Salvatore Iannotta

Cluster Beam Synthesis of Nanostructured Materials

1. Introduction.- 2. Molecular Beams and Cluster Nucleation.- 2.1 Molecular Beams.- 2.1.1 Continuous Effusive Beams.- 2.1.2 Continuous Supersonic Beams.- 2.1.3 Pulsed Beams.- 2.2 Nucleation and Aggregation Processes.- 2.2.1 Classical Theory.- 2.2.2 Homogeneous Nucleation by Monomer Addition.- 2.2.3 Homogeneous Nucleation by Aggregation.- 2.2.4 Nucleation of Clusters in Beams.- 2.2.5 Semi-empirical Approach to Clustering in Free Jets.- 3. Cluster Sources.- 3.1 Vaporization Methods.- 3.1.1 Joule Heating.- 3.1.2 Plasma Generation for Cluster Production.- 3.1.3 Laser Vaporization.- 3.1.4 Glow and Arc Discharges.- 3.2 Continuous Sources.- 3.2.1 Effusive Joule-Heated Gas Aggregation Sources.- 3.2.2 Magnetron Plasma Sources.- 3.2.3 Supersonic Sources.- 3.3 Pulsed Sources.- 3.3.1 Pulsed Valves.- 3.3.2 Laser Vaporization Sources.- 3.3.3 Arc Pulsed Sources.- 4. Characterization and Manipulation of Cluster Beams.- 4.1 Mass Spectrometry.- 4.1.1 Quadrupole Mass Spectrometry.- 4.1.2 Time-of-Flight Mass Spectrometry.- 4.1.3 Retarding Potential Mass Spectrometry.- 4.2 Detection Methods.- 4.2.1 Ionization of Clusters.- 4.2.2 Charged Cluster Detection.- 4.2.3 Cluster Beam Characterization.- 4.3 Cluster Selection and Manipulation.- 4.3.1 Size and Energy Selection.- 4.3.2 Quadrupole Filter.- 4.3.3 Separation of Gas Mixtures in Supersonic Beams.- 5. Thin Film Deposition and Surface Modification by Cluster Beams.- 5.1 Kinetic Energy Regimes.- 5.2 Diffusion and Coalescence of Clusters on Surfaces.- 5.3 Low-Energy Deposition.- 5.3.1 Cluster Networks and Porous Films.- 5.3.2 Composite Nanocrystalline Materials.- 5.4 High-Energy Deposition.- 5.4.1 Implantation, Sputtering, Etching.- 5.4.2 Thin Film Formation.- 6. Outlook and Perspectives.- 6.1 Cluster Beam Processing of Surfaces.- 6.2 Nanostructured Materials Synthesis.- 6.3 Perspectives.- References.

Effect of the gate electrode on the response of organic electrochemical transistors

Organic electrochemical transistors (OECTs) are attracting a great deal of interest for biosensing and bioelectronics applications. However, their device physics is not yet well-understood. In this paper, we focus on the effect of the gate electrode material on the response of OECTs. We studied OECTs made from the conducting polymer poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulfonate), and which utilized halide electrolytes. We demonstrate that OECTs with Ag gate electrodes show larger current modulation compared to OECTs with Pt gate electrodes. This effect is due to a change in the OECT regime of operation from capacitive, in case of a Pt gate electrode, to Faradaic, in the case of an Ag electrode.

New opportunities for organic electronics and bioelectronics: ions in action

This perspective deals with the coupling of ionic and electronic transport in organic electronic devices, focusing on electrolyte-gated transistors. These include electrolyte-gated organic field-effect transistors (EG-OFETs) and organic electrochemical transistors (OECTs). EG-OFETs, based on molecules and polymers, can be operated at low electrical bias (about 1 V or below) and permit unprecedented charge carrier densities within the transistor channel. OECTs can be operated in aqueous environment as efficient ion-to-electron converters, thus providing an interface between the worlds of biology and electronics. The exploration and the exploitation of coupled ionic and electronic transport in organic materials brings together different disciplines such as materials science, physics, chemistry, electrochemistry, organic electronics and biology.

The mozzarella cheese flavour profile: a comparison between judge panel analysis and proton transfer reaction mass spectrometry

Described in this paper is a comparison of results obtained in flavour profiling with two different approaches: classical sensory analysis and a novel instrumental technique. The mozzarella cheese flavour profile of seven different brands has been described by a sensory panel of eight judges. The same brands have been studied by means of proton transfer reaction mass spectrometry (PTR-MS), a novel technique well suited for detecting volatile organic compounds (VOCs) down to the pptv level in air, without any need for sample concentration or trapping. The PTR mass spectra of the headspace of mozzarella samples held at 36 °C have been compared with the judge panel flavour profile. Multivariate statistical data analysis shows that the two methods perform comparable sample discrimination. Even though several questions are still open (definition of better instrumental parameters, improvements in sampling set-up, spectral interpretation), the PTR-MS technique appears to be a very promising method for the instrumental evaluation of the flavour sensory profile of food. This opens up new opportunities both in the control of quality and technological processes as well in the fundamental comprehension of the physiological processes of aroma perception. © 2000 Society of Chemical Industry

Ambipolar copper phthalocyanine transistors with carbon nanotube array electrodes

We report on organic thin film transistors (OTFTs) based on copper phthalocyanine (CuPc) having electrodes consisting of isolated carbon nanotube (CNT) arrays embedded in the organic layer. CuPc OTFT with CNT array electrodes show p-type behavior with Ohmic hole injection, high hole mobility, and enhanced switching characteristics at low voltage. The p-type devices are converted to ambipolar OTFT by vacuum annealing. Despite the large offset between the CNT work function and the CuPc energy levels, electron injection characteristics are also Ohmic. The extension of CNT electrodes to the phthalocyanine family confirms the validity of this contact approach for organic electronic devices.

Optical enhancement of diode laser-photoacoustic trace gas detection by means of external Fabry-Perot cavity

An optical enhancement method applied to a diode laser photoacoustic trace gas detector is presented. In order to improve the detection sensitivity, the light intensity inside the acoustic resonator is amplified using a Fabry-Perot cavity. A feedback signal stabilizes the laser frequency to the optical cavity length, in order to maintain the light amplification constant during the probe frequency scan. The usefulness of the optical amplifier is demonstrated by showing two ethylene spectra obtained at 1.624μm with and without the optical enhancement. Tens to hundreds ppb (part per billion) sensibility for molecules absorbing in the region between 1.5–1.7μm can be obtained.An optical enhancement method applied to a diode laser photoacoustic trace gas detector is presented. In order to improve the detection sensitivity, the light intensity inside the acoustic resonator is amplified using a Fabry-Perot cavity. A feedback signal stabilizes the laser frequency to the optical cavity length, in order to maintain the light amplification constant during the probe frequency scan. The usefulness of the optical amplifier is demonstrated by showing two ethylene spectra obtained at 1.624μm with and without the optical enhancement. Tens to hundreds ppb (part per billion) sensibility for molecules absorbing in the region between 1.5–1.7μm can be obtained.

A single cotton fiber organic electrochemical transistor for liquid electrolyte saline sensing

A single natural cotton fiber has been functionalized with poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulfonate) (PEDOT:PSS) conductive polymer by a simple soaking process and used as a channel of an organic electrochemical transistor (OECT), directly interfaced with a liquid electrolyte in contact with an Ag wire gate. The device shows a stable and reproducible current modulation and has been demonstrated to be very effective for electrochemical sensing of NaCl concentration in water. The single wire cotton fiber OECT results to be a simple and low cost device, which is very attractive for wearable electronics in fitness and healthcare.

Organic electrochemical transistors monitoring micelle formation

Organic electrochemical transistors (OECTs) exploit electrolyte gating to achieve the transduction of ionic currents. Therefore, they are ideally suitable to sense different chemo/bio species dissolved in the electrolyte. Current modulation in OECTs relies on doping or dedoping of the OECT channel by electrolyte ions. Nevertheless the role played by the specific physicochemical properties of an electrolyte on OECT operation is largely unknown. Here we investigate OECTs, making use of aqueous solutions of the micelle-forming cationic surfactant cetyltrimethylammonium bromide (CTAB) as the electrolyte. Micelle-forming salts are remarkable model systems to study the doping and dedoping mechanism of OECTs, because the aggregation of dissociated ions into micelles at the critical micelle concentration permits to modify the size and the type of the species that dope or dedope the OECT channel in situ. The current modulation of OECTs using a CTAB electrolyte shows a marked increase close to the critical micellar concentration. The measurement of the transistors drain current as a function of CTAB concentration provides a simple, fast method to detect the formation of micelles from dissociated ions.

Liposome sensing and monitoring by organic electrochemical transistors integrated in microfluidics

BACKGROUND Organic electrochemical transistors (OECTs), which are becoming more and more promising devices for applications in bioelectronics and nanomedicine, are proposed here as ideally suitable for sensing and real time monitoring of liposome-based structures. This is quite relevant since, currently, the techniques used to investigate liposomal structures, their stability in different environments as well as drug loading and delivery mechanisms, operate basically off-line and/or with pre-prepared sampling. METHODS OECTs, based on the PEDOT:PSS conductive polymer, have been employed as sensors of liposome-based nanoparticles in electrolyte solutions to assess sensitivity and monitoring capabilities based on ion-to-electron amplified transduction. RESULTS We demonstrate that OECTs are very efficient, reliable and sensitive devices for detecting liposome-based nanoparticles on a wide dynamic range down to 10(-5)mg/ml (with a lowest detection limit, assessed in real-time monitoring, of 10(-7)mg/ml), thus matching the needs of typical drug loading/drug delivery conditions. They are hence particularly well suited for real-time monitoring of liposomes in solution. Furthermore, OECTs are shown to sense and discriminate successive injection of different liposomes, so that they could be good candidates in quality-control assays or in the pharmaceutical industry. GENERAL SIGNIFICANCE Drug loading and delivery by liposome-based structures is a fast growing and very promising field that will strongly benefit from real-time, highly sensitive and low cost monitoring of their dynamics in different pharma and biomedical environments, with a particular reference to the pharmaceutical and production processes, where a major issue is monitoring and measuring the formation and concentration of liposomes and the relative drug load. The demonstrated ability to sense and monitor complex bio-structures, such as liposomes, paves the way for very promising developments in biosensing and nanomedicine. This article is part of a Special Issue entitled Organic Bioelectronics-Novel Applications in Biomedicine.

Human stress monitoring through an organic cotton-fiber biosensor

Selective detection of bioanalytes in physiological fluids, such as blood, sweat or saliva, by means of low-cost and non-invasive devices, is of crucial importance to improve diagnosis and prevention in healthcare. To be really useful in everyday life a sensing system needs to be handy, non-invasive, easy to read and possibly wearable. Only a sensor that satisfies these requirements could be eligible for applications in healthcare and physiological condition monitoring. Herein an organic electrochemical transistor has been investigated as a simple, low-cost and e-textile biosensor, fully integrated on a single cotton yarn. The biosensor has been used for real-time detection of adrenaline, selectively compared to the saline content in human physiological fluids. The sensing mechanism is based on the oxidation of adrenaline at the Pt-gate electrode surface, with the formation of adrenaline-quinone and adrenochrome. Two independent organic electrochemical transistors, characterized by different gate-electrode materials, detect saline and adrenaline concentrations, respectively, in real human sweat. Measurements performed in real-time mode show the complete independence of adrenaline detection from NaCl and, hence, guarantee the simultaneous monitoring of both concentrations. The oxidation of adrenaline has been studied by means of absorption spectroscopy in air, with either silver or platinum working electrodes. Our results confirm that the oxidation reaction driven by the Pt-electrode leads to the formation of adrenochrome, while with the Ag-electrode the oxidation is similar to the spontaneous one occurring in air. The cotton-based biosensor shows the possibility of monitoring human performances (hydration and stress) in situ and using a non-invasive approach, opening new unexplored opportunities in healthcare, fitness and work safety.