Synthesis and analysis of silicon nanowires grown on Si (111) substrate at different silane gas flow rate

Silicon nanowires were grown on Si (111) substrates by very high frequency plasma enhanced chemical vapor deposition (VHF-PECVD). The nanowires were grouted at 450 °C and 21 watt RF power. Pure silane (99.9995%) and gold colloid were used as precursor and catalyst respectively for growth of wires. The nanowires were investigated using scanning electron microscopy (SEM). Their crystallity and compositions were studied using X-ray diffraction method and energy dispersive X-ray (EDX) spectroscopy. The growth of Si nanowires is controlled by conventional vapor- liquid-solid (VLS) mechanism. The results show ed that there were gold particle on the top of wires. The silane flow rates does effect the quantity of Si nanowire. The Si nanowires length changes from 350 nm to 5.5 μm for Si flow rate of 5 to 20 sccm, respectively. XRD and EDX results revealed that the nanowires composed of mainly Si with small percent of Au and oxygen

Silicon self-assembled growth of quantum dots grown on corning glass (7059) substrate

Silicon quantum dots have been grown on corning glass(7059) substrate using a self-assembly method of physical vapour deposition. The samples were fabricated at sufficiently low sputtering rate and varying experimental conditions. Apparently, the onset of nucleation took place during the first 5 minutes of deposition, followed by a further growth of stable islands known as quantum dots, with the measured radii comparable to the predicted values. Other measurement results confirmed the existence of these dots, including the bandgap energy ∼ 1.80 eV from PL and a 2% at. silicon from EDX and possible amorphous from XRD. The nucleation parameters were predicted as follows: Free energy change per unit volume ∆Gv = 2.64x104 Jmol-1; Surface energies per unit area, γLN = 1.48 Jm-2, γNS = 20.0 - 90.0 Jm-2 and γLS = 0.42 x 10-2 Jm-2; Critical energies ∆G* = 7.53x10-17 - 8.31x10-14 J; Critical radii r* = 9.0- 97.0 nm. This experimental evidence strongly support the early stage growth model of silicon quantum dot deposited on corning glass substrat

Improvement of catalytic activity in styrene oxidation of carbon-coated titania by formation of porous carbon layer

Porous carbon layer has been formed by treating the carbon-coated titania (C@TiO2) with KOH solution. Carbon-coated titania (C@TiO2) was obtained by pyrolysis of polystyrene-coated titania (PS@TiO2), which was produced by in situ polymerization of styrene by using aqueous hydrogen peroxide. The presence of polystyrene and carbon on the surface of titania were confirmed by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy techniques. Carbon content was about 2.2 wt.% with thickness of carbon layer ca. 5 nm. After treating with KOH solution, PC@TiO2 with the pore size of ca. 5 nm, total pore volume of 0.05 cm2 g-1 and Brunauer–Emmett–Teller (BET) specific surface area of 46 m2 g-1 has been obtained. Catalytic activity results showed that PC@TiO2 gave a higher activity in styrene oxidation compared to bare TiO2, and C@TiO2. The highest catalytic activity was obtained by using PC@TiO2 that obtained after treating C@TiO2 with 1.0 M KOH solution with benzaldehyde and phenylacetaldehyde as the main reaction products. At the higher concentration of KOH solution, the catalytic activity decreased when crystallinity of TiO2 decreased

Photoluminescence studies of silicon self-assembled quantum dots

Silicon self-assembled nanodots have been fabricated on corning (7059) and quartz glass substrates using a magnetron sputtering method at different experimental conditions, including the deposition time, RF power and substrate temperature. It was observed that, as the deposition time increases, PL intensities increased with deposition time. However, the full width at half maximum of individual spectra was observed to decrease with time. This occurs because the nature of PL is such that an improvement in the number of carriers (electron and holes) results in enhanced PL intensities. An increase in the deposition time allows more silicon attached to substrate and forming the nanodots, thus increasing the number of atoms as well as carriers. The effect of RF power was indicated by increasing trends in PL intensities. Higher deposition power appeared to increase the ratio of Si atomic concentration and, hence, an increasing number of silicon nanodots. On the other hand, the results showed that, the PL intensity decreased as the substrate temperatures were increased caused by an activated non-radiative recombination process and decrease of crystal quality. It was also observed that the peak of PL wavelength centered at 693 nm or 1.78eV energy bandgap did not differ much from those peaks obtained by varying the RF power and substrate temperature. The suggested that deposition time up to 5 min, RF power of 200 W and substrate temperature of 400°C as optimum conditions for the growth of dome-shaped silicon nanodots, with sizes between 40-80 nm. Generally the shifts in PL intensities are attributed to the structural changes which occurs during the growth processes

The advantage of low growth temperature and V/III ratio for In(x)Ga(1-x)As nanowires growth

Cylindrical InxGa1-xAs nanowires (NWs) perpendicular to the substrate have been successfully grown using MOCVD. Morphology of InxGa1-xAs NWs has been observed using Field Emission-Scanning Electron Microscopy (FE-SEM) and Transmission Electron Microscopy (TEM). Both FE-SEM and TEM results show that the NWs grown at low growth temperature and V/III ratio were via direct impinging mechanism. Energy Dispersive X-ray spectroscopy (EDX) results confirm that the cylindrical NWs grown via direct impinging mechanism and tends to have uniform chemical composition

Effect of plasma power and flow rate of silane gas on diameter of silicon nanowires grown by plasma enhanced chemical vapor deposition

Silicon nanowires (SiNWs) have been synthesized by plasma enhanced chemical vapor deposition (PECVD) at different power for generation of plasma and different flow rate of silane gas. Silane (10% SiH4 in Ar) gas with flow rate ranging between 6-15 standard cubic centimeter per minute(sccm) were employed as the source and gold colloid as the catalyst. A p-type Si (100) wafer was used as substrate in this experiment and the substrate’s temperature was 370°C.The plasma power range was 12-17 watts. The grown silicon nanowires were analyzed using field emission scanning electron microscopy (FESEM) and energy dispersive X-ray spectroscopy (EDX). FESEM results show that some silicon nanowires are cone like and some of them are cylindrical. The EDX result revealed that the existence of silicon and oxygen elements in the nanowires. The silicon nanowires obtained have different diameters and lengths and the SiNWs consist of silicon core which are surrounded by oxide sheath. It has been found that the plasma power and flow rate of the silane gas influence the size of silicon nananowires growth by PECVD. The diameter of wires decreased from 140 nm to 80 nm averagely when plasma power was increased from 12 to 17 watts. The diameter also increased about 90 nm to 150 nm when the flow rate of silane gas is increased from 6 to 15 scc

Studies of the self-assembled growth mechanism on nanocrystalline silicon nanodots

Nanocrystalline silicon (nc-Si) nanodots have been grown on corning glass (7059) substrate using a self-assembly VHF-PECVD method under the following experimental conditions: Fixed deposition temperatures of 300/400 °C, deposition times 30/60 s, plasma power of 10 W, silane gas flow rate of 10 sccm, as well as deposition pressure of 10-2 torr. It is predicted that the onset of nucleation began immediately after the deposition and start to appear clearly after 20-60 s during which growth mechanisms occur. Essentially, the nanodots were formed onto the substrate in dome-like shapes by virtue of equilibrium surface energies, yLS, yLN and yNS. The associated liquid/solid nucleation mechanism was then simulated and related parameters were obtained: Free energy change per unit volume ?Gv ~-104 Jmol-1; Surface energies per unit area, ?LN = 1.44 Jm-2, ?NS = 19 - 60 Jm-2 and ?LS = 0.74 Jm-2; Critical energies ?G* ~10-15 J; Critical radii r* = 16 - 48 nm. These results were experimentally verified, in particular for selected critical radius r* less than 50 nm. Other measurements were also carried out: PL analysis gave bandgap energies ~ 1.8-2.4 eV, whilst Raman spectra revealed the coexistence of nc-Si and amorphous Si. It is strongly suggested that, the nc-Si nanodot grown on glass substrate fulfills the Volmer-Weber growth mode with a minor modification

Morphology and chemical composition of inxGa1-xAs NWs Au-assisted grown at low growth temperature using MOCVD

Cylindrical InxGa1-xAs NWs have been successfully grown at low growth temperature using MOCVD. Field Emission-Scanning Electron Microscopy (FE-SEM) characterization and Energy Dispersive X-ray (EDX) analysis have been used to investigate the morphology and chemical composition of NWs, respectively. Both characterization results consistently reinforce that the NWs growth were via direct impinging mechanism and NW have relatively uniform chemical composition

A review on effect of plasma power density and gas flow rate on structural properties of nanocrystalline silicon

Effects of plasma power density and gas density on structural properties of nanocrystalline silicon grown by Plasma Enhanced Chemical Vapor Deposition (PECVD)are discussed in this paper. It has been found that both gas flow rates and plasma power density have an opposite effect on the film’s crystallinity. It was observed that higher plasma power density tend to increase the degree of crystallinity, while higher gas flow rates appeared to decrease its curves. It was also observed that microstructural defects were lower for samples with lower crystallinity