Search results for "grafeeni"

Laser-induced tuning of graphene field-effect transistors for pH sensing

2023

Here we demonstrate, using pulsed femtosecond laser-induced two-photon oxidation (2PO), a novel method of locally tuning the sensitivity of solution gated graphene field-effect transistors (GFETs) without sacrificing the integrity of the carbon network of chemical vapor deposition (CVD) grown graphene. The achieved sensitivity with 2PO was (25 ± 2) mV pH−1 in BIS-TRIS propane HCl (BTPH) buffer solution, when the oxidation level corresponded to the Raman peak intensity ratio I(D)/I(G) of 3.58. Sensitivity of non-oxidized, residual PMMA contaminated GFETs was 20–22 mV pH−1. The sensitivity decreased initially by 2PO to (19 ± 2) mV pH−1 (I(D)/I(G) = 0.64), presumably due to PMMA residue remova…

Experimental studies on carbon nanotubes and graphene functionalized via physical adsorption with cellulose and avidin

2018

In this Thesis I have experimentally studied structural, electronic, and optical properties of hybrids of nanocarbon materials, carbon nanotubes (CNT) and graphene, and certain biomacromolecules. The latter are especially xylan, a type of hemicellulose, and avidin, an important protein. Complexes of CNT with hemicellulose are attractive because the hybrid material is soluble in water. The conductive transport properties of thin films of CNT /hemicellulose have been systematically studied with different experimental tools. These are low temperature DC conduction measurements, Kelvin probe microscopy, and optical conductivity measurements at terahertz frequencies. The results clearly indicate …

The role of oxidation treatments before and after CVD synthesis of graphene on copper catalytic surface

2021

Graphene is a sheet of honeycomb bonded carbon, that is only one atom thick. Aside from its remarkable strength, graphene has great conducting and photochemical prop erties. Due to its unique properties, it can be used as viable option for rare metals in circuits and in new type of measuring components. To express these properties at their best, graphene should be single crystal and as clean as possible. In this bachelor thesis, different treatment options for catalytic metal surface for graphene synthesis are studied in chemical vapor deposition growth. Different options to treat the catalytic metal layer were studied, such as changes in gas compositions in annealing process, electropolish…

From Seeds to Islands: Growth of Oxidized Graphene by Two-Photon Oxidation

2016

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. Sha…

Electronic structure of triangular, hexagonal and round graphene flakes

2009

Revealing lattice disorder, oxygen incorporation and pore formation in laser induced two-photon oxidized graphene

2019

Laser induced two-photon oxidation has proven to be a reliable method to pattern and control the level of oxidation of single layer graphene, which in turn allows the development of graphene-based electronic and optoelectronic devices with an all-optical method. Here we provide a full structural and chemical description of modifications of air-suspended graphene during the oxidation process. By using different laser irradiation doses, we were able to show via transmission electron microscopy, electron energy loss spectroscopy, electron diffraction and Raman spectroscopy how graphene develops from its pristine form up to a completely oxidized, porous and amorphous carbon layer. Furthermore, …

Grafeenioksidin luminesenssiominaisuudet

2016

Grafeeni on yksikerroksinen hiililevy, joka muodostuu toisiinsa sp2-sidoksilla kiinnittyneistä hiilistä. Grafeenioksidi on grafeenin hapettunut muoto, jossa levyn pintaan on liittynyt funktionaalisia happiryhmiä. Grafeenioksidilla on havaittu laaja luminesenssi, joka riippuu sen hapetusasteesta, pH:sta, viritysaallonpituudesta ja konsentraatiosta. Luminesenssin on arveltu aiheutuvan mm. grafeenioksidin sp2-alueista kvanttirajoituksen takia. Energia voi kvantituttua näillä pienillä alueilla happialueiden muodostaessa potentiaaliseinät niille. Luminesenssin on myös ehdotettu aiheutuvan rakennevirheistä aiheutuvista lokalisoiduista tiloista, funktionaalisten happiryhmien protonaatiosta ja depr…

Transparent hemicellulose-DWCNT electrode

2015

Carbon nanotubes (CNTs) and graphene have shown promising potential as next-generation transparent conducting materials due to their high electrical and thermal conductance, flexibility and transparency in both visible and infrared spectral regions. In this study transparent and conductive thin films with a novel hemicellulose and double-walled carbon nanotube (HC-DWCNT) hybrid material were produced with spray-coating, droplet casting and vacuum filtration deposition methods. HC-DWCNT material is easily dispersed in water and usable for mass-production. These films showed good conductivity, stability at ambient air, very good transparency in the visible and excellent transparency in the in…

Manufacturing of graphene nanodisks for surface plasmon measurements

2017

Grafeeni on ilmestynyt tieteen rintamalle kovalla ryminällä vasta viimeisen 13 vuoden aikana, mutta on jo nyt yksi mielenkiintoisimmista tutkimuskohteista, jolla voisi olla lukuisia sovelluksia tulevaisuudessa. Grafeeni on ilmestynyt myös plasmoniikan tutkimuskohteeksi sen lukuisten ainutlaatuisten sähköisten ja optisten ominaisuuksien takia ja sen ominaisuuksien muokattavuuden helppouden takia. Grafeeni voisi mahdollisesti korvata yleisesti käytössä olleet jalot metallit kuten kullan ja hopean pintaplasmonien tuotossa ja tutkimuksessa ja voisi johtaa uudenlaiseen valon kontrollointiin nanoskaalassa ja optiikan ja elektroniikan yhdistämiseen tässä pienessä mittakaavassa. Tässä työssä tavoit…

Measuring optical anisotropy in poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) films with added graphene

2015

Abstract Graphene is a 2D nanomaterial having a great potential for applications in electronics and optoelectronics. Composites of graphene with conducting polymers have shown high performance in practical devices and their solution-processability enables low-cost and high-throughput mass manufacturing using printing techniques. Here we measure the effect of incorporation of graphene into poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) to the optical anisotropy, absorbance and conductivity of the film. Uniaxial anisotropy in PEDOT:PSS films has been thought to be caused by the spin-coating process used in fabrication. We have characterized spray- and spin-coated films …