摘要:

The superconducting compound YBa2Cu3O7and the insulating material La2CuO4have been examined using liquid-metal ion-induced secondary-ion mass spectrometry. The results revealed surface reactions with moisture as well as some contamination by hydrocarbons. These surface layers were readily sputtered away, but the apparent presence of yttrium, barium and lanthanum hydroxides could play a significant part in their surface conduction characteristics. The relative intensity of the sputtered ion MO+was found to be a logarithmic function of its dissociation energy.

ISSN:0950-0839    

DOI:10.1080/09500838808214756

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

The complex chemical and physical processes occurring in hydrating cement pastes are not fully understood. The properties of cement setting and the influence of different additives are encompassed by the delayed nucleation and the protective layer theories. Each of these two theories is supported by several different experimental observations. In order to resolve this question further, the proton nuclear magnetic resonance (NMR) data of the hydrating cement pastes are analysed and discussed. This analysis shows that NMR data favour the osmotic model of cement setting.

ISSN:0950-0839    

DOI:10.1080/09500838808214757

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

The photoinduced changes of the optical properties of Ge27S73thin films have been examined using visible and infrared spectroscopy. It was found that illumination of the virgin thin film in vacuum is accompanied by a blue shift of the optical gap and by an increase of the Ge─S bond density. If the film is illuminated in air, the blue shift of the gap is observed too, but the density of Ge─S bonds decreases and new extrinsic absorption bands around 820 and 695 cm−1appear in the spectrum, indicating most probably the presence of Ge─O bonds. It is supposed that in the former case the photoinduced changes are most probably intrinsic (decreases of the randomness of the film structure), while in the second case the photoinduced bleaching is accompanied by photoinduced oxidation of the film.

ISSN:0950-0839    

DOI:10.1080/09500838808214758

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Key results of recent transport measurements on the silicon backbone polymer, poly(methylphenylsilylene) (PMPS) are reviewed. The hole drift mobility is characterized by a convoluted yet familiar pattern of electric field and temperature dependences. This behaviour in PMPS is remarkably similar to transport behaviour reported in a diverse collection of disordered solids ranging from poly(vinylcarbazole) (PVK) to molecularly doped polymers and even glassy selenium. The latter, however, all share the feature that transport is in part controlled by thermal emission from localized states which act as traps or by field-enhanced thermally assisted electron transfer among such states. The present results thus continue to suggest that a common but incompletely understood mechanism of field-enhanced thermal emission operates to influence transport in a broad class of amorphous solids.

ISSN:0950-0839    

DOI:10.1080/09500838808214759

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

We study the question of whether the metal-insulator transition in a doped semiconductor takes place in a conduction band or in an impurity band. Our calculations of the Knight shift and the specific heat indicate that the transition takes place in an impurity band. We use a tight-binding model to calculate the electron wavefunctions and density of states and obtain good agreement with the measured Knight shift and specific heat of Si: P. By contrast, the nearly-free-electron model, appropriate to a conduction band, fails to account for the Knight shift measured at the phosphorus nuclei in Si: P.

ISSN:0950-0839    

DOI:10.1080/09500838808214760

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

The existence of cusps in the interfacial energy against misorientation curve has been studied for Ag/Si(l00) and Ag/Si(111) interfaces using the modified sphere-plate technique. The following preferred orientations were obtained: Ag(100)//Si(100) with Ag[011]//Si[011], and Ag(111)//Si(111) with Ag[110]//Si[114]. These are the same preferred orientation relationships previously found in studies of thin-film growth and appear to be due to low interfacial energies. In addition, preferred orientations Ag(100)//Si(100), Ag(111)//Si(100) and Ag(111)//Si(111) without any preferred directional alignment were observed. These latter orientations are believed to be the result of the native silicon oxide layer present between silver and the silicon single crystals.

ISSN:0950-0839    

DOI:10.1080/09500838808214761

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

ISSN:0950-0839    

DOI:10.1080/09500838808214762

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor