The rise of flexible electronics in neuroscience, from materials selection to in vitro and in vivo applications

Neuroscience deals with one of the most complicate system we can study: the brain. The huge amount of connections among the cells and the different phenomena occurring at different scale give rise to a continuous flow of data that have to be collected, analyzed and interpreted. Neuroscientists try to interrogate this complexity to find basic principles underlying brain electrochemical signalling and human/animal behaviour to disclose the mechanisms that trigger neurodegenerative diseases and to understand how restoring damaged brain circuits. The main tool to perform these tasks is a neural interface, a system able to interact with brain tissue at different levels to provide a uni/bidirectional communication path. Recently, breakthroughs coming from various disciplines have been combined to enforce features and potentialities of neural interfaces. Among the different findings, flexible electronics is playing a pivotal role in revolutionizing neural interfaces. In this work, we review the most recent advances in the fabrication of neural interfaces based on flexible electronics. We define challenges and issues to be solved for the application of such platforms and we discuss the different parts of the system regarding improvements in materials selection and breakthrough in applications both for in vitro and in vivo tests

Polarization-maintaining reflection-mode THz time-domain spectroscopy of a polyimide based ultra-thin narrow-band metamaterial absorber

This paper reports the design, the microfabrication and the experimental characterization of an ultra-thin narrow-band metamaterial absorber at terahertz frequencies. The metamaterial device is composed of a highly flexible polyimide spacer included between a top electric ring resonator with a four-fold rotational symmetry and a bottom ground plane that avoids misalignment problems. Its performance has been experimentally demonstrated by a custom polarization-maintaining reflection-mode terahertz time-domain spectroscopy system properly designed in order to reach a collimated configuration of the terahertz beam. The dependence of the spectral characteristics of this metamaterial absorber has been evaluated on the azimuthal angle under oblique incidence. The obtained absorbance levels are comprised between 67% and 74% at 1.092 THz and the polarization insensitivity has been verified in transverse electric polarization. This offers potential prospects in terahertz imaging, in terahertz stealth technology, in substance identification, and in non-planar applications. The proposed compact experimental set-up can be applied to investigate arbitrary polarization-sensitive terahertz devices under oblique incidence, allowing for a wide reproducibility of the measurements

Efficient Photothermal Generation by Nanoscale Light Trapping in a Forest of Silicon Nanowires

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Spitzer-IRAC survey of molecular jets in Vela-D

We present a survey of H2 jets from young protostars in the Vela-D molecular cloud (VMR-D), based on Spitzer -IRAC data between 3.6 and 8.0 micron. Our search has led to the identification of 15 jets and about 70 well aligned knots within 1.2 squared degree. We compare the IRAC maps with observations of the H2 1-0 S(1) line at 2.12 micron, with a Spitzer-MIPS map at 24 and 70 micron, and with a map of the dust continuum emission at 1.2 mm. We find a association between molecular jets and dust peaks. The jet candidate exciting sources have been searched for in the published catalog of the Young Stellar Objects of VMR-D. We selected all the sources of Class II or earlier which are located close to the jet center and aligned with it.The association between jet and exciting source was validated by estimating the differential extinction between the jet opposite lobes. We are able to find a best-candidate exciting source in all but two jets. Four exciting sources are not (or very barely) observed at wavelengths shorter than 24 micron, suggesting they are very young protostars. Three of them are also associated with the most compact jets. The exciting source Spectral Energy Distributions have been modeled by means of the photometric data between 1.2 micron and 1.2 mm. From SEDs fits we derive the main source parameters, which indicate that most of them are low-mass protostars. A significant correlation is found between the projected jet length and the [24] - [70] color, which is consistent with an evolutionary scenario according to which shorter jets are associated with younger sources. A rough correlation is found between IRAC line cooling and exciting source bolometric luminosity, in agreement with the previous literature. The emerging trend suggests that mass loss and mass accretion are tightly related phenomena and that both decrease with time.Comment: Accepted by The Astrophysical Journa

SEM characterization and ageing analysis on two generation of invisible aligners

Abstract Background: The purpose of the in vitro study is to investigate and compare the morphological features and the chemical stability in weight of two different polyurethane-based blends, Smart Track (LD30) and Exceed30 (EX30), used for orthodontic aligners manufacture before and after the oral usage. Methods: Twenty orthodontic aligners were randomly selected: 10 LD30 and 10 EX30, each group was divided in two subgroups, never used and intra-orally aged. By the employment of a Stereomicroscope, a section of 5 × 5 mm was cut from the buccal surface of the incisal region of each aligner. All samples were subjected to Scanning Electron Microscopy and Ageing tests in different solutions to simulate the hostility of the oral environment. The statistical method used was t-test. Results: At SEM images, LD30 appears more homogeneous in texture respect to EX30. However, after clinical usage, both materials show significant structural alterations: findings have been supported by higher magnifications at SEM, by which it is clearly to observe many superficial cracks cross through the polymer structures of LD30U, absent in never used samples. LD30U surface becomes also smoother due to the disappearance of most of the conglomerates, but at the same time also rougher while EX30U shows a greater irregularity and porosity in which large and deep cracks are also highlighted. Although these changes occur persistently, in the aging tests no significant weight loss from both materials has been found, confirming the initial hypothesis of a good chemical stability and safety of both polyurethane mixtures even in conditions of severe hostility. Conclusion: LD30 is the expression of the technological evolution of EX30, this is made evident above all by its morphological architecture, more homogeneous and defined but also by the chemical stability that can be appreciated even in evident critic situations

In vitro evaluation of structural factors favouring bacterial adhesion on orthodontic adhesive resins

Bacterial adhesion to the surface of orthodontic materials is an important step in the formation and proliferation of plaque bacteria, which is responsible for enamel demineralization and periodontium pathologies. With the intent of investigating if adhesive resins used for bracket bonding are prone to bacteria colonization, the surface roughness of these materials has been analyzed, combining information with a novel methodology to observe the internal structures of orthodontic composites. Scanning electron microscopy, combined with focus ion bean micromachining and stylus profilometry analyses, were performed to evaluate the compositional factors that can influence specific pivotal properties facilitating the adhesion of bacteria to the surface, such as surface roughness and robustness of three orthodontic adhesive composite resins. To confirm these findings, contact angle measurements and bacteria incubation on resin slide have been performed, evaluating similarities and differences in the final achievement. In particular, the morphological features that determine an increase in the resins surface wettability and influence the bacterial adhesion are the subject of speculation. Finally, the focused ion beam technique has been proposed as a valuable tool to combine information coming from surface roughness with specific the internal structures of the polymers

In-flight calibration system of imaging x-ray polarimetry explorer

The NASA/ASI Imaging X-ray Polarimetry Explorer, which will be launched in 2021, will be the first instrument to perform spatially resolved X-ray polarimetry on several astronomical sources in the 2-8 keV energy band. These measurements are made possible owing to the use of a gas pixel detector (GPD) at the focus of three X-ray telescopes. The GPD allows simultaneous measurements of the interaction point, energy, arrival time, and polarization angle of detected X-ray photons. The increase in sensitivity, achieved 40 years ago, for imaging and spectroscopy with the Einstein satellite will thus be extended to X-ray polarimetry for the first time. The characteristics of gas multiplication detectors are subject to changes over time. Because the GPD is a novel instrument, it is particularly important to verify its performance and stability during its mission lifetime. For this purpose, the spacecraft hosts a filter and calibration set (FCS), which includes both polarized and unpolarized calibration sources for performing in-flight calibration of the instruments. In this study, we present the design of the flight models of the FCS and the first measurements obtained using silicon drift detectors and CCD cameras, as well as those obtained in thermal vacuum with the flight units of the GPD. We show that the calibration sources successfully assess and verify the functionality of the GPD and validate its scientific results in orbit; this improves our knowledge of the behavior of these detectors in X-ray polarimetry

Calibration of the IXPE instrument

IXPE scientific payload comprises of three telescopes, each composed of a mirror and a photoelectric polarimeter based on the Gas Pixel Detector design. The three focal plane detectors, together with the unit which interfaces them to the spacecraft, are named IXPE Instrument and they will be built and calibrated in Italy; in this proceeding, we will present how IXPE Instrument will be calibrated, both on-ground and in-flight. The Instrument Calibration Equipment is being finalized at INAF-IAPS in Rome (Italy) to produce both polarized and unpolarized radiation, with a precise knowledge of direction, position, energy and polarization state of the incident beam. In flight, a set of four calibration sources based on radioactive material and mounted on a filter and calibration wheel will allow for the periodic calibration of all of the three IXPE focal plane detectors independently. A highly polarized source and an unpolarized one will be used to monitor the response to polarization; the remaining two will be used to calibrate the gain through the entire lifetime of the mission

Realizzazione e caratterizzazione di TFTs in polisilicio su substrati in polyimide per elettronica su plastica

In questo lavoro di tesi, svoltosi principalmente presso l'Istituto di Fotonica e Nanotecnologie e l'Istituto per la Microelettronica e Microsistemi del CNR, si sono studiate le possibilità di integrazione di componenti elettronici quali transistor a film sottile (TFTs) in polisilicio e altri dispositivi più complessi come circuiti oscillanti, porte logiche e sensori di gas su substrati flessibili polimerici. In una prima fase del lavoro si sono investigate le proprietà fisiche e chimiche di numerosi polimeri quali Polyethylene terephthalate (PET), Polyethylene naphthalate (PEN), Polycarbonate (PC), Polyethersulfone (PES), Polycyclic Olefin (PCO), Polyarylite (PAR) e Polyimide (PI). Si sono studiate poi le caratteristiche di diversi tipi di PI depositati da fase solida o da fase liquida, essendo questo un polimero particolarmente interessante per la sua alta temperatura di vetrificazione (Tg>350°C) e per il suo basso coefficiente termico di espansione (CTE~3-20 ppm/°C). E' stato individuato, infine, un tipo di PI depositato da fase liquida, con caratteristiche fisiche e chimiche soddisfacenti per il processo di integrazione con i dispositivi in polisilicio. Nella seconda fase del lavoro si è messo a punto un processo fabbricativo a bassa temperatura (<350°C) compatibile con il substrato polimerico di PI. Per raggiungere tale obiettivo sono state utilizzate svariate tecniche di deposizione di film sottili e ricristallizzazione con l'unico scopo di ottenere buone performance in termini di caratteristiche elettriche dei dispositivi in polisilicio minimizzando il budget termico a carico del substrato plastico. A tal fine si è usata la tecnica di ricristallizzazione del silicio amorfo da laser ad eccimeri, proteggendo tale polimero con una serie di strati dielettrici in nitruro di silicio e ossido di silicio dello spessore complessivo di circa 500 nm depositati a bassa temperatura (<300°C) da sistemi assistiti da plasma (ECR-PECVD, rf-PECVD). Tali materiali dielettrici depositati a bassa temperatura non solo si sono dimostrati particolarmente utili come strati inorganici barriera o di incapsulamento, ma hanno anche mostrato caratteristiche elettriche e morfologiche adeguate per il loro impiego come dielettrici di gate nei TFTs. Attraverso una serie di misure di rigidità dielettrica e di densità di stati eseguite su strutture capacitive è stato possibile, inoltre, verificare che film di ossido di silicio, di circa 100 nm di spessore, depositati a temperatura ambiente in sistemi ECR-PECVD e successivamente trattati termicamente in atmosfera controllata di azoto a temperature inferiori ai 350°C, mostrano iniezione di carica per campi elettrici di circa 7 MV/cm e tensioni di breakdown per campi >10 MV/cm. I transistor in polisilicio così realizzati, presentano correnti di perdita <10-12 A, rapporto Ion/Ioff pari a 106, mobilità superiori a 50 cm2/Vs, subthrehold slope di circa 1V/dec e tensioni di soglia di 6 V. I TFTs fabbricati su PI non hanno evidenziato, inoltre, apprezzabili variazioni nelle loro caratteristiche di uscita e di trasferimento una volta sottoposti a stress meccanico di tipo tensile o compressivo per raggi di curvatura fino a R=1.3 cm. Sono stati, infine, eseguiti sui TFTs test di stabilità elettrica ed è stato analizzato il fenomeno del self-heating: per tempi crescenti (fino a 104 s) sono state esaminate le caratteristiche di trasferimento e di uscita dei transistor fabbricati su PI osservando un progressivo danneggiamento delle curve a causa della formazione di stati all.interfaccia ossido/semiconduttore, principalmente nella regione di drain dove i campi elettrici sono sensibilmente più elevati: tale fenomeno risulta del tutto simile a quello osservato sui TFTs realizzati su substrati convenzionali. Il fenomeno del self-heating si è invece dimostrato particolarmente critico per questi dispositivi, in quanto il calore generato durante il funzionamento dei transistor si dissipa molto lentamente a causa della scarsa conduzione termica del substrato isolante. Nella terza ed ultima fase di questo lavoro di ricerca abbiamo progettato e caratterizzato dispositivi elettronici basati su polisilicio, più complessi come porte logiche, oscillatori, circuiti di lettura di diversa configurazione e sensori di gas. Questi circuiti in polisilicio realizzati su polyimide hanno costituito il punto di partenza per la fabbricazione di dispositivi su plastica più complessi quali touch-key e dispositivi a radio-frequenza (RF-ID): tali apparati elettronici sono stati progettati in collaborazione con STMicroelectronics e sono attualmente in fase di valutazione brevettuale. Sono stati, infine, progettati e realizzati su PI, sensori di gas di tipo resistivo (IDE) e capacitivo (IDC) con elettrodo patternato a pettine o a griglia e tali strutture sono state integrate con circuiti di lettura basati su transistor in polisilicio realizzati su un film di PI di 8 .m di spessore. Per la rilevazione dell.ammoniaca è stata impiegata la struttura IDE, scegliendo come materiale attivo un film di polyanilina; tale struttura è stata integrata con un circuito di lettura dalla configurazione a micro-bridge e ha mostrato una risposta soddisfacente anche per concentrazioni di ammoniaca molto basse (0.5 ppm). Utilizzando, invece, un film isolante di BCB, spesso circa 1 .m, abbiamo realizzato un sensore di umidità del tipo IDC: tale dispositivo è stato integrato con un circuito di lettura formato da un ring oscillator a tre stadi con carico passivo, realizzato su PI, e ha mostrato una sensitività pari a 7 Hz/RH%, e caratteristiche di stabilità e velocità di risposta del tutto compatibili con i sensori oggi in commercio