Name: preparation of liquid-exfoliated transition metal dichalcogenide nanosheets with controlled size and thickness: a state of the art protocol
Uploaded: 2016-12-20T12:00:00
Description: Watch this Scientific Journal Video about Preparation of Liquid-exfoliated Transition Metal Dichalcogenide Nanosheets with Controlled Size and Thickness: A State of the Art Protocol at JoVE.com

The research leading to these results has received funding from the European Union Seventh Framework Program under grant agreement n&#176;604391 Graphene Flagship. C.B. acknowledges the German Research Foundation, DFG, under grant BA 4856/2-1.

1. Flydende Eksfoliering - Udarbejdelse af Egnede Stock dispersioner <ol><li> Monter en metal kop under en sonotrode i et isbad. </li><li> Fordybe 1,6 g af TMD pulver i 80 ml vandig opløsning af natriumcholat (SC) overfladeaktivt middel (natriumcholat koncentration, C SC = 6 g L-1) i metallet cup. </li><li> Flyt sonic spids til bunden af ​​metallet cup og derefter op af ~ 1 cm. Wrap aluminiumsfolie omkring den soniske probe for at undgå spild. </li><li> Sonikeres blandingen under isafkølin...

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Prøveforberedelse De her beskrevne prøver fremstilles ved spids lydbehandling. Alternative exfoliation fremgangsmåder kan anvendes, men vil føre til forskellige koncentrationer, laterale størrelser og grader af delaminering. Højere amplituder og længere på pulser under lydbehandling bør undgås for at forhindre beskadigelse af den sonikator. Lignende resultater blev opnået under anvendelse af 500 W processorer. Men sonication tid og amplitude har en indvirkning på nanosheet eksfolier...

Muligheden for at producere og proces graphene, beslægtet todimensionale (2D) krystaller i den flydende fase gør dem lovende materialer til et stadigt voksende vifte af applikationer som kompositmaterialer, sensorer, i energilagring og konvertering og fleksible (opto) elektronik. 1-6 For at udnytte 2D nanomaterialer inden applikationer som disse vil kræve billige og pålidelige funktionelle blæk med on-demand lateral størrelse og tykkelse af de nanoskala bestanddele, samt kontrollerede reologiske og morfologiske egenskaber som kan underkastes industriel skala udskrivning / overfladebehandling. 7 I denne henseende har væskefase exfoliation blevet en vigtig produktionsteknik giver adgang til en lang række nanostrukturer i store mængder. 6,8,9 Denne fremgangsmåde involverer sonikering eller forskydning af lagdelte krystaller i væsker. Hvis væsken passende vælges (dvs. egnede opløsningsmidler eller overfladeaktive midler) de nanosheets vil være stabilized mod reaggregation. Talrige applikationer og proof-of-principle enheder er blevet påvist af sådanne teknikker. 6 Sandsynligvis den største styrke i denne strategi er dens alsidighed, som mange lagdelte forælder krystaller kan afstødes og behandles på en lignende måde, der giver adgang til en bred palet af materialer, som kan skræddersys til det ønskede program. Men trods dette nylige fremskridt, den resulterende polydispersitet, der opstår som følge af disse flydende fase produktionsmetoder (i form af nanosheet længde og tykkelse) stadig udgør en flaskehals i realiseringen af ​​højtydende enheder. Dette er for det meste fordi udviklingen af ​​nye og innovative udvalg størrelse teknikker har hidtil krævet nanosheets længde og tykkelse karakterisering ved hjælp kedelige statistisk mikroskopi (atomic force mikroskopi, AFM og / eller transmission elektronmikroskopi, TEM). På trods af disse udfordringer, Several centrifugeringsteknikker er blevet rapporteret at opnå længde og tykkelse sortering. 6,10-13 Den enkleste scenario er homogen centrifugering, hvor dispersionen centrifugeres ved en given centrifugalacceleration og supernatanten dekanteres til analyse. Centrifugeringen hastighed indstiller størrelsen afskæringen, hvorved højere hastigheden er, jo mindre er de nanosheets i supernatanten. Denne teknik lider to store ulemper; dels når større nanosheets udvælges (dvs. dispersionen centrifugeres ved lav hastighed, og supernatanten dekanteres) alle mindre nanosheets vil holde prøven. For det andet, uanset centrifugeringen hastighed, en betydelig del af materialet tendens til at blive brændt i sedimentet. En alternativ strategi til udvælgelse størrelse er densitetsgradient (eller isopyknisk) centrifugering. 11,14 I dette tilfælde er dispersionen sprøjtes i et centrifugerør containing en densitetsgradient medium. Under ultracentrifugering (typisk&gt; 200.000 xg), er en densitetsgradient dannet, og de nanosheets flytte til det punkt i centrifugen, hvor deres opdrift densitet (tæthed herunder stabilisator og skallen opløsningsmiddel) matcher tætheden af ​​gradienten. Bemærk, at nanomateriale også kan bevæge sig opad under denne proces (afhængigt af hvor det blev injiceret). På en sådan måde bliver nanosheets effektivt sorteret efter tykkelse snarere end masse (i modsætning til homogen centrifugering). Mens denne fremgangsmåde giver en unik mulighed for at sortere nanosheets ved tykkelse, det lider bemærkelsesværdige ulemper. For eksempel er udbytterne er meget lave og i øjeblikket ikke muliggør masseproduktion af adskilte nanosheets. Dette er til dels relateret til lavt indhold af monolag på lager dispersioner efter væske-eksfoliering og kan potentielt forbedres ved optimering af eksfoliering procedurer i fremtiden. Derudover er det typisk en tidskrævende flertrins-ultracentrifugering proces, der involverer flere gentagelser for at opnå en effektiv udvælgelse størrelse. Endvidere i tilfælde af uorganiske nanomaterialer, er den begrænset til polymer-stabiliserede dispersioner til opnåelse af de nødvendige opdrift densiteter og gradienten medium i dispersionen kan forstyrre yderligere behandling. Vi har for nylig vist, at en procedure, vi udtrykket flydende kaskade centrifugering (LCC) tilbyder et spændende alternativ, 13 som vi vil også detaljer i dette manuskript. Dette er en multi-trins procedure, som er yderst alsidigt tillade forskellige kaskader, der skal udformes i henhold til det ønskede resultat. For at demonstrere denne proces, er en standard kaskade portrætteret i figur 1, og involverer flere centrifugeringstrin hvorved hver har et højere hastighed end den sidste. Efter hvert trin sedimentet lagret, og den ovenstående væske anvendes derefter i proceduren fase. Som følge heraf hver sediment indeholder nanosheets i en givenstørrelsesorden, der er blevet &quot;fanget&quot; mellem to centrifugeringer med forskellige hastigheder; den nederste fjernelse af større nanosheets i det foregående sediment mens højere hastighed fjerner de mindre nanosheets i supernatanten. Kritisk til LCC, kan den resulterende sediment gendispergeres fuldstændigt ved mild sonikering i det respektive medium, som i dette tilfælde er vandig natriumcholat H2O-SC (ved SC koncentrationer så lave som 0,1 g L -1). Resultatet er dispersioner med stort set alle valgte koncentration. Vigtigere, er stort set ingen materiale spildt i LCC, hvilket resulterer i samlingen af ​​relativt store masser af størrelse valgt nanosheets. Som vist her, har vi anvendt denne procedure på en række af flydende-ekspanderet nanosheets herunder MoS2 og WS 2 samt gas, 15 sorte fosfor 16 og graphene 17 i både opløsningsmiddel og overfladeaktive systemer. Denne unikke centrifugering procedure muliggør effektiv størrelse udvælgelse af flydende afstødes nanosheets og har efterfølgende muliggjort en betydelig fremgang i kraft af deres størrelse og tykkelse bestemmelse. Især med denne fremgangsmåde, vi demonstreret tidligere, at optisk ekstinktion (og absorbans-spektre) af nanosheets ændres systematisk som funktion af begge nanosheets laterale dimensioner og nanosheets tykkelse. Som vi opsummere her, har dette tilladt os at knytte nanosheet spektrale profil (specifikt intensitetsforholdet ved to positioner på udtømning spektrum) til middelværdien nanosheet længde som følge af nanosheet randeffekter. 12,13 vigtigere er, kan den samme ligning anvendes til at kvantificere størrelsen af MoS2 og WS 2. Endvidere viser vi, at A-exciton holdning ændrer mod lavere bølgelængder som en funktion af gennemsnitlig nanosheet tykkelse som følge af indeslutning effekter. Selvom peeling, samt størrelse udvælgelse og bestemmelse er generelt temmelig røveUST procedurer, den kvantitative resultat afhænger af finesser i protokollen. Men især for nytilkomne til feltet, er det vanskeligt at vurdere, hvilken proces parametre er mest relevante. Det kommer ned til det faktum, at eksperimentelle afsnit af forskningsrapporter kun give et groft protokol, uden at diskutere, hvad resultatet kan forventes, når ændrer proceduren eller give en rationel bag protokollen. I dette bidrag, vi har til hensigt at løse dette samt give en detaljeret vejledning og diskussion til fremstilling af flydende-ekspanderet nanosheets af kontrolleret størrelse og til den nøjagtig bestemmelse af størrelse ved enten statistisk mikroskopi eller analyse af udslettelse spektre. Vi er overbeviste om, at dette vil bidrage til at forbedre reproducerbarhed og håber, at det vil være en nyttig vejledning for andre eksperimentalister på dette forskningsområde. <img alt="figur 1" src="/files/ftp_upload/54806/54806fig1.jpg" /> FiguAd 1: Skematisk af udvælgelsen størrelse ved flydende kaskade centrifugering. Størrelsesselekteret nanosheets opsamles som sedimenter. Hver sediment opsamles eller &quot;fanget&quot; mellem to centrifugering hastigheder (w) startende fra lave hastigheder og går til højere dem fra trin til trin. Sedimentet kasseres efter den første centrifugering indeholder unexfoliated lagdelte krystallitter mens supernatanten kasseres efter det sidste centrifugeringstrin indeholder ekstremt små nanosheets. Størrelsesselekteret dispersioner fremstilles ved igen at dispergere de indsamlede sedimenter i det samme medium (her vandig opløsning af overfladeaktivt middel) ved reducerede mængder. Tilpasset med tilladelse fra 13. <a href="http://ecsource.jove.com/files/ftp_upload/54806/54806fig1large.jpg" target="_blank">Klik her for at se en større version af dette tal.</a>

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		<tr height="42">
			<td height="42" style="height:42px;width:233px;">Sodium cholate hydrate, from ox and/or sheep bile</td>
			<td style="width:105px;">Sigma Aldrich</td>
			<td style="width:127px;">C1254-100G</td>
			<td style="width:523px;">Surfactant used as stabilizer in the form of an aqueous solution (i.e. after dissolving the powder in millipore water)</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:233px;">MoS2 powder</td>
			<td style="width:105px;">Sigma Aldrich</td>
			<td style="width:127px;">69860-100G</td>
			<td style="width:523px;">Other distributors available, but exfoliation and outcome of size selection can vary</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:233px;">WS2, powder 2 um</td>
			<td style="width:105px;">Sigma Aldrich</td>
			<td style="width:127px;">243639-50G</td>
			<td style="width:523px;">Other distributors available, but exfoliation and outcome of size selection can vary</td>
		</tr>
		<tr height="84">
			<td height="84" style="height:84px;width:233px;">ImageJ Software</td>
			<td style="width:105px;">Developer: National Insitutes of Health</td>
			<td style="width:127px;">64-bit Java version 2.45 1.6.0_24</td>
			<td style="width:523px;">Image processing software used for TEM analysis, free download</td>
		</tr>
		<tr height="84">
			<td height="84" style="height:84px;width:233px;">Gwyddion Software</td>
			<td style="width:105px;">Developer: Czech Metrology Institute</td>
			<td style="width:127px;">64-bit Java version 2.45</td>
			<td style="width:523px;">Image processing software used for AFM analysis, free download</td>
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			<td height="42" style="height:42px;width:233px;">Origin Pro Software</td>
			<td style="width:105px;">OriginLab</td>
			<td style="width:127px;">Version 2016</td>
			<td style="width:523px;">Software used for data analysis such as differntiation and fitting of the extinction spectra</td>
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			<td height="21" style="height:21px;width:233px;">Centrifuge&#160;</td>
			<td style="width:105px;">HettichLab</td>
			<td style="width:127px;">Mikro 220R</td>
			<td style="width:523px;">any other benchtop centrifuge is suitable</td>
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			<td height="21" style="height:21px;width:233px;">Rotor 1</td>
			<td style="width:105px;">Hettich</td>
			<td style="width:127px;">Rotor 1016</td>
			<td style="width:523px;">for centrifugation &#60; 5000 x g</td>
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			<td height="21" style="height:21px;width:233px;">Rotor 2</td>
			<td style="width:105px;">Hettich</td>
			<td style="width:127px;">Rotor 1195-A</td>
			<td style="width:523px;">for centrifugation &#62; 5000 x g</td>
		</tr>
	</tbody>
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preparation of liquid-exfoliated transition metal dichalcogenide nanosheets with controlled size and thickness: a state of the art protocol

We summarize recent advances in the production of liquid-exfoliated transition metal dichalcogenide (TMD) nanosheets with controlled size and thickness. Layered crystals of molybdenum disulphide (MoS2) and tungsten disulphide (WS2) are exfoliated in aqueous surfactant solution by sonication. This yields highly polydisperse mixtures containing nanosheets with broad size and thickness distributions. However, for most purposes, specific sizes (in terms of both lateral dimension and thickness) are required. For example, large and thin nanosheets are desired for (opto) electronic applications, while laterally small nanosheets are interesting for catalytic applications. Therefore, post-exfoliation size selection is an important step that we address here. We provide a detailed protocol on the efficient size selection in large quantities by liquid cascade centrifugation and the size and thickness quantification by statistical microscopic analysis (atomic force microscopy and transmission electron microscopy). The comparison of MoS2 and WS2 shows that both materials are size-selected in a similar way by the same procedure. Importantly, the dispersions of size-selected nanosheets show systematic changes in their optical extinction spectra with size due to edge and confinement effects. We show how these optical changes are related quantitatively to the nanosheets dimensions and describe how mean nanosheets length and layer number can be extracted reliably from the extinction spectra. The exfoliation and size selection protocol can be applied to a broad range of layered crystals as we have previously demonstrated for graphene, gallium sulphide (GaS) and black phosphorus.

Flydende kaskade centrifugering (figur 1) er en kraftfuld teknik til at sortere væske-ekspanderet nanosheets efter størrelse og tykkelse som illustreret i figur 2 for både MoS2 og WS 2. Nanosheet laterale størrelser og tykkelser kan karakteriseres ved statistisk TEM og AFM hhv. En typisk AFM billede er vist i figur 2A. Den tilsyneladende nanosheet tykkelse omdannes til lag nummer ved hjælp af trinhøjde analyse...

Watch this Scientific Journal Video about Preparation of Liquid-exfoliated Transition Metal Dichalcogenide Nanosheets with Controlled Size and Thickness: A State of the Art Protocol at JoVE.com

Preparation of Liquid-exfoliated Transition Metal Dichalcogenide Nanosheets with Controlled Size and Thickness: A State of the Art Protocol

En protokol for væsken eksfoliering af lagdelte materialer til nanosheets, er deres størrelse udvælgelse og måling størrelse ved mikroskopiske og spektroskopiske teknikker præsenteres.

Udarbejdelse af Liquid-afstødes Transition Metal Dichalcogenide Nanosheets med kontrolleret størrelse og tykkelse: En State of the Art protokollen

We summarize recent advances in the production of liquid-exfoliated transition metal dichalcogenide (TMD) nanosheets with controlled size and thickness. ...

The goal of this protocol is to produce two dimensional nanosheets stabalized in liquid with controlled lateral size and thickness from bulk crystals. We also demonstrate methods to characterize the morphology and quantitatively determine the nanosheet dimensions from extinction spectra. This method can help answer key questions in nanoscience, such as the influence of nanosheet dimensions on the properties of structures and composites containing these sheets exfoliated in liquid.The main advantage of this technique is that it's applicable to many different true day materials and only requires commonplace laboratory equipment. In particular, the spectroscopic metrics allow rapid assessment of the dispersions that are produced. Demonstrating the procedure will be Farnia Rashvand, a PhD student, and Kevin Synnatschke, a Master's student from my laboratory.To begin this procedure, mount a metal cup underneath a sonotrode in an ice bath. Immerse 0.6 grams of a transition metal dichalcogenide or TMD powder in 80 milliliters of an aqueous solution of sodium cholate surfactant in the metal cup. Move the solid flathead tip to the bottom of the metal cup and then raise it approximately one centimeter.Wrap aluminum foil around the sonic probe to avoid spillage. To sonicate the mixture by probe sonication, set the amplitude to 60%and the pulsing to six seconds on, and two seconds off. Then switch on the sonicator and run the process for one hour.Next, centrifuge the dispersion at 2, 660 times g for 1.5 hours. After discarding the supernatant, add 80 milliliters of fresh surfactant solution to the sediment and agitate the mixture. Then, transfer the mixture back to the metal cup.Now, subject the dispersion to a second, longer sonication using the solid flathead tip for five hours at 60%amplitude under ice cooling. After every two hours, pause the sonication and replace the ice bath. Remove unexfoliated particles by centrifugation at 240 times g for two hours.When finished, discard the sediment. Following this, centrifuge the supernatant at higher centrifugal acceleration. Collect the sediment in three to eight millileters of fresh surfactant solution.Centrifuge the supernatant at an even higher centrifugal acceleration of 950 times g for two hours. Then collect the sediment in three to eight milliliters of fresh surfactant solution. For atomic force microscopy, dilute the dispersion so that it is almost transparent to the human eye.Following this, heat a wafer to approximately 170 degrees Celsius on a hot plate. Then deposit the dispersion on the preheated wafer. Rinse the wafer thoroughly with a minimum of five milliliters of water and three milliliters of 2-Propanol to remove residual surfactant and other impurities.Following this, load the sample in AFM instrument. Scan and save multiple images across the sample with the atomic force microscope in tapping mode. For samples containing larger nanosheets, increase the field of view up to eight by eight micrometers squared and use scan rates of 0.4 to 0.7 hertz.To perform the thickness measurement, open the software and select the relevant AFM image via File and Open. Correct the background using the level data by mean plane subtraction, align rows, and correct horizontal scars in the data process section of the Home menu. Apply the corrections, change the image color for better contrast by right-clicking on the the legend and set the Z plane to zero.Next, zoom into the region of choice by first clicking on the Crop tool in the Home menu. Then drag the cursor over the image to mark the region of choice and press Apply. Check the create new channel to open the selected region in a new window.Select extract profiles from the Tools menu and draw a line across the nanosheet. After the window showing the thickness length profile opens, enter the thickness value in a table. Take the approximate median value of the thickness profile across the nanosheet, taking extreme care to measure only individually deposited and non-aggregated nanosheets.For spectral acquisition, dilute the high concentration sample with the respective medium to yield extinctions below two across the entire spectral range. Set the increments for spectral acquisition to 0.5 nanometers in the instruments setting. Choose subtract baseline in the instruments settings.After placing a cuvette containing the aqueous sodium cholate solution in the spectrometer, run the measurement. Following this, remove the cuvette from the spectrometer and empty it. Add the sample to the cuvette and place the cuvette in the spectrometer.Then run the measurement. Using the data analysis and graphing software, select the column containing the extinction intensity. Click on the Analysis tab, select Mathematics from the dropdown menu, and click on Differentiate.Then select Open Dialog. After the new window opens, set the derivative order to two and press OK.Select the column containing the derivative, click on Analysis and choose Signal Processing. Click on Smooth and then select Open Dialog from the dropdown menu.Next, choose Adjacent Averaging as the smoothing method and set the points to 20. Plot the resultant smoothed spectrum, which is displayed as new columns. Finally, read off the peak position from the second derivative by placing the cursor in the center of the peak.Liquid cascade centrifugation is used to sort liquid-exfoliated nanosheets by size and thickness as demonstrated for molybdenum and tungsten disulfide. A typical AFM image is shown here. And the nanosheet thickness is converted to layer number using step height analysis.Statistical microscopic analysis yields length and number of layer histograms. The mean nanosheet length and layer number plotted as a function of central acceleration shows a similar trend for both materials. The length plotted as a function of nanosheet layer number confirms that smaller, thinner nanosheets are separated from larger, thicker ones.Optical extinction spectra of molybdenum and tungsten disulfide with different mean nanosheet sizes and thicknesses are shown here. The corresponding fitted second derivatives of the A-exciton region illustrate well-defined peak shifts of the transition. Data for both materials collapses on the same curve if appropriate peak positions are chosen and means that the nanosheet size can be quantitatively linked to the nanosheet length via the same equations.The A-exciton extinction coefficient is length dependent except at certain positions, so that the corresponding extinction coefficient can be used as measure for nanosheet concentration. The number of layers can be quantitatively related to the A-exciton peak position. Once mastered, large quantities of liquid-exfoliated nanosheet dispersions with controlled and known dimensions can be produced in only a couple of days.This is enabled by the high throughput size determination based on the optical extinction spectra. Since the nanosheet size determines its properties, the size control is crucial. After the development of the metrics, this technique paved the way for researchers to explore them in a number of applications, from electrocatalysis to electronics to composite reinforcement.After watching this video, you should have a good understanding of how to produce size selected nanosheet dispersions using liquid phase exfoliation and liquid cascade centrifugation procedures. Following the dispersion preparation, it's very important to perform basic characterization using statistical microscopy and optical extinction spectroscopy to confirm the nature of the dispersion constituents. Most excitingly, the resulting size selected nanosheet dispersions can then be subject to various liquid phase processing methods to produce thin films and other nanosheet containing structures for a wide range of potential applications.

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