Synthesis of Large-Area Tungsten Disulfide Films on Pre-Reduced Tungsten Suboxide Substrates

Choi, Soo Ho,Boandoh, Stephen,Lee, Young Ho,Lee, Joo Song,Park, Ji-Hoon,Kim, Soo Min,Yang, Woochul,Kim, Ki Kang American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.49

<P>We report a facile method for the synthesis of large-area tungsten disulfide (WS2) films by means of chemical vapor deposition (CVD). To promote WS2 film growth, the precursor solution, which includes pre-reduced tungsten. suboicides, is prepared by using hydrazine as the strong reducing agent and spin-coated onto the growth substrate. Growth is then carried out in a CVD chamber vaporized with dimethyl disulfide as the sulfur precursor. Although only WS2 flakes are grown with unreduced tungsten precursors under a hydrogen atmosphere, WS2 films are readily attained on pre-reduced tungsten suboxide substrates without the need for further reduction by hydrogen, which is noted to induce discontinuity of the grown film. The result presents the coverage of WS2 to be proportional to the amount of reduced tungsten suboxides, which is revealed by X-ray photoelectron spectroscopy. Furthermore, it is found that the multilayer WS2 flakes grow along the grain boundary, which allows the analysis of the grain size of WS2 films by optical microscopy images only. WS2 field effect transistors are fabricated by conventional photolithography and show an average electron mobility of 0.4 cm(2) V-1 s(-1) and a high on/off ratio of 10(6) at room temperature.</P>

Electrical modulation of excitonic transition in monolayer tungsten disulfide on periodically poled ferroelectric substrates

Seo Changwon,Kim Jung Ho,Lee Jubok,Yun Seok Joon,Kim Teun-Teun,Kim Jeongyong 한국물리학회 2022 Current Applied Physics Vol.43 No.-

Although the spectral investigation of monolayer two-dimensional transition metal dichalcogenide (1L-TMD) has been extensively performed for identifying modulation of excitonic transition, study of excitonic transition in ferroelectric/TMD hybrid structure is essential to understand and design high speed and low loss devices based on in-plane junctions. Here, we demonstrate electrical modulation of excitonic transition by transferring 1L-tungsten disulfide (WS2) onto a ferroelectric domain surface, a periodically poled lithium niobate (PPLN). We observe that exciton (A0) and trion (A-) emissions of 1L-WS2 are spatially modulated depending on the sign of the phase domain, such that A0 and A- emission is stronger at the positive (D+) and negative (D-) domain, respectively. In addition, different trends of excitonic transition of 1L-WS2 between D+ and D- domain are demonstrated by applying a back-gate bias voltage. The spatial modulation of electrical and optical characteristics of 1L-TMDs will help to design the homo- or hetero p-n junctions based on TMDs.

Synthesis of Tungsten Disulfide for Electrocatalysts

Keshab PANDEY,Hae Kyung JEONG 한국물리학회 2023 새물리 Vol.73 No.5

Variation of photoluminescence spectral line shape of monolayer WS2

권용재,김강원,김원택,류순민,정현식 한국물리학회 2018 Current Applied Physics Vol.18 No.8

The origin of the variation of photoluminescence (PL) spectra of monolayer tungsten disulfide (WS2) is investigated systematically. Dependence of the PL spectrum on the excitation power show that the relatively sharp component corresponds to excitons whereas the broader component at slightly lower energy corresponds to negatively charged trions. PL imaging and second harmonic generation measurements show that the trion signals are suppressed more than the exciton signals near the edges, thereby relatively enhancing the excitonic feature in the PL spectrum and that such relative enhancement of the exciton signals is more pronounced near approximately armchair edges. This effect is interpreted in terms of depletion of free electrons near the edges caused by structural defects and adsorption of electron acceptors such as oxygen atoms.

Synthesis and Characterization of Cobalt-Doped WS ₂ Nanorods for Lithium Battery Applications

Wang, Shiquan,Li, Guohua,Du, Guodong,Li, Li,Jiang, Xueya,Feng, Chuanqi,Guo, Zaiping,Kim, Seungjoo Springer 2010 NANOSCALE RESEARCH LETTERS Vol.5 No.8

<P>Cobalt-doped tungsten disulfide nanorods were synthesized by an approach involving exfoliation, intercalation, and the hydrothermal process, using commercial WS<SUB>2</SUB> powder as the precursor and <I>n</I>-butyllithium as the exfoliating reagent. XRD results indicate that the crystal phase of the sample is 2H-WS<SUB>2</SUB>. TEM images show that the sample consists of bamboo-like nanorods with a diameter of around 20 nm and a length of about 200 nm. The Co-doped WS<SUB>2</SUB> nanorods exhibit the reversible capacity of 568 mAh g<SUP>−1</SUP> in a voltage range of 0.01–3.0 V versus Li/Li<SUP>+</SUP>. As an electrode material for the lithium battery, the Co-doped WS<SUB>2</SUB> nanorods show enhanced charge capacity and cycling stability compared with the raw WS<SUB>2</SUB> powder.</P>

Ultrafast Pulsed All-Fiber Laser Based on Tapered Fiber Enclosed by Few-Layer WS₂ Nanosheets

Khazaeinezhad, Reza,Kassani, Sahar Hosseinzadeh,Hwanseong Jeong,Kyung Jun Park,Byoung Yoon Kim,Dong-Il Yeom,Kyunghwan Oh IEEE 2015 IEEE photonics technology letters Vol.27 No.15

<P>We demonstrate all-fiber mode-locked laser based on a tapered optical fiber saturable absorber (SA) enclosed in tungsten disulfide (WS<SUB>2</SUB>) nanosheets. Tapered fibers were fabricated using the standard flame brushing method to an interaction length of 3 mm with waist diameters of 10 and 15 μm. WS<SUB>2</SUB> nanosheets were prepared via a liquid phase exfoliation method to form a uniform dispersion. Subsequently, the WS<SUB>2</SUB> nanosheets were optically deposited along the interaction length of the tapered fibers by evanescent field interactions. We built a ring laser including the fabricated mode-lockers. The SA with a 10-μm taper diameter delivers the pulses with a pulse duration of 369 fs and 3-dB spectral bandwidth of 7.5 nm; on the other hand, the output pulses using the mode-locker with 15-μm waist diameter were found to have 563-fs pulse duration and 5.2 nm of 3-dB bandwidth. It is shown that the smaller waist diameter of tapered fiber causes wider spectral bandwidth of the ultrafast pulses and narrower 3-dB bandwidth.</P>

Femtosecond Soliton Pulse Generation Using Evanescent Field Interaction Through Tungsten Disulfide (WS ₂) Film

Khazaeinezhad, Reza,Hosseinzadeh Kassani, Sahar,Hwanseong Jeong,Dong-Il Yeom,Kyunghwan Oh IEEE 2015 Journal of lightwave technology Vol.33 No.17

<P>We investigated nonlinear optical characteristics of Tungsten disulfide (WS<SUB>2</SUB>) films and experimentally demonstrated their high potential for application as nonlinear saturable absorbers in passively mode-locked fiber lasers. Side polished fiber (SPF) was fabricated and WS<SUB>2</SUB> film was overlaid to provide an efficient evanescent field interaction. The WS<SUB>2</SUB> film was prepared using two methods: liquid phase exfoliation to form few-layer nano-sheets, and chemical vapor deposition (CVD) to grow uniform multilayer WS<SUB>2</SUB> on a SiO<SUB>2</SUB> substrate. Two SPF saturable absorbers were prepared by either spin coating WS<SUB>2</SUB> solution or lifting off the multilayer CVD WS<SUB>2</SUB> on SPF. An all-fiber ring cavity was built and the WS<SUB>2</SUB> film overlaid on SPF was employed as a mode locker along with Er-doped fiber as a gain medium. Using the spin-coated WS<SUB>2</SUB> SPF, stable soliton-like pulses were generated with a spectral width of 5.6 nm and 467 fs pulse duration. The fiber laser cavity containing CVD WS<SUB>2</SUB> SPF generated a transform-limited soliton pulse train with a spectral width of 8.23 nm and a pulse duration of 332 fs. Our study confirmed a high potential of WS<SUB>2</SUB> film as a novel 2-D nonlinear optical material for laser applications.</P>

이황화텅스텐 나노시트 제조를 위한 기계화학적 볼밀링 공정 연구

김슬기,안윤희,이동주 한국분말재료학회 2022 한국분말재료학회지 (KPMI) Vol.29 No.5

Tungsten disulfide (WS2) nanosheets have attracted considerable attention because of their unique optical and electrical properties. Several methods for fabrication of WS2 nanosheets have been developed. However, methods for mass production of high-quality WS2 nanosheets remain challenging. In this study, WS2 nanosheets were fabricated using mechano-chemical ball milling based on the synergetic effects of chemical intercalation and mechanical exfoliation. The ball-milling time was set as a variable for the optimized fabricating process of WS2 nanosheets. Under the optimized conditions, the WS2 nanosheets had lateral sizes of 500–600 nm with either a monolayer or bilayer. They also exhibited high crystallinity in the 2H semiconducting phase. Thus, the proposed method can be applied to the exfoliation of other transition metal dichalcogenides using suitable chemical intercalants. It can also be used with highperformance WS2-based photodiodes and transistors used in practical semiconductor applications.

의사 커패시터를 위한 WS₂ 나노입자가 내제된 탄소나노섬유

성기욱,이정수,이태근,안효진,Sung, Ki-Wook,Lee, Jung Soo,Lee, Tae-Kum,Ahn, Hyo-Jin 한국재료학회 2021 한국재료학회지 Vol.31 No.8

Tungsten disulfide (WS₂), a typical 2D layerd structure, has received much attention as a pseudocapacitive material because of its high theoretical specific capacity and excellent ion diffusion kinetics. However, WS₂ has critical limits such as poor long-term cycling stability owing to its large volume expansion during cycling and low electrical conductivity. Therefore, to increase the high-rate performance and cycling stability for pseudocapacitors, well-dispersed WS₂ nanoparticles embedded in carbon nanofibers (WS₂-CNFs), including mesopores and S-doping, are prepared by hydrothermal synthesis and sulfurizaiton. These unique nanocomposite electrodes exhibit a high specific capacity (159.6 F g^-1 at 10 mV s^-1), excellent high-rate performance (81.3 F g^-1 at 300 mV s^-1), and long-term cycling stability (55.9 % after 1,000 cycles at 100 mV s^-1). The increased specific capacity is attributed to well-dispersed WS₂ nanoparticles embedded in CNFs that the enlarge active area; the increased high-rate performance is contributed by reduced ion diffusion pathway due to mesoporous CNFs and improved electrical conductivity due to S-doped CNFs; the long-term cycling stability is attributed to the CNFs matrix including WS₂ nanoparticles, which effectively prevent large volume expansion.

Synthesis of Centimeter-Scale Monolayer Tungsten Disulfide Film on Gold Foils

Yun, Seok Joon,Chae, Sang Hoon,Kim, Hyun,Park, Jin Cheol,Park, Ji-Hoon,Han, Gang Hee,Lee, Joo Song,Kim, Soo Min,Oh, Hye Min,Seok, Jinbong,Jeong, Mun Seok,Kim, Ki Kang,Lee, Young Hee American Chemical Society 2015 ACS NANO Vol.9 No.5

<P>We report the synthesis of centimeter-scale monolayer WS<SUB>2</SUB> on gold foil by chemical vapor deposition. The limited tungsten and sulfur solubility in gold foil allows monolayer WS<SUB>2</SUB> film growth on gold surface. To ensure the coverage uniformity of monolayer WS<SUB>2</SUB> film, the tungsten source-coated substrate was placed in parallel with Au foil under hydrogen sulfide atmosphere. The high growth temperature near 935 °C helps to increase a domain size up to 420 μm. Gold foil is reused for the repeatable growth after bubbling transfer. The WS<SUB>2</SUB>-based field effect transistor reveals an electron mobility of 20 cm<SUP>2</SUP> V<SUP>–1</SUP> s<SUP>–1</SUP> with high on–off ratio of ∼10<SUP>8</SUP> at room temperature, which is the highest reported value from previous reports of CVD-grown WS<SUB>2</SUB> samples. The on–off ratio of integrated multiple FETs on the large area WS<SUB>2</SUB> film on SiO<SUB>2</SUB> (300 nm)/Si substrate shows within the same order, implying reasonable uniformity of WS<SUB>2</SUB> FET device characteristics over a large area of 3 × 1.5 cm<SUP>2</SUP>.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2015/ancac3.2015.9.issue-5/acsnano.5b01529/production/images/medium/nn-2015-01529j_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn5b01529'>ACS Electronic Supporting Info</A></P>