SEPARATION OF SEMI-CONDUCTING AND METALLIC SINGLE-WALLED CARBON NANOTUBES USING A POLYTUNGSTATE

Abstract

The present invention relates to a method for separating semi-conducting and metallic single-walled carbon nanotubes from each other and, if present, from other carbonaceous material, or for separating semi-conducting or metallic single-walled carbon nanotubes from other carbonaceous material via density separation using a solution of a polytungstate; to semi-conducting or metallic single-walled carbon nanotubes obtained by this method; and to the use of these semi-conducting or metallic single-walled carbon nanotubes. The invention further relates to the use of a polytungstate, particularly sodium polytungstate, for separating semi-conducting single-walled carbon nanotubes from metallic single-walled carbon nanotubes, or for separating semi-conducting single-walled carbon nanotubes from undesired carbonaceous material, particularly from metallic single-walled carbon nanotubes, or for separating metallic single-walled carbon nanotubes from undesired carbonaceous material, particularly from semi-conducting single-walled carbon nanotubes. The invention also relates to specific polyarylethers containing phosphate groups and their use as surface-active compounds.

Claims

1. A method for separating semi-conducting and metallic single-walled carbon nanotubes from each other and optionally from other carbonaceous material, or for separating semi-conducting single-walled carbon nanotubes or metallic single-walled carbon nanotubes from other carbonaceous material, the method comprising: contacting a) a composition containing semi-conducting and metallic single-walled carbon nanotubes and optionally other carbonaceous material, or b) a composition containing semi-conducting carbon nanotubes and other carbonaceous material, or c) a composition containing metallic single-walled carbon nanotubes and optionally other carbonaceous material, with at least one surface-active compound and a solution of a polytungstate, to obtain a composition, and subjecting the obtained composition to a density separation treatment.

2. A method for obtaining semi-conducting or metallic single-walled carbon nanotubes, the method comprising: contacting a composition containing semi-conducting or metallic single-walled carbon nanotubes and undesired carbonaceous material with at least one surface-active compound and then with a solution of a polytungstate, and subjecting the obtained composition to a density separation treatment.

3. The method of claim 1, comprising: (i) dispersing a first composition containing the semi-conducting and/or metallic single-walled carbon nanotubes and optionally other carbonaceous material in a liquid medium containing at least one surface-active compound to obtain a dispersion; (ii) providing a solution of a polytungstate; (iii) placing the dispersion obtained in (i) on or into the solution provided in (ii) to obtain a second composition; (iv) submitting the second composition obtained in (iii) to the density separation treatment; (v) separating a fraction or fractions enriched in the semi-conducting single-walled carbon nanotubes from a fraction or fractions enriched in other carbonaceous material; or separating a fraction or fractions enriched in the metallic single-walled carbon nanotubes from a fraction or fractions enriched in other carbonaceous material and (vi) optionally repeating (i) to (iv) with one or more of the fractions obtained in (v).

4. The method of claim 3, wherein in (i) the composition containing the semi-conducting and/or metallic single-walled carbon nanotubes, calculated as solid carbon matter, is used in an amount of from 0.01 to 2% by weight, based on a total weight of the dispersion.

5. The method of claim 3, wherein in (i) the at least one surface-active compound is used in an amount of from 0.05 to 5% by weight, based on a total weight of the dispersion.

6. The method of claim 3, wherein (i) comprises: providing a mixture containing the semi-conducting and/or metallic single-walled carbon nanotubes and optionally other carbonaceous material, water and at least one surface-active compound and subjecting the mixture to an ultrasonic treatment.

7. The method of claim 1, wherein the polytungstate is sodium polytungstate.

8. The method of claim 1, wherein the solution of the polytungstate is an aqueous solution.

9. The method of claim 1, wherein the solution of the polytungstate contains at least one surface-active compound.

10. The method of claim 1, wherein the solution of the polytungstate has at least one zone with a density which corresponds to a density of a complex formed by the semi-conducting single-walled carbon nanotubes and the at least one surface-active compound, or has at least one zone with a density which corresponds to a density of a complex formed by the metallic single-walled carbon nanotubes and the at least one surface-active compound.

11. The method of claim 10, wherein the solution of the polytungstate has at least one zone with a density of from 1.05 to 1.3 g/cm.sup.3.

12. The method of claim 1, wherein in case that the solution of the polytungstate has at least one zone with a pH of below 5, the density separation treatment is centrifugation, filtration, or sedimentation; and in case that the solution of the polytungstate has a pH of at least 5, the density separation treatment is density gradient centrifugation.

13. The method of claim 1, wherein centrifugation is used as the density separation treatment, wherein one or more layers of the solution of the polytungstate are placed in a centrifugation tube on top of each other, where in case that two or more layers are used, the layers have different densities and are placed in order of decreasing densities with the layer with the highest density at the bottom of the centrifugation tube and the layer with the lowest density at the top of the centrifugation tube; and wherein in case that the solution of the polytungstate has or is to have a pH of at least 5, two or more layers are used.

14. The method of claim 13, wherein 1, 2, 3, 4 or 5 layers of a solution of a polytungstate are used.

15. The method of claim 13, wherein densities of the bottom layer and the top layer differ by at least 0.1 g/cm.sup.3.

16. The method of claim 1, wherein the at least one surface-active compound is selected from the group consisting of a polyarylether, a polyarylsulfonate, a poly(alkyleneoxide) blockcopolymer, a condensation product of at least one arylsulfonic acid, at least one aldehyde and optionally at least one other compound different from the arylsulfonic acid and aldehyde which is capable of undergoing condensation with the arylsulfonic acid and/or the aldehyde; and a salt thereof.

17. The method of claim 16, wherein in case that the semi-conducting single-walled carbon nanotubes are to be obtained, the surface-active compound is a polyarylether containing a phosphate group —O—P(═O)(OR).sub.2 and/or a phosphonate group —O—P(═O)(R′)OR, where each R is independently hydrogen, a cationic equivalent, C.sub.1-C.sub.4-alkyl, or optionally substituted phenyl; and R′ is C.sub.1-C.sub.4-alkyl or phenyl.

18. The method of claim 17, wherein the surface-active compound is a polyarylether having a backbone formed by 2 or more aryl groups selected from the group consisting of a phenyl ring and a naphthyl ring bound to each other via at least one C.sub.1-C.sub.5-alkylene group as a linking group, where at least a part of the aryl groups carry one or more ether groups of formula O-A.sub.x—Y, wherein each A is independently selected from C.sub.2-C.sub.5-alkylene, each x is independently 1 to 50, in a first part of the ether groups Y is OH, in a second part of the ether groups Y is —O—P(═O)(OR).sub.2, and in a third part of the ether groups Y is —O—S(═O).sub.2OR, —O—S(═O).sub.2—R′, —O—P(═O)(R′)OR, —O—C(═O)—R′ or —O—C(═O)—OR, where each R is independently hydrogen, C.sub.1-C.sub.4-alkyl, optionally substituted phenyl, or a cationic equivalent and R′ is C.sub.1-C.sub.4-alkyl or phenyl.

19. The method of claim 18, where the polyarylether is obtained by a process comprising: obtaining a condensation product of (1) at least one monohydroxyaromatic derivative in which the hydroxyl group is etherified with a C.sub.2-C.sub.5-alkyl group which carries a phosphate group —O—P(═O)(OR).sub.2, with each R being independently H, a cationic equivalent, C.sub.1-C.sub.4-alkyl or optionally substituted phenyl; (2) at least one monohydroxyaromatic derivative in which the hydroxyl group is etherified by reaction with at least one diol precursor selected from the group consisting of ethylene oxide, propylene oxide, tetrahydrofuran and 1,2-pentylene oxide; (3) at least one monohydroxyaromatic compound carrying one or more C.sub.4-C.sub.20-alkyl groups; and (4) an aldehyde source; and optionally partially or completely neutralizing the condensation product.

20. The method of claim 19, wherein the at least one monohydroxyaromatic derivative (1) is obtained by reacting phenoxyethanol and phosphoric acid or polyphosphoric acid; the at least one monohydroxyaromatic derivative (2) is obtained by reacting phenol and ethylene oxide; component (3) is dodecylphenol; and component (4) is a formaldehyde source.

21. The method of claim 19, wherein the at least one monohydroxyaromatic derivative (1) is used in a molar excess to an overall amount of (2) and (3).

22. The method of claim 16, wherein in case that the metallic single-walled carbon nanotubes are to be obtained, the surface-active compound is a polyarylsulfonate, a poly(alkyleneoxide) blockcopolymer, or a condensation product of at least one arylsulfonic acid, at least one aldehyde and optionally other compounds.

23. The method of claim 12, wherein the density separation treatment is centrifugation, which is carried out with a mean acceleration of from 100 to 300000 g.

24-26. (canceled)

27. A semi-conducting single-walled carbon nanotube, obtained by the method of claim 1.

28. An electronic device, optical device, optoelectronic device or energy storage device, comprising: the semi-conducting single-walled carbon nanotubes of claim 27.

29. A metallic single-walled carbon nanotube, obtained by the method of claim 1.

30. An electric conductor, a touch screen, a RFID antenna, an interconnect device, a sensor, a photodetector, a solar cell, a battery device, a capacitor device, or a catalyst, comprising: the metallic carbon nanotube of claim 29.

31. A polyarylether, obtained by a process comprising: obtaining a condensation product of (1) at least one monohydroxyaromatic derivative in which the hydroxyl group is etherified with a C.sub.2-C.sub.5-alkyl group which carries a phosphate group —O—P(═O)(OR).sub.2, with each R being independently H, a cationic equivalent, C.sub.1-C.sub.4-alkyl or optionally substituted phenyl; (2) at least one monohydroxyaromatic derivative in which the hydroxyl group is etherified by reaction with at least one diol precursor selected from the group consisting of ethylene oxide, propylene oxide, tetrahydrofuran and 1,2-pentylene oxide; (3) at least one monohydroxyaromatic compound carrying one or more C.sub.4-C.sub.20-alkyl groups; and (4) an aldehyde source; and optionally partially or completely neutralizing the condensation product.

32. A surface-active compound, comprising: the polyarylether of claim 31.

Description

FIGURES

[0178] FIG. 1 shows the UV/Vis/NIR spectrum of the bluish layer obtained in example 2.1 (continuous line). As can be seen, the band between 400 and 550 nm belonging to metallic SWCNTs has disappeared; cf. with spectrum of raw material containing dispersion of CNT starting material in water containing 2% by weight of PAE1, based on the total weight of the dispersion (dotted line).

[0179] FIG. 2 compares the UV/Vis/NIR spectrum of the two bluish bands obtained in example 2.2 (continuous line) and the spectrum of the reddish band obtained in example 2.2 (dotted line).

[0180] FIG. 3 compares the UV/Vis/NIR spectrum of the sheet formed in the top part of the centrifugation tubes of example 2.3 (dotted line) with the spectrum of the bluish layer obtained in example 2.1 (continuous line). As can be seen, in both spectra, the band between 400 and 550 nm belonging to metallic SWCNTs has disappeared.

[0181] FIG. 4 shows the UV/Vis/NIR spectrum of the bluish layer obtained in example 2.5 (dotted line). As can be seen, the band between 400 and 550 nm belonging to metallic SWCNTs has disappeared; cf. with spectrum of raw material containing dispersion of CNT starting material in water containing 2% by weight of PAE1, based on the total weight of the dispersion (continuous line).

[0182] FIG. 5 shows the UV/Vis/NIR spectrum of the reddish-brown layer obtained in example 2.7.

[0183] FIG. 6 shows the input curve of the transistor prepared in example 3.1.

[0184] FIG. 7 shows the output curve of the transistor prepared in example 3.1.

[0185] FIG. 8 shows a darkfield microscopic picture of a working FET of example 3.2 with SWNT sheet channel, top gold contacts and top ionic liquid gating. The nanotube sheet is overlapping itself in the lower right corner, but not in the channel.

[0186] FIG. 9 shows the transfer curve of the transistor of example 3.2 with channel length of 50 μm.

[0187] FIG. 10 shows the output curve of the transistor of example 3.2 with channel length of 50 μm.

EXAMPLES

1. Preparation of Polyarylether Surfactants PAE1 and PAE2

[0188] A reactor, equipped with heating and stirrer was charged with 127 g of polyphosphoric acid (specified to have 85% P.sub.2O.sub.5 content). The content was heated to 60-100° C. 1 mol of phenoxyethanol was added to the stirred reaction mixture through a period of 1 to 3 hours. After the addition was finished, the reaction mix was stirred for an additional hour. The reaction product contained 75%-wt. of phenoxyethanol phosphoric acid monoester (ester of 1 mol of phenoxyethanol with 1 mol of phosphoric acid), 5%-wt. of bis(phenoxyethanol)phosphoric acid ester (ester of 2 mols phenoxyethanol with 1 mol of phosphoric acid), 1%-wt. of unreacted phenoxyethanol and 19%-wt. of unreacted phosphoric acid. The reaction product of the phosphorylation was used without further purification as starting material for the following polycondensation step.

General Polycondensation Procedure:

[0189] A corrosion-resistant reactor equipped with a stirrer and temperature control was charged with the starting materials listed in table 1 in the given order:

[0190] 1. poly(ethylenoxide)monophenylether (Ph-PEG), 2. phosphorylated phenoxyethanol (PPE), 3. dodecylphenol, 4. paraformaldehyde or trioxan, 5. methansulfonic acid 98%. Upon completion of the addition of the acid, the reaction mix was heated to 115-120° C. After 3 hours the polycondensation reaction was finished and water was added. The polycondensate PAE2 (only this) was neutralized with NaOH to pH 6-8. Finally the solid content of the product was adjusted with water to 30-35%.

TABLE-US-00001 TABLE 1 M.sub.w.sup.2 CH.sub.3SO.sub.3H Reaction Ph-PEG PPE.sup.1) Dodecylphenol Trioxan Paraformaldehyde 98% product Product M.sub.w [D] [g] [g] [g] [g] [g] [g] [D] PAE 1 750 37.51 54.55 13.51 9.03 0 2.92 6981 PAE 2 1500 60.7 87.20 20.40 0 16.33 2.39 12587 .sup.1)contains 75%-wt. of phenoxyethanol phosphoric acid monoester, 5%-wt. of bis(phenoxyethanol)phosphoric acid ester, 1%-wt. of phenoxyethanol and 19%-wt. of phosphoric acid. .sup.2The molecular weights of the polymers were determined by using gel permeation chromatography method (GPC) as described below: Column combination: OH-Pak SB-G, OH-Pak SB 804 HQ and OH-Pak SB 802.5 HQ by Shodex, Japan; eluent: 80 Vol.-% aqueous solution of HCO2NH4 (0.05 mol/l) and 20 Vol.-% acetonitrile; injection volume 100 μl; flow rate 0.5 ml/min. The molecular weight calibration was performed with poly(styrene sulphonate) standards for the UV detector and poly(ethylene oxide) standards for the RI detector. Both standards were purchased from PSS Polymer Standards Service, Germany. In order to determine the molecular weight of the polymers, result based on UV-detection (254 nm) was used, because the UV detector is only responsive towards the aromatic compounds and neglects inorganic impurities, that otherwise could falsify the results for the molecular weights. The dispersity was in each case 1.3.

2. Separation Examples

[0191] The starting carbon nanotube material was a HiPCO (high pressure CO conversion) material from Nanolntegris (SWNTs-Raw batch no. R1-912).

Example 2.1

[0192] The CNT raw material was dispersed in deionized water containing PAE1 from example 1 as surface-active compound under permanent tip sonication (Dr. Hielscher Up 200 s; tip: S2; amplitude: 195 μm, depth of immersion: ca. 2 cm) for 1 h under ice cooling. The obtained dispersion contained 0.5% by weight of the CNT raw material and 2% by weight of PAE, based on the total weight of the dispersion.

[0193] Four solutions containing sodium polytungstate (SPT) in different concentrations (see table 2 below) and 2% by weight of PAE1, based on the overall weight of the solution, and thus having different densities were prepared:

TABLE-US-00002 TABLE 2 SPT concentration [% by weight] pH of solution Density of solution [g/cm.sup.3] 21 2.4 1.20 34 2.4 1.37 43 2.3 1.51 64 2.3 2.04

[0194] The different SPT solutions were placed in centrifugation tubes of ca. 6 cm×1 cm (6 ml) in layers of between 0.5 and 1.6 ml on top of each other in order of decreasing density (0.5 ml of 64% SPT solution, 1.2 ml of 43% SPT solution, 1.6 ml of 34% SPT solution and 0.7 ml of 21% SPT solution), and on top of the SPT layers were injected 0.5 ml of the CNT dispersion. Centrifugation was carried out in a Beckmann Ultima-XL Ultracentrifuge for 18 h at 10,000×g.

[0195] After centrifugation the tubes were first analyzed visually. All tubes showed a bluish layer in the top zone of the tubes, a middle zone without any specific color (the color of the SPT solution) and a dark layer at the bottom of the tubes.

[0196] The top, bluish layer, the middle layer and the bottom dark layer were extracted separately from the tubes. For analysis the extracted bluish fraction had to be freed of the remaining SPT content, which absorbs light, thus interfering with the nanotube transitions, and also inhibits transistor measurements by being an insulator once dried. To remove the SPT, the bluish fraction (ca 0.5 ml) was loaded onto a centrifugation tube. The tube was then filled with 4 ml of deionized water. A centrifugation run was performed at 250.000×g for 4 h to force the nanotubes towards the bottom of the centrifuge tube. After the run, the supernatant was extracted using a pipette. About 0.1 ml of liquid phase and the nanotubes that agglomerated on the bottom of the tube were left. The centrifugation tube was again filled with water, ensuring that the nanotubes were re-dispersed and also the remaining SPT was mixed over the whole tube volume. These steps were repeated with 4 centrifugation steps in total. Then the tube was refilled to a volume of 0.5 ml with water containing 2% of sodium cholate hydrate (a well-known surfactant for nanotube dispersion). A total of 6 centrifugation tubes were used, all with the same parameters. The contents of the 6 tubes were transferred to a vial and tip-sonicated for 15 minutes to re-disperse the nanotubes.

Analytics of the Blue Fraction/UV-Vis-NIR:

[0197] The characterization of SWCNTs according to their electronic behavior (i.e. semi-conducting and metallic species) was carried out by recording the absorbance spectra of individualized SWCNTs with a UV/Vis/NIR spectrometer (PerkinElmer UV/Vis/NIR Spectrometer 750). The accessible range of wavelength reaches from 200-3000 nm and is therefore able to cover the characteristic absorption peaks of individualized HiPco SWCNTs (400-1400 nm). All samples were background-corrected to a reference sample, which was measured at the same time and contained 2% of sodium cholate hydrate, the surfactant used, in water. All spectra of the listed experiments are shown in FIG. 1.

[0198] To record the spectra of the sample and the reference they were filled in a 0.5 ml cuvette and placed in the beamline of the spectrometer. The measuring range was set to 200 nm to 1400 nm to cover all transitions of the nanotubes.

[0199] As FIG. 1 shows, essentially no metallic SWNTs are present (these have typical absorption bands at 400-550 nm). Thus, the bluish layer contains virtually only semi-conducting SWNTs.

[0200] In sum, the bluish layer was identified to contain the separated semi-conducting SWCNTs in a purity of 99.2%. The dark bottom layer, in a density region of ca. 2 g/cm.sup.3, was identified to contain the remaining CNT material, including the metallic SWCNTs. The middle layer was essentially devoid of any CNT material.

Example 2.2

[0201] In order to prove that the bluish layer of example 2.1 consists indeed essentially of semi-conducting SWNTs, this was freed from SPT and the surfactant and re-dispersed in a 2% sodium cholate hydrate solution as described in example 2.1 and then subjected to a “standard” density gradient ultracentrifugation using a Nycodenz® gradient (50%/40%/27.5%/22.5% by weight of Nyodenz in H.sub.2O) containing 2% sodium cholate hydrate at pH 7; see table 3.

TABLE-US-00003 TABLE 3 Nycodenz concentration [% by weight] pH of solution Density of solution [g/cm.sup.3] 22.5 7 1.14 27.5 7 1.18 40 7 1.27 50 7 1.35

[0202] Centrifugation was carried out at 25,000×g for 18 h. Centrifugation resulted in 2 bluish bands, which were analyzed with UV/Vis/NIR.

[0203] The same treatment was applied to the bottom layer of example 2.1. Centrifugation resulted in multiple bands of which a reddish one was the largest. This reddish band was isolated and analyzed with UV/Vis/NIR.

[0204] As FIG. 2 shows, the spectrum of the two bluish bands corresponds essentially to the spectrum of the bluish layer of example 2.1. Thus, indeed the bluish layer of example 2.1 consists essentially of semi-conducting SWNTs. The spectrum of the reddish band, by contrast, shows absorption bands in the range of 400-550 nm, which means that the reddish band (and therefore a substantial fraction of the bottom layer of example 2.1) mainly consists of metallic SWNTs (plus other carbonaceous material). This proves that the simplified separation method of example 2.1 results in a top layer consisting essentially of semi-conducting SWNTs which is essentially devoid of metallic SWNTs, while the latter concentrate in the bottom layer.

Example 2.3

[0205] The separation was carried out in analogy to example 2.1, applying however 72 h of centrifugation, using larger centrifugation tubes of up to 30 ml, using only two layers of SPT (6 ml of 64% by weight SPT solution; 9 ml of 43% by weight of SPT solution), and using 15 ml of the SWNT dispersion. In this case, in addition to the bluish layer formed in the top region of the centrifugation tube, a dark, free-standing sheet of SWNTs formed on the surface of the tube.

[0206] For analysis, smaller parts of the sheets were placed in 150 ml of deionized water in a vial and extracted only after a few days to get rid of remaining SPT. Each part was then stored in 10 ml of deionized water for further analysis. Data was then collected from one part of the sheet. The sheet was carefully extracted with a pipette from its 10 ml water bath and then placed on a quartz glass, which itself was placed on a hot plate, but still freely floating in approximately 1 ml of water. The sheet was then manually unfolded and carefully smoothed. The hot plate was heated to 90° C., thus removing the water and leaving the sheet flat on the surface of the quartz. The sheet was then subjected to a UV/Vis/NIR analysis. The reference (blank quartz) was manually subtracted from the spectrum. The spectrum is shown in FIG. 3; this reveals that the sheet is composed of semi-conducting SWNTs.

[0207] Moreover, Raman spectra were recorded, which clearly confirmed that the sheet is composed of semi-conducting SWNTs

Example 2.4

[0208] The separation was carried out in analogy to example 2.1, however the layer containing 43% SPT was omitted and the SPT/PAE1 solutions were neutralized with aqueous NaOH to pH 7 before they were loaded to the centrifugation tubes. Centrifugation resulted in multiple bands at the place one would expect SWCNTs sorted with respect to their density, analogously to prior art separations using Nycodenz gradients. The topmost layer was bluish; the layer below orange.

Example 2.5

[0209] The separation was carried out similarly to example 2.1. However, only one SPT layer was used (25% by weight of SPT), and PAE2 was used as surfactant instead of PAE1. The SPT/PAE2 solution was set to pH 1.9 with HCl. After centrifugation, like in example 2.1, all tubes contained a bluish layer in the top zone of the tubes, a middle zone without any specific color (the color of the SPT solution) and a dark layer at the bottom of the tubes. The bluish fraction was purified in analogy to example 2.1 and analyzed via UV/Vis/NIR. As FIG. 4 shows, essentially no metallic SWNTs are present. Thus, the bluish layer contains virtually only semi-conducting SWNTs.

Example 2.6

[0210] The separation was carried out similarly to example 2.5. However, instead of surfactant PAE2, Tamol® NN9401, a condensation product of 2-naphthylsulfonic acid and formaldehyde from BASF SE, Germany, was used, and the SPT/Tamol solution was set to pH 1.5 with HCl. Here, after centrifugation, the tubes contained a reddish-brown layer in the top zone of the tubes, a middle zone without any specific color (the color of the SPT solution) and a dark layer at the bottom of the tubes. The reddish-brown fraction was purified in analogy to example 2.1 and analyzed with UV/Vis/NIR. The spectra proved that this fraction was significantly depleted of semi-conducting SWNTs and contained essentially metallic SWNTs.

Example 2.7

[0211] The separation was carried out similarly to example 2.6. However, instead of surfactant Tamol® NN9401, Glydol® N1055, a polyarylsulfonate from Zschimmer & Schwarz, Germany, was used. Here, after centrifugation, the tubes contained a reddish layer in the top zone of the tubes, a middle zone without any specific color (the color of the SPT solution) and a dark layer at the bottom of the tubes. The reddish fraction was purified in analogy to example 2.1 and analyzed with UV/Vis/NIR. As FIG. 5 shows, this fraction contains essentially metallic SWNTs.

3. Application Examples

[0212] 3.1 Transistors with Semi-Conducting SWNTs from Example 2.1

[0213] Transistors measurements provide a simple method for performance analysis of the separation of semiconducting SWCNTs from metallic ones. For purely semi-conducting samples, high On/Off ratios are typically observed. On the contrary, metallic impurities limit the On/Off ratio by creating short-circuits, which lead to stable currents that flow between source and drain electrodes; thus decreasing the On/Off ratio.

Drop Casting Nanotubes onto a Si/SiO.sub.2 or Si/Al.sub.2O.sub.3 Wafer

[0214] For the testing the wafers consisting of degenerately doped Si with an insulator (either SiO.sub.2 or Al.sub.2O.sub.3) were equipped with gold contacts by vaporizing gold contacts through shadow masks onto the respective dielectric surface. A shadow mask was used to create multiple possible channels of same length and width to enable a variety of possible channels that can be easily compared. The wafers as produced were cut into 2×2 cm pieces. Drop casting denotes in this context the process of depositing single drops using a 1 ml syringe with needle (Braun 4657519) of the extracted aqueous SWNTs bands (from example 2.1) onto the Si-wafer. To do so, the wafers were placed on a hot plate and heated to approximately 70° C., thus causing the water of the single drops to evaporate slowly (within about 5 min). After each drop and dry step the wafer was dipped into deionized water to eliminate residual surfactant and SPT particles. The wafers were additionally dipped into a beaker with deionized water and dried by placing a piece of drying paper near the surface to lead the water cautiously off the surface. In the following step the wafers were placed back on the hot plate to completely remove remaining trace amounts of water. A percolating network resulted after 0.2 ml had been deposited in a drop-wise manner.

[0215] For all experiments, two opposing gold contacts (channel width: 100 μm channel length: 200 μm) were contacted as source and drain. The Si side of the Si/SiO.sub.2 or Si/A1203 wafer was contacted as the gate electrode. The voltage between source and drain was −1V and the voltage between the channel and the gate was varied between +8 V and −8 V. The mobility was determined to be 1 cm.sup.2/Vs and the On/Off ratio was found to be 5E4 (see FIGS. 6 and 7).

[0216] The characteristic transistor curves are shown in FIGS. 6 and 7. These results confirm that the semi-conducting SWNTs from example 2.1 are highly enriched and suitable as active material in transistor applications.

3.2 Transistors with Semi-Conducting SWNT Sheet from Example 2.2

[0217] The quartz substrate of example 3.1 with the sheet on it was also used for this experiment. Gold contacts were placed on top of the sheet as shown in FIG. 8. 50 nm thick gold contacts were evaporated through a shadow mask onto the SWCNT film to yield a 50 μm long, 1000 μm wide channel. A liquid gate material was placed directly over the channel partially overlapping the metal contacts (FIG. 8). FIGS. 9 and 10 show the transfer and the output curve for different applied voltages between source and drain. From the output curve it can be seen that for higher V.sub.gs the drain current ID saturates at higher V.sub.ds. This can be ascribed to parasitic effects of contact resistance due to the top gate top contact geometry. The overall best performance measured with this transistor was 12.6 cm.sup.2/Vs as mobility and 10E3 as the On/Off ratio using V.sub.ds=−1V.