**2. Emerging etch technologies of graphene surfaces**

Graphene layers have a number of independent bandgaps, e.g., single layer has no bandgap, but a bilayer has bandgap, and could be utilized to make transistor a superior performance. The layer-by-layer graphene etching would form (i) a cleaner surface with removed residues and (ii) thinner graphene film leading to smaller bandgap value until there is no bandgap at a single layer. Depending on the types of defects such as disorder [33], doping [34], external field [35] and mechanic strain [36–40], the etching can make the host material (e.g., graphene) very useful (high conductivity, high mobility, high work function, etc.) [41]. As a result, bandgap can be higher (or lower) depending on the types of vacancy defects and etching rates [41].

## **2.1 O2 plasma etching**

Plasma etch technology presents many advantages such as easy scale-up, manipulation and mass production. Under O2 plasma exposure, graphene multilayers were well-etched on SiO2 [23, 25] or SiC [24]. In 2014, the etching of host bilayer graphene was carried out by O2 using ICP and RIE apparatuses on the vertical and horizontal etch directions (**Figure 2a, b**) [23]. However, this approach formed defects during the use of RIE, but the defects were very few in the ICP case because of the high damage energy of RIE. Raman data provided the proof through disorder characteristics based on ID/IG ratio (0.94 and 1.18) when utilizing RIE and ICP, respectively [23]. Treating another substrate, SiC, the contact angle changed from 92.7° (multilayer), 91.9° (bilayer) and 92.5° (single layer) down to 70° when one layer epitaxial graphene etched away at 10 W and 2 min (**Figure 2c, d**) [24]. In 2011, through nanosphere lithography with low-power O2 plasma, Liu et al. found out the etched ordering of graphene nanoribbons (GNRs) on SiO2, which performed well in various shapes such as branches, chains, connected rings and circular rings (**Figure 2e**) [25].

#### **2.2 N2 plasma etching and postannealing**

Yang et al. utilized N2 plasma and postannealing (Ar/O2, 900°C), another technology in integration of layer-by-layer thinned plasma and post-annealing.

**65**

**Figure 2.**

D-peak (**Figure 3c**) [27].

*Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim).*

*The New Etching Technologies of Graphene Surfaces DOI: http://dx.doi.org/10.5772/intechopen.92627*

As a result, this dry-etching thinned regarding layer-by-layer easily from intrinsic multilayer graphene (**Figure 3a**–**c**) [26]. In another innovative etch technology by Lim et al. [27] and Kim et al. [28], Lim et al. utilized a neutral beam ALE via two-step process of O2 radical absorption and Ar neutral beam desorption, and multilayer graphene was well-etched for each layer (**Figure 3d**). Although this etching was much more effective than the previous study [24–27], defects formed slightly on graphene lattice as high Raman

*(a) Sequence of graphene etching via O2 plasma. (b) Schematic of two etching mechanisms of O2 plasma: vertical etching and horizontal etching. (c, d) The contact angle of graphene/SiC without/with O2 plasma, respectively. (e) On-chip device assisted by O2-etched nanosphere graphene ((a) and (b) are reproduced with permission from [23], Copyright 2014, Springer; (c) and (d) are reproduced with permission from [24], Copyright 2010, American Chemical Society; (e) is reproduced with permission from [25], Copyright 2011,* 

**2.3 Cyclic etching (O2 adsorption and Ar desorption by ion beam)**

of Ar ion beam at optimized plasma energy (11.2 eV).

In 2017, Kim et al. newly innovated by adding two mesh grids between the plasma source and the substrate holder in the ICP chamber (**Figure 3e**–**j**) [28]. Consequently, the damage on graphene surface disappeared after the two-step plasma etching process of chemical absorption of O2 radical and physical desorption *The New Etching Technologies of Graphene Surfaces DOI: http://dx.doi.org/10.5772/intechopen.92627*

#### **Figure 2.**

*21st Century Surface Science - a Handbook*

*chemistry to tune its electronics and optoelectronics.*

**2. Emerging etch technologies of graphene surfaces**

Graphene layers have a number of independent bandgaps, e.g., single layer has no bandgap, but a bilayer has bandgap, and could be utilized to make transistor a superior performance. The layer-by-layer graphene etching would form (i) a cleaner surface with removed residues and (ii) thinner graphene film leading to smaller bandgap value until there is no bandgap at a single layer. Depending on the types of defects such as disorder [33], doping [34], external field [35] and mechanic strain [36–40], the etching can make the host material (e.g., graphene) very useful (high conductivity, high mobility, high work function, etc.) [41]. As a result, bandgap can be higher (or lower) depending on the types of vacancy defects

*Etch processing of graphene few-layer or graphene nanoribbon on various substrates through plasma, physic,* 

Plasma etch technology presents many advantages such as easy scale-up, manipulation and mass production. Under O2 plasma exposure, graphene multilayers were well-etched on SiO2 [23, 25] or SiC [24]. In 2014, the etching of host bilayer graphene was carried out by O2 using ICP and RIE apparatuses on the vertical and horizontal etch directions (**Figure 2a, b**) [23]. However, this approach formed defects during the use of RIE, but the defects were very few in the ICP case because of the high damage energy of RIE. Raman data provided the proof through disorder characteristics based on ID/IG ratio (0.94 and 1.18) when utilizing RIE and ICP, respectively [23]. Treating another substrate, SiC, the contact angle changed from 92.7° (multilayer), 91.9° (bilayer) and 92.5° (single layer) down to 70° when one layer epitaxial graphene etched away at 10 W and 2 min (**Figure 2c, d**) [24]. In 2011, through nanosphere lithography with low-power O2 plasma, Liu et al. found out the etched ordering of graphene nanoribbons (GNRs) on SiO2, which performed well in various shapes such as branches, chains, connected rings and

Yang et al. utilized N2 plasma and postannealing (Ar/O2, 900°C), another technology in integration of layer-by-layer thinned plasma and post-annealing.

**64**

and etching rates [41].

**Figure 1.**

**2.1 O2 plasma etching**

circular rings (**Figure 2e**) [25].

**2.2 N2 plasma etching and postannealing**

*(a) Sequence of graphene etching via O2 plasma. (b) Schematic of two etching mechanisms of O2 plasma: vertical etching and horizontal etching. (c, d) The contact angle of graphene/SiC without/with O2 plasma, respectively. (e) On-chip device assisted by O2-etched nanosphere graphene ((a) and (b) are reproduced with permission from [23], Copyright 2014, Springer; (c) and (d) are reproduced with permission from [24], Copyright 2010, American Chemical Society; (e) is reproduced with permission from [25], Copyright 2011, Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim).*

As a result, this dry-etching thinned regarding layer-by-layer easily from intrinsic multilayer graphene (**Figure 3a**–**c**) [26]. In another innovative etch technology by Lim et al. [27] and Kim et al. [28], Lim et al. utilized a neutral beam ALE via two-step process of O2 radical absorption and Ar neutral beam desorption, and multilayer graphene was well-etched for each layer (**Figure 3d**). Although this etching was much more effective than the previous study [24–27], defects formed slightly on graphene lattice as high Raman D-peak (**Figure 3c**) [27].

### **2.3 Cyclic etching (O2 adsorption and Ar desorption by ion beam)**

In 2017, Kim et al. newly innovated by adding two mesh grids between the plasma source and the substrate holder in the ICP chamber (**Figure 3e**–**j**) [28]. Consequently, the damage on graphene surface disappeared after the two-step plasma etching process of chemical absorption of O2 radical and physical desorption of Ar ion beam at optimized plasma energy (11.2 eV).

#### **Figure 3.**

*(a) Sequence of layer-by-layer etching via N2 irradiative and oxidative etch. (b, c) Raman data of pristine, irradiated and annealed multilayer graphene. (d) Schematic of ALE process of graphene via O2 radical absorption and Ar neutral beam desorption. (e) A double-grid ICP ion beam apparatus for graphene etching via chemical O2 absorption and physical low-energy Ar ion beam desorption. (f, g) OM and (h, i) AFM data of pristine bilayer graphene, and after an ALE cycle. (j) Raman data of pristine bilayer graphene after an ALE cycle for white dots of (f, g) ((a–c) are reproduced with permission from [26], Copyright 2011, IOP Publishing; (d) is reproduced with permission from [27], Copyright 2012, Elsevier; (e–j) are reproduced with permission from [28], Copyright 2017, Nature Publishing Group).*

### **2.4 Others (RIE, H2, CH4/H2 and Fe NPs)**

In addition, there are still strategies for graphene surface etching such as Ar/H2 mixture in reactive ion etching (RIE) (**Figure 4a**) [29], H2 etching during CVD graphene growth (**Figure 4b**–**e**) [30], CH4/H2 etching during CVD graphene growth (**Figure 4f**) [31] or thermally activated Fe nanoparticles (NPs) (**Figure 4g, h**) [32]. However, the demonstrated results showed high defects through very high D-peak intensity in Raman spectra [29] or the random and nonuniform nanoribbon-etched graphene [28] and nanotrench-etched graphene based on Fe NPs [32]. Compared with the developed etch technologies above, the etching method by Kim et al. [28] revealed to be the best to date because of perfectly no damage and layer-by-layer etching from an innovative ion beam ICP.

### **3. Applications based on etched graphene**

In **Table 1**, applications associated with the above etched-graphene investigations are briefly summarized. A chip utilized nanosphere-etched GNRs by O2 plasma at low power [25] and revealed the high-performance electronic device

**67**

mechanically.

*American Chemical Society).*

**Figure 4.**

*The New Etching Technologies of Graphene Surfaces DOI: http://dx.doi.org/10.5772/intechopen.92627*

with the exotic GNR architectures (chain, branch and circle ring). In another application, a metal oxide semiconductor (MOS)-like transistor was made; although the etched effect was formed, it simultaneously produced a high-energy plasma damage that induced poor electrical characteristics [27]. One more application related to the monolayer deep patterning was fabricated by etching (N2) and annealing (Ar/O2), and this pattern presented good quality for slight defects [26]. In 2015, Papon et al. fabricated the Y- and Z-shaped GNRs during CVD graphene growth, and the etching effect vehemently happened at high H2 concentrations [30]. But these shapes were random and not well-controlled

*(a) An RIE apparatus using Ar/H2 to etch graphene on SiO2. OM data of H2-etched graphene during CVD growth and then annealing (Ar/H2, 1000°C) under ambient atmosphere (b–d). (e) Raman data of etched graphene and partially oxidized Cu surface. (f) Schematic of few-layer graphene etching by thermally activated iron nanoparticles. (g) SEM data of etched few-layer graphene as nanotrench; tiny dots are iron NPs; scale bar is 0.8 μm. Inset is AFM data of few-layer graphene after being etched ((a) is reproduced with permission from [29], Copyright 2011, AIP Publishing; (b–e) are reproduced with permission from [30], Copyright 2015, the Royal Society of Chemistry; (f) is reproduced with permission from [31], Copyright 2018, American Chemical Society; (g) and (h) are reproduced with permission from [32], Copyright 2008,* 

*The New Etching Technologies of Graphene Surfaces DOI: http://dx.doi.org/10.5772/intechopen.92627*

*21st Century Surface Science - a Handbook*

**2.4 Others (RIE, H2, CH4/H2 and Fe NPs)**

*permission from [28], Copyright 2017, Nature Publishing Group).*

etching from an innovative ion beam ICP.

**3. Applications based on etched graphene**

In addition, there are still strategies for graphene surface etching such as Ar/H2 mixture in reactive ion etching (RIE) (**Figure 4a**) [29], H2 etching during CVD graphene growth (**Figure 4b**–**e**) [30], CH4/H2 etching during CVD graphene growth (**Figure 4f**) [31] or thermally activated Fe nanoparticles (NPs) (**Figure 4g, h**) [32]. However, the demonstrated results showed high defects through very high D-peak intensity in Raman spectra [29] or the random and nonuniform nanoribbon-etched graphene [28] and nanotrench-etched graphene based on Fe NPs [32]. Compared with the developed etch technologies above, the etching method by Kim et al. [28] revealed to be the best to date because of perfectly no damage and layer-by-layer

*(a) Sequence of layer-by-layer etching via N2 irradiative and oxidative etch. (b, c) Raman data of pristine, irradiated and annealed multilayer graphene. (d) Schematic of ALE process of graphene via O2 radical absorption and Ar neutral beam desorption. (e) A double-grid ICP ion beam apparatus for graphene etching via chemical O2 absorption and physical low-energy Ar ion beam desorption. (f, g) OM and (h, i) AFM data of pristine bilayer graphene, and after an ALE cycle. (j) Raman data of pristine bilayer graphene after an ALE cycle for white dots of (f, g) ((a–c) are reproduced with permission from [26], Copyright 2011, IOP Publishing; (d) is reproduced with permission from [27], Copyright 2012, Elsevier; (e–j) are reproduced with* 

In **Table 1**, applications associated with the above etched-graphene investigations are briefly summarized. A chip utilized nanosphere-etched GNRs by O2 plasma at low power [25] and revealed the high-performance electronic device

**66**

**Figure 3.**

#### **Figure 4.**

*(a) An RIE apparatus using Ar/H2 to etch graphene on SiO2. OM data of H2-etched graphene during CVD growth and then annealing (Ar/H2, 1000°C) under ambient atmosphere (b–d). (e) Raman data of etched graphene and partially oxidized Cu surface. (f) Schematic of few-layer graphene etching by thermally activated iron nanoparticles. (g) SEM data of etched few-layer graphene as nanotrench; tiny dots are iron NPs; scale bar is 0.8 μm. Inset is AFM data of few-layer graphene after being etched ((a) is reproduced with permission from [29], Copyright 2011, AIP Publishing; (b–e) are reproduced with permission from [30], Copyright 2015, the Royal Society of Chemistry; (f) is reproduced with permission from [31], Copyright 2018, American Chemical Society; (g) and (h) are reproduced with permission from [32], Copyright 2008, American Chemical Society).*

with the exotic GNR architectures (chain, branch and circle ring). In another application, a metal oxide semiconductor (MOS)-like transistor was made; although the etched effect was formed, it simultaneously produced a high-energy plasma damage that induced poor electrical characteristics [27]. One more application related to the monolayer deep patterning was fabricated by etching (N2) and annealing (Ar/O2), and this pattern presented good quality for slight defects [26]. In 2015, Papon et al. fabricated the Y- and Z-shaped GNRs during CVD graphene growth, and the etching effect vehemently happened at high H2 concentrations [30]. But these shapes were random and not well-controlled mechanically.


**Table 1.**

*Graphene etching methods and their applications. Source: "NA" is "not applicable".*
