method. Surfactant concentration was manipulated as an important variable to tailor different mesostructure designs. The deposition of coatings was performed by sequential spin-coating method. The effects of layers arrangement on light transmittance and water absorption were investigated. The fabricated transparent multi-layer coatings showed to have a uniform pore size of about 3 nm and a thickness of about 450 nm. The average transmittance of the coatings was approximately 96% in the wavelength range of 400–800 nm. It was concluded that the optical properties and water absorption of multi-layer coatings depend on the porosity of each layer and the interconnections of the layers upon which the desired properties can be tailored. The maximum constant transmittance in a wavelength range from 400 to 800 nm of tri-layer coatings was obtained when layer of lower porosity was at the bottom next to the glass. Fabricated samples with high smoothness, high transmittance, and low water absorption indicate positive prospects for solar glass applications.

Near-infrared light emitting devices from Er doped silica thin films via introducing SnO2 nanocrystals

To get high performance light emitting devices on Si platform with emission wavelength at 1.55 μm is a challenge for future Si-based opto-electronic integration chips. In this paper, we fabricated near-infrared light-emitting devices based on Er/SnO2 co-doped silica thin films. The introduction of SnO2 nanocrystals with controllable size and density not only contributes to the near-infrared light emission enhancement of Er3+ ions at 1.55 μm, but also provides an effective carrier transport channel to realize efficient and stable electro-luminescence. The corresponding devices exhibit an external quantum efficiency of 5.4% at near infrared light region and the power efficiency is about 1.52 × 10−3. Our present work lays a solid foundation for facilitating Si-based light source towards practical application in the field of optoelectronic interconnection.

A Comparative Study of PMETAC-Modified Mesoporous Silica and Titania Thin Films for Molecular Transport Manipulation.

The manipulation and understanding of molecular transport across functionalized nanopores will take us closer to mimicking biological membranes and thus to design high-performance permselective separation systems. In this work, Surface-initiated atom transfer radical polymerization (SI-ATRP) of (2-methacryloyloxy)-ethyltrimethylammonium chloride (METAC) was performed on both mesoporous silica and mesoporous titania thin films. Pores were proven to be filled using ellipsometry and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Furthermore, the employed method leads to a polymer overlayer, whose thickness could be discriminated using a double-layer ellipsometry model. Cyclic voltammetry experiments reveal that the transport of electrochemically active probes is affected by the PMETAC presence, both due to the polymer overlayer and the confined charge of the pore-tethered PMETAC. A more detailed study demonstrates that ion permeability depends on the combined role of the inorganic scaffolds' (titania and silica) surface chemistry and the steric and charge exclusion properties of the polyelectrolyte. Interestingly, highly charged negative walls with positively charged polymers may resemble zwitterionic polymer behavior in confined environments.