The Role of Korean Diaspora in Central Asia as an Incentive for South Korea`s Policy in the Region: a Framework for Analysis

( George Kallander ),( Pierre Chabal ) 아시아.유럽미래학회 2004 유라시아연구 Vol.1 No.2

Realistic Metal–Graphene Contact Structures

Gong, Cheng,McDonnell, Stephen,Qin, Xiaoye,Azcatl, Angelica,Dong, Hong,Chabal, Yves J.,Cho, Kyeongjae,Wallace, Robert M. American Chemical Society 2014 ACS NANO Vol.8 No.1

<P>The contact resistance of metal–graphene junctions has been actively explored and exhibited inconsistencies in reported values. The interpretation of these electrical data has been based exclusively on a <I>side</I>-contact model, that is, metal slabs sitting on a pristine graphene sheet. Using <I>in</I> <I>situ</I> X-ray photoelectron spectroscopy to study the wetting of metals on as-synthesized graphene on copper foil, we show that side-contact is sometimes a misleading picture. For instance, metals like Pd and Ti readily react with graphitic carbons, resulting in Pd- and Ti-carbides. Carbide formation is associated with C–C bond breaking in graphene, leading to an <I>end</I>-contact geometry between the metals and the periphery of the remaining graphene patches. This work validates the <I>spontaneous</I> formation of the metal–graphene end-contact during the metal deposition process as a result of the metal–graphene reaction instead of a simple carbon diffusion process.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2014/ancac3.2014.8.issue-1/nn405249n/production/images/medium/nn-2013-05249n_0005.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn405249n'>ACS Electronic Supporting Info</A></P>

Recovery of Nonwetting Characteristics by Surface Modification of Gallium-Based Liquid Metal Droplets Using Hydrochloric Acid Vapor

Kim, Daeyoung,Thissen, Peter,Viner, Gloria,Lee, Dong-Weon,Choi, Wonjae,Chabal, Yves J.,Lee, Jeong-Bong (J.B.) American Chemical Society 2013 ACS APPLIED MATERIALS & INTERFACES Vol.5 No.1

<P>The applicability of gallium-based liquid metal alloy has been limited by the oxidation problem. In this paper, we report a simple method to remove the oxide layer on the surface of such alloy to recover its nonwetting characteristics, using hydrochloric acid (HCl) vapor. Through the HCl vapor treatment, we successfully restored the nonwetting characteristics of the alloy and suppressed its viscoelasticity. We analyzed the change of surface chemistry before and after the HCl vapor treatment using X-ray photoelectron spectroscopy (XPS) and low-energy ion-scattering spectroscopy (LEIS). Results showed that the oxidized surface of the commercial gallium-based alloy Galinstan (Ga<SUB>2</SUB>O<SUB>3</SUB> and Ga<SUB>2</SUB>O) was replaced with InCl<SUB>3</SUB> and GaCl<SUB>3</SUB> after the treatment. Surface tension and static contact angle on a Teflon-coated glass of the HCl-vapor-treated Galinstan were measured to be 523.8 mN/m and 152.5°. A droplet bouncing test was successfully carried out to demonstrate the nonwetting characteristics of the HCl-vapor-treated Galinstan. Finally, the stability of the transformed surface of the HCl-vapor-treated Galinstan was investigated by measuring the contact angle and LEIS spectra after reoxidation in an ambient environment.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2013/aamick.2013.5.issue-1/am302357t/production/images/medium/am-2012-02357t_0010.gif'></P>

Rational design of common transition metal-nitrogen-carbon catalysts for oxygen reduction reaction in fuel cells

Zheng, Yongping,Yang, Dae-Soo,Kweun, Joshua M.,Li, Chenzhe,Tan, Kui,Kong, Fantai,Liang, Chaoping,Chabal, Yves J.,Kim, Yoon Young,Cho, Maenghyo,Yu, Jong-Sung,Cho, Kyeongjae Elsevier 2016 Nano energy Vol.30 No.-

<P><B>Abstract</B></P> <P>Bio-inspired non-precious-metal catalysts based on iron and cobalt porphyrins are promising alternatives to replace costly platinum-based catalysts for oxygen reduction reaction (ORR) in fuel cells. However, the exact nature of the active sites is still not clearly understood, and further optimization design is needed for practical applications. Here, we report a rational catalyst design process by combining density functional theory (DFT) calculations and experimental validations. Two sets of square-planar (MN<SUB>x</SUB>C<SUB>4−x</SUB>) and square-pyramid (MN<SUB>x</SUB>C<SUB>5−x</SUB>) active centers (M=Mn, Fe, Co, Ni) incorporated in graphene were examined using DFT. Fe-N<SUB>5</SUB> and Co-N<SUB>4</SUB> sites were identified theoretically to have the best performance in fuel cells, while Ni-N<SUB>x</SUB>C<SUB>4−x</SUB> sites catalyze the most H<SUB>2</SUB>O<SUB>2</SUB> byproduct. Graphene samples with well-dispersed incorporations of metals were synthesized, and the following electrochemical measurements show an excellent agreement with the theoretical predictions, indicating that a successful design framework and systematic understanding toward the catalytic nature of these materials are established.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Graphene based catalysts design for ORR is demonstrated by combining experiments and modellings. </LI> <LI> Iron porphyrin like active site is unraveled to be five nitrogen coordinated as FeN<SUB>5</SUB>. </LI> <LI> Cobalt porphyrin like active site is shown to be four nitrogen coordinated as CoN<SUB>4</SUB>. </LI> <LI> Nickel porphyrin like catalyst is potentially used for catalytic synthesis of H<SUB>2</SUB>O<SUB>2</SUB>. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Silicon Interfacial Passivation Layer Chemistry for High-<i>k</i>/InP Interfaces

Dong, Hong,Cabrera, Wilfredo,Qin, Xiaoye,Brennan, Barry,Zhernokletov, Dmitry,Hinkle, Christopher L.,Kim, Jiyoung,Chabal, Yves J.,Wallace, Robert M. American Chemical Society 2014 ACS APPLIED MATERIALS & INTERFACES Vol.6 No.10

<P>The interfacial chemistry of thin (1 nm) silicon (Si) interfacial passivation layers (IPLs) deposited on acid-etched and native oxide InP(100) samples prior to atomic layer deposition (ALD) is investigated. The phosphorus oxides are scavenged completely from the acid-etched samples but not completely from the native oxide samples. Aluminum silicate and hafnium silicate are possibly generated upon ALD and following annealing. The thermal stability of a high-<I>k</I>/Si/InP (acid-etched) stack are also studied by in situ annealing to 400 and 500 °C under ultrahigh vacuum, and the aluminum oxide/Si/InP stack is the most thermally stable. An indium out-diffusion to the sample surface is observed through the Si IPL and the high-<I>k</I> dielectric, which may form volatile species and evaporate from the sample surface.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2014/aamick.2014.6.issue-10/am500752u/production/images/medium/am-2014-00752u_0010.gif'></P>

Atomic Layer Deposition of Dielectrics on Graphene Using Reversibly Physisorbed Ozone

Jandhyala, Srikar,Mordi, Greg,Lee, Bongki,Lee, Geunsik,Floresca, Carlo,Cha, Pil-Ryung,Ahn, Jinho,Wallace, Robert M.,Chabal, Yves J.,Kim, Moon J.,Colombo, Luigi,Cho, Kyeongjae,Kim, Jiyoung American Chemical Society 2012 ACS NANO Vol.6 No.3

<P>Integration of graphene field-effect transistors (GFETs) requires the ability to grow or deposit high-quality, ultrathin dielectric insulators on graphene to modulate the channel potential. Here, we study a novel and facile approach based on atomic layer deposition through ozone functionalization to deposit high-κ dielectrics (such as Al<SUB>2</SUB>O<SUB>3</SUB>) without breaking vacuum. The underlying mechanisms of functionalization have been studied theoretically using <I>ab initio</I> calculations and experimentally using <I>in situ</I> monitoring of transport properties. It is found that ozone molecules are physisorbed on the surface of graphene, which act as nucleation sites for dielectric deposition. The physisorbed ozone molecules eventually react with the metal precursor, trimethylaluminum to form Al<SUB>2</SUB>O<SUB>3</SUB>. Additionally, we successfully demonstrate the performance of dual-gated GFETs with Al<SUB>2</SUB>O<SUB>3</SUB> of sub-5 nm physical thickness as a gate dielectric. Back-gated GFETs with mobilities of ∼19 000 cm<SUP>2</SUP>/(V·s) are also achieved <I>after</I> Al<SUB>2</SUB>O<SUB>3</SUB> deposition. These results indicate that ozone functionalization is a promising pathway to achieve scaled gate dielectrics on graphene without leaving a residual nucleation layer.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2012/ancac3.2012.6.issue-3/nn300167t/production/images/medium/nn-2012-00167t_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn300167t'>ACS Electronic Supporting Info</A></P>

Critical Role of Mullite-type Oxides’ Surface Chemistry on Catalytic NO Oxidation Performance

Thampy, Sampreetha,Ashburn, Nickolas,Dillon, Sean,Liu, Chengfa,Xiong, Ka,Mattson, Eric C.,Zheng, Yongping,Chabal, Yves J.,Cho, Kyeongjae,Hsu, Julia W. P. American Chemical Society 2019 The Journal of Physical Chemistry Part C Vol.123 No.9

<P>By combining low energy ion scattering spectroscopy and density functional theory calculation, we study the surface composition and surface formation energy of AMn<SUB>2</SUB>O<SUB>5</SUB> (A = Sm, Bi) mullite-type oxides synthesized by different methods and their effects on NO catalytic performance. It is well-known that hydrothermal (HT) synthesis at low temperatures produces materials with higher specific surface areas (SSAs) compared with those synthesized by coprecipitation (CP) and high-temperature calcination; however, it is less clear how synthesis methods affect surface chemistry. We find that the NO oxidation performance of SmMn<SUB>2</SUB>O<SUB>5</SUB>-HT does not match the SSA increase when compared to the lower SSA SmMn<SUB>2</SUB>O<SUB>5</SUB>-CP. Combined experimental and theoretical investigation reveals that SmMn<SUB>2</SUB>O<SUB>5</SUB>-HT includes a higher fraction of inactive Sm-terminated surfaces, which explains its lower than expected activity. However, the surface chemistry change depends strongly on the A-site element. The exposed surfaces of BiMn<SUB>2</SUB>O<SUB>5</SUB>-CP are predominantly terminated by Bi and exhibit a very low activity, while BiMn<SUB>2</SUB>O<SUB>5</SUB>-HT contains active Mn-terminated surfaces. This study shows that catalytic performance is determined predominantly by surface chemistry, which depends critically on the A-site element and synthesis method and less by physical surface area.</P> [FIG OMISSION]</BR>

Stable and Active Oxidation Catalysis by Cooperative Lattice Oxygen Redox on SmMn₂O₅ Mullite Surface

Zheng, Yongping,Thampy, Sampreetha,Ashburn, Nickolas,Dillon, Sean,Wang, Luhua,Jangjou, Yasser,Tan, Kui,Kong, Fantai,Nie, Yifan,Kim, Moon J.,Epling, William S.,Chabal, Yves J.,Hsu, Julia W. P.,Cho, Kye American Chemical Society 2019 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.141 No.27

<P>The correlation between lattice oxygen (O) binding energy and O oxidation activity imposes a fundamental limit in developing oxide catalysts, simultaneously meeting the stringent thermal stability and catalytic activity standards for complete oxidation reactions under harsh conditions. Typically, strong O binding indicates a stable surface structure, but low O oxidation activity, and <I>vice</I><I>versa</I>. Using nitric oxide (NO) catalytic oxidation as a model reaction, we demonstrate that this conflicting correlation can be avoided by cooperative lattice oxygen redox on SmMn<SUB>2</SUB>O<SUB>5</SUB> mullite oxides, leading to stable and active oxide surface structures. The strongly bound neighboring lattice oxygen pair cooperates in NO oxidation to form bridging nitrate (NO<SUB>3</SUB><SUP>-</SUP>) intermediates, which can facilely transform into monodentate NO<SUB>3</SUB><SUP>-</SUP> by a concerted rotation with simultaneous O<SUB>2</SUB> adsorption onto the resulting oxygen vacancy. Subsequently, monodentate NO<SUB>3</SUB><SUP>-</SUP> species decompose to NO<SUB>2</SUB> to restore one of the lattice oxygen atoms that act as a reversible redox center, and the vacancy can easily activate O<SUB>2</SUB> to replenish the consumed one. This discovery not only provides insights into the cooperative reaction mechanism but also aids the design of oxidation catalysts with the strong O binding region, offering strong activation of O<SUB>2</SUB>, high O activity, and high thermal stability in harsh conditions.</P> [FIG OMISSION]</BR>