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Controlling work function of reduced graphite oxide with Au-ion concentration
Benayad, Anass,Shin, Hyeon-Jin,Park, Hyeon Ki,Yoon, Seon-Mi,Kim, Ki Kang,Jin, Mei Hua,Jeong, Hae-Kyung,Lee, Jae Cheol,Choi, Jae-Young,Lee, Young Hee Elsevier 2009 Chemical physics letters Vol.475 No.1
<P><B>Graphical abstract</B></P><P>The spontaneous electrons transfer from the specific bands in RGOs to Au-ions and their reduction induced a downshift of the Fermi level and contributed to tailoring the work function of the RGOs films. The sheet resistance of those films was decreased by the increase of the hole concentration at the pristine RGOs’ surface as a result of the p-type doping.</P><ce:figure></ce:figure> <P><B>Abstract</B></P><P>We have investigated the effect of Au-ion treatment on the work function and the electronic structure change of reduced graphite oxides (RGOs). Au-ions were reduced spontaneously by extracting electrons (i) from sp<SUP>2</SUP> carbons of RGO at low concentration and (ii) from some oxygen-related functional groups at high concentration. This implies that the work function was modulated by the amount of charges transferred to Au-ions. The sheet resistance of the RGO film was improved with Au-ion treatment. This was explained in terms of electron donation to Au-ions that eventually led to a p-type doping in RGO film.</P>
Electronic structure of (Ge2Sb2Te5)1−x(In3SbTe2)x investigated by x-ray photoelectron spectroscopy
Benayad, Anass,Kang, YounSeon,Shin, Hyun-Joon,Kim, Kihong,Suh, Dong-Seok,Kim, KiJoon,Kim, CheolKyu,Lee, Tae-Yon,Noh, Jin-Seo,Lee, JaeCheol,Khang, YoonHo American Institute of Physics 2009 JOURNAL OF APPLIED PHYSICS - Vol.106 No.4
Bulliard, Xavier,Benayad, Anass,Lee, Kwang-Hee,Choi, Yun-Hyuk,Lee, Jae Cheol,Park, Jong-Jin,Kim, Jong-Min IOP Pub 2011 Nanotechnology Vol.22 No.47
<P>We report on a method for surface nano-texturing on a plastic substrate. Nano-objects with a silica nanoparticle core and a textured cobalt oxide crown are created with selectable density on the plastic substrate. The resulting dual morphology is easily tuned over large areas, either by changing the parameters directing nanoparticle deposition through electrostatic self-arrangement for nano-object density control, or the parameter directing cobalt oxide deposition for shape control. The entire process takes place at room temperature, with no chemicals harmful to the plastic substrate. The ready modulation of the dual morphology is used to control the wettability properties of the plastic film, which is covered by nano-objects. </P>
New dry carbon nanotube coating of over-lithiated layered oxide cathode for lithium ion batteries
Mun, Junyoung,Park, Jin-Hwan,Choi, Wonchang,Benayad, Anass,Park, Jun-Ho,Lee, Jae-Myung,Doo, Seok-Gwang,Oh, Seung M. The Royal Society of Chemistry 2014 Journal of Materials Chemistry A Vol.2 No.46
<▼1><P>For high rate capability and energy density of lithium ion batteries, over-lithiated layered cathodes coated by multiwall carbon nanotube were prepared by a novel dry method without decay in the structure.</P></▼1><▼2><P>Carbon serves as one of the best coating materials for the cathode in lithium ion batteries. This is because it can solve two main problems, which are surface deterioration and poor electrical conductivity. However, the conventional carbon coating procedures and, chemical carbonization processes, are especially difficult to implement for the oxide cathode, which could thereby deteriorate the oxide structure. We prepared a new dry 100 nm-thick homogeneous multi-walled carbon nanotube (MWCNT) coating on the high-capacity oxide cathode material, Li1.17Ni0.17Co0.1Mn0.56O2, by applying shear stress without breaking down the crystal structure or morphology of the cathode. The electronic conductivity of the carbon composite with the coated sample is 170 mS cm<SUP>−1</SUP>, which is over 40 times as much as the conductivity of the pristine cathode containing the same amount of carbon. In addition, at a high current condition of 2450 mA g<SUP>−1</SUP>, a specific capacity of 103 mA h g<SUP>−1</SUP> is observed even with 3 percent of the carbon (in weight) constituting the coated MWCNT. The unconventionally improved performances are explained by the suppression of the electronic resistance and surface charge transfer resistance by electrochemical analyses.</P></▼2>
Efficient Reduction of Graphite Oxide by Sodium Borohydride and Its Effect on Electrical Conductance
Shin, Hyeon-Jin,Kim, Ki Kang,Benayad, Anass,Yoon, Seon-Mi,Park, Hyeon Ki,Jung, In-Sun,Jin, Mei Hua,Jeong, Hae-Kyung,Kim, Jong Min,Choi, Jae-Young,Lee, Young Hee WILEY-VCH Verlag 2009 Advanced functional materials Vol.19 No.12
<P>The conductivity of graphite oxide films is modulated using reducing agents. It is found that the sheet resistance of graphite oxide film reduced using sodium borohydride (NaBH<SUB>4</SUB>) is much lower than that of films reduced using hydrazine (N<SUB>2</SUB>H<SUB>4</SUB>). This is attributed to the formation of C&n.bond;N groups in the N<SUB>2</SUB>H<SUB>4</SUB> case, which may act as donors compensating the hole carriers in reduced graphite oxide. In the case of NaBH<SUB>4</SUB> reduction, the interlayer distance is first slightly expanded by the formation of intermediate boron oxide complexes and then contracted by the gradual removal of carbonyl and hydroxyl groups along with the boron oxide complexes. The fabricated conducting film comprising a NaBH<SUB>4</SUB>-reduced graphite oxide reveals a sheet resistance comparable to that of dispersed graphene.</P> <B>Graphic Abstract</B> <P>Reduced graphite oxide films obtained using NaBH<SUB>4</SUB> exhibit much lower sheet resistance than films obtained using N<SUB>2</SUB>H<SUB>4</SUB> because the latter results in the formation of C–N groups, which may act as donors compensating the hole carriers in the film and increasing resistivity. A transparent conducting film prepared using optimized NaBH<SUB>4</SUB> reduction reveals a sheet resistance comparable to that observed in dispersed graphene. <img src='wiley_img/1616301X-2009-19-12-ADFM200900167-content.gif' alt='wiley_img/1616301X-2009-19-12-ADFM200900167-content'> </P>
Ultrafast photocarrier dynamics in nanocrystalline ZnOxNy thin films.
Shin, Taeho,Lee, Eunha,Sul, Soohwan,Lee, Hyungik,Ko, Dong-Su,Benayad, Anass,Kim, Hyun-Suk,Park, Gyeong-Su Optical Society of America 2014 Optics letters Vol.39 No.17
<P>We examined the ultrafast dynamics of photocarriers in nanocrystalline ZnOxNy thin films as a function of compositional variation using femtosecond differential transmittance spectroscopy. The relaxation dynamics of photogenerated carriers and electronic structures are strongly dependent on nitrogen concentration. Photocarriers of ZnOxNy films relax on two different time scales. Ultrafast relaxation over several picoseconds is observed for all chemical compositions. However, ZnO and oxygen-rich phases show slow relaxation (longer than several nanoseconds), whereas photocarriers of films with high nitrogen concentrations relax completely on subnanosecond time scales. These relaxation features may provide a persistent photocurrent-free and prompt photoresponsivity for ZnOxNy with high nitrogen concentrations, as opposed to ZnO for display applications.</P>