Alessio Verna

Bio: Alessio Verna is an academic researcher from Polytechnic University of Turin. The author has contributed to research in topics: Graphene & PEDOT:PSS. The author has an hindex of 10, co-authored 23 publications receiving 296 citations. Previous affiliations of Alessio Verna include Istituto Italiano di Tecnologia.

Effect of the fabrication method on the functional properties of BaTiO3: PVDF nanocomposites

Abstract: This paper deals with the preparation and characterization of nanocomposite (NC) materials, comparing different technologies for sample fabrication, in view of their possible application as piezoelectric sensors. Those NCs consist on BaTiO3 nanoparticles embedded into a polyvinylidene fluoride matrix, where both the ceramic and the polymeric phases could exhibit ferroelectricity. In particular, we compare the properties of samples prepared through three different methods, i.e., solvent casting, enabling a fast realization, spin-coating, which allows to realize thin flexible films particularly interesting for large area sensors, and hot embossing, which is exploited to modify the residual porosity in the thick films. The influence of the fabrication techniques on the physical and chemical properties is investigated. Different electrode materials have been tested and compared, ranging from sputtered Pt to an engineered thermally evaporated Ti/Au bilayer. Leakage current, polarization, displacement curves, and piezoelectric coefficient d 33 are evaluated by small signal indirect measurements, comparing the properties of different materials and understanding how processing technologies influence the sensor performances by acting on the functional materials.

Evidence of Negative Capacitance in Piezoelectric ZnO Thin Films Sputtered on Interdigital Electrodes.

Abstract: The scaling paradigm known as Moore’s Law, with the shrinking of transistors and their doubling on a chip every two years, is going to reach a painful end. Another less-known paradigm, the so-called Koomey’s Law, stating that the computing efficiency doubles every 1.57 years, poses other important challenges, since the efficiency of rechargeable energy sources is substantially constant, and any other evolution is based on device architecture only. How can we still increase the computational power/reduce the power consumption of our electronic environments? A first answer to this question comes from the quest for new functionalities. Within this aim, negative capacitance (NC) is becoming one of the most intriguing and studied phenomena since it can be exploited for reducing the aforementioned limiting effects in the downscaling of electronic devices. Here we report the evidence of negative capacitance in 80 nm thick ZnO thin films sputtered on Au interdigital electrodes (IDEs). Highly (002)-oriented ZnO th...

Different scale confinements of PVDF-TrFE as functional material of piezoelectric sensor devices

Abstract: In this paper, we report on the effect of micro- and nano-structuration on the piezoelectric properties of polymeric samples. We prepare micro-sized pillars and nano-wires (thus 1-D structures) of a piezoelectric polymer Poly(VinyliDene Fluoride-Tri FluoroEthylene) PVDF-TrFE and we compare their structural and piezoelectrical properties with a thin film (thus 2-D) of the same material. X-ray diffraction and infrared spectroscopy measurements show that the crystallization of the polymer into the ferroelectric $\beta$ -phase is affected by the size of the confinement. The direct and converse piezoelectric characterization of the three polymeric structures shows important improvements as far as the nano-structuration is reached. As a proof of concept, we demonstrate the use of the three polymeric structures as potential flexible tactile sensors and bendable energy harvesters, showing a profound effect of the micro- and nano-structuration on the device performances.

Development of a Flexible Lead-Free Piezoelectric Transducer for Health Monitoring in the Space Environment

Abstract: In this work we report on the fabrication process for the development of a flexible piezopolymeric transducer for health monitoring applications, based on lead-free, piezoelectric zinc oxide (ZnO) thin films. All the selected materials are compatible with the space environment and were deposited by the RF magnetron sputtering technique at room temperature, in view of preserving the total flexibility of the structures, which is an important requirement to guarantee coupling with cylindrical fuel tanks whose integrity we want to monitor. The overall transducer architecture was made of a c-axis-oriented ZnO thin film coupled to a pair of flexible Polyimide foils coated with gold (Au) electrodes. The fabrication process started with the deposition of the bottom electrode on Polyimide foils. The ZnO thin film and the top electrode were then deposited onto the Au/Polyimide substrates. Both the electrodes and ZnO layer were properly patterned by wet-chemical etching and optical lithography. The assembly of the final structure was then obtained by gluing the upper and lower Polyimide foils with an epoxy resin capable of guaranteeing low outgassing levels, as well as adequate thermal and electrical insulation of the transducers. The piezoelectric behavior of the prototypes was confirmed and evaluated by measuring the mechanical displacement induced from the application of an external voltage.

Organic and hybrid resistive switching materials and devices

Abstract: The explosive increase in digital communications in the Big Data and internet of Things era spurs the development of universal memory that can run at high speed with high-density and nonvolatile storage capabilities, as well as demonstrating superior mechanical flexibility for wearable applications. Among various candidates for the next-generation information storage technology, resistive switching memories distinguish themselves with low power consumption, excellent downscaling potential, easy 3D stacking, and high CMOS compatibility, fulfilling key requirements for high-performance data storage. Employing organic and hybrid switching media in addition allows light weight and flexible integration of molecules with tunable device performance via molecular design-cum-synthesis strategy. In this review, we present a timely and comprehensive review of the recent advances in organic and hybrid resistive switching materials and devices, with particular attention on their design principles for electronic property tuning and flexible device performance. The current challenges posed with development of organic and hybrid resistive switching materials and flexible memory devices, together with their future perspectives, are also discussed.

Robust Resistive Memory Devices Using Solution-Processable Metal-Coordinated Azo-aromatics

Abstract: Non-volatile memories will play a decisive role in the next generation of digital technology. Flash memories are currently the key player in the field, yet they fail to meet the commercial demands of scalability and endurance. Resistive memory devices, and in particular memories based on low-cost, solution-processable and chemically tunable organic materials, are promising alternatives explored by the industry. However, to date, they have been lacking the performance and mechanistic understanding required for commercial translation. Here we report a resistive memory device based on a spin-coated active layer of a transition-metal complex, which shows high reproducibility (∼350 devices), fast switching (≤30 ns), excellent endurance (∼1012 cycles), stability (>106 s) and scalability (down to ∼60 nm2). In situ Raman and ultraviolet-visible spectroscopy alongside spectroelectrochemistry and quantum chemical calculations demonstrate that the redox state of the ligands determines the switching states of the device whereas the counterions control the hysteresis. This insight may accelerate the technological deployment of organic resistive memories.

Self-powered flexible pressure sensors with vertically well-aligned piezoelectric nanowire arrays for monitoring vital signs

Abstract: Human vital signs such as the heartbeat and respiration are important physiological parameters for public health care. Precisely monitoring these very minute and complex time-dependent signals in a simple, low-cost way is still a challenge. This study shows a novel fabrication of vertically well-aligned piezoelectric nanowire arrays with preferential polarization orientation as highly sensitive self-powered sensors for monitoring vital signs. The process realizes in situ poling of the P(VDF-TrFE) nanowires within the nanopores of the anodized aluminium oxide (AAO) template to yield a preferential alignment of both nanowires and the polymer chains required for superior sensitivity in one step. The resulting self-powered flexible sensor shows high sensitivity, good stability and strong power-generating performance. Under bending conditions, the device exhibits a maximum voltage of ∼4.8 V and a current density of ∼0.11 μA cm−2. The fabricated self-powered sensor shows a linear relationship of output voltage versus compressive force with a high sensitivity, and the piezoelectric voltage of the P(VDF-TrFE) nanowire array is enhanced 9 times that of conventional spin-coated bulk films. Furthermore, the highly sensitive vertically well-aligned nanowire array can be applied as a self-powered sensor for detecting some tiny human activities including breath, heartbeat pulse, and finger movements, which may possibly serve for medical diagnostics as sensors, robotics and smart electronic devices.

Carbon-based materials for stable, cheaper and large-scale processable perovskite solar cells

Abstract: Almost ten years after their first use in the photovoltaic (PV) field, perovskite solar cells (PSCs) are now hybrid devices that, in addition to having reached silicon performance, can accelerate the energy transition and boost the use of abundant elements for their manufacturing process. However, noble metals (in particular gold) represent the most typically used sources for back electrode fabrication, and this issue has been intensively considered by the research community in the last five years. This review shows how the most promising solution, considering also the need to develop a large-scale production process, is based on the use of carbon-based materials for the preparation of back electrodes. Graphite, carbon black, graphene and carbon nanotubes (CNTs) have been proposed, functionalized and characterized, leading to laboratory-scale solar cells and modules capable of providing excellent efficiencies and ensuring stability greater than those of gold-based devices. Strengthened by these results and its hydrophobizing properties, carbon has also started to be used as an electron transporting material (ETM), with excellent results on both rigid and flexible substrates. This review discusses the major advances and the updated state-of-the-art in the carbon-based PSC scenario, keeping a solid trajectory where the accessibility, low cost, high electrical conductivity, chemical stability and controllable porosity of carbon are highlighted and exploited in the design of upscalable hybrid solar cells.

Flourishing Bioinspired Antifogging Materials with Superwettability: Progresses and Challenges

Abstract: Antifogging (AF) structure materials found in nature have great potential for enabling novel and emerging products and technologies to facilitate the daily life of human societies, attracting enormous research interests owing to their potential applications in display devices, traffics, agricultural greenhouse, food packaging, solar products, and other fields. The outstanding performance of biological AF surfaces encourages the rapid development and wide application of new AF materials. In fact, AF properties are inextricably associated with their surface superwettability. Generally, the superwettability of AF materials depends on a combination of their surface geometrical structures and surface chemical compositions. To explore their general design principles, recent progresses in the investigation of bioinspired AF materials are summarized herein. Recent developments of the mechanism, fabrication, and applications of bioinspired AF materials with superwettability are also a focus. This includes information on constructing superwetting AF materials based on designing the topographical structure and regulating the surface chemical composition. Finally, the remaining challenges and promising breakthroughs in this field are also briefly discussed.