Browsing by Author "Etula, Jarkko"
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Item Accurate Computational Prediction of Core-Electron Binding Energies in Carbon-Based Materials: A Machine-Learning Model Combining Density-Functional Theory and GW(AMERICAN CHEMICAL SOCIETY, 2022-07-13) Golze, Dorothea; Hirvensalo, Markus; Hernández-León, Patricia; Aarva, Anja; Etula, Jarkko; Susi, Toma; Rinke, Patrick; Laurila, Tomi; Caro, Miguel A.; Department of Applied Physics; Department of Electrical Engineering and Automation; Department of Chemistry and Materials Science; Computational Electronic Structure Theory; Microsystems Technology; Physical Characteristics of Surfaces and Interfaces; Centre of Excellence in Quantum Technology, QTF; Department of Applied Physics; University of ViennaWe present a quantitatively accurate machine-learning (ML) model for the computational prediction of core-electron binding energies, from which X-ray photoelectron spectroscopy (XPS) spectra can be readily obtained. Our model combines density functional theory (DFT) with GW and uses kernel ridge regression for the ML predictions. We apply the new approach to disordered materials and small molecules containing carbon, hydrogen, and oxygen and obtain qualitative and quantitative agreement with experiment, resolving spectral features within 0.1 eV of reference experimental spectra. The method only requires the user to provide a structural model for the material under study to obtain an XPS prediction within seconds. Our new tool is freely available online through the XPS Prediction Server.Item Aluminum Nitride Transition Layer for Power Electronics Applications Grown by Plasma-Enhanced Atomic Layer Deposition(MDPI AG, 2019-02-01) Seppänen, Heli; Kim, Iurii; Etula, Jarkko; Ubyivovk, Evgeniy; Buravlev, Alexey; Lipsanen, Harri; Department of Electronics and Nanoengineering; Department of Chemistry and Materials Science; Harri Lipsanen Group; Markku Sopanen Group; Physical Characteristics of Surfaces and Interfaces; St. Petersburg National Research University of Information Technologies, Mechanics and Optics (ITMO)Aluminum nitride (AlN) films have been grown using novel technological approaches based on plasma-enhanced atomic layer deposition (PEALD) and in situ atomic layer annealing (ALA). The growth of AlN layers was carried out on Si<100> and Si<111> substrates at low growth temperature. The investigation of crystalline quality of samples demonstrated that PEALD grown layers were polycrystalline, but ALA treatment improved their crystallinity. A thick polycrystalline AlN layer was successfully regrown by metal-organic chemical vapor deposition (MOCVD) on an AlN PEALD template. It opens up the new possibilities for the formation of nucleation layers with improved quality for subsequent growth of semiconductor nitride compounds.Item Application-Specific Catalyst Layers: Pt-Containing Carbon Nanofibers for Hydrogen Peroxide Detection(2017-02-13) Laurila, Tomi; Sainio, Sami; Jiang, Hua; Isoaho, Noora; Koehne, Jessica; Etula, Jarkko; Koskinen, Jari; Meyyappan, M.; Department of Electrical Engineering and Automation; Department of Applied Physics; Department of Chemistry and Materials Science; NanoMaterials; Microsystems Technology; NASA Ames Research CenterComplete removal of metal catalyst particles from carbon nanofibers (CNFs) and other carbon nanostructures is extremely difficult, and the envisioned applications may be compromised by the left-over impurities. To circumvent these problems, one should use, wherever possible, such catalyst materials that are meant to remain in the structure and have some application-specific role, making any removal steps unnecessary. Thus, as a proof-of-concept, we present here a nanocarbon-based material platform for electrochemical hydrogen peroxide measurement utilizing a Pt catalyst layer to grow CNFs with intact Pt particles at the tips of the CNFs. Backed by careful scanning transmission electron microscopy analysis, we show that this material can be readily realized with the Pt catalyst layer thickness impacting the resulting structure and also present a growth model to explain the evolution of the different types of structures. In addition, we show by electrochemical analysis that the material exhibits characteristic features of Pt in cyclic voltammetry and it can detect very small amounts of hydrogen peroxide with very fast response times. Thus, the present sensor platform provides an interesting electrode material with potential for biomolecule detection and in fuel cells and batteries. In the wider range, we propose a new approach where the selection of catalytic particles used for carbon nanostructure growth is made so that (i) they do not need to be removed and (ii) they will have essential role in the final application.Item Characterization and electrochemical properties of iron-doped tetrahedral amorphous carbon (ta-C) thin films(2018-01-01) Etula, Jarkko; Wester, Niklas; Sainio, Sami; Laurila, Tomi; Koskinen, Jari; Department of Chemistry and Materials Science; Department of Chemistry; Department of Electrical Engineering and Automation; Physical Characteristics of Surfaces and Interfaces; Microsystems TechnologyIron-doped tetrahedral amorphous carbon thin films (Fe/ta-C) were deposited with varying iron content using a pulsed filtered cathodic vacuum arc system (p-FCVA). The aim of this study was to understand effects of iron on both the physical and electrochemical properties of the otherwise inert sp3-rich ta-C matrix. As indicated by X-ray photoelectron spectroscopy (XPS), even ∼0.4 at% surface iron had a profound electrochemical impact on both the potential window of ta-C in H2SO4 and KOH, as well as pseudocapacitance. It also substantially enhanced the electron transport and re-enabled facile outer sphere redox reaction kinetics in comparison to un-doped ta-C, as measured with electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) using outer-sphere probes Ru(NH3)6, IrCl6, and FcMeOH. These increases in surface iron loading were linked to increased surface oxygen content and iron oxides. Unlike few other metals, an iron content even up to 10 at% was not found to result in the formation of sp2-rich amorphous carbon films as investigated by Raman spectroscopy. Atomic force microscopy (AFM) and transmission electron microscopy (TEM) investigations found all films to be amorphous and ultrasmooth with Rq values always in the range of 0.1-0.2 nm. As even very small amounts of Fe were shown to dominate the electrochemistry of ta-C, implications of this study are very useful e.g. in carbon nanostructure synthesis, where irregular traces of iron can be readily incorporated into the final structures.Item Comparison of mechanical properties and composition of magnetron sputter and plasma enhanced atomic layer deposition aluminum nitride films(2018-09-01) Sippola, Perttu; Pyymaki Perros, Alexander; Ylivaara, Oili M.E.; Ronkainen, Helena; Julin, Jaakko; Liu, Xuwen; Sajavaara, Timo; Etula, Jarkko; Lipsanen, Harri; Puurunen, Riikka L.; Department of Electronics and Nanoengineering; Department of Chemical and Metallurgical Engineering; Department of Chemistry and Materials Science; Physical Characteristics of Surfaces and Interfaces; Catalysis; Harri Lipsanen Group; VTT Technical Research Centre of Finland; University of JyväskyläA comparative study of mechanical properties and elemental and structural composition was made for aluminum nitride thin films deposited with reactive magnetron sputtering and plasma enhanced atomic layer deposition (PEALD). The sputtered films were deposited on Si (100), Mo (110), and Al (111) oriented substrates to study the effect of substrate texture on film properties. For the PEALD trimethylaluminum-ammonia films, the effects of process parameters, such as temperature, bias voltage, and plasma gas (ammonia versus N2/H2), on the AlN properties were studied. All the AlN films had a nominal thickness of 100 nm. Time-of-flight elastic recoil detection analysis showed the sputtered films to have lower impurity concentration with an Al/N ratio of 0.95, while the Al/N ratio for the PEALD films was 0.81-0.90. The mass densities were ∼3.10 and ∼2.70 g/cm3 for sputtered and PEALD AlN, respectively. The sputtered films were found to have higher degrees of preferential crystallinity, whereas the PEALD films were more polycrystalline as determined by x-ray diffraction. Nanoindentation experiments showed the elastic modulus and hardness to be 250 and 22 GPa, respectively, for sputtered AlN on the (110) substrate, whereas with PEALD AlN, values of 180 and 19 GPa, respectively, were obtained. The sputtered films were under tensile residual stress (61-421 MPa), whereas the PEALD films had a residual stress ranging from tensile to compressive (846 to −47 MPa), and high plasma bias resulted in compressive films. The adhesion of both films was good on Si, although sputtered films showed more inconsistent critical load behavior. Also, the substrate underneath the sputtered AlN did not withstand high wear forces as with the PEALD AlN. The coefficient of friction was determined to be ∼0.2 for both AlN types, and their wear characteristics were almost identical.Item 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; NanoMaterialsSingle 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.Item Enhanced Thermoelectric Transport and Stability in Atomic Layer Deposited HfO2/ZnO and TiO2/ZnO Sandwiched Multilayer Thin Films(AMERICAN CHEMICAL SOCIETY, 2020-10-28) Clairvaux Felizco, Jenichi; Juntunen, Taneli; Uenuma, Mutsunori; Etula, Jarkko; Tossi, Camilla; Ishikawa, Yasuaki; Tittonen, Ilkka; Uraoka, Yukiharu; Department of Electronics and Nanoengineering; Department of Chemistry and Materials Science; Ilkka Tittonen Group; Physical Characteristics of Surfaces and Interfaces; Nara Institute of Science and TechnologyHerein, enhancements in thermoelectric (TE) performance, both the power factor (PF) and thermal stability, are exhibited by sandwiching HfO2 and TiO2 layers onto atomic layer deposited-ZnO thin films. High-temperature TE measurements from 300 to 450 K revealed an almost two-fold improvement in electrical conductivity for TiO2/ZnO (TZO) samples, primarily owing to an increase in carrier concentration by Ti doping. On the other hand, HfO2/ZnO (HZO) achieved the highest PF values owing to maintaining Seebeck coefficients comparable to pure ZnO. HZO also exhibited excellent stability after multiple thermal cycles, which has not been previously observed for pure or doped ZnO thin films. Such improvement in both TE properties and thermal stability of HZO can be attributed to a shift in crystalline orientation from the a axis to c axis, as well as the high bond dissociation energy of Hf-O, stabilizing the ZnO structure. These unique properties exhibited by HZO and TZO thin films synthesized by atomic layer deposition pave the way for next-generation transparent TE devices.Item Exploring the envelope of physical vapor deposition: Nano- and microstructured films for electrochemical applications(Aalto University, 2023) Etula, Jarkko; Kemian ja materiaalitieteen laitos; Department of Chemistry and Materials Science; Physical Characteristics of Surfaces and Interfaces; Kemian tekniikan korkeakoulu; School of Chemical Technology; Koskinen, Jari Prof., Aalto University, School of Chemical Engineering, Head of Department of Chemistry and Materials Science, Finland; Laurila, Tomi, Prof., Aalto University, Department of Electrical Engineering and Automation, FinlandPhysical vapor deposition (PVD) methods are established scalable industrial processes for creating high-quality functional films in various industries. PVD deposited films are commonly dense and smooth with structural features in the nanoscale, but by variation of deposition parameters, film properties and structure can be modified to enhance application-specific performance. In electrode materials for electrochemistry, for instance, a larger accessible surface area commonly increases the number of electrochemical reactions occurring at the same time on the electrode. In this work, PVD methods are used to deposit film materials for electrochemical applications: Nanostructured carbon thin films are investigated as electrochemical biosensors, and microstructured titanium oxide films are demonstrated in microbattery and photocatalysis applications. The aim is to explore and determine how PVD methods can be utilized to construct film structures with a high degree of application-specific tailorability in terms of nano- and microstructural features. Comprehensive structural and physicochemical characterization is carried out for the deposited materials, providing the fundamental tools and insight required to understand and link the observed application performance to changes in material properties. In the first part, the nanostructure of thin and ultrasmooth chemically inert carbon films high in sp3-bonded carbon are modified by alloying with iron, doping with nitrogen, and by embedding carbon nanodiamonds into the film structure. The addition of iron into the films as well as doping with nitrogen are found to enhance the performance of electron transfer on the carbon electrodes in electrochemical sensing applications. It is however also found that these modifications open and alter the initially high sp3-carbon nanostructure, exposing it to atmospheric contaminants. In the second part, a higher gas pressure is applied during PVD deposition, inducing cluster and nanoparticle formation of the deposited material. This gas nucleation technique is leveraged with titanium oxide as the deposition material to construct thick and porous microstructures. In the first subsection, a large permanent magnet is used to collect and self-assemble the gas nucleated titanium oxide nanoparticles into a hierarchical film structure several micrometers in thickness comprising particle clusters of varying sizes. This microstructure offers a considerably large specific surface area, which is important in its application as a photocatalyst. In the second subsection, in an otherwise conventional PVD process, substrate biasing in combination with gas nucleation of lithium-titanate-carbon material is found to result in an unidentified growth mechanism of micrometer-sized pillars. The performance of this micropillar structure is demonstrated as an anode material in Li-ion microbattery. These findings showcase the adaptability of conventional PVD methods for depositing films with diverse nano- and microscale features. Thorough characterization is essential for understanding material changes and in uncovering unidentified phenomena in films deposited via physical vapor deposition.Item Functionalized Nanocellulose/Multiwalled Carbon Nanotube Composites for Electrochemical Applications(AMERICAN CHEMICAL SOCIETY, 2021-06-25) Durairaj, Vasuki; Li, Panpan; Liljeström, Touko; Wester, Niklas; Etula, Jarkko; Leppänen, Ilona; Ge, Yanling; Kontturi, Katri S.; Tammelin, Tekla; Laurila, Tomi; Koskinen, Jari; Department of Chemistry and Materials Science; Department of Electrical Engineering and Automation; Physical Characteristics of Surfaces and Interfaces; Microsystems Technology; VTT Technical Research Centre of FinlandFour different types of crystalline and fibrillar nanocellulosic materials with different functional groups (sulfate, carboxylate, amino-silane) are produced and used to disperse commercial multiwalled carbon nanotubes (MWCNT). Aqueous nanocellulose/MWCNT dispersions are drop-cast on tetrahedral amorphous carbon (ta-C) substrates to obtain highly stable composite electrodes. Their electrochemical properties are studied using cyclic voltammetry (CV) measurements with Ru(NH3)62+/3+, IrCl62-/3- redox probes, in electrolytes of different ionic strengths. All studied nanocellulose/MWCNT composites show excellent stability over a wide potential range (-0.6 to +1 V) in different electrolytes. Highly anionic and more porous fibrillar nanocellulosic composites indicate strong electrostatic and physical enrichment of cationic Ru(NH3)62+/3+ in lower-ionic-strength electrolytes, while lesser anionic and denser crystalline nanocellulosic composites show no such effects. This study provides essential insights into developing tailorable nanocellulose/carbon nanomaterial hybrid platforms for different electrochemical applications, by altering the constituent nanocellulosic material properties.Item Heat treatment of copper-doped tetrahedral amorphous carbon thin films(2019-05-07) Grahn, Julius; Etula, Jarkko; Kemian tekniikan korkeakoulu; Koskinen, JariItem In Situ Bioprocessing of Bacterial Cellulose with Graphene: Percolation Network Formation, Kinetic Analysis with Physicochemical and Structural Properties Assessment(AMERICAN CHEMICAL SOCIETY, 2019-01-01) Dhar, Prodyut; Etula, Jarkko; Bankar, Sandip Balasaheb; Department of Chemistry and Materials Science; Department of Bioproducts and Biosystems; Physical Characteristics of Surfaces and Interfaces; Bioprocess engineeringThe understanding of microbial growth dynamics during in situ fermentation and production of bacterial cellulose (BC) with impressive properties mimicking artificial nacre, suitable for commodity applications remains fundamentally challenging. Fabrication of BC/graphene films through a single step in situ fermentation with improved properties provides a sustainable replacement to the conventional chemical-based modification using toxic compounds. This work reports the effect of reduced graphene oxide (RGO) on in situ fermentation kinetics and demonstrates the formation of percolated-network in BC/RGO nanostructures. The evaluation of kinetic parameters shows that the specific growth rate reaches optimal values at 3 wt % RGO loadings, with mixed growth associated BC production behavior. The two-dimensional graphene sheets uniformly dispersed into a three-dimensional matrix of BC nanofibers via hydrogen-bonded interactions along with in situ reductions of RGO sheets, as confirmed from spectroscopic studies. This study also demonstrates the presence of percolated network-like structures between BC fibers and RGO platelets, which resulted in the formation of nanostructures with exceptional mechanical robustness and electrical conductivity. The physicochemical and structural properties of fabricated BC/RGO films were found to significantly depend upon the RGO compositions as well as fermentation conditions. We envision that the proposed ecofriendly and scalable technology for the formation of BC/RGO films with excellent inherent properties and performance will attract great interest for its prospective applications in flexible electronics.Item Insights into corrosion in dye solar cells(Wiley-Blackwell, 2015) Miettunen, Kati; Etula, Jarkko; Saukkonen, Tapio; Jouttijärvi, Sami; Halme, Janne; Romu, Jyrki; Lund, Peter; Teknillisen fysiikan laitos; Department of Applied Physics; Perustieteiden korkeakoulu; School of ScienceThe main issue in using low cost metals in dye solar cells is the corrosion caused by the liquid electrolyte. Contrary to typical applications of metals, the adverse effects of corrosion in dye solar cells are related to irreversible depletion of charge carriers from the electrolyte rather than consumption of the metal itself. It is calculated that the penetration rate due to corrosion should not exceed 10−4 mpy (a couple of nanometers per year) to ensure device lifetime longer than 1 year. This is 10 000 times slower rate than what is considered to be a general benchmark value for very low corrosion rate in the field of corrosion science and has a major effect on how corrosion should be investigated in the case of dye solar cells. Different methods, their applicability, and limitations to investigate corrosion in dye solar cells are evaluated here. The issue with most techniques is that they can detect metals that are clearly corroding, but they have significant limitations in proving a metal stable. Our investigation shows that the most reliable information on corrosion is obtained from complete dye solar cells that are exposed to working conditions. A combination of color analysis of the electrolyte to such measurement is proposed as a means to extrapolate future performance of the cells and estimate potential lifetimes of the dye solar cells in regards to corrosion.Item Integrating Carbon Nanomaterials with Metals for Bio-sensing Applications(Humana Press, 2019-01-01) Sainio, Sami; Leppänen, Elli; Mynttinen, Elsi; Palomäki, Tommi; Wester, Niklas; Etula, Jarkko; Isoaho, Noora; Peltola, Emilia; Koehne, Jessica; Meyyappan, M.; Koskinen, Jari; Laurila, Tomi; Department of Chemistry and Materials Science; Department of Electrical Engineering and Automation; Physical Characteristics of Surfaces and Interfaces; Microsystems Technology; NASA Ames Research CenterAge structure in most developed countries is changing fast as the average lifespan is increasing significantly, calling for solutions to provide improved treatments for age-related neurological diseases and disorders. In order to address these problems, a reliable way of recording information about neurotransmitters from in vitro and in vivo applications is needed to better understand neurological diseases and disorders as well as currently used treatments. Likewise, recent developments in medicine, especially with the opioid crisis, are demanding a swift move to personalized medicine to administer patient needs rather than population-wide averages. In order to enable the so-called personalized medicine, it is necessary to be able to do measurements in vivo and in real time. These actions require sensitive and selective detection of different analytes from very demanding environments. Current state-of-the-art materials are unable to provide sensitive and selective detection of neurotransmitters as well as the required time resolution needed for drug molecules at a reasonable cost. To meet these challenges, we have utilized different metals to grow carbon nanomaterials and applied them for sensing applications showing that there are clear differences in their electrochemical properties based on the selected catalyst metal. Additionally, we have combined atomistic simulations to support optimizing materials for experiments and to gain further understanding of the atomistic level reactions between different analytes and the sensor surface. With carbon nanostructures grown from Ni and Al + Co + Fe hybrid, we can detect dopamine, ascorbic acid, and uric acid simultaneously. On the other hand, nanostructures grown from platinum provide a feasible platform for detection of H2O2 making them suitable candidates for enzymatic biosensors for detection of glutamate, for example. Tetrahedral amorphous carbon electrodes have an ability to detect morphine, paracetamol, tramadol, and O-desmethyltramadol. With carbon nanomaterial-based sensors, it is possible to reach metal-like properties in sensing applications using only a fraction of the metal as seed for the material growth. We have also seen that by using nanodiamonds as growth catalyst for carbon nanofibers, it is not possible to detect dopamine and ascorbic acid simultaneously, although the morphology of the resulting nanofibers is similar to the ones grown using Ni. This further indicates the importance of the metal selection for specific applications. However, Ni as a continuous layer or as separate islands does not provide adequate performance. Thus, it appears that metal nanoparticles combined with fiber-like morphology are needed for optimized sensor performance for neurotransmitter detection. This opens up a new research approach of application-specific nanomaterials, where carefully selected metals are integrated with carbon nanomaterials to match the needs of the sensing application in question.Item Ionic cross-linked polyvinyl alcohol tunes vitrification and cold-crystallization of sugar alcohol for long-term thermal energy storage(ROYAL SOC CHEMISTRY, 2020-08-21) Yazdani, Maryam Roza; Etula, Jarkko; Zimmerman, Julie Beth; Seppala, Ari; Department of Mechanical Engineering; Department of Chemistry and Materials Science; Energy Conversion; Physical Characteristics of Surfaces and Interfaces; Yale UniversityA new sustainable material for storing heat and releasing it on demand has been demonstrated for long-term latent heat storage (LLHS). The material consists of a high-latent-heat sugar alcohol phase change material (PCM) dispersed within ionic cross-linked matrices of polyvinyl alcohol (PVA). This material's unique property is the inhibition of undesired crystallization of the PCM during cooling due to the strong intermolecular interactions of the polymeric matrices, which leads to vitrification instead of crystallization. The release of latent heat can be controlled due to the PCM's stability below its cold-crystallization, which is triggered by reheating, as demonstrated by differential scanning calorimetry (DSC), optical microscopy (OM) and in situ X-ray diffraction (XRD). The addition of an ionic citrate cross-linker further tunes the vitrification and cold-crystallization properties of the PCM. Homogeneity and the presence of hydrogen bonding of the cold-crystalizing PCM (CC-PCM) were studied by scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX), Fourier transform infrared spectroscopy (FTIR) and XRD. Thermal stability was confirmed by thermogravimetric analysis (TGA) and 100 consecutive DSC heating-cooling cycles. The CC-PCM demonstrated high latent heat of fusion, up to 266 J g(-1), depending on the composition. As a super-adsorbent, PVA was able to swell and hold the liquid PCM resulting in form-stability and leakage-preventive properties above the melting temperature. Taken together, these results confirm that PVA matrices are promising for the thermal and structural stabilization of sugar alcohol PCMs, overcoming unexpected heat release and phase separation, and withstanding repeated melting-cooling cycles for LLHS.Item Multiwalled Carbon Nanotubes/Nanofibrillar Cellulose/Nafion Composite-Modified Tetrahedral Amorphous Carbon Electrodes for Selective Dopamine Detection(AMERICAN CHEMICAL SOCIETY, 2019-01-01) Durairaj, Vasuki; Wester, Niklas; Etula, Jarkko; Laurila, Tomi; Lehtonen, Janika; Rojas, Orlando J.; Pahimanolis, Nikolaos; Koskinen, Jari; Department of Chemistry and Materials Science; Department of Electrical Engineering and Automation; Department of Bioproducts and Biosystems; Physical Characteristics of Surfaces and Interfaces; Biohybrid Materials; Microsystems Technology; Bio-based Colloids and MaterialsWe introduce a composite membrane comprised of multiwalled carbon nanotubes (MWCNTs) dispersed in a matrix of sulfated nanofibrillar cellulose (SNFC) and Nafion. The high negative charge densities of the SNFC and Nafion ionomers enhance the cationic selectivity of the composite. The composite is characterized by scanning electron (SEM) and transmission electron (TEM) microscopies as well as Fourier transform infrared (FTIR) and Raman spectroscopies. Tetrahedral amorphous carbon (ta-C) electrodes modified with the composite are investigated as potential dopamine (DA) electrochemical sensors. The composite-modified electrodes show significant selectivity and sensitivity toward DA in the presence of ascorbic acid (AA) and uric acid (UA) in physiologically relevant concentrations. A linear dopamine detection range of 0.05-100 μM with detection limits of 65 nM in PBS and 107 nM in interferent solution was determined using 100 mV/s cyclic voltammetry (CV) measurements. These results highlight the potential of the composite membrane for in vivo detection of neurotransmitters.Item Nanodiamond embedded ta-C composite film by pulsed filtered vacuum arc deposition from a single target(2016-11) Iyer, Ajai; Etula, Jarkko; Ge, Yanling; Liu, Xuwen; Koskinen, Jari; Department of Materials Science and Engineering; Department of Chemistry and Materials ScienceDetonation Nanodiamonds (DNDs) are known to have sp3 core, sp2 shell, small size (few nm) and are gaining importance as multi-functional nanoparticles. Diverse methods have been used to form composites, containing DNDs embedded in conductive and dielectric matrices for various applications. Here we show a method, wherein DND-ta-C composite film, consisting of DNDs embedded in ta-C matrix have been co-deposited from the same cathode by pulsed filtered cathodic vacuum arc (p-FCVA) method. Transmission Electron Microscope (TEM) analysis of these films revel the presence of DNDs embedded in the matrix of amorphous carbon. Raman spectroscopy indicates that the presence of DNDs does not adversely affect the sp3 content of DND-ta-C composite film compared to ta-C film of same thickness. Nanoindentation and nanowear tests indicate that DND-ta-C composite films possess improved mechanical properties in comparison to ta-C films of similar thickness.Item Novel iron doped tetrahedral amorphous carbon films for electrochemical drug sensing applications(2017-10-03) Etula, Jarkko; Wester, Niklas; Kemian tekniikan korkeakoulu; Koskinen, JariItem Ohjausjärjestelmä metalliseostettujen FCVA-pinnoitteiden valmistamiseen(2014-12-30) Etula, Jarkko; Protopopova, Vera; Kemiantekniikan korkeakoulu; Forsén, OlofItem Peri-implanttimukoosan kiinnittyminen abutmenttiin sekä sähköisten ominaisuuksien muutokset perimukosiitin edetessä(2021-01-10) Palkama, Miila; Etula, Jarkko; Kemiantekniikan korkeakoulu; Aromaa, JariItem Rapid industrial scale synthesis of robust carbon nanotube network electrodes for electroanalysis(Elsevier Science, 2021-09-01) Leppänen, Elli; Etula, Jarkko; Engelhardt, Peter; Sainio, Sami; Jiang, Hua; Mikladal, Björn; Peltonen, Antti; Varjos, Ilkka; Laurila, Tomi; Microsystems Technology; Physical Characteristics of Surfaces and Interfaces; OtaNano; Stanford University; NanoMaterials; Canatu Oy; Aalto Nanofab; Department of Electrical Engineering and Automation; Department of Chemistry and Materials Science; Department of Applied PhysicsCarbon nanotubes (CNT) have been extensively investigated for various electroanalytical applications. As the properties of CNTs heavily depend on the fabrication conditions, it is expected that the electrochemical performance will also vary between CNTs from different processes. However, it is still not well known how the different synthesis conditions affect the electrochemical properties of CNTs. Thus, here we investigate the effect of synthesis rate on the physicochemical properties of CNT networks. Through extensive structural and chemical analysis, we show that the widely different synthesis rates, fast and slow, produced CNT networks with surprisingly similar properties. The only distinct differences were seen in the TEM tomography 3D reconstructions, where the faster synthesis produced a less dense network with larger bundle size. Moreover, minor changes were seen in the composition of Fe catalyst particles where the faster rate network mainly exhibited metallic Fe, whereas carbide and oxidized Fe phases were observed in the slower rate network. Although no changes were seen in the electron transfer kinetics with outer-sphere probes, it was clear that even these small changes in physicochemical properties affected the surface sensitive inner-sphere analytes. With slower synthesis rate i) sensitivity towards all analgesics, especially oxycodone, was enhanced and ii) oxidation potential of all analytes shifted to cathodic direction in comparison to higher synthesis rate. In the wider context, we propose that good quality CNTs can be fabricated rapidly in industrial scale for biosensing purposes. However, in electroanalytical applications properties of CNTs should be optimized for the analyte of interest.