Philosophical Magazine Part B最新文献

{"title":"Coulomb couplings in positively charged fullerene","authors":"M. Lueders, A. Bordoni, N. Manini, A. D. Corso, M. Fabrizio, E. Tosatti","doi":"10.1080/13642810208220729","DOIUrl":"https://doi.org/10.1080/13642810208220729","url":null,"abstract":"Abstract We compute, based on density-functional electronic-structure calculations, the Coulomb couplings in the hu highest occupied orbital of molecular C60. We obtain a multiplet-averaged Hubbard U ≈ 3 eV, and four Hund-rule-like intramolecular multiplet-splitting terms, each of the order of a few hundred millielectronvolts. According to these couplings, all Cn+ 60 ions should possess a high-spin ground state if kept in their rigid undistorted form. Even after molecular distortions are allowed, however, the Coulomb terms still appear to be somewhat stronger than the previously calculated Jahn–Teller couplings, the latter favouring low-spin states. Thus for example in C2+ 60, unlike C2- 60, the balance between the Hund rule and Jahn–Teller yields, even if marginally, a high-spin ground state. That seems surprising in view of reports of superconductivity in field-doped Cn+ 60 systems.","PeriodicalId":20016,"journal":{"name":"Philosophical Magazine Part B","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2002-07-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87417860","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}

{"title":"Potential fluctuations, diffusion length and lateral photovoltage in hydrogenated amorphous silicon and silicon–germanium thin films","authors":"A. Srivastava, S. Agarwal","doi":"10.1080/13642810208223161","DOIUrl":"https://doi.org/10.1080/13642810208223161","url":null,"abstract":"Abstract The lateral photovoltage (LPV) has been measured between coplanar electrodes by illuminating hydrogenated amorphous silicon samples at various positions with a red laser spot. We find that the LPV decreases at higher temperatures and increases upon light soaking. Similar results are obtained for hydrogenated amorphous silicon–germanium alloys. The diffusion length of carriers in our samples is measured by the steady-state photocarrier grating technique and the LPV is calculated. The calculated LPV is much smaller than that experimentally measured. We propose that the potential fluctuations present in the samples might be responsible for the large LPV. We have measured the ambipolar diffusion lengths in a-Si : H and a-SiGe : H samples by the SSPG technique. The ambipolar diffusion length decreases with increasing germanium incorporation in the films while keeping the other deposition parameters the same. This decrease in the ambipolar diffusion length with increasing germanium incorporation is attributed to the increase in the DOS as evident from our CPM measurements. Moreover, for all the samples studied, we found that the diffusion length decreases with LS and this is also explained on the basis of the rise in the DOS. These findings are as expected and are in agreement with the published results (Ritter et al. 1987, Weiser and Ritter 1989, Sakata et al. 1997). A LPV is observed in all the samples studied. The LPV decreases upon increasing the temperature of measurement but increases upon LS. In all cases the magnitude of the LPV is found to be much larger than expected from the measured L. The observations are explained on the basis of the potential fluctuations present in the material. These arise from the heterogeneities, that is non-uniform distribution of hydrogen and variation in silicon and germanium concentrations from point to point in the a-SiGe: H film. In our model, the effect of these potential fluctuations is twofold. The electrons and holes become separated spatially in the presence of the potential fluctuations. This tends to reduce their recombination probability and might increase L. Secondly, there is an accumulation of localized charges in the states that coexist above the percolation edge with the extended states. Although these charges do not participate in conduction, they will give a contribution to the LPV. Other factors, for example band bending at the surface might also contribute by separating the carriers. Hence larger potential fluctuations are likely to give a large LPV, since both N and L in equation (14) are expected to be larger. Since the presence of a bias light is expected to reduce the potential fluctuations, the LPV should also be reduced. This explanation of the LPV in terms of potential fluctuations agrees with the observation that the value of L measured by SSPG decreases as the light intensity increases (Weiser and Ritter 1989). Further, we note that SSPG is always carried out in the presence o","PeriodicalId":20016,"journal":{"name":"Philosophical Magazine Part B","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2002-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"72927182","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}

{"title":"Electronic and magnetic properties and phase diagrams of (La1–XRX)0.7Ca0.3MnO3 compounds with R ˭ Sm, Gd, Ho or Er","authors":"T. Terai, T. Kakeshita, T. Fukuda, K. Kindo, M. Honda, K. Kishio","doi":"10.1080/13642810208223152","DOIUrl":"https://doi.org/10.1080/13642810208223152","url":null,"abstract":"Abstract Electronic and magnetic properties of the perovskite-like compounds of (La1–xRx)0.7Ca0.3MnO3 (R ˭ Sm, Gd, Ho or Er; 0 ⩽ x ⩽ 1) have been studied by measuring electrical resistance and magnetization. Depending on x in all the compounds examined, a transition from a ferromagnetic metal to a paramagnetic insulator or to a spin-glass insulator state appears. These electronic and magnetic properties are found to depend not only on the tolerance factor t but also on the variance (second moment) [sgrave]2 of the A-site ion radii distribution, and the phase diagram has been established by using t and [sgrave]2 based on the results of the study and the results previously obtained by the present authors and many other researchers.","PeriodicalId":20016,"journal":{"name":"Philosophical Magazine Part B","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2002-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84306200","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}

{"title":"Ferromagnetic phases in the Kondo lattice model","authors":"A. Juozapavičius, I. McCulloch, M. Gulácsi, A. Rosengren","doi":"10.1080/13642810208223159","DOIUrl":"https://doi.org/10.1080/13642810208223159","url":null,"abstract":"Abstract Using an SO(4) invariant density-matrix renormalization group algorithm a sufficient numerical accuracy is achieved to demonstrate new ferromagnetic phase regions inside the paramagnetic area of the one-dimensional antiferromagnetic Kondo lattice model phase diagram. Spin-spin correlation functions, energy gap, number of singlets and other physical properties are investigated in detail. Direct measurements of the magnetization reveal continuous paramagnetic-ferromagnetic phase transitions.","PeriodicalId":20016,"journal":{"name":"Philosophical Magazine Part B","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2002-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90075802","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}

{"title":"Effect of interstitial hydrogen on structural and electronic properties of BaTiO3","authors":"A. Stashans, J. Chimborazo","doi":"10.1080/13642810208223155","DOIUrl":"https://doi.org/10.1080/13642810208223155","url":null,"abstract":"Abstract We investigate the geometry and electronic structure of an interstitial H atom in the BaTiO3 crystal considering both cubic and tetragonal crystallographic lattices. A quantum-chemical method based on the Hartree-Fock formalism is used throughout the study. Interstitial H is found to bind to one of the O atoms, forming the so-called OH group. At equilibrium, the O-H distances are found to be 0.89 and 0.91 Å for cubic and tetragonal lattices respectively. The performed automated geometry optimization procedure of the defective region shows considerable outward movements of atoms closest to the impurity. The role of the H impurity in ferroelectric polarization in the BaTiO3 crystal is analysed using the results obtained in connection with the available experimental data on ferroelectric perovskites.","PeriodicalId":20016,"journal":{"name":"Philosophical Magazine Part B","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2002-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"72840268","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}

{"title":"Fokker–Planck transport simulation tool for semiconductor devices","authors":"E. Bringuier","doi":"10.1080/13642810208223153","DOIUrl":"https://doi.org/10.1080/13642810208223153","url":null,"abstract":"Abstract The paper investigates a new method for simulating carrier transport in semiconductor devices where the field may be high and strongly inhomogeneous. The simulator is based upon a deterministic equation of the Fokker–Planck type reproducing the predictions of a Monte Carlo simulation using the same material model. The equation deals with the spectral carrier density which consists of the carrier density and the local energy distribution. As input data the equation uses the energy-band diagram and functions of energy describing the carrier–lattice interaction in the relevant energy range. The numerical solution is found in detail in the case of a metal–insulator–metal structure used in electroluminescence devices. The proposed algorithm uses a finite-volume scheme which yields a code much faster than a Monte Carlo simulator, and without statistical noise.","PeriodicalId":20016,"journal":{"name":"Philosophical Magazine Part B","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2002-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78702798","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}

{"title":"On the phase diagram of a ‘collapsing’ hard-sphere system","authors":"S. Stishov","doi":"10.1080/13642810208223165","DOIUrl":"https://doi.org/10.1080/13642810208223165","url":null,"abstract":"Abstract The principal phase diagram of a system with a repulsive step potential is built using the properties of a hard-sphere system as a starting point. The behaviour of the melting curve is discussed and the possibility of a phase transition in the liquid phase is indicated.","PeriodicalId":20016,"journal":{"name":"Philosophical Magazine Part B","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2002-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75784004","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}

{"title":"Carrier generation in polycrystalline MgIn2O4 thin films by proton implantation","authors":"M. Miyakawa, H. Un'no, K. Ueda, H. Kawazoe, H. Hosono, N. Matsunami","doi":"10.1080/13642810208223156","DOIUrl":"https://doi.org/10.1080/13642810208223156","url":null,"abstract":"Abstract Thin films of polycrystalline MgIn2O4 (spinel structure; bandgap, 3.5 eV) were prepared on silica glass by the rf sputtering technique. The thin films were insulating in the as-deposited state, and proton implantation was carried out in the fluence range from 1 × 1015 to 1 × 1018 cm−2 at room temperature to introduce carrier electrons in the films. Upon implantation at a fluence of 1 × 1015 cm−2, the electrical conductivity increased to as high as approximately 3 × 1015 cm−1 and saturated at this level even for higher fluences. Carrier generation efficiency was about 100 % at a fluence of 1 × 1015 cm−2 but monotonically decreased with increasing fluence. Nuclear reaction analysis on deuteron-implanted specimens revealed that the depth profile of D concentration for all specimens was almost the same in the as-implanted state, and the D fraction retained in the films was about 80 % for a D+ fluence of 1 × 1016 cm−2, about 70 % for 1 × 1017 cm−2, and about 65 % for 1 × 1018 cm−2. After post-annealing at 300°C, the width of the D distribution became broader, and the retained D fraction was reduced to 50 % for a D+ fluence of 1 × 1017 cm−2 or 17 % for 1 × 1018 cm−2. These results strongly suggest that the majority of H+ ions implanted at high fluences are present in the films as neutral species such as H2 molecules. Therefore, the formation of these species, which are inactive for carrier generation, is responsible for the decrease in carrier generation efficiency.","PeriodicalId":20016,"journal":{"name":"Philosophical Magazine Part B","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2002-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90079433","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}

{"title":"Strongly correlated electron behaviour in stoichiometric CeRhSn and non-stoichiometric CexRhSn","authors":"A. Lebarski, N. A. Frederick, M. Maple","doi":"10.1080/13642810208223164","DOIUrl":"https://doi.org/10.1080/13642810208223164","url":null,"abstract":"Abstract We have recently shown that CeRhSn exhibits non-Fermi-liquid temperature dependences in its low-temperature physical properties. Here we suggest that the non-Fermi-liquid behaviour observed in CexRhSn may be due to the existence of a Griffiths phase in the vicinity of a quantum critical point, based on electrical resistivity, magnetic susceptibility and specific heat measurements carried out on off-stoichiometric CexRhSn alloys. We also discuss the influence of disorder on the low-temperature properties of CexRhSn.","PeriodicalId":20016,"journal":{"name":"Philosophical Magazine Part B","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2002-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83503013","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}

{"title":"Photoinduced defects in wide-gap materials: Hydrogenated amorphous silicon-carbon and silicon-nitrogen films","authors":"M. Fathallah, M. Mars, C. Pirri, E. Tresso","doi":"10.1080/13642810208223163","DOIUrl":"https://doi.org/10.1080/13642810208223163","url":null,"abstract":"Abstract Wide-bandgap hydrogenated amorphous silicon-carbon and silicon-nitrogen films having optical gaps in the range 1.9–4.0eV have been deposited by the 13.56 MHz plasma-enhanced chemical vapour deposition technique from SiH4 + C2H2 (+H2), SiH4 + NH3 (+H2), gas mixtures. The deposition conditions have been chosen so as to obtain device-quality films already successfully applied in optoelectronic technology. The films have been light soaked in the average weather conditions solar spectrum (air mass 2.0) for times up to 90 h, monitoring the absorbed energy. The optical properties have been measured after each occurrence of damage, and the defect density evolution due to light soaking was determined by photothermal deflection spectroscopy. An increase in the density of defects with light exposure was observed in all samples strongly dependent on carbon or nitrogen gas sources, plasma conditions and initial properties.","PeriodicalId":20016,"journal":{"name":"Philosophical Magazine Part B","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2002-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79577171","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}