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In recent years, there has been a dramatic progress in the photonics field of disordered media, ranging from applications in solar collectors, photocatalyzers, random lasing, and other novel photonic devices, to investigations into fundamental topics, such as localization of light and other phenomena involving photon interactions. Anderson localization of light is an open researcher frontier, which has greatly attracted the attention of researchers in the past few decades. In this work, we study the transport of light in a strongly disordered optical medium composed by core-shell nanoparticles (TiO 2 cSilica) suspended in ethanol solution. We demonstrate the crossover from a diffusive transport to a localization transition regime as TiO 2 cSilica nanoparticle concentration is increased. A striking phenomenon of enhanced absorption, mainly near the input border, arises at the localization transition, from which an increase of refractive index was inferred. An increase of the density of localized states and absorption near the input border is reported when the incidence angle is increased. The specular reflection, measured for the photons that enter the sample, is considerably lower than the effective internal reflection undergone by the coherently backscattered photons in the exact opposite direction, indicating a nonreciprocal propagation of light (parity-symmetry breaking). A theoretical simulation, performed through random-matrix theory, agrees satisfactorily with the experimental results, showing the generality of this approach to address transport phenomena.

A new approach for electrical and thermal improvement of contacts between carbon nanostructures (multi-wall carbon nanotubes - MWCNTs and multi-layer graphene - MLG) and metal electrodes by localized laser heating is presented. The nanostructures were deposited over electrodes using the dielectrophoresis (DEP) technique. A focused laser beam was used for direct heating the samples in ambient atmosphere. The Raman spectroscopy was used to determine the process temperature by observations of the graphitic G-line downshift. In the laser annealing experiments, the G-line position was found first to downshift linearly with laser power indicating gradual heating of the sample proportional to the absorbed power. However, with increasing power the shift was found to saturate at levels that depend on the metal and the contact area. This saturation was attributed to gradual increase of the contact area and improvement of the thermal contacts between the nanostructures and metal electrode that can occur during sample heating. The maximum sample temperature in the beginning of the annealing process was always higher for MLG samples, due to smaller area of contact established between rigid multi-layer graphene and initially rough metal surface. The final result is the increased heat losses to the electrodes and, subsequently, the reduction of the samples temperature. The main advantage of this method, when compared with traditional and rapid thermal annealing, is that the thermal treatment is localized in a small pre-determined region, allowing individually controlled annealing process.

A characteristic feature near ∼255 nm has been revealed in the optical absorption spectra of nano-graphite aqueous suspensions. This is a broad absorption peak, which is due to the surface plasmon resonance in nanographite particles. The peak shape and intensity depend on the structural quality and aggregate state of onion-like nanographite particles in suspension.

There has been a growing interest in disordered optical media in recent years due to their potential applications in solar collectors, random lasers, light confinement, and other advanced photonic functions. This paper studies the transport of light for different incidence angles in a strongly disordered optical medium composed of core-shell TiO2@Silica nanoparticles suspended in an ethanol solution. A decrease of optical conductance and an increase of absorption near the input border are reported when the incidence angle increases. The specular reflection, measured for the photons that enter the sample, is lower than the effective internal reflection undergone by the coherently backscattered photons in the exact opposite direction, indicating a nonreciprocal propagation of light. This study represents a novel approach in order to understand the complex physics involved at the phase transition to localization.

The conditions of formation of deep periodic trenches by photoelectrochemical etching of n-Si (100) with linear seeds on the surface are analyzed. Criteria for the proper choice of the period of seed grooves and the etching current density in relation to the doping level of the substrate are formulated. Corrugation of walls is a characteristic feature of the obtained structures; this corrugation is caused by traces of merged macropores. Atomic-force microscopy is used to study roughness of the side-walls in relation to the etching conditions; the current density at which one can obtain the smoothest side-walls is determined. The roughness of the side walls in structures with periods of 7 and 9 μm on Si with the resistivity of 15 Ω cm amounts to ∼40 nm. It is shown that additional treatment of the structures in alkaline solutions can decrease the side-wall roughness by approximately a factor of 2.

Made available in DSpace on 2015-10-21T20:15:17Z (GMT). No. of bitstreams: 0 Previous issue date: 2015-06-23. Added 1 bitstream(s) on 2015-10-22T09:48:15Z : No. of bitstreams: 1 WOS000356663700001.pdf: 1328411 bytes, checksum: 2d01feaf14a69ea302c9623eac68234d (MD5) Graphene, in single layer or multi-layer forms, holds great promise for future electronics and high-temperature applications. Resistance to oxidation, an important property for high-temperature applications, has not yet been extensively investigated. Controlled thinning of multi-layer graphene (MLG), e.g., by plasma or laser processing is another challenge, since the existing methods produce non-uniform thinning or introduce undesirable defects in the basal plane. We report here that heating to extremely high temperatures (exceeding 2000 K) and controllable layer-by-layer burning (thinning) can be achieved by low-power laser processing of suspended high-quality MLG in air in "cold-wall" reactor configuration. In contrast, localized laser heating of supported samples results in non-uniform graphene burning at much higher rates. Fully atomistic molecular dynamics simulations were also performed to reveal details of oxidation mechanisms leading to uniform layer-by-layer graphene gasification. The extraordinary resistance of MLG to oxidation paves the way to novel high-temperature applications as continuum light source or scaffolding material. Univ Estadual Campinas, Ctr Semicond Components, BR-13083870 Campinas, SP, Brazil Univ Estadual Campinas, Inst Fis Gleb Wataghin, BR-13083970 Campinas, SP, Brazil UNESP, Univ Estadual Paulista, Dept Fis, IGCE, BR-13506900 Rio Claro, SP, Brazil UNESP, Univ Estadual Paulista, Dept Fis, IGCE, BR-13506900 Rio Claro, SP, Brazil

We present technique of obtaining complex hybrid structures combining the multi-walled carbon nanotubes or multi-layer graphene and luminescent hydrophobic semiconductor core/shell quantum dots CdSe/ZnS. As a result, a formation of quantum dot decorated carbon nanotubes and graphene films is evidenced by 2D microluminescence and micro-Raman mapping of quantum dots and nanocarbons, respectively, where a spatial correlation between the luminescence and Raman signals is found.

We investigate electrical photoresponse of multilayer graphene decorated with CdSe/ZnS quantum dots. Itwas found that photoresponse of these hybrid structures depends on quantum dot photoluminescence quantumyield. We demonstrate inuence of external factors (light exposure and treatment with ammonia vapors) onphotoluminescence quantum yield of quantum dots and electrical photoresponse of the hybrid structures.Keywords: Graphene, quantum dots, hybrid structures, photocurrent, ammonia sensor 1. INTRODUCTION Hybrid structures based on graphene and semiconductor quantum dots is a hot research spot during the lastyears. 1{5 Such structures do not combine unique properties of graphene and quantum dots only, but possessemergent properties. For example, matching remarkable electronic properties of graphene 6,7 and outstandingoptical properties of semiconductor quantum dots (QD) 8{10 allows formation of hybrid structures with enhancedphotoresponse. 5 Such structures are promising as light harvesting systems

The quality of thermal contacts between a graphene flake and metal electrodes was shown to improve strongly by laser annealing. The improvement of thermal contacts to initially rough metal electrodes is attributed to local melting of the metal surface under laser heating, and increased area of real metal-graphene contact. Improvement of the thermal contacts was observed also between multi-layer graphene and silicon oxide surface, with more efficient heat transfer from graphene as compared with the graphene-metal case.

We report on the enhancement of the electrical photoresponse in a hybrid structure composed of multi-layer graphene flakes covered by a layer of CdSe/ZnS quantum dots (QDs) and placed between metal electrodes. The rate of the photoexcitation energy transfer from QDs to graphene, (0.5–2)×109 s−1 which controls the photoelectrical response of the structure, was found from the analysis of photoluminescence intensities and decay times for QDs in solution, on a bare glass substrate and on the surface of multilayer graphene, and in the presence of ammonia vapors.

Lenses with variable focus may find extensive applications in industrial production of optical devices. The variable-focus lenses considered in this work may be used most efficiently in laser systems wherein the radiation initially has linear polarization. Consideration is being given to the principles of operation of switchable lenses. The aberration of such lenses is analyzed, the data on control elements having a large angular aperture are presented, and a practical example of a variable-focus lens is given.© (1992) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.