One-dimensional Porous Silicon Photonic Crystals Research Articles

Influence of One-Dimensional Photonic Crystal on Raman Signal Enhancement: A Detailed Experimental Study

The enhancement of Raman signals using photonic crystal structures has been the subject of numerous experimental and theoretical studies, leading to a variety of issues and inconsistencies. This paper presents a comprehensive experimental investigation into the impact of alignment between the laser excitation wavelength and the specific position of the photonic band gap on signal enhancement in Raman spectroscopy. By employing one-dimensional (1D) porous silicon photonic crystals, a systematic analysis across a large number of spectra was conducted. The study focused on examining the signal enhancement of both the Raman ∼520 cm–1 silicon band, representing the constituent material of photonic crystal, and the most prominent Raman bands of crystal violet, used as a probe molecule. The probe molecules were both infiltrated into and adsorbed on top of the photonic crystal structure. The obtained experimental results for the contribution of 1D photonic crystals to Raman signal enhancement are much smaller compared to most predictions. The Raman signal of silicon and the signal from the probe molecule are enhanced ≤2.5 times when the laser excitation aligns with the edge of the photonic band gap, strictly defined as the position at the very bottom of the reflectance peak. The results have been discussed within the context of theoretical explanations.

One-dimensional porous silicon photonic crystals for chemosensors: Geometrical factors influencing the sensitivity

One-dimensional photonic crystals with microcavity were prepared to be used as optical chemosensors. The experimental reflectance of the as-etched devices immersed in solvent solutions appear greater than the theoretical one. The fitting procedure of the experimental data using the transfer matrix method together with the Looyenga effective medium approach reveals that the deviation of the experimental data occurs because of the expansion-contraction effect of the high and low porosity layers, respectively, caused by the presence of the solvent into the porous matrix and is proportional to the solvent effective refractive index. Due to this phenomenon, the sensitivity of the as-etched photonic crystals increases about two times but is not stable because of the aging effect. To avoid this effect, the photonic crystal structures were passivated by thermally silicon oxide growing, gold thin film and titanium oxide deposition. After thermal treatment in an air environment, the optical response achieves its stabilization even after long storage times, thus showing the importance of the passivation procedure. Among them, the passivation by TiO2 shows better performance and lower loss in sensitivity in comparison to the as-etched devices.

Optical and structural characterization of one-dimensional porous silicon photonic crystals made in single and double electrochemical cells: Study on the back contact effect

One-dimensional porous silicon photonic crystals with microcavity were fabricated using single and double electrochemical cells and the same electrochemical parameters. Devices with better optical quality can be achieved when liquid acids are used as back contacts for current flow. Optical analysis of them shows that devices with less rough interfaces and layers with negligible in-depth inhomogeneities are formed. However, the etch rate and porosity depend strongly on the acid strength, the diffusion of the acid species from the liquid bulk to the interface, and the anodization temperature. Strong acids promote a higher etch rate. Thinner films with lower porosity and rougher interfaces are observed for devices fabricated in substrates with aluminum or platinum as solid ohmic contacts compared to devices fabricated in unmetallized substrates, as shown by optical analysis, such that devices with aluminum as the ohmic contact have about 80% of the reflectance, while with platinum shows 94%.

Enhanced spontaneous emission from two-photon-pumped quantum dots in a porous silicon microcavity.

Photoluminescence (PL)-based sensing techniques have been significantly developed in practice due to their key advantages in terms of sensitivity and versatility of the approach. Recently, various nanostructured and hybrid materials have been used to improve the PL quantum yield and the spectral resolution. The near-infrared (NIR) fluorescence excitation has attracted much attention because it offers deep tissue penetration and it avoids the autofluorescence of the biological samples. In our study, we have shown both spectral and temporal PL modifications under two-photon excitation of quantum dots (QDs) placed in one-dimensional porous silicon photonic crystal (PhC) microcavities. We have demonstrated an up-to-4.3-fold Purcell enhancement of the radiative relaxation rate under two-photon excitation. The data show that the use of porous silicon PhC microcavities operating in the weak coupling regime permits the enhancement of the PL quantum yield of QDs under two-photon excitation, thus extending the limits of their biosensing applications in the NIR region of the optical spectrum.

Additive Combination of Spectra Reflected from Porous Silicon and Carbon/Porous Silicon Rugate Filters to Improve Vapor Selectivity.

Selectivity remains a challenge for rapid optical vapor sensing via light reflected from porous silicon photonic crystals. This work highlights a method to increase optical vapor selectivity of porous silicon rugate filters by analyzing additive spectra from two rugate filter substrates with different functionalities, an oxidized and carbonized surface. Individually, both porous silicon rugate filters demonstrated sensitivity but not selectivity toward the vapor analytes. However, differences in peak shift trends between the two substrates suggested differences in vapor affinities for the surfaces. By adding the two spectra, improvements to selectivity relative to the individual surfaces were observed even at low vapor pressures and for analytes of similar polarity, refractive index, and concentration. These results are expected to contribute toward optical vapor selectivity improvements in one-dimensional porous silicon photonic crystals.

Enhancement of spontaneous emission of semiconductor quantum dots inside one-dimensional porous silicon photonic crystals.

Controlling spontaneous emission by modifying the local electromagnetic environment is of great interest for applications in optoelectronics, biosensing and energy harvesting. Although the development of devices based on one-dimensional porous silicon photonic crystals with embedded luminophores is a promising approach for applications, the efficiency of the embedded luminophores remains a key challenge because of the strong quenching of the emission due to the contact of the luminophores with the surface of porous silicon preventing the observation of interesting light-matter coupling effects. Here, we experimentally demonstrate an increase in the quantum dot (QD) spontaneous emission rate inside a porous silicon microcavity and almost an order of magnitude enhancement of QD photoluminescence intensity in the weak light-matter coupling regime. Furthermore, we have demonstrated drastic alteration of the QD spontaneous emission at the edge of the photonic band gap in porous silicon distributed Bragg reflectors and proved its dependence on the change in the density of photonic states.

Refractive index gas sensor based on the Tamm state in a one-dimensional photonic crystal: Theoretical optimisation

Gas sensors are important in many fields such as environmental monitoring, agricultural production, public safety, and medical diagnostics. Herein, Tamm plasmon resonance in a photonic bandgap is used to develop an optical gas sensor with high performance. The structure of the proposed sensor comprises a gas cavity sandwiched between a one-dimensional porous silicon photonic crystal and an Ag layer deposited on a prism. The optimised structure of the proposed sensor achieves ultra-high sensitivity (S = 1.9×105 nm/RIU) and a low detection limit (DL = 1.4×10−7 RIU) compared to the existing gas sensor. The brilliant sensing performance and simple design of the proposed structure make our device highly suitable for use as a sensor in a variety of biomedical and industrial applications.

Enhancement of the quantum dot photoluminescence using transfer-printed porous silicon microcavities

Enhancement of the photoluminescence signal intensity from organic and inorganic fluorophores increases the sensitivity of operation of optical sensors, detectors, and photonic diagnostic assays. Here, we have engineered and compared optical and fluorescence-enhancing properties of two types of one-dimensional porous silicon photonic crystals: a transfer-printed microcavity based on the freestanding photonic crystal and a conventional “one-piece” microcavity created on a monocrystalline silicon substrate. Comparative analysis of the eigenmodes and the photonic bandgaps of both types of microcavities demonstrated a high quality of transfer-printed microcavities and good correlation of their reflection spectra with the spectra of “one-piece” microcavities. Moreover, embedding of a highly concentrated solution of quantum dots (QDs) in the eigenmode localization region of transfer-printed microcavity was followed by three-fold reduction of the full-width-at-half-maximum of their luminescence spectrum at the microcavity eigenmode wavelength, thus confirming a weak coupling regime of QD exciton and microcavity eigenmode interaction and significant enhancement of QD luminescence within the microcavity.

Design, fabrication, and optical characterization of one-dimensional photonic crystals based on porous silicon assisted by in-situ photoacoustics

We present a methodology to fabricate one-dimensional porous silicon (PSi) photonic crystals in the visible range by controlled etching and monitored by photoacoustics. Photoacoustic can record in-situ information about changes in the optical path and chemical reaction as well as in temperature, refractive index, and roughness during porous layers formation. Radiometry imaging can determine the carrier distribution of c-Si substrate that is a fundamental parameter to obtain high-quality PSi films. An electrochemical cell was calibrated through a series of single PSi layers that allows knowing the PA amplitude period, porosity, and roughness as a function of the current density. Optical properties of single layers were determined using the reflectance response in the UV-Vis range to solve the inverse problem through genetic algorithms. PhC structures were designed using the transfer matrix method and effective media approximation.Based on the growth kinetics of PSi single layers, those structures were fabricated by electrochemical etching monitored and controlled by in-situ photoacoustics.

Porous Silicon Photonic Crystal as a Substrate for High Efficiency Biosensing

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C-Si hybrid photonic structures by full infiltration of conjugated polymers into porous silicon rugate filters

Loading of one-dimensional (1-D) porous silicon photonic crystals (PS-PhCs), known as rugate filters, with luminescent materials is generally limited by the potential for (undesired) “pore clogging,” in relation to the size of the nanoparticles (e.g. quantum dots) or molecular species, and so far mainly restricted to small molecular weight materials or small nanocrystals, or in situ polymerized dyes. Here we report the infiltration 1-D PS-PhCs with a green-emitting commercial luminescent polymer (F8BT, poly[(9,9-di-n-octylfluorenyl-2,7-diyl)-alt-(benzo[2,1,3]thiadiazol-4,8-diyl)]), with a molecular weight of approximately 46 kDa across their whole depth (approximately 7.5 μm), thereby showing that pore clogging is not a concern for these structures. We also characterize the modification of the photoluminescence (PL) and decay rates, and investigate the detailed inner morphology of the filters with the help of (scanning) transmission electron microscopy. We observe both suppression (in the stop-band) and enhancement (at the high-energy band-edge) of the PL. We also find that the photonic stop-band is red-shifted after polymer infiltration, due to the increased effective refractive index of the polymer-infiltrated nanostructured system. The presence of just one unbroadened peak in the reflectance spectra after infiltration confirms that infiltration extends for the whole depth of the rugate filters.

Angle-resolved diffraction grating biosensor based on porous silicon

In this study, an optical biosensor based on a porous silicon composite structure was fabricated using a simple method. This structure consists of a thin, porous silicon surface diffraction grating and a one-dimensional porous silicon photonic crystal. An angle-resolved diffraction efficiency spectrum was obtained by measuring the diffraction efficiency at a range of incident angles. The angle-resolved diffraction efficiency of the 2nd and 3rd orders was studied experimentally and theoretically. The device was sensitive to the change of refractive index in the presence of a biomolecule indicated by the shift of the diffraction efficiency spectrum. The sensitivity of this sensor was investigated through use of an 8 base pair antifreeze protein DNA hybridization. The shifts of the angle-resolved diffraction efficiency spectrum showed a relationship with the change of the refractive index, and the detection limit of the biosensor reached 41.7 nM. This optical device is highly sensitive, inexpensive, and simple to fabricate. Using shifts in diffraction efficiency spectrum to detect biological molecules has not yet been explored, so this study establishes a foundation for future work.

Optical characterization of one-dimensional porous silicon photonic crystals with effective refractive index gradient in depth

In this paper, we report the results of the investigation about the optical properties of one-dimensional photonic crystals based on porous silicon multilayer structures having unit cells with optical properties that vary as a function of the device thickness. These devices were obtained by anodizing crystalline silicon in electrolyte aqueous solution of HF at different concentrations. The effective refractive index and extinction coefficients, of porous silicon layers of unit cells had been obtained by fitting the experimental reflectance spectra using the transfer matrix method. The effective–refractive indexes, for devices obtained in electrolyte solution of high HF concentration, were shown to have a significant gradient in the depth of the layers, whereas it was low (negligible) for devices obtained in electrolyte solution with low HF concentration, but the mechanical stability of these latter devices is poor. It was found that this fragility depends on the layer number and upon their physical thicknesses ratio.

A compact dual-band bandpass filter based on porous silicon dual-microcavity of one-dimensional photonic crystal

We propose a compact dual-band bandpass filter (BPF) based on one-dimensional porous silicon (PS) photonic crystal by electrochemical etching. By inserting three periods of high and low reflective index layers in the center of porous silicon microcavity (PSM), two sharp resonant peaks appear in the high reflectivity stop band on both sides of the resonance wavelength. Through simulation and experiment, the physical mechanisms of the two resonance peaks and the resonance wavelength are also studied. It is found that the resonance wavelength can be tuned only by adjusting the effective optical thickness (EOT) of each PS layer, in which different resonance wavelengths have different widths between the two sharp resonance peaks. Besides, the analysis indicates that oxidization makes the blue shift become larger for high wavelength than that for low wavelength. Such a fabricated BPF based on PS dual-microcavity is easy to be fabricated and low cost, which benefits the application of integrated optical devices.

Fabrication of arrays of one-dimensional porous silicon photonic crystal

PDF HTML阅读 XML下载 导出引用 引用提醒 应用于中红外波段的阵列化多孔硅一维光子晶体的制备 DOI: 作者: 作者单位: 齐齐哈尔大学通信与电子工程学院,齐齐哈尔;齐齐哈尔大学通信与电子工程学院,齐齐哈尔,齐齐哈尔大学通信与电子工程学院,齐齐哈尔;齐齐哈尔大学通信与电子工程学院,齐齐哈尔,中国科学院上海技术物理研究所,红外物理国家重点实验室,上海 作者简介: 通讯作者: 中图分类号: 基金项目: Fabrication of array of one-dimensional porous silicon photonic crystal Author: Affiliation: Qiqihar University,Qiqihar University,Shanghai Institute of Technical Physics Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:首先通过光刻工艺制作了阵列化岛状硅衬底，然后利用交替变换阳极腐蚀电流, 通过合理的控制制备参数，适当的热氧化条件，成功地制备了禁带中心位于5μm、6μm、7μm、10μm的阵列化多孔氧化硅一维光子晶体. 随后在其表面淀积一层低应力的Si3N4，通过原子力显微镜(AFM)和傅里叶红外反射谱(FTIR)测试证明, 沉积Si3N4后该结构仍然具有良好的平整度和较高的反射特性。该阵列结构不但具有较好的隔热和高反射特性，而且岛状的阵列结构可使其与其他器件互联变得简单易行，必将为制备多功能、一体化器件提供有利条件。 Abstract:With the aid of photolithography, arrays of one-dimensional porous silicon photonic crystal with the middle infrared mid-gap (λ=5、6、7、10 μm) were fabricated successfully by the combination of microelectronic technique and the electrochemical etching method. For practical use, the roughness of the surface was improved by deposited a Si3N4 thin film with 5000 ?. Then their optical and roughness properties were characterized by FTIR and AFM, respectively. As a result of the synergetic effects rendered by heat isolation and high reflection properties, the array of the one-dimensional porous silicon photonic crystal exhibit feasibility as the substrate for pyroelectric infrared sensor. 参考文献 相似文献 引证文献

Anomalous patterned scattering spectra of one-dimensional porous silicon photonic crystals

Far-field secondary emission spectra of one-dimensional periodic photonic structures based on porous silicon show characteristic co-focal rings centered close to the structure plane normal. The rings appear when the frequency of picosecond excitation laser pulses is tuned to the edges of the fourth photonic band gap. They can be clearly distinguished from the typical reflected and transmitted light in the oblique incidence geometry. The rings number is dependent on the excitation frequency and the incidence angle. We explain these anomalous spectral features of porous silicon structures by the spectral filtering of light elastically scattered inside the photonic structure by the narrow photonic bands. The elastic scattering of light due to the photonic disorder in the structure causes the appearance of secondary waves propagating in any direction. But only those waves which fall into the allowed photonic bands penetrate through the whole structure and move through its front or back surfaces. The observed patterned secondary emission is an example of efficient photonic engineering by simple means of multilayer porous silicon structures.

Spatially localized one-dimensional porous silicon photonic crystals

The authors report a straightforward method to achieve spatially localized photonic band-gap structures in porous silicon. This photonic band-gap lithography technique consists of local photo-oxidation followed by exposure to methanol solvent. Reflectance measurements show that the oxidized porous silicon regions maintain their photonic band structure with only a slight blueshift while there is significant spectral degradation in the nonoxidized regions. Fourier transform infrared spectroscopy and scanning electron microscopy were performed to investigate this phenomenon. The significant spectral change in the nonoxidized regions is attributed to chemical modification of the porous silicon.

Coupling of surface waves in highly defined one-dimensional porous silicon photonic crystals for gas sensing applications

We describe the use of one-dimensional porous silicon (p-Si) photonic crystals for guiding TE-polarized surface electromagnetic waves (SEWs). Although bulk and interface roughnesses might deteriorate the optical response of photonic structures, we observed reflection spectra presenting narrow (≲6nm) reflectivity anomalies associated with SEWs. In analogy with surface plasmons, SEWs are strongly sensitive to surface modifications. As a proof of principle for a sensor, we provide a direct real-time monitoring of the reversible interactions of organic vapors with the p-Si multilayer. We highlight the higher sensitivity of the SEW-based detection scheme as compared to a method exploiting perturbations of waveguide modes.

One‐dimensional porous silicon photonic crystals for visible and NIR applications

We present one-dimensional porous silicon photonic crystals that exhibit two band gaps in the NIR region and two band gaps in the visible region. These photonic crystals are made by periodically repeating two porous silicon layers with different refractive index. Theoretical analysis demonstrates that they are suitable for obtaining omnidirectional mirrors to be applied in the infrared region, especially for the wavelength of 1.55 µm. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)