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167 results on '"Myllyperkiö, Pasi"'

1. Optically Forged Diffraction-Unlimited Ripples in Graphene

Author

Koskinen, Pekka, Karppinen, Karoliina, Myllyperkiö, Pasi, Hiltunen, Vesa-Matti, Johansson, Andreas, and Pettersson, Mika

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

In nanofabrication, just as in any other craft, the scale of spatial details is limited by the dimensions of the tool at hand. For example, the smallest details for direct laser writing with far-field light are set by the diffraction limit, which is approximately half of the used wavelength. In this work, we overcome this universal assertion by optically forging graphene ripples that show features with dimensions unlimited by diffraction. Thin sheet elasticity simulations suggest that the scaled-down ripples originate from the interplay between substrate adhesion, in-plane strain, and circular symmetry. The optical forging technique thus offers an accurate way to modify and shape two-dimensional materials and facilitates the creation of controllable nanostructures for plasmonics, resonators, and nano-optics., Comment: 19 pages, 4 figures (1 TOC figure)

Published
2018
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3. Patterning and tuning of electrical and optical properties of graphene by laser induced two-photon oxidation

Author

Aumanen, Jukka, Johansson, Andreas, Koivistoinen, Juha, Myllyperkiö, Pasi, and Pettersson, Mika

Subjects
Condensed Matter - Materials Science
Abstract

Graphene, being an ultrathin, durable, flexible, transparent material with superior conductivity and unusual optical properties, promises many novel applications in electronics, photonics and optoelectronics. For applications in electronics, patterning and modification of electrical properties is very desirable since pristine graphene has no band gap. Here we demonstrate a simple all-optical patterning method for graphene, based on laser induced two-photon oxidation. By tuning the intensity of irradiation and the number of pulses the level of oxidation can be controlled to high precision and, therefore, a band gap can be introduced and electrical and optical properties can be continuously tuned. Arbitrary complex patterning can be performed for air-suspended monolayer graphene or for graphene on substrates. The method works at room temperature in ambient air and no additional processing step is needed. The presented concept allows development of all-graphene electronic and optoelectronic devices and complex circuits with an all-optical method., Comment: 24 pages, 9 figures

Published
2014
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4. Ultrastiff graphene

Author

Hiltunen, Vesa-Matti, Koskinen, Pekka, Mentel, Kamila K., Manninen, Jyrki, Myllyperkiö, Pasi, Pettersson, Mika, and Johansson, Andreas

Published
2021
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6. Fabrication and characterization of vacuum deposited fluorescein thin films

Author

Jalkanen, Pasi, Kulju, Sampo, Arutyunov, Konstantin, Antila, Liisa, Myllyperkiö, Pasi, Korppi-Tommola, Jouko, Ihalainen, Teemu, Kääriäinen, Tommi, and Kääriäinen, Marja-Leena

Subjects
Condensed Matter - Materials Science, Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

Simple vacuum evaporation technique for deposition of dyes on various solid surfaces has been developed. The method is compatible with conventional solvent-free nanofabrication processing enabling fabrication of nanoscale optoelectronic devices. Thin films of fluorescein were deposited on glass, fluorine-tin-oxide (FTO) coated glass with and without atomically layer deposited (ALD) nanocrystalline 20 nm thick anatase TiO2 coating. Surface topology, absorption and emission spectra of the films depends on their thickness and the material of supporting substrate. On a smooth glass surface the dye initially formes islands before merging into a uniform layer after 5 to 10 monolayers. On FTO covered glass the absorption spectra are similar to fluorescein solution in ethanol. Absorption spectra on ALD-TiO2 is red shifted compared to the film deposited on bare FTO. The corresponding emission spectra at {\lambda} = 458 nm excitation show various thickness and substrate dependent features, while the emission of films deposited on TiO2 is quenched due to the effective electron transfer to the semiconductor conduction band., Comment: 24 pages including 5 figures

Published
2011
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19. Tuning protein adsorption on graphene surfaces via laser-induced oxidation

Author

Sitsanidis, Efstratios D., Schirmer, Johanna, Lampinen, Aku, Mentel, Kamila K., Hiltunen, Vesa-Matti, Ruokolainen, Visa, Johansson, Andreas, Myllyperkiö, Pasi, Nissinen, Maija, and Pettersson, Mika

Subjects
spektroskopia, grafeeni, hapettuminen, proteiinit, atomivoimamikroskopia, lasertekniikka, mikrosirut, fluoresenssimikroskopia
Abstract

An approach for controlled protein immobilization on laser-induced two-photon (2P) oxidation patterned graphene oxide (GO) surfaces is described. Selected proteins, horseradish peroxidase (HRP) and biotinylated bovine serum albumin (b-BSA) were successfully immobilized on oxidized graphene surfaces, via non-covalent interactions, by immersion of graphene-coated microchips in the protein solution. The effects of laser pulse energy, irradiation time, protein concentration and duration of incubation on the topography of immobilized proteins and consequent defects upon the lattice of graphene were systemically studied by atomic force microscopy (AFM) and Raman spectroscopy. AFM and fluorescence microscopy confirmed the selective aggregation of protein molecules towards the irradiated areas. In addition, the attachment of b-BSA was detected by a reaction with fluorescently labelled avidin-fluorescein isothiocyanate (Av-FITC). In contrast to chemically oxidized graphene, laser-induced oxidation introduces the capability for localization on oxidized areas and tunability of the levels of oxidation, resulting in controlled guidance of proteins by light over graphene surfaces and progressing towards graphene microchips suitable for biomedical applications. peerReviewed

Published
2021

30. Time-resolved coherent anti-Stokes Raman-scattering measurements of I2 in solid Kr: Vibrational dephasing on the ground electronic state at 2.6–32 K.

Author

Kiviniemi, Tiina, Aumanen, Jukka, Myllyperkiö, Pasi, Apkarian, V. A., and Pettersson, Mika

Subjects
RAMAN effect, LIGHT scattering, IODINE, KRYPTON, MATRICES (Mathematics), TEMPERATURE, PHONONS
Abstract

Time-resolved coherent anti-Stokes Raman-scattering (CARS) measurements are carried out for iodine (I2) in solid krypton matrices. The dependence of vibrational dephasing time on temperature and vibrational quantum number v is studied. The v dependence is approximately quadratic, while the temperature dependence of both vibrational dephasing and spectral shift, although weak, fits the exponential form characteristic of dephasing by pseudolocal phonons. The analysis of the data indicates that the frequency of the pseudolocal phonons is ∼30 cm-1. The longest dephasing times are observed for v=2 being ∼300 ps and limited by inhomogeneous broadening. An increase in the dephasing rate of v=2 as the temperature is lowered to T=2.6 K is taken as a clear indication of lattice-strain-induced inhomogeneity of the ensemble coherence. [ABSTRACT FROM AUTHOR]

Published
2005
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31. From Seeds to Islands: Growth of Oxidized Graphene by Two-Photon Oxidation

Author

Koivistoinen, Juha, Sládková, Lucia, Aumanen, Jukka, Koskinen, Pekka, Roberts, Kevin, Johansson, Andreas, Myllyperkiö, Pasi, and Pettersson, Mika

Subjects
kuviointi, oxidation, grafeeni
Abstract

The mechanism of two-photon induced oxidation of single-layer graphene on Si/SiO2 substrates is studied by atomic force microscopy (AFM) and Raman microspectroscopy and imaging. AFM imaging of areas oxidized by using a tightly focused femtosecond laser beam shows that oxidation is not homogeneous but oxidized and nonoxidized graphene segregate into separate domains over the whole irradiated area. The oxidation process starts from point-like “seeds” which grow into islands finally coalescing together. The size of islands before coalescence is 30–40 nm, and the density of the islands is on the order of 1011 cm–2. Raman spectroscopy reveals growth of the D/G band ratio along the oxidation. Sharpness of the D-band which persists over a large range of oxidation and the maximal value of the intensity ratio of the D- and G-bands (∼0.8) indicates that graphene oxidation proceeds by an increase of the oxidized area rather than progression of oxidized areas to fully disordered structure. A phenomenological model is developed which explains the observations. According to the model, the probability for oxidation of a site next to an already oxidized site is 5 orders of magnitude higher than oxidation of pristine graphene. Irradiation of an extended area by raster scanning leads to a formation of an irregular nanomesh of oxide islands with a narrow size distribution. The phenomenological model yields similar results as the experiment. This study forms a basis for controlled use of two-photon oxidation for tailoring properties of graphene and patterning it with submicrometer resolution. peerReviewed

Published
2016

33. Optical Forging of Graphene into Three-Dimensional Shapes

Author

Johansson, Andreas, primary, Myllyperkiö, Pasi, additional, Koskinen, Pekka, additional, Aumanen, Jukka, additional, Koivistoinen, Juha, additional, Tsai, Hung-Chieh, additional, Chen, Chia-Hao, additional, Chang, Lo-Yueh, additional, Hiltunen, Vesa-Matti, additional, Manninen, Jyrki J., additional, Woon, Wei Yen, additional, and Pettersson, Mika, additional

Published
2017
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37. Electronic spectroscopy of I2-Xe complexes in solid Krypton

Author

Hulkko, Eero, Ahokas, Jussi, Lindgren, Johan, Myllyperkiö, Pasi, and Pettersson, Mika

Subjects
jodi, Electronic spectroscopy, varauksensiirto, charge-transfer, Elektroninen spektroskopia, complex, kompleksi
Abstract

In the present work, we have studied ion-pair states of matrix-isolated I2 with vacuum-UV absorption and UV-vis-NIR emission, where the matrix environment is systematically changed by mixing Kr with Xe, from pure Kr to a more polarizable Xe host. Particular emphasis is put on low doping levels of Xe that yield a binary complex I2–Xe, as verified by coherent anti-Stokes Raman scattering (CARS) measurements. Associated with interaction of I2 with Xe we can observe strong new absorption in vacuum-UV, redshifted 2400 cm−1 from the X → D transition of I2. Observed redshift can be explained by symmetry breaking of ion-pair states within the I2–Xe complex. Systematic Xe doping of Kr matrices shows that at low doping levels, positions of I2 ion-pair emissions are not significantly affected by complexation with Xe, but simultaneous increase of emissions from doubly spin-excited states indicates non-radiative relaxation to valence states. At intermediate doping levels ion-pair emissions shift systematically to red due to change in the average polarizability of the environment. We have conducted spectrally resolved ultrafast pump-probe ion-pair emission studies with pure and Xe doped Kr matrices, in order to reveal the influence of Xe to I2 dynamics in solid Kr. Strikingly, relaxed emission from the ion-pair states shows no indication of complex presence. It further indicates that the complex escapes detection due to a non-radiative relaxation. peerReviewed

Published
2012

50. Second-harmonic Generation Microscopy of Carbon Nanotubes

Author

Huttunen, Mikko J., primary, Herranen, Olli, additional, Johansson, Andreas, additional, Jiang, Hua, additional, Mudimela, Prasantha R., additional, Myllyperkiö, Pasi, additional, Bautista, Godofredo, additional, Nasibulin, Albert G., additional, Kauppinen, Esko I., additional, Ahlskog, Markus, additional, Kauranen, Martti, additional, and Pettersson, Mika, additional

Published
2012
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