[en] High Energy Ion Implantation (HEII) of both medium and light mass ions has been successfully applied for the surface micromachining of single crystal LiNbO₃ (LN) substrates. It has been demonstrated that the ion implantation process generates high differential etch rates in the LN implanted areas, when suitable implantation parameters, such as ion species, fluence and energy, are chosen. In particular, when traditional LN etching solutions are applied to suitably ion implanted regions, etch rates values up to three orders of magnitude higher than the typical etching rates of the virgin material, are registered. Further, the enhancement in the etching rate has been observed on x, y and z-cut single crystalline material, and, due to the physical nature of the implantation process, it is expected that it can be equivalently applied also to substrates with different crystallographic orientations. This technique, associated with standard photolithographic technologies, allows to generate in a fast and accurate way very high aspect ratio relief micrometric structures on LN single crystal surface. In this work a description of the developed technology is reported together with some examples of produced micromachined structures: in particular very precisely defined self sustaining suspended structures, such as beams and membranes, generated on LN substrates, are presented. The developed technology opens the way to actual three dimensional micromachining of LN single crystals substrates and, due to the peculiar properties characterising this material, (pyroelectric, electro-optic, acousto-optic, etc.), it allows the design and the production of complex integrated elements, characterised by micrometric features and suitable for the generation of advanced Micro Electro Optical Systems (MEOS).

[en] A study on LiNbO₃ crystal irradiation by pulsed KrF excimer laser beam is presented. The interaction with the 248 nm laser light modifies the material properties so that, when the irradiation is switched off, a time-periodic variation in the material reflectivity, depending on the irradiation conditions, was observed. This phenomenon can be explained in terms of the electro-optic effect induced by the buildup of internal electric fields since the compositional characterization, performed by the secondary ion mass spectrometry, showed no modification in the element concentration and the high resolution x-ray diffraction did not detect any structural deformation within the crystal

[en] The damage effects produced in the near-surface region of x-cut LiNbO₃ by low dose, high energy implantation of carbon, nitrogen, oxygen, and fluorine ions are investigated as a function of the dose and substrate temperature during the implant process. The damage profiles were obtained by the Rutherford backscattering RBS-channeling technique, whereas the compositional profiles were performed by secondary ion mass spectrometry. The experimental results showed that the mechanisms governing the damage formation at the surface are strongly connected to the interaction of defects produced when the electronic energy loss exceeds a given threshold close to 220 eV/A. In particular, we observed a damage pileup compatible with a growth of three-dimensional defect clusters

[en] In this work x-cut Lithium Niobate crystals were implanted with 0.5 MeV O ions (nuclear stopping regime), 5 MeV O ions (sub-threshold electronic stopping regime) and 12.5 MeV Ti ions (ion track regime) at the fluences required for the formation of a surface fully disordered layer. The damage depth profiles were determined by RBS-channeling. Wet etching was performed at room temperature in 50% HF:H₂O solution. The data indicated an exponential dependence of the etching rate on the damage concentration. Independently of the damage regime, once random level in the RBS-channeling spectra was attained we measured the same etching rate (50-100 nm/s) and the same volume expansion (∼10%) in all samples. These results indicate that the fully disordered layers obtained by electronic damage accumulation have the same chemical properties of those obtained by conventional nuclear damage accumulation and therefore they can be defined 'amorphous'. The impressive etching selectivity of ion implanted regions makes this process suitable for sub-micro machining of Lithium Niobate

[en] The damage induced by 5 MeV oxygen ion implantation in x-cut congruent LiNbO₃ has been investigated by Rutherford backscattering spectrometry channeling technique. The dynamics of the damage growth has been described by an analytical formula considering the separate contributions of nuclear and electronic energy deposition. It has been hypothesized that the nuclear damage provides the localization of the energy released to the electronic subsystem necessary for the conversion into atomic displacements. The strong influence of the preexisting defects on the damage pileup, foreseen by the analytical formula, has been experimentally verified by pre-implanting the samples with 500 keV oxygen ions. It has been shown that a subsequent 5 MeV oxygen implantation step gives rise to an impressive damage accumulation, eventually leading to the total amorphization of the surface, even at moderate fluences

[en] High energy implantation of medium-light elements such as oxygen and carbon was performed in X-cut LiNbO₃ single crystals in order to prepare high quality optical waveguides. The compositional and damage profiles, obtained by exploiting the secondary ion mass spectrometry and Rutherford back-scattering techniques respectively, were correlated to the structural properties measured by the high resolution X-ray diffraction. This study evidences the development of tensile strain induced by the ion implantation that can contribute to the decrease of the ordinary refractive index variation through the photo-elastic effect

[en] The assembly and testing of the components which make up a detector plane for the Leading Proton Spectrometer is described. The spectrometer, a part of the ZEUS detector, utilizes single-sided DC-coupled silicon strip detectors and custom VLSI front-end electronics for readout. (orig.)

[en] The damage formation by implantation of energetic (∼5 MeV) low Z ions (C, N, O, F) in LiNbO₃ has been investigated. The surface damage growth as a function of the fluence is consistent with a mechanism of nucleation and 3D growth of fully disordered clusters. It is possible to describe this behaviour by considering two processes: the first one is the direct generation of nuclear damage whereas the second one is the partial conversion of the electronic excitation into atomic displacements, mediated by the local concentration of defects. Within this simple scenario the damage evolution has been described by an analytical formula. This formula suggested that the existence of pre-damage in the surface region can boost the damage growth. This was demonstrated by introducing nuclear damage in the first 0.6 μm surface layer by 500 keV O implantation followed by a subsequent 5 MeV O implantation. The final surface damage is not the mere sum of the two implantation steps, but it is strongly enhanced by the interaction of the two damage mechanisms (nuclear and electronic) and it is in very good quantitative agreement with the proposed analytical formula. A strong non-linear dependence of the electronic damage formation cross-section on the stopping power was evidenced by repeating the same experiment with carbon ions

[en] A gas vertex detector, operated with dimethylether (DME) at atmospheric pressure, is presently being built for the ZEUS experiment at HERA. Its main design features, together with the performances of a prototype measured at various operating voltages, particle rates and geometrical conditions on a CERN Proton Synchrotron test beam, are presented. A spatial resolution down to 35 μm and an average wire efficiency of 96% have been achieved, for a 3 mm gas gap relative to each sense wire. (orig.)

[en] We show that the approximations used to extract the damage depth profiles from the RBS-channeling spectra of high energy ion implanted lithium niobate lead to incorrect results when two defective regions containing damage generated by electronic and nuclear energy deposition are produced. We demonstrate by high resolution X-ray diffraction analysis that the end-of-range defects formation is not influenced by the onset of different defects in the surface region and it is thus independent of the implantation energy. We propose universal curves, valid for ions Z ≤ 14, for the end-of-range defective fraction and the maximum strain as a function of the density of energy deposited by nuclear processes