Jouni Ahopelto

Learn More
Nanofibrillated cellulose, a polymer that can be obtained from one of the most abundant biopolymers in nature, is being increasingly explored due to its outstanding properties for packaging and device applications. Still, open challenges in engineering its intrinsic properties remain to address. To elucidate the optical and mechanical stability of(More)
In magnetocardiography (MCG) the magnetic field, produced by the electrical activity of the heart, is measured. This paper presents the preliminary results of the human fetal magnetocardiography (FMCG). The MCG of an adult heart was first recorded by BAULE and McFEE [1]. Recently, several research groups have utilized the superconducting quantum(More)
We present an approach where biomolecular self-assembly is used in combination with lithography to produce patterns of metallic nanoparticles on a silicon substrate. This is achieved through a two-step method, resulting in attachment of nanoparticles on desired sites on the sample surfaces, which allowed a detailed characterization. First, a genetically(More)
We study the relaxation of coherent acoustic phonon modes with frequencies up to 500 GHz in ultrathin free-standing silicon membranes. Using an ultrafast pump-probe technique of asynchronous optical sampling, we observe that the decay time of the first-order dilatational mode decreases significantly from ~4.7 ns to 5 ps with decreasing membrane thickness(More)
We report the changes in dispersion relations of hypersonic acoustic phonons in free-standing silicon membranes as thin as ∼8 nm. We observe a reduction of the phase and group velocities of the fundamental flexural mode by more than 1 order of magnitude compared to bulk values. The modification of the dispersion relation in nanostructures has important(More)
Citation Cuffe, John, Jeffrey K. Eliason, A. A. Maznev, Kimberlee C. Collins, Jeremy A. Johnson, Andrey Shchepetov, Mika Prunnila, et al. “Reconstructing Phonon Mean-Free-Path Contributions to Thermal Conductivity Using Nanoscale Membranes.” Phys. Rev. B 91, no. 24 (June 2015). © 2015 American Physical Society As Published(More)
A detailed understanding of the connections of fabrication and processing to structural and thermal properties of low-dimensional nanostructures is essential to design materials and devices for phononics, nanoscale thermal management, and thermoelectric applications. Silicon provides an ideal platform to study the relations between structure and heat(More)
control A. Shchepetov, M. Prunnila, F. Alzina, L. Schneider, J. Cuffe, H. Jiang, E. I. Kauppinen, C. M. Sotomayor Torres, and J. Ahopelto VTT Technical Research Centre of Finland, P.O. Box 1000, FI-02044 VTT, Espoo, Finland Catalan Institute of Nanotechnology, Campus de la UAB, 08193 Bellaterra (Barcelona), Spain Nanomaterials Group, Department of Applied(More)
We report on stress induced changes in the dispersion relations of acoustic phonons propagating in 27 nm thick single crystalline Si membranes. The static tensile stress (up to 0.3GPa) acting on the Si membranes was achieved using an additional strain compensating silicon nitride frame. Dispersion relations of thermally activated hypersonic phonons were(More)