• Journal of Integrative Natural Science
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• v.2 no.4
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• pp.275-279
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• 2009

Recently, number of studies for porous silicon (PSi) have been investigated by many researchers. Multistructured porous silicon such as a distributed Bragg reflector (DBR) PSi, has been a topic of interest, because of its unique optical properties. DBR PSi were prepared by using an electrochemical etch of $P{^+}{^+}$-type silicon wafer with resistivity between 0.1 and $10m{\Omega}cm$. The electrochemical etch with square wave current density results in two different refractive indices in the porous layer. In this work, DBR porous silicon chips for a simple and portable organic vapor-sensing device have fabricated. The optical characteristics of DBR PSi have been investigated. DBR porous silicon have been characterized by FT-IR and Ocean optics 2000 spectrometer. The device used DBR PSi chip has been demonstrated as an excellent gas sensor, showing a great senstivity to organic vapor at room temperature.

• Journal of Integrative Natural Science
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• v.2 no.2
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• pp.82-85
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• 2009

Distributed Bragg reflector (DBR) porous silicon (PSi) was generated by an electrochemical etching a bragg structure into a silicon wafer through electrode current in aqueous ethanolic HF solution. DBR PSi exhibiting unique reflectivity was successfully obtained by an electrochemical etching of silicon wafer using square current waveform. The multilayered photonic crystals of DBR PSi exhibited the reflection of a specific wavelength with high reflectivity in the optical reflectivity spectrum. In this work, we have developed a method to create refractive index in Si substrate through intensity of an electric current. The electrochemical process allows for precise control of the structural properties of DBR PSi such as thickness of the porous layer, porosity, and average pore diameter. The number of reflection peak of DBR PSi and its pore size increased as the intensity of electric current increased. This might be a demonstration for the fabrication of specific reflectors or filters.

• Journal of Integrative Natural Science
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• v.8 no.1
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• pp.67-74
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• 2015

Sensing characteristics for porous smart particle based on DBR smart particles were reported. Optically encoded porous silicon smart particles were successfully fabricated from the free-standing porous silicon thin films using ultrasono-method. DBR PSi was prepared by an electrochemical etch of heavily doped $p^{++}$-type silicon wafer. DBR PSi was prepared by using a periodic pseudo-square wave current. The surface-modified DBR PSi was prepared by either thermal oxidation or thermal hydrosilylation. Free-standing DBR PSi films were generated by lift-off from the silicon wafer substrate using an electropolishing current. Free-standing DBR PSi films were ultrasonicated to create DBR-structured porous smart particles. Three different surface-modified DBR smart particles have been prepared and used for sensing volatile organic vapors. For different types of surface-modified DBR smart particles, the shift of reflectivity mainly depends on the vapor pressure of analyte even though the surfaces of DBR smart particles are different. However huge difference in the shift of reflectivity depending on the different types of surface-modified DBR smart particles was obtained when the vapor pressures are quite similar which demonstrate a possible sensing application to specify the volatile organic vapors.

• Journal of the Korean Vacuum Society
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• v.16 no.3
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• pp.221-226
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• 2007

DBR (distributed Bragg reflectors) PSi (porous silicon) composite films displaying dual optical properties, both optical reflectivity and photoluminescence had been developed. DBR PSi samples were prepared by electrochemical etch of heavily doped $p^{++}-type$ silicon wafers (boron doped, polished on the <100> face, resistivity of $0.8-1.2m{\Omega}-cm$, Siltronix, Inc.). Free-standing DBR PSi films were treated with PMMA (polymethyl methacrylate) to produce flexible, stable composite materials in which the PSi matrix is covered with PMMA containing photoluminescent polysiloles. Optical characteristics of DBR PSi/polysilole-impregnated PMMA composite materials exhibit both their photonic reflectivity at 565 nm and photoluminescence at 510 nm, simultaneously. A possible application of this materials will be discussed.

• Journal of Integrative Natural Science
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• v.7 no.4
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• pp.221-226
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• 2014

Optically encoded porous silicon smart particles were successfully fabricated from the free-standing porous silicon thin films using ultrasono-method. DBR PSi was prepared by an electrochemical etch of heavily doped $p^{{+}{+}}$-type silicon wafer. DBR PSi was prepared by using a periodic pseudo-square wave current. The surface-modified DBR PSi was prepared by either thermal oxidation or thermal hydrosilylation. Free-standing DBR PSi films were generated by lift-off from the silicon wafer substrate using an electropolishing current. Free-standing DBR PSi films were ultrasonicated to create DBR-structured porous smart particles. Optical characteristics of porous smart particles were measured by FT-IR spectroscopy. The surface morphology of porous smart particles was determined by FE-SEM.

• Journal of Integrative Natural Science
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• v.3 no.4
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• pp.237-240
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• 2010

Recently, number of studies for porous silicon have been investigated by many researchers. Multistructured porous silicon (PSi), distributed Bragg reflector (DBR) PSi, has been a topic of interest, because of its unique optical properties. DBR PSi were prepared by an electrochemical etch of $P^{{+}{+}}$-type silicon wafer of resistivity between 0.1 $m{\Omega}cm$ with square wave current density, resulting two different refractive indices. In this work, We have fabricated a simple and portable organic vapor-sensing device based on DBR porous silicon and investigated the optical characteristics of DBR porous silicon. DBR porous silicon have been characterized by FT-IR, Ocean optics 2000 spectrometer. The device used DBR PSi chip has been demonstrated as an excellent gas sensor, showing a great senstivity to a toxic vapor (TEP, DMMP, DEEP) at room temperature.

• Journal of Sensor Science and Technology
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• v.15 no.6
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• pp.391-396
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• 2006

Free-standing multilayer distributed Bragg reflectors (DBR) porous silicon dielectric mirrors, prepared by electrochemical etching of crystalline silicon using square wave currents are treated with polystyrene to produce flexible, stable composite materials in which the porous silicon matrix is covered with caffeine-impregnated polystyrene. Optically encoded DBR PSi/polystyrene composite films retain the optical reflectivity. Optical characteristics of DBR PSi/polystyrene composite films are stable and robust for 2 hrs in a pH=7 aqueous buffer solution. The appearance of caffeine and change of DBR peak were simultaneously measured by UV-vis spectrometer and Ocean optics 2000 spectrometer, respectively.

• Journal of Integrative Natural Science
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• v.4 no.1
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• pp.11-14
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• 2011

Free-standing multilayer distributed Bragg reflectors (DBR) porous silicon dielectric mirrors, prepared by electrochemical etching of crystalline silicon using square wave currents are treated with polymethylmethacrylate (PMMA) to produce flexible, stable composite materials in which the porous silicon matrix is covered with caffeine-impregnated PMMA. Optically encoded free-standing DBR PSi dielectric mirrors retain the optical reflectivity. Optical characteristics of free-standing DBR PSi dielectric mirrors are stable and robust for 24 hrs in a pH 12 aqueous buffer solution. The appearance of caffeine and change of DBR peak were simultaneously measured by UV-vis spectrometer and Ocean optics 2000 spectrometer, respectively.

• Journal of Integrative Natural Science
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• v.4 no.3
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• pp.187-191
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• 2011

The differences of properties for both single-layered and multi-layered porous silicon were investigated. Multistructured porous silicons such as DBR or rugate porous silicon exhibit strong reflection resonances providing the reflection of a specific wavelength in the optical reflectivity spectrum. DBR PSi displays a square varying porosity gradient in the direction perpendicular to the plane of the filter but a sinusoidally varying porosity gradient was obtained for rugate PSi.