Browsing by Author "Karppinen, Maarit"

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  • 151Eu Mössbauer spectroscopy and x-ray-diffraction studies on the Pb2Ba2EuCu3O8+[delta] system
    (1994) Lindén, J.; Lippmaa, M.; Miettinen, J.; Tittonen, I.; Katila, T.; Karppinen, Maarit; Niinistö, L.
     School of Chemical Technology | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Simultaneous replacement of Sr by Ba and Y by Eu in the Pb-2213 system was found to yield single-phase Pb2Ba2EuCu3O8+δ samples, suitable for Eu151 Mössbauer measurements. The samples were synthesized by a solid-state reaction of metal oxides and carbonates under an inert atmosphere. An oxygen-rich sample corresponding to δ=1.79 was obtained by annealing the as-synthesized material (δ=0.16) in oxygen. The oxygen annealing increased the size of the lattice constants and led to an orthorhombic-to-tetragonal phase transition of the structure. The samples were also oriented in an 11.7-T magnetic field. The x-ray-diffraction spectra showed that the c axes tended to orient perpendicular to the applied field. The measured Mössbauer spectra exhibited an electric quadrupole interaction typical of the Eu site in high-Tc cuprates. The average orientation angles obtained from fittings of the Mössbauer spectra were in accordance with the results from the x-ray-diffraction measurements.
  • Advances in upconversion enhanced solar cell performance
    (2021-09-15) Ghazy, Amr; Safdar, Muhammad; Lastusaari, Mika; Savin, Hele; Karppinen, Maarit
     A2 Katsausartikkeli tieteellisessä aikakauslehdessä
    Photovoltaics (PV) is the leading renewable energy harvesting technology. Thus, there is a remarkable strive to enhance the light harvesting capability of the state-of-the-art solar cells. The major issue common to all solar cell types is that they utilize only a limited portion of the solar spectrum, mostly in the visible range, as the active semiconductor materials suffer from intrinsic light absorption thresholds. As a result, photons below and above these threshold values do not contribute to the electricity generation. A plausible solution to enhance the performance is to integrate the PV cell with an upconverting (UC) component capable of harvesting lower energy photons in the infrared (IR) range and emitting visible light. The concept was first introduced in 1990s, but major progress in the field has been made in particular in the recent few years. In this overview our intention is to provide the readers with a comprehensive account of the progress in the research on the UC-enhanced solar cells. Lanthanide ions embedded in different host lattices constitute the most important UC material family relevant to the PV technology; we first summarize the design principles and fabrication routes of these materials. Then discussed are the different approaches taken to integrate the UC layers in actual PV device configurations. Finally, we will highlight the most prominent results obtained, give some future perspectives and outline the remaining challenges in this scientifically intriguing and application-wise important field.
  • Al2O3 coating grown on Nafion membranes by atomic layer deposition
    (2015-12-01) Toikkanen, Outi; Nisula, Mikko; Pohjalainen, Elina; Hietala, Sami; Havansi, Hannele; Ruotsalainen, Jussi; Halttunen, Sakari; Karppinen, Maarit; Kallio, Tanja
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Nafion membranes were shown to be suitable substrates for atomic layer deposition (ALD) process. ALD utilising trimethyl aluminum as a precursor leads to well reproducible formation of smooth single-sided Al2O3 coating on the membranes. Physicochemical and mechanical properties of the coated membranes were compared to those of the unmodified ones. The coating reduced water uptake and thus also conductivity. Moreover, the Al2O3 coating decreased the oxygen permeability of the membrane by 10 % and the methanol permeability 30-50 %. The mechanical properties of the Nafion® membrane were improved. The resulting membranes were successfully applied in hydrogen fuel cells, direct methanol fuel cells and microbial fuel cells. In the microbial fuel cell, the Al2O3 coated membrane showed stable performance during long-term measurements of more than 100 d and doubled power densities in comparison to a cell equipped with a pristine membrane. The membrane modification strategy has potential for improving the performance of various types of membrane fuel cells and could be used for several types of functional membranes containing active groups for ALD growth.
  • Alkali- ja maa-alkalimetalleihin perustuvat metalli-orgaanisen runkorakenteen ohutkalvot ALD/MLD-menetelmällä
    (2016-10-04) Penttinen, Jenna
     Kemian tekniikan korkeakoulu | Master's thesis
    Metalli-orgaaniset runkorakenteet (MOF) soveltuvat niiden huokoisuudesta, muunneltavuudesta ja kiteisyydestä johtuen moniin käyttökohteisiin. Alkali- ja maa-alkalimetalleihin perustuvat MOF-rakenteet soveltuvat esimerkiksi kaasun varastoimiseen, sensoreiksi ja akkuihin elektrodimateriaaleiksi. Tämä diplomityö vertailee alkali- ja maa-alkalimetalleihin perustuvia metalli-orgaanisia runkorakenteita. MOF-rakenteen kasvatus ohutkalvomuotoon luo uusia sovelluskohteita. Mikroakuissa orgaanisen elektrodin vaatimuksena on ohutkalvon kolmiulotteinen rakenne, mikä lisää sen pinta-alaa, jolloin tehotiheys on suurempi ja varauksen kuljettajan diffuusioreitti lyhempi. Yhdistetyllä atomi- ja molekyylikerroskasvatusmenetelmällä (ALD/MLD) voidaan kasvattaa laadukasta ohutkalvoa kolmiulotteiselle substraatille. Diplomityön kokeellisessa osuudessa tavoitteena oli kasvattaa natriumiin, kaliumiin ja magnesiumiin perustuvia kiteisiä metalli-orgaanisen runkorakenteen ohutkalvoja yhdistetyllä ALD/MLD-menetelmällä. Orgaanisina lähtöaineina kasvatuksissa käytettiin tereftalaattihappoa ja 3,5-pyridiinidikarboksyylihappoa. Ohutkalvonäytteiden paksuutta, kiteisyyttä ja koostumusta analysoitiin. Näytteiden kiteisyyttä ja stabiilisuutta kosteus- ja lämpökäsittelyissä tutkittiin. Tuloksia vertailtiin keskenään ja kirjallisuuslähteisiin. Kokeellisessa osuudessa löydettiin kuusi uutta MOF-ohutkalvorakennetta.
  • Alucone and alumina thin films grown on bio-based packaging materials by atomic layer deposition and molecular layer deposition techniques
    (2011) Kauppi, Emilia
     School of Chemical Engineering | Master's thesis
    Biopolymers are good candidates for use in packaging applications to resolve the environmental problems related to petroleum-based polymers. In order to extend the use of biopolymers to more demanding packaging applications, barrier properties of the biopolymer films are often in need of improvement. Inorganic Al2O3 thin films deposited by atomic layer deposition (ALD) have been shown to significantly improve the barrier properties of various polymer films without sacrificing their biodegradability and recyclability. The ALD is a thin film deposition technique based on self saturated gas-solid surface reactions. The ALD produces pinhole-free inorganic thin films uniform in thicknesses. One disadvantage is that the inorganic thin films tend to be brittle, and the barrier properties are lost when such thin films are exposed to mechanical stresses. The ALD can be combined with molecular layer deposition (MLD) which is a similar technique except that it uses organic reactants. Inorganic-organic hybrid thin films grown by ALD/MLD have properties of both inorganic and organic components. The inorganic component provides stability, while the organic compound enhances the flexibility of the thin film. In the experimental part, alumina (Al2O3) and alucone (AIOCH2CH2O) thin-film coatings were deposited on biopolymers using the ALD and the ALD/MLD techniques, respectively. Plain Al2O3 film was brittle as straining of this film by mere 2% led to cracking and defects, and thus to deteriorated barrier properties. Unlike Al2O3, plain alucone films formed poor barrier against oxygen and water vapour. The alucone films were also more brittle than Al2O3. Multilayer films of Al2O3/AlOCH2CH2O /AhO3/AIOCH2CH2O/ Al2O3 were deposited on biaxially oriented polylactic acid film by utilizing both the ALD and the ALD/MLD techniques. These multilayer thin films improved the oxygen barrier property as well as flexibility compared to the Al2O3 thin films.
  • Amorphous-to-crystalline transition and photoluminescence switching in guest-absorbing metal-organic network thin films
    (2020-01-07) Ghazy, Amr; Safdar, Muhammad; Lastusaari, Mika; Karppinen, Maarit
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    An amorphous metal-organic framework (aMOF) is an oxymoron as the porosity derived from the ordered network of the metal and organic moieties is the main characteristic of conventional crystalline MOFs. However, amorphous metal-organic materials can be synthesized from gaseous precursors through atomic/molecular layer deposition (ALD/MLD). We demonstrate an exciting interplay between luminescence properties and amorphous-to-crystalline transition realized upon water absorption in ALD/MLD aMOF films.
  • Anisotropic thermoelectric properties associated with dimensional crossover in quasi-one-dimensional SrNbO3.4+d (d ~ 0.03)
    (2011) Kobayashi, W; Hayashi, Y; Matsushita, M; Yamamoto, Y; Terasaki, I; Nakao, A; Nakao, H; Murakami, Y; Moritomo, Y; Yamauchi, Hisao; Karppinen, Maarit
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We have grown large single crystals of SrNbO3.4+d (d∼0.03) with n=5 in the homologous series SrnNbnO3n+2 by using a traveling solvent floating-zone method and measured resistivity, thermopower, and thermal conductivity along all crystallographic axes. The thermoelectric properties are found to be highly anisotropic, which reflects a quasi-one-dimensional electronic structure. In particular, the thermopower along the b axis is −170 μV/K at 300 K, which is 1 order of magnitude higher than the −15 μV/K along the a axis and −25 μV/K along the c axis. A possible origin of the high anisotropy in the thermopower is discussed in terms of dimensional crossover associated with a structural modification.
  • Anisotropic thermoelectric properties associated with dimensional crossover in quasi-one-dimensional SrNbO3.4+d(d~0.03)
    (2011) Kobayashi, W.; Hayashi, Y.; Matsushita, M.; Yamamoto, Y.; Terasaki, I.; Nakao, A.; Nakao, H.; Murakami, Y.; Moritomo, Y.; Yamauchi, H.; Karppinen, Maarit
     School of Chemical Technology | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We have grown large single crystals of SrNbO3.4+d (d~0.03) with n=5 in the homologous series SrnNbnO3n+2 by using a traveling solvent floating-zone method and measured resistivity, thermopower, and thermal conductivity along all crystallographic axes. The thermoelectric properties are found to be highly anisotropic, which reflects a quasi-one-dimensional electronic structure. In particular, the thermopower along the b axis is −170 μV/K at 300 K, which is 1 order of magnitude higher than the −15 μV/K along the a axis and −25 μV/K along the c axis. A possible origin of the high anisotropy in the thermopower is discussed in terms of dimensional crossover associated with a structural modification.
  • Aqueous-based processing of lithium titanate (Li4Ti5O12) negative electrodes
    (2014-04-08) Kannisto, Klaara
     Kemian tekniikan korkeakoulu | Master's thesis
  • Area-Selective Atomic Layer Deposition on Functionalized Graphene Prepared by Reversible Laser Oxidation
    (2022-10-13) Mentel, Kamila K.; Emelianov, Aleksei V.; Philip, Anish; Johansson, Andreas; Karppinen, Maarit; Pettersson, Mika
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Area-selective atomic layer deposition (ALD) is a promising “bottom-up” alternative to current nanopatterning techniques. While it has been successfully implemented in traditional microelectronic processes, selective nucleation of ALD on 2D materials has so far remained an unsolved challenge. In this article, a precise control of the selective deposition of ZnO on graphene at low temperatures (<250 °C) is demonstrated. Maskless femtosecond laser writing is used to locally activate predefined surface areas (down to 300 nm) by functionalizing graphene to achieve excellent ALD selectivity (up to 100%) in these regions for 6-nm-thick ZnO films. The intrinsic conductive properties of graphene can be restored by thermal annealing at low temperature (300 °C) without destroying the deposited ZnO patterns. As the graphene layer can be transferred onto other material surfaces, the present patterning technique opens new attractive ways for various applications in which the functionalized graphene is utilized as a template layer for selective deposition of desired materials.
  • Artificial SEI layers for sodium-ion battery through ALD/MLD
    (2022-08-23) Meier-Merziger, Jule
     Kemian tekniikan korkeakoulu | Master's thesis
    Sodium-ion batteries suffer from dendrite growth, resulting in safety issues and a short cycle life. A stable solid electrolyte interphase (SEI) layer could solve these problems. The literature part of this thesis presents the variety of different methods and materials investigated for artificial SEI layers. It is demonstrated that the atomic/molecular layer deposition (ALD/MLD) technique is particularly promising for the deposition of defect-free artificial SEI layers due to its atomically precise layer thickness and composition control. Based on the materials considered, it appears that Li-EG (EG: ethylene glycol) is an interesting candidate material for protecting the lithium anode. This hybrid film deposited through ALD/MLD provided the framework for the experimental part of this thesis. The experiments proved that it was straightforward to reproduce the Li-EG and Li-EG-CO films. Additionally, the preparation of novel sodium hybrid films via ALD/MLD was successful, and the process parameters could be optimized towards growth rates up to 3 Å/C. A film transformation into crystalline Na2CO3 and Na3H(CO2)3 in a humid environment was detected. The attempt to convert the Na-EG films into sodium ethylene carbonate films was not successful. The results of this work are expected to provide a promising starting point for the deposition of hybrid sodium-organic coatings for next generation sodium-ion battery applications.
  • Assessment of magnetic properties of A2B′B′′O6 double perovskites by multivariate data analysis techniques
    (2019-01-01) Tiittanen, Taneli; Vasala, Sami; Karppinen, Maarit
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Multivariate data analysis is a promising tool for structure-property data mining and new-material prediction in the field of inorganic materials chemistry. Here we demonstrate its usability in assessing the magnetic properties of one of the most intriguing and plural functional inorganic material families, the ordered perovskite oxides of the A2B′B′′O6 type.
  • Atomic and Molecular Layer Deposition of Alkali Metal Based Thin Films
    (2021-12-08) Madadi, Milad; Heiska, Juho; Multia, Jenna; Karppinen, Maarit
     A2 Katsausartikkeli tieteellisessä aikakauslehdessä
    Atomic layer deposition (ALD) is the fastest growing thin-film technology in microelectronics, but it is also recognized as a promising fabrication strategy for various alkali-metal-based thin films in emerging energy technologies, the spearhead application being the Li-ion battery. Since the pioneering work in 2009 for Li-containing thin films, the field has been rapidly growing and also widened from lithium to other alkali metals. Moreover, alkali-metal-based metal-organic thin films have been successfully grown by combining molecular layer deposition (MLD) cycles of the organic molecules with the ALD cycles of the alkali metal precursor. The current literature describes already around 100 ALD and ALD/MLD processes for alkali-metal-bearing materials. Interestingly, some of these materials cannot even be made by any other synthesis route. In this review, our intention is to present the current state of research in the field by (i) summarizing the ALD and ALD/MLD processes so far developed for the different alkali metals, (ii) highlighting the most intriguing thin-film materials obtained thereof, and (iii) addressing both the advantages and limitations of ALD and MLD in the application space of these materials. Finally, (iv) a brief outlook for the future perspectives and challenges of the field is given.
  • Atomic and Molecular Layer Deposition of Functional Thin Films Based on Rare Earth Elements
    (2024-08-23) Ghazy, Amr; Zanders, David; Devi, Anjana; Karppinen, Maarit
     A2 Katsausartikkeli tieteellisessä aikakauslehdessä
    High-quality rare earth element (R) based thin films are in demand for applications ranging from (opto)electronics and energy conversion/storage to medical diagnostics, imaging and security technologies. Atomic layer deposition (ALD) offers large-area homogeneous and conformal ultrathin films and is uniquely suited to address the requirements set by the potential applications of R-based thin films. The history starts from the 1990s, when the first electroluminescent R-doped thin films were grown with ALD. The interest soon expanded to rare earth element oxide layers as high-k gate dielectrics in semiconductor devices, and later to complex ternary and quaternary perovskite oxides with novel functional properties. The most recent advancements related to the combined atomic/molecular layer deposition (ALD/MLD) have rapidly expanded the family of R-organic hybrid materials with intriguing luminescence and up-conversion properties. This review provides up-to-date insights to the current state of ALD and ALD/MLD research of R-based thin films and highlights their application potential.
  • Atomic layer deposited aluminum oxide mitigates outgassing from fused filament fabrication–based 3-D printed components
    (2020-03-25) Heikkinen, Ismo T.S.; Marin, Giovanni; Bihari, Nupur; Ekstrum, Craig; Mayville, Pierce J.; Fei, Yuhuan; Hu, Yun Hang; Karppinen, Maarit; Savin, Hele; Pearce, Joshua M.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Open-source scientific hardware based on affordable fused filament fabrication (FFF) 3-D printing has the potential to reduce the cost of research tools considerably. So far, development has focused on tools that do not require compatibility with vacuum environments. Highly porous 3-D printed plastics require surface treatments to mitigate their outgassing, and in this study we explored the outgassing reduction from 3-D printed black-colored acrylonitrile butadiene styrene (ABS) and polycarbonate (PC) using a commercial vacuum sealing resin as well as atomic layer deposited (ALD) aluminum oxide (AlOx). The outgassing properties of uncoated plastics could not be measured due to a too high level of outgassing, which was attributed to their high porosity and high specific surface area. However, both the commercial resin and the ALD coatings reduced the extent of outgassing from both ABS and PC, which enabled their comparison by residual gas analysis (RGA). Remarkably, the outgassing performance achieved with ALD AlOx was superior to the performance of the commercial vacuum resin across a temperature range of 40 to 100 °C for both plastics, despite the uneven coverage of the plastic surface with AlOx. Results indicated that both ABS and PC could be made compatible with at least moderate vacuums using ALD AlOx. Thus, the fabrication of laboratory vacuum tools can be realized with affordable 3-D printed plastics. However, further studies on the physical mechanisms behind the outgassing reduction and the durability of the coatings are required.
  • Atomic layer deposition and characterization of BiFeO3 thin films
    (2007) Ollikainen, Antti Eino
     Helsinki University of Technology | Master's thesis
    Vismuttirautaoksidiperovskiitti BiFeO3 on ferrosähköinen, antiferromagneettinen ja ferroelastinen materiaali. Tällaista materiaalia kutsutaan multiferromateriaaliksi, jos sen ferro-ominaisuudet ovat toisiinsa kytkeytyneitä, eli yhden ominaisuuden muutos vaikuttaa samanaikaisesti muihin ominaisuuksiin. BiFeO3-kiteenmagneettisuuden muuttaminen ulkoisella magneettikentällä aiheuttaa kiteessä myös sähköisen polarisaation ja rakennemuutoksen. Nämä ominaisuudet tekevät BiFeO3:sta lupaavan materiaalin tulevaisuuden spintroniikan sovelluksiin. Sovelluksia varten BiFeO3 halutaan usein ohutkalvomuodossa. BiFeO3-ohutkalvoja on aikaisemmin kasvatettu useilla kemiallisilla ja fysikaalisilla menetelmillä, mutta ei nk. atomikerroskasvatusmenetelmällä (ALD). Diplomityön kirjallisuusosassa on tarkasteltu kasvatuslämpötilan ja substraatin sekä mahdollisen jälkilämpökäsittelyn vaikutusta BiFeO3-kalvojen kiteytymiseen ja koostumukseen. Lisäksi kalvojen multiferro-ominaisuuksia on vertailtu keskenään. Mahdollisia vismutti- ja rautalähdeaineita, joita on aikaisemmin kokeiltu ALD ja CVD(kemiallinen kaasufaasikasvatus) menetelmillä, on tarkasteltu työn kokeellista osaa varten. Kokeellisessa osassa käytettiin ALD-menetelmää BiFeO3-ohutkalvojen kasvattamiseen Si-substraateille. Valituilla lähtöaineilla (Fe(thd)3, Fe(C5H5)2, Bi(thd)3, BiC13, O3) kasvatettiin ensin binäärisiä metallioksidikalvoja tarkoituksena optimoida kasvatusprosessit ternäärisiä Bi-Fe-O-ohutkalvoja varten. Optimointi tehtiin kasvatus- ja sublimointilämpötilojen ja lähdeainepulssien pituuksien osalta. Bi(thd)3 muodosti monikiteistä Bi-O-kalvoa 160 °C:n lämpötilassa, kun taas BiCl3 muodosti BIOCI-faasia. Fe(thd)3:n havaittiin kemisorboituvan Bi-O-pinnalle mutta ei suoraan Si-substraatille. Sen sijaan Fe(C5H5)2 muodosti 250°C:ssa tasaista ja amorfista Fe-O-kalvoa kummallekin pinnalle. Binääriprosessit, joiden kasvatuslämpötilat kohtasivat, yhdistettiin ternääriprosesseiksi. Kalvojen kiteisyyttä ja faasikoostumusta tutkittiin röntgendiffraktiolla (XRD). Kalvojen kemiallinen koostumus määritettiin röntgenfluoresenssilla (XRF) ja Rutherford backscattering spektroskopialla (RBS). Työssä onnistuttiin valmistamaan BiFeO3-ohutkalvoja ensimmäistä kertaa ALD-menetelmällä. Lähtöaineina käytettiin Bi(thd)3:tä ja Fe(thd)3:tä ja otsonia. Ohutkalvon paksuus oli n. 200 nm. Lämpökäsittelemällä 160 °C:ssa kasvatettuja Bi-Fe-O-kalvoja 500 °C:ssa happi-ilmakehässä 10 minuutin ajan havaittiin kalvojen kiteytyvän romboedrisenä BiFeO3-perovskiittina. XRF-mittausten perusteella voitiin todeta kalvojen olevan koostumukseltaan stoikiometrisiä ennen ja jälkeen lämpökäsittelyn.
  • Atomic layer deposition and wet etching of aluminum-doped zinc oxide films for transparent electroluminescent displays
    (2024-08-29) Karis, Azad
     Kemian tekniikan korkeakoulu | Master's thesis
    This research explores the atomic layer deposition (ALD) technique and transparent conductive oxides, particularly focusing on aluminum-doped zinc oxide (AZO) films for their application in transparent electroluminescent displays. AZO is identified as a cost-effective, environmentally friendly, and efficient alternative to indium tin oxide (ITO), offering significant advancements in display technology through optimized deposition and wet etching processes. Through the ALD, the effects of varying the ZnO to Al ratio, film thickness, deposition temperatures, and annealing on the films’ physical, optical, and electrical properties were investigated. Optimal deposition conditions were established, notably at a deposition temperature of 250 °C with a ZnO:Al ratio of 20:1 and a film thickness of approximately 400 nm, good optical and electrical properties were achieved, balancing between transparency (83 %) and resistivity (1.08×10−3 Ω cm). Preliminary wet etching studies highlighted the role of different acids and concentrations, with acetic acid showing promising etching rates, surface quality, and anisotropic etching characteristics. Notably, etching experiments with hydrochloric and nitric acid unveiled a distinctive phenomenon where etching rates were higher adjacent to the patterned AZO features. A significant milestone was achieved by manufacturing a segmented transparent electroluminescent display using AZO as an electrode for the first time, demonstrating the practical application of the findings and the potential of AZO in display technologies.
  • Atomic layer deposition of Al-doped ZnO thin films
    (2013) Tynell, Tommi; Yamauchi, Hisao; Karppinen, Maarit; Okazaki, Ryuji; Terasaki, Ichiro
     School of Chemical Technology | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Atomic layer deposition has been used to fabricate thin films of aluminum-doped ZnO by depositing interspersed layers of ZnO and Al 2O3 on borosilicate glass substrates. The growth characteristics of the films have been investigated through x-ray diffraction, x-ray reflection, and x-ray fluorescence measurements, and the efficacy of the Al doping has been evaluated through optical reflectivity and Seebeck coefficient measurements. The Al doping is found to affect the carrier density of ZnO up to a nominal Al dopant content of 5 at. %. At nominal Al doping levels of 10 at. % and higher, the structure of the films is found to be strongly affected by the Al 2O3 phase and no further carrier doping of ZnO is observed.
  • Atomic Layer Deposition of Conducting CuS Thin Films from Elemental Sulfur
    (2018-05) Tripathi, Tripurari S.; Lahtinen, Jouko; Karppinen, Maarit
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    A facile, yet precisely controlled and efficient atomic layer deposition (ALD) process is reported for high-quality copper(II) sulfide thin films based on elemental solid sulfur as the source for sulfur; Cu(acac)2 (acac: acetylacetonate) is used as the copper precursor. In the deposition temperature range as low as 140-160 °C, the process proceeds in an essentially ideal ALD manner and yields single-phase CuS thin films with appreciably high growth rate of ≈4 Å per cycle. When the deposition temperature is increased above 160 °C the growth rate considerably increases and flake-like nanostructures evolve. All the as-deposited films are crystalline, highly conducting, and specularly reflecting. Seebeck coefficient measurements confirm the p-type conducting nature of the films. The direct optical bandgap as determined from UV-vis spectroscopic measurements varies in the range of 2.40-2.54 eV, depending on the deposition temperature.
  • Atomic Layer Deposition of Copper Metal Films from Cu(acac)2 and Hydroquinone Reductant
    (2021-10) Tripathi, Tripurari Sharan; Wilken, Martin; Hoppe, Christian; de los Arcos, Teresa; Grundmeier, Guido; Devi, Anjana; Karppinen, Maarit
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    High-quality copper metal thin films are demanded for a number of advanced technologies. Herein, a facile ALD (atomic layer deposition) process for the fabrication of Cu metal films directly from two solid readily usable precursors, copper acetylacetonate as the source of copper and hydroquinone as the reductant is reported. This process yields highly crystalline, dense, specularly reflecting, and electrically conductive Cu films with an appreciably high growth rate of 1.8 Å/cycle at deposition temperatures as low as 160 to 240 °C.