Graphene–Ferroelectric Hybrid Structure for Flexible Transparent Electrodes

Ni, Guang-Xin,Zheng, Yi,Bae, Sukang,Tan, Chin Yaw,Kahya, Orhan,Wu, Jing,Hong, Byung Hee,Yao, Kui,Ö,zyilmaz, Barbaros American Chemical Society 2012 ACS NANO Vol.6 No.5

<P>Graphene has exceptional optical, mechanical, and electrical properties, making it an emerging material for novel optoelectronics, photonics, and flexible transparent electrode applications. However, the relatively high sheet resistance of graphene is a major constraint for many of these applications. Here we propose a new approach to achieve low sheet resistance in large-scale CVD monolayer graphene using nonvolatile ferroelectric polymer gating. In this hybrid structure, large-scale graphene is heavily doped up to 3 × 10<SUP>13</SUP> cm<SUP>–2</SUP> by nonvolatile ferroelectric dipoles, yielding a low sheet resistance of 120 Ω/□ at ambient conditions. The graphene–ferroelectric transparent conductors (GFeTCs) exhibit more than 95% transmittance from the visible to the near-infrared range owing to the highly transparent nature of the ferroelectric polymer. Together with its excellent mechanical flexibility, chemical inertness, and the simple fabrication process of ferroelectric polymers, the proposed GFeTCs represent a new route toward large-scale graphene-based transparent electrodes and optoelectronics.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2012/ancac3.2012.6.issue-5/nn3010137/production/images/medium/nn-2012-010137_0008.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn3010137'>ACS Electronic Supporting Info</A></P>

A Eu^III Tetrakis(β-diketonate) Dimeric Complex: Photophysical Properties, Structural Elucidation by Sparkle/AM1 Calculations, and Doping into PMMA Films and Nanowires

Biju, Silvanose,Freire, Ricardo O.,Eom, Yu Kyung,Scopelliti, Rosario,Bu&#x308,nzli, Jean-Claude G.,Kim, Hwan Kyu American Chemical Society 2014 Inorganic Chemistry Vol.53 No.16

<P>Reaction of Ln<SUP>III</SUP> with a tetrakis(diketone) ligand H<SUB>4</SUB>L [1,1′-(4,4′-(2,2-bis((4-(4,4,4-trifluoro-3-oxobutanoyl) phenoxy)methyl)propane-1,3-diyl)bis(oxy)bis(4,1-phenylene))bis(4,4,4-trifluorobutane-1,3-dione)] gives new podates which, according to mass spectral data and Sparkle/AM1 calculations, can be described as dimers, (NBu<SUB>4</SUB>[LnL])<SUB>2</SUB> (Ln = Eu, Tb, Gd:Eu), in both solid-state and dimethylformamide (DMF) solution. The photophysical properties of the Eu<SUP>III</SUP> podate are compared with those of the mononuclear diketonate (NBu<SUB>4</SUB>[Eu(BTFA)<SUB>4</SUB>], BTFA = benzoyltrifluoroacetonate), the crystal structure of which is also reported. The new Eu<SUP>III</SUP> dimeric complex displays bright red luminescence upon irradiation at the ligand-centered band in the range of 250–400 nm, irrespective of the medium. The emission quantum yields and the luminescence lifetimes of (NBu<SUB>4</SUB>[EuL])<SUB>2</SUB> (solid state: 51% ± 8% and 710 ± 2 μs; DMF: 31% ± 5% and 717 ± 1 μs) at room temperature are comparable to those obtained for NBu<SUB>4</SUB>[Eu(BTFA)<SUB>4</SUB>] (solid state: 60 ± 9% and 730 ± 5 μs; DMF: 30 ± 5% and 636 ± 1 μs). Sparkle/AM1 calculations were utilized for predicting the ground-state geometries of the Eu<SUP>III</SUP> dimer. Theoretical Judd–Ofelt and photoluminescence parameters, including quantum yields, predicted from this model are in good agreement with the experimental values, proving the efficiency of this theoretical approach implemented in the LUMPAC software (<uri xlink:href='http://lumpac.pro.br' xlink:type='simple'>http://lumpac.pro.br</uri>). The kinetic scheme for modeling energy transfer processes show that the main donor state is the ligand triplet state and that energy transfer occurs on both the <SUP>5</SUP>D<SUB>1</SUB> (44.2%) and <SUP>5</SUP>D<SUB>0</SUB> (55.8%) levels. Furthermore, the newly obtained Eu<SUP>III</SUP> complex was doped into a PMMA matrix to form highly luminescent films and one-dimensional nanowires having emission quantum yield as high as 67%–69% (doping concentration = 4% by weight); these materials display bright red luminescence even under sunlight, so that interesting photonic applications can be foreseen.</P><P>A red-emitting dimeric Eu<SUP>III</SUP> podate based on a tetrakis(β-diketonate) ligand emits highly monochromatic red light and features the highest quantum yield reported so far for dinuclear Eu<SUP>III</SUP> bis(β-diketonates); doping into a PMMA matrix results in thin films and one-dimensional nanowires, the luminescence of which can be seen under sunlight illumination.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/inocaj/2014/inocaj.2014.53.issue-16/ic500966z/production/images/medium/ic-2014-00966z_0012.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ic500966z'>ACS Electronic Supporting Info</A></P>

Phonon Modes of Organic Electro-Optic Molecular Crystals for Terahertz Photonics

Kim, Jongtaek,Kwon, O-Pil,Brunner, Fabian D. J.,Jazbinsek, Mojca,Lee, Seung-Heon,Gu&#x308,nter, Peter American Chemical Society 2015 The Journal of Physical Chemistry Part C Vol.119 No.18

<P>We investigate theoretically and experimentally the phonon modes of organic electro-optic crystals for THz-wave photonics. THz phonon modes significantly influence the characteristics of THz-wave generation and detection through the THz absorption and refractive-index dispersion. For a model as THz generation material, electro-optic PNP (2-(<I>N</I>-prolinol)-5-nitropyridine) molecular crystal containing a relatively small numbers of atoms in the unit cell is chosen for phonon-mode calculation. THz phonon modes with their frequencies and intensities are calculated by periodic density functional theory, and the resulting spectrum exhibits a good agreement with the experimental absorption spectrum measured by THz time-domain spectroscopy. THz-wave generation experiment is performed with PNP as THz generator and the organic electro-optic OH1 (2-(3-(4-hydroxystyryl)-5,5-dimethylcyclohex-2-enylidene)malononitrile) crystal as THz detector. Considering the phase matching condition and THz absorption, which are both influenced by the THz phonon modes of THz generation and detection materials, the calculated THz generation spectrum also matches well with the experimental THz spectrum obtained by optical rectification at the pump wavelength of 1300 nm. Therefore, the phonon mode identification is very important for optimizing and designing new THz source and detection materials as well as for THz spectroscopy.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2015/jpccck.2015.119.issue-18/acs.jpcc.5b02445/production/images/medium/jp-2015-02445p_0004.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jp5b02445'>ACS Electronic Supporting Info</A></P>

Reconciling reported and unreported HFC emissions with atmospheric observations

Lunt, Mark F.,Rigby, Matthew,Ganesan, Anita L.,Manning, Alistair J.,Prinn, Ronald G.,O’Doherty, Simon,Mu&#x308,hle, Jens,Harth, Christina M.,Salameh, Peter K.,Arnold, Tim,Weiss, Ray F.,Saito, Takuya,Y National Academy of Sciences 2015 PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF Vol.112 No.19

<P><B>Significance</B></P><P>Hydrofluorocarbons (HFCs) are among the atmosphere’s fastest growing, and most potent, greenhouse gases. Proposals have been made to phase down their use over the coming decades. Such initiatives may largely be informed by existing emissions inventories, which, we show, are the subject of significant uncertainty. In this work, we use atmospheric models and measurements to examine the accuracy of these inventories for five major HFCs. We show that, when aggregated together, reported emissions of these HFCs from developed countries are consistent with the atmospheric measurements, and almost half of global emissions now originate from nonreporting countries. However, the agreement between our results and the inventory breaks down for individual HFC emissions, suggesting inaccuracies in the reporting methods for individual compounds.</P><P>We infer global and regional emissions of five of the most abundant hydrofluorocarbons (HFCs) using atmospheric measurements from the Advanced Global Atmospheric Gases Experiment and the National Institute for Environmental Studies, Japan, networks. We find that the total CO<SUB>2</SUB>-equivalent emissions of the five HFCs from countries that are required to provide detailed, annual reports to the United Nations Framework Convention on Climate Change (UNFCCC) increased from 198 (175–221) Tg-CO<SUB>2</SUB>-eq⋅y<SUP>–1</SUP> in 2007 to 275 (246–304) Tg-CO<SUB>2</SUB>-eq⋅y<SUP>–1</SUP> in 2012. These global warming potential-weighted aggregated emissions agree well with those reported to the UNFCCC throughout this period and indicate that the gap between reported emissions and global HFC emissions derived from atmospheric trends is almost entirely due to emissions from nonreporting countries. However, our measurement-based estimates of individual HFC species suggest that emissions, from reporting countries, of the most abundant HFC, HFC-134a, were only 79% (63–95%) of the UNFCCC inventory total, while other HFC emissions were significantly greater than the reported values. These results suggest that there are inaccuracies in the reporting methods for individual HFCs, which appear to cancel when aggregated together.</P>

Porphyrins Fused with Strongly Electron-Donating 1,3-Dithiol-2-ylidene Moieties: Redox Control by Metal Cation Complexation and Anion Binding

Bill, Nathan L.,Ishida, Masatoshi,Ba&#x308,hring, Steffen,Lim, Jong Min,Lee, Sangsu,Davis, Christina M.,Lynch, Vincent M.,Nielsen, Kent A.,Jeppesen, Jan O.,Ohkubo, Kei,Fukuzumi, Shunichi,Kim, Dongho,S American Chemical Society 2013 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.135 No.29

<P>A new class of redox-active free base and metalloporphyrins fused with the 1,3-dithiol-2-ylidene subunits present in tetrathiafulvalene, termed MTTFP (M = H<SUB>2</SUB>, Cu, Ni, Zn), have been prepared and characterized. The strong electron-donating properties of MTTFP were probed by electrochemical measurement and demonstrated that oxidation potentials can be tuned by metalation of the free base form, H<SUB>2</SUB>TTFP. X-ray crystal structures of H<SUB>2</SUB>TTFP, ZnTTFP, and CuTTFP revealed that a severe saddle-shape distortion was observed with the dithiole rings bent out of the plane toward one another in the neutral form. In contrast, the structure of the two-electron oxidized species (CuTFFP<SUP>2+</SUP>) is planar, corresponding to a change from a nonaromatic to aromatic structure upon oxidation. A relatively large two-photon absorption (TPA) cross-section value of H<SUB>2</SUB>TTFP<SUP>2+</SUP> (1200 GM) was obtained for the free base compound, a value that is much higher than those typically seen for porphyrins (<100 GM). Augmented TPA values for the metal complexes were also seen. The strong electron-donating ability of ZnTTFP was further enhanced by binding of Cl<SUP>–</SUP> and Br<SUP>–</SUP> as revealed by thermal electron-transfer between ZnTTFP and Li<SUP>+</SUP>-encapsulated C<SUB>60</SUB> (Li<SUP>+</SUP>@C<SUB>60</SUB>) in benzonitrile, which was “switched on” by the addition of either Cl<SUP>–</SUP> or Br<SUP>–</SUP> (as the tetrabutylammonium salts). The X-ray crystal structure of Cl<SUP>–</SUP>-bound ZnTTFP was determined and provided support for the strong binding between the Cl<SUP>–</SUP> anion and the Zn<SUP>2+</SUP> cation present in ZnTTFP.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2013/jacsat.2013.135.issue-29/ja404830y/production/images/medium/ja-2013-04830y_0015.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja404830y'>ACS Electronic Supporting Info</A></P>

Efficient Excitonic Photoluminescence in Direct and Indirect Band Gap Monolayer MoS₂

Steinhoff, A.,Kim, J.-H.,Jahnke, F.,Rö,sner, M.,Kim, D.-S.,Lee, C.,Han, G. H.,Jeong, M. S.,Wehling, T. O.,Gies, C. American Chemical Society 2015 NANO LETTERS Vol.15 No.10

<P>We discuss the photoluminescence (PL) of semiconducting transition metal dichalcogenides on the basis of experiments and a microscopic theory. The latter connects ab initio calculations of the single-particle states and Coulomb matrix elements with a many-body description of optical emission spectra. For monolayer MoS<SUB>2</SUB>, we study the PL efficiency at the excitonic A and B transitions in terms of carrier populations in the band structure and provide a quantitative comparison to an (In)GaAs quantum well-structure. Suppression and enhancement of PL under biaxial strain is quantified in terms of changes in the local extrema of the conduction and valence bands. The large exciton binding energy in MoS<SUB>2</SUB> enables two distinctly different excitation methods: above-band gap excitation and quasi-resonant excitation of excitonic resonances below the single-particle band gap. The latter case creates a nonequilibrium distribution of carriers predominantly in the K-valleys, which leads to strong emission from the A-exciton transition and a visible B-peak even if the band gap is indirect. For above-band gap excitation, we predict a strongly reduced emission intensity at comparable carrier densities and the absence of B-exciton emission. The results agree well with PL measurements performed on monolayer MoS<SUB>2</SUB> at excitation wavelengths of 405 nm (above) and 532 nm (below the band gap).</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2015/nalefd.2015.15.issue-10/acs.nanolett.5b02719/production/images/medium/nl-2015-02719d_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl5b02719'>ACS Electronic Supporting Info</A></P>

Interconnectable Dynamic Compression Bioreactors for Combinatorial Screening of Cell Mechanobiology in Three Dimensions

Seo, Jungmok,Shin, Jung-Youn,Leijten, Jeroen,Jeon, Oju,Bal Ö,ztu&#x308,rk, Ayc&#x327,a,Rouwkema, Jeroen,Li, Yuancheng,Shin, Su Ryon,Hajiali, Hadi,Alsberg, Eben,Khademhosseini, Ali American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.16

<P>Biophysical cues can potently direct a cell’s or tissue’s behavior. Cells interpret their biophysical surroundings, such as matrix stiffness or dynamic mechanical stimulation, through mechanotransduction. However, our understanding of the various aspects of mechanotransduction has been limited by the lack of proper analysis platforms capable of screening three-dimensional (3D) cellular behaviors in response to biophysical cues. Here, we developed a dynamic compression bioreactor to study the combinational effects of biomaterial composition and dynamic mechanical compression on cellular behavior in 3D hydrogels. The bioreactor contained multiple actuating posts that could apply cyclic compressive strains ranging from 0 to 42% to arrays of cell-encapsulated hydrogels. The bioreactor could be interconnected with other compressive bioreactors, which enabled the combinatorial screenings of 3D cellular behaviors simultaneously. As an application of the screening platform, cell spreading, and osteogenic differentiation of human mesenchymal stem cells (hMSCs) were characterized in 3D gelatin methacryloyl (GelMA) hydrogels. Increasing hydrogel concentration from 5 to 10% restricted the cell spreading, however, dynamic compressive strain increased cell spreading. Osteogenic differentiation of hMSCs was also affected by dynamic compressive strains. hMSCs in 5% GelMA hydrogel were more sensitive to strains, and the 42% strain group showed a significant increase in osteogenic differentiation compared to other groups. The interconnectable dynamic compression bioreactor provides an efficient way to study the interactions of cells and their physical microenvironments in three dimensions.</P> [FIG OMISSION]</BR>

Source Forensics of Black Carbon Aerosols from China

Chen, Bing,Andersson, August,Lee, Meehye,Kirillova, Elena N.,Xiao, Qianfen,Krusa&#x30a,, Martin,Shi, Meinan,Hu, Ke,Lu, Zifeng,Streets, David G.,Du, Ke,Gustafsson, Ö,rjan American Chemical Society 2013 Environmental science & technology Vol.47 No.16

<P>The limited understanding of black carbon (BC) aerosol emissions from incomplete combustion causes a poorly constrained anthropogenic climate warming that globally may be second only to CO<SUB>2</SUB> and regionally, such as over East Asia, the dominant driver of climate change. The relative contribution to atmospheric BC from fossil fuel versus biomass combustion is important to constrain as fossil BC is a stronger climate forcer. The source apportionment is the underpinning for targeted mitigation actions. However, technology-based “bottom-up” emission inventories are inconclusive, largely due to uncertain BC emission factors from small-scale/household combustion and open burning. We use “top-down” radiocarbon measurements of atmospheric BC from five sites including three city sites and two regional sites to determine that fossil fuel combustion produces 80 ± 6% of the BC emitted from China. This source-diagnostic radiocarbon signal in the ambient aerosol over East Asia establishes a much larger role for fossil fuel combustion than suggested by all 15 BC emission inventory models, including one with monthly resolution. Our results suggest that current climate modeling should refine both BC emission strength and consider the stronger radiative absorption associated with fossil-fuel-derived BC. To mitigate near-term climate effects and improve air quality in East Asia, activities such as residential coal combustion and city traffic should be targeted.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/esthag/2013/esthag.2013.47.issue-16/es401599r/production/images/medium/es-2013-01599r_0005.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/es401599r'>ACS Electronic Supporting Info</A></P>

Toward Wafer Scale Fabrication of Graphene Based Spin Valve Devices

Avsar, Ahmet,Yang, Tsung-Yeh,Bae, Sukang,Balakrishnan, Jayakumar,Volmer, Frank,Jaiswal, Manu,Yi, Zheng,Ali, Syed Rizwan,Gu&#x308,ntherodt, Gernot,Hong, Byung Hee,Beschoten, Bernd,Ö,zyilmaz, Barb American Chemical Society 2011 Nano letters Vol.11 No.6

<P>We demonstrate injection, transport, and detection of spins in spin valve arrays patterned in both copper based chemical vapor deposition (Cu-CVD) synthesized wafer scale single layer and bilayer graphene. We observe spin relaxation times comparable to those reported for exfoliated graphene samples demonstrating that chemical vapor deposition specific structural differences such as nanoripples do not limit spin transport in the present samples. Our observations make Cu-CVD graphene a promising material of choice for large scale spintronic applications.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2011/nalefd.2011.11.issue-6/nl200714q/production/images/medium/nl-2011-00714q_0001.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl200714q'>ACS Electronic Supporting Info</A></P>

Graphene-P(VDF-TrFE) Multilayer Film for Flexible Applications

Bae, Sang-Hoon,Kahya, Orhan,Sharma, Bhupendra K.,Kwon, Junggou,Cho, Hyoung J.,Ö,zyilmaz, Barbaros,Ahn, Jong-Hyun American Chemical Society 2013 ACS NANO Vol.7 No.4

<P>A flexible, transparent acoustic actuator and nanogenerator based on graphene/P(VDF-TrFE)/graphene multilayer film is demonstrated. P(VDF-TrFE) is used as an effective doping layer for graphene and contributes significantly to decreasing the sheet resistance of graphene to 188 ohm/sq. The potentiality of graphene/P(VDF-TrFE)/graphene multilayer film is realized in fabricating transparent, flexible acoustic devices and nanogenerators to represent its functionality. The acoustic actuator shows good performance and sensitivity over a broad range of frequency. The output voltage and the current density of the nanogenerator are estimated to be similar to 3 V and similar to 0.37 mu Acm(-2), respectively, upon the application of pressure. These values are comparable to those reported earlier for Zn0- and PIT-based nanogenerators. Finally, the possibility of rollable devices based on graphene/P(VDF-TrfE)/graphene structure is also demonstrated under a dynamic mechanical loading condition.</P>