D. Vincenzi

Gas sensing through thick film technology

Abstract We report in our research on semiconductor-based sensing layers deposited via thick-film technique. Particular focus was devoted to achieve nanosized films through proper processing and to study their morphological and structural features. Nanosized powders were prepared by sol–gel method or laser-assisted spray pyrolysis. We also considered some techniques to maintain the stability of a nanostructure for long-term usage of the sensing layers. We detailed the preparation of screen printing pastes suitable for gas sensing application. Implementation of the sensing film on a low-power-consumption micromachined hotplate has also been addressed. The performance of such devices is presented and compared to that of conventional units.

Experimental study for the feasibility of a crystalline undulator

We present an idea for creation of a crystalline undulator and report its first realization. One face of a silicon crystal was given periodic microscratches (grooves) by means of a diamond blade. The x-ray tests of the crystal deformation due to a given periodic pattern of surface scratches have shown that a sinusoidal-like shape is observed on both the scratched surface and the opposite (unscratched) face of the crystal; that is, a periodic sinusoidal-like deformation goes through the bulk of the crystal. This opens up the possibility for experiments with high-energy particles channeled in a crystalline undulator, a novel compact source of radiation.

Shaping of silicon crystals for channelling experiments through anisotropic chemical etching

We present an idea and its development to realize crystals for channelling experiments, which result in significant improvement of the crystal quality with respect to the traditional methods of fabrication. The technique relies on non-conventional usage of the established technique of the anisotropic etching of silicon in micro-machining. Morphological and structural analyses were carried out through electron and scanning-probe microscopy to show that the crystal exhibited flat surfaces with atomically sharp termination, i.e. no appreciable surface damage was induced by the preparation. Thereby, the crystal meets the stringent requirements that are demanded for operation with high-energy beams and in particular for halo collimation in modern hadron colliders.

Development of a low-power thick-film gas sensor deposited by screen-printing technique onto a micromachined hotplate

Abstract We report on the design, implementation and characterisation of a thick-film gas sensor deposited for the first time by screen-printing technique onto a micromachined hotplate, the microheater maintains a film temperature as high as 400°C with 2 was achieved by computer-aided screen-printing. The films were then fired through the microheater itself to guarantee thermodynamic stability for long time exploitation. The response of the device to CO, CH 4 and NO 2 at concentrations typical for indoor and outdoor applications was recorded by measuring the film resistance through ultra high impedance CMOS circuit.

Crystal deflector for highly efficient channeling extraction of a proton beam from accelerators

The design and manufacturing details of a new crystal deflector for proton beams are reported. The technique allows one to manufacture a very short deflector along the beam direction (2 mm). Thanks to that, multiple encounters of circulating particles with the crystal are possible with a reduced probability of multiple scattering and nuclear interactions per encounter. Thus, drastic increase in efficiency for particle extraction out of the accelerator was attained (85%) on a 70 GeV proton beam. We show the characteristics of the crystal deflector and the technology behind it.

Low-power thick-film gas sensor obtained by a combination of screen printing and micromachining techniques

Abstract A novel prototype of low-power thick-film gas sensor deposited by screen-printing onto a micromachined hotplate is presented. The micro-heater is designed to maintain a film temperature of 400°C with less than 30 mW of input power. The fabrication process involves a combination of standard, VLSI-compatible, micromachining procedures and computer-aided screen-printing. A dielectric membrane of Si 3 N 4 and SiO 2 has been obtained with an embedded poly-Si resistor acting as a heating element. The bonding pad and contacts have been realised by a Ti/TiN/Cr/Au structure and the sensing film has been deposited by a screen-printing technique. Here follows a characterisation of a device, based on SnO 2 sensing film, at working conditions together with the response curve for CH 4 and NO 2 . We will also address some important improvements to the micro-hotplate structure, which leads to an increased flexibility of the device.

Crystal undulator as a novel compact source of radiation

A crystalline undulator (CU) with periodically deformed crystallographic planes is capable of deflecting charged particles with the same strength as an equivalent magnetic field of 1000 T and could provide quite a short period L in the sub-millimeter range. We present an idea for creation of a CU and report its first realization. One face of a silicon crystal was given periodic micro-scratches (grooves), with a period of 1 mm, by means of a diamond blade. The X-ray tests of the crystal deformation have shown that a sinusoidal-like shape of crystalline planes goes through the bulk of the crystal. This opens up the possibility for experiments with high-energy particles channeled in CU, a novel compact source of radiation. The first experiment on photon emission in CU has been started at LNF with 800 MeV positrons aiming to produce 50 keV undulator photons.

Mechanical effects of chemical etchings on monocrystalline silicon for photovoltaic use

The mechanical effects of two etching treatments commonly applied on silicon wafers for the PV industry, are considered. The failure characteristics of this material under concentrated load are shown . In both cases, the maximum elongation and sustainable load of the etched wafers were measured to be higher than those of the original sample. The employed experimental procedure and results are presented here and a statistical data analysis substantiates the results observed. An attempt of explanation for this effect is offered based on the removal of a shallow highly defective layer induced by the etching of the material.

Observation of multiple volume reflection by different planes in one bent silicon crystal for high-energy negative particles

Multiple volume reflection by different planes passing through the 〈111〉 axis in a bent silicon crystal was observed for the first time for 150 GeV/c negative particles, π- mesons, at one of the se ...

Ge growth on porous silicon: The effect of buffer porosity on the epilayer crystalline quality

We report on the epitaxial growth of Ge virtual substrates directly on Si (001) and on different porosity porous silicon (pSi) buffers. Obtained results indicate that Ge grown on low porosity (22%) pSi buffer has a better crystalline quality compared to Ge grown on bulk Si and on higher porosity buffers. This result is attributed to the compliant nature of pSi and to its reduced Youngs modulus, which leads to plastic tensile deformation of the 22% porosity buffer under the in-plane tensile stress introduced by Ge lattice. The same result is not observed for higher porosity buffers, this effect being attributed to the higher buffer fragility. A low porosity pSi layer can hence be used as buffer for the growth of Ge on Si virtual substrates with reduced dislocation content and for the growth of Ge based devices or the successive integration of III-V semiconductors on Si.