The present study focuses on two aspects of heavy metals and radionuclide fluxes to lake Annecy: a long term. secular evolution by analysing dated sediment cores, and a short term, seasonal evolution through the analysis of settling particles collected by sediment traps. Compared to background values prior to 1900, sediment cores reveal a two-fold (Cd, Cu, Zn) to a four-fold (Pb) increase in heavy metal concentration after the 40s, and a smaller decrease after the 70s except for Cu, which does not decrease. Sediment traps moored from April 1998 to November 2000 record strong variations of particles (range: 0.5 - 6.1 g m(-2) d(-1)), organic matter (range 0.03 - 0.27 g m(-2) d(-1)) and carbonate fluxes (range: 0.2 - 4.9 g m(-2) d(-1)). The maximum fluxes are observed at the end of spring and summer, related to increased phytoplankton production. Mean annual heavy metal fluxes (0.014 mug.cm(-2).y(-1) for Cd, 1 mug.cm(-2). y(-1) for Ph and Cu and 2.8 mug.cm(-2).y(-1) for Zn) are lower than those recorded in the surface layers of the sediment cores. No relation has been observed between fluxes of heavy metal and of particles. Comparison of heavy metal fluxes in Lake Annecy with two other peri-alpine lakes show that this lake receive more Cu and Ph of anthropogenic origin, in spite of the sewage collector built around the lake.
{"title":"Recent and present sedimentary fluxes of heavy metals and radionuclides in oligotrophic Lake Annecy, France","authors":"J. Loizeau, P. Arpagaus, D. Mathieu, J. Dominik","doi":"10.1051/JP4:20030419","DOIUrl":"https://doi.org/10.1051/JP4:20030419","url":null,"abstract":"The present study focuses on two aspects of heavy metals and radionuclide fluxes to lake Annecy: a long term. secular evolution by analysing dated sediment cores, and a short term, seasonal evolution through the analysis of settling particles collected by sediment traps. Compared to background values prior to 1900, sediment cores reveal a two-fold (Cd, Cu, Zn) to a four-fold (Pb) increase in heavy metal concentration after the 40s, and a smaller decrease after the 70s except for Cu, which does not decrease. Sediment traps moored from April 1998 to November 2000 record strong variations of particles (range: 0.5 - 6.1 g m(-2) d(-1)), organic matter (range 0.03 - 0.27 g m(-2) d(-1)) and carbonate fluxes (range: 0.2 - 4.9 g m(-2) d(-1)). The maximum fluxes are observed at the end of spring and summer, related to increased phytoplankton production. Mean annual heavy metal fluxes (0.014 mug.cm(-2).y(-1) for Cd, 1 mug.cm(-2). y(-1) for Ph and Cu and 2.8 mug.cm(-2).y(-1) for Zn) are lower than those recorded in the surface layers of the sediment cores. No relation has been observed between fluxes of heavy metal and of particles. Comparison of heavy metal fluxes in Lake Annecy with two other peri-alpine lakes show that this lake receive more Cu and Ph of anthropogenic origin, in spite of the sewage collector built around the lake.","PeriodicalId":17944,"journal":{"name":"Le Journal De Physique Colloques","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2003-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77457076","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 refers to the characterization of plane masonry behaviour under the assumption of plane stress. Masonry may be seen as a two-phase (bricks and mortar) periodic anisotropic material with complex macroscopic behaviour due to the possible occurrence of cracking in each of the phases. Non-linear constitutive equations have thus to be used in order to realistically represent masonry structures. Most existing macroscopic models defined for such materials are by essence phenomenological. This leads to weakly motivated frameworks and rather complex models, especially if one wants to account for material symmetry evolution due to cracking. The aim of this paper is to identify a simple set of damage mechanics variables for the constituents that could be used in homogenization procedures to infer the overall behaviour of the material from its mesostructural features (geometrical arrangement and mechanical properties of the constituents). Based on unit cell computations, it is shown that scalar damage mesomodels allow to obtain realistic damage patterns encountered in experiments. Results suggest that at the meso-scale, it is possible to use a scalar damage model for the individual phases which naturally leads to the desired anisotropy evolution into the macroscopic descriptions. This macroscopic anisotropy evolution is illustrated using a numerical homogenization procedure to identify the degraded stiffness associated to damage patterns. The influence of variations in the constituent characteristics is also correctly captured as illustrated for some of the loading schemes.
{"title":"Anisotropic damage effects in masonry walls","authors":"T. Massart, P. Bouillard, M. Geers, R. Peerlings","doi":"10.1051/JP4:20030182","DOIUrl":"https://doi.org/10.1051/JP4:20030182","url":null,"abstract":"This paper refers to the characterization of plane masonry behaviour under the assumption of plane stress. Masonry may be seen as a two-phase (bricks and mortar) periodic anisotropic material with complex macroscopic behaviour due to the possible occurrence of cracking in each of the phases. Non-linear constitutive equations have thus to be used in order to realistically represent masonry structures. Most existing macroscopic models defined for such materials are by essence phenomenological. This leads to weakly motivated frameworks and rather complex models, especially if one wants to account for material symmetry evolution due to cracking. The aim of this paper is to identify a simple set of damage mechanics variables for the constituents that could be used in homogenization procedures to infer the overall behaviour of the material from its mesostructural features (geometrical arrangement and mechanical properties of the constituents). Based on unit cell computations, it is shown that scalar damage mesomodels allow to obtain realistic damage patterns encountered in experiments. Results suggest that at the meso-scale, it is possible to use a scalar damage model for the individual phases which naturally leads to the desired anisotropy evolution into the macroscopic descriptions. This macroscopic anisotropy evolution is illustrated using a numerical homogenization procedure to identify the degraded stiffness associated to damage patterns. The influence of variations in the constituent characteristics is also correctly captured as illustrated for some of the loading schemes.","PeriodicalId":17944,"journal":{"name":"Le Journal De Physique Colloques","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2003-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85276695","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 : 1996-03-01DOI: 10.1051/JPHYSCOL/1979250
H. Winkler, P. Alwardt, E. Gerdau
The temperature dependence of the relaxation rates in YbCl 3 .6H 2 O up to 45 K can be explained by the Raman pro cess if phonon dispersion is considered. The analysis of the measured Mossbauer spectra has been performed by means of the field up-down model. It is pointed out that there are found "dispersionlike" terms in the spectra in addition to the usual Lorentzians.
{"title":"THE FIELD UP-DOWN MODEL AND ITS APPLICATION TO PARAMAGNETIC RELAXATION IN YbCl3.6H2O","authors":"H. Winkler, P. Alwardt, E. Gerdau","doi":"10.1051/JPHYSCOL/1979250","DOIUrl":"https://doi.org/10.1051/JPHYSCOL/1979250","url":null,"abstract":"The temperature dependence of the relaxation rates in YbCl 3 .6H 2 O up to 45 K can be explained by the Raman pro cess if phonon dispersion is considered. The analysis of the measured Mossbauer spectra has been performed by means of the field up-down model. It is pointed out that there are found \"dispersionlike\" terms in the spectra in addition to the usual Lorentzians.","PeriodicalId":17944,"journal":{"name":"Le Journal De Physique Colloques","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1996-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87223441","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 : 1996-03-01DOI: 10.1051/JPHYSCOL/1979243
J. Friedt, G. Shenoy, B. D. Dunlap
The electric quadrupole and magnetic hyperfine interactions rneasured from the 161 Dy Mossbauer resonance in crystalline Dy(OH)3 and from the 166 Er resonance in crystalline Ho(OH)3 and Er(OH)3 are interpreted using the crystal field and molecular exchange field model . The crystal field parameters established from previous optical spectroscopy results account weIl for these hyperfine parameters. The crystal-field and magnetic properties of these ferromagnetic insulators are described weIl within the model.
{"title":"CRYSTAL FIELD AND MAGNETIC PROPERTIES OF Dy(OH)3, Ho(OH)3 AND Er(OH)3","authors":"J. Friedt, G. Shenoy, B. D. Dunlap","doi":"10.1051/JPHYSCOL/1979243","DOIUrl":"https://doi.org/10.1051/JPHYSCOL/1979243","url":null,"abstract":"The electric quadrupole and magnetic hyperfine interactions rneasured from the 161 Dy Mossbauer resonance in crystalline Dy(OH)3 and from the 166 Er resonance in crystalline Ho(OH)3 and Er(OH)3 are interpreted using the crystal field and molecular exchange field model . The crystal field parameters established from previous optical spectroscopy results account weIl for these hyperfine parameters. The crystal-field and magnetic properties of these ferromagnetic insulators are described weIl within the model.","PeriodicalId":17944,"journal":{"name":"Le Journal De Physique Colloques","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1996-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"74418580","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 : 1996-03-01DOI: 10.1051/JPHYSCOL/1979237
G. Belozerskii, S. Simonyan
It is shown, that the description of the time development of the magnetic moment of superparamagnetic particles in terms of the dis crete orientations model is the main reason of the distinction between the theoretical and experimental spectra. The model of the time development of magnetic moment which takes into account the jumps from one easy direction to another as weIl as the precession at the time between the jumps, gives a reasonable explanation for the broadening and the asymmetry of the experimental lines.
{"title":"THE EFFECT OF PRECESSION OF MAGNETIZATION VECTOR ON THE MÖSSBAUER SPECTRA OF SUPERPARAMAGNETIC PARTICLES","authors":"G. Belozerskii, S. Simonyan","doi":"10.1051/JPHYSCOL/1979237","DOIUrl":"https://doi.org/10.1051/JPHYSCOL/1979237","url":null,"abstract":"It is shown, that the description of the time development of the magnetic moment of superparamagnetic particles in terms of the dis crete orientations model is the main reason of the distinction between the theoretical and experimental spectra. The model of the time development of magnetic moment which takes into account the jumps from one easy direction to another as weIl as the precession at the time between the jumps, gives a reasonable explanation for the broadening and the asymmetry of the experimental lines.","PeriodicalId":17944,"journal":{"name":"Le Journal De Physique Colloques","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1996-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80989453","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 : 1996-03-01DOI: 10.1051/JPHYSCOL/1979234
W. Reiff, H. Wong, M. Tuiroc, G. Eisman
The temperature dependence of the zero field Mossbauer spectrum of [ϕ 4 As] 2 [Fe(N 3 ) 5 ] il has been determined over the range 300 K to 1.60 K and exhibits the effects of paramagnetic relaxation broadening and magnetic hyperfine splitting (H n ~ 486 kG a 4,2 K) at low temperatures corresponding to a negative zero field splitting, D ~ -1 cm -l . These results are consistent with the isolated trigonal bipyramidal Fe(N 3 ) 5 2- anion known to be present in this compound and slow spin-spin relaxation between highly separated (11 A or greater) metal centers. D || > µ ⊥ with [Formula: see PDF file] at ~5 K. The X and Q band ESR spectra of the system over the range 300 to 3.6 K indicate a typical axial Fe 3+ compound but with slight rhombicity of the local FeN 5 coordination environment.
在300 K ~ 1.60 K范围内测定了[φ 4 As] 2 [Fe(N 3) 5] il的零场穆斯堡尔谱的温度依赖性，并在低温下显示出顺磁弛豫展宽和磁超细分裂(H N ~ 486 kG a 4,2 K)的效应，对应于负零场分裂，D ~ -1 cm -1。这些结果与已知在该化合物中存在孤立的三角双锥体Fe(n3) 5 -阴离子和高度分离的(11a或更大)金属中心之间的缓慢自旋-自旋弛豫一致。D || >µ与[公式:见PDF文件]在~ 5k处。在300 ~ 3.6 K范围内，体系的X和Q波段ESR谱显示为典型的轴向fe3 +化合物，但具有局部fe5配位环境的轻微菱形。
{"title":"SLOW PARAMAGNETIC RELAXATION OF HIGH-SPIN IRON III IN A TRIGONAL BIPYRAMIDAL ENVIRONMENT A STUDY OF THE PENTA-AZIDO FERRATE ION, FE(N3)52-","authors":"W. Reiff, H. Wong, M. Tuiroc, G. Eisman","doi":"10.1051/JPHYSCOL/1979234","DOIUrl":"https://doi.org/10.1051/JPHYSCOL/1979234","url":null,"abstract":"The temperature dependence of the zero field Mossbauer spectrum of [ϕ 4 As] 2 [Fe(N 3 ) 5 ] il has been determined over the range 300 K to 1.60 K and exhibits the effects of paramagnetic relaxation broadening and magnetic hyperfine splitting (H n ~ 486 kG a 4,2 K) at low temperatures corresponding to a negative zero field splitting, D ~ -1 cm -l . These results are consistent with the isolated trigonal bipyramidal Fe(N 3 ) 5 2- anion known to be present in this compound and slow spin-spin relaxation between highly separated (11 A or greater) metal centers. D || > µ ⊥ with [Formula: see PDF file] at ~5 K. The X and Q band ESR spectra of the system over the range 300 to 3.6 K indicate a typical axial Fe 3+ compound but with slight rhombicity of the local FeN 5 coordination environment.","PeriodicalId":17944,"journal":{"name":"Le Journal De Physique Colloques","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1996-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75617061","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 : 1996-03-01DOI: 10.1051/JPHYSCOL/1979247
M. Tanaka
Mossbauer measurements have been done for 2% 57 Fe at A site in NiCr 2 O 4 . Spectra in a finite temperature range around the distortion temperature have shown that the transition has the characteristics of the first order one, and that cubic regions and tetragonal regions coexist with strong interactions between them. From an anomalous spectrum at 4.2 K a plausible spin configuration for Fe 2+ spins has been proposed.
{"title":"MÖSSBAUER STUDY OF Fe57 IN NiCr2O4","authors":"M. Tanaka","doi":"10.1051/JPHYSCOL/1979247","DOIUrl":"https://doi.org/10.1051/JPHYSCOL/1979247","url":null,"abstract":"Mossbauer measurements have been done for 2% 57 Fe at A site in NiCr 2 O 4 . Spectra in a finite temperature range around the distortion temperature have shown that the transition has the characteristics of the first order one, and that cubic regions and tetragonal regions coexist with strong interactions between them. From an anomalous spectrum at 4.2 K a plausible spin configuration for Fe 2+ spins has been proposed.","PeriodicalId":17944,"journal":{"name":"Le Journal De Physique Colloques","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1996-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88982397","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:19955102
V. Cimalla, J. Pezoldt, G. Ecke, H. Rössler, G. Eichhorn
Silicon Carbide has been grown by rapid thermal carbonization of (100) and (111) Si surfaces at atmospheric pressure using 1 lpm hydrogen (H 2 ) as a carrier gas and propane (C 3 H 8 ) with concentrations ranging from 0.025-1.5%. RHEED investigations have shown single crystalline SiC as well as additional phases depending on the propane concentration. A set of kinetic phase diagrams were determined. The chemical nature was examined by AES. At concentrations below 0.1% additional silicon and an increasing number of defects were found. The growth on (100) substrates has shown a change in orientation toward (111). Above 0.6% a carbon rich polycrystalline layer covering completely the surface was formed. The carbon has both graphitic and carbidic nature. The graphitic content could be decreased by post deposition H 2 annealing without changing the polycrystalline nature of this top layer. Best crystallinity were found at 1250 °C, 0.15% propane and 30-90 s.
{"title":"Characterization of Buffer Layers for SiC CVD","authors":"V. Cimalla, J. Pezoldt, G. Ecke, H. Rössler, G. Eichhorn","doi":"10.1051/JPHYSCOL:19955102","DOIUrl":"https://doi.org/10.1051/JPHYSCOL:19955102","url":null,"abstract":"Silicon Carbide has been grown by rapid thermal carbonization of (100) and (111) Si surfaces at atmospheric pressure using 1 lpm hydrogen (H 2 ) as a carrier gas and propane (C 3 H 8 ) with concentrations ranging from 0.025-1.5%. RHEED investigations have shown single crystalline SiC as well as additional phases depending on the propane concentration. A set of kinetic phase diagrams were determined. The chemical nature was examined by AES. At concentrations below 0.1% additional silicon and an increasing number of defects were found. The growth on (100) substrates has shown a change in orientation toward (111). Above 0.6% a carbon rich polycrystalline layer covering completely the surface was formed. The carbon has both graphitic and carbidic nature. The graphitic content could be decreased by post deposition H 2 annealing without changing the polycrystalline nature of this top layer. Best crystallinity were found at 1250 °C, 0.15% propane and 30-90 s.","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":"73738404","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:1995596
M. Nadal, F. Teyssandier
TiN has been used in numerous technological applications including: cutting or milling tools and inserts, cold extrusion nozzles and punches, forming or stamping tools, and diffusion barrier. It is currently deposited from an initial gas mixture composed of hydrogen, ammonia and titanium tetrachloride. This paper reports on the optimization of its deposition conditions at atmospheric pressure. A complete factorial design with three factors and two levels, thus requiring 2 3 =8 experiments, has been carried out. The following parameters were selected: the deposition temperature, the molar fraction of titanium tetrachloride and the molar fraction of ammonia. The influence of these factors on the deposition rate, the grain size estimated by the Scherrer method and the texture coefficient as determined by X-ray diffraction were studied. The mechanical properties of the coatings (microhardness, Young's modulus) were measured by depth-sensing indentation.
{"title":"Optimization of the Deposition Conditions of Titanium Nitride from Ammonia and Titanium Tetrachloride","authors":"M. Nadal, F. Teyssandier","doi":"10.1051/JPHYSCOL:1995596","DOIUrl":"https://doi.org/10.1051/JPHYSCOL:1995596","url":null,"abstract":"TiN has been used in numerous technological applications including: cutting or milling tools and inserts, cold extrusion nozzles and punches, forming or stamping tools, and diffusion barrier. It is currently deposited from an initial gas mixture composed of hydrogen, ammonia and titanium tetrachloride. This paper reports on the optimization of its deposition conditions at atmospheric pressure. A complete factorial design with three factors and two levels, thus requiring 2 3 =8 experiments, has been carried out. The following parameters were selected: the deposition temperature, the molar fraction of titanium tetrachloride and the molar fraction of ammonia. The influence of these factors on the deposition rate, the grain size estimated by the Scherrer method and the texture coefficient as determined by X-ray diffraction were studied. The mechanical properties of the coatings (microhardness, Young's modulus) were measured by depth-sensing indentation.","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":"75186126","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:1995518
A. Jörg, D. Neuschütz, E. Zimmermann
The kinetics of CVD of boron nitride from a gas mixture of 1,3,5-tri(N-methyl)borazine (TMB), ammonia, and hydrogen were studied at 900 to 1050°C and a total pressure of 1 bar. TMB, a liquid between -3 and 136°C, is assumed to be a single source precursor for CVD of BN. However, to suppress gas phase nucleation, one has to add sufficiently large amounts of ammonia. Below 900°C no deposition was observed within 10 hours. Between 900 and 980°C the deposition rate was controlled by a surface reaction with an apparent activation energy of 145 kJ mol -1 . The reaction was found to be first-order with respect to TMB and zero-order in both NH 3 and H 2 . Above 1000°C the activation energy decreased to 26 kJmol -1 which corresponds to gas diffusion as the rate-determining step. Gas phase nucleation makes it difficult to produce smooth films above 1000°C. The reaction product was turbostratic hexagonal boron nitride with about 52 at.-% nitrogen, 46 at.-% boron, and 1-2 at.-% codeposited carbon.
{"title":"Kinetics of Chemical Vapour Deposition of Boron Nitride from a Gas Mixture of Trimethylborazine, Ammonia, and Hydrogen at 900 to 1050 °C and 1 Bar Total Pressure","authors":"A. Jörg, D. Neuschütz, E. Zimmermann","doi":"10.1051/JPHYSCOL:1995518","DOIUrl":"https://doi.org/10.1051/JPHYSCOL:1995518","url":null,"abstract":"The kinetics of CVD of boron nitride from a gas mixture of 1,3,5-tri(N-methyl)borazine (TMB), ammonia, and hydrogen were studied at 900 to 1050°C and a total pressure of 1 bar. TMB, a liquid between -3 and 136°C, is assumed to be a single source precursor for CVD of BN. However, to suppress gas phase nucleation, one has to add sufficiently large amounts of ammonia. Below 900°C no deposition was observed within 10 hours. Between 900 and 980°C the deposition rate was controlled by a surface reaction with an apparent activation energy of 145 kJ mol -1 . The reaction was found to be first-order with respect to TMB and zero-order in both NH 3 and H 2 . Above 1000°C the activation energy decreased to 26 kJmol -1 which corresponds to gas diffusion as the rate-determining step. Gas phase nucleation makes it difficult to produce smooth films above 1000°C. The reaction product was turbostratic hexagonal boron nitride with about 52 at.-% nitrogen, 46 at.-% boron, and 1-2 at.-% codeposited carbon.","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":"72926559","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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