Workshop Nanoscience B: Self-Assembly-from molecules to materials

In recent years, there has been growing interest in the design of electron accelerators in order to reduce beam emittance and to increase photon brilliance (from third-generation synchrotron sources to free electron lasers). This has increased the coherent properties of the beam and has opened up new branches of microscopy and spectroscopy at nanometer-length scales. The X-ray nano probe is going to be an important tool for future research, hence there has been substantial research carried out in order to develop nano focusing optics of diffraction-limited performance.     

Nanoscience: The quantum frontier

This overview begins with some historical comments and then describes some recent work on theoretical and experimental nanoscience advances. The focus is mainly on nanotubes and fullerenes. Electronic, optical, structural, mechanical, and superconducting properties of these systems are discussed.     

Nanoscience in Latin America

Journal of Nanoparticle Research -     

Nanoscience and nanotechnology in Venezuela

Nanoscale research in Venezuela is briefly reviewed, with emphasis on research groups, research lines, and institutions involved. A summary exploration is made of international collaboration through scientific co-authorship, as well of the efforts to build nano capacities, available infrastructure, relationships to the productive sector and a weak presence in Venezuelan public policies, although there is some expectation that the situation may soon begin to change.     

Controlling self-organized criticality in complex networks

A control scheme to reduce the size of avalanches of the Bak-Tang-Wiesenfeld model on complex networks is proposed. Three network types are considered: those proposed by Erdős-Renyi, Goh-Kahng-Kim, and a real network representing the main connections of the electrical power grid of the western United States. The control scheme is based on the idea of triggering avalanches in the highest degree nodes that are near to become critical. We show that this strategy works in the sense that the dissipation of mass occurs most locally avoiding larger avalanches. We also compare this strategy with a random strategy where the nodes are chosen randomly. Although the random control has some ability to reduce the probability of large avalanches, its performance is much worse than the one based on the choice of the highest degree nodes. Finally, we argue that the ability of the proposed control scheme is related to its ability to reduce the concentration of mass on the network.     

Nanoscience and Engineering: The Next Five Years

The current and planned research in nanoscience and engineering will make possible a paradigm shift in nanoscale devices and structures.     

玻色-爱因斯坦凝聚体中的双孤子相互作用操控

考虑周期性驱动线性势, 利用Darboux变换法解析地研究了玻色-爱因斯坦凝聚体(BEC)中的双孤子相互作用, 得到了S-波散射长度的临界值. 结果表明: 当S-波散射长度高于临界值时, BEC中的两个亮孤子相互吸引并融合; 而当S-波散射长度低于临界值时, 两个亮孤子保持局域稳定. 此外, 在外部势阱的驱动下, 两个稳定的亮孤子产生周期性振荡行为.     

Mixed hyperfine interactions in amorphous materials: A model study

⁵⁷Fe Mössbauer absorption profiles were calculated supposing distributions of all hyperfine parameters: hyperfine magnetic fields, isomer shifts, and electric field gradients. The effect of mixed hyperfine interactions was taken into account in all orders of perturbation theory. The shapes of the spectra were systematically studied for varying average values and widths of the hyperfine magnetic field distribution (HMFD). From the simulated spectra, the shapes of the HMFD were reconstructed using standard techniques of Mössbauer spectra processing which neglect the effects of random isomer shifts and electric field gradients. It has been shown that the reconstructed shapes of the HMFD differ qualitatively from the original single-peaked distributions and exhibit a double-peaked structure similar to the distributions found in many experiments on amorphous alloys with low iron content. A brief review of various mechanisms responsible for either apparent or real double-peaked structure of HMFD has been given.     

Surface Science: Foundations of Catalysis and Nanoscience

Journal of Nanoparticle Research -     

Geometry of interactions in complex bodies

We analyze geometrical structures necessary to represent bulk and surface interactions of standard and substructural nature in complex bodies. Our attention is mainly focused on the influence of diffuse interfaces on sharp discontinuity surfaces. In analyzing this phenomenon, we prove the covariance of surface balances of standard and substructural interactions.     

Controlling electron-phonon interactions in graphene at ultrahigh carrier densities

We report on the temperature dependent electron transport in graphene at different carrier densities n. Employing an electrolytic gate, we demonstrate that n can be adjusted up to 4 × 10(14) cm(-2) for both electrons and holes. The measured sample resistivity ρ increases linearly with temperature T in the high temperature limit, indicating that a quasiclassical phonon distribution is responsible for the electron scattering. As T decreases, the resistivity decreases more rapidly following ρ(T) ～ T(4). This low temperature behavior can be described by a Bloch-Grüneisen model taking into account the quantum distribution of the two-dimensional acoustic phonons in graphene. We map out the density dependence of the characteristic temperature Θ(BG) defining the crossover between the two distinct regimes, and show that, for all n, ρ(T) scales as a universal function of the normalized temperature T/Θ(BG).     

Progress of Nanoscience and Nanotechnology in China

Nanoscience and nanotechnology has been attracting wide attention and is becoming an active frontier area. Chinese scientists have followed with the main stream interest in the development of Nanoscience and nanotechnology since its initial stage. In the present paper, the achievements and present status of China in relative researches such as nanomaterials, nanodevices and characterization of nanostructure are described.     

Controlling the diffused nonlinear light generated in random materials

We describe a method for shaping the wavefront of the second-harmonic light generated in nonlinear materials with a disordered structure using a spatial light modulator on the fundamental beam. We show that, for the case of a transparent strontium-barium niobate crystal with a random distribution of antiparallel domains, the speckle generation can be concentrated into a single spot.     

Controlling spin exchange interactions of ultracold atoms in optical lattices

We describe a general technique that allows one to induce and control strong interaction between spin states of neighboring atoms in an optical lattice. We show that the properties of spin exchange interactions, such as magnitude, sign, and anisotropy, can be designed by adjusting the optical potentials. We illustrate how this technique can be used to efficiently "engineer" quantum spin systems with desired properties, for specific examples ranging from scalable quantum computation to probing a model with complex topological order that supports exotic anyonic excitations.     

High-power laser interactions with nanostructured materials

We use short-pulse high-power lasers to selectively modify the structure of nanolaminates and nanocrystals. It is demonstrated that femtosecond pulses can achieve excellent results for microscopic thin film removal. Laser pulses can also be used to modify the crystal structure of thin films. It is also demonstrated that coherent laser excitation promotes a selective modification of nanocrystals, resulting in changes of size, shape, and crystal structure. Received: 7 October 2002 / Accepted: 20 January 2003 / Published online: 28 May 2003 RID="*" ID="*"Corresponding author. Fax: +1-414/229-5589, E-mail: yakovlev@uwm.edu     

Focus on Research in Nanoscience and Nanotechnology in Switzerland

Journal of Nanoparticle Research -     

A new method to study complex materials in solid state chemistry: application to chalcogenide materials

We show that a combined application of Mössbauer spectroscopy and other experimental tools such as X‐ray photoelectron spectroscopy, X‐ray absorption spectroscopy and nuclear magnetic resonance provides a coherent picture of the local electronic structure in chalcogenide materials. In order to develop this idea we propose an analysis of the Sn, Sb and Te local electronic structures for three different systems of materials. The first example concerns the In–Sn–S system. We show that Li insertion in In₁₆Sn₄S₃₂ leads to changes of the Sn oxidation states from Sn(IV) to Sn(II). The second example concerns materials of the Tl–Sb–S system. We show that variations of the ¹²¹Sb Mössbauer isomer shift and surface of the first peak of the X‐ray absorption spectra at the Sb L_III edge can be linearly correlated because of the main influence of the Sb 5s electrons. This is explained by changes in the local environment of the Sb atoms. The last example concerns the crystalline phases of the Tl–Sn–Te system. The formal oxidation numbers of the Te atoms are determined from ¹²⁵Te Mössbauer spectroscopy and X‐ray photoelectron spectroscopy. They are related to the different types of bonds involving the Te atoms in the Tl–Sn–Te compounds.