SiO2 Cavity Research Articles

Water-Resistant Subwavelength Perovskite Lasing from Transparent Silica-Based Nanocavity.

Great research efforts are devoted to exploring the miniaturization of chip-scale coherent light sources possessing excellent lasing performance. Despite the indispensablerole in Si photonics, SiO2 is generally considered not contributing to the starting up and operation of integrated lasers. Here, this work demonstrates an extraordinary-performance subwavelength-scale perovskite vertical cavity laser with all-transparent SiO2 cavity, whose cavity is ultra-simple and composed of only two parallel SiO2 plates. By introducing a ligand-assisted thermally co-evaporation strategy, highly luminescent perovskite film with high reproducibility and excellent optical gain is grown directly on SiO2 . Benefitting from their high-refractive-index contrast, low-threshold, high-quality factor, and single-mode lasing is achieved in subwavelength range of ≈120nm, and verified by long-range coherence distance (115.6µm) and high linear polarization degree (82%). More importantly, the subwavelength perovskite laser device could operate in water for 20 days without any observable degradation, exhibiting ultra-stable water-resistant performance. These findings would provide a simple but robust and reliable strategy for the miniaturized on-chip lasers compatible with Si photonics.

Thermal dynamics of few-layer-graphene seals.

Being of atomic thickness, graphene is the thinnest imaginable membrane. While graphene's basal plane is highly impermeable at the molecular level, the impermeability is, in practice, compromised by leakage pathways located at the graphene-substrate interface. Here, we provide a kinetic analysis of such interface-mediated leakage by probing gas trapped in graphene-sealed SiO2 cavities versus time and temperature using electron energy loss spectroscopy. The results show that gas leakage exhibits an Arrhenius-type temperature dependency with apparent activation energies between 0.2 and 0.7 eV. Surprisingly, the interface leak rate can be improved by several orders of magnitude by thermal processing, which alters the kinetic parameters of the temperature dependency. The present study thus provides fundamental insight into the leakage mechanism while simultaneously demonstrating thermal processing as a generic approach for tightening graphene-based-seals with applications within chemistry and biology.

Gas permeation rates of ultrathin graphite sealed SiO2 cavities.

Despite the proven impermeability of graphene toward most standard gases, graphene/graphite sealed SiO2 cavities always exhibit a nonzero leak rate, and the physical leakage mechanism is still unclear. By measuring leak rates of different gases for the same cavities sealed by ultrathin graphite under identical conditions, we find that the leak rates generally depend on the kinetic diameter of the gas molecules, which implies that the leakage is caused by a molecular sieving mechanism. By comparing different samples, we find that the leak rate of any gas in a particular sample is well predicted by the leak rate of N2 in that sample. In addition, we observe enhanced leak rates of water-soluble molecules. We infer that the leakage path (i.e., the graphene/graphite-SiO2 interface) favors hydrophilic species.

High‐Chroma Color Coatings Based on Ag/SiO2/Ti/SiO2 Structures

A four‐layer metal–dielectric–metal–dielectric (MDMD) stack design for color control is demonstrated. This stack incorporates Ag, SiO2, and Ti as materials, enabling wide absorbance bands, high reflectance peaks, and a strongly tunable color. A wide gamut is obtained by varying the thickness of the SiO2 cavity layer, and the resulting colors exhibit outstanding luminance and chroma. Coatings of red, green, and blue colors are designed and deposited. These coatings demonstrate a very close agreement between the simulated and experimental results. The chroma of the coatings is found to be similar to or exceeded the limits of the Pointer gamut, an empirical gamut of colors in reflectance. This shows that, in the generation of surface color, even for a simple four‐layer stack, the performance of thin‐film coatings can rival or exceed that of traditional paints and dyes.

Fabrication of multi-nanocavity and multi-reflection interface in rGO for enhanced EMI absorption and reduced EMI reflection

Through inserting SiO2@Au into the reduced graphene oxide (rGO) layers, the rGO-SiO2@Au composites were prepared via the vacuum-assisted electrostatic self-assembly method. The obtained composites exhibit excellent electromagnetic interference (EMI) shielding effectiveness due to the successful construction of multi-nanocavities (spherical SiO2 cavities and layered air cavities between rGO), multi-reflection interfaces (rGO and Au shell) and continuous conductive network (rGO-Au-rGO). Among them, the total shielding effectiveness (SET) of the composites with 75.78 wt% SiO2 and 19.38 wt% rGO can reach 38.4 dB at 18 GHz. Thereinto, the shielding effectiveness absorption (SEA) is 36.4 dB, 1.3 and 13.5 times higher than that of rGO and SiO2@Au. And the shielding effectiveness reflection (SER) is always below 5 dB from 1 to 18 GHz, much lower than that of rGO (about 15 dB). Further studies found that the SEA values were enhanced at 12.6 GHz and 6.2 GHz due to the construction of cavities and location of Au nanoparticles between the rGO layers. This study provides a simple and mild method to prepare high-performance thin-layered materials with applications in the field of EMI absorption shielding.

Hollow double-shell structured Void@SiO2@Co-C composite for broadband electromagnetic wave absorption

Current electromagnetic wave (EMW) absorbing materials generally face the problem of narrow absorption bandwidth, which is the bottleneck in practical applications. Exploring new strategies and designing new architectures to overcome this problem is urgent but challenging. Here, a hollow double-shell structured magneto-electric composite, composed of an internal hollow cavity, a middle SiO2 matching shell and an outer Co-C porous shell ([email protected]2@Co-C), was prepared by assembling metal–organic-framework particles on hollow SiO2 cavity and pyrolysis. The multiple magnetic resonances, magneto-electric interface polarization, defect dipole polarization and conductivity of the composite can be well tuned by controlling the pyrolysis temperature. In particular, the hollow SiO2 cavity plays an essential role in improving impedance matching. Benefitting from the synergistic effect between hollow SiO2 cavity, porous carbon shell and Co particles, the [email protected]2@Co-C composite exhibits a broad effective absorption bandwidth above 7 GHz at a thin thickness of 2.2 mm, which is superior to other Co-C composites (less than 6 GHz). This work provides an effective solution for broadening the EMW absorption bandwidth.

Farfield Under Small Scattering Angle in the Rectangular Ag–Si–SiO2 Cavity

In this paper, the farfield under small scattering angle was investigated in the rectangular Ag–Si–SiO2 cavity by FDTD. The simulation results showed that Re(E) of the farfield was related to the monitoring wavelength and was a function of monitoring wavelengths. Moreover, in the rectangular Ag–Si–SiO2 cavity, the amplitude of Re(E) changed as the silicon height d varied, and maximum amplitude A of Re(E) could be approximated as the functions of transverse length l and thickness t of silver film under small scattering angle. Re(E) was independent of the transverse length w2 and the longitudinal length d of the cavity in RCM and was also irrelevant with the dielectric constant of silver films. The amplitude A of Re(E) increased as l and t of silver film increased.

Integrated structural color array enabled by ultrathin silver film via cavity-enhanced absorption

In this work, we experimentally demonstrate enhanced absorption resonance enabled by the deconstructive interference of the reflected light in a sandwiched nanostructures composing of the ultrathin silver layer, transparent SiO2 cavity, and the opaque metallic substrate (e.g., 300-nm Ag). Such cavity-enhanced absorption is tunable via modulating the thickness of the absorptive ultrathin silver layer or the embedded transparent SiO2 cavity, giving rise to tunable structural coloration. Through five deposition processes, a 32-channel colorful sample is successfully fabricated. We believe the concepts and results make it evident that such ultrathin absorptive film offers us unprecedented opportunities on developing various photonic applications such as labeling, visual arts, and optical filters.

Time-resolved spectral response of asymmetrical optical microcavity structures under laser-driven shock compression

The time-resolved spectral responses of three asymmetrical optical microcavity (AOMC) structures under laser-driven shock compression were investigated. The objective was to compare the performance of these multilayer structures and explore the potential in dynamic shock “pressure” sensing, given their unique ability to capture spatially heterogeneous pressure distributions across 2D surfaces. Different AOMC structures were fabricated, with amorphous SiO2, amorphous Al2O3, and PMMA cavity layers between deposited silver reflecting layers producing the characteristic spectral features of the structures. An experimental setup employing laser-driven shock compression was used to generate nanosecond scale pressure loads of ∼1-10 GPA, and the corresponding time-resolved spectral response and in-situ particle velocity of the AOMCs was simultaneously recorded. Each of the AOMC multilayers showed clear spectral shifts as a function of pressure with nanosecond level correlation to the independently measured velocimetry data. These results indicate that the time-resolved physical state of the cavity layer drives the spectral response of the optical microcavity structures. The results also validate qualitative predictions of the multilayer structures’ response to dynamic compressive loads and their potential for use in time-resolved sensing of pressure.

Asymmetrical optical microcavity structures for dynamic pressure sensing: design, fabrication, validation.

Optical microcavity (OMC) structures have spectral properties that are directly related to their physical dimensions and material refractive indices. Their intrinsically fast optical response to mechanically-induced changes in these parameters makes OMCs uniquely suited for dynamic sensing when paired with a suitably fast streak camera and spectrograph. Various designs and processes of fabrication for asymmetrical OMC (AOMC) structures were investigated to optimize and assess their feasibility for dynamic sensing. Structural and material effects were studied in terms of spectral properties, structure stabilities and fabrication process. From this study, it was shown that an AOMC structure with a SiO2 cavity layer and Ag mirror layers, fabricated with thin adhesion Al2O3 layers exhibited the best structural stability and spectral properties. Under dynamic compressive loading of ~4 GPa, the structure exhibited a blueshift of 22 nm and a temporal response time of < 3.3 ns, thus demonstrating the potential of AOMC based dynamic pressure sensing.

Coalescence of planar GaAs nanowires into strain-free three-dimensional crystals on exact (001) silicon

We report three dimensional (3D) disk-shaped GaAs crystals on V-groove patterned (001) Si substrates by metalorganic chemical vapor deposition. Planar GaAs nanowires with triangular cross-sections were grown inside Si V-grooves by nano-scale selective heteroepitaxy. These nanowires were then partially confined in micro-sized SiO2 cavities and coalesced into uniform arrays of 3D crystals. Scanning electron microscope and atomic force microscopy inspection showed the absence of antiphase-domains and smooth top surface morphology. Superior structural and optical properties over GaAs thin films on planar Si were also demonstrated. More remarkably, by growing the 3D crystals on V-grooved Si, we were able to overcome the residual tensile stress induced by the thermal mismatch between GaAs and Si. Strain-free GaAs was uncovered in the crystals with a dimension of 3×3µm2.

Electrochemical behaviors of polyaniline confined in highly ordered micro-sized SiO2 cavities

An array of microelectrodes is fabricated with highly ordered SiO2 cavities modified on an indium-doped tin oxide (ITO) electrode, benefiting from the confinement of the insulating SiO2 cavities. Aniline can be electrochemically polymerized to form polyaniline (PANI) independently inside each SiO2 cavity. The edge effect of the microelectrodes leads to the radial diffusion of aniline in the SiO2 cavities; as a result, the PANI grows uniformly along the wall of the cavities and eventually covers the whole surface area of the SiO2 cavities to form an array of PANI cavities. Thus, the effective area of the PANI modified electrode could be greatly enlarged through such a surface structure modification. Moreover, it is demonstrated that the electrochemical reaction of ascorbic acid can be enhanced due to the radial diffusion of ascorbic acid inside PANI cavities. The specific features of the PANI cavity array enables us to develop a sensing platform of ascorbic acid detection with a detection limit of 0.14μM (S/N=3) and a linear range of 0.5–131μM.

SIMS depth profiling and topography studies of repetitive III–V trenches under low energy oxygen ion beam sputtering

Chemical depth profiling of III–V trenches containing InGaAs quantum wells with AlAs barriers selectively grown inside SiO2 cavities was studied using magnetic secondary ion mass spectrometry (SIMS). The authors show that the depth resolution of SIMS profiles of III-As layers degrades under extremely low energy oxygen beam sputtering (&amp;lt;500 eV) due to ripple formation and an increase in surface roughness. Improved SIMS depth resolution was observed by increasing the incident angle (∼50°–65°). Finally, the authors report the effect of sample rotation and orientation of the ion beam with respect to the trenches on depth profiling of III-As layers using time-of-flight SIMS.

Formation of silver single crystal polyhedra with high catalytic activity toward oxidation of ascorbic acid in highly ordered SiO2 cavities

Two-dimensional array of SiO2 cavities is fabricated on an indium-doped tin oxide (ITO) electrode by using highly ordered self-assembly of polystyrene spheres as a template. Silver nanoparticles electrodeposited at the bottom of the SiO2 cavities are fused and recrystallized via aggregative and Ostwald ripening mechanisms under annealing treatment conditions. Due to the confinement effect of the SiO2 cavity, the vaporized silver atoms preferentially deposit on the surface of the relative large silver particles at near equilibrium state, leading to the formation of silver single crystal polyhedron dominated with (111) facets in each SiO2 cavity, which can functionalize as a nanoelectrode and exhibit excellent electrocatalytic activity toward oxidation of ascorbic acid. Based on the array of the silver single crystal polyhedra, an electrochemical sensing platform of ascorbic acid is developed with high sensitivity and rapid response.

Core/Shell Structured Rattle-Type Multifunctional Spheres: Synthesis, Magnetic, and Fluorescent Properties

In this study, we prepared the core/shell structured rattle-type multifunctional composites Fe3O4@H SiO2@YVO4:Eu3+. It is composed of Fe3O4 crystals as cores, YVO4:Eu3+ phosphors as shell, and an SiO2 cavity in between. The formation of SiO2 cavity between magnetic core and fluorescent shell is based on the SiO2 structural difference by the selective ammonium etching method. The composites were characterized by the X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, N2 adsorption-desorption, photoluminescence spectroscopy, and vibrating sample magnetometer. The results indicate that the multifunctional composites exhibit obvious cavity, typical mesoporous structure, narrow size distribution, excellent luminescent properties, and magnetic features. The composites may have potential applications in catalytic, drug delivery, and controlled storage and release.

Two-Dimensional Ordered Silicon Dioxide Cavities Array as Matrix for the Immobilization of Horseradish Peroxidase and Its Direct Electrochemistry

A silicon dioxide (SiO2) cavities array was fabricated on indium-tin oxide (ITO) electrode with polystyrene (PS) particles array as template by using sol-gel technique. The electrochemical properties of SiO2 cavities array indicated that it acted as microelectrode array. Horseradish peroxidase (HRP) was immobilized on the surface of SiO2 cavities by adsorption method. Direct electrochemistry of HRP modified SiO2 cavities array was studied. The results showed that the microenvironment of SiO2 cavities can accelerate electron transfer of HRP efficiently and the electron transfer rate was calculated to be 1.98 s(-1).

Low defect InGaAs quantum well selectively grown by metal organic chemical vapor deposition on Si(100) 300 mm wafers for next generation non planar devices

Metal organic chemical vapor deposition of GaAs, InGaAs, and AlGaAs on nominal 300 mm Si(100) at temperatures below 550 °C was studied using the selective aspect ratio trapping method. We clearly show that growing directly GaAs on a flat Si surface in a SiO2 cavity with an aspect ratio as low as 1.3 is efficient to completely annihilate the anti-phase boundary domains. InGaAs quantum wells were grown on a GaAs buffer and exhibit room temperature micro-photoluminescence. Cathodoluminescence reveals the presence of dark spots which could be associated with the presence of emerging dislocation in a direction parallel to the cavity. The InGaAs layers obtained with no antiphase boundaries are perfect candidates for being integrated as channels in n-type metal oxide semiconductor field effect transistor (MOSFET), while the low temperatures used allow the co-integration of p-type MOSFET.

Structure and SO3 decomposition activity of nCuO–V2O5/SiO2 (n = 0, 1, 2, 3 and 5) catalysts for solar thermochemical water splitting cycles

SiO2-supported nCuO–V2O5 catalysts with different ratios (n=0, 1, 2, 3 and 5) were prepared to study their catalytic activity for SO3 decomposition, which is a key reaction necessary for solar thermochemical H2 production. Although four binary compounds, CuV2O6, Cu2V2O7, Cu3V2O8 and Cu5V2O10, were formed on three-dimensional (3-D) mesoporous SiO2 depending on the ratio (n), the thermal ageing caused their incongruent melting and precipitation of Cu2V2O7. The highly corrosive molten vanadate phase resulted in mesopore-to-macropore conversion of SiO2, which was accompanied by significant decrease of BET surface area and pore volume. Nevertheless, the structural conversion yielded copper vanadate with a high surface coverage of SiO2 cavity walls enabling efficient catalytic SO3 decomposition at moderated reaction temperatures (∼600°C). Among nCuO–V2O5/SiO2 catalysts, the highest catalytic activity was achieved for n=1, which corresponds to the phase with the lowest melting point (630°C) of the present system.

Electrochemical detection of free glycerol in biodiesel using electrodes with single gold particles in highly ordered SiO2 cavities

In the present work, we report a direct electrochemical glycerol detection method using thermally annealed, facet-specific, single gold particles, Au (111), located in the cavities of a highly ordered SiO2 cavity array on an indium-doped tin oxide (ITO) electrode. We fabricated an interconnected array structure comprised of SiO2 cavities onto ITO electrodes via monolayer colloidal crustal (MCC) templates. Gold nanoparticles (Au NPs) were electrodeposited at the bottom of the SiO2 cavities in direct contact with the ITO electrodes (Au (poly)/SiO2 cavity/ITO electrode). Upon annealing the electrodes at 700°C, single gold particles were formed, dominated by the (111) facet (Au (111)/SiO2 cavity/ITO electrode). The Au (111)/SiO2 cavity/ITO electrode exhibited satisfactory electrocatalytic activity to the oxidation of glycerol. More importantly, each cavity of the SiO2 possibly behaves as an independent electrochemical cell in which the glycerol molecules are trapped; this produces a microenvironment advantageous to catalyze electrooxidation. Moreover, Au (111)/SiO2 cavity/ITO electrode design gave a wide linear range from 0.01mM to 0.8mM, and a low detection limit of 1.49μM. As a glycerol sensor, the electrode displayed good reproducibility and long-term stability. The electrode was applied to directly determine the free glycerol in the biodiesel samples. This strategy might provide an approach to study electrochemical reactions on single particles in a microenvironment and offers a method for constructing alcohols sensors.

Antenna-enhanced and polarization sensitive photoresponse in arrays of silicon P–i–N nanowires

We analyze a novel antenna effect that resonantly enhances the photocurrent response of end-contacted P–i–N junction nanowire gratings, due to coupling of incident radiation into the grating's multiple-scattering electromagnetic modes. Quantitative characterization of these resonances was performed by spectral and polarization-resolved photocurrent measurements on gratings with N = 500, 200 and 100 nanowires, aided by electron beam-induced current measurements, and in excellent agreement with electromagnetic scattering theory. Despite the small scattering cross-section of each nanowire, with triangular cross-section (height 8 nm, width 6 nm), the measured quality factor of the resonances Q ≈ 10 exceeds that of the empty SiO2 cavity without degradation for gratings of as few as 100 nanowires. Photoresponse retains sinusoidal polarization anisotropy characteristic of single nanowires. We discuss strategies for improving Q and present a grating design tailoring resonant field enhancement at red, green or blue wavelengths, for three different grating periods of ℓ = 460, 400 and 320 nm.