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1.
U. Kunze 《Zeitschrift für Physik B Condensed Matter》1989,76(4):463-472
Metal/insulator/semiconductor junctions are prepared on degeneratep-type InAs substrates with hole concentrations ranging from 2.3×1017 cm–3 to 2.7×1018 cm–3. The low work function of the top metal Yb, Al, or Au and charged interface states influence a two-dimensional (2D) electron inversion layer at the InAs surface. The insulator barrier that is formed by thermal oxidation is designed sufficiently thin, so that the bias voltage applied at the metal electrode mainly drops across the depletion layer separating the electron channel from the bulk. The current-voltage (I–V) characteristics exhibit strong negative differential conductance due to interband, tunneling from the 2D subband into the 3D valence band with peak-to-valley current ratios up to 3.1, 18, and 32 at 300 K, 77 K, and 4.2 K, respectively. In agreement with a theoretical model based on coherentelastic tunneling, the form of the I–V curves resembles those of double-barrier resonant tunnel devices rather than those of 3D Esaki diodes. The series resistance is obtained from the saturation of the differential conductance dI/dV at high forward bias and from the shift of structures in d2
I/dV
2 arising from phonon assisted tunneling.Dedicated to G. Lautz on the occasion of his 65th birthday 相似文献
2.
3.
Stefan Pitsch Sebastian Wendeborn Ramanarayanan Krishnamurthy Armin Holzner Mark Minton Martin Bolli Christian Miculca Norbert Windhab Ronald Micura Michael Stanek Bernhard Jaun Albert Eschenmoser 《Helvetica chimica acta》2003,86(12):4270-4363
Pyranosyl‐RNA (‘p‐RNA’ ) is an oligonucleotide system isomeric to natural RNA and composed of the very same building blocks as RNA. Its generational, chemical, and informational properties are deemed to be those of an alternative nucleic acid system that could have been a candidate in Nature's evolutionary choice of the molecular basis of genetic function. We consider the study of the chemistry of p‐RNA as etiologically relevant in the sense that knowledge of its structural, chemical, and informational properties on the chemical level offers both a perspective and reference points for the recognition of specific structural assets of the RNA structure that made it the (supposedly) superior system among possible alternatives and, therefore, the system that became part of biology as we know it today. The paper describes the chemical synthesis of β‐d‐ (and L )‐ribopyranosyl‐(4′→2′)‐oligonucleotide sequences, presents a resume of their structural and chemical properties, and cautiously discusses what we may and may not have learned from the pyranosyl isomer of RNA with respect to the conundrum of RNA's origin. 相似文献
4.
We consider solutions bifurcating from a spatially
homogeneous equilibrium under the assumption that the associated
linearization possesses continuous spectrum up to the imaginary
axis, for all values of the bifurcation parameter, and that a real
eigenvalue crosses the imaginary axis. For a model we investigate
the nonlinear stability of the trivial solution with respect to
spatially localized perturbations, prove the occurrence of a
pitchfork bifurcation of equilibria and the nonlinear stability of
the bifurcating equilibria, again with respect to spatially
localized perturbations. 相似文献
5.
6.
H. Günther M. Foerste M. Kunze G. zu Putlitz U. von Stein 《Zeitschrift für Physik B Condensed Matter》1996,100(4):613-617
We review the previous conclusion [J.Y. Ryu, Y.C. Chung and S.D. Choi, Phys. Rev. B 32, 7769 (1984)] that the trace property Tr(ABC) = Tr(CAB) leads to two different cyclotron transition absorption formulae in the electron-phonon systems in the lowest order approximation. The pictorial expression and the calculated linewidths in Ge and Si show that the socalled EWC scheme is more seeming than the socalled MWC scheme. The difference is expected to disappear if we take into account all the higher order perturbation terms or start with the many body formalism in the complete scheme. 相似文献
7.
H. Hofsäss H. Feldermann R. Merk M. Sebastian C. Ronning 《Applied Physics A: Materials Science & Processing》1998,66(2):153-181
T /nS of nT rearrangements and nS atoms in the spike volume as the crucial parameter characterizing the ability of a given ion–target combination to achieve
complete rearrangement of the spike volume. nT/nS>1 is the optimum condition for diamondlike film growth. For aC films the ion energy dependence of nT/nS agrees well with the measured sp3 bond fraction. For Ar+-ion-assisted deposition of aC we find nT/nS>1 above 50 eV with no pronounced ion energy dependence. Furthermore, our model predicts optimum conditions for the formation
of cubic boron nitride between 50 eV and 3 keV.
Accepted: 14 October 1997 相似文献
8.
Phosphine Substituted Chelate Ligands. XVIII. Penta- and Tetracarbonylmetal Complexes of Chromium, Molybdenum, and Tungsten with Secondary and Tertiary Phosphinothioformamide Ligands Mono- and bidentately coordinated phosphinothioformamide complexes are obtained by photochemical substitution of the metal hexacarbonyls M(CO)6 (M ? Cr ( a ), Mo ( b ), W ( c )). The M(CO)5 · THF adducts react with secondary thioamides under exclusion of light to give the P-coordinate pentacarbonyl complexes [(CO)5MPPh2C(S)NHR1] (R1 ? Ph ( 1a – c ), Me ( 2a )). The photoreaction of M(CO)5 · THF with secondary and tertiary thioamides at low temperatures leads to the formation of the P, S-chelate complexes . The corresponding N-silylated complexes 6a – c (R1 ? Me3Si, R2 ? Ph) are obtained by direct photosubstitution of M(CO)6 in cyclohexane solution. The labile bis(thioformamide) complexes [(CO)4M(PPh2C(S)NHMe)2] ( 7a – c , cis-trans isomers) are synthesized in low yields according to the same procedure. The attempted alkylation of the chelate complexes 3a – c remains unsuccessful, whereas the secondary thioformamides react with n-BuLi/CH2Br2 to give the methylene bis(thioformirnidoesters) [Ph2PC(NR1)S]2CH2 (R1 ? Ph (8), Me ( 9 )) in quantitative yields. 相似文献
9.
57Fe electric and magnetic hyperfine parameters were calculated for a series of 10 iron model complexes, covering a wide range of oxidation and spin states. Employing the B3LYP hybrid method, results from nonrelativistic density functional theory (DFT) and quasi-relativistic DFT within the zero-order regular approximation (ZORA) were compared. Electron densities at the iron nuclei were calculated and correlated with experimental isomer shifts. It was shown that the fit parameters do not depend on a specific training set of iron complexes and are, therefore, more universal than might be expected. The nonrelativistic and quasi-relativistic electron densities gave fit parameters of similar quality; the ZORA densities are only shifted by a factor of 1.32, upward in the direction of the four-component Dirac-Fock value. From a correlation of calculated electric field gradients and experimental quadrupole splittings, the value of the 57Fe nuclear quadrupole moment was redetermined to a value of 0.16 barn, in good agreement with other studies. The ZORA approach gave no additional improvement of the calculated quadrupole splittings in comparison to the nonrelativistic approach. The comparison of the calculated and measured 57Fe isotropic hyperfine coupling constants (hfcc's) revealed that both the ZORA approach and the inclusion of spin-orbit contributions lead to better agreement between theory and experiment in comparison to the nonrelativistic results. For all iron complexes with small spin-orbit contributions (high-spin ferric and ferryl systems), a distinct underestimation of the isotropic hfcc's was found. Scaling factors of 1.81 (nonrelativistic DFT) and 1.69 (ZORA) are suggested. The calculated 57Fe isotropic hfcc's of the remaining model systems (low-spin ferric and high-spin ferrous systems) contain 10-50% second-order contributions and were found to be in reasonable agreement with the experimental results. This is assumed to be the consequence of error cancellation because g-tensor calculations for these systems are of poor quality with the existing DFT approaches. Excellent agreement between theory and experiment was found for the 57Fe anisotropic hfcc's. Finally, all of the obtained fit parameters were used for an application study of the [Fe(H2O)6]3+ ion. The calculated spectroscopic data are in good agreement with the Mossbauer and electron paramagnetic resonance results discussed in detail in a forthcoming paper. 相似文献
10.
Die freie Oberflächenenergie binärer Systeme als Funktion der zwischen den Molekeln wirkenden Kräfte
F. Kunze 《Monatshefte für Chemie / Chemical Monthly》1948,78(5-6):362-375
Zusammenfassung Die freien molaren Oberflächenenergien binärer Systemea
M werden durch Anteilwerte der Mischungskomponenten ausgedrückt. Diese Anteilwerte setzen sich proportional den Molenbrüchen aus dena-Werten der reinen Komponenten und einem Wechselwirkungsglieda
GL zusammen. Die Formel füra
M, bzw.
M
enthält daher außer den Molenbrüchen unda-Werten der reinen Komponenten nur die Größea
GL.Diese Gleichung ermöglicht es daher, mit Hilfe einereinzigen Messung bei beliebiger Konzentration den Gesamtverlauf der freien Oberflächenenergie bei allen Konzentrationen zu berechnen. Die Gleichung ist auch bei Dipolstoffen, welche in Lösung assoziiert sind, anwendbar. Die Dipolassoziation wirkt sich nur dann aus, wenn die betreffende Molekel klein oder das Moment besonders groß ist. In diesem Falle kann unter Annahme einer empirisch zu ermittelnden wirksamen Assoziationszahl eine Korrektur der Molenbrüche vorgenommen werden. 相似文献