One-dimensional heterostructures, based on functionalities of dissimilar materials within a monolithic structure, are promising building blocks for different applications. Herein, utilizing surface decoration of multiwalled carbon nanotubes (MWCNTs) with hydrogenated graphitic carbon layers (HGCLs), the realization of a vertically aligned MWCNT/amorphous-silicon (a-Si) core/shell heterostructure is reported. The proposed method enables the formation of conformal, continuous, and all-around silicon deposition on the carbon nanotube and eliminates any signature of line-of-sight deposition problem, even for thicknesses as low as a few nanometers. Precise elaboration using comparative Raman analysis reveals that the HGCLs play a major role in the construction of such structures. Evidence of direct binding between Si and C, a missing remarkable feature in previous reports, has been observed in high-resolution transmission electron microscope images and X-ray photoelectron spectroscopy. Monitoring time evolution during the formation of the silicon shell declares a diffusive mechanism for the deposition of Si on the surface of MWCNTs. Furthermore, the electro-optical proficiency of the MWCNT/a-Si heterostructure was studied by fabrication of a photodiode. Unlike previous attempts, a naturally formed Schottky junction at the high-quality a-Si/nanotube interface is exploited for charge separation in this photodiode, which provides a sensitivity of >10⁷% in the reverse saturation current for a wavelength of λ = 405 nm.

Metal-assisted etching of silicon in HF/H₂O₂ aqueous solutions has been used to fabricate luminescent silicon nanowires (SiNWs) and porous silicon. The impact of the gold catalyst layer thickness and the etching solution on the morphology of the synthesized nanostructures and the diameter of the obtained nanowires were systematically investigated. Scanning electron microscopy (SEM) analyses reveal that the morphology of the fabricated structures strongly depends on the composition of the solution and the thickness of the catalyst layer. It has been observed that SiNWs are formed in solutions with H₂O₂ ratios (ξ) below 10 %; increasing the H ₂O₂ concentration above this critical value leads to mesoporous (10 % < ξ < 14 %) and macroporous (14 % < ξ < 17 %) structures. Photoluminescence measurements show that SiNWs emit light at about 430 nm. Fourier transform infrared (FTIR) spectroscopy and transmission electron microscopy (TEM) analyses were utilized to determine the origin of the emission in the silicon nanostructures. TEM imaging demonstrates that SiNWs are covered by a thin layer of porous silicon, which is assumed to be responsible for their light emission.

The formation of high sensitivity-wide dynamic range field emission pressure sensors based on carbon nanotubes (CNTs) is reported. In this work, CNTs are grown inside an array of micromachined holes in order to ensure a high sensitivity and a wide dynamic range by allowing anode-cathode proximity while preventing anode-cathode direct contact simultaneously. External pressure is applied to a Si-based flexible anode, which results in consequent variations in emission current, due to electric field changes. Microcavities in this structure have been formed by a Si deep vertical etching process, while the CNTs have been grown by direct current plasma-enhanced chemical vapour deposition. Also, it is demonstrated that a similar fabrication process can be applied to implement a device with an electrically controllable emission current. A high sensitivity of 1.5-13.7 μA kPa^-1 (with V_{anode/cathode} < 100 V) within a dynamic range from around 0.1 to 1 GPa, is measured in this experiment.

We report a novel method for the formation of hollow rod silicon nanostructures via plasma treated nanosphere lithography and reactive ion etching. The plasma treatment of polystyrene nanospheres (PS-NS) with O ₂ and methanol-O₂ gases is studied as a function of nanosphere size, plasma power and treatment time on a silicon substrate covered by a thin layer of nickel. Applying hydrogen or HCl plasma to already treated polystyrenes, nano-rings and nano-dots can be obtained without any physical or sputtering damage. Large area silicon nano-pillars and hollow silicon nano-structures with inner diameters of 50 nm were obtained by using optimized plasma treatment. These nanostructures show a hexagonal order with good fidelity to the PS-NS patterns. Various characterization techniques such as AFM, SEM, TEM, XPS and FTIR spectroscopy have been exploited to study the samples. The hollow rod structures made using this method will have applications in low power high performance electronic devices, optoelectronic and lithium ion battery devices. Also, a model for the formation of hollow rings is presented. This journal is

Silicon nanocrystals with dimensions of about 3 to 4 nm are fabricated by hydrogenation of amorphous silicon layers with thickness of about 15 nm. The strong binding of nanocrystals to the amorphous matrix, which prevents them from showing luminescence, is broken up by a plasma treatment process in the presence of H₂, N₂O, and SF₆. Regions with high nanocrystal density show more resistance against plasma etching. By controlling the etching parameters such as precursor flow rates during hydrogenation and plasma treatment processes, it seems possible to realize luminescent layers. Photoluminescence (PL) studies show that nanocrystals emit light around a wavelength of 550 nm. Multilayer structures have been fabricated to increase the PL intensity by separating luminescent nanocrystal layers with a 5 nm-thick layer of silicon oxynitride. The entire fabrication process has been performed in a conventional RF-PECVD reactor offering hope for realization of cost-effective silicon lightemitting structures. The low temperature nature of the proposed process could lead to the fabrication of light-emitting devices on low cost substrates like glass or even plastic.