Marco Negri

Porphyrin conjugated SiC/SiOx nanowires for X-ray-excited photodynamic therapy

The development of innovative nanosystems opens new perspectives for multidisciplinary applications at the frontier between materials science and nanomedicine. Here we present a novel hybrid nanosystem based on cytocompatible inorganic SiC/SiOx core/shell nanowires conjugated via click-chemistry procedures with an organic photosensitizer, a tetracarboxyphenyl porphyrin derivative. We show that this nanosystem is an efficient source of singlet oxygen for cell oxidative stress when irradiated with 6 MV X-Rays at low doses (0.4–2 Gy). The in-vitro clonogenic survival assay on lung adenocarcinoma cells shows that 12 days after irradiation at a dose of 2 Gy, the cell population is reduced by about 75% with respect to control cells. These results demonstrate that our approach is very efficient to enhance radiation therapy effects for cancer treatments.

Activation and control of visible single defects in 4H-, 6H-, and 3C-SiC by oxidation

In this work, we present the creation and characterisation of single photon emitters at the surface of 4H- and 6H-SiC, and of 3C-SiC epitaxially grown on silicon. These emitters can be created by annealing in an oxygen atmosphere at temperatures above 550 °C. By using standard confocal microscopy techniques, we find characteristic spectral signatures in the visible region. The excited state lifetimes are found to be in the nanosecond regime in all three polytypes, and the emission dipoles are aligned with the lattice. HF-etching is shown to effectively annihilate the defects and to restore an optically clean surface. The defects described in this work have ideal characteristics for broadband single photon generation in the visible spectral region at room temperature and for integration into nanophotonic devices.

Carbon-doped SiO x nanowires with a large yield of white emission

The growth of SiOx nanowires (NWs) with intense white emission is reported. Due to carbon monoxide gas being used as a dopant precursor, carbon-doped under-stoichiometric silicon dioxide NWs are obtained. The doping of the NWs is studied by means of x-ray photoelectron spectroscopy, which allows to assess the presence of carbon atoms in the silicon oxide amorphous structure. The light emission properties are studied by means of cathodoluminescence spectroscopy, which shows three main emission bands set at 2.7 eV (blue), 2.3 eV (green) and 1.9 eV (red), resulting in the white emission.

Cold field electron emission of large-area arrays of SiC nanowires: photo-enhancement and saturation effects

This paper explores the cold field emission (CFE) properties of SiC nanowire (NW) arrays. The CFE currents were studied in the dark and under ultra-violet (UV) irradiation conditions. An increase in CFE current was observed when the SiC NW arrays were illuminated, with a consequent decrease in the values of the turn-on field and the threshold field. Furthermore, while dark CFE currents were well described by the standard Fowler–Nordheim (FN) theory for metals, the photo-enhanced CFE currents showed nonlinearity in FN plots. Specifically, a voltage range of current saturation appeared, which is appealing for nanotechnological applications, and it is indeed an essential prerequisite for realizing devices such as FE photocathodes.

3C–SiC nanowires luminescence enhancement by coating with a conformal oxides layer

In this work, we report the light emission properties of different classes of 3C–SiC nanowires. We compare the luminescence of core/shell nanowires where the 3C–SiC core is covered by a SiOx shell of different thickness, or coated with different conformal oxide layers (aluminium oxide and gallium oxide), grown by atomic layer deposition. The main result is the enhancement of the 3C–SiC near-band-edge emission at room temperature with the nanowires surface coating, due to carriers diffusion from the shell to the core, promoted by the alignment between the oxides and SiC bands in a type I quantum-well.

Effects of Growth Parameters on SiC/SiO2 Core/Shell Nanowires Radial Structures

Cubic silicon carbide - silicon dioxide core-shell nanowires have been synthesized in a thermal CVD system from carbon monoxide on silicon substrate. Using a non-ionic surfactant during the coating process of the substrate by the catalyst, the uniformity of the catalytic layer was improved, resulting in a more uniform nanowires growth. It is demonstrated that the core diameter is strongly correlated with the precursor concentration.

Silicon Carbide in Microsystem Technology — Thin Film Versus Bulk Material

This chapter looks at the role of silicon carbide (SiC) in microsystem technology. It starts with an introduction into the wide bandgap (WBG) materials and the properties that make them potential candidates to enable the development of harsh environment microsystems. The future commercial success of WBG microsystems depends mainly on the availability of high-quality materials, well-established microfabrication processes, and economic viability. In such aspects SiC platform, in relation to other WBG materials, provides a clear and competitive advantage. The reasons for this will be detailed. Furthermore, the current status of the SiC thin film and bulk material technologies will also be discussed. Both SiC material forms have played important roles in different microsystem types.

Effect of a halogen-based precursor on dopant incorporation in 3C-SiC film epitaxy

Silicon carbide thin films were synthesised by vapour phase epitaxy technique on silicon substrates using silane and propane as precursors. Methyltrichlorosilane (MTS) was added, and nitrogen was used as dopant precursor. Samples with different doping concentrations were obtained varying the nitrogen flow during the growth. Doping level for each sample was assessed using Raman technique, and a correlation between dopant flow and doping level was confirmed. The influence of MTS on nitrogen incorporation is analysed and discussed: the introduction of MTS increases the growth rate and increases the doping level. We exclude a direct doping effect by the MTS, but we think that it promotes the incorporation of nitrogen doping species. The crystalline quality of the as-grown films was evaluated using X-ray diffraction, assessing the good crystalline quality even in samples obtained using high growth rates and high doping level.

Engineering single defects in silicon carbide bulk, nanostructures and devices

We will review recent demonstrations of single photon emission in different silicon carbide (SiC) polytypes, in both bulk and nano-structured form. Due to well established doping, and micro- and nanofabrication procedures deep defects photoluminescence (PL) can be electrically excited and incorporated in SiC nanomaterials. Finally we will report on preliminary results to incorporate near infrared defects in SiC nanoparticles.

SiC NWs Grown on Silicon Substrate Using Fe as Catalyst

We report on the synthesis of SiC nanowires (NWs) using iron as catalyst. The NWs were grown on silicon substrate by vapour-liquid-solid (VLS) mechanism with propane and silane as precursors, both 3% diluted in hydrogen, and hydrogen as carrier gas. The growth temperature was 1250°C, to reach the eutectic values of the Si-Fe alloy and to permit the VLS mechanism. The as-grown SiC nanowires were characterized by scanning and transmission electron microscopy. The nanowires are from 30 to 100 nm in diameter and several μm in length, with <111> growth direction.