Detection of nanoparticles by means of reflection electron energy loss spectroscopy depth profiling

The various studies of nanoparticles are of great importance because of the wide application of nanotechnology. The shape and structure of the nanoparticles can be determined by transmission electron microscopy (TEM) and their chemistry by electron energy loss spectroscopy. TEM sample preparation is an expensive and difficult procedure, however. Surface sensitive, analytical techniques, such as Auger electron spectroscopy (AES) and x-ray photoelectron spectroscopy (XPS) are well applicable to detect the atoms that make up the nanoparticles, but cannot determine whether particle formation occurred. On the other hand, reflection electron energy loss spectroscopy (REELS) probes the electronic structures of atoms, which are strongly different for the atoms being in solution or in precipitated form. If the particle size is in the nm range, plasmon resonance can be excited in it, which appears as a loss feature in REELS spectrum. Thus, by measuring AES (XPS) spectra parallel with those of REELS, besides the atomic concentrations the presence of the nanoparticles can also be identified. As an example, the appearance of nanoparticles during ion beam induced mixing of C/Si layer will be shown

Anomalous Temperature Dependence of Isotactic Polypropylene \uce\ub1-on-\uce\ub2 Cross-Nucleation Kinetics

A particular kind of heterogeneous nucleation, i.e., cross-nucleation, is sometimes observed in polymorphic substances, when a new crystal structure nucleates on the surface of a crystal of a different modification. Here we show a unique and apparently incongruous nucleation behavior in polymorphic isotactic polypropylene (i-PP). The rate of cross-nucleation of the monoclinic \uce\ub1-phase on the trigonal \uce\ub2-phase crystals increases with increasing temperature, in the vicinity of the \uce\ub1-crystals melting point. This behavior is contrary to that of the heterogeneous nucleation kinetics of the same crystal on various solid substrates, and also to the previously reported cases of cross-nucleation rate of other polymorphic systems, both exhibiting the expected decrease with temperature in the same range of undercoolings. i-PP \uce\ub1-on-\uce\ub2 cross-nucleation apparently eludes the nucleation theory. The results are explained as a manifestation of a kinetic competition between \uce\ub1-on-\uce\ub2 cross-nucleation and growth of \uce\ub2-crystalline seeds, and finally reconciled with the current understanding of nucleation. These new findings indicate that further theoretical efforts are needed to include the cross-nucleation phenomenon in the framework of a comprehensive understanding of polymorphic crystallization. Incidentally, this study highlights the intrinsic limits of the, industrially desirable, promotion of \uce\ub2-phase formation in polypropylene

Non-equilibrium phase transitions in one-dimensional kinetic Ising models

A family of nonequilibrium kinetic Ising models, introduced earlier, evolving under the competing effect of spin flips at {\it zero temperature} and nearest neighbour random spin exchanges is further investigated here. By increasing the range of spin exchanges and/or their strength the nature of the phase transition 'Ising-to-active' becomes of (dynamic) mean-field type and a first order tricitical point is located at the Glauber ($\delta=0$) limit. Corrections to mean-field theory are evaluated up to sixth order in a cluster approximation and found to give good results concerning the phase boundary and the critical exponent $\beta$ of the order parameter which is obtained as $\beta\simeq1.0$.Comment: 15 pages, revtex file, figures available at request from [email protected] in postscript format, submitted to J.Phys.

Three-Dimensional Ordering in Weakly Coupled Antiferromagnetic Ladders and Chains

A theoretical description is presented for low-temperature magnetic-field induced three-dimensional (3D) ordering transitions in strongly anisotropic quantum antiferromagnets, consisting of weakly coupled antiferromagnetic spin-1/2 chains and ladders. First, effective continuum field theories are derived for the one-dimensional subsystems. Then the Luttinger parameters, which determine the low-temperature susceptibilities of the chains and ladders, are calculated from the Bethe ansatz solution for these effective models. The 3D ordering transition line is obtained using a random phase approximation for the weak inter-chain (inter-ladder) coupling. Finally, considering a Ginzburg criterion, the fluctuation corrections to this approach are shown to be small. The nature of the 3D ordered phase resembles a Bose condensate of integer-spin magnons. It is proposed that for systems with higher spin degrees of freedom, e.g. N-leg spin-1/2 ladders, multi-component condensates can occur at high magnetic fields.Comment: RevTex, 18 pages with 7 figure

Quasi-static intergranular cracking in a Cu-Sn alloy: An analog of stress relief cracking of steels

Intergranular cracking in a laboratory-made Cu-8wt%Sn alloy at 265 to 300{degree}C in vacuum was studied in order to explore the hypothesis that this could serve as an analog to the brittle mode of stress-relief cracking in steels and to test the mechanism proposed earlier to explain that phenomenon. This mechanism involves the stress-induced intergranular penetration along grain boundaries of a surface-adsorbed embrittling element. Sulfur is the active element in this regard in steels, and tin was envisioned as playing the same role in Cu-Sn alloys. Auger spectroscopy was used to confirm earlier reports of the surface activity of tin and to determine the segregation kinetics in the present polycrystals; no other elements were found to segregate to surfaces to any significant degree in the present alloy. Crack growth measurements showed that intergranular cracking occurs in an intermittent manner at an average rate on the order of 0.1 {mu}m/sec over a range of crack length. Crack initiation was found to be remarkably sensitive to the stress intensity, implying the existence of a threshold. The fracture appearance in the regions of slow crack growth was similar to that observed in steels undergoing stress-relief cracking at 500--600{degree}C. It was concluded that the quasi-static intergranular cracking in the steels and in the Cu-Sn alloy represent two aspects of the same generic phenomenon and that the proposed mechanism of stress-induced intergranular impurity penetration is valid. It is believed that liquid-and solid-metal embrittlement are closely related to the type of intergranular cracking described here

On the nature of different types of absorbing states

We present a comparison of three different types of Langevin equation exhibiting absorbing states: the Langevin equation defining the Reggeon field theory, one with multiplicative noise, and a third type in which the noise is complex. Each one is found to describe a different underlying physical mechanism; in particular, the nature of the different absorbing states depends on the type of noise considered. By studying the stationary single-site effective potential, we analyze the impossibility of finding a reaction-diffusion model in the multiplicative noise universality class. We also discuss some theoretical questions related to the nature of complex noise, as for example, whether it is necessary or not to consider a complex equation in order to describe processes as the annihilation reaction, $A +A \to 0$.Comment: 7 figures, Latex fil

Interface depinning versus absorbing-state phase transitions

According to recent numerical results from lattice models, the critical exponents of systems with many absorbing states and an order parameter coupled to a non-diffusive conserved field coincide with those of the linear interface depinning model within computational accuracy. In this paper the connection between absorbing state phase transitions and interface pinning in quenched disordered media is investigated. For that, we present a mapping of the interface dynamics in a disordered medium into a Langevin equation for the active-site density and show that a Reggeon-field-theory like description, coupled to an additional non-diffusive conserved field, appears rather naturally. Reciprocally, we construct a mapping from a discrete model belonging in the absorbing state with-a-conserved-field class to a discrete interface equation, and show how a quenched disorder is originated. We discuss the character of the possible noise terms in both representations, and overview the critical exponent relations. Evidence is provided that, at least for dimensions larger that one, both universality classes are just two different representations of the same underlying physics.Comment: 8 page

Rare region effects at classical, quantum, and non-equilibrium phase transitions

Rare regions, i.e., rare large spatial disorder fluctuations, can dramatically change the properties of a phase transition in a quenched disordered system. In generic classical equilibrium systems, they lead to an essential singularity, the so-called Griffiths singularity, of the free energy in the vicinity of the phase transition. Stronger effects can be observed at zero-temperature quantum phase transitions, at nonequilibrium phase transitions, and in systems with correlated disorder. In some cases, rare regions can actually completely destroy the sharp phase transition by smearing. This topical review presents a unifying framework for rare region effects at weakly disordered classical, quantum, and nonequilibrium phase transitions based on the effective dimensionality of the rare regions. Explicit examples include disordered classical Ising and Heisenberg models, insulating and metallic random quantum magnets, and the disordered contact process.Comment: Topical review, 68 pages, 14 figures, final version as publishe