Tactile sensor devices exploiting the tunnelling conduction in piezoresistive composites

The thesis reports on the preparation of three piezoresistive composites using different metal particles as filler in a silicone (PDMS) matrix. The results obtained from the functional characterizations performed under compressive and tensile stresses are well supported by the theoretical models and showed that the conduction mechanism in the metal-polymer composites is based on a quantum tunnelling effect. The phenomenon is further enhanced by the sharp tip morphology of the metal particles used. In particular when using spiky nickel particles, the composites undergo a variation of resistance up to nine orders of magnitude under an applied pressure. The possibility to obtain a huge variation in resistance upon a small deformation of the samples makes these composites a well performing functional material for sensor applications. Moreover the simplicity of the synthesis process, the low cost of the materials and the mechanical flexibility favor their choice among the possible sensing materials for tactile sensors. Piezoresistive composites were subsequently implemented in two different sensor architectures. The first measures the resistance variation of a 8x8 array of sensing element and reproduces the pressure distribution on a 3D graphic software. The second exploits both the resistance and capacitance variation of the tunnelling conductive material with an extremely low power quasi-digital frequency converter methods. Thanks to this measuring methods, the sensor was able to resolve 1 gr of applied load

Spontaneous Conversion from Virtual to Real Photons in the Ultrastrong Coupling Regime

We show that a spontaneous release of virtual photon pairs can occur in a quantum optical system in the ultrastrong coupling regime. In this regime, which is attracting interest both in semiconductor and superconducting systems, the light-matter coupling rate {\Omega}R becomes comparable to the bare resonance frequency of photons {\omega}0. In contrast to the dynamical Casimir effect and other pair creation mechanisms, this phenomenon does not require external forces or time dependent parameters in the Hamiltonian.Comment: To appear on Phys. Rev. Let

Crystallization of TiO2 nanotubes by in situ heating TEM

The thermally-induced crystallization of anodically grown TiO2 amorphous nanotubes has been studied so far under ambient pressure conditions by techniques such as differential scanning calorimetry and in situ X-ray diffraction, then looking at the overall response of several thousands of nanotubes in a carpet arrangement. Here we report a study of this phenomenon based on an in situ transmission electron microscopy approach that uses a twofold strategy. First, a group of some tens of TiO2 amorphous nanotubes was heated looking at their electron diffraction pattern change versus temperature, in order to determine both the initial temperature of crystallization and the corresponding crystalline phases. Second, the experiment was repeated on groups of few nanotubes, imaging their structural evolution in the direct space by spherical aberration-corrected high resolution transmission electron microscopy. These studies showed that, differently from what happens under ambient pressure conditions, under the microscope’s high vacuum (p < 10−5 Pa) the crystallization of TiO2 amorphous nanotubes starts from local small seeds of rutile and brookite, which then grow up with the increasing temperature. Besides, the crystallization started at different temperatures, namely 450 and 380 °C, when the in situ heating was performed irradiating the sample with electron beam energy of 120 or 300 keV, respectively. This difference is due to atomic knock-on effects induced by the electron beam with diverse energy

Silicon and Silicon Carbide Recrystallization by Laser Annealing: A Review

Modifying material properties within a specific spatial region is a pivotal stage in the fabrication of microelectronic devices. Laser annealing emerges as a compelling technology, offering precise control over the crystalline structure of semiconductor materials and facilitating the activation of doping ions in localized regions. This obviates the necessity for annealing the entire wafer or device. The objective of this review is to comprehensively investigate laser annealing processes specifically targeting the crystallization of amorphous silicon (Si) and silicon carbide (SiC) samples. Silicon finds extensive use in diverse applications, including microelectronics and solar cells, while SiC serves as a crucial material for developing components designed to operate in challenging environments or high-power integrated devices. The review commences with an exploration of the underlying theory and fundamentals of laser annealing techniques. It then delves into an analysis of the most pertinent studies focused on the crystallization of these two semiconductor materials

PDMS/Polyimide Composite as an Elastomeric Substrate for Multifunctional Laser-Induced Graphene Electrodes

Laser-induced graphene (LIG) emerged as one of the most promising materials for flexible functional devices. However, the attempts to obtain LIG onto elastomeric substrates never succeed, hindering its full exploitation for stretchable electronics. Herein, a novel polymeric composite is reported as a starting material for the fabrication of graphene-based electrodes by direct laser writing. A polyimide (PI) powder is dispersed into the poly(dimethylsiloxane) (PDMS) matrix to achieve an easily processable and functional elastomeric substrate, allowing the conversion of the polymeric surface into laser-induced graphene (LIG). The mechanical and electrical properties of the proposed material can be easily tuned by acting on the polyimide powder concentration. The reported procedure takes advantage from the simple casting process, typical of silicone elastomer, allowing to produce electrodes conformable to any kind of shape and surface as well as complex three-dimensional structures. Electrochemical capacitors and strain gauges are selected as flexible prototypes to demonstrate the multifunctional properties of the obtained LIG on the PDMS/PI composite substrate