INVERSION OF THE ELECTRICAL AND OPTICAL PROPERTIES OF PARTIALLY OXIDIZED HEXAGONAL BORON NITRIDE

AVINASH P. NAYAK,DEJI AKINWANDE,ANDREI DOLOCAN,JONGHO LEE,HSIAO-YU CHANG,TWINKLE PANDHI,MILO HOLT 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2014 NANO Vol.9 No.1

By acoustically irradiating pristine, white, electrically insulating h-BN in aqueous environmentwe were able to invert its material properties. The resulting dark, electrically conductive h-BN(referred to as partially oxidized h-BN or PO-hBN) shows a signi¯cant decrease in opticaltransmission ( > 60%) and bandgap (from 5.46 eV to 3.97 eV). Besides employing a wide variety ofanalytical techniques (optical and electrical measurements, Raman spectroscopy, SEM imaging,EDS, X-Ray di®raction, XPS and TOF-SIMS) to study the material properties of pristine andirradiated h-BN, our investigation suggests the basic mechanism leading to the dramatic changesfollowing the acoustic treatment. We ¯nd that the degree of inversion arises from the degree of h-BN surface or edge oxidation which heavily depends on the acoustic energy density provided tothe pristine h-BN platelets during the solution-based process. This provides a facile avenue for therealization of materials with tuned physical and chemical properties that depart from the intrinsicbehavior of pristine h-BN.

Enhanced heat dissipation performance of chemical-doped graphene for flexible devices

Chung Yung-Bin,Kireev Dmitry,Kim Myungsoo,Akinwande Deji,Kwon Sung-Joo 한국물리학회 2021 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.78 No.1

As the rapid development of electronic technology, the amount of unavoidable heat from electronic components is also increasing. Therefore, the demand for efficient heat dissipation materials with high performance is continuously increasing. Graphene is one of the best candidates in terms of heat dissipation property and intrinsic flexibility. In this work, we show that chemical doping is an effective way to additionally improve the heat dissipation property of large-scale CVD grown monolayer graphene. We found that heat dissipation property of monolayer graphene, chemically doped with HNO3 and PFSA improves by the 9.94% and 4.12% compared with pristine graphene, respectively. Moreover, it shows the stable heat dissipation property after bending test.

Selective-Area Fluorination of Graphene with Fluoropolymer and Laser Irradiation

Lee, Wi Hyoung,Suk, Ji Won,Chou, Harry,Lee, Jongho,Hao, Yufeng,Wu, Yaping,Piner, Richard,Akinwande, Deji,Kim, Kwang S.,Ruoff, Rodney S. American Chemical Society 2012 Nano letters Vol.12 No.5

<P>We have devised a method to selectively fluorinate graphene by irradiating fluoropolymer-covered graphene with a laser. This fluoropolymer produces active fluorine radicals under laser irradiation that react with graphene but only in the laser-irradiated region. The kinetics of C–F bond formation is dependent on both the laser power and fluoropolymer thickness, proving that fluorination occurs by the decomposition of the fluoropolymer. Fluorination leads to a dramatic increase in the resistance of the graphene while the basic skeletal structure of the carbon bonding network is maintained. Considering the simplicity of the fluorination process and that it allows patterning with a nontoxic fluoropolymer as a solid source, this method could find application to generate fluorinated graphene in graphene-based electronic devices such as for the electrical isolation of graphene.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2012/nalefd.2012.12.issue-5/nl300346j/production/images/medium/nl-2012-00346j_0004.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl300346j'>ACS Electronic Supporting Info</A></P>

Support-Free Transfer of Ultrasmooth Graphene Films Facilitated by Self-Assembled Monolayers for Electronic Devices and Patterns

Wang, Bin,Huang, Ming,Tao, Li,Lee, Sun Hwa,Jang, A-Rang,Li, Bao-Wen,Shin, Hyeon Suk,Akinwande, Deji,Ruoff, Rodney S. American Chemical Society 2016 ACS NANO Vol.10 No.1

<P>We explored a support-free method for transferring large area graphene films grown by chemical vapor deposition to various fluoric self-assembled mono layer (F-SAM) modified substrates including SiO2/Si wafers, polyethylene terephthalate films, and glass. This method yields clean, ultrasmooth, and high-quality graphene films for promising applications such as transparent, conductive, and flexible films due to the absence of residues and limited structural defects such as cracks. The F-SAM introduced in the transfer process can also lead to graphene transistors with enhanced field-effect mobility (up to 10,663 cm(2)/Vs) and resistance modulation (up to 12x) on a standard silicon dioxide dielectric. Clean graphene patterns can be realized by transfer of graphene onto only the F-SAM modified surfaces.</P>

Simultaneous Transfer and Doping of CVD-Grown Graphene by Fluoropolymer for Transparent Conductive Films on Plastic

Lee, Wi Hyoung,Suk, Ji Won,Lee, Jongho,Hao, Yufeng,Park, Jaesung,Yang, Jae Won,Ha, Hyung-Wook,Murali, Shanthi,Chou, Harry,Akinwande, Deji,Kim, Kwang S.,Ruoff, Rodney S. American Chemical Society 2012 ACS NANO Vol.6 No.2

<P>Chemical doping can decrease sheet resistance of graphene while maintaining its high transparency. We report a new method to simultaneously transfer and dope chemical vapor deposition grown graphene onto a target substrate using a fluoropolymer as both the supporting and doping layer. Solvent was used to remove a significant fraction of the supporting fluoropolymer, but residual polymer remained that doped the graphene significantly. This contrasts with a more widely used supporting layer, polymethylmethacrylate, which does not induce significant doping during transfer. The fluoropolymer doping mechanism can be explained by the rearrangement of fluorine atoms on the graphene basal plane caused by either thermal annealing or soaking in solvent, which induces ordered dipole moments near the graphene surface. This simultaneous transfer and doping of the graphene with a fluoropolymer increases the carrier density significantly, and the resulting monolayer graphene film exhibits a sheet resistance of ∼320 Ω/sq. Finally, the method presented here was used to fabricate flexible and a transparent graphene electrode on a plastic substrate.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2012/ancac3.2012.6.issue-2/nn203998j/production/images/medium/nn-2011-03998j_0003.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn203998j'>ACS Electronic Supporting Info</A></P>

Thermal Oxidation of WSe₂ Nanosheets Adhered on SiO₂/Si Substrates

Liu, Yingnan,Tan, Cheng,Chou, Harry,Nayak, Avinash,Wu, Di,Ghosh, Rudresh,Chang, Hsiao-Yu,Hao, Yufeng,Wang, Xiaohan,Kim, Joon-Seok,Piner, Richard,Ruoff, Rodney S.,Akinwande, Deji,Lai, Keji American Chemical Society 2015 NANO LETTERS Vol.15 No.8

<P>Because of the drastically different intralayer versus interlayer bonding strengths, the mechanical, thermal, and electrical properties of two-dimensional (2D) materials are highly anisotropic between the in-plane and out-of-plane directions. The structural anisotropy may also play a role in chemical reactions, such as oxidation, reduction, and etching. Here, the composition, structure, and electrical properties of mechanically exfoliated WSe<SUB>2</SUB> nanosheets on SiO<SUB>2</SUB>/Si substrates were studied as a function of the extent of thermal oxidation. A major component of the oxidation, as indicated from optical and Raman data, starts from the nanosheet edges and propagates laterally toward the center. Partial oxidation also occurs in certain areas at the surface of the flakes, which are shown to be highly conductive by microwave impedance microscopy. Using secondary ion mass spectroscopy, we also observed extensive oxidation at the WSe<SUB>2</SUB>–SiO<SUB>2</SUB> interface. The combination of multiple microcopy methods can thus provide vital information on the spatial evolution of chemical reactions on 2D materials and the nanoscale electrical properties of the reaction products.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2015/nalefd.2015.15.issue-8/acs.nanolett.5b02069/production/images/medium/nl-2015-02069p_0005.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl5b02069'>ACS Electronic Supporting Info</A></P>