W. M. Liu

Chinese Academy of Sciences, Peping, Beijing, China

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Publications (31)101.65 Total impact

  • L. Shi · C. F. Sun · P. Gao · F. Zhou · W. M. Liu ·
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    ABSTRACT: Ni–Co–carbon nanotubes composite coatings were prepared by electrodeposition in a Ni–Co plating bath containing carbon nanotubes (CNTs) to be co-deposited. The polarization behavior of the composite plating bath was examined on a PAR-273A potentiostat/galvanostat device. The friction and wear behaviors of the Ni–Co–CNTs composite coatings were evaluated on a UMT-2MT test rig in a ball-on-disk contact mode. The morphologies of the original and worn surfaces of the composite coatings were observed on an atom force microscope (AFM) and scanning electron microscope. It was found that the introduction of the carbon nanotubes in the electrolyte caused the shift towards larger negatives of the reduction potential of the Ni–Co alloy coating, and the co-deposited CNTs had no significant effect on the electrodeposition process of the Ni–Co alloy coating. However, the co-deposited CNTs led to changes in the composition and structure of the composite coatings as well. Namely, the peak width of the Ni–Co solid solution for the composite coating is broader than that of the Ni–Co alloy coating and the composite coating possess higher microhardness and elastic modulus than Ni–Co alloy coating. The co-deposited CNTs were uniformly distributed in the Ni–Co matrix and contributed to greatly increase the microhardness and tribological properties of the Ni–Co alloy coating.
    Surface and Coatings Technology 04/2006; 200(16):4870-4875. DOI:10.1016/j.surfcoat.2005.04.037 · 2.00 Impact Factor
  • PQ La · J. Yang · D. J. H. Cockayne · WM Liu · QJ Xue · YD Li ·
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    ABSTRACT: The preparation of bulk naocrystalline Fe3Al-based material by aluminothermic reaction was described. Ferric sesquioxide and aluminum powders were weighed according to the stoichiometry of the aluminothermic reaction. Metallographic investigations and chemical analysis of the polished cross sections of the Fe3Al product are performed on an electron probe microanalyzer. EPMA examination revealed that the bright phase consists of Fe and Al elements and the black phase consists of Mn, Al, and S elements.
    Advanced Materials 02/2006; 18(6):733 - 737. DOI:10.1002/adma.200501684 · 17.49 Impact Factor
  • Z.-G. Guo · F. Zhou · W.-M. Liu ·
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    ABSTRACT: A superhydrophobic silica film was prepared by means of sol-gel and self-assembly techniques, with a very high water contact angle (155°-157°) and a small sliding angle (3°-5°), making water droplet move readily on the surface. The film surface morphologies were observed with scanning electron microscope, and the elements on surface were determined by X-ray photoelectron spectroscopy. It was found that there were many microconvexities with binary structure uniformly distributed on the surface atop of the film with the average diameter of about 0.2 μm and nanoconvexities on the lower surface layer of the film with the average diameter of about 13 nm, and the film surface structure was similar to that of lotus surface. Many elements such as F and Cl were observed on the film surface, which could make the film surface energy decreased dramatically. The possible reason of leading to superhydrophobic properties on the as-prepared film is due to form an appropriate surface roughness after sol-gel method, and its surface energy will be further decreased after being modified with perfluorooctyltrichloromethoxysilane (FOTMS). These two formed conditions of surface roughness and low surface energy on the film will make the film formed on silicon exhibit good superhydrophobic properties.
  • Jun Liang · B. G. Guo · Jun Tian · H. W. Liu · J. F. Zhou · W. M. Liu · Tao Xu ·
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    ABSTRACT: Microarc oxidation coatings on AM60B magnesium alloy were prepared in phosphate-KOH electrolytes with and without NaAlO2 addition. The effect of NaALO(2) on the characteristic of breakdown voltage in different concentrations of NaAlO2 has been studied. The compositions, structure and morphologies of the oxide coatings formed in different concentrations of NaAlO2 were determined by energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The corrosion resistance of the oxide coatings was evaluated in 3.5 wt.% NaCl solution using potentiodynamic polarization tests. The results showed that the solution conductivity increased while the values of breakdown voltage decreased with the increase of concentration of NaAlO2. In both cases the coatings contained Mg, Al, O and P as well as a trace amount of Na and K, and were mainly composed of MgO and spinel MgAl2O4. The addition of NaAlO2 into the base electrolyte resulted in the increase of spinel MgAl2O4 in the oxide coating. Furthermore, the number and size of micropores on top of the surface decreased with the increasing concentration of NaAlO2, though the surface roughness increased with the NaAlO2 addition. The coating formed in the electrolyte containing 8.0 g/L NaAlO2 exhibited the highest corrosion resistance in NaCl solution. (c) 2005 Elsevier B.V All rights reserved.
    Surface and Coatings Technology 09/2005; 199(2-2-3):121-126. DOI:10.1016/j.surfcoat.2005.03.020 · 2.00 Impact Factor
  • L. Shi · C.F. Sun · F. Zhou · W.M. Liu ·
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    ABSTRACT: Ni–Co/Si3N4 composite coatings with various contents of Si3N4 nano-particulates were prepared by electrodeposition in a Ni–Co plating bath containing Si3N4 nano-particulates to be co-deposited. The shape and size of the Si3N4 nano-particulates were observed and determined on a transmission electron microscope. The polarization behavior of the composite plating bath was examined on a PAR-273A potentiostat/galvanostat device. The friction and wear behaviors of the Ni–Co/Si3N4 composite coatings were evaluated on a ball-on-disk UMT-2MT test rig. The worn surface morphologies of the Ni–Co/Si3N4 composite coatings wear observed using a scanning electron microscope. It was found that the Si3N4 nano-particulates appeared as microspheres of a diameter about 20 nm. The cathodic polarization potential of the composite electrolyte increased with increasing Si3N4 concentration in the plating bath, and the addition of Si3N4 particulates led to changes in the morphologies of the composite coatings. Namely, the Ni–Co alloy coating was composed of needle-like micro-crystallites, while the Ni–Co/Si3N4 composite coatings were characterized by particulate-like structure and had more compact and fine granular morphologies. At the same time, the morphologies of the composite coatings changed from fibril to granular, which implied that the co-deposited Si3N4 nano-particulates at a larger content could agglomerate to some extent. The co-deposited Si3N4 nano-particulates were uniformly distributed in the Ni–Co matrix and contributed to greatly increasing the microhardness and tribological properties of the Ni–Co alloy. The microhardness of the composite coatings increased and the friction coefficients and wear rates decreased with increasing content of the nano-Si3N4 in the composite coatings. This was attributed to the grain fining and dispersive strengthening effects of the co-deposited hard Si3N4 nano-particulates. At the same time, the hydroxylated silicon oxide formed by the tribochemical reaction between the nano-Si3N4 of high reactivity and water vapor in the air also contributed to decreasing the friction coefficient.
    Materials Science and Engineering A 04/2005; 397(1-2-397):190-194. DOI:10.1016/j.msea.2005.02.009 · 2.57 Impact Factor
  • J. X. Liao · W. M. Liu · T. Xu · C. R. Yang · H. W. Chen · C. L. Fu · W. J. Leng ·
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    ABSTRACT: DLC films ranging from 5 to 180 nm in thickness have been prepared by plasma-based ion implantation (PBII) with C on Si. The structures of the films were studied with XPS and Raman spectroscopy. The nanohardness and the intrinsic stress of the films were measured. Dry sliding wear experiments have been carried out, using a ball-on-disc tester, to investigate the tribological properties of DLC films against alumina balls, employing various normal applied loads and reciprocating frequencies. For comparison, DLC films prepared by plasma-assisted chemical vapor deposition (PACVD) on Si were also investigated. The results show that the films prepared by PBII exhibit more significant improvement in tribological properties than the films prepared by PACVD because the former present higher sp3/sp2 ratio, higher hardness and lower stress than the latter. The effects of the film thickness, the applied loads and the reciprocating frequencies on the tribological properties are also presented.
    Surface and Coatings Technology 02/2005; 191(1):90-95. DOI:10.1016/j.surfcoat.2004.06.039 · 2.00 Impact Factor
  • X. H. Li · W. M. Liu · H. L. Li ·
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    ABSTRACT: TiO 2 nanotubes of the anatase form have been synthesized by sol-gel chemical method using anodic aluminum oxide (AAO) as a template. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray diffraction were used to investigate the structure and morphology of the TiO 2 nanotubes. The results showed that TiO 2 nanotubes obtained are highly ordered and uniform. The diameter and length of the obtained nanotubes were determined by the pore size and the thickness of AAO template. It was found that through control of immersion time of AAO membrane in sol, both tubules and fibrils can be prepared.
    Applied Physics A 02/2005; 80(2):317-320. DOI:10.1007/s00339-003-2183-8 · 1.70 Impact Factor
  • J.X. Liao · L.F. Xia · M.R. Sun · W.M. Liu · T. Xu · C.R. Yang · H.W. Chen · C.L. Fu · W.J. Leng ·
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    ABSTRACT: As an interlayer in the gradient layers such as AlN/Ti/TiN/DLC prepared by plasma-based ion implantation (PBII) on 2024 aluminum alloy, titanium layer plays an important role in enhancing adhesion, reducing thermal stress, limiting the crack propagation, etc. A series of dual-layers prepared by PBII with nitrogen then titanium at various sputtering currents of titanium target on 2024 aluminum alloy have been reported in this paper. The composition distributions and the chemical states are analyzed using X-ray photoelectron spectroscopy (XPS). The structures are studied with grazing X-ray diffraction (GXRD). The results show that PBII with titanium strongly depends on the sputtering current. It is found that there exists a critical sputtering current corresponding only to a titanium-implanted layer containing TiAl3. When the sputtering current exceeds the critical value, a titanium-deposited layer rich in α-Ti is formed on a titanium-implanted layer. By controlling the sputtering current an appropriate titanium interlayer can be prepared to meet the requirement of forming a proper gradient layer.
    Applied Surface Science 02/2005; 240(1-4-240):71-76. DOI:10.1016/j.apsusc.2004.06.145 · 2.71 Impact Factor
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    ABSTRACT: High-quality titanium nitride (TiN) films with nano-structure were prepared at ambient temperature on (111) silicon substrates by filtered cathodic arc plasma (FCAP) technology with an in-plane “S” filter. The effects of substrate bias and argon flux on the crystal grain size, roughness and preferred orientation were systematically investigated. It was found that the substrate bias and argon flux can affect the properties of TiN films effectively. Transmission electron microscope images showed that the crystal grain size was uniform and ranged from 10 nm to 5 nm. The results of X-ray diffraction and electron diffraction indicated that the degree of preferred orientation was more evident under high substrate bias and high argon flux. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
    Physica Status Solidi (A) Applications and Materials 01/2005; 202(1):95 - 101. DOI:10.1002/pssa.200406902 · 1.62 Impact Factor
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    YJ Zhang · P. X. Yan · Z. G. Wu · J. W. Xu · W. W. Zhang · X Li · W. M. Liu · Q. J. Xue ·
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    ABSTRACT: High-quality TiN films were successfully deposited on silicon and stainless-steel substrates at low temperature using an improved filtered cathode arc plasma technique developed in our lab. Atomic force microscope, x-ray diffractometer, x-ray photoelectron spectroscopy, and a nanoindenter were employed to characterize the TiN thin films. The microhardness of the TiN films have a high value up to 41 GPa, which is far higher than that of TiN compounds deposited by conventional chemical vapor deposition and physical vapor deposition methods (20 Gpa or so). The films are of a stronger preferred crystalline orientation, very smooth surface, and high reflectivity. The effects of the negative substrate bias on the preferred crystalline orientation, surface roughness, deposition rate, and microhardness of Tin thin films are discussed in detail.
    Journal of Vacuum Science & Technology A Vacuum Surfaces and Films 11/2004; 22(6):2419-2423. DOI:10.1116/1.1807836 · 2.32 Impact Factor
  • P. Liu · W. M. Liu · Q. J. Xue ·
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    ABSTRACT: The preparation of hyperbranched poly(amine ester) (HPAE) grafted silica nanoparticles (HPAE-SN) from methyl acrylate (MA) and diethanol amine (DEA) was analyzed. HPAE-SN was separated from the non-grafted HPAE by several cycles of dispersion in methanol with ultrasonic vibrations for 30 min and precipitated by centrifugation at 104 rpm for 30 min. It was shown that the 'grafting onto' procedure is simpler and the percentage of grafting (PG) obtained is satisfactory. The results show that the modification of silica nanoparticles with HPAE could improve its dispersibility in polar organic solvents.
    Journal of Materials Science 06/2004; 39(11):3825-3827. DOI:10.1023/B:JMSC.0000030749.58598.e8 · 2.37 Impact Factor
  • H Xie · G.C Yang · P.Q La · W.X Hao · J.F Fan · W.M Liu · L.J Xu ·
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    ABSTRACT: The tribological properties of Ni–20 wt.% Pb alloys were measured by using a ball-on-disc reciprocating tribo-tester. The effects of load, sliding speed and melt undercooling on wear rate of the sample were investigated. The worn surface of Ni–20 wt.% Pb was examined using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The results show that the wear properties of the samples undercooled by 85 and 390 K are obviously superior, which is attributed to more efficient transfer of Pb from the bulk material to the worn surface. The lubricating film is identified as a mixture of Ni2O3 and lead oxide by XPS analysis. At the same load or sliding speed, the predominant wear mechanisms can be identified as oxidative wear for the lower and larger undercooling and plastic deformation for the medium undercooling.
    Materials Characterization 05/2004; 52(2):153–158. DOI:10.1016/j.matchar.2004.04.008 · 1.85 Impact Factor
  • J. X. Liao · L. F. Xia · M. R. Sun · W. M. Liu · T. Xu · Q. J. Xue ·
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    ABSTRACT: DLC films can play an important role in tribological properties of Al-alloys. A gradient layer of AlN/Ti/TiN/DLC film has been prepared by plasma-based ion implanted N, followed by Ti, and N and Ti, and finally C on 2024 Al-alloy. Emphasis has been placed on the tribological properties of the gradient layer. Its composition depth profile and chemical structure were characterized using X-ray photoelectron spectroscopy (XPS), the surface C-layer and the wear tracks were analyzed by laser Raman spectroscopy. The morphologies of the C-layer were observed by atomic force microscopy (AFM), the hardness of the gradient layer was measured with the mechanical property microprobe and the dry wear tests against AISI steel ball at different sliding loads were performed with a ball-on-disk wear tester in ambient environment. The results indicate that the gradient layer shows a gradual change in hardness, compact surface appearance and good tribological properties owing to the gradient structure. As the number of the sliding cycles or the load is increasing, the tribological properties decrease due to the graphitization of the DLC films. Meanwhile, the gradient layer can be controlled by PBII processing parameters, thus an optimized gradient layer can be obtained to offer the possibility of making aluminum alloys and other soft alloys qualified candidates for particular engineering applications.
    Surface and Coatings Technology 05/2004; 183(2):157-164. DOI:10.1016/j.surfcoat.2003.10.003 · 2.00 Impact Factor
  • J. X. Liao · L. F. Xia · M. R. Sun · Y. Sun · W. M. Liu · T. Xu · Q. J. Xue ·
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    ABSTRACT: The N-pre-implanted 2024 aluminum alloy was implanted with Ti and N, or implanted with Ti, and then with Ti and N by plasma-based ion implantation (PBII) to form two gradient layers, respectively. The composition depth profiles of the gradient layers were characterized by X-ray photoelectron spectroscopy. A series of ball-on-disk wear experiments have been carried out in ambient air, to investigate the tribological behavior of the gradient layer against steel ball under dry and un-lubricated conditions, employing various applied loads and a constant sliding speed. The results revealed that tribological properties of the gradient layers were improved markedly in contrast with those of the unmodified sample, and strongly dependent on their composition depth profiles. The gradient layer implanted with Ti, and then with Ti and N was much thicker and contains higher N, thus it corresponded to higher hardness which slowly decrease from surface to substrate and the optimal tribological properties including higher load carrying capacity. As load was increasing, the tribological properties decreased, and the adhesive degree increased since the gradient layer became thinner rapidly. Of course, more proper gradient layers will be obtained as the qualified candidates in some particular engineering applications by optimizing PBII parameters.
    Wear 04/2004; 256(7):840-845. DOI:10.1016/S0043-1648(03)00521-0 · 1.91 Impact Factor
  • J.X. Liao · W.M. Liu · T. Xu · Q.J. Xue ·
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    ABSTRACT: Four carbon nanometer films ranging from 5 to 60 nm have been prepared by plasma-based ion implantation (PBII) with C on Si (1 0 0) wafers. Raman spectra and X-ray photoelectron spectroscopy (XPS) indicate these films are diamond-like carbon (DLC) films with high sp3/sp2 bonds ratio. Atomic force microscopy shows that their appearances are smooth and compact, and improved to some extent. Meanwhile, XPS displays that they are naturally connected with the Si substrate by a C–Si transition layer where the implanted C+ ions react with Si to form SiCx. Infrared spectra reveal they contain some hydrogen, and hydrogen mainly combines with carbon to form sp3 CH, CH2 and CH3 bonds. Proper DLC films will be obtained and used as the qualified candidates in some particular engineering applications by actively optimizing PBII parameters.
    Applied Surface Science 03/2004; 226(4-226):387-392. DOI:10.1016/j.apsusc.2003.10.039 · 2.71 Impact Factor
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    P. Liu · W.M. Liu · Q.J. Xue ·
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    ABSTRACT: The in situ radical transfer addition polymerization of styrene from silica nanoparticles was carried out by the free radical polymerized of styrene in the presence of mercaptopropyl-modified silica nanoparticles as chain-transfer agent. The effects of the amount of the initiator, polymerizing temperature and polymerizing time on the convention of styrene (C) and the percentage of grafting were investigated. Results of elemental analysis, IR, X-ray photoelectron spectrometer and transmission electron microscope demonstrated that the desired polymer chains have been covalently bonded to the surface of the silica nanoparticles. A C of 42.56% and a PG of 38.10% could be achieved with the optimal condition. The polystyrene grafted silica nanoparticles could be separated and used as nanofiller for polymers.
    European Polymer Journal 02/2004; 40(2):267-271. DOI:10.1016/j.eurpolymj.2003.10.003 · 3.01 Impact Factor
  • J X Liao · L F Xia · M R Sun · W M Liu · T Xu · Q J Xue ·
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    ABSTRACT: Using plasma-based ion implantation, two types of gradient layers have been prepared on 2024 Al alloy. One is prepared by N-implantation then C-deposition, the other adds an interlayer composed of a Ti layer and a Ti–N layer between N-implantation and C-deposition. C-deposition is carried out at various implanting voltages or C2H2/H2 ratios. The composition depth profiles of these layers were characterized by x-ray photoelectron spectroscopy. The structure, morphologies and microstructure of the C layers were studied using Raman spectroscopy, atomic force microscope and transmission electron microscope, respectively. The surface hardness was measured with a Knoop tester and a mechanical property microprobe. The dry ball-on-disc wear tests were performed in ambient air. The gradient layer without interlayer is composed of an N-implanted layer rich in AlN and a diamond-like carbon (DLC) layer (film), and the two layers are connected with a C–Al transition layer containing Al4C3. The Ti layer rich in α -Ti and the N-implanted layer are connected by a Ti–Al transition layer containing TiAl3, while the Ti–N layer rich in TiN and the DLC film are connected by a C–Ti transition layer containing TiC, TiCN, etc. Thus, the gradient layer with interlayers has optimized the gradient structure. DLC films are compact and amorphous, contain high sp3/sp2 ratios and depend on the implanting voltage and the C2H2/H2 ratio. Similarly, these gradient layers exhibit significant improvement in morphologies, surface hardness and tribological properties; the interlayer, the implanting voltage and the C2H2/H2 ratio all have prominent effects on these properties.
    Journal of Physics D Applied Physics 01/2004; 37(3):392. DOI:10.1088/0022-3727/37/3/014 · 2.72 Impact Factor
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    J. X. Liao · W. M. Liu · T. Xu · Q. J. Xue ·
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    ABSTRACT: A series of carbon films have been prepared by plasma-based ion implantation (PBII) with C on pure Al and Si. Emphasis has been placed on the effect of implanting voltage on the characteristics of these films. The structures of the films were analyzed by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The morphologies were observed by atomic force microscope (AFM). Surface hardness and electrical resistivity were also measured. The results indicate that the characteristics of these films are strongly dependent on the implanting voltage. An implanting voltage threshold value ranging from 3 to 5 kV starts to form a C-substrate transition layer owing to C+ ions implanted into the substrate. The transition layer exhibits a gradual change in composition and structure and effectively connects the carbon film and the substrate. Also, an implanting voltage threshold value ranging from 5 to 10 kV starts to form diamond-like carbon (DLC) films. An increasing voltage causes the resultant DLC films to be smoother and more compact. Moreover, Raman spectrum, chemical state of C1s, surface hardness and electrical resistivity all prove an optimum voltage of approximately 30 kV corresponding to the lowest ratio of sp2/sp3.
    Carbon 01/2004; 42(2):387-393. DOI:10.1016/j.carbon.2003.11.013 · 6.20 Impact Factor
  • F. Zhou · WM Liu · JC Hao · T. Xu · M. Chen · QJ Xue ·
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    ABSTRACT: This article describes a strategy to fabricate a conducting polymer and complementary gold microstructures through selective electrodeposition and wet chemical etching on a chemically tethered polymer brush template that is prepared by surface-initiated atomic transfer radical polymerization (ATRP) and subsequent photopatterning. The polymer brush acts as a sufficient insulating barrier and thus the polypyrrole (PPy) can be grown from the exposed area of the polymer brush template. Different polymer brushes provide different protection actions in selective etching, which is utilized to generate complementary (negative or positive) gold pattern on a single template in different manners.
    Advanced Functional Materials 12/2003; 13(12):938 - 942. DOI:10.1002/adfm.200304469 · 11.81 Impact Factor
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    F. Zhou · M. Chen · WM Liu · JX Liu · ZL Liu · ZG Mu ·
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    ABSTRACT: One-step electrodeposition of pyrrole on octadecyltrichlorosilane- (OTS) patterned silicon wafers results in positively patterned polypyrrole (PPy) structures, i.e., PPy deposits on the OTS-covered area. In contrast, negative patterns are obtained on an indium. tin oxide surface. The Figure shows electrically isolated positive PPy microwires on a silicon wafer.
    Advanced Materials 08/2003; 15(16):1367 - 1370. DOI:10.1002/adma.200304466 · 17.49 Impact Factor