Nanoshaping field emitters from glassy carbon sheets: a new functionality induced by H-plasma etching.

This paper reports on the morphological and electrical characterization at the nanometer scale and the investigation of the field emission characteristics of glassy carbon (GC) plates which underwent H-induced physical/chemical processes occurring in a dual-mode MW-RF plasma reactor. Plasma treatment produced on the GC surface arrays of vertically aligned conically shaped nanostructures, with density and height depending on the plasma characteristics. Two kinds of samples obtained under two different bias regimes have been deeply analyzed using an AFM apparatus equipped with tools for electric forces and surface potential measurements. The features of electron emission via the Field Emission (FE) mechanism have been correlated with the morphology and the structure at the nanoscale of the treated glassy carbon samples. The measured current density and the characteristics of the emission, which follow the Fowler-Nordheim law, indicate that the plasma-based methodology utilized for the engineering of the GC surfaces is able to turn conventional GC plates into efficient emission devices. The outstanding properties of GC suggest the use of such nanostructured materials for the assembling of cold cathodes to be used in a harsh environment and under extreme P/T conditions.

Rhodamine/Nanodiamond as a System Model for Drug Carrier.

In this paper we present some strategies that are being developed in our labs towards enabling nanodiamond-based applications for drug delivery. Rhodamine B (RhB) has been choosen as model molecule to study the loading of nanodiamonds with active moieties and the conditions for their controlled release. In order to test the chemical/physical interactions between functionalized detonation nanodiamond (DND) and complex molecules, we prepared and tested different RhB@DND systems, with RhB adsorbed or linked by ionic bonding to the DND surface. The chemical state of the DND surfaces before conjugation with the RhB molecules, and the chemical features of the DND-RhB interactions have been deeply analysed by coupling DND with Au nanoparticles and taking advantage of surface enhanced Raman spectroscopy SERS. The effects due to temperature and pH variations on the process of RhB release from the DND carrier have been also investigated. The amounts of released molecules are consistent with those required for effective drug action in conventional therapeutic applications, and this makes the DND promising nanostructured cargos for drug delivery applications.

Diamond layers grown by chemical vapor deposition on NbN systems and NbN/SiO2-based devices.

Deposits of individual diamond grains and continuous polycrystalline diamond layers have been generated by means of a HFCVD technique onto different types of untreated or seeded NbN surfaces. To test the feasibility of using diamond layers as protective coatings for aerospace applications, we carried out diamond deposition onto the lithographically defined NbN microelectrodes of a NbN/SiO2 multifinger device. The morphological and structural features of the diamond deposits and of the substrates were characterized by FE-SEM, XRD and Raman spectroscopy. The preferential growth of diamond on the superconductive NbN enables the selective coating of the NbN microstripes sputtered on the insulating SiO2. Moreover the diamond coating procedure is able to preserve the structural integrity of the substrate material and to retain the shaped architecture of the device. For the polycrystalline diamond layers grown on NbN a residual stress of -9.8 GPa, largely due to thermal stress, has been estimated by Raman analysis. The diamond coatings of the NbN-based architectures result to be mechanically stable.

Low temperature conductivity of carbon nanotube aggregates.

We compare, over wide temperature ranges, the transport properties of single-wall carbon nanotubes arranged in the form of aligned arrays or in the form of fibres. The experimental data show that both the forms of aggregates present a crossover in the transport mechanism from three-dimensional hopping of the electrons between localized states at high temperature to fluctuation-induced tunnelling across potential barriers at low temperature. The role of the junctions formed between the bundles in the array and between the nanotubes inside the fibres is discussed on the basis of the experimental results.

An innovative and viable route for the realization of ultra-thin supercapacitors electrodes assembled with carbon nanotubes.

Electrochemical Double Layer Capacitors (EDLC), also known as supercapacitors, have been fabricated using Single Walled Carbon Nanotubes (SWCNTs) as active material for electrode assembling. In particular a new way of fabrication of ultra-thin electrodes (< or = 25 microm) directly formed on the separator has been proposed, and a prototype of EDLC has been realized and tested. For such devices the specific capacitance is in the range 40-45 F/g and the internal resistances in the range 6-8 omega x cm2, at current density of 2 mA x cm-2.

Charge transport and tunneling in single-walled carbon nanotube bundles.

We investigate experimentally the transport properties of single-walled carbon nanotube bundles as a function of temperature and applied current over broad intervals of these variables. The analysis is performed on arrays of nanotube bundles whose axes are aligned along the direction of the externally supplied bias current. The data are found consistent with a charge transport model governed by the tunneling between metallic regions occurring through potential barriers generated by a nanotube's contact areas or bundle surfaces. Based on this model and on experimental data, we describe quantitatively the dependencies of the height of these barriers upon bias current and temperature.

Nanocrystalline diamond films grown in nitrogen rich atmosphere: structural and field emission properties.

The field emission behaviour of a series of nanocrystalline N-doped diamond films has been investigated and interpreted on the basis of the structural and compositional characteristics of the layers. The diamond films, formed by crystallites with grain size in the range 20-100 nm were produced from CH4/H2 mixtures using a HF-CVD apparatus. Nitrogen was added to the gaseous reactants in form of both N2 and of Urea. Micro-Raman spectroscopy and cathodoluminescence have been used to define the structure of the deposits on a nanometric scale. The field emission measurements have been carried out under a pressure of 10(-6) mbar using a sphere-to-plane anode-cathode configuration. The characteristics of the emission from the various nanodiamond samples and from different regions of the same sample are discussed in terms of field threshold, current density, current stability.

Hybrid carbon nanotube/nanodiamond structures as electron emitters for cold cathodes.

The field emission properties of hybrid carbon nanotubes/nanodiamond structures produced by one-step chemical vapor deposition (CVD) process have been investigated in order to assess their application as electron emitters for cold cathodes. The electron emission properties of a series of samples have been investigated by current-pressure, current-voltage and current-time measurements with the aim of testing the emission stability under working conditions relevant to technological applications. Stable emission, high values of current density and lack of arcing have been observed during prolonged working cycles, and without degradation of the material structure.

Polycrystalline diamond on self-assembled detonation nanodiamond: a viable route for fabrication of all-diamond preformed microcomponents.

Surface assisted self-assembly of detonation nanodiamond particles (with typical sizes in the range 4-10 nm) has been obtained using different fractions of colloidal aqueous dispersions as starting material. The relationship between dispersion properties and structure/geometry of the aggregates deposited on Si or glass plates has been investigated. A series of differently shaped free-standing nanodiamond structures has been prepared, analysed and used as templates for the growth of polycrystalline diamond layers by the chemical vapour deposition (CVD) technique. The possibility of obtaining textured coating with a relatively strong [Formula: see text] preferred orientation (within a solid angle of about 0.6 srad) is also reported. Overall, the coupling of nanodiamond self-assembling to the CVD diamond growth enables one to produce specimens with complex 3D architectures. The proposed microfabrication methodology could represent a viable route for the production of free-standing all-diamond microcomponents, with tailored shapes and predefined crystalline features, to be used for advanced electronic applications.