Growth of nano-graphene on SrTiO3 (110) substrates by chemical vapour deposition

Transfer of graphene from metal catalyst to dielectrics is a complicated procedure which affects the quality of graphene. In the present work, direct growth of graphene was established on strontium titanate (SrTiO3) substrates with the means of chemical vapour deposition (CVD). The graphene growth on catalyst free dielectric substrates were carried out for 3, 4 and 7 h at 1000 degrees C. Raman spectrum showed D, G and 2D peaks of graphene for the samples. Scanning electron microscope (SEM) was used to get an initial measurement about the morphological structure. Energy Dispersive X-ray spectrometer attached with SEM was also used to get information about the composition of carbon content which showed a considerable increase for the CVD grown sample as compare to bare substrate. Atomic force microscope (AFM) images of the samples surface clearly showed multilayer graphene domains of different sizes and height for different growth time. AFM height profile showed an increase in vertical growth with the increase in growth time. X-ray photoelectron spectroscopy (XPS) was used to get further information about the presence of necessary elements like graphene (carbon), its bonding with STO substrates and the shift in position of fermi level of graphene layers. XPS mapping was also done to get information about the non-uniform growth of carbon surface grown on SrTiO3 surface

Multilayer graphene growth on polar dielectric substrates using chemical vapour deposition

High quality of graphene is necessary for its applications at industrial scale production. The most convenient way is its direct growth on dielectrics which avoid the transfer route of graphene from metal to dielectric substrate usually followed by graphene community. The choice of a suitable dielectric for the gate material which can replace silicon dioxide (SiO2) is in high demand. Various properties like permittivity, thermodynamic stability, film morphology, interface quality, bandgap and band alignment of other dielectrics with graphene needs more exploration. A potential dielectric material is required which could be used to grow graphene with all these qualities. Direct growth of graphene on magnesium oxide (MgO) substrates is an interesting idea and will be a new addition in the library of 2D materials. The present work is about the direct growth of graphene on MgO substrates by an ambient pressure chemical vapour deposition (CVD) method. We address the surface instability issue of the polar oxides which is the most challenging factor in MgO. Atomic force microscopy (AFM) measurements showed the topographical features of the graphene coated on MgO. X-ray photoelectron spectroscopy (XPS) study is carried out to extract information regarding the presence of necessary elements, their bonding with substrates and to confirm the sp-2 hybridization of carbon, which is a characteristic feature of graphene film. The chemical shift is due to the surface reconstruction of MgO in the prepared samples. For graphene-MgO interface, valence band offset (VBO) and conduction band offset (CBO) extracted from valence band spectra reported. Further, we predicted the energy band diagram for single layer and thin film of graphene. By using the room-temperature energy band gap values of MgO and graphene, the CBO is calculated to be 6.85 eV for single layer and 5.66 eV for few layer (1-3) of graphene layers

Suitable alkaline for graphene peeling grown on metallic catalysts using chemical vapor deposition

In chemical vapor deposition, the higher growth temperature roughens the surface of the metal catalyst and a delicate method is necessary for the transfer of graphene from metal catalyst to the desired substrates. In this work, we grow graphene on Pt and Cu foil via ambient pressure chemical vapor deposition (AP-CVD) method and further alkaline water electrolysis was used to peel off graphene from the metallic catalyst. We used different electrolytes i.e., sodium hydroxide (NaOH), potassium hydroxide (KOH), lithium hydroxide (LiOH) and barium hydroxide Ba(OH)(2) for electrolysis, hydrogen bubbles evolved at the Pt cathode (graphene/Pt/PMMA stack) and as a result graphene layer peeled off from the substrate without damage. The peeling time for KOH and LiOH was similar to 6 min and for NaOH and Ba(OH)(2) it was similar to 15 min. KOH and LiOH peeled off graphene very efficiently as compared to NaOH and Ba(OH)(2) from the Pt electrode. In case of copper, the peeling time is similar to 35 min. Different characterizations like optical microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and atomic force microscopy were done to analyze the as grown and transferred graphene samples

Coalescence of few layer graphene grains grown by chemical vapor deposition and their stacking sequence

Few layer graphene is attractive due to its extraordinary electronic and optical properties, which are strongly influenced by the orientation between the layers called as stacking sequence. It is challenging to synthesize high quality large size single or multi layer graphene crystals on the metal catalyst using chemical vapor deposition technique. The present work is about synthesis of few layer graphene grains on platinum foil using ambient pressure chemical together vapor deposition technique. The main focus is how the different grains coalesced and maintain the stacking sequence. Different characterization techniques are used to analyze the grains when they are in the process of merging to make a bigger grain. Scanning electron microscopy clearly shows different stacking sequences and merging of different nucleation sites of different grains. Interestingly, different stacking sequences are observed during the process of coalescence of grains. Raman spectroscopy gives accurate information about the number of layers and their stacking sequence. We observed Bernal AB and twisted layer stacking in the grains when they were combining together to grow into a bigger size. The full width at half maximum (FWHM) value of 2D Raman peaks appeared in the range of 52-69 cm(-1) which shows an increase from the value of single layer graphene (30.18 cm(-1)) and identifies Bernal stacking in grains. For twisted stacking FWHM values lie in the range of 19-32 cm(-1).Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) ; European Union (EU

Coalescence of few layer graphene grains grown by chemical vapor deposition and their stacking sequence

Few layer graphene is attractive due to its extraordinary electronic and optical properties, which are strongly influenced by the orientation between the layers called as stacking sequence. It is challenging to synthesize high quality large size single or multi layer graphene crystals on the metal catalyst using chemical vapor deposition technique. The present work is about synthesis of few layer graphene grains on platinum foil using ambient pressure chemical together vapor deposition technique. The main focus is how the different grains coalesced and maintain the stacking sequence. Different characterization techniques are used to analyze the grains when they are in the process of merging to make a bigger grain. Scanning electron microscopy clearly shows different stacking sequences and merging of different nucleation sites of different grains. Interestingly, different stacking sequences are observed during the process of coalescence of grains. Raman spectroscopy gives accurate information about the number of layers and their stacking sequence. We observed Bernal AB and twisted layer stacking in the grains when they were combining together to grow into a bigger size. The full width at half maximum (FWHM) value of 2D Raman peaks appeared in the range of 52-69 cm(-1) which shows an increase from the value of single layer graphene (30.18 cm(-1)) and identifies Bernal stacking in grains. For twisted stacking FWHM values lie in the range of 19-32 cm(-1).Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) ; European Union (EU

Synthesis of Graphene-MoS2 composite based anode from oxides and their electrochemical behavior

High energy storage capacity and longer life span make rechargeable Li-ion batteries the first choice in portable electronics. Here, a graphene-MoS2 composite material is investigated as a potential electrode material which enhances the electrochemical storage ability of the Li-ion batteries (LIBs). Graphene-MoS2 composite is synthesized from graphene oxide (GO), molybdenum trioxide and thiourea via hydrothermal route. Formation of graphene-MoS2 composite (molar ratio 1:2) is confirmed by X-ray diffraction (XRD). The characteristic phonons modes of graphene (D and G bands) and MoS2 (A1g and E2g) are observed in the Raman spectra of the synthesized graphene-MoS2 composite. Fourier- transform infrared (FTIR) spectroscopy showed reduction from GO to graphene in composite due to absence of C = O bond while the peaks observed at 900 cm−1 and 1095 cm−1 of Mo-O and S = O, respectively, supports the formation composite material. To investigate the diffusion rate of Li+ ions for anode material, the electrochemical impedance spectroscopy (EIS) measurements modeled with equivalent circuit has been performed, which showed the high diffusion rate of Li ions but with less cyclic stability due to drastic change in surface film resistance for increased number of cycles. The value of discharge capacity obtained for the first cycle is ~ 975 mAh/g, which dropped to 250 mAh/g after executing 80 cycles. For different cycles, rate capabilities have also been measured at different current densities. At initial current density of 100 mAh/g, the highest discharge capacity of 975 mAh/g is obtained. The current density dropped to 200 mAh/g from the highest current density of 1000 mAh/g after 40 cycles with a retention capacity of 20%. The present study confirmed that composite synthesized from precursors, namely, molybdenum trioxide and thiourea has the potential as an electrode for LIBs

Graphene/SrTiO3 hetero interface studied by X-ray photoelectron spectroscopy

The present paper focuses on study of graphene and strontium titanate (SrTiO3 or STO) interface. An ambient pressure chemical vapour deposition (AP-CVD) setup is used to grow graphene on STO (110) substrates in the presence of methane, argon and hydrogen gases at 1000 degrees C for 4 h. Raman spectroscopy measurements confirm the presence of graphene on STO substrates due to the existence of typical D and G peaks referring to graphene. These characteristic peaks are missing in the spectrum for bare substrates. X-ray photoelectron spectroscopy (XPS) is carried out for elemental analysis of samples, and study their bonding with STO substrates. We employed the valence band spectrum to calculate the valence band offset (VBO) and conduction band offset (CBO) at the G-STO interface. Also, we present an energy band diagram for Bi-layer and ABC (arranging pattern of carbon layers) stacked graphene layers. (C) 2016 Chinese Materials Research Society. Production and hosting by Elsevier B.V