Thickness Of Silica Layer Research Articles

Stepwise ordering under nano-scale confinement in thin silica films

The phase transition from an amorphous 2D structure to a crystalline 3D structure under confinement is a fascinating and challenging problem in materials science and condensed matter physics. This work reports the Field Emission Scanning Electron Microscopy (FESEM) and energy dispersive analysis of X-rays (EDAX), X-ray diffraction (XRD), X-ray reflectivity (XRR), Fourier Transform Infrared Spectroscopy (FTIR) studies on pristine silica thin films. Silica was deposited on pristine Al (001) substrate (Alfa-Aesar) from tetraethyl orthosilicate (TEOS) precursor and thin films were spin-coated at different spinning frequencies under ambient conditions. The samples are highly porous and in-plane porosity varies from 30% to 60% as analyzed from both the FESEM and XRR and with increasing spinning frequency pores become more ordered. XRR shows that the samples are composed of two layers, a thick layer of aluminum oxide (Al2O3) as buffer layer and a layer of SiO2 on the top of the film. XRR shows sharp ordering rather than any layering. The film thickness varies from 90[Formula: see text]Å to 200[Formula: see text]Å and it shows a linear decay in the thickness of silica layer. In between 1000 and 1500[Formula: see text]rpm, XRR shows a sharp drop in the thickness of silica layer where thickness of this layer falls below the unit-cell dimension indicating higher-ordered crystallization under strained condition. XRD shows that there are no crystalline peaks coming from silica at lower rpm except the peaks of Al coming from the substrate. At 1000, 1200 and 1500[Formula: see text]rpm there is peak corresponding to the quartz, highly crystalline phase of SiO2 and where the substrate is slightly modified Al2O3. Reflection from (101) plane is prominent in all the films and it gives indication of formation 3D crystalline phase. Whereas FTIR shows that the Si–O stretching modes exhibit sharper and more defined reflectance peak compared to the broad bands observed in the samples in lower rpm. Observations suggest a clear indication of progressive ordering under confinement. To one extent, the results of XRR and FESEM will suggest the mechanism of transition from 2D amorphous to 3D crystalline phase under geometrical confinement effect and total confinement effect arising from thinning of the films with the increasing rpm, interfacial effect and on the other hand XRD and FTIR results will explain high ordering under confinement without any layering.

Exploring the relationship between seed weight and seed coat characteristics in the adlay (Coix lacryma-jobi L.) cultivar WATANI-2 through N, P and K treatment compositions

Adlay plant (Coix lacryma-jobi) grown in many Asian countries, as a source of carbohydrates. The cultivation of adlay faces challenges such as long growth periods, low yields, and hard seeds. Efforts to enhance productivity are crucial, specifically by applying Nitrogen, Phosphorus, and Potassium fertilizers at the appropriate and balanced doses that have not yet been established. Therefore, this study aimed to investigate the relationship between seed weight and seed coat characteristics under optimal N, P, and K fertilizer doses. The exploration process was conducted at the Research Station and Plant Production Technology Laboratory, Faculty of Agriculture, Padjadjaran University, from April 2019 to November 2020. Features of the location included an altitude of 750 – 800 m above sea level, a climate type C3 (Oldeman), an average temperature of 23.8oC, and a soil classified as Inceptisols with a pH of 5.83. The experimental design incorporated several treatments at minimum, optimum, and maximum dosage levels, namely N (90kg/ha, 180 kg/ha, and 270 kg/ha), P (37.5kg/ha, 75 kg/ha, and 150 kg/ha), and K (60 kg/ha, 120 kg/ha and 240 kg/ha) fertilizers, each was repeated twice. Fertilizer application was administered at the beginning of growth and the late vegetative phase, while P was given during the late vegetative phase and before seed formation. Subsequently, a regression analysis was performed to determine the relationship of the weight of 100 seeds with thickness and hardness, generating the equation: Y = 13.755 + 0.061 X1 + 0.012 X2, where X1 = seed hardness and X2 = seed coat thickness. Observations were carried out on the weight, thickness, and hardness of adlay seeds, both macroscopically by measuring length and width or diameter and microscopically through the evaluation of coat and silica layer thickness). The results showed a significant relationship between seed weight, thickness, and hardness, yielding 5.56 t/ha with an 80% land efficiency.

SOI Based metasurface for broadband perfect reflection in visible spectrum

We propose modeling and design of a low-loss all-dielectric metasurface (DM), comprised of Silicon on Insulator (SiO2) substrate to demonstrate a perfect reflector in the visible spectrum. The proposed metasurface unit cell consists of V and W shapes arranged in a mirror image configuration, with nanometre-sized gaps (g) between them. A narrow peak with a nearly 100% reflectance and a broad perfect reflectance spectrum is observed within the visible region (400–700 nm) of the electromagnetic spectrum. The effective electromagnetic parameters were also analyzed for electric and magnetic dipole resonance. The electric and magnetic field distributions at the resonant wavelength were also analyzed for the proposed structure. By altering the gap region ‘g’, the thickness of the dielectric Silica layer (ts ), and the Si resonator (t m), the proposed structure exhibits tunable characteristics. We have successfully illustrated the consistent position of the scattering parameter’s response, regardless of the structure’s rotation, concluding the homogeneity of the designed structure across the entire visible spectrum. The all-DM exhibits a unique combination of features, including a distinct and wide reflectance spectrum as well as a tuned and enhanced electric field which makes it an ideal platform for the applications in filters, color printing, low-loss slow-light devices, and nonlinear optics.

Ultra-narrowband, electrically switchable, and high-efficiency absorption in monolayer graphene resulting from lattice plasmon resonance

We propose a novel approach to obtain the ultra-narrowband, electrically switchable, and high-efficiency absorption in the monolayer graphene. The monolayer graphene is sandwiched between the silica substrate and a square array of silver nanospheres, which is covered by a very thick silica layer. The fundamental role of the thick silica cover layer is to homogenize the surrounding medium of the silver nanospheres, and thus efficiently exciting the lattice plasmon resonance. The lattice plasmon resonance arising from the coupling between the dipolar plasmon resonance of silver nanospheres and the zero-order diffraction wave at Wood anomaly can enhance the electromagnetic fields at the graphene surface, and thus greatly improve the near-infrared light absorption of the monolayer graphene with the maximum absorption efficiency up to 45%. Owing to the low radiation loss of the lattice plasmon resonance, the absorption linewidth of the monolayer graphene can be largely compressed to only several nanometers (3.2 nm ∼ 7.4 nm). Moreover, the absorption of the monolayer graphene in our proposed nanostructures has a nearly 100% modulation depth to exhibit an excellent switching property. Our work will be helpful for some graphene-based photoelectric devices.

Zeta potential and nanodiamond self assembly assisted diamond growth on lithium niobate and lithium tantalate single crystal

This study focuses on the self-assembly and subsequent diamond growth on SiO2 buffered lithium niobate (LNO) and lithium tantalate (LTO) single crystals. The zeta-potential of LNO and LTO single crystal were measured as a function of pH. They were found to be negative in the pH range 3.5–9.5. The isoelectric point for LNO was found to be at pH ∼ 2.91 and that of LTO to be at pH ∼ 3.20. X-ray photoelectron spectroscopy performed on the surfaces show presence of oxygen groups which may be responsible for the negative zeta potential of the crystals. Self-assembly of nanodiamond particles on LTO and LNO, using nanodiamond colloid, were studied. As expected, high nanodiamond density was seen when self-assembly was done using a positively charged nanodiamond particles. Diamond growth was attempted on the nanodiamond coated substrates but they were found to be unsuitable for direct growth due to disintegration of substrates in diamond growth conditions. A ∼100 nm thick silicon dioxide layer was deposited on the crystals, followed by nanodiamond self assembly and diamond growth. Thin diamond films were successfully grown on both coated crystals. The diamond quality was analysed by Raman spectroscopy and atomic force microscopy.

An anisotropic nanobox based core-shell-satellite nanoassembly of multiple SERS enhancement with heterogeneous interface for stroke marker determination

Herein, A novel gold-silver alloy nanobox (AuAgNB)@SiO2-gold nanosphere (AuNP) nanoassembly based on core–shell-satellite structure is fabricated and applied to the surface-enhanced Raman scattering (SERS) detection of S100 calcium-binding protein B protein (S100B). It contains an anisotropic hollow porous AuAgNB core with rough surface, an ultrathin silica interlayer labeled with reporter molecules, and AuNP satellites. The nanoassemblies were systematically optimized by tuning the reporter molecules concentration, silica layer thickness, AuAgNB size, and the size and number of AuNP satellite size. Remarkably, AuNP satellites are adjacent to AuAgNB@SiO2, developing AuAg-SiO2-Au heterogeneous interface. With the strong plasmon coupling between AuAgNB and AuNP satellites, chemical enhancement from heterogeneous interface, and the tip “hot spots” of AuAgNB, the SERS activity of the nanoassemblies was multiply enhanced. Additionally, the stability of nanostructure and Raman signal was significantly improved by the silica interlayer and AuNP satellites. Eventually, the nanoassemblies were applied for S100B detection. It demonstrated satisfactory sensitivity and reproducibility with a wide detection range of 10 fg/mL-10 ng/mL and a limit of detection (LOD) of 1.7 fg/mL. This work based on the AuAgNB@SiO2-AuNP nanoassemblies with multiple SERS enhancements and favorable stability demonstrates the promising application in stroke diagnosis.

Neglected Applications of Monolithic Structures: The Beginnings of Planar Chromatography with Mass Spectrometric Detection

Thin layer chromatography (TLC) has been first reported by N. A. Izmailov and M. S. Schreiber in the late 1930s. The liquid mobile phase usually moves in pores of a layer supported by a rigid plate placed vertically in a simple container, e.g., a beaker. The flow is driven by capillary forces in the pores only and no sophisticated instrumentation is required. The individual components of the mixture are separated based on differences in their affinity for the solid stationary and the liquid mobile phases. The typical format of the stationary phase represents a thin layer coated on a glass, aluminium, or plastic plate. The porous sorbents can be silicon dioxide (silica), aluminium oxide (alumina), and cellulose, held together, e.g., with gypsum. The main advantages of TLC are the ease of carrying out the separations, which can also take place in parallel lines on the same plate, simple equipment, stationary phase for single use, static detection, and the possibility of archiving the separation result in a dried layer. However, the typical 100–250 μm thick layers are not well suited for combination of TLC with mass spectrometry (MS). This has led to the commercialization of ultrathin 10 μm thick monolithic silica layers. Unfortunately, their production was soon discontinued. Alternative solutions to that problem originated from the academic environment. In one approach, the layers were formed from nanofibers prepared by electrospinning. Alternatively, the layers were porous monolithic polymers produced by polymerization in situ and a variety of separations of both small and large molecules was demonstrated. The use of MS detection then enabled determination of molecular mass of the compounds in the separated spots. Although preparation of the thin monolithic layers originally appeared straightforward, some unexpected problems had to be solved. This review details issues related to the history of the monolithic TLC and presents approaches leading to well behaving layers suitable for the desired separations.

(Invited, Digital Presentation) Low Voltage Operation of CMOS Inverter Based on WSe2 n/p FETs

Transition metal dichalcogenides (TMDC) have remarkable properties for the next generation of electronic devices [1]. A complementary metal-oxide-semiconductor (CMOS) inverter consisting of pairs of p-type and n-type field-effect transistor (FET) is a fundamental building block in modern digital electronics [2]. Therefore, realization of both p-type and n-type FETs based on semiconducting TMDC is of particular importance. Among various semiconducting TMDC, tungsten diselenide (WSe2) is a promising candidate for constructing a CMOS inverter because of its high mobility, symmetric electron and hole effective mass and ambipolar transport [3]. These prominent features of WSe2 motivates the fabrication and characterization of a CMOS inverter. One of the significant challenges is to develop a high-gain CMOS inverter for operation at a low power supply voltage (Vdd) for future low power digital electronics. Previous studies on a WSe2 CMOS inverter were limited to operation with a low gain of 3 or a high Vdd of more than 1 V under conditions of relatively low gate capacitance and degraded interfacial properties [3-5]. This study addressed these issues by developing a doping technique and gate stack technology to demonstrate the high-gain with low-Vdd operation of a WSe2 CMOS inverter [6]. The focus is on the doping technique of both electrons and holes to a WSe2 layer by simple spin-coating. Of particular interest in this study is the impact of gate stack technology on the CMOS inverter characteristics in low-Vdd operation. In this study, a hybrid self-assembled monolayer (SAM)/aluminum oxide (AlOx) gate dielectric is applied to a WSe2 CMOS inverter for high-gain low-Vdd operation since superior interfacial properties with high gate capacitance have been reported in molybdenum disulfide (MoS2) FETs.For p-type WSe2 FETs, the fluoropolymer CYTOP (AGC, CTX-809A) was applied since polarization in CYTOP due to the difference in electronegativity between C–F bonds generates holes in WSe2. On the other hand, poly(vinyl alcohol) (PVA) was utilized for n-type WSe2 FETs because positive charges in PVA accumulates electrons in WSe2. The resin solutions of both CYTOP and PVA were purchased from a commercial supplier. A heavily doped p-type silicon substrate (p+-Si) was thermally oxidized to form a 60 nm thick silicon dioxide (SiO2) layer for the global back-gate architecture. Palladium (Pd) and gold (Au) as the source and drain contacts for p-type and n-type WSe2 FETs were fabricated by the lift-off process, respectively. An aluminum (Al) gate was prepared and a hybrid SAM/AlOx gate dielectric was formed by oxygen (O2) plasma and an immersion process. After that, mechanically exfoliated WSe2 was transferred with a poly(dimethylsiloxane) (PDMS) stamp. Finally, CYTOP and PVA were deposited by spin-coating for p-type and n-type WSe2 FETs, respectively.Figures 1 (a) and (b) show the Id–Vg characteristics of fabricated FETs. For the p-type WSe2 FET, a small SS of 78 mV/dec and an on/off ratio of about 106 order were observed. On the other hand, the Id–Vg characteristics of the n-type WSe2 FET were degraded compared with those of the p-type WSe2 FET because of the Schottky contacts.Figures 2 (a) and (b) show the transfer characteristics and gain as a function of Vdd in CMOS inverter. The gain of the CMOS inverter increased to as high as 9 at Vdd of 0.5 V.Figure 3 shows the benchmark of this study. Our proposed concepts enabled the operation with high gain at a low Vdd as low as 0.5 V for the WSe2 CMOS inverter, which had not been realized in previous studies. The dangling-bond-free and ultrathin SAM/AlOx gate dielectric has an important role in the low-Vdd operation of the WSe2 CMOS inverter. This study opens up interesting directions for the research and development of TMDC-based devices and circuits.

Design of functionalized magnetic silica multi-core composite nanoparticles for synergistic magnetic hyperthermia/radiotherapy in cancer cells

Nanomaterials in particular the magnetic nanoparticles (MNPs) offer tremendous potential for cancer treatment due to their unique intrinsic properties. Combining materials with a variety of functional groups, and forming a multifunctional nanosystem to overcome the limitations of monotherapy for cancer treatment has always been a research focus with notable difficulties. Considering the many challenges faced by radiotherapy and hyperthermia, in this study, we designed a rational strategy for magnetic hyperthermia using Fe3O4@SiO2@Sec2@FA nanoparticles as a novel nano-radiosensitizer to simultaneously enhance the therapeutic effects of radiotherapy in the future. Fe3O4@SiO2 core–shell structured nanoparticles were synthesized with an appropriate silica layer thickness to maintain good saturation magnetization. The as-prepared Fe3O4@SiO2@Sec2@FA nanoparticles had the specific absorption rate (SAR)value of 57 W/g, which was below the clinically acceptable alternating magnetic field value of 4.9 × 109 Am−1s−1, indicating good heat generation efficiency (the temperature level ΔT=6–10 °C). Moreover, Folate-modified nanoparticles exhibited approximately 6-fold higher cellular internalization of Hela cells with no obvious cytotoxicity for the Hela and MDA-MB-231 cells, and lower cytotoxicity for the HUVECs in a concentration range of 0–150 µg/mL. In addition, these nanoparticles were modified on the silica surface by L-selenocystine, which could enhance the elimination of tumor cells by producing reactive oxygen species under X-rays, resulting in a novel radiosensitization effect. Therefore, the as-prepared Fe3O4@SiO2@Sec2@FA nanoparticles with good biocompatibility and active targeting would possess synergistic magnetic hyperthermia/radiotherapy effect.

Tunable multiband metamaterial coherent perfect absorber based on graphene and vanadium dioxide

In this paper, we propose a tunable multiband metamaterial coherent perfect absorber, where vanadium dioxide (VO2) square particles are periodically arranged on the two sides of polysilicon–silica–graphene–silica–polysilicon​ structure. The absorption spectrum of our absorber exhibits three peaks with high absorptivity which are originated from the plasmon resonance modes of graphene and VO2 particle. Benefitting from the tunable conductivity of graphene, the adjustment range of the absorption peak based on the first-order plasmon resonance mode of graphene is as much as 7.88μm when the Fermi level of graphene is increased from 0.3 to 1 eV. As VO2 is changed from metal phase to insulating phase, the absorption peak stemming from the plasmon resonance mode of VO2 particle disappears. The modulation depth of absorption peak can achieve up to 98.85% by tuning the relative phase of two coherent light beams. The resonance wavelengths and intensities of absorption peaks are also dependent on the array period, side length of VO2 particle and the thickness of silica layer. In addition, the change of surrounding refractive index causes a shift of the absorption peak corresponding to VO2 particle. Our findings are helpful for the engineering of actively tunable nano plasmonic devices and metamaterials.

Design and fabrication of a tapered fiber bundle for a pump combiner with a uniform splicing region

A process of fabricating tapered fiber bundle (TFB) consisting of a set of input pump fibers, stacked inside a low-OH silica capillary, has been optimized to combine multiple multimode pump powers into different output fibers having cladding diameters of 400, 250, and 125 µm. Instead of individual input and output fiber processing, here pump combiner fabrication is based on the processing of the TFB to match its diameter with the output fiber to eliminate any perturbation in light guidance. Fabrication of the TFB includes multiple fusing steps and tapering with brightness conservation, followed by reduction of the outer silica layer through chemical etching to obtain the desired outer diameter. To reduce pump power leakage, the optimum fluorine cladding layer thickness outside the pump fiber cores and outer silica layer thickness have been estimated through numerical simulations using a finite element solver. The influence of fabrication parameters such as interstitial gaps between the input pump fibers, taper ratio, fluorine cladding, outer silica layer thickness, and non-uniformity of splicing region has been characterized in terms of transmission efficiency per port, as well as cumulative power handling along with the operating temperature at maximum power.

An aqueous gold nanorod and CdSe quantum dots hybrid nanomaterial: A potential plasmon enhanced fluorescence structure for bio-probe fabrication

We reported an aqueous plasmon enhanced fluorescence (PEF) nanomaterial, termed as O113A11F19@QDs@SiO2@AuNR, where the fluorescence enhancement fold was highly dependent on the distance between cadmium selenide quantum dots (CdSe QDs) and the plasmonic gold nanorod (AuNR). The distance between AuNR and CdSe QDs was controlled by adjusting the thickness of the silica layer. When the thickness of silica layer was 22 ± 1.2 nm, the maximum fluorescence enhancement of O113A11F19@QDs@SiO2@AuNR was 3.30 times that of bare CdSe QDs. Moreover, O113A11F19@QDs@SiO2@AuNR also showed colloidal stability even when diluted to 5 times. The O113A11F19@QDs@SiO2@AuNR could be used as advanced bio-probe for sophisticated medical diagnosis. The interaction between CdSe QDs and AuNR was investigated using a finite difference time domain (FDTD) simulation. The simulation results demonstrated that the electromagnetic field generated from AuNR can enhance the excitation and radiation decay rate of CdSe QDs, which results in the fluorescence enhancement. The spectra overlap of CdSe QDs with longitudinal localized surface plasmon resonance band (L-SPR) of AuNR and an appropriate distance between AuNR and QDs were both crucial factors for the fluorescence enhancement. The reported findings provide a valuable guidance to rationally design advanced bio-probe for sophisticated medical diagnosis.

Influence of the thickness of silica layer on the radiative relaxation of AuNR@SiO2 core–shell nanostructures upon photoexcitation

AbstractSilica‐coated gold nanorods with different silica thicknesses (AuNR@X‐SiO2, X = 20, 35, 50 and 65, denoting the SiO2 thickness in nm on the longitudinal side) were excited with a 7‐ns pulsed 1064‐nm laser. The infrared emissions of AuNR@X‐SiO2, probed with a step‐scan Fourier‐transform interferometer, enveloped the optical phonon modes of the Si‐O‐Si bridge (1250–1000 cm−1) and adsorbed water (1700–1550 cm−1) within silica pores and minute blackbody radiation, indicating the capability of populating the optical phonon energy of capping layers in core‐shelled nanostructures upon photoexcitation. The decay of the emission at 1250–1000 cm−1 was decelerated as the thickness of silica increased. The kinetic analysis on the emission evolutions provided the thermalization properties of SiO2 on a microsecond timescale, including the intrinsic spontaneous radiation and the non‐radiative thermal conduction. The vibrational energy stored in the solid SiO2 and the embedded water might be capable of serving as an energy donor, that is, an optically‐energized catalyst, for vibrationally‐assisted chemical reactions.

A Magnetic Nanocomposite Modifier for Improved Ultrasensitive Detection of Hexavalent Chromium in Water Samples

In this work, different electrodes were employed for the determination of Cr(VI) by the cathodic square-wave voltammetry (SWV) technique and the square-wave adsorptive stripping voltammetry (SWAdSV) technique in combination with diethylenetriaminepentaacetic acid. Using SWV, a comparison of the analytical performance of the bare glassy carbon electrode (GCE), ex situ electrodes (antimony-film—SbFE, copper-film—CuFE, and bismuth-film—BiFE), and the GCE modified with a new magnetic nanocomposite (MNC) material was performed. First, the MNC material was synthesized, i.e., MNPs@SiO2@Lys, where MNPs stands for magnetic maghemite nanoparticles, coated with a thin amorphous silica (SiO2) layer, which was additionally functionalized with derived lysine (Lys). The crystal structure of the prepared MNCs was confirmed by X-ray powder diffraction (XRD), while the morphology and nano-size of the MNCs were investigated by field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM), where TEM was additionally used to observe the MNP core and silica layer thickness. The presence of functional groups of the MNCs was investigated by attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and surface analysis was performed by X-ray photoelectron spectroscopy (XPS). The hydrophilicity of the modified electrodes was also tested by static contact angle measurements. Then, MNPs@SiO2@Lys was applied onto the electrodes and used with the SWV and SWAdSV techniques. All electrodes tested with the SWV technique were effective for Cr(VI) trace determination. On the other hand, the SWAdSV technique was required for ultra-trace determination of Cr(VI). Using the SWAdSV technique, it was shown that a combination of ex situ BiFE with the deposited MNPs@SiO2@Lys resulted in excellent analytical performance (LOQ = 0.1 µg/L, a linear concentration range of 0.2–2.0 µg/L, significantly higher sensitivity compared to the SWV technique, an RSD representing reproducibility of 9.0%, and an average recovery of 98.5%). The applicability of the latter system was also demonstrated for the analysis of a real sample.

Deep Silicon Amorphization Induced by Femtosecond Laser Pulses up to the Mid‐Infrared

AbstractDirect laser writing of amorphous lines in crystalline silicon has the potential for becoming a flexible alternative to silicon‐on‐insulator technology for photonic integrated circuits. Yet, the maximum amorphous layer thickness achieved is 60 nm, which is below the requirements for waveguiding at telecom wavelengths. Here, the authors report on different strategies to push the layer thickness beyond today's limit. To this end, irradiation with femtosecond laser pulses covering an extremely broad wavelength range (515 nm–4 µm) up to the yet unexplored near‐ and mid‐infrared region of silicon transparency is investigated. The results show that much thicker amorphous layers can be obtained upon multipulse irradiation at 3‐µm wavelength. The deepest amorphization is achieved in silicon wafers covered with a thick silicon dioxide layer that strongly assists the heat extraction, yielding steep index profiles with a maximum amorphous layer thickness of 128 nm. This superior thickness is compatible with single mode waveguiding for a symmetric waveguide configuration. This study also contributes to a better understanding of the mechanisms involved in laser‐induced amorphization.

Low-Temperature Deep Ultraviolet Laser Polycrystallization of Amorphous Silicon for Monolithic 3-Dimension Integration

Monolithic 3-dimensional integration (M3D) requires heat treatment techniques that should not degrade the device performance of the lower layers when applied to device fabrication in the upper layers. Deep ultraviolet (DUV) laser annealing was implemented in the crystallization of amorphous silicon and source/drain junction activation to fabricate polycrystalline silicon (poly-Si) metal-oxide-semiconductor field-effect-transistors (MOSFETs) for upper-layer devices. The poly-Si MOSFET devices were fabricated successfully on top of the bottom electronic circuit layer (isolated by a thick silicon dioxide layer). Devices on the upper and lower layers were connected through interlayer vias to form a current-starved ring oscillator. The current-to-frequency converter on the bottom layer showed a reasonable increase in frequency as the current of the poly-Si MOSFET on the upper layer increased with increasing silicon grain size, confirming that DUV laser annealing did not degrade the performance of the bottom layer devices. This opens more opportunities for using DUV laser annealing in the M3D integration.

Suppressing the Photocatalytic Activity of Titania by Precisely Controlled Silica Coating.

A homogeneous thin silica layer with the thickness of a few nanometers was successfully deposited on an anatase particle by the hydrolysis and condensation of tetraethyl orthosilicate. The heat treatment of the titania/silica hybrid at 1000 °C led to the densification of the silica layer on the anatase particles. The anatase particle after the silica coating did not transform to rutile, and no change in the crystallite size was seen by the heat treatment at 1000 °C. The coating and subsequent heating were repeated to vary the thickness of the silica layer to obtain each coating with similar thickness by each coating procedure (ca. 3 and 2 nm, before and after the heat treatment). The samples were evaluated for the photocatalytic decomposition of methylene blue by the UV irradiation to find that the decomposition became slower after the coating and subsequent heat treatment, and the repeated procedures led to further suppression of the photocatalytic decomposition of methylene blue. The quite small decomposition rate constant (0.01 h-1) was successfully achieved by the coating and subsequent heating for three times (the thickness of the dense silica layer was ca. 7 nm).

Investigation of physico-chemical and catalytic properties of the coating layer of silica-coated iron oxide magnetic nanoparticles

Silica-coated iron oxide magnetic nanoparticles to be employed as the starting core for easily-recoverable heterogeneous catalysts supports, were synthesized. We tuned both the properties of the magnetic core and of the covering shell, with particular emphasis on the optimization of the silica layer thickness. Afterwards, structural-sensitive techniques (XRD, BET surface area analysis), surface-sensitive techniques (ATR-IR, XPS), imaging (SEM, TEM), elemental analyses (ICP-MS) and magnetization analyses (AGFM), were employed to unravel the features of the synthesized materials. The oxidation of cis-cyclooctene with tert-butyl hydroperoxide in presence of MNPs was used as probe reaction to check the reactivity of the NPs and the effectiveness of the silica shield. The results of these tests showed its chemical inertia confirming the absence of any detrimental iron oxide catalyzed side-reactions or magnetic core modification.

Magnetic nanostructures functionalized with a derived lysine coating applied to simultaneously remove heavy metal pollutants from environmental systems

ABSTRACT The pollution of environmental systems with heavy metals is becoming a serious problem worldwide. These contaminants are one of the main issues in sludge (which is considered waste) and can even have harmful effects if the sludge is not treated properly. Thus, the development of a novel functional magnetic nanoadsorbent based on a derived lysine is reported here, which can be efficiently applied for metal removal from sludge. Magnetic nanoparticles were coated with silica layer and further modified by covalent bonding of derived lysine. The morphology of the nanomaterial, its nano-size and the silica layer thickness were analyzed by transmission electron microscopy. The successful silanization of the lysine derivative to the silica-coated magnetic nanostructures was investigated by several physicochemical characterization techniques, while the magnetic properties were measured with a vibrating sample magnetometer. The synthesized nanostructures were used as adsorbents for simultaneous removal of most critical heavy metals (Cr, Zn, Cu) from real complex sludge suspensions. The main practical adsorption parameters, pH of the native stabilized sludge, adsorbent amount, time, and adsorbent regeneration were investigated. The results show promising adsorption properties among currently available adsorbents (the total equilibrium adsorption capacity was 24.5 mg/g) from the sludge with satisfactory nanoadsorbent reusability and its rapid removal. The stability of the nanoadsorbent in the sludge, an important but often neglected practical parameter for efficient removal, was verified. This work opens up new possibilities for the development of high-quality magnetic nanoadsorbents for metal pollutants applied in various complicated environmental fields and enables waste recovery.

Effect of different silica coatings on the toxicity of upconversion nanoparticles on RAW 264.7 macrophage cells.

Upconversion nanoparticles (UCNPs), consisting of NaYF4 doped with 18% Yb and 2% Er, were coated with microporous silica shells with thickness values of 7 ± 2 and 21 ± 3 nm. Subsequently, the negatively charged particles were functionalized with N-(6-aminohexyl)-3-aminopropyltrimethoxysilane (AHAPS), which provide a positive charge to the nanoparticle surface. Inductively coupled plasma optical emission spectrometry (ICP-OES) measurements revealed that, over the course of 24h, particles with thicker shells release fewer lanthanide ions than particles with thinner shells. However, even a 21 ± 3 nm thick silica layer does not entirely block the disintegration process of the UCNPs. 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays and cell cytometry measurements performed on macrophages (RAW 264.7 cells) indicate that cells treated with amino-functionalized particles with a thicker silica shell have a higher viability than those incubated with UCNPs with a thinner silica shell, even if more particles with a thicker shell are taken up. This effect is less significant for negatively charged particles. Cell cycle analyses with amino-functionalized particles also confirm that thicker silica shells reduce cytotoxicity. Thus, growing silica shells to a sufficient thickness is a simple approach to minimize the cytotoxicity of UCNPs.