Marco Natali

Low-threshold blue lasing from silk fibroin thin films

Silk is a natural biocompatible material that can be integrated in a variety of photonic systems and optoelectronic devices. The silk replication of patterned substrates with features down to tens of nanometers is exploited to realize highly transparent, mechanically stable, and free-standing structures with optical wavelength size. We demonstrate organic lasing from a blue-emitting stilbene-doped silk film spin-coated onto a one-dimensional distributed feedback grating (DFB). The lasing threshold is lower than that of organic DFB lasers based on the same active dye. These findings pave the way to the development of an optically active biocompatible technological platform based on silk.

Mapping of charge distribution in organic field-effect transistors by confocal photoluminescence electromodulation microscopy.

A novel method for mapping the charge density spatial distribution in organic field-effect transistors based on the electromodulation of the photoluminescence is demonstrated. In field-effect transistors exciton quenching is dominated by exciton-charge carrier interaction so that it can be used to map the charge distribution in different operating conditions. From a quantitative analysis of the photoluminescence quenching, the thickness of the charge carrier accumulation layer is derived. The injection of minority charge carriers in unipolar conditions is unexpectedly evidenced, which is not displayed by the electrical characteristics.

N-type perylene-based organic semiconductors for functional neural interfacing

The bioelectrical signalling within neural networks has to be monitored in real-time and localized in space in order to unravel the mechanisms behind pathologies and diseases of the nervous systems. Organic materials have significant potential for bio-functional neural interfacing given that their soft nature offers better mechanical compatibility with the nerve tissues than conventional semiconductors, and their flexibility allows realization of the non-planar forms typically required for biomedical implants. The integration of living cells into organic semiconductors is an important step towards the development of bio-organic electronic transducers of cellular activity from neurons. Here, we report on the use and characterization of n-type perylene derivatives as a suitable interface platform for organic neuro-electronic devices. We demonstrate that primary neurons can adhere, grow and differentiate on a suitably engineered perylene-based field-effect transistor platform, while maintaining their firing properties even after a prolonged time of cell-culturing. It is noteworthy that the field-effect transistors preserve their electrical characteristics even after 10 days of incubation in cell culture media. These results validate n-type perylene derivatives as a suitable long-term interface platform for organic neuro-electronic devices, which is particularly relevant in view of the recently reported perylene-based field-effect transistor structure capable of providing bidirectional stimulation and recording of primary neurons.

Characterization of nanostructured copper films for electromagnetic shield

Purpose – The purpose of this paper is to obtain a multidisciplinary characterization of nanostructured copper films for electromagnetic shields.Design/methodology/approach – Structural and electrical analysis have been applied, on copper nanometric films produced by a magnetron sputtering device.Findings – Data are provided for copper films realized by magnetron sputtering deposition on glass, in different operating conditions.Practical implications – A multidisciplinary comprehension of shielding effectiveness of nanostructured thin films can be important in many applications where there are electromagnetic compatibility problems.Originality/value – The paper gives a valuable set of information for the characterization of nanometric copper thin films.

On the Pulsed and Transient Characterization of Organic Field-Effect Transistors

We performed pulsed measurements on organic transistors presenting four different active materials. All the devices show a strong correlation between the drain-source current and the pulse width. We attributed this phenomenon to the long time needed for channel formation and depletion. These transient effects may have a severe impact on device characterization and application development.

Contact Resistance in Ambipolar Organic Field-Effect Transistors Measured by Confocal Photoluminescence Electro-Modulation Microscopy

Although it is theoretically expected that all organic semiconductors support ambipolar charge transport, most organic transistors either transport holes or electrons effectively. Single-layer ambipolar organic field-effect transistors enable the investigation of different mechanisms in hole and electron transport in a single device since the device architecture provides a controllable planar pn-junction within the transistor channel. However, a direct comparison of the injection barriers and of the channel conductivities between electrons and holes within the same device cannot be measured by standard electrical characterization. This article introduces a novel approach for determining threshold gate voltages for the onset of the ambipolar regime from the position of the pn-junction observed by photoluminescence electro-modulation (PLEM) microscopy. Indeed, the threshold gate voltage in the ambipolar bias regime considers a vanishing channel length, thus correlating the contact resistance. PLEM microscopy is a valuable tool to directly compare the contact and channel resistances for both carrier types in the same device. The reported results demonstrate that designing the metal/organic–semiconductor interfaces by aligning the bulk metal Fermi levels to the highest occupied molecular orbital or lowest unoccupied molecular orbital levels of the organic semiconductors is a too simplistic approach for optimizing the charge-injection process in organic field-effect devices.

Investigation of Mobility Transient on Organic Transistor by Means of DLTS Technique

We analyzed the transient response of organic transistors by means of the deep-level transient spectroscopy technique. We showed how the current transient can be related to a mobility transient from which we estimated two different kinds of activation energies as well as information to the density of states.

An organic transistor architecture for stimulation of calcium signalling in primary rat cortical astrocytes

In this work we report the stimulation of astrocytic calcium signalling using an organic cell sensing and stimulating transistor (O-CST). We demonstrate that astroglial cells can adhere and proliferate on these devices giving us the possibility to stimulate bioelectrical activity in this type of cells. By the use of a microfluorimetric calcium imaging approach we show that our device is able to evoke an increase in intracellular calcium levels. This research opens a new path in the study of glial cells and their bioelectrical activity.