Porous silicon: a quantum sponge structure for silicon based optoelectronics

Bisi, O.; Ossicini, Stefano; Pavesi, L.

doi:10.1016/s0167-5729(99)00012-6

Cited by 1,351 publications

(993 citation statements)

References 408 publications

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“…MS-MPs are characterized by an average pore diameter of 22.5 nm (N2 adsorption, BJH calculation scheme) and a BET Surface Area of 341.5219 m²/g. It is known that porous silicon prepared with p + -type doped wafer consists on long tubular cavities running perpendicular to the surface, another distinctive feature of MS-MPs as compared to silicon particles prepared by supramolecular chemistry [34]. Figure 2C and 2D substantiate the order of magnitude of this pore size and this regular pore arrangement.…”

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confidence: 56%

Protein delivery based on uncoated and chitosan-coated mesoporous silicon microparticles

Pastor

Matveeva

Valle-Gallego

et al. 2011

Colloids and Surfaces B: Biointerfaces

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Mesoporous silicon is a biocompatible, biodegradable material that is receiving increased attention for pharmaceutical applications due to its extensive specific surface. This feature enables to load a variety of drugs in mesoporous silicon devices by simple adsorption-based procedures. In this work, we have addressed the fabrication and characterization of two new mesoporous silicon devices prepared by electrochemistry and intended for protein delivery, namely: (i) mesoporous silicon microparticles and (ii) chitosan-coated mesoporous silicon microparticles. Both carriers were investigated for their capacity to load a therapeutic protein (insulin) and a model antigen (bovine serum albumin) by adsorption. Our results show that mesoporous silicon microparticles prepared by electrochemical methods present moderate affinity for insulin and high affinity for albumin. However, mesoporous silicon presents an extensive capacity to load both proteins, leading to systems were protein could represent the major mass fraction of the formulation. The possibility to form a chitosan coating on the microparticles surface was confirmed both qualitatively by atomic force microscopy and quantitatively by a colorimetric method.Mesoporous silicon microparticles with mean pore size of 35 nm released the loaded insulin quickly, but not instantaneously. This profile could be slowed to a certain extent by the chitosan coating modification. With their high protein loading, their capacity to provide a controlled release of insulin over a period of 60-90 min, and the potential mucoadhesive effect of the chitosan coating, these composite devices comprise several features that render them interesting candidates as transmucosal protein delivery systems.

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confidence: 56%

Protein delivery based on uncoated and chitosan-coated mesoporous silicon microparticles

Pastor

Matveeva

Valle-Gallego

et al. 2011

Colloids and Surfaces B: Biointerfaces

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“…With this in mind, different mechanisms for silicon dissolution have been proposed, in which some basic requirements need to be satisfied. 7,8,10 The mechanism for the oxidation and dissolution of (100) silicon is discussed in light of experimental finding supported by the divalent dissolution mechanism that is, in aqueous solution, initiated by holes supplied from the Si bulk. 10 The holes concentration may be thermally generated or photogenerated.…”

Section: Resultsmentioning

confidence: 99%

“…7,8 In general, it is discussed and accepted in the literature that holes (h+) are required for both electropolishing and pores formation, where two hydrogen atoms are evolved for Morphological and Optical Characteristics of Porous Silicon Produced by Anodization Process J. Braz. Chem.…”

Section: Introductionmentioning

confidence: 99%

“…7,8 In general, it is discussed and accepted in the literature that holes (h+) are required for both electropolishing and pores formation, where two hydrogen atoms are evolved for each dissolved Si atom. 7 As a consequence, for the pore formation process, the current efficiencies are due to two electrons per dissolved Si atom, whereas four electrons are necessary for the electropolishing regime.…”

Section: Introductionmentioning

confidence: 99%

“…This argument was supported in the literature, from the chemical composition studies of PS layer, using IR spectroscopy measurements showing that the silicon surface is terminated with hydrogen, although the Si-F (6 eV) bond is much strong than Si-H bond. 7,12,14,[18][19][20][21][22][23][24] Figure 1 shows top view images of typical PS samples prepared by photoelectrochemical oxidation of n-type silicon, etching time of 60 min and current density of 11 mA cm -2 . The samples were prepared with two different solutions of HF-ethanol and HF-MeCN, for two types of Si resistivity.…”

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Morphological and optical characteristics of porous silicon produced by anodization process in HF-acetonitrile and HF-ethanol solutions

Miranda¹,

Baldan²,

Beloto³

et al. 2008

J. Braz. Chem. Soc.

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Amostras de silício poroso (PS) foram obtidas pelo processo de anodização em lâminas de Si tipo n, dopadas com fósforo. A oxidação eletroquímica do PS foi obtida utilizando-se solução de ácido fluorídrico (HF) contendo aditivos como etanol e acetonitrila (MeCN). A formação dos poros foi estudada com a variação da resistividade das laminas de Si e parâmetros de processo como: concentração do ácido, densidade de corrente e tempo de anodização. As técnicas de Microscopia Eletrônica de Varredura (MEV) e Espectroscopia de Espalhamento Raman foram utilizadas para a investigação da morfologia e fotoluminescência, respectivamente. A camada de PS formada com o uso da solução de HF-MeCN mostrou maior uniformidade e homogeneidade na distribuição dos macroporos com diferentes tipos e tamanhos. Esse comportamento pode ser explicado devido a tensão superficial da MeCN ser maior que a do etanol. Consequentemente, as moléculas de MeCN podem passivar a superfície do silício durante o processo de anodização.Porous silicon (PS) samples were obtained by anodization etching process of n-type silicon wafer phosphorus-doped. Electrochemical oxidation of PS was investigated in aqueous hydrofluoric acid (HF) containing additive such as ethanol or acetonitrile. Pore formation was studied with the variation of type and resistivity of the silicon wafer, taking into account the most important anodization process parameters such as: acid concentration, current density and anodization time. Scanning Electron Microscopy (SEM) and Raman Scattering Spectroscopy measurements were used to characterize the macropore morphology changes and sample photoluminescense responses, respectively. PS layer formed in HF-acetonitrile solution showed more uniform and homogeneous macropore distributions with different shapes and sizes. Behavior may be explained because acetonitrile surface tension is greater than that of ethanol. Therefore, acetonitrile molecules might passivate the silicon surface dissolved during the anodization process. Keywords: porous silicon, HF-acetonitrile, HF-ethanol IntroductionSince the discovery of its visible photoluminescence (PL) at room temperature, porous silicon (PS) has been intensively studied. Nowadays, PS is considered a very attractive material for the sensing layer in a chemical sensor, sacrificial layer in micromachining, and light emitting diode (LED) in optoelectronic devices. [1][2][3][4] Porous Si might be formed by electrochemical etching of single monocrystalline Si in HF solutions containing additives as ethanol or acetonitrile (MeCN). However, the anodization process was firstly studied by Bomchil et al., 5 in 1983, using HF and ethanol solution and they reported that ethanol improved the homogeneity of PS layer. Consequently, HF-ethanol has been used by most research groups as the standard electrolyte for PS formation process. After that, Propst et al. 6 have reported the electrochemical oxidation of p-and n-type silicon in nonaqueous electrolyte of HF-MeCN and discussed their singular and large porous structure...

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From Undulating Si Quantum Wires to Si Quantum Dots: A Model for Porous Silicon

Degoli

Luppi

Ossicini

2000

phys. stat. sol. (a)

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Freshly etched porous silicon shows the structure of a crystalline silicon skeleton with a connected undulating-wire morphology; in aged porous silicon samples the presence of Si dots is predominant. In this paper we present, for the first time, ab-initio results of the electronic and optical properties of undulating Si quantum wires, moreover, the transition from Si quantum wires to Si quantum dots is also discussed.Introduction It is now well accepted that the striking luminescence properties of porous silicon (PS) are due to the quantum confinement effects in nanometer-sized silicon crystallites that compose this complex material [1]. A lot of experimental results have actually shown, for a recent review see [1], that PS is characterized by a complicated network of silicon pillar structures of nanometrical dimension crossing each other to form a sponge-like material. In aged samples the cross-section dimensions of the wirelike silicon structures are reduced down to a dot-like situation. From a theoretical point of view fresh structures can be modelled as quantum wires, while heavily aged structures are modelled as dot-like. The modelling of PS both as Si quantum wires and Si quantum dots has been recently reviewed [1±3]. All the calculations show that the electronic states and the optical properties of Si quantum wires and dots are influenced by quantum confinement, symmetry features and passivation regimes. Quantum confinement effects result in an enlargement of the band gap, in a relaxation of the momentum conserving role, and in a size dependence of the absorption and luminescence energy. Nevertheless, no attempt has been made until now to perform calculations which try to simulate the real morphology of PS that is those of undulating wires, the only calculation, to our knowledge, of the electronic properties of an idealised undulating-wire structure is that done by Tigelis et al.[4] 2 , using the effective-mass theory. Moreover, no attempt has been made in order to model the transition from wires to dots. The reason lies in the formidable computational burden that has obliged theoretical calculations to use a simplified model of wires with constant cross section. Here we will present first-principle

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Porous silicon: a quantum sponge structure for silicon based optoelectronics

Cited by 1,351 publications

References 408 publications

Protein delivery based on uncoated and chitosan-coated mesoporous silicon microparticles

Protein delivery based on uncoated and chitosan-coated mesoporous silicon microparticles

Morphological and optical characteristics of porous silicon produced by anodization process in HF-acetonitrile and HF-ethanol solutions

From Undulating Si Quantum Wires to Si Quantum Dots: A Model for Porous Silicon

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