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Exfoliated MoS2 in Water without Additives
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.ORCID iD: 0000-0003-2873-7875
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
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2016 (Swedish)In: PLOS ONE, E-ISSN 1932-6203, Vol. 11, no 4, article id 0154522Article in journal (Refereed) Published
Abstract [en]

Many solution processing methods of exfoliation of layered materials have been studied during the last few years; most of them are based on organic solvents or rely on surfactants andother funtionalization agents. Pure water should be an ideal solvent, however, it is generallybelieved, based on solubility theories that stable dispersions of water could not be achievedand systematic studies are lacking. Here we describe the use of water as a solvent and thestabilization process involved therein. We introduce an exfoliation method of molybdenumdisulfide (MoS2) in pure water at high concentration (i.e., 0.14±0.01 g L−1). This was achieved by thinning the bulk MoS2by mechanical exfoliation between sand papers and dis-persing it by liquid exfoliation through probe sonication in water. We observed thin MoS2nanosheets in water characterized by TEM, AFM and SEM images. The dimensions of thenanosheets were around 200 nm, the same range obtained in organic solvents. Electropho-retic mobility measurements indicated that electrical charges may be responsible for the sta-bilization of the dispersions. A probability decay equation was proposed to compare thestability of these dispersions with the ones reported in the literature. Water can be used as asolvent to disperse nanosheets and although the stability of the dispersions may not be ashigh as in organic solvents, the present method could be employed for a number of applications where the dispersions can be produced on site and organic solvents are not desirable.

Place, publisher, year, edition, pages
2016. Vol. 11, no 4, article id 0154522
Keywords [en]
liquid exfoliation; MoS2; solar cells; water exfoliation
National Category
Condensed Matter Physics
Identifiers
URN: urn:nbn:se:miun:diva-27560DOI: 10.1371/journal.pone.0154522ISI: 000374976200086Scopus ID: 2-s2.0-85002584946OAI: oai:DiVA.org:miun-27560DiVA, id: diva2:924456
Projects
Paper Solar CellsAvailable from: 2016-04-28 Created: 2016-04-28 Last updated: 2022-04-04Bibliographically approved
In thesis
1. Liquid Exfoliation of Molybdenum Disulfide for Inkjet Printing
Open this publication in new window or tab >>Liquid Exfoliation of Molybdenum Disulfide for Inkjet Printing
2016 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Since the discovery of graphene, substantial effort has been put toward the synthesis and production of 2D materials. Developing scalable methods for the production of high-quality exfoliated nanosheets has proved a significant challenge. To date, the most promising scalable method for achieving these materials is through the liquid-based exfoliation (LBE) of nanosheetsin solvents. Thin films of nanosheets in dispersion can be modified with additives to produce 2D inks for printed electronics using inkjet printing. This is the most promising method for the deposition of such materials onto any substrate on an industrial production level. Although well-developed metallic and organic printed electronic inks exist on the market, there is still a need to improve or develop new inks based on semiconductor materials such as transition metal dichalcogenides (TMDs) that are stable, have good jetting conditions and deliver good printing quality.The inertness and mechanical properties of layered materials such as molybdenum disulfide (MoS2) make them ideally suited for printed electronics and solution processing. In addition,the high electron mobility of the layered semiconductors, make them a candidate to become a high-performance semiconductor material in printed electronics. Together, these features make MoS2 a simple and robust material with good semiconducting properties that is also suitable for solution coating and printing. It is also environmentally safe.The method described in this thesis could be easily employed to exfoliate many types of 2D materials in liquids. It consists of two exfoliation steps, one based on mechanical exfoliation of the bulk powder utilizing sand paper, and the other inthe liquid dispersion, using probe sonication to liquid-exfoliate the nanosheets. The dispersions, which were prepared in surfactant solution, were decanted, and the supernatant was collected and used for printing tests performed with a Dimatix inkjetprinter. The printing test shows that it is possible to use the MoS2 dispersion as a printed electronics inkjet ink and that optimization for specific printer and substrate combinations should be performed. There should also be advances in ink development, which would improve the drop formation and break-off at the inkjet printing nozzles, the ink jetting and, consequently, the printing quality.

Abstract [sv]

Sedan upptäckten av grafen har mycket arbete lagts på framställning och produktion av 2D-material. En viktig uppgift har varit att ta fram skalbara metoder för produktion av högkvalitativa  nanosheets via exfoliering. Den mest lovande skalbarametoden hittills har varit vätskebaserad exfoliering av nanosheets i lösningsmedel. Tunna filmer av nanosheets i dispersion kan anpassas med hjälp av tillsatser och användas för tillverkning av halvledare strukturer med inkjet-skrivare, vilket är den mest lovande metoden för på en industriell produktions nivå beläggaden typen av material på substrat. Även om det finns välutvecklade metalliska och organiskabläck för tryckt elektronik, så finns det fortfarande ett behov av att förbättra eller utveckla nya bläck baserade på halvledarmaterial som t.ex. TMD, som är stabila, har goda bestryknings  egenskaper och ger bra tryckkvalitet. Den inerta naturen tillsammans med de mekaniska egenskaperna som finns hosskiktade material, som t.ex. molybdendisulfid (MoS2), gör demlämpliga för flexibel elektronik och bearbetning i lösning. Dessutom gör den höga elektronmobiliteten i dessa 2D-halvledaredem till en stark kandidat som halvledarmaterial inom trycktelektronik. Det betyder att MoS2 är ett enkelt och robust material med goda halvledaregenskaper som är lämpligt för bestrykning från lösning och tryck, och är miljömässigt säker.Den metod som beskrivs här kan med fördel användas föratt exfoliera alla typer av 2D-material i lösning. Exfolieringensker i två steg; först mekanisk exfoliering av torr bulk med sandpapper, därefter används ultraljudsbehandling i lösning för att exfoliera nanosheets. De dispersioner som framställts i lösning med surfaktanter dekanterades och det övre skiktetanvändes i trycktester med en Dimatix inkjet-skrivare.Tryckprovet visar att det är möjligt att använda MoS2 -dispersion som ett inkjet-bläck och att optimering för särskildaskrivar- och substratkombinationer borde göras, såsom förbättringav bläcksammansättningen med avseende på droppbildning och break-off vid skrivarmunstycket, vilket i sin tur skulleförbättra tryckkvaliteten.

Place, publisher, year, edition, pages
Sundsvall: Mid Sweden University, 2016. p. 85
Series
Mid Sweden University licentiate thesis, ISSN 1652-8948 ; 123
Keywords
MoS2, Exfoliation, Inkjet Printing, 2D materials, Environmental Friendly, TMD, thin films, industrial printing, 2D inks, printed electronics, thin films carrier mobility, large-area electronics, graphene analogues, solar cells
National Category
Physical Sciences
Identifiers
urn:nbn:se:miun:diva-29181 (URN)978-91-88025-71-5 (ISBN)
Presentation
2016-09-09, O111, Holmgatan 10, Sundsvall, 10:15 (English)
Opponent
Supervisors
Projects
KM2Paper Solar Cells
Funder
Swedish Energy AgencyKnowledge Foundation
Available from: 2016-11-02 Created: 2016-11-02 Last updated: 2016-11-02Bibliographically approved
2. Liquid-Phase Exfoliation of Two-Dimensional Materials: Applications, deposition methods and printed electronics on paper
Open this publication in new window or tab >>Liquid-Phase Exfoliation of Two-Dimensional Materials: Applications, deposition methods and printed electronics on paper
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

After the unprecedented success of graphene research, other materials that can also be exfoliated into thin layers, like Transition metal dichalcogenides (TMDs) such as molybdenum disulfide (MoS2), have also become the subjects of extensive studies. As one of the most promising methods for large scale production of such materials, liquid-phase exfoliation (LPE) has also been the subject of extensive research and is maturing as a field to the point that devices using additive manufacturing and printed nanosheets are often reported. The stability of the nanosheets in environmentally friendly solvents, particularly in water, with or without stabilizers, is still a focus of great interest for sustainable and commercial production. In this thesis, different methods of LPE in water with and without stabilizers are investigated and discussed. Stabilizers such as surfactant sodium dodecyl sulfate (SDS) and modified cellulose2-hydroxyethyl cellulose (HEC), were employed. Because waterdoes not have surface energy parameters that match those of2D materials, the dispersions in water do not usually have a high yield. Therefore, to circumvent the use of organic solvents that are known to be able to successfully exfoliate and stabilize nanosheets of two-dimensional materials, this thesis focuses on water as the solution-process medium for exfoliation and the assisting stabilizers used to keep the exfoliated nanomaterials in dispersion with a long half-time. Surfactant-assisted dispersions are discussed together with test-printing resultsusing inkjet to deposit the material. Process parameters for the LPE method using HEC as a stabilizer are presented together with thin nanosheets characterized by Raman spectroscopy. Dispersions using HEC presented the longest half-time among the studied methods, higher than previously reported values for methods using mixed low-boiling-point solvents. Devices using exfoliated nanosheets have been fabricated and presented in the present study. The photoconductivity of MoS2 using a device fabricated with LPE MoS2 nanosheets and the cathodoluminescence of LPE MoS2 are discussed. Although fabricated with mechanically exfoliated nanosheets and not LPE ones, another photodetector fabricated with one of the MoS2 grades used in this thesis is presented to highlight the excellent photoresponse of this material. A method of producing thin nanosheets with-out stabilizers by pre-processing the MoS2 grades withs and papers is introduced. With this method, nanosheets with a lateral size of around 200nm and a concentration around 0.14 g L−1 - that is half the concentration at the same processing conditions in solvent n-methyl pyrrolidone (NMP) - are discussed. Inkjet printing as a deposition method is discussed together with the requirements for the 2D inks. Printed organic electronics using the conductive polymer PEDOT:PSS are compared to those using commercially-available graphene ink, with a focus on printing on paper substrates. In order to bring the thesis into perspective from materials to device fabrication, I study the suitability of inkjet paper substrates for printed electronics, by extensively characterizing the chemical and physical properties of their ink-receiving layers (IRLs) and their impact on the electronic properties of the conductive printed lines.

Place, publisher, year, edition, pages
Sundsvall: Mid Sweden University, 2019. p. 125
Series
Mid Sweden University doctoral thesis, ISSN 1652-893X ; 305
Keywords
molybdenum disulfide (MoS2), transition metal dichalcogenide (TMD), thin films, inkjet printing, 2D inks, liquid-phase exfoliation, shear exfoliation, printed electronics, organic electronics, PEDOT:PSS, photoresponse, photocurrent, cathodoluminescence
National Category
Natural Sciences
Identifiers
urn:nbn:se:miun:diva-37287 (URN)978-91-88947-19-2 (ISBN)
Public defence
2019-10-18, O102, Sundsvall, 10:15 (English)
Opponent
Supervisors
Note

Vid tidpunkten för disputationen var följande delarbete opublicerat: delarbete 3 (inskickat).

At the time of the doctoral defence the following paper was unpublished: paper 3 (submitted).

Available from: 2019-09-23 Created: 2019-09-23 Last updated: 2019-09-23Bibliographically approved

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Forsberg, VivianeZhang, RenyunJoakim, BäckströmDahlström, ChristinaAndres, BrittaNorgren, MagnusAndersson, MattiasHummelgård, MagnusOlin, Håkan

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