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ABSTRACT: In the present paper, vertically aligned arrays of zinc nanowires were synthesized by electrochemical deposition into ion track-etched polycarbonate membranes in the ionic liquid electrolyte 1-ethyl-3-methylimidazolium trifluoromethylsulfonate ([EMIm]TfO)/zinc triflate. Cyclic voltammetry and chronoamperometry were performed to investigate the electrochemical growth of zinc nanowires inside of the membranes. The transport processes and mechanisms of the nanowires growth in the membranes are also discussed. Zinc nanowires with a diameter of 90 nm and a length of up to 18 µm were obtained after removing of the template. The zinc nanowires were more uniform on copper than on gold sputtered membranes, likely due to a good alloying between zinc and copper. Furthermore, a supporting zinc or copper layer was deposited on the sputtered side in order to make the back layer thick enough to stabilize the wires. Dendritic structures were obtained for zinc deposition while more compact structures were obtained for copper deposition on both sputtered gold and copper, respectively. Vertically aligned zinc nanowires on such a substrate might show a good performance in future generation lithium ion batteries.
Physical Chemistry Chemical Physics 05/2013; · 3.57 Impact Factor
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ABSTRACT: The binary alloy system Si(x)Ge(1-x) provides a continuous series of materials with gradually varying properties. In this paper, we report on a fundamental basis a method to make large-area macroporous Si(x)Ge(1-x) films with variable Ge content by electrodeposition in an ionic liquid, with SiCl(4) and GeCl(4) as precursors. The chemical composition of the products can be modified by changing the molar ratio of the precursors. Periodical macroporous Si(x)Ge(1-x) was made by a multilayer polystyrene (PS) template assembled as face-centered cubic lattice. Two-dimensional (2-D) Si(x)Ge(1-x) bowl-like and fishing-net structures can be obtained by applying different deposition temperatures. The results highlight the potential applications, including photonic bandgap and battery materials, as well as ultra-thin gratings, due to the effect of modification of light and improved tunability of composition, although Si(x)Ge(1-x) made by our method is sensitive to oxidation by air.
Physical Chemistry Chemical Physics 01/2013; · 3.57 Impact Factor
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ABSTRACT: The lubricating properties of an ionic liquid on gold surfaces can be controlled through application of an electric potential to the sliding contact. A nanotribology approach has been used to study the frictional behavior of 1-butyl-1-methylpyrrolidinium tris(pentafluoroethyl) trifluorophosphate ([Py_{1,4}]FAP) confined between silica colloid probes or sharp silica tips and a Au(111) substrate using atomic force microscopy. Friction forces vary with potential because the composition of a confined ion layer between the two surfaces changes from cation-enriched (at negative potentials) to anion-enriched (at positive potentials). This offers a new approach to tuning frictional forces reversibly at the molecular level without changing the substrates, employing a self-replenishing boundary lubricant of low vapor pressure.
Physical Review Letters 10/2012; 109(15):155502. · 7.37 Impact Factor
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ABSTRACT: The electrical double layer at ionic liquid (IL)-Au(111) interfaces is composed of alternating ion layers. Interfacial layering is markedly weaker when small amounts of LiCl are dissolved in the IL for all potential between -2.0 V and +2.0 V (vs. Pt). This means that models developed for pure IL electrical double layers may not be valid when solutes are present.
Chemical Communications 09/2012; 48(82):10246-8. · 6.17 Impact Factor
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ABSTRACT: Vanadium pentoxide (V2O5) nanoparticles were synthesized at moderate reaction temperatures by hydrolysis of VO[OCH(CH3)2]3 in two different air- and water-stable ionic liquids with the same anion: 1-butyl-1-methyl pyrrolidinium bis(trifluoromethylsulfonyl)amide
([Py1,4]Tf2N) and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide ([EMIM]Tf2N) via the sol–gel method using acetone and isopropanol either as refluxing solvents or as co-solvents. The cation type of
the ionic liquid affects the crystallinity, morphology, and surface area of the produced nanoparticles: [Py1,4]Tf2N gave products with higher crystallinity especially with acetone as a refluxing and co-solvent, while [EMIM]Tf2N gave a clear mesoporous morphology with isopropanol as a refluxing solvent. Ionic liquids affect the key factors (morphology
and surface area) that make V2O5 an attractive material as catalyst and/or cathodic material for lithium ion batteries.
Journal of Materials Science 04/2012; 44(5):1363-1373. · 2.02 Impact Factor
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ABSTRACT: Recently we reported our results on the successful synthesis of 3-D highly ordered macroporous (3DOM) structure of germanium via the template-assisted electrochemical deposition from air- and water stable ionic liquids. Herein we report our new results on the photoluminescence (PL) properties of the obtained ordered macroporous Ge and the Ge/polystyrene composite opal structure. The latter showed a strong green emission compared to a Ge film and a Ge inverse opal. The enhancement of PL intensity was ascribed to the disorder multiple scattering in polystyrene colloidal crystal structure which increased both the excitation light absorption efficiency and the light extraction efficiency. The X-ray photoelectron spectroscopy (XPS) results suggested that the ordered macroporous Ge was capped with an oxide layer including a considerable amount of GeO(2). The observed green emission (539 nm) was related to GeO(2), likely resulting from the Ge-O bond related intrinsic defects.
Optics Express 04/2012; 20(9):9421-30. · 3.59 Impact Factor
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ABSTRACT: Ionic liquids are of high interest for the development of safe electrolytes in modern electrochemical cells, such as batteries, supercapacitors and dye-sensitised solar cells. However, electrochemical applications of ionic liquids are still hindered by the limited understanding of the interface between electrode materials and ionic liquids. In this article, we first review the state of the art in both experiment and theory. Then we illustrate some general trends by taking the interface between the extremely pure ionic liquid 1-butyl-1-methylpyrrolidinium tris(pentafluoroethyl)trifluorophosphate and an Au(111) electrode as an example. For the study of this interface, electrochemical impedance spectroscopy was combined with in situ STM and in situ AFM techniques. In addition, we present new results for the temperature dependence of the interfacial capacitance and dynamics. Since the interfacial dynamics are characterised by different processes taking place on different time scales, the temperature dependence of the dynamics can only be reliably studied by recording and carefully analysing broadband capacitance spectra. Single-frequency experiments may lead to artefacts in the temperature dependence of the interfacial capacitance. We demonstrate that the fast capacitive process exhibits a Vogel-Fulcher-Tamman temperature dependence, since its time scale is governed by the ionic conductivity of the ionic liquid. In contrast, the slower capacitive process appears to be Arrhenius activated. This suggests that the time scale of this process is determined by a temperature-independent barrier, which may be related to structural reorganisations of the Au surface and/or to charge redistributions in the strongly bound innermost ion layer.
Physical Chemistry Chemical Physics 03/2012; 14(15):5090-9. · 3.57 Impact Factor
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ABSTRACT: In this paper we report on the electrodeposition of lithium on a polystyrene sphere modified electrode from an ionic liquid. By a simple dipping process, polystyrene (PS) spheres with an average diameter of 600 nm arrange in a hexagonal close packed structure onto an electrode surface. Surprisingly, lithium does not grow uniformly from the electrode surface to the electrolyte within the voids of the PS structure. Depending on the experimental conditions a more or less good inverse opal structure made of lithium, lithium spheres or hollow lithium half-spheres can be obtained showing that the growth of lithium in the employed ionic liquid is more complicated than expected. Somehow lithium tends to push away the PS spheres during growth. Applying a slight mechanical pressure on the PS spheres during deposition improves the growth within the voids of the opal structure. Despite this complicated behaviour the PS opal structure seems to suppress a vertical dendritic growth, thus, a lithium/PS composite electrode or other lithium/polymer composite electrodes might be of some interest in rechargeable lithium metal microbatteries where a dendritic vertical growth has to be avoided.
Australian Journal of Chemistry 01/2012; · 2.34 Impact Factor
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ABSTRACT: The structure of the interfacial layer(s) between the extremely pure air- and water-stable ionic liquid 1-butyl-1-methylpyrrolidinium tris(pentafluoroethyl) trifluorophosphate and Au(111) has been investigated using in situ scanning tunneling microscopy (STM) at electrode potentials more positive than the open circuit potential. The in situ STM measurements show that layers/islands form with increasing electrode potential. According to recently published atomic force microscopy (AFM) data the anion is adsorbed even at low anodic overvoltages and adsorption becomes slightly stronger with increasing electrode potential. Furthermore, the number of interfacial layers increases with increasing electrode potential. The present discussion paper shows that these layers are not uniform and have a structure on the nanoscale, supporting earlier results that the interface electrode/ionic liquid is highly complex. It is also shown that the addition of solutes changes this structure considerably. AFM results reveal that in the pure liquid, interfacial layers lead to a repulsive force but the addition of 10 wt% of LiCl leads to an attractive force close to the surface. These preliminary results show that solutes strongly alter the interfacial structure of the ionic liquid/ electrode interface.
Faraday Discussions 01/2012; 154:221-33; discussion 313-33, 465-71. · 5.00 Impact Factor
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ABSTRACT: Herein the structure of the interfacial layer between the air- and water-stable ionic liquid 1-ethyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate ([EMIM]FAP) and Au(111) is investigated using in situ scanning tunneling microscopy (STM), distance tunneling spectroscopy (DTS) and cyclic voltammetry (CV) measurements. The in situ STM measurements reveal that structured interfacial layers can be probed in both cathodic and anodic regimes at the IL/Au(111) interface. The structure of these layers is dependent on the applied electrode potential, the number of subsequent STM scans and the scan rate. Furthermore, first DTS results show that the tunneling barrier during the 1st STM scan does not seem to change significantly in the cathodic potential regime between the ocp (-0.2 V) and -2.0 V.
ChemPhysChem 12/2011; 13(7):1736-42. · 3.41 Impact Factor
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ABSTRACT: Three dimensionally ordered macroporous (3DOM) silicon films have been made via ordered polystyrene (PS) templates by electrodeposition from an ionic liquid (IL). For this purpose, the ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide ([Py(1,4)]Tf(2)N) with SiCl(4) dissolved in it was used as an electrolyte and the electrodeposition of macroporous silicon could be achieved at room temperature (~20 °C). Self-assembled PS colloidal crystals with different diameters were used as templates. Scanning electron microscopy and X-ray photoelectron spectroscopy confirm the quality of the samples, and the optical transmission measurement demonstrates that the 3DOM silicon film has a bandgap in the near infrared regime. Such a material has the potential to make 3DOM silicon feasible for electrical and optical applications.
Physical Chemistry Chemical Physics 12/2011; 14(15):5100-5. · 3.57 Impact Factor
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ABSTRACT: We report on the electrochemical synthesis of free-standing aluminium nanowire architectures through a template-assisted electrodeposition technique. For this purpose, nuclear track-etched polycarbonate membranes were employed as templates. One side of the template was sputtered with a thin gold film to serve as a working electrode. Subsequently the nanowires were made in the ionic liquid 1-ethyl-3-methylimidazolium chloride ([EMIm]Cl)/AlCl(3) (40/60 mol %) under potentiostatic conditions. Two different electrodeposition procedures were employed to fabricate strongly adherent Al nanowire structures on an electrodeposited Al layer. In the first procedure, electrodeposition simultaneously occurs along the pores of the template and on the Au-sputtered side of the template. In the second procedure, electrodeposition takes place in two different steps: first a thick supporting film of Al is deposited on the sputtered side of the membrane and second Al nanowires are grown within the pores. After chemical dissolution of the membrane in dichloromethane, an aluminium foil of a controlled thickness with a three-dimensional nanowire structure on one side was obtained. Different nanowire architectures, such as free-standing nanowires, vertically aligned tree-shaped arrays, and bunched nanowire films, were obtained. Such nanowire architectures are of particular interest for applications in Li-ion micro-batteries.
ChemPhysChem 11/2011; 13(1):250-5. · 3.41 Impact Factor
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ABSTRACT: We have recently measured core level and valence band XPS, UPS, and MIES spectra of two room temperature ionic liquids composed of bis(trifluoromethylsulfonyl)imide anions ([Tf(2)N](-)) and either 1-ethyl-3-methyl-imidazolium ([EMIm](+)) or 1-octyl-3-methyl-imidazolium cations ([OMIm](+)). [T. Ikari, A. Keppler, M. Reinmöller, W. J. D. Beenken, S. Krischok, M. Marschewski, W. Maus-Friedrichs, O. Höfft and F. Endres, e-J. Surf. Sci. Nanotechnol., 2010, 8, 241.] In the present work we analyze these spectra by means of partial density of states (pDOS) as calculated from a single ion pair of the respective ionic liquid using density functional theory (DFT). Subsequently we reconstruct the XPS and UPS spectra by considering photoemission cross sections and analyze the MIES spectra by pDOS, which provides us decisive hints to the ionic liquid surface structure.
Physical Chemistry Chemical Physics 11/2011; 13(43):19526-33. · 3.57 Impact Factor
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ABSTRACT: The electrochemical synthesis of gallium nanostructures in an ionic liquid is presented. Gallium nanowires and macroporous structures were synthesized by the template-assisted electrodeposition in the ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide ([Py(1,4)]TFSA) containing GaCl(3) as the precursor. Track-etched polycarbonate membranes with an average pore diameter of 90 nm and a thickness of 21 μm were used as templates for the nanowire synthesis. Ga nanowires with a length of more than 4 μm and an average diameter corresponding to that of the template's pores were easily obtained by this method. Macroporous structures with an average pore diameter of 600 nm were obtained by the electrochemical deposition of Ga inside polystyrene colloidal crystal templates and the subsequent removal of the template by THF. The macroporous deposit showed a granular morphology with smallest grain sizes of about 40 nm and light reflections. The nanostructures of Ga were characterized by HR-SEM and EDX analysis.
ChemPhysChem 10/2011; 12(15):2751-4. · 3.41 Impact Factor
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ChemPhysChem 07/2011; 12(14):2565-7. · 3.41 Impact Factor
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ABSTRACT: In this perspective, the application of stable glow discharge plasmas as free electrodes for the generation of nanoparticles in ionic liquids is reported. The basic concepts of plasma electrochemistry as well as a few other concepts in this field will be presented. One focus is the interaction of the plasma with the ionic liquids itself and possible influences on the production process of the particles. Several examples of the plasma generation and characterisation of nanoparticles in ionic liquids will be presented. The starting point is thereby the generation of noble metals and at the end the efforts to synthesize semiconductor nanoparticles will be discussed. In all examples the benefits, the difficulties and the challenges of this method and the outcome for the future will be addressed.
Physical Chemistry Chemical Physics 06/2011; 13(30):13472-8. · 3.57 Impact Factor
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ABSTRACT: The double layer structure of two ionic liquids (ILs), 1-butyl-1-methylpyrrolidinium tris(pentafluoroethyl)trifluorophosphate ([Py1,4]FAP) and 1-ethyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate ([EMIm]FAP) at the polarized Au(111) electrode interface is probed using Atomic Force Microscopy force measurements. The force-separation profiles suggest a multilayered morphology is present at the electrified Au(111)−IL interface, with more near surface layers detected at higher potentials. At the (slightly negative) open circuit potential, multiple ion layers are present, and the innermost layer, in contact with the Au(111) surface, is enriched in the cation due to electrostatic adsorption. Upon applying negative electrode potentials (−1.0 V, −2.0 V), stronger IL near surface structure is detected: both the number of ion layers and the force required to rupture these layers increases. Positive electrode potentials (+1.0 V, +2.0 V) also enhance IL near surface structure, but not as much as negative potentials, because surface-adsorbed anions are less effective at templating structure in subsequent layers than cations. This interfacial structure is not consistent with a double layer in the Stern−Gouy−Chapman sense, as there is no diffuse layer. The structure is consistent with a capicitative double-layer model, with a very small separation distance between the planes of charge.
03/2011;
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ABSTRACT: The structure and dynamics of the interfacial layers between the extremely pure air- and water-stable ionic liquid 1-butyl-1-methylpyrrolidinium tris(pentafluoroethyl)trifluorophosphate and Au(111) has been investigated using in situ scanning tunneling microscopy, cyclic voltammetry, electrochemical impedance spectroscopy, and atomic force microscopy measurements. The in situ scanning tunnelling microscopy measurements reveal that the Au(111) surface undergoes a reconstruction, and at -1.2 V versus Pt quasi-reference the famous (22 × √3) herringbone superstructure is probed. Atomic force microscopy measurements show that multiple ion pair layers are present at the ionic liquid/Au interface which are dependent on the electrode potential. Upon applying cathodic electrode potentials, stronger ionic liquid near surface structure is detected: both the number of near surface layers and the force required to rupture these layers increases. The electrochemical impedance spectroscopy results reveal that three distinct processes take place at the interface. The fastest process is capacitive in its low-frequency limit and is identified with electrochemical double layer formation. The differential electrochemical double layer capacitance exhibits a local maximum at -0.2 V versus Pt quasi-reference, which is most likely caused by changes in the orientation of cations in the innermost layer. In the potential range between -0.84 V and -1.04 V, a second capacitive process is observed which is slower than electrochemical double layer formation. This process seems to be related to the herringbone reconstruction. In the frequency range below 1 Hz, the onset of an ultraslow faradaic process is found. This process becomes faster when the electrode potential is shifted to more negative potentials.
Physical Chemistry Chemical Physics 03/2011; 13(15):6849-57. · 3.57 Impact Factor
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ABSTRACT: In this paper we report on recent results from our group, namely on the interface ionic liquid/electrode,
plasma electrochemistry and electrodeposition of selenium and of macroporous structures. Ionic liquids
showan interesting and liquid dependent surface chemistry: insomeliquids the long range “herringbone”
superstructure of Au(1 1 1) is visible, in others it is not. Glow discharge plasmas can be employed as a
contact free electrode to make nanoparticles in solutions, e.g. nanoparticles of germanium. Selenium can
be electrodeposited from ionic liquids under environmental conditions in an open cell and both the red
and the grey phases of selenium are feasible. With the help of self organized opal structures of polystyrene
spheres macroporous materials of Ag, Al and conducting polymers can be made. The prospects and limits
of ionic liquids in surface electrochemistry and electrodeposition are shortly discussed.
Electrochimica Acta 01/2011; 56:10295-10305. · 3.83 Impact Factor
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Plasma Processes and Polymers 12/2010; 8(1):32 - 37. · 2.47 Impact Factor
