Silvia Orlanducci

Effect of tip geometry on local indentation modulus measurement via atomic force acoustic microscopy technique

Atomic force acoustic microscopy (AFAM) is a dynamical AFM-based technique very promising for nondestructive analysis of local elastic properties of materials. AFAM technique represents a powerful investigation tool in order to retrieve quantitative evaluations of the mechanical parameters, even at nanoscale. The quantitative determination of elastic properties by AFAM technique is strongly influenced by a number of experimental parameters that, at present, are not fully under control. One of such issues is that the quantitative evaluation require the knowledge of the tip geometry effectively contacting the surface during the measurements. We present and discuss an experimental approach able to determine, at first, tip geometry from contact stiffness measurements and, on the basis of the achieved information, to measure sample indentation modulus. The reliability and the accuracy of the technique has been successfully tested on samples (Si, GaAs, and InP) with very well known structural and morphological ...

Nanodiamonds coupled with plant bioactive metabolites: A nanotech approach for cancer therapy

Nanodiamond application in biotechnological and medical fields is nowadays in continuous progress. In fact, biocompatibility, reduced dimensions and high surface chemical interaction are specific features that make nanodiamonds perfect intracellular carriers of bioactive compounds. By confocal microscopy, we confirmed that nanodiamonds were able to penetrate in cell cytoplasm but we also demonstrated how they remained embedded in nuclear membrane just exposing some little portions into nuclear area, definitively clarifying this topic. In this work, for the first time, nanodiamonds were conjugated with plant secondary metabolites, ciproten and quercetin. Moreover, since drug-loading on nanoparticles was strongly conditioned by their chemical surface, different types of nanodiamonds (oxidized, wet chemical reduced and plasma reduced) were synthesized in this work and then functionalized with plant compounds. We found that ciproten and quercetin antiproliferative effects, on human (HeLa) and murine (B16F10) tumor cells, were improved after nanodiamond conjugation. Moreover, plant molecules highly reduced their in vitro pro-oxidant, cytotoxic and pro-apoptotic activity when associated with nanodiamond. We are led to suppose that natural drug-nanodiamond adducts would act at cellular level by different molecular mechanisms with respect to plant metabolite pure forms. Finally, our results showed that chemical and structural modifications of nanodiamond surfaces influenced the bioactivity of transported drugs. According to all these evidences, this work can be considered as a promotional research to favor the use of bioactive plant molecules associated with nanodiamonds for therapeutic purposes.

Carbon nanotube/nanodiamond structures: An innovative concept for stable and ready-to-start electron emitters

Efficient and robust cold cathodes have been assembled using as emitting material mats of single wall carbon nanotubes (SWCNTs) coated with nanodiamonds. The preparation of the hybrid nanotube/nanodiamond structures by chemical vapor deposition is a route suitable to be scaled up and adapted to the electronic industry requirements. Turn-on field of 1.7 V/μm and emission current density J of 6 mA/cm2 at applied field E of 6.2 V/μm were measured. The field emission properties of SWCNT coated with nanodiamond are very attractive in terms of reproducibility, current stability under medium vacuum and lack of arcing. Moreover, the diamond coating acts against the adsorption of chemical species, making it possible to avoid the outgassing procedures usually needed for current stabilization and allowing to reduce the time response for electron sources assembled with these hybrid materials.

Characterization of carbon structures produced by graphene self-assembly

Low-dimensional carbon-based materials, in particular two-dimensional graphenic carbon structures, have been produced from single-walled carbon nanotube disruption using high-shear mixing and/or treatments in sulfonitric acid mixtures at both room and high temperature. Among other two-dimensional graphenic carbon structures, colloidal dispersions of graphenic nanoflakes have been obtained. Different structural arrangements, resulting from the reorganization of carbon because of the disruption procedures applied, were observed through selected area electron diffraction (SAED) and through reflection high-energy electron diffraction (RHEED) analyses coupled to transmission and scanning electron microscopy observations. Such combined investigations in the real and reciprocal space provided structural information at the nanoscale on the clustering of graphene layers in nanoplatelets or/and on their assembly into highly ordered (single-crystal) nanosheets. Furthermore, a different carbon phase exhibiting an orthorhombic cell with Cmma symmetry has been detected by SAED and RHEED analyses. In addition, a variety of self-assemblies of hexagonal basal planes have been observed to occur as the result of their different rotational and/or translational stacking faults. Overall, the reported results contribute to define the conditions for a controlled self-assembly of graphene-based structures with tailored dimensions, which is an important technological challenge, as their structure at the nanoscale dramatically affects their electrical properties.

Photoconductivity of packed homotype bundles formed by aligned single-walled carbon nanotubes.

Photoconductivity properties of aggregated single-walled carbon nanotubes have been studied by performing measurements on macroscopic ribbons, obtained by the aggregation of a large number of SWCNT bundles. Structural analysis performed by electron diffraction revealed that the nanotubes forming each bundle have the same chirality. The experimental results, regarding the region 1.2-3.6 eV and the pressure range 10(3)-10(-3) mbar, suggest that the photoexcitation of nanotubes, packed in bundles and organized in ribbons, generates electron-hole pairs within a band structure and that bond excitons are formed by Coulomb interactions between spatially confined charge carriers.

Nanodiamonds coupled with 5,7-dimethoxycoumarin, a plant bioactive metabolite, interfere with the mitotic process in B16F10 cells altering the actin organization.

For the first time, we coupled reduced detonation nanodiamonds (NDs) with a plant secondary metabolite, citropten (5,7-dimethoxycoumarin), and demonstrated how this complex was able to reduce B16F10 tumor cell growth more effectively than treatment with the pure molecule. These results encouraged us to find out the specific mechanism underlying this phenomenon. Internalization kinetics and quantification of citropten in cells after treatment with its pure or ND-conjugated form were measured, and it was revealed that the coupling between NDs and citropten was essential for the biological properties of the complex. We showed that the adduct was not able to induce apoptosis, senescence, or differentiation, but it determined cell cycle arrest, morphological changes, and alteration of mRNA levels of the cytoskeletal-related genes. The identification of metaphasic nuclei and irregular disposition of β-actin in the cell cytoplasm supported the hypothesis that citropten conjugated with NDs showed antimitotic properties in B16F10 cells. This work can be considered a pioneering piece of research that could promote and support the biomedical use of plant drug-functionalized NDs in cancer therapy.

Modulation of charge transport in diamond-based layers

Doping of diamond by substitutional insertion of metallic species or production of diamond/metals nanocomposite layers has been obtained by a hybrid chemical vapor deposition based technique. The potential of such an approach makes it possible to obtain a wide class of purposely designed diamond-based structures characterized by specific properties of charge transport. Reflection high-energy electron diffraction, scanning electron microscopy and x-ray dispersive spectrometry have been used to study the structural and compositional characteristics of some Nd-, W- and Ti-containing diamond films. The peculiar electrical properties conferred to the host diamond layers by the insertion of various metals have been investigated in the range of 25–500 K by performing Hall effect and conductivity measurements. The mechanism of charge transport and the electrical properties of these materials are found to be mainly governed by organization of the metallic species, which can be in different forms, such as dispersio...

Field emission from silicon nanowires: Conditioning and stability

We report the low-pressure chemical vapor deposition growth and field emission characterization of silicon nanowires (SiNWs). Our field emission results show the importance of the so called conditioning process on the reproducibility of the emission performance itself; this effect has proven to be reversible for the investigated current regime. We explained this behavior by invoking a current-driven desorption of residual adsorbed gases. A highly reproducible turn-on electric field of 27 V∕μm is found for a diode-connected SiNW planar sample. Furthermore, stability analysis is performed showing the technologically promising field emission behavior of the samples.

Magnetic resonance study of Ni nanoparticles in single-walled carbon nanotube bundles

We present a detailed study of the electron magnetic resonance EMR properties of Ni nanoparticles NPs placed in the bundles of single-walled carbon nanotubes produced by arc discharge with Ni catalyst. The behavior of EMR signals has been investigated in the 10–300 K temperature range for the initial powderlike materials and those diluted in a nonmagnetic matrix. The magnetic response evolves between two modes, ferromagnetic and superparamagnetic, depending on both the temperature and distribution of Ni nanoparticles in the sample. The behavior of EMR spectra shows that the initial materials retain the ferromagnetic character of the NP ensemble even at room temperature. This is most likely due to dipole-dipole interactions and macroscopic demagnetizing fields stemming from powderlike composition of the samples. For the diluted materials, the actual superparamagnetic signal is observed at room temperature. As temperature is reduced, the behavior of the EMR parameters reflects a gradual transition from free rotated magnetic moments of NPs to those ordered along the “easy” magnetic axes blocked state . In the 300–130 K temperature range, anomalous temperature dependence of the resonance magnetic field Hres was observed. It is examined in terms of competition between the single-particle anisotropy energy and dipole interactions between the Ni nanoparticles. Finally, a transition to a blocked state occurs at blocking temperature estimated as Tb 40 K. At lower temperatures, both the dense and diluted samples behave identically.

Evaluation of the gauge factor for membranes assembled by single-walled carbon nanotubes

Samples of single-walled carbon nanotubes (SWCNTs) organized in the form of thin membranes have been investigated in order to correlate the mechanical deformation and conductivity behavior of such nanosized material. The nanotubes gauge factor of piezoresistivity has been evaluated by comparing the electrical responses induced by the deformation in SWCNT membranes and in Si substrates with the same electrical characteristics. The gauge factor of the SWCNT–Si systems was found to be a factor 2.3–2.5 larger than that of the Si substrates. We have also observed that temperature slightly enhances the piezoresistive response of the SWCNT.