CVD growth

2010

Cross-sectional transmission electron microscopy of thin graphite films grown by chemical vapor deposition.

Robert Colby, Qingkai Yu, Helin Cao, Steven S. Pei, Eric A. Stach, and Yong P. Chen

Diamond and Related Materials Volume 19, Issues 2-3, February-March 2010, Pages 143-146

 

 

Graphene has been the subject of an extraordinary upsurge of interest due to its intriguing properties and potential applications. Recent work has shown that excellent electronic properties are exhibited by large-scale ultrathin graphite films, grown by chemical vapor deposition on a polycrystalline metal and transferred to a device-compatible surface. The properties of such multilayered graphene films could depend strongly on film thickness and uniformity. Unlike the other common methods for analysis in the literature, cross-sectional transmission electron microscopy (TEM) would provide direct, straightforward analysis of film thickness and quality, as well as provide a means to investigate specific defect structures (e.g. wrinkles). However, this approach has not often been pursued due to the sensitivity of graphite to the electron and ion beam damage in such a procedure. Here, an approach to creating cross-sectional TEM samples using a focused ion beam lift-out method is presented, along with the resulting TEM images of thin graphite films and several wrinkle defects. Samples removed from as-grown films on polycrystalline nickel and films removed from measured devices are presented. The benefits and limitations to this approach are discussed.

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Scalable growth of free-standing graphene wafers with copper(Cu) catalyst on SiO2/Si substrate: Thermal conductivity of the wafers

Yun-Hi Lee and Jong-Hee Lee

Appl. Phys. Lett. 96, 083101 (2010)

 

 

The authors report scalable growth of free-standing graphene wafers with copper(Cu) catalyst on SiO2/Si substrate at low temperature and investigation of their thermal conductivity. The Cu is the most common and the cheapest catalyst among electronic materials. Our process for producing the graphene with the Cu is based on a low-pressure, fast-heating chemical vapor deposition method. Thermal conductivity measurements with nondestructive Raman spectroscopy showed that the free-standing-graphene is a good thermal conductor. The possibility of growing graphene wafer at low temperatures by using a Cu thin film should accelerate research and facilitate the development of graphene for practical applications.

 

 

Wafer-Scale Synthesis and Transfer of Graphene Films

Nano Lett., 2010, 10 (2), pp 490–493

 

Youngbin Lee, Sukang Bae, Houk Jang, Sukjae Jang, Shou-En Zhu, Sung Hyun Sim, Young Il Song, Byung Hee Hong and Jong-Hyun Ahn

 

We developed means to produce wafer scale, high-quality graphene films as large as 3 in. wafer size on Ni and Cu films under ambient pressure and transfer them onto arbitrary substrates through instantaneous etching of metal layers. We also demonstrated the applications of the large-area graphene films for the batch fabrication of field-effect transistor (FET) arrays and stretchable strain gauges showing extraordinary performances. Transistors showed the hole and electron mobilities of the device of 1100 ± 70 and 550 ± 50 cm2/(V s) at drain bias of 0.75 V, respectively. The piezo-resistance gauge factor of strain sensor was 6.1. These methods represent a significant step toward the realization of graphene devices in wafer scale as well as application in optoelectronics, flexible and stretchable electronics.

 

 

2009

Transfer of Large-Area Graphene Films for High-Performance Transparent Conductive Electrodes

Nano Lett., 2009, 9 (12), pp 4359–4363

 

Xuesong Li, Yanwu Zhu, Weiwei Cai, Mark Borysiak, Boyang Han, David Chen, Richard D. Piner, Luigi Colombo and Rodney S. Ruoff

Graphene, a two-dimensional monolayer of sp2-bonded carbon atoms, has been attracting great interest due to its unique transport properties. One of the promising applications of graphene is as a transparent conductive electrode owing to its high optical transmittance and conductivity. In this paper, we report on an improved transfer process of large-area graphene grown on Cu foils by chemical vapor deposition. The transferred graphene films have high electrical conductivity and high optical transmittance that make them suitable for transparent conductive electrode applications. The improved transfer processes will also be of great value for the fabrication of electronic devices such as field effect transistor and bilayer pseudospin field effect transistor devices.

Chemical vapor deposition of large area few layer graphene on Si catalyzed with nickel films

Thin Solid Films Volume 518, Issue 6, Supplement 1, 1 January 2010, Pages S128-S132

 

Wei Liu, Choong-Heui Chung, Cong-Qin Miao, Yan-Jie Wang, Bi-Yun Li, Ling-Yan Ruana Ketan Patel, Young-Ju Park, Jason Woob and Ya-Hong Xie

 

We present the results of a systematic study of chemical vapor deposition of graphene on silicon substrates. The silicon substrate is covered with SiO2 and capped with an electron-beam evaporator deposited nickel film, which serves as the catalyst for carbon precursor decomposition. Methane is used as the carbon precursor. Three key parameters of CVD growths, the growth temperature, time, and the post-growth cooling rate are studied and the optimized combination of the three allowed for the reproducible fabrication of single layer graphene of larger than 100 ?m2 covering more than 50% of the surface of 1-in. diameter Si wafers. We further demonstrate the transfer of CVD graphene onto SiO2/Si surfaces with higher than 95% success rate. Our result together with those reported by other research groups shows real promise of the integration of carbon electronics with silicon integrated circuit technology.

Synthesis, Transfer, and Devices of Single- and Few-Layer Graphene byChemical Vapor Deposition

IEEE Trans. Nanotech, 2009

 

Lewis Gomez De Arco, Yi Zhang, Akshay Kumar, and Chongwu Zhou

 

The advance of graphene-based nanoelectronics hasbeen hampered due to the difficulty in producing single- or few-layer graphene over large areas. We report a simple, scalable, andcost-efficient method to prepare graphene using methane-basedCVD on nickel films deposited over complete Si/SiO2 wafers. Byusing highly diluted methane, single- and few-layer graphene wereobtained, as confirmed by micro-Raman spectroscopy. In addition,a transfer technique has been applied to transfer the graphene filmto target substrates via nickel etching. FETs based on the graphenefilms transferred to Si/SiO2 substrates revealed a weak p-type gatedependence, while transferring of the graphene films to glass sub-strate allowed its characterization as transparent conductive films,exhibiting transmittance of 80% in the visible wavelength range

 

Large Area, Few-Layer Graphene Films on Arbitrary Substrates by Chemical Vapor Deposition

Nano Lett., 2009, 9 (1), pp 30–35

 

Alfonso Reina, Xiaoting Jia, John Ho, Daniel Nezich, Hyungbin Son, Vladimir Bulovic, Mildred S. Dresselhaus and Jing Kong

In this work we present a low cost and scalable technique, via ambient pressure chemical vapor deposition (CVD) on polycrystalline Ni films, to fabricate large area (cm2) films of single- to few-layer graphene and to transfer the films to nonspecific substrates. These films consist of regions of 1 to 12 graphene layers. Single- or bilayer regions can be up to 20 ?m in lateral size. The films are continuous over the entire area and can be patterned lithographically or by prepatterning the underlying Ni film. The transparency, conductivity, and ambipolar transfer characteristics of the films suggest their potential as another materials candidate for electronics and opto-electronic applications

Large-scale pattern growth of graphene films for stretchable transparent electrodes

Nature 457, 706-710 (5 February 2009)

 

Keun Soo Kim, Yue Zhao, Houk Jang, Sang Yoon Lee, Jong Min Kim, Kwang S. Kim, Jong-Hyun Ahn, Philip Kim, Jae-Young Choi & Byung Hee Hong

 

Problems associated with large-scale pattern growth of graphene constitute one of the main obstacles to using this material in device applications. Recently, macroscopic-scale graphene films were prepared by two-dimensional assembly of graphene sheets chemically derived from graphite crystals and graphene oxides. However, the sheet resistance of these films was found to be much larger than theoretically expected values. Here we report the direct synthesis of large-scale graphene films using chemical vapour deposition on thin nickel layers, and present two different methods of patterning the films and transferring them to arbitrary substrates. The transferred graphene films show very low sheet resistance of 280 per square, with 80 per cent optical transparency. At low temperatures, the monolayers transferred to silicon dioxide substrates show electron mobility greater than 3,700 cm2 V-1 s-1 and exhibit the half-integer quantum Hall effect, implying that the quality of graphene grown by chemical vapour deposition is as high as mechanically cleaved graphene6. Employing the outstanding mechanical properties of graphene7, we also demonstrate the macroscopic use of these highly conducting and transparent electrodes in flexible, stretchable, foldable electronics

Large-Area Synthesis of High-Quality and Uniform Graphene Films on Copper Foils

Science,Vol. 324. pp. 1312 - 1314 (5 June 2009)

 

Xuesong Li, Weiwei Cai, Jinho An, Seyoung Kim, Junghyo Nah, Dongxing Yang, Richard Piner, Aruna Velamakanni, Inhwa Jung, Emanuel Tutuc, Sanjay K. Banerjee, Luigi Colombo, Rodney S. Ruoff

 

Graphene has been attracting great interest because of its distinctive band structure and physical properties. Today, graphene is limited to small sizes because it is produced mostly by exfoliating graphite. We grew large-area graphene films of the order of centimeters on copper substrates by chemical vapor deposition using methane. The films are predominantly single-layer graphene, with a small percentage (less than 5%) of the area having few layers, and are continuous across copper surface steps and grain boundaries. The low solubility of carbon in copper appears to help make this growth process self-limiting. We also developed graphene film transfer processes to arbitrary substrates, and dual-gated field-effect transistors fabricated on silicon/silicon dioxide substrates showed electron mobilities as high as 4050 square centimeters per volt per second at room temperature.

Graphene segregated on Ni surfaces and transferred to insulators

Appl. Phys. Lett. 93, 113103 (2008)

 

Qingkai Yu, Jie Lian, Sujitra Siriponglert, Hao Li, Yong P. Chen and Shin-Shem Pei

 

We report an approach to synthesize high quality graphene by surface segregation and substrate transfer. Graphene was segregated from Ni surface under the ambient pressure by dissolving carbon in Ni at high temperatures followed by cooling down with various rates. Different cooling rates led to different segregation behaviors, strongly affecting the thickness and quality of the graphene films. Electron microscopy and Raman spectroscopy indicated that the graphene films synthesized with medium cooling rates have high quality crystalline structure and well-controlled thicknesses. The graphene films were transferred to insulating substrates by wet etching and found to maintain their high quality.

 

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