A.P. Caricato

Poly-(3-hexylthiophene)/[6,6]-phenyl-C61-butyric-acid-methyl-ester bilayer deposition by matrix-assisted pulsed laser evaporation for organic photovoltaic applications

A poly-(3-hexylthiophene) (P3HT)/[6,6]-phenyl-C61-butyric-acid-methyl-ester (PCBM) bilayer structure has been realized by single step matrix-assisted pulsed laser evaporation (ss-MAPLE) technique using the same solvent for both the polymers under vacuum conditions. Our ss-MAPLE procedure allows the fabrication of polymeric multilayer device stacks, which are very difficult to realize with the conventional solvent assisted deposition methods. A proof of concept bilayer P3HT/PCBM solar cell based on ss-MAPLE deposition has been realized and characterized. This demonstration qualifies ss-MAPLE as a general and alternative technique for the implementation of polymeric materials in hetero-structure device technology.

Realistic absorption coefficient of ultrathin films

Both a theoretical algorithm and an experimental procedure are discussed of a new route to determine the absorption/scattering properties of thin films deposited on transparent substrates. Notably, the non-measurable contribution of the film–substrate interface is inherently accounted for. While the experimental procedure exploits only measurable spectra combined according to a very simple algorithm, the theoretical derivation does not require numerical handling of the acquired spectra or any assumption on the film homogeneity and substrate thickness. The film absorption response is estimated by subtracting the measured absorption spectrum of the bare substrate from that of the film on the substrate structure but in a non-straightforward way. In fact, an assumption about the absorption profile of the overall structure is introduced and a corrective factor accounting for the relative film-to-substrate thickness. The method is tested on films of a well known material (ITO) as a function of the film structural quality and influence of the film–substrate interface, both deliberately changed by thickness tuning and doping. Results are found fully consistent with information obtained by standard optical analysis and band gap values reported in the literature. Additionally, comparison with a conventional method demonstrates that our route is generally more accurate even if particularly suited for very thin films.

Low electrode induced optical losses in organic active single layer polyfluorene waveguides with two indium tin oxide electrodes deposited by pulsed laser deposition

We demonstrate that 20nm thick indium tin oxide (ITO) layers deposited by pulsed laser deposition present sheet resistance as low as 130Ω∕◻ and very uniform morphology, with an average roughness of about 0.4nm, and peak-to-valley roughness as low as 8.2nm. This good uniformity allowed us to realize a single layer polyfluorene active waveguide with both top and bottom ITO electrodes showing clear amplified spontaneous emission and electrode induced losses as low as 3.0cm−1. We investigated the effects of hole injection in the ASE intensity concluding that complete gain suppression due to polaron absorption would take place for current density of about 360mAcm−2.

TiO2 brookite nanostructured thin layer on magneto-optical surface plasmon resonance transductor for gas sensing applications

The sensing performance comparisons presented in this work were carried out by exploiting a suitable magneto-plasmonic sensor in both the traditional surface plasmon resonance configuration and the innovative magneto-optic surface plasmon resonance one. The particular multilayer transducer was functionalized with TiO2 Brookite nanorods layers deposited by matrix assisted pulsed laser evaporation, and its sensing capabilities were monitored in a controlled atmosphere towards different concentrations of volatile organic compounds mixed in dry air.

Very low roughness MAPLE-deposited films of a light emitting polymer: an alternative to spin coating

The matrix assisted pulsed laser evaporation (MAPLE) technique is emerging as an alternative route to conventional deposition methods of organic materials (solution-phase and thermal evaporation approaches). However, the high surface roughness of the films deposited by MAPLE makes this technique not compatible with applications in electronics and photonics. In this paper we report the deposition of MAPLE-films of a green light emitting polymer, commercially named ADS125GE, with remarkable low roughness values, down to about 10 nm at the thickness conventionally used in photonic devices (~40 nm). This issue is discussed as a function of polymer concentration, target-substrate distance and substrate rotation based on AFM topography images, roughness estimation and optical (absorption and luminescent) measurements. In addition we have fabricated an organic light emitting diode with this technique using the best deposition parameters which guarantee the lowest roughness. These results open the way to MAPLE applications in organic photonics and opto-electronics.

Nanoparticle and nanorod films deposited by matrix assisted pulsed laser evaporation

The promising results obtained with the MAPLE-deposition of nanostructured thin films, to be used in different fields, are reviewed. Nanoparticles (TiO2, SnO2, CdS) and nanorods (TiO2) with well defined dimensions were suspended in appropriate solvents (distilled water, toluene) with low concentration (1wt% or less). The solutions were flash frozen at the liquid nitrogen temperature to form the targets to be laser irradiated. The MAPLE process allowed a successful transfer from the target to rough and flat substrates, preserving the starting composition and crystalline phase of the nanostructures in a wide range of experimental conditions. In contrast, a careful choice of the laser fluence is mandatory to avoid shape modifications. Growth of metal nanoparticles with a low dispersion in size was also obtained by the MAPLE technique, starting from target solutions of a metallorganic element (AcPd) diluted in different solvents (acetone, diethyl ether). It seems that selecting the solvent with appropriate va...

Realistic absorption coefficient of each individual film in a multilayer architecture

A spectrophotometric strategy, termed multilayer-method (ML-method), is presented and discussed to realistically calculate the absorption coefficient of each individual layer embedded in multilayer architectures without reverse engineering, numerical refinements and assumptions about the layer homogeneity and thickness. The strategy extends in a non-straightforward way a consolidated route, already published by the authors and here termed basic-method, able to accurately characterize an absorbing film covering transparent substrates. The ML-method inherently accounts for non-measurable contribution of the interfaces (including multiple reflections), describes the specific film structure as determined by the multilayer architecture and used deposition approach and parameters, exploits simple mathematics, and has wide range of applicability (high-to-weak absorption regions, thick-to-ultrathin films). Reliability tests are performed on films and multilayers based on a well-known material (indium tin oxide) by deliberately changing the film structural quality through doping, thickness-tuning and underlying supporting-film. Results are found consistent with information obtained by standard (optical and structural) analysis, the basic-method and band gap values reported in the literature. The discussed example-applications demonstrate the ability of the ML-method to overcome the drawbacks commonly limiting an accurate description of multilayer architectures.

Realistic reflectance spectrum of thin films covering a transparent optically thick substrate

A spectrophotometric strategy is presented and discussed for calculating realistically the reflectance spectrum of an absorbing film deposited over a thick transparent or semi-transparent substrate. The developed route exploits simple mathematics, has wide range of applicability (high-to-weak absorption regions and thick-to-ultrathin films), rules out numerical and curve-fitting procedures as well as model-functions, inherently accounts for the non-measurable contribution of the film-substrate interface as well as substrate backside, and describes the film reflectance spectrum as determined by the experimental situation (deposition approach and parameters). The reliability of the method is tested on films of a well-known material (indium tin oxide) by deliberately changing film thickness and structural quality through doping. Results are found consistent with usual information yielded by reflectance, its inherent relationship with scattering processes and contributions to the measured total reflectance.

Graphitization of Diamond by Means of UV Laser Writing: A Transmission Electron Microscopy Study

A.Taurino, M. Catalano , M. De Feudis , A.P. Caricato , M. Martino , Q. Wang and M. J. Kim 1. CNR IMM, Institute for Microelectronics and Microsystems, Via Monteroni, Lecce, Italy. 2. Dep. of Materials Science and Engineering, Univ. of Texas at Dallas, Richardson, Texas, USA. 3. Department of Mathematics and Physics, University of Salento, Lecce, Italy. 4. INFN National Institute of Nuclear Physics, Lecce, Italy.