Decoration of graphene sheets with metal and metal oxide nanostructures by low-pressure plasma deposition

Khan , Hafeez Ullah (2017) Decoration of graphene sheets with metal and metal oxide nanostructures by low-pressure plasma deposition. PhD thesis, University of Trento.

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Abstract

This thesis was dedicated to decorate graphene sheets with metal and metal oxide nanostructures by RF sputtering technique. Two main objectives were focused in this thesis. 1) To decorate graphene sheets uniformly with metal and metal oxide nanostructure without agglomeration. 2) To explore different kinds of application of decorated graphene sheets with metal and metal oxide nanostructures In the first step, we presented the experimental study results about Nb2O5 deposition onto graphite nanoplatelets (GNPs) by the variation of the deposition process parameters. The structural, chemical and electronic properties of the decorated GNPs with Nb2O5 layers were studied. It was found that with deposition of Nb2O5 layers onto GNPs, tensile strain was developed into the planes of the GNPs. The induced tensile strain in and between the planes of GNPs increased with raising the amount of the Nb2O5 concentration. TEM images shows that GNPs decorated with around 5 to10 nm uniform layer of Nb2O5 at 100 W on their surface were successfully fabricated. From the XPS analysis it was confirmed that, by increasing Nb2O5 layer thickness on the GNPs surface with rising RF power values binding energy downshift in C 1s peak suggests a p-type doping of GNPs due to charge transfer at the interface as a consequence of the higher work function difference between the Nb2O5 (4.70 eV) and GNPs (4.33 eV). In the second step, the interface between the graphene sheets and Nb2O5 nanoparticles were studied. It was established that the structural defects were pronounced with increasing amounts of the Nb2O5 concentration. XPS measurement on graphene/Nb2O5 suggests p-type doping of graphene due to charge transfer at the interface as a consequence of the high work function of Nb2O5. The strong p-doping effect was also confirmed by Raman analysis where the positions of the G and 2D peaks of graphene gradually upshifted upon increasing the Nb2O5 concentration. The uniform distribution of decorated Nb2O5 nanoparticles onto graphene was confirmed from TEM analysis. The ferromagnetic behavior was observed for the undecorated graphene and decorated graphene with Nb2O5 nanoparticles. The ferromagnetic behavior of graphene was enhanced with decoration of the Nb2O5 nanoparticles. In the third step, the effect of the Mg concentration on the structural, chemical and morphological properties of the graphene was described. Well dispersed Mg nanoparticles were decorated onto graphene sheets. It was found that from the XRD results, different sizes of the crystalline Mg nanoparticles were obtained onto graphene sheets with variation of the process parameters.. Raman spectra indicated that G and 2D bands of the graphene were shifted to higher wavenumber with deposition of Mg nanoparticles. The well dispersed and small size of Mg nanoparticles in the range of (8-12 nm) onto graphene sheets was decorated by using a high powder vibration frequency. No agglomeration of the sputtered particles was observed with high powder vibration frequency. This observation was confirmed by TEM micrographs. XPS analysis revealed that the decorated Mg nanoparticles onto graphene were oxidized due to exposure to the atmosphere. The well dispersed decorated Mg nanoparticles onto graphene sheets were studied for the hydrogen absorption and desorption at two different temperatures 330 oC and 360 oC at 2 and 8 bars pressure. The hydrogen up taking capacity for the decorated graphene sheets with Mg nanoparticles was 3 wt. % in whole composite. However, the up taking hydrogen storage capacity of the only Mg nanoparticles was 6.6 wt. %. In the last step, the interaction of the graphene sheets with TiO2 nanoparticles was studied. The XRD results indicated that the lattice of the graphene sheets was distorted with increasing amount of the TiO2 concentration. The particle nature of the deposited TiO2 was confirmed by TEM examination and also the TEM analysis shows that TiO2 nanoparticles were uniformly distributed onto graphene sheets. The Raman analysis showed that the G and 2D bands of graphene were shifted to higher wavenumber with increasing TiO2 concentration onto graphene sheet confirming the p doped graphene with TiO2 nanoparticles. The XPS analysis further confirmed the p doping of graphene upon the deposition of the TiO2 nanoparticles. The binding energy downshift the C 1s core level of was observed after charge transfer from graphene to TiO2 nanoparticles due to the larger work function of TiO2 relatively to that of graphene. It was observed that decorated graphene sheets with TiO2 nanoparticles shows reasonably catalytic activity.

Item Type:Doctoral Thesis (PhD)
Doctoral School:Physics
PhD Cycle:29
Subjects:Area 02 - Scienze fisiche > FIS/01 FISICA SPERIMENTALE
Area 09 - Ingegneria industriale e dell'informazione > ING-IND/22 SCIENZA E TECNOLOGIA DEI MATERIALI
Area 02 - Scienze fisiche > FIS/03 FISICA DELLA MATERIA
Repository Staff approval on:20 Apr 2017 11:23

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