**4. Graphene oxide nanosheets for surface and interfacial engineering**

#### **4.1. Atomically thin graphene oxide as a multifunctional dopant**

Highly oxidized GO with electron-withdrawing groups can be utilized as a strong p-type dopant of nanocarbon materials such as carbon nanotubes (CNTs) and graphene because of the charge transfer interactions between sp2 carbon and the oxidative functional groups in GO [20, 21]. Doping nanocarbon materials with GO nanosheets have advantages: stable and strong p-doping that maintains the intrinsic properties of pristine CNT films and chemical vapor deposition (CVD)-graphene. Controlling the surface wetting properties of nanocarbon films is very important for their use in optoelectronic devices, which are fabricated by layering a hydrophilic material on top of hydrophobic carbon electrodes. Moreover, deposited GO nanosheets on porous CNT networks can reduce the surface roughness of the film. Further, it is worth noting that the doping state assisted by GO nanosheets is stable for more than 40 days at room temperature and atmospheric pressure compared to that doped with nitric acid. **Figure 8** illustrates the advantage of GO nanosheets as p-type dopants for CVDgraphene. Graphene oxide doping decreased the sheet resistance of CVD-graphene from 600 to 292 Ω/sq. The doping effect of GO nanosheets on the CVD-graphene was demonstrated using Kelvin probe force microscopy (KPFM) and Raman spectroscopy results. The KPFM images associated with AFM images show that the surface potential of the graphene/single GO sheet is negatively shifted by 120 mV. The bright region in the Raman map of the 2D peak shows a p-doped area in a single GO nanosheet. The gate-dependent I-V characteristics of CVD-graphene and GO-doped CVD-graphene show that the hole mobility of CVD-graphene is almost unaffected by doping. The hole mobility of GO-coated graphene was found to be 3330 cm2 /Vs, which is only slightly lower than that of pristine graphene (under equivalent device positions before GO coating), 3500 cm2 /Vs. Graphene oxide nanosheets can be also used to modify the properties of single-walled carbon nanotube networks by p-doping, flattening the network surface, and making it hydrophilic. This is useful for fabricating optoelectronic devices onto GO modified graphene or single-walled carbon nanotube (SWCNT) films.

### **4.2. Graphene oxide as an interfacial modifier**

For the fabrication of SWCNT patterns on hydrophilic substrates, partially reduced GO nanosheets are used as interfacial adhesive layers on hydrophilic SiO2 surfaces. Hydrophobic materials can be easily detached from hydrophilic substrates. Thus, to obtain stable interfacial structure, hydrophilic substrates are usually treated with surface modifiers such as silane coupling agents. In this context, the deposition of GO onto substrates and its partial reduction has several advantages. The partially reduced GO having hydroxyl and carboxyl groups can play as a role of the interfacial adhesive between the substrate and the deposited materials. Moreover, this process is scalable and straightforward because uniform SWCNT networks can be formed even by spraying on plastic substrates. In terms of optoelectronic device application, partially reduced GO can be used for the work function engineering with the conducting and semiconducting materials. Uniform GO films and patterns can be fabricated by blow-assisted

spin coating and inkjet printing, respectively, and the surface energy of the GO surface can be modulated by thermal treatment in vacuum. The SWCNTs were selectively deposited onto partially reduced GO films with moderately hydrophobic properties as shown in **Figure 9**.

**Figure 9.** FESEM images of selectively deposited single-walled CNT films on partially reduced GO surfaces [22].

of CVD-grown graphene transferred on a GO sheet. (c) Atomic force microscope image and height profile showing the thickness of GO nanosheet, (d) kelvin probe force microscopy, and (e) Raman map of the 2D-band shift of CVD-

Chemically Exfoliated Graphene Nanosheets for Flexible Electrode Applications

http://dx.doi.org/10.5772/intechopen.77284

137

at atmospheric pressure and room temperature. (g) Gate-dependent I-V characteristics of CVD-grown graphene and

/Si substrate. (b) SEM image


**Figure 8.** (a) Schematic diagram of graphene/GO film fabricated on an HMDS-treated SiO<sup>2</sup>

grown graphene on a GO single sheet. (f) Electrical conductance variation of GO- and HNO3

GO-doped graphene. (h) AFM images of CVD-grown graphene with and without GO [21].

Chemically Exfoliated Graphene Nanosheets for Flexible Electrode Applications http://dx.doi.org/10.5772/intechopen.77284 137

**4. Graphene oxide nanosheets for surface and interfacial** 

Highly oxidized GO with electron-withdrawing groups can be utilized as a strong p-type dopant of nanocarbon materials such as carbon nanotubes (CNTs) and graphene because of

GO [20, 21]. Doping nanocarbon materials with GO nanosheets have advantages: stable and strong p-doping that maintains the intrinsic properties of pristine CNT films and chemical vapor deposition (CVD)-graphene. Controlling the surface wetting properties of nanocarbon films is very important for their use in optoelectronic devices, which are fabricated by layering a hydrophilic material on top of hydrophobic carbon electrodes. Moreover, deposited GO nanosheets on porous CNT networks can reduce the surface roughness of the film. Further, it is worth noting that the doping state assisted by GO nanosheets is stable for more than 40 days at room temperature and atmospheric pressure compared to that doped with nitric acid. **Figure 8** illustrates the advantage of GO nanosheets as p-type dopants for CVDgraphene. Graphene oxide doping decreased the sheet resistance of CVD-graphene from 600 to 292 Ω/sq. The doping effect of GO nanosheets on the CVD-graphene was demonstrated using Kelvin probe force microscopy (KPFM) and Raman spectroscopy results. The KPFM images associated with AFM images show that the surface potential of the graphene/single GO sheet is negatively shifted by 120 mV. The bright region in the Raman map of the 2D peak shows a p-doped area in a single GO nanosheet. The gate-dependent I-V characteristics of CVD-graphene and GO-doped CVD-graphene show that the hole mobility of CVD-graphene is almost unaffected by doping. The hole mobility of GO-coated graphene was found to be

/Vs, which is only slightly lower than that of pristine graphene (under equivalent

used to modify the properties of single-walled carbon nanotube networks by p-doping, flattening the network surface, and making it hydrophilic. This is useful for fabricating optoelectronic devices onto GO modified graphene or single-walled carbon nanotube (SWCNT) films.

For the fabrication of SWCNT patterns on hydrophilic substrates, partially reduced GO

materials can be easily detached from hydrophilic substrates. Thus, to obtain stable interfacial structure, hydrophilic substrates are usually treated with surface modifiers such as silane coupling agents. In this context, the deposition of GO onto substrates and its partial reduction has several advantages. The partially reduced GO having hydroxyl and carboxyl groups can play as a role of the interfacial adhesive between the substrate and the deposited materials. Moreover, this process is scalable and straightforward because uniform SWCNT networks can be formed even by spraying on plastic substrates. In terms of optoelectronic device application, partially reduced GO can be used for the work function engineering with the conducting and semiconducting materials. Uniform GO films and patterns can be fabricated by blow-assisted

nanosheets are used as interfacial adhesive layers on hydrophilic SiO2

carbon and the oxidative functional groups in

/Vs. Graphene oxide nanosheets can be also

surfaces. Hydrophobic

**4.1. Atomically thin graphene oxide as a multifunctional dopant**

the charge transfer interactions between sp2

device positions before GO coating), 3500 cm2

**4.2. Graphene oxide as an interfacial modifier**

**engineering**

136 Graphene Oxide - Applications and Opportunities

3330 cm2

**Figure 8.** (a) Schematic diagram of graphene/GO film fabricated on an HMDS-treated SiO<sup>2</sup> /Si substrate. (b) SEM image of CVD-grown graphene transferred on a GO sheet. (c) Atomic force microscope image and height profile showing the thickness of GO nanosheet, (d) kelvin probe force microscopy, and (e) Raman map of the 2D-band shift of CVDgrown graphene on a GO single sheet. (f) Electrical conductance variation of GO- and HNO3 -doped graphene with time at atmospheric pressure and room temperature. (g) Gate-dependent I-V characteristics of CVD-grown graphene and GO-doped graphene. (h) AFM images of CVD-grown graphene with and without GO [21].

**Figure 9.** FESEM images of selectively deposited single-walled CNT films on partially reduced GO surfaces [22].

spin coating and inkjet printing, respectively, and the surface energy of the GO surface can be modulated by thermal treatment in vacuum. The SWCNTs were selectively deposited onto partially reduced GO films with moderately hydrophobic properties as shown in **Figure 9**.
