Scanning ion conductance microscopy (SICM) is a type of scanning probe microscopy based on the continuous measurement of an ion current flowing through a pipette filled with an electrolyte solution, while the pipette apex approaches a non-conductive sample. This technique can be operated in environmental conditions such as those of cell cultures and does not require a direct contact between probe and sample. It is therefore particularly suitable for the investigation of living specimens. SICM was initially proposed as an instrument that could obtain topographic 3D images with high resolution. Later, simple modifications have been devised to apply a mechanical stimulus to the specimen via a solution flux coming out from the pipette aperture. This modified setup has been employed to measure cell membrane elasticity and to guide the growth cones of neurons for tens of micrometers, by means of repeated non-contact scanning. Both these applications require an accurate measurement of the mechanical forces acting on the cell surface, which can be obtained by combining SICM, Atomic force microscopy (AFM) and inverted optical microscopy in the same apparatus. In this configuration, a SICM pipette is approached to an AFM cantilever while monitoring the cantilever deflection as a function of the pressure applied to the pipette and the relative distance. In addition, the pipette aperture can be imaged in situ by exploiting the AFM operation, so that all the experimental parameters can be effectively controlled in the investigation of pressure effects on living cells.
We report on the influence of the dielectric/organic interface properties on the electrical characteristics of field-effect
transistors based on Poly-phenylenevinylene derivatives. We observe a direct influence of the dielectric surface on the
field-effect mobility as well as on the charge injection at the source electrode, despite the fact that we used a top contact
transistor structure.
We find that the presence of traps at the dielectric surface, decreases the hole mobility and increases the threshold
voltages. By treating the silicon dioxide dielectric surface with gas phase molecules such as octadecyltrichlorosilane
(OTS) and hexamethyldisilazane (HMDS) the hole mobility improves and the threshold voltage slightly increases.
The effects of a dielectric polymer layer spin coated onto silicon dioxide substrates before deposition of the
semiconductor polymer can be related to the density of the oxydryl groups (-OH ), which are the most efficient traps for the charges flowing in the device. We use different polymer species such as polyvinylalchol (PVA),
polymethylmetacrilate (PMMA) and a cyclotene derivative (B-staged bisbenzocyclobutene or BCB). The elimination of
the -OH groups and of other traps, produces the same effect observed with HMDS coupled to a more pronounced
enhancement of the threshold voltage, with the exception of PMMA. The electrical characteristics obtained with HMDS
and PMMA polymer dielectrics are the highest reported to date for PPV-based field-effect transistors.
We confirm that the purification of the active material is crucial to enhance the device performances and to achieve a
better device to device reproducibility.
We also investigated the effect of the dispersion of a phosphorescent dye into the active polymeric material. The
electrical characteristics of OFETs with HMDS or PMMA dielectric with and without dye doping are compared.
Organic light-emitting field-effect transistors are a new class of electrooptical devices that could
provide a novel architecture to address open questions concerning fundamental optoelectronic
phenomena in organic semiconductors, and can be potentially used as key components in optical
communication systems, advanced display technology, solid-state lighting and organic lasers.
The realisation of Organic Light-Emitting Transistors (OLETs) with high quantum efficiency and
fast switching time is crucial for the development of highly integrated organic optoelectronic
systems. Organic molecular materials having intrinsically ambipolar transport and high charge
mobility values are restricted in number and show poor light-emission efficiency. Here, we describe
the device operation principles of OLETs and report on the approach of combining p-type and n-type
molecular materials in a layered structure to achieve ambipolar transport and light emission. Imaging
of the individual layers and a correlation between active layer structure and device electrical
performances is achieved by means of the Laser Scanning Confocal Microscopy.
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