Imaging electronic structure of carbon nanotubes by voltage-contrast scanning electron microscopy

Vijayaraghavan, Aravind; Blatt, Sabine; Marquardt, Christoph; Dehm, Simone; Wahi, Rajeev K.; Hennrich, Frank; Krupke, Ralph

doi:10.1007/s12274-008-8034-3

Cited by 29 publications

(37 citation statements)

References 34 publications

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“…Methods for measuring m-SWCNT content can be divided into bulk sample techniques and countingbased techniques. Counting-based techniques more accurately enumerate m-and sc-nanotubes and typically rely on their electrical and/or optical performance [20][21][22][23][24][25][26][27][28][29]. Although these methods give relatively accurate results, they involve tedious fabrication processes and costly instruments.…”

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Raman microscopy mapping for the purity assessment of chirality enriched carbon nanotube networks in thin-film transistors

Ding

Finnie

et al. 2015

Nano Res.

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With recent improvements in carbon nanotube separation methods, the accurate determination of residual metallic carbon nanotubes in a purified nanotube sample is important, particularly for those interested in using semiconducting single-walled carbon nanotubes (SWCNTs) in electronic device applications such as thin-film transistors (TFTs). This work demonstrates that Raman microscopy mapping is a powerful characterization tool for quantifying residual metallic carbon nanotubes present in highly enriched semiconducting nanotube networks. Raman mapping correlates well with absorption spectroscopy, yet it provides greater differentiation in purity. Electrical data from TFTs with channel lengths of 2.5 and 5 μm demonstrate the utility of the method. By comparing samples with nominal purities of 99.0% and 99.8%, a clear differentiation can be made when evaluating the current on/off ratio as a function of channel length, and thus the Raman mapping method provides a means to guide device fabrication by correlating SWCNT network density and purity with TFT channel scaling.As-prepared single-walled corbon nanotube (SWCNT) raw materials contain bundles of nanotubes with a 2:1 semiconducting (sc-) to metallic (m-) ratio and other impurities such as catalysts and amorphous carbon [1][2][3]. For electrical devices, these raw materials must be debundled, purified, and enriched [4][5][6][7][8][9][10][11]. It has been demonstrated that for network thin-film transistors (TFTs), the m-tube content should be less than 2% [3]. For more demanding applications, such as high-frequency logic circuits and display backplanes, the m-tube content should be less than a few ppm given the need for high mobility and high current on/off ratios [12]. In recent years, multiple efforts have led to significant progress in solution-based enrichment techniques, with sc-SWCNT purities in excess of 99% routinely achieved. This leap, however, has now started to reveal the limits of common characterization methods, and other tools are required to provide accurate purity assessment [13,14].Typically, the purity of enriched sc-SWCNTs is Nano Research 2 Nano Res. estimated from the UV absorption spectrum by comparing the peak areas associated with the m-or sc-species [12,[15][16][17]. This method works well for samples whose peaks are well defined and for which background absorption is not dominant. However, as the sc-species purity increases, the features associated with m-tube absorption will gradually disappear and the precise subtraction of the background absorption will dramatically influence the calculated results and introduce uncertainty [18]. As an alternative, we have previously used a different purity metric, denoted as φ, which is based on the ratio of the sc-peak area over the total absorption background from the metallic (M 11 ) and semiconducting (S 22 ) absorption bands [16].Although we presume that φ correlates well with purity for highly pure samples, it does not provide a quantitative assessment. Furthermore, a solution sample is not nece...

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confidence: 99%

Raman microscopy mapping for the purity assessment of chirality enriched carbon nanotube networks in thin-film transistors

Ding

Finnie

et al. 2015

Nano Res.

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“…15 In our devices, this was realized by grounding one of the two metal electrodes. The other electrode remained floating, albeit connected to the grounded electrode by the mSWNT.…”

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Fabrication of carbon nanotube nanogap electrodes by helium ion sputtering for molecular contacts

et al. 2014

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“…3c, it is found that the invisible CNTs in the SEM images are semiconducting ones, which is in consistence with previous studies. 28,[44][45][46][47][48] Obviously, our approach, which is not influenced by the electrical conductivity of the CNTs, provides a more accurate data on the number of the CNTs and represents a valuable complementor of the SEM technique.…”

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confidence: 99%

Volatile-nanoparticle-assisted optical visualization of individual carbon nanotubes and other nanomaterials

et al. 2016

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The development of nanomaterials has put forward high requirements for characterization techniques. Optical microscopy (OM), with easy accessibility and open operating spaces as compared to scanning electron microscopy, is a good choice to quickly locate materials and to be integrated with other equipment. However, OM is limited by its low resolution. Herein, we present a facile and non-destructive approach for optical observation of nanomaterials under conventional OMs with the aid of volatile nanoparticles (NPs), which can be deposited and removed in a controlled manner. The NPs deposited on the surface of nanomaterials render strong light scattering to enable the nanomaterials to become optically visible. For example, this approach enables the observation of individual carbon nanotubes (CNTs) with OMs at low magnification or even with the naked eye. Both supported CNTs on various substrates and suspended CNTs can be observed with this approach. Most importantly, the NPs can be completely removed through moderate heat treatment or laser irradiation, avoiding potential influence on the properties or subsequent applications of nanomaterials. Furthermore, we systematically investigate the deposition of various volatile NPs (up to 14 kinds) for the optical observation of nanomaterials. We also demonstrated the application of this approach on other nanomaterials, including nanowires and graphene. We showed that this approach is facile, controllable, non-destructive, and contamination-free, indicating wide potential applications.

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Imaging electronic structure of carbon nanotubes by voltage-contrast scanning electron microscopy

Cited by 29 publications

References 34 publications

Raman microscopy mapping for the purity assessment of chirality enriched carbon nanotube networks in thin-film transistors

Raman microscopy mapping for the purity assessment of chirality enriched carbon nanotube networks in thin-film transistors

Fabrication of carbon nanotube nanogap electrodes by helium ion sputtering for molecular contacts

Volatile-nanoparticle-assisted optical visualization of individual carbon nanotubes and other nanomaterials

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