Efficient n-Doping and Hole Blocking in Single-Walled Carbon

Subscriber access provided by Washington University | Libraries

Article

Efficient n-Doping and Hole-Blocking in Single-Walled Carbon Nanotube Transistors with 1,2,4,5-Tetrakis(tetramethyl-guanidino)benzene Severin Schneider, Maximilian Brohmann, Roxana Lorenz, Yvonne J. Hofstetter, Marcel Rother, Eric Sauter, Michael Zharnikov, Yana Vaynzof, Hans-Joerg Himmel, and Jana Zaumseil ACS Nano, Just Accepted Manuscript • DOI: 10.1021/acsnano.8b02061 • Publication Date (Web): 22 May 2018 Downloaded from http://pubs.acs.org on May 22, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Nano

Efficient n-Doping and Hole-Blocking in SingleWalled Carbon Nanotube Transistors with 1,2,4,5Tetrakis(tetramethyl-guanidino)benzene

Severin Schneider1, Maximilian Brohmann1, Roxana Lorenz2, Yvonne J. Hofstetter3,4, Marcel Rother1, Eric Sauter1, Michael Zharnikov1, Yana Vaynzof3,4, Hans-Jörg Himmel2 and Jana Zaumseil1,4* 1

Institute for Physical Chemistry, Universität Heidelberg, D-69120 Heidelberg, Germany

2

Institute for Inorganic Chemistry, Universität Heidelberg, D-69120 Heidelberg, Germany

3

Kirchhoff-Institute for Physics, Universität Heidelberg, D-69120 Heidelberg, Germany

4

Centre for Advanced Materials, Universität Heidelberg, D-69120 Heidelberg, Germany

KEYWORDS. Single-walled carbon nanotube, n-type, doping, guanidino-functionalized aromatic compound, field-effect transistor, complementary inverter

1 ACS Paragon Plus Environment

ACS Nano 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 24

ABSTRACT Efficient, stable and solution-based n-doping of semiconducting single-walled carbon nanotubes (SWCNTs) is highly desired for complementary circuits but remains a significant challenge. Here we present 1,2,4,5-tetrakis(tetramethyl-guanidino)benzene (ttmgb) as a strong two-electron donor that enables the fabrication of purely n-type SWCNT field-effect transistors (FETs). We apply ttmgb to networks of monochiral, semiconducting (6,5) SWCNTs that show intrinsic ambipolar behavior in bottom-contact/top-gate FETs and obtain unipolar n-type transport with 3 to 5 fold enhancement of electron mobilities (approx. 10 cm2V-1s-1), while completely suppressing hole currents, even at high drain voltages. These n-type FETs show excellent on/off current ratios of up to 108, steep subthreshold swings (80 – 100 mV/dec) and almost no hysteresis. Their excellent device characteristics stem from the reduction of the work function of the gold electrodes via contact doping, blocking of hole injection by ttmgb2+ on the electrode surface and removal of residual water from the SWCNT network by ttmgb protonation. The ttmgb-treated SWCNT FETs also display excellent environmental stability under bias stress in ambient conditions. Complementary inverters based on n- and p-doped SWCNT FETs exhibit rail-to-rail operation with high gain and low power dissipation. The simple and stable ttmgb molecule thus serves as an example for the larger class of guanidinofunctionalized aromatic (GFA) compounds as promising electron donors for high performance thin film electronics.


Page 3 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Nano

Networks of purely semiconducting single-walled carbon nanotubes (SWCNTs) are an ideal material for thin film transistors. They are solution-processable, printable, chemically stable, mechanically flexible and even stretchable while maintaining high charge-carrier mobilities for fast switching and large drive currents.1,2 The problem of separating semiconducting from metallic nanotubes in dispersion has been solved over the last few years using various methods such as density gradient ultracentrifugation,3 gel-chromatography,4 aqueous two-phase separation5 and highly-selective dispersion with conjugated polymers.6 The purity of thin films of semiconducting SWCNTs is nowadays sufficiently high7-9 to rival the performance parameters of conventional inorganic semiconductors10 and to enable digital logic,11 radiofrequency circuits and highly flexible electronics.12,13 However, for complementary and low power digital circuits, the intrinsically ambipolar (both hole and electron) charge transport properties of SWCNTs remain a significant drawback. Typically, only purely p-type or n-type transistors with high on/off current ratios are desired, which, in conventional inorganic electronics, can be easily obtained by doping the semiconductor. While p-type SWCNT transistors can be attained rather easily by exposure to air and are frequently used for circuits,14 in combination with, for example, semiconducting metal oxides (ZnO, IGZO) as the corresponding n-type transistors,15,16 stable and reliable n-doping of SWCNTs remains very challenging. Moreover, efficient n-doping of SWCNTs is important not only for transistor applications, but also for their potential use as thermoelectric materials.17,18 Common strategies for n-doping include doping by alkali metals,19 polyethylene imine,20 ethanolamine,21 silicon nitride,22 deposition of certain metal oxides,23 low work function electrodes (e.g., Sc or Y) 24 and a number of electron-donating small molecules such as NADH,25 viologen,26 dimethyldihydro-1H-benzoimidazole

(DMBI)

derivatives,27

or

metallocene

compounds.28,29

Unfortunately, all of these n-doping methods suffer from at least one of the following drawbacks: high cost, insufficient air stability of the dopant or final device during operation, 3 ACS Paragon Plus Environment

ACS Nano 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 4 of 24

limited carrier concentration modulation or undesired onset voltage shifts. Often the hole current is not fully suppressed, i.e., the device maintains its ambipolar nature, albeit with shifted onset voltages, or the on/off current ratio and current modulation suffer as a result of degenerate doping. As a strategy to overcome these issues that have so far prevented the general application of n-type SWCNT transistors in complementary circuits, we present guanidino-functionalized aromatic compounds (GFAs) as an alternative class of highly efficient n-dopants for SWCNTs. GFAs are known as strong organic electron donors.30,31 Reversible oxidation leads to a stable cation with charge delocalization across the extended π-system. Originally developed to be used as highly versatile redox-active ligands for transition metals32,33 and as redox catalysts,34 GFAs are highly alkaline and strong reducing agents. Due to their multistage redox behavior they are also being considered for use as high charge capacity materials for organic batteries.31 The synthesis of most GFAs is inexpensive, easy and scalable. Many of them are fairly stable and can even be handled in air for short periods of time. Moreover, the modification of the guanidino-groups or the aromatic core facilitates fine-tuning of their redox potentials.30 In this work, we treat ambipolar networks of polymer-sorted (6,5) SWCNTs with the GFA compound 1,2,4,5-tetrakis(tetramethyl-guanidino)benzene (ttmgb)35 (Figure 1) to obtain purely n-type field-effect transistors with fully suppressed hole injection/transport, excellent on/off current ratios, a 3- to 5-fold increase of the electron mobility compared to untreated reference samples, a steep subthreshold swing and excellent stability even under extended bias stress in ambient conditions. We fabricate truly complementary inverters, which show full railto-rail operation with high gain and very low power dissipation. The origins of the observed impact of the ttmgb treatment on device performance are investigated and revealed by ultraviolet photoemission spectroscopy (UPS).


Page 5 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Nano

RESULTS AND DISCUSSION The focus of this study lies on the modification of ambipolar SWCNT network FETs to achieve unipolar electron transport, i.e. pure n-type behavior. As shown in Figure 1a, networks of polymer-sorted (6,5) SWCNTs (see Methods and Supporting Information, Figure S1) with a linear density of (11.5 ± 2.5) µm-1 served as the active semiconducting layer in topgate/bottom-contact transistors with a hybrid dielectric of poly(methyl methacrylate) (PMMA) and HfOx (Figure 1b) as previously demonstrated.36,37

Figure 1. Device geometry and dopant. (a) Representative atomic force micrograph of a sparse (6,5) SWCNT network; inset: structure of a (6,5) SWCNT. (b) Schematic device layout of a SWCNT FET with dopant ttmgb (red). (c) Molecular structure of ttmgb and reversible twoelectron transfer to form ttmgb2+.

When processed in dry nitrogen, this type of nanotube transistor always exhibits the intrinsic ambipolar transport characteristics of semiconducting SWCNTs, which leads to poor on/off current ratios at high source-drain bias even when no metallic nanotubes are present. These ambipolar transistors can only be fully turned off at very low drain voltages (Vd). To accomplish the conversion from ambipolar to purely n-type behavior, we applied ttmgb (Figure 1c) as a 5 ACS Paragon Plus Environment

ACS Nano 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 24

dopant. The entire substrate with gold electrodes and nanotube network was dipped into a ttmgb solution in anhydrous toluene followed by annealing at 150 °C before the dielectric and gate electrode were added (for details see Methods). The dopant ttmgb is a strongly reducing and highly alkaline GFA compound. Its alkalinity facilitates a quick and efficient deprotonation of any trace amounts of water that are typically present on polar substrates (e.g., glass) and difficult to remove only by annealing. As shown previously, ttmgb is also an excellent twoelectron donor forming a dication (ttmgb2+) after oxidation. The first oxidation potential as measured by cyclic voltammetry in acetonitrile (vs. Fc/Fc+) is -0.69 V.30, 35 Figure 2a shows representative transfer characteristics of a transistor (channel length L = 40 µm, channel width W = 5 mm) with an untreated (6,5) SWCNT network. It features fairly balanced transport of holes and electrons. The current hysteresis can be attributed to the presence of adsorbed water on the polar glass substrate, which gives rise to shallow trap states.38,39 An identical but ttmgb-treated sample shows drastically different behavior, as demonstrated in Figure 2b. There is no detectable hole current (i.e., above the gate leakage current) even at large negative gate voltages (Vg = -5 V) and large positive drain voltages (Vd = +4 V). The drain current in the electron accumulation regime shows a very steep increase (subthreshold slope of (94 ± 6) mV/dec) with an onset voltage close to 0 V. It is noteworthy that the high on-current and complete off-state even at high drain voltages lead to on/off current ratios of 107 for transistors with L = 40 µm and up to 2·108 for L = 20 µm. There is almost no current hysteresis.


Page 7 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Nano

Figure 2. Device characteristics with and without doping. (a) Transfer curves of an untreated (6,5) SWCNT network FET as reference at low (Vd = 0.1 V) and high (Vd = 4.0 V) drain voltages (L = 40 µm, W = 5 mm). (b) Transfer curves of a ttmgb-treated (6,5) SWCNT network FET (cttmgb = 2.5 g·L-1). (c) Corresponding output characteristics. (d) Electron mobility (linear and saturation) of untreated reference and ttmgb-treated samples for three different dopant concentrations. Error bars indicate standard deviation for at least 8 devices.

Figure 2c shows the corresponding output characteristics for the ttmgb-treated transistor with nearly textbook-like unipolar behavior including a linear current increase at low drain voltages and current saturation for high drain voltages, without visible hysteresis. The extracted electron mobility values are shown in Figure 2d (linear and saturation regime, average values from 8 devices per substrate) without and with ttmgb-treatment at different concentrations (1.5 to 2.5 g·L-1). For all tested concentrations the electron mobility is 3 to 5 times higher after ttmgbtreatment as compared to the untreated reference samples, reaching values of (10 ± 2) cm2V-1s-1. In all cases, linear and saturation mobilities are very similar. These excellent device characteristics place ttmgb-treated (6,5) SWCNT FETs close to state-of-theart metal oxide n-type transistors40 and would be suitable, for example, for active-matrix OLED display backplanes that require high drive currents and high on/off ratios.41 7 ACS Paragon Plus Environment

ACS Nano 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 8 of 24

As shown in Figure 2b, the ttmgb-treatment suppresses the hole current without creating undesired threshold shifts or high off-currents due to degenerate n-doping. The impact of the ttmgb, however, strongly depends on its optimized concentration in the toluene solution. Low concentrations (3 mg·mL-1) result in onset voltage shifts toward negative gate voltages. At very high concentrations the SWCNT network becomes degenerately doped with high conductivity and limited gate modulation. While this doping regime is not useful for FETs, it is desired for thermoelectric applications of SWCNTs.18 The near-ideal n-type characteristics of ttmgb-treated SWCNT network transistors raise questions about the underlying mechanism, which is clearly different from previously reported n-dopants. We could quickly disprove the unlikely notion that charge transport may occur directly through the ttmgb. FETs with only a ttmgb layer as the semiconductor did not show any charge transport. Next, we wanted to exclude that electron-density transfer by the four guanidino groups of the ttmgb - acting as Lewis bases - was responsible for the observed device characteristics after ttmgb-treatment. Electron transfer by the free electron pair of the nitrogen is considered to be the primary doping mechanism when using ethanolamine or polyethyleneimine as n-dopants for SWCNT networks.21, 42


Page 9 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Nano

Figure 3. Reference samples and contact resistance. (a) Transfer characteristics of a tetramethylguanidine (Me4G)-treated (6,5) SWCNT network FET. (b) Transfer characteristics of a hexahydropyrimido-pyrimidine (hpp)-treated (6,5) SWCNT network FET. (c) Direct comparison of the gate-voltage-dependent contact resistance in the electron accumulation regime of an untreated reference (6,5) SWCNT (black) and a ttmgb-treated (blue) FET as determined by the gated four point probe measurements (inset: schematic electrode layout).

To disprove this possible mechanism, we fabricated SWCNT transistors treated with tetramethylguanidin (Figure 3a) and hexahydropyrimidopyrimidine (Figure 3b), which contain guanidine structures very similar to ttmgb. Both are also highly alkaline and strong Lewis bases but cannot act as direct electron donors except via the free electron pair of the amine groups. In both cases the hole current decreased to some degree, while the electron current increased compared to the untreated nanotube networks (see Supporting Information, Discussion and Figure S3). A threshold voltage shift for electron transport toward negative gate voltages was also evident. However, even at very high concentrations no exclusive n-type behavior was observed. Consequently, the origin for the modification of charge transport in SWCNT


ACS Nano 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 24

transistors with ttmgb cannot be solely attributed to its Lewis base character and must be related to its ability to fully donate two electrons to form ttmgb2+. One of the common methods for obtaining n-type SWCNT transistors is the use of low work function (WF) electrodes (e.g., Sc) that favor electron injection over hole injection.12, 43 For (6,5) nanotubes with a bandgap of ~1.27 eV, the injection barriers for holes and electrons from gold are roughly equal and lead to measurable, but ohmic contact resistance. The gate voltagedependent contact resistance in a field-effect transistor can be measured directly using a gated four-point probe geometry (see Figure 3c) with voltage probes (VP1 and VP2) within the active channel.44 For untreated (6,5) SWCNT transistors with gold electrodes we found a contact resistance (for electrons) in the on-state (Vg = 5.0 V) of 3.6·104 Ω·cm. For ttmgb-treated devices, this value dropped by two orders of magnitude to just 4.0·102 Ω·cm. This drastically lowered contact resistance must be the result of significantly improved electron injection (i.e., lower injection barrier), which might be achieved by contact doping and thus a substantially reduced work function of the gold electrodes. A lower work function would likewise impede hole injection. To understand the impact of ttmgb treatment on the energetic alignment between the gold electrodes and SWCNT network, we performed UPS measurements. The work function of all samples was calculated from the secondary photoemission onset (Figure 4a) and the highest occupied molecular orbital (HOMO) position was obtained from the low binding energy edge of the valence band45 (Figure 4b). The energies of all unoccupied states were derived from the corresponding UV-VIS-nIR absorption spectroscopy data. Solvent-cleaned gold electrodes gave a typical WF of 4.7 eV. Depositing the SWCNT network on the electrodes resulted in a 0.5 eV hole injection barrier and a corresponding ~0.7 eV electron injection barrier, consistent with the ambipolar device characteristics of the untreated FETs. Upon treatment with ttmgb the WF of the gold was drastically reduced to 3.5 eV. This decrease in work function was 10 ACS Paragon Plus Environment

Page 11 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Nano

further corroborated by Kelvin probe measurements of untreated and ttmgb-treated gold, which showed a WF reduction of 0.6 eV. We interpret this decrease in work function as arising from an interfacial dipole pointing away from the ttmgb molecule. This dipole can be attributed to a corresponding ground state electron charge transfer from the ttmgb molecule to the Au substrate (i.e. contact doping).

Figure 4. (a) Secondary photoemission onset spectra and (b) valance band spectra of Au, CNTs/Au, ttmgb on gold (already oxidized due to electron transfer to gold, ttmgb*) and ttmgb2+ samples. (c) Summary of the energy level diagrams obtained from the UPS measurements.

Unexpectedly, the measured ionization potential of ttmgb on gold was found to be 5.0 eV, which is not in agreement with the HOMO of a strong electron donor. Based on the interfacial dipole and the donor strength of ttmgb, we believe that this value does not represent the HOMO energy of ttmgb, but rather that electron transfer to the gold has already taken place and we observe HOMO-1, i.e. the HOMO of ttmgb2+. The value is consistent with cyclic voltammetry data of ttmgb30 and was further corroborated by UPS measurements on ttmgb-bishexafluorophoshate (i.e., a ttmgb2+ salt), which resulted in a similar ionization potential value of 5.05 eV. These data may also serve as an explanation for the absence of hole injection and 11 ACS Paragon Plus Environment

ACS Nano 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 24

transport for the ttmgb-treated FETs. With an energy difference of 1.5 eV between the gold electrodes and the HOMO of ttmgb2+, the latter serves as a highly efficient hole blocker, suppressing hole injection and transport in the SWCNT network. The energy level diagrams obtained from these measurements are summarized in Figure 4c. Finally, the substantial decrease in hysteresis and significant increase of electron mobility upon ttmgb treatment of the SWCNT network is highly interesting. Typically, the presence of water or hydroxyl groups on polar substrate surfaces (e.g. glass or SiO2) is suspected to be the origin of electron traps and hysteresis in carbon nanotube transistors.46,47 A complete removal of water and passivation of electron traps would thus facilitate faster electron transport and suppress hysteresis. The ttmgb may saturate all remaining electron traps via electron donation and its reaction with any residual water on the surface via protonation would also eliminate this source of potential trap sites. Overall, at optimum concentration the ttmgb treatment improves electron injection into the SWCNT network by contact doping of the gold electrodes, the formed ttmgb2+ efficiently blocks hole injection and potential electron trap states in the channel are neutralized by reaction with ttmgb. We conclude that the combination of these three factors leads to the excellent n-type transistor characteristics for ttmgb-treated (6,5) nanotube networks. Only at higher ttmgb concentrations actual n-doping of the SWCNTs takes place, leading to threshold shifts and overall higher conductivity.


Page 13 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Nano

Figure 5. Complementary inverters. (a) Single sweep voltage transfer characteristics of a complementary inverter based on ttmgb-treated n-type SWCNT FET and (Mo(tfd-COCF3)3) treated p-type SWCNT FET (inset: inverter circuit diagram). (b) Corresponding gains at different supply voltages (VDD).

To demonstrate the applicability of the ttmgb-treated n-type nanotube FETs in circuits, we fabricated complementary inverters by connecting a p-type and n-type transistor of equal channel length and width as shown in the inset of Figure 5a. The SWCNT p-type transistors were fabricated identically to the n-type FETs, but using molybdenum tris(1-(trifluoroacetyl)2-(trifluoromethyl)ethane-1,2-dithiolene) (Mo(tfd-COCF3)3) as a molecular p-dopant48 for the carbon nanotube networks (see Supporting Information, Figure S4a). The inverter characteristics depicted in Figure 5a show full rail-to-rail operation with gains of up to 52 (Figure 5b) depending on the supply voltage (VDD). At a supply voltage of 1.0 V (gain = 18), the maximum power consumption during switching reached a very low value of just 45 nW 13 ACS Paragon Plus Environment

ACS Nano 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 24

(see Supporting Information, Figure S4b). Molecular p- and n-doping of SWCNT networks is thus a useful platform for fabrication of complementary circuits with low power dissipation. Furthermore, environmental stability is one of the key challenges for n-type SWCNT FETs. The bottom-contact/top-gate device geometry with a bilayer dielectric of PMMA/HfOx already provides very good self-encapsulation as shown previously.49 However, to test environmental stability under bias stress conditions, we measured the ttmgb-treated FETs in ambient atmosphere in their on-state for several hours. Figure 6a shows transfer characteristics (saturation regime) before and after ten hours of continuous bias stress (Vd = 1.0 V, Vg = 4.0 V) in air. A direct comparison of these two curves shows that there is virtually no change in transistor performance (hysteresis, subthreshold swing, mobility) except a slight onset voltage shift toward negative gate voltages by about 0.4 V, which leads to an increase of the on-current at Vg = 4.0 V by a factor of 1.6 (Figure 6b). However, this shift is fully reversible after letting the sample rest in air without bias (see Supporting Information, Figure S5). This excellent stability against bias stress for the ttmgb-treated SWCNT network transistors rules out any undesired dopant diffusion or degradation and further highlights the suitability of these n-type nanotube FETs for practical device operation and circuit applications.


Page 15 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Nano

Figure 6. Environmental stability. (a) Transfer characteristics of a ttmgb-treated (6,5) SWCNT network FET (cttmgb = 2.5 g·L-1) in saturation regime before (red line) and after (orange line) 10 hours of continuous bias stress (Vd = 1.0 V, Vg = 4.0 V) in air. (b) Change of drain current in on-state over time during bias stress measurement.

CONCLUSION In summary, we have introduced the GFA compound ttmgb as an efficient n-dopant for semiconducting SWCNT networks that enables unipolar n-type SWCNT transistors with excellent on/off current ratios, high electron mobility, steep subthreshold slopes and a complete suppression of hole injection/transport. We have shown that contact doping of the gold electrodes by the ttmgb plays a key role in reducing the injection barrier for electrons while the formation of ttmgb2+ blocks the injection of holes. The removal of electron traps (water etc.) 15 ACS Paragon Plus Environment

ACS Nano 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 24

within the channel by the ttmgb leads to hysteresis-free current-voltage characteristics that are very stable against bias stress even under ambient conditions. Complementary inverters based on p-doped and n-doped nanotube FETs with full rail-to-rail operation and low power dissipation exemplify the application potential of this n-doping concept. The application of the n-dopant ttmgb and other tailored GFA compounds in field-effect transistors and in thermoelectric devices is highly promising not only in the context of other types of semiconducting SWCNTs, but also for other functional materials such as semiconducting polymers and monolayered inorganic semiconductors.

MATERIALS & METHODS Preparation of SWCNT Dispersions. As previously described,50,51 SWCNTs were selectively dispersed from CoMoCAT raw material (Chasm Advanced Materials, SG65i-L58, 0.38 mg mL-1) by shear-force mixing (Silverson L2/Air, 10,230 rpm, 72 hours) with poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt-co-(6,6’)-(2,2’-bipyridine)] (PFO-BPy, American Dye Source, Mw = 34 kg mol-1, 0.5 g L-1) in toluene. Subsequently, the dispersion was centrifuged at 60,000 g (Beckman Coulter Avanti J26XP centrifuge) for 30 min and the supernatant was collected. This process was repeated several times. The supernatant was then passed through a PTFE membrane filter (Merck Millipore, JGWP, 0.1 µm pore size) to obtain a (6,5) SWCNT filter cake. Excess polymer was removed by washing with hot (80 °C) toluene. The filter cake was redispersed in pure toluene (1 mL) by bath sonication for 30 min at 20 °C. For spin-coating, the concentration was adjusted to an absorbance of 3.0 (1 cm path length) at the E11 absorption of (6,5) SWCNTs. For aerosol jet printing (AJP) with an Optomec Inc. Aerosol Jet 200 printer (200 μm inner diameter nozzle, ultrasonic atomizer) the dispersion was diluted to an absorbance at the E11 transition (at 997 nm) of 2.0 and 5 vol% of terpineol were added as described previously.36


Page 17 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Nano

Dopants. 1,2,4,5-tetrakis(tetramethyl-guanidino)benzene (ttmgb) was synthesized and purified as described previously;35 the colorless crystals were stored in dry nitrogen. Solutions of ttmgb in anhydrous toluene were prepared immediately before application. Tetramethylguanidine (99 %) was purchased from ACROS and was used without further purification. Hexahydropyrimido-pyrimidine (hpp) was purchased from Sigma Aldrich and sublimated at 100 °C under vacuum before use. FET Fabrication. Interdigitated source-drain electrodes (L = 40 µm, W = 5 mm) were patterned on AF32eco Thin Glass (SCHOTT AG) by standard photolithography combined with electron-beam evaporation of chromium (2 nm) and gold (30 nm) followed by lift-off in Nmethyl-2-pyrrolidone. SWCNT dispersions were spin-coated at 2000 rpm for 30 s with subsequent annealing at 100 °C (3 times). After rinsing with tetrahydrofuran and isopropanol, the films were patterned using standard photolithography and oxygen plasma etching. After the substrates were annealed at 300 °C for 30 min in dry nitrogen the respective dopant was applied by dipping the substrates in solutions of anhydrous toluene for 20 min followed by an annealing step (see Supporting Information, Table S1). Spin-coating of 6 g L−1 PMMA (syndiotactic poly(methyl methacrylate), Polymer Source, Mw = 350 kg mol−1) in n-butyl acetate at 4000 rpm for 60 s and atomic layer deposition of HfOx (Ultratech Savannah S100) with tetrakis(dimethylamino)-hafnium precursor (Strem Chemicals Inc.) yielded a hybrid dielectric with layer thicknesses of 11 nm (PMMA) and 61 nm (HfOx).49 Thermal evaporation of silver (30 nm) gate electrodes completed the devices. Inverters were obtained by connecting n-type and p-type transistors of equal channel length and width. Characterization. Ultraviolet Photoemission Spectroscopy. Substrates were prepared by evaporation of chromium (5 nm) and gold (50 nm) on silicon (with native oxide). Films were produced by spin-coating (ttmgb, ttmgb(PF6)2) in a dry nitrogen glovebox, (6,5) SWNT were aerosol-jet 17 ACS Paragon Plus Environment

ACS Nano 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 24

printed using an Aerosol Jet 200 printer (Optomec Inc., for details see Supporting Information, Table S2). Samples were transferred into an ultrahigh vacuum chamber (ESCALAB 250Xi) without exposure to air for UPS measurements. The measurements were performed using a He I photon line (hν = 21.22 eV) of a double-differentially pumped He discharge lamp with an analyzer pass energy of 2 eV. Kelvin Probe. Work function measurements were carried out using a Kelvin Probe 2001 system (KP technology Ltd., U.K.) in an ultrahigh vacuum chamber (∼10−8 mbar). Freshly sputtered gold and 1-hexadecanethiol self-assembled monolayers on gold were used as references. AFM. Atomic force micrographs were recorded with a Bruker Dimension Icon atomic force microscope in tapping mode. Electrical Characterization. Current-Voltage characteristics were measured in dry nitrogen (for environmental stability measurements also in ambient air) with an Agilent 4155C semiconductor parameter analyzer. The device capacitance was determined using an impedance spectrometer (ModuLab XM MTS System, Solartron Analytical). Measurements were conducted at 1.0 kHz and the maximum capacitance was extracted in the on-state (+5 V). Charge carrier mobilities were calculated from the linear regime at Vd = 0.1 V and for the saturation regime at Vd = 4.0 V. Contact resistances were determined from gated four-pointprobe measurements (L = 40 µm, W = 1 mm, pair of voltage probes with channel positions LP1 = 6 µm, LP2 = 34 µm and probe widths WP1 = WP2 = 4 µm). In order to evaluate environmental stability, transfer curves were measured before and after subjecting a device to continuous bias stress at Vd = 1.0 V and Vg = 4.0 V for 10 hours in ambient air.


Page 19 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Nano

ASSOCIATED CONTENT Supporting Information. UV-vis-nIR absorption and Raman spectra of (6,5) SWCNT dispersions/filter cakes, transfer characteristics of ttmgb-treated (6,5) SWCNT network FETs for ttmgb concentration range from 0.1 to 10 g·L-1; comparison of charge carrier mobilities and threshold voltages of ttmgb to non-redox active bases; transfer characteristics of a p-type SWCNT FET and power consumption of inverter; reversibility of onset voltage shift; experimental details on annealing and UPS sample fabrication (PDF).

AUTHOR INFORMATION Corresponding Author *[email protected] ORCID Jana Zaumseil: 0000-0002-2048-217X Yana Vaynzof: 0000-0002-0783-0707 Michael Zharnikov: 0000-0002-3708-7571

ACKNOWLEDGMENT This research was funded by the Deutsche Forschungsgemeinschaft via the Collaborative Research Center “N-Heteropolycycles as Functional Materials” (SFB 1249, B03, C04, C06).


ACS Nano 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 24

REFERENCES (1) Zaumseil, J., Single-Walled Carbon Nanotube Networks for Flexible and Printed Electronics. Semicond. Sci. Technol. 2015, 30, 074001. (2) Cao, Y.; Cong, S.; Cao, X.; Wu, F.; Liu, Q.; Amer, M. R.; Zhou, C., Review of Electronics Based on Single-Walled Carbon Nanotubes. Top. Curr. Chem. 2017, 375, 75. (3) Arnold, M. S.; Green, A. A.; Hulvat, J. F.; Stupp, S. I.; Hersam, M. C., Sorting Carbon Nanotubes by Electronic Structure Using Density Differentiation. Nat. Nanotechnol. 2006, 1, 60-65. (4) Liu, H.; Nishide, D.; Tanaka, T.; Kataura, H., Large-Scale Single-Chirality Separation of Single-Wall Carbon Nanotubes by Simple Gel Chromatography. Nat. Commun. 2011, 2, 309. (5) Fagan, J. A.; Khripin, C. Y.; Silvera Batista, C. A.; Simpson, J. R.; Hároz, E. H.; Hight Walker, A. R.; Zheng, M., Isolation of Specific Small-Diameter Single-Wall Carbon Nanotube Species via Aqueous Two-Phase Extraction. Adv. Mater. 2014, 26, 2800-2804. (6) Nish, A.; Hwang, J. Y.; Doig, J.; Nicholas, R. J., Highly Selective Dispersion of Singlewalled Carbon Nanotubes Using Aromatic Polymers. Nat. Nanotechnol. 2007, 2, 640646. (7) Derenskyi, V.; Gomulya, W.; Gao, J.; Bisri, S. Z.; Pasini, M.; Loo, Y.-L.; Loi, M. A., Semiconducting Swnts Sorted by Polymer Wrapping: How Pure Are They? Appl. Phys. Lett. 2018, 112, 072106. (8) Noh-Hwal, P.; Seung-Hoon, L.; Seung-Hyeon, J.; Dongyoon, K.; Yun Ho, K.; Sungmi, Y.; Yong-Young, N.; Jang-Joo, K., Heterostructured Semiconductor Single-Walled Carbon Nanotube Films for Solution-Processed High-Performance Field-Effect Transistors. Semicond. Sci. Technol. 2018, 33, 035017. (9) Ji, D.; Lee, S.-H.; Noh, Y.-Y., Selective Dispersion of High-Purity Semiconducting Carbon Nanotubes Using Indacenodithiophene-Based Conjugated Polymer. Appl. Phys. Lett. 2018, 112, 033103. (10) Brady, G. J.; Way, A. J.; Safron, N. S.; Evensen, H. T.; Gopalan, P.; Arnold, M. S., Quasi-Ballistic Carbon Nanotube Array Transistors with Current Density Exceeding Si and GaAs. Sci. Adv. 2016, 2, e1601240. (11) Tulevski, G. S.; Franklin, A. D.; Frank, D.; Lobez, J. M.; Cao, Q.; Park, H.; Afzali, A.; Han, S.-J.; Hannon, J. B.; Haensch, W., Toward High-Performance Digital Logic Technology with Carbon Nanotubes. ACS Nano 2014, 8, 8730-8745. (12) Zhang, H.; Xiang, L.; Yang, Y.; Xiao, M.; Han, J.; Ding, L.; Zhang, Z.; Hu, Y.; Peng, L.-M., High-Performance Carbon Nanotube Complementary Electronics and Integrated Sensor Systems on Ultrathin Plastic Foil. ACS Nano 2018, 12, 2773–2779. (13) Wang, C.; Chien, J.-C.; Takei, K.; Takahashi, T.; Nah, J.; Niknejad, A. M.; Javey, A., Extremely Bendable, High-Performance Integrated Circuits Using Semiconducting Carbon 20 ACS Paragon Plus Environment

Page 21 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Nano

Nanotube Networks for Digital, Analog, and Radio-Frequency Applications. Nano Lett. 2012, 12, 1527-1533. (14) Cong, S.; Cao, Y.; Fang, X.; Wang, Y.; Liu, Q.; Gui, H.; Shen, C.; Cao, X.; Kim, E. S.; Zhou, C., Carbon Nanotube Macroelectronics for Active Matrix Polymer-Dispersed Liquid Crystal Displays. ACS Nano 2016, 10, 10068–10074. (15) Chen, H.; Cao, Y.; Zhang, J.; Zhou, C., Large-Scale Complementary Macroelectronics Using Hybrid Integration of Carbon Nanotubes and IGZO Thin-Film Transistors. Nature Comm. 2014, 5, 4097. (16) Kim, B.; Jang, S.; Geier, M. L.; Prabhumirashi, P. L.; Hersam, M. C.; Dodabalapur, A., High-Speed, Inkjet-Printed Carbon Nanotube/Zinc Tin Oxide Hybrid Complementary Ring Oscillators. Nano Lett. 2014, 14, 3683-3687. (17) Brownlie, L.; Shapter, J., Advances in Carbon Nanotube n-Type Doping: Methods, Analysis and Applications. Carbon 2018, 126, 257-270. (18) Blackburn, J. L.; Ferguson, A. J.; Cho, C.; Grunlan, J. C., Carbon-Nanotube-Based Thermoelectric Materials and Devices. Adv. Mater. 30, 1704386. (19) Derycke, V.; Martel, R.; Appenzeller, J.; Avouris, P., Controlling Doping and Carrier Injection in Carbon Nanotube Transistors. Appl. Phys. Lett. 2002, 80, 2773-2775. (20) Shim, M.; Javey, A.; Shi Kam, N. W.; Dai, H., Polymer Functionalization for Air-Stable n-Type Carbon Nanotube Field-Effect Transistors. J. Am. Chem. Soc. 2001, 123, 11512-11513. (21) Xu, Q.; Zhao, J.; Pecunia, V.; Xu, W.; Zhou, C.; Dou, J.; Gu, W.; Lin, J.; Mo, L.; Zhao, Y.; Cui, Z., Selective Conversion from p-Type to n-Type of Printed Bottom-Gate Carbon Nanotube Thin-Film Transistors and Application in Complementary Metal-OxideSemiconductor Inverters. ACS Appl. Mater. Interfaces 2017, 9, 12750-12758. (22) Ha, T.-J.; Chen, K.; Chuang, S.; Yu, K. M.; Kiriya, D.; Javey, A., Highly Uniform and Stable n-Type Carbon Nanotube Transistors by Using Positively Charged Silicon Nitride Thin Films. Nano Lett. 2014, 15, 392-397. (23) Zhang, J.; Wang, C.; Fu, Y.; Che, Y.; Zhou, C., Air-Stable Conversion of Separated Carbon Nanotube Thin-Film Transistors from p-Type to n-Type Using Atomic Layer Deposition of High-k Oxide and Its Application in CMOS Logic Circuits. ACS Nano 2011, 5, 3284-3292. (24) Ding, L.; Wang, S.; Zhang, Z.; Zeng, Q.; Wang, Z.; Pei, T.; Yang, L.; Liang, X.; Shen, J.; Chen, Q.; Cui, R.; Li, Y.; Peng, L.-M., Y-Contacted High-Performance n-Type SingleWalled Carbon Nanotube Field-Effect Transistors: Scaling and Comparison with Sc-Contacted Devices. Nano Lett. 2009, 9, 4209-4214. (25) Kang, B. R.; Yu, W. J.; Kim, K. K.; Park, H. K.; Kim, S. M.; Park, Y.; Kim, G.; Shin, H. J.; Kim, U. J.; Lee, E. H., Restorable Type Conversion of Carbon Nanotube Transistor Using Pyrolytically Controlled Antioxidizing Photosynthesis Coenzyme. Adv. Funct. Mater. 2009, 19, 2553-2559. 21 ACS Paragon Plus Environment

ACS Nano 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 24

(26) Lee, S. Y.; Lee, S. W.; Kim, S. M.; Yu, W. J.; Jo, Y. W.; Lee, Y. H., Scalable Complementary Logic Gates with Chemically Doped Semiconducting Carbon Nanotube Transistors. ACS Nano 2011, 5, 2369-2375. (27) Wang, H.; Wei, P.; Li, Y.; Han, J.; Lee, H. R.; Naab, B. D.; Liu, N.; Wang, C.; Adijanto, E.; Tee, B. C.-K., Tuning the Threshold Voltage of Carbon Nanotube Transistors by n-Type Molecular Doping for Robust and Flexible Complementary Circuits. Proc. Natl. Acad. Sci. U. S. A. 2014, 111, 4776-4781. (28) Geier, M. L.; Moudgil, K.; Barlow, S.; Marder, S. R.; Hersam, M. C., Controlled nType Doping of Carbon Nanotube Transistors by an Organorhodium Dimer. Nano Lett. 2016, 16, 4329-4334. (29) Fukumaru, T.; Fujigaya, T.; Nakashima, N., Development of n-Type CobaltoceneEncapsulated Carbon Nanotubes with Remarkable Thermoelectric Property. Sci. Rep. 2015, 5, 7951. (30) Eberle, B.; Hübner, O.; Ziesak, A.; Kaifer, E.; Himmel, H. J., What Makes a Strong Organic Electron Donor (or Acceptor)? Chem. Eur. J. 2015, 21, 8578-90. (31) Eberle, B.; Kaifer, E.; Himmel, H.-J., A Stable Hexakis(Guanidino)Benzene: Realization of the Strongest Neutral Organic Four-Electron Donor. Angew. Chem. Int. Ed. 2017, 56, 3360-3363. (32) Eberle, B.; Damjanović, M.; Enders, M.; Leingang, S.; Pfisterer, J.; Krämer, C.; Hübner, O.; Kaifer, E.; Himmel, H.-J., Radical Monocationic Guanidino-Functionalized Aromatic Compounds (GFAs) as Bridging Ligands in Dinuclear Metal Acetate Complexes: Synthesis, Electronic Structure, and Magnetic Coupling. Inorg. Chem. 2016, 55, 1683-1696. (33) Wiesner, S.; Wagner, A.; Kaifer, E.; Himmel, H. J., A Valence Tautomeric Dinuclear Copper Tetrakisguanidine Complex. Chem. Eur. J. 2016, 22, 10438-10445. (34) Wild, U.; Schön, F.; Himmel, H. J., Oxidation of Organic Molecules with a Redox‐ Active Guanidine Catalyst. Angew. Chem. Int. Ed. 2017, 56, 16410-16413. (35) Peters, A.; Kaifer, E.; Himmel, H.-J., 1,2,4,5-Tetrakis(Tetramethylguanidino)Benzene: Synthesis and Properties of a New Molecular Electron Donor. Eur. J. Org. Chem. 2008, 2008, 5907-5914. (36) Rother, M.; Brohmann, M.; Yang, S.; Grimm, S. B.; Schießl, S. P.; Graf, A.; Zaumseil, J., Aerosol-Jet Printing of Polymer-Sorted (6,5) Carbon Nanotubes for Field-Effect Transistors with High Reproducibility. Adv. Electron. Mater. 2017, 3, 1700080. (37) Schießl, S. P.; Fröhlich, N.; Held, M.; Gannott, F.; Schweiger, M.; Forster, M.; Scherf, U.; Zaumseil, J., Polymer-Sorted Semiconducting Carbon Nanotube Networks for HighPerformance Ambipolar Field-Effect Transistors. ACS Appl. Mater. Interfaces 2015, 7, 682689. (38) Kim, W.; Javey, A.; Vermesh, O.; Wang, Q.; Li, Y.; Dai, H., Hysteresis Caused by Water Molecules in Carbon Nanotube Field-Effect Transistors. Nano Lett. 2003, 3, 193-198. 22 ACS Paragon Plus Environment

Page 23 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Nano

(39) Schießl, S. P.; Rother, M.; Lüttgens, J.; Zaumseil, J., Extracting the Field-Effect Mobilities of Random Semiconducting Single-Walled Carbon Nanotube Networks: A Critical Comparison of Methods. Appl. Phys. Lett. 2017, 111, 193301. (40) Petti, L.; Münzenrieder, N.; Vogt, C.; Faber, H.; Büthe, L.; Cantarella, G.; Bottacchi, F.; Anthopoulos, T. D.; Tröster, G., Metal Oxide Semiconductor Thin-Film Transistors for Flexible Electronics. Appl. Phys. Rev. 2016, 3, 021303. (41) Nathan, A.; Striakhilev, D.; Chaji, R.; Ashtiani, S.; Lee, C.-H.; Sazonov, A.; Robertson, J.; Milne, W., Backplane Requirements for Active Matrix Organic Light Emitting Diode Displays. Mater. Res. Soc. Symp. Proc. 2011, 910, 0910-A16-01-L09-01. (42) Zhou, Y.; Gaur, A.; Hur, S.-H.; Kocabas, C.; Meitl, M. A.; Shim, M.; Rogers, J. A., pChannel, n-Channel Thin Film Transistors and p−n Diodes Based on Single Wall Carbon Nanotube Networks. Nano Lett. 2004, 4, 2031-2035. (43) Yang, Y.; Ding, L.; Han, J.; Zhang, Z.; Peng, L.-M., High-Performance Complementary Transistors and Medium-Scale Integrated Circuits Based on Carbon Nanotube Thin Films. ACS Nano 2017, 11, 4124-4132. (44) Richards, T. J.; Sirringhaus, H., Analysis of the Contact Resistance in Staggered, TopGate Organic Field-Effect Transistors. J. Appl. Phys. 2007, 102, 094510. (45) Kahn, A.; Koch, N.; Gao, W., Electronic Structure and Electrical Properties of Interfaces between Metals and Π-Conjugated Molecular Films. J. Polym. Sci., Part B: Polym. Phys. 2003, 41, 2529-2548. (46) Aguirre, C. M.; Levesque, P. L.; Paillet, M.; Lapointe, F.; St‐Antoine, B. C.; Desjardins, P.; Martel, R., The Role of the Oxygen/Water Redox Couple in Suppressing Electron Conduction in Field‐Effect Transistors. Adv. Mater. 2009, 21, 3087-3091. (47) Kim, W.; Javey, A.; Vermesh, O.; Wang, O.; Li, Y. M.; Dai, H. J., Hysteresis Caused by Water Molecules in Carbon Nanotube Field-Effect Transistors. Nano Lett. 2003, 3, 193198. (48) Qi, Y.; Sajoto, T.; Kröger, M.; Kandabarow, A. M.; Park, W.; Barlow, S.; Kim, E.-G.; Wielunski, L.; Feldman, L. C.; Bartynski, R. A.; Brédas, J.-L.; Marder, S. R.; Kahn, A., A Molybdenum Dithiolene Complex as p-Dopant for Hole-Transport Materials: A Multitechnique Experimental and Theoretical Investigation. Chem. Mat. 2010, 22, 524-531. (49) Held, M.; Schießl, S. P.; Miehler, D.; Gannott, F.; Zaumseil, J., Polymer/Metal Oxide Hybrid Dielectrics for Low Voltage Field-Effect Transistors with Solution-Processed, HighMobility Semiconductors. Appl. Phys. Lett. 2015, 107, 083301. (50) Graf, A.; Zakharko, Y.; Schießl, S. P.; Backes, C.; Pfohl, M.; Flavel, B. S.; Zaumseil, J., Large Scale, Selective Dispersion of Long Single-Walled Carbon Nanotubes with High Photoluminescence Quantum Yield by Shear Force Mixing. Carbon 2016, 105, 593-599. (51) Ozawa, H.; Ide, N.; Fujigaya, T.; Niidome, Y.; Nakashima, N., One-Pot Separation of Highly Enriched (6,5)-Single-Walled Carbon Nanotubes Using a Fluorene-Based Copolymer. Chem. Lett. 2011, 40, 239-241. 23 ACS Paragon Plus Environment

ACS Nano 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Table of Contents Figure 344x174mm (143 x 143 DPI)

ACS Paragon Plus Environment

Page 24 of 24

Efficient n-Doping and Hole Blocking in Single-Walled Carbon

Recommend Documents