Find Professionals
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Do you want to be introduced as a Young Professional?
Nanotechnology Center of Expertise is offering young researchers a chance to present their expertise under the title ”Find Professionals”. If you have defended your dissertation within the last two years or if you are going to have your dissertation ready within the next half a year you have a chance to be introduced as a “Young Professional” under the nanobusiness.fi website.
Read more » Young Professionals
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Dr. Tiina Rasilainen - Controlling water on polypropylene surfaces with micro- and micro/nanostructures
31.1.2012
During recent years, surface structuring has become a common method to modify the surface properties of materials. Especially fabrication of biomimetic micro-, nano- and hierarchical structures in polymers has gained attention when aiming to create water-repellent and self-cleansing surfaces. In this work, polypropylene surfaces were furnished with several types of micro- and hierarchical micro/nanostructures, and contact and sliding angles of water were measured. Protrusive structures comprised micropillars or micropillars covered with nanobumps. On some surfaces, the pillars were arranged isotropically, on the rest the patterns were anisotropic, with parallel stripe- or zone-like structures. Hollow structures were isotropic and consisted of micropits or of micropits covered with nanodepressions.
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Dr. Minna Piispanen - Characterization of Functional Coatings on Ceramic Surfaces
20.12.2011 -
Glass and glazes are easy-to-clean surfaces often used in everyday environments where the surface needs to repel soils and deposits. In general, these surfaces also have a very good chemical durability. The durability, however, is rapidly degraded in solutions of high or low pH. This kind of surface corrosion diminishes the cleanability. The surface topography also influences the soil resistance and cleanability of the surface. To enhance the surface cleanability and chemical resistance, self-cleaning and/or easy-to-clean coatings have been employed to glass and glazes. The coatings we studied were a commercial hydrophobic fluoropolymer coating, two experimental coatings based on titania, and one experimental sol-gel based zirconia coating applied on glazed tiles and sanitary ware ceramics and float glass. The effect of a smooth transparent glaze was also tested on an opaque glaze surface containing zircon. One of the titania coatings was applied via the sol-gel route, while the other one also containing silver was manufactured via the liquid flame spray method.
Some of the studied coatings show promise regarding self-cleaning and easy-to-clean properties of the surfaces. As the results showed, however, the functionality of the surfaces can easily diminish as a result of chemical and mechanical loading. Since ceramic surfaces are often subjected to mechanical abrasion and different aqueous solutions, the long term performance of the coatings should be known. Our results provide guidelines for selecting additional coatings on ceramic silicate surfaces used in different environments.
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Dr. Minna Toivola - Dye-sentisized solar cells on alternative substrates
27.05.2010
The Thesis of Dr. Minna Toivola concentrates on dye solar cells (DSC) prepared on alternative substrates to glass, i.e. plastic foils and metal sheets. Integration of a cylindrical DSC structure on optical fibers has also been investigated. Flexible, light weight plastic foils enable roll-to-roll (R2R) type, industrial scale manufacturing of the cells though their obvious challenge is their low temperature tolerance, which is why development of room temperature processable cell materials was a part of this study. Flexible metal sheets can be coated with R2R methods as well, and in addition to that, their superior electrical conductivity enables drastic upscaling of the cell size. Metals are also cost-effective and mechanically robust substrate materials. Depositing the DSC structure directly on metal sheets could realize electricity-producing roofing and façade materials and lead to substantial savings when additional support structures normally used in the panel mounting would not be needed.
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Dr. Sami Suihkonen – InGaN quantum wells for LED applications
25.03.2010
The Thesis of Dr. Sami Suihkonen studies the fabrication and properties of InGaN quantum wells (QWs) for light emitting diode (LED) applications. Metal-organic vapor phase epitaxy (MOVPE) is used to grow InGaN/(InAl)GaN multiple quantum well (MQW) and LED structures on GaN/sapphire substrates. Also a multistep growth method for the growth of GaN on sapphire is investigated. The method enables a tenfold reduction of threading dislocation (TD) density in the GaN layer compared to conventional growth methods. The objective of this work is to study the physics of InGaN QWs and to improve the performance of InGaN MQW structures used in near-UV, blue and green LEDs. The quality of quantum wells is analyzed by x-ray diffraction (XRD), atomic force microscopy (AFM), and photoluminescence (PL) measurements. The LED structures are characterized also by electroluminescence (EL) measurements.
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Dr. Olli Punkkinen – Strongly charged biolomecules
25.03.2010
The Thesis of Dr. Olli Punkkinen is based on analytical and numerical calculations concerning strongly charged biomolecules. The study concentrates on statistical properties of strongly charged biopolymers in the presence of neutralizing counterions and reservoir salt ions, involving applications on deoxyribonucleic acid (DNA), which is a key molecule in human cells. The Thesis starts from constructing a theory that explains the counter- and coion distributions around an arbitrary strongly charged surface, and moves to applications involving statistical conformations of highly stretched DNA, and dynamics of settling the DNA chain in the presence of a large amount of reservoir salt.
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Dr. Lauri Sainiemi – Silicon micro and nanostructures by cryogenic deep reactive ion etching
25.03.2010
The Thesis of Dr. Lauri Sainiemi focuses on cryogenic deep reactive ion etching (DRIE) and presents how it can be applied to the fabrication of silicon micro- and nanostructures that have applications in microfluidics and micromechanics. The cryogenic DRIE process relies on inductively coupled SF6/O2 plasma at temperatures below −100 °C. Low etching temperatures can cause some photoresist materials to crack, but Al2O3 has been shown to be a very well-suited masking material for cryogenic etching. The anisotropy of the etching process is enhanced by a thin passivation layer on sidewalls that prevents lateral etching. The main parameters that are used to adjust the thickness of the passivation layer are the process temperature and the O2 flow. Under adequate conditions vertical sidewalls are obtained, whereas passivation layers that are too thin result in negatively tapered sidewall slopes. Under conditions where a passivation layer is not formed, at higher temperatures and/or without oxygen flow, the etching profiles are isotropic. On the other hand, too high oxygen flow results in over passivation. Under conditions where the sidewall is slightly over passivated, its slopes are positively tapered, while more pronounced over passivation results in the formation of black silicon (or silicon nanograss, silicon nanoturf or columnar microstructures).
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Dr. Abuduwayiti Aierken – GaAs surfaces and In(Ga)As quantum ring structures
25.03.2010
In the Thesis of Dr. Abuduwayiti Aierken work concentrates on two topics: (i) GaAs surface passivation methods using different materials and (ii) formation of InAs islands on GaAs and transformation of InAs islands into quantum rings (QRs). All the samples are fabricated by metalorganic vapor phase epitaxy and characterized by optical spectroscopy and atomic force microscopy.
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Dr. Marko Peura – Mechanical properties and cell wall structure of Norway Spruce
25.03.2010
The Thesis of Dr. Marko Peura studies the structure and the mechanical properties of wood of Norway spruce (Picea abies [L.] Karst.) using small samples from Finland and Sweden. X-ray diffraction (XRD) was used to determine the orientation of cellulose microfibrils (microfibril angle, MFA), the dimensions of cellulose crystallites and the average shape of the cell cross-section. X-ray attenuation and x-ray fluorescence measurements were used to study the chemical composition and the trace element content. Tensile testing with in situ XRD was used to characterise the mechanical properties of wood and the deformation of crystalline cellulose within the wood cell walls.
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Dr. Janne Halme – Flexible dye solar cells
25.03.2010
The Thesis of Dr. Janne Halme studies the preparation of dye solar cells (DSC) on flexible plastic and metal substrates. The study concentrates on the factors limiting the energy conversion efficiency of the cells. Flexible substrates enable manufacturing of solar cells with cost-effective roll-to-roll techniques, but set restrictions to their materials and fabrication processes. An improved method for the preparation of nanoparticle films on plastic was developed using spray deposition and mechanical pressing at room-temperature. With the method, deposition of nanostructured TiO2 photoelectrodes was fast but their photocurrent output was low.
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Dr. Päivi Laaksonen – Self-Assembled Metal Nanoparticle Superstructures
25.03.2010
The Thesis of Dr. Päivi Laaksonen approaches the formation of functional nanoscale devices from the self-assembly of molecules and metallic monolayer capped nanoparticles into superstructures consisting of numerous nanoparticles. Stabilisation of the individual nanosized particles is based on bonding between noble metals and thiol ligands. The desired chemical characteristics and functionality of the nanoparticles is achieved by choosing the capping ligand layer and thus, directing the interactions between the nanoparticles.
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Dr. Kati Miettunen – Nanostructured dye solar cells
25.03.2010
The Thesis of Dr. Kati Miettunen presents a study is on nanostructured dye solar cells which are easy to manufacture and use low cost materials. Dye solar cells have conventionally been deposited on conductive glass sheets. To reduce the costs and enable roll-to-roll mass production, the glass substrates should be replaced with flexible metal and plastic substrates. The change of the substrates has a profound effect on the cell, e.g. on electrochemical properties, optics, temperature treatments, and lifetime which all change when using alternative substrates.
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Dr. Samuli Hirsjärvi – Nanoparticles for pharmaceutical use
25.03.2010
The Thesis of Dr. Samuli Hirsjärvi studies nanoparticles that were prepared from a biodegradable poly(lactic acid) (PLA) polymer. Knowledge and understanding of properties of the materials used in the particle preparation as well as behavior of the nanoparticles in different environments are essential in order to create successful nanoparticle formulations and to predict their performance in the body. Therefore, the effect nanoprecipitation, a nanoparticle preparation method, on the physicochemical properties of the polymer and model drugs encapsulated in the nanoparticles as well as the effect of the drugs on the polymer were studied by thermoanalytical and spectroscopic methods. The suitability of capillary electrophoresis for drug quantitation in the nanoparticle formulations was estimated. Surface pressure measurements were applied for the assessment of stability and aggregation of the nanoparticles. The protective ability of carbohydrates to improve the freeze-drying process of the nanoparticles was evaluated. Finally, a layer-by-layer polyelectrolyte coating process, which modifies the particle surface properties, was introduced. Analytical methods such as electron microscopy, size measurements and zeta potential determinations were included in the nanoparticle characterization.
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Dr. Tero Pilvi – Atomic layer deposition for optical applications
25.03.2010
The Thesis of Dr. Tero Pilvi presents novel metal fluoride processes that have been developed for atomic layer deposition (ALD), which is a gas phase thin film deposition method based on alternate saturative surface reactions. Surface controlled self-limiting film growth results in conformal and uniform films. Other strengths of ALD are precise film thickness control, repeatability and dense and pinhole free films. All these make the ALD technique an ideal choice also for depositing metal fluoride thin films. Metal fluoride ALD processes have been largely missing, which is mostly due to a lack of a good fluorine precursor. In this thesis, TiF4 precursor was used for the first time as the fluorine source in ALD for depositing CaF2, MgF2, LaF3 and YF3 thin films. TaF5 was studied as an alternative novel fluorine precursor only for MgF2 thin films.
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Dr. Antti Kemppinen – Tunnel Junction Devices for Quantum Metrology
25.03.2010
The Thesis of Dr. Antti Kemppinen studies opportunities to create a quantum standard for the electric current with the help of tunnel junctions. We use two types of tunnel junctions: superconducting Josephson junctions and NIS junctions where one of the electrodes is normal (N) and the other one superconducting (S). In both cases, tunnel junctions are employed in a single-electron transistor (SET) structure, which is used to transfer a controlled number k of electrons (e) with the repetition frequency f. The magnitude of the resulting current is thus I = kef.
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Dr. Andrey Timofeev – Low temperature nanoelectronics
25.03.2010
The Thesis of Dr. Andrey Timofeev addresses the fundamental aspects of modern low temperature mesoscopic physics and nano-electronics. It focuses on noise and full counting statistics of electrical charge, and heat transport in superconducting circuits with sub-micron tunnel junctions. The Thesis summarizes the experiments on shot noise asymmetry, heat relaxation in a superconductor, and radiative electronic refrigeration, which are performed at sub-kelvin temperatures, when quantum phenomena of charge and energy transport take place.