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Now showing items 1 - 16 of 16

  • In Situ STM Study of Cu Electrodeposition on TBPS-Modified Au(111) Electrodes

    Liu, Yung-Fang   Krug, Klaus   Lin, Pin-Chun   Chiu, Yong-Da   Dow, Wei-Ping   Yau, Shueh-Lin   Lee, Yuh-Lang  

    The impact of 3,3'-thiobis(1-propanesulfonic acid, sodium salt) (TBPS) on Cu/Au(111) electrodeposition has been investigated by electrochemical methods and scanning tunneling microscopy (STM). Cyclic voltammetry and galvanostatic experiments indicate that Cu growth on Au(111) - which is known to be strongly kinetically hindered in additive-free, aqueous perchloric acid solutions - proceeds significantly faster in the presence of TBPS. The TBPS molecules either "float" on top of the growing film or become incorporated into the deposit. Complementary in situ STM studies show that Cu underpotential deposition (UPD) proceeds via two distinct mechanisms. One-dimensional growth of Cu stripes was observed between 0.05 and 0.35 V-RHE for TBPS-modified Au(111) electrodes. Each stripe is composed of two or three parallel rows of Cu atoms oriented along the main crystallographic directions of the Au(111) substrate. An increase of the TBPS concentration near the solid/liquid interface restricts the Cu stripe growth to a narrow potential regime between 0.3 and 0.35 V-RHE and two-dimensional Cu island growth becomes the favored growth mechanism. The latter fully dominates in TBPS-containing electrolyte. Cu growth in the overpotential deposition (OPD) regime results in a smooth Cu film with low surface roughness, in contrast to defect-mediated 3D island growth in additive-free electrolytes. (C) 2011 The Electrochemical Society. [DOI: 10.1149/2.057202jes] All rights reserved.
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  • Potential-Induced Adsorption Behavior of Carboxyl-Terminated Alkanethiol on Au(111) Surfaces

    Liu, Yung-Fang   Chen, Liang-Huei   Yoshimura, Masahiro   Yau, Shueh-Lin   Lee, Yuh-Lang  

    The adsorption and self-assembly behaviors of a carboxyl-group-terminated alkanethiol, 11-mercaptoundecanoic acid (MUA), on Au(111) electrodes in an electrochemical system are studied using in situ scanning tunneling microscopy. The effect of applied potential on the phase evolution of the MUA adlayer is investigated and compared with those reported for alkanethiols with various terminal groups. The results show that the MUA molecules initially adsorb in a lie-down orientation, organizing into ordered domains with a stripe structure. With further adsorption of MUA molecules, the alkyl chains lift off from the substrate, forming a more condensed phase with an arrangement of (root 3 x root 3). This phase evolution is similar to those reported for other alkanethiols. However, the adsorption process of MUA is much slower and a disordered transition phase (gamma phase) exists between the stripe and saturation phases. The gamma phase converts back to the stripe phase when the electrode potential is shifted from 0.2 to 0.4 V, following which the phase evolution cannot proceed further to the saturation phase. These results are contrary to those observed for other alkanethiols and are attributed to the interaction of the terminal COOH group with the substrate at positive potentials. Under the electrode potential, the molecules bind to the substrate via both head and end groups, triggering a lie-down orientation and decreasing the mobility of adsorbed molecules. As a result, the adlayer remains in the stripe phase and further phase evolution is inhibited.
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  • Epitaxial Electrodeposition of Cobalt on a Pt(111) Electrode Covered with a Cu(111) Film

    Yen, Po-Yu   Chen, Sihzih   Tu, Hsin-Ling   Wu, Hengliang   Yau, Shueh-Lin   Tsay, Jyh-Shen  

    Electrodeposition is an inexpensive alternative to the conventional molecular beam epitaxy technique used to fabricate artificial magnetic materials, such as cobalt thin film. Reported here is a scanning tunneling microscopy (STM) study on the electrodeposition of Co on a Pt(111) single-crystal electrode precoated with a Cu thin film in 0.1 M KClO(4) + 1 mM HCl + 0.04 M CoCl(2) (pH 3). Deposition of Co started with the nucleation of nanometer-sized clusters preferentially at pits on the Cu support, followed by lateral expansion and coalescence of Co nuclei to form a uniform Co layer. Normally a few Co layers would grow simultaneously to produce a smooth Co deposit until the 12th layer. Cobalt grew in three dimensions afterward. Atomic-resolution STM imaging showed that the first Co layer assumed a double-lined pattern, which was lifted by the deposition of another layer of Co. The second Co layer exhibited a hollow-ring pattern, which transformed into a moire pattern and triangular pits at the third Co layer. The moire pattern gained prominence at the expense of the triangular pits as the Co deposit thickened. The amplitude of the intensity modulation of the moire pattern decreased with the thickness of the Co deposit and eventually became indiscernible at the 12th layer. These restructuring events resulted from a gradual release of the stress at the Co/Cu interface. Since the morphology of the copper substrate was hardly changed by the deposition of cobalt, mixing at the Co/Cu interface seems to be negligible. Similar to the deposition process, dissolution of Co deposit proceeded in layers also.
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  • In situ STM observation with atomic resolution on platinum film electrodes formed by a sputtering method

    Yau, Shueh-Lin   Moriyama, Takahiro   Uchida, Hiroyuki   Watanabe, Masahiro  

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  • In Situ Scanning Tunneling Microscopy of Benzene Adsorbed on Rh(111) and Pt(111) in HF Solution

    Yau, Shueh-Lin   Kim, Youn-Geun   Itaya, Kingo  

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  • Electrochemical etching of Si(001) in NH4F solutions: Initial stage and {111} microfacet formation

    Yau, Shueh-Lin   Kaji, Kazutoshi   Itaya, Kingo  

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  • Adlayer structure of octa-alkoxy-substituted copper(II) phthalocyanine on Au(111) by electrochemical scanning tunneling microscopy

    Wang, Li   Ou-Yang, Liangyue   Yau, Shueh-Lin  

    Electrochemical scanning tunneling microscopy (ECSTM) has been used to examine the adlayer of octa-alkoxy-substituted copper(II) phthalocyanines (CuPc(OC8H17)(8)) on Au(111) in 0.1 M HClO4, where the molecular adlayer was prepared by spontaneous adsorption from a benzene solution containing this molecule. Topography STM scans revealed long-range ordered, interweaved arrays of CuPc(OC8H17)(8) with coexistent rectangular and hexagonal symmetries. High-quality STM molecular resolution yielded the internal molecular structure and the orientation of CuPc(OC8H17)(8) admolecules. These STM results could shed insight into the method of generating ordered molecular assemblies of phthalocyanine molecules with long-chained substitutes on metal surface.
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  • Structures and dynamic processes of molecular adlayers on Rh(111) and Pt(111) in HF solution: naphthalene and biphenyl

    Yau, Shueh-Lin   Itaya, Kingo  

    Adlayer structures of naphthalene and biphenyl on well-defined Rh(111) and Pt(111) electrodes were investigated in HF solution using in situ scanning tunneling microscopy (STM). A highly ordered adlayer of naphthalene was found to form on Rh(111) with a (33 × 33)R30° structure, whereas disordered adlayers were observed on Pt(111). The longer molecular axis of naphthalene was aligned along the close-packed atomic rows of both Rh and Pt. On the other hand, the molecular axis of biphenyl was aligned along the 3 direction on Rh(111). The influence of molecular structure on the arrangement of adsorbates is discussed, based on the adlayer structures of naphthalene and biphenyl. The desorption process of naphthalene was carefully investigated at potentials near the hydrogen evolution reaction. On Rh(111), it was found that the desorption of naphthalene occurred preferentially near defects at terraces in the early stages, followed by the formation of ordered islands on terraces at more cathodic potentials. Naphthalene adsorbed at step edges or holes on terraces was more stable against replacement by hydrogen. On Pt(111), desorption occurred more randomly, resulting in the formation of an adlayer with isolated molecules. These isolated molecules were clearly discerned by in situ STM, indicating that naphthalene is strongly attached on Pt(111).
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  • Electrochemical performance and safety features of high-safety lithium ion battery using novel branched additive for internal short protection

    Li, Yu-Han   Lee, Meng-Lun   Wang, Fu-Ming   Yang, Chang-Rung   Chu, Peter P. J.   Yau, Shueh-Lin   Pan, Jing-Pin  

    In this study, we have investigated N-phenylmaleimide/bismaleimide-containing branched oligomer (BO1) as additive in Li-ion batteries to increase the safety performance by reducing the probability of batteries suffering an internal short circuit. In the nail penetration test, a LiCoO2/MCMB full battery with N-phenylmaleimide/bismaleimide-containing branched oligomer (BO1) showed a significant improvement in thermal stability and was able to restrain the temperature of the battery at about 85 degrees C. Furthermore, we found that N-phenylmaleimide/bismaleimide-containing branched oligomer (BO1) contained battery revealed better cycling and electrochemical performance, compared with the battery with bismaleimide-containing branched oligomer (BO3) in the electrolyte. The improvement might result from the favorable ionic conductivity, Li ion mobility and lower resistance in the battery. This additive can meet the cycling performance and safety requirements for Li-ion batteries. (C) 2012 Elsevier B. V. All rights reserved.
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  • High-Resolution Imaging of Aromatic Molecules Adsorbed on Rh(111) and Pt(111) in Hydrofluoric Acid Solution:? In Situ STM Study

    Yau, Shueh-Lin   Kim, Youn-Geun   Itaya, Kingo  

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  • In situ scanning tunneling microscopy imaging of electropolymerized poly(3,4-ethylenedioxythiophene) on an iodine-modified Au(111) single crystal electrode

    Lapitan, Lorico D. S., Jr.   Tongol, Bernard John V.   Yau, Shueh-Lin  

    The electrochemical polymerization of 3,4-ethylenedioxythiophene (EDOT) on an iodine-modified Au(1 1 1) single crystal electrode in aqueous 0.10 M HClO4 was investigated by cyclic voltammetry (CV) and electrochemical scanning tunneling microscopy (EC-STM). The cyclic voltammetric and EC-STM data revealed the stability of the iodine adlayer provided a suitable potential range for EDOT electropolymerization was controlled at 1.20V (vs. the reversible hydrogen electrode). EC-STM was used to examine the formation of the PEDOT adlayer on the iodine-modified Au(1 1 1) electrode. In situ electropolymerization of EDOT was carried out by slowly increasing the electrode potential to 1.20V. This process resulted in the formation of single molecular chains of PEDOT with a diameter of 0.90 nm and lengths of 5-7 nm. Higher resolution STM images further revealed PEDOT nanostructures with bent polymer backbones at angles of 105 degrees, 144 degrees and 180 degrees. The growth of PEDOT multi-layers was observed when the potential was held for a longer time. (C) 2011 Elsevier Ltd. All rights reserved.
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  • Substrate-Induced Varied Conformation and Molecular Assemblies: In Situ STM Observation of beta-Substituted Oligothiophene Adlayers on Au(111) RID A-6557-2010

    Wang, Li   Tongol, Bernard John V.   Yau, Shueh-Lin   Otsubo, Tetsuo   Itaya, King  

    The adsorption of 3,3"'-dihexy1-2,2':5',2 '':5 '',2'''-quaterthiophene (4T) molecules on an Au(111) electrode was examined by using in situ scanning tunneling microscopy in 0.10 M HClO(4), revealing internal molecular structures oldie tetrathiophene backbones and the hexyl side chains. The 4T admolecules were packed in lamellae with their molecular axis aligned along the main axis of the Au(111) substrate and their hexyl side chains interdigitated to enhance intermolecular interaction. Dynamics of molecular organization incurred by the shifting of potential was also observed in this study. By examining and comparing the adsorption of 4T on HOPG and Au(111), we address the role of the substrate in understanding the arrangement of 4T admolecules.
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  • Molecular Assembly and Electropolymerization of 3,4-Ethylenedioxythiophene on Au(111) Single Crystal Electrode as Probed by In Situ Electrochemical STM in 0.10 M HClO(4)

    Lapitan, Lorico D. S., Jr.   Tongol, Bernard John V.   Yau, Shueh-Lin  

    We have used electrochemical scanning tunneling microscopy (EC-STM) to obtain molecular insights on the adlayer structures and electrochemical polymerization of 3,4-ethylenedioxythiophene (EpoT) on a bare Au(111) single crystal electrode in 0.1 M HClO(4) solution. Cyclic voltammetric (CV) studies showed an increase in anodic current at 0.90 V with the oxidation of EDOT monomer occurring at E = 1.10 V (vs reversible hydrogen electrode). In situ STM revealed, for the first time, that EDOT molecules can spontaneously form organized adlayers on a bare Au(111) surface with 18 mu M concentration of EpoT in aqueous solution. Molecularly resolved STM images of the EDOT adlayer showed two domains consisting of disordered and ordered structures with the formation of vacancy islands or "etch pits". Several EpoT structures were observed at +0.60 V. namely, (4 x 7), (5 x root 37), and (root 7 x 3) with calculated coverages of 0.107, 0.114, and 0.111 ML, respectively. Electropolymerization was also carried out using in situ STM in 0.10 M HClO(4) under potential control.
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  • Dynamic self-assembly and electropolymerization processes of 3,4-ethylenedioxythiophene on Au(100) single crystal electrode as probed by in situ scanning tunneling microscopy

    Garcia, Jonyl L.   Tongol, Bernard John V.   Yau, Shueh-Lin  

    Electrochemical scanning tunneling microscopy (EC-STM) was employed to examine the molecular assembly and electropolymerization processes of 3,4-ethylenedioxythiophene (EDOT) onto reconstructed and unreconstructed Au(1 0 0) single crystal electrodes in a 0.1 M HClO4 electrolyte solution. The EDOT adsorption onto the Au(1 0 0)-hex surface induced lifting of the reconstruction at potentials as low as E = 0.150 V (vs. reversible hydrogen electrode (RHE)), which is clear evidence of the strong EDOT-Au interaction that was also observed by cyclic voltammetry (CV). EC-STM was also able to reveal, for the first time, the dynamic process of EDOT molecular self-assembly onto the Au(1 0 0)-(1 x 1) surface. The EDOT adlayer was found to fit into a 4 root 2 x 3 root 2 unit cell. High-resolution STM imaging revealed a vertically tilted geometry for the EDOT molecules. Electropolymerization was also performed, revealing the solution-process formation of polymer bundles. (C) 2012 Elsevier Ltd. All rights reserved.
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  • Direct Observation of Conformational Changes of beta-Substituted Duodecithiophene on a Au(111)-(root 3 x 22) Substrate Using in Situ Electrochemical STM in 0.1 M HClO(4) RID A-6557-2010

    Tongol, Bernard John V.   Wang, Li   Yau, Shueh-Lin   Otsubo, Tetsuo   Itaya, Kingo  

    The adsorption of hexahexylduodecithiophene (12T) on a Au(111) electrode was investigated by using Cyclic voltammetry (CV) and in situ electrochimal scanning tunneling microscopy (EC-STM) in 0.10 M HClO(4). Potential control at 0.20 V (vs RHE) revealed adlayer structures of mostly folded and rarely angular (oblique) and extended conformations on a reconstructed Au(111)-(root 3x22) surf ace. The angular and extended conformations predominate when the electrode potential is increased to 0.35 and 0.60 V. Folded structures are still evident, but dynamic STM studies showed unfolding of this conformation. With molecular STM imaging of 12T adlayers, we address the packing arrangement and conformational changes of 12T admolecules on the reconstructed Au(111) electrode Surface.
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  • Nanostructures and Molecular Assembly of beta-Blocked Long Oligothiophenes up to the 96-Mer on Au(111) as Probed by in Situ Electrochemical Scanning Tunneling Microscopy RID A-6557-2010

    Tongol, Bernard John V.   Wang, Li   Yau, Shueh-Lin   Otsubo, Tetsuo   Itaya, Kingo  

    The electrochemistry and adsorption of a series of beta-blocked long oligothiophenes up to the 96-mer (96T) on Au(111) electrode were examined by using cyclic voltammetry (CV) and in situ electrochemical scanning tunneling microscopy (EC-STM), respectively, in 0.10 M HClO(4), CV characterization presents the electrochemical behavior and stability of the oligothiophene-modified Au(111) in aqueous perchloric acid solution, EC-STM characterization revealed lamella-type molecular arrangement with the molecular axis aligned along the main crystallographic axis of the Au(111) substrate. High-quality STM molecular resolution imaging was obtained to reveal details of conformation, dimension, and packing habit of the oligothiophene nanostructures.
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