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Magnetic and Optical Studies of Hydrogenated Cu-doped ZnO Film
Tong Li,Wen Xiao,Tun Seng Herng,Nina Bao,Jun Ding 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.62 No.12
Significantly enhanced ferromagnetism and strong green emission were observed for Cu-dopedZnO films undergoing a hydrogenation process. After H2 treatment at 500 C, the saturation magnetizationof 2 at% Cu-doped ZnO film (50 nm) is significantly increased from 1.65 emu cm−3(0.3 µB/Cu) to 11.7 emu cm−3 (1.5 µB/Cu). The areal magnetization of the hydrogenated CudopedZnO is dependent on the film thickness, thus suggesting that it is Cu dopants that playdominant roles rather than surface magnetism arising from OH attachment. Detailed XPS and Ramananalysis demonstrated that H2 treatment may introduce more Cu (Cu1+ -like) impurities andoxygen vacancies that coupled with each other, resulting in ferromagnetic ordering. Furthermore,strong green emission can be obtained in hydrogenated Cu-doped ZnO films. The green emissionis unlikely related with Cu dopants, but H2 treatment can generate a unique structure with porousmorphology and coexistence of complex defects that favors the green emission. The “green defects”are not simple O vacancies or H-incorporation and are stable after annealing at 700 C underO2 atmosphere. The high room temperature ferromagnetism and strong green light emission ofhydrogenated Cu-doped ZnO film pave a way to its novel applications in future spintronics andoptoelectronic devices.
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Zeng, Zebing,Sung, Young Mo,Bao, Nina,Tan, Davin,Lee, Richmond,Zafra, José,L.,Lee, Byung Sun,Ishida, Masatoshi,Ding, Jun,Ló,pez Navarrete, Juan T.,Li, Yuan,Zeng, Wangdong,Kim, Dongho,Huang American Chemical Society 2012 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.134 No.35
<P>Stable open-shell polycyclic aromatic hydrocarbons (PAHs) are of fundamental interest due to their unique electronic, optical, and magnetic properties and promising applications in materials sciences. Chichibabin’s hydrocarbon as a classical open-shell PAH has been investigated for a long time. However, most of the studies are complicated by their inherent high reactivity. In this work, two new stable benzannulated Chichibabin’s hydrocarbons <B>1-CS</B> and <B>2-OS</B> were prepared, and their electronic structure and geometry in the ground state were studied by various experiments (steady-state and transient absorption spectra, NMR, electron spin resonance (ESR), superconducting quantum interference device (SQUID), FT Raman, X-ray crystallographic etc.) and density function theory (DFT) calculations. <B>1-CS</B> and <B>2-OS</B> exhibited tunable ground states, with a closed-shell quinoidal structure for <B>1-CS</B> and an open-shell biradical form for <B>2-OS</B>. Their corresponding excited-state forms <B>1-OS</B> and <B>2-CS</B> were also chemically approached and showed different decay processes. The biradical <B>1-OS</B> displayed an unusually slow decay to the ground state (<B>1-CS</B>) due to a large energy barrier (95 ± 2.5 kJ/mol) arising from severe steric hindrance during the transition from an orthogonal biradical form to a butterfly-like quinoidal form. The quick transition from the quinoidal <B>2-CS</B> (excited state) to the orthogonal biradicaloid <B>2-OS</B> (ground state) happened during the attempted synthesis of <B>2-CS</B>. Compounds <B>1-CS</B> and <B>2-OS</B> can be oxidized into stable dications by FeCl<SUB>3</SUB> and/or concentrated H<SUB>2</SUB>SO<SUB>4</SUB>. The open-shell <B>2-OS</B> also exhibited a large two-photon absorption (TPA) cross section (760 GM at 1200 nm).</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2012/jacsat.2012.134.issue-35/ja3050579/production/images/medium/ja-2012-050579_0017.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja3050579'>ACS Electronic Supporting Info</A></P>
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Li, Yuan,Heng, Wee-Kuan,Lee, Byung Sun,Aratani, Naoki,Zafra, José,L.,Bao, Nina,Lee, Richmond,Sung, Young Mo,Sun, Zhe,Huang, Kuo-Wei,Webster, Richard D.,Ló,pez Navarrete, Juan T.,Kim, Dongh American Chemical Society 2012 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.134 No.36
<P>Polycyclic aromatic hydrocarbons with an open-shell singlet biradical ground state are of fundamental interest and have potential applications in materials science. However, the inherent high reactivity makes their synthesis and characterization very challenging. In this work, a convenient synthetic route was developed to synthesize two kinetically blocked heptazethrene (<B>HZ-TIPS</B>) and octazethrene (<B>OZ-TIPS</B>) compounds with good stability. Their ground-state electronic structures were systematically investigated by a combination of different experimental methods, including steady-state and transient absorption spectroscopy, variable temperature NMR, electron spin resonance (ESR), superconducting quantum interfering device (SQUID), FT Raman, and X-ray crystallographic analysis, assisted by unrestricted symmetry-broken density functional theory (DFT) calculations. All these demonstrated that the heptazethrene derivative <B>HZ-TIPS</B> has a closed-shell ground state while its octazethrene analogue <B>OZ-TIPS</B> with a smaller energy gap exists as an open-shell singlet biradical with a large measured biradical character (<I>y</I> = 0.56). Large two-photon absorption (TPA) cross sections (σ<SUP>(2)</SUP>) were determined for <B>HZ-TIPS</B> (σ<SUP>(2)</SUP><SUB>max</SUB> = 920 GM at 1250 nm) and <B>OZ-TIPS</B> (σ<SUP>(2)</SUP><SUB>max</SUB> = 1200 GM at 1250 nm). In addition, <B>HZ-TIPS</B> and <B>OZ-TIPS</B> show a closely stacked 1D polymer chain in single crystals.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2012/jacsat.2012.134.issue-36/ja304618v/production/images/medium/ja-2012-04618v_0015.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja304618v'>ACS Electronic Supporting Info</A></P>
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Zeng, Zebing,Ishida, Masatoshi,Zafra, José,L.,Zhu, Xiaojian,Sung, Young Mo,Bao, Nina,Webster, Richard D.,Lee, Byung Sun,Li, Run-Wei,Zeng, Wangdong,Li, Yuan,Chi, Chunyan,Navarrete, Juan T. Lo American Chemical Society 2013 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.135 No.16
<P><I>p</I>-Quinodimethane (<I>p</I>-QDM) is a fundamental building block for the design of π-conjugated systems with low band gap and open-shell biradical character. However, synthesis of extended <I>p</I>-QDMs has usually suffered from their intrinsic high reactivity and poor solubility. In this work, benzannulation together with terminal cyano-substitution was demonstrated to be an efficient approach for the synthesis of a series of soluble and stable tetracyano-oligo(<I>N</I>-annulated perylene)quinodimethanes <B><I>n</I>Per-CN</B> (<I>n</I> = 1–6), with the longest molecule having 12 <I>para</I>-linked benzenoid rings! The geometry and electronic structures of these oligomers were investigated by steady-state and transient absorption spectroscopy, nuclear magnetic resonance, electron spin resonance, superconducting quantum interference device, and FT Raman spectroscopy assisted by density functional theory calculations. They showed tunable ground states, varying from a closed-shell quinoidal structure for monomer, to a singlet biradical for dimer, trimer, and tetramer, and to a triplet biradical for pentamer and hexamer. Large two-photon absorption cross-section values were observed in the near-infrared range, which also exhibited a clear chain-length dependence.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2013/jacsat.2013.135.issue-16/ja402467y/production/images/medium/ja-2013-02467y_0010.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja402467y'>ACS Electronic Supporting Info</A></P>
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