0000000000289362
AUTHOR
Jyrki Manninen
showing 6 related works from this author
Making Graphene Luminescent by Direct Laser Writing
2020
Graphene is not intrinsically luminescent, due to a lack of bandgap, and methods for its creation are tricky for device fabrication. In this study, we create luminescent graphene patterns by a simple direct laser writing method. We analyze the graphene using Raman spectroscopy and find that the laser writing leads to generation of line defects after initial formation of point defects. This Raman data enables us to create a model that explains the luminescence by a formation of small domains due to confinement of graphene by line defects, which is conceptually similar to the mechanism of luminescence in graphene quantum dots. peerReviewed
Unusually high frequency natural VLF radio emissions observed during daytime in Northern Finland
2016
Geomagnetic field variations and electromagnetic waves of different frequencies are ever present in the Earth's environment in which the Earth's fauna and flora have evolved and live. These waves are a very useful tool for studying and exploring the physics of plasma processes occurring in the magnetosphere and ionosphere. Here we present ground-based observations of natural electromagnetic emissions of magnetospheric origin at very low frequency (VLF, 3–30 kHz), which are neither heard nor seen in their spectrograms because they are hidden by strong impulsive signals (sferics) originating in lightning discharges. After filtering out the sferics, peculiar emissions are revealed in these dig…
Ultrastiff graphene
2021
Graphene has exceptionally high in-plane strength, which makes it ideal for various nanomechanical applications. At the same time, its exceptionally low out-of-plane stiffness makes it also flimsy and hard to handle, rendering out-of-plane structures unstable and difficult to fabricate. Therefore, from an application point of view, a method to stiffen graphene would be highly beneficial. Here we demonstrate that graphene can be significantly stiffened by using a laser writing technique called optical forging. We fabricate suspended graphene membranes and use optical forging to create stable corrugations. Nanoindentation experiments show that the corrugations increase graphene bending stiffn…
Shaping graphene with optical forging: from a single blister to complex 3D structures
2020
Properties of graphene, such as electrical conduction and rigidity can be tuned by introducing local strain or defects into its lattice. We used optical forging, a direct laser writing method, under an inert gas atmosphere, to produce complex 3D patterns of single layer graphene. We observed bulging of graphene out of the plane due to defect induced lattice expansion. By applying low peak fluences, we obtained a 3D-shaped graphene surface without either ablating it or deforming the underlying Si/SiO2 substrate. We used micromachining theory to estimate the single-pulse modification threshold fluence of graphene, which was 8.3 mJ cm−2, being an order of magnitude lower than the threshold for…
Optical Forging of Graphene into Three-Dimensional Shapes
2017
Atomically thin materials, such as graphene, are the ultimate building blocks for nanoscale devices. But although their synthesis and handling today are routine, all efforts thus far have been restricted to flat natural geometries, since the means to control their three-dimensional (3D) morphology has remained elusive. Here we show that, just as a blacksmith uses a hammer to forge a metal sheet into 3D shapes, a pulsed laser beam can forge a graphene sheet into controlled 3D shapes in the nanoscale. The forging mechanism is based on laser-induced local expansion of graphene, as confirmed by computer simulations using thin sheet elasticity theory. peerReviewed
Electrical measurements of femtosecond laser treated graphene
2017
Tutkielman pääasiallinen tavoite oli valmistaa sähköisiin mittauksiin sopivia grafeenilaitteita ja tutkia femtosekuntilaserkäsittelyn vaikutusta grafeenin sähköisiin ominaisuuksiin. Tutkielmassa käsitellään grafeenin valmistamista kemiallisella kaasufaasipinnoituksella, laitegeometrian määrittelyä ja käsittelemättömän, sekä femtosekuntilaserilla käsitellyn grafeenin sähköisiä mittauksia. Grafeenin synteesin alustana käytettiin kupariohutkalvoja ja pääasiallisena lähtöaineena oli etanoli tai metaani. Metaanin käyttö grafeenin synteesissä johti paremmin toistettaviin tuloksiin. Lisäksi havaittiin, että synteesissä käytetyn uunin latausjärjestelmän teräksinen osa lisäsi kupariohutkalvon reikii…