Surface Science Group
The Surface Science Group, led by Prof. Mika Valden, conducts research on the phenomena at surfaces and interfaces of biomaterials, nanostructured materials and semiconductor materials.The main objectives are to gain insights into the physicochemical surface and interface properties at molecular level and to develop novel materials by functionalizing surfaces on the nanometer scale.
The Surface Science Group, formerly Surface Science Laboratory, has been part of the following organizations at TUT:
- 1999-2010 Surface Science Laboratory, Department of Physics
- 2011-2016 Surface Science Laboratory, Optoelectronics Research Centre
- 2017- Surface Science Group, Photonics Laboratory
- Main research areas
- Research methods
- Recent publications
The use of solar power in energy production is increasing every year. The majority of new installations use well-established methods for solar energy conversion, such as photovoltaic solar cells. Unfortunately, they are intermittent energy sources that lack an inherent ability to store energy. In Surface Science research group, we have adopted a nature-based approach to the problem - artificial photosynthesis. With help of specifically tailored photoelectrode materials, energy of the Sun can be effectively used to split water and carbon dioxide into hydrogen, carbon monoxide and oxygen, much like plants do. The reaction products can then be used, for example, in conjuction with traditional fuel-cell technology to produce electrical energy on demand.
Fig.1: H. Ali-Löytty et al., Ambient-Pressure XPS Study of a Ni–Fe Electrocatalyst for the Oxygen Evolution Reaction [J. Phys. Chem. C 2016]
Recently, we have shown techniques for ambient-pressure X-ray photoelectron spectropscopy (APXPS) studies of water splitting catalysts [J. Phys. Chem. C 2016], allowing for monitoring of chemical nature of the catalyst on the solid-liquid interface during the reaction, and experimentally applied them to analysis of a Ni-Fe OER electrocatalyst.
Nanostructured materials are indispensable for many applications, especially for production of photonic devices. Their functional properties can be easily modified by controlling the structure of the material on the surface, which strongly affects the interaction of light with the material. The chemical composition and morphology of surface nanostructures influence many important interactions with other phases or materials, allowing applications in photoelectrochemistry.
Fig.2: SEM image of TiSi microstructure on Si, compositional contrast
Recently, we have demonstrated that microstructured TiSi films (Fig.2) form during annealing of TiO2 ALD films on Si [Scr. Mat. 2016]. This knowledge allows for creation of a scalable process for augmenting TiSi heterostructures for photovoltaic and photoelectrochemical applications and shines light on role of TiO2 reduction and Si diffusion in formation of such films.
Surface of metals is a host to a multitude of physical and chemical processes. Metals, due to their mechanical properties and chemical stability are commonly used for demanding high-temperature applications. For example, special grades of stainless steel are used as interconnect materials in solid-oxide fuel cells, where in normal operation temperatures can be as high as 800°C. In such harsh environment, it is ultimately important to understand the oxidation processes on the metal surface which give the corrosion resistant properties to the stainless steels, in order to optimize the production and treatment of such high-performance materials.
In our recent work, we have demonstrated a pathway for enhancement of oxidation resistance of Ti–Nb stabilized ferritic stainless steels [Corrosion Science 2016] by optimizing the microstructure of the surface to favor surface segregation of particular alloying elements. By control of surface precipitates, uniform protective oxide formation on the surface of steels can be effectively managed without any changes to composition of the source material.
Stainless steel is inherently excellent material choice for applications where the material is in contact with biological substances due to the properties of the few nanometre thick passive oxide surface layer. As a result, specific steel grades have been successfully used in applications where corrosion resistance and biocompatibility is required. What steel surfaces lack, though, is biofunctionality. Therefore, creation of stable organic-inorganic interfaces is paramount to functionalizing the steel surfaces and simultaneously taking advantage of the aforementioned properties of the steel itself.
Recently, we have presented a solution-based deposition method for fabricating novel uniform organosilane monolayers on stainless steel [Nanotechnology 2014], and shown further developments of steel biofunctionalisation based on such an organic-inorganic interface. The method demonstrates efficient growth of organosilane monolayers on steel under ambient conditions, as compared to competing methods which require vacuum-deposited buffer layers for priming the steel surface.
Surface coatings are indispensable in combining desirable properties in a single material composite. Coatings are widely used to modify hardness, wettability, abrasion and corrosion resistance, and chemical stability of materials. For example, galvanised steels employ thin organic coatings to improve the anti-corrosion properties of the zinc galvanizing layer. In such a system, the adhesive and anticorrosive properties of the hybrid organic-inorganic interface ultimately define the longevity and stability of the material, simply by preventing delamination of the coating off the steel substrate. It is thus crucial to understand and be able to effectively modify the properties of the interface for creation of durable and functional coatings. Recently, we have demonstrated a novel method of improving coatings on the surface of hot-dip galvanised steel [Corrosion 2017] by manufacturing a nanomolecular silane film to work as an interfacial layer, improving anti-corrosion and adhesion properties across a wide range of electrolyte solution pH.
Recently we have been utilizing atomic layer deposition (ALD) to grow, e.g., (1) antireflective coatings on laser chips, (2) dielectric layers between semiconductor distributed Bragg reflector and metallization interface in optically pumped semiconductor disk lasers [Applied Physics Letters 2014], and (3) titanium dioxide ultrathin films for dye-sensitized solar cells [ChemPhysChem 2017] and other photonic applications [Scripta Materialia 2016].
The ALD technique allows for growth of atomically thin films in a precisely controlled manner. ALD is based on exposing the substrate to separate pulses of gaseous precursors, which react chemically to form the desired film. ALD is applicable to deposit oxides (dielectrics, semiconductors), nitrides, sulfides, III-V compounds, ternary compounds, and elements, to produce, e.g., passivation and interface layers, diffusion barriers, metallization, and antireflective coatings, including multilayered structures. Layer thicknesses from one monolayer to hundreds of nanometers can be grown to an atomically specified thickness.
Experimentally, the group relies on various surface sensitive methods operating in ultrahigh vacuum.
Surface Science Laboratory at TUT
- Spectromicroscopy: Photoemission electron microscopy (PEEM), Small spot spectroscopy XPS/UPS, Energy-filtered imaging XPS/UPS, Chemical mapping, Momentum microscopy in k-space
- Electron spectroscopy: X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), Ultraviolet photoelectron spectroscopy (UPS)
- Scanning tunneling microscopy (STM)
- Molecular beam surface scattering (MBSS)
- Low energy electron diffraction (LEED)
Thermal desorption spectroscopy (TDS)
Electrochemical instruments: Potentiostat/galvanostat, Electrochemical impedance spectroscopy (EIS), Electrochemical quartz crystal microbalance (EQCM)
Solar simulator for photonics research
Optical contact angle meter for measurement of static contact angle, dynamic contact angles, surface free energy, surface tension, interfacial tension, batch contact angle
Pull-off adhesion gauge
Various sample preparation and surface modification methods in UHV and low pressure: Sputtering, Annealing, Physical vapour deposition (PVD), Activated ion bombardment, Evaporation, Electrospraying, Oxidation, Reduction, Gas exposures, Atomic hydrogen cleaning, etching and passivation, Atomic layer deposition (ALD)
Various sample preparation and surface modification methods in liquid phase: Electrochemical deposition and treatments, Liquid phase deposition of molecules
MAX IV Laboratory
MAX IV Laboratory is a Swedish national laboratory, operating one of the strongest synchrotron radiation facilities in the world. The new facilities of MAX IV, superseding the previous three, have been officially inaugurated in June 2016. MAX IV consists of two storage rings, operating at 1.5 and 3 GeV, and a full-energy linac. The 1.5 and 3 GeV rings are optimized, respectively, for production of brilliant soft and hard X-ray beams, allowing a wide range of experimental methods to be utilised at the beamlines of the facility. Access to facilities of MAX IV Laboratory allows Surface Science Group to augment research methods available locally at Tampere University of Technology with ones available at MAX IV, extending the expertise of the group in areas such as High-resolution photoelectron spectroscopy (PES), X-ray absorption spectroscopy (XAS), Photoemission electron microscopy (LEEM, PEEM, XPEEM) and Near-ambient-pressure X-ray photoelectron spectroscopy (APXPS). Surface Science Group is also actively involved in advancement of capabilities of MAX IV Laboratory, through participation in development of FinEstBeaMS - a Finnish-Estonian Beamline for Materials Science[Nucl. Instrum. Methods Phys. Res. A 2017] . Currently under construction at the 1.5GeV ring of MAX IV, the beamline will cover a wide range of photon energies - from ultraviolet to soft X-rays in a continuous range of 4.3-1000eV, with addition of Al and Mg Kα energies. Beamline will consist of two branches, one of which will investigate free atoms, molecules and clusters with photoelectron photoion coincidence spectroscopy as well as solids with photoluminescence spectroscopy. The second branch will be dedicated to surface and interface studies in ultrahigh vacuum - with X-ray photoelectron spectroscopy as well as X-ray absorption spectroscopy. Both branches will have the possibility to attach user setups to the end stations for maximum flexibility.
At present, Surface Science Group is engaged in the following projects:
- STEELY: Steely way to sustainable hydrogen economy - Thermally grown oxides on advanced iron alloys for photoelectrochemical hydrogen production by solar water splitting
- FinEstBeaMS: MAX IV Infrastructure - FinEstBeaMS Solid State Materials Research (FIRI project)
- PerforMant: Enhancing performance of artificial photosynthesis by engineered nanomaterials and photon management
- Synchrotron radiation mediated research at MAX IV Laboratory (Lund University, Sweden):
- The effect of minor alloying elements on the initial stages of surface oxide formation on FeCr alloys for biomedical applications
- Core-level photoelectron and x-ray absorption spectroscopy of biofunctional layers on advanced metal alloys
- Adsorption geometry and electronic structure of maleimide on silanized FeCr single crystal surface
- FABRICS: Fabrication and service performance of advanced stainless steels for demanding exhaust applications
- NanoFinish: Nanostructures and finishing of advanced stainless steel surfaces
- KURKO: Composites for tissue construction
- NANOmat: Modular spectromicroscopy system for nanomaterials synthesis and characterization (FIRI project)
- Biofunc: Biofunctionalization of stainless steel surfaces using novel electrospray mediated supersonic molecular beam deposition technique
- SR-MAXIV: Synchrotron radiation based studies at MAX IV Laboratory (FIRI project)
- HYBRIDS: Multifunctional thin coatings - Creating innovative and sustainable solutions with multifunctional properties
For more information of our research contact Prof. Mika Valden.
T.-P. Ruoko, A. Hiltunen, T. Iivonen, R. Ulkuniemi, K. Lahtonen, H. Ali-Löytty, M. Valden, M. Leskelä, and N. Tkachenko, Charge carrier dynamics in tantalum oxide overlayered and doped hematite photoanodes, Submitted.
H. Ali-Löytty, M. Hannula, J. Saari, L. Palmolahti, B. Bhuskute, R. Ulkuniemi, T. Nyyssönen, K. Lahtonen, and M. Valden, Diversity of TiO2: Controlling the molecular and electronic structure of atomic layer deposited black TiO2, Submitted.
M. Hannula, H. Ali-Löytty, K. Lahtonen, J. Saari, A. Tukiainen, and M. Valden, Highly efficient charge separation in Z-scheme TiO2/TiSi2/Si photoanode by micropatterned titanium silicide interlayer, Submitted.
M. Kanerva, S. Korkiakoski, K. Lahtonen, J. Jokinen, E. Sarlin, S. Palola, A. Iyer, P. Laurikainen, L. Xuwen, S. Tervakangas, and M. Valden, DLC-treated aramid-fibre composites: tailoring nanoscale-coating for macroscale performance, Submitted to Composites Science and Technology.
A. Hiltunen, T.-P. Ruoko, T. Iivonen, K. Lahtonen, H. Ali-Löytty, E. Sarlin, M. Valden, M. Leskelä, and N. Tkachenko, Design aspects of all atomic layer deposited TiO2-Fe2O3 scaffold-absorber photoanodes for water splitting, Sustainable Energy & Fuels 2, 2124–2130 (2018). [abstract]
M. Sorvali, L. Vuori, M. Pudas, J. Haapanen, R. Mahlberg, H. Ronkainen, M. Honkanen, M. Valden, and J. Mäkelä, Fabrication of ultrathin multilayered superomniphobic nanocoatings by liquid flame spray, atomic layer deposition and silanization, Nanotechnology 29, 185708 (2018). [Abstract]
M. Hannula, H. Ali-Löytty, K. Lahtonen, E. Sarlin, J. Saari, and M. Valden, Improved stability of ALD grown amorphous TiO2 photoelectrode coatings by thermally induced oxygen defects, Chemistry of Materials 30(4), 1199–1208 (2018). [Abstract]
H. Ali-Löytty, M. Hannula, T. Juuti, Y. Niu, A. A. Zakharov, and M. Valden, The role of (FeCrSi)2(MoNb)-type Laves phase on the formation of Mn-rich protective oxide scale on ferritic stainless steel, Corrosion Science 132, 214–222 (2018). [Abstract]
A. T. Aho, J. Viheriälä, V.-M. Korpijärvi, M. Koskinen, H. Virtanen, M. Christensen, T. Uusitalo, K. Lahtonen, M. Valden, and M. Guina, High-power 1180 nm GaInNAs DBR laser diodes, IEEE Photonics Technology Letters 29(23), 2023–2026 (2017). [Abstract]
R. Pärna, R. Sankari, E. Kukk, E. Nõmmiste, M. Valden, M. Lastusaari, K. Kooser, K. Kokko, M. Hirsimäki, S. Urpelainen, P. Turunen, A. Kivimäki, V. Pankratov, L. Reisberg, F. Hennies, H. Tarawneh, R. Nyholm, and M. Huttula, FinEstBeaMS - a Wide-range Finnish-Estonian Beamline for Materials Science at the 1.5 GeV Storage Ring at the MAX IV Laboratory, Nuclear Instruments and Methods in Physics Research A: Accelerators, Spectrometers, Detectors and Associated Equipment 859, 83–89 (2017). [Abstract]
L. George, E. Efimova, E. Sariola-Leikas, K. Lahtonen, M. Valden, P. Vivo, H. Hakola, A. Hiltunen, and A. Eﬁmov, Building up colors: multilayered arrays of peryleneimides on flat surfaces and on mesoporous layers, ChemPlusChem 82, 1–12 (2017). [Abstract]
M. Kuzmin, K. Lahtonen, L. Vuori, R. Sánchez-de-Armas, M. Hirsimäki, and M. Valden, Investigation of the structural anisotropy in a self-assembling glycinate layer on Cu(100) by scanning tunneling microscopy and density functional theory calculations, Applied Surface Science 409, 111–116 (2017). [Abstract]
L. Vuori, H. Ali-Löytty, K. Lahtonen, M. Hannula, E. Lehtonen, Y. R. Niu, and M. Valden, Hot dip galvanized steel by nanomolecular silane layers as hybrid interface between zinc and top coatings, Corrosion 73(2), 169–180 (2017). [Abstract]
A. Hiltunen, K. Lahtonen, J. Saari, A. Ojanperä, E. Sarlin, H. Wondraczek, A. Eﬁmov, K. Kaunisto, P. Vivo, C. Maccato, D. Barreca, P. Fardim, N. Tkachenko, M. Valden, and H. Lemmetyinen, Tailored fabrication of transferable and hollow weblike titanium dioxide structures, ChemPhysChem 18, 64–71 (2017). [Abstract]
L. Reisberg, R. Pärna, A. Kikas, I. Kuusik, V. Kisand, M. Hirsimäki, M. Valden, and E. Nõmmiste, UPS and DFT investigation of the electronic structure of gas-phase trimesic acid, Journal of Electron Spectroscopy and Related Phenomena 213, 11–16 (2016). [Abstract]
H. Ali-Löytty, M. Hannula, M. Honkanen, K. Östman, K. Lahtonen, and M. Valden, Grain orientation dependent Nb–Ti microalloying mediated surface segregation on ferritic stainless steel, Corrosion Science 112, 204–213 (2016). [Abstract]
V. Hynninen, L. Vuori, M. Hannula, K. Tapio, K. Lahtonen, T. Isoniemi, E. Lehtonen, M. Hirsimäki, J. J. Toppari, M. Valden, and V. Hytönen, Improved antifouling properties and selective biofunctionalization of stainless steel by employing heterobifunctional silane-polyethylene glycol overlayers and avidin-biotin technology, Scientific Reports 6, 29324 (2016). [Abstract]
M. Hannula, K. Lahtonen, H. Ali-Löytty, A. A. Zakharov, T. Isotalo, J. Saari, and M. Valden, Fabrication of topographically microstructured titanium silicide interface for advanced photonic applications, Scripta Materialia 119, 76 (2016). [Abstract]
H. Ali-Löytty, M. W. Louie, M. R. Singh, L. Li, H. G. Sanchez Casalongue, H. Ogasawara, E. J. Crumlin, Z. Liu, A. T. Bell, A. Nilsson, and D. Friebel, Ambient-pressure XPS study of a Ni–Fe electrocatalyst for the oxygen evolution reaction, Journal of Physical Chemistry C 120 (4), 2247 (2016). [Abstract]
E. Sariola-Leikas, Z. Ahmed, P. Vivo, A. Ojanperä, K. Lahtonen, J. Saari, M. Valden, H. Lemmetyinen, and A. Efimov, Color bricks: Building highly organized and strongly absorbing multicomponent arrays of terpyridyl perylenes on metal oxide surfaces, Chemistry - A European Journal 22, 1501 (2016). [Abstract]