Position-resolved charge collection of silicon carbide detectors with an epitaxially-grown graphene layer.

Silicon carbide (SiC) has outstanding physical properties therefore, diodes based on SiC are being considered for many radiation detection applications such as particle accelerator experiments and medical dosimetry. Moreover, by reducing the metal on the surface of the diode there is the potential to enhance its performance in some fields where the presence of metal is detrimental. To this end, SiC detectors with an epitaxially-grown graphene layer (EG), that substitutes the metallic contact, in the sensitive region were produced at IMB-CNM, profiting from the conductivity of the mono-atomic layer material. To isolate the effect of the graphene on the charge collection, samples without graphene were produced in parallel. In this paper, the effect of EG on Silicon Carbide p-in-n radiation detectors is studied in terms of charge collection with a radioactive source and by means of the transient current technique (TCT), which allows for position-dependent signal formation analysis. As a result of the former, we show the capability of the EG-SiC sensor for charge collection after signal integration, to a resolution close to that of a sensor fully metallised. Moreover, from the TCT studies, we observe uniform charge collection across the active region, as well as an up-to ∼ 40% transient amplitude damping which, compared with the ∼ 90% on the sample containing no metallic contact, proves that the presence of graphene benefits the performance of the device and that the technology is viable for radiation detection as an alternative to metal.

Single-Step Functionalization Strategy of Graphene Microtransistor Array with Chemically Modified Aptamers for Biosensing Applications.

Graphene solution-gated field-effect transistors (gSGFETs) offer high potential for chemical and biochemical sensing applications. Among the current trends to improve this technology, the functionalization processes are gaining relevance for its crucial impact on biosensing performance. Previous efforts are focused on simplifying the attachment procedure from standard multi-step to single-step strategies, but they still suffer from overreaction, and impurity issues and are limited to a particular ligand. Herein, a novel strategy for single-step immobilization of chemically modified aptamers with fluorenylmethyl and acridine moieties, based on a straightforward synthetic route to overcome the aforementioned limitations is presented. This approach is benchmarked versus a standard multi-step strategy using thrombin as detection model. In order to assess the reliability of the functionalization strategies 48-gSGFETs arrays are employed to acquire large datasets with multiple replicas. Graphene surface characterization demonstrates robust and higher efficiency in the chemical coupling of the aptamers with the single-step strategy, while the electrical response evaluation validates the sensing capability, allowing to implement different alternatives for data analysis and reduce the sensing variability. In this work, a new tool capable of overcome the functionalization challenges of graphene surfaces is provided, paving the way toward the standardization of gSGFETs for biosensing purposes.

Editorial for the Special Issue on "10th Anniversary of Nanomaterials-Recent Advances in Nanocomposite Thin Films and 2D Materials".

As a way to celebrate the 10th anniversary of the journal Nanomaterials, this Special Issue within the section 'Nanocomposite thin film and 2D materials' provides an overview of the wide spectrum of research challenges and applications in the field, represented by a collection of 12 contributions, including three up-to-date review articles plus nine original works, in different targeted topics as described below [...].

Characterization of optogenetically-induced cortical spreading depression in awake mice using graphene micro-transistor arrays.

Objective.The development of experimental methodology utilizing graphene micro-transistor arrays to facilitate and advance translational research into cortical spreading depression (CSD) in the awake brain.Approach.CSDs were reliably induced in awake nontransgenic mice using optogenetic methods. High-fidelity DC-coupled electrophysiological mapping of propagating CSDs was obtained using flexible arrays of graphene soultion-gated field-effect transistors (gSGFETs).Main results.Viral vectors targetted channelrhopsin expression in neurons of the motor cortex resulting in a transduction volume ⩾1 mm3. 5-10 s of continous blue light stimulation induced CSD that propagated across the cortex at a velocity of 3.0 ± 0.1 mm min-1. Graphene micro-transistor arrays enabled high-density mapping of infraslow activity correlated with neuronal activity suppression across multiple frequency bands during both CSD initiation and propagation. Localized differences in the CSD waveform could be detected and categorized into distinct clusters demonstrating the spatial resolution advantages of DC-coupled recordings. We exploited the reliable and repeatable induction of CSDs using this preparation to perform proof-of-principle pharmacological interrogation studies using NMDA antagonists. MK801 (3 mg kg-1) suppressed CSD induction and propagation, an effect mirrored, albeit transiently, by ketamine (15 mg kg-1), thus demonstrating this models' applicability as a preclinical drug screening platform. Finally, we report that CSDs could be detected through the skull using graphene micro-transistors, highlighting additional advantages and future applications of this technology.Significance.CSD is thought to contribute to the pathophysiology of several neurological diseases. CSD research will benefit from technological advances that permit high density electrophysiological mapping of the CSD waveform and propagation across the cortex. We report anin vivoassay that permits minimally invasive optogenetic induction, combined with multichannel DC-coupled recordings enabled by gSGFETs in the awake brain. Adoption of this technological approach could facilitate and transform preclinical investigations of CSD in disease relevant models.

Bidirectional Modulation of Neuronal Cells Electrical and Mechanical Properties Through Pristine and Functionalized Graphene Substrates.

In recent years, the quest for surface modifications to promote neuronal cell interfacing and modulation has risen. This course is justified by the requirements of emerging technological and medical approaches attempting to effectively interact with central nervous system cells, as in the case of brain-machine interfaces or neuroprosthetic. In that regard, the remarkable cytocompatibility and ease of chemical functionalization characterizing surface-immobilized graphene-based nanomaterials (GBNs) make them increasingly appealing for these purposes. Here, we compared the (morpho)mechanical and functional adaptation of rat primary hippocampal neurons when interfaced with surfaces covered with pristine single-layer graphene (pSLG) and phenylacetic acid-functionalized single-layer graphene (fSLG). Our results confirmed the intrinsic ability of glass-supported single-layer graphene to boost neuronal activity highlighting, conversely, the downturn inducible by the surface insertion of phenylacetic acid moieties. fSLG-interfaced neurons showed a significant reduction in spontaneous postsynaptic currents (PSCs), coupled to reduced cell stiffness and altered focal adhesion organization compared to control samples. Overall, we have here demonstrated that graphene substrates, both pristine and functionalized, could be alternatively used to intrinsically promote or depress neuronal activity in primary hippocampal cultures.

Self-assembly of block copolymers under non-isothermal annealing conditions as revealed by grazing-incidence small-angle X-ray scattering.

An accurate knowledge of the parameters governing the kinetics of block copolymer self-assembly is crucial to model the time- and temperature-dependent evolution of pattern formation during annealing as well as to predict the most efficient conditions for the formation of defect-free patterns. Here, the self-assembly kinetics of a lamellar PS-b-PMMA block copolymer under both isothermal and non-isothermal annealing conditions are investigated by combining grazing-incidence small-angle X-ray scattering (GISAXS) experiments with a novel modelling methodology that accounts for the annealing history of the block copolymer film before it reaches the isothermal regime. Such a model allows conventional studies in isothermal annealing conditions to be extended to the more realistic case of non-isothermal annealing and prediction of the accuracy in the determination of the relevant parameters, namely the correlation length and the growth exponent, which define the kinetics of the self-assembly.

Direct Visualization of Current-Stimulated Oxygen Migration in YBa2Cu3O7-δ Thin Films.

The past years have witnessed major advancements in all-electrical doping control on cuprates. In the vast majority of cases, the tuning of charge carrier density has been achieved via electric field effect by means of either a ferroelectric polarization or using a dielectric or electrolyte gating. Unfortunately, these approaches are constrained to rather thin superconducting layers and require large electric fields in order to ensure sizable carrier modulations. In this work, we focus on the investigation of oxygen doping in an extended region through current-stimulated oxygen migration in YBa2Cu3O7-δ superconducting bridges. The underlying methodology is rather simple and avoids sophisticated nanofabrication process steps and complex electronics. A patterned multiterminal transport bridge configuration allows us to electrically assess the directional counterflow of oxygen atoms and vacancies. Importantly, the emerging propagating front of current-dependent doping δ is probed in situ by optical microscopy and scanning electron microscopy. The resulting imaging techniques, together with photoinduced conductivity and Raman scattering investigations, reveal an inhomogeneous oxygen vacancy distribution with a controllable propagation speed permitting us to estimate the oxygen diffusivity. These findings provide direct evidence that the microscopic mechanism at play in electrical doping of cuprates involves diffusion of oxygen atoms with the applied current. The resulting fine control of the oxygen content would permit a systematic study of complex phase diagrams and the design of electrically addressable devices.

High-resolution mapping of infraslow cortical brain activity enabled by graphene microtransistors.

Recording infraslow brain signals (<0.1 Hz) with microelectrodes is severely hampered by current microelectrode materials, primarily due to limitations resulting from voltage drift and high electrode impedance. Hence, most recording systems include high-pass filters that solve saturation issues but come hand in hand with loss of physiological and pathological information. In this work, we use flexible epicortical and intracortical arrays of graphene solution-gated field-effect transistors (gSGFETs) to map cortical spreading depression in rats and demonstrate that gSGFETs are able to record, with high fidelity, infraslow signals together with signals in the typical local field potential bandwidth. The wide recording bandwidth results from the direct field-effect coupling of the active transistor, in contrast to standard passive electrodes, as well as from the electrochemical inertness of graphene. Taking advantage of such functionality, we envision broad applications of gSGFET technology for monitoring infraslow brain activity both in research and in the clinic.

Boosting the local anodic oxidation of silicon through carbon nanofiber atomic force microscopy probes.

Many nanofabrication methods based on scanning probe microscopy have been developed during the last decades. Local anodic oxidation (LAO) is one of such methods: Upon application of an electric field between tip and surface under ambient conditions, oxide patterning with nanometer-scale resolution can be performed with good control of dimensions and placement. LAO through the non-contact mode of atomic force microscopy (AFM) has proven to yield a better resolution and tip preservation than the contact mode and it can be effectively performed in the dynamic mode of AFM. The tip plays a crucial role for the LAO-AFM, because it regulates the minimum feature size and the electric field. For instance, the feasibility of carbon nanotube (CNT)-functionalized tips showed great promise for LAO-AFM, yet, the fabrication of CNT tips presents difficulties. Here, we explore the use of a carbon nanofiber (CNF) as the tip apex of AFM probes for the application of LAO on silicon substrates in the AFM amplitude modulation dynamic mode of operation. We show the good performance of CNF-AFM probes in terms of resolution and reproducibility, as well as demonstration that the CNF apex provides enhanced conditions in terms of field-induced, chemical process efficiency.

Evaporation of femtoliter sessile droplets monitored with nanomechanical mass sensors.

We present a time-resolved study of the evaporation in air of minuscule sessile droplets deposited by nanodispensing techniques. Highly sensitive nanomechanical resonators are designed to monitor in time the mass variation of evaporating liquid droplets. The precision of the measurement setup enables the study of droplets with diameters in the 1 mum range, which correspond to volumes of femtoliters and smaller, 9 orders of magnitude smaller than most of presently published data. Experimental data are compared with macroscopic models.