Andrea Di Donato

Tomographic effects of near-field microwave microscopy in the investigation of muscle cells interacting with multi-walled carbon nanotubes

In this work, we introduce a hybrid atomic-force/near-field scanning microwave microscope, exploiting the tomographic capabilities of the microwave microscopy to explore structures of relevant interest, namely, samples involving both biological and non-biological materials at the same time. In particular, we show imaging of C2C12 muscle cells grown in the presence of bundles of multi-walled carbon nanotubes: here, the microwave microscopy, by virtue of its tomographic potentiality, highlights how cells incorporate some nanotubes in their fibers.

Broadband Scanning Microwave Microscopy investigation of graphene

In this work we describe the application of a dual-channel scanning probe microscope performing simultaneously Scanning Tunneling Microscopy (STM) and wide-band Near Field Scanning Microwave Microscopy (wide-band SMM) - developed by ourselves- to a graphene flake. In our system we introduce a conversion in Time-Domain to discriminate the desired information, achieving high quality microwave images with nanometric resolution. The graphene sample is deposited on a substrate of SiO2 with an additional deposition of gold (a contact finger). The preliminary measurements seem to show evidence of localized change of impedance near the edge of the flake.

Stationary Mode Distribution and Sidewall Roughness Effects in Overmoded Optical Waveguides

In this paper, the authors investigate analytically the transformation from the initial guided mode distribution to the stationary state and the effects of the bidimensional roughness profile, in multimode polymeric buried waveguides. In these structures, due to the geometrical dimensions and the operating wavelength, about a thousands of guided modes can propagate, even for weak core/cladding dielectric contrast. The coupling coefficients are computed by exploiting the geometrical features of the optical channels, such as the waveguide dimensions and the roughness surface statistics. The analysis gives insight on the guided/guided and guided/radiated mode interaction, and higher order solution is proposed, in the case of a great number of modes interacting over distances that are extremely long as compared to the signal wavelength and the roughness correlation length. Experimental results are valuated by means of semicontact atomic force microscopy as well as compared with existing numerical models.

Near-Field Microwave Investigation of Electrical Properties of Graphene-ITO Electrodes for LED Applications

We propose a method to evaluate the electrical properties of nanoscale layered materials. This study is important for the potential application of these structures in light emitting diode electrodes. For this purpose we measure the reflection coefficient of a microwave signal recorded by a near-field Scanning Microwave Microscope. This method allows the non-contact measurement of the sheet resistance of the material under analysis. It provides detailed maps of the electrical properties of a micrometric area under test to assay its uniformity. In particular, we have applied this technique to a multilayer material composed by an Indium–Tin–Oxide film and few layer graphene.

Fast ultrahigh-density writing of low-conductivity patterns on semiconducting polymers.

The exceptional interest in improving the limitations of data storage, molecular electronics and optoelectronics has promoted the development of an ever increasing number of techniques used to pattern polymers at micro and nanoscale. Most of them rely on atomic force microscopy to thermally or electrostatically induce mass transport, thereby creating topographic features. Here we show that the mechanical interaction between the tip of the atomic force microscope and the surface of π-conjugated polymeric films produces a local increase of molecular disorder, inducing a localized lowering of the semiconductor conductivity, not associated to detectable modifications in the surface topography. This phenomenon allows for the swift production of low-conductivity patterns on the film surface at a speed exceeding 20 μm s⁻¹; paths have a resolution in the order of the tip size (20 nm) and are detected by a conducting-atomic force microscopy tip in the conductivity maps.

Self-consistent simulation of multi-walled CNT nanotransistors

We present detailed results of the self-consistent analysis of carbon nanotube (CNT) field-effect transistors (FET), previously extended by us to the case of multi-walled/multi-band coherent carrier transport. The contribution to charge transport, due to different walls and sub-bands of a multi-walled CNT, is shown to be generally non-negligible. In order to prove the effectiveness of our simulation tool, we provide interesting examples about current–voltage characteristics of four-walled semi-conducting nanotubes, including details of numerical convergence and contribution of sub-bands to the calculation.

Time-Domain Reflectometry for Near-Field Scanning Microwave Microscopy

Time-Domain Reflectometry (TDR) is a well-well known technique, widely used in several fields, such as signal integrity and remote sensing. Here we show that TDR can be conveniently used in the Near-Field Scanning Microwave Microscopy, regardless the apparent mismatch between timescales involved at nanoscale and the period of a microwave signal. The technique is demonstrated on Highly Oriented Pyrolitic Graphite (HOPG) and CVD graphene.

Graphene etching by a Near-Field Scanning Microwave Microscope

Significant efforts are being invested in investigation of graphene, as well as its nanopatterning and shaping, owing to its promising properties. Here we present a study of hexagonal graphene flakes, deposited on a copper foil by chemical vapor deposition. In particular we have exploited a Near-Field Scanning Microwave Microscope, and investigated the impact of the microwave power on the sample. From preliminary data, we found the possibility of inducing a localized destruction of the graphene by means of the near-field microwave probe. We exploited this effect to create a recognizable pattern on a flake. A discussion of the roles of concurrent physical phenomena is also presented.

Infrared imaging in liquid through an extrinsic optical microcavity

The mutual interference of light scattered inside an extrinsic Fabry-Perot microcavity, fed by a low-coherence light, is exploited to achieve infrared imaging in a liquid environment. The transverse field distribution inside a cavity is shaped by the effect of scattered interfering waves in a lens-free system. Reflectivity and contrast phase maps are extracted through the analysis of the cavity response in the time domain. This approach allows to conjugate noninvasivity, subdiffraction imaging, possible quantitative evaluation of dielectric constants and infrared spectroscopy, making it suitable for biological applications.

Near field microwave microscopy for nanoscale characterization, imaging and patterning of graphene

This paper reports images of reproducible nanopatterns on hexagonal graphene flakes, produced by modulating the input power of a Near-Field Scanning Microwave Microscope, used at the same time for the characterization of the samples. We have studied the impact of different time exposures to the microwave field, and of different power levels. A possible explanation of the patterning mechanism is given by the heating-induced oxidation of the exposed graphene flakes. In order to confirm this assumption, we have developed a simplified model for the analysis of the heat distribution, and for the estimation of the temperature under the microscope probe. This effect could be the basis for an alternative nanolithographic technique.