Publications by authors named "Laurent Cagnon"

7 Publications

  • Page 1 of 1

Nanowire forest of pnictogen-chalcogenide alloys for thermoelectricity.

Nanoscale 2019 Jul;11(28):13423-13430

Institut Néel, CNRS, 25 avenue des Martyrs, F-38042 Grenoble, France. and Univ. Grenoble Alpes, Grenoble, France.

Pnictogen and chalcogenide compounds have been seen as high-potential materials for efficient thermoelectric conversion over the past few decades. It is also known that with nanostructuration, the physical properties of these pnictogen-chalcogenide compounds can be further enhanced towards a more efficient heat conversion. Here, we report the reduced thermal conductivity of a large ensemble of Bi2Te3 alloy nanowires (70 nm in diameter) with selenium for n-type and antimony for p-type (Bi2Te3-ySey and Bi2-xSbxTe3 respectively). The nanowire growth was carried out through electrodeposition in nanoporous aluminium oxide templates with high aspect ratios leading to a forest (109 per centimetre square) of nearly identical nanowires. The temperature dependence of thermal conductivity for the nanowire ensembles was acquired through a highly sensitive 3ω measurement technique. The change in the thermal conductivity of nanowires is largely affected by the roughness in addition to the size effect due to enhanced boundary scattering. The major factor that influences the thermal conductivity was found to be the ratio of the rms roughness to the correlation length of the nanowire. With a high Seebeck coefficient and electrical conductivity at room temperature, the overall thermoelectric figure of merit ZT allows the consideration of such forests of nanowires as efficient potential building blocks of future TE devices.
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http://dx.doi.org/10.1039/c9nr01566cDOI Listing
July 2019

A robust ALD-protected silicon-based hybrid photoelectrode for hydrogen evolution under aqueous conditions.

Chem Sci 2019 Apr 12;10(16):4469-4475. Epub 2019 Mar 12.

Université Grenoble Alpes , CNRS , CEA , Laboratoire de Chimie et Biologie des Métaux , 17 rue des Martyrs , 38000 Grenoble , France . Email:

Hydrogen production through direct sunlight-driven water splitting in photo-electrochemical cells (PECs) is a promising solution for energy sourcing. PECs need to fulfill three criteria: sustainability, cost-effectiveness and stability. Here we report an efficient and stable photocathode platform for H evolution based on Earth-abundant elements. A p-type silicon surface was protected by atomic layer deposition (ALD) with a 15 nm TiO layer, on top of which a 300 nm mesoporous TiO layer was spin-coated. The cobalt diimine-dioxime molecular catalyst was covalently grafted onto TiO through phosphonate anchors and an additional 0.2 nm ALD-TiO layer was applied for stabilization. This assembly catalyzes water reduction into H in phosphate buffer (pH 7) with an onset potential of +0.47 V RHE. The resulting current density is -1.3 ± 0.1 mA cm at 0 V RHE under AM 1.5 solar irradiation, corresponding to a turnover number of 260 per hour of operation and a turnover frequency of 0.071 s.
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http://dx.doi.org/10.1039/c8sc05006fDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6482884PMC
April 2019

Measurement of anisotropic thermal conductivity of a dense forest of nanowires using the 3 method.

Rev Sci Instrum 2018 Aug;89(8):084902

Institut Néel, CNRS, 38000 Grenoble, France.

The 3 method is a dynamic measurement technique developed for determining the thermal conductivity of thin films or semi-infinite bulk materials. A simplified model is often applied to deduce the thermal conductivity from the slope of the real part of the ac temperature amplitude as a function of the logarithm of frequency, which in-turn brings a limitation on the kind of samples under observation. In this work, we have measured the thermal conductivity of a forest of nanowires embedded in nanoporous alumina membranes using the 3 method. An analytical solution of 2D heat conduction is then used to model the multilayer system, considering the anisotropic thermal properties of the different layers, substrate thermal conductivity, and their thicknesses. Data treatment is performed by fitting the experimental results with the 2D model on two different sets of nanowires (silicon and BiSbTe) embedded in the matrix of nanoporous alumina templates, having thermal conductivities that differ by at least one order of magnitude. These experimental results show that this method extends the applicability of the 3 technique to more complex systems having anisotropic thermal properties.
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http://dx.doi.org/10.1063/1.5025319DOI Listing
August 2018

Direct electrical transport measurement on a single thermoelectric nanowire embedded in an alumina template.

Phys Chem Chem Phys 2016 04;18(17):12332-7

CNRS, Inst. NEEL, F-38042 Grenoble, France. and Univ. Grenoble Alpes, Inst. NEEL, F-38042 Grenoble, France.

Electrical conductivity is a key parameter to increase the performance of thermoelectric materials. However, the measurement of such performance remains complex for 1D structures, involving tedious processing. In this study, we present a non-destructive, rapid and easy approach for the characterization of electrical conductivity of Bi2Te3 based single nanowires. By controlling the nanowire overgrowth, each nanowire emerges in the form of a micrometric hemisphere constituting a unique contact zone for direct nanoprobing. As nanowires need no preliminary preparation and remain in their template during measurement, we avoid oxidation effects and time-consuming processing. Electrical transport results show a low nanowire resistivity for compact nanowires obtained at low overpotential. Such values are comparable to bulk materials and thin films. This method not only confirmed its reliability, but it could also be adopted for other semiconducting or metallic electrodeposited nanowires.
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http://dx.doi.org/10.1039/c6cp00972gDOI Listing
April 2016

Disproportionation of thermoelectric bismuth telluride nanowires as a result of the annealing process.

Phys Chem Chem Phys 2010 Dec 2;12(46):15247-50. Epub 2010 Nov 2.

Ertl Center for Electrochemistry and Catalysis, Gwangju Institute of Science and Technology, Gwangju 500-712, South Korea.

P-type thermoelectric bismuth telluride nanowires were fabricated by pulsed electrodeposition in anodic aluminium oxide (AAO) membranes. Subsequently, the nanowires were annealed at 423, 523 and 673 K in an inert atmosphere for 4 h. With increasing temperature, it was observed that the Te compound incongruently sublimates due to its high vapor pressure, leading to disproportionation (from Bi(2)Te(3) to Bi(4)Te(3)via Bi(4)Te(5)). The crystalline structure of the nanowires was then investigated using XRD and SAED, with nanowire compositions investigated using an EDX attached to a TEM. The crystallinity of the nanowires was found to be enhanced with increased annealing temperature, and nanowires annealed at 673 K were stably maintained in the Bi(4)Te(3) phase. Additionally, the Seebeck coefficient was determined and the thermopower of nanowires annealed at a temperature of 423 K was shown to be slightly enhanced. Significantly suppressed Seebeck values for annealing temperatures of 523 K and 673 K were also observed.
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http://dx.doi.org/10.1039/c0cp00749hDOI Listing
December 2010

Tuning the crystallinity of thermoelectric Bi(2)Te(3) nanowire arrays grown by pulsed electrodeposition.

Nanotechnology 2008 Sep 28;19(36):365701. Epub 2008 Jul 28.

Max-Planck-Institut für Mikrostrukturphysik, Weinberg 2, D-06120 Halle, Germany.

Arrays of thermoelectric bismuth telluride (Bi(2)Te(3)) nanowires were grown into porous anodic alumina (PAA) membranes prepared by a two-step anodization. Bi(2)Te(3) nanowire arrays were deposited by galvanostatic, potentiostatic and pulsed electrodeposition from aqueous solution at room temperature. Depending on the electrodeposition method and as a consequence of different growth mechanisms, Bi(2)Te(3) nanowires exhibit different types of crystalline microstructure. Bi(2)Te(3) nanowire arrays, especially those grown by pulsed electrodeposition, have a highly oriented crystalline structure and were grown uniformly as compared to those grown by other electrodeposition techniques used. X-ray diffraction (XRD) analyses are indicative of the existence of a preferred growth orientation. High resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) confirm the formation of a preferred orientation and highly crystalline structure of the grown nanowires. The nanowires were further analyzed by scanning electron microscopy (SEM). Energy dispersive x-ray spectrometry (EDX) indicates that the composition of Bi-Te nanowires can be controlled by the electrodeposition method and the relaxation time in the pulsed electrodeposition approach. The samples fabricated by pulsed electrodeposition were electrically characterized within the temperature range 240 K≤T≤470 K. Below T≈440 K, the nanowire arrays exhibited a semiconducting behavior. Depending on the relaxation time in the pulsed electrodeposition, the semiconductor energy gaps were estimated to be 210-290 meV. At higher temperatures, as a consequence of the enhanced carrier-phonon scattering, the measured electrical resistances increased slightly. The Seebeck coefficient was measured for every Bi(2)Te(3) sample at room temperature by a very simple method. All samples showed a positive value (12-33 µV K(-1)), indicating a p-type semiconductor behavior.
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http://dx.doi.org/10.1088/0957-4484/19/36/365701DOI Listing
September 2008

Enhanced fluid flow through nanoscale carbon pipes.

Nano Lett 2008 Sep 5;8(9):2632-7. Epub 2008 Aug 5.

Chemistry Department, Imperial College, South Kensington, London SW7 2AZ, United Kingdom.

Recent experimental and theoretical studies demonstrate that pressure driven flow of fluids through nanoscale ( d < 10 nm) carbon pores occurs 4 to 5 orders of magnitude faster than predicted by extrapolation from conventional theory. Here, we report experimental results for flow of water, ethanol, and decane through carbon nanopipes with larger inner diameters (43 +/- 3 nm) than previously investigated. We find enhanced transport up to 45 times theoretical predictions. In contrast to previous work, in our systems, decane flows faster than water. These nanopipes were composed of amorphous carbon deposited from ethylene vapor in alumina templates using a single step fabrication process.
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http://dx.doi.org/10.1021/nl080705fDOI Listing
September 2008