The electrical properties of graphene layers on SiO2/Si obtained at low temperature (T ≤ 260 °C) were evaluated with back-gated graphene-based field effect transistors (FET) and using the transmission line model method. We also find that the obtained graphene films in the range of 25 °C to 260 °C have similar structural quality, but the surface coverage of graphene on SiO2 shows a strong dependence on the growth temperature. The inset shows an optical microscopy image of this device and the scale bar is 10 μm……….41 Figure 3-11 Large-scale grain image of graphene grown at 160°C on SiO2 using DF-TEM.
Optical microscopy image of graphene-free surface showing traces of graphene ridges grown at temperature T = 160 °C for 2 min on SiO2. T =160°C for 10 minutes on SiO2..60 Figure 3-22 Schematics of graphene growth mechanisms in the DAS process, depending on the growth. The red arrows in the Raman spectrum of graphene on PMMA originate from local vibrational modes of PMMA substrate. (c) Representative optical microscopy image of graphene film grown at temperature T = 60 °C for 10 min on PMMA after removal of PMMA (scale bar, 100 µm).
Introduction
The brief procedure is as follows: (1) the mesa structures on top of the HOPG are prepared using dry etching in oxygen plasma. In the method using graphite oxide, graphite is first oxidized in the presence of strong acids and oxidizing agents, proposed by Brodie [16], Staudenmaier [17] and Hummers [18]. Thus, the reduction processes of the graphene oxide are required by using chemical methods [22-24] (using reducing agents such as hydrazine, dimethylhydrazine, hydroquinone and NaBH4), thermal methods [25].
In the case of the low carbon solubility metal, graphene is grown by a surface adsorption process, namely the dissolution of a precursor, surface diffusions, nucleation, island growth and island fusion to yield a continuous graphene film (see Figure 1-7b). Furthermore, the deposition of a continuous graphene layer leads to passivation of the metal surface, dramatically hindering multilayer growth. To tune the structural and optoelectronic properties of the resulting graphene layers, we designed the grain sizes of the nickel films on the substrate of choice.
Experimental Methods and Equipments
After carbon-Ni/substrate diffusion couplings have been heated for 1-60 min, the samples are rapidly cooled to room temperature under an Ar atmosphere by removing them from the hot zone of the furnace using a stainless rod to control carbon diffusion time (growth time of DAS graphene films). Schematic drawing of the DAS process for the direct deposition of graphene films on non-conductive substrates. A depth profile of the Ni films was obtained by combining a series of gun etch cycles interleaved with XPS measurements from the present surface.
The sheet resistance of the graphene layers was measured using transmission line model measurement (TLM), which is the way to accurately measure the contact resistance and sheet resistance of the graphene layer. After the total resistance of the TLM structure was measured as a function of distance, we derived a value of the resistance of the graphene sheet from the slope. We used a wet transfer TEM sampling method for planar imaging of graphene films grown on SiO2 to minimize damage and/or contamination of the films.
Results and Discussions
Set of XPS spectra corresponding to (a) C1s and (b) O1s peak from a depth profile experiment of the as-deposited Ni film. A low intensity of the disorder-induced D band (~ 1351 cm − 1 ) is observed by plotting the peak intensity ratios of D to G (ID/IG), obtaining 0.1 ≤ ID/IG≤0.4 in layers of graphene grown at 160 °C, which are comparable to those of films grown in elevated temperature CVD (~1000 °C) on polycrystalline nickel surfaces [61]. Interestingly, we find that the morphologies of the monolayer (red dot in Figure 3-9b) and bilayer (blue dot in Figure 3-9b) regions covered by graphene resemble those of grains, and the graphene ridges with many layers, grain boundaries in Ni thin films.
As shown in Figure 3-10a, the plot shows total resistance of the TLM structure as a function of distance. Due to thickness variation in the graphene channel, it is possible that the gating effect is screened by other graphene layers in multilayer regions of the film [72]. From this dark-field image, we estimate that the maximum grain size of the DAS graphene is around a few micrometers.
The corresponding OM images of graphene on SiO2 grown at different growth temperatures are shown in Figure 3-13. As shown in Figure 3-13, the graphene surface coverage on SiO2/Si substrates increases linearly from ~60 % to. Finally, we tested our DAS method in the high temperature growth range (300 °C ≤ T ≤ 600 °C) and evaluated the structural quality and surface morphology of the synthesized graphene film using SEM, Raman spectroscopy and TEM analysis.
To obtain the prefactor for the Arrhenius equation, the vibrational frequency of the added carbon atom at the adsorption site was calculated [97]. The adsorption energy and vibration frequency of the added carbon atom at the site were found to be 1.65 eV and 22.8 THz, respectively. In Figure 3-26, the calculated diffusion barrier from the HCP location to the FCC location of the Ni (111) surface along the interface between graphene and the Ni (111) surface is found to be ~ 0.51 eV, which is slightly is higher than that on a free Ni(111) surface.
These grain sizes are at least two orders of magnitude smaller than the annealed Ni films on SiO2/Si substrates. This result indicates that the crystal quality of Ni films on plastic and glass for the DAS process is worse than that of annealed Ni films on SiO2/Si substrates because there is no recrystallization process. We confirmed that centimeter-scale graphene was grown on PMMA/SiO2/Si by detecting D-band and G-band signals with Raman spectroscopy, as shown in Figure 3-28b.
Conclusions
에스; Akinwande, D., 박리된 단층에 필적하는 품질을 갖는 증발된 Cu(111) 필름에 그래핀의 균일한 웨이퍼 규모 화학 기상 증착. 성공을 꿈꾸며 대학원에 입학한 지 많은 시간이 흘렀습니다. 이 과정에서 무한한 자신감으로 응원해주시고 늘 빛의 등불이 되어주시고 이끌어주신 많은 분들께 짧은 시간이라도 감사하다는 말씀 전하고 싶습니다. 길을 잃지 마세요.
먼저, 늦게 인생을 시작한 저에게 끝없는 관심과 격려를 주시고, 무한한 자신감을 가지고 다시 한 번 연구자의 길을 나아갈 수 있는 기회를 주신 권순용 교수님께 깊은 감사의 말씀을 전하고 싶습니다. 저도 박사님께 머리 숙여 감사의 말씀을 드리고 싶습니다. 평가에 대한 지도를 제공하기 위해 더욱 노력한 한국전기연구원 주성재 연구원. 또한, 연구자로서 롤모델이 되어주시고 세심하게 배려해주신 캠퍼스 내 다른 교수님들께도 깊은 사과와 감사의 말씀을 전하고 싶습니다.
집보다 같은 공간에서 보내는 시간이 더 많은 FIND 연구실에서의 생활은 제 인생에서 잊지 못할 소중한 시간이었습니다. 나와 함께 고민하고 옆에 있어준 의사선생님께 깊은 감사의 말씀을 전하고 싶습니다. 그리고 우리 FIND 연구실의 미래를 책임질 고명, 세양 님도 선배님들의 지도 아래 좋은 연구를 하시길 바랍니다.
힘든 생활 속에서도 대학 생활의 향수와 열정, 위로를 함께 나눠준 친구 용현, 홍삼, 반장 철, 성오, 현욱에게 감사 인사를 전하고 싶습니다. 함께여서 늘 즐거웠고 행복했어요 . 바쁜 일상 속에서도 가끔 친구로서 제 속 깊은 이야기를 들어주시고 도움을 주시는 중앙계측센터 김영기, 임동주, 박지혜 교수님들께도 감사의 말씀을 전하고 싶습니다. 좋은 연구 결과를 만들어내겠습니다. 클린룸의 장비가 다 소진되더라도 항상 든든한 힘이 되어준 형일님께 깊은 감사의 말씀을 드리며, 이들의 앞날에 희망이 가득하길 바랍니다. 누구보다 이날을 손꼽아 기다려주셨던 사랑하는 아버지, 어머니, 그리고 대신 집안의 크고 작은 일들을 맡아주신 남동생에게 이 자리를 빌려 머리 숙여 감사의 말씀을 드립니다. 결석한 형의..
또한 오랜 시간 변함없는 믿음과 사랑으로 저를 기다려주신 시아버지, 시어머니, 처가 식구들에게도 감사하다는 말씀 전하고 싶습니다.
