Charge carrier production by singlet excitons striking an anthracene/aluminium interface is investigated. Two possibilities are considered: (i) non-radiative energy transfer creates hot electrons and holes in the metal, which can be injected into the crystal by analogy with the photoemission process; (ii) charge transfer, efficiently competing with energy transfer, takes place, in course of which the exciton donates its electron to an empty metal state, the hole remaining within the crystal. Experimental evidence for the second mechanism is presented based on (i) the magnitude of the photocarrier production efficiency, (ii) its polarity dependence and, essentially, (iii) its reduction upon inserting a bimolecular fatty-acid layer between metal and crystal.
{"title":"Exciton-induced photocurrents in molecular crystals","authors":"H. Baessler, H. Killesreiter, G. Vaubel","doi":"10.1039/DF9715100048","DOIUrl":"https://doi.org/10.1039/DF9715100048","url":null,"abstract":"Charge carrier production by singlet excitons striking an anthracene/aluminium interface is investigated. Two possibilities are considered: (i) non-radiative energy transfer creates hot electrons and holes in the metal, which can be injected into the crystal by analogy with the photoemission process; (ii) charge transfer, efficiently competing with energy transfer, takes place, in course of which the exciton donates its electron to an empty metal state, the hole remaining within the crystal. Experimental evidence for the second mechanism is presented based on (i) the magnitude of the photocarrier production efficiency, (ii) its polarity dependence and, essentially, (iii) its reduction upon inserting a bimolecular fatty-acid layer between metal and crystal.","PeriodicalId":11262,"journal":{"name":"Discussions of The Faraday Society","volume":"1998 1","pages":"48-53"},"PeriodicalIF":0.0,"publicationDate":"1971-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90454437","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 interaction of the homogeneous series of primary, secondary and tertiary amines with the free hydroxyls (A-type) and hydrogen-bonded hydroxyls (B-type) of an Aerosil silica is investigated by i.-r.-spectroscopy. The shift Δν of the 3750 cm–1 band (A-type OH) toward lower frequency on adsorption of amines is correlated with the ionization potential I(eV), indicating that charge-transfer contributes strongly to the hydrogen bonding interaction. To investigate the possibility that steric effects of substituent groups in the adsorbate molecule influence the hydrogen-bonding interaction, Δν was also related to the Taft factors σ* and Es, which reflect the polar and steric effects of the substituent groups. A linear (Δν, σ*) relation is found with strong deviation for the tertiary amines. This deviation can be explained either by a steric effect between adsorbate molecule and surface groups, or by the different molecular symmetry of tertiary amines which gives this series a separate but parallel behaviour to the two other series. The extent of interaction of the amines with the B-type hydroxyls is greater for ammonia and the primary amines, than for the secondary and tertiary. This different behaviour is explained by the different packing of the adsorbing molecule. The higher the packing, the lower the proportion of species reacting.
{"title":"Infra-red spectroscopic study of the adsorption of amines on the A-type and B-type hydroxyls of an aerosil silica gel","authors":"F. V. Cauwelaert, F. Vermoortele, J. Uytterhoeven","doi":"10.1039/DF9715200066","DOIUrl":"https://doi.org/10.1039/DF9715200066","url":null,"abstract":"The interaction of the homogeneous series of primary, secondary and tertiary amines with the free hydroxyls (A-type) and hydrogen-bonded hydroxyls (B-type) of an Aerosil silica is investigated by i.-r.-spectroscopy. The shift Δν of the 3750 cm–1 band (A-type OH) toward lower frequency on adsorption of amines is correlated with the ionization potential I(eV), indicating that charge-transfer contributes strongly to the hydrogen bonding interaction. To investigate the possibility that steric effects of substituent groups in the adsorbate molecule influence the hydrogen-bonding interaction, Δν was also related to the Taft factors σ* and Es, which reflect the polar and steric effects of the substituent groups. A linear (Δν, σ*) relation is found with strong deviation for the tertiary amines. This deviation can be explained either by a steric effect between adsorbate molecule and surface groups, or by the different molecular symmetry of tertiary amines which gives this series a separate but parallel behaviour to the two other series. The extent of interaction of the amines with the B-type hydroxyls is greater for ammonia and the primary amines, than for the secondary and tertiary. This different behaviour is explained by the different packing of the adsorbing molecule. The higher the packing, the lower the proportion of species reacting.","PeriodicalId":11262,"journal":{"name":"Discussions of The Faraday Society","volume":"1 1","pages":"66-76"},"PeriodicalIF":0.0,"publicationDate":"1971-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88700667","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 micro-Brownian motion of a polymer chain in sheared solutions has been studied by means of fluorescence depolarization. An apparatus for determining the degree of polarization of sheared solutions was designed, and measurements were made on fluorescein in aqueous hydroxyethyl cellulose solutions, both tagged to the polymer chains and freely dispersed. The degree of polarization was independent of rate of shear in the region studied, 0-104 s–1, though the flow viscosity of the solutions showed marked non-Newtonian nature. Similar behaviour was observed for concentrated solutions of dextran and polystyrene.
{"title":"Fluorescence depolarization in sheared solutions of dye-tagged polymers","authors":"S. Claesson, H. Odani","doi":"10.1039/DF9704900268","DOIUrl":"https://doi.org/10.1039/DF9704900268","url":null,"abstract":"The micro-Brownian motion of a polymer chain in sheared solutions has been studied by means of fluorescence depolarization. An apparatus for determining the degree of polarization of sheared solutions was designed, and measurements were made on fluorescein in aqueous hydroxyethyl cellulose solutions, both tagged to the polymer chains and freely dispersed. The degree of polarization was independent of rate of shear in the region studied, 0-104 s–1, though the flow viscosity of the solutions showed marked non-Newtonian nature. Similar behaviour was observed for concentrated solutions of dextran and polystyrene.","PeriodicalId":11262,"journal":{"name":"Discussions of The Faraday Society","volume":"6 1","pages":"268-276"},"PeriodicalIF":0.0,"publicationDate":"1970-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79776800","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}
An attempt has been made to describe the vibrational spectrum of a vitreous material in terms of a simple model based on the unit cell of the crystal. The model has been adapted to include broad distributions of intertetrahedral angles and configurations which are salient features of the structures of silicate glasses. Normal coordinate calculations of the spectra of models representing vitreous chain silicates and vitreous silica have been performed. The results show that some detailed structural information is accessible using this approach and it has been possible to provide explanations for the shape of the infra-red spectrum of vitreous silica and sodium metasilicate at high frequencies and to offer a reason for the low-frequency Raman continuum and excess infra-red absorption which are features of the spectra of all silicate glasses.
{"title":"Vibrational spectra of simple silicate glasses","authors":"P. Gaskell","doi":"10.1039/DF9705000082","DOIUrl":"https://doi.org/10.1039/DF9705000082","url":null,"abstract":"An attempt has been made to describe the vibrational spectrum of a vitreous material in terms of a simple model based on the unit cell of the crystal. The model has been adapted to include broad distributions of intertetrahedral angles and configurations which are salient features of the structures of silicate glasses. Normal coordinate calculations of the spectra of models representing vitreous chain silicates and vitreous silica have been performed. The results show that some detailed structural information is accessible using this approach and it has been possible to provide explanations for the shape of the infra-red spectrum of vitreous silica and sodium metasilicate at high frequencies and to offer a reason for the low-frequency Raman continuum and excess infra-red absorption which are features of the spectra of all silicate glasses.","PeriodicalId":11262,"journal":{"name":"Discussions of The Faraday Society","volume":"54 1","pages":"82-93"},"PeriodicalIF":0.0,"publicationDate":"1970-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77059388","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}
Frequency spectra and normal modes of vibration have been computed for vitreous silica. They have been calculated from atomic arrangements in physical models based on the random network theory. The positions of bands in the computed spectra agree well with observed features in the experimental infra-red and Raman spectra of the glass. Detailed analysis of the normal modes indicates that the bands at 1050, 750 and 400 cm–1 are associated with bond-stretching, bending and rocking motions, respectively, of the oxygen atoms. Atomic vibrations in the glass are, on the whole, less extended in space than the plane wave-like modes which prevail in perfect crystals. The spatial localization tends to be greatest at high frequencies and near band edges. If non-bridging oxygen atoms are present in the structure, the frequenncy spectrum exhibits an additional band of very intense localization, associated with bond-stretching vibrations of the non-bridging atoms.
{"title":"Atomic vibrations in vitreous silica","authors":"R. J. Bell, P. Dean","doi":"10.1039/DF9705000055","DOIUrl":"https://doi.org/10.1039/DF9705000055","url":null,"abstract":"Frequency spectra and normal modes of vibration have been computed for vitreous silica. They have been calculated from atomic arrangements in physical models based on the random network theory. The positions of bands in the computed spectra agree well with observed features in the experimental infra-red and Raman spectra of the glass. Detailed analysis of the normal modes indicates that the bands at 1050, 750 and 400 cm–1 are associated with bond-stretching, bending and rocking motions, respectively, of the oxygen atoms. Atomic vibrations in the glass are, on the whole, less extended in space than the plane wave-like modes which prevail in perfect crystals. The spatial localization tends to be greatest at high frequencies and near band edges. If non-bridging oxygen atoms are present in the structure, the frequenncy spectrum exhibits an additional band of very intense localization, associated with bond-stretching vibrations of the non-bridging atoms.","PeriodicalId":11262,"journal":{"name":"Discussions of The Faraday Society","volume":"78 1","pages":"55-61"},"PeriodicalIF":0.0,"publicationDate":"1970-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84060984","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 efficiency of TiO2 as a nucleating agent in the Li2O—Al2O3—SiO2 system is explored over a wide composition range. Sharp changes in crystal growth rate, which strongly influence nucleation rate, are observed near the Li2O·Al2O3—SiO2 composition line and are ascribed to changes in fluidity of the glass at the crystal growth front caused by rejection of lithia-rich material by the growing crystals. A mechanism for triggered nucleation at the growth front is advanced to explain a discrepancy between crystal growth rate and final particle size. The general implications of the results are briefly discussed.
{"title":"Nucleation efficiency in lithia-alumina-silica glasses","authors":"T. I. Barry, L. Lay, R. Miller","doi":"10.1039/DF9705000214","DOIUrl":"https://doi.org/10.1039/DF9705000214","url":null,"abstract":"The efficiency of TiO2 as a nucleating agent in the Li2O—Al2O3—SiO2 system is explored over a wide composition range. Sharp changes in crystal growth rate, which strongly influence nucleation rate, are observed near the Li2O·Al2O3—SiO2 composition line and are ascribed to changes in fluidity of the glass at the crystal growth front caused by rejection of lithia-rich material by the growing crystals. A mechanism for triggered nucleation at the growth front is advanced to explain a discrepancy between crystal growth rate and final particle size. The general implications of the results are briefly discussed.","PeriodicalId":11262,"journal":{"name":"Discussions of The Faraday Society","volume":"23 1","pages":"214-221"},"PeriodicalIF":0.0,"publicationDate":"1970-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83545401","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 role of short-range order in determining the density of states of disordered covalent semiconductors is investigated using the multiple scattering formalism. Detailed calculations of an approximate density of states for a model consisting of clusters of carbon atoms in configurations found in amorphous and crystalline germanium are reported. These calculations suggest that the energy gap in amorphous covalent semi-conductors is a result of the short-range order.
{"title":"Role of short-range order in producing an energy gap in amorphous covalent semiconductors","authors":"J. Klima, T. C. Mcgill, J. Ziman","doi":"10.1039/DF9705000020","DOIUrl":"https://doi.org/10.1039/DF9705000020","url":null,"abstract":"The role of short-range order in determining the density of states of disordered covalent semiconductors is investigated using the multiple scattering formalism. Detailed calculations of an approximate density of states for a model consisting of clusters of carbon atoms in configurations found in amorphous and crystalline germanium are reported. These calculations suggest that the energy gap in amorphous covalent semi-conductors is a result of the short-range order.","PeriodicalId":11262,"journal":{"name":"Discussions of The Faraday Society","volume":"164 1","pages":"20-26"},"PeriodicalIF":0.0,"publicationDate":"1970-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76598484","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}
Direct analysis of the separated phases in unmixed sodium borosilicate glasses has been carried out using an electron microprobe analyzer. The results are discussed in relation to the tie-lines proposed by Charles, Tran, and Mazurin.
{"title":"Glassy phase separation in sodium borosilicate glasses","authors":"S. Scholes, F. Wilkinson","doi":"10.1039/DF9705000175","DOIUrl":"https://doi.org/10.1039/DF9705000175","url":null,"abstract":"Direct analysis of the separated phases in unmixed sodium borosilicate glasses has been carried out using an electron microprobe analyzer. The results are discussed in relation to the tie-lines proposed by Charles, Tran, and Mazurin.","PeriodicalId":11262,"journal":{"name":"Discussions of The Faraday Society","volume":"35 1","pages":"175-181"},"PeriodicalIF":0.0,"publicationDate":"1970-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80287845","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}
In the system Ge + As + Te, the heavy Te atom facilitates the formation of mesomeric pσ-bonding systems. The glass forming regions are thus small and depend strongly on the quenching conditions. As in the systems Ge + Sb + Se and Ge + As + Se all metallically conducting melts in the system Ge + As + Te solidify to a crystallline structure even when quenched in water. However, not all semiconducting melts belonging to this system become glassy under these conditions. As expected, the transition from melts solidifying to a glass structure to those solidifying to a crystalline structure is more gradual, as is also the transition from metallic to semiconducting melts. All the semiconducting melts become more or less metallically conducting at temperatures between 900 and 1000 °C. The transition can be described by a parabolical or a log log dependence on temperature.In the chalcogenide systems the melting process often enforces the same bonding mechanism with similar atomic short range order as does the application of high pressures or of strong electric fields. This is especially the case at high temperatures. The enforced mobility of the atoms, their tighter packing and the effect of electrical conductivity often act in the same direction, enhancing structural changes in the same direction.
在Ge + As + Te体系中，重Te原子有利于中间体pσ成键体系的形成。因此，玻璃形成区域很小，并且强烈依赖于淬火条件。与Ge + Sb + Se和Ge + As + Se体系一样，Ge + As + Te体系中的金属导电熔体即使在水中淬火也会凝固成结晶结构。然而，并不是所有属于这个系统的半导体熔体在这些条件下都变成玻璃状。正如预期的那样，从熔体固化到玻璃结构到那些固化到晶体结构的转变更加缓慢，从金属熔体到半导体熔体的转变也是如此。所有的半导体熔体在900到1000°C之间的温度下都或多或少地具有金属导电性。这种转变可以用对温度的抛物线依赖性或对数依赖性来描述。在硫族化合物体系中，熔炼过程往往与施加高压或强电场一样，具有相同的键合机制，具有类似的原子短程有序。这在高温下尤其如此。原子的强制迁移，它们更紧密的包装和电导率的影响通常在同一方向上起作用，增强了同一方向上的结构变化。
{"title":"Electrical conductivity of melts and their ability to form glasses in the system Ge + As + Te","authors":"H. Krebs, P. Fischer","doi":"10.1039/DF9705000035","DOIUrl":"https://doi.org/10.1039/DF9705000035","url":null,"abstract":"In the system Ge + As + Te, the heavy Te atom facilitates the formation of mesomeric pσ-bonding systems. The glass forming regions are thus small and depend strongly on the quenching conditions. As in the systems Ge + Sb + Se and Ge + As + Se all metallically conducting melts in the system Ge + As + Te solidify to a crystallline structure even when quenched in water. However, not all semiconducting melts belonging to this system become glassy under these conditions. As expected, the transition from melts solidifying to a glass structure to those solidifying to a crystalline structure is more gradual, as is also the transition from metallic to semiconducting melts. All the semiconducting melts become more or less metallically conducting at temperatures between 900 and 1000 °C. The transition can be described by a parabolical or a log log dependence on temperature.In the chalcogenide systems the melting process often enforces the same bonding mechanism with similar atomic short range order as does the application of high pressures or of strong electric fields. This is especially the case at high temperatures. The enforced mobility of the atoms, their tighter packing and the effect of electrical conductivity often act in the same direction, enhancing structural changes in the same direction.","PeriodicalId":11262,"journal":{"name":"Discussions of The Faraday Society","volume":"73 1","pages":"35-44"},"PeriodicalIF":0.0,"publicationDate":"1970-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88522715","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}
It is frequently stated that amorphous semiconductors have, in contrast to crystals, a value of the conductivity which is relatively insensitive to composition. This is explained by assuming that each atom in a glass has as many nearest neighbours as the number of bonds it can from (Ge, 4; As, 3; Te, 2), so that there are no free electrons available to carry a current. The validity of this concept will be examined; it is not true for some amorphous films (Mg-Bi) which are not strongly bonded. Also some glasses, when heated above the softening point, seem to change their coordination numbers and become metallic.The theoretical models necessary to describe these results are outlined. In liquid metals and most amorphous metal films, the Ziman theory should be applicable, giving a conductivity equal to Se2L/12π3ħ, where S is the Fermi surface area and L the mean free path. When this is about 3000 Ω–1 cm–1, L is comparable with the distance between atoms and it cannot be smaller. For materials such as liquid Te for which the conductivity is lower, a “pseudogap” affects the conductivity. The lowest possible metallic conductivity is about 200 Ω–1 cm–1. For materials (liquids or non-crystalline solids) with lower conductivity, the current is due either to electrons excited to the “mobility shoulder” or to hopping conduction of the kind familiar in impurity conduction. A real gap (as contrasted with a pseudogap) must exist in transparent materials, and can be understood in terms of the tight-binding approximation.
{"title":"Conduction in glassy and liquid semiconductors","authors":"N. Mott","doi":"10.1039/DF9705000007","DOIUrl":"https://doi.org/10.1039/DF9705000007","url":null,"abstract":"It is frequently stated that amorphous semiconductors have, in contrast to crystals, a value of the conductivity which is relatively insensitive to composition. This is explained by assuming that each atom in a glass has as many nearest neighbours as the number of bonds it can from (Ge, 4; As, 3; Te, 2), so that there are no free electrons available to carry a current. The validity of this concept will be examined; it is not true for some amorphous films (Mg-Bi) which are not strongly bonded. Also some glasses, when heated above the softening point, seem to change their coordination numbers and become metallic.The theoretical models necessary to describe these results are outlined. In liquid metals and most amorphous metal films, the Ziman theory should be applicable, giving a conductivity equal to Se2L/12π3ħ, where S is the Fermi surface area and L the mean free path. When this is about 3000 Ω–1 cm–1, L is comparable with the distance between atoms and it cannot be smaller. For materials such as liquid Te for which the conductivity is lower, a “pseudogap” affects the conductivity. The lowest possible metallic conductivity is about 200 Ω–1 cm–1. For materials (liquids or non-crystalline solids) with lower conductivity, the current is due either to electrons excited to the “mobility shoulder” or to hopping conduction of the kind familiar in impurity conduction. A real gap (as contrasted with a pseudogap) must exist in transparent materials, and can be understood in terms of the tight-binding approximation.","PeriodicalId":11262,"journal":{"name":"Discussions of The Faraday Society","volume":"42 1","pages":"7-12"},"PeriodicalIF":0.0,"publicationDate":"1970-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87099963","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}
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：