Aging and stationary properties of non-equilibrium symmetrical three-state models

We consider a non-equilibrium three-state model whose dynamics is Markovian and displays the same symmetry as the three-state Potts model, i.e. the transition rates are invariant under the cyclic permutation of the states. Unlike the Potts model, detailed balance is, in general, not satisfied. The aging and the stationary properties of the model defined on a square lattice are obtained by means of large-scale Monte Carlo simulations. We show that the phase diagram presents a critical line, belonging to the three-state Potts universality class, that ends at a point whose universality class is that of the Voter model. Aging is considered on the critical line, at the Voter point and in the ferromagnetic phase.

Transport Properties and Novel Sensing Applications of Organic Semiconducting Crystals

The present thesis is focused on the study of Organic Semiconducting Single Crystals (OSSCs) and crystalline thin films. In particular solution-grown OSSC, e.g. 4-hdroxycyanobenzene (4HCB) have been characterized in view of their applications as novel sensors of X-rays, gamma-rays, alpha particles radiations and chemical sensors. In the field of ionizing radiation detection, organic semiconductors have been proposed so far mainly as indirect detectors, i.e. as scintillators or as photodiodes. I first study the performance of 4HCB single crystals as direct X-ray detector i.e. the direct photon conversion into an electrical signal, assessing that they can operate at room temperature and in atmosphere, showing a stable and linear response with increasing dose rate. A dedicated study of the collecting electrodes geometry, crystal thickness and interaction volume allowed us to maximize the charge collection efficiency and sensitivity, thus assessing how OSSCs perform at low operating voltages and offer a great potential in the development of novel ionizing radiation sensors. To better understand the processes generating the observed X-ray signal, a comparative study is presented on OSSCs based on several small-molecules: 1,5-dinitronaphthalene (DNN), 1,8-naphthaleneimide (NTI), Rubrene and TIPS-pentacene. In addition, the proof of principle of gamma-rays and alpha particles has been assessed for 4HCB single crystals. I have also carried out an investigation of the electrical response of OSSCs exposed to vapour of volatile molecules, polar and non-polar. The last chapter deals with rubrene, the highest performing molecular crystals for electronic applications. We present an investigation on high quality, millimeter-sized, crystalline thin films (10 – 100 nm thick) realized by exploiting organic molecular beam epitaxy on water-soluble substrates. Space-Charge-Limited Current (SCLC) and photocurrent spectroscopy measurements have been carried out. A thin film transistor was fabricated onto a Cytop® dielectric layer. The FET mobility exceeding 2 cm2/Vs, definitely assess the quality of RUB films.

Luminescence and non-radiative processes in lanthanide squarate hydrates

The luminescence properties of solid hydrated lanthanide squarates (Ln2(C4O4)3(H2O) x; x = 8 or 13;Ln3+ = Gd, La, Eu, Tb, Pr) are reported for temperatures down to 4.2K. The luminescence of the squarate group is observed for the Gd3+ and La3+ compounds at low temperatures (below 150K). The Pr3+ compound does not show any emission at all, not even at 4.2K. This is ascribed to the quenching of the Pr3+ emission by multiphonon relaxation and/or concentration quenching. The quantum efficiencies of the 5D0 emission of Eu3+ and of the 5D4 emission of Tb3+ in these squarate complexes are strikingly different. Whereas the Tb3+ emission shows a temperature independent quantum efficiency of 50% upon ligand excitation, the Eu3+ emission is strongly quenched, showing a temperature dependent quantum efficiency of 0.8% at 4.2K upon ligand excitation. This quenching is ascribed to the low energy position of the charge-transfer state of Eu3+ in these compounds.

Response theory for equilibrium and non-equilibrium statistical mechanics: causality and generalized Kramers-Kronig relations

We consider the general response theory recently proposed by Ruelle for describing the impact of small perturbations to the non-equilibrium steady states resulting from Axiom A dynamical systems. We show that the causality of the response functions entails the possibility of writing a set of Kramers-Kronig (K-K) relations for the corresponding susceptibilities at all orders of nonlinearity. Nonetheless, only a special class of directly observable susceptibilities obey K-K relations. Specific results are provided for the case of arbitrary order harmonic response, which allows for a very comprehensive K-K analysis and the establishment of sum rules connecting the asymptotic behavior of the harmonic generation susceptibility to the short-time response of the perturbed system. These results set in a more general theoretical framework previous findings obtained for optical systems and simple mechanical models, and shed light on the very general impact of considering the principle of causality for testing self-consistency: the described dispersion relations constitute unavoidable benchmarks that any experimental and model generated dataset must obey. The theory exposed in the present paper is dual to the time-dependent theory of perturbations to equilibrium states and to non-equilibrium steady states, and has in principle similar range of applicability and limitations. In order to connect the equilibrium and the non equilibrium steady state case, we show how to rewrite the classical response theory by Kubo so that response functions formally identical to those proposed by Ruelle, apart from the measure involved in the phase space integration, are obtained. These results, taking into account the chaotic hypothesis by Gallavotti and Cohen, might be relevant in several fields, including climate research. In particular, whereas the fluctuation-dissipation theorem does not work for non-equilibrium systems, because of the non-equivalence between internal and external fluctuations, K-K relations might be robust tools for the definition of a self-consistent theory of climate change.

Transport properties and equation of state of quark-nuclear matter

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Optical properties and energy transfer processes in (Tm3+, Nd3+) doped tungstate fluorophosphate glass

We investigate the linear optical properties and energy transfer processes in tungstate fluorophosphate glass doped with thulium (Tm3+) and neodymium (Nd3+) ions. The linear absorption spectra from 370 to 3000 nm were obtained. Transitions probabilities, radiative lifetimes, and transition branching ratios were determined using the Judd-Ofelt [Phys. Rev. 127, 750 (1962); J. Chem. Phys. 37, 511 (1962)] theory. Frequency up-conversion to the blue region and fluorescence in the infrared were observed upon pulsed excitation in the range of 630-700 nm. The excitation spectra of the luminescence were obtained to understand the origin of the signals. The temporal decay of the fluorescence was measured for different concentrations of the doping ions. Energy transfer rates among the Tm3+ and Nd3+ ions were also determined.

Towards an Exergy Analysis of Diffusive and Non-Diffusive Processes in Living Organisms

Living organisms are open dissipative thermodynamic systems that rely on mechanothermo-electrochemical interactions to survive. Plant physiological processes allow plants to survive by converting solar radiation into chemical energy, and store that energy in form that can be used. Mammals catabolize food to obtain energy that is used to fuel, build and repair the cellular components. The exergy balance is a combined statement of the first and second laws of thermodynamics. It provides insight into the performance of systems. In this paper, exergy balance equations for both mammal’s and green plants are presented and analyzed.

Electronic transport properties of ascorbic acid and nicotinamide adsorbed on single-walled carbon nanotubes

Ab initio simulations of carbon nanotubes interacting with ascorbic acid and nicotinamide are reported. The electronic transport properties of these systems are studied using a combination of density functional theory and non-equilibrium Green`s functions methods. The adsorptions of both molecules are observed to depend strongly on their functionalization. The interaction through the appropriate functionalized species modifies the structural and electronic properties of the original system, resulting in a chemisorption regime. Changes in the electronic transport properties are also observed, with reductions on the total electronic transmission probabilities. Nevertheless, when the molecules interact through the pristine form, a physisorption interaction is observed with insignificant structural and electronic transport changes. (c) 2011 Elsevier B.V. All rights reserved.

Spin Orbit Effects in the Electronic Transport Properties of Adsorbed Graphene Nanoribbons

Graphene has received great attention due to its exceptional properties, which include corners with zero effective mass, extremely large mobilities, this could render it the new template for the next generation of electronic devices. Furthermore it has weak spin orbit interaction because of the low atomic number of carbon atom in turn results in long spin coherence lengths. Therefore, graphene is also a promising material for future applications in spintronic devices - the use of electronic spin degrees of freedom instead of the electron charge. Graphene can be engineered to form a number of different structures. In particular, by appropriately cutting it one can obtain 1-D system -with only a few nanometers in width - known as graphene nanoribbon, which strongly owe their properties to the width of the ribbons and to the atomic structure along the edges. Those GNR-based systems have been shown to have great potential applications specially as connectors for integrated circuits. Impurities and defects might play an important role to the coherence of these systems. In particular, the presence of transition metal atoms can lead to significant spin-flip processes of conduction electrons. Understanding this effect is of utmost importance for spintronics applied design. In this work, we focus on electronic transport properties of armchair graphene nanoribbons with adsorbed transition metal atoms as impurities and taking into account the spin-orbit effect. Our calculations were performed using a combination of density functional theory and non-equilibrium Greens functions. Also, employing a recursive method we consider a large number of impurities randomly distributed along the nanoribbon in order to infer, for different concentrations of defects, the spin-coherence length.

Non-Equilibrium Reaction Rates in the Macroscopic Chemistry Method for DSMC Calculations

The Direct Simulation Monte Carlo (DSMC) method is used to simulate the flow of rarefied gases. In the Macroscopic Chemistry Method (MCM) for DSMC, chemical reaction rates calculated from local macroscopic flow properties are enforced in each cell. Unlike the standard total collision energy (TCE) chemistry model for DSMC, the new method is not restricted to an Arrhenius form of the reaction rate coefficient, nor is it restricted to a collision cross-section which yields a simple power-law viscosity. For reaction rates of interest in aerospace applications, chemically reacting collisions are generally infrequent events and, as such, local equilibrium conditions are established before a significant number of chemical reactions occur. Hence, the reaction rates which have been used in MCM have been calculated from the reaction rate data which are expected to be correct only for conditions of thermal equilibrium. Here we consider artificially high reaction rates so that the fraction of reacting collisions is not small and propose a simple method of estimating the rates of chemical reactions which can be used in the Macroscopic Chemistry Method in both equilibrium and non-equilibrium conditions. Two tests are presented: (1) The dissociation rates under conditions of thermal non-equilibrium are determined from a zero-dimensional Monte-Carlo sampling procedure which simulates ‘intra-modal’ non-equilibrium; that is, equilibrium distributions in each of the translational, rotational and vibrational modes but with different temperatures for each mode; (2) The 2-D hypersonic flow of molecular oxygen over a vertical plate at Mach 30 is calculated. In both cases the new method produces results in close agreement with those given by the standard TCE model in the same highly nonequilibrium conditions. We conclude that the general method of estimating the non-equilibrium reaction rate is a simple means by which information contained within non-equilibrium distribution functions predicted by the DSMC method can be included in the Macroscopic Chemistry Method.

Minimum distance estimation of stationary and non-stationary ARFIMA processes

A new parametric minimum distance time-domain estimator for ARFIMA processes is introduced in this paper. The proposed estimator minimizes the sum of squared correlations of residuals obtained after filtering a series through ARFIMA parameters. The estimator iseasy to compute and is consistent and asymptotically normally distributed for fractionallyintegrated (FI) processes with an integration order d strictly greater than -0.75. Therefore, it can be applied to both stationary and non-stationary processes. Deterministic components are also allowed in the DGP. Furthermore, as a by-product, the estimation procedure provides an immediate check on the adequacy of the specified model. This is so because the criterion function, when evaluated at the estimated values, coincides with the Box-Pierce goodness of fit statistic. Empirical applications and Monte-Carlo simulations supporting the analytical results and showing the good performance of the estimator in finite samples are also provided.

Optical and Carrier Transport Properties of Cosputtered Zn–In–Sn–O Films and Their Applications to TFTs

The optical and carrier transport properties of amorphous transparent zinc indium tin oxide (ZITO)(a-ZITO) thin films and the characteristics of the thin-film transistors TFTs were examined as a function of chemical composition. The as-deposited films were very conductive and showed clear free carrier absorption FCA . The analysis of the FCA gave the effective mass value of 0.53 me and a momentum relaxation time of 3.9 fs for an a-ZITO film with Zn:In:Sn = 0.35:0.35:0.3. TFTs with the as-deposited channels did not show current modulation due to the high carrier density in the channels. Thermal annealing at 300°C decreased the carrier density and TFTs fabricated with the annealed channels operated with positive threshold voltages VT when Zn contents were 25 atom % or larger. VT shifted to larger negative values, and subthreshold voltage swing increased with decreasing the Zn content, while large on–off current ratios 107–108 were kept for all the Zn contents. The field effect mobilities ranged from 12.4 to 3.4 cm2 V−1 s−1 for the TFTs with Zn contents varying from 5 to 48 atom %. The role of Zn content is also discussed in relation to the carrier transport properties and amorphous structures.

Effects of drilling and stress release on hydraulic properties and porewater chemistry of crystalline rocks

The experimental verification of matrix diffusion in crystalline rocks largely relies on indirect methods performed in the laboratory. Such methods are prone to perturbations of the rock samples by collection and preparation and therefore the laboratory-derived transport properties and fluid composition might not represent in situ conditions. We investigated the effects induced by the drilling process and natural rock stress release by mass balance considerations and sensitivity analysis of analytical out-diffusion data obtained from originally saturated, large-sized drillcore material from two locations drilled using traced drilling fluid. For in situ stress-released drillcores of quartz-monzodiorite composition from the Aspo HRL, Sweden, tracer mass balance considerations and 1D and 2D diffusion modelling consistently indicated a contamination of <1% of the original pore water. This chemically disturbed zone extends to a maximum of 0.1 mm into the drillcore (61.8 mm x 180.1 mm) corresponding to about 0.66% of the total pore volume (0.77 vol.%). In contrast, the combined effects of stress release and the drilling process, which have influenced granodioritic drillcore material from 560 m below surface at Forsmark. Sweden, resulted in a maximum contamination of the derived porewater Cl(-) concentration of about 8%. The mechanically disturbed zone with modified diffusion properties covers the outermost similar to 6 mm of the drillcore (50 mm x 189 mm), whereas the chemically disturbed zone extends to a maximum of 0.3 mm based on mass balance considerations, and to 0.15 mm to 0.2 mm into the drillcore based on fitting the observed tracer data. This corresponds to a maximum of 2.4% of the total pore volume (0.62 vol.%) being affected by the drilling-fluid contamination. The proportion of rock volume affected initially by drilling fluid or subsequently with experiment water during the laboratory diffusion and re-saturation experiments depends on the size of the drillcore material and will become larger the smaller the sample used for the experiment. The results are further in support of matrix diffusion taking place in the undisturbed matrix of crystalline rocks at least in the cm range.

Non-destructive evaluation of carrier transport properties in CuInS2 and CuInSe2 thin films using photothermal deflection technique

Photothermal deflection technique (PTD) is a non-destructive tool for measuring the temperature distribution in and around a sample, due to various non-radiative decay processes occurring within the material. This tool was used to measure the carrier transport properties of CuInS2 and CuInSe2 thin films. Films with thickness <1 μm were prepared with different Cu/In ratios to vary the electrical properties. The surface recombination velocity was least for Cu-rich films (5×105 cm/s for CuInS2, 1×103 cm/s for CuInSe2), while stoichiometric films exhibited high mobility (0.6 cm2/V s for CuInS2, 32 cm2/V s for CuInSe2) and high minority carrier lifetime (0.35 μs for CuInS2, 12 μs for CuInSe2

On the statistical and transport properties of a non-dissipative Fermi-Ulam model

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)