Mikko Heikkilä

University of Helsinki | HY · Department of Chemistry

The development of deposition processes for metal carbide thin films is rapidly advancing, driven by their potential for applications including catalysis, batteries, and semiconductor devices. Within this landscape, atomic layer deposition (ALD) offers exceptional conformality, uniformity, and thickness control on spatially complex structures. This...

Coinage metals Cu, Ag, and Au are essential for modern electronics and their recycling from waste materials is becoming increasingly important to guarantee the security of their supply. Designing new sustainable and selective procedures that would substitute currently used processes is crucial. Here, we describe an unprecedented approach for the se...

Coinage metals Cu, Ag and Au are essential for modern electronics and their recycling from waste materials is becoming increasingly important to guarantee the security of their supply. Designing new sustainable and selective procedures that would substitute currently used processes is crucial. Here, we describe an unprecedented approach for the seq...

In this paper, we present an ALD process for ScF3 using Sc(thd)3 and NH4F as precursors. This is the first material made by ALD that has a negative thermal expansion over a wide-temperature range. Crystalline films were obtained at the deposition temperatures of 250–375 °C, with a growth per cycle (GPC) increasing along the deposition temperature f...

In this paper, we introduce a vacuum cluster tool designed specifically for studying reaction mechanisms in atomic layer deposition (ALD) and atomic layer etching (ALE) processes. In the tool, a commercial flow-type ALD reactor is in vacuo connected to a set of UHV chambers so that versatile surface characterization is possible without breaking the...

In this paper, the deposition of pyrrone thin film materials by molecular layer deposition (MLD) is reported for the first time using pyromellitic dianhydride (PMDA) and 3,3'‐diaminobenzidine (DAB) as monomers, and ozone as a promoting precursor. Besides ozone, the effect of water, hydrogen peroxide, and oxygen is also tested to promote the growth...

Nuclear power is a clean alternative to fossil fuels. However, the use of nuclear energy generates hazardous fission products of which ⁹⁰Sr is the second most important. To remove Sr²⁺ from aqueous solutions, we synthesized submicron TiO2 and TiO2/SiO2 composite fibers with Ti: Si molar ratios of 3: 1 (3TiO2-1SiO2) and 1: 1 (1TiO2-1SiO2) utilizing...

In this paper we present laboratory-scale X-ray absorption spectroscopy applied to the research of nanometer-scale thin films. We demonstrate the Cu K edge X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) of CuI and CuO thin films grown with atomic layer deposition. Film thicknesses in the investigat...

Stoichiometric troilite (FeS) is a common phase in differentiated and undifferentiated meteorites. It is the endmember of the iron sulfide system. Troilite is important for investigating shock metamorphism in meteorites and studying spectral properties and space weathering of planetary bodies. Thus, obtaining coarse-grained meteoritic troilite in q...

Nanoscale SnO2 has many important properties ranging from sorption of metal ions to gas sensing. Using a novel electroblowing method followed by calcination, we synthesized SnO2 and composite SnO2/SiO2 submicron fibers with a Sn : Si molar ratio of 3 : 1. Different calcination temperatures and heating rates produced fibers with varying structures a...

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...

This article describes the deposition of AlF3/polyimide nanolaminate film by inorganic-organic atomic layer deposition (ALD) at 170 °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 scann...

Lanthanide fluoride thin films have gained interest as materials for various optical applications, including electroluminescent displays and mid-IR lasers. However, the number of atomic layer deposition (ALD) processes for lanthanide fluorides has remained low. In this work, we present an ALD process for TbF3 using tris(2,2,6,6-tetramethyl-3,5-hept...

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 switch...

Shock darkening is caused by two distinct mechanisms with characteristic pressure regions, which are separated by an interval where the darkening ceases. This implies a reduced amount of shock-darkened material produced during the asteroid collisions.

SiO2-Fe2O3 mixture films and nanolaminates were grown by atomic layer deposition from iron trichloride, hexakis(ethylamino)disilane, and ozone at 300 °C. Orthorhombic ɛ-Fe2O3 was identified in Fe2O3 reference films and in Fe2O3 layers grown to certain thicknesses between amorphous SiO2 layers. SiO2-Fe2O3 films could be magnetized in external fields...

Context. Shock-induced changes in ordinary chondrite meteorites related to impacts or planetary collisions are known to be capable of altering their optical properties. Thus, one can hypothesize that a significant portion of the ordinary chondrite material may be hidden within the observed dark C/X asteroid population. Aims: The exact pressure-temp...

Stress corrosion cracking (SCC) of oxygen‐free phosphorous‐alloyed copper was investigated in sulphide‐ and chloride‐containing deoxygenated water at 90°C with sulphide concentrations of 0.001 and 0.00001 M. Several intergranular defects were found in the specimen exposed to the high sulphide environment. Similar defects were not found in the low s...

Context. Shock-induced changes in ordinary chondrite meteorites related to impacts or planetary collisions are known to be capable of altering their optical properties. Thus, one can hypothesize that a significant portion of the ordinary chondrite material may be hidden within the observed dark C/X asteroid population. Aims. The exact pressure-temp...

Shock-induced changes in ordinary chondrite meteorites related to impacts or planetary collisions are known to be capable of altering their optical properties. Thus, one can hypothesize that a significant portion of the ordinary chondrite material may be hidden within the observed dark C/X asteroid population. The exact pressure-temperature conditi...

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...

Amorphous SiO2-Nb2O5 nanolaminates and mixture films were grown by atomic layer deposition. The films were grown at 300 oC from Nb(OC2H5)5, Si2(NHC2H5)6, and O3 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...

Stress corrosion cracking (SCC) of oxygen-free phosphorous-alloyed copper was investigated in sulphide- and chloride-containing deoxygenated water at 90°C with sulphide concentrations of 0.001 and 0.00001 M. Several intergranular defects were found in the specimen exposed to the high sulphide environment. Similar defects were not found in the low s...

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...

Both stable and radioactive antimony are common industrial pollutants. For antimonate (Sb(V)) removal from industrial waste water, we synthesized submicron zirconium dioxide (ZrO2) fibers by electroblowing and calcination of the as-electroblown fibers. The fibers are amorphous after calcination at 300 and 400 °C and their average diameter is 720 nm...

In this paper, a combined H2O thermal atomic layer deposition of Al2O3 with in‐situ N2 plasma treatment process at 90 °C for encapsulation applications is reported. The effect of process parameters on the growth behavior and properties of Al2O3 thin films, such as elemental composition, residual stress, moisture permeation barrier ability, density...

The application of scandium (Sc) is hindered by insufficient supply. The majority of the world Sc supply is sourced from industrial by-products, where Sc needs to be separated from other components. Phosphate precipitation is an effective separation and purification method to harvest dissolved Sc ions from acidic leachate solutions, however the obt...

Herein, we report an atomic layer deposition (ALD) process for Cu2O thin films using copper(II) acetate [Cu(OAc)2] and water vapor as precursors. This precursor combination enables the deposition of phase-pure, polycrystalline, and impurity-free Cu2O thin films at temperatures of 180–220 °C. The deposition of Cu(I) oxide films from a Cu(II) precurs...

This work presents preparation of nickel germanide (Ni2Ge) thin films by atomic layer deposition (ALD). The films were grown using NiCl2(tmpda) (tmpda = N,N,N’,N’,-tetramethyl-1,3-propanediamine) and tributylgermanium hydride (TBGH) serving as a new, efficient reducing agent. This is the first time ALD NixGey films are prepared directly upon the co...

LiMn2O4 is a promising candidate for a cathode material in lithium ion batteries (LIBs) due to its ability to intercalate lithium ions reversibly through its three-dimensional manganese oxide network. One of the promising techniques for depositing LiMn2O4 thin film cathodes is atomic layer deposition (ALD). Due to its unparalleled film thickness co...

This article describes the atomic layer deposition (ALD) of nickel nitride and nickel thin films using a diamine adduct of Ni(II) chloride, NiCl2(TMPDA) (TMPDA = N,N,N′,N′,‐tetramethyl‐1,3‐propanediamine), as the metal precursor. Owing to the high reducing power of tert‐butylhydrazine (TBH), the films are grown at low temperatures of 190–250 °C. Th...

The authors demonstrate multilayer epitaxial films by atomic layer deposition and postdeposition annealing. Their example features two ABO3 type perovskite oxide films with different materials properties - a conductor (LaNiO3) and an insulator (SrTiO3) - that can be integrated epitaxially once the geometric interaction between the two oxides' latti...

In this paper, results on the solid state reactions of atomic layer deposited Li 2 CO 3 with HfO 2 and ZrO 2 are reported. An Li 2 CO 3 film was deposited on top of hafnia and zirconia, and the stacks were annealed at various temperatures in air to remove the carbonate and facilitate lithium diffusion into the oxides. It was found that Li ⁺ ions ar...

Thermal ageing promotes intergranular carbide precipitation and atomic ordering reaction in most commercial nickel-base alloys, and it affects the long-term primary water stress corrosion cracking (PWSCC) resistance of pressurized water reactor components. Alloy 690 with 9.8 wt% Fe was solution annealed and heat-treated at low temperature, then age...

Molybdenum forms a range of oxides with different stoichiometries and crystal structures, which lead to different properties and performance in diverse applications. Herein, crystalline molybdenum oxide thin films with controlled phase composition are deposited by atomic layer deposition. The MoO2(thd)2 and O3 as precursors enable well-controlled g...

Thin mixed and nanolaminate films of ZrO2 and Al2O3 were grown by atomic layer deposition from the corresponding metal chlorides and water. The films were grown at 350◦C in order to ensure ZrO2 crystallization in the as-deposited state. The relative thicknesses of layers in the structure of the nanolaminates were controlled in order to maximize the...

In this paper, we introduce a new Co precursor for the atomic layer deposition (ALD) of Co metal and other Co containing materials. CoCl2(TMEDA) (TMEDA = N,N,N',N'-tetramethylethylenediamine) is a diamine adduct of cobalt(II) chloride that is inexpensive and easy to synthesize making it an industrially viable precursor. Furthermore, CoCl2(TMEDA) sh...

Electroblowing was used to prepare ZnO and aluminum doped zinc oxide (AZO, 1–3 cation-% of Al) fibers. The as-blown fibers were calcined at 500 °C to obtain the target material. The average fiber diameters ranged from 240 ± 60 nm for ZnO fibers to 330 ± 80 nm for AZO with 3% Al. Smaller crystallite size was measured with x-ray diffraction for the A...

Several alloys including Al-alloyed austenitic and ferritic stainless steels, Ni-based alloy and Si-alloyed ferritic stainless steel were annealed at 550, 750, and 950 °C for up to 700 h. AISI 347HFG and 10CrMo910 were used as reference materials. Weight gain was measured and the samples were analyzed with SEM/EDS and XRD. Materials having high eno...

Low ionic conductivity and slow reaction kinetics often limit the performance of a ceramic nanocomposite fuel cell (CNFC). Here, we report a novel synthesis method, freeze-dried method, to achieve a record high ionic conductivity for nanocomposite electrolytes (>0.5 S/cm) based on Ce0.85Sm0.15O2 (SDC) and a eutectic mixture of Na2CO3, Li2CO3, K2CO3...

Deposition of zinc glutarate thin films by atomic layer deposition is studied at 200–250 °C using zinc acetate and glutaric acid as the precursors. The films are characterized by UV–vis spectrophotometry, X-ray diffraction, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, at...

Supporting information - EFTEM, HRSEM, Phi scan XRD, EBSD of IMF sample, choice of materials, lattice matching heteroepitaxial assembly

Herein, we describe an efficient two-step pathway for isosorbide synthesis from cellulose with the use of new recyclable Ru-catalysts. We show that the oxidative and sulfonation treatments of the new Ru-catalysts increase the acidity and the hydrophilicity of the activated carbon support material, thus reducing the catalyst fouling caused by build-...

We introduce a new approach to creating low-resistance metal-semiconductor ohmic contacts, illustrated using high conductivity Au Island Metal Films (IMFs) on Ge, with hot carrier injection initiated at low applied voltage. The same metallization process simultaneously allows ohmic contact to n-Ge and p-Ge, because hot carriers circumvent the Schot...

The ternary lithium aluminum fluoride Li3AlF6 is formed from two optically interesting fluorides, LiF and AlF3. It has been reported to have a large electronic bandgap with a reasonable lithium-ion conductivity at room temperature, making it a potential electrolyte material for solid state lithium-ion batteries. Because of complications during atte...

Thermal ageing of Alloy 690 triggers an intergranular (IG) carbide precipitation and is known to promote an ordering reaction causing lattice contraction. It may affect the long-term primary water stress corrosion cracking (PWSCC) resistance of pressurized water reactor (PWR) components. Four conditions of Alloy 690 (solution annealed, cold-rolled...

Thin solid films consisting of ZrO2 and Ta2O5 were grown by atomic layer deposition at 300 °C. Ta2O5 films doped with ZrO2, TaZr2.75O8 ternary phase, or ZrO2 doped with Ta2O5 were grown to thickness and composition depending on the number and ratio of alternating ZrO2 and Ta2O5 deposition cycles. All the films grown exhibited resistive switching ch...

Lithium containing multicomponent oxides are important materials for both lithium-ion batteries and optical applications. In most cases thin films of these materials are desired. Atomic layer deposition (ALD) is a thin film deposition method that is known to deposit high quality films by sequential self-limiting surface reactions. However, the reac...

As2S3 thin films were deposited on glass and silicon (100) substrates by atomic layer deposition from tris(dimethylamino)arsine [(CH3)2N)3As] and H2S. Amorphous films were deposited at an exceptionally low temperature of 50 °C. No film growth was observed at higher temperatures. The films were amorphous and contained H and C as the main impurities....

Atomic layer deposition (ALD) is an advanced thin film deposition method based on self-limiting surface reactions, which allow controlled deposition of conformal, high-quality thin films of various materials. In this study we aimed to explore how modifying the deposition chemistry affects the growth and properties of iridium films. We demonstrated...

The photocatalytic activity of TiO2 based nanotube (TNT) and nanofiber (TNF) coatings has been investigated, in corelation to their structure, morphology, specific surface area, acidity and the amount of surface H2O molecules and –OH groups. Characterization of these materials was carried out using grazing incidence X-ray diffraction (GIXRD), X-ray...

Base-free oxidation of glucose to gluconic acid with supported gold catalysts was studied using microwave heating. High conversion and selectivity were obtained in a remarkably shortened reaction time; in 10 min gluconic acid was obtained with up to 76% yields with 0.09 mol%Au/Al2O3 and hydrogen peroxide as oxidant. Very high turn-over frequencies...

Cellulose is mainly utilized by industry for paper and packaging materials. Due to ecological awareness this biopolymer has recently received an increasing amount of attention as a renewable alternative for replacing traditional oil based products. In this work, hydrophobic cellulose based materials were prepared by acylation of cellulose with tall...

Alloy 690 was developed to improve the corrosion resistance of components in nuclear power systems since the 90s. Its composition is close to the Ni2Cr stoichiometry which promotes an ordering reaction upon ageing at temperatures below 550 °C with a maximum effect at 475 °C. Atomic ordering promotes lattice contraction and brittle intergranular fra...

Stress corrosion cracking (SCC) susceptibility of austenitic EN 1.4301 (AISI 304, UNS S30400) stainless steel was studied as a function of electrode potential at T = 190°C in 15 g/kg NaOH + 150 g/kg Na2S containing caustic environment simulating heavy black liquors (HBL) of the pulp industry. Severe cracking was detected at the corrosion potential...

Aluminum fluoride thin films have potential in both optic and lithium-ion battery applications. AlF3 thin films have mostly been deposited using physical vapor deposition methods. In this study, we present a new atomic layer deposition process for AlF3. Our method makes use of a halide-halide exchange reaction with AlCl3 and TiF4 as the precursors....

The polarity of the resistive switching (RS) characteristic of metal-oxide-metal devices from atomic layer deposited polycrystalline ZrO2 films was studied by means of impedance spectroscopy. Pt/ZrO2/Ti/Pt cells made with 10 nm Ti and 30 nm Pt capping top electrodes, served as unipolar switching (US) devices. Bipolar switching (BS) devices were rep...

We introduce a flame based aerosol method to fabricate thin films consisting of binary TiO2/SiO2 nanoparticles deposited directly from the flame onto the paperboard. Nanocoatings were prepared with Liquid Flame Spray (LFS) in a roll-to-roll process with the line speed of 50 m/min. Surface wetting behavior of nanocoated paperboard was studied for di...

Calcium carbonate (CaCO3) fibers were prepared by electrospinning followed by annealing. Solutions consisting of calcium nitrate tetrahydrate (Ca(NO3)2·4H2O) and polyvinylpyrrolidone (PVP) dissolved in ethanol or 2-methoxyethanol were used for the fiber preparation. By varying the precursor concentrations in the electrospinning solutions CaCO3 fibe...

Nanocrystalline hydroxyapatite thin films were fabricated on silicon and titanium by atomic layer deposition (ALD) of CaCO3 and its subsequent conversion to hydroxyapatite by diammonium hydrogen phosphate (DAP) solution. The effects of conversion process parameters to crystallinity and morphology of the films were examined. DAP concentration was fo...

Nanolaminate (nanomultilayer) thin films of TiO2 and Ho2O3 were grown on Si(001) substrates by atomic layer deposition at 300 °C from alkoxide and β-diketonate based metal precursors and ozone. Individual layer thicknesses were 2 nm for TiO2 and 4.5 nm for Ho2O3. As-deposited films were smooth and X-ray amorphous. After annealing at 800 °C and high...

One main limiting factor for the technoeconomics of future bioprocesses that use ionic liquids (ILs) is the recovery of the expensive and potentially toxic IL. We have demonstrated a new series of phase-separable ionic liquids, based on the hydrophobic tetraalkylphosphonium cation ([PRRRR]+), that can dissolve lignin in the neat state but also hemi...

Thin ZrO2 films and ZrO2/TiO2 bilayers grown by atomic layer deposition (ALD) are integrated into metal–oxide–metal (MOM) structures for investigation of resistive switching (RS) properties. The films have different microstructure depending on the used ALD oxygen source and stacking sequence for the bilayers. Pt/ZrO2/Ti/Pt devices show unipolar RS...

Deposition of MOF-5 thin films from vapor phase by atomic layer deposition (ALD) was studied at 225–350 °C. Zinc acetate (ZnAc 2 ) and 1,4-benzenedicarboxylic acid (1,4-BDC) were used as the precursors. The resulting films were characterized by UV–Vis spectrophotometry, Fourier transform infrared spectroscopy (FTIR), optical microscopy, X-ray diffr...

In this study, VOx films were grown by atomic layer deposition (ALD) using V(NEtMe)4 as the vanadium precursor and either ozone or water as the oxygen source. V(NEtMe)4 is liquid at room temperature and shows good evaporation properties. The growth was investigated at deposition temperatures from as low as 75 [degree]C, up to 250 [degree]C. When us...

Core WO3 nanofibers (140–300 nm in diameter, several hundred µm long) are made by a novel, water-based electrospinning process using ammonium metatungstate (AMT) and polyvinylpyrrolidone (PVP) as precursors. TiO2 shells (1.5–20 nm) are grown by atomic layer deposition (ALD) using TiCl4 and water at 250°C. The WO3/TiO2 composite fibers are analyzed...

This chapter contains five sections related to advances in technology and characterization. The first section investigates influence of Ti top electrodes on the oxidation state of epi-taxially grown STO thin films and the corresponding resistive switching devices. The second section shows comparison of work diode- and CO2-laser heater versions. The...

Corrosion behavior of austenitic stainless steel UNS( 1 ) S30403, duplex stainless steels UNS S32101, UNS S32304, UNS S32205 and UNS S32507 as well as ferritic stainless steels UNS S43932 and ASTM(2) 444 was evaluated with U-bend specimens in alkaline solutions containing 500 g/l NaOH, 100 g/l NaOH + 55 g/l Na2S (hot white liquor [HWL]) and 15 g/l...

A highly efficient, selective and green catalytic protocol for open air oxidation of primary benzylic alcohols into aldehydes by in situ made N-isopropyl-3,5-di-tert-butylsalicylaldimine (HL3)–Cu(II) complexes and TEMPO (2,2,6,6-tetramethyl-piperidinyloxyl radical) is introduced herein. Distilled water as a solvent the reaction proceeds at 80 °C te...

Reaction mechanisms in the Al(CH3)(3)-D2O-Si-2(NHEt)(6)-D2O ALD process for AlxSiyOz, were studied in situ with a quartz crystal microbalance (QCM) and a quadrupole mass spectrometer (QMS) at 200 degrees C. Two other pulsing sequences were investigated too to assess the surface reactivity of Si-2(NHEt)(6) and Al(CH3)(3). The resulting films were ex...

The atomic layer deposition of Ta2O5 thin films was studied using a novel imido–amido precursor tBuN = Ta(NEt2)3. This precursor is liquid at room temperature, possesses good volatility and is reactive toward both water and ozone as the oxygen sources. The deposition temperature was varied from 125 to 475 °C. Saturated film growth was confirmed at...

Atomic layer deposition (ALD) of Nb2O5 thin films was studied using three novel precursors, namely, tBuN═Nb(NEt2)3, tBuN═Nb(NMeEt)3, and tamylN═Nb(OtBu)3. These precursors are liquid at room temperature, present good volatility, and are reactive toward both water and ozone as the oxygen sources. The deposition temperature was varied from 150 to 375...

The atomic layer deposition (ALD) of phosphate containing thin films using reactions between the metal halide and the phosphorus source without any additional oxygen sources was examined. Two very common metal halides, AlCl3 and TiCl4, were used in conjunction with trimethyl phosphate (TMPO) to grow corresponding metal phosphate films. Aluminum pho...