Investigating the Effect of Cu Pre-Cleaning on the Graphene Structural Defects Synthesized by Chemical Vapor Deposition

Name: Ghaith Nadhreen 201142310 ME 495 Section: 3 Advisor: Prof. Tahar Laoui Instructor: Dr. Ahmad Ibrahim

INTRODUCTION

EFFECT OF PRE-CLEANING ON AS-GROWN GRAPHENE ON CU FOILS

ABSTRACT

METHODS AND MATERIALS

SUMMARY

This project aims to Investigate Cu precleaning -induced structural defects in graphene film synthesized by chemical vapor deposition (CVD). This is achieved by observing the impact of different etchants on the morphology of copper foils, the formation of particles and the deposited graphene characteristics. Here, we report that ammonium persulfate (APS) etching for short time (30s) efficiently reduced the surface particles and yielded smooth Cu surface as well. As a result, CVD-synthesized graphene was dominated by clean, large area and single layer graphene with good quality upon transfer onto SiO2/Si wafers, with minimal wrinkles, tears and cracks. • Bare-Cu foils were pre-cleaned first by acetone, Iso-propanol (ISP)

and deionized (DI) water 5 min each, and then dried with nitrogen gas. Then, they were etched using the following chemicals; APS (0.3 M), FeCl3 (1M) and HNO3 (1M).

• Cu samples were etched for 30s, and 5 min to achieve slight and harsh cleaning conditions.

• Then, Cu foils were cleaned again with DI water for 5 min to remove any etchants contaminants and finally dried with nitrogen gas.

• 30s samples yielded thinner graphene with fewer bi/multilayer domains compared to the thicker and more multilayer domains obtained in case of longer etching time

• Shorter etching time gave smoother surface structure with more uniform graphene film

• Longer etching yielded rougher Cu of step-like structure with more non-uniform graphene film

• APS sample showed cleaner, more uniform graphene with fewer wrinkles and holes/pores

• FeCl3 etching exhibited the roughest surface dominated with the highest density of surface particles

Graphene has many potential applications because of its excellent mechanical and electrical properties. Therefore, producing deformation free graphene sheets is of vital importance. Copper foils (Cu) serve as a catalyst for graphene production. Cu surface consists of the following features rolling marks, oxide layer, coating layer, organic and inorganic contaminants.

Improper elimination of the above features may lead to formation of complex surface structure consisting of dense surface steps, kinks and particles. Consequently, evolved Cu may have significant effects not only on deposited graphene characteristics but also on the transferred graphene films.

OBJECTIVES• Explore the impact of APS, FeCl3 and HNO3 as etching reagents on

Cu surface morphology before and after graphene growth.• Find out their influences on the characteristics of both deposited

and transferred graphene films.

Etchant Name Pre-cleaning Etchant conc. DI conc.

Etching Time

Ferric Chloride

Acetone + ISP + D.I water (5 min each)

3.5g FeCl3 + 10ml HCl

100 ml 30s & 5minNitric Acid 7g HNO3

Ammonium Persulfate 7g (NH4)2S2O8

EFFECT OF PRE-CLEANING ON CU SURFACE MORPHOLOGY

50 m

(a) RMS = 360 nm

20 m

(b)

Fig 3: SEM and optical surface topography for Cu surface morphology of as-received Cu foil

(e)

5 m

(d) (f)Cu-FeCl3-5min Cu-HNO3-5minCu-APS-5min

RMS= 517 nm RMS= 573 nm RMS= 337 nm(a) (b) (c)

Cu-FeCl3-5min Cu-HNO3-5minCu-APS-5min

Fig 4: Cu surface morphology after etching for 5min

Cu-APS-30s(d) Cu-FeCl3-30s(e) Cu-HNO3-30s(f)

5 m

Cu-APS-30s Cu-FeCl3-30s

RMS= 421 nm RMS= 524 nm RMS= 326 nm

Cu-HNO3-30s(a) (b) (c)

Fig 5: Cu surface morphology after etching for 30 sec

(b) G/Cu-FeCl3-5min (c) G/Cu-HNO3-5min

20 µm

(a) G/Cu-APS-5min

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(e)G/Cu-FeCl3-5min

(f)G/Cu-HNO3-5min

(d)G/Cu-APS-5min

(h) (i)(g)

Raman shift (cm-1) Raman shift (cm-1) Raman shift (cm-1)

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Fig 6: Cu surface morphology after graphene growth on Cu (etched for 5min)

(d) (e) (f)G/Cu-APS-30s G/Cu-FeCl3-30s G/Cu-HNO3-30s

G/Cu-APS-30s(a) G/Cu-FeCl3-30s(b) G/Cu-HNO3-30s(c)

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Fig 7: Cu surface morphology after graphene growth on Cu (etched for 30 sec)

EFFECT OF PRE-CLEANING ON AS-TRANSFERRED GRAPHENE ON SIO2/SI

(g) (i)(h)G/SiO2-APS-30s G/SiO2-FeCl3-30s G/SiO2-HNO3-30s

(d) (e) (f)G/SiO2-APS-5min G/SiO2-FeCl3-5min

G/SiO2-HNO3-5min

G/SiO2-APS-30s

(a) G/SiO2-FeCl330s

(b) G/SiO2-HNO330s

(c)

20 µm

Fig 8: optical images and AFM of transferred G on SiO2/Si wafer

12 3

2

4

4

1- Adsorption 2- Diffusion 3- Attachment 4- Desorption

Quartz TubeAr+H2+CH4

1000 oC

Cu

Cu foil

OrganicInorganic Coating layer

Oxide layer

Fig 1: CVD schematics

Fig 2: Surface characteristics of Alfa Aesar (AA) foil

REFERENCES1. Kim, Soo Min. "The Effect of Copper Pre-cleaning on Graphene

Synthesis." IOPscience. 13 Aug. 2013. Web. 2 May 2016.

2. Han, Gang Hee. "Influence of Copper Morphology in Forming Nucleation Seeds for Graphene Growth." ACS Publications. 24 Aug. 2011. Web. 2 May 2016.

3. Lupina, Grzegorz. "Residual Metallic Contamination of Transferred Chemical Vapor Deposited Graphene." ArXiv. 2015. Web. 2 May 2016.

ME495-02-A

RESULTS AND DISCUSSION