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Choi, Hyun Joo,Nam, Seung Jin,Hofstetter, Jasmin,Buonassisi, Tonio,Bae, Dong Hyun SAGE Publications 2015 Journal of composite materials Vol.49 No.22
<P>The present study investigates the effect of multi-walled carbon nanotubes (MWCNTs) on atomic diffusion processes in the metal matrix, by comparing growth kinetics of interfacial phases in Al–Cu and Al/MWCNT–Cu diffusion couples. Multiple intermetallic layers such as Al<SUB>2</SUB>Cu, AlCu, Al<SUB>3</SUB>Cu<SUB>4</SUB>, Al<SUB>2</SUB>Cu<SUB>3</SUB>, and Al<SUB>4</SUB>Cu<SUB>9</SUB> are formed at the interface between Al and Cu during heat treatment of an Al/Cu diffusion couple at 530. For the diffusion couple of ultrafine-grained Al and cast Cu, the growth rate of intermetallic layers is comparable with theoretical expectations based on Fick’s second law. On the other hand, MWCNTs significantly restrict the diffusion of Al atoms in the composite because the atoms tend to detour around the long tube for diffusion, particularly when MWCNTs are oriented perpendicular to the atomic diffusion path. This accelerates the growth of voids at the contact interface of the diffusion couple during heat treatment.</P>
An insight into dislocation density reduction in multicrystalline silicon
Woo, Soobin,Bertoni, Mariana,Choi, Kwangmin,Nam, Seungjin,Castellanos, Sergio,Powell, Douglas Michael,Buonassisi, Tonio,Choi, Hyunjoo Elsevier 2016 Solar energy materials and solar cells Vol.155 No.-
<P><B>Abstract</B></P> <P>Dislocations can severely limit the conversion efficiency of multicrystalline silicon (mc-Si) solar cells by reducing minority carrier lifetime. As cell performance becomes increasingly bulk lifetime–limited, the importance of dislocation engineering increases too. This study reviews the literature on mc-Si solar cells; it focuses on the (i) impact of dislocations on cell performance, (ii) dislocation diagnostic skills, and (iii) dislocation engineering techniques during and after crystal growth. The driving forces in dislocation density reduction are further discussed by examining the dependence of dislocation motion on temperature, intrinsic and applied stresses, and on other defects, such as vacancies and impurities.</P>
Jo, Won Jun,Kang, Hyun Joon,Kong, Ki-Jeong,Lee, Yun Seog,Park, Hunmin,Lee, Younghye,Buonassisi, Tonio,Gleason, Karen K.,Lee, Jae Sung National Academy of Sciences 2015 PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF Vol.112 No.45
<P><B>Significance</B></P><P>Hydrogen has been recognized as one of the most promising energy carriers for the future, because it can generate enormous energy by clean combustion chemistry without any greenhouse gas emissions. Water splitting under visible light irradiation is an ideal route to cost-effective, large-scale, and sustainable hydrogen production, but it is challenging, because it requires a rare photocatalyst that carries a combination of suitable band gap energy, appropriate band positions, and photochemical stability. To create this rare photocatalyst, we engineered the band edges of BiVO<SUB>4</SUB> by simultaneously substituting In<SUP>3+</SUP> for Bi<SUP>3+</SUP> and Mo<SUP>6+</SUP> for V<SUP>5+</SUP> in the host lattice of monoclinic BiVO<SUB>4</SUB>, which induced partial phase transformation from pure monoclinic BiVO<SUB>4</SUB> to a mixture of monoclinic BiVO<SUB>4</SUB> and tetragonal BiVO<SUB>4</SUB>.</P><P>Through phase transition-induced band edge engineering by dual doping with In and Mo, a new greenish BiVO<SUB>4</SUB> (Bi<SUB>1-X</SUB>In<SUB>X</SUB>V<SUB>1-X</SUB>Mo<SUB>X</SUB>O<SUB>4</SUB>) is developed that has a larger band gap energy than the usual yellow scheelite monoclinic BiVO<SUB>4</SUB> as well as a higher (more negative) conduction band than H<SUP>+</SUP>/H<SUB>2</SUB> potential [0 V<SUB>RHE</SUB> (reversible hydrogen electrode) at pH 7]. Hence, it can extract H<SUB>2</SUB> from pure water by visible light-driven overall water splitting without using any sacrificial reagents. The density functional theory calculation indicates that In<SUP>3+</SUP>/Mo<SUP>6+</SUP> dual doping triggers partial phase transformation from pure monoclinic BiVO<SUB>4</SUB> to a mixture of monoclinic BiVO<SUB>4</SUB> and tetragonal BiVO<SUB>4</SUB>, which sequentially leads to unit cell volume growth, compressive lattice strain increase, conduction band edge uplift, and band gap widening.</P>