• 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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• 2012.08a
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• pp.376-376
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• 2012

Semiconductor nanowires (NWs) are future building block for nano-scale devices. Especially, Ge NWs are fascinated material due to the high electrical conductivity with high carrier mobility. It is strong candidate material for post-CMOS technology. However, thermal stability of Ge NWs are poor than conventional semiconductor material such as Si. Especially, when it reduced size as small as nano-scale it will be melted around CMOS process temperature due to the melting point depression. Recently, Graphene have been intensively interested since it has high carrier mobility with single atomic thickness. In addition, it is chemically very stable due to the $sp^2$ hybridization. Graphene films shows good protecting layer for oxidation resistance and corrosion resistance of metal surface using its chemical properties. Recently, we successfully demonstrated CVD growth of monolayer graphene using Ge catalyst. Using our growth method, we synthesized Ge/graphene core/shell (Ge@G) NW and conducted it for highly thermal stability required devices. We confirm the existence of graphene shell and morphology of NWs using SEM, TEM and Raman spectra. SEM and TEM images clearly show very thin graphene shell. We annealed NWs in vacuum at high temperature. Our results indicated that surface melting phenomena of Ge NWs due to the high surface energy from curvature of NWs start around $550^{\circ}C$ which is $270^{\circ}C$ lower than bulk melting point. When we increases annealing temperature, tip of Ge NWs start to make sphere shape in order to reduce its surface energy. On the contrary, Ge@G NWs prevent surface melting of Ge NWs and no Ge spheres generated. Furthermore, we fabricated filed emission devices using pure Ge NWs and Ge@G NWs. Compare with pure Ge NWs, graphene protected Ge NWs show enhancement of reliability. This growth approach serves a thermal stability enhancement of semiconductor NWs.

• Transactions on Electrical and Electronic Materials
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• v.14 no.3
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• pp.148-151
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• 2013

The control of Ga doping in ZnO nanowires (NWs) by physical vapor deposition has been implemented and characterized. Various Ga-doped ZnO NWs were grown using the vapor-liquid-solid (VLS) method, with Au catalyst on c-plane sapphire substrate by hot-walled pulsed laser deposition (HW-PLD), one of the physical vapor deposition methods. The structural, optical and electrical properties of Ga-doped ZnO NWs have been systematically analyzed, by changing Ga concentration in ZnO NWs. We observed stacking faults and different crystalline directions caused by increasing Ga concentration in ZnO NWs, using SEM and HR-TEM. A $D^0X$ peak in the PL spectra of Ga doped ZnO NWs that is sharper than that of pure ZnO NWs has been clearly observed, which indicated the substitution of Ga for Zn. The electrical properties of controlled Ga-doped ZnO NWs have been measured, and show that the conductance of ZnO NWs increased up to 3 wt% Ga doping. However, the conductance of 5 wt% Ga doped ZnO NWs decreased, because the mean free path was decreased, according to the increase of carrier concentration. This control of the structural, optical and electrical properties of ZnO NWs by doping, could provide the possibility of the fabrication of various nanowire based electronic devices, such as nano-FETs, nano-inverters, nano-logic circuits and customized nano-sensors.

• Transactions on Electrical and Electronic Materials
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• v.15 no.5
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• pp.262-264
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• 2014

Pristine ZnO, 3 wt.% Ga-doped (3GZO) and 3 wt.% Ag-doped (3SZO) ZnO nanowires (NWs) were grown using the hot-walled pulse laser deposition (HW-PLD) technique. The doping of Ga and Ag in ZnO NWs was observed by analyzing the optical and chemical properties. We optimized the synthesis conditions, including processing temperature, time, gas flow, and distance between target and substrate for the growth of pristine and doped ZnO NWs. The diameter and length of pristine and doped ZnO NWs were controlled under 200 nm and several ${\mu}m$, respectively. Low temperature photoluminescence (PL) was performed to observe the optical property of doped NWs. We clearly observed the shift of the near band edge (NBE) emission by using low temperature PL. In the case of 3GZO and 3SZO NWs, the center photon energy of the NBE emissions shifted to low energy direction using the Burstein Moss effect. A strong donor-bound exciton peak was found in 3 GZO NWs, while an acceptor-bound exciton peak was found in 3SZO NWs. X-ray photoelectron spectroscopy (XPS) also indicated that the shift of binding energy was mainly attributed to the interaction between the metal ion and ZnO NWs.

• Interaction and multiscale mechanics
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• v.5 no.2
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• pp.115-129
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• 2012

Nanowires (NWs) have attracted intensive researches owing to the broad applications that arise from their remarkable properties. Over the last decade, immense numerical studies have been conducted for the numerical investigation of mechanical properties of NWs. Among these numerical simulations, the molecular dynamics (MD) plays a key role. Herein we present a brief review on the current state of the MD investigation of nanowires. Emphasis will be placed on the FCC metal NWs, especially the Cu NWs. MD investigations of perfect NWs' mechanical properties under different deformation conditions including tension, compression, torsion and bending are firstly revisited. Following in succession, the studies for defected NWs including the defects of twin boundaries (TBs) and pre-existing defects are discussed. The different deformation mechanism incurred by the presentation of defects is explored and discussed. This review reveals that the numerical simulation is an important tool to investigate the properties of NWs. However, the substantial gaps between the experimental measurements and MD results suggest the urgent need of multi-scale simulation technique.

• 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.

• Journal of the Semiconductor & Display Technology
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• v.19 no.4
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• pp.6-10
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• 2020

The silver nanowires (AgNWs) were synthesized by the conventional polyol process, which revealed 25 ㎛ and 30 nm of average length and diameter, respectively. The synthesized AgNWs were applied to the CdSe/CdZnS quantum dot (QD) based transparent light-emitting device (LED). The device using a randomly networked AgNWs electrode had some problems such as the high threshold voltage (for operating the device) due to the random pores from the networked AgNWs. As a method of improvement, a composite electrode was formed by overlaying the ZnO:Ga on the AgNWs network. The device used the composite electrode revealed a low threshold voltage (4.4 Vth) and high current density compared to the AgNWs only electrode device. The brightness and current density of the device using composite electrode were 55.57 cd/㎡ and 41.54 mA/㎠ at the operating voltage of 12.8 V, respectively, while the brightness and current density of the device using (single) AgNWs only were 1.71 cd/㎡ and 2.05 mA/㎠ at the same operating voltage. The transmittance of the device revealed 65 % in a range of visible light. Besides the reliability of the devices was confirmed that the device using the composite electrode revealed 2 times longer lifetime than that of the AgNWs only electrode device.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.379.1-379.1
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• 2016

Recently, new types of wearable devices such as textile electronics are considered as the next generation wearable electronics. To realize the textile electronics, conductive fibers are required to supply the power and for signal processing. Conventionally, silver nanowires (Ag NWs) have been attracted as one of the conductive additives in the fibers, however, using the Ag NWs may lead to high production cost since it is a noble metal. Many researches have been done to replace the Ag NWs into a cheaper materials such as copper nanowires (Cu NWs). Here, we synthesized ultra-long Cu NWs for a conductive filler material in conductive fibers, taking advantages of their structural features. To investigate the effect of capping agents on the aspect ratio of the synthesized Cu NWs, we used various capping agents such as hexadecylamine, butylamine, ethylenedilamine and oleylamine in the Cu NW synthesis. In this research, the effects of capping agents on the structure and the synthesis of Cu NWs are presented.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.328.2-328.2
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• 2014

Semiconductor nanowires (NWs) have attracted research interests due to the distinct physical properties that can lead to variousoptical and electrical applications. In this paper, we have grown InAs NWs viagold (Au)-assisted vapor-liquid-solid (VLS) and catalyst-free vapor-solid (VS) mechanisms and investigated on the p-type doping profile of the NWs. Metal-organic chemical vapor deposition (MOCVD) is used for the growth of the NWs. Trimethylindium (TMIn) and arsine (AsH3) were used for the precursor and diethyl zinc (DEZn) was used for the p-type doping source of the NWs. The effectiveness of p-type doping was confirmed by electrical measurement, showing an increase of the electron density with the DEZn flow. The structural properties of the InAs NWs were examined using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). In addition, we characterize atomic distribution of InAs NWs using energy-dispersive X-ray spectroscopy (EDX) analysis.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.289-289
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• 2013

While there are plenty of studies on synthesizing semiconducting germanium nanowires (Ge NWs) by vapor-liquid-solid (VLS) process, it is difficult to inject dopants into them with uniform dopants distribution due to vapor-solid (VS) deposition. In particular, as precursors and dopants such as germane ($GeH_4$), phosphine ($PH_3$) or diborane ($B_2H_6$) incorporate through sidewall of nanowire, it is hard to obtain the structural and electrical uniformity of Ge NWs. Moreover, the drastic tapered structure of Ge NWs is observed when it is synthesized at high temperature over $400^{\circ}C$ because of excessive VS deposition. In 2006, Emanuel Tutuc et al. demonstrated Ge NW pn junction using p-type shell as depleted layer. However, it could not be prevented from undesirable VS deposition and it still kept the tapered structures of Ge NWs as a result. Herein, we adopt $C_2H_2$ gas in order to passivate Ge NWs with carbon sheath, which makes the entire Ge NWs uniform at even higher temperature over $450^{\circ}C$. We can also synthesize non-tapered and uniformly doped Ge NWs, restricting incorporation of excess germanium on the surface. The Ge NWs with carbon sheath are grown via VLS process on a $Si/SiO_2$ substrate coated 2 nm Au film. Thin Au film is thermally evaporated on a $Si/SiO_2$ substrate. The NW is grown flowing $GeH_4$, HCl, $C_2H_2$ and PH3 for n-type, $B_2H_6$ for p-type at a total pressure of 15 Torr and temperatures of $480{\sim}500^{\circ}C$. Scanning electron microscopy (SEM) reveals clear surface of the Ge NWs synthesized at $500^{\circ}C$. Raman spectroscopy peaked at about ~300 $cm^{-1}$ indicates it is comprised of single crystalline germanium in the core of Ge NWs and it is proved to be covered by thin amorphous carbon by two peaks of 1330 $cm^{-1}$ (D-band) and 1590 $cm^{-1}$ (G-band). Furthermore, the electrical performances of Ge NWs doped with boron and phosphorus are measured by field effect transistor (FET) and they shows typical curves of p-type and n-type FET. It is expected to have general potentials for development of logic devices and solar cells using p-type and n-type Ge NWs with carbon sheath.