Browsing by Subject "ALD"

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  • Li, Xinzhi; Vehkamaki, Marko; Heikkila, Mikko; Mattinen, Miika; Putkonen, Matti; Leskela, Markku; Ritala, Mikko (2021)
    This article describes the deposition of AlF3/polyimide nanolaminate film by inorganic-organic atomic layer deposition (ALD) at 170 degrees C. AlCl3 and TiF4 were used as precursors for AlF3. Polyimide layers were deposited from PMDA (pyromellitic dianhydride, 1,2,3,5-benzenetetracarboxylic anhydride) and DAH (1,6-diaminohexane). With field-emission scanning electron microscopy (FESEM) and X-ray reflection (XRR) analysis, it was found that the topmost layer (nominally 10 nm in thickness) of the nanolaminate film (100 nm total thickness) changed when exposed to the atmosphere. After all, the effect on roughness was minimal. The length of a delay time between the AlF3 and polyimide depositions was found to affect the sharpness of the nanolaminate structure. Electrical properties of AlF3/polyimide nanolaminate films were measured, indicating an increase in dielectric constant compared to single AlF3 and a decrease in leakage current compared to polyimide films, respectively.
  • Hämäläinen, Jani; Mattinen, Miika; Mizohata, Kenichiro; Meinander, Kristoffer; Vehkamäki, Marko; Räisänen, Jyrki; Ritala, Mikko; Leskelä, Markku (2018)
    2D materials research is advancing rapidly as various new “beyond graphene” materials are fabricated, their properties studied, and materials tested in various applications. Rhenium disulfide is one of the 2D transition metal dichalcogenides that has recently shown to possess extraordinary properties such as that it is not limited by the strict monolayer thickness requirements. The unique inherent decoupling of monolayers in ReS2 combined with a direct bandgap and highly anisotropic properties makes ReS2 one of the most interesting 2D materials for a plethora of applications. Here, a highly controllable and precise atomic layer deposition (ALD) technique is applied to deposit ReS2 thin films. Film growth is demonstrated on large area (5 cm × 5 cm) substrates at moderate deposition temperatures between 120 and 500 °C, and the films are extensively characterized using field emission scanning electron microscopy/energy‐dispersive X‐ray spectroscopy, X‐ray diffractometry using grazing incidence, atomic force microscopy, focused ion beam/transmission electron microscopy, X‐ray photoelectron spectroscopy, and time‐of‐flight elastic recoil detection analysis techniques. The developed ReS2 ALD process highlights the potential of the material for applications beyond planar structure architectures. The ALD process also offers a route to an upgrade to an industrial scale.
  • Heikkilä, Mikko J.; Hämäläinen, Jani; Puukilainen, Esa; Leskelä, Markku; Ritala, Mikko (2020)
    IrO2 is an important material in numerous applications ranging from catalysis to the microelectronics industry, but despite this its behaviour upon annealing under different conditions has not yet been thoroughly studied. This work provides a detailed investigation of the annealing of IrO2 thin films using in situ high-temperature X-ray diffraction and X-ray reflectivity (HTXRR) measurements from room temperature up to 1000 degrees C in oxygen, nitrogen, forming gas and vacuum. Complementary ex situ scanning electron microscopy and atomic force microscopy measurements were conducted. The combined data show the dependencies of crystalline properties and surface morphology on the annealing temperature and atmosphere. The reduction of IrO2 to Ir takes place at a temperature as low as 150 degrees C in forming gas, but in oxygen IrO2 is stable up to 800 degrees C and evaporates as a volatile oxide at higher temperatures. The IrO2 crystallite size remains constant in oxygen up to 400 degrees C and increases above that, while in the more reducing atmospheres the Ir crystallites grow continuously above the phase-change temperature. The role of HTXRR in the analysis is shown to be important since its high sensitivity allows one to observe changes taking place in the film at temperatures much below the phase change.
  • Keränen, Laura (Helsingin yliopisto, 2021)
    Tutkielman kirjallisuusosassa tarkastellaan johtavien metalli-, oksidi- ja nitridikalvojen kasvattamista epitaksiaalisesti strontiumtitanaatille. Epitaksiaalisia kalvoja on kasvatettu fysikaalisilla kasvatusmenetelmillä, kuten laserpulssikasvatuksella, elektronisuihkuhöyrystyksellä ja sputteroimalla, sekä kemiallisilla kasvatusmenetelmillä, kuten atomikerroskasvatuksella, sooli-geeli-menetelmällä sekä metalliorgaanisella kemiallisella kaasufaasikasvatuksella. Useiden tekijöiden, kuten substraattien lämpötilan ja esikäsittelyn todettiin vaikuttavan kalvojen orientaatioon. Kokeellisessa osassa iridium- ja platinaohutkalvoja kasvatettiin (100)-orientoiduille strontiumtitanaattisubstraateille atomikerroskasvatuksella. Iridiumkalvojen lähtöaineina käytettiin iridiumasetyyliasetonaattia sekä happea tai otsonia ja vetyä. Platinakalvojen lähtöaineina käytettiin platina-asetyyliasetonaattia, otsonia ja vetyä tai metyylisyklopentadienyylitrimetyyliplatinaa ja happea. Kalvojen rakennetta ja tekstuuria tutkittiin θ-2θ- ja in plane -röntgendiffraktiolla. Osaa iridiumkalvojen poikkileikkauksista tutkittiin myös läpäisyelektronimikroskopialla. Iridiumkalvojen todettiin olevan vahvasti (100)-orientoituneita, mutta monikiteisiä. Platinan (h00)-piikkejä ei kyetty erottamaan substraatin (h00)-piikeistä, mutta vahvojen (111)-piikkien perusteella kalvot eivät olleet epitaksiaalisia. Kalvojen kuumentaminen lisäsi (111)-orientaatiota molemmissa metalleissa.
  • Zhu, Zhen; Sippola, Perttu; Ylivaara, Oili M E; Modanese, Chiara; Di Sabatino, Marisa; Mizohata, Kenichiro; Merdes, Saoussen; Lipsanen, Harri; Savin, Hele (Springer US, 2019)
    Abstract In this work, we report the successful growth of high-quality SiO2 films by low-temperature plasma-enhanced atomic layer deposition using an oxidant which is compatible with moisture/oxygen sensitive materials. The SiO2 films were grown at 90 °C using CO2 and Bis(tertiary-butylamino)silane as process precursors. Growth, chemical composition, density, optical properties, and residual stress of SiO2 films were investigated. SiO2 films having a saturated growth-per-cycle of ~ 1.15 Å/cycle showed a density of ~ 2.1 g/cm3, a refractive index of ~ 1.46 at a wavelength of 632 nm, and a low tensile residual stress of ~ 30 MPa. Furthermore, the films showed low impurity levels with bulk concentrations of ~ 2.4 and ~ 0.17 at. % for hydrogen and nitrogen, respectively, whereas the carbon content was found to be below the measurement limit of time-of-flight elastic recoil detection analysis. These results demonstrate that CO2 is a promising oxidizing precursor for moisture/oxygen sensitive materials related plasma-enhanced atomic layer deposition processes.
  • Heikkinen, Niko; Keskivali, Laura; Eskelinen, Patrik; Reinikainen, Matti; Putkonen, Matti (2021)
    Atomic layer deposition (ALD) was used to prepare a thin alumina layer on Fischer-Tropsch catalysts. Co-Pt-Si/gamma-Al2O3 catalyst was overcoated with 15-40 cycles of Al2O3 deposited from trimethylaluminum (TMA) and water vapor, followed by thermal annealing. The resulting tailored Fischer-Tropsch catalyst with 35 cycle ALD overcoating had increased activity compared to unmodified catalyst. The increase in activity was achieved without significant loss of selectivity towards heavier hydrocarbons. Altered catalyst properties were assumed to result from cobalt particle stabilization by ALD alumina overcoating and nanoscale porosity of the overcoating. In addition to optimal thickness of the overcoat, thermal annealing was an essential part of preparing ALD overcoated catalyst.
  • Ahaliabadeh, Zahra; Miikkulainen, Ville; Mäntymäki, Miia; Mousavihashemi, Seyedabolfazl; Lahtinen, Jouko; Lide, Yao; Jiang, Hua; Mizohata, Kenichiro; Kankaanpää, Timo; Kallio, Tanja (2021)
    Nickel-rich layered oxides, such as LiNi0.6Co0.2Mn0.2O2 (NMC622), are high-capacity electrode materials for lithium-ion batteries. However, this material faces issues, such as poor durability at high cut-off voltages (>4.4 V vs Li/Li+), which mainly originate from an unstable electrode-electrolyte interface. To reduce the side reactions at the interfacial zone and increase the structural stability of the NMC622 materials, nanoscale (