Effect of the microstructure of Ag catalysts in the fabricating process of silicon nanowires

Fei Zhao,Guo-an Cheng,Rui-ting Zheng,Le-yang Xia 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.52 No.-

In this paper, well-aligned silicon nanowire (SiNW) arrays have been directly synthesized on single crystal silicon wafer at room temperature via a simple chemical etching method, and the effect of the microstructure of Ag catalysts on the fabricating process of the silicon nanowires has been systematically investigated. The experimental results show that different microstructures of Ag catalysts have been observed with different concentration of AgNO3/HF solution for different deposition times. The diameters of Ag particles and the mean interstitial sizes among Ag particles are relatively small for a short deposition time, and some large particles are formed when the deposition time increases. A much longer deposition time caused the substrate to be covered with a large amount of Ag dendrite. It can be inferred that 4 min is a good deposition time, because of the proportioned structure of particles and interstitial size, according to our experimental results. Nanostructures of Ag catalyst also vary with a change of concentration of AgNO3/HF solution. Ag dendrite may be formed at high concentration and affect the fabrication of SiNWs. In this paper, well-aligned silicon nanowire (SiNW) arrays have been directly synthesized on single crystal silicon wafer at room temperature via a simple chemical etching method, and the effect of the microstructure of Ag catalysts on the fabricating process of the silicon nanowires has been systematically investigated. The experimental results show that different microstructures of Ag catalysts have been observed with different concentration of AgNO3/HF solution for different deposition times. The diameters of Ag particles and the mean interstitial sizes among Ag particles are relatively small for a short deposition time, and some large particles are formed when the deposition time increases. A much longer deposition time caused the substrate to be covered with a large amount of Ag dendrite. It can be inferred that 4 min is a good deposition time, because of the proportioned structure of particles and interstitial size, according to our experimental results. Nanostructures of Ag catalyst also vary with a change of concentration of AgNO3/HF solution. Ag dendrite may be formed at high concentration and affect the fabrication of SiNWs.

Synthesis and Spectral Analysis of Head-to-Tail Shaped Ag2S/ZnS Near-Infrared Quantum Dots with Manganese Dopant.

Zhao, Fei,Kim, Jongsung American Scientific Publishers 2015 Journal of nanoscience and nanotechnology Vol.15 No.7

<P>Silver sulfide (Ag2S) near-infrared quantum dots have been synthesized by one pot process and the water solubility of the quantum dots was enhanced by ligand exchange. With the addition of zinc source, zinc sulfide (ZnS) nanocrystals grew like a link with the Ag2S in head-to-tail structure. Furthermore, in the presence of manganese dopants, particles exhibited twice the length of previous size. The optical and structural properties of these three kinds of quantum dots (Ag2S, Ag2S/ZnS, and Mn-doped Ag2S/ZnS) were characterized through photoluminescence spectra, UV-Vis absorption spectra, and transmission electron microscopy. It has been found that a linked structure is formed in ZnS-Ag2S-ZnS by manganese doping.</P>

Fabrication of the optical fiber pH sensor based on CdSe/ZnS quantum dot.

Zhao, Fei,Kim, Inyea,Kim, Jongsung American Scientific Publishers 2014 Journal of nanoscience and nanotechnology Vol.14 No.8

<P>During the past decade, there has been a lot of research on the application of quantum dots (QDs) in photonics and biotechnology. QDs are semiconductor nanocrystals which show many peculiar optical and electrical properties due to their quantum confinement effects. In this work, the correlation of the fluorescence intensity of QDs and the pH under ambient temperature was studied. An optical fiber pH sensor was prepared using CdSe/ZnS carboxyl quantum dots as sensing media. QDs with different sizes and emission colors (green, yellow, and red) were immobilized on the surface of the optical fiber through EDC/sulfo-NHS coupling reaction. The optical fiber was immersed in water, and the photoluminescence (PL) spectra of QDs were obtained at ambient temperature under various pH conditions. The photoluminescence (PL) intensity of QDs increased linearly with the increase of pH, and among the QDs, the red emitting QDs show the largest change in PL intensity with pH. This shows that QDs can be used as pH sensing media and optical fiber pH probe can be prepared.</P>

Optimum Design for a Double-excitation Spoke-array Permanent Magnet Vernier Machine by Tooth Modification

Fei ZHAO(조비),Thomas Anthony Lipo,Byung-il Kwon(권병일) 대한전기학회 2013 대한전기학회 학술대회 논문집 Vol.2013 No.7

Design Consideration to Improve Torque in Axial Flux PM Vernier Machine

Fei zhao(조비),Byung-il Kwon(권병일) 대한전기학회 2014 대한전기학회 학술대회 논문집 Vol.2014 No.10

Improved Reversible Cross-Linking-Based Solid-Phase RNA Extraction for Pathogen Diagnostics

Zhao, Fei,Lee, Eun Yeong,Shin, Yong American Chemical Society 2018 ANALYTICAL CHEMISTRY - Vol.90 No.3

<P>In this study, we developed an amine-functionalized, diatomaceous earth-based, dimethyl suberimidate assisted (ADD) system as a novel binding strategy to improve the solid-phase extraction method for rapid and simple purification of RNA from biological samples including human cells and pathogenic bacteria. This ADD system is based on reversible cross-linking reactions between RNA and the silica matrix. The formation of robust covalent bonds protects RNA from both the sufferance of washing steps and isolation with ribonuclease (RNase)-rich samples, leading to the extraction of higher quality RNA. This improved RNA extraction system integrated with quantitative real-time reverse transcription polymerase chain reaction (RT-qPCR) is evaluated for pathogen diagnostics. Compared to standard solid-phase extraction based commercial kits, this improved method shows highly enhanced sensitivity with 1000-fold higher sensitivity for human cells and 100-fold higher sensitivity for <I>Brucella</I> bacteria, according to the cycle threshold value of RT-qPCR. We envision that the ADD system can be tailored for commercial applications for RNA expression analysis in forensics studies, as well as for disease diagnostics in clinical applications.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancham/2018/ancham.2018.90.issue-3/acs.analchem.7b03493/production/images/medium/ac-2017-03493v_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ac7b03493'>ACS Electronic Supporting Info</A></P>

Fabrication of a Dopamine Sensor Based on Carboxyl Quantum Dots

Zhao, Fei,Kim, Jongsung American Scientific Publishers 2015 Journal of nanoscience and nanotechnology Vol.15 No.10

Fabrication and Electron Field Emission of Silicon Nanowires Synthesized by Chemical Etching

Fei Zhao,Dan-dan Zhao,Shao-long Wu,Guo-an Cheng,Rui-ting Zheng 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.55 No.6

Vertically aligned silicon nanowire arrays, which were synthesized by using a Ag catalyst deposited with magnetron sputtering and an electrochemical etching process were investigated. The thickness of the Ag catalyst affects the microstructure of aligned silicon nanowire array. Vertically aligned silicon nanowire arrays with more uniform morphology structures were synthesized with a catalyst thickness of 40 nm on a single crystal silicon wafer at room temperature. The electron field emission data showed a lower turn-on field for silicon nanowire arrays fabricated with the electrochemical etching process. The field enhancement factor of the silicon nanowire arrays is as high as 1637. These data indicate that electrochemical etching technology is a cheap and good method for fabricating vertically aligned silicon nanowire arrays for applications in field emission devices. Vertically aligned silicon nanowire arrays, which were synthesized by using a Ag catalyst deposited with magnetron sputtering and an electrochemical etching process were investigated. The thickness of the Ag catalyst affects the microstructure of aligned silicon nanowire array. Vertically aligned silicon nanowire arrays with more uniform morphology structures were synthesized with a catalyst thickness of 40 nm on a single crystal silicon wafer at room temperature. The electron field emission data showed a lower turn-on field for silicon nanowire arrays fabricated with the electrochemical etching process. The field enhancement factor of the silicon nanowire arrays is as high as 1637. These data indicate that electrochemical etching technology is a cheap and good method for fabricating vertically aligned silicon nanowire arrays for applications in field emission devices.

A Small Axial-Flux Vernier Machine With Ring-Type Magnets for the Auto-Focusing Lens Drive System

Zhao, Fei,Kim, Min-Soo,Kwon, Byung-Il,Baek, Jong-Ho IEEE 2016 IEEE transactions on magnetics Vol.52 No.7

<P>A small axial-flux permanent magnet vernier motor (PMVM) is investigated to satisfy the requirements of high drive torque, low speed, low noise, and low-power consumption for application in the camera auto-focusing lens drive. The proposed axial-flux PMVM is constructed with ring-type magnets in the rotor and has strict dimensional constraints due to its location in the lens barrel. The design approach is an alternative motor design method coupled with the analytical method or the finite-element method. The proposed motor's electromagnetic performance was verified by means of both methods. Finally, a prototype was built and tested, showing an adequate range of speed while also meeting the noise limits, and consuming less than 2 W of power.</P>

Fabrication of CdSeS Alloyed Quantum Dots and Study on Fluorescence Lifetime

Zhao, Fei,Kim, Jong Sung Informa UK (TaylorFrancis) 2012 Molecular Crystals and Liquid Crystals Vol.566 No.1