미리보기
서지주요정보
Defect healing of CVD graphene by selective electroplating for mechanically robust and transparent electrodes = 선택적 전기도금법을 이용한 합성 그래핀의 결함 치유 및 강건 투명 전극 설계
서명 / 저자 Defect healing of CVD graphene by selective electroplating for mechanically robust and transparent electrodes = 선택적 전기도금법을 이용한 합성 그래핀의 결함 치유 및 강건 투명 전극 설계 / Minsun Cho.
발행사항 [대전 : 한국과학기술원, 2019].
Online Access 원문보기 원문인쇄

소장정보

등록번호

8033568

소장위치/청구기호

학술문화관(문화관)B1층 보존서고

MME 19042

휴대폰 전송

도서상태

이용가능(대출불가)

사유안내

반납예정일

리뷰정보

초록정보

Due to outstanding electrical and optical properties with flexibility, graphene has become a promising material for mechanically robust and transparent electronics. In addition, the development of chemical vapor deposition (CVD) method has enabled the production of high quality, large area graphene. Nevertheless, few industrial applications use graphene. This is because it is difficult to achieve the theoretical performance of graphene. The difference between theory and reality comes from intrinsic defects during the synthesis and integration of graphene. Mechanically robust and transparent electrodes applied to advanced electronic devices must satisfy high transmittance and robustness as well as conductivity. In this study, it was first optimized that the selective electroplating for a robust and transparent electrode. Optimum conditions for a robust and transparent electrode were determined in consideration of electroplating time, concentration, and potential difference. Then, the selective electroplating was improved using surface treatment and mechanical bending. The first method, surface treatment enhanced the wettability of graphene. The improved wettability affected electroplating quality. Also, a mechanical strain was applied. Applying a strain to the graphene changes the electrical band structure It was found that the properties of healed graphene electrode with surface treatment and mechanical bending were improved while maintaining a high level of transmittance. In addition, multilayer structure was applied to overcome the low conductivity compared to indium tin oxide (ITO), a widely used transparent electrode. The multilayered graphene electrode fabricated with optimized electroplating had enhanced mechanical robustness while maintaining the transmittance and conductivity of indium tin oxide. The proposed graphene electrode can be effectively used in various fields requiring both electrical and mechanical properties.

그래핀은 뛰어난 전기, 광학적 성질과 함께 유연하다는 특징으로 인해 신축성을 가지는 전자 장치를 위한 재료로 주목받고 있다. 게다가, 화학적 기상 증착법의 발전으로 좋은 품질의 대면적 그래핀을 생산할 수 있게 되었다. 하지만 이와 같은 활발한 연구에도 불구하고 아직 그래핀의 산업적인 활용은 거의 존재하지 않는다. 이는 그래핀에 존재하는 불가피한 결함들로 인해 이론적인 물성을 실제로 구현하기 어렵기 때문이다. 본 연구에서는 그래핀의 결함 치유 목적으로 연구되었던, 선택적 전기 도금법을 강건 투명 전극에의 적용을 목표로 최적화를 진행했다. 이에 더해 도금 효과를 높이기 위한 전처리, 구조적인 설계를 추가해 널리 사용되어온 투명 전극인 인듐 주석 산화물과 유사한 저항 그리고 투과도를 가지면서도 기계적으로 강건한 특성을 갖는 전극을 제작했다. 본 연구에서 제안한 그래핀 기반 전극은 전기, 기계적인 성질이 동시에 요구되는 차세대 디스플레이와 같은 분야에서 효과적으로 사용될 수 있을 것이다.

서지기타정보

서지기타정보
청구기호 {MME 19042
형태사항 iv, 34 p. : 삽화 ; 30 cm
언어 영어
일반주기 저자명의 한글표기 : 조민선
지도교수의 영문표기 : Taek-Soo Kim
지도교수의 한글표기 : 김택수
학위논문 학위논문(석사) - 한국과학기술원 : 기계공학과,
서지주기 References : p. 29-34
QR CODE

책소개

전체보기

목차

전체보기

이 주제의 인기대출도서

표/그림

모든 표/그림 보기

Various types of cracks which are produced duringsynthesis and transfer process. Vacancy (a), grain boundary (b), wrinkle (c), and crack (d). Images from [24, 25, 27, 29], respectively.

Schematic of the transfer process, which is the graphene on thermal release film to a PET film.

Hot lamination machine for detaching thermal release film (TRF) from graphene. graphene on the TRF pre-contacted to target substrate, and pressed by roller with elevated temperati

Schematic of the electroplating process in silver nitrate solutio

Setup for tensile testing. Electrical resistance was measured simultaneously by connecting four-point probes with conductive loading grips.

The load-displacement curve of the graphene on PET, bilayer specimen

In - situ images of specimen with applied tensile strain. Although plastic deformation was occurred, no critical deformation had occurred during the test area that affects the properties.

Normalized resistance while tensile test ofpristine graphene and ITO on the plastic substrate Failure strain was defined as a strain which the resistance became ten times of the initial resistance.

SEM images of the graphene surface after the electroplating with repect to time. After 10 minutes, the microstructure of electroplated silver on the graphene was maintained.

SEMimages ofthegraphenesurface after the electroplating with respect to concentraion and voltage. According to change in voltage and concentration, the microstructure of silver on the graphene varied significantly. Electroplating time was fixed as 10 minutes.

Schematic of reduction mechanism with respect to concentration. At a high concentration, silver was dendritic and uniformly reduced on the graphene surface. On the other hand, the silver selectively deposited at a low concentration.

Transmittance and surface roughness with respect to concentration and voltage. The blue dotted lines in the graph indicate the transmittance and roughness ofITO, respectively.

SEM images ofthe characteristic region in Figure2.4. The microstructure of silver on the graphene surface was significantly changed between 5 and 10 voltages.

Sheet resistances after electroplating measured according to applied voltages. The sheet resistance ofhealed graphene decreased in the initial region. Afterthat, the sheet resistance was saturated until 10 voltages.

SEM images and schematic for why the increase in sheet resistance by electroplating was not large. The electroplating with the conditions proposed in this study was selectively electroplated on the surface of graphene. Therefore, most of the electrons flow through the graphene as in the schematic below, SO the sheet resistance did not improve dramatically.

Failure strain measured according to applied voltage. The failure strain of healed graphene increased with voltage up to 10 voltages. After that, the failure strain was drastically reduced.

The SEM Images of the graphene surface after healing with 10 and 15 voltages with a low concentration. At 10 voltages, the silver was reduced selectively at the defect sites. The silver was selectively deposited at 15 voltages, but many areas of the surface were damaged.

Effects of surface tension during electroplaitng. If the surface tension is too high, electro- plating solution is difficult to penetrate into the electrode surface, from ref. [57].

Effects of UV/Ozone treatment on graphene surface. The inset show optical images and values of the contact angle.

Contact angle of the graphene on PET with respect to UV/Ozone treatment time. The 5 minutes treatment time showed the highest wettability.

XPS results ofthe UV/Ozone treated graphenesurface. (a) Deconvoluted peaks were marked and (b) The Normalized intensity ratios of the XPS results was plotted. Oxygen functional groups kept increasing while the ratio of C-C/C=0 was saturated.

Failure strain with respect to UV/Ozone treatment time. It was demonstrated that the tendency of failure strain agreed well with the change in wettability of the graphene surface.

The transmittance change after healing graphene on PET was plotted as a function of UV/Ozone treatment time. UV/Ozone treatment did not significantly deteriorate the transmittance.

The SEM images of healed graphene after UV/Ozone as a pre-treatment with 5 minutes (a), 15 minutes (b).

Effects of mechanical strain on the graphene. Mechanical deformation lowers the activation energy ofgraphene, whichimproves the chemical reactivity (a), from ref. [65]. Themethod also improving work function and electron mobility (b), from ref. [66].

(a) The graph shows normalized resistance change of graphene on PET with applied strain Resistance remained almost constant until 1% strain. So, in this research, the upper limit value of the applied pre-strain was selected as 1%. (b) An experiment setting for applying strain on the bi-layer specimen, graphene on PET. Electroplating was conducted while applying bending. Change in neutral plane of

Work function of the graphene on PET with respect to applied strain

Raman spectra of graphene at 0% and 1% strain (a), from ref. [71]. Another Raman spectra of graphene as a function ofstrain (b), from ref. [72].

Images showing local work function changes due to defect ofgraphene surface, from ref [75

The failure strain a and transmittance (b) as a function of pre-strain

Effects of multilayer structure on a graphene-based electrode. (a) Conductivity ofa single layer graphene increased because it did not have an electrical path when electrons face an disconnected section. However, multilayer graphene had an additional conductive path in the out-of-plane direction. (b) From ref. [42], graphene has weak interlaminar interaction due to its stable characteristics. As a

Sheet resistance ofa graphene with respect to the number oflayers. As a layer was added the conductivity was increased.

Schematic of a multilayer graphene-based electrode. Since the transmittance after electro- plating was comparable to that ofITO, additional healing and graphene transfer were possible.

The initial resistance (a) and transmittance (b) ofa multilayer graphene-based electrode as a function of the number of graphene layers.

SEM images of healed 1-layer and 3-layer graphene. It was confirmed that critical defects on a graphene were covered at a multilayer graphene-based electrode.

Failure strain measured according to the number of graphene layers. As the number of layers increased, the failure strain gradually increased. During the first electroplating process, critical defects were almost healed. The effects ofsubsequent processes were weaker than the first process because it covered a few minor defects.