The optical response of 200nm thick La0.7Sr0.3MnO(3−δ) films, deposited by pulsed laser deposition on amorphous silica substrates heated at nearly 600°C, under different oxygen pressures (0.1Pa, ...0.5Pa, 1Pa, 5Pa and 10Pa), is reported. The effects of the oxygen non-stoichiometry are investigated at room temperature dealing with the absorption coefficient and the Tauc's plot method rather than conventional optical conductivity. The absorption curves are evaluated by an algorithm able to realistically describe the behavior of thin films without exploiting numerical extrapolations or simplified theoretical models or ab-initio calculations. Optical features, tunable by the growth oxygen pressure, are discussed based on the known theoretical and experimental scenario.
•Overview of the La0.7Sr0.3MnO3 basics to highlight basic questions to be assessed.•Optical analysis by the absorption coefficient rather than optical conductivity.•Realistic absorption response that avoids numerical refinements and simulations.•Analysis of the role of oxygen vacancies in tuning the electronic dispersion.•First investigation of direct and indirect transitions by the Tauc's plot.
The PADME beam line Monte Carlo simulation Bossi, F.; Branchini, P.; Buonomo, B. ...
The journal of high energy physics,
09/2022, Letnik:
2022, Številka:
9
Journal Article
Recenzirano
Odprti dostop
A
bstract
The PADME experiment at the DAΦNE Beam-Test Facility (BTF) of the INFN Laboratory of Frascati is designed to search for invisible decays of dark sector particles produced in ...electron-positron annihilation events with a positron beam and a thin fixed target, by measuring the missing mass of single-photon final states. The presence of backgrounds originating from beam halo particles can significantly reduce the sensitivity of the experiment. To thoroughly understand the origin of the beam background contribution, a detailed G
eant
4-based Monte Carlo simulation has been developed, containing a full description of the detector together with the beam line and its optical elements. This simulation allows the full interactions of each particle to be described, both during beam line transport and during detection, a possibility which represents an innovative way to obtain reliable background predictions.
The surface of a detector grade CVD polycrystalline diamond sample (5×5×0.05mm3) was irradiated by an ArF excimer laser (λ=193nm, τ=20ns) to produce graphitic conductive layers.
In particular, two ...sets of four parallel graphitic strip-like contacts, with 1mm pitch, were created along the whole sample on the top and on the rear surfaces of the sample respectively. The two series of stripes lie normally to each other. Such a grid allows to obtain a segmented all-carbon device capable of giving bi-dimensional information on particle detection processes in nuclear applications.
Afterwards, an extensive characterization of the samples was performed: SEM and micro-Raman investigations to study the morphological and structural evolution of the irradiated areas, EDS measurements to individuate any absorption phenomena from environment associated to laser treatment, and nanoindentation mapping to understand how the hard-soft transformation occurred depending on the locally transferred energy. Finally, current-voltage analyses were carried out checking the ohmic behavior of the diamond-graphite contact. By comparing the results of the different characterization analyses, a strong periodicity of the modified surface properties was found, confirming the reliability and reproducibility of the laser-induced graphitization process.
The results demonstrate that the laser-writing technique is a good and fast solution to produce graphitic contacts on diamond surface and therefore represents a promising way to fabricate segmented all-carbon devices.
Hardness and reduced elastic modulus mappings of a graphitic strip induced by laser on diamond surface. Display omitted
•The manufacturing of strip-like graphitic contacts on diamond surface by laser-writing was carried out.•The contacts were created on diamond surface of both sides, with orthogonal orientation, to obtain a segmented all-carbon device capable to give bi-dimensional information during detection processes.•SEM and micro-Raman Spectroscopy analyzes allowed understanding the physical evolution of the graphitization process, and how the morphological and structural changes depend on laser processing.•Phenomena of chemical modifications were found by EDS: oxidation reactions were present on all the irradiated areas, with increasing intensity values for the most damaged zones.•Nano-indentation investigations were performed showing that hard-soft transformation occurred depending on the locally deposited energy and in agreement with the changes of hybridization (sp3→sp2) of carbon atoms.•Current-voltage analyses allowed to verify the ohmic behavior of the contacts and to evaluate the resistivity values of every strip, which range from 2.5 × 10-5 Ωm up to 3 × 10-5 Ωm.
Matrix assisted pulsed laser evaporation (MAPLE) is a new promising laser-based technique thought for polymer or biomaterial thin films deposition. In this work, the MAPLE technique has been used for ...the deposition of titania (TiO2) nanoparticle thin films to be used for gas sensor applications. For this purpose, an aqueous solution of TiO2 nanoparticles, synthesized by a novel chemical route, was frozen at the liquid nitrogen temperature and introduced in a vacuum chamber to be irradiated with a pulsed ArF excimer laser. The volatile solvent was pumped away while the TiO2 nanoparticles were deposited on Si and Al2O3 substrates. A uniform distribution of TiO2 nanoparticles with an average size of about 10nm was obtained, as demonstrated by high resolution scanning electron microscopy (SEM-FEG) inspection. We realized gas-sensing devices based on resistive transduction mechanism by using the TiO2 nanoparticles thin films deposited by the MAPLE technique onto suitable rough alumina substrates equipped with interdigitated electrical contacts (IDC) and heating elements. Electrical characterization measurements were carried out in controlled environment. The results of the gas-sensing tests towards low concentrations of ethanol and acetone vapors are reported. Typical gas sensor parameters (gas responses, response/recovery time, sensitivity, and low detection limit) towards ethanol were extracted and compared with to the corresponding parameters towards acetone.
Diamond-Like Carbon for the Fast Timing MPGD Colaleo, A.; De Robertis, G.; Licciulli, F. ...
Journal of physics. Conference series,
04/2020, Letnik:
1498, Številka:
1
Journal Article
Recenzirano
Odprti dostop
The present generation of Micro-Pattern Gaseous Detectors (MPGDs) are radiation hard detectors, capable of detecting effciently particle rates of several MHz/cm2, while exhibiting good spatial ...resolution (≤ 50 µm) and modest time resolution of 5-10 ns, which satisfies the current generation of experiments (High Luminosity LHC upgrades of CMS and ATLAS) but it is not sufficient for bunch crossing identification of fast timing systems at FCC-hh. Thanks to the application of thin resistive films such as Diamond-Like Carbon (DLC) a new detector concept was conceived: Fast Timing MPGD (FTM). In the FTM the drift volume of the detector has been divided in several layers each with their own amplification structure. The use of resistive electrodes makes the entire structure transparent for electrical signals. After some first initial encouraging results, progress has been slowed down due to problems with the wet-etching of DLC-coated polyimide foils. To solve these problems a more in-depth knowledge of the internal stress of the DLC together with the DLC-polyimide adhesion is required. We will report on the production of DLC films produced in Italy with Ion Beam Sputtering and Pulsed Laser Deposition, where we are searching to improve the adhesion of the thin DLC films, combined with a very high uniformity of the resistivity values.
In this work graphitic structures were fabricated on high quality polycrystalline CVD diamond by using a UV laser beam (λ=193nm). Two different kinds of structures were realized on diamond to study ...the evolution from diamond to graphite at different irradiation conditions (spot like structures) and to study their electrical transport properties (strip like structures). The graphitic structures were characterized structurally and morphologically by micro-Raman spectroscopy and atomic force microscopy. The electrical properties were evaluated using the transmission line model. Finally, a full carbon detector was built and tested showing good nuclear detection properties.
When a diamond graphitization process is induced, for example by excimer laser which irradiates the diamond surface, two phenomena occur: diamond graphititization and graphite ablation. The figure shows the physical evolution of the average height of the graphitic spots obtained after laser-diamond interaction, at laser fluence of 5J/cm2, with respect to the number of pulses. The measurements were obtained by AFM investigations (zero level refers flat unirradiated diamond surface). For one and two pulses it dominates a swelling phenomenon which represents the diamond graphitization process (the swelling is due to different mass density between diamond and graphite phases), while for four and eight pulses the graphite ablation dominates generating crates with increasing depth. Display omitted
•The physical evolution of the diamond graphitization process was studied.•The characterizations of graphitization and ablation processes of diamond were made by AFM and micro-Raman investigations.•The realization and optimization of ohmic graphitic contacts on diamond surface were done.•The response of full carbon detector to an ionizing particle and estimation of its CCE were reported.
PDF
