Pub Date : 1995-06-01DOI: 10.1051/JPHYSCOL:19955115
L. Cognolato
At the beginning of the seventies, a break-through took place in the telecommunication research. The introduction of Chemical Vapour Deposition technology in the manufacture of optical fibres allowed both technical quality and economical convenience to realise optical networks, thus beginning the telecommunication revolution. Since that moment, a great development of the CVD techniques has been performed, introducing several methods to produce fibres with geometry and optical properties optimised for different applications. An overview of the different methods is given, and the problems which have been to be solved in these years are described.
{"title":"Chemical Vapour Deposition for Optical Fibre Technology","authors":"L. Cognolato","doi":"10.1051/JPHYSCOL:19955115","DOIUrl":"https://doi.org/10.1051/JPHYSCOL:19955115","url":null,"abstract":"At the beginning of the seventies, a break-through took place in the telecommunication research. The introduction of Chemical Vapour Deposition technology in the manufacture of optical fibres allowed both technical quality and economical convenience to realise optical networks, thus beginning the telecommunication revolution. Since that moment, a great development of the CVD techniques has been performed, introducing several methods to produce fibres with geometry and optical properties optimised for different applications. An overview of the different methods is given, and the problems which have been to be solved in these years are described.","PeriodicalId":17944,"journal":{"name":"Le Journal De Physique Colloques","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1995-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"74945472","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}
Pub Date : 1995-06-01DOI: 10.1051/JPHYSCOL:1995549
N. Didier, B. Chenevier, O. Thomas, J. Sénateur, F. Weiss, A. Gaskov
[(YBaCuO) m /(PrBaCuO) n ] 10 multilayers have been deposited by Metal Organic Chemical Vapor Deposition (MOCVD). The films grow on SrTiO 3 (100) and MgO (100) substrates and have c-axis perpendicular to the substrate. A serie of superlattices has been synthesised with different deposition temperatures ranging between 700 and 850°C with different modulations (the thickness of YBCO layers staying unchanged and equal to 100A). The elements concentrations profiles at the interfaces and the interdiffusion were determined by secondary neutral mass spectroscopy (SNMS). X-ray diffraction show satellite peaks (characteristic of superlattice modulation) around 001 and 002 reflections. Moreover, the samples show a good in-plane orientation. The superconducting properties are analysed by AC screening. The critical temperature reaches 88K in the case of m=8 and n=2 (n and m being the numbers of units cells along c-axis for YBCO layer and PBCO one respectively).
采用金属有机化学气相沉积(MOCVD)技术沉积了[(YBaCuO) m /(PrBaCuO) n] 10多层膜。薄膜生长在srtio3(100)和MgO(100)衬底上，其c轴垂直于衬底。在不同的沉积温度(700 ~ 850℃)和不同的调制下合成了一系列的超晶格(YBCO层的厚度保持不变，等于100A)。用二次中性质谱(SNMS)测定了界面和相互扩散处的元素浓度谱。x射线衍射在001和002反射附近显示卫星峰(超晶格调制的特征)。此外，样品具有良好的面内取向。用交流筛选法对其超导性能进行了分析。当m=8和n=2 (n和m分别为YBCO层和PBCO层沿c轴的单位胞数)时，临界温度达到88K。
{"title":"Growth of (YBaCuO)m/(PrBaCuO)n Superlattices by MOCVD","authors":"N. Didier, B. Chenevier, O. Thomas, J. Sénateur, F. Weiss, A. Gaskov","doi":"10.1051/JPHYSCOL:1995549","DOIUrl":"https://doi.org/10.1051/JPHYSCOL:1995549","url":null,"abstract":"[(YBaCuO) m /(PrBaCuO) n ] 10 multilayers have been deposited by Metal Organic Chemical Vapor Deposition (MOCVD). The films grow on SrTiO 3 (100) and MgO (100) substrates and have c-axis perpendicular to the substrate. A serie of superlattices has been synthesised with different deposition temperatures ranging between 700 and 850°C with different modulations (the thickness of YBCO layers staying unchanged and equal to 100A). The elements concentrations profiles at the interfaces and the interdiffusion were determined by secondary neutral mass spectroscopy (SNMS). X-ray diffraction show satellite peaks (characteristic of superlattice modulation) around 001 and 002 reflections. Moreover, the samples show a good in-plane orientation. The superconducting properties are analysed by AC screening. The critical temperature reaches 88K in the case of m=8 and n=2 (n and m being the numbers of units cells along c-axis for YBCO layer and PBCO one respectively).","PeriodicalId":17944,"journal":{"name":"Le Journal De Physique Colloques","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1995-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77376563","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}
Pub Date : 1995-06-01DOI: 10.1051/JPHYSCOL:1995551
G. Garcia, J. Casado, J. Llibre, M. Doudkowski, J. Santiso, A. Figueras, S. Schamm, D. Dorignac, C. Grigis, M. Aguiló
YSZ buffer layers were deposited on silicon and sapphire by MOCVD. The layers deposited on silicon were highly oriented along [100] direction without in-plane orientation, probably because the existence of the SiO2 amorphous interlayer. In contrast, epitaxial YSZ was obtained on (1-102) sapphire showing an inplane texture defined by the following relationships : (100) YSZ // (1-102) sapphire and (110) YSZ // (01-12) sapphire. Subsequently, YBCO films were deposited on YSZ by MOCVD. Structural, morphological and electrical characterization of the superconducting layers were correlated with the in-plane texture of the buffer layers.
{"title":"Preparation of YBCO on YSZ Layers Deposited on Silicon and Sapphire by MOCVD : Influence of the Intermediate Layer on the Quality of the Superconducting Film","authors":"G. Garcia, J. Casado, J. Llibre, M. Doudkowski, J. Santiso, A. Figueras, S. Schamm, D. Dorignac, C. Grigis, M. Aguiló","doi":"10.1051/JPHYSCOL:1995551","DOIUrl":"https://doi.org/10.1051/JPHYSCOL:1995551","url":null,"abstract":"YSZ buffer layers were deposited on silicon and sapphire by MOCVD. The layers deposited on silicon were highly oriented along [100] direction without in-plane orientation, probably because the existence of the SiO2 amorphous interlayer. In contrast, epitaxial YSZ was obtained on (1-102) sapphire showing an inplane texture defined by the following relationships : (100) YSZ // (1-102) sapphire and (110) YSZ // (01-12) sapphire. Subsequently, YBCO films were deposited on YSZ by MOCVD. Structural, morphological and electrical characterization of the superconducting layers were correlated with the in-plane texture of the buffer layers.","PeriodicalId":17944,"journal":{"name":"Le Journal De Physique Colloques","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1995-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"74364838","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}
Pub Date : 1995-06-01DOI: 10.1051/JPHYSCOL:19955120
Kai-Erik Elers, M. Ritala, M. Leskelä, Leena‐Sisko Johansson
AlN thin films were grown by the Atomic Layer Epitaxy (ALE) technique employing AlCl 3 and NH 3 as precursors. A growth rate of 1.0 A/cycle was obtained in experiments carried out at 500 °C. The films deposited onto soda lime glass substrates were polycrystalline exhibiting a strong preferred orientation in the [001] direction. X-ray Photoelectron Spectroscopy (XPS) measurements revealed that the films contained oxygen and chlorine as impurities.
{"title":"Atomic Layer Epitaxy Growth of AIN Thin Films","authors":"Kai-Erik Elers, M. Ritala, M. Leskelä, Leena‐Sisko Johansson","doi":"10.1051/JPHYSCOL:19955120","DOIUrl":"https://doi.org/10.1051/JPHYSCOL:19955120","url":null,"abstract":"AlN thin films were grown by the Atomic Layer Epitaxy (ALE) technique employing AlCl 3 and NH 3 as precursors. A growth rate of 1.0 A/cycle was obtained in experiments carried out at 500 °C. The films deposited onto soda lime glass substrates were polycrystalline exhibiting a strong preferred orientation in the [001] direction. X-ray Photoelectron Spectroscopy (XPS) measurements revealed that the films contained oxygen and chlorine as impurities.","PeriodicalId":17944,"journal":{"name":"Le Journal De Physique Colloques","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1995-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87857043","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}
Pub Date : 1995-06-01DOI: 10.1051/JPHYSCOL:19955106
R. Loo, L. Vescan, C. Dieker, D. Freundt, A. Hartmann, A. Mück
The paper reports a study of the quality of the substrate/epilayer interface. Before growing the Si or Si/Si 1-x Ge x structures by low pressure chemical vapour deposition, Si(100) substrates were cleaned by a modified RCA-cleaning and just before epitaxy different ex-situ and in-situ processes were applied to remove the oxide layer grown on the wafer substrates in the last step of the RCA-cleaning. The effect of interfacial contamination on electrical and optical properties were studied. By a wet-chemical removal of the oxide layer an interfacial oxygen level of 1.3 x 10 13 atoms/cm 2 is found, while a thermal removal leads to an interfacial oxygen level below 6 x 10 12 atoms/cm 2 . In both cases carbon levels of (1-2)x10 14 atoms/cm 2 have been detected. By electrochemical capacitance-voltage profiling it was found that these contaminations are connected with electrically active donors. According to our investigations, electrochemical capacitance-voltage profiling is suitable to give a quick indication on the quality of the substrate/epitaxial interface. In addition, the removal of the oxide layer was investigated by high resolution electron energy loss spectroscopy on cleaned Si-surfaces.
本文报道了衬底/脱膜界面质量的研究。在通过低压化学气相沉积生长Si或Si/Si 1-x Ge x结构之前，用改良的rca清洗方法清洗Si(100)衬底，在外延之前，在rca清洗的最后一步，采用不同的非原位和原位工艺去除生长在晶圆衬底上的氧化层。研究了界面污染对材料电学和光学性能的影响。通过湿法化学去除氧化层，发现界面氧水平为1.3 x 1013原子/ cm2，而热去除导致界面氧水平低于6 x 1012原子/ cm2。在这两种情况下，碳水平均为(1-2)× 10 14原子/平方厘米。通过电化学电容电压谱分析，发现这些污染物与电活性供体有关。根据我们的研究，电化学电容电压谱适合于快速指示衬底/外延界面的质量。此外，用高分辨电子能量损失谱法研究了氧化层的去除。
{"title":"Investigation of the substrate/epitaxial interface of Si/Si1−xGex layers grown by LPCVD","authors":"R. Loo, L. Vescan, C. Dieker, D. Freundt, A. Hartmann, A. Mück","doi":"10.1051/JPHYSCOL:19955106","DOIUrl":"https://doi.org/10.1051/JPHYSCOL:19955106","url":null,"abstract":"The paper reports a study of the quality of the substrate/epilayer interface. Before growing the Si or Si/Si 1-x Ge x structures by low pressure chemical vapour deposition, Si(100) substrates were cleaned by a modified RCA-cleaning and just before epitaxy different ex-situ and in-situ processes were applied to remove the oxide layer grown on the wafer substrates in the last step of the RCA-cleaning. The effect of interfacial contamination on electrical and optical properties were studied. By a wet-chemical removal of the oxide layer an interfacial oxygen level of 1.3 x 10 13 atoms/cm 2 is found, while a thermal removal leads to an interfacial oxygen level below 6 x 10 12 atoms/cm 2 . In both cases carbon levels of (1-2)x10 14 atoms/cm 2 have been detected. By electrochemical capacitance-voltage profiling it was found that these contaminations are connected with electrically active donors. According to our investigations, electrochemical capacitance-voltage profiling is suitable to give a quick indication on the quality of the substrate/epitaxial interface. In addition, the removal of the oxide layer was investigated by high resolution electron energy loss spectroscopy on cleaned Si-surfaces.","PeriodicalId":17944,"journal":{"name":"Le Journal De Physique Colloques","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1995-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81092094","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}
Pub Date : 1995-06-01DOI: 10.1051/JPHYSCOL:1995506
S. Eroglu
Thermodynamic analysis of the chemical vapor deposition (CVD) of P 3 N 5 has been performed using the method of the minimization of the Gibbs' free energy in order to evaluate the PH 3 -NH 3 -N 2 , PCl 3 -NH 3 -H 2 and PBr 3 -NH 3 -H 2 gaseous mixtures for their potential to synthesize single-phase P 3 N 5 films at high yields. The conditions for the deposition of P 3 N 5 have been determined as a function of input reactant gas ratio of PX 3 /(PX 3 +NH 3 ) (X=H or Cl or Br) and deposition temperature at atmospheric pressure. A single phase P 3 N 5 is deposited at almost all reactant ratios and at temperatures below about 700 K when the PH 3 -NH 3 -N 2 system is used. The use of halide gas mixtures limits the formation of single phase P 3 N 5 to narrow regions of temperature and input reactant gas ratio. The gaseous species generally present in greatest abundance are H 2 , N 2 , NH 3 , PH 3 , HCl, P 4 , PCl 3 , P 2 , HBr, PBr 3 and PN. The thermodynamic analysis suggests that among the systems investigated here, the PH 3 -NH 3 -N 2 mixture is the most promising because simultaneously it gives the highest P 3 N 5 deposition yield and allows better control of the CVD process for the synthesis of P 3 N 5 films.
{"title":"Thermodynamic Analysis of the Chemical Vapor Deposition of Phosphorus Nitride (P3N5) Thin Films","authors":"S. Eroglu","doi":"10.1051/JPHYSCOL:1995506","DOIUrl":"https://doi.org/10.1051/JPHYSCOL:1995506","url":null,"abstract":"Thermodynamic analysis of the chemical vapor deposition (CVD) of P 3 N 5 has been performed using the method of the minimization of the Gibbs' free energy in order to evaluate the PH 3 -NH 3 -N 2 , PCl 3 -NH 3 -H 2 and PBr 3 -NH 3 -H 2 gaseous mixtures for their potential to synthesize single-phase P 3 N 5 films at high yields. The conditions for the deposition of P 3 N 5 have been determined as a function of input reactant gas ratio of PX 3 /(PX 3 +NH 3 ) (X=H or Cl or Br) and deposition temperature at atmospheric pressure. A single phase P 3 N 5 is deposited at almost all reactant ratios and at temperatures below about 700 K when the PH 3 -NH 3 -N 2 system is used. The use of halide gas mixtures limits the formation of single phase P 3 N 5 to narrow regions of temperature and input reactant gas ratio. The gaseous species generally present in greatest abundance are H 2 , N 2 , NH 3 , PH 3 , HCl, P 4 , PCl 3 , P 2 , HBr, PBr 3 and PN. The thermodynamic analysis suggests that among the systems investigated here, the PH 3 -NH 3 -N 2 mixture is the most promising because simultaneously it gives the highest P 3 N 5 deposition yield and allows better control of the CVD process for the synthesis of P 3 N 5 films.","PeriodicalId":17944,"journal":{"name":"Le Journal De Physique Colloques","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1995-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78497161","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}
Pub Date : 1995-06-01DOI: 10.1051/JPHYSCOL:19955139
T. Nagatomo, O. Omoto
The optical and electrical properties, crystallinity, and photoluminescence of GaInN epitaxial films were remarkably improved by photo-assited MOVPE using ultraviolet (UV) light from a deuterium (D 2 ) lamp. The dissociation of NH 3 is promoted by irradiation with a D 2 lamp and indiun atoms are effectively incorporated into the crystal lattice of GaInN. Good-quality epitaxial GaInN films were obtained at higher growth temperature of 800°C increasing the now rate of trimethylindium (TMIn). The photoluminescence peak intensity (band-edge emission) of GaInN films grown at 800°C is 14 times as great as that of 675°C.
{"title":"Physical Properties of Gallium Indium Nitride Films Prepared by Photo-Assisted MOVPE","authors":"T. Nagatomo, O. Omoto","doi":"10.1051/JPHYSCOL:19955139","DOIUrl":"https://doi.org/10.1051/JPHYSCOL:19955139","url":null,"abstract":"The optical and electrical properties, crystallinity, and photoluminescence of GaInN epitaxial films were remarkably improved by photo-assited MOVPE using ultraviolet (UV) light from a deuterium (D 2 ) lamp. The dissociation of NH 3 is promoted by irradiation with a D 2 lamp and indiun atoms are effectively incorporated into the crystal lattice of GaInN. Good-quality epitaxial GaInN films were obtained at higher growth temperature of 800°C increasing the now rate of trimethylindium (TMIn). The photoluminescence peak intensity (band-edge emission) of GaInN films grown at 800°C is 14 times as great as that of 675°C.","PeriodicalId":17944,"journal":{"name":"Le Journal De Physique Colloques","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1995-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82835561","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}
Pub Date : 1995-06-01DOI: 10.1051/JPHYSCOL:1995525
A. E. Turgambaeva, A. Bykov, I. Igumenov
Vapour thermolysis processes of copper(II) bis-chelate complexes with different β-diketones in the 160-640°C temperature range were studied by using the high-temperature source of a molecular beam with mass spectrometric recording of the gas phase composition directly at the outlet from the thermal reactor. Schemes of a heterogeneous decomposition of these compounds vapour were suggested on the basis of temperature dependences of the thermolysis gaseous products composition. It was established that the mechanisms of thermal conversion of copper(II) complexes with fluorinated and non-fluorinated ligands were not similar. A comparison of the thermal behaviour of the complexes with fluorinated and non-fluorinated ligands in vacuum, hydrogen and oxygen was carried out. Effective values of kinetic parameters in the Arrhenius equation were calculated for the first-order reaction on initial compound from the temperature dependence of the rate constant. The sequence of copper(II) complexes with β-diketones having different end substituents according to the thermal stability was revealed from the values of the thermal decomposition activation energy.
{"title":"Mass Spectrometric Study of Copper(II) β-Diketonates Vapour Thermolysis Mechanism and Kinetics","authors":"A. E. Turgambaeva, A. Bykov, I. Igumenov","doi":"10.1051/JPHYSCOL:1995525","DOIUrl":"https://doi.org/10.1051/JPHYSCOL:1995525","url":null,"abstract":"Vapour thermolysis processes of copper(II) bis-chelate complexes with different β-diketones in the 160-640°C temperature range were studied by using the high-temperature source of a molecular beam with mass spectrometric recording of the gas phase composition directly at the outlet from the thermal reactor. Schemes of a heterogeneous decomposition of these compounds vapour were suggested on the basis of temperature dependences of the thermolysis gaseous products composition. It was established that the mechanisms of thermal conversion of copper(II) complexes with fluorinated and non-fluorinated ligands were not similar. A comparison of the thermal behaviour of the complexes with fluorinated and non-fluorinated ligands in vacuum, hydrogen and oxygen was carried out. Effective values of kinetic parameters in the Arrhenius equation were calculated for the first-order reaction on initial compound from the temperature dependence of the rate constant. The sequence of copper(II) complexes with β-diketones having different end substituents according to the thermal stability was revealed from the values of the thermal decomposition activation energy.","PeriodicalId":17944,"journal":{"name":"Le Journal De Physique Colloques","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1995-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82884891","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}
Pub Date : 1995-06-01DOI: 10.1051/JPHYSCOL:1995517
G. Vignoles
The problem of gaseous diffusion inside complex porous media arises in the modeling of many chemical processes (e.g. Chemical Vapor Infiltration (CVI), heterogeneous catalysis in porous catalysts, filtration, etc...). A program computing effective diffusivities in the bulk, Knudsen and transition regimes has been designed and tested, which uses a Monte-Carlo mean-square-displacement algorithm. The porous medium has been represented from a special interpretation of a computer 3D discretized image. Simulations were carried out in a typical case of complex structured porous medium: a stacking of tissues (e. g. 2D woven fiber preform for CVI-densified composite materials). The results are presented as tortuosity factors, i.e. deviations from an equivalent medium made of straight cylindrical pores. The evolution of the diffusivities with the geometrical parameters of the tissues, and with the stacking mode has also been studied. It appears that the perpendicular diffusivity is closely related to the proportion of matching holes between different layers of tissue. The intermediate regime appears for Knudsen numbers lying between 100 and 10 -1 . In this domain, the Bosanquet formula only gives a good description if the Knudsen number is multiplied by a factor γ = 1/4. This phenomenon had been reported, to a lesser extent, for unidirectional random fiber packings.
{"title":"Modelling binary, Knudsen and transition regime diffusion inside complex porous media","authors":"G. Vignoles","doi":"10.1051/JPHYSCOL:1995517","DOIUrl":"https://doi.org/10.1051/JPHYSCOL:1995517","url":null,"abstract":"The problem of gaseous diffusion inside complex porous media arises in the modeling of many chemical processes (e.g. Chemical Vapor Infiltration (CVI), heterogeneous catalysis in porous catalysts, filtration, etc...). A program computing effective diffusivities in the bulk, Knudsen and transition regimes has been designed and tested, which uses a Monte-Carlo mean-square-displacement algorithm. The porous medium has been represented from a special interpretation of a computer 3D discretized image. Simulations were carried out in a typical case of complex structured porous medium: a stacking of tissues (e. g. 2D woven fiber preform for CVI-densified composite materials). The results are presented as tortuosity factors, i.e. deviations from an equivalent medium made of straight cylindrical pores. The evolution of the diffusivities with the geometrical parameters of the tissues, and with the stacking mode has also been studied. It appears that the perpendicular diffusivity is closely related to the proportion of matching holes between different layers of tissue. The intermediate regime appears for Knudsen numbers lying between 100 and 10 -1 . In this domain, the Bosanquet formula only gives a good description if the Knudsen number is multiplied by a factor γ = 1/4. This phenomenon had been reported, to a lesser extent, for unidirectional random fiber packings.","PeriodicalId":17944,"journal":{"name":"Le Journal De Physique Colloques","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1995-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84810463","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}
Pub Date : 1995-06-01DOI: 10.1051/JPHYSCOL:1995569
J. Salge
In plasma-assisted deposition methods the activation energy necessary for the initiation of chemical reactions is transferred via charged particles. Due to this fact in many cases the process temperature can be kept small, if gas discharges at pressures below 1 hPa are used. On the other hand low pressure requires a great deal of vacuum equipment. Processes at atmospheric pressure are more favourable, if similar results compared to existing methods can be achieved. Basis for a new plasma-assisted deposition method at atmospheric pressure are barrier discharges. Those discharges consist of a large number of transient microdischarges in parallel which are distributed statistically on the surface to be coated. Starting with some basic considerations on the repetitive generation of microdischarges, the deposition of thin polymeric films on glass surfaces is described, using barrier discharges at atmospheric pressure and acetylene. Uniform polymeric films up to 1 μm are obtained, if trains of voltage pulses are used. Parameters influencing the deposition rate and the film quality are discussed. In addition, it is estimated whether further improvements of the deposition process are possible.
{"title":"Plasma-Assisted Deposition at Atmospheric Pressure","authors":"J. Salge","doi":"10.1051/JPHYSCOL:1995569","DOIUrl":"https://doi.org/10.1051/JPHYSCOL:1995569","url":null,"abstract":"In plasma-assisted deposition methods the activation energy necessary for the initiation of chemical reactions is transferred via charged particles. Due to this fact in many cases the process temperature can be kept small, if gas discharges at pressures below 1 hPa are used. On the other hand low pressure requires a great deal of vacuum equipment. Processes at atmospheric pressure are more favourable, if similar results compared to existing methods can be achieved. Basis for a new plasma-assisted deposition method at atmospheric pressure are barrier discharges. Those discharges consist of a large number of transient microdischarges in parallel which are distributed statistically on the surface to be coated. Starting with some basic considerations on the repetitive generation of microdischarges, the deposition of thin polymeric films on glass surfaces is described, using barrier discharges at atmospheric pressure and acetylene. Uniform polymeric films up to 1 μm are obtained, if trains of voltage pulses are used. Parameters influencing the deposition rate and the film quality are discussed. In addition, it is estimated whether further improvements of the deposition process are possible.","PeriodicalId":17944,"journal":{"name":"Le Journal De Physique Colloques","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1995-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83131241","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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