Search results for "Feen"
showing 10 items of 53 documents
Suspended graphene device fabrication
2016
Tämän pro gradu -tutkielman aiheena oli tutkia itsekantavien grafeeninäytteiden valmistusta. Grafeeni syntetisoitiin kaasufaasikasvatuksella ilmakehän paineessa kupariohutkalvoille. Kupariohutkalvot valmistattiin käyttämällä elektronisuihkuhöyrystystä. Projektin aikana synteesiprosessia parannettiin optimoimalla synteesiparametreja. Syntetisoinnin jälkeen grafeeninäytteet siirrettiin piinitridikalvoille, joihin oli valmistettu reikiä. Viimeinen vaihe siirrossa on PMMA tukikerroksen poisto grafeenin päältä, jota tutkittiin käyttämällä kahta eri menetelmää. Näistä ensimmäinen menetelmä oli lämpökäsittely ja toinen kriittisen pisteen kuivaus PMMA:n asetoniin liuottamisen jälkeen. Näytteet kuva…
Reduction-oxidation dynamics of oxidized graphene: Functional group composition dependent path to reduction
2018
Micrometer-sized oxidation patterns containing varying composition of functional groups including epoxy, ether, hydroxyl, carbonyl, carboxyl, were created in chemical vapor deposition grown graphene through scanning probe lithography and pulsed laser two-photon oxidation. The oxidized graphene films were then reduced by a focused x-ray beam. Through in-situ x-ray photoelectron spectroscopy measurement, we found that the path to complete reduction depends critically on the total oxygen coverage and concentration of epoxy and ether groups. Over the threshold concentrations, a complex reduction-oxidation process involving conversion of functional groups of lower binding energy to higher bindin…
Revealing lattice disorder, oxygen incorporation and pore formation in laser induced two-photon oxidized graphene
2019
Abstract 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. Furt…
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…
Heterogeneous fenton oxidation using magnesium ferrite nanoparticles for ibuprofen removal from wastewater: optimization and kinetics studies
2020
In this study, the catalytic properties of Fenton-like catalyst based on magnesium ferrite nanoparticles for IBP degradation were examined. Structural and morphological studies showed the low crystallinity and mesoporous structure for the catalyst obtained via a glycine-nitrate method. The influences of catalyst dosage, oxidant concentration, and solution pH on the pollutant degradation were investigated. The pseudo-first-order model describes kinetic data, and under optimal condition (catalyst dose of 0.5 g L-1, H2O2 concentration of 20.0 mM, and pH of 8.0), apparent rate constant reached 0.091 min-1. It was shown that Fenton reaction was mainly induced by iron atoms on the catalyst surfac…
Ion pair recognition by ditopic crown ether based bis-urea and uranyl salophen receptors
2016
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…