Flexible CMOS-Like Circuits Based on Printed P-Type and N-Type Carbon Nanotube Thin-Film Transistors.

P-type and n-type top-gate carbon nanotube thin-film transistors (TFTs) can be selectively and simultaneously fabricated on the same polyethylene terephthalate (PET) substrate by tuning the types of polymer-sorted semiconducting single-walled carbon nanotube (sc-SWCNT) inks, along with low temperature growth of HfO2 thin films as shared dielectric layers. Both the p-type and n-type TFTs show good electrical properties with on/off ratio of ≈105 , mobility of ≈15 cm2 V-1 s-1 , and small hysteresis. Complementary metal oxide semiconductor (CMOS)-like logic gates and circuits based on as-prepared p-type and n-type TFTs have been achieved. Flexible CMOS-like inverters exhibit large noise margin of 84% at low voltage (1/2 Vdd = 1.5 V) and maximum voltage gain of 30 at Vdd of 1.5 V and low power consumption of 0.1 µW. Both of the noise margin and voltage gain are one of the best values reported for flexible CMOS-like inverters at Vdd less than 2 V. The printed CMOS-like inverters work well at 10 kHz with 2% voltage loss and delay time of ≈15 µs. A 3-stage ring oscillator has also been demonstrated on PET substrates and the oscillation frequency of 3.3 kHz at Vdd of 1 V is achieved.

Selective extraction of large-diameter single-wall carbon nanotubes with specific chiral indices by poly(9,9-dioctylfluorene-alt-benzothiadiazole).

Semiconducting single-wall carbon nanotubes (SWCNTs) having large diameters (d(t) > 1.3 nm) are successfully extracted in toluene by fluorene-based polymers. In particular, poly(9,9-dioctylfluorene-alt-benzothiadiazole) shows excellent selectivity for (15,4) SWCNTs. Although the importance of structural matching between the fluorene backbone and the tube surface has already been discussed, the present photoluminescence studies reveal that matching the energy levels between fluorene-based polymers and SWCNTs is crucial for selective nanotube extractions.

Room-temperature Y-type emission of perylenes by encapsulation within single-walled carbon nanotubes.

Fluorescent materials that exhibit large Stokes shifts are useful for suppressing aggregation-caused quenching. Controlling the self-trapped exciton (STE) states in organic dyes with a dimeric structure is one way of tuning Stokes shifts. However, this leads to the spectral broadening of the emissions at room temperature owing to the effects of the surrounding materials on the excited dimers. Here, we demonstrate the effects of confining organic dyes on their optical properties via the encapsulation of perylene molecules within single-walled carbon nanotubes. The encapsulated dimeric perylene exhibits fluorescence with large Stokes shifts and long lifetimes through the STE states. In particular, a noticeable emission of dimeric perylene is observed with a vibronic structure at room temperature; this resembles the Y-type emission of dimeric α-perylene crystals observed only at low temperatures. The results suggest that the isolation of the excited perylene dimers plays an important role in the occurrence of the room-temperature Y-emission.

Near-Infrared Photoluminescence Properties of Endohedral Mono- and Dithulium Metallofullerenes.

The optical properties of endohedral metallofullerene molecules can be tuned by changing the fullerene size as well as the number of metal atoms inside the fullerene cages. In this work we have synthesized and isolated a series of mono- and dithulium metallofullerenes, including Tm@C82 (isomers I, II, III, IV), Tm@C88 (I-IV), Tm2@C82 (I-III), and (Tm2C2)@C82 (I-III). Near-infrared photoluminescence is observed from the thulium metallofullerenes. By changing the number of Tm ion in the fullerene cage, we have found that one can vary and tune the photoluminescence from 1200 to 1300-2000 nm observed for Tm(2+) (4f(13)) in Tm@C88 and Tm(3+) (4f(12)) in (Tm2C2)@C82, respectively. The photoluminescence intensity depends sensitively on the fullerene cages. (Tm2C2)@C82 (III) exhibits the highest photoluminescence intensity among the three structural isomers because of its large HOMO-LUMO energy gap.

Printed thin film transistors and CMOS inverters based on semiconducting carbon nanotube ink purified by a nonlinear conjugated copolymer.

Two innovative research studies are reported in this paper. One is the sorting of semiconducting carbon nanotubes and ink formulation by a novel semiconductor copolymer and second is the development of CMOS inverters using not the p-type and n-type transistors but a printed p-type transistor and a printed ambipolar transistor. A new semiconducting copolymer (named P-DPPb5T) was designed and synthesized with a special nonlinear structure and more condensed conjugation surfaces, which can separate large diameter semiconducting single-walled carbon nanotubes (sc-SWCNTs) from arc discharge SWCNTs according to their chiralities with high selectivity. With the sorted sc-SWCNTs ink, thin film transistors (TFTs) have been fabricated by aerosol jet printing. The TFTs displayed good uniformity, low operating voltage (±2 V) and subthreshold swing (SS) (122-161 mV dec(-1)), high effective mobility (up to 17.6-37.7 cm(2) V(-1) s(-1)) and high on/off ratio (10(4)-10(7)). With the printed TFTs, a CMOS inverter was constructed, which is based on the p-type TFT and ambipolar TFT instead of the conventional p-type and n-type TFTs. Compared with other recently reported inverters fabricated by printing, the printed CMOS inverters demonstrated a better noise margin (74% 1/2 Vdd) and was hysteresis free. The inverter has a voltage gain of up to 16 at an applied voltage of only 1 V and low static power consumption.

Influence of structure-selective fluorene-based polymer wrapping on optical transitions of single-wall carbon nanotubes.

To understand how fluorene-based polymers selectively extract specific semiconducting single-wall carbon nanotubes (SWCNTs), we compared the optical transitions of SWCNTs wrapped with poly(9,9-dioctylfluorene-alt-pyridine) (PFOPy), i.e., structure-selective polymers, with those wrapped with poly(9,9-di-n-dodecylfluorene) (PFD), i.e., non-selective polymers, in organic solvents by using photoluminescence (PL) excitation spectroscopy. Two (n,m) species of PFOPy-wrapped SWCNTs with intermediate chiral angles exhibited blue-shifted emissions compared with the PFD-wrapped SWCNTs. The shifts in the peaks of PL signals cannot be explained in terms of the dielectric screening effect, but can plausibly be explained in terms of the strains of specific SWCNTs due to the PFOPy wrapping. Moreover, the emissions of specific SWCNTs wrapped with PFOPy were not blue-shifted as much when the solvent was changed from toluene to p-xylene, and this result could be accounted for by a change in the rigidity of the fluorene backbone. Moreover, using p-xylene instead of toluene lowered the selectivity of the SWCNT extraction, thereby suggesting the importance of having a rigid fluorene backbone for selective extraction of SWCNTs.

Diameter selective electron transfer from encapsulated ferrocenes to single-walled carbon nanotubes.

The diameter selective photoluminescence quenching of single-walled carbon nanotubes (SWCNTs) is observed upon ferrocene encapsulation, which can be attributed to electron transfer from the encapsulated ferrocenes to the SWCNTs. Interestingly, the dependence of the electron transfer process on the nanotube diameter is governed by the molecular orientation of the ferrocenes in the SWCNT rather than the reduction potentials of the SWCNT.

Selective extraction of semiconducting single-wall carbon nanotubes by poly(9,9-dioctylfluorene-alt-pyridine) for 1.5 µm emission.

For applications in standard optical devices, single-wall carbon nanotubes (SWCNTs) exhibiting emissions near 1500 nm are potentially feasible because silicon semiconductors efficiently transmit the light in this region. However, techniques to extract such semiconducting SWCNTs have not been reported thus far. In this study, using poly(9,9-dioctylfluorene-alt-pyridine) (PFOPy) as a dispersant in organic solvent, we succeeded in selectively dispersing SWCNTs which show near-infrared fluorescence around 1500 nm. On the basis of optical absorption and photoluminescence excitation spectroscopy, we revealed that the outstanding tube-structure preference of PFOPy can be interpreted by a characteristic "wavy" conformation of PFOPy on the tube wall.