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Electrical Properties of Surface-Passivated GaAs Nanowires
신재철,Rochelle S. Lee,김태겸,이상원,조규연,최종현,김미영 한국진공학회 2018 Applied Science and Convergence Technology Vol.27 No.6
The electrical properties of surface-passivated GaAs nanowires (NWs) were investigated and compared with those of unpassivated NWs. Surface passivation was carried out by chemically etching the native oxide of the GaAs NWs with ammonium polysulfide, (NH4)2Sx, while the native oxide of the unpassivated NWs was etched in hydrochloric acid solution. The GaAs NWs were grown by metal-organic chemical vapor deposition via a Au-catalyzed vapor-liquidsolid growth method. Sulfur-passivated single-GaAs NWs showed 3-fold increase in mobility, indicating that sulfur passivation reduces the presence of surface states, contact resistance, and the Schottky barrier at NW-metal contacts.
Pawar, Sachin A.,Kim, Donghwan,Lee, Rochelle,Kang, Sang-Woo,Patil, Dipali S.,Kim, Tae Wan,Shin, Jae Cheol Elsevier 2019 CHEMICAL ENGINEERING JOURNAL -LAUSANNE- Vol.371 No.-
<P><B>Abstract</B></P> <P>Te-based transitional metal dichalcogenides (TMDs) as supercapacitors are gaining substantial attention with a few reports. The integration of 1T′-Mo<SUB>6</SUB>Te<SUB>6</SUB> nanoplates (NPs) into few-atomic-layered two dimensional (2D) 2H-MoTe<SUB>2</SUB> thin film has not been realized in supercapacitive studies. Herein, we demonstrate the growth of 1T′-Mo<SUB>6</SUB>Te<SUB>6</SUB> NP/2H-MoTe<SUB>2</SUB> thin film polymorphic structure through metal organic chemical vapor deposition (MOCVD) on Si/SiO<SUB>2</SUB> and thereby, the successful transfer of these polymorphic structure on a flexible nickel (Ni) foam current collector by simple chemical etching protocol for high performance supercapacitors. A layer by layer study of the Mo<SUB>6</SUB>Te<SUB>6</SUB>/MoTe<SUB>2</SUB> polymorphic structure is carried out by varying the number of transfer layers on the Ni foam. The resultant supercapacitors demonstrate a three-fold enhancement in areal capacitance (1542 mFcm<SUP>−2</SUP> at 10 mVs<SUP>−1</SUP>) compared to a single layer transferred electrode, together with remarkable electrochemical stability (96%) and high energy density (140.36 mWcm<SUP>−2</SUP> at 4 mA). These supercapacitors outperform the TMD-based (Te-based) supercapacitors presented in the past, demonstrating the high potential for their application in energy conversion devices.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Integration of 1T′-Mo<SUB>6</SUB>Te<SUB>6</SUB> NP/2H-MoTe<SUB>2</SUB> thin film polymorphic structure. </LI> <LI> Transfer of polymorphic structure on a flexible nickel (Ni) foam current collector. </LI> <LI> A three-fold enhancement in areal capacitance (1542 mFcm<SUP>−2</SUP> at 10 mVs<SUP>−1</SUP>). </LI> <LI> The specific capacitances of 3816 Fg<SUP>−1</SUP> at 10 mVs<SUP>−1</SUP> for optimized electrode. </LI> <LI> An excellent cycling stability with a capacitance retention of 96% is observed. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>The growth of 1T′-Mo<SUB>6</SUB>Te<SUB>6</SUB> NP/2H MoTe<SUB>2</SUB> thin film polymorphic structure through MOCVD on Si/SiO<SUB>2</SUB> and thereby, the successful transfer of these polymorphic structure on flexible nickel (Ni) foam current collector by simple chemical etching protocol for high performance supercapacitor is demonstrated.</P> <P>[DISPLAY OMISSION]</P>
Quantum Dot Sensitized Solar Cells Based on TiO2/AgInS2
Sachin A. Pawar,정재필,Dipali S. Patil,Vivek M. More,Rochelle S. Lee,신재철,최원준 한국물리학회 2018 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.72 No.10
Quantum dot heterojunctions with type-II band alignment can efficiently separate photogenerated electron-hole pairs and, hence, are useful for solar cell studies. In this study, a quantum dot sensitized solar cell (QDSSC) made of TiO2/AgInS2 is achieved to boost the photoconversion efficiency for the TiO2-based system by varying the AgInS2 layer’s thickness. The TiO2 nanorods array film is prepared by using a simple hydrothermal technique. The formation of a AgInS2 QD-sensitized TiO2-nanorod photoelectrode is carried out by successive ionic layer adsorption and reaction (SILAR) technique. The effect of the QD layer on the performance of the solar cell is studied by varying the SILAR cycles of the QD coating. The synthesized electrode materials are characterized by using X-ray diffraction, X-ray photoelectron spectroscopy, field emission scanning electron microscopy, high resolution transmission electron microscopy and solar cell performances. The results indicate that the nanocrystals have effectively covered the outer surfaces of the TiO2 nanorods. The interfacial structure of quantum dots (QDs)/TiO2 is also investigated, and the growth interface is verified. A careful comparison between TiO2/AgInS2 sensitized cells reveals that the trasfer of electrons and hole proceeds efficiently, the recombination is suppressed for the optimum thickness of the QD layer and light from the entire visible spectrum is utilised. Under AM 1.5G illumination, a high photocurrent of 1.36 mAcm−2 with an improved power conversion efficiency of 0.48% is obtained. The solar cell properties of our photoanodes suggest that the TiO2 nanorod array films co-sensitized by AgInS2 nanoclusters have potential applications in solar cells.