Entity

Time filter

Source Type

Tampere, Finland

Hakala T.J.,VTT Technical Research Center of Finland | Metsajoki J.,VTT Technical Research Center of Finland | Granqvist N.,BioNavis Ltd | Milani R.,VTT Technical Research Center of Finland | And 5 more authors.
Tribology International | Year: 2015

In a metal forming process the adhesion between the workpiece and the tool needs to be minimised, which can be achieved by use of lubricants and coatings. Here adsorption and lubrication properties of HFBII hydrophobins and diblock copolymer poly(methyl methacrylate-b-sodium acrylate) in water-lubricated copper vs. a-C:H coating contacts were studied by Surface Plasmon Resonance (SPR) and by a pin-on-disc (POD) tribometer. Hydrophobins formed a dense monolayer film on a-C:H surface and reduced friction by 13-30% but increased the wear of copper compared to pure water lubrication. Poly(methyl methacrylate-b-sodium acrylate) formed a sparse lubricating layer compared to HFBII lubricated contacts, but the friction coefficient was lower. HFBII molecules prevented copper oxide tribofilm formation on the copper pin. © 2015 Elsevier Ltd. All rights reserved. Source


Jussila H.,Aalto University | Yang H.,Aalto University | Granqvist N.,BioNavis Ltd | Sun Z.,Aalto University
Optica | Year: 2016

Characterization of large-area thin films with atomic-scale resolution is challenging but in great demand for diverse applications (e.g., nanotechnology and sensing). Here, we use the Surface Plasmon Resonance (SPR) method to characterize both the thickness and refractive index of chemical-vapor-deposition (CVD)-grown graphene films. The measured refractive index and extinction coefficient values of the CVD-grown graphene monolayer at 670 nm wavelength are 3.135 and 0.897, respectively. Our results demonstrate that SPR shifts generated by graphene films are large (i.e., ~1°/nm), almost tenfold larger than that observed in SPR measurements of organic monolayers. We find that this significantly large SPR shift easily enables the thickness of a large area sample (i.e., ~mm2) to be determined with subnanometer-scale resolution. We show that the SPR method can identify thickness of different graphene layers and give an estimate of ~0.37 nm for the thickness of the CVD-grown graphene layer, which agrees extremely well with the 0.335 nm reported for layer-to-layer carbon atom distance of graphite crystals. Our results open the avenue to fast and cost-effective simultaneous characterization of various parameters (including thickness and optical constants) of thin films at the atomic-scale resolution. The presented characterization method can be applied both to physical characterizations of various two-dimensional layered materials as well as to the use of these layered materials for biosensing applications as shown earlier, due to the favorable properties of graphene plasmons. © 2016 Optical Society of America. Source


Galvan M.V.,National University of Santa | Peresin M.S.,VTT Technical Research Center of Finland | Mocchiutti P.,National University of Santa | Granqvist N.,BioNavis Ltd | And 2 more authors.
Cellulose | Year: 2015

The adsorption behavior of polyelectrolyte complexes (PECs) of poly(allylamine hydrochloride) (PAH) and 4-O-methylglucuronoxylan (Xyl) onto silica surface, cellulose nanofibrils (CNFs) model surfaces, and unbleached softwood kraft fibers was studied. Different charge ratios and ionic strengths of the liquid medium (q−/q+: 0.3, 0.5 and 0.8 in 1 mM NaCl, and q−/q+: 0.2, 0.3 and 0.5 in 10 mM NaCl), at pH 7.5 were considered. First, the complexes obtained were characterized by measuring the charge density, the particle size and the zeta potential. Then, the adsorption of PAH alone and PECs on silica and CNF model surfaces were studied by quartz crystal microbalance with dissipation monitoring (QCM-D) and surface plasmon resonance (SPR). The QCM-D test indicated that: (a) adsorbed cationic layers of PECs were soft in 10 mM NaCl, (b) higher adsorption was observed at higher ionic strength and (c) the highest adsorption of complex and coupled water was found at a charge ratio of 0.3. The SPR results analyzed together with the corresponding QCM-D results revealed that a significant portion of the adsorbed layers corresponded to coupled water on the cationic PEC structures. Morphology and structures of the adsorbed PEC layers studied using atomic force microscopy showed that the majority of the PECs were spherical, while some bigger aggregates were also found. Finally, the retention of different PECs on an unbleached softwood pulp was determined and the maximum retention was obtained when the PEC charge ratio was 0.5 in a 10 mM NaCl solution. © 2015, Springer Science+Business Media Dordrecht. Source


Liang H.,Chongqing University | Liang H.,University of Helsinki | Miranto H.,University of Helsinki | Miranto H.,BioNavis Ltd | And 6 more authors.
Sensors and Actuators, B: Chemical | Year: 2010

A surface plasmon resonance (SPR) setup in Kretschmann configuration is being utilized as a refractometer for both liquids as well as ultrathin films. The SPR signal detection technology used is based on a goniometer approach providing a wide angular scan range which facilitates highly accurate liquid and gas phase measurements. Attention was paid to improve sample handling and preparation. In order to avoid cross-contamination between measurements an easily removable and exchangeable molded PDMS flow cell was used during the measurements. By careful choice of components for liquid handling the dead volume of the system could be reduced down to some microliters. The angular change and thus the refractive index for sucrose, ethylene glycol (EG) and ethanol solutions with different concentrations, the thickness and refractive index of deposited Langmuir-Blodgett (LB) films, and the interaction kinetics between a biotin containing self-assembled monolayer (SAM) and streptavidin were determined. The measured refractive indices of sucrose, EG and ethanol solutions corresponded well with literature values. LB films were characterized by measuring the complete SPR curve in an angular scan range from 40 to 78°. A two-color SPR approach combined with two-media measurements was successfully employed for simultaneous and unambiguous determination of both refractive index and thickness of stearic acid monolayers. The thickness obtained for the stearic acid monolayer was 2.66 nm, and the refractive indices at 635 and 670 nm were 1.5800 and 1.4138, respectively. The developed sensor-plate holder enabled functionalization of the SPR gold chip outside the instrument, therefore making the sample handling more flexible. The affinity constant obtained for the streptavidin-biotin interaction was 1.01 × 10-8 M. The total angle SPR method used in this study clearly shows its potential to be used as a refractometer for both liquids and ultrathin films, as well as for traditional liquid phase biomolecular kinetic studies. © 2010 Elsevier B.V. All rights reserved. Source


Kuncova-Kallio J.,BioNavis Ltd | Jokinen A.,BioNavis Ltd | Sadowski J.W.,BioNavis Ltd | Granqvist N.,University of Helsinki
2013 International Conference on Manipulation, Manufacturing and Measurement on the Nanoscale, 3M-NANO 2013 - Conference Proceedings | Year: 2013

Nanolaminates play a significant role in the precision optical components, and protective barrier coatings. We present a new non-destructive method for characterization of nanolaminates in terms of thickness and refractive index based on Multi-Parametric Surface Plasmon Resonance (MP-SPR). In this paper, we briefly compare novel MP-SPR technology and traditional ellipsometry approach and then show MP-SPR on three examples that would be difficult-to-measure with ellipsometry. In the first case, MP-SPR is used to measure thickness of Langmuir-Blodgett multilayer film of Cr-Au-SACd, where each SACd layer can be measured individually without averaging. In the second case, vacuum deposited Cr-Au-TaC (tetragonal amorphous carbon) is measured. In the third case, alternating nanolayers of Al2O3-Pt deposited by Atomic Layer Deposition are measured. This shows that Multi-Parametric Surface Plasmon Resonance (MP-SPR) overcomes drawbacks of traditional optical methods and enables measurements of metal (light absorbing) nanolaminates and of ultrathin nanolayers. © 2013 IEEE. Source

Discover hidden collaborations