Aaltodoc Repository :: Browsing by Author "Kauppinen, Esko I."

Browsing by Author "Kauppinen, Esko I."

Now showing 1 - 20 of 89

Ambient-Dried Cellulose Nanofibril Aerogel Membranes with High Tensile Strength and Their Use for Aerosol Collection and Templates for Transparent, Flexible Devices
(2015) Toivonen, Matti S.; Kaskela, Antti; Rojas, Orlando J.; Kauppinen, Esko I.; Ikkala, Olli; Department of Forest Products Technology; Department of Applied Physics; Department of Bioproducts and Biosystems; Molecular Materials
The application potential of cellulose nanofibril (CNF) aerogels has been hindered by the slow and costly freeze- or supercritical drying methods. Here, CNF aerogel membranes with attractive mechanical, optical, and gas transport properties are prepared in ambient conditions with a facile and scalable process. Aqueous CNF dispersions are vacuum-filtered and solvent exchanged to 2-propanol and further to octane, followed by ambient drying. The resulting CNF aerogel membranes are characterized by high transparency (>90% transmittance), stiffness (6 GPa Young's modulus, 10 GPa cm3 g−1 specific modulus), strength (97 MPa tensile strength, 161 MPa m3 kg−1 specific strength), mesoporosity (pore diameter 10–30 nm, 208 m2 g−1 specific surface area), and low density (≈0.6 g cm−3). They are gas permeable thus enabling collection of nanoparticles (for example, single-walled carbon nanotubes, SWNT) from aerosols under pressure gradients. The membranes with deposited SWNT can be further compacted to transparent, conductive, and flexible conducting films (90% specular transmittance at 550 nm and 300 Ω ◻−1 sheet resistance with AuCl3-salt doping). Overall, the developed aerogel membranes pave way toward use in gas filtration and transparent, flexible devices.
Atomic layer etching of gallium nitride (0001)
(2017-11-01) Kauppinen, Christoffer; Khan, Sabbir Ahmed; Sundqvist, Jonas; Suyatin, Dmitry B.; Suihkonen, Sami; Kauppinen, Esko I.; Sopanen, Markku; Department of Electronics and Nanoengineering; Department of Applied Physics; Aalto Nanofab; NanoMaterials; Markku Sopanen Group; Fraunhofer Institute for Ceramic Technologies and Systems; Lund University
In this work, atomic layer etching (ALE) of thin film Ga-polar GaN(0001) is reported in detail using sequential surface modification by Cl2 adsorption and removal of the modified surface layer by low energy Ar plasma exposure in a standard reactive ion etching system. The feasibility and reproducibility of the process are demonstrated by patterning GaN(0001) films by the ALE process using photoresist as an etch mask. The demonstrated ALE is deemed to be useful for the fabrication of nanoscale structures and high electron mobility transistors and expected to be adoptable for ALE of other materials.
Atomic-Scale Deformations at the Interface of a Mixed-Dimensional van der Waals Heterostructure
(AMERICAN CHEMICAL SOCIETY, 2018-07-17) Mustonen, Kimmo Aleksi; Hussain, Aqeel; Hofer, Christoph; Reza Ahmadpour Monazam, Mohammad; Mirzayev, Rasim; Elibol, Kenan; Laiho, Patrik; Mangler, Clemens; Jiang, Hua; Susi, Toma; Kauppinen, Esko I.; Kotakoski, Jani; Meyer, Jannik C.; Department of Applied Physics; NanoMaterials; University of Vienna
Molecular self-assembly due to chemical interactions is the basis of bottom-up nanofabrication, whereas weaker intermolecular forces dominate on the scale of macromolecules. Recent advances in synthesis and characterization have brought increasing attention to two- and mixed-dimensional heterostructures and it has been recognized that van der Waals (vdW) forces within the structure may have a significant impact on their morphology. Here, we suspend single-walled carbon nanotubes (SWCNTs) on graphene to create a model system for the study of a 1D-2D molecular interface through atomic resolution scanning transmission electron microscopy observations. When brought in contact, we observe radial deformation of SWCNTs and the emergence of long-range linear grooves in graphene revealed by three-dimensional reconstruction of the heterostructure. These topographic features are strain-correlated but show no sensitivity to carbon nanotube helicity, electronic structure, or stacking order. Finally, despite random deposition of the nanotubes, we show that the competition between strain and vdW forces results in aligned carbon-carbon interfaces spanning hundreds of nanometers.
Broadband laser polarization control with aligned carbon nanotubes
(ROYAL SOC CHEMISTRY, 2015) Yang, He; Fu, Bo; Li, Diao; Tian, Ying; Chen, Ya; Mattila, Marco; Yong, Zhenzhong; Li, Ru; Hassanien, Abdou; Yang, Changxi; Tittonen, Ilkka; Zhaoyu, Re; Bai, Jintao; Li, Qingwen; Kauppinen, Esko I.; Lipsanen, Harri; Sun, Zhipei; Department of Micro and Nanosciences; Department of Applied Physics; NanoMaterials; Ilkka Tittonen Group; Harri Lipsanen Group; Zhipei Sun Group; Tsinghua University
Broadband synchronization of ultrafast pulse generation with double-walled carbon nanotubes
(De Gruyter, 2023-08-02) Zheng, Jiancheng; Li, Diao; Liu, Peng; Cui, Xiaoqi; Zhang, Bin; Geng, Wei; Zhang, Qiang; Xu, Zhenyu; Kauppinen, Esko I.; Sun, Zhipei; Department of Electronics and Nanoengineering; Department of Applied Physics; Centre of Excellence in Quantum Technology, QTF; Zhipei Sun Group; NanoMaterials
Double-walled carbon nanotubes have shown competitive properties in broadband optical pulse generation owning to the intrinsic electronic properties. Synchronization of ultrafast optical pulses in multiple wavelengths is a key technique for numerous applications, such as nonlinear frequency conversion, ultrafast pump-probe, coherent Raman scattering spectroscopy, coherent optical synthesis, etc. In this work, we demonstrate the mode-locking and synchronization of 1.55 μm pulses with 1 μm and 1.9 μm pulses via a single saturable absorber based on double-walled carbon nanotubes. The large optical nonlinearity and broadband optical absorption in the double-walled carbon nanotubes enable independent and synchronized mode-locking in >900 nm bandwidth. In addition, we present a creative concept to realize multi-wavelength synchronization from a single laser system. Our results demonstrate a straightforward and feasible approach towards pulse synchronization over ultra-broad bandwidth with flexible wavelength selection in the near-infrared region.
Carbon Nanotube/Nanofibers and Graphite Hybrids for Li-Ion Battery Application
(Hindawi Publishing Corporation, 2014) Nomura, Yosuke; Anoshkin, Ilya V.; Okuda, Chikaaki; Iijima, Motoyuki; Ukyo, Yoshio; Kamiya, Hidehiro; Nasibulin, Albert G.; Kauppinen, Esko I.; Teknillisen fysiikan laitos; Department of Applied Physics; Perustieteiden korkeakoulu; School of Science
To improve the electrical conductivity of negative electrodes of lithium ion batteries, we applied a direct CVD synthesis of carbon nanomaterials on the surface of graphite particles. To prepare a catalyst, two alternative approaches were utilized: colloidal nanoparticles (NPs) and metal (Ni and Co) nitrate salt precursors deposited on the graphite surface. Both colloidal and precursor systems allowed us to produce carbon nanofibers (CNFs) on the graphite surface with high coverage under the optimum CVD conditions. Electrical measurements revealed that the resistivity of the actual electrodes fabricated from CNFs coated graphite particles was about 40% lower compared to the original pristine graphite electrodes.
Carbon Nanotubes and Related Nanomaterials: Critical Advances and Challenges for Synthesis toward Mainstream Commercial Applications
(AMERICAN CHEMICAL SOCIETY, 2018) Rao, Rahul; Pint, Cary L.; Islam, Ahmad E.; Weatherup, Robert S.; Hofmann, Stephan; Meshot, Eric R.; Wu, Fanqi; Zhou, Chongwu; Dee, Nicholas; Amama, Placidus B.; Carpena-Nunez, Jennifer; Shi, Wenbo; Plata, Desiree L.; Penev, Evgeni S.; Yakobson, Boris I.; Balbuena, Perla B.; Bichara, Christophe; Futaba, Don N.; Noda, Suguru; Shin, Homin; Kim, Keun Su; Simard, Benoit; Mirri, Francesca; Pasquali, Matteo; Fornasiero, Francesco; Kauppinen, Esko I.; Arnold, Michael; Cola, Baratunde A.; Nikolaev, Pavel; Arepalli, Sivaram; Cheng, Hui Ming; Zakharov, Dmitri N.; Stach, Eric A.; Zhang, Jin; Wei, Fei; Terrones, Mauricio; Geohegan, David B.; Maruyama, Benji; Maruyama, Shigeo; Li, Yan; Adams, W. Wade; Hart, A. John; Department of Applied Physics; NanoMaterials; Wright-Patterson AFB; Vanderbilt University; University of Manchester; University of Cambridge; Lawrence Livermore National Laboratory; University of Southern California; Massachusetts Institute of Technology; Kansas State University; Yale University; Rice University; Texas A&M University; CNRS; National Institute of Advanced Industrial Science and Technology; Waseda University; National Research Council of Canada; University of Wisconsin-Madison; Georgia Institute of Technology; Tsinghua University; Brookhaven National Laboratory; University of Pennsylvania; Peking University; Pennsylvania State University; Oak Ridge National Laboratory; University of Tokyo
Advances in the synthesis and scalable manufacturing of single-walled carbon nanotubes (SWCNTs) remain critical to realizing many important commercial applications. Here we review recent breakthroughs in the synthesis of SWCNTs and highlight key ongoing research areas and challenges. A few key applications that capitalize on the properties of SWCNTs are also reviewed with respect to the recent synthesis breakthroughs and ways in which synthesis science can enable advances in these applications. While the primary focus of this review is on the science framework of SWCNT growth, we draw connections to mechanisms underlying the synthesis of other 1D and 2D materials such as boron nitride nanotubes and graphene.
Catalyst-free growth of In(As)P nanowires on silicon
(AIP Publishing, 2006) Mattila, M.; Hakkarainen, T.; Lipsanen, Harri; Jiang, H.; Kauppinen, Esko I.; Mikro- ja nanotekniikan laitos; Department of Micro and Nanosciences; Sähkötekniikan korkeakoulu; School of Electrical Engineering
The catalyst-free metal organic vapor phase epitaxialgrowth of In(As)P nanowires on silicon substrates is investigated using in situ deposited In droplets as seeds for nanowiregrowth. The thin substrate native oxide is found to play a crucial role in the nanowire formation. The structure of the nanowires is characterized by photoluminescence and electron microscopy measurements. The crystal structure of the InPnanowires is wurtzite with its c axis perpendicular to the nanowire axis. Adding arsenic precursor to the gas phase during growth results in a bimodal photoluminescence spectrum exhibiting peak at the InAsP and InP band gap energies.
Chiral-Selective Growth of Single-Walled Carbon Nanotubes on Lattice-Mismatched Epitaxial Cobalt Nanoparticles
(Nature Publishing Group, 2013) He, Maoshuai; Jiang, Hua; Liu, Bilu; Fedotov, Pavel V.; Chernov, Alexander I.; Obraztsova, Elena D.; Cavalca, Filippo; Wagner, Jakob B.; Hansen, Thomas W.; Anoshkin, Ilya V.; Obraztsova, Ekaterina A.; Belkin, Alexey V.; Sairanen, Emma; Nasibulin, Albert G.; Lehtonen, Juha; Kauppinen, Esko I.; Teknillisen fysiikan laitos; Department of Applied Physics; Perustieteiden korkeakoulu; School of Science
Controlling chirality in growth of single-walled carbon nanotubes (SWNTs) is important for exploiting their practical applications. For long it has been conceptually conceived that the structural control of SWNTs is potentially achievable by fabricating nanoparticle catalysts with proper structures on crystalline substrates via epitaxial growth techniques. Here, we have accomplished epitaxial formation of monometallic Co nanoparticles with well-defined crystal structure, and its use as a catalyst in the selective growth of SWNTs. Dynamics of Co nanoparticles formation and SWNT growth inside an atomic-resolution environmental transmission electron microscope at a low CO pressure was recorded. We achieved highly preferential growth of semiconducting SWNTs (~90%) with an exceptionally large population of (6, 5) tubes (53%) in an ambient CO atmosphere. Particularly, we also demonstrated high enrichment in (7, 6) and (9, 4) at a low growth temperature. These findings open new perspectives both for structural control of SWNTs and for elucidating the growth mechanisms.
Colors of Single-Wall Carbon Nanotubes
(WILEY-V C H VERLAG GMBH, 2021-02-24) Wei, Nan; Tian, Ying; Liao, Yongping; Komatsu, Natsumi; Gao, Weilu; Lyuleeva-Husemann, Alina; Zhang, Qiang; Hussain, Aqeel; Ding, Er Xiong; Yao, Fengrui; Halme, Janne; Liu, Kaihui; Kono, Junichiro; Jiang, Hua; Kauppinen, Esko I.; Department of Applied Physics; Dalian Maritime University; NanoMaterials; Rice University; Peking University
Although single-wall carbon nanotubes (SWCNTs) exhibit various colors in suspension, directly synthesized SWCNT films usually appear black. Recently, a unique one-step method for directly fabricating green and brown films has been developed. Such remarkable progress, however, has brought up several new questions. The coloration mechanism, potentially achievable colors, and color controllability of SWCNTs are unknown. Here, a quantitative model is reported that can predict the specific colors of SWCNT films and unambiguously identify the coloration mechanism. Using this model, colors of 466 different SWCNT species are calculated, which reveals a broad spectrum of potentially achievable colors of SWCNTs. The calculated colors are in excellent agreement with existing experimental data. Furthermore, the theory predicts the existence of many brilliantly colored SWCNT films, which are experimentally expected. This study shows that SWCNTs as a form of pure carbon, can display a full spectrum of vivid colors, which is expected to complement the general understanding of carbon materials.
Controlling supercurrents using single-walled carbon nanotube weak links
(IOP Publishing, 2009) Wu, F.; Danneau, R.; Queipo, P.; Kauppinen, Esko I.; Tsuneta, T.; Hakonen, Pertti J.; Teknillisen fysiikan laitos; Department of Applied Physics; Perustieteiden korkeakoulu; School of Science
We have investigated proximity-induced supercurrents in single-walled carbon nanotubes. Phase diffusion is found to be present in the maximum measured supercurrent of 4.8 nA, which results in a minimum of 100Ω zero bias resistance in superconducting state. We also observe that the supercurrent is very sensitive to the measurement bandwidth and large phase fluctuations can even destroy the supercurrents. Our results shed light on the methods of how to improve the performance of high frequency superconducting single-walled nanotube devices.
Core level binding energies of functionalized and defective graphene
(Beilstein Institut, 2014) Susi, Toma; Kaukonen, Markus; Havu, Paula; Ljungberg, Mathias P.; Ayala, Paola; Kauppinen, Esko I.; Teknillisen fysiikan laitos; Department of Applied Physics; Perustieteiden korkeakoulu; School of Science
X-ray photoelectron spectroscopy (XPS) is a widely used tool for studying the chemical composition of materials and it is a standard technique in surface science and technology. XPS is particularly useful for characterizing nanostructures such as carbon nanomaterials due to their reduced dimensionality. In order to assign the measured binding energies to specific bonding environments, reference energy values need to be known. Experimental measurements of the core level signals of the elements present in novel materials such as graphene have often been compared to values measured for molecules, or calculated for finite clusters. Here we have calculated core level binding energies for variously functionalized or defected graphene by delta Kohn–Sham total energy differences in the real-space grid-based projector-augmented wave density functional theory code (GPAW). To accurately model extended systems, we applied periodic boundary conditions in large unit cells to avoid computational artifacts. In select cases, we compared the results to all-electron calculations using an ab initio molecular simulations (FHI-aims) code. We calculated the carbon and oxygen 1s core level binding energies for oxygen and hydrogen functionalities such as graphane-like hydrogenation, and epoxide, hydroxide and carboxylic functional groups. In all cases, we considered binding energy contributions arising from carbon atoms up to the third nearest neighbor from the functional group, and plotted C 1s line shapes by using experimentally realistic broadenings. Furthermore, we simulated the simplest atomic defects, namely single and double vacancies and the Stone–Thrower–Wales defect. Finally, we studied modifications of a reactive single vacancy with O and H functionalities, and compared the calculated values to data found in the literature.
CVD Synthesis of Hierarchical 3D MWCNT/Carbon-Fiber Nanostructures
(Hindawi Publishing Corporation, 2008) Susi, Toma; Nasibulin, Albert G.; Jiang, Hua; Kauppinen, Esko I.; Teknillisen fysiikan laitos; Department of Applied Physics; Perustieteiden korkeakoulu; School of Science
Multiwalled carbon nanotubes (MWCNTs) were synthesized by CVD on industrially manufactured highly crystalline vapor-grown carbon fibers (VGCFs). Two catalyst metals (Ni and Fe) and carbon precursor gases (C2H2 and CO) were studied. The catalysts were deposited on the fibers by sputtering and experiments carried out in two different reactors. Samples were characterized by electron microscopy (SEM and TEM). Iron was completely inactive as catalyst with both C2H2 and CO for reasons discussed in the paper. The combination of Ni and C2H2 was very active for secondary CNT synthesis, without any pretreatment of the fibers. The optimal temperature for CNT synthesis was 750 ∘C, with total gas flow of 650 cm exp 3 min exp -1 of C2H2, H2, and Ar in 1.0:6.7:30 ratio.
Design of nano deposition device
(2010) Toivonen, Axel; Kauppinen, Esko I.; Koneenrakennustekniikan laitos; Insinööritieteiden korkeakoulu; School of Engineering; Coatanea, Eric
The objective of this work is to create a device that deposits carbon nanotubes from a floating catalyst chemical vapour deposition reactor to a substrate in one process, without extra steps. This will create a conductive transparent thin film which can be used as raw material for the electronics industry. The device works as proof of concept for a novel collection method. The theoretical part of this work describes properties and applications for carbon nanotubes and the dominant production methods. Product development methods are also presented and a deeper analysis of methods presented by Otto & Wood. Utilizing impaction and an electric field the device collects the nanotubes from the aerosol straight to the substrate. The produced thin film is conducting and a uniform nanotubes layer covers the film. Most of the customer needs were satisfied and the product development project was a success. The device can work as a modular test platform in the future
Determination of helicities in unidirectional assemblies of graphitic or graphiticlike tubular structures
(AIP Publishing, 2008) Jiang, H.; Brown, D. P.; Nikolaev, P.; Nasibulin, Albert G.; Kauppinen, Esko I.; Teknillisen fysiikan laitos; Department of Applied Physics; Perustieteiden korkeakoulu; School of Science
Here we propose a universal method for the determination of all helicities present in unidirectional assemblies of hexagon-based graphitic or graphiticlike tubular structures, e.g., multiwalled or bundled carbon nanotubes(CNTs) or boron-nitride nanotubes and their structural analogs. A critical dimension characteristic of a fundamental structural property, i.e., the atomic bond length, is discerned from electron diffraction patterns by which all helicities present in the assemblies are identified. Using this method, we determine the helicity population in a single-walled CNT sample produced by laser ablation technique.
Direct Synthesis of Colorful Single-Walled Carbon Nanotube Thin Films
(2018-08-08) Liao, Yongping; Jiang, Hua; Wei, Nan; Laiho, Patrik; Zhang, Qiang; Khan, Sabbir A.; Kauppinen, Esko I.; Department of Applied Physics; NanoMaterials
In floating catalyst chemical vapor deposition (FC-CVD), tuning chirality distribution and obtaining narrow chirality distribution of single-walled carbon nanotubes (SWCNTs) is challenging. Herein, by introducing various amount of CO2 in FC-CVD using CO as a carbon source, we have succeeded in directly synthesizing SWCNT films with tunable chirality distribution as well as tunable colors. In particular, with 0.25 and 0.37 volume percent of CO2, the SWCNT films display green and brown colors, respectively. We ascribed various colors to suitable diameter and narrow chirality distribution of SWCNTs. Additionally, by optimizing reactor temperature, we achieved much narrower (n,m) distribution clustered around (11,9) with extremely narrow diameter range (>98% between 1.2 and 1.5 nm). We propose that CO2 may affect CO disproportionation and nucleation modes of SWCNTs, resulting in SWCNTs' various diameter ranges. Our work could provide a new route for high-yield and direct synthesis of SWCNTs with narrow chirality distribution and offer potential applications in electronics, such as touch sensors or transistors.
Direct Synthesis of Semiconducting Single-Walled Carbon Nanotubes Toward High-Performance Electronics
(Wiley-VCH Verlag, 2023-07) Liu, Peng; Khan, Abu Taher; Ding, Er Xiong; Zhang, Qiang; Xu, Zhenyu; Bai, Xueyin; Wei, Nan; Tian, Ying; Li, Diao; Jiang, Hua; Lipsanen, Harri; Sun, Zhipei; Kauppinen, Esko I.; Department of Electronics and Nanoengineering; Department of Applied Physics; Zhipei Sun Group; Centre of Excellence in Quantum Technology, QTF; Harri Lipsanen Group; NanoMaterials; Aalto University; Department of Electronics and Nanoengineering; Peking University; Dalian Maritime University
The large-scale synthesis of high-purity semiconducting single-walled carbon nanotubes (s-SWCNTs) plays a crucial role in fabricating high-performance and multiapplication-scenario electronics. This work develops a straightforward, continuous, and scalable method to synthesize high-purity and individual s-SWCNTs with small-diameters distribution (≈1 nm). It is believed that the water and carbon dioxide resulting from the decomposition of isopropanol act as oxidizing agents and selectively etch metallic SWCNTs, hence enhancing the production of s-SWCNTs. The performance of individual-SWCNTs field effect transistors confirms the high abundance of s-SWCNTs, presenting a mean mobility of 376 cm2 V−1 s−1 and a high mobility of 2725 cm2 V−1 s−1 with an on-current to off-current (Ion/Ioff) ratio as high as 2.51 × 107. Moreover, thin-film transistors based on the as-synthesized SWCNTs exhibit excellent performance with a mean mobility of 9.3 cm2 V−1 s−1 and Ion/Ioff ratio of 1.3× 105, respectively, verifying the enrichment of s-SWCNTs. This work presents a simple and feasible route for the sustainable synthesis of high-quality s-SWCNTs for electronic devices.
Effect of Carbon Nanotube Aqueous Dispersion Quality on Mechanical Properties of Cement Composite
(Hindawi Publishing Corporation, 2012) Nasibulina, Larisa I.; Anoshkin, Ilya V.; Nasibulin, Albert G.; Cwirzen, Andrzej; Penttala, Vesa; Kauppinen, Esko I.; Teknillisen fysiikan laitos; Department of Applied Physics; Perustieteiden korkeakoulu; School of Science
An effect of the quality of carbon nanotube (CNT) dispersions added to cement on paste mechanical properties has been studied. High-quality dispersions of few-walled CNT (FWCNTs) were produced in two steps. First, FWCNTs were functionalized in a mixture of nitric and sulfuric acids (70 wt.% and 96 wt.%, resp.) at 80 ∘C . Second, functionalized FWCNTs were washed out by acetone to remove carboxylated carbonaceous fragments (CCFs) formed during CNT oxidation. Mechanical test results showed 2-fold increase in the compressive strength of the cement paste prepared from the dispersion of acetone-washed functionalized FWCNTs, which is believed to occur due to the chemical interaction between cement matrix and functional groups (–COOH and –OH). Utilisation of unwashed FWCNTs led to a marginal improvement of mechanical properties of the cement pastes, whereas surfactant-treated functionalized FWCNT dispersions only worsened the mechanical properties.
The effect of Nafion content in a graphitized carbon nanofiber-based anode for the direct methanol fuel cell
(2012-12) Kanninen, Petri; Borghei, Maryam; Ruiz, Virginia; Kauppinen, Esko I.; Kallio, Tanja; Department of Chemistry; Department of Applied Physics
The performance and stability of a direct methanol fuel cell (DMFC) with membrane electrode assemblies (MEA) using different Nafion® contents (30, 50 and 70 wt% or MEA30, MEA50 and MEA70, respectively) and graphitized carbon nanofiber (GNF) supported PtRu catalyst at the anode was investigated by a constant current measurement of 9 days (230 h) in a DMFC and characterization with various techniques before and after this measurement. Of the pristine MEAs, MEA50 reached the highest power and current densities. During the 9-day measurement at a constant current, the performance of MEA30 decreased the most (−124 μV h−1), while the MEA50 was almost stable (−11 μV h−1) and performance of MEA70 improved (+115 μV h−1). After the measurement, the MEA50 remained the best MEA in terms of performance. The optimum anode Nafion content for commercial Vulcan carbon black supported PtRu catalysts is between 20 and 40 wt%, so the GNF-supported catalyst requires more Nafion to reach its peak power. This difference is explainedby the tubular geometry of the catalyst support, which requires more Nafion to form a penetrating proton conductive network than the spherical Vulcan. Mass transfer limitations are mitigated by the porous 3D structure of the GNF catalyst layer and possible changes in the compact Nafion filled catalyst layers during constant current production.
Effect of tetrahedral amorphous carbon coating on the resistivity and wear of single-walled carbon nanotube network
(2016-05-14) Iyer, Ajai; Kaskela, Antti; Novikov, Serguei; Etula, Jarkko; Liu, Xuwen; Kauppinen, Esko I.; Koskinen, Jari; Department of Materials Science and Engineering; Department of Applied Physics; Department of Micro and Nanosciences; Department of Chemistry and Materials Science; NanoMaterials
Single walled carbon nanotube networks (SWCNTNs) were coated by tetrahedral amorphous carbon (ta-C) to improve the mechanical wear properties of the composite film. The ta-C deposition was performed by using pulsed filtered cathodic vacuum arc method resulting in the generation of C+ ions in the energy range of 40-60 eV which coalesce to form a ta-C film. The primary disadvantage of this process is a significant increase in the electrical resistance of the SWCNTN post coating. The increase in the SWCNTN resistance is attributed primarily to the intrinsic stress of the ta-C coating which affects the inter-bundle junction resistance between the SWCNTN bundles. E-beam evaporated carbon was deposited on the SWCNTNs prior to the ta-C deposition in order to protect the SWCNTN from the intrinsic stress of the ta-C film. The causes of changes in electrical resistance and the effect of evaporated carbon thickness on the changes in electrical resistance and mechanical wear properties have been studied.

Browsing by Author "Kauppinen, Esko I."

Results Per Page

Sort Options