Influence of electrostatic interactions on spin-assembled single-walled carbon nanotube networks on amine-functionalized surfaces.
ABSTRACT Preferential interactions between self-assembled monolayers (SAMs) terminated with amine functional groups and single-walled carbon nanotubes (SWNTs) were exploited to produce nanotube networks (SWNTnts) via spin coating. We provide insight into the mechanisms of this system while simultaneously demonstrating a facile approach toward controllable arrays of SWNTnts. The chirality, density, and alignment of the SWNTnt was heavily influenced by adsorption onto amine-functionalized surfaces that were exposed to varying pH solutions, as evidenced by atomic force microscopy (AFM) and Raman spectroscopy. This pH treatment altered the charge density on the surface, allowing for the examination of the contribution from electrostatic interaction to SWNT adsorption and SWNTnt characteristics. Secondary and tertiary amines with methyl substitutions were utilized to confirm that adsorption and chirality specific adsorption is largely due to the nitrogen lone pair, not the neighboring hydrogen atoms. Thus, the nature of adsorption is predominantly electrostatic and not due to van der Waals forces or localized polarization on the SWNTs. Moreover, the overall density of SWNTnts is different for the various amines, indicating that the accessibility to the lone pair electrons on the nitrogen plays a crucial role in SWNT adsorption. With greater understanding of the amine-SWNT interaction, these findings can be utilized to control SWNTnt formation for the precise integration into electronic devices.
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ABSTRACT: The large-scale application of semiconducting single walled carbon nanotubes (s-SWCNTs) for printed electronics requires scalable, repeateable, as well as non-contaminating, assembly techniques. Previously explored nanotube deposition methods include serial methods such as inkjet printing and parallel methods such as spin coating with photolithography. The serial methods are usually slow while the photolithography-related parallel methods result in contamination of the nanotubes. In this paper, we report a reliable clean parallel method for fabrication of arrays of carbon nanotube-based field effect transistors (CNTFETs) involving shadow mask patterning of a passivating layer of Hafnium oxide (HfO(2)) over the nanotube (CNT) active channel regions and plasma etching of the unprotected nanotubes. Pure (99%) semiconducting SWCNTs are first sprayed over the entire surface of a wafer substrate followed by a two-step shadow masking procedure to first deposit metal electrodes and then a HfO(2) isolation/passivation layer over the device channel region. The exposed SWCNT network outside the HfO(2) protected area is removed with oxygen plasma etching. The HfO(2) thus serves as both the device isolation mask during the plasma etching and as a protective passivating layer in subsequent use. The fabricated devices on SiO(2)/Si substrate exhibit good device performance metrics, with on/off ratio ranging from 1x10(1) to 3x10(5) and mobilities of 4 to 23 cm(2)/V-s. The HfO(2)/Si devices show excellent performance with on/off ratios of 1x10(2) to 2x10(4) and mobilities of 8 to 56 cm(2)/V-s. The optimum devices (on HfO(2)/Si) have on/off ratio of 10(4) and mobility as high as 46 cm(2)/V-s. This HfO(2)-based patterning method enables large scale fabrication of CNTFETs with no resist residue or other contamination on the device channel. Further, shadow masking circumvents the need for expensive and area-limited lithography patterning process. The device channel is also protected from external environment by the HfO(2) film and the passivated device shows similar (or slightly improved) performance after 300-day exposure to ambient conditions.ACS Applied Materials & Interfaces 11/2012; 4(12). DOI:10.1021/am302431e · 5.90 Impact Factor
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ABSTRACT: Photoelectric heat effect induce instability on the negative bias temperature illumination stress for InGaZnO thin film transistors Appl. Phys. Lett. 101, 253502 (2012) Thin film transistors based on zinc nitride as a channel layer for optoelectronic devices Appl. Phys. Lett. 101, 253501 (2012) Flicker noise in n-channel nanoscale tri-gate fin-shaped field-effect transistors Appl. Phys. Lett. 101, 243512 (2012) Effect of H and OH desorption and diffusion on electronic structure in amorphous In-Ga-Zn-O metal-oxide-semiconductor diodes with various gate insulators We study the impact of thermal boundary conductance (TBC) at carbon nanotube (CNT)-substrate interfaces and CNT junctions on power dissipation and breakdown in CNT network based thin film transistors (CN-TFTs). Comparison of our results from an electro-thermal transport model of CN-TFTs to experimental measurements of power dissipation and temperature profiles allows us to estimate the average CNT-SiO 2 TBC as g $ 0.16 Wm À1 K À1 and the TBC at CNT junctions as G C $ 2.4 pWK À1 . We find the peak power dissipation in CN-TFTs is more strongly correlated to the TBC of the CNT-substrate interface than to the TBC at CNT junctions. Molecular dynamics simulations of crossed CNT junctions also reveal that the top CNT is buckled over $30 nm lengths, losing direct contact with the substrate and creating highly localized hot-spots. Our results provide new insights into CNT network properties which can be engineered to enhance performance of CN-TFTs for macro and flexible electronics applications. V C 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4767920]Journal of Applied Physics 12/2012; 112:124506. DOI:10.1063/1.4767920 · 2.19 Impact Factor
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ABSTRACT: Four custom-designed bidentate adsorbates having either ammonium or Boc-protected amino termini and either methanethiol or ethanethioate headgroups were prepared for the purpose of generating amine-terminated self-assembled monolayers (SAMs) on evaporated gold surfaces. These adsorbates utilize a phenyl-based framework to connect the headgroups to a single hexadecyloxy chain, extending the amino functionality away from the surface of gold, providing two regions within the adsorbate structure where intermolecular interactions contribute to the stability of the fully formed thin film. The structural features of the resulting SAMs were characterized by ellipsometry, X-ray photoelectron spectroscopy, and polarization modulation infrared reflection-absorption spectroscopy. The collected data were compared to those of eight additional SAMs formed from analogous monodentate alkanethiols and alkanethioacetates having either a similar aromatic framework or a simple alkyl chain connecting the headgroup to the tailgroup. Analysis of the data obtained for the full set of SAMs revealed that both the tailgroup and headgroup influenced the formation of a well-packed monolayer, with the Boc-protected amine-terminated alkanethiols producing films with superior surface bonding and adsorbate packing as compared to those formed with ammonium tailgroups or alkanethioacetate headgroups. Comparison of the structural differences before and after deprotection of the Boc-protected amine-terminated thiolate SAMs revealed that the bidentate adsorbate was the most resistant to desorption during the Boc-deprotection procedure. Furthermore, solution-phase thermal desorption tests performed to evaluate the thermal stability of the Boc-deprotected amine-terminated alkanethiolate films provided further evidence of the enhanced stability associated with SAMs formed from these bidentate adsorbates.Langmuir 01/2015; 31(7). DOI:10.1021/la5044359 · 4.38 Impact Factor