Analysis and optimization of propagation losses in LiNbO3 optical waveguides produced by swift heavy-ion irradiation

The propagation losses (PL) of lithium niobate optical planar waveguides fabricated by swift heavy-ion irradiation (SHI), an alternative to conventional ion implantation, have been investigated and optimized. For waveguide fabrication, congruently melting LiNbO3 substrates were irradiated with F ions at 20 MeV or 30 MeV and fluences in the range 1013–1014 cm−2. The influence of the temperature and time of post-irradiation annealing treatments has been systematically studied. Optimum propagation losses lower than 0.5 dB/cm have been obtained for both TE and TM modes, after a two-stage annealing treatment at 350 and 375∘C. Possible loss mechanisms are discussed

Change and continuity in managerialism: 100 years of administrative history at the International Museum of Ceramics in Faenza

This paper offers a long-term perspective on the debate on managerial transformations in the public sector: how public sector organisations actually arrived at such changes, what processes, discourses and practices are transformed and how. This is investigated through archival research and a longitudinal analysis of 100 years of the administrative history of an Italian museum. Taking a historical perspective allows us to account for organisational changes that occurred over time, including major reforms in the governance structure and the dynamics of some core managerial features. Such an approach enables a more in-depth, empirically grounded and historically aware discussion on the so-called rise of managerial issues in the public secto

Recrystallization of amorphous nano-tracks and uniform layers generated by swift-ion-beam irradiation in lithium niobate.

The thermal annealing of amorphous tracks of nanometer-size diameter generated in lithium niobate (LiNbO3) by Bromine ions at 45 MeV, i.e., in the electronic stopping regime, has been investigated by RBS/C spectrometry in the temperature range from 250°C to 350°C. Relatively low fluences have been used (<1012 cm−2) to produce isolated tracks. However, the possible effect of track overlapping has been investigated by varying the fluence between 3×1011 cm−2 and 1012 cm−2. The annealing process follows a two-step kinetics. In a first stage (I) the track radius decreases linearly with the annealing time. It obeys an Arrhenius-type dependence on annealing temperature with activation energy around 1.5 eV. The second stage (II) operates after the track radius has decreased down to around 2.5 nm and shows a much lower radial velocity. The data for stage I appear consistent with a solid-phase epitaxial process that yields a constant recrystallization rate at the amorphous-crystalline boundary. HRTEM has been used to monitor the existence and the size of the annealed isolated tracks in the second stage. On the other hand, the thermal annealing of homogeneous (buried) amorphous layers has been investigated within the same temperature range, on samples irradiated with Fluorine at 20 MeV and fluences of ∼1014 cm−2. Optical techniques are very suitable for this case and have been used to monitor the recrystallization of the layers. The annealing process induces a displacement of the crystalline-amorphous boundary that is also linear with annealing time, and the recrystallization rates are consistent with those measured for tracks. The comparison of these data with those previously obtained for the heavily damaged (amorphous) layers produced by elastic nuclear collisions is summarily discussed

Del restauro di tre lapidi con epigrafe di pietra calcarea risalenti ai secoli XV e XVI

Storia critica delle indagini conservative e dell'intervento di restauro di tre lapidi riferibili ai secoli XV e XVI conservate nel Museo Civico di mirandola

A 6-18 GHz GaAs multifunctional chip for transmit/receive modules

In this contribution the development, design, fabrication and test of a highly integrated broadband multifunctional chip is presented. The MMIC covers the C-, X-And Ku-Band and it is suitable for applications in high performance Transmit/Receive Modules. In less than 26 mm2, the MMIC embeds several T/R switches, low noise/medium power amplifiers, a stepped phase shifter and analog/digital attenuators in order to perform the RF signal routing and phase/amplitude conditioning. Besides, an embedded serial-to-parallel converter drives the phase shifter and the digital attenuator leading to a reduction in complexity of the digital control interfac

A 6-18 GHz GaAs multifunctional chip for transmit/receive modules

In this contribution the development, design, fabrication and test of a highly integrated broadband multifunctional chip is presented. The MMIC covers the C-, X-and Ku- Band and it is suitable for applications in high performance Transmit/Receive Modules. In less than 26 mm 2 , the MMIC embeds several T/R switches, low noise/medium power amplifiers, a stepped phase shifter and analog/digital attenuators in order to perform the RF signal routing and phase/amplitude conditioning. Besides, an embedded serial-to-parallel converter drives the phase shifter and the digital attenuator leading to a reduction in complexity of the digital control interfac

NATIVE OXIDES BEHAVIOR DURING PULSED LASER IRRADIATION OF GaAs

Nous avons utilisé des techniques d'analyses nucléaires et de spectrométrie de masse d'ions secondaires pour étudier le comportement d'oxydes natifs de GaAs enrichis à l'18O et irradiés sous vide au moyen d'un laser à Rubis déclenché. Nous avons examiné l'incorporation d'16O, l'incorporation et les pertes d'18O ainsi que le déplacement des cations As et Ga hors des sites du réseau en fonction de la densité d'énergie du faisceau laser. Nos résultats démontrent qu'il est nécessaire d'irradier avec une densité d'énergie de l'ordre de 0,8 J/cm2, afin d'éliminer complètement les oxydes de surface. Toutefois, avant élimination complète, nous observons une dissolution partielle de ces oxydes dans le matériau liquide sous-jacent, ce qui a pour effet d'induire un important piégeage d'oxygène dans les couches resolidifiées. Nous observons de plus que la surface passe de façon continue d'un état riche en Ga à un état riche en As, tandis que la densité d'énergie du faisceau laser croît de 0,4 J/cm2 à 1 J/cm2.Nuclear Microanalysis and Secondary Ion Mass Spectroscopy have been used to study the behavior of GaAs 18O enriched native oxides irradiated with a pulsed Ruby laser under vacuum. We have analyzed 16O incorporation, 18O losses and incorporation and Ga and As atoms out of crystallographic sites as a function of laser energy density. Our results demonstrate that an energy density of 0.8 J/cm2 is needed to completely remove the native oxides. However, before complete evaporation, part of these oxides are dissolved in the layer melted by the laser pulse, leading to oxygen trapping in the resolidified material. We also find that the surface composition varies continuously from Ga rich to As rich when the laser energy density is raised from 0.4 J/cm2 up to 1 3/cm2

EFFECT OF OXYGEN PRESSURE ON OXYGEN INCORPORATION IN Si AND Ga As DURING Q SWITCHED LASER IRRADIATION

Nous avons étudié l'incorporation d'oxygène et sa relation avec la stabilité de l'oxyde de surface dans des échantillons d'Arseniure de Gallium et de silicium, soumis à des irradiations laser pulsées (≈ 15 ns) intenses (≈ 1 J/cm2), dans le visible, sous fortes pressions d'oxygène. A cet effet, nous avons utilisé la microanalyse nucléaire (rétrodiffusion, réactions nucléaires, canalisation) et des techniques de traçage isotopique à l'18O. Dans le cas de Ga As il existe un seuil de densité d'énergie (Eth ≥ ~ 1.1 J/cm2) au-dessus duquel se produit une forte incorporation d'oxygène. Cette incorporation est pratiquement proportionnelle à la pression du gaz. Des résultats similaires sont observés pour Si, mais dans ce cas la reproductivité est mauvaise. Le rôle de l'oxyde de surface a été mis en évidence en étudiant des échantillons recouverts d'une mince couche d'oxyde enrichie en 18O (= 100 Å), formée par oxydation anodique. On constate dans le cas de Ga As une importante perte d'18O pour des irradiations au-dessus du seuil Eth correspondant à l'incorporation. La relation entre cette dernière et la destruction de l'oxyde de surface est discutée.Nuclear microanalysis (R.B.S., Nuclear reactions, channeling) combined with 18O tracing techniques have been used to study oxygen incorporation and native oxide stability for Ga As and Si submitted to intense pulse laser irradiation under high oxygen pressure (pulse duration = 15 ns of either Ruby or frequency doubled Nd:YAG laser). We have found an energy threshold for Ga As (Eth ≥ ~ 1.1 J/cm2) above which an important oxygen uptake is observed during laser irradiation. The oxygen incorporation for pulse laser energy density E > Eth is a quasi linear function of oxygen pressure. Similar results have been found for Si although an important scattering in experimental results is observed. The role of native oxide films has been studied by using samples covered with thin (~ 100 Å) 18O enriched surface oxide layers. We have found (for Ga As) that for E > Eth 18O is lost. The possible relation between the oxygen uptake (16O) from gas phase and the loss of native oxide is discussed