Jari E M Malm
University of Jyväskylä, Physics, Post-Doc
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In microelectromechanical system devices, thin films experience thermal processing at temperatures some cases exceeding the growth or deposition temperature of the film. In the case of the thin film grown by atomic layer deposition (ALD)... more
In microelectromechanical system devices, thin films experience thermal processing at temperatures some cases exceeding the growth or deposition temperature of the film. In the case of the thin film grown by atomic layer deposition (ALD) at relatively low temperatures, post-ALD thermal processing or high device operation temperature might cause performance issues at device level or even device failure. In this work, residual stress and the role of intrinsic stress in ALD Al2O3 films grown from Me3Al and H2O, O3, or O2 (plasma ALD) were studied via post-ALD thermal processing. Thermal expansion coefficient was determined using thermal cycling and the double substrate method. For some samples, post-ALD thermal annealing was done in nitrogen at 300, 450, 700, or 900 °C. Selected samples were also studied for crystallinity, composition, and optical properties. Samples that were thermally annealed at 900 °C had increased residual stress value (1400–1600 MPa) upon formation of denser Al2O3 phase. The thermal expansion coefficient varied somewhat between Al2O3 made using different oxygen precursors. For thermal-Al2O3, intrinsic stress decreased with increasing growth temperature. ALD Al2O3 grown with plasma process had the lowest intrinsic stress. The results show that ALD Al2O3 grown at 200 and 300 °C is suitable for applications, where films are exposed to post-ALD thermal processing even at temperature of 700 °C without a major change in optical properties or residual stress.
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Aalto University, P.O. Box 11000, FI-00076 Aalto www.aalto.fi Author Jari Malm Name of the doctoral dissertation Surface Functionalization by Atomic Layer Deposited Binary Oxide Thin Films Publisher School of Chemical Technology Unit... more
Aalto University, P.O. Box 11000, FI-00076 Aalto www.aalto.fi Author Jari Malm Name of the doctoral dissertation Surface Functionalization by Atomic Layer Deposited Binary Oxide Thin Films Publisher School of Chemical Technology Unit Department of Chemistry Series Aalto University publication series DOCTORAL DISSERTATIONS 57/2013 Field of research Inorganic Chemistry Manuscript submitted 14 January 2013 Date of the defence 3 May 2013 Permission to publish granted (date) 19 March 2013 Language English Monograph Article dissertation (summary + original articles) Abstract The materials of today have intriguing properties. The mastering of phenomena at the nanometer range often forms the basis for the understanding of novel materials and their functional properties. In this thesis three materials zinc oxide (ZnO), titanium dioxide (TiO2) and tungsten trioxide (WO3) in the form of thin films less than 100 nanometers in thickness are being studied from the surface functionalization point ...
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Carbon nanotubes (CNTs) and carbon nanofibers (CNFs) are known to possess exceptional tensile strength, elastic modulus and electrical and thermal conductivity. They are promising candidates for the next-generation high-performance... more
Carbon nanotubes (CNTs) and carbon nanofibers (CNFs) are known to possess exceptional tensile strength, elastic modulus and electrical and thermal conductivity. They are promising candidates for the next-generation high-performance structural and multi-functional composite materials. However, one of the largest obstacles to creating strong, electrically or thermally conductive CNT/CNF composites is the difficulty of getting a good dispersion of the carbon nanomaterials in a matrix. Typically, time-consuming steps of purification and functionalization of the carbon nanomaterial are required. We propose a new approach to grow CNTs/CNFs directly on the surface of matrix particles. 8 Author to whom any correspondence should be addressed. New Journal of Physics 11 (2009) 023013 1367-2630/09/023013+11$30.00 © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft
1 NanoMaterials Group, Department of Applied Physics and Center for New Materials, Helsinki University of Technology, P.O. Box 5100, 02150 Espoo, Finland 2 Laboratory of Building Materials Technology, Faculty of Engineering and... more
1 NanoMaterials Group, Department of Applied Physics and Center for New Materials, Helsinki University of Technology, P.O. Box 5100, 02150 Espoo, Finland 2 Laboratory of Building Materials Technology, Faculty of Engineering and Architecture, Helsinki University of Technology, P.O. Box 5100, 02150 Espoo, Finland 3 Laboratory of Inorganic Chemistry, Department of Chemistry, Helsinki University of Technology, P.O. Box 6100, 02150 Espoo, Finland 4 Material Science Faculty, State Polytechnical University, Polytechnicheskaya 29, Saint Petersburg 195251, Russia 5 VTT Biotechnology, P.O. Box 1000, 02044 VTT, Espoo, Finland
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Area-selective atomic layer deposition (ALD) allows the growth of highly uniform thin inorganic films on certain parts of the substrate while preventing the film growth on other parts. Although the selective ALD growth is working well at... more
Area-selective atomic layer deposition (ALD) allows the growth of highly uniform thin inorganic films on certain parts of the substrate while preventing the film growth on other parts. Although the selective ALD growth is working well at the micron and submicron scale, it has failed at the nanoscale, especially near the interface where there is growth on one side and no-growth on the other side. The reason is that methods so far solely rely on the chemical modification of the substrate, while neglecting the occurrence of lateral ALD growth at the nanoscale. Here we present a proof-of-concept for blocking the lateral ALD growth also at the nanoscale by combining the chemical surface modification with topographical features. We demonstrate that area-selective ALD of ZnO occurs by applying the diethylzinc/water ALD process on cicada wings that contain a dense array of nanoscopic pillars. The sizes of the features in the inorganic film are down to 25 nm which is, to the best of our knowledge, the smallest obtained by area-selective ALD. Importantly, our concept allows the synthesis of such small features even though the film is multiple times thicker.
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This master's thesis has been performed between November 2004 œ May 2005 at Planar Systems Oy and at Helsinki University of Technology (TKK), Department of Chemical Technology, Laboratory of Inorganic and Analytical Chemistry. The... more
This master's thesis has been performed between November 2004 œ May 2005 at Planar Systems Oy and at Helsinki University of Technology (TKK), Department of Chemical Technology, Laboratory of Inorganic and Analytical Chemistry. The work was funded by a ...
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ABSTRACT ZnO films were grown by atomic layer deposition at 35 °C on poly(methyl methacrylate) substrates using diethylzinc and water precursors. The film growth, morphology, and crystallinity were studied using Rutherford backscattering... more
ABSTRACT ZnO films were grown by atomic layer deposition at 35 °C on poly(methyl methacrylate) substrates using diethylzinc and water precursors. The film growth, morphology, and crystallinity were studied using Rutherford backscattering spectrometry, time-of-flight elastic recoil detection analysis, atomic force microscopy, scanning electron microscopy, and x-ray diffraction. The uniform film growth was reached after several hundreds of deposition cycles, preceded by the precursor penetration into the porous bulk and island-type growth. After the full surface coverage, the ZnO films were stoichiometric, and consisted of large grains (diameter 30 nm) with a film surface roughness up to 6 nm (RMS). The introduction of Al 2O3 seed layer enhanced the initial ZnO growth substantially and changed the surface morphology as well as the crystallinity of the deposited ZnO films. Furthermore, the water contact angles of the ZnO films were measured, and upon ultraviolet illumination, the ZnO films on all the substrates became hydrophilic, independent of the film crystallinity.
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ABSTRACT Amorphous Ca–P–O films were deposited on titanium substrates using atomic layer deposition, while maintaining a uniform Ca/P pulsing ratio of 6/1 with varying number of atomic layer deposition cycles starting from 10 up to 208.... more
ABSTRACT Amorphous Ca–P–O films were deposited on titanium substrates using atomic layer deposition, while maintaining a uniform Ca/P pulsing ratio of 6/1 with varying number of atomic layer deposition cycles starting from 10 up to 208. Prior to film deposition the titanium substrates were mechanically abraded using SiC abrasive paper of 600, 1200, 2000 grit size and polished with 3 μm diamond paste to obtain surface roughness Rrms values of 0.31 μm, 0.26 μm, 0.16 μm, and 0.10 μm, respectively. The composition and film thickness of as-deposited amorphous films were studied using Time-Of-Flight Elastic Recoil Detection Analysis. The results showed that uniform films could be deposited on rough metal surfaces with a clear dependence of substrate roughness on the Ca/P atomic ratio of thin films. The in vitro cell-culture studies using MC3T3 mouse osteoblast showed a greater coverage of cells on the surface polished with diamond paste in comparison to rougher surfaces after 24 h culture. No statistically significant difference was observed between Ca–P–O coated and un-coated Ti surfaces for the measured roughness value. The deposited 50 nm thick films did not dissolve during the cell culture experiment.
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... Jari Malm, Elina Sahramo, Maarit ... The TMA, DEZ, and water precursors were evaporated by means of their vapor pressure from external reservoirs kept at 23 °C. Furthermore, Al 2 O 3 and ZnO films were deposited on 5 × 5 cm 2... more
... Jari Malm, Elina Sahramo, Maarit ... The TMA, DEZ, and water precursors were evaporated by means of their vapor pressure from external reservoirs kept at 23 °C. Furthermore, Al 2 O 3 and ZnO films were deposited on 5 × 5 cm 2 Si(100) and soda lime glass substrates for ...
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Self-erasing patterns allow a substrate to be patterned multiple times or could store temporary information for secret communications, and are mostly based on photochromic molecules to change the color of the pattern. Herein we... more
Self-erasing patterns allow a substrate to be patterned multiple times or could store temporary information for secret communications, and are mostly based on photochromic molecules to change the color of the pattern. Herein we demonstrate self-erasing patterns of wettability on thin ZnO films made by atomic layer deposition. Hydrophilic patterns are written using UV light and decay spontaneously, i.e. become hydrophobic, or are erased aided by vacuum conditions or heat. We demonstrate that these patterns can be applied for channels to confine flow of water without physical walls.
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Research Interests: Kinetics, Pharmaceutical Technology, Powder Diffraction, Crystallization, Nanoparticles, and 11 morePharmaceutical Chemistry, Macromolecular X-Ray Crystallography, Aerosols, Differential scanning calorimetry, Temperature, Solubility, Thermogravimetry, Particle Size, AAPS PharmSciTech, Powders, and Sulfates
Hollow nano-objects have raised interest in applications such as sensing, encapsulation, and drug-release. Here we report on a new class of porous materials, namely inorganic nanotube aerogels that, unlike other aerogels, have a framework... more
Hollow nano-objects have raised interest in applications such as sensing, encapsulation, and drug-release. Here we report on a new class of porous materials, namely inorganic nanotube aerogels that, unlike other aerogels, have a framework consisting of inorganic hollow nanotubes. First we show a preparation method for titanium dioxide, zinc oxide, and aluminum oxide nanotube aerogels based on atomic layer deposition (ALD) on biological nanofibrillar aerogel templates, that is, nanofibrillated cellulose (NFC), also called microfibrillated cellulose (MFC) or nanocellulose. The aerogel templates are prepared from nanocellulose hydrogels either by freeze-drying in liquid nitrogen or liquid propane or by supercritical drying, and they consist of a highly porous percolating network of cellulose nanofibrils. They can be prepared as films on substrates or as freestanding objects. We show that, in contrast to freeze-drying, supercritical drying produces nanocellulose aerogels without major interfibrillar aggregation even in thick films. Uniform oxide layers are readily deposited by ALD onto the fibrils leading to organic-inorganic core-shell nanofibers. We further demonstrate that calcination at 450 °C removes the organic core leading to purely inorganic self-supporting aerogels consisting of hollow nanotubular networks. They can also be dispersed by grinding, for example, in ethanol to create a slurry of inorganic hollow nanotubes, which in turn can be deposited to form a porous film. Finally we demonstrate the use of a titanium dioxide nanotube network as a resistive humidity sensor with a fast response.