Syntheses of semiconductor nanoparticles using single-molecular precursors

Methods for the preparation of II-VI, III-V, and II-V as well as other compound semiconductor nanoparticles using main group single-molecular precursors have been developed. The work involves the design and synthesis of compounds containing all the elements required within the desired nanoparticulate material. Precursors are tailored to give reproducible, clean decomposition at moderate temperatures, leading to high quality, defect free, mono-dispersed nanoparticles. In this article we cover key aspects of precursor and nanoparticle synthesis. One of the more successful and reproducible series of single-source precursors used, and the one on which we have concentrated our research efforts, is the bis(dialkyldithio-/diseleno-carbamato)cadmium(II)/zinc(II) compounds, M(E(2)CNR(2))(2) (M = Zn or Cd, E = S or Se, and R = alkyl) for the preparation of chalcogenide nanoparticulate materials. Preliminary mechanistic studies suggest that the precursor to nanoparticle deposition route is strongly influenced by the alkyl substituent groups present, and may well determine the phase and quality of the final metal chalcogenide nanoparticles produced. Herein we discuss the synthesis of semiconductor nanoparticles using such single-molecular precursors.     

Studies on the conformation of α-arylcinnamic acids and their esters: Crystal structures of methyl (E)-2,3-bis(3,4-dimethoxyphenyl)propenoate and methyl (Z)-2,3-bis(3,4-dimethoxyphenyl)propenoate

The conformations of stereoisomers of -arylcinnamic acids and their esters are discussed based on crystal structures of the E and Z forms of 2,3-bis(3,4-dimethoxyphenyl)propenoic acid and its methyl ester. In the E forms of the cinnamic acid and the cinnamic acid ester, the plane of the -aryl substituent is approximately perpendicular to that of the rest of the molecule. In the Z forms the plane of the carboxyl or methoxycarbonyl group is approximately perpendicular to that of the ethylenic group, and both the aromatic group planes are significantly twisted out of the ethylenic group plane. Crystal structures of methyl (E)-2,3-bis(3,4-dimethoxyphenyl)propenoate (space group P2₁/n with a = 8.1697(5), b = 11.3882(9), c = 19.7766(9) Å, = 90.058(4)°, V = 1840.0(2) ų, and Z = 4), monoclinic methyl (Z)-2,3-bis(3,4-dimethoxyphenyl)propenoate (space group P2₁/n with a = 11.183(2), b = 5.640(2), c = 29.737(7) Å, = 99.19(2)°, V = 1851.4(9) ų, and Z = 4), and orthorhombic methyl (Z)-2,3-bis(3,4-dimethoxyphenyl)propenoate (space group P2₁2₁2₁ with a = 8.849(4), b = 24.288(9), c = 8.734(3) Å, V = 1877(1) ų, and Z = 4) are reported.     

Statistical properties of eigenvalues for an operating quantum computer with static imperfections

We investigate the transition to quantum chaos, induced by static imperfections, for an operating quantum computer that simulates efficiently a dynamical quantum system, the sawtooth map. For the different dynamical regimes of the map, we discuss the quantum chaos border induced by static imperfections by analyzing the statistical properties of the quantum computer eigenvalues. For small imperfection strengths the level spacing statistics is close to the case of quasi-integrable systems while above the border it is described by the random matrix theory. We have found that the border drops exponentially with the number of qubits, both in the ergodic and quasi-integrable dynamical regimes of the map characterized by a complex phase space structure. On the contrary, the regime with integrable map dynamics remains more stable against static imperfections since in this case the border drops only algebraically with the number of qubits. Received 19 June 2002 / Received in final form 30 September 2002 Published online 17 Decembre 2002 RID="a" ID="a"e-mail: dima@irsamc.ups-tlse.fr RID="b" ID="b"UMR 5626 du CNRS     

Non-adiabatic quantum molecular dynamics: General formalism and case study H<Subscript>2</Subscript><Superscript>+</Superscript> in strong laser fields

In Rydberg atoms subject to static and harmonic collinear electric fields, intrashell transition can be induced by the first order perturbation from a small perpendicular electric or magnetic field, or by effects of the second order in the major fields. Both mechanisms lead to resonances that are suppressed under certain conditions, and high-frequency interference oscillations in case of non-adiabatic field switching. Recent measurements of microwave ionization signals show very rich and fascinating structures similar to the ones predicted for intrashell mixing. We show that the observed ionization structures may be explained by diabatic electric-field ionization and the consistent use of perturbation theory for intrashell mixing. In particular, the dominant oscillation frequency is successfully interpreted in terms of interference between first and second order transition amplitudes. New predictions are provided. The present approach gives a comprehensive picture of intrashell transitions, which may be tested in future experiments designed to observe such transitions directly. Received 2 May 2002 / Received in final form 23 September 2002 Published online 21 January 2003 RID="a" ID="a"e-mail: Valentin.Ostrovsky@pobox.spbu.ru RID="b" ID="b"e-mail: horsdal@ifa.au.dk     

Study of the electric capacitance spectra on symmetric quantum-dot pattern

We have calculated the ground-state energy of the symmetric quantum-dot pattern by the ab initio calculation method, i.e. unrestricted Hartree-Fock-Roothaan (UHFR) method based on the Gaussian basis, and studied their electric capacitance spectra, assuming each quantum dot of quantum-dot pattern to be confined in a three-dimensional spherical potential well of finite depth. For the systems in question, our results show that our method and theoretical model not only give the electric capacitance peaks similar to s-shell and p-shell atom-like quantum dot, but also show some new fine-structure of electric capacitance in the symmetric quantum-dot pattern system. This method might be a feasible tool to study few-electron problems on the symmetric quantum-dot pattern system.     

Organic quantum well and superlattice characteristics in quasi-one-dimensional multiblock copolymers

A tight-binding calculation was presented to describe multiblock copolymers, such as [...-(PA)x-(PPP)y-...] composed of PA (polyacetylene) and PPP (poly(p-phenylene). It is found that a copolymer has a quantum well and superlattice characteristics, and evident is the effect of the composite lengths, the interfacial couplings and the electron-phonon interactions on the electronic properties of a copolymer. The quantum tunneling, the Franz-Keldysh effect and the quantum confinement can be generated under an applied electric field. These results were compared to those of traditional inorganic quantum well and superlattice systems.     

Crystal Bases for Quantum Affine Algebras and Combinatorics of Young Walls

In this paper we give a realization of crystal bases for quantumaffine algebras using some new combinatorial objects which wecall the Young walls. The Young walls consist of colored blockswith various shapes that are built on a given ground-state walland can be viewed as generalizations of Young diagrams. Therules for building Young walls and the action of Kashiwara operatorsare given explicitly in terms of combinatorics of Young walls.The crystal graph of a basic representation is characterizedas the set of all reduced proper Young walls. The characterof a basic representation can be computed easily by countingthe number of colored blocks that have been added to the ground-statewall. 2000 Mathematical Subject Classification: 17B37, 17B65,81R50, 82B23.     

Intersection Local Times of Independent Brownian Motions as Generalized White Noise Functionals

A 'chaos expansion' of the intersection local time functional of two independent Brownian motions in R ^d is given. The expansion is in terms of normal products of white noise (corresponding to multiple Wiener integrals). As a consequence of the local structure of the normal products, the kernel functions in the expansion are explicitly given and exhibit clearly the dimension dependent singularities of the local time functional. Their L ^p -properties are discussed. An important tool for deriving the chaos expansion is a computation of the 'S-transform' of the corresponding regularized intersection local times and a control about their singular limit.     

Thin-Film Luminescent UV Radiation Converters Based on Europium Chelates

This paper considers the possibility of using tris--diketonate complexes of europium in polymethylmettacrylate as luminescent UV radiation converters for widening the range of spectral sensitivity of photodetectors (including TV ones). The absolute quantum yields of luminescence have been determined. Converters for the 220–380-nm range providing a quantum efficiency of the silicon photodiode and the CCD matrix in the UV range up to 40% of the efficiency at the maximum of the spectral characteristic have been devised.     

Generalized Quantum Mechanics for Separated Systems

We give seven necessary physical conditions on a property lattice for to describe two quantum systems when they are separated.