The induced contaminations (e.g polymer residues or impurities in air) on nanomaterial surfaces have been a serious problem to probe their intrinsic properties and for unique applications in surface chemistry, electronic, and optoelectronic. The polymer residues still presented on chemical vapor deposited graphene surface after its wet transfer (e.g. poly(methyl methacrylate) (PMMA)) on the arbitrary substrates tends to cause problems such as electrical degradation and unwanted intentional doping. Polymer residues (e.g PMMA), defects, and other contaminations are commonly leaving the thin layers or the particles as residues on nanomaterials. Nowadays, the nanomaterials are receiving broad interests. Among them, grapheme [1-36], hexagonal-boron nitride (h-BN) [37-40], carbon nanotubes (CNTs) [41,42], and graphene oxide [43] are emerging as many promising potential materials with novel properties in electronics and optoelectronics (Figure 1). These nanomaterials have attracted a huge research interest in recent decades due to its anomalous properties such as very high carrier mobility, extremely high mechanical strength and optical transparency, electrical conductivity, chemical stability and thermal conductivity [1-43] and that is the reason above nanomaterials are being observed as a potential material for next-generation semiconductor devices that would replace silicon-based technology. Due to being an atomically thin material, every atom of nanomaterials has an access to surface that is directly responsible for its electronic and chemical activity. However, for many applications, the nanomaterials in pristine form cannot be used due to high resistance and performance degradation on poor nanomaterial quality. 

Thereby, the exploration of new methods in order to mitigation as much polymer residues as possible on nanomaterials (CVD Graphene, CNT, GO, h-BN) is highly desirable (Figure 2). For instance on CVD graphene material, many reports have demonstrated to remove poly(methyl methacrylate) (PMMA) residues and other impurities on surface achieved the significant achievements such as wet chemical by acetone [25,26], cleaning by chloroform or toluene [44], by N-methyl-2-pyrrolidone [45], by diazonium salt [46], a modified RCA cleaning process and mechanically sweeping away the contamination [47], oxygen plasma and reactive ion etching treatment for a short time [25,26,46], mechanical method: AFM tip can remove all resist (theoretically without damaging the sample) in a contact mode [34], annealing in high temperature [18,25,26,48], current annealing [49], by acetic acid [50], by electrostatic force [16], by lithography resist [17], by annealing [18], by electric current [19], by electrolytic [20], by titanium sacrificial layer [22], by heat treatment in air and vacuum [23], by dry-cleaning [24]. Very recently, a superior technique for cleaning of nanomaterials using plasma (Ar, oxygen) proved extremely efficient in residue cleaning from graphene surface and tuning the graphene properties [25-29,51]. 


Figure 1: Schematic of cleaning of various nanomaterial surfaces (CVD graphene, CNTs, GO, h-BN) by chemistry, physic, nanotechnology, and engineering for tuning their electronics and optoelectronics.



Figure 2: Cleaning process of various nanomaterial surfaces such as carbon nanotubes (a-c), graphene (d-e), h-BN (f,g), and GO (i,j). (a-c) reproduced with permission from [41]. (d,e) reproduced with permission from [17]. (f,g) reproduced with permission from [40]. (i,j) reproduced with permission from [43].

The cleaning of CNT materials surface by cyclic Ar plasma and nitric acid treatment for enhancing the electrical conductivity of flexible transparent conducting film [41], or by RF-PECVD technique [42], has also well-investigated. Or the surface of the h-BN material was cleaned greatly by wet chemical (HF solution) and annealing in vacuum at 10500C [52], or annealing at 4500C in air and ozone [40]. In addition, the contamination on GO surface was removed significantly assisted by an oxidation process and washing-centrifugation cycles which is controlled by pH of the supernatant. The cleaning of nanomaterials (CVD Graphene, CNT, h-BN, GO) using various strategies related to chemistry, physic, nanotechnology, and engineering in order to obtain the ultra-clean material layer and resulting in improving their electrical characteristics is highly desiring with targeting toward practical applications in the industry to serve human society. The enhancing of electrical properties of cleaned nanomaterials would be raising up the current on-off ratio, photoluminescence, and other unexploited and unexplored exotic properties. Consequently, it could unlock and take a leap forward on developing superior plasma-based cleaning methods [15,32], for other TMDs and low-dimensional materials in various advanced devices and applications.

References

1.              Novoselov KS, Geim AK, Morozov SV, Jiang D, Zhang Y, et al. Electric field effect in atomically thin carbon films (2004) Science 306: 666-669. https://doi.org/10.1126/science.1102896

2.              Pham VP, Jang HS, Whang D AND Choi JY. Direct growth of graphene on rigid and flexible substrates: progress, applications and challenges (2017) Chem Soc Rev 46: 6276-6300. https://doi.org/10.1039/c7cs00224f

3.              Pham VP, Nguyen MT, Park JW, Kwak SS, Nguyen DHT, et al. Chlorine-trapped CVD bilayer graphene for resistive pressure sensor with high detection limit and high sensitivity (2017) 2D Materials 4: 025049. https://doi.org/10.1088/2053-1583/aa6390

4.              Pham VP, Kim KN, Jeon MH, Kim KS, Yeom GY, et al. Cyclic chlorine trap-doping for transparent, conductive, thermally stable and damage-free graphene (2014) Nanoscale 6: 15301-15308. https://doi.org/10.1039/c4nr04387a

5.              Pham VP, Kim KH, Jeon MH, Lee S H, Kim KN, et al. Low damage pre-doping on CVD graphene/Cu using a chlorine inductively coupled plasma (2015) Carbon 95: 664-671. https://doi.org/10.1016/j.carbon.2015.08.070

6.              Pham VP, Mishra A and Yeom GY. The enhancement of Hall mobility and conductivity of CVD graphene through radical doping and vacuum annealing (2017) RSC Adv 7: 16104-16108. DOI: 10.1039/C7RA01330B

7.              Pham VP, Kim DS, Kim KS, Park JW, Yang KC, et al. Low energy BCl3 plasma doping of few-layer graphene (2016) Sci Adv Mater 8: 884-890. https://doi.org/10.1166/sam.2016.2549

8.              Pham VP. Chemical vapor deposited graphene synthesis with same-oriented hexagonal domains (2017) Eng Press 1: 39-42. DOI: 10.28964/EngPress-1-107

9.              Kim KN, Pham VP and Yeom GY. Chlorine radical doping of a few layer graphene with low damage (2015) ECS J Solid State Sci. Technol. 4: N5095-N5097. DOI: 10.1149/2.0141506jss

10.           Pham VP and Yeom GY. Recent advances in doping of molybdenum disulphide: industrial applications and future prospects (2016) Adv Mater 28: 9024-9059. https://doi.org/10.1002/adma.201506402

11.           Ferrari AC, Bonaccorso F, Falko V, Novoselov KS, Roche S, et al. Science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems (2015) Nanoscale 7: 4587-5062. https://doi.org/10.1039/c4nr01600a

12.           Butler SZ, Hollen SM, Cao L, Cui Y, Gupta JA, et al. Progress, challenges, and opportunities in two-dimensional materials beyond graphene (2013) ACS Nano 7: 2898-2926. https://doi.org/10.1021/nn400280c

13.           Geim AK and Novoselov KS. The rise of graphene (2007) Nat Mater 6: 183-191. https://doi.org/10.1038/nmat1849

14.           Zhang H, Yang P and Prato M. Grand challenges for nanoscience and nanotechnology (2015) ACS Nano 9: 6637-6640. DOI: 10.1021/acsnano.5b04386

15.           Kim KS, Ji YJ, Nam Y, Kim KH, Singh E, et al. Atomic layer etching of graphene through controlled ion beam for graphene-based electronics (2017) Sci Rep 7: 2462. https://doi.org/10.1038/s41598-017-02430-8

16.           Choi WJ, Chung YJ, Park S, Yang CS, Lee YK, et al. A simple method for cleaning graphene surfaces with an electrostatic force (2014) Adv Mater 26: 637-644. https://doi.org/10.1002/adma.201303199

17.           Ishigami M, Chen JH, Cullen WG, Fuhrer MS and Williams ED. Atomic structure of graphene on SiO₂ (2007) Nano Lett 7: 1643-1648. https://doi.org/10.1021/nl070613a

18.           Lin YC, Lu CC, Yeh CH, Jin C, Suenaga K, et al. Graphene annealing: how clean can it be? (2011) Nano Lett. 12: 414-419. http://dx.doi.org/10.1021/nl203733r

19.           Moser J, Barreiro A and Bachtold A. Current-induced cleaning of graphene (2007) Appl Phys Lett 91: 161513. https://doi.org/10.1063/1.2789673

20.           Sun J, Finklea HO and Liu Y. Characterization and electrolytic cleaning of poly(methyl methacrylate) residues on transferred chemical vapor deposited graphene (2017) Nanotech 28: 125703. https://doi.org/10.1088/1361-6528/aa5e55

21.           Wood JD, Doidge GP, Carrion EA, Koepke JC, Kaitz JA, et al. Annealing free, clean graphene transfer using alternative polymer scaffolds (2015) Nanotech 26: 055302. https://doi.org/10.1088/0957-4484/26/5/055302

22.           Joiner CA, Roy T, Hesabi ZR, Chakrabarti B and Vogel EM. Cleaning graphene with a titanium sacrificial layer (2014) Appl Phys Lett 104: 223109. https://doi.org/10.1063/1.4881886

23.           Tripathy M, Mittelberge A, Mustonen K, Mangler C, Kotakoski J, et al. Cleaning graphene: comparing heat treatments in air and in vacuum (2017) Phys Status Solidi RRL 11: 1700124. https://doi.org/10.1002/pssr.201700124

24.           Siller GA, Lehtinen O, Turchanin A and Kaiser U. Dry-cleaning of graphene (2014) Appl Phys Lett 104: 153115. https://doi.org/10.1063/1.4871997

25.           Peltekis N, Kumar S, McEvoy N, Lee K, Weidlich A, et al. The effect of downstream plasma treatments on graphene surfaces (2011) Carbon 50: 395-403. https://doi.org/10.1016/j.carbon.2011.08.052

26.           McEvoy N, Nolan H, Kumar NA, Hallam T and Duesberg GS. Functionalisation of graphene surfaces with downstream plasma treatments (2013) Carbon 54: 282-290. http://dx.doi.org/10.1016/j.carbon.2012.11.040

27.           Prudkovskiy VS, Katin KP, Maslov MM, Puech P and Yakimova R. Efficient cleaning of graphene from residual lithographic polymers by ozone treatment (2016) Carbon 109 : 221-226. https://doi.org/10.1016/j.carbon.2016.08.013

28.           Hadish F, Jou S, Huang BR, Kuo HA and Tu CW. Functionalization of CVD grown graphene with downstream oxygen plasma treatment for glucose sensors (2017) J Electrochem. Soc. 164: B336-B341. doi: 10.1149/2.0601707jes

29.           Mumen HA, Rao F, Li W and Dong L. Singular sheet etching of graphene with oxygen plasma (2014) Nano-Micro Lett 6: 116-124. https://doi.org/10.1007/BF03353775

30.           Sun H, Chen D, Wu Y, Yuan Q, Guo L, et al. High quality graphene films with a clean surface prepared by an UV/ozone assisted transfer process (2017) J. Mater. Chem. C 5: 1880-1884. DOI: 10.1039/C6TC05505B

31.           Choi W, Shehzad MA, Park S and Seo Y. Influence of removing PMMA residues on surface of CVD graphene using a contact-mode atomic force microscope (2016) RSC Adv. 7: 6943-6949. DOI: 10.1039/C6RA27436F

32.           Kim KS, Hong HK, Jung H, Of IK, Lee Z, et al. Surface treatment process applicable to next generation graphene-based electronics (2016) Carbon 104: 119-124. https://doi.org/10.1016/j.carbon.2016.03.054

33.           Jia Y, Gong X, Peng P, Wang Z, Tian Z, et al. Toward high carrier mobility and low contact resistance: laser cleaning of PMMA residues on graphene surfaces (2016) Nano-Micro Lett 8: 336-346. https://doi.org/10.1007/s40820-016-0093-5

34.           Goossens AM, Calado VE, Barreiro A, Watanabe K, Taniguchi T, et al. Mechanical cleaning of graphene (2012) Appl Phys Lett 100: 073110. https://doi.org/10.1063/1.3685504

35.           Choi H, Kim JA, Cho Y, Hwang T, Lee J, et al. Surface cleaning of graphene by CO₂ cluster (2015) Solid State Phenomena 219: 68-70. https://doi.org/10.4028/www.scientific.net/SSP.219.68

36.           Kumar K, Kim YS and Yang EH. The influence of thermal annealing to remove polymeric residue on the electronic doping and morphological characteristics of graphene (2013) Carbon 65: 35-45. https://doi.org/10.1016/j.carbon.2013.07.088

37.           Dean CR, Young AF, Lee C, Wang L, Sorgenfrei S, et al. Boron nitride substrates for high-quality graphene electronics (2010) Nature Nanotech 5 :722-726. https://doi.org/10.1038/nnano.2010.172

38.           Elbadawi C, Tran TT, Kolibal M, Sikola T, Scott, et al. Electron beam directed etching of hexagonal boron nitride (2016) Nanoscale 8: 16182-16196. DOI: 10.1039/C6NR04959A

39.           Liao Y, Tu K, Han X, Hu L, Connell JW, et al. Oxidative etching of hexagonal boron nitride towards nanosheets with defined edges and holes (2015) Sci. Rep. 5: 14510. https://doi.org/10.1038/srep14510

40.           Bueno JC, Cavalieri M, Wang R, Houri S, Hofmann S, et al. Mechanical characterization and cleaning of CVD single-layer h-BN resonators (2017) npj 2D materials and applications 1: 16. https://doi.org/10.1038/s41699-017-0020-8

41.           Phuong VP, Jo YW, Oh JS, Kim SM, Park JW, et al. Effect of plasma-nitric acid treatment on the electrical conductivity of flexible transparent conductive films (2013) Jpn J Appl Phys 52: 075102. https://doi.org/10.7567/JJAP.52.075102

42.           Di H, Li M, Li H, Huang B and Yang B. Purification and characterization of carbon nanotubes synthesized by RF-PECVD (2012) ECS Trans. 44: 499-504. http://dx.doi.org/10.1149/1.3694360

43.           Barbolina I, Woods CR, Lozano N, Kostarelos K, Novoselov KS, et al. Purity of graphene oxide determines its antibacterial activity (2016) 2D Materials 3: 025025. https://doi.org/10.1088/2053-1583/3/2/025025

44.           Niranan P, Marco S, Alberto D and Athanasia A. Effect of solvents on the dynamic behavior of poly(methyl methacrylate) film prepared by solvent casting (2011) J Mater Sci 46: 5044-5049. https://doi.org/10.1007/s10853-011-5424-9

45.           Xuelei L, Brent AS, Irene C, Guangjun C, Christina AH, et al. Toward clean and crackles transfer of graphene (2011) ACS Nano 5: 9144-9153. https://doi.org/10.1021/nn203377t

46.           Xiao YF, Ryo N and Li CY, Katsumi T. Effects of electron-transfer chemical modification on the electrical characteristics of graphene (2010) Nanotech 21: 475208. https://doi.org/10.1088/0957-4484/21/47/475208

47.           Stephen C, Peter RK and Preston JR. Nanoimprint lithography (1996) J Vac Sci Technol B 14: 4129-4133.

48.           Wei SL, Chang TN and John TLT. What does annealing do to metal-graphene contacts? (2014) Nano Lett 14: 3840-3847. http://dx.doi.org/10.1021/nl500999r

49.           Moser J, Barreiro A and Bachtold A. Current-induced cleaning of graphene (2007) Appl Phys Lett 91: 163513. https://doi.org/10.1063/1.2789673

50.           Michael H, Ryan B, Lukas N. Graphene transfer with reduced residue (2013) Phys Lett A 377: 1455-1458. https://doi.org/10.1016/j.physleta.2013.04.015

51.           Lim YD, Lee DY, Shen TZ, Ra CH, Choi JY, et al. Si-compatible cleaning process for graphene using low-density inductively coupled plasma (2012) ACS Nano 6, 4410-4417. http://dx.doi.org/10.1021/nn301093h

52.           King SW, Nemanich RJ and Davis RF. Cleaning of pyrolytic hexagonal boron nitride surfaces (2015) Surf Interface Anal 47: 798-803. https://doi.org/10.1002/sia.5781

Keywords

Polymer, Nano material, Graphene