Search results for "grafeeni"
showing 10 items of 48 documents
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
Real-time monitoring of graphene patterning with wide-field four-wave mixing microscopy
2016
The single atom thick two-dimensional graphene is a promising material for various applications due to its extraordinary electronic, optical, optoelectronic, and mechanical properties. The demand for developing graphene based applications has entailed a requirement for development of methods for fast imaging techniques for graphene. Here, we demonstrate imaging of graphene with femtosecond wide-field four-wave mixing microscopy. The method provides a sensitive, non-destructive approach for rapid large area characterization of graphene. We show that the method is suitable for online following of a laser patterning process of microscale structures on single-layer graphene. peerReviewed
Preparation of graphene nanocomposites from aqueous silver nitrate using graphene oxide’s peroxidase-like and carbocatalytic properties
2020
AbstractThe present study evaluates the role of graphene oxide’s (GO’s) peroxidase-like and inherent/carbocatalytic properties in oxidising silver nitrate (AgNO3) to create graphene nanocomposites with silver nanoparticles (GO/Ag nanocomposite). Activation of peroxidase-like catalytic function of GO required hydrogen peroxide (H2O2) and ammonia (NH3) in pH 4.0 disodium hydrogen phosphate (Na2HPO4). Carbocatalytic abilities of GO were triggered in pH 4.0 deionised distilled water (ddH2O). Transmission electron microscope (TEM), scanning electron microscope (SEM), cyclic voltammetry (CV) and UV-Vis spectroscopy aided in qualitatively and quantitatively assessing GO/Ag nanocomposites. TEM and …
Rippling of two-dimensional materials by line defects
2020
Two-dimensional materials and their mechanical properties are known to be profoundly affected by rippling deformations. However, although ripples are fairly well understood, less is known about their origin and controlled modification. Here, motivated by recent reports of laser-controlled creation of line defects in graphene, we investigate how line defects could be used to control rippling in graphene and other two-dimensional materials. By sequential multi-scale coupling of density-functional tight-binding and continuum elasticity simulations, we quantify the amount of rippling when the number and the cumulative length of the line defects increase. Simulations show that elastic sheets wit…
Microwave photoassisted dissipation and supercurrent of a phase-biased graphene-superconductor ring
2021
Irradiating normal-superconducting junctions with microwave photons produce spectacular effects, such as Shapiro steps and photoinduced modifications of the dc supercurrent. Moreover, microwave irradiation can also have other, hitherto unexplored consequences, such as a photoassisted dissipation which is phase dependent. Here we present a finite-frequency measurement of both the dissipation and the supercurrent of a phase-biased graphene-superconductor junction in response to microwave photons. We find that, while the supercurrent response is well described by existing theory, the dissipation exhibits unexpected effects which need new theoretical elucidation. Especially with high frequency …
Stability limits of elemental 2D metals in graphene pores
2019
Two-dimensional (2D) materials can be used as stabilizing templates for exotic nanostructures, including pore-stabilized, free-standing patches of elemental metal monolayers. Although these patches represent metal clusters under extreme conditions and are thus bound for investigations, they are poorly understood as their energetic stability trends and the most promising elements remain unknown. Here, using density-functional theory simulations and liquid drop model to explore the properties of 45 elemental metal candidates, we identify metals that enable the largest and most stable patches. Simulations show that pores can stabilize patches up to $\sim 8$ nm$^2$ areas and that the most promi…
Time-Resolved Coherent Anti-Stokes Raman Scattering of Graphene: Dephasing Dynamics of Optical Phonon.
2017
We report dynamics of the G-mode in graphene probed with time-resolved coherent anti-Stokes Raman scattering measurements. By applying BOXCARS excitation geometry with three different excitation wavelengths, various nonlinear processes can be selectively detected due to energy and momentum conservation and temporal sequence of the pulses. The Raman signal due to resonant coherent excitation of the G-mode shows exponential decay with lifetime of ∼325 ± 50 fs. This decay time is shorter than expected based on the line width of the G-mode in the Raman spectrum. We propose that the unexpectedly short dephasing time is a result of dynamic variation of nonadiabatic coupling of the photoexcited el…
Limits of lateral expansion in two-dimensional materials with line defects
2021
The flexibility of two-dimensional (2D) materials enables static and dynamic ripples that are known to cause lateral contraction, shrinking of the material boundary. However, the limits of 2D materials' \emph{lateral expansion} are unknown. Therefore, here we discuss the limits of intrinsic lateral expansion of 2D materials that are modified by compressive line defects. Using thin sheet elasticity theory and sequential multiscale modeling, we find that the lateral expansion is inevitably limited by the onset of rippling. The maximum lateral expansion $\chi_{max}\approx 2.1\cdot t^2\sigma_d$, governed by the elastic thickness $t$ and the defect density $\sigma_d$, remains typically well belo…
Phase-dependent microwave response of a graphene Josephson junction
2021
Gate-tunable Josephson junctions embedded in a microwave environment provide a promising platform to in situ engineer and optimize novel superconducting quantum circuits. The key quantity for the circuit design is the phase-dependent complex admittance of the junction, which can be probed by sensing a radio frequency SQUID with a tank circuit. Here, we investigate a graphene-based Josephson junction as a prototype gate-tunable element enclosed in a SQUID loop that is inductively coupled to a superconducting resonator operating at 3 GHz. With a concise circuit model that describes the dispersive and dissipative response of the coupled system, we extract the phase-dependent junction admittanc…
Grafeenioksidin funktionalisointi
2014
Tämän pro gradu -tutkielman aiheena on grafeenioksidin kiehtova maailma. Tutkielman tavoitteena oli tehdä kattava kirjallisuuskatsaus grafeenioksidin funktionalisoinnista. Tutkielmassa käydään läpi grafeenioksidin tärkeimmät rakenteelliset piirteet, fysikaalis-kemialliset ominaisuudet, kemialliset funktionalisointimenetelmät sekä sovelluskohteet bioteknologiassa ja muualla. Ominaisuuksien tarkastelussa on kiinnitetty erityistä huomiota hapetusasteen merkitykseen sekä grafeenioksidin fluoresenssiin. Kemiallisten funktionalisointimenetelmien osiossa keskitytään lähinnä epoksidi- ja hydroksyyliryhmien funktionalisointireaktioihin. Karboksyylihapporyhmien reaktioista on annettu myös muutamia es…