Browsing by Author "Jiang, Hua"
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Item Amorphous carbon modulated-quantum dots NiO for efficient oxygen evolution in anion exchange membrane water electrolyzer(Elsevier BV, 2024-12-05) Jin, Benjin; Wang, Qian; Sainio, Jani; Saveleva, Viktoriia A.; Jiang, Hua; Shi, Junjie; Ali, Basit; Kallio, Antti Jussi; Huotari, Simo; Sundholm, Dage; Han, Nana; Kallio, Tanja; Department of Chemistry and Materials Science; Department of Applied Physics; OtaNano; Electrochemical Energy Conversion; Surface Science; NanoMaterials; Inorganic Materials Chemistry; University of Helsinki; European Synchrotron Radiation FacilityDeveloping efficient electrocatalysts of elements that are abundant on earth crust is crucial for green hydrogen generation technologies. In particular, the oxygen evolution reaction (OER) under alkaline plays a key role in anion exchange membrane (AEM) electrolyzer to produce green hydrogen but suffers from low kinetic. Herein, nickel oxide quantum dots with highly uniform size distribution on ultrathin amorphous carbon nanosheets (NiO dots/a-carbon) were successfully prepared by a one-step method. Introducing NiO quantum dots onto amorphous carbon modifies the local coordination environment of Ni promoting it into a higher valence state. Benefitting from the promoted Niδ+ (2<δ<3) and the strong connection between Ni and amorphous carbon though Ni-O-C and Ni-C bonds, NiO dots/a-carbon exhibits excellent activity and stability towards OER in 0.1 M KOH using the rotating disk electrode. Moreover, a challenging current density of 500 mA cm−2 is achieved at 1.7 V with a lab-scale AEM electrolyzer.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 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 ViennaMolecular 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.Item Blistering mechanisms of atomic-layer-deposited AlN and Al2O3 films(2017-10-02) Broas, Mikael; Jiang, Hua; Graff, Andreas; Sajavaara, Timo; Vuorinen, Vesa; Paulasto-Kröckel, Mervi; Department of Electrical Engineering and Automation; Department of Applied Physics; Aalto Nanofab; NanoMaterials; Electronics Integration and Reliability; Fraunhofer Institute for Microstructure of Materials and Systems; University of JyväskyläBlistering of protective, structural, and functional coatings is a reliability risk pestering films ranging from elemental to ceramic ones. The driving force behind blistering comes from either excess hydrogen at the film-substrate interface or stress-driven buckling. Contrary to the stress-driven mechanism, the hydrogen-initiated one is poorly understood. Recently, it was shown that in the bulk Al-Al2O3 system, the blistering is preceded by the formation of nano-sized cavities on the substrate. The stress-and hydrogen-driven mechanisms in atomic-layer-deposited (ALD) films are explored here. We clarify issues in the hydrogen-related mechanism via high-resolution microscopy and show that at least two distinct mechanisms can cause blistering in ALD films. Published by AIP Publishing.Item Catalyst Support Effect on the Activity and Durability of Magnetic Nanoparticles: Toward Design of Advanced Electrocatalyst for Full Water Splitting(2018-09-19) Davodi, Fatemeh; Mühlhausen, Elisabeth; Tavakkoli, Mohammad; Sainio, Jani; Jiang, Hua; Gökce, Bilal; Marzun, Galina; Kallio, Tanja; Department of Chemistry and Materials Science; Department of Applied Physics; Electrochemical Energy Conversion; Surface Science; NanoMaterials; University of Duisburg-EssenEarth-abundant element-based inorganic-organic hybrid materials are attractive alternatives for electrocatalyzing energy conversion reactions. Such material structures do not only increase the surface area and stability of metal nanoparticles (NPs) but also modify the electrocatalytic performance. Here, we introduce, for the first time, multiwall carbon nanotubes (MWNTs) functionalized with nitrogen-rich emeraldine salt (ES) (denoted as ES-MWNT) as a promising catalyst support to boost the electrocatalytic activity of magnetic maghemite (γ-Fe2O3) NPs. The latter component has been synthesized by a simple and upscalable one-step pulsed laser ablation method on Ni core forming the core-shell Niγ-Fe2O3 NPs. The catalyst (Niγ-Fe2O3/ES-MWNT) is formed via self-assembly as strong interaction between ES-MWNT and Niγ-Fe2O3 results in NPs' encapsulation in a thin C-N shell. We further show that Ni does not directly function as an active site in the electrocatalyst but it has a crucial role in synthesizing the maghemite shell. The strong interaction between the NPs and the support improves notably the NPs' catalytic activity toward oxygen evolution reaction (OER) in terms of both onset potential and current density, ranking it among the most active catalysts reported so far. Furthermore, this material shows a superior durability to most of the current excellent OER electrocatalysts as the activity, and the structure, remains almost intact after 5000 OER stability cycles. On further characterization, the same trend has been observed for hydrogen evolution reaction, the other half-reaction of water splitting.Item 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 ScienceControlling 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.Item 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 UniversityAlthough 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.Item Core-Selective Silver-Doping of Gold Nanoclusters by Surface-Bound Sulphates on Colloidal Templates: From Synthetic Mechanism to Relaxation Dynamics(WILEY-VCH VERLAG, 2023-01-04) Chandra, Sourov; Sciortino, Alice; Shandilya, Shruti; Fang, Lincan; Chen, Xi; Nonappa; Jiang, Hua; Johansson, Leena Sisko; Cannas, Marco; Ruokolainen, Janne; Ras, Robin H.A.; Messina, Fabrizio; Peng, Bo; Ikkala, Olli; Department of Applied Physics; Department of Bioproducts and Biosystems; Center of Excellence in Life-Inspired Hybrid Materials, LIBER; Molecular Materials; Computational Electronic Structure Theory; NanoMaterials; Bioproduct Chemistry; Soft Matter and Wetting; University of PalermoUltra-small luminescent gold nanoclusters (AuNCs) have gained substantial interest owing to their low photobleaching and high biocompatibility. While the substitution of silver for gold at the central core of AuNCs has shown significant augmentation of photoluminescence with enhanced photostability, selective replacement of the central atom by silver is, however, energetically inhibited. Herein, a new strategy for in situ site-selective Ag-doping exclusively at the central core of AuNCs using sulphated colloidal surfaces as the templates is presented. This approach exceedingly improves the photoluminescence quantum efficiency of AuNCs by eliminating nonradiative losses in the multi-step relaxation cascade populating the emissive state. Density functional theory predicts the mechanism of specific doping at the central core, endorsing the preferential bonding between Ag+ ions and sulphates in water. Finally, the generic nature of the templating concept to allow core-specific doping of nanoclusters is unraveled.Item Correlation between microstructure and surface chemistry of carbon nanofibers grown using different adhesive layers(Elsevier BV, 2023-03) Pande, Ishan; Sainio, Sami; Sainio, Jani; Liljeström, Ville; Jiang, Hua; Laurila, Tomi; Department of Chemistry and Materials Science; Department of Electrical Engineering and Automation; Department of Applied Physics; OtaNano; Microsystems Technology; Surface Science; NanoMaterialsCarbon nanofibers (CNFs) have applications in a wide range of technological and scientific fields. The connections between their micro- and macrostructure and observed performance are, however, currently lacking. This hinders the realization of their full potential. In this paper, we correlate the microstructure of CNFs grown on two types of substrates: (1) Si + 20 nm Ti + 20 nm Ni, and (2) Si + 80 nm Cr + 20 nm Ni, to their surface chemistry. We use transmission electron microscopy (TEM), supported by energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) analysis, to describe the morphology and structure of CNFs as well as the underlying interfacial layers. Then, we study the similarities and differences in chemistry of these two types of CNFs using X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) and correlate them with the observed structural features of the fibers. Vertically aligned, tip-type fiber growth was observed on both substrates. TEM micrographs show that the CNFs grown on the Cr + Ni substrates have a slightly distorted herringbone-like structure, whereas fibers grown on the Ti + Ni substrates have relatively ill-defined structure with basal planes pointing outwards. Consequently, the latter possess a richer surface chemistry, which is apparent from the wider peaks and more spectral features observed during XAS and XPS measurements. This analysis provides us with some of the missing structure-chemistry connections, which can subsequently be expanded towards including correlations of these features with observed performance of the CNFs in different applications. Ultimately, this enables us to tailor features of the CNFs for specific target fields.Item 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 ScienceMultiwalled 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.Item Designing of low Pt electrocatalyst through immobilization on metal@C support for efficient hydrogen evolution reaction in acidic media(Elsevier Science, 2021-09-01) Davodi, Fatemeh; Cilpa-Karhu, Geraldine; Sainio, Jani; Tavakkoli, Mohammad; Jiang, Hua; Mühlhausen, Elisabeth; Marzun, Galina; Gökce, Bilal; Laasonen, Kari; Kallio, Tanja; Department of Chemistry and Materials Science; Department of Applied Physics; Electrochemical Energy Conversion; Computational Chemistry; Surface Science; NanoMaterials; University of Duisburg-EssenNanoparticles comprising of transition metals encapsulated in an ultrathin graphene layer (NiFe@UTG) are utilized to anchor very low amount of finely dispersed pseudo-atomic Pt to function as a durable and active electrocatalyst (Pt/NiFe@UTG) for the hydrogen evolution reaction (HER) in acidic media. Our experiments show the vital role of the carbon shell thickness for efficient utilization of Pt. Furthermore, density functional theory calculations suggest that the metal-core has a crucial role in achieving promising electrocatalytic properties. The thin carbon shell allows the desired access of Pt atoms to the vicinity of the NiFe core while protecting the metallic core from oxidation in the harsh acidic media. In acidic media, the performance of this Pt/NiFe@UTG catalyst with 0.02 at% Pt is the same as that of commercial Pt/C (10 and 200 mV overpotential to reach 10 and 200 mA cm−2, respectively) with promising durability (5000 HER cycles). Our electrochemical characterization (cyclic voltammetry) shows no Pt specific peaks, indicating the existence of a very low Pt loading on the surface of the catalyst. Hence, this conductive core-shell catalyst support enables efficient utilization of Pt for electrocatalysis.Item Direct observation of nanowire growth and decomposition(2017-12-01) Rackauskas, Simas; Shandakov, Sergey D.; Jiang, Hua; Wagner, Jakob B.; Nasibulin, Albert G.; Department of Applied Physics; NanoMaterials; Kemerovo State University; Technical University of DenmarkFundamental concepts of the crystal formation suggest that the growth and decomposition are determined by simultaneous embedding and removal of the atoms. Apparently, by changing the crystal formation conditions one can switch the regimes from the growth to decomposition. To the best of our knowledge, so far this has been only postulated, but never observed at the atomic level. By means of in situ environmental transmission electron microscopy we monitored and examined the atomic layer transformation at the conditions of the crystal growth and its decomposition using CuO nanowires selected as a model object. The atomic layer growth/decomposition was studied by varying an O2 partial pressure. Three distinct regimes of the atomic layer evolution were experimentally observed: growth, transition and decomposition. The transition regime, at which atomic layer growth/decomposition switch takes place, is characterised by random nucleation of the atomic layers on the growing {111} surface. The decomposition starts on the side of the nanowire by removing the atomic layers without altering the overall crystal structure, which besides the fundamental importance offers new possibilities for the nanowire manipulation. Understanding of the crystal growth kinetics and nucleation at the atomic level is essential for the precise control of 1D crystal formation.Item 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; NanoMaterialsIn 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.Item 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 UniversityThe 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.Item Effect of atomic layer deposited zinc promoter on the activity of copper-on-zirconia catalysts in the hydrogenation of carbon dioxide to methanol(Elsevier BV, 2023-02) Arandia, Aitor; Yim, Jihong; Warraich, Hassaan; Leppäkangas, Emilia; Bes, René; Lempelto, Aku; Gell, Lars; Jiang, Hua; Meinander, Kristoffer; Viinikainen, Tiia; Huotari, Simo; Honkala, Karoliina; Puurunen, Riikka L.; Department of Chemical and Metallurgical Engineering; Department of Applied Physics; OtaNano; Department of Bioproducts and Biosystems; Catalysis; NanoMaterials; Department of Chemical and Metallurgical Engineering; University of Jyväskylä; University of Helsinki; Helsinki Institute of PhysicsThe development of active catalysts for carbon dioxide (CO2) hydrogenation to methanol is intimately related to the creation of effective metal-oxide interfaces. In this work, we investigated how the order of addition of copper and zinc on zirconia influences the catalytic properties, the catalytic activity and selectivity toward methanol. Regarding the carbon dioxide conversion and methanol production, the catalysts on which the promoter (zinc) was atomically deposited after copper impregnation (i.e., ZnO/Cu/ZrO2 and ZnO/Cu/ZnO/ZrO2) were superior catalysts compared to the reverse copper-after-zinc catalyst (Cu/ZnO/ZrO2). Temperature-programmed experiments and in situ diffuse reflectance infrared Fourier transform-spectroscopy (DRIFTS) experiments allowed us to elucidate the benefits of the zinc-after-copper pair to store CO2 as carbonate species and further convert them into formate species, key intermediates in the formation of methanol. This research provides insights into the potential of atomic layer deposition in the development of tailored heterogeneous catalysts for efficient CO2 valorization to methanol.Item Effect of Electrochemical Oxidation on Physicochemical Properties of Fe-Containing Single-Walled Carbon Nanotubes(John Wiley and Sons Ltd, 2020-10-01) Leppänen, Elli; Sainio, Sami; Jiang, Hua; Mikladal, Bjørn; Varjos, Ilkka; Laurila, Tomi; Department of Electrical Engineering and Automation; Department of Applied Physics; Microsystems Technology; NanoMaterials; Canatu Oy; SLAC National Accelerator LaboratoryMetal catalysts are necessary for fabricating carbon nanotubes, but are often considered impurities in the end products, and arduous steps are used to remove catalyst residues from the nanotube structure. However, as metals can be electrocatalytic, instead of removing them we can utilize their role in detection of analgesics. Herein, we study the physicochemical properties of Fe-containing single-walled carbon nanotubes (SWCNTs), and the effect of simple oxidative pretreatment on them. We show that a gentle anodic pretreatment i) increased the amount of oxidized Fe nanoparticles, most likely exhibiting phases Fe3O4 and Fe2O3 and ii) effectively removed disordered carbonaceous material from SWCNT bundles surfaces. Pretreatment had only a marginal effect on sensitivity towards analgesics. However, interestingly, selectivity of Fe-SWCNTs towards paracetamol and morphine could be modified with pretreatment. Through this kind of in-depth investigation, we can, to a certain extent, correlate various material properties of SWCNTs with the observed electrochemical performance. This approach allows us to evaluate what factors in SWCNTs truly affect the electrochemical detection of biomolecules.Item Effect of etchant gases on the structure and properties of carbon nanofibers(Elsevier BV, 2024-04) Pande, Ishan; Pascual, Laura Ferrer; Kousar, Ayesha; Sainio, Jani; Jiang, Hua; Laurila, Tomi; Department of Electrical Engineering and Automation; Department of Applied Physics; OtaNano; Microsystems Technology; Surface Science; NanoMaterialsThe utilization of plasma-enhanced chemical vapor deposition (PECVD) for carbon nanofiber (CNF) growth using NH3 as the etchant gas has been extensively documented. Notably, NH3 serves a dual role by etching excess carbon and providing N heteroatoms. Most studies neglect to address this phenomenon, despite the well-known impact of N-doping on CNF properties. Furthermore, NH3 exhibits specific interactions with C2H2—it not only etches excess carbon, but also suppresses the dissociation of C2H2. The implications of this phenomenon on CNF micro- and macroscale morphology have not been comprehensively investigated. To elucidate the influence of etchant gases on CNF structure and properties, we fabricated two types of CNFs - N-doped CNFs (N-CNF) and undoped CNFs (U-CNF). Both were grown on identical substrates using the same carbon source (C2H2) but different etchants (NH3 and H2). Their microstructure and surface chemistry were analyzed using transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). Electrochemical properties were investigated using cyclic voltammetry (CV). U-CNFs were found to have a larger population density and a more disordered structure than N-CNFs. N-doping was confirmed in N-CNFs using XPS analysis, which also revealed differences in relative amounts of sp2 C and O functional groups. U-CNFs exhibited distinct electrochemical properties, including smaller pseudocapacitance, larger potential window, slower outer sphere redox (OSR) kinetics, and diminished dopamine sensitivity. Electrochemical differences were rationalized based on CNF structure and surface chemistry, which, in turn, were attributed to how different etchant gases influence the PECVD process.Item An efficient approach toward production of near-zigzag single-chirality carbon nanotubes(American Association for the Advancement of Science, 2024-04) Li, Yahan; Li, Linhai; Jiang, Hua; Qian, Liu; He, Maoshuai; Zhou, Duanliang; Jiang, Kaili; Liu, Huaping; Qin, Xiaofan; Gao, Yan; Wu, Qianru; Chi, Xinyan; Li, Zhibo; Zhang, Jin; Department of Applied Physics; OtaNano; NanoMaterials; Qingdao University of Science and Technology; CAS - Institute of Physics; Peking University; Tsinghua UniversitySynthesizing single-walled carbon nanotubes (SWCNTs) with a narrow chirality distribution is essential for obtaining pure chirality materials through postgrowth sorting techniques. Using carbon monoxide chemical vapor deposition, we devise a ruthenium (Ru) catalyst supported by silica for the bulk production of SWCNTs containing only a few (n, m) species. The result is attributed to the limited carbon dissociation on the supported Ru clusters, favoring the growth of only small-diameter SWCNTs at comparable growth rates. The resulting materials expedite high-purity single chirality separation using gel chromatography, leading to unprecedented yields of 3.5% for (9, 1) and 5.2% for (9, 2) nanotubes, which surpass those separated from HiPco SWCNTs by two orders of magnitude. This work sheds light on the large-quantity synthesis of SWCNTs with enriched species beyond near-armchair ones for their high-yield separation.Item Electrochemical Detection of Oxycodone and Its Main Metabolites with Nafion-Coated Single-Walled Carbon Nanotube Electrodes(AMERICAN CHEMICAL SOCIETY, 2020-05-15) Mynttinen, Elsi; Wester, Niklas; Lilius, Tuomas; Kalso, Eija; Mikladal, Bjørn; Varjos, Ilkka; Sainio, Sami; Jiang, Hua; Kauppinen, Esko; Koskinen, Jari; Laurila, Tomi; Department of Electrical Engineering and Automation; Department of Chemistry and Materials Science; Department of Applied Physics; Microsystems Technology; Physical Characteristics of Surfaces and Interfaces; NanoMaterials; University of Helsinki; Canatu Oy; SLAC National Accelerator LaboratoryOxycodone is a strong opioid frequently used as an analgesic. Although proven efficacious in the management of moderate to severe acute pain and cancer pain, use of oxycodone imposes a risk of adverse effects such as addiction, overdose, and death. Fast and accurate determination of oxycodone blood concentration would enable personalized dosing and monitoring of the analgesic as well as quick diagnostics of possible overdose in emergency care. However, in addition to the parent drug, several metabolites are always present in the blood after a dose of oxycodone, and to date, there is no electrochemical data available on any of these metabolites. In this paper, a single-walled carbon nanotube (SWCNT) electrode and a Nafion-coated SWCNT electrode were used, for the first time, to study the electrochemical behavior of oxycodone and its two main metabolites, noroxycodone and oxymorphone. Both electrode types could selectively detect oxycodone in the presence of noroxycodone and oxymorphone. However, we have previously shown that addition of a Nafion coating on top of the SWCNT electrode is essential for direct measurements in complex biological matrices. Thus, the Nafion/SWCNT electrode was further characterized and used for measuring clinically relevant concentrations of oxycodone in buffer solution. The limit of detection for oxycodone with the Nafion/SWCNT sensor was 85 nM, and the linear range was 0.5–10 μM in buffer solution. This study shows that the fabricated Nafion/SWCNT sensor has potential to be applied in clinical concentration measurements.Item GaAs nanowires grown on Al-doped ZnO buffer layer(2013) Haggren, Tuomas; Pyymaki Perros, Alexander; Dhaka, Veer; Huhtio, Teppo; Jussila, Henri; Jiang, Hua; Ruoho, Mikko; Kakko, Joona-Pekko; Kauppinen, Esko; Lipsanen, Harri; Department of Micro and Nanosciences; Department of Applied PhysicsWe report a pathway to grow GaAs nanowires on a variety of substrates using a combination of atomic layer deposition and metallo-organic vapor phase epitaxy (MOVPE). GaAs nanowires were grown via MOVPE at 430–540 °C on an atomic-layer-deposited Al:ZnO buffer layer. The resulting nanowires were affected only by the properties of the buffer layer, allowing nanowire growth on a number of substrates that withstand ∼400 °C. The growth occurred in two phases: initial in-plane growth and subsequent out-plane growth. The nanowires grown exhibited a strong photoluminescence signal both at room temperature and at 12 K. The 12 K photoluminescence peak was at 1.47 eV, which was attributed to Zn autodoping from the buffer layer. The crystal structure was zincblende plagued with either twin planes or diagonal defect planes, which were related to perturbations in the seed particle during the growth. The used method combines substrates with variable properties to nanowire growth on a transparent and conductive Al:ZnO buffer layer.
