Browsing by Subject "atomic layer deposition"

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  • Kalam, Kristjan; Seemen, Helina; Ritslaid, Peeter; Rähn, Mihkel; Tamm, Aile; Kukli, Kaupo; Kasikov, Aarne; Link, Joosep; Stern, Raivo; Duenas, Salvador; Castan, Helena; Garcia, Hector (2018)
    Thin solid films consisting of ZrO2 and Fe2O3 were grown by atomic layer deposition (ALD) at 400 degrees C. Metastable phases of ZrO2 were stabilized by Fe2O3 doping. The number of alternating ZrO2 and Fe2O3 deposition cycles were varied in order to achieve films with different cation ratios. The influence of annealing on the composition and structure of the thin films was investigated. Additionally, the influence of composition and structure on electrical and magnetic properties was studied. Several samples exhibited a measurable saturation magnetization and most of the samples exhibited a charge polarization. Both phenomena were observed in the sample with a Zr/Fe atomic ratio of 2.0.
  • Mattinen, Miika; Leskelä, Markku; Ritala, Mikko (2021)
    2D transition metal dichalcogenides (TMDCs) are among the most exciting materials of today. Their layered crystal structures result in unique and useful electronic, optical, catalytic, and quantum properties. To realize the technological potential of TMDCs, methods depositing uniform films of controlled thickness at low temperatures in a highly controllable, scalable, and repeatable manner are needed. Atomic layer deposition (ALD) is a chemical gas-phase thin film deposition method capable of meeting these challenges. In this review, the applications evaluated for ALD TMDCs are systematically examined, including electronics and optoelectonics, electrocatalysis and photocatalysis, energy storage, lubrication, plasmonics, solar cells, and photonics. This review focuses on understanding the interplay between ALD precursors and deposition conditions, the resulting film characteristics such as thickness, crystallinity, and morphology, and ultimately device performance. Through rational choice of precursors and conditions, ALD is observed to exhibit potential to meet the varying requirements of widely different applications. Beyond the current state of ALD TMDCs, the future prospects, opportunities, and challenges in different applications are discussed. The authors hope that the review aids in bringing together experts in the fields of ALD, TMDCs, and various applications to eventually realize industrial applications of ALD TMDCs.
  • Mattinen, Miika; Hatanpaa, Timo; Sarnet, Tiina; Mizohata, Kenichiro; Meinander, Kristoffer; King, Peter J.; Khriachtchev, Leonid; Räisänen, Jyrki; Ritala, Mikko; Leskelä, Markku (2017)
    Molybdenum disulfide (MoS2) is a semiconducting 2D material, which has evoked wide interest due to its unique properties. However, the lack of controlled and scalable methods for the production of MoS2 films at low temperatures remains a major hindrance on its way to applications. In this work, atomic layer deposition (ALD) is used to deposit crystalline MoS2 thin films at a relatively low temperature of 300 degrees C. A new molybdenum precursor, Mo(thd)(3) (thd = 2,2,6,6-tetramethylheptane-3,5-dionato), is synthesized, characterized, and used for film deposition with H2S as the sulfur precursor. Self-limiting growth with a low growth rate of approximate to 0.025 angstrom cycle(-1), straightforward thickness control, and large-area uniformity are demonstrated. Film crystallinity is found to be relatively good considering the low deposition temperature, but the films have significant surface roughness. Additionally, chemical composition as well as optical and wetting properties are evaluated. MoS2 films are deposited on a variety of substrates, which reveal notable differences in growth rate, surface morphology, and crystallinity. The growth of crystalline MoS2 films at comparably low temperatures by ALD contributes toward the use of MoS2 for applications with a limited thermal budget.
  • Väyrynen, Katja; Hatanpää, Timo; Mattinen, Miika; Mizohata, Kenichiro; Meinander, Kristoffer; Räisänen, Jyrki; Link, Joosep; Stern, Raivo; Ritala, Mikko; Leskela, Markku (2019)
    Intermetallics form a versatile group of materials that possess unique properties ranging from superconductivity to giant magnetoresistance. The intermetallic Co-Sn and Ni-Sn compounds are promising materials for magnetic applications as well as for anodes in lithium- and sodium-ion batteries. Herein, a method is presented for the preparation of Co3Sn2 and Ni3Sn2 thin films using diamine adducts of cobalt(II) and nickel(II) chlorides, CoCl2(TMEDA) and NiCl2(TMPDA) (TMEDA = N,N,N ',N '-tetramethylethylenediamine, TMPDA = N,N,N ',N '-tetramethyl-1,3-propanediamine) combined with tributyltin hydride. The films are grown by atomic layer deposition (ALD), a technique that enables conformal film deposition with sub-nanometer thickness control. The Co3Sn2 process fulfills the typical ALD qualifications, such as self-limiting growth, excellent film uniformity, and conformal coverage of a trench structure. X-ray diffraction (XRD) shows reflections characteristic to the hexagonal Co3Sn2 phase, which confirms that the films are, indeed, intermetallic instead of being mere alloys of Co and Sn. The films are extremely pure with impurity levels each below 1.0 at.%. Ni3Sn2 films similarly exhibit the expected XRD reflections for the intermetallic phase and are of high purity. The Co3Sn2 film show magnetic hysteresis with high coercivity values exceeding 500 Oe, indicating great potential in terms of applicability of the films.
  • 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.
  • Keskivali, Laura; Heikkila, Pirjo; Kentta, Eija; Virtanen, Tommi; Rautkoski, Hille; Pasanen, Antti; Vaha-Nissi, Mika; Putkonen, Matti (2021)
    The growth mechanism of Atomic Layer Deposition (ALD) on polymeric surfaces differs from growth on inorganic solid substrates, such as silicon wafer or glass. In this paper, we report the growth experiments of Al2O3 and ZnO on nonwoven poly-L-lactic acid (PLLA), polyethersulphone (PES) and cellulose acetate (CA) fibres. Material growth in both ALD and infiltration mode was studied. The structures were examined with a scanning electron microscope (SEM), scanning transmission electron microscope (STEM), attenuated total reflectance-fourier-transform infrared spectroscopy (ATR-FTIR) and Al-27 nuclear magnetic resonance (NMR). Furthermore, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) analysis were used to explore the effect of ALD deposition on the thermal properties of the CA polymer. According to the SEM, STEM and ATR-FTIR analysis, the growth of Al2O3 was more uniform than ZnO on each of the polymers studied. In addition, according to ATR-FTIR spectroscopy, the infiltration resulted in interactions between the polymers and the ALD precursors. Thermal analysis (TGA/DSC) revealed a slower depolymerization process and better thermal resistance upon heating both in ALD-coated and infiltrated fibres, more pronounced on the latter type of structures, as seen from smaller endothermic peaks on TA.
  • Mattinen, Miika; King, Peter J.; Bruener, Philipp; Leskelä, Markku; Ritala, Mikko (2020)
    Semiconducting 2D materials, such as SnS2, hold great promise in a variety of applications including electronics, optoelectronics, and catalysis. However, their use is hindered by the scarcity of deposition methods offering necessary levels of thickness control and large-area uniformity. Herein, a low-temperature atomic layer deposition (ALD) process is used to synthesize up to 5x5 cm(2)continuous, few-layer SnS(2)films on a variety of substrates, including SiO2/Si, Si-H, different ALD-grown films (Al2O3, TiO2, and Ir), sapphire, and muscovite mica. As a part of comprehensive film characterization, the use of low energy ion scattering (LEIS) is showcased to determine film continuity, coverage of monolayer and multilayer areas, and film thickness. It is found that on sapphire substrate, continuous films are achieved at lower thicknesses compared to the other substrates, down to two monolayers or even less. On muscovite mica, van der Waals epitaxial growth is realized after the post-deposition annealing, or even in the as-deposited films when the growth is performed at 175 to 200 degrees C. This work highlights the importance of the substrate choice for 2D materials and presents a practical low-temperature method for the deposition of high-quality SnS(2)films that may be further evaluated for a range of applications.
  • Rontu, Ville; Nolvi, Anton; Hokkanen, Ari; Haeggström, Edward; Kassamakov, Ivan; Franssila, Sami (2018)
    We have investigated elastic and fracture properties of amorphous Al2O3 thin films deposited by atomic layer deposition (ALD) with bulge test technique using a free-standing thin film membrane and extended applicability of bulge test technique. Elastic modulus was determined to be 115 GPa for a 50 nm thick film and 170 GPa for a 15 nm thick film. Residual stress was 142 MPa in the 50 nm Al2O3 film while it was 116 MPa in the 15 nm Al2O3 film. Density was 3.11 g cm(-3) for the 50 nm film and 3.28 g cm(-3) for the 15 nm film. Fracture strength at 100 hPa s(-1) pressure ramp rate was 1.72 GPa for the 50 nm film while for the 15 nm film it was 4.21 GPa, almost 2.5-fold. Fracture strength was observed to be positively strain-rate dependent. Weibull moduli of these films were very high being around 50. The effective volume of a circular film in bulge test was determined from a FEM model enabling future comparison of fracture strength data between different techniques.
  • 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.
  • Miikkulainen, Ville; Vehkamäki, Marko; Mizohata, Kenichiro; Hatanpää, Timo; Ritala, Mikko (2021)
    There is a growing need for bottom-up fabrication methods in microelectronic industry as top-down, lithography-based methods face increasing challenges. In Photo-assisted atomic layer deposition (Photo-ALD), photons supply energy to the deposition reactions on the surface. Here, a process and patterning for Photo-ALD of copper is reported, with inherently selective, self-aligned film growth without any photomasking or additive layers. Highly conductive and pure copper films are selectively deposited on tantalum oxide for over hundred nanometers of film thickness, while no copper deposits on silicon or aluminum oxide. On anatase titanium dioxide, copper deposition is crystal-facet selective. Selective deposition of a metal is realized on oxides, which has been especially challenging for ALD. This study indicates that the growth mechanism is closely related to photocatalysis: the photons interact with the material under the growing copper film, enabling the inherent selectivity. The findings provide promising material engineering schemes for microelectronics, photocatalysis, and photovoltaics.
  • Mattinen, Miika; King, Peter J.; Khriachtchev, Leonid; Meinander, Kristoffer; Gibbon, James T.; Dhanak, Vin R.; Räisänen, Jyrki; Ritala, Mikko; Leskelä, Markku (2018)
    Semiconducting 2D materials, such as SnS2, hold immense potential for many applications ranging from electronics to catalysis. However, deposition of few-layer SnS2 films has remained a great challenge. Herein, continuous wafer-scale 2D SnS2 films with accurately controlled thickness (2 to 10 monolayers) are realized by combining a new atomic layer deposition process with low-temperature (250 degrees C) postdeposition annealing. Uniform coating of large-area and 3D substrates is demonstrated owing to the unique self-limiting growth mechanism of atomic layer deposition. Detailed characterization confirms the 1T-type crystal structure and composition, smoothness, and continuity of the SnS2 films. A two-stage deposition process is also introduced to improve the texture of the films. Successful deposition of continuous, high-quality SnS2 films at low temperatures constitutes a crucial step toward various applications of 2D semiconductors.
  • Bakos, Laszlo Peter; Justh, Nora; da Costa, Ulisses Carlo Moura da Silva Bezerra; Laszlo, Krisztina; Labar, Janos Laszlo; Igricz, Tamas; Varga-Josepovits, Katalin; Pasierb, Pawel; Farm, Elina; Ritala, Mikko; Leskelä, Markku; Szilagyi, Imre Miklos (2020)
    TiO2 and ZnO single and multilayers were deposited on hydroxyl functionalized multi-walled carbon nanotubes using atomic layer deposition. The bare carbon nanotubes and the resulting heterostructures were characterized by TG/DTA, Raman, XRD, SEM-EDX, XPS, TEM-EELS-SAED and low temperature nitrogen adsorption techniques, and their photocatalytic and gas sensing activities were also studied. The carbon nanotubes (CNTs) were uniformly covered with anatase TiO2 and wurtzite ZnO layers and with their combinations. In the photocatalytic degradation of methyl orange, the most beneficial structures are those where ZnO is the external layer, both in the case of single and double oxide layer covered CNTs (CNT-ZnO and CNT-TiO2-ZnO). The samples with multilayer oxides (CNT-ZnO-TiO2 and CNT-TiO2-ZnO) have lower catalytic activity due to their larger average densities, and consequently lower surface areas, compared to single oxide layer coated CNTs (CNT-ZnO and CNT-TiO2). In contrast, in gas sensing it is advantageous to have TiO2 as the outer layer. Since ZnO has higher conductivity, its gas sensing signals are lower when reacting with NH3 gas. The double oxide layer samples have higher resistivity, and hence a larger gas sensing response than their single oxide layer counterparts.
  • Rosa, Jose; Heikkilä, Mikko J.; Sirkia, Mika; Merdes, Saoussen (2021)
    Y2O3:Eu is a promising red-emitting phosphor owing to its high luminance efficiency, chemical stability, and non-toxicity. Although Y2O3:Eu thin films can be prepared by various deposition methods, most of them require high processing temperatures in order to obtain a crystalline structure. In this work, we report on the fabrication of red Y2O3:Eu thin film phosphors and multilayer structure Y2O3:Eu-based electroluminescent devices by atomic layer deposition at 300 degrees C. The structural and optical properties of the phosphor films were investigated using X-ray diffraction and photoluminescence measurements, respectively, whereas the performance of the fabricated device was evaluated using electroluminescence measurements. X-ray diffraction measurements show a polycrystalline structure of the films whereas photoluminescence shows emission above 570 nm. Red electroluminescent devices with a luminance up to 40 cd/m(2) at a driving frequency of 1 kHz and an efficiency of 0.28 Lm/W were achieved.
  • Napari, Mari; Huq, Tahmida N.; Meeth, David J.; Heikkilä, Mikko J.; Niang, Kham M.; Wang, Han; Iivonen, Tomi; Wang, Haiyan; Leskelä, Markku; Ritala, Mikko; Flewitt, Andrew J.; Hoye, Robert L. Z.; MacManus-Driscoll, Judith L. (2021)
    High-performance p- type oxide thin film transistors (TFTs) have great potential for many semiconductor applications. However, these devices typically suffer from low hole mobility and high off-state currents. We fabricated p-type TFTs with a phase-pure polycrystalline Cu2O semiconductor channel grown by atomic layer deposition (ALD). The TFT switching characteristics were improved by applying a thin ALD Al2O3 passivation layer on the Cu2O channel, followed by vacuum annealing at 300 degrees C. Detailed characterization by transmission electron microscopy-energy dispersive X-ray analysis and X-ray photoelectron spectroscopy shows that the surface of Cu2O is reduced following Al2O3 deposition and indicates the formation of a 1-2 nm thick CuAlO2 interfacial layer. This, together with field-effect passivation caused by the high negative fixed charge of the ALD Al2O3, leads to an improvement in the TFT performance by reducing the density of deep trap states as well as by reducing the accumulation of electrons in the semiconducting layer in the device off-state.
  • Kukli, Kaupo; Kemell, Marianna; Heikkilä, Mikko J.; Castan, Helena; Duenas, Salvador; Mizohata, Kenichiro; Ritala, Mikko; Leskelä, Markku (2020)
    Amorphous SiO2-Nb2O5 nanolaminates and mixture films were grown by atomic layer deposition. The films were grown at 300 degrees C from Nb(OC2H5)(5), Si-2(NHC2H5)(6), and O-3 to thicknesses ranging from 13 to 130 nm. The niobium to silicon atomic ratio was varied in the range of 0.11-7.20. After optimizing the composition, resistive switching properties could be observed in the form of characteristic current-voltage behavior. Switching parameters in the conventional regime were well defined only in a SiO2:Nb2O5 mixture at certain, optimized, composition with Nb:Si atomic ratio of 0.13, whereas low-reading voltage measurements allowed recording memory effects in a wider composition range.
  • 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.
  • Radtke, Aleksandra; Ehlert, Michalina; Jcdrzejewski, Tomasz; Sadowska, Beata; Wieckowska-Szakiel, Marzena; Holopainen, Jani; Ritala, Mikko; Leskelä, Markku; Bartmanski, Michal; Szkodo, Marek; Piszczek, Piotr (2019)
    Titanium dioxide nanotubes/hydroxyapatite nanocomposites were produced on a titanium alloy (Ti6Al4V/TNT/HA) and studied as a biocompatible coating for an implant surface modification. As a novel approach for this type of nanocomposite fabrication, the atomic layer deposition (ALD) method with an extremely low number of cycles was used to enrich titania nanotubes (TNT) with a very thin hydroxyapatite coating. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used for determination of the structure and the surface morphology of the fabricated nanocoatings. The biointegration activity of the layers was estimated based on fibroblasts' proliferation on the TNT/HA surface. The antibacterial activity was determined by analyzing the ability of the layers to inhibit bacterial colonization and biofilm formation. Mechanical properties of the Ti6Al4V /TNT/HA samples were estimated by measuring the hardness, Young's module, and susceptibility to scratching. The results revealed that the nanoporous titanium alloy coatings enriched with a very thin hydroxyapatite layer may be a promising way to achieve the desired balance between biofunctional and biomechanical properties of modern implants.
  • Mattinen, Miika; King, Peter J.; Popov, Georgi; Hämäläinen, Jani; Heikkilä, Mikko J.; Leskelä, Markku; Ritala, Mikko (2020)
    Van der Waals epitaxy holds great promise in producing high-quality films of 2D materials. However, scalable van der Waals epitaxy processes operating at low temperatures and low vacuum conditions are lacking. Herein, atomic layer deposition is used for van der Waals epitaxy of continuous multilayer films of 2D materials HfS2, MoS2, SnS2, and ZrS2 on muscovite mica and PbI2 on sapphire at temperatures between 75 degrees C and 400 degrees C. For the metal sulfides on mica, the main epitaxial relation is MS2 mica. Some domains rotated by 30 degrees are also observed corresponding to the MS2 mica alignment. In both cases, the presence of domains rotated by 60 degrees (mirror twins) is also expected. For PbI2 on sapphire, the epitaxial relation is PbI2 Al2O3 with no evidence of 30 degrees domains. For all of the studied systems there is relatively large in-plane mosaicity and in the PbI2/Al2O3 system some non-epitaxial domains are also observed. The study presents first steps of an approach towards a scalable and semiconductor industry compatible van der Waals epitaxy method.