Piero Morales

Liquid crystal-carbon nanotube dispersions

Parallel alignment of nanotubes can be obtained by dispersion in a self-organizing anisotropic fluid such as a nematic liquid crystal. Exploiting the cooperative reorientation of liquid crystals, the overall direction of the nanotube alignment can be controlled both statically and dynamically by the application of external fields. These can be electric, magnetic, mechanic, or even optic in nature. Employing multiwall as well as single-wall carbon nanotubes, we show their parallel alignment along a uniform liquid crystal director field and electrically verify their reorientation behavior for two complementary geometries. These demonstrate electrically controlled carbon nanotube OFF–ON and ON–OFF switches. Further applicational potential will be outlined.

Fabrication of 5 nm Resolution Electrodes for Molecular Devices by Means of Electron Beam Lithography

Electron beam lithography is used to fabricate two-metal electrode tip-shaped structures. The distance between the tips is continuously controlled to be between 5 and 70 nm. The electron beam lithography process is robust and the tip separation is well controlled in the sense that the smallest distance between the tips is a consequence of the design and not a consequence of randomly distributed metal spots around the tip area. Interest in these structures is due to the fact that they can be used to fabricate rectifiers, working with single molecule, designed to exhibit semiconductor properties.

Nanometer biodevice fabrication by electron beam lithography

A conventional electron beam lithography machine operated at 50 kV is used in this work to fabricate devices and structures for biophysical and molecular electronics applications featuring critical dimensions down to the nanometer region. Such nanostructures are used for deposition and manipulation of organic molecules; fabricated devices include fine pitch self-standing meshes for laser deposition of molecules, a bimetallic miniaturized glucose sensor and nanogaps for molecular trapping and probing. The developed process is described in detail and by means of Monte Carlo simulation, the various electron scattering processes are modelled. Critical issues, such as fabrication of nanogaps with dimension down to 5 nm, are also addressed.

Self-assembled ordered structures in thin films of HAT5 discotic liquid crystal

Summary Thin films of the discotic liquid crystal hexapentyloxytriphenylene (HAT5), prepared from solution via casting or spin-coating, were investigated by atomic force microscopy and polarizing optical microscopy, revealing large-scale ordered structures substantially different from those typically observed in standard samples of the same material. Thin and very long fibrils of planar-aligned liquid crystal were found, possibly formed as a result of an intermediate lyotropic nematic state arising during the solvent evaporation process. Moreover, in sufficiently thin films the crystallization seems to be suppressed, extending the uniform order of the liquid crystal phase down to room temperature. This should be compared to the bulk situation, where the same material crystallizes into a polymorphic structure at 68 °C.

Synthesis and field-effect properties of α,ω -disubstituted sexithiophenes bearing polar groups

The synthesis of sexithiophenes bearing amide or ester groups in the α,ω-terminal positions is described, along with their characterization in the solid state. The influence of the functional group on mobilities and on/off ratios of the organic FET devices was investigated. The oligomer bearing the ester functional group separated from the sexithiophene core by an ethylene spacer showed a hole field-effect mobility as high as 0.012 cm2 V−1 s−1, which is among the highest reported so far for organic FETs using sexithiophenes modified with polar groups.

New method of deposition of biomolecules for bioelectronic purposes

A laser induced plasma vaporization and ionization technique is proposed for electric field assisted deposition of proteins. Experiments were carried out depositing thick layers of lysozyme on metal, creating submillimeter patterns. The enzymatic activity of horseradish peroxidase deposited by this method was tested, together with that of the enzyme laccase from a micro‐organism. The applicability of this method to the construction of nanometric patterns for bioelectronic purposes is discussed.

Laser-Assisted Fabrication of Biomolecular Sensing Microarrays

With the aim of obtaining high density biosensing arrays we use pulsed laser deposition to immobilize functional biomolecules on useful surfaces, and micro- and nanopatterning techniques for fabrication of prototype immunosensing bioarrays. We report biological activity tests demonstrating the functional properties of the immobilized proteins and atomic force microscopy characterization of films of nanometric dimensions. Laser-fabricated immunofluorescent arrays are analyzed to check that the intensity and contrast of the sensing sites allow efficient device fabrication. We have also developed an elementary array of heterogeneous reaction sites and tested its performance by simultaneous incubation with the different specific antigens.

Microstructural and morphological properties of homoepitaxial (001)ZnTe layers investigated by x-ray diffuse scattering

The microstructural and morphological properties of homoepitaxial (001)ZnTe layers grown by metalorganic vapor phase epitaxy at a temperature (TG) between 325°C and 400°C are investigated by x-ray diffuse scattering. High resolution reciprocal space maps (RSMs) recorded close to the ZnTe (004) Bragg peak show different diffuse scattering features that can be ascribed to (i) the specific surface morphology of the sample, and (ii) the presence of extended lattice defects in the epilayers. One kind of cross-shaped diffuse scattering streaks, appearing for TG⩾350°C, extend along ⟨111⟩ directions and can be attributed to stacking faults (SFs) occurring at the epilayer–substrate interface, within the epilayers. The SF diameter was estimated around 200–300nm, while their density increases with TG. Another kind of cross-shaped diffuse streaks, inclined at an angle β≈80° with respect to the ⟨110⟩ in-plane direction, arises from the morphology of epilayers grown above 360°C, their surfaces being covered by pairs of...

MICROLITHOGRAPHIC TECHNIQUES FOR LASER ASSISTED FABRICATION OF BIOELECTRONIC DEVICES

Microlithographic techniques are described for the fabrication of removable stencils to be used in micropatterning by laser deposition of organic and biological matter. Patterned layers are shown together with same atomic force microscope preliminary characterization. Also, a lithographically fabricated micron size glucose biosenser is shown, together with first assays of its performance.

Suspending DNA origami between four gold nanodots

Rectangular DNA origami functionalized with thiols in each of the four corners immobilizes by self-assembly between lithographically patterned gold nanodots on a silicon oxide surface.