Atomic layer deposition of W on nanoporous carbon aerogels

Elam, Jeffrey W.; Libera, Joseph A.; Pellin, Michael J.; Zinovev, A. V.; Greene, J. P.; Nolen, J.A.

doi:10.1063/1.2245216

Cited by 57 publications

(68 citation statements)

References 33 publications

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“…This model is consistent with mass initially increasing with the square of the ALD film thickness, and subsequently becoming constant, as we have previously observed. [14,20] In fact, the absorbance decreased monotonically for the electrodes coated with ZnO layer thicknesses larger than 2.1 nm indicating that the usable surface area was decreasing, presumably due to pore filling (Table 1). Alternatively, since the porosity decreases with increasing ZnO thickness, poor diffusion of the dye throughout the aerogel membrane may be responsible for the decrease of dye loading with more ZnO.…”

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confidence: 92%

Aerogel Templated ZnO Dye‐Sensitized Solar Cells

et al. 2008

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Dye-sensitized solar cells (DSSCs) based on nanocrystalline TiO 2 have exhibited solar energy-conversion efficiencies of over 10% and remain one of the most promising candidates for cost-effective solar energy conversion devices. [1,2] The most efficient DSSCs reported to date utilize a high surface area photoanode, which allows for good light harvesting with a moderate extinction dye, in contact with the I 3 À /I À couple which acts as a redox mediator.[3] The good performance of DSSCs is partially attributed to the slow dark reaction, i.e., electron transfer from TiO 2 to I 3 À via a potentially multielectron process. The slow dark reaction kinetics allows for excellent charge collection despite the relatively slow (millisecond) transport through the nanoparticle network.[4]The I 3 À /I À couple, however, has several disadvantages, including limitations on the open-circuit voltage related to the redox potential of the mediator species. In order to push device performance beyond its current limits, a faster redox shuttle, which requires a smaller overpotential to reduce the oxidized dye, is likely necessary, either to increase the photovoltage (provided that the dark current in not enhanced) or to allow alternate dyes with increased spectral coverage to be used. Replacing iodide/ triiodide with faster one-electron, outer-sphere redox reagents such as ferrocene, however, has resulted in significantly worse overall performance. [5,6] Although such fast redox species efficiently reduce the oxidized dye, rapid recombination between electrons in the TiO 2 and the redox shuttle results in poor electron collection. [5][6][7] Therefore, an alternate redox shuttle will concomitantly require faster charge transport through the metal oxide frameworks to allow for complete charge collection under cell operating conditions. Several interesting photoanode architectures have been fabricated with reduced dimensionality, a design feature that is expected to accelerate charge transport. Among these new architectures are hydrothermally grown ZnO nanorod arrays, ZnO nanotubes, and TiO 2 nanotubes. [8][9][10] The ZnO nanorod arrays have been shown to exhibit much faster transport than comparable ZnO nanoparticle networks. [11,12] While nanorod devices showed promising efficiencies of 1.5%, further improvement requires overcoming the technical challenge of increasing the relatively low surface area that currently limits light-harvesting.[8] Nominally one-dimensional ZnO nanotubes showed efficiencies of 1.6%, but with limited lightharvesting again a significant performance limiting factor.[9]Here we introduce a new core-shell material as a pseudo-one dimensional ZnO photoanode produced from coating templates of high aspect ratio substructures, exhibiting initial efficiencies up to 2.4% under AM 1.5 illumination when incorporated in a DSSC. Inert low density, high surface area silica aerogel films, featuring a large range of controllable thickness and porosity, are prepared as substructure templates. The aerogel templates are coated wi...

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confidence: 92%

Aerogel Templated ZnO Dye‐Sensitized Solar Cells

et al. 2008

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“…Therefore it is an ideal tool to coat uniformly polymer and carbon aerogels. By now, there have been several ALD depositions of semiconductor oxides on carbon substrates [3,31], however; there have been only a few metal and semiconductor oxide depositions on aerogels [32][33][34][35], and these composites were not used as photocatalysts, to the best of our knowledge.Hence, our aim was to prepare polymer and carbon aerogel/TiO2 composites from resorcinolformaldehyde aerogel (RFA) and its carbon aerogel (RFCA) derivative by ALD. The RF hydrogel was prepared by sol-gel method from resorcinol and formaldehyde.…”

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confidence: 99%

Photocatalytic properties of TiO2@polymer and TiO2@carbon aerogel composites prepared by atomic layer deposition

Justh

Mikula

Bakoš

et al. 2019

Carbon

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Monolithic structured TiO2/aerogel composites were prepared from resorcinol-formaldehyde polymer aerogel (RFA) and its carbon aerogel (RFCA) derivative. A resorcinol-formaldehyde hydrogel was synthesized in a sol-gel reaction and transformed into polymer aerogel by supercritical drying. The RFA was converted to carbon aerogel by pyrolysis at 900 °C in dry N2.Amorphous and crystalline TiO2 layers were grown from TiCl4 and H2O precursors by atomic layer deposition (ALD) at 80 °C and 250 °C, respectively, on both RFA and RFCA. The substrates and the composites were studied by N2 adsorption, TG/DTA-MS, Raman, SEM-EDX and TEM techniques. Their photocatalytic activity was compared in the UV catalyzed decomposition reaction of methyl orange dye. Keywordsresorcinol-formaldehyde polymer aerogel, carbon aerogel, photocatalysis, ALD, TiO2 IntroductionBeside crystalline carbonaceous nanomaterials such as fullerene, graphene, graphene oxide, nanodiamond, carbon nanospheres, carbon nanotubes; mesoporous carbon aerogels have attracted a great deal of attention. Carbon aerogels, available also in monolithic form, have several favorable properties, for example they can be used as adsorbents or as substrates for catalysts, because of their robustness and high specific surface area [1,2]. They are also excellent thermal and phonic insulators, while conduct electricity. These properties can be tuned through their synthesis conditions. [3][4][5][6][7] Resorcinol-formaldehyde (RF) organic aerogels, that Pekala and co-workers synthetized for the first time [8], undergo two main stages during preparation. In the first stage a hydrogel is prepared by a sol-gel process and in the second stage after drying the aerogel is obtained. The resorcinol-formaldehyde polymer aerogel becomes a carbon aerogel in a consecutive third stage, which is carbonization occasionally followed by activation. Depending on the conditions carbonization or activation influence the structural and performance characteristics, like the specific surface area, significantly [9][10][11][12].Photocatalytic carbon nanocomposites have great potential in the field of environmental remediation, water splitting and self-cleaning surfaces [13,14]. Among the various semiconductor oxide photocatalysts TiO2 is researched widely, due to being stable and nontoxic. TiO2 has ideal band gap width for the half reactions of water splitting and its composites with other nanomaterials, such as carbon nanostructures, may enhance the photocatalytic activity. However, its use still faces some difficulties, such as a narrow light response range limited to UV. The carbon nanostructure inhibits the recombination by promoting the charge separation as an electron acceptor. This effect and the widening of the wavelength response range through Ti-O-C bonds as well as modifying the photocatalytic selectivity are three advantages of TiO2 composites [3,[15][16][17][18]. Moreover, a number of studies indicates that nanoporous or nanostructured carbon materials, such as activated carbon or graphene-oxide...

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“…A 2-4 lL drop of the suspension was deposited onto a clean silicon substrate and evaporated with a heat lamp. To fill open pore space and stabilize the samples, atomic layer deposition (ALD; Elam et al 2006) was performed at Argonne National Laboratory to deposit Al 2 O 3 (approximately 3.6 nm thickness) and tungsten (approximately 1.3 nm thickness) onto the tips. We also prepared control samples that consisted only of deposited Al 2 O 3 .…”

Section: Chicago Methodsmentioning

confidence: 99%

Atom‐probe analyses of nanodiamonds from Allende

Heck

Stadermann

Isheim

et al. 2014

Meteorit & Planetary Scien

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Abstract-Atom-probe tomography (APT) is currently the only analytical technique that, due to its spatial resolution and detection efficiency, has the potential to measure the carbon isotope ratios of individual nanodiamonds. We describe three different sample preparation protocols that we developed for the APT analysis of meteoritic nanodiamonds at sub-nm resolution and present carbon isotope peak ratios of meteoritic and synthetic nanodiamonds. The results demonstrate an instrumental bias associated with APT that needs to be quantified and corrected to obtain accurate isotope ratios. After this correction is applied, this technique should allow determination of the distribution of 12 C/ 13 C ratios in individual diamond grains, solving the decades-old question of the origin of meteoritic nanodiamonds: what fraction, if any, formed in the solar system and in presolar environments? Furthermore, APT could help us identify the stellar sources of any presolar nanodiamonds that are detected.

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Atomic layer deposition of W on nanoporous carbon aerogels

Cited by 57 publications

References 33 publications

Aerogel Templated ZnO Dye‐Sensitized Solar Cells

Aerogel Templated ZnO Dye‐Sensitized Solar Cells

Photocatalytic properties of TiO2@polymer and TiO2@carbon aerogel composites prepared by atomic layer deposition

Atom‐probe analyses of nanodiamonds from Allende

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