[show abstract][hide abstract] ABSTRACT: A new class of nanostructured hybrid materials is developed by direct grafting of a model thiophene-based organic dye on the surface of 3C-SiC/SiO2 core/shell nanowires. TEM-EDX analysis reveals that the carbon distribution is more spread than it would be, considering only the SiC core size, suggesting a main contribution from C of the oligothiophene framework. Further, the sulfur signal found along the treated wires is not detected in the as-grown samples. In addition, the fluorescent spectra are similar for the functionalized nanostructures and T3Pyr in solution, confirming homogeneous molecule grafting on the nanowire surface. Chemical and luminescence characterizations confirm a homogeneous functionalization of the nanowires. In particular, the fluorophore retains its optical properties after functionalization.
Nanoscale Research Letters 12/2012; 7(1):680. · 2.52 Impact Factor
[show abstract][hide abstract] ABSTRACT: In this work we report the enhancement of the 3C-SiC band edge luminescence induced by the SiO2 shell in a SiC/SiO2 core/shell nanowires (NWs) system. We demonstrate that the shell enhances the SiC near band edge luminescence and we argue the formation of a type-I quantum well between the SiC core and the SiO2 shell, with the consequent injection of carriers from the larger band-gap shell to the narrower band-gap core.
[show abstract][hide abstract] ABSTRACT: The luminescence properties of SiC/SiO 2 core/shell nanowires with different core to shell thickness ratio are analysed by SEM-Cathodoluminescence spectroscopy. The different radial NW structure, studied by trans-mission electron microscopy, deeply influences the efficiency of competitive radiative transitions. As the core to shell ratio decreases, the increase of a UV emission component is observed indicating that the elec-tron–hole pairs recombine directly in the silicon dioxide and the beneficial effect of shell-induced enhance-ment of the core emissions is less efficient.
[show abstract][hide abstract] ABSTRACT: beta-SiC nanowires were synthesized on different monocrystalline substrates: Si (001), Si (111), 3C-SiC (001), 4H-SiC (0001), 6H-SiC (0001). The SiC nanowire growth was carried out using a Chemical Vapor Deposition method, with silane and propane diluted in hydrogen (3%) as precursors. The deposition was performed at atmospheric pressure and at 1100 degrees C, after dewetting of the Ni catalyst, which had been previously evaporated onto the substrate, to induce 1D growth according to a VLS process. The crystal structure of the nanowires, as determined by X-ray diffraction and High Resolution Transmission Electron Microscopy, corresponds to 3C-SiC polytype growing along a (111) direction, irrespective of the substrate. The occurrence of (111) stacking faults was observed, partly reduced for samples grown on 3C-SiC substrate. The growth on (111) substrate allowed to achieve a good vertical alignment of the nanowires, as investigated by Scanning Electron Microscopy. High Angle Annular Dark Field imaging and Energy Dispersive X-Ray spectroscopy were performed to study the catalyst particle on top of the wires and showed the formation of a nickel-silicon alloy.
Journal of Nanoscience and Nanotechnology 05/2011; 11(5):4109-13. · 1.15 Impact Factor
[show abstract][hide abstract] ABSTRACT: To assess deformation issues in the vapor phase epitaxy of 3C-SiC on (001) and (111) Si substrates, we investigated different pre-growth (carburisation) procedures, adding various amount of SiH4 to C3H8. The mechanical deformation of the samples was measured by quantitative Makyoh topography, through which 3D deformation maps of the entire wafers were obtained. X-ray diffraction was used to check the crystal quality of the layers and, in transmission geometry, to assess whether the observed deformation was plastic or elastic. Residual stress of the deposited 3C-SiC layers was investigated across the entire wafer substrates by using Raman spectroscopy and values between 0.5 and 1GPa were found. It was observed that, for a given carburisation procedure, the crystalline orientation of the Si substrates plays an important role in the substrate curvature (convex and concave). The addition of SiH4 during carburisation ramp leads to increased deformation for SiC/Si (001), while decreased deformation for SiC/Si (111).
Journal of Crystal Growth 01/2011; 318(1):401-405. · 1.55 Impact Factor
[show abstract][hide abstract] ABSTRACT: We report the influence of the native amorphous SiO(2) shell on the cathodoluminescence emission of 3C-SiC/SiO(2) core/shell nanowires. A shell-induced enhancement of the SiC near-band-edge emission is observed and studied as a function of the silicon dioxide thickness. Since the diameter of the investigated SiC cores rules out any direct bandgap optical transitions due to confinement effects, this enhancement is ascribed to a carrier diffusion from the shell to the core, promoted by the alignment of the SiO(2) and SiC bands in a type I quantum well. An accurate correlation between the optical emission and structural and SiO(2)-SiC interface properties is also reported.
[show abstract][hide abstract] ABSTRACT: Nanowires (NWs) open promising near-future perspectives for the design and fabrication of nano-scale devices. In this paper we discussed the 3C-SiC NW preparation obtained by three different growth procedures:
[show abstract][hide abstract] ABSTRACT: This paper reviews the most important properties of germanium, gives an insight into the newer techniques and technology for the growth of epitaxial Ge thin layers and focuses on some applications of this material, with a special emphasis on recent achievements in electronics and photovoltaics. We will highlight the recent development of Ge research and will give an account of the most important Ge applications that emerged in the last two decades.Germanium is a key material in modern material science and society: it is used as a dopant in fiber optic glasses and in semiconductor devices, both in activating conduction in layers and also as a substrate for III–V epitaxy. Ge is also widely used in infrared (IR) detection and imaging and as a polymerization catalyst for polyethylene terephthalate (PET). Moreover, high-speed electronics for cell phone communications relies heavily on SiGe alloys. Ge electronics is nowadays gaining new interest because of the enhanced electronic properties of this material compared to standard silicon devices, but the lack of a suitable gate oxide still limits its development. High efficiency solar cells, mainly for space use but also for terrestrial solar concentration have surpassed 40% efficiency and Ge has a lead role in achieving this goal.The main focus of the paper is on Ge epitaxy. Since epitaxy starts from the surface of the substrate, different studies on substrate pre-epitaxy, surface analysis and preparations are reviewed, covering the most common substrates for Ge deposition such as Ge, Si and GaAs. The most used Ge precursors such as GeH4 and GeCl4 are described, but several novel precursors, mostly metal-organic, have recently been developed and are becoming more common in epitaxial Ge deposition. Epitaxial growth of Ge by means of the most common methods, including Chemical Vapour Deposition and Molecular Beam Epitaxy is discussed, along with some recent advances in Ge deposition, such as Atomic Layer Deposition and Low Energy Plasma-Enhanced Chemical Vapour Deposition.Several Ge applications are finally discussed, with the aim of providing insights into the potential of this material for the development of novel devices that are able to surpass the current limits of standard device design. Ge in microelectronics is becoming more and more important, thanks to the possibilities offered by bandgap engineering of strained SiGe/Si. However, lack of a good Ge oxide is posing several problems in device improvement. In the field of photovoltaics Ge is mainly used as a substrate for high efficiency III–V solar cells and for the development of thermophotovoltaic devices instead of the most expensive and scarcer GaSb. In this field, Ge epitaxy is very rare but the development of an epitaxial Ge process may help in developing new solar cells concepts and to improve the efficiency of thermophotovoltaic converters. Ge may play a role even in new spintronics devices, since a GeMn alloy was found to have a higher Curie temperature than GaAsMn.
Progress in Crystal Growth and Characterization of Materials - PROG CRYST GROWTH CHARACT. 01/2010; 56(3):146-174.
[show abstract][hide abstract] ABSTRACT: A new method has been developed to grow nickel-catalysed SiC nanowires on silicon, by a chemical reaction involving carbon tetrachloride as a single precursor. This produces long crystalline 3C–SiC nanowires with <111> axis, as verified by transmission electron microscopy. A broad optical emission centred at about 2 eV is detected by cathodoluminescence spectroscopy. The Gaussian component at about 2.2 eV corresponds to the indirect 3C–SiC band gap emission, while the dominant red emission is related to oxygen incorporation.
[show abstract][hide abstract] ABSTRACT: Wafer bending is a serious problem that affects the growth of cubic silicon carbide on silicon. Thermal and lattice mismatch are often cited as the causes of stress in this system, but they alone cannot account for severe wafer warp seen in many cases. This work proposes diffusion-induced stress as a new mechanism that can explain the extreme degree of bending observed.
Materials Letters - MATER LETT. 01/2008; 62(14):2129-2131.