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51.
The paper deals with conductivity, thermoelectric power and field effect measurements on amorphous Ge specimens prepared by the decomposition of germane gas in a rf glow discharge. Substrate temperatures Td of 300, 400 and 500 K were used during deposition. The sign of the thermoelectric power S is negative throughout the temperature range investigated (200–500 K). Above 300 K, the conductivity activation energy in specimens prepared at Td = 500 K lies between 0.40 and 0.43 eV; it is equal to the gradient of the S versus 1/T curves, suggesting transport in the extended electron states. Below room temperature there is an increasing contribution in all specimens from electron hopping transport in localized states lying about 0.25 eV below ?C. Both conductivity and thermoelectric power results can be interpreted satisfactorily in terms of these two current paths. Hopping at the Fermi level has not been observed. The preliminary field effect measurements indicate that, as in amorphous Si, ?f lies near a density of state minimum. The density of states at ?f is appreciably higher than that in similarly prepared Si specimens. 相似文献
52.
M.T. Esat M.P. Fewell R.H. Spear T.H. Zabel A.M. Baxter S. Hinds 《Nuclear Physics A》1981,362(1):227-240
The static electric quadrupole moment Q2+ and the B(E2; 0+ → 2+) value of the 2+ first excited state of 204Hg have been determined using the reorientation effect in Coulomb excitation. An annular Si surface-barrier detector was used to detect back-scattered 4He, 12C and 16O projectiles. In a subsidiary experiment, spectra were obtained from 204Hg(p, p')204Hg using Si surface-barrier detectors, and the results were used in conjunction with previously existing data to provide information on higher states of 204Hg which might participate in the Coulomb excitation of the 2+ state. From a 3-level analysis, we find Q2+ = +0.40 ± 0.20 e · b and B(E2; 0+ → 2+) = 0.423 ± 0.005 e2 · b2. These results are in good agreement with the predictions of particle-vibrational coupling calculations. The value obtained for is substantially smaller in magnitude than values of Q2+ previously determined for 198, 200, 202Hg. 相似文献
53.
It is shown that the electrical conductivity of a tetrahedral amorphous semiconductor can be controlled over many orders of magnitude by doping with substitutional impurities. Experiments were carried out on a-Si specimens prepared by the glow discharge technique, with phosphorus and boron impurity levels between 5 × 10?6 and 10?2 ppv. 相似文献
54.
Absolute cross sections are presented for the reactions 37Cl(α, γ)41K for 2.90 MeV ≦ Elabα ≦ 5.23 MeV, for energies near the (α, n0) threshold at , and for 64Ni(α, n)67N from Eαlab = 5.30 MeV up to Eα = 7.45 MeV. Substantial competition cusps were observed in the excitation function for all three (α, γ) reactions. The data were found to be in reasonable agreement with the predictions of the current versions of global Hauser-Feshbach models used in nucleosynthesis calculations. Including width fluctuation corrections and realistic neutron strength functions generally improves the ability of the models to predict the depth of the (α, γ) competition cusps; the depths of the predicted (α,γ) cusps are insensitive to the degree of isospin mixing. Taken together with studies of competition effects in proton-induced reactions, the present data confirm the importance of width fluctuation and strength function effects, and indicate essentially complete isospin mixing between T< and T> states in the compound nucleus. 相似文献
55.
R.H. Spear 《Physics Reports》1981,73(5):369-390
Available experimental information on the static electric quadrupole moments Q2+ of the 2+ first excited states of even-mass nuclei in the 2s1d shell is tabulated and critically reviewed, and “adopted values” are presented. The results reveal a well defined pattern for the variation of Q2+ through the shell. Predictions of Q2+ made from various nuclear models are tabulated and compared with experiment. For each nucleus the qua ty and quality of the existing data for Q2+, together with the current theoretical significance of the result, are used as criteria to determi whether new experimental work is desirable. 相似文献
56.
Swatloski RP Spear SK Holbrey JD Rogers RD 《Journal of the American Chemical Society》2002,124(18):4974-4975
We report here initial results that demonstrate that cellulose can be dissolved without activation or pretreatment in, and regenerated from, 1-butyl-3-methylimidazolium chloride and other hydrophilic ionic liquids. This may enable the application of ionic liquids as alternatives to environmentally undesirable solvents currently used for dissolution of this important bioresource. 相似文献
57.
Barbara O. Scott Aaron C. Siegmund Charles K. Marlowe Yazhong Pei Kerry L. Spear 《Molecular diversity》1996,1(2):125-134
Summary The solid phase synthesis of libraries containing a 1,3,4,6-tetrasubstituted-2,5-diketo-1,4-piperazine scaffold (DKP) or a 3,4,6-trisubstituted-2,5-diketo-1,4-morpholme scaffold (DKM) from -bromocarboxylic acids and amines is described. Using a design strategy which we refer to as divergent library design, both templates were prepared from a common intermediate. The general utility of this synthetic route in creating novel, non-peptidyl chemical libraries is discussed. 相似文献
58.
Identical extraction behavior and coordination of trivalent or hexavalent f-element cations using ionic liquid and molecular solvents 总被引:2,自引:0,他引:2
Cocalia VA Jensen MP Holbrey JD Spear SK Stepinski DC Rogers RD 《Dalton transactions (Cambridge, England : 2003)》2005,(11):1966-1971
The extraction of both UO2(2+) and trivalent lanthanide and actinide ions (Am3+, Nd3+, Eu3+) by dialkylphosphoric or dialkylphosphinic acids from aqueous solutions into the ionic liquid, 1-decyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide has been studied and compared to extractions into dodecane. Radiotracer partitioning measurements show comparable patterns of distribution ratios for both the ionic liquid/aqueous and dodecane/aqueous systems, and the limiting slopes at low acidity indicate the partitioning of neutral complexes in both solvent systems. The metal ion coordination environment, elucidated from EXAFS and UV-visible spectroscopy measurements, is equivalent in the ionic liquid and dodecane solutions with coordination of the uranyl cation by two hydrogen-bonded extractant dimers, and of the trivalent cations by three extractant dimers. This is the first definitive report of a system where both the biphasic extraction equilibria and metal coordination environment are the same in an ionic liquid and a molecular organic solvent. 相似文献
59.
60.
Contrary to theoretical predictions and previous experimental results, a new systematic study of the static quadrupole moments Q2+ in the even-mass cadmium isotopes using the re-orientation effect shows no evidence of significant variation in Q2+ with mass number. For 116Cd, B(E2: 0+ → 2+) is found to be 20% lower than the previously adopted value. 相似文献