• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.11a
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• pp.278-278
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• 2009

A photovoltaic device consisting of arrays of radial p-n junction wires enables a decoupling of the requirements for light absorption and carrier extraction into orthogonal spatial directions. Each individual p-n junction wire in the cell is long in the direction of incident light, allowing for effective light absorption, but thin in orthogonal direction, allowing for effective carrier collection. To fabricate radial p-n junction solar cells, p or n-type vertical Si wire cores need to be produced. The majority of Si wires are produced by the vapor-liquid-solid (VLS) method. But contamination of the Si wires by metallic impurities such as Au, which is used for metal catalyst in the VLS technique, results in reduction of conversion efficiency of solar cells. To overcome impurity issue, top-down methods like noble metal catalytic etching is an excellent candidate. We used noble metal catalytic etching methods to make Si wire arrays. The used noble metal is two; Au and Pt. The method is noble metal deposition on photolithographycally defined Si surface by sputtering and then etching in various BOE and $H_2O_2$ solutions. The Si substrates were p-type ($10{\sim}20ohm{\cdot}cm$). The areas that noble metal was not deposited due to photo resist covering were not etched in noble metal catalytic etching. The Si wires of several tens of ${\mu}m$ in height were formed in uncovered areas by photo resist. The side surface of Si wires was very rough. When the distance of Si wires is longer than diameter of that Si nanowires are formed between Si wires. Theses Si nanowires can be removed by immersing the specimen in KOH solution. The optimum noble metal thickness exists for Si wires fabrication. The thicker or the thinner noble metal than the optimum thickness could not show well defined Si wire arrays. The solution composition observed in the highest etching rate was BOE(16.3ml)/$H_2O_2$(0.44M) in Au assisted chemical etching method. The morphology difference was compared between Au and Pt metal assisted chemical etching. The efficiencies of radial p-n junction solar Cells made of the Si wire arrays were also measured.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.30 no.3
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• pp.185-191
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• 2017

Cadmium compounds with one dimension (1D) nanostructures have attracted attention for their excellent electrical and optical properties. In this study, vertically aligned CdTe-Si nanostructures with high density were synthesized by several simple chemical reactions. First, l D Te nanostructures were synthesized by silver assisted chemical Si wafer etching followed by a galvanic displacement reaction of the etched Si nanowires. Nanowire length was controlled from 1 to $25{\mu}m$ by adjusting etching time. The Si nanowire galvanic displacement reaction in $HTeO_2{^+}$ electrolyte created hybrid 1D Te-branched Si nanostructures. The sequential topochemical reaction resulted in $Ag_2Te-Si$ nanostructures, and the cation exchange reaction with the hybrid 1D Te-branched Si nanostructures resulted in CdTe-Si nanostructures. Wet chemical processes including metal assisted etching, galvanic displacement, topochemical and cation exchange reactions are proposed as simple routes to fabricate large scale, vertically aligned CdTe-Si hybrid nanostructures with high density.

• Korean Journal of Materials Research
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• v.22 no.4
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• pp.180-184
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• 2012

Nanostructures of ZnO, such as nanowires, nanorods, nanorings, and nanobelts have been actively studied and applied in electronic or optical devices owing to the increased surface to volume ratio and quantum confinement that they provide. ZnO seed layer (about 40 nm thick) was deposited on Si(100) substrate by RF magnetron sputtering with power of 60 W for 5 min. ZnO nanorods were grown on ZnO seed layer/Si(100) substrate at $95^{\circ}C$ for 5 hr by hydrothermal method with concentrations of $Zn(NO_3)_2{\cdot}6H_2O$ [ZNH] and $(CH_2)_6N_4$ [HMT] precursors ranging from 0.02M to 0.1M. We observed the microstructure, crystal structure, and photoluminescence of the nanorods. The ZnO nanorods grew with hexahedron shape to the c-axis at (002), and increased their diameter and length with the increase of precursor concentration. In 0.06 M and 0.08 M precursors, the mean aspect ratio values of ZnO nanorods were 6.8 and 6.5; also, ZnO nanorods had good crystal quality. Near band edge emission (NBE) and a deep level emission (DLE) were observed in all ZnO nanorod samples. The highest peak of NBE and the lower DLE appeared in 0.06 M precursor; however, the highest peak of DLE and the lower peak of NBE appeared in the 0.02 M precursor. It is possible to explain these phenomena as results of the better crystal quality and homogeneous shape of the nanorods in the precursor solution of 0.06 M, and as resulting from the bed crystal quality and the formation of Zn vacancies in the nanorods due to the lack of $Zn^{++}$ in the 0.02 M precursor.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.325-325
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• 2012

1차원구속 반도체인 nanowires (NWs)는 전기적, 광학적으로 일반 bulk구조와 다른 특성을 가지고 있어서 현재 많은 연구가 되고 있다. 일반적으로 NWs는 Au 등의 금속 촉매를 이용하여 성장을 하게 되는데 이때 촉매가 오염물로 작용을 해서 결함을 만들어서 bandgap내에 defect level을 형성하게 된다. 본 연구는 Si (111) 기판 위에 GaAs NWs 와 InAs NWs를 촉매를 이용하지 않고 성장 하였다. vapour-liquid-solid (VLS)방법으로 성장하는 GaAs NWs는 Ga의 droplet을 이용하게 되는데 Ga이 Si 기판위에 자연 산화막에 존재하는 핀홀(pinhole)로 이동하여 1차적으로 Ga droplet 형성하고 이후 공급되는 Ga과 As은 SiO2 보다 GaAs와 sticking coefficient 가 좋기 때문에 Ga drolept을 중심으로 빠른 선택적 성장을 하게 되면서 NWs로 성장을 하게 된다. 반면에 InAs NWs를 성장 할 시에 droplet 방법으로 성장을 하게 되면 NWs가 아닌 박막 형태로 성장을 하게 되는데 이것으로 InAs과 GaAs의 $SiO_2$와의 sticking coefficient 의 차이를 추측을 할 수 있다. InAs NWs는 GaAs NWs는 달리 native oxide를 이용하지 않고 InAs 과 Si 사이의 11.5%의 큰 lattice mismatch를 이용한다. 이종의 epitaxy 방법에는 크게 3종류 (Frank-van der Merwe mode, Stranski-Krastanov mode, Volmer-Weber mode)가 있는데 각기 다른 adatom 과 surface의 adhesive force로 나누어지게 된다. 이 중 Volmer-Weber mode epitaxy는 adatom 의 cohesive force가 surface와의 adhesive force보다 큰 경우 성장 되는 방식으로 InAs NWs 는 이 방식을 이용한다. 즉 droplet을 이용하지 않는 vapour-solid (VS) 방법으로 성장을 하였다. 이 때 In 의 migration을 억제하기 위해서 VLS mode 의 GaAs NWs 보다 As의 공급을 10배 이상 하였다. FE-SEM 분석 결과 GaAs NWs는 Ga droplet을 확인 할 수 있었고 InAs NWs는 droplet이 존재하지 않았다. GaAs와 InAs NW는 density와 length가 V/III가 높을수록 증가 하였다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.9
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• pp.502-507
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• 2016

Vanadium dioxide, $VO_2$, is a thermochromic material that exhibits a reversible metal-insulator phase transition at $68^{\circ}C$, which accompanies rapid changes in the optical and electronic properties. To decrease the transition temperature around room temperature, a number of studies have been performed. The phase transition temperature of 1D nanowire $VO_2$ with a 100 nm diameter was reported to be approximately $29^{\circ}C$. In this study, 1D or 2D nanostructured $VO_2$ was grown using the vapor transport method. Vanadium dioxide has a different morphology with the same growth conditions for different substrates. The 1D nanowires $VO_2$ were grown on a Si substrate ($Si{\setminus}SiO_2$(300 nm), whereas the 2D & 3D nanostructured $VO_2$ were grown on an exfoliated graphene nanosheet. The crystallographic properties of the 1D or 2D & 3D nanostructured $VO_2$, which were grown by thermal CVD, and exfoliated-transferred graphene nanosheets on a Si wafer which was used as substrate for the vanadium oxide nanostructures, were analyzed by Raman spectroscopy. The as-grown vanadium oxide nanostructures have a $VO_2$ phase, which are confirmed by Raman spectroscopy.

• Transactions of the Korean hydrogen and new energy society
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• v.19 no.6
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• pp.498-504
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• 2008

Metal-reducing bacterium, Geobacter sulfurreducens is available for mediator-less microbial fuel cell (MFC) because it has biological nanowires(pili) which transfer electrons to outside the cell. In this study, in the anode chamber of the MFC system using G. sulfurreducens, the concentrations of NaCl, sodium phosphate and sodium bicarbonate as electrolytes were mainly optimized for the generation of electricity from acetate. 0.4%(w/v) NaClO and 0.5M $H_2SO_4$ could be utilized for the sterilization of acrylic plates and proton exchange membrane (major construction materials of the MFC reactor), respectively. When NaCl concentration in anode phosphate buffer increased from 5 to 50 mM, power density increased from 6 to $20\;mW/m^2$. However, with increasing sodium phosphate buffer concentration from 5 to 50 mM, power density significantly decreased from 18 to $1\;mW/m^2$. Twenty-four mM sodium bicarbonate did not affect electricity generation as well as pH under 50 mM phosphate buffer condition. Optimized anode chamber of MFC using G. sulfurreducens generated relatively high power density ($20\;mW/m^2$) with the maximum coulombic efficiency (41.3%).

• Journal of the Korean Vacuum Society
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• v.19 no.4
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• pp.307-313
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• 2010

One-dimensional cubic phase silicon carbide nanowires (${\beta}$-SiC NWs) were efficiently synthesized by thermal chemical vapor deposition (TCVD) with mixtures containing Si powders and nickel chloride hexahydrate $(NiCl_2{\cdot}6H_2O)$ in an alumina boat with a carbon source of methane $(CH_4)$ gas. SEM images are shown that the growth temperature (T) of $1,300^{\circ}C$ is not enough to synthesize the SiC NWs owing to insufficient thermal energy for melting down a Si powder and decomposing the methane gas. However, the SiC NWs could be synthesized at T>$1,300^{\circ}C$ and the most efficient temperature for growth of SiC NWs is T=$1,400^{\circ}C$. The synthesized SiC NWs have the diameter with an average range between 50~150 nm. Raman spectra clearly revealed that the synthesized SiC NWs are forming of a cubic phase (${\beta}$-SiC). Two distinct peaks at 795 and $970 cm^{-1}$ in Raman spectra of the synthesized SiC NWs at T=$1,400^{\circ}C$ represent the TO and LO mode of the bulk ${\beta}$-SiC, respectively. XRD spectra are also supported to the Raman spectra resulting in the strongest (111) peaks at $2{\Theta}=35.7^{\circ}$, which is the (111) plane peak position of 3C-SiC. Moreover, the gas flow rate of 300 sccm for methane is the optimal condition for synthesis of a large amount of ${\beta}$-SiC NW without producing the amorphous carbon structure shown at a high methane flow rate of 800 sccm. TEM images are shown two kinds of the synthesized ${\beta}$-SiC NWs structures. One is shown the defect-free ${\beta}$-SiC NWs with a (111) interplane distance of 0.25 nm, and the other is the stacking-faulted ${\beta}$-SiC NWs. Also, TEM images exhibited that two distinct SiC NWs are uniformly covered with $SiO_2$ layer with a thickness of less 2 nm.