Browsing by Author "Khan, Abu Taher"

Filter results by typing the first few letters
Now showing 1 - 6 of 6
  • Direct Synthesis of Semiconducting Single-Walled Carbon Nanotubes Toward High-Performance Electronics
    (2023-07) Liu, Peng; Khan, Abu Taher; Ding, Er Xiong; Zhang, Qiang; Xu, Zhenyu; Bai, Xueyin; Wei, Nan; Tian, Ying; Li, Diao; Jiang, Hua; Lipsanen, Harri; Sun, Zhipei; Kauppinen, Esko I.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    The large-scale synthesis of high-purity semiconducting single-walled carbon nanotubes (s-SWCNTs) plays a crucial role in fabricating high-performance and multiapplication-scenario electronics. This work develops a straightforward, continuous, and scalable method to synthesize high-purity and individual s-SWCNTs with small-diameters distribution (≈1 nm). It is believed that the water and carbon dioxide resulting from the decomposition of isopropanol act as oxidizing agents and selectively etch metallic SWCNTs, hence enhancing the production of s-SWCNTs. The performance of individual-SWCNTs field effect transistors confirms the high abundance of s-SWCNTs, presenting a mean mobility of 376 cm2 V−1 s−1 and a high mobility of 2725 cm2 V−1 s−1 with an on-current to off-current (Ion/Ioff) ratio as high as 2.51 × 107. Moreover, thin-film transistors based on the as-synthesized SWCNTs exhibit excellent performance with a mean mobility of 9.3 cm2 V−1 s−1 and Ion/Ioff ratio of 1.3× 105, respectively, verifying the enrichment of s-SWCNTs. This work presents a simple and feasible route for the sustainable synthesis of high-quality s-SWCNTs for electronic devices.
  • Fast and Ultraclean Approach for Measuring the Transport Properties of Carbon Nanotubes
    (2020-01-01) Wei, Nan; Laiho, Patrik; Khan, Abu Taher; Hussain, Aqeel; Lyuleeva, Alina; Ahmed, Saeed; Zhang, Qiang; Liao, Yongping; Tian, Ying; Ding, Er Xiong; Ohno, Yutaka; Kauppinen, Esko I.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    In this work, a fast approach for the fabrication of hundreds of ultraclean field-effect transistors (FETs) is introduced, using single-walled carbon nanotubes (SWCNTs). The synthesis of the nanomaterial is performed by floating-catalyst chemical vapor deposition, which is employed to fabricate high-performance thin-film transistors. Combined with palladium metal bottom contacts, the transport properties of individual SWCNTs are directly unveiled. The resulting SWCNT-based FETs exhibit a mean field-effect mobility, which is 3.3 times higher than that of high-quality solution-processed CNTs. This demonstrates that the hereby used SWCNTs are superior to comparable materials in terms of their transport properties. In particular, the on–off current ratios reach over 30 million. Thus, this method enables a fast, detailed, and reliable characterization of intrinsic properties of nanomaterials. The obtained ultraclean SWCNT-based FETs shed light on further study of contamination-free SWCNTs on various metal contacts and substrates.
  • High-performance single-walled carbon nanotube transparent conducting film fabricated by using low feeding rate of ethanol solution
    (2018-06-18) Ding, Er Xiong; Zhang, Qiang; Wei, Nan; Khan, Abu Taher; Kauppinen, Esko I.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We report floating catalyst chemical vapour deposition synthesis of single-walled carbon nanotubes (SWCNTs) for high-performance transparent conducting films (TCFs) using low feeding rate of precursor solution. Herein, ethanol acts as carbon source, ferrocene and thiophene as catalyst precursor and growth promoter, respectively. By adopting a low feeding rate of 4 μl min-1, the fabricated TCFs present one of the lowest sheet resistances of ca 78Ωsq.-1. at 90% transmittance. Optical characterizations demonstrate that the mean diameter of high-quality SWCNTs is up to 2 nm. Additionally, electron microcopy observations provide evidence that the mean length of SWCNT bundles is as long as 28.4 μm while the mean bundle diameter is only 5.3 nm. Moreover, very few CNT loops can be found in the film. Remarkably, the fraction of individual SWCNTs reaches 24.6%. All those morphology data account for the superior optoelectronic performance of our SWCNT TCFs.
  • Hybrid Low-Dimensional Carbon Allotropes Formed in Gas Phase
    (2020-11-04) Ahmad, Saeed; Mustonen, Kimmo; McLean, Ben; Jiang, Hua; Zhang, Qiang; Hussain, Aqeel; Khan, Abu Taher; Ding, Er Xiong; Liao, Yongping; Wei, Nan; Monazam, Mohammad R.A.; Nasibulin, Albert G.; Kotakoski, Jani; Page, Alister J.; Kauppinen, Esko I.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Graphene, carbon nanotubes (CNTs) and fullerenes are the basic set of low-dimensional carbon allotropes. The latter two arise from the former by selective removal and addition of carbon atoms. Nevertheless, given their morphological disparities, the production of each is typically devised from entirely different starting points. Here, it is demonstrated that all three allotropes can nucleate from (pseudo-)spherical, nanometer-sized transition metal clusters in a gas-suspension when the chemical conditions are favorable. The experimental results indicate that graphitic carbon embryos nucleate on the catalyst particles and sometimes transform into 2D graphene flakes through chain polymerization of carbon fragments forming in the surround gas atmosphere. It is further shown that hydrogenation reactions play an essential role by stabilizing the emerging flakes by mitigating the pentagon and heptagon defects that lead into evolution of fulleroids. Ab initio molecular dynamics simulations show that the ratio of hydrogen to carbon in the reaction is a key growth parameter. Since structural formation takes place in a gas-suspension, graphene accompanied by fullerenes and single-walled CNTs can be deposited on any surface at ambient temperature with arbitrary layer thicknesses. This provides a direct route for the production and deposition of graphene-based hybrid thin films for various applications.
  • Large-Diameter Carbon Nanotube Transparent Conductor Overcoming Performance–Yield Tradeoff
    (2022-03-09) Zhang, Qiang; Nam, Jeong Seok; Han, Jiye; Datta, Sukanta; Wei, Nan; Ding, Er Xiong; Hussain, Aqeel; Ahmad, Saeed; Skakalova, Viera; Khan, Abu Taher; Liao, Yong Ping; Tavakkoli, Mohammad; Peng, Bo; Mustonen, Kimmo; Kim, Dawoon; Chung, In; Maruyama, Shigeo; Jiang, Hua; Jeon, Il; Kauppinen, Esko I.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    The floating catalyst chemical vapor deposition (FCCVD) method for producing single-walled carbon nanotubes (SWNTs) has demonstrated great potential in transparent conductive film (TCF) application. In FCCVD, reducing the concentration of carbon nanotubes (CNTs) is a well-agreed method of improving the conductivity of SWNT TCF, achieved by producing thinner and longer CNT bundles. However, this method decreases the yield dramatically, which has persisted throughout the TCF development. Here, the production of large-diameter double-walled CNT (DWNT) TCFs via FCCVD is reported, which overcomes the tradeoff between performance and yield. These TCFs of DWNTs with an average diameter of approximate to 4 nm have a low sheet resistance of 35 omega sq(-1) at 90% transmittance. The conductivity here aligns with the best-performing SWNT TCFs reported to date, showing a production yield greater than two orders of magnitude. The main factor contributing to the high performance and yield is considered to be the large tube diameter, which greatly improves the yield threshold of CNT bundling and leads to long tube length and unique junctions broadening. Moreover, the application of DWNT TCFs in perovskite solar cells exhibits a power conversion efficiency of 17.4%, which has not been reported yet in indium-free CNT-based solar cells.
  • Towards the synthesis of semiconducting single-walled carbon nanotubes by floating-catalyst chemical vapor deposition: Challenges of reproducibility
    (2022-08-15) Ding, Er Xiong; Liu, Peng; Khan, Abu Taher; Zhang, Qiang; Wei, Nan; Jiang, Hua; Kauppinen, Esko I.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    High-purity semiconducting single-walled carbon nanotubes (s-SWCNTs) are of paramount significance for the fabrication of high-performance electronics. Here, we present continuous production of high-purity, long, and isolated s-SWCNTs by gas-phase synthesis, retaining the pristine morphologies of as-synthesized nanotubes. The s-SWCNTs were synthesized at ca. 920 °C using ethanol and methanol as carbon source and growth enhancer, respectively in N2 and H2. The purity of as-produced s-SWCNTs with a mean length of 15.2 μm can reach 98% as determined by optical absorption spectroscopy. We observed that the overpressure in the reactor and methanol are the principal causes of the enrichment of s-SWCNTs. Specifically, the s-SWCNTs were found to be more negatively charged, and oxygen-contained species play critical roles in the s-SWCNT synthesis. Through the demonstration of field-effect transistors, the s-SWCNTs exhibit a high mean charge carrier mobility of 453.3 cm2 V−1 s−1 which is 2.27 times higher than that of the transistors fabricated with high-quality dispersion-processed SWCNTs. Additionally, we discuss the challenges of synthesis repeatability and recommend a few tips to improve reproducibility. Our study represents an important step towards the scalable production of clean, long, and isolated s-SWCNTs with high purity and narrow bandgap distribution.