The as-grown vertically aligned single-wall carbon nanotube (SWNT) arrays are transferred from the original silicon substrate to a poly(ethylene terephthalate) (PET) substrate, which acts as a stamp. Thin SWNT films can be applied from the stamp to the target substrate and subsequently treated by an ultrasonic process to reduce their thickness to 6.6 nm. The transferred SWNT thin film retains the advantageous super-alignment and high-density properties of the vertical SWNT arrays. The linear density, transmittance, and square resistance of the thin film are as high as 15 tubes per micrometer, 99% at 550 nm, and 16 kΩ, respectively.
To improve the therapeutic efficacy of anticancer agents and extend their application, mussel-inspired chemical modifications have attracted considerable attention. Surface modification based on polydopamine (PDA) has been a facile and versatile method to immobilize biomolecules on substrates for targeted drug delivery. To better analyze pharmaceutical differences between PDA-based surface modification and traditional synthesis methods, we prepared two kinds of folate (FA)-targeted nanoparticles (NPs) loaded with paclitaxel (PTX). The resultant PTX-PDA-FA NPs and PTX-FA NPs represented PDA and synthesis strategies, respectively. PTX-PDA-FA NPs and PTX-FA NPs have been characterized. The particle size of PTX-PDA-FA NPs was smaller than that of PTX-FA NPs. The two kinds of NPs both exhibited long-rod morphology, good colloidal stability and sustained slow drug release. Cytotoxicityin vitrowas evaluated, and antitumor efficacy was investigated against 4T1 tumor-bearing mice. The tumor targeting therapeutic index of PTX-PDA-FA NPs and PTX-FA NPs showed equivalent superior specificity compared to nontargeted groups, which indicated that FA successfully attached to the surface of NPs by the PDA method and that the antitumor effect was equivalent to that of FA-modified NPs prepared by the chemical synthesis method. These results further indicated that PDA, as a simple and effective chemical surface modification platform, could be developed and applied in targeted delivery systems.
We focused on controlling the diameter of single-walled carbon nanotubes (SWNTs) by controlling the ferritin catalyst diameter using reactive ion etching (RIE). The average diameter of ferritin decreased by about 26.5% upon RIE treatment, which resulted in the decrease of the mean diameter of the SWNTs by about 34% with a small diameter distribution. This was demonstrated by both atomic force microscopic and Raman spectroscopic measurements. We found that the current on/off ratio of the SWNT thin film transistors was significantly improved after the catalyst treatment. It was estimated that the purity of the semiconducting SWNT also increased from 58.8 to 92.4%.
The often observed p-type conduction of single carbon nanotube field-effect transistors is usually attributed to the Schottky barriers at the metal contacts induced by the work function differences or by the doping effect of the oxygen adsorption when carbon nanotubes are exposed to air, which cause the asymmetry between electron and hole injections. However, for carbon nanotube thin-film transistors, our contrast experiments between oxygen doping and electrostatic doping demonstrate that the doping-generated transport barriers do not introduce any observable suppression of electron conduction, which is further evidenced by the perfect linear behavior of transfer characteristics with the channel length scaling. On the basis of the above observation, we conclude that the environmental adsorbates work by more than simply shifting the Fermi level of the CNTs; more importantly, these adsorbates cause a poor gate modulation efficiency of electron conduction due to the relatively large trap state density near the conduction band edge of the carbon nanotubes, for which we further propose quantitatively that the adsorbed oxygen–water redox couple is responsible.
We derived an analytical expression based on the Pao-Sah theory to characterize the electric conduction of ambipolar graphene transistors. We included and solved exactly the contact resistance, thermal excitation of carrier density, quantum capacitance, and the velocity saturation effect. Our model agreed with the experimental results for ion-gel gated graphene transistors. The microscopic conduction behavior was calculated and proved to be helpful for understanding the weak current saturation observed because of the “kink effect.” To achieve a high voltage gain for radio-frequency or analog circuit applications, the carrier velocity should be facilitated to reach saturation before the formation of the minimal carrier point inside the channel, which can be realized by decreasing the channel length and the series contact resistance. Given a finite channel length and the series contact resistance, the optimized gate capacitance can be solved analytically. Considering state-of-the-art device parameters, we find that maintaining a low contact resistance is vital for further improvement of the device performance.
'/%3e%3cuse xlink:href='%23a' transform='rotate(23.036 .093 25.536)'/%3e%3cuse xlink:href='%23a' transform='rotate(45.87 1.273 16.18)'/%3e%3cuse xlink:href='%23a' transform='rotate(69.945 .996 12.078)'/%3e%3cuse xlink:href='%23a' transform='rotate(20.66 -19.689 31.932)'/%3e%3c/svg%3e)
