Ajellium model analysis on quantum growth of metal nanowires and nanomesas

A simple jellium model is used to investigate the stability of a metal nanowire as a function of its size. The theoretical results from the model indicate the quantum selectivity of preferable radii of nanowires, in apparent agreement with the experimental observations. It is consequently suggested that a series of stable “magic numbers” and “instability gaps” observed in the synthesis experiments of Au nanowires is mainly attributed to the quantum-mechanical behavior. These stable radii can be achieved by rearranging atoms during the formation of nanowires. The model is also used to analyze the growth of Au nanomesas on a graphite surface, and the puzzling growth behavior of Au nanomesas can be reasonably explained.     

Dipoles and band alignment for benzene/Au(111) and C<Subscript>60</Subscript>/Au(111) interfaces

A local orbital DFT-approach combined with a “scissor”-operator is used to obtain the Charge Neutrality Level and the screening parameter in the benzene/Au(111) and C₆₀/Au(111) interfaces. The “pillow” dipole and interface Fermi level are also calculated. The total dipole induced across the interface is compared with the experimental evidences: while the agreement for C₆₀/Au(111) is excellent, for benzene/Au(111), some discrepancies appear that are discussed in the light of other models.     

Magnetostatics dualism in a one-dimensional chain of classical magnetic moments

Magnetostatic interaction in polycrystalline nanowires manifests itself in two competing ways, providing the existence of a stable domain structure even in the absence of exchange interaction between crystals. It has been found that not only the domain structure but also the block magnetization structure of the nanowire consisting of exchange-noninteracting crystallites are of magnetostatic nature. The average domain wall width and magnetization correlation length have been calculated analytically and validated by simulation. The feasibility of the “easy axis” and “easy plane” phases of the effective anisotropy for different crystallite shapes has been demonstrated.     

Electrochemically grown rough-textured nanowires

Nanowires with a rough surface texture show unusual electronic, optical, and chemical properties; however, there are only a few existing methods for producing these nanowires. Here, we describe two methods for growing both free standing and lithographically patterned gold (Au) nanowires with a rough surface texture. The first strategy is based on the deposition of nanowires from a silver (Ag)–Au plating solution mixture that precipitates an Ag–Au cyanide complex during electrodeposition at low current densities. This complex disperses in the plating solution, thereby altering the nanowire growth to yield a rough surface texture. These nanowires are mass produced in alumina membranes. The second strategy produces long and rough Au nanowires on lithographically patternable nickel edge templates with corrugations formed by partial etching. These rough nanowires can be easily arrayed and integrated with microscale devices.     

On the Study of Jamming Percolation

We investigate kinetically constrained models of glassy transitions, and determine which model characteristics are crucial in allowing a rigorous proof that such models have discontinuous transitions with faster than power law diverging length and time scales. The models we investigate have constraints similar to that of the knights model, introduced by Toninelli, Biroli, and Fisher (TBF), but differing neighbor relations. We find that such knights-like models, otherwise known as models of jamming percolation, need a “No Parallel Crossing” rule for the TBF proof of a glassy transition to be valid. Furthermore, most knights-like models fail a “No Perpendicular Crossing” requirement, and thus need modification to be made rigorous. We also show how the “No Parallel Crossing” requirement can be used to evaluate the provable glassiness of other correlated percolation models, by looking at models with more stable directions than the knights model. Finally, we show that the TBF proof does not generalize in any straightforward fashion for three-dimensional versions of the knights-like models.     

Convenient approaches for the synthesis of gold nanowires by successive utilization of two kinds of reducing agents in the solution of hexadecyl-trimethylammonium bromide

In spite that several empirical approaches for the synthesis of gold nanowires have been reported, there still remains ambiguity and controversy for their mechanisms. In this study, we report very easy and highly-reproducible synthetic method of gold (Au) nanowires with the size and the length of 40–50 nm and several micrometers, respectively. The method includes an extremely higher concentration of hexadecyl-trimethylammonium bromide (CTAB) at room temperature. We successively used two kinds of reducing agents, firstly sodium borohydride for the reduction of Au(III) ion into mostly Au(I) ion, and secondly triethylamine (TEA) leading Au(I) ion to Au(0) and its growth to Au nanowires. The former should be added very slowly, while the latter at once. Effects of oxygen were crucial for the growth to nanowires, and copper ion was quite effective for reductive scavenging of unwanted oxygen. It is strongly suggested that Cu(I) ion first generates the complex with TEA and then reduces Au(I) ion to Au(O). Thus, the Au nanowires grow in higher concentrations of Cu(I) ion. The concentration of CTAB was also found to be very important for the generation of Au nanowires.     

Mesoscopic and macroscopic dipole clusters: Structure and phase transitions

A two dimensional (2D) classical system of dipole particles confined by a quadratic potential is studied. This system can be used as a model for rare electrons in semiconductor structures near a metal electrode, indirect excitons in coupled quantum dots etc. For clusters of N ≤ 80 particles ground state configurations and appropriate eigenfrequencies and eigenvectors for the normal modes are found. Monte-Carlo and molecular dynamic methods are used to study the order-disorder transition (the “melting” of clusters). In mesoscopic clusters (N < 37) there is a hierarchy of transitions: at lower temperatures an intershell orientational disordering of pairs of shells takes place; at higher temperatures the intershell diffusion sets in and the shell structure disappears. In “macroscopic” clusters (N > 37) an orientational “melting” of only the outer shell is possible. The most stable clusters (having both maximal lowest nonzero eigenfrequencies and maximal temperatures of total melting) are those of completed crystal shells which are concentric groups of nodes of 2D hexagonal lattice with a number of nodes placed in the center of them. The picture of disordering in clusters is compared with that in an infinite 2D dipole system. The study of the radial diffusion constant, the structure factor, the local minima distribution and other quantities shows that the melting temperature is a nonmonotonic function of the number of particles in the system. The dynamical equilibrium between “solid-like” and “orientationally disordered” forms of clusters is considered.     

Hysteresis Phenomenon in Deterministic Traffic Flows

We study phase transitions of a system of particles on the one-dimensional integer lattice moving with constant acceleration, with a collision law respecting slower particles. This simple deterministic “particle-hopping” traffic flow model being a straightforward generalization to the well known Nagel–Schreckenberg model covers also a more recent slow-to-start model as a special case. The model has two distinct ergodic (unmixed) phases with two critical values. When traffic density is below the lowest critical value, the steady state of the model corresponds to the “free-flowing” (or “gaseous”) phase. When the density exceeds the second critical value the model produces large, persistent, well-defined traffic jams, which correspond to the “jammed” (or “liquid”) phase. Between the two critical values each of these phases may take place, which can be interpreted as an “overcooled gas” phase when a small perturbation can change drastically gas into liquid. Mathematical analysis is accomplished in part by the exact derivation of the life-time of individual traffic jams for a given configuration of particles. This research has been partially supported by Russian Foundation for Fundamental Research and French Ministry of Education grants.     

“Hot spots” induced near-field enhancements in Au nanoshell and?Au nanoshell dimer

The influence of “hot spots” on the near-field properties of Au nanoshell and Au nanoshell dimers have been investigated by means of the finite element method. It is found with increasing the pinhole radius R that the maximal enhancement of near-field for Au nanoshell with pinhole parallel to the polarization increases from 17.906 at R=0 nm to 36.979 at R=0.8 nm, and then almost shows a negligible radius dependence. Large electric fields also can be observed inside the pinhole perpendicular to the polarization, which increases with increasing the pinhole radius. The near-field of Au nanoshell dimer depends strongly on the polarization and propagation directions of the incident light. Exponential decay behavior is found for the maximal enhancement of the electric field in the dimer junction as a function of the dimer separation. Furthermore, a very strong electric field is found in the junction between two Au nanoshells when the pinholes are located near the gap between the nanoshells.     

Thermodynamics of the HMF model with a magnetic field

We study the thermodynamics of the Hamiltonian mean field (HMF) model with an external potential playing the role of a “magnetic field”. If we consider only fully stable states, the caloric curve does not present any phase transition. However, if we take into account metastable states (for a restricted class of perturbations), we find a very rich phenomenology. In particular, the caloric curve displays a region of negative specific heat in the microcanonical ensemble in which the temperature decreases as the energy increases. This leads to ensembles inequivalence and to zeroth order phase transitions similar to the “gravothermal catastrophe” and to the “isothermal collapse” of self-gravitating systems. In the present case, they correspond to the reorganization of the system from an “anti-aligned” phase (magnetization pointing in the direction opposite to the magnetic field) to an “aligned” phase (magnetization pointing in the same direction as the magnetic field). We also find that the magnetic susceptibility can be negative in the microcanonical ensemble so that the magnetization decreases as the magnetic field increases. The magnetic curves can take various shapes depending on the values of energy or temperature. We describe first order phase transitions and hysteretic cycles involving positive or negative susceptibilities. We also show that this model exhibits gaps in the magnetization at fixed energy, resulting in ergodicity breaking.     

Dark matter and dark energy of the universe

A possibility of existing spheres filled with a uniform constant scalar field in the Universe is shown. These spheres can act as “dark matter” and can be responsible for a decreasing behavior of the “ rotational” curved galaxies observed. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 9–19, April, 2006.     

Investigation on non-LTE radiation emitted from a laser-irradiated Au disk

1 Introduction The laser-target coupling physics is a key topic in indirect-driven inertial confinement fusion (ICF) and X-ray application research[1―3]. When intense laser light irradiates the solid target, the plasmas are produced rapidly on the surface of the target. The laser en-ergy is mainly absorbed by inverse bremsstrahlung absorption, and a coronal region with high-temperature and low-density plasma is formed. Electron thermal conduction proc-ess transfers energy into over-dense re…     

Growth and use of metal nanocrystal assemblies on high-density silicon nanowires formed by chemical vapor deposition

In this paper, we describe the growth and potential application of metal nanocrystal assemblies on metal-catalyzed, CVD-grown silicon nanowires (SiNWs). The nanowires are decorated by chemical assembly of closely spaced (1–5 nm) Ag (30–100 nm diameter) and Au (5–25 nm diameter) nanocrystals formed from solutions of AgNO₃ and NaAuCl₄·2H₂O, respectively. The formation and growth of metal nanocrystals is believed to involve the galvanic reduction of metal ions from solution and the subsequent oxidation of available Si-hydride sites on the surfaces of the nanowires. A native oxide layer suppresses formation of metal nanocrystals; adding HF to the ionic solutions significantly increases the density of nanocrystals on the surfaces of the nanowires. The nanocrystals coating the nanowires were characterized by X-ray photoelectron spectroscopy, scanning electron microscopy, and X-ray diffraction. Ag nanocrystals on the nanowires afford sensitive detection of Rhodamine 6G (R6G) molecules in the 100 picomolar–micromolar range by surface enhanced Raman spectroscopy. In addition, Au nanocrystals formed on selected surfaces of a substrate of arbitrary shape can serve as effective nuclei for localized nanowire growth. PACS 81.07.b; 81.15.Gh     

Search for Hawking radiation in heavy ion collisions

The creation of “white holes” that decay by Hawking radiation has been proposed as one way to achieve the very early thermalization observed in heavy ion collisions at RHIC. The charartistic temperature of the radiations depends only on the ratio of the baryon number to the transverse energy. The yields of pions, kaons, protons and antiprotons measured by BRAHMS in central Au+Au collisions can be described within a thermal model where T drops with rapidity, and beam energy. We find that the chemical freeze-out temperature drops as the ratio of baryon number to energy increases but much more rapidly than predicted by the model.     

Structure and fragmentation in colloidal artificial molecules and nuclei

Motivated by recent experiments on colloidal systems with competing attractive and repulsive interactions, we simulate a two-dimensional system of colloids with competing interactions that can undergo fragmentation. In the absence of any other confining potential, the colloids can form stable clusters depending on the strength of the short range attractive term. By suddenly changing the strength of one of the interaction terms we find a rich variety of fragmentation behavior which is affected by the existence of “magic” cluster numbers. Such soft matter systems can be used to construct artificial nuclei.     

Solution templating of Au and Ag nanoparticles by linear poly[2-(diethylamino)ethyl methacrylate]

Abstract  

Linear poly[2-(diethylamino)ethyl methacrylate], poly(DEAMA), is an uncommon example of a homopolymer that can reduce salts of Au and Ag in solution to yield stable dispersions of nanoparticles (5–25 nm typical size). Poly(DEAMA)-stabilized Au and Ag nanoparticles were prepared in a mixture of water and 2-butoxyethanol, an amphiphilic organic solvent. The “loading ratio” (mole ratio of metal atoms to amines), a key parameter influencing particle size and clustering, was systematically varied. The size distribution and clustering of the nanoparticles were characterized by transmission electron microscopy and small-angle X–ray scattering. The maximum loading ratio achievable without inducing precipitation was approximately 0.3 for Au, but the maximum loading ratio for Ag was only about 0.04. The preparation of both Au and Ag nanoparticles in solution with a linear polymeric template illustrates that dendritic or hyperbranched architecture of the polymer is not a prerequisite for obtaining stable, non-aggregated dispersions. From a practical standpoint, poly(DEAMA) is an inexpensive template material that is readily immobilized on silica, which could facilitate development of novel, nanoparticle-based heterogeneous catalysts.     

Lateral field instability and six-wave mixing in a diode laser with broad active area

The electromagnetic field inside a nonlinear active medium of a laser is considered as a system of counterpropagating waves. Such an approach changes radically an earlier studied behavior of the lateral field instability due to self-deformaion (or self-focusing). In our calculations we used an expression for a laser field in the form of two “strong” counterpropagating waves whose complex amplitudes have weak perturbations. Amplitude perturbations of each of the “strong” waves can be presented by two spatial harmonics corresponding to two weak perturbation waves with wave vectors making some tilted angle ±φ with the cavity axis. Thus six waves would participate in the interaction: two counterpropagating strong waves and two pairs of weak waves. Using this approach, we have developed a theory for the propagation of four “weak” perturbation waves in a nonlinear amplifying medium in the presence of two counterpropagating “strong” waves. It is shown that perturbation waves with tilted angle φ⋍0.5–1.2° inside the active region, and respecively, with the side lobes of the far-field pattern at ∼1.7–4°, have the greatest growth increment. These perturbation waves produce lateral intensity modulation with period 10–30 μm for the 0.85 μm lasing wavelength. The appearance of such waves corresponds to the instability threshold of a homogeneous lateral distribution of optical power in a diode laser. The present theory makes it possible to investigate the stability of the homogeneous lateral optical intensity distribution in a diode laser of any design. This allows one to choose a suitable design of a laser with a homogeneous lateral distribution at high radiation power. Translated from Preprint No. 43 (1992) of the Lebedev Physics Institute, Russian Academy of Sciences.     

Phase Transitions for the Growth Rate of Linear Stochastic Evolutions

We consider a discrete-time stochastic growth model on d-dimensional lattice. The growth model describes various interesting examples such as oriented site/bond percolation, directed polymers in random environment, time discretizations of binary contact path process and the voter model. We study the phase transition for the growth rate of the “total number of particles” in this framework. The main results are roughly as follows: If d≥3 and the system is “not too random”, then, with positive probability, the growth rate of the total number of particles is of the same order as its expectation. If on the other hand, d=1,2, or the system is “random enough”, then the growth rate is slower than its expectation. We also discuss the above phase transition for the dual processes and its connection to the structure of invariant measures for the model with proper normalization. Supported in part by JSPS Grant-in-Aid for Scientific Research, Kiban (C) 17540112.     

Pulse applications of electrochemical cells - materials aspects

There is a rapidly increasing need for energy sources that are optimized to provide electrical energy at high power for short times. The terms “ultracapacitor” and “supercapacitor” are often used to describe some types of such devices. Applications include the requirement for very short pulses for digital electronic devices, the somewhat longer power pulse demands of heart defibrillators and other implantable medical devices, and the much larger transient power needs in connection with electric vehicle traction. The several mechanisms that can be used to store and provide pulse energy in electrochemical systems are reviewed. Their fundamental characteristics, as well as their applicability to the different types of pulse output requirements, are discussed. The use of spreadsheet techniques to model transient transport behavior in solids under various conditions, as well as the use of Laplace transform methods to convert information about the physical mechanisms and parameters of individual components into the dynamic response of an electrochemical system are demonstrated. Paper presented at the 1st Euroconference on Solid State Ionics, Zakynthos, Greece, 11 – 18 Sept. 1994     

“Non-Gibbsian” States and their Gibbs Description

The driving principle behind this paper is the following thesis: “Every physically reasonable random field has to be a Gibbs random field”. In this paper the so-called “non-Gibbsian” random fields are considered. The usual definition of the Gibbs field is generalized in such a way so as to include some of the discovered “non-Gibbsian” fields. The new definition is then used to show that the projection of the two-dimensional Ising model onto the one-dimensional sublattice ℤ¹ falls into the class of the generalized Gibbs fields. Received: 13 March 1998 / Accepted: 19 June 1998