Publications (26)71.25 Total impact
-
Article: Spectroscopic ellipsometry analysis of amorphous silicon thin films for Si-nanocrystals.
[show abstract] [hide abstract]
ABSTRACT: Hydrogenated amorphous and nano-crocrystalline silicon thin films were grown by very-high-frequency plasma-enhanced chemical vapor deposition (VHF-PECVD, 60 MHz). In this paper, we report the defects of nano-crystallites embedded in an amorphous matrix of hydrogenated silicon alloy (a-Si:H) thin film as investigated by spectroscopic ellipsometry (SE). The peak intensity and position of the imaginary part of the dielectric constant (epsilon2) as a function of the energy show various material states, including a-Si:H (3.5 eV) and nc-Si (4.2 eV), along with the absorption coefficient, thickness, optical gap, and the characteristics of the defects. The ratio of the characteristic Raman features, the TA/LO and LA/LO ratio, is related to the defect states in the films. It was correlated to the SE data. Following this, we look into the systematic change in the crystallinity of the film from the SE results. Quantized crystallinity values from the SE data show good agreement by more than 88.75% with the crystallinity information obtained through Raman spectroscopy.Journal of Nanoscience and Nanotechnology 04/2012; 12(4):3228-32. · 1.56 Impact Factor -
Article: Doping-free fabrication of silicon thin films for schottky solar cell.
[show abstract] [hide abstract]
ABSTRACT: Thin film Schottky solar cells were fabricated without doping processes, which may provide an alternative approach to the conventional thin film solar cells in the n-i-p configuration. A thin Co layer was coated on a substrate, which worked as a back contact metal and then Si film was grown above it. Deposition condition may modulate the Si film structure to be a fully amorphous Si (a-Si) or a mixing of microcrystalline Si (mc-Si) and a-Si. A thin Au layer was deposited above the grown Si films, which formed a Schottky junction. Two types of Schottky solar cells were prepared on a fully a-Si film and a mixing of mc-Si and a-Si film. Under one sun illumination, the mixing of mc-Si and a-Si device provided 35% and 68.4% enhancement in the open circuit voltage and fill factor compared to that of the amorphous device.Journal of Nanoscience and Nanotechnology 02/2012; 12(2):1371-4. · 1.56 Impact Factor -
Article: Efficient three-dimensional nanostructured photoelectric device by Al-ZnO coating on lithography-free patterned Si nanopillars
[show abstract] [hide abstract]
ABSTRACT: An efficient three-dimensional (3D) nanostructure photoelectric device is presented. An Al-doped ZnO (AZO) coating was applied to lithography-free patterned Si nanopillars and spontaneously formed a radial heterojunction (n-AZO/p-Si) photodiode having a quality ideality factor of 1.64. A significantly enhanced photocurrent of 5.45 mA/cm2 was obtained from the 3D nanostructure relative to that of a planar substrate (1.1 mA/cm2). This enhancement is induced by enlargement of the light-active surface area and an anti-reflection effect. Due to the intermediate refractive index of AZO, the reflection was distinctively reduced in the air-Si system. It discusses an effective approach for realizing nanostructured photoelectric device.Applied Physics Letters 08/2011; 99(5):053118-053118-3. · 3.84 Impact Factor -
Article: Rapid thermal annealed Al-doped ZnO film for a UV detector
[show abstract] [hide abstract]
ABSTRACT: A low-resistive Al-doped ZnO (AZO) film was achieved by rapid thermal annealing. A co-sputtering method was used in the initial growth of AZO films and a rapid annealing process was performed on the as-deposited AZO film under N2 atmosphere for 3 min. An as-deposited AZO film had an optical transmittance of 84.78% at 550 nm and a resistivity of 7.8103 cm. A rapid annealing process significantly improved the optical transmittance and electrical resistivity of the AZO film to 99.67% and 1103 cm, respectively. The structural changes of the AZO films were investigated by X-ray diffraction and transmission electron microscopy. The high quality AZO film was used to fabricate a metalsemiconductormetal (MSM) structure for aUV detector. TheMSMdevice provided a stable current of 25 A at a bias of 2 V in a dark condition. Under UV illumination, theMSMdevice was highly responsive to UV light uniformly and repeatedly, and it enhanced the current by 80% at 45 A. This rapid thermal annealing process may provide a useful method to fabricate quality AZO films for photoelectric applications with a low thermal budget.Materials Letters. 01/2011; 65:786-789. -
Book: Efficient three-dimensional nanostructured photoelectric device by Al-ZnO coating on lithography-free patterned Si nanopillars
01/2011; AIP. -
Article: Double Transparent Conducting Oxide Films for Photoelectric Devices
Materials Letters 01/2011; · 2.31 Impact Factor -
Article: Rapid thermal annealed Al-doped ZnO film for a UV detector
Materials Letters. 01/2011; 65(4):786-789. -
Article: Solution-processed germanium nanowire-positioned Schottky solar cells.
[show abstract] [hide abstract]
ABSTRACT: Germanium nanowire (GeNW)-positioned Schottky solar cell was fabricated by a solution process. A GeNW-containing solution was spread out onto asymmetric metal electrodes to produce a rectifying current flow. Under one-sun illumination, the GeNW-positioned Schottky solar cell yields an open-circuit voltage of 177 mV and a short-circuit current of 19.2 nA. Schottky and ohmic contacts between a single GeNW and different metal electrodes were systematically investigated. This solution process may provide a route to the cost-effective nanostructure solar architecture.Nanoscale Research Letters 01/2011; 6(1):287. · 2.73 Impact Factor -
Article: Fast and Efficient Purification for Highly Conductive Transparent Carbon Nanotube Films
[show abstract] [hide abstract]
ABSTRACT: A combination of thermal oxidation and thermal recovery was used to obtain transparent single-walled carbon nanotube (SWCNT) films with low sheet resistance. The process resulted in the effective removal of impurities and healing of defects in the SWCNTs, thus markedly increasing their conductivity. SWCNT samples before and after the process were analyzed by Raman spectroscopy, scanning and transmission electron microscopy, thermogravimetric analysis, contact angle measurement, and transparent conductive film fabrication. Following purification, the sheet resistance decreased from 5380 to 187 Ω/sq at 80% optical transmittance and at a wavelength of 550 nm. The process requires a short time of about 3 h and produces 30% yield of the as-produced sample.10/2010; -
Article: Ni-catalyzed growth of silicon wire arrays for a Schottky diode
[show abstract] [hide abstract]
ABSTRACT: Vertically grown Si wire arrays were fabricated on a large scale by the Ni-catalyzed vapor-liquid-solid method. A single Si wire has a length of several tens of micrometers with a pure Si stem and a NiSi <sub>2</sub> tip. The NiSi <sub>2</sub> tip was spontaneously formed on a Si wire due to a slight lattice mismatch relative to Si. Further, this system provides a Schottky contact having a rectifying ratio of ∼10<sup>2</sup> with a low leakage current of about 2.88×10<sup>-10</sup> A . The growth mechanism of vertical Si wires and the performance of a Schottky diode are discussed.Applied Physics Letters 08/2010; · 3.84 Impact Factor -
Article: Functional microscopy tip fabrication by an electric conductive nanowire.
[show abstract] [hide abstract]
ABSTRACT: The functional microscopy tip was fabricated by an electric conductive nanowire (NW). Single crystalline nickel silicide (NiSi) NW grown by plasma-enhanced chemical vapor deposition has an excellent electrical conductivity. On behalf of the advantages in tiny size and conductivity of NiSi NW, it was utilized as a nanoscale probe. Dielectrophoretic method was applied to position the NW. The NiSi NW containing solution was dropped in an ac electric field applying system to align the NiSi NW on a Si cantilever. The fabricated NiSi NW-sitting functional microscopy tip obtained the information of topography and electrical signals from a nanoscale structure. It shows the high potential of nanoscale microscopy tip fabrication at reduced processing steps.Journal of Nanoscience and Nanotechnology 05/2010; 10(5):3207-10. · 1.56 Impact Factor -
Article: ZnO nanowire-embedded Schottky diode for effective UV detection by the barrier reduction effect.
[show abstract] [hide abstract]
ABSTRACT: A zinc oxide nanowire (ZnO NW)-embedded Schottky diode was fabricated for UV detection. Two types of devices were prepared. The ZnO NW was positioned onto asymmetric metal electrodes (Al and Pt) for a Schottky device or symmetric metal electrodes (Al and Al) for an ohmic device, respectively. The Schottky device provided a rectifying current flow and was more sensitive to UV illumination than the ohmic device. The Schottky barrier plays an important role for UV detection by a UV-induced barrier reduction effect. The fabrication of the ZnO NW-embedded Schottky diode and the UV reaction mechanism are discussed in light of the UV light-induced Schottky barrier reduction effect.Nanotechnology 02/2010; 21(11):115205. · 3.98 Impact Factor -
Book: Ni-catalyzed growth of silicon wire arrays for a Schottky diode
01/2010; AIP. -
Article: Highly sensitive carbon nanotube-embedding gas sensors operating at atmospheric pressure.
[show abstract] [hide abstract]
ABSTRACT: Highly sensitive palladium (Pd) decorated carbon nanotube (CNT) embedding gas sensors working at atmospheric pressure were fabricated. Two types of gas sensors of bare CNTs and Pd nanoparticle decorated CNTs were synthesized by dielectrophoresis. The CNT-containing solution was dropped onto the patterned-platinum electrodes with ac bias. The CNT-embedding sensors sensitively detected 100 ppb level of NO(2) in an atmospheric pressure condition. The Pd decoration on CNTs forming the depletion region was found to be an effective way to enhance the sensor response by the control of carrier mobility and density. Raman spectroscopy revealed a low defect ratio of D/G(-) by heat treatment at 450 degrees C. Moreover, it was investigated that there exists an optimum temperature to enhance the sensor response.Nanotechnology 03/2009; 20(5):055503. · 3.98 Impact Factor -
Article: Continuous extraction of highly pure metallic single-walled carbon nanotubes in a microfluidic channel.
[show abstract] [hide abstract]
ABSTRACT: Highly pure metallic single-walled carbon nanotubes were continuously extracted from a mixture of semiconducting and metallic species using a nondestructive, scalable method. Two laminar streams were generated in an H-shaped microfluidic channel with two inlets and two outlets. The flow conditions were carefully controlled to minimize diffusive and convective transport across the boundary between the two flows. Dielectrophoretic force from the embedded electrode at the junction extracted metallic nanotubes from a stream of nanotube suspension toward the other stream of buffer solution without nanotubes. The highly pure metallic and enriched semiconducting nanotubes were obtained simultaneously at each outlet using this novel approach. Excellent selectivity was verified by electrical transport measurement, absorption, and Raman spectroscopic analysis.Nano Letters 01/2009; 8(12):4380-5. · 13.20 Impact Factor -
Article: The spontaneous metal-sitting structure on carbon nanotube arrays positioned by inkjet printing for wafer-scale production of high sensitive gas sensor units
[show abstract] [hide abstract]
ABSTRACT: Highly sensitive single wall carbon nanotube (CNT)-embedded gas sensor units were fabricated by the mass production scheme. The wafer-scale produced sensor units provide repeatable sensing performances to 10 ppb level of NO2 and the distinctive response to CO. Inkjet approach was applied to deposit CNTs to be arrayed on a 4 in. wafer at designated positions and controlled the density of CNT arrays with reliable accuracy. Metal deposition above the CNT arrays forms the metal-sitting structure providing a good Ohmic contact formation, which also ensures the active CNT responses to gas molecules with less effect from the metal contacts.Sensors and Actuators B: Chemical. 01/2009; 135:587-591. -
Article: Nanomaterial-embedded gas sensor fabrication
[show abstract] [hide abstract]
ABSTRACT: Nanomaterial-embedded gas sensors were fabricated on a 4-in. Si wafer counting 200 units. Carbon nanotubes (CNTs) and tin oxide (SnO) nanoparticles were prepared as hosts to detect NO2 gas molecules at room temperature. Ink-jet approach was applied to deposit nanomaterials on a Si wafer. Metal deposition above the nanomaterials formed the metal-sitting structure providing spontaneous passivation. The performance of the CNT sensor and SnO sensor showed distinctive responses to NO2 gas depending on the type of semiconductor. The sensor is highly sensitive, to detect a 10 ppb level of NO2. It offers massive production of nanomaterial gas sensor units, and the performance is discussed.Current Applied Physics. 01/2009; 9:e38-e41. -
Article: Multiple silicon nanowires-embedded Schottky solar cell
[show abstract] [hide abstract]
ABSTRACT: Large area applicable silicon nanowire (SiNW)-embedded Schottky solar cell (SC) is fabricated. Multiple semiconducting SiNWs were positioned on two different metals. SiNW forms a Schottky or an Ohmic contact to each metal according to the Fermi level lineup. Electrons or holes have a barrier to transport resulting in a rectifying flow. Under 1 sun illumination, the SiNW Schottky SC provided 0.167 V of photovoltage and 91.91 nA of photocurrent with an ideality factor of 1.2. It discusses the fabrication scheme and mechanism of multiple SiNWs-embedded Schottky SC.Applied Physics Letters 01/2009; 95:143112. · 3.84 Impact Factor -
Article: A nickel silicide nanowire microscopy tip obtains nanoscale information.
[show abstract] [hide abstract]
ABSTRACT: An electric conductive Ni silicide nanowire (NiSi NW) embedding electric force microscopy (EFM) tip was fabricated by the dielectrophoretic method and was used to obtain electric information. Due to the geometric and electric excellence, the NiSi NW provides advantages in imaging and fabrication of the microscopy tip. A lead zirconate titanate (PZT) ferroelectric thin film was positively and negatively polarized, and the polarities were obtained by probing of the NiSi NW EFM tip to give distinctive charging information of the PZT film. Moreover, the NiSi NW EFM probing was adopted to achieve the electrical signal from the NW interconnect. The NiSi NW EFM probe confirmed the uniform electric-potential distribution through the NiSi NW interconnect with a small standard deviation. This demonstrates the feasibility of functional utilizations of the NiSi NW.Nanotechnology 12/2008; 19(48):485713. · 3.98 Impact Factor -
Article: Synthesis of Vertically Aligned Manganese-Doped Fe3O4 Nanowire Arrays and Their Excellent Room-Temperature Gas Sensing Ability
[show abstract] [hide abstract]
ABSTRACT: Vertically aligned Mn (10%)-doped Fe3O4 (Fe2.7Mn0.3O4) nanowire arrays were produced by the reduction/substitution of pregrown Fe2O3 nanowires. These nanowires were ferromagnetic with a Verwey temperature of 129 K. X-ray magnetic circular dichroism measurements revealed that the Mn2+ ions preferentially occupy the tetrahedral sites, substituting for the Fe3+ ions. We observed that the Mn substitution decreases the magnetization, but increases the electrical conductivity. We developed highly sensitive gas sensors using these nanowire arrays, operating at room temperature, whose sensitivity showed a correlation with their bond strength of diatomic/triatomic molecules.08/2008;
Top co-authors
Top Journals
Institutions
-
2007–2012
-
Korea Institute of Machinery and Materials
Seoul, Seoul, South Korea
-
-
2010
-
Hanyang University
- Department of Materials & Chemical Engineering
Ansan, Gyeonggi, South Korea
-
-
2006
-
State University of New York
New York City, NY, USA
-
