Conversion of Amorphous Carbon on Silicon Nanostructures into Similar Shaped Semi-Crystalline Graphene Sheets.

Graphene sheets displaying partial crystallinity and nanowire structures were formed on a silicon substrate with silicon nanowires by utilizing an amorphous carbon source. The carbon source was deposited onto the silicon nanostructured substrate by breaking down a polymer precursor and was crystallized by a nickel catalyst during relatively low temperature inert gas annealing. The resulting free-standing graphene-based material can remain on the substrate surface after catalyst removal or can be removed as a separate film. The film is flexible, continuous, and closely mimics the silicon nanostructure. This follows research on similar solid carbon precursor derived semi-crystalline graphene synthesis procedures and applies it to complex silicon nanostructures. This work examined the progression of the carbon, finding that it migrates through the thin film catalyst and forms the graphene only on the other side, and that the process can successfully be used to form 3D shaped graphene films. Semi-crystalline graphene has the possible application of being flexible transparent electrodes, and the 3D shaping opens the possibility of more complex configurations and applications.

Solar Cell Based on Hybrid Structural SiNW/Poly(3,4 ethylenedioxythiophene): Poly(styrenesulfonate)/Graphene.

Solar energy is considered as a potential alternative energy source. The solar cell is classified into three main types: i) solar cells based on bulk silicon materials (monocrystalline, polycrystalline), ii) thin-film solar cells (CIGS, CdTe, DSSC, etc.), and iii) solar cells based on nanostructures and nanomaterials. Nowadays, commercial solar cells are usually made by bulk silicon material, which requires not only high fabrication costs but also limited performance. In this study, the fabrication of high-performance solar cells based on hybrid structure of silicon nanowires/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)/graphene (SiNW/PEDOT:PSS/Gr) is focused upon. SiNWs with different lengths of 125, 400, 800 nm, and 2 µm are fabricated by a metal-assisted chemical etching method, and their influence on the performance of the hybrid solar cells is studied and investigated. The experimental results indicate that the suitable SiNW length for the fabrication of the hybrid solar cells is about 400 nm and the best power conversion efficiency obtained is about 9.05%, which is about 2.1 times higher than that of the planar Si solar cell.

Surface-Enhanced Raman Spectroscopy (SERS) of Neonicotinoid Insecticide Thiacloprid Assisted by Silver and Gold Nanostructures.

This study expresses our results on surface-enhanced Raman spectroscopy (SERS) analyses of neonicotinoid insecticide thiacloprid, i.e., Calypso 480 SC, in quantities much smaller than usually applied in the agricultural medicine. Advanced Ag and Au nanostructures created by the thermal deposition technique on Al2O3 ceramic were applied as active substrates for SERS analyses. The minimum concentration of thiacloprid detected was 380 µM and the enhancement factor was estimated to be about 3 × 103. The intensity of the SERS peaks increased by an order of magnitude after pulsed laser annealing of the films and formation of nanoparticle arrays and the enhancement factor reached ≈104, respectively. The proposed study has direct bearing on the environment and human health by detection of small amounts or residue of harmful pollutants using a relatively cheap and easy method to produce active SERS substrates.

Three-dimensional radial junction solar cell based on ordered silicon nanowires.

Highly ordered silicon nanowires (SiNWs) were fabricated by nanoimprint lithography and Bosch etching methods. A polycrystalline silicon shell was grown to form a radial p-n junction. To enhance its anti-reflection properties and conductivity, a thin ITO layer was deposited on the SiNWs solar cell, then a micro-grid electrode was introduced to minimize the metal areas to maximize carrier collection. Finally, shorter nanowires were used to reduce surface recombination and achieve an efficiency of 10.5%. This work is expected to show some possible techniques to improve the performance of silicon nanostructure solar cell.

Surface-Enhanced Raman Spectroscopy (SERS) of Mancozeb and Thiamethoxam Assisted by Gold and Silver Nanostructures Produced by Laser Techniques on Paper.

Advanced gold (Au) and silver (Ag) nanostructures were produced by laser techniques on printer paper substrate. Surface-enhanced Raman spectroscopy (SERS) analyses of the fungicide mancozeb (Dithane DG) and insecticide thiamethoxam (Aktara 25 BG) in quantities smaller than usually applied in agricultural medicine were performed for the first time assisted by the structures fabricated. The investigations and results show an easy alternative and cheap way to detect small amounts or residue of harmful environmental pollutants, which has a direct bearing on food quality and thus on human health.

Hole gas accumulation in Si/Ge core-shell and Si/Ge/Si core-double shell nanowires.

Core-shell nanowires (NWs) composed of silicon and germanium can be used to realize high electron (hole) mobility transistors (HEMTs) by suppressing impurity scattering due to their band offset structure and selective doping. Boron doped p-type Si/intrinsic-Ge (i-Ge) core-shell NW structures are selected to study this phenomenon. To produce HEMT devices, hole gas accumulation must be controlled in the impurity undoped i-Ge shell layers. Spectral change in the Ge optical phonon is detected with increased B doping in p-Si core NWs, showing hole gas accumulation in this system. We also fabricate p-Si/i-Ge/p-Si core-double shell NWs to more clearly demonstrate hole gas accumulation in the i-Ge layers.

Functionalization of Silicon Nanostructures for Energy-Related Applications.

Silicon (Si) is used in various application fields such as solar cells and electric devices. Functionalization of Si nanostructures is one way to further improve the properties of these devices such as these. This Review summarizes recent results of solar cell and Li-ion battery applications using Si-related nanostructures. In solar cell applications, the light trapping effect is increased and the carrier recombination rate is decreased due to the short carrier collection path achieved by radially constructed p-n junction in Si nanowires, resulting in higher power conversion efficiency. The nonradiative energy transfer effect created by nanocrystalline Si is a novel way of improving solar cell properties. Si-related nanostructures are also anticipated as new anode materials with higher capacity in Li-ion batteries. Si-related nanocomposite materials which show densely packed microparticle structures agglomerated with small nanoparticles are described here as a promising challenge. These unique structures show higher capacity and longer cycle properties.

Low-Pressure-Assisted Coating Method To Improve Interface between PEDOT:PSS and Silicon Nanotips for High-Efficiency Organic/Inorganic Hybrid Solar Cells via Solution Process.

Nanostructured silicon hybrid solar cells are promising candidates for a new generation photovoltaics because of their light-trapping abilities and solution processes. However, the performance of hybrid organic/Si nanostructure solar cells is hindered because of carrier recombination at surface and poor coverage of organic material poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) ( PEDOT: PSS) on nanostructures. Here we demonstrate low-pressure-assisted coating method of PEDOT: PSS on surface-modified silicon nanotips with broadband light-trapping characteristics to improve interface property and to achieve high-efficiency hybrid solar cells through a solution process. The approach enhances the effective minority-carrier lifetime and the coverage of PEDOT: PSS on the surface of nanostructures. Hybrid solar cells fabricated with surface-modified nanotips exhibit a high fill factor of 70.94%, short-circuit current density of 35.36 mA/cm(2), open-circuit voltage of 0.528 V, and power conversion efficiency of 13.36%. The high efficiency and the high fill factor are achieved because of conformal coating of PEDOT: PSS via a low-pressure-assisted coating process, excellent light harvesting without sacrificing the minority-carrier lifetime, and efficient charge separation/collection of photogenerated carriers.