Oxidized Porous Silicon Research Articles

Oxidized Porous Silicon Nanoparticles Covalent-Bonded with Levofloxacin in Hydrogel Polymer as a Drug Delivery System.

Oxidized porous silicon (OPS) nanoparticles covalent-bonded with levofloxacin in hydrogel polymer are prepared and used to measure the efficiency for the controlled release drug delivery. Levofloxacin is covalently bonded to a Si-OH surface of OPS nanoparticles by catalytic condensation. The average size of these particles is about 100 nm. Since levofloxacin has a fluorescence property, the release of levofloxacin has been measured by fluorescence spectrometer. The quantity of levofloxacin release from the OPS nanoparticles is measured at the emission wavelength at 455 nm with an excitation wavelength of 330 nm on a time scale in pH 7 aqueous buffer solution. The analysis of release profile reveals that the OPS covalently bonded with levofloxacin (Levo-OPS) exhibits a great potential candidate for controlled release. The drug-release rate depends on the hydrolysis of silyl ester from the surface of OPS nanoparticles.

Thermally Carbonized Porous Silicon for Robust Label-Free DNA Optical Sensing.

In this work, thermal carbonization is shown to provide the necessary surface passivation to enable highly robust DNA detection on a porous silicon (PSi) platform, overcoming previous corrosion challenges with detection of negatively charged biomolecules. The stability of thermally carbonized PSi (TCPSi), oxidized PSi (OPSi), and undecylenic acid-modified PSi (UAPSi) is compared in phosphate-buffered saline and during DNA sensing experiments. Reflectance measurements reveal an improvement in stability and DNA sensor response for TCPSi compared to OPSi and UAPSi. TCPSi exhibits a large positive sensor response with >90% DNA hybridization efficiency. In comparison, UAPSi shows a smaller positive DNA sensor response, likely lessened by a small corrosion effect, while OPSi exhibits a large negative sensor response, indicating significant induced PSi corrosion that confounds the ability of OPSi to yield meaningful readouts of DNA hybridization events. This work expands the application of TCPSi for its more widespread usage in sensing applications where competing substrate corrosion may influence device stability.

The luminescence properties of colloidal quantum dots

Luminescent properties of systems containing lead sulfide (PbS) nanoparticles deposited on substrates of porous silicon (p-Si), oxidized porous silicon (OPS) and have been studied. It was shown that structure of the matrix and its composition are of crucial importance affecting luminescence spectra of colloidal quantum dots by setting their radiation wavelength.

FUNCTIONALIZATION OF BIOMOLECULES WITH NANOSTRUCTURED POROUS SILICON FOR BIOMEDICAL APPLICATION

Porous silicon (PS) fabrication, changes in the optical properties and surface modification in the oxidized PS (dipped into the Glucose oxide) due to the infiltration of biomolecules using Luminescence Spectrophotometer [Photoluminescence (PL)], Fourier Transform Infrared Spectroscopy (FTIR), and Scanning Electron Microscope (SEM) were studied. The surface morphology of oxidized PS (OPS) and treated with Glucose have been studied by SEM. Spontaneous imbibition weight was calculated theoretically using imbibition equation for the porous medium using glucose solution as the wetting liquid. FTIR analysis revealed that, the strong Si–H, Si–O–Si bonds which covered most of the OPS surface. In the glucose treated PS layer, the amide I (C=O) stretch and amide II (C=N) stretch (1690 cm−1 and 1551 cm−1) groups were appeared in the spectrum which confirmed the coupling reaction. Efficient visible Photoluminescence was obtained at around 624 nm from glucose treated porous silicon. The functionalization of glucose with nano structured PS, changes light emission over the surface of OPS. It can be applied in optical biosensor and which can be used in biomedical applications.

Comparative SERS study carried out on unsilanized and silanized oxidized porous silicon surface coated by small gold nanoparticles

Porous silicon (PSi) was formed by electrochemical anodization and was oxidized before silanization and immersion in colloidal gold nanoparticles (GNP) (5 nm size) solution. The oxidized PSi (OPSi) coated with nanoparticles was used as surface enhanced Raman scattering (SERS) substrate, where bovine serum albumin (BSA) was used as a target molecule. Also, rhodamine 6G (R6G) dyes were used to confirm the SERS efficiency. Firstly, the bio-conjugation between protein and GNP was investigated by localized surface plasmon resonance spectroscopy. Then a comparative SERS study from silanized and unsilanized OPSi was performed and showed a good vibrational BSA bands resolution with the unsilanized one. The silanized surface did not show any improvement on the SERS enhancement of the BSA due to the interferences between the vibrational modes of 3-aminopropyltriethoxysilane and BSA. Furthermore, we have investigated the BSA solution pH effect on the SERS results in the case of unsilanized OPSi surface. The results prove the efficiency of the SERS substrate at pH 4.9, corresponding to BSA iso-electric point. A detection limit of about 10−8 M was obtained for both BSA and R6G molecules.

Oxidized Porous Silicon Particles Covalently Grafted with Daunorubicin as a Sustained Intraocular Drug Delivery System

To test the feasibility of covalent loading of daunorubicin into oxidized porous silicon (OPS) and to evaluate the ocular properties of sustained delivery of daunorubicin in this system. Porous silicon was heat oxidized and chemically functionalized so that the functional linker on the surface was covalently bonded with daunorubicin. The drug loading rate was determined by thermogravimetric analysis. Release of daunorubicin was confirmed in PBS and excised rabbit vitreous by mass spectrometry. Daunorubicin-loaded OPS particles (3 mg) were intravitreally injected into six rabbits, and ocular properties were evaluated through ophthalmic examinations and histology during a 3-month study. The same OPS was loaded with daunorubicin using physical adsorption and was evaluated similarly as a control for the covalent loading. In the case of covalent loading, 67 ± 10 μg daunorubicin was loaded into each milligram of the particles while 27 ± 10 μg/mg particles were loaded by physical adsorption. Rapid release of daunorubicin was observed in both PBS and excised vitreous (~75% and ~18%) from the physical adsorption loading, while less than 1% was released from the covalently loaded particles. Following intravitreal injection, the covalently loaded particles demonstrated a sustained degradation of OPS with drug release for 3 months without evidence of toxicity; physical adsorption loading revealed a complete release within 2 weeks and localized retinal toxicity due to high daunorubicin concentration. OPS with covalently loaded daunorubicin demonstrated sustained intravitreal drug release without ocular toxicity, which may be useful to inhibit unwanted intraocular proliferation.

High-density oxidized porous silicon

We have studied oxidized porous silicon (OPS) properties using Fourier transform infraRed (FTIR) spectroscopy and capacitance–voltage C–V measurements. We report the first experimental determination of the optimum porosity allowing the elaboration of high-density OPS insulators. This is an important contribution to the research of thick integrated electrical insulators on porous silicon based on an optimized process ensuring dielectric quality (complete oxidation) and mechanical and chemical reliability (no residual pores or silicon crystallites). Through the measurement of the refractive indexes of the porous silicon (PS) layer before and after oxidation, one can determine the structural composition of the OPS material in silicon, air and silica. We have experimentally demonstrated that a porosity approaching 56% of the as-prepared PS layer is required to ensure a complete oxidation of PS without residual silicon crystallites and with minimum porosity. The effective dielectric constant values of OPS materials determined from capacitance–voltage C–V measurements are discussed and compared to FTIR results predictions.

Luminescence properties of Bi-doped oxidized porous silicon thin films

Luminescence properties of Bi-doped oxidized porous silicon (OPS) thin films were studied. It was found that this material shows two broad luminescence bands centered at 845nm with the FWHM of 120nm and at 1410nm with that of 220nm under 488nm excitation. A detailed analysis of the 3D plot of PL intensities versus excitation and emission wavelengths revealed that these luminescence bands arise from at least two different kinds of Bi luminescence centers. The broad luminescence covering the whole telecommunication window (1.2–1.6μm) suggests that Bi-doped OPS thin films can be a candidate material for a broadband waveguide-type optical amplifier at optical telecommunication wavelengths.

New Type of Thermal-Isolation Structure Based on PI and OPS Used in Uncooled Infrared Detector

A new type of thermal-isolation structure based on polyimide (PI) and oxidized porous silicon (OPS) is presented. The structure has the advantage of simpler process, lower cost, and higher yield. The mechanism is described briefly in this paper and the process is studied in detail. The thermal-isolation capability of the structure is verified by a-Si bolometer with PI and OPS complex thermal isolation structure and excellent performance has been achieved.

Effect of atmospheric-air pressure on charge transport in structures with oxidized porous silicon

The electron-transport processes in structures with oxidized porous silicon (OPS) are investigated during adsorption and desorption of polar molecules from atmosphere when the air pressure varies. It is shown that the cause of the existence of the open-circuit voltage in Pd-OPS-p+-Si-Al structures in the initial state is the surface-charge change on the Pd-OPS interface due to the polar-molecule adsorption from atmospheric air. The desorption of atmospheric-air molecules leads to a change in the current-voltage characteristics of structures, growth of the metal-OPS barrier in samples with the Schottky barrier, and initiation of current instabilities. The nanocrystalline nature of OPS manifests itself in the charge-carrier localization in quantum dots (QDs) during desorption in samples with space-charge-limited currents.

New Through-Wafer Via Interconnections with Thick Oxidized Porous Silicon Sidewall Via

In this paper, we present the detailed fabrication process and high-frequency characterization of a new silicon through-wafer via interconnection and a low pass filter module flip-chip bonded to these via interconnections. An oxide liner of 18 µm thick for the via was fabricated on a complementary metal–oxide–semiconductor (CMOS)-grade low-resistivity 5 Ω·cm silicon wafer using the oxidized porous silicon (OPS) process. The through-wafer vias were filled with copper by electroplating. For a via interconnection of 240 µm length and 70 µm diameter, the series inductance and resistance are 0.079 nH and 0.059 Ω each. A coplanar waveguide (CPW) and a RF low pass filter (LPF) module were assembled on this through-wafer via interconnection substrate.

Form birefringence of oxidized porous silicon

A network of preferentially oriented pores is shown to induce anisotropy of linear and nonlinear optical properties of oxidized porous silicon (OPS) films. Although the x-ray diffraction indicates the presence of amorphous phase in OPS samples, the near-infrared and visible transmission measurements reveal a strong in-plane anisotropy exceeding that for the crystalline quartz. This anisotropy modifies dramatically polarization properties of the nonlinear optical properties resulting in a strong anisotropy of the third-harmonic signal generated from these films.

Photoluminescence from erbium incorporated in oxidized porous silicon

In the present work, photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopy were used to study oxidized porous silicon (OPS) doped with Er by electrochemical migration. Three types of OPS were investigated: (a) partially oxidized PS (POPS); (b) fully oxidized PS (FOPS); (c) oxidized PS co-doped with Fe (OPS:Fe). The OPS consists of oxide, Si nanoclusters and voids, and their composing fractions are dependent on the PS porosity and oxidation regime. The main result of this work is the assessment that the location of Er ions in composing fractions of OPS has a profound effect on the PL and PLE spectra. We show that for both POPS and FOPS, Er exhibits a broad 1530 nm PL spectrum similar to that observed in the Er-doped silica glasses. For POPS, the PLE spectrum of the 1530 nm Er PL band consists of a superposition of sharp peaks, which are attributed to the absorption transitions of Er ions incorporated into the oxide fraction, and a broad band, which is related to the absorption band of Si nanoclusters. For FOPS, the PLE spectrum consists just of sharp peaks. In contrast to POPS and FOPS, for OPS:Fe, Er PL spectrum consists of 21 highly resolved peaks. PLE spectrum of the strongest 1535 nm PL peak represents a wide band which is attributed to the absorption band of Fe:O nanoclusters formed inside OPS:Fe. Mechanism of excitation and luminescence of Er ions in OPS is presented.

Nano-composite of porous silicon and organic dye molecules for optical gas sensor and lasing medium

The present work reports the infrared spectra (FTIR) studied and the optical properties of nano-composite structures obtained from Porous silicon (PS) films and thermally oxidized PS (Ox-PS) films with tetrasulfonated Zinc phthalocyanines (ZnPc) or Rhodamine-6G (Rh-6G) dye molecules (nano-composites: PS/dye and Ox-PS)/dye). The dye adsorption on the PS and Ox-PS surfaces conserved their monomer characteristics preserving the optical absorption and emission features of the dye molecules, i.e., non-dimmer, non-trimmer or non-cluster formation were observed. The PL spectra, of the nano-composites structures, showed highly intensity emission, suggesting a possible application of this material for lasing devices fabrication. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Fabrication of Three-Dimensional Cu Coaxial Cable Using Porous Silicon Technology

This paper presents the fabrication of a three-dimensional Cu coaxial cable with a thick oxidized porous silicon (OPS) layer for application of microwave and RF integrated circuit technology. The structure was fabricated by hydrofluoric acid, nitric acid, acetic acid (HNA) etching, followed by the OPS process, electroplating and photoresist (PR) reflow. The return loss of the Cu coaxial cable on the OPS layer is -35.53 dB at 13 GHz and the insertion loss of Cu coaxial cable on OPS layer is -0.17 dB at 5.5 GHz. Therefore, the fabricated devices are expected to improve the characteristic of the insertion loss and the transmission line dispersion. Also, it is possible that the cable can be used as the microsize coaxial cable.

An Oxidized Porous Silicon (OPS) Microlens Implemented on Thick OPS Membrane for a Silicon-Based Optoelectronic-Multichip Module (OE-MCM)

Using the silicon bulk micromachining and selectively oxidized porous silicon (SOPS) technology, a silicon dioxide microlens was implemented on thick oxidized porous silicon (OPS) membrane. Because the surface of microlens was the interface of OPS-Si, the surface roughness of lens was directly affected by the anodization current density, substrate resistivity, and high-frequency percent in ethanol-contained electrolyte. In the SOPS technology, the porous silicon layer (PSL) was formed under the mask layer with its horizontal-vertical ratio of about 0.8. During the formation of lens part, Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> mask layer was also etched with constant etch rate and the PSL formed on the masked area was used as a membrane supporter. The initial open area and the thickness of the mask layer controlled the focal length of the OPS lens and its range was from 20 to 110 μm. By using these microlenses, a new silicon-based optoelectronic-multichip module configuration was proposed.

Fine structure of photoluminescence spectra from erbium incorporated with iron in oxidized porous silicon

We report 77 K Photoluminescence (PL) and Photoluminescence Excitation (PLE) spectroscopies of Er ions incorporated with Fe in oxidized porous silicon (OPS) in the form of 5-50 nm sized clusters containing Fe, O, and Er. Twenty sharp (FWHM of about 0.4 meV) PL peaks related to the transitions between highly split levels of 4 I 13/2 and 4 I 15/2 multiplets were observed. Two different Er centers having cubic and lower than cubic symmetries were identified. The photoluminescence excitation spectrum of the 1533 nm PL peak comprises no resonant features but a broad band spanning from 300 to 570 nm. The mechanism of excitation of Er ions through Fe : O : Er nanoclusters in the OPS host is presented.

Fabrication of Thick Silicon Dioxide Air-Bridge for RF Application Using Micromachining Technology

This paper proposes a 10 µm thick oxide air-bridge structure which can be used as a substrate for RF circuits. The structure was fabricated by anodic reaction, multi-step thermal oxidation and micromachining technology using tetramethylammonium hydroxide (TMAH) etching. This structure is mechanically stable because of thick oxide layer up to 10 µm and is expected to solve the problem of high dielectric loss of silicon substrate in RF region. The properties of the transmission line formed on the oxidized porous silicon (OPS) air-bridge were investigated and compared with those of the transmission line formed on the OPS layers. The insertion loss of coplanar waveguide (CPW) on OPS air-bridge is (about -2 dB) lower than that of CPW on OPS layers. Therefore, this technology is very promising for extending the use of complementary metal oxide (CMOS) circuitry to higher RF frequencies.

복합 산화법과 MEMS 기술을 이용한 RF용 두꺼운 산화막 에어 브리지 및 공면 전송선의 제조

본 논문에서는 양극반응과 복합 산화법(<TEX>$H_2O/O_2$</TEX> 분위기에서 <TEX>$500^{\circ}C$</TEX>, 1시간 열산화와 <TEX>$1050^{\circ}C$</TEX>, 2분간 RTO(Rapid Thermal Oxidation) 공정)을 이용한 두꺼운 OPSL(Oxidized Porous Silicon Layer)을 형성하여 이를 마이크로머시닝 기술을 이용함으로써 <TEX>$10\;{\mu}m$</TEX> 두께의 OPS(Oxidized Porous Silicon) 에어 브리지를 제조하고, 그 위에 전송선로를 형성하여 그 RF 특성을 조사하였다. OPS 에어 브리지 위에 형성된 CPW(Coplanar Waveguide)의 손실이 OPSL 위에 형성된 전송선의 삽입손실보다 약 2dB 정도 적은 것을 보여주었으며, 반사손실은 OPSL 위에 형성된 전송선의 반사손실보다 적으며 약 -20 dB를 넘지 않고 있다. 본 연구에서 개발한 산화된 다공질 실리콘 멤브레인 및 에어 브리지 구조는 CMOS 공정 후에 사용 가능하며, 초고주파 회로 설계시 편리성과 유용성을 제시하고 있다. This paper proposes a <TEX>$10\;{\mu}m$</TEX> thick oxide air-bridge structure which can be used as a substrate for RF circuits. The structure was fabricated by anodic reaction, complex oxidation and micromachining technology using TMAH etching. High quality films were obtained by combining low temperature thermal oxidation (<TEX>$500^{\circ}C$</TEX>, 1 hr at <TEX>$H_2O/O_2$</TEX>) and rapid thermal oxidation (RTO) process (<TEX>$1050^{\circ}C$</TEX>, 2 min). This structure is mechanically stable because of thick oxide layer up to <TEX>$10\;{\mu}m$</TEX> and is expected to solve the problem of high dielectric loss of silicon substrate in RF region. The properties of the transmission line formed on the oxidized porous silicon (OPS) air-bridge were investigated and compared with those of the transmission line formed on the OPS layers. The insertion loss of coplanar waveguide (CPW) on OPS air-bridge was (about 2dB) lower than that of CPW on OPS layers. Also, the return loss of CPW on OPS air-bridge was less than about -20 dB at measured frequency region for 2.2 mm. Therefore, this technology is very promising for extending the use of CMOS circuitry to higher RF frequencies.

Oxidized Porous Silicon: From Dielectric Isolation to Integrated Optical Waveguides

A brief review of 20-years research of formation, processing and utilizing of oxidized porous silicon (OPS) is presented. Electrolytes to form porous silicon (PS) layers, special features of PS chemical cleaning and thermal oxidation are discussed. OPS application for dielectric isolation of components of bipolar ICs and for the formation of silicon-on-insulator structures has been demonstrated. Although these OPS-based techniques have found limited current commercial use, experience gained is applicable to the fabrication of optoelectronic devices. Specifically, integrated optical waveguides based on OPS have been developed.