Browsing by Author "Mustonen, Kimmo"

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  • Automation of WAP Gateway Testing
    (2002) Mustonen, Kimmo
     Helsinki University of Technology | Master's thesis
  • Puhe- ja lauluärsykkeiden luominen ja MEG-mittauksia
    (2004) Mustonen, Kimmo
     Helsinki University of Technology | Master's thesis
    Kiinnostus musiikin aivotutkimukseen on ollut kasvussa, sillä musiikin avulla voidaan tutkia aivojen järjestäytyneisyyttä. Musiikin aivotutkimus auttaa myös ymmärtämään puheeseen liittyviä aivotoimintoja paremmin. Tässä työssä on luotu suomen- ja ranskankieliset puhe- ja lauluärsykkeet MEG- menetelmällä tehtävää aivotutkimusta varten. Ärsykkeistä tehtiin lisäksi kaksi variaatiota. Ensimmäisessä poistettiin prosodiainformaatiota muuttamalla ärsykesignaalin perustaajuus vakioksi, toisessa poistettiin merkitysinformaatiota alipäästösuodattamalla formanttitaajuudet pois signaalista. Luoduista ärsykkeistä valittiin pilottitutkimukseen suomenkieliset ärsykkeet, ja niillä suoritettiin viisi MEG-mittausta aikuisilla ja kaksi vastasyntyneillä. Sekä aikuisilta että vastasyntyneiltä onnistuttiin mittaamaan kuuloaivokuoren ärsykkeisiin liittyvää toimintaa. Aikuisten vasteista mallinnettujen dipolien mukaan näyttää alustavasti siltä, että laululle vasteet ovat hieman puheen vasteita suurempia ja laulun prosessointi kestää pidempään kuin puheen. Aivopuoliskojen välillä ei näin pienellä koehenkilöjoukolla havaittu systemaattista eroa puhe- ja lauluärsykkeiden käsittelyyn liittyen. Tutkimuksessa saatiin mitattua kuuloaivokuoren toimintaa jatkuvalle puheelle ja laululle myös molemmilta tutkituilta vastasyntyneiltä. Kokonaisuutena voidaan todeta, että tutkimus osoittaa jatkuvien puhe- ja lauluärsykkeiden soveltuvan kuuloaivokuoren sähköisen toiminnan tutkimiseen. Tulos avaa uusia mahdollisuuksia elektro- ja magnetoenkefalografian käyttöön ja luonnollisempien koetilanteiden kautta aivojen toiminnan parempaan ymmärtämiseen.
  • Electron-Beam Manipulation of Silicon Impurities in Single-Walled Carbon Nanotubes
    (2019-01-01) Mustonen, Kimmo; Markevich, Alexander; Tripathi, Mukesh; Inani, Heena; Ding, Er Xiong; Hussain, Aqeel; Mangler, Clemens; Kauppinen, Esko I.; Kotakoski, Jani; Susi, Toma
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    The recent discovery that impurity atoms in crystals can be manipulated with focused electron irradiation has opened novel perspectives for top-down atomic engineering. These achievements have been enabled by advances not only in electron optics and microscope stability but also in the preparation of suitable materials with impurity elements incorporated via ion and electron-beam irradiation or chemical means. Here it is shown that silicon heteroatoms introduced via plasma irradiation into the lattice of single-walled carbon nanotubes (SWCNTs) can be manipulated using a focused 55–60 keV electron probe aimed at neighboring carbon sites. Moving the silicon atom mainly along the longitudinal axis of large 2.7 nm diameter tubes, more than 90 controlled lattice jumps are recorded and the relevant displacement cross sections are estimated. Molecular dynamics simulations show that even in 2 nm diameter SWCNTs, the threshold energies for out-of-plane dynamics are different than in graphene, and depend on the orientation of the silicon-carbon bond with respect to the electron beam as well as the local bonding of the displaced carbon atom and its neighbors. Atomic-level engineering of SWCNTs where the electron wave functions are more strictly confined than in 2D materials may enable the fabrication of tunable electronic resonators and other devices.
  • Ethylene assisted floating catalyst synthesis of single-walled carbon nanotubes with a spark discharge reactor
    (2014-12-27) Aapro, Markus
     Perustieteiden korkeakoulu | Bachelor's thesis
  • Highly efficient bilateral doping of single-walled carbon nanotubes
    (2021-04-07) Goldt, Anastasia E.; Zaremba, Orysia T.; Bulavskiy, Mikhail O.; Fedorov, Fedor S.; Larionov, Konstantin V.; Tsapenko, Alexey P.; Popov, Zakhar I.; Sorokin, Pavel; Anisimov, Anton S.; Inani, Heena; Kotakoski, Jani; Mustonen, Kimmo; Nasibulin, Albert G.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    A boost in the development of flexible and wearable electronics facilitates the design of new materials to be applied as transparent conducting films (TCFs). Although single-walled carbon nanotube (SWCNT) films are the most promising candidates for flexible TCFs, they still do not meet optoelectronic requirements demanded for their successful industrial integration. In this study, we proposed and thoroughly investigated a new approach that comprises simultaneous bilateral (outer and inner surface) SWCNT doping after their opening by thermal treatment at 400 °C under an ambient air atmosphere. Doping by a chloroauric acid (HAuCl4) ethanol solution allowed us to achieve the record value of equivalent sheet resistance of 31 ± 4 Ω sq-1 at a transmittance of 90% in the middle of the visible spectrum (550 nm). The strong p-doping was examined by open-circuit potential (OCP) measurements and confirmed by ab initio calculations demonstrating a downshift of the Fermi level of around 1 eV for the case of bilateral doping.
  • Hybrid Low-Dimensional Carbon Allotropes Formed in Gas Phase
    (2020-11-04) Ahmad, Saeed; Mustonen, Kimmo; McLean, Ben; Jiang, Hua; Zhang, Qiang; Hussain, Aqeel; Khan, Abu Taher; Ding, Er Xiong; Liao, Yongping; Wei, Nan; Monazam, Mohammad R.A.; Nasibulin, Albert G.; Kotakoski, Jani; Page, Alister J.; Kauppinen, Esko I.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Graphene, carbon nanotubes (CNTs) and fullerenes are the basic set of low-dimensional carbon allotropes. The latter two arise from the former by selective removal and addition of carbon atoms. Nevertheless, given their morphological disparities, the production of each is typically devised from entirely different starting points. Here, it is demonstrated that all three allotropes can nucleate from (pseudo-)spherical, nanometer-sized transition metal clusters in a gas-suspension when the chemical conditions are favorable. The experimental results indicate that graphitic carbon embryos nucleate on the catalyst particles and sometimes transform into 2D graphene flakes through chain polymerization of carbon fragments forming in the surround gas atmosphere. It is further shown that hydrogenation reactions play an essential role by stabilizing the emerging flakes by mitigating the pentagon and heptagon defects that lead into evolution of fulleroids. Ab initio molecular dynamics simulations show that the ratio of hydrogen to carbon in the reaction is a key growth parameter. Since structural formation takes place in a gas-suspension, graphene accompanied by fullerenes and single-walled CNTs can be deposited on any surface at ambient temperature with arbitrary layer thicknesses. This provides a direct route for the production and deposition of graphene-based hybrid thin films for various applications.
  • Hydrogen evolution in alkaline medium on intratube and surface decorated PtRu catalyst
    (2022-10-15) Ali, Farhan S. M.; Arevalo, Ryan Lacdao; Vandichel, Matthias; Speck, Florian; Rautama, Eeva-Leena; Jiang, Hua; Sorsa, Olli; Mustonen, Kimmo; Cherevko, Serhiy; Kallio, Tanja
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    For anion exchange membrane (AEM) electrolysis, challenges include finding an optimal catalyst for hydrogen evolution reaction (HER), as the noble metals are scarce while non-noble metals are inferior. Here, the noble metal amount is reduced in a straightforward solution synthesis which produces Pt-Ru surface nanoparticles and unique intratube nanowires decorated on single walled carbon nanotubes (SWNT). In half-cell tests, 5 wtPtRu-% Pt-Ru SWNT demonstrates stable 10 mA cm−2 HER current at 46 mV overpotential and outperforms commercial electrocatalysts. When integrated in an AEM electrolyser, a high current density of 500 mA cm−2 at a low voltage of 1.72 V is achieved with 34 µg cm−2 metal loading. First-principles calculations reveal that both the Pt-Ru alloy nanoparticle and intratube nanowires promote near optimal H* binding energy, thereby releasing the H2 faster. Thus, our approach yields an active low metal loading alkaline HER catalyst without sacrificing the performance in an AEM electrolyser.
  • Influence of the diameter of single-walled carbon nanotube bundles on the optoelectronic performance of dry-deposited thin films
    (2012) Mustonen, Kimmo; Susi, Toma; Kaskela, Antti; Laiho, Patrik; Tian, Ying; Nasibulin, Albert G.; Kauppinen, Esko I.
     School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    The optoelectronic performance of thin films of single-walled carbon nanotubes (SWCNTs) was studied with respect to the properties of both individual nanotubes and their bundles. The SWCNTs were synthesized in a hot wire generator aerosol reactor, collected by gas filtration and dry-transferred onto various substrates. By thus completely avoiding liquid dispersion steps, we were able to avoid any artifacts from residual surfactants or sonication. We found that bundle lengths determined the thin-film performance, as would be expected for highly resistive bundle–bundle junctions. However, we found no evidence that contact resistances were affected by the bundle diameters, although they did play a secondary role by simply affecting the absorption. The individual SWCNT diameters and their graphitization level as gauged by the Raman D band intensity did not show any clear correlation with the overall performance.
  • Kiimingin kunnan kyläkeskusten kehittämissuunnitelma
    (1977) Mustonen, Kimmo
     Helsinki University of Technology | Master's thesis
  • Large-Diameter Carbon Nanotube Transparent Conductor Overcoming Performance–Yield Tradeoff
    (2022-03-09) Zhang, Qiang; Nam, Jeong Seok; Han, Jiye; Datta, Sukanta; Wei, Nan; Ding, Er Xiong; Hussain, Aqeel; Ahmad, Saeed; Skakalova, Viera; Khan, Abu Taher; Liao, Yong Ping; Tavakkoli, Mohammad; Peng, Bo; Mustonen, Kimmo; Kim, Dawoon; Chung, In; Maruyama, Shigeo; Jiang, Hua; Jeon, Il; Kauppinen, Esko I.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    The floating catalyst chemical vapor deposition (FCCVD) method for producing single-walled carbon nanotubes (SWNTs) has demonstrated great potential in transparent conductive film (TCF) application. In FCCVD, reducing the concentration of carbon nanotubes (CNTs) is a well-agreed method of improving the conductivity of SWNT TCF, achieved by producing thinner and longer CNT bundles. However, this method decreases the yield dramatically, which has persisted throughout the TCF development. Here, the production of large-diameter double-walled CNT (DWNT) TCFs via FCCVD is reported, which overcomes the tradeoff between performance and yield. These TCFs of DWNTs with an average diameter of approximate to 4 nm have a low sheet resistance of 35 omega sq(-1) at 90% transmittance. The conductivity here aligns with the best-performing SWNT TCFs reported to date, showing a production yield greater than two orders of magnitude. The main factor contributing to the high performance and yield is considered to be the large tube diameter, which greatly improves the yield threshold of CNT bundling and leads to long tube length and unique junctions broadening. Moreover, the application of DWNT TCFs in perovskite solar cells exhibits a power conversion efficiency of 17.4%, which has not been reported yet in indium-free CNT-based solar cells.
  • Mesoporous Single-Atom-Doped Graphene-Carbon Nanotube Hybrid: Synthesis and Tunable Electrocatalytic Activity for Oxygen Evolution and Reduction Reactions
    (2020-04-17) Tavakkoli, Mohammad; Flahaut, Emmanuel; Peljo, Pekka; Sainio, Jani; Davodi, Fatemeh; Lobiak, Egor V.; Mustonen, Kimmo; Kauppinen, Esko I.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Mesoporous heteroatom-doped carbon-based nanomaterials are very promising as catalysts for electrochemical energy conversion and storage. We have developed a one-step catalytic chemical vapor deposition method to grow a highly graphitized graphene nanoflake (GF)-carbon nanotube (CNT) hybrid material doped simultaneously with single atoms of N, Co, and Mo (N-Co-Mo-GF/CNT). This high-surface-area material has a mesoporous structure, which facilitates oxygen mass transfer within the catalyst film, and exhibits a high electrocatalytic activity and stability in oxygen reduction and evolution reactions (ORR and OER) in alkaline media. We have shown that in this metal (M)-N-C catalyst, M (Co, Mo)-C centers are the main sites responsible for OER, while, for ORR, both M and N-C centers synergistically serve as the active sites. We systematically investigated tuning of the ORR and OER activity of the porous catalyst depending on the choice of the underlying substrate. The ORR kinetic current and OER activity for N-Co-Mo-GF/CNT were significantly enhanced when the catalyst was deposited onto a Ni substrate, resulting in an advanced electrocatalytic performance compared to the best bifunctional ORR/OER catalysts reported so far. Using a developed scanning electrochemical microscopy analysis method, we demonstrated that the higher OER reactivity on Ni was attributable to the formation of underlying catalyst/Ni interfacial sites, which are accessible due to the porous, electrolyte-permeable structure of the catalyst.
  • Novel nanoparticle production method
    (2013-09-02) Inkinen, Sampo
     Perustieteiden korkeakoulu | Bachelor's thesis
  • On the limit of single-walled carbon nanotube random network conductivity
    (2015) Mustonen, Kimmo
     School of Science | Doctoral dissertation (article-based)
    Single-walled carbon nanotubes (SWCNTs) are one of the most interesting emerging materials for practical applications. As transparent conductive films (TCFs) and thin film transistors (TFTs) they provide prospects for both improved flexibility and conductivity over established metal oxide and silicon-based materials. Technologically crucial performance optimizations, however, require a coherent picture how the SWCNT network properties, specifically sheet conductance, absorbance and spatial uniformity, emerge from individual nanotubes. Here, a new kind of floating catalyst approach based on a spark discharge generator (SDG) is presented for the synthesis of predominantly individual SWCNTs in the gas phase. In this process, Brownian diffusion is identified as the major cause behind nanotube gas-phase aggregation (bundling). This can be avoided by limiting the SWCNT number concentration down to ~105 cm-3, yielding a high fraction of 60-80 % of individual tubes on substrates. For mostly individual 3-4 μm long SWCNTs, the observed aggregation rate matches a mobility diameter of 20 nm. The synthesized tubes exhibit a pre-eminence of near-armchair chiralities, up to 70 % having chiral angles ≥20°, with an unconventionally high fraction of semiconducting tube species, 80 %, at a growth temperature of 750 °C. Furthermore, by optical and electrical characterization of networks fabricated from individual tubes and small diameter bundles, unambiguous experimental evidence of the detrimental nature of SWCNT bundling on TCF performance is found. The performance loss is explained to be due to gratuitous absorbance in large diameter bundles, without a compensating conductivity gain. An absorbance-conductance model is presented, assuming that the Beer-Lambert law applies independent of the TCFs’ internal geometry, whereas at room temperature a significant charge carrier transport is allowed only through metallic-metallic tube junctions. The maximum network conductivity is expected where the nanotube lengthwise resistances between the junctions become as large as the junction resistances, providing the ultimate performance limit for metallicity-mixed SWCNT networks of 80 Ω/☐ at 90 % transparency. For all-metallic and doped networks, the limit is expected at 25 Ω/☐. In correspondence, nitric acid treated TCFs fabricated using individual 4 μm long SWCNTs are demonstrated with a sheet resistance of 63 Ω/☐ at 90 % transparency. Finally, random-network TFTs fabricated from the individual tubes approach the uniformity of ideal computer-simulated systems. The TFTs exhibit On/Off current ratios between 104 and 106 and simultaneous charge carrier mobilities up to 100 cm2 V-1s-1 combined with a fabrication yield of >99%. The normalized On-current shows standard deviation of ~25%, showing unprecedently high uniformity for random network TFTs.
  • Photon-Pair Generation with a 100 nm Thick Carbon Nanotube Film
    (2017-06-27) Lee, Kim Fook; Tian, Ying; Yang, He; Mustonen, Kimmo; Martinez, Amos; Dai, Qing; Kauppinen, Esko I.; Malowicki, John; Kumar, Prem; Sun, Zhipei
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Nonlinear optics based on bulk materials is the current technique of choice for quantum-state generation and information processing. Scaling of nonlinear optical quantum devices is of significant interest to enable quantum devices with high performance. However, it is challenging to scale the nonlinear optical devices down to the nanoscale dimension due to relatively small nonlinear optical response of traditional bulk materials. Here, correlated photon pairs are generated in the nanometer scale using a nonlinear optical device for the first time. The approach uses spontaneous four-wave mixing in a carbon nanotube film with extremely large Kerr-nonlinearity (≈100 000 times larger than that of the widely used silica), which is achieved through careful control of the tube diameter during the carbon nanotube growth. Photon pairs with a coincidence to accidental ratio of 18 at the telecom wavelength of 1.5 μm are generated at room temperature in a ≈100 nm thick carbon nanotube film device, i.e., 1000 times thinner than the smallest existing devices. These results are promising for future integrated nonlinear quantum devices (e.g., quantum emission and processing devices).
  • Scalable growth of single-walled carbon nanotubes with a highly uniform structure
    (2020-06-21) Hussain, Aqeel; Ding, Er Xiong; McLean, Ben; Mustonen, Kimmo; Ahmad, Saeed; Tavakkoli, Mohammad; Page, Alister J.; Zhang, Qiang; Kotakoski, Jani; Kauppinen, Esko I.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Here, a scalable floating catalyst chemical vapor deposition (FCCVD) method is developed for the production of single-walled carbon nanotubes (SWCNTs) with a controlled structure. For the first time, water is used as the growth promoter in the FCCVD process to modulate the growth of SWCNTs. At an optimum water concentration of ca. 115 ppm, the water-assisted FCCVD process synthesizes SWCNTs with a significantly narrow chirality distribution. In particular, the proportion of (9,8) and (8,7) semiconducting tubes was dramatically enhanced to 45% with 27% of the (9,8) tube in the end product. This is attributed to the changes in both the SWCNT diameter and the chiral angle. The experiment results and accurate quantum chemical molecular dynamics simulations show that the addition of water affects the nucleation and the size distribution of nanoparticle catalysts, thus resulting in the growth of SWCNTs with a highly uniform structure. This direct and continuous water-assisted FCCVD provides the possibility for the mass production of high-quality SWCNTs with a controlled structure.
  • Silicon Substitution in Nanotubes and Graphene via Intermittent Vacancies
    (2019-05-23) Inani, Heena; Mustonen, Kimmo; Markevich, Alexander; Ding, Er Xiong; Tripathi, Mukesh; Hussain, Aqeel; Mangler, Clemens; Kauppinen, Esko I.; Susi, Toma; Kotakoski, Jani
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    The chemical and electrical properties of single-walled carbon nanotubes (SWCNTs) and graphene can be modified by the presence of covalently bound impurities. Although this can be achieved by introducing chemical additives during synthesis, it often hinders growth and leads to limited crystallite size and quality. Here, through the simultaneous formation of vacancies with low-energy argon plasma and the thermal activation of adatom diffusion by laser irradiation, silicon impurities are incorporated into the lattice of both materials. After an exposure of ∼1 ion/nm2, we find Si-substitution densities of 0.15 nm-2 in graphene and 0.05 nm-2 in nanotubes, as revealed by atomically resolved scanning transmission electron microscopy. In good agreement with predictions of Ar irradiation effects in SWCNTs, we find Si incorporated in both mono- and divacancies, with ∼2/3 being of the first type. Controlled inclusion of impurities in the quasi-1D and -2D carbon lattices may prove useful for applications such as gas sensing, and a similar approach might also be used to substitute other elements with migration barriers lower than that of carbon.