Influence of the diameter of single-walled carbon nanotube bundles on the optoelectronic performance of dry-deposited thin films

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.Peer reviewe

Characterization of sedimentary depositional environments for land use and urban planning in Espoo, Finland

AbstractThe capital region of Finland is growing rapidly and into areas with challenging construction conditions such as deep fine-grained sediments. In the coastal city of Espoo, present land use is mainly focused in the southern and central parts, which were submerged by the Baltic Sea during the early and mid-Holocene. These areas have experienced saline and brackish water phases during the history of the Baltic Sea Basin. The deposition environments of the presently studied onshore areas are an analogue for the present day offshore Baltic Sea sedimentation settings for fine-grained material. The results from Baltic Sea studies have demonstrated that the seabed topography has a significant role in the deposition of sediments and their properties. In this study, paleotopographic models were created for the ancient Baltic Sea Basin in the Espoo area 1) after deglaciation and 2) during the Litorina transgression and classified into bathymetric (terrain) zones and structures. Topographic classification was combined with the water depth of the Litorina stage, the thickness of fine-grained deposits and wind fetch to establish the overall characteristics of sedimentary environments in the coastal area. Fine-grained sediments can be found mainly in depressions that are classified here as broad, narrow or local. The study found the most challenging environments for construction purposes in sheltered narrow depressions that contain thick layers of fine-grained sediments deposited during the Litorina transgression. These are mainly located in the southern and central parts of Espoo. Minor deep canyons were also found in the northern parts of Espoo. This study provides new prior knowledge for urban planning and construction design in Espoo. The methodology could be applied to other Baltic Sea coastal cities and areas with fine-grained sediments.</p

Conditions for forming composite carbon nanotube-diamond like carbon material that retain the good properties of both materials

Peer reviewe

Understanding the impact of brain disorders: Towards a 'horizontal epidemiology' of psychosocial difficulties and their determinants

Objective To test the hypothesis of ‘horizontal epidemiology’, i.e. that psychosocial difficulties (PSDs), such as sleep disturbances, emotional instability and difficulties in personal interactions, and their environmental determinants are experienced in common across neurological and psychiatric disorders, together called brain disorders. Study Design A multi-method study involving systematic literature reviews, content analysis of patientreported outcomes and outcome instruments, clinical input and a qualitative study was carried out to generate a pool of PSD and environmental determinants relevant for nine different brain disorders, namely epilepsy, migraine, multiple sclerosis, Parkinson’s disease, stroke, dementia, depression, schizophrenia and substance dependency. Information from these sources was harmonized and compiled, and after feedback from external experts, a data collection protocol including PSD and determinants common across these nine disorders was developed. This protocol was implemented as an interview in a cross-sectional Objective To test the hypothesis of ‘horizontal epidemiology’, i.e. that psychosocial difficulties (PSDs), such as sleep disturbances, emotional instability and difficulties in personal interactions, and their environmental determinants are experienced in common across neurological and psychiatric disorders, together called brain disorders. Study Design A multi-method study involving systematic literature reviews, content analysis of patientreported outcomes and outcome instruments, clinical input and a qualitative study was carried out to generate a pool of PSD and environmental determinants relevant for nine different brain disorders, namely epilepsy, migraine, multiple sclerosis, Parkinson’s disease, stroke, dementia, depression, schizophrenia and substance dependency. Information from these sources was harmonized and compiled, and after feedback from external experts, a data collection protocol including PSD and determinants common across these nine disorders was developed. This protocol was implemented as an interview in a cross-sectionalThe PARADISE project is supported by the Coordination Theme 1 (Health) of the European Community’s FP7, Grant Agreement No. HEALTHF2- 2009-241572

Läpinäkyvät, johtavat ja joustavat yksiseinäiset hiilinanoputkikalvot

Single-walled carbon nanotube (SWCNT) networks have a large application potential for future electronics as transparent conductive films. SWCNT networks (SWCNT-N) offer improved flexibility when compared to the current industry standard transparent conductive films (TCF), an example of which is indium tin oxide (ITO). SWCNTs can be synthesised from abundant raw materials, whereas indium supply is limited and has been a target of aggressive trade policies, thus increasing supply risks and price volatility. In order to make the SWCNT-Ns suitable for industrial applications, their performance must be made competitive with ITO and other TCF materials, whilst their manufacturing costs have to be minimised. Understanding the performance limiting factors is important when it comes to the development of high performance SWCNT networks. The results presented here show that the bundle length has a major impact on the electrical performance of SWCNT networks. Optimisation of SWCNT growth conditions in aerosol-CVD reactors used for SWCNT synthesis led to an increase in SWCNT bundle length from 1.3 μm to 9.4 μm. Bundle diameter distributions were found to overlap, with mean bundle diameter measuring approximately 10 nm, and mean SWCNT diameters ranging from 1.4 to 1.7 nm. The increased bundle length led to a reduction in the number of the highly resistive bundle-bundle contacts and to improved performance. When the SWCNT-TCFs were chemically doped by nitric acid, sheet resistance was reduced down to 84 Ω/sq. at 90% transparency, thus making the SWCNT TCFs competitive with ITO on polymer films. The intertube and interbundle contact resistances together with the effect of nitric acid treatment were studied by using conductive atomic force microscopy. The contact resistance values of pristine junctions were within the range of 29 kΩ - 532 kΩ for contacts between individual tubes and small bundles with less than 5 nm diameter. The contact resistance decreased with increasing tube or bundle diameter. Contact morphology had a major impact on the contact resistance values as X- contacts exhibited higher mean contact resistance of 180 kΩ, while the Y-contacts had mean contact resistance of 60 kΩ. When the contacts were exposed to strong nitric acid, the mean contact resistance was reduced by a factor of 3, although the length resistivity remained largely unchanged at around 8 kΩ/μm. The results indicate that the contact morphology and the diameter of contacting SWCNTs and bundles had a significant impact on the electrical transport across the contacts and that the nitric acid treatment mainly affected the network performance by modulating the contacts and reducing their contact resistances. Furthermore, a novel room-temperature press transfer technique was developed. This dry, ambient temperature deposition method allowed for the rapid and direct deposition of variable thickness SWCNT networks to a wide range of substrates, from flexible polymers to glass, silicon and metals. The developed process eliminates harsh and detrimental purification and dispersion steps, thus maintaining the high intrinsic performance of SWCNTs. Fabrication of novel freestanding SWCNT networks was also demonstrated. The freestanding SWCNT networks can be used for a wide range of novel applications. The aerosol-CVD synthesized SWCNTs were also demonstrated as flexible counter-electrodes in dye-sensitised solar cells. The SWCNT-network was combined with electrochemically deposited PEDOT, reaching comparable performance with standard platinum catalyst with energy conversion efficiencies of up to 4%. Fabrication and properties of hybrid materials consisting of SWCNT networks coated with amorphous carbon deposited by low energy plasma were studied. The carbon coating improved the mechanical durability of SWCNT films under nanoindentation and scratching.Yksiseinämäisillä hiilinanoputkilla on merkittävä sovelluspotentiaali tulevaisuuden elektroniikassa läpinäkyvänä johdemateriaalina. Nanoputkiverkot ovat merkittävästi tällä hetkellä käytössä olevia läpinäkyviä johdemateriaaleja, kuten indium-tinaoksidia, taipuisampia. Ne voidaan valmistaa laajasti saatavilla olevista raaka-aineista, kun taas hyödynnetyt indium-resurssit ovat voimakkaasti keskittyneet ja indium on ollut aggressiivisten vientirajoitusten kohteena, mikä puolestaan on lisännyt saatavuusriskejä ja aiheuttanut hinnanvaihteluita. Jotta hiilinanoputkiverkkoihin pohjautuvat materiaalit voivat kilpailla teollisissa sovelluksissa indium-tina-oksidin kanssa, niiden suorituskykyä on parannettava nykyisten teollisten materiaalien kanssa kilpailukykyiselle tasolle. Myös hiiliputkien valmistus ja prosessointimenetelmiä on kehitettävä, jotta madaltuvat tuotantokustannukset parantaisivat valmistuksen kannattavuutta. Hiilinanoputkiverkkojen suorituskyvyn parantamiseksi on tärkeää ymmärtää paremmin tärkeimpiä suorituskykyä rajoittavia tekijöitä. Tämän väitöskirjan tulokset osoittavat, että hiilinanoputkien muodostamien kimppujen pituus on erittäin merkittävä verkkojen suorituskykyyn vaikuttava tekijä. Optimoimalla aerosolipohjaisen synteesireaktorin reaktio-olosuhteet, onnistuttiin hiilinanoputkien kimppujen pituutta kasvattamaan 1.3 μm:stä 9.4 μm:iin. Kimppujen halkaisijajakaumat olivat eri kasvatusolosuhteissa päällekkäisiä, keskihalkaisijan ollessa noin 10 nm. Yksittäisten hiilinanoputkien halkaisijat olivat tyypillisesti 1.4 to 1.7 nm välillä. Pidempi kimppupituus vähentää korkean vastuksen omaavien kimppu-kimppu-liitosten lukumäärää ja pienentää näin verkon kokonaisvastusta. Kun pisimmät verkot altistettiin typpihappokäsitettelylle, onnistuttiin verkon pintavastus pienentämään tasolle 84 Ω/neliö 90 % valonläpäisyllä, tehden verkoista suorituskyvyltään kilpailukykyisiä polymeerikalvoille kasvatetun indium-tina- oksidipinnoitteen kanssa. Putkien ja kimppujen välisiä liitoksia sekä typpihappokäsittelyn vaikutusta tutkittiin käyttäen johtavaa atomivoimamikroskopiaa. Käsittelemättömien liitoksien liitosvastukset vaihtelivat 29 kΩ ja 532 kΩ välillä, pääosin yksittäisistä nanoputkista ja halkaisijaltaan pienistä, alle 5 nm kimpuista, koostuvalle näytepopulaatiolle. Liitosvastuksen havaittiin pienenevän kasvavan putki- ja kimppuhalkaisijan mukana. Liitoksen geometrialla havaittiin olevan merkittävä vaikutus liitosvastukseen ja X-tyyppiset liitokset omasivat keskimäärin 180 kΩ liitosvastuksen, kun taas Y-tyyppisten liitoksen keskimääräinen vastus oli 60 kΩ. Kun X-tyyppiset liitokset käsiteltiin voimakkaalla typpihapolla, liitosvastus pieneni tekijällä 3x, kun taas pituusvastus pysyi lähes vakiona noin 8 kΩ/μm tasolla. Tulosten mukaan typpihappokäsittely parantaa verkon suorituskykyä lähinnä pienentämällä liitosvastuksia. Lisäksi tässä väitöskirjassa tutkittiin useita hiilinanoputkiverkkojen sovellusalueita ja niiden toteuttamisessa tarvittavia tekniikoita. Osana työtä kehitettiin uusi, huoneenlämpötilassa toimiva valmistusmenetelmä hiiliputkiverkkojen siirtämiseen keräyssuodattimelta sovelluksissa tarvittaville pohjamateriaaleille. Menetelmän osoitettiin mahdollistavan eri paksuuksien hiilinanoputkiverkkojen nopea ja suoraviivainen siirto laajalle joukolle pohjamateriaaleja, mukaan lukien joustavat polymeerit, lasi, pii sekä metallikalvot. Menetelmän merkittävä etu on, että se poistaa tarpeen haitallisille ja aikaa vieville puhdistus- ja dispersointikäsittelyille, joita tarvitaan muiden hiilinanoputkien keräys- ja prosessointimenetelmien kanssa ja mahdollistaa siten hiiliputkien korkean ominaisjohtavuuden hyödyntämisen. Osana väitöskirjaa valmistettiin myös uudenlaisia itsekantavia nanoputkiverkkoja. Hiilinanoputkiverkkoja käytettiin lisäksi myös joustavina väriaineherkistetyn aurinkokennon vastaelektrodimateriaalina. Yhdistämällä hiilinanoputkiverkko elektropolymerisoidun PEDOT-polymeerin kanssa saavutettiin standardia platinakatalyyttiä vastaava suorituskyky, parhaimmillaan 4 % energiakonversiotehokkuudella. Viimeisenä aihealueena tutkittiin hiilinanoputkien ja amorfisten plasmakasvatuksella valmistettujen hiilipinnoitteiden yhdistämistä hybridirakenteeksi. Hiilipinnoitteen käyttö paransi merkittävästi hiilinanoputkiverkon mekaanista kestävyyttä, hybridimateriaalin säilyttäessä sähköisen johtavuuden sekä optisen läpinäkyvyytensä