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In this paper, we demonstrate the first example of phonon-assisted hot luminescence (PAHL) emission from silicon (Si) spheres (diameter > 100nm) without using the plasmonic effect or quantum confinement effect. Instead, we excite the hot luminescence of Si by a strong thin-film-cavity-enhanced magnetic dipole resonance. The thin-film cavity (80 nm SiO2/Ag) shows a strong co-enhancement with the magnetic dipole resonance of Si sphere (diameter = 120 nm). The concentrated electromagnetic fields induce significant light–matter interaction. Our Si sphere coupled with a thin-film cavity achieves a 10-fold field enhancement relative to the Si sphere without an enhancement substrate. Furthermore, we experimentally use cavity-enhanced magnetic dipole resonance to a 50-fold enhancement in PAHL. The measured internal quantum efficiency for the visible light emitted from the Si spheres was approximately 2.4%. Furthermore, we demonstrate the tunability of emission peaks merely by adjusting the sizes of Si spheres using thermal oxidation and etching processes. For comparison, we calculated the peak wavelength (λ peak) sensitivities (Δλ peak/ΔDiameter) of Si spheres and Si QDs through Mie theory and effective mass approximation, respectively. The predicated peak sensitivities of the Si spheres ranged from 1.3 to 3.2; they were much more controllable than those of the Si QDs (200–400). Thus, the peak wavelengths of the PAHL of the Si spheres could be modulated and controlled much more precisely and readily than that of the Si QDs. With the tunability and strong electromagnetic field confinement, the cavity-enhanced magnetic dipole resonance appears to have great potential in the development of all-optical processing based on Si photonics.

The localized surface plasmon resonance of plasmonic nanoparticles (NPs) can be coupled with a noble metal substrate (S) to induce a localized augmented electric field (E-field) concentrated at the NP-S gap. Herein, we analyzed the fundamental near-field properties of metal NPs on diverse substrates numerically (using the 3D finite-difference time-domain method) and experimentally [using surface-enhanced Raman scattering (SERS)]. We systematically examined the effects of plasmonic NPs on noble metals (Ag and Au), non-noble metals (Al, Ti, Cu, Fe, and Ni), semiconductors (Si and Ge), and dielectrics (TiO2, ZnO, and SiO2) as substrates. For the AgNPs, the Al (11,664 times) and Si (3969 times) substrates produced considerable E-field enhancements, with Al in particular generating a tremendous E-field enhancement comparable in intensity to that induced by a Ag (28,224 times) substrate. Notably, we found that a superior metallic character of the substrate gave rise to easier induction of image charges within the metal substrate, resulting in a greater E-field at the NP-S gap; on the other hand, the larger the permittivity of the nonmetal substrate, the greater the ability of the substrate to store an image charge distribution, resulting in stronger coupling to the charges of localized surface plasmon resonance oscillation on the metal NP. Furthermore, we measured the SERS spectra of rhodamine 6G (a commonly used Raman spectral probe), histamine (a biogenic amine used as a food freshness indicator), creatinine (a kidney health indicator), and tert-butylbenzene [an extreme ultraviolet (EUV) lithography contaminant] on AgNP-immobilized Al and Si substrates to demonstrate the wide range of potential applications. Finally, the NP-S gap hotspots appear to be widely applicable as an ultrasensitive SERS platform (∼single-molecule level), especially when used as a powerful analytical tool for the detection of residual contaminants on versatile substrates.

Perovskite materials prepared in the form of solution-processed nanocrystals and used in top-down fabrication techniques are very attractive to develop low-cost and high-quality integrated optoelectronic circuits. Particularly, integrated miniaturized coherent light sources that can be connected to light-guiding structures on a chip are highly desired. To control light propagating on a small footprint with low-loss optical modes, long-range surface plasmon polariton (LRSPP) waveguides are employed. Herein, we demonstrate an on-chip fabricated photonic-plasmonic hybrid system consisting of a perovskite lasing structure coupled to an LRSPP waveguide achieving a low lasing threshold and a propagation length over 100 μm. Preventing perovskite material degradation and the formation of surface roughness of the laser cavity during fabrication is made possible by designing a fabrication technique without any etching step.

Extensive studies on lead halide perovskites have shown that these materials are excellent candidates as gain mediums. Recently, many efforts have been made to incorporate perovskite lasers in integrated optical circuits. Possible solutions would be to utilize standard lithography with an etching/lift-off process or a direct laser etching technique. However, due to the fragile nature of the lead halide perovskites which gives rise to significant material deterioration during the lithography and etching processes, realizing a small-size, low-roughness, and single-mode laser remains a challenge. Here, a lithographic in-mold patterning method realized by nanocrystal concentration control and a multi-step filling-drying process is proposed to demonstrate CsPbBr3 nanocrystals distributed-Bragg-reflector (DBR) waveguide lasers. This method realizes the patterning of the CsPbBr3 nanocrystal laser cavity and DBR grating without lift-off and etching processes, and the smallest fabricated structures are obtained in a few hundred nanometers. The single-mode lasing is demonstrated at room temperature with a threshold of 23.5 μJ cm-2. The smallest full width at half maximum FWHM of the laser output is 0.4 nm. Due to the fabrication process and the DBR laser geometry, the lasers can be fabricated in a compact array, which is important for incorporating perovskite-based lasers in complex optoelectronic circuits.

The recent development of perovskite-based lasers showcased the outstanding optical properties of the material such as high absorption coefficient and high quantum yield. The lasers were demonstrated in the form of nanowires and nanoplates, which are difficult to be integrated on a chip in the form of high-density arrays due to the difficulties in positioning them on the chip. The solution to this problem should be to use the well-known lithography process in the fabrication process of the lasers. In this work, we demonstrate several perovskite-based plasmonic lasers that were fabricated by using the lithographic in-mold patterning method that relies on the electron beam lithography process. The lasers utilized CsPbBr3 perovskite nanocrystals as the gain material and plasmonic distributed Bragg reflector grating structure as the optical feedback provider to achieve a low lasing threshold of 42.5 μJ/cm2 with a linewidth of 0.6 nm (FWHM) at room temperature. The use of the lithographic process in the fabrication of the lasers makes it possible to fabricate and integrate them on a chip in a relatively high-density manner, so that they can be used extensively in quantum optics and on-chip integrated photonics applications.

Extensive studies on lead halide perovskites have shown that these materials are excellent candidates as gain mediums. Recently, many efforts have been made to incorporate perovskite lasers in integrated optical circuits. Possible solutions would be to utilize standard lithography with an etching/lift-off process or a direct laser etching technique. However, due to the fragile nature of the lead halide perovskites which gives rise to significant material deterioration during the lithography and etching processes, realizing a small-size, low-roughness, and single-mode laser remains a challenge. Here, a lithographic in-mold patterning method realized by nanocrystal concentration control and a multi-step filling-drying process is proposed to demonstrate CsPbBr

The properties of two-dimensional (2D) materials are readily affected by their surroundings. Therefore, the underlying substrates and surrounding materials always disturb the pristine properties of 2D materials. Herein, we describe how the pristine properties of suspended 2D materials can be precisely extracted from Raman and photoluminescence (PL) spectra with great signal enhancements by taking advantage of both air gap suspension and nanocavity enhancement effects. The modes of the Raman emission lines were enhanced to almost the same degree when the 2D materials were positioned over the nanocavity: the 2D/G peaks of suspended single-layer graphene (SLG) and the E12g/A1g peaks of MoS2 were significantly enhanced almost equally. Moreover, recording Raman and PL spectra at different positions of the suspended 2D materials was a very powerful tool for observing charge transfer between the pristine 2D materials and the surrounding materials. We also found that the residual holes of the suspended SLG could ...

Solution-process perovskite quantum dots (QDs) are promising materials to be utilized in photovoltaics and photonics with their superior optical properties. Advancements in top-down nanofabrication for perovskite are thus important for practical photonic and plasmonic devices. However, different from the chemically synthesized nano/micro-structures that show high quality and low surface roughness, the perovskite QD thin film prepared by spin-coating or the drop-casting process shows a large roughness and inhomogeneity. Low-roughness and low-optical loss perovskite QD thin film is highly desired for photonic and optoelectronic devices. Here, this work presents a pressure-assisted ligand engineering/recrystallization process for high-quality and well-thickness controlled CsPbBr

Plasmonic nanolasers provide a valuable opportunity for expanding sub-wavelength applications in the fields of biosensing,[1] nonlinear frequency generation,[2] and optical switching.[3]

Large-area graphene is commonly prepared through chemical vapor deposition (CVD); in situ and nondestructive methods for its characterization are desirable. In this paper, we demonstrate a practical method—exploiting magnetic dipole resonance and coupling effects—with which the Raman signals of graphene on copper (Cu) foil can be directly, faithfully, and greatly enhanced. The magnetic dipole resonance of a silicon nanoparticle (SiNP) can effectively couple its electromagnetic field with the Cu foil to induce an enormous electric field located solely at the position of the SiNP on the graphene. The coupled electromagnetic field can lead to hot spots of high electric field intensity (E2/E02 = 123.2) within the graphene. Even when we positioned only a few SiNPs upon the graphene/Cu foil, we obtained a Raman signal enhancement (ca. 206 times) much greater than that of graphene transferred onto a 300 nm oxide film (ca. 12 times). From a series of experiments comparing the Raman signals of graphene before and ...

A broadband perfect absorber based on loading effect–induced single-layer/trench-like thin metallic (LISTTM) structures is demonstrated. These LISTTM structures take advantage of both surface plasmon resonance and three-dimensional cavity effects to provide efficient, tunable, polarization-insensitive absorption from the ultraviolet (UV) to the infrared (IR) regime. The optimized hole-width of the LISTTM arrays was approximately one half of the designed wavelength. Therefore, even when the designed absorption band was in the visible regime, the feature sizes of the LISTTM structure could remain on the order of several hundred nanometers. Moreover, the loading effects, which were generated during the etching and deposition processes, further improved the maximum absorption to greater than 95% and widened the absorption bandwidth of the structures significantly. These LISTTM structures exhibited superior photothermal performance; they also displayed very low emissivity, thereby decreasing heat dispersion through thermal radiation. Therefore, the LISTTM arrays could efficiently absorb light of higher photon energy in the UV, visible, and near-IR regimes, effectively conduct the generated heat through the continuous metal films, and barely disperse any heat through thermal radiation. Accordingly, these attractive properties suggest that such LISTTM absorbers might have promising applications in many fields related to energy harvesting.

Carbon nanotube (CNT) meshes have optical and electrical properties that make them suitable for use in next-generation transparent conductive electrodes (TCEs). Although circuit modeling of CNT meshes has been studied widely, very few researchers have modeled the optical properties of the horizontally and regular arrangement of CNT arrays. The behavior of light propagating through a CNT mesh is complex, with no straightforward rules established to provide simple analytical solutions. In this study, we used the three-dimensional finite difference time domain (3D-FDTD) method to model the optical properties of regular arrays of CNTs, based on the calculated refractive indices and extinction coefficients of multi-walled CNTs (MWCNTs). One-dimensional regular arrays of CNTs displayed strong anisotropic optical behavior. Moreover, by adjusting the spacing and arrangement of two-dimensional regular arrays of CNTs, we could identify the optimal structure for a CNT-based TCE displaying excellent optical and electrical performance. We have also developed the concept of the “optical threshold,” which defines the most effective charge transport channels possessing sufficiently open areas. This concept solves the trade-off between the two key parameters—the light transmittance and the sheet resistance—in TCEs. The optimal geometry provided a CNT mesh with not only the most effective charge transport channels but also very high optical transmittance, CNT network with a diameter of 10 nm (specific conductivity of 0.385 Ω−1 nm−1) has light transparency and low sheet resistance T > 90% and Rs < 1.6 Ω/sq, such that the ratio of the direct current conductivity to the optical conductivity (σDC/σop) reached as high as 2077. This value is far greater than previously reported simulated and experimental values for TCEs based on various materials.

In this study we developed a method, using a simple two-layer nanocavity structure, to significantly enhance light outcoupling from two-dimensional (2D) materials. Because the surface electric fields (E-fields) of the nanocavities were enhanced greatly over ultrabroadband regimes, the excitation of various 2D materials with laser light and their Raman and photoluminescence (PL) light emissions were all enhanced dramatically while maintaining band-to-band ratios and peak positions precisely. At the same time, the optical visibility of the 2D materials was also enhanced significantly over a broad spectral regime. Using a single type of Ag/SiO2 nanocavity structure, we obtained a 475-fold, equal enhancement in the intensities of the main Raman peaks of single-layer graphene (SLG) and more than a 350-fold increase in the intensities of both the Raman and PL signals of single-layer tungsten disulfide (WS2). Notably, the light outcouplings of these 2D materials were enhanced dramatically without any spectral di...

In this study, we developed a simple approach, using a nanocavity structure, to increase the light absorption of graphene in an ultra-broadband and omnidirectional manner. We determined the light absorption of graphene by calculating the surface electric fields (E-fields) of various underlying substrates. Although the surface E-field was maximized for both one-dimensional photonic crystals and a metal/dielectric nanocavity structure, the much simpler two-layer nanocavity configuration also provided ultra-broadband and omnidirectional enhancement of absorption. By selecting a suitable metal as the back reflector and controlling the thickness of the single-layer dielectric spacer in the nanocavity structure, we found experimentally that the light absorption of graphene could be enhanced approximately fivefold, with full widths at half maximum of 200 nm in the ultraviolet, 400 nm in the visible, and greater than 1000 nm in the infrared regime. Moreover, we observed a significantly enhanced photo–heat response from the greater light absorption of graphene in the nanocavity structure. The absorbance spectrum of graphene in the nanocavity structure perfectly matched the air mass 1.5 solar spectrum, suggesting that such systems might be very useful for harvesting solar energy in optoelectronic devices.

In this study we developed an approach to identify the surface polarity of silicon carbide (SiC) by using an excitation laser possessing a photon energy (2.33 eV) much lower than the band gap of 4H-SiC (3.30 eV). By gradually attenuating the intensity of the excitation laser, the effective depth that the laser could generate Raman signals could eventually be limited to within the ultrashallow region of the SiC wafer. Through three-dimensional finite-difference-time-domain (3D-FDTD) simulations, we found that the depth of the high electric field region could be limited from several micrometers below the surface to the near-surface region of 4H-SiC, merely by attenuating the power of the incident laser. Experimentally, we observed a clear trend in the Raman peak intensity ratio of the signals at 210 and 203 cm–1 in the FTA mode: the intensity ratio of the Si face was always higher than that of the C face regardless of the measurement position on the 4H-SiC wafer. Even through the carrier concentrations in t...

In this study, we found that an astronomical liquid mirror can be prepared as a highly ultrasensitive, low-cost, highly reproducible, broadband-operational surface-enhanced Raman scattering (SERS)-active substrate. Astronomical liquid mirrors are highly specularly reflective because of their perfectly dense-packed silver nanoparticles; they possess a large number and high density of hot spots that experience a very high intensity electric field, resulting in excellent SERS performance. When using the liquid mirror-based SERS-active substrate to detect 4-aminothiophenol (4-ATP), we obtained measured analytical enhancement factors (AEFs) of up to 2.7×10(12) and detection limits as low as 10(-15) M. We also found that the same liquid mirror could exhibit superior SERS capability at several distinct wavelengths (532, 632.8, and 785 nm). The presence of hot spots everywhere in the liquid mirror provided highly repeatable Raman signals from low concentrations of analytes. In addition, the astronomical liquid mirrors could be transferred readily onto cheap, flexible, and biodegradable substrates and still retain their excellent SERS performance, suggesting that they might find widespread applicability in various (bio)chemical detection fields.

Fluorescent nanodiamonds (FNDs) having nitrogen-vacancy (NV) centers have drawn much attention for their biocompatibility and stable optical properties. Nevertheless, the NV centers are located in the interior of the FNDs, and it has not been possible to increase the fluorescence intensity of FNDs efficiently using previously developed enhancement methods. In this paper, we present a simple nanocavity structure that enhances the fluorescence intensity of FNDs. The designed Al/SiO2 nanocavities are stable and inexpensive, and provide a large region for efficient enhancement of fluorescence that can cover most 100 nm FNDs. By tuning the thickness of the capping SiO2 layer of the Al/SiO2 nanocavities, the distributions of both the spatial and spectral electric field intensities of the FNDs could be controlled and manipulated. In general, the FNDs were excited using a green-yellow laser; the broadband fluorescence of the FNDs comprised the emissions from neutral (NV0) and negatively charged (NV−) NV centers. To enhance the fluorescence intensity from the NV− centers of the FNDs, we designed an Al/70 nm SiO2 nanocavity to function at excitation and emission wavelengths of 633 and 710 nm, respectively, allowing the NV− centers to be excited efficiently; as a result, we achieved an enhancement in fluorescence intensity of 11.2-fold. Moreover, even when we covered 100 nm FNDs with polyglycerol (forming p-FND), the fluorescence intensities of the p-FND particles placed on the nanocavities remained greatly enhanced.

We developed a nanocavity structure to enhance light outcoupling from different two-dimensional (2D) materials. The Raman and photoluminescence (PL) light emissions from 2D materials were enhanced dramatically while maintaining band-to-band ratios and peak positions precisely.

In this study, we developed a reliable method to analyze the interference-enhanced Raman scattering (IERS) effect on graphene by considering the surface electric field (E-field), which can be calculated precisely by measuring the optical admittance of the thin-film assembly. Through accurate tuning of the optical properties of one-dimensional photonic crystals (1D-PhCs), the strong and controllable interference effect allowed the surface E-field to be maximized and, thereby, to optimize the enhancement factors of the Raman scattering signals of graphene. Using this approach, we could enhance both the G and the 2D bands of graphene largely, uniformly, and equally, by about 180 times relative to those obtained on a silicon substrate. Under certain conditions, the Raman peak of graphene could even be enhanced by over 400 times. After transferring single-layer graphene (SLG) and few-layer graphene (FLG) onto various substrates, we found that the Raman spectra of both SLG and FLG on the 1D-PhCs substrate were ...

In this study, we found that the large area of electromagnetic field hot zone induced through magnetic dipole resonance of metal-free structures can greatly enhance Raman scattering signals. The magnetic resonant nanocavities, based on high-refractive-index silicon nanoparticles (SiNPs), were designed to resonate at the wavelength of the excitation laser of the Raman system. The well-dispersed SiNPs that were not closely packed displayed significant magnetic dipole resonance and gave a Raman enhancement per unit volume of 59 347. The hot zones of intense electric field were generated not only within the nonmetallic NPs but also around them, even within the underlying substrate. We observed experimentally that gallium nitride (GaN) and silicon carbide (SiC) surfaces presenting very few SiNPs (coverage: 50%) Raman signals. In contrast, the Raman signals of the underlying substrates were not enhanced by gold nanoparticles (AuNPs), even though these NPs displayed a localized surface plasmon resonance (LSPR) phenomenon. A comparison of the areas of the electric field hot zones (E 2 > 10) generated by SiNPs undergoing magnetic dipole resonance with the electric field hot spots (E 2 > 10) generated by AuNPs undergoing LSPR revealed that the former was approximately 70 times that of the latter. More noteworthily, the electromagnetic field hot zone generated from the SiNP is able to extend into the surrounding and underlying media. Relative to metallic NPs undergoing LSPR, these nonmetallic NPs displaying magnetic dipole resonance were more effective at enhancing the Raman scattering signals from analytes that were underlying, or even far away from, them. This application of magnetic dipole resonance in metal-free structures appears to have great potential for use in developing next-generation techniques for Raman enhancement.

In this paper, we describe a high-reflectance liquid mirror prepared from densely packed silver nanoparticles (AgNPs) of two different sizes. We controlled the particle size during the synthetic process by controlling the temperature. Varying the concentration of the ligand also allowed us to optimize the arrangement of the AgNPs to achieve liquid mirrors exhibiting high specular reflectance. Scanning electron microscopy and atomic force microscopy confirmed that the particles of the liquid mirror were well-packed with an interparticle distance of merely 2 nm; thus, the interstices and surface roughness of the NPs were effectively minimized. As a result of decreased scattering loss, the reflectance in the shorter wavelength regime was increased effectively. The AgNP film was also sufficiently thick to reflect the light in the longer wavelength regime. In addition, we used three-dimensional finite-difference time domain simulations and experimental measurements to investigate the relationship between the localized surface plasmon resonance (LSPR) and the specular reflection of the liquid mirrors. By changing the packing density of the AgNPs, we found that the LSPR effect could yield either a specular reflection peak or dip at the LSPR wavelengths in the reflection spectra of the liquid mirrors. Relative to previously reported liquid mirrors, the reflectance of our system is obviously much greater, especially in the shorter wavelength regime. The average reflectance in the range from 400 to 1000 nm could reach 77%, comparable with that of mercury-based liquid mirrors.

A Bloch surface wave (BSW) platform opens up new possibilities in the design of sensors and components for photonic circuits owing to its superior properties such as low propagation losses that enable long optical communication lengths and large surface sensing areas. However, most of the reported BSW platforms require a large number of alternating layers to realize the coupling of the surface wave mode. Additionally, although BSW modes have been investigated in the visible region and the near-infrared (NIR) region, only limited reports are available in the important mid-infrared (MIR) region. In this study, we demonstrated a BSW platform consisting of only two Ge/SiO2 pairs and realizing well-coupled BSW in a wide spectral range from the NIR to the MIR. Exploiting the large refractive index difference between Ge and SiO2, the proposed BSW multilayer structure is designed to possess only two pairs of layers with a smaller total thickness than any of the reported BSW platforms. The reported MIR BSW mode shows potential for determination of trace elements and molecule species attached on the surface of the proposed BSW structure.A Bloch surface wave (BSW) platform opens up new possibilities in the design of sensors and components for photonic circuits owing to its superior properties such as low propagation losses that enable long optical communication lengths and large surface sensing areas. However, most of the reported BSW platforms require a large number of alternating layers to realize the coupling of the surface wave mode. Additionally, although BSW modes have been investigated in the visible region and the near-infrared (NIR) region, only limited reports are available in the important mid-infrared (MIR) region. In this study, we demonstrated a BSW platform consisting of only two Ge/SiO2 pairs and realizing well-coupled BSW in a wide spectral range from the NIR to the MIR. Exploiting the large refractive index difference between Ge and SiO2, the proposed BSW multilayer structure is designed to possess only two pairs of layers with a smaller total thickness than any of the reported BSW platforms. The reported MIR BSW mode sh...

Although silicon carbide (SiC) possesses excellent material properties and is a good candidate to replace sapphire as the substrate material for high-power light emitting diodes (HP-LEDs), the light extraction behavior of SiC substrate-based gallium nitride (GaN) LEDs had not been reported in detail previously. In this study, we measured the optical properties of SiC substrates and determined their effects on SiC substrate-based LEDs. Because the optical constants of SiC are very different from those of sapphire substrates, the light propagating and light extracting behavior of SiC substrate-based LEDs differs dramatically from that of traditional sapphire substrate-based LEDs. Herein, we used rigorous coupled-wave analysis and finite-difference time domain methods to systematically analyze the light propagating behavior of flip-chip and conventional-type SiC substrate-based LEDs. Our measured and simulated data revealed that the absorption of the SiC substrate would seriously affect the light extraction efficiency of flip-chip SiC LEDs. For the conventional-type LEDs, on the other hand, because the refractive index of SiC is greater than that of GaN, light readily propagates through the GaN–SiC interface into the SiC substrate to form the SiC substrate guided mode, which cannot be extracted. Therefore, maximizing the first direct extraction light from conventional-type SiC LEDs would be the most effective approach toward increasing the light extraction efficiency. Accordingly, we analyzed some periodic structures that enhanced the light extraction efficiency of SiC substrate-based LEDs.

In this study, nanoparticles (NPs) of various types and sizes are arranged to enhance both the omnidirectional light harvesting of solar cells and the light extraction of light emitting diodes (LEDs). A graded-refractive-index NP stack can minimize reflectance, not only over a broad range of wavelengths but also at different incident angles; the photocurrent of silicon-based solar cells an also be significantly improved omnidirectionally. In addition, the optical gradient of an NP stack can also enhance the light-extraction efficiency of LEDs, due to both the graded refractive index and the moderate surface roughness. Large particles having sizes on the same order of the wavelength of the incident light roughen the LED surfaces further and extract light from beyond the critical angle, as supported by three-dimensional finite-difference time-domain simulations. Using this approach, the photoluminescence intensity can be increased by up to sevenfold. The developed technique: arranging sequences of different NPs in graded-refractive-index stacks, and considering their ability to scatter light due to their sizes and optical constants, may also significantly improve the performance of various optoelectronic devices.

The external quantum efficiency of a light-emitting diode (LED) is strictly limited by total internal reflection and Fresnel reflection effects. In this study, we sought to optimize light extraction by monitoring the shape effects of four kinds of periodic textured structures (nanorod, inverted rod, pyramid, inverted pyramid) on the surface of gallium nitride (GaN)-based LEDs. We employed the three-dimensional rigorous coupled waves approach to calculate the direct emissions at different incident angles on the various textured structures, and then determined an optimized structure that would improve the extraction efficiency of LEDs. The optical gradient of the inverted pyramid structure could decrease not only the Fresnel reflection at incident angles less than the critical angle but also the total internal reflection at incident angles greater than the critical angle. Many inverted pyramid structures at the GaN–air interface, with various sizes and periods, provided enhancement factors of greater than 150%.

Despite the efficiency of gallium nitride (GaN)-based blue light-emitting diodes (LEDs), the light extraction arising from the packaging of the phosphor remains an important issue when enhancing the performance of dichromatic white LEDs. In this study, we employed a simple, inexpensive nanoimprinting process to increase both the light extraction efficiency and color rendering of dichromatic white LEDs. We employed the rigorous coupled wave approach (RCWA) to optimize the light extraction efficiency of yellow and blue light. We found that the presence of the light extracting structures could also improve the color rendering of the dichromatic white LEDs, due to the different light extraction efficiencies of the textured structures at different wavelengths. After fabricating inverted pyramid structures on the surface of the encapsulation layer, the intensity of the blue light at 455 nm increased by 20%. When we further considered the color rendering and correlated color temperature (CCT), the enhancement of blue light was 15% and that of yellow light was 4%. Meanwhile, the light extraction of the intensity dip near 490 nm was enhanced significantly (by 25%), resulting in an increased dip-intensity of light at 490 nm relative to the intensities of the blue and yellow light. Accordingly, the color rendering index (CRI) of this dichromatic white LED increased from 69 to 73. Because it improved both the light extraction efficiency and color rendering of dichromatic white LEDs, this simple method should be very helpful for enhancing their applications in solid state illumination.

A study of male sterility over a period of three consecutive years on a conifer species endemic to Taiwan, Taiwania cryptomerioides Hayata (Taxodiaceae), was done for this article. With the aids of fluorescence and electron microscopic observations, the ontogenic processes in the fertile and sterile microsporangia are compared, using samples collected from Chitou Experimental Forest and Yeou-Shoei-Keng Clonal Orchard of the National Taiwan University, Nantou, Taiwan. The development of male strobili occurred from August to the end of March. Microsporogenesis starts with the formation of the archesporium and ends with the maturation of 2-celled pollen grains within the dehiscing microsporangium. Before meiosis, there was no significant difference in ultrastructure between the fertile and sterile microsporangia. Asynchronous pollen development with various tetrad forms may occur in the same microsporangium of either fertile or sterile strobili. However, a callose wall was observable in the fertile dyad and tetrad, but not in the sterile one. After dissolution of the callose wall, the fertile microspores were released into the locule, while some sterile microspores still retained as tetrads or dyads with intertwining of exine walls in the proximal faces. As a result, there was no well developed lamellated endexine and no granulate ectexine or intine in the sterile microspores. Eventually, the intracellular structures in sterile microspores were dramatically collapsed before anthesis. The present study shows that the abortion in pollen development is possibly attributed to the absence of the callose wall. The importance of this structure to the male sterility of T. cryptomerioides is discussed.

The separation distance between the electron channel at oxide∕Si interface and the strained-Si∕relaxed-SiGe heterojunction can significantly affect the effective electron mobility of metal–oxide–silicon field-effect transistors due to the roughness scattering of the underneath Si∕SiGe heterojunction. The mobility degradation due to the Si∕SiGe heterojunction with the roughness of 7 nm becomes insignificant when the strained-Si thickness is larger than ∼20nm. A clear hole confinement shoulder is observed in the accumulation region of the capacitance–voltage curves, indicating that the abrupt transition from the SiGe buffer to strained Si is maintained at the rough heterojunction. The heterojunction roughness scattering not only degrades the electron mobility, but also degrades the device characteristics such as the transconductance and cut-off frequency.

In this study, we combined intruded nanocluster (INC)-based catalysts with ultrasound-assisted etching to obtain, within only a few seconds, wafer-scale nanostructures exhibiting excellent antireflective properties. We chose the INC catalysts because their high density of atomic-scale gold nanoclusters could be used to prepare highly dense silicon nanostalactite (SNS) structures, which can exhibit excellent antireflective properties even at relatively shallow etching depths. By applying ultrasonic oscillation during the etching process, gas bubbles were detached instantly and the exchange rate of the etching solution was improved significantly. Using this approach, we could prepare antireflective SNS structures with an average reflectance of approximately 2% over the range of 350 to 1000 nm within an etching time of 10 s. We also constructed INC-based SNS structures on the surfaces of micrometer-scale silicon pyramids to decrease the angular dependence of their surface reflection. These micro/nano hybrid structures effectively suppressed the average reflectance to 1.6% at normal incidence and to approximately 3.5% at an incident angle of 60°—excellent omnidirectional and broadband antireflective properties. Notably, such micro/nano hybrid structures could also be prepared within very short etching times.