• Bulletin of the Korean Chemical Society
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• v.34 no.11
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• pp.3451-3455
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• 2013

Single-crystalline silicon nanowires (SiNWs) were fabricated by using an electroless metal-assisted etching of bulk silicon wafers with silver nanoparticles obtained by wet electroless deposition. The etching of SiNWs is based on sequential treatment in aqueous solutions of silver nitrate followed by hydrofluoric acid and hydrogen peroxide. SEM observation shows that well-aligned nanowire arrays perpendicular to the surface of the Si substrate were produced. Free-standing SiNWs were then obtained using ultrasono-method in toluene. Alkyl-derivatized SiNWs were prepared to prevent the aggregation of SiNWs and obtained from the reaction of SiNWs and dodecene via hydrosilylation. Optical characterizations of SiNWs were achieved by FT-IR spectroscopy and indicated that the surface of SiNWs is terminated with hydrogen for fresh SiNWs and with dodecyl group for dodecyl-derivatized SiNWs, respectively. The main structures of dodecyl-derivatized SiNWs are wires and rods and their thicknesses of rods and wire are typically 150-250 and 10-20 nm, respectively. The morphology and chemical state of dodecyl-derivatized SiNWs are characterized by scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.499-499
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• 2011

Silicon nanowires (Si NWs) have been extensively studied for nanoelectronics owing to their unique optical and electrical properties different from those of bulk silicon. For the development of Si NW devices, better understanding of oxidation behavior in Si NWs would be an important issue. For example, it is widely known that atomic scale roughness at the dielectric (SiOx)/channel (Si) interface can significantly affect the device performance in the nano-scale devices. However, the oxidation process at the atomic-scale is still unknown because of its complexity. In the present work, we investigated the oxidation behavior of Si NW in atomic scale by simulating the dry oxidation process using a reactive molecular dynamics simulation technique. We focused on the residual stress evolution during oxidation to understand the stress effect on oxidation behavior of Si NWs having two different diameters, 5 nm and 10 nm. We calculated the charge distribution according to the oxidation time for 5 and 10 nm Si NWs. Judging from this data, it was observed that the surface oxide layer started to form before it is fully oxidized, i.e., the active diffusion of oxygen in the surface oxide layer. However, it is well-known that the oxide layer formation on the Si NWs results in a compressive stress on the surface which may retard the oxygen diffusion. We focused on the stress evolution of Si NWs during the oxidation process. Since the surface oxidation results in the volume expansion of the outer shell, it shows a compressive stress along the oxide layer. Interestingly, the stress for the 10 nm Si NW exhibits larger compressive stress than that of 5 nm Si NW. The difference of stress level between 5 an 10 anm Si NWs is approximately 1 or 2 GPa. Consequently, the diameter of Si NWs could be a significant factor to determine the self-limiting oxidation behavior of Si NWs when the diameter was very small.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.10a
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• pp.27.1-27.1
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• 2011

The recent extensive research of one-dimensional (1D) nanostructures such as nanowires (NWs) and nanotubes (NTs) has been the driving force to fabricate new kinds of nanoscale devices in electronics, optics and bioengineering. We attempt to produce silicon oxide nanowires (SiOxNWs) in a simple way without complicate deposition process, gaseous Si containing precursors, or starting material of $SiO_2$. Nickel (Ni) nanoparticles (NPs) were applied on Si wafer and thermally treated in a furnace. The temperature in the furnace was kept in the ranges between 900 and $1,100^{\circ}C$ and a mixture of nitrogen ($N_2$) and hydrogen ($H_2$) flowed through the furnace. The SiOxNWs had widths ranging from 100 to 200 nm with length extending up to ~10 ${\mu}m$ and their structure was amorphous. Ni NPs were acted as catalysts. Since there were no other Si materials introduced into the furnace, the Si wafer was the only Si sources for the growth of SiOxNWs. When the Si wafer with deposition of Ni NPs was heated, the liquid Ni-Si alloy droplets were formed. The droplets as the nucleation sites induce an initiation of the growth of SiOxNWs and absorb oxygen easily. As the droplets became supersaturated, the SiOxNWs were grown, by the reaction between Si and O and continuously dissolving Si and O onto NPs. Photoluminescence (PL) showed that blue emission spectrum was centered at the wavelength of 450 nm (2.76 eV). The details of growth mechanism of SiOxNWs and the effect of Ni NPs on the formation of SiOxNWs will be presented.

• Korean Journal of Materials Research
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• v.24 no.10
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• pp.509-514
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• 2014

We demonstrate a simple and effective method to accurately position silicon nanowires (Si NWs) at desirable locations using drop-casting of Si NW inks; this process is suitable for applications in nanoelectronics or nanophotonics. Si NWs were assembled into a lithographically patterned sacrificial photoresist (PR) template by means of capillary interactions at the solution interface. In this process, we varied the type of solvent of the SiNW-containing solution to investigate different assembly behaviors of Si NWs in different solvents. It was found that the assembly of Si NWs was strongly dependent on the surface energy of the solvents, which leads to different evaporation modes of the Si NW solution. After Si NW assembly, the PR template was cleanly removed by thermal decomposition or chemical dissolution and the Si NWs were transferred onto the underlying substrate, preserving its position without any damage. This method enables the precise control necessary to produce highly integrated NW assemblies on all length scales since assembly template is easily fabricated with top-down lithography and removed in a simple process after bottom-up drop-casting of NWs.

• Journal of the Korean Vacuum Society
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• v.17 no.1
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• pp.51-57
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• 2008

we have demonstrated structural evolution and optical properties of Si-nanowires (NWs) synthesized on Si (111) substrates with nanoscale Au-Si islands by rapid thermal chemical vapor deposition (RTCVD). The Au-Si nano-islands (10-50nm in diameter) were employed as a liquid-droplet catalysis to grow Si-NWs via vapor-liquid-solid mechanism. The Si-NWs were grown by a mixture gas of SiH4 and H2 at a pressure of 1.0 Torr and temperatures of $500{\sim}600^{\circ}C$. Scanning electron microscopy measurements showed that the Si-NWs are uniformly sized and vertically well-aligned along <111> direction on Si (111) surfaces. The resulting NWs are ${\sim}60nm$ in average diameter and ${\sim}5um$ in average length. High resolution transmission microscopy measurements indicated that the NWs are single crystals covered with amorphous SiOx layers of ${\sim}3nm$ thickness. In addition, the optical properties of the NWs were investigated by micro-Raman spectroscopy. The downshift and asymmetric broadening of the Si main optical phonon peak were observed in Raman spectra of Si-NWs, which indicates a minute stress effects on Raman spectra due to a slight lattice distortion led by lattice expansion of Si-NW structures.

• Journal of the Korean Vacuum Society
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• v.16 no.4
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• pp.279-285
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• 2007

We have demonstrated structural evolution and optical properties of the Si-NWs on Si (111) substrates with synthesized nanoscale Au-Si islands by rapid thermal chemical vapor deposition(RTCVD). Au nano-islands (10-50nm in diameter) were employed as a liquid-droplet catalysis to grow Si-NWs via vapor-liquid-solid mechanism. Si-NWs were grown by a mixture gas of $SiH_4\;and\;H_2$ at pressures of $0.1{\sim}1.0$Torr and temperatures of $450{\sim}650^{\circ}C$. SEM measurements showed the formation of Si-NWs well-aligned vertically for Si (111) surfaces. The resulting NWs are 30-100nm in diameter and $0.4{\sim}12um$ in length depending on growth conditions. HR-TEM measurements indicated that Si-NWs are single crystals convered with about 3nm thick layers of amorphous oxide. In addition, optical properties of NWs were investigated by micro-Raman spectroscopy. The downshift and asymmetric broadening of the Si optical phonon peak with a shoulder at $480cm^{-1}$ were observed in Raman spectra of Si-NWs.

• Journal of Integrative Natural Science
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• v.5 no.4
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• pp.211-215
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• 2012

Single-crystalline silicon nanowire arrays (SiNWAs) using electroless metal-assisted etchings of p-type silicon were successfully fabricated. Ag nanoparticle deposition on silicon wafers in HF solution acted as a localized micro-electrochemical redox reaction process in which both anodic and cathodic process took place simultaneously at the silicon surface to give SiNWAs. The growth effect of SiNWs was investigated by changing of etching times. The morphologies of SiNWAs were obtained by SEM observation. Well-aligned nanowire arrays perpendicular to the surface of the silicon substrate were produced. Optical characteristics of SiNWs were measured by FT-IR spectroscopy and indicated that the surface of SiNWs are terminated with hydrogen. The thicknesses and lengths of SiNWs are typically 150-250 nm and 2 to 5 microns, respectively.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.74-74
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• 2010

One-dimensional nanosturctures such as nanowires and nanotube have been mainly proposed as important components of nano-electronic devices and are expected to play an integral part in design and construction of these devices. Silicon carbide(SiC) is one of a promising wide bandgap semiconductor that exhibits extraordinary properties, such as higher thermal conductivity, mechanical and chemical stability than silicon. Therefore, the synthesis of SiC-based nanowires(NWs) open a possibility for developing a potential application in nano-electronic devices which have to work under harsh environment. In this study, one-dimensional nanowires(NWs) of cubic phase silicon carbide($\beta$-SiC) were efficiently produced by thermal chemical vapor deposition(T-CVD) synthesis of mixtures containing Si powders and hydrocarbon in a alumina boat about $T\;=\;1400^{\circ}C$ SEM images are shown that the temperature below $1300^{\circ}C$ is not enough to synthesis the SiC NWs due to insufficient thermal energy for melting of Si Powder and decomposition of methane gas. However, the SiC NWs are produced over $1300^{\circ}C$ and the most efficient temperature for growth of SiC NWs is about $1400^{\circ}C$ with an average diameter range between 50 ~ 150 nm. Raman spectra revealed the crystal form of the synthesized SiC NWs is a cubic phase. Two distinct peaks at 795 and $970\;cm^{-1}$ over $1400^{\circ}C$ represent the TO and LO mode of the bulk $\beta$-SiC, respectively. In XRD spectra, this result was also verified with the strongest (111) peaks at $2{\theta}=35.7^{\circ}$, which is very close to (111) plane peak position of 3C-SiC over $1400 ^{\circ}C$ TEM images are represented to two typical $\beta$-SiC NWs structures. One is shown the defect-free $\beta$-SiC nanowire with a (111) interplane distance with 0.25 nm, and the other is the stacking-faulted $\beta$-SiC nanowire. Two SiC nanowires are covered with $SiO_2$ layer with a thickness of less 2 nm. Moreover, by changing the flow rate of methane gas, the 300 sccm is the optimal condition for synthesis of a large amount of $\beta$-SiC NWs.

• Proceedings of the Materials Research Society of Korea Conference
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• 2012.05a
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• pp.88.1-88.1
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• 2012

Silicon nanowires (SiNWs), due to their unusual quantum-confinement effects that lead to superior electrical and optical properties compared to those of the bulk silicon, have been widely researched as a potential building block in a variety of novel electronic devices. The conventional means for the synthesis of SiNWs has been the vapor-liquid-solid method using chemical vapor deposition; however, this method is time consuming, environmentally unfriendly, and do not support vertical growth. As an alternate, the electroless etching method has been proposed, which uses metal catalysts contained in aqueous hydrofluoric acids (HF) for vertically etching the bulk silicon substrate. This new method can support large-area growth in a short time, and vertically aligned SiNWs with high aspect ratio can be readily synthesized with excellent reproducibility. Nonetheless, there still are rooms for improvement such as the poor surface characteristics that lead to degradation in electrical performance, and non-uniformity of the diameter and shapes of the synthesized SiNWs. Here, we report a facile method of SiNWs synthesis having uniform sizes, diameters, and shapes, which may be other than just cylindrical shapes using a modified nanosphere lithography technique. The diameters of the polystyrene nanospheres can be adjustable through varying the time of O2 plasma treatment, which serve as a mask template for metal deposition on a silicon substrate. After the removal of the nanospheres, SiNWs having the exact same shape as the mask are synthesized using wet etching technique in a solution of HF, hydrogen peroxide, and deionized water. Different electrical and optical characteristics were obtained according to the shapes and sizes of the SiNWs, which implies that they can serve specific purposes according to their types.

• Korean Journal of Materials Research
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• v.21 no.2
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• pp.115-119
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• 2011

Si Nanowire (NW) field effect transistors (FETs) were fabricated on hard Si and flexible polyimide (PI) substrates, and their electrical characteristics were compared. Si NWs used as channels were synthesized by electroless etching method at low temperature, and these NWs were refined using a centrifugation method to get the NWs to have an optimal diameter and length for FETs. The gate insulator was poly(4-vinylphenol) (PVP), prepared using a spin-coating method on the PI substrate. Gold was used as electrodes whose gap was 8 ${\mu}m$. These gold electrodes were deposited using a thermal evaporator. Current-voltage (I-V) characteristics of the device were measured using a semiconductor analyzer, HP-4145B. The electrical properties of the device were characterized through hole mobility, $I_{on}/I_{off}$ ratio and threshold voltage. The results showed that the electrical properties of the TFTs on PVP were similar to those of TFTs on $SiO_2$. The bending durability of SiNWs TFTs on PI substrate was also studied with increasing bending times. The results showed that the electrical properties were maintained until the sample was folded about 500 times. But, after more than 1000 bending tests, drain current showed a rapid decrease due to the defects caused by the roughness of the surface of the Si NWs and mismatches of the Si NWs with electrodes.