Synthesis and characterization of large-area and continuous MoS2atomic layers by RF magnetron sputtering

Hussain, Sajjad,Shehzad, Muhammad Arslan,Vikraman, Dhanasekaran,Khan, Muhammad Farooq,Singh, Jai,Choi, Dong-Chul,Seo, Yongho,Eom, Jonghwa,Lee, Wan-Gyu,Jung, Jongwan The Royal Society of Chemistry 2016 Nanoscale Vol.8 No.7

<P>In this article, we report layer-controlled, continuous and large-area molydenum sulfide (MoS2) growth onto a SiO2/Si substrate by RF sputtering combined with sulfurization. A two-step process was employed to synthesize MoS2 films. In the first step, an atomically thin MoO3 film was deposited by RF magnetron sputtering at 300 degrees C. Subsequently, the as-sputtered MoO3 film was further subjected to post-annealing and sulfurization processes at 650 degrees C for 1 hour. It was observed that the number of layers of MoS2 can be controlled by adjusting the sputtering time. The fabricated MoS2 transistors exhibited high mobility values of similar to 21 cm(2) V-1 s(-1) (bilayer) and similar to 25 cm(2) V-1 s(-1) (trilayer), on/off ratios in the range of similar to 10(7) (bilayer) and 10(4)-10(5) (trilayer), respectively. We believe that our proposed paradigm can start a new method for the growth of MoS2 in future electronics and optoelectronics applications.</P>

Controlled synthesis and optical properties of polycrystalline molybdenum disulfide atomic layers grown by chemical vapor deposition

Hussain, Sajjad,Shehzad, Muhmmad Arslan,Vikraman, Dhanasekaran,Iqbal, Muhmmad Zahir,Singh, Jai,Khan, Muhmmad Farooq,Eom, Jonghwa,Seo, Yongho,Jung, Jongwan Elsevier 2015 JOURNAL OF ALLOYS AND COMPOUNDS Vol.653 No.-

<P><B>Abstract</B></P> <P>We report a scalable growth of mono to few-layer molybdenum disulfide (MoS<SUB>2</SUB>) atomic layers on different substrates by chemical vapor deposition (CVD). The effects of the source material (sulfur and MoO<SUB>3</SUB> powder) and the growth temperature were systematically optimized for the growth of both highly crystalline and large area MoS<SUB>2</SUB>. The deposited film thickness could be precisely controlled by varying the growth temperatures, and this was confirmed by Raman and AFM results. The monolayer, bilayer, and multilayer MoS<SUB>2</SUB> could be obtained at 650 °C, 700 °C, and 750–800 °C, respectively. The mobility value of ∼0.89 cm<SUP>2</SUP>/V s and current on/off ratio in the order of ∼10<SUP>4</SUP> was estimated for monolayer MoS<SUB>2</SUB>. The mobility value increased to ∼7.6 cm<SUP>2</SUP>/V s for the bilayer MoS<SUB>2</SUB>. Our results pave the way for the controlled synthesis of high-quality transition metal dichalcogenide materials, which are an attractive option for applications in electronic and optoelectronic devices.</P> <P><B>Highlights</B></P> <P> <UL> <LI> MoS<SUB>2</SUB> films were characterized by AFM, Raman, XRD, SEM, UV–visible, PL and XPS. </LI> <LI> Monolayer MoS<SUB>2</SUB> FET electron mobility is ∼0.89 cm<SUP>2</SUP>/V s with the on/off ratio of 10<SUP>4</SUP>. </LI> <LI> MoS<SUB>2</SUB> bilayer back-gate transistors showed quite a high mobility of ∼7.6 cm<SUP>2</SUP>/V s. </LI> <LI> Raman shift variations are deeply investigated by variation of laser power. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Physical and electrical properties of graphene grown under different hydrogen flow in low pressure chemical vapor deposition

Hussain, Sajjad,Iqbal, Muhmmad Waqas,Park, Jaehyun,Ahmad, Muneer,Singh, Jai,Eom, Jonghwa,Jung, Jongwan Springer 2014 NANOSCALE RESEARCH LETTERS Vol.9 No.1

<P>Hydrogen flow during low pressure chemical vapor deposition had significant effect not only on the physical properties but also on the electrical properties of graphene. Nucleation and grain growth of graphene increased at higher hydrogen flows. And, more oxygen-related functional groups like amorphous and oxidized carbon that probably contributed to defects or contamination of graphene remained on the graphene surface at low H<SUB>2</SUB> flow conditions. It is believed that at low hydrogen flow, those remained oxygen or other oxidizing impurities make the graphene films p-doped and result in decreasing the carrier mobility.</P>

CuS/WS₂ and CuS/MoS₂ heterostructures for high performance counter electrodes in dye-sensitized solar cells

Hussain, Sajjad,Patil, Supriya A.,Memon, Anam Ali,Vikraman, Dhanasekaran,Naqvi, Bilal Abbas,Jeong, Sung Hoon,Kim, Hyun-Seok,Kim, Hak-Sung,Jung, Jongwan Elsevier 2018 SOLAR ENERGY -PHOENIX ARIZONA THEN NEW YORK- Vol.171 No.-

<P><B>Abstract</B></P> <P>In this work, we demonstrated CuS/WS<SUB>2</SUB> and CuS/MoS<SUB>2</SUB> heterostructures via a sputtering-CVD process for dye-sensitized solar cells (DSSCs) as a counter electrode (CE) to replace the currently preferred expensive platinum (Pt). The cyclic voltammetry, electrochemical impedance spectroscopy, and Tafel curve studies revealed that the unique CuS/WS<SUB>2</SUB> and CuS/MoS<SUB>2</SUB> heterostructures were beneficial in achieving high electrocatalytic activity, low charge-transfer resistance at the CE/electrolyte interface, and fast reaction kinetics for the reduction of triiodide to iodide at the CE. The constructed DSSCs using these CuS/WS<SUB>2</SUB> and CuS/MoS<SUB>2</SUB> CEs exhibited high-power conversion efficiencies (PCEs) of 8.21% and 7.12%, respectively, which are comparable to conventional Pt CE (8.74%) and pristine WS<SUB>2</SUB>, MoS<SUB>2</SUB>, and CuS CEs (6.0%, 6.3% and 6.4%). This novel sulfur based heterostructure opens up opportunities for a variety of optoelectronic and photoelectrochemical applications.</P> <P><B>Highlights</B></P> <P> <UL> <LI> CuS/WS<SUB>2</SUB> heterostructure was synthesized via a sputtering-CVD process for counter electrode in DSSCs. </LI> <LI> It showed low charge transfer resistance, good electrocatalytic activity and strong electrochemical stability. </LI> <LI> The constructed DSSC using CuS/WS<SUB>2</SUB> CE achieved high power conversion efficiency of 8.21% </LI> <LI> That value is comparable to that of Pt CE (8.74%) and higher than that of pristine WS<SUB>2</SUB>, MoS<SUB>2</SUB>, and CuS CEs. </LI> <LI> CuS/WS<SUB>2</SUB> CE shows promising counter electrode for DSSCs. </LI> </UL> </P>

Facile and cost-effective growth of MoS₂ on 3D porous graphene-coated Ni foam for robust and stable hydrogen evolution reaction

Hussain, Sajjad,Vikraman, Dhanasekaran,Truong, Linh,Akbar, Kamran,Rabani, Iqra,Kim, Hyun-Seok,Chun, Seung-Hyun,Jung, Jongwan Elsevier 2019 JOURNAL OF ALLOYS AND COMPOUNDS Vol.788 No.-

<P><B>Abstract</B></P> <P>To replace the costly, noble platinum electrocatalyst, the inexpensive, earth abundant and highly efficient electrocatalysts of layered transition metal dichalcogenides (TMDs) are explored for the hydrogen evolution reaction (HER). This paper describes cost-effective synthesis of 1T-MoS<SUB>2</SUB> on 3D-graphene/Ni foam (NF) via a facile solution bath approach as an electrocatalyst for HER. The improved HER performances were observed due to the 3D-structure of MoS<SUB>2</SUB>/graphene. HER performance of MoS<SUB>2</SUB>/graphene/NF electrocatalyst exposed a superior catalytic performance with the low overpotential (−89 mV vs RHE) to drive the 10 mA cm<SUP>−2</SUP>, steep Tafel slope (45 mV dec<SUP>−1</SUP>), large exchange current density (4.16 × 10<SUP>−1</SUP> mA cm<SUP>−2</SUP>), and robust stability over 18 h. Density functional theory (DFT) calculations also confirmed the reduced Gibbs free energy for H-adsorption (ΔG<SUB>H</SUB>) for MoS<SUB>2</SUB>/graphene compared to MoS<SUB>2</SUB>. The observed results suggest that the 1T-MoS<SUB>2</SUB>/graphene/NF is an interesting alternative to platinum-based catalyst for boosting HER efficiency.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Active electrocatalyst of MoS<SUB>2</SUB> decorated on graphene/NF by chemical route. </LI> <LI> Raman and XRD results confirmed the observation of 1T-MoS<SUB>2</SUB>. </LI> <LI> The robust stability over 18 h with over potential of 89 mV vs RHE was observed. </LI> <LI> DFT calculations explained in terms of density of states for high HER performance. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

WS2/CoSe2 heterostructure: A designed structure as catalysts for enhanced hydrogen evolution performance

Sajjad Hussain,Kamran Akbar,Dhanasekaran Vikraman,Hailiang Liu,천승현,정종완 한국공업화학회 2018 Journal of Industrial and Engineering Chemistry Vol.65 No.-

The development of hydrogen-evolving catalysts based on transition metal dichalchogenides (TMDs) is receiving a great attention for practical application of water-splitting devices and fuel cells due to their high electrocatalytic activity. Herein, we synthesized tungsten disulfide (WS2)/cobalt diselenide (CoSe2) hybrid catalyst for hydrogen evolution reaction (HER). CoSe2 films were first deposited via electrodeposition of Co and followed by selenization process. And, the surface of the synthesized CoSe2 films was covered with WS2 via combined process of sputtering and sulfurization. In acidic media, the WS2/CoSe2 heterostructure catalyst exhibited fast hydrogen evolution kinetics of onset potential and Tafel slope were at 95 mV and 44 mV decade−1, respectively with the excellent electrocatalytic stability over 20 h. WS2/CoSe2 heterostructure electrode demonstrates an excellent HER activity and long-term stability owing to their abundant active edge sites, and the strong chemical and electronic coupling between the CoSe2 and WS2.

EBCO - Efficient Boundary Detection and Tracking Continuous Objects in WSNs

( Sajjad Hussain Chauhdary ),( Jeongjoon Lee ),( Sayed Chhattan Shah ),( Myong-soon Park ) 한국인터넷정보학회 2012 KSII Transactions on Internet and Information Syst Vol.6 No.11

Recent research in MEMS (Micro-Electro-Mechanical Systems) and wireless communication has enabled tracking of continuous objects, including fires, nuclear explosions and bio-chemical material diffusions. This paper proposes an energy-efficient scheme that detects and tracks different dynamic shapes of a continuous object (i.e., the inner and outer boundaries of a continuous object). EBCO (Efficient Boundary detection and tracking of Continuous Objects in WSNs) exploits the sensing capabilities of sensor nodes by automatically adjusting the sensing range to be either a boundary sensor node or not, instead of communicating to its neighboring sensor nodes because radio communication consumes more energy than adjusting the sensing range. The proposed scheme not only increases the tracking accuracy by choosing the bordering boundary sensor nodes on the phenomenon edge, but it also minimizes the power consumption by having little communication among sensor nodes. The simulation result shows that our proposed scheme minimizes the energy consumption and achieves more precise tracking results than existing approaches.

WS₂/CoSe₂ heterostructure: A designed structure as catalysts for enhanced hydrogen evolution performance

Hussain, Sajjad,Akbar, Kamran,Vikraman, Dhanasekaran,Liu, Hailiang,Chun, Seung-Hyun,Jung, Jongwan THE KOREAN SOCIETY OF INDUSTRIAL AND ENGINEERING 2018 JOURNAL OF INDUSTRIAL AND ENGINEERING CHEMISTRY -S Vol.65 No.-

<P><B>Abstract</B></P> <P>The development of hydrogen-evolving catalysts based on transition metal dichalchogenides (TMDs) is receiving a great attention for practical application of water-splitting devices and fuel cells due to their high electrocatalytic activity. Herein, we synthesized tungsten disulfide (WS<SUB>2</SUB>)/cobalt diselenide (CoSe<SUB>2</SUB>) hybrid catalyst for hydrogen evolution reaction (HER). CoSe<SUB>2</SUB> films were first deposited via electrodeposition of Co and followed by selenization process. And, the surface of the synthesized CoSe<SUB>2</SUB> films was covered with WS<SUB>2</SUB> via combined process of sputtering and sulfurization. In acidic media, the WS<SUB>2</SUB>/CoSe<SUB>2</SUB> heterostructure catalyst exhibited fast hydrogen evolution kinetics of onset potential and Tafel slope were at 95mV and 44mVdecade<SUP>−1</SUP>, respectively with the excellent electrocatalytic stability over 20h. WS<SUB>2</SUB>/CoSe<SUB>2</SUB> heterostructure electrode demonstrates an excellent HER activity and long-term stability owing to their abundant active edge sites, and the strong chemical and electronic coupling between the CoSe<SUB>2</SUB> and WS<SUB>2</SUB>.</P> <P><B>Graphical abstract</B></P> <P>WS<SUB>2</SUB>/CoSe<SUB>2</SUB> hybrid structure was implemented to enhance HER electrocatalytic activity. The WS<SUB>2</SUB>/CoSe<SUB>2</SUB> catalyst exhibited low overpotentials of 95mV (@1mAcm<SUP>−2</SUP>) and 160mV (@ 10mAcm<SUP>−2</SUP>), a high exchange current density of ∼1.0×10<SUP>−2</SUP> mAcm<SUP>−2</SUP>, and a small Tafel slope of 44mVdecade<SUP>−1</SUP>. In addition, WS<SUB>2</SUB>/CoSe<SUB>2</SUB> hybrid electrode was stable over 20h of sustained hydrogen production in 0.5M H<SUB>2</SUB>SO<SUB>4</SUB> acidic medium.</P> <P>[DISPLAY OMISSION]</P>

High Performance MoSe₂/Mo Counter Electrodes Based- Dye-Sensitized Solar Cells

Hussain, Sajjad,Patil, Supriya A.,Vikraman, Dhanasekaran,Liu, Hailiang,Kim, Hak-Sung,Jung, Jongwan The Electrochemical Society 2017 Journal of the Electrochemical Society Vol.164 No.2

<P>In the present study, multilayer MoSe2/Mo nanostructures fabricated by surface selenization of Mo-coated glass substrates using magnetron sputtering, was proposed as a counter electrode (CE) catalyst in dye-sensitized solar cells (DSSCs) to speed up the reduction of triiodide I-3(-) to iodide I-. The extensive cyclic voltammograms (CV) and Tafel curve analysis indicated that the current density of the optimized MoSe2/Mo CE was higher than Pt CEs due to the fast reduction species. Furthermore, the peak current densities of theMoSe(2)/Mo CE showed little degradation after consecutive 100 CV cycles, suggesting high electrochemical stability of the MoSe2/Mo CE. In addition, MoSe2/Mo CE exhibited lower charge-transfer resistance than Pt CEs. Finally, the DSSC assembled with the MoSe2/Mo CE showed a high power conversion efficiency of 9.57% under illumination of 100 mW.cm(-2) (DSSC with Pt CE: 9.15%). (C) 2017 The Electrochemical Society. All rights reserved.</P>

QUASI AND BI IDEALS IN LEFT ALMOST RINGS

Hussain, Fawad,Khan, Walayat,Khan, Muhammad Sajjad Ali,Abdullah, Saleem The Honam Mathematical Society 2019 호남수학학술지 Vol.41 No.3

The aim of this paper is to extend the concept of quasi and bi-ideals from left almost semigroups to left almost rings which are the generalization of one sided ideals. Further, we discuss quasi and bi-ideals in regular left almost rings and intra regular left almost rings. We then explore many interesting and elegant properties of quasi and bi-ideals.