Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session B6: Focus Session: CVD Graphene - Growth and Characterization |
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Sponsoring Units: DMP Chair: Luigi Colombo, Texas Instruments Room: 302 |
Monday, March 18, 2013 11:15AM - 11:27AM |
B6.00001: Ultrafast dynamics of non-thermal hot electrons in chemical vapor deposited graphene Kuan-Chun Lin, Ming-Yang Li, Cheng-Chung Chi, Jeng-Chung Chen The relaxation dynamics of photoexcited carriers in a chemical vapor deposited graphene transferred on quartz substrate are investigated using ultrafast optical-pump terahertz (THz)-probe spectroscopy. Terahertz transmission through graphene sample is reduced by optical pumping. The change of transmission decays exponentially after the optical pulse. We find the decay time is insensitive to the substrate temperatures from 10~K to 300~K, but increases sublinearly with pump flunce. We model the relaxation process involving electron-phonon coupling together with a set of rate equations to describe the transient responses of quasi-particals and optical phonons. We can fit the observered transient terahertz transmission very well. The extracted carrier temperature follows the same trend of decay time as a function of fluence. High pump fluence can significantly increase the carrier temperature and broaden the carrier distributions, consequently causing the reduction of optical phonon emission efficiency and slowing down cooling rate. The differences of our results in comparison to similar measurements of expitaxial graphene on SiC will be disscussed. [Preview Abstract] |
Monday, March 18, 2013 11:27AM - 11:39AM |
B6.00002: Raman Spectroscopic Studies of Room-Temperature-Grown Graphene by Plasma-Assisted Chemical Vapor Deposition Chen-Chih Hsu, David Boyd, Wei-Hsiang Lin, Jong Yeon Lee, Nai-Chang Yeh We have synthesized graphene using plasma-assisted chemical vapor deposition (CVD) at room temperature (RT). Structural analysis through Raman spectroscopy reveals that high quality large-area graphene can be grown reproducibly. From the frequency shifts of the G-band and 2D-band, it is evident that the average strain of RT-grown graphene becomes much reduced relative to the high-temperature (1000$^{\circ}C)$ CVD-grown graphene. This finding is confirmed by the atomically resolved images taken with scanning tunneling microscopy (STM). To investigate the effect of different substrates on the resulting strain in graphene, we have grown graphene on Cu(111) and Cu(100) single crystals and polycrystalline Cu foils. Compared to high temperature CVD-grown graphene, strain is reduced no matter which substrate was used for the RT growth. However, graphene grown on Cu(111) is more inhomogeneous because anisotropic plasma etching of the substrate results in excess steps on the surface and creates stripe-like superstructures in graphene. Upon transferring the RT-grown graphene to SiO2 substrates, we find the average strain minimized. Our results suggest a promising pathway to inexpensive growth of high-quality large-area graphene. This work was supported by NSF through IQIM at Caltech. [Preview Abstract] |
Monday, March 18, 2013 11:39AM - 11:51AM |
B6.00003: Carbon atom bonding processes in CVD graphene growth on copper surface: A first principles study Takahisa Ohno, Nobuo Tajima, Tomoaki Kaneko, Jun Nara Graphene has attracted considerable research interest due to potential application to future electronic devices. Large area and high-quality graphene is needed for device applications. Chemical vapor deposition using copper surface with hydrocarbon source is one of the practical methods to produce graphene. This method is appropriate for creating large area graphene, and the graphene growth control to obtain high quality product is a challenge. The carbon atom nucleation and cluster growth processes in the CVD reactions have been studied extensively as key steps to control graphene growth. In the present study, first principles molecular dynamics calculations are performed to obtain fundamental insight into these C-C bonding process. First principles simulation code PAHSE (http://www.ciss.iis.u-tokyo.ac.jp/english/project/device/) was used in these calculations. [Preview Abstract] |
Monday, March 18, 2013 11:51AM - 12:27PM |
B6.00004: Probing dynamics in graphene with infrared spectroscopy Invited Speaker: Jie Shan Infrared and far-infrared spectroscopy provides an attractive approach for examining the properties of charge carriers in solids. For the case of graphene, while these possibilities had been recognized, experiments were hindered by the lack of samples of sufficient lateral extent to be probed by standard far-field techniques. Now, with the advent of high-quality graphene grown by chemical vapor deposition (CVD), researchers are able to overcome these limitations. Analysis of optical conductivity by infrared spectroscopy provides direct information about the carrier scattering rate, as well as the intraband and interband transition strength in graphene. Furthermore, when combined with a femtosecond excitation pulse, time-resolved terahertz (or far-infrared) spectroscopy allows us to probe the ultrafast relaxation dynamics of electrons in graphene. In this talk, I will discuss recent results on infrared spectroscopy and dynamics studies of CVD graphene, with an emphasis on identifying the role of electron-phonon and electron-electron interactions and the influence of doping on these interactions. [Preview Abstract] |
Monday, March 18, 2013 12:27PM - 12:39PM |
B6.00005: Graphene originated 3D structures grown on the assembled nickel particles Tereza Paronyan, Avetik Harutyunyan Recently, the fabrication of various morphologies of graphene originated structures became very important due to the perspective of wide range of new applications. Particularly, free standing 3D structured graphene foams could be imperative in energy related areas$.$ Here, we present the new approach of the CVD growth of 3D graphene network by using primarily sintered Ni particle's ($\sim$40$\mu $m size) assembles as a template-catalyst via decomposition of low rate of CH$_{4}$ at 1100$^{\circ}$ C based on synthesis method described earlier [1]. SEM and Raman spectra analysis revealed the formation of graphene structure containing a single up to few layers grown on the sintered metal particles served as a catalyst-template. After etching the metal frame without using any support polymer, 3D free-standing graphene microporous structure was formed demonstrating high BET surface area. Two probe measurements of frame resistance were $\sim$2-8$\Omega $. Our approach allows controllable tune the pore size and thereby the surface area of 3D graphene network through the variation of the template-catalyst particles size. \\[4pt] [1]. T. M. Paronyan et al. ACS Nano, \textbf{5}, p. 9619 (2011) [Preview Abstract] |
Monday, March 18, 2013 12:39PM - 12:51PM |
B6.00006: Improving the quality of CVD graphene-based devices: synthesis, transfer, fabrication and measurement Junjie Wang, Bei Wang, Anna Skinner, Jun Zhu Graphene synthesized by chemical vapor deposition (CVD) is potentially useful in a wide range of electronic and optoelectronic applications. In order to obtain CVD-graphene based devices with performance comparable to their exfoliated counterparts, improvement needs to be made on the synthesis and transfer of graphene, as well as device fabrication and measurement techniques. Here we report on a low-pressure growth procedure, which successfully suppresses the growth of multilayer patches, resulting in large-scale single-layer graphene production. By following the etching of the copper substrate with a HCl/H$_{\mathrm{2}}$O$_{\mathrm{2}}$ cleaning step similar to the RCA-2 procedure used in Silicon industry, metal particle contamination is reduced. By applying the gate voltage in pulse, we eliminate the hysteresis commonly observed in the transfer curve of graphene field effect transistors. This allows us to accurately determine the charge neutrality point and carrier mobility of the device. We are able to achieve high-quality CVD-graphene devices with average carrier mobility of 7,000 cm$^{\mathrm{2}}$V$^{\mathrm{-1}}$s$^{\mathrm{-1}}$. [Preview Abstract] |
Monday, March 18, 2013 12:51PM - 1:03PM |
B6.00007: Linear magnetoresistance of graphene in contact with inhomogeneous disordered graphitic carbon Jinglei Ping, Michael Fuhrer We synthesized graphene via chemical vapor deposition(CVD) on platinum foils and transferred graphene to Si$_{\mathrm{3}}$N$_{\mathrm{4}}$ membranes for inspection by transmission electron microscope (TEM), or to SiO$_{\mathrm{2}}$/Si for fabricating field-effect transistors. Dark-field TEM shows that the graphene is decorated with disordered (nanocrystalline) graphitic carbon which is spatially inhomogeneous. The impurity layer can easily be mistaken for a second graphene layer in optical microscopy. Atomic force microscopy shows that impurities form between graphene and Pt, supporting a ``growth-from-below'' model. The impurity-decorated graphene exhibits linear magnetoresistance (LMR) which is carrier-density-dependent and nonsaturating up to 8 Tesla. No LMR is observed with graphene samples with little impurities, or in exfoliated graphene. We understand the LMR as due to an effective inhomogeneous random-resistor network arising from the spatially inhomogeneous nature of the graphene/impurity system. The results may shed light on the previously-observed LMR in graphene on Si-face SiC. [Preview Abstract] |
Monday, March 18, 2013 1:03PM - 1:15PM |
B6.00008: Triggering the Growth of Large Single Crystal Graphene by Chemical Vapor Deposition Tianru Wu, Haomin Wang, Guqiao Ding, Da Jiang, Xiaoming Xie, Mianheng Jiang Graphene, a monolayer of sp2 carbon atoms, has been attracting great interests as an ideal two dimensional crystalline material. Fabrication technique for wafer scale graphene via chemical vapor deposition (CVD) was developed several years ago [1]. However, large scale graphene films from CVD method so far are found to be polycrystalline, consisting of numerous grain boundaries, which greatly degrade the electrical and mechanical properties of graphene [2]. Recently, we obtained hexagonal-shaped single-crystal monolayer graphene domains ($\sim $1.2 mm) [3]. We adapted a strategy to synthesize larger size single crystal grains by regulating the supply of reactants and hytrogen. Nucleation density can be decreased to less than 1000 nuclei /m2. Gradually increase in the supply of reactants could break the equilibrium of growth and etching at the edge of hexagonal-shaped graphene grains. It drives the reaction toward quick growth of graphene domains during the whole CVD process. The graphene grains we obtained show high crystalline quality with high mobility of $\sim$13000 cm2V-1s-1, which is comparable to that of exfoliated graphene. The results achieved will definitely benefit for further practical application of graphene electronics. [1] Li X S, et al. Science, 2009, 324: 1312$\sim$1314. [2] Huang PY, et al. Nature 2011, 469: 389-392. [3] Wu T R, et al. Adv. Func. Mater. 2012, Doi: 10.1002/adfm.201201577. [Preview Abstract] |
Monday, March 18, 2013 1:15PM - 1:27PM |
B6.00009: Superior properties of plasma-assisted room-temperature-grown graphene from STM studies M.L. Teague, W.-H. Lin, D.A. Boyd, N.-C. Yeh, Y.-Y. Lo, C.-I. Wu, W.-Y. Chan, W.-B. Su, C.-S. Chang We report scanning tunneling microscopic and spectroscopic (STM/STS) studies of large-area monolayer graphene grown at room temperature (RT) on Cu foils, Cu (100) and Cu (111) single crystals, and compare the properties of these samples with high-temperature (1000 $^{\circ}$C) CVD-grown graphene. All RT-grown graphene exhibit highly ordered honeycomb structures over $\sim$ 1 cm$^{2}$ areas, smooth surface morphology, much reduced strain (\textless\ 0.1{\%}) and additional Moire patterns for samples grown on single crystals. The structural quality and reduced strain obtained from STM studies are consistent with finds from Raman spectra. In contrast, high-temperature CVD-grown graphene revealed strongly distorted atomic structures and large strain, giving rise to giant pseudo-magnetic fields and charging effects as manifested by the conductance peaks at quantized energies and the strongly enhanced local conductance in highly strained regions. These strain-induced effects are believed to be responsible for the reduced electrical mobility in typical CVD-grown graphene. The superior structural and electronic properties demonstrated by our RT-grown graphene are promising for a wide range of applications. This work was supported by NSF through IQIM at Caltech. [Preview Abstract] |
Monday, March 18, 2013 1:27PM - 1:39PM |
B6.00010: Structural and Electrical Properties of CVD and PECVD Grown Graphene Michelle Langhoff, W. Mitchel, E. Gallo, G. Tompa, N. Sbrockey, T. Salagaj, K. Ghosh There is a robust research effect on graphene due to its unique properties. While the ultimate goal of this research is to study the electrical properties of graphene, a multistep process of research is require to reach the point at which it is possible to make the necessary measurements. Graphene is typically grown using CVD on a copper substrate: this substrate has been found to offer the best results to date. Unfortunately, this requires the transfer to alternate, non-conducting, substrates in order to effect electrical measurements. This work seeks to determine the optimal transfer process of graphene using Raman spectroscopy and analyzing the prominence of the defect peak. Upon the success of the transfer, electrical properties are evaluated using AFM. This work will discuss the difference in growth quality between standard CVD growth and PECVD, evaluate the success of transfer to alternate substrates, and provide results from preliminary electrical measurements using AFM. We would like to acknowledge Structured Materials Industries Inc. for providing graphene samples. [Preview Abstract] |
Monday, March 18, 2013 1:39PM - 1:51PM |
B6.00011: Catalyst-free growth of nanographene and its application Dongxia Shi, Wei Yang, Donghua Liu, Rong Yang, Guangyu Zhang A new method was developed to synthesis graphene films on various substrates without catalyst at low temperature, which was performed using our home-made remote plasma enhanced chemical vapor deposition system (r-PECVD). The fabricated graphene film is composed of nanographene islands with hexagonal shape and size of several hundred nanometers. Through the adjustment of temperature, the nucleation and growth were fully controlled, in this way, nanographene films with expected crystal size and layers can be obtained. Furthermore, the fabricated nanographene films was also investigated in strain sensors, which shows ultra-sensitive properties with the highest gauge factor over 300 so far for graphene-based strain sensors. The piezoresistive characteristics of nanographene films are based on charge tunneling from neighboring nanographene islands. Besides strain sensors, this simple and scalable graphene fabrication also provides a potential way in many applications fields, such as electrode materials, transparent conductive films, thin film resistors, gas sensors and so on. [Preview Abstract] |
Monday, March 18, 2013 1:51PM - 2:03PM |
B6.00012: Engineering epitaxial graphene with oxygen Amina Kimouche, Sylvain Martin, Clemens Winkelmann, Olivier Fruchart, Herv\'e Courtois, Johann Coraux Almost free-standing graphene can be obtained on metals by decoupling graphene from its substrate, for instance by intercalation of atoms beneath graphene, as it was shown with oxygen atoms [1]. We show that the interaction of oxygen with epitaxial graphene on iridium leads to the formation of an ultrathin crystalline oxide extending between graphene and the metallic substrate via the graphene wrinkles. Graphene studied in this work was prepared under ultra-high vacuum by CVD [2,3]. The samples were studied by combining scanning probe microscopy (STM, AFM) and spatially resolved spectroscopy (Raman, STS). The ultrathin oxide forms a decoupling barrier layer between graphene and Ir, yielding truly free-standing graphene whose hybridization and charge transfers with the substrate have been quenched [4]. Our work presents novel types of graphene-based nanostructures, and opens the route to the transfer-free preparation of graphene directly onto an insulating support contacted to the metallic substrate which could serve as a gate electrode. References [1] Sutter, P. \textit{et al. }J. Am. Chem. Soc. 132, 8135 (2010). [2] Coraux, J. \textit{et al.} Nano Lett. 8, 565 (2008). [3] Vo-Van, C~; Kimouche, A \textit{et al. } Appl. Phys. Lett. 98, 181903 (2011). [4] Kimouche, A\textit{ et al. }Fully decoupling graphene from its substrate via wrinkles. \textit{Submitted} [Preview Abstract] |
Monday, March 18, 2013 2:03PM - 2:15PM |
B6.00013: Graphene growth using Pulsed Laser Deposition Gautam Hemani, Manuel Quevedo-Lopez, Massimo V. Fischetti To obtain improved electrical performance in graphene, an unconventional growth process using pulsed laser deposition (PLD) where graphene is grown directly on a silicon substrate is proposed. Using PLD, graphene was grown directly on device quality wafer using nickel metal and then characterized with Raman spectroscopy. Also, the Electron Backscatter Diffraction technique was used to characterize the grain structure of the Nickel after deposition in order to understand how the high temperatures affected the graphene growth process. Attempts have also been made to integrate this unconventional growth with standard semiconductor device fabrication in order to explore transfer free graphene based devices. Raman spectroscopy revealed that we have well defined spectra indicating from monolayer to few layer graphene, with minimum defects. [Preview Abstract] |
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