Browsing by Author "Lin, Chi-Yuan"

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Core-Level Shift of Graphene with Number of Layers Studied by Microphotoelectron Spectroscopy and Electrostatic Force Microscopy
(2014-10-30)
Lin, Chi-Yuan
;
Shiu, Hung-Wei
;
Chang, Lo-Yueh
;
Chen, Chia-Hao
;
Chang, Chen-Shiung
The dependence of C-1s core-level shift (CLS) of graphene on the number of layer (NL) is significant information to derive the coordination-resolved C1s core-level energy (E-1s) of carbon allotropes. To observe the variation of CLS of graphene with NL, binding energy and work function of graphene with various NL were examined by scanning photoelectron microscopy/spectroscopy and electrostatic force microscopy. E1s of grounded graphene decreased as NL increased. The E-1s of single-layer graphene and multilayer graphene (MLG) is 289.42 and 289.13 eV, respectively. Based on the NL-dependent E1s of graphene, the CLS of C-1s between a free carbon atom and diamond is 0.74 eV, calculated by the bond-order-length-strength correlation theory. The CLS of graphene with NL supported the existence of surface core-level shift (SCLS) on graphite. The magnitude of SCLS in MLG was +0.09 eV. The effective coordination number is 3.68 for bilayer graphene and 4.31 for the surface carbon layer in MLG.
Fabrication of Ni Nanostructures on p-Si by Scanning Probe Lithography on Si(3)N(4) Films and Selective Electrodeposition
(2010-07-01)
Lin, Chi-Yuan
;
Chang, Chung-Shun
;
Chien, Forest S. -S.
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光電工程學系
;
Department of Photonics
Ni-Si nano Schottky junctions are fabricated by the combined process of scanning probe lithography and electrodeposition. The Si(3)N(4) film was patterned by probe-induced oxidation and became a mask for selective electrodeposition of Ni on p-Si substrate. The Ni pattern consists of Ni nano dots, whose diameter is less then 60 nm. The composition and ferromagnetism of Ni dots are verified by energy dispersive spectrum and magnetic force microscopy. The schottky barrier of Ni-Si nano contact is 0.52 V determined by the I-V measurement of conducting atomic force microscopy (CAFM). From current mapping images, it shows that chemical impurity at the Ni-Si interfaces can result in the poor conductance of the junctions.
Fabrication of Ni Nanostructures on p-Si by Scanning Probe Lithography on Si3N4 Films and Selective Electrodeposition
(2010-07-01)
Lin, Chi-Yuan
;
Chang, Chung-Shun
;
Chien, Forest S. -S.
;
光電工程學系
;
光電工程研究所
Ni-Si nano Schottky junctions are fabricated by the combined process of scanning probe lithography and electrodeposition. The Si3N4 film was patterned by probe-induced oxidation and became a mask for selective electrodeposition of Ni on p-Si substrate. The Ni pattern consists of Ni nano dots, whose diameter is less then 60 nm. The composition and ferromagnetism of Ni dots are verified by energy dispersive spectrum and magnetic force microscopy. The schottky barrier of Ni-Si nano contact is 0.52 V determined by the I-V measurement of conducting atomic force microscopy (CAFM). From current mapping images, it shows that chemical impurity at the Ni-Si interfaces can result in the poor conductance of the junctions.
Graphene On Au-Coated SiOx Substrate: Its Core-Level Photoelectron Microspectroscopy Study
(2012-08-01)
Chen, Jhih-Wei
;
Wang, Chiang-Lun
;
Shiu, Hung Wei
;
Lin, Chi-Yuan
;
Chang, Chen-Shiung
"The core-level electronic structures of exfoliated graphene sheets on a Au-coated SiOx substrate have been studied using synchrotron radiation photoelectron spectroscopy (SR-PES) on a micron scale. The graphene's visibility on the Au-coated SiOx substrate was first demonstrated by micro optical characterization, and then an SR-PES study was conducted. Because of the elimination of charging effect, a precise C 1s core-level characterization shows graphitic and contaminated carbon states of graphene. Different levels of Au-coating-induced p-type doping on single-and double-layer graphene sheets were also examined in the C 1s core-level shift. The Au-coated SiOx substrate can be treated as a simple but high-throughput platform for in situ studying graphene under further hybridization by PES. (C) 2012 The Japan Society of Applied Physics"
Optical controlled graphene-based nonvolatile ternary-logic transistor with azobenzene copolymer
(2013-01-07)
Lin, Chi-Yuan
;
Chang, Chen-Shiung
;
Lin, Jian Hung
;
Hsu, Chia-Chen
;
Chien, Forest Shih-Sen
We demonstrated optical-controlled graphene-based nonvolatile transistors incorporated with azobenzene copolymer. The transistor was gated by the quasi remnant polarization of azobenzene copolymer, which was built by photo-assisted poling and erased by photo-depoling at room temperature. By taking the nature of polymer electret of azobenzene copolymer, the graphene-based device can perform ternary logic, and the resistance change ratio of the written status "+/- 1" to the erased status "0" was -/+ 60%. The device can retain its statuses against an electric field as high as 0.2 MV/cm because the azobenzene molecules were frozen in copolymer at room temperature. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4773984]
Optical-power-dependent photodesorption kinetics of graphene studied by conductance response
(2015-06-01)
Hsu, Yang-Yang
;
Lin, Chi-Yuan
;
Lai, Yi-Chun
;
Wu, Kun-Rui
;
Ng, Kwai-Kong
The photodesorption kinetics of graphene with various UV laser power is studied by conductance response. Analytical expressions of the power-dependent photodesorption kinetics of graphene in ambience are derived. The photodesorption time constant tau(d), steady current, and magnitude of modulation current, can be expressed as functions of the adsorption time constant tau(a), desorption cross section sigma, and photon flux density. Under illumination the steady occupation ratio of adsorbed O-2 on graphene is equal to tau(d)/tau(a). It is suggested that the photodesorption of O-2 on graphene is attributed the injection of photogenerated hot electrons and is restricted by the density of antibonding states of O-2. (C) 2015 Optical Society of America
Platinum-graphene counter electrodes for dye-sensitized solar cells
(2013-07-07)
Cheng, Cheng-En
;
Lin, Chi-Yuan
;
Shan, Chien-Hsun
;
Tsai, Shang-Yi
;
Lin, Ko-Wei
This paper describes the photovoltaic performance of dye-sensitized solar cells (DSSCs) containing graphene-incorporated counter electrodes (CEs). The location and thickness of graphene in CEs are optimized to improve the photovoltaic performance of DSSCs, compared with typical Pt CEs. The DSSC, with a Pt/few-layer graphene (FLG) CE, achieved 8% in short-circuit current density and 13% in power conversion efficiency (PCE). Electrochemical impedance spectroscopy shows that the DSSC, with a Pt/FLG CE, exhibits a series resistance lower than that with a Pt CE. The lower series resistance is attributed to the contact resistance at the interface of platinum and fluorine doped tin oxide. The contact resistance is reduced by the formation of the thin platinum-carbon composite layer. It is demonstrated that the consumption of Pt could be reduced with a Pt/FLG CE. However, graphene/Pt CEs resulted in a slow charge-transfer process and consequently a worse photovoltaic performance of DSSCs. (C) 2013 AIP Publishing LLC.
Surface-enhanced Raman scattering of graphene with photo-assisted-synthesized gold nanoparticles
(2013-03-11)
Cheng, Cheng-En
;
Lin, Chi-Yuan
;
Chang, Hao-Yu
;
Huang, Chen-Han
;
Lin, Hsing-Ying
This paper presents a convenient and reliable method to prepare gold nanoparticles (AuNPs) on graphene. Photo-assisted synthesis (PAS) was employed to grow AuNPs in AuCl4- electrolyte on graphene. The size of AuNPs could be as large as 130 nm. This optical method had a steady growth rate of AuNPs. The distribution of AuNPs was well controlled by focusing the laser for PAS. The minimum diameter of the distribution was approximately 1 mu m. Surface-enhanced Raman scattering of graphene due to AuNPs was observed. Electrical fields near AuNPs calculated by the finite-difference time-domain algorithm ensured that the Raman enhancement was attributed to the localized surface plasmons of AuNPs. (c) 2013 Optical Society of America
Synchrotron Radiation Soft X-ray Induced Reduction in Graphene Oxide Characterized by Time-Resolved Photoelectron Spectroscopy
(2015-06-11)
Lin, Chi-Yuan
;
Cheng, Cheng-En
;
Wang, Shuai
;
Shiu, Hung Wei
;
Chang, Lo Yueh
Synchrotron radiation soft X-ray was employed to reduce graphene oxide (GO) films in ultrahigh vacuum. The dissociation of oxygen-containing functional groups, and the formation of sp(2) C-C bonds were revealed by time-resolved in situ X-ray photoelectron spectroscopy, demonstrating the X-ray reduction of GO. The number of C-O bonds of G-O exhibited an exponential decay with exposure time. The X-ray reduction rate of G-O was positively correlated with the intensity of low-energy secondary electrons excited from substrates by soft X-ray, indicating the C-O bonds were dissociated by secondary electrons.
The effect of thermal annealing on the optical and electrical properties of ZnO epitaxial films grown on n-GaAs (001)
(2015-01-01)
Liu, Wei-Rein
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Lin, Bi-Hsuan
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Lin, Chi-Yuan
;
Yang, Song
;
Kuo, Chin-Chia
Wurtzite ZnO epitaxial layers grown on n-type GaAs (001) by pulsed laser deposition (PLD) exhibited n-type conductivity. Post-growth annealing leads the conversion of carrier type from electron to hole, as revealed by Hall effect measurements, although only moderate structural improvement was observed. The carrier type conversion is attributed to thermally activated arsenic diffusion from the substrate, confirmed by secondary ion mass spectrometry and photoluminescence. The surface electrical properties of both the as-deposited n-type and annealed p-type ZnO epitaxial layers were thoroughly characterized by Kelvin force microscopy (KFM) and electrostatic force microscopy (EFM). The results indicated the existence of a high density of surface states close to the ZnO midgap with a density of a few 10(14) cm(-2) eV(-1). The Fermi levels (E-F) of n- and p-type ZnO epitaxial layers were found to be 1.06 eV below the conduction-band minimum (CBM) and 1.612-1.769 eV above the valence-band maximum (VBM), respectively. The small EF difference between the n- and p-type ZnO epitaxial layers implies Fermi level pinning at the surface of both n-and p-type ZnO epitaxial layers.