Far-infrared probe of size dispersion and population fluctuations in doped self-assembled quantum dots

We investigate the FIR magneto-optical transitions in doped self-assembled InAs quantum dots with an average filling ranging from 0.6 to 6 electrons per dot. Significant changes in the magnetic field dispersion, the line-width and the amplitude of the transitions are observed as the doping level is varied, in agreement with our theoretical calculations. We show that our technique is an effective tool to obtain informations regarding the dot size homogeneity and the electron filling uniformity.Received: 22 July 2003, Published online: 2 October 2003PACS: 73.21.La Quantum dots - 78.20.Ls Magnetooptical effects - 78.30.Fs III-V and II-VI semiconductors - 78.67.Hc Quantum dotsE. Deleporte: Present address: Laboratoire de Photonique Quantique et Moleculaire, École Normale Superieure de Cachan, 94235 Cachan Cedex, FranceJ.M. Gérard: Present address: CEA-Grenoble DRFMC/SP2M/PSC, Laboratoire de Physique des semiconducteurs, 38054 Grenoble, France     

Theoretical evaluation of sensitivity and thermal stability for high explosives based on quantum chemistry methods: A brief review

Over the past 20 years, a number of scientists have conducted numerous fundamental investigations based on quantum chemistry theory into various mechanistic processes that seems to contribute to the sensitivity of energetic materials. A large number of theoretical methods that have been used to predict their mechanical and spark sensitivity are summarized in this article, in which the advantages and disadvantages of these methods, together with their scope of use are clarified. In addition, the theoretical models for thermal stability of explosives are briefly introduced as a supplement. It has been concluded that the current ability to predict sensitivity is merely based on a series of empirical rules, such as simple oxygen balance, molecular properties, and the ratios of C and H to oxygen for different classes of explosive compounds. These are valid only for organic classes of explosives, though some special models have been proposed for inorganic explosives, such as azides. An exact standard for sensitivity should be established experimentally by some new techniques for both energetic compounds and their mixtures. © 2013 Wiley Periodicals, Inc.     

Hydrogen-antihydrogen interactions at low energies

The main cause of loss of trapped AH is due to collisions with H₂ and He. As a first step towards treating these reactions we are studying the interaction of AH with H. We have carried out variational calculations to determine an upper bound to the smallest internuclear distance at which the light particles are still bound to the nuclei. We are currently in the process of taking into account the motion of the nuclei. This will enable us to calculate cross-sections for low energy H-AH scattering. This revised version was published online in August 2006 with corrections to the Cover Date.     

A Galerkin Approximation for the Initial-Value Problem for Linear Second-Order Differential Equations

In this paper, a Galerkin type algorithm is given for the numerical solution of L(x)=(r(t)x'(t))'-p(t)x(t)=g(t); x(a)=x_a, x'(a)=x'_a, where r (t)>f0, and Spline hat functions form the approximating basis. Using the related quadratic form, a two-step difference equation is derived for the numerical solutions. A discrete Gronwall type lemma is then used to show that the error at the node points satisfies e_k=0(h²). If e(t) is the error function on a?t?b; it is also shown (in a variety of norms) that e(t)?Ch² and e'(t)?C₁h. Test case runs are also included. A (one step) Richardson or Rhomberg type procedure is used to show that e^R_k=0(h⁴). Thus our results are comparable to Runge-Kutta with half the function evaluations.     

Recombination efficacy in a-Si:H p-i-n devices

The performance of hydrogenated amorphous silicon solar cells (a-Si:H) is limited due to the relatively high defect concentration in the intrinsic layer, leading to high recombination rates. The dark current-voltage (JV) characteristics of these cells are mainly determined by recombination processes. Several parameters influence these processes: the density-of-states distribution in the mobility gap, the spatial distribution of recombination centers, and the recombination efficacy. As a result the ideality factor is non-integer and varies with voltage. The temperature dependence of the dark JV curves reveals the bias dependent activation energy, a measure for the mobility gap, and the temperature dependence of the recombination efficacy.In this contribution we present results of accurate dark JV measurements at different temperatures and a comparison to computer simulations. By analyzing the temperature dependence we study the influence of the recombination efficacy on the recombination rate and determine where in the device recombination is most effective. Simulations show that the shape of the recombination efficacy curve depends on the cross-section ratio for electron and hole trapping. Whereas the recombination rate is mainly determined by the local defect density in the device and controls the JV characteristic, the recombination efficacy controls the temperature dependence.     

Magneto infrared absorption in high electron density GaAs quantum wells

Magneto infrared absorption measurements have been performed in a highly doped GaAs quantum well which has been lifted off and bonded to a silicon substrate, in order to study the resonant polaron interaction. It is found that the pinning of the cyclotron energy occurs at an energy close to that of the transverse optical phonon of GaAs. This unexpected result is explained by a model taking into account the full dielectric constant of the quantum well.     

Nonlinear volterra integrodifferential equations in a Banach space

We study the Cauchy problem associated with the Volterra integrodifferential equation u\left( t \right) \in Au\left( t \right) + \int {_0^1 B\left( {t - s} \right)u\left( s \right)ds + f\left( t \right),} u\left( 0 \right) = u_0 \in D\left( A \right), whereA is anm-dissipative non-linear operator (or more generally, anm-D(ω) operator), defined onD(A) ⊂X, whereX is a real reflexive Banach space. We show that ifB is of the formB=FA+K, whereF, K :X →D(D _s), whereD _s is the differentiation operator, withF bounded linear andK andD _sK Lipschitz continuous, then the Cauchy problem is well-posed. In addition we obtain an approximation result for the Cauchy problem.     

Identifizierung von Aminen

Zusammenfassung 4-Dimethylamino-3,5-dinitrobenzoyl-Derivate von Aminen (DADB-Amine) verschiedener chemischer Struktur wurden dünnschicht-chromatographisch und massenspektrometrisch untersucht. Die Fragmentierung dieser Verbindungen bei Elektronenbeschuß wird diskutiert. Aus den Massenspektren der DADB-Amine kann die Struktur eines unbekannten Amins weitgehend abgeleitet werden. In einzelnen Fällen, z.B. bei manchen iso- und n-Alkylaminen, sind zusätzliche NMR-Messungen nützlich. Die Massenspektrometrie erlaubt, besonders in Kombination mit der Dünnsehicht-Chromatographie, unbekannte Amine in komplexen Gemischen schnell und sicher zu identifizieren.

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Identification of aminesIII. Thin-layer chromatography and mass spectrometry of 4-dimethylamino-3,5-dinitrobenzoyl derivatives (DADS-amines)

4-Dimethylamino-3,5-dinitrobenzoyl derivatives of amines (DADB-amines) having different chemical structures were examined via thin-layer chromatography and mass spectrometry. The fragmentation of these compounds due to electron bombardment is discussed. On the basis of mass spectra of the DADB-amines, the structure of an unknown amine can be derived to a great extent. In some cases, e.g. many isoand n-alkyl amines, additional NMR-measurements are usefull. Mass Spectrometry makes it possible, particularly in combination with thin-layer chromatography, to identify unknown amines in complex mixtures rapidly and accurately.

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Teil I: diese Z. 247, 155 (1969). Teil II: diese Z. 247, 158 (1969).

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Auszugsweise vorgetragen: Hauptversammlung GDCh, Karlsruhe, September 1971.