摘要:

Samples of CdS doped silica thin films have been prepared with weight concentrations ranging from 0.5 to 20% (CdO/SiO2). Nanocrystal structure and size distribution are determined by Transmission Electron Microscopy (TEM) and image analysis. The mean size is the same for all concentrations (4 nm) and is related to the matrix porosity. The linear absorption shows characteristic features of the excitonic level and the gap blue shift due to the quantum confinement. Non-linear optical properties are studied by Degenerate Four Waves Mixing (DFWM) to measure the third order susceptibility χ(3)which is high (typically 10−7esu) and depends linearly of the volume fraction of the semiconductor particles.

ISSN:1042-0150    

DOI:10.1080/10420159508222703

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The hole paramagnetic center (S = 1/2, g = 2.0028) was observed in undoped C70fullerite for the first time. It was shown that the possible model of this center is C60+-hole center with charge compensation at the surface.

ISSN:1042-0150    

DOI:10.1080/10420159508222704

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Nanosized carbon π-clusters have been identified in implanted nonconjugated polymers by means of small angle X-ray scattering. The consistency of obtained numerical data with results of optical absorption spectra analysis and measurements of electrical conductivity has been shown.

ISSN:1042-0150    

DOI:10.1080/10420159508222705

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

We have studied electrical transport phenomena after ion implantation in sublimed C60films. A n type doping exists with 30 KeV potassium ion irradiations and low fluences (D < 1015ions/cm2). However degradation effects have been noted. So we have tried to discriminate doping and damage effects. Studies about the compensation phenomenum have been performed in order to prove the chemical role of the potassium atoms. An electron transfer from the alkali metal is sure; but a strong competition exists between degradation and doping phenomena. Finally, the intact C60molecules are the insulator barriers, K3C60and isolated carbon atoms are the conductor phase for an heterogeneous media model.

ISSN:1042-0150    

DOI:10.1080/10420159508222706

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The results of thermopower S measurements performed on implanted polyparaphenylene and polyimide films between 150 K and 450 K are presented. The implantations of Caesium or Iodine ions in polyparaphenylene with low parameters induce a sign of S characteristic to chemical nature of the implanted ions and an increase of ISI at around 350 K due to a transition from a VRH process to a polaronic conduction. With Iodine implanted sample at higher energy (E = 250 keV) and low dose (D = 2 × 1015ions/cm2) a transition from p type to n type doping at 400 K is attributed to a migration of negative oxygen ions as in the case of polyimide samples implanted with Caesium and Iodine ions where a similar behaviour of S is found.

ISSN:1042-0150    

DOI:10.1080/10420159508222707

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Ultra thin polyimide layers have been prepared by the Langmuir Blodgett method and bombarded with a beam of 170 keV Ne+. Optical absorption and specular reflectance studies have been performed in the spectral domain 2.5–6.5 eV. The energy loss function is deduced and shows the development of a new absorption band at 3 eV, which accounts for the shift of the absorption edge towards the visible in thick films. An effective medium calculation shows that this resonance can be attributed to graphitic nanoparticles dispersed in the polymeric matrix. The development of these conducting domains accounts for the transition to a conducting regime at high irradiation fluence.

ISSN:1042-0150    

DOI:10.1080/10420159508222708

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Nuclear spin relaxation (NSR) and electrical conductivity measurements were performed between about 1 K and room temperature in various fluoride glasses. The19F NSR rates are found to exhibit a pronounced peak around 10 K which is not observed by conductivity experiments. The underlying relaxation process is interpreted by magnetic fluctuations between neighbouring19F nuclear probes without accompanying charge motions. The observed NSR rates and conductivities can be described phenomenologically in the context of excitations of asymmetric double well potential (ADWP) configurations intrinsic to the glassy state.

ISSN:1042-0150    

DOI:10.1080/10420159508222709

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A study is made of temperature and pressure dependence of impedance spectroscopy and x-ray analysis for lead fluoride doped with various concentrations of scandium fluoride for samples with mixed orthorhombic/cubic phase composition.

ISSN:1042-0150    

DOI:10.1080/10420159508222710

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A study has been made of the effect of local light irradiation and silver saturation on the contact photo-emf excitation spectrum of α-RbAg4I5superionic crystals at room temperature. It was found that irradiation with light having energies 2.75 eV and 2.92 eV causes color centers formation in the crystals. The possible nature of the bands in the photo-emf excitation spectrum is discussed. Time dependences of the photo-emf for the main excitation bands were measured at various illumination levels. A characteristic asymmetry of the relaxation curves governed by the excitation kinetics was observed at high illumination intensities. The estimation of the photon capture cross sections for the electronic transitions gives the values of the order of magnitude of 10−17cm2. The transient experiments have shown that the photocarrier lifetimes in the crystals are of the order of 1000 sec.

ISSN:1042-0150    

DOI:10.1080/10420159508222711

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The local evironments of Cd and Pb cations in the system Cd1−xPbxF2(x = 0.6) have been measured by means of EXAFS. A comparative analysis of the Fourier transforms of the experimental data provides evidence of the Pb-F bond length being longer than the Cd-F one. Furthermore, our studies show a loss of structure around the Pb(L111) edge with increasing temperature. This suggests that the temperature-induced vacancies on the anion sub-lattice are preferentially located adjacent to Pb ions as previously observed in PbSnF4mixed-metal fluorides. The results obtained accord well with our computer simulation findings.

ISSN:1042-0150    

DOI:10.1080/10420159508222712

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor