Memory effects are commonly seen in organic thin-film transistor (OTFT) characteristics. In the absence of memory effects associated with the gate dielectric, the hysteresis in p-channel pentacene-based OTFTs, as measured in air and under illumination, was found to be dominated by trapped electrons, rather than trapped holes, in the semiconductor. The responsible acceptor type traps have very long lifetime. The immobile, previously stored negative charge requires extra holes to balance it, resulting in early establishment of the channel and extra drain current. This model is unique in that it discusses the majority carrier population influenced by trapped charge opposite in sign to the majority carriers in a simple electrostatic manner, to explain history dependence. The model was supported by drain current transient decay data. This memory effect is ambient and illumination sensitive. We studied the presence or absence of this effect under various ambient and illumination conditions, and found the responsible acceptor type traps mostly extrinsic and their formation reversible. Efforts were taken in the quantitative analysis to exclude the bias stress effect from the memory effect due to the charged acceptors.
{"title":"Hysteresis in pentacene-based organic thin-film transistors","authors":"G. Gu, M. Kane","doi":"10.1117/12.679661","DOIUrl":"https://doi.org/10.1117/12.679661","url":null,"abstract":"Memory effects are commonly seen in organic thin-film transistor (OTFT) characteristics. In the absence of memory effects associated with the gate dielectric, the hysteresis in p-channel pentacene-based OTFTs, as measured in air and under illumination, was found to be dominated by trapped electrons, rather than trapped holes, in the semiconductor. The responsible acceptor type traps have very long lifetime. The immobile, previously stored negative charge requires extra holes to balance it, resulting in early establishment of the channel and extra drain current. This model is unique in that it discusses the majority carrier population influenced by trapped charge opposite in sign to the majority carriers in a simple electrostatic manner, to explain history dependence. The model was supported by drain current transient decay data. This memory effect is ambient and illumination sensitive. We studied the presence or absence of this effect under various ambient and illumination conditions, and found the responsible acceptor type traps mostly extrinsic and their formation reversible. Efforts were taken in the quantitative analysis to exclude the bias stress effect from the memory effect due to the charged acceptors.","PeriodicalId":406438,"journal":{"name":"SPIE Optics + Photonics","volume":"407 30","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2006-09-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114008012","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
U. Efron, B. Apter, R. Israeli, I. David, I. Baal-Zedaka
One of the key factors affecting the performance of liquid crystal devices is the fringing field effect. This effect is the principal cause for the current resolution limitations of LCDs as well as the reduction in both the maximum deflection angle and the diffraction efficiency of beam steering devices. Recent studies in the reduction of the fringing field effects will be presented with applications in the development of ultra-small pixel sizes in LCD's and high performance LC-beam steering devices. A particular implementation using Gires-Tournois structure will be discussed. Another area of research to be discussed is a study of the fundamental limits of LCs and other electro-optic materials, with respect to their electro-optic coefficient. Fundamental physical limitations based on material stability considerations will be presented.
{"title":"Recent studies in LC devices and technology","authors":"U. Efron, B. Apter, R. Israeli, I. David, I. Baal-Zedaka","doi":"10.1117/12.680995","DOIUrl":"https://doi.org/10.1117/12.680995","url":null,"abstract":"One of the key factors affecting the performance of liquid crystal devices is the fringing field effect. This effect is the principal cause for the current resolution limitations of LCDs as well as the reduction in both the maximum deflection angle and the diffraction efficiency of beam steering devices. Recent studies in the reduction of the fringing field effects will be presented with applications in the development of ultra-small pixel sizes in LCD's and high performance LC-beam steering devices. A particular implementation using Gires-Tournois structure will be discussed. Another area of research to be discussed is a study of the fundamental limits of LCs and other electro-optic materials, with respect to their electro-optic coefficient. Fundamental physical limitations based on material stability considerations will be presented.","PeriodicalId":406438,"journal":{"name":"SPIE Optics + Photonics","volume":"36 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2006-09-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123300123","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
M. Mestre, B. Viaris de Lesegno, R. Farcy, L. Pruvost, J. Bourderionnet, A. Delboulbé, B. Loiseaux, D. Dolfi
We demonstrate the use of an acousto-optic modulator to enhance the refresh rate and dynamic properties of a liquid-crystal spatial light modulator (SLM). The useful area of the SLM surface is split in several zones which are addressed separately, and read in a sequence by a steered laser beam. This configuration allows to increase the refresh rate by five orders of magnitude. Furthermore, improvements on the nature of the transition between different holograms are experimentally shown. The advantages of this technique are discussed in the particular context of cold atom manipulation with holographic optical tweezers.
{"title":"Improvements on the refresh rate and dynamical properties of a SLM by sequential readout using an acousto-optic modulator","authors":"M. Mestre, B. Viaris de Lesegno, R. Farcy, L. Pruvost, J. Bourderionnet, A. Delboulbé, B. Loiseaux, D. Dolfi","doi":"10.1117/12.680458","DOIUrl":"https://doi.org/10.1117/12.680458","url":null,"abstract":"We demonstrate the use of an acousto-optic modulator to enhance the refresh rate and dynamic properties of a liquid-crystal spatial light modulator (SLM). The useful area of the SLM surface is split in several zones which are addressed separately, and read in a sequence by a steered laser beam. This configuration allows to increase the refresh rate by five orders of magnitude. Furthermore, improvements on the nature of the transition between different holograms are experimentally shown. The advantages of this technique are discussed in the particular context of cold atom manipulation with holographic optical tweezers.","PeriodicalId":406438,"journal":{"name":"SPIE Optics + Photonics","volume":"6 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2006-09-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114268417","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We have developed liquid crystalline retardation films to improve quality of images of LCDs such as their viewing angle performance and coloration. We have achieved to make many types of optical retardation films by using rod-like liquid crystalline polymer (LCP). The resulting liquid crystalline polyesters film has several advantages over conventional uni- or biaxial stretched retardation film. Optical well-controlled structures such as twisted nematic, hybrid nematic and homeotropic structures could be stabilized for ideal compensation of various LCD modes including TN, STN, ECB, VA and IPS modes. Twisted nematic film is effective to cancel coloration in STN mode that is a fatal drawback for color representation. Hybrid nematic film is quite unique film because the film works not only as a wave plate but also as a viewing angle compensator for TN and ECB modes. By using rod-like LCP, it is also possible to make negative-C plate and positive-C plate. Negative-C plate could be realized by using a short pitch cholesteric alignment and positive-C plate could be realized by using homeotropic alignment. Viewing angle performances of various LCD modes compensated with the LCP films are reported in this study.
{"title":"Viewing angle compensation of various LCD modes by using a liquid crystalline polymer film Nisseki LC film","authors":"S. Nishimura, H. Mazaki","doi":"10.1117/12.681705","DOIUrl":"https://doi.org/10.1117/12.681705","url":null,"abstract":"We have developed liquid crystalline retardation films to improve quality of images of LCDs such as their viewing angle performance and coloration. We have achieved to make many types of optical retardation films by using rod-like liquid crystalline polymer (LCP). The resulting liquid crystalline polyesters film has several advantages over conventional uni- or biaxial stretched retardation film. Optical well-controlled structures such as twisted nematic, hybrid nematic and homeotropic structures could be stabilized for ideal compensation of various LCD modes including TN, STN, ECB, VA and IPS modes. Twisted nematic film is effective to cancel coloration in STN mode that is a fatal drawback for color representation. Hybrid nematic film is quite unique film because the film works not only as a wave plate but also as a viewing angle compensator for TN and ECB modes. By using rod-like LCP, it is also possible to make negative-C plate and positive-C plate. Negative-C plate could be realized by using a short pitch cholesteric alignment and positive-C plate could be realized by using homeotropic alignment. Viewing angle performances of various LCD modes compensated with the LCP films are reported in this study.","PeriodicalId":406438,"journal":{"name":"SPIE Optics + Photonics","volume":"122 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2006-09-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127583504","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A. Geiss, M. Schinhaerl, E. Pitschke, R. Rascher, P. Sperber, J. Slabeycius
Magnetorheological finishing (MRF) is a computer controlled polishing (CCP) technique for high precision surfaces. The process uses a magnetorheological fluid which stiffens in a magnetic field and thus acts as the polishing tool. A standard MR fluid consists of magnetic carbonyl iron (CI) particles, nonmagnetic polishing abrasives and liquid. To delaying oxidation of the iron particles and avoiding agglomeration the liquid consists of water completed with stabilizers. For the material removal and smoothing of the surface mostly cerium oxide or diamond is used. The materials to be polished may tend toward to different sedimentations of the MR fluid on the machined surface. These sedimentations result from the machining and may develop a polishing layer with MR fluid components. At the University of Applied Sciences Deggendorf analysis of the machined surface are made by the scanning electronic microscope (SEM) to determine the sedimentations of the finishing. The results of the research display the influence for the surface properties due to developing polishing layer by magnetorheological finishing.
{"title":"Sedimentations on high-precision surfaces of advanced materials by magnetorheological finishing","authors":"A. Geiss, M. Schinhaerl, E. Pitschke, R. Rascher, P. Sperber, J. Slabeycius","doi":"10.1117/12.680247","DOIUrl":"https://doi.org/10.1117/12.680247","url":null,"abstract":"Magnetorheological finishing (MRF) is a computer controlled polishing (CCP) technique for high precision surfaces. The process uses a magnetorheological fluid which stiffens in a magnetic field and thus acts as the polishing tool. A standard MR fluid consists of magnetic carbonyl iron (CI) particles, nonmagnetic polishing abrasives and liquid. To delaying oxidation of the iron particles and avoiding agglomeration the liquid consists of water completed with stabilizers. For the material removal and smoothing of the surface mostly cerium oxide or diamond is used. The materials to be polished may tend toward to different sedimentations of the MR fluid on the machined surface. These sedimentations result from the machining and may develop a polishing layer with MR fluid components. At the University of Applied Sciences Deggendorf analysis of the machined surface are made by the scanning electronic microscope (SEM) to determine the sedimentations of the finishing. The results of the research display the influence for the surface properties due to developing polishing layer by magnetorheological finishing.","PeriodicalId":406438,"journal":{"name":"SPIE Optics + Photonics","volume":"90 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2006-09-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131897222","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Generally, optical feedback and/or two counter-propagating beams are necessary to form high-definition patterns in the cross section of a laser beam after passing through a nonlinear medium. In this paper we present an observation of pattern formation in liquid crystal media in a single laser beam without any external feedback. We found that after irradiation of a dye-doped liquid crystal cell with repetitive nanosecond pulses, the beam coming out of the liquid crystal cell exhibits a spectacular kaleidoscopic change of beam patterns in the far field. The patterns vary from pulse to pulse in an ordered manner cycling through a variety of complicated forms. We speculate that localized phase separation of the dye from the liquid crystal host occurs in the focal region of the beam in our experiments, and that the observed far-field patterns result from the laser-beam diffraction on these absorptive and refractive inhomogeneities.
{"title":"Feedback-free single-beam pattern formation by nanosecond pulses in dye-doped liquid crystals","authors":"N. Lepeshkin, S. Lukishova, R. Boyd, K. Marshall","doi":"10.1117/12.679738","DOIUrl":"https://doi.org/10.1117/12.679738","url":null,"abstract":"Generally, optical feedback and/or two counter-propagating beams are necessary to form high-definition patterns in the cross section of a laser beam after passing through a nonlinear medium. In this paper we present an observation of pattern formation in liquid crystal media in a single laser beam without any external feedback. We found that after irradiation of a dye-doped liquid crystal cell with repetitive nanosecond pulses, the beam coming out of the liquid crystal cell exhibits a spectacular kaleidoscopic change of beam patterns in the far field. The patterns vary from pulse to pulse in an ordered manner cycling through a variety of complicated forms. We speculate that localized phase separation of the dye from the liquid crystal host occurs in the focal region of the beam in our experiments, and that the observed far-field patterns result from the laser-beam diffraction on these absorptive and refractive inhomogeneities.","PeriodicalId":406438,"journal":{"name":"SPIE Optics + Photonics","volume":"166 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2006-09-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116403285","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The superprism and lasing devices were demonstrated using holographic polymer-dispersed liquid crystal (HPDLC) films. The HPDLC film for superprism application was designed and fabricated using three coplanar beams. The fabricated HPDLC film contained two-dimensional (2D) ordered nano-sized LC domains (~150nm in diameter) embedded in a polymer matrix; its periodicity was estimated using a scanning electron microscope to be ~350nm. The dispersion of white light from this HPDLC superprism was ~50°, and the deflection of light output from it was consistent with the theoretical value obtained by the pland wave expansion method. HPDLC for laser application was fabricated using two counter-propagation laser beams similar to those used in standard holography. The structure has a periodicity in the range of optical wavelength, and reflects light selectively as governed by Bragg reflection. Doped with a laser dye whose emission spectrum overlaps the reflection spectrum of the grating, the HPDLC reflection grating can be lased at the band edges of the reflection band gap. The details of the experiments, results will be reported.
{"title":"Photonic crystals based on holographic polymer-dispersed liquid crystal films and applications","authors":"M. Li, S. T. Wu, A. Fuh","doi":"10.1117/12.677625","DOIUrl":"https://doi.org/10.1117/12.677625","url":null,"abstract":"The superprism and lasing devices were demonstrated using holographic polymer-dispersed liquid crystal (HPDLC) films. The HPDLC film for superprism application was designed and fabricated using three coplanar beams. The fabricated HPDLC film contained two-dimensional (2D) ordered nano-sized LC domains (~150nm in diameter) embedded in a polymer matrix; its periodicity was estimated using a scanning electron microscope to be ~350nm. The dispersion of white light from this HPDLC superprism was ~50°, and the deflection of light output from it was consistent with the theoretical value obtained by the pland wave expansion method. HPDLC for laser application was fabricated using two counter-propagation laser beams similar to those used in standard holography. The structure has a periodicity in the range of optical wavelength, and reflects light selectively as governed by Bragg reflection. Doped with a laser dye whose emission spectrum overlaps the reflection spectrum of the grating, the HPDLC reflection grating can be lased at the band edges of the reflection band gap. The details of the experiments, results will be reported.","PeriodicalId":406438,"journal":{"name":"SPIE Optics + Photonics","volume":"13 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2006-09-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122210630","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
M. Astafieva, R. Hoover, A. Y. Rozanov, A. B. Vrevskiy
Ancient Archaean and Proterozoic rocks are model objects for the investigation of rocks comprising astromaterials. Three types of fossil microorganisms found in Archaean rocks of Karelia are determined: 1. forms found in situ, in other words microorganisms of the same-age as the rock matrix, that is valid Archaean fossils, 2. endolithic fossil microorganisms, that is to say forms inhabited early formed rocks, and 3. younger than Archaean-Proterozoic mineralised microorganisms, that is later contamination. The structures belong (from our point of view) to the first type, or genuine Archaean forms were mainly under our examination. Practical investigation of ancient microorganisms from Greenstone-Belt of Northern Karelia turns to be very perspective. It shows that even in such ancient period as the Archaean an ancient diverse world existed. Moreover probably such relatively highly organised forms as cyanobacteria and perhaps eukaryotic forms existed in Archaean world.
{"title":"Fossil microorganisms in the Archaean","authors":"M. Astafieva, R. Hoover, A. Y. Rozanov, A. B. Vrevskiy","doi":"10.1117/12.681660","DOIUrl":"https://doi.org/10.1117/12.681660","url":null,"abstract":"Ancient Archaean and Proterozoic rocks are model objects for the investigation of rocks comprising astromaterials. Three types of fossil microorganisms found in Archaean rocks of Karelia are determined: 1. forms found in situ, in other words microorganisms of the same-age as the rock matrix, that is valid Archaean fossils, 2. endolithic fossil microorganisms, that is to say forms inhabited early formed rocks, and 3. younger than Archaean-Proterozoic mineralised microorganisms, that is later contamination. The structures belong (from our point of view) to the first type, or genuine Archaean forms were mainly under our examination. Practical investigation of ancient microorganisms from Greenstone-Belt of Northern Karelia turns to be very perspective. It shows that even in such ancient period as the Archaean an ancient diverse world existed. Moreover probably such relatively highly organised forms as cyanobacteria and perhaps eukaryotic forms existed in Archaean world.","PeriodicalId":406438,"journal":{"name":"SPIE Optics + Photonics","volume":"3 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2006-09-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127481580","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This paper reviews our recent progress of micro and nanolithography techniques for the fabrications of planar photonic meta-materials and other nano photonic structures. The nanotechnologies involved in this development include the state-of-the-art electron-beam lithography (EBL), nanoimprint lithography (NIL), hot embossing, soft lithography and hybrid lithography, which is the combination of different lithography processes. Using these technologies, various meta-materials in sizes from micrometres down to sub-100 nm were successfully fabricated. Characterisations of these meta-materials have revealed a wealth of novel phenomena in nanophotonics. This paper will also discuss the advantages, disadvantages and suitability of each technology involved, trying to give a fair judgement for the applicability of the developed techniques. It can be concluded that micro and nanolithography are capable of achieving functional planar optic meta-materials in both single layer and multiple layer. Especially the developed manufacture processes using nanoimprint lithography and hot embossing technique may lead to fast speed patterning for high throughput and low cost mass production for broad applications.
{"title":"Micro and nanolithography for photonic meta-materials and photonic nanostructures","authors":"Yifang Chen, A. S. Schwanecke, N. Zheludev","doi":"10.1117/12.678172","DOIUrl":"https://doi.org/10.1117/12.678172","url":null,"abstract":"This paper reviews our recent progress of micro and nanolithography techniques for the fabrications of planar photonic meta-materials and other nano photonic structures. The nanotechnologies involved in this development include the state-of-the-art electron-beam lithography (EBL), nanoimprint lithography (NIL), hot embossing, soft lithography and hybrid lithography, which is the combination of different lithography processes. Using these technologies, various meta-materials in sizes from micrometres down to sub-100 nm were successfully fabricated. Characterisations of these meta-materials have revealed a wealth of novel phenomena in nanophotonics. This paper will also discuss the advantages, disadvantages and suitability of each technology involved, trying to give a fair judgement for the applicability of the developed techniques. It can be concluded that micro and nanolithography are capable of achieving functional planar optic meta-materials in both single layer and multiple layer. Especially the developed manufacture processes using nanoimprint lithography and hot embossing technique may lead to fast speed patterning for high throughput and low cost mass production for broad applications.","PeriodicalId":406438,"journal":{"name":"SPIE Optics + Photonics","volume":"15 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2006-09-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130525410","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
K. Kolasinski, I. Harrison, A. Gavrilenko, C. Bonner, V. Gavrilenko
Sum Frequency Generation (SFG) spectra of nanocrystalline porous silicon (por-Si) exposed to different chemical treatments are studied. We report the first SFG studies of por-Si in direct contact with a liquid. SFG is excited by a regeneratively amplified Ti:sapphire system (787 nm, 120 fs, 1 kHz). The sum frequency is generated by combining this light with infrared that is generated with an optical parametric amplifier (OPA) that delivers 100-200 μJ pulses at 1370-1770 nm. Por-Si is made from a 10-20 Ω cm p-type Si(001) wafer. Comparisons are made to planar Si(001) as well as GaAs(001). First principle electronic structure theory based on density functional theory (DFT) is used to study the adsorption and optical response functions from the system of ethanol molecule adsorbed on Si(001) and Si(111) surfaces. Equilibrium atomic geometries are obtained through molecular dynamics and total energy minimization methods. Electron energy structure and optical properties are calculated using generalized gradient approximation method with ab initio pseudopotentials. Predicted differential optical absorption spectra for chemisorbed Si(001) and Si(111) surfaces are analyzed in comparison with SFG data measured on differently treated porous silicon. Substantial modifications of the surface atomic and electron energy structures of silicon surfaces due to chemisorption are shown to provide the dominant contributions to the SFG response.
{"title":"Characterization of chemisorption on porous silicon by sum frequency generation","authors":"K. Kolasinski, I. Harrison, A. Gavrilenko, C. Bonner, V. Gavrilenko","doi":"10.1117/12.681142","DOIUrl":"https://doi.org/10.1117/12.681142","url":null,"abstract":"Sum Frequency Generation (SFG) spectra of nanocrystalline porous silicon (por-Si) exposed to different chemical treatments are studied. We report the first SFG studies of por-Si in direct contact with a liquid. SFG is excited by a regeneratively amplified Ti:sapphire system (787 nm, 120 fs, 1 kHz). The sum frequency is generated by combining this light with infrared that is generated with an optical parametric amplifier (OPA) that delivers 100-200 μJ pulses at 1370-1770 nm. Por-Si is made from a 10-20 Ω cm p-type Si(001) wafer. Comparisons are made to planar Si(001) as well as GaAs(001). First principle electronic structure theory based on density functional theory (DFT) is used to study the adsorption and optical response functions from the system of ethanol molecule adsorbed on Si(001) and Si(111) surfaces. Equilibrium atomic geometries are obtained through molecular dynamics and total energy minimization methods. Electron energy structure and optical properties are calculated using generalized gradient approximation method with ab initio pseudopotentials. Predicted differential optical absorption spectra for chemisorbed Si(001) and Si(111) surfaces are analyzed in comparison with SFG data measured on differently treated porous silicon. Substantial modifications of the surface atomic and electron energy structures of silicon surfaces due to chemisorption are shown to provide the dominant contributions to the SFG response.","PeriodicalId":406438,"journal":{"name":"SPIE Optics + Photonics","volume":"18 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2006-09-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130288010","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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