Flexible hybrid nanostructures for applications as ultraviolet radiation protection optical filters

The escalating applications of ultraviolet light, specifically in the UVA and UVB part of the spectrum, in medicine, cosmetics, or for industrial and commercial purposes in general demand deeper studies of the hazards involved in the use of this type of electromagnetic radiation as well as further research in the development of new materials for selectively protecting against it. It is well-known that UV radiation causes damage to organic materials like plastics, woods, or polymers, among others. In general, the formation of free radicals, due to light absorption induced chemical reactions, results in subsequent polymer photodegradation. Regarding the effect on human tissue, there is a vast and growing literature regarding the harmful effects of ultraviolet radiation on the skin, as more epidemiologic and basic research continues to illustrate the impact of sun exposure and other sources of UV radiation upon the appearance of cutaneous neoplasm and a variety of photosensitive dermatoses or skin cancer. Films used for UV blocking can be classified according to the physical mechanism responsible for the protection effect, namely, optical absorption or reflection. This fundamental difference determines that a completely diverse materials design will have to be used to achieve control over spectral selectivity. From a different perspective, when reflection, rather than absorption, of UV wavelengths is sought after, more complex multilayered architectures must be employed, so that interference effects can give rise to the desired blocking effect. In this context, the development of polymer films that act as shields against ultraviolet (UV) radiation constitutes nowadays an active and interesting field of research, since they could be used as adaptable coatings for a wide variety of UV sensitive environments. The main objective of this thesis is the development of nanoparticle based flexible structures with photonic crystal properties that shield against UV radiation through optical reflection phenomena. The suggested approach will allow to accurately select the range of wavelengths blocked. This represents a much more efficient alternative to UV absorbing compounds, whose protection mechanism gives rise to secondary undesirable chemical reactions with the consequent photodegradation of these materials. Most of the mentioned drawbacks could be overcome with the use of the sheets whose evaluation in a real system, protecting epithelial cells from UV radiation, will be provided here. The versatility of the proposed photonic structures, due to their flexibility, transferability and adaptability to all kinds of substrates, enables them for interesting applications as UV optical filters. First of all, TiO2, ZrO2, Nb2O5 nanoparticles were successfully synthesized as suitable building blocks for one dimensional photonic crystals. Rigid coatings and flexible self-standing films were designed to be capable of efficiently protecting against UV radiation in selected wavelength ranges entirely through optical reflection phenomena. It was demonstrated that these films may equal or outperform layers of similar thickness made of purely absorbing materials in terms of the degree of radiation protection achieved

Form factors of boundary exponential operators in the sinh-Gordon model

Using the recently introduced boundary form factor bootstrap equations, the form factors of boundary exponential operators in the sinh-Gordon model are constructed. The ultraviolet scaling dimension and the normalization of these operators are checked against previously known results. The construction presented in this paper can be applied to determine form factors of relevant primary boundary operators in general integrable boundary quantum field theories.Comment: 22 pages, LaTeX2e fil

Higher particle form factors of branch point twist fields in integrable quantum field theories

In this paper we compute higher particle form factors of branch point twist fields. These fields were first described in the context of massive 1+1-dimensional integrable quantum field theories and their correlation functions are related to the bi-partite entanglement entropy. We find analytic expressions for some form factors and check those expressions for consistency, mainly by evaluating the conformal dimension of the corresponding twist field in the underlying conformal field theory. We find that solutions to the form factor equations are not unique so that various techniques need to be used to identify those corresponding to the branch point twist field we are interested in. The models for which we carry out our study are characterized by staircase patterns of various physical quantities as functions of the energy scale. As the latter is varied, the beta-function associated to these theories comes close to vanishing at several points between the deep infrared and deep ultraviolet regimes. In other words, renormalisation group flows approach the vicinity of various critical points before ultimately reaching the ultraviolet fixed point. This feature provides an optimal way of checking the consistency of higher particle form factor solutions, as the changes on the conformal dimension of the twist field at various energy scales can only be accounted for by considering higher particle form factor contributions to the expansion of certain correlation functions.Comment: 25 pages, 4 figures; v2 contains small correction

Boundary form factors of the sinh-Gordon model with Dirichlet boundary conditions at the self-dual point

In this manuscript we present a detailed investigation of the form factors of boundary fields of the sinh-Gordon model with a particular type of Dirichlet boundary condition, corresponding to zero value of the sinh-Gordon field at the boundary, at the self-dual point. We follow for this the boundary form factor program recently proposed by Z. Bajnok, L. Palla and G. Takaks in hep-th/0603171, extending the analysis of the boundary sinh-Gordon model initiated there. The main result of the paper is a conjecture for the structure of all n-particle form factors of two particular boundary operators in terms of elementary symmetric polynomials in certain functions of the rapidity variables. In addition, form factors of boundary "descendant" fields have been constructedComment: 14 pages LaTex. Version to appear in J. Phys.

Minimum Conductivity and Evidence for Phase Transitions in Ultra-clean Bilayer Graphene

Bilayer graphene (BLG) at the charge neutrality point (CNP) is strongly susceptible to electronic interactions, and expected to undergo a phase transition into a state with spontaneous broken symmetries. By systematically investigating a large number of singly- and doubly-gated bilayer graphene (BLG) devices, we show that an insulating state appears only in devices with high mobility and low extrinsic doping. This insulating state has an associated transition temperature Tc~5K and an energy gap of ~3 meV, thus strongly suggesting a gapped broken symmetry state that is destroyed by very weak disorder. The transition to the intrinsic broken symmetry state can be tuned by disorder, out-of-plane electric field, or carrier density

Vertically aligned carbon nanotubes for microelectrode arrays applications

In this work a methodology to fabricate carbon nanotube based electrodes using plasma enhanced chemical vapour deposition has been explored and defined. The final integrated microelectrode based devices should present specific properties that make them suitable for microelectrode arrays applications. The methodology studied has been focused on the preparation of highly regular and dense vertically aligned carbon nanotube (VACNT) mat compatible with the standard lithography used for microelectrode arrays technology

Form factors of boundary fields for A(2)-affine Toda field theory

In this paper we carry out the boundary form factor program for the A(2)-affine Toda field theory at the self-dual point. The latter is an integrable model consisting of a pair of particles which are conjugated to each other and possessing two bound states resulting from the scattering processes 1 +1 -> 2 and 2+2-> 1. We obtain solutions up to four particle form factors for two families of fields which can be identified with spinless and spin-1 fields of the bulk theory. Previously known as well as new bulk form factor solutions are obtained as a particular limit of ours. Minimal solutions of the boundary form factor equations for all A(n)-affine Toda field theories are given, which will serve as starting point for a generalisation of our results to higher rank algebras.Comment: 24 pages LaTeX, 1 figur

Thermodynamic Bethe ansatz for the AII sigma-models

We derive thermodynamic Bethe ansatz equations describing the vacuum energy of the SU(2N)/Sp(N) nonlinear sigma model on a cylinder geometry. The starting points are the recently-proposed amplitudes for the scattering among the physical, massive excitations of the theory. The analysis fully confirms the correctness of the S-matrix. We also derive closed sets of functional relations for the pseudoenergies (Y-systems). These relations are shown to be the k-->infinity limit of the Sp(k+1)-related systems studied some years ago by Kuniba and Nakanishi in the framework of lattice models.Comment: 11 pages, 1 figure, Latex 2e, uses amssymb, graphicx. v2: typos correcte

Exact form factors for the scaling Z{N}-Ising and the affine A{N-1}-Toda quantum field theories

Previous results on form factors for the scaling Ising and the sinh-Gordon models are extended to general $Z_{N}$-Ising and affine $A_{N-1}$-Toda quantum field theories. In particular result for order, disorder parameters and para-fermi fields $\sigma_{Q}(x), \mu_{\tilde{Q}}(x)$ and $\psi_{Q}(x)$ are presented for the $Z_{N}$-model. For the $A_{N-1}$-Toda model all form factors for exponentials of the Toda fields are proposed. The quantum field equation of motion is proved and the mass and wave function renormalization are calculated exactly.Comment: Latex, 11 page

Bi-partite entanglement entropy in integrable models with backscattering

In this paper we generalise the main result of a recent work by J. L. Cardy and the present authors concerning the bi-partite entanglement entropy between a connected region and its complement. There the expression of the leading order correction to saturation in the large distance regime was obtained for integrable quantum field theories possessing diagonal scattering matrices. It was observed to depend only on the mass spectrum of the model and not on the specific structure of the diagonal scattering matrix. Here we extend that result to integrable models with backscattering (i.e. with non-diagonal scattering matrices). We use again the replica method, which connects the entanglement entropy to partition functions on Riemann surfaces with two branch points. Our main conclusion is that the mentioned infrared correction takes exactly the same form for theories with and without backscattering. In order to give further support to this result, we provide a detailed analysis in the sine-Gordon model in the coupling regime in which no bound states (breathers) occur. As a consequence, we obtain the leading correction to the sine-Gordon partition function on a Riemann surface in the large distance regime. Observations are made concerning the limit of large number of sheets.Comment: 22 pages, 2 figure