Electronic devices relying on the combination of different conjugated organic materials are considerably appealing for their potential use in many applications such as photovoltaics, light emission, ...and digital/analog circuitry. In this study, the electrical response of field-effect transistors achieved through the evaporation of picene and PDIF-CN2 molecules, two well-known organic semiconductors with remarkable charge transport properties, was investigated. With the main goal to get a balanced ambipolar response, various device configurations bearing double-layer, triple-layer, and codeposited active channels were analyzed. The most suitable choices for the layer deposition processes, the related characteristic parameters, and the electrode position were identified to this purpose. In this way, ambipolar organic field-effect transistors exhibiting balanced mobility values exceeding 0.1 cm2 V–1 s–1 for both electrons and holes were obtained. These experimental results highlight also how the combination between picene and PDIF-CN2 layers allows tuning the threshold voltages of the p-type response. Scanning Kelvin probe microscopy (SKPM) images acquired on picene/PDIF-CN2 heterojunctions suggest the presence of an interface dipole between the two organic layers. This feature is related to the partial accumulation of space charge at the interface being enhanced when the electrons are depleted in the underlayer.
The diketopyrrolopyrrole (DPP) unit represents one of the building blocks more widely employed in the field of organic electronics; in most of the reported DPP-based small molecules, this unit ...represents the electron acceptor core symmetrically coupled to donor moieties, and the solubility is guaranteed by functionalizing lactamic nitrogens with long and branched alkyl tails. In this paper, we explored the possibility of modulating the solubility by realizing asymmetric DPP derivatives, where the molecular structure is extended in just one direction. Four novel derivatives have been prepared, characterized by a common dithyenil-DPP fragment and functionalized on one side by a thiophene unit linked to different auxiliary electron acceptor groups. As compared to previously reported symmetric analogs, the novel dyes showed an increased solubility in chloroform and proved to be soluble in THF as well. The novel dyes underwent a thorough optical and electrochemical characterization. Electronic properties were studied at the DFT levels. All the dyes were used as active layers in organic field effect transistors, showing balanced charge transport properties.
In this work, a microfluidic system to investigate the flow behavior of red blood cells in a microcirculation-mimicking network of PDMS microchannels with thickness comparable to cell size is ...presented. We provide the first quantitative description of cell velocity and shape as a function of the applied pressure drop in such devices. Based on these results, a novel methodology to measure cell membrane viscoelastic properties in converging/diverging flow is developed, and the results are in good agreement with data from the literature. In particular, in the diverging channel the effect of RBC surface viscosity is dominant with respect to shear elasticity. Possible applications include measurements of cell deformability in pathological samples, where reliable methods are still lacking.
A novel methodology to measure red blood cell surface viscosity
η
and membrane shear elasticity
µ
in converging/diverging microfluidic channel is developed.
In this paper, Scanning Kelvin Probe Microscopy (SKPM) was applied in combination with standard current-voltage measurements to assess the contact resistance (RC) effects and to estimate the ...contact-free charge carrier mobility in n-type transistors based on evaporated films of PDIF-CN2. This analysis was carried out in particular as a function of the applied polarization voltages. The separate contributions to the RC phenomenon coming from the injecting (source) and extracting (drain) electrodes were investigated with the possibility to separately analyze the specific electrical behaviour of these two regions. In agreement with previous results, the experimental data here discussed show that the devices under analysis are not simply injected limited. Voltage drops at both the injecting and extracting contacts must be taken into consideration. However, it is worth to mention that for the bottom-contact devices here investigated, a minimum RC of 5.5 kΩ cm was found in linear regime. These values are significantly lower (i.e. by a factor 5×) than those previously reported for other perylene dimiide thin-film devices with bottom-contact configuration.
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•Contact resistances (RC) in PDIF-CN2 bottom-contact bottom-gate OTFT have been evaluated by Scanning Kelvin Probe Microscopy.•For the device architecture here investigated, a minimum RC of 5.5 kΩ cm was found in linear regime.•Devices are not purely injection-limited at the source and the role of the drain electrode must be considered.
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•Flame synthesized soot nanoparticles.•Self-assembled nanostructured carbon thin films produced by thermophoretic particle deposition.•Morphological, structural and electrical film ...characterization.
Carbon nanoparticles, with diameter d ∼10nm, were produced in a premixed ethylene-air flame and used to grow self-assembled thin films by thermophoretic deposition on Si++/SiO2/Gold multilayer substrates inserted in flame.
The particles’ size was measured by a Scanning Mobility Particle Sizer. UV–vis light absorption, Raman spectroscopy and Atomic Force Microscopy were used for the chemico-physical and morphological investigation of the carbon nanoparticle thin films. The electrical characterization was then performed in different environmental conditions with the basic aim to assess the potentiality of these films to be employed as electrically-active components in electronic and sensing applications.
The films are composed by the aggregation of nanoscale grains whose size increases with the deposition time and are consequently highly porous with the electrical conduction properties showing a dependence on thickness suggesting a percolation-like behavior. Raman spectrum indicates that the chemical/structural composition of the film does not change with deposition time and consists in small graphitic crystallites with constant size.
The electrical measurements show also the ohmic behavior of the IV curves. Moreover, an ambipolar response of the CNPs channels, when investigated in the field-effect configuration, was observed and, in parallel with conductivity, charge carrier mobility values were found to increase with thickness.
Contact resistance effects in n-type organic field-effect transistors (OFETs) based on perylene-diimide thin films and monolayer CVD graphene electrodes have been investigated by using Scanning ...Kelvin Probe Force Microscopy (SKPFM). SKPFM voltage profiles were acquired as a function of the applied drain-source (
V
ds
) and gate-source (
V
gs
) voltages and in the temperature range between 300 and 360 K. The results were compared with those obtained for hybrid devices bearing contemporarily a gold and a graphene electrode, in order to highlight the specific behaviors of the graphene/organic and gold/organic interfaces. Despite the fact that overall electrical performances of devices based on gold and graphene contacts are fully comparable, the SKPFM analysis demonstrates unambiguously that the physical mechanisms driving the charge injection and extraction phenomena are distinctive based on the electrode type. While for OFETs with gold electrodes, the
R
C
effect is mainly ascribable to the degraded quality of the charge transport in the semiconducting film regions close to the electrodes, for graphene-based devices, it is related to the presence of a Schottky-like barrier at the injecting electrode.
Contact effects occurring at organic-semiconductor/graphene-electrode interfaces are directly analyzed in unprecedented detail in n-type OFETs
via
scanning Kelvin probe force microscopy.
Homocysteine (Hcy) is a non-protein, sulfur-containing amino acid, which is recognized as a possible risk factor for coronary artery and other pathologies when its levels in the blood exceed the ...normal range of between 5 and 12 μmol/L (hyperhomocysteinemia). At present, standard procedures in laboratory medicine, such as high-performance liquid chromatography (HPLC), are commonly employed for the quantitation of total Hcy (tHcy), i.e., the sum of the protein-bound (oxidized) and free (homocystine plus reduced Hcy) forms, in biological fluids (particularly, serum or plasma). Here, the response of Aerosol Jet-printed organic electrochemical transistors (OECTs), in the presence of either reduced (free) and oxidized Hcy-based solutions, was analyzed. Two different experimental protocols were followed to this end: the former consisting of gold (Au) electrodes' biothiol-induced thiolation, while the latter simply used bare platinum (Pt) electrodes. Electrochemical impedance spectroscopy (EIS) analysis was performed both to validate the gold thiolation protocol and to gain insights into the reduced Hcy sensing mechanism by the Au-gated OECTs, which provided a final limit of detection (LoD) of 80 nM. For the OECT response based on Platinum gate electrodes, on the other hand, a LoD of 180 nM was found in the presence of albumin-bound Hcy, with this being the most abundant oxidized Hcy-form (i.e., the protein-bound form) in physiological fluids. Despite the lack of any biochemical functionalization supporting the response selectivity, the findings discussed in this work highlight the potential role of OECT in the development of low-cost point-of-care (POC) electronic platforms that are suitable for the evaluation, in humans, of Hcy levels within the physiological range and in cases of hyperhomocysteinemia.
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•Non passivated flexible OTFTs were studied through ToF-SIMS.•Two hybrid interfaces were succesfully characterized in a single run.•The hydrophobic treatment was detected and mapped ...in the multilayer structure.•Multivariate analysis applied to 3D ToF-SIMS datasets revealed chemical treatments.
Here, electron-transporting semiconducting organic channels made of N,N′-1H, 1H-perfluorobutyl dicyanoperylenecarboxydiimmide (PDIF-CN2) molecules were thermally evaporated on flexible polyethylene-naphtalate (PEN) plastic substrates equipped with gold (Au) electrodes. This multilayer structure represents the basic component for the fabrication of staggered top-gate n-type organic thin-film transistors (OTFTs) to be completed with the addition of a polymeric dielectric layer and an aluminum gate electrode. PEN substrate was treated with hexamethyldisilazane (HMDS) in order to make it more hydrophobic. Indeed, the hydrophobized surface of the plastic substrate was shown to induce a more ordered supramolecular structure of the semiconductor layer during the evaporation process. The hybrid organic/inorganic formally trilayer non-passivated OTFT structure was successfully profiled in a single run through ToF-SIMS depth profiling experiments with low energy cesium ions. High mass molecular fragment ions were obtained and used as indicators of interfaces, leading to an increase of information on molecular specificity. The HMDS surface modification was clearly detected and spatially located. Finally, a chemometric approach was also adopted to evaluate depth profiling data. In particular, principal component analysis (PCA) and K-means algorithm were tested as innovative method for the identification of molecular fragments useful for the OTFT multi-layer structure characterization and the determination of the number of OTFT layers, respectively.
We discuss the formation and post-deposition instability of nanodrop-like structures in thin films of PDIF-CN2 (a perylene derivative) deposited via supersonic molecular beam deposition technique on ...highly hydrophobic substrates at room temperature. The role of the deposition rate on the characteristic lengths of the organic nanodrops has been investigated by a systematic analysis of atomic force microscope images of the thin films and through the use of the height-height correlation function. The nanodrops appear to be a metastable configuration for the freshly-deposited films. For this reason, post-deposition wetting effect has been examined with unprecedented accuracy throughout a year of experimental observations. The observed time scales, from few hours to months, are related to the growth rate, and characterize the thin films morphological reordering from three-dimensional nanodrops to a well-connected terraced film. While the interplay between adhesion and cohesion energies favors the formation of 3D-mounted structures during the growth, wetting phenomenon following the switching off of the molecular flux is found to be driven by an instability. A slow rate downhill process survives at the molecular flux shutdown and it is accompanied and maybe favored by the formation of a precursor layer composed of more lying molecules. These results are supported by simulations based on a non-linear stochastic model. The instability has been simulated, for both the growth and the post-growth evolution. To better reproduce the experimental data it is needed to introduce a surface equalizer term characterized by a relaxation time taking into account the presence of a local mechanism of molecular correlation.
The global COVID-19 pandemic has had severe consequences from the social and economic perspectives, compelling the scientific community to focus on the development of effective diagnostics that can ...combine a fast response and accurate sensitivity/specificity performance. Presently available commercial antigen-detecting rapid diagnostic tests (Ag-RDTs) are very fast, but still face significant criticisms, mainly related to their inability to amplify the protein signal. This translates to a limited sensitive outcome and, hence, a reduced ability to hamper the spread of SARS-CoV-2 infection. To answer the urgent need for novel platforms for the early, specific and highly sensitive detection of the virus, this paper deals with the use of organic electrochemical transistors (OECTs) as very efficient ion-electron converters and amplifiers for the detection of spike proteins and their femtomolar concentration. The electrical response of the investigated OECTs was carefully analyzed, and the changes in the parameters associated with the transconductance (i.e., the slope of the transfer curves) in the gate voltage range between 0 and 0.3 V were found to be more clearly correlated with the spike protein concentration. Moreover, the functionalization of OECT-based biosensors with anti-spike and anti-nucleocapside proteins, the major proteins involved in the disease, demonstrated the specificity of these devices, whose potentialities should also be considered in light of the recent upsurge of the so-called "long COVID" syndrome.
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