Electrochwmical Deposition of ZnO Nanorod on Graphene

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Electrochemical Deposition of ZnO Nanorods on Transparent Reduced Graphene Oxide Electrodes for Hybrid Solar Cells

Inter science. 2010A

PresentationTran Ngoc Cuong

2010/11/27

Abstract

Monocrystalline ZnO nanorods with high donor concentration areelectrochemically deposited reduced graphene oxide films on quartz.

Vertically aligned ZnO nanorod arrays were grown on a glass subtrate by using hydrothermal method.

The GO sheet were physically attached to the tip by assembling the sheets on the nanorod.

Graphene nanomesh is treated by using the photocatalytic property of the ZnO nanorod contained smaller oxygen.

Graphene nanomesh reduced by hydrazine showed as a broad sheet of P-type semiconductor

Method analysis and results

The apparatus in used: X-ray diffraction,transmission electron microscopy, photoluminescence, and Raman spectra.

Results:

- The obtained ZnO NRs on rGO are usedto fabricate inorganic–organic hybrid solar cells.- The rGO films with a higher conductivity have asmaller work function and show a better performance in the fabricated solarcells.-XPS and showed that partical photocatalytic reduction of GO during the local photo-degradation of graphene sheet at the contact place with the tip of the ZnO nanorod.

- The Graphene nanomesh presented a P-type semiconducting behavior in a wide sheet with no doping.

Fabrication of GNM

1. Mechanically peeled off GO as the starting material.

2. GO were assembled on ZnO nanorods using PMMA

etch transfer method.

3. Removing PMMA in water.

4. illuminated by UV-Led source (5 mW/cm2, 255 nm)

for 10 h.

5. GNM obtain were also reduced by hydrazine vapor for 1h.

PMMA block

SiO2 wafer

ZnO nanorods

Glass subtrate

Mechanically peel off

Transfer

Removing PMMA

UV source

C-OH

C=O

Results and discussion

Fig a: AFM images of the GO sheets.

Height show the thickness of the sheet was 0.9nm

Fig b: AFM images of the graphene nanomeshes- Some pores are clearly seen on the sheet, formating of porous sheet- Thickness of the over sheets were smaller than GO.

The GO nanosheets deposited on the TiO2 thin film

Fig a: as-deposited

Fig b: annealed at 400 °C

Fig c: exposed to UV-visible light irradiation for 4 h in the photocatalytic reduction process.

Graphene oxide structure

Chemical reduction such as hydrazine, hydroquinone, sodium borohydride(NaBH4) has been presented as an effective way to remove oxygen functional groups from GO

Schematic of graphene oxide structure

Raman spectra

GO sheet

GNM

After reduced by hydrazine

-Raman spectroscopy was used to study the ordered/disordered crystal structures .

- The ratio ID/IG increased due to creating of the pores (as defects and disorders) in the graphenesheets

1583 cm-1

2683 cm-1

2673 cm-1

1348 cm-1

Mechanism of photocatalyst

Electron will move easily from ZnO nanorods to Graphene, and global reduction of the sheets.The holes accumulated in the tip of the ZnO nanorods could produce ac-tive OH- radicals near the surface of the tip for the local oxidation and the local degradation of the sheets

The larger diameter of the pores due to higher humidity near the hy-drophilic tip of the nanorods.

XPS valence spec-tra

Sumary

Advantage:

-Graphene nanomesh were synthesized using local photodegradation of GO sheets by the tip of vertically aligned ZnO nanorod arrays.

-The graphene nanomeshes presented a p-type semiconducting behavior in a wide sheet and with no doping .Therefore the Nanomeash structure is able to open up a band gap in a large sheet of graphene.

Disadvantage:

- The asymmetrical shape of the 2D band is clearly seen, showing the presence of the multilayer graphene nanomesh in the samples.