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.

Species Diversity, Relative Abundance, and Decline of Flying Insects in a Fragmented Forest in Futa Akure, Ondo State, Nigeria

Temitope A. Olatoye,권오석,Kayode L. Akinwande 국립생태원 2024 국립생태원회보(PNIE) Vol.5 No.1

The study investigated species diversity, relative abundance, and decline of flying insects and plants within a fragmented forest in the Federal University of Technology Akure (FUTA), Ondo State, Nigeria. It is known that habitat fragmentation can reduce biodiversity. Thus, it is important to perform comprehensive assessments to understand implications of the habitat fragmentation for flora and fauna. Species richness and abundance of flying insects and plants across fragmented forest patches were quantified using field surveys and taxonomic identification. This study revealed shifts in species diversity, with fragmented areas exhibiting reduced biodiversity compared to contiguous forest ecosystems. Flying insects crucial for ecosystem functioning and pollination services demonstrated decreased species richness and relative abundance within fragmented habitats. This decline was attributed to habitat loss, altered microclimates, and limited movement pathways known to hinder insect dispersal. Similarly, plant species richness and abundance showed decline in fragmented forest due to disrupted mutualistic interactions with pollinators, altered nutrient cycling, and increased competition among plant species. This study underscores the importance of maintaining intact forest habitats to sustain healthy ecosystems and preserve biodiversity. Effective conservation strategies should focus on habitat connectivity, reforestation efforts, and protection of essential ecological corridors to mitigate effects of fragmentation. In conclusion, this investigation provides empirical evidence for effects of habitat fragmentation on flying insects and plants in a forest ecosystem in FUTA Akure, Nigeria. Findings emphasize an urgency of adopting conservation measures to safeguard these invaluable components of biodiversity and ecosystem stability in the face of ongoing habitat loss and fragmentation.

Low-voltage organic transistors and depletion-load inverters with high-K pyrochlore BZN gate dielectric on polymer substrate

Choi, YongWoo,Kim, Il-Doo,Tuller, H.L.,Akinwande, A.I. Institute of Electrical and Electronics Engineers 2005 IEEE transactions on electron devices Vol.52 No.12

Pentacene organic thin-film transistors (OTFTs) have demonstrated the highest performance among TFTs with an organic semiconductor channel. High operating voltages (20-100 V), stemming from poor capacitive coupling between gate electrode and channel, are a major limitation, particularly for portable battery-powered device applications. OTFTs fabricated on flexible polymer substrates, often characterized by rough surfaces, benefit from the use of high-K dielectrics given the ability to accommodate thicker films which ensure the pinhole-free and good coverage without need to increase operating voltage. As we demonstrate, pyrochlore structured thin films can provide the requisite high dielectric constant coupled with excellent leakage current characteristics, while remaining compatible with the processing requirements of flexible OTFTs. The introduction of an extremely thin parylene film between the BZN dielectric and the pentacene semiconductor markedly shifts the threshold voltage, making it possible to fabricate both enhancement (E) and depletion (D) TFTs. We report the successful fabrication of low-voltage (<2 V) organic transistors and depletion-load inverter using a 200-nm-thick pyrochlore gate dielectric, Bi<SUB>1.5</SUB>Zn<SUB>1.0</SUB>Nb<SUB>1.5</SUB>O<SUB>7</SUB> (BZN), prepared by a room temperature process. The inverters with depletion load were successfully operated under 5 V with excellent noise margin.

Recent development of two-dimensional transition metal dichalcogenides and their applications

Choi, W.,Choudhary, N.,Han, G.H.,Park, J.,Akinwande, D.,Lee, Y.H. Elsevier Science Ltd 2017 Materials today Vol.20 No.3

<P>Recent advances in atomically thin two-dimensional transition metal dichalcogenides (2D TMDs) have led to a variety of promising technologies for nanoelectronics, photonics, sensing, energy storage, and opto-electronics, to name a few. This article reviews the recent progress in 2D materials beyond graphene and includes mainly transition metal dichalcogenides (TMDs) (e.g. MoS2, WS2, MoSe2, and WSe2). These materials are finding niche applications for next-generation electronics and optoelectronics devices relying on ultimate atomic thicknesses. Albeit several challenges in developing scalable and defect-free TMDs on desired substrates, new growth techniques compatible with traditional and unconventional substrates have been developed to meet the ever-increasing demand of high quality and controllability for practical applications. The fabrication of novel 2D TMDs that exhibit exotic functionalities and fundamentally new chemistry is highlighted. And finally, in parallel with the electronics, the considerable effort devoted to using these materials for energy and sensing applications is discussed in detail.</P>

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>

Hepatoprotective and Antioxidant Activities of Vernonia amygdalina on Acetaminophen-Induced Hepatic Damage in Mice

B.A. Iwalokun,B.U. Efedede,J.A. Alabi-Sofunde,T.Oduala,O.A. Magbagbeola,A.I.Akinwande 한국식품영양과학회 2006 Journal of medicinal food Vol.9 No.4

Vernonia amygdalinaDel. (Family Compositae) is used in Nigerian folk medicine as a tonic and remedy againstconstipation, fever, high blood pressure, and many infectious diseases. We have evaluated the hepatoprotective and antioxi-dant effects of an aqueous extract of V. amygdalinaleaves against acetaminophen-induced hepatotoxicity and oxidative stressin mice in vivo. Activities of liver marker enzymes in serum (glutamate-oxaloacetate transaminase, glutamate-pyruvate transam-inase, lactate dehydrogenase, and alkaline phosphatase) and bilirubin levels were determined colorimetrically, while catalaseactivity, lipid peroxidation products, thiobarbituric acid-reactive substances (TBARS), iron, and total protein concentrationswere measured in liver homogenate. Acetaminophen challenge (300 mg/kg, i.p) for 7 days caused significant (P. .01) in-creases in the levels of bilirubin, liver enzymes, TBARS, and iron, while catalase activity and total protein level were reducedsignificantly (P. .01). Preadministration of V. amygdalinaresulted in a dose-dependent (50100 mg/kg) reversal of aceta-minophen-induced alterations of all the liver function parameters by 51.984.9%. Suppression of acetaminophen-induced lipidperoxidation and oxidative stress by the extract was also dose-dependent (50100 mg/kg). The results of this study suggestthat V. amygdalinaelicits hepatoprotectivity through antioxidant activity on acetaminophen-induced hepatic damage in mice.

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>

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>