Xuesong Li
University of Texas at Austin
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Featured researches published by Xuesong Li.
Science | 2009
Xuesong Li; Weiwei Cai; Jinho An; Seyoung Kim; Dongxing Yang; Richard D. Piner; Aruna Velamakanni; Inhwa Jung; Emanuel Tutuc; Sanjay K. Banerjee; Luigi Colombo; Rodney S. Ruoff
Growing Graphene The highest quality graphene samples, single-atom-thick layers of carbon, are suspended flakes exfoliated from graphite, but these samples are very small in size (square micrometers). For many electronics applications, larger areas are needed. Li et al. (p. 1312, published online 7 May) show that graphene grows in a self-limiting way on copper films as large-area sheets (one square centimeter) from methane through a chemical vapor deposition process. The films, which are mainly one layer in thickness, can be transferred to other substrates and have electron mobilities as high as 4300 square centimeters per volt second. Predominantly single-layer graphene films grow in a self-limited manner on copper and can be transferred to other substrates. 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.
Advanced Materials | 2010
Yanwu Zhu; Shanthi Murali; Weiwei Cai; Xuesong Li; Ji Won Suk; Jeffrey R. Potts; Rodney S. Ruoff
There is intense interest in graphene in fields such as physics, chemistry, and materials science, among others. Interest in graphenes exceptional physical properties, chemical tunability, and potential for applications has generated thousands of publications and an accelerating pace of research, making review of such research timely. Here is an overview of the synthesis, properties, and applications of graphene and related materials (primarily, graphite oxide and its colloidal suspensions and materials made from them), from a materials science perspective.
Nano Letters | 2009
Xuesong Li; Yanwu Zhu; Weiwei Cai; Mark Borysiak; Boyang Han; David J. Chen; Richard D. Piner; Luigi Colombo; Rodney S. Ruoff
Graphene, a two-dimensional monolayer of sp(2)-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.
Science | 2010
Jae Hun Seol; Insun Jo; Arden L. Moore; Lucas Lindsay; Zachary H. Aitken; Michael T. Pettes; Xuesong Li; Zhen Yao; Rui Huang; David Broido; Natalio Mingo; Rodney S. Ruoff; Li Shi
Heat Flow in Graphene Unsupported graphene sheets show exceptional thermal transport properties, but are these properties maintained when a graphene sheet is in contact with a substrate? Seol et al. (p. 213; see the Perspective by Prasher) measured the thermal conductivity of graphene supported on silicon dioxide and found that, while the conductivity was considerably lower than that of free-standing graphene, it was still greater than that of metals such as copper. A theoretical model suggested that the out-of-plane flexing vibrations of the graphene play a key role in thermal transport. Thus, graphene may help in applications such as conducting heat away from electronic circuits. The thermal conductivity of graphene supported on silicon dioxide remains high, despite phonon scattering by the substrate. The reported thermal conductivity (κ) of suspended graphene, 3000 to 5000 watts per meter per kelvin, exceeds that of diamond and graphite. Thus, graphene can be useful in solving heat dissipation problems such as those in nanoelectronics. However, contact with a substrate could affect the thermal transport properties of graphene. Here, we show experimentally that κ of monolayer graphene exfoliated on a silicon dioxide support is still as high as about 600 watts per meter per kelvin near room temperature, exceeding those of metals such as copper. It is lower than that of suspended graphene because of phonons leaking across the graphene-support interface and strong interface-scattering of flexural modes, which make a large contribution to κ in suspended graphene according to a theoretical calculation.
Nano Letters | 2009
Xuesong Li; Weiwei Cai; Luigi Colombo; Rodney S. Ruoff
Large-area graphene growth is required for the development and production of electronic devices. Recently, chemical vapor deposition (CVD) of hydrocarbons has shown some promise in growing large-area graphene or few-layer graphene films on metal substrates such as Ni and Cu. It has been proposed that CVD growth of graphene on Ni occurs by a C segregation or precipitation process whereas graphene on Cu grows by a surface adsorption process. Here we used carbon isotope labeling in conjunction with Raman spectroscopic mapping to track carbon during the growth process. The data clearly show that at high temperatures sequentially introduced isotopic carbon diffuses into the Ni first, mixes, and then segregates and precipitates at the surface of Ni forming graphene and/or graphite with a uniform mixture of (12)C and (13)C as determined by the peak position of the Raman G-band peak. On the other hand, graphene growth on Cu is clearly by surface adsorption where the spatial distribution of (12)C and (13)C follows the precursor time sequence and the linear growth rate ranges from about 1 to as high as 6 mum/min depending upon Cu grain orientation. This data is critical in guiding the graphene growth process as we try to achieve the highest quality graphene for electronic devices.
Journal of the American Chemical Society | 2011
Xuesong Li; Carl W. Magnuson; Archana Venugopal; Rudolf M. Tromp; James B. Hannon; Eric M. Vogel; Luigi Colombo; Rodney S. Ruoff
Graphene single crystals with dimensions of up to 0.5 mm on a side were grown by low-pressure chemical vapor deposition in copper-foil enclosures using methane as a precursor. Low-energy electron microscopy analysis showed that the large graphene domains had a single crystallographic orientation, with an occasional domain having two orientations. Raman spectroscopy revealed the graphene single crystals to be uniform monolayers with a low D-band intensity. The electron mobility of graphene films extracted from field-effect transistor measurements was found to be higher than 4000 cm(2) V(-1) s(-1) at room temperature.
ACS Nano | 2011
Shanshan Chen; Lola Brown; Mark Levendorf; Weiwei Cai; Sang Yong Ju; Jonathan Edgeworth; Xuesong Li; Carl W. Magnuson; Aruna Velamakanni; Richard D. Piner; Junyong Kang; Jiwoong Park; Rodney S. Ruoff
The ability to protect refined metals from reactive environments is vital to many industrial and academic applications. Current solutions, however, typically introduce several negative effects, including increased thickness and changes in the metal physical properties. In this paper, we demonstrate for the first time the ability of graphene films grown by chemical vapor deposition to protect the surface of the metallic growth substrates of Cu and Cu/Ni alloy from air oxidation. In particular, graphene prevents the formation of any oxide on the protected metal surfaces, thus allowing pure metal surfaces only one atom away from reactive environments. SEM, Raman spectroscopy, and XPS studies show that the metal surface is well protected from oxidation even after heating at 200 °C in air for up to 4 h. Our work further shows that graphene provides effective resistance against hydrogen peroxide. This protection method offers significant advantages and can be used on any metal that catalyzes graphene growth.
Nano Letters | 2010
Xuesong Li; Carl W. Magnuson; Archana Venugopal; Jinho An; Ji Won Suk; Boyang Han; Mark Borysiak; Weiwei Cai; Aruna Velamakanni; Yanwu Zhu; Lianfeng Fu; Eric M. Vogel; Edgar Voelkl; Luigi Colombo; Rodney S. Ruoff
The fundamental properties of graphene are making it an attractive material for a wide variety of applications. Various techniques have been developed to produce graphene and recently we discovered the synthesis of large area graphene by chemical vapor deposition (CVD) of methane on Cu foils. We also showed that graphene growth on Cu is a surface-mediated process and the films were polycrystalline with domains having an area of tens of square micrometers. In this paper, we report on the effect of growth parameters such as temperature, and methane flow rate and partial pressure on the growth rate, domain size, and surface coverage of graphene as determined by Raman spectroscopy, and transmission and scanning electron microscopy. On the basis of the results, we developed a two-step CVD process to synthesize graphene films with domains having an area of hundreds of square micrometers. Scanning electron microscopy and Raman spectroscopy clearly show an increase in domain size by changing the growth parameters. Transmission electron microscopy further shows that the domains are crystallographically rotated with respect to each other with a range of angles from about 13 to nearly 30°. Electrical transport measurements performed on back-gated FETs show that overall films with larger domains tend to have higher carrier mobility up to about 16,000 cm(2) V(-1) s(-1) at room temperature.
Nano Letters | 2010
Weiwei Cai; Arden L. Moore; Yanwu Zhu; Xuesong Li; Shanshan Chen; Li Shi; Rodney S. Ruoff
Graphene monolayer has been grown by chemical vapor deposition on copper and then suspended over a hole. By measuring the laser heating and monitoring the Raman G peak, we obtain room-temperature thermal conductivity and interface conductance of (370 + 650/-320) W/m K and (28 + 16/-9.2) MW/m(2) K for the supported graphene. The thermal conductivity of the suspended graphene exceeds (2500 + 1100/-1050) W/m K near 350 K and becomes (1400 + 500/-480) W/m K at about 500 K.
Applied Physics Letters | 2009
Weiwei Cai; Yanwu Zhu; Xuesong Li; Richard D. Piner; Rodney S. Ruoff
By dissolving carbon atoms decomposed from methane in a metal substrate at high temperatures, large area uniform few-layer graphene (FLG)/graphite films were precipitated on metal surfaces upon cooling. The thickness could be controlled by varying the amount of carbon atoms in the metal. Such films were transferred to glass slides after dissolving the metal substrate in an aqueous solution of Fe(NO3)3. Sheet resistances as low as 200 Ω/◻ with a transmittance of 85% were obtained from FLG films. The resistance and transmittance can be changed over one order of magnitude, making such films potentially useful for transparent thin conducting electrodes.