Browsing by Author "Wei, Nan"

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Colors of Single-Wall Carbon Nanotubes
(2021-02-24) Wei, Nan; Tian, Ying; Liao, Yongping; Komatsu, Natsumi; Gao, Weilu; Lyuleeva-Husemann, Alina; Zhang, Qiang; Hussain, Aqeel; Ding, Er Xiong; Yao, Fengrui; Halme, Janne; Liu, Kaihui; Kono, Junichiro; Jiang, Hua; Kauppinen, Esko I.
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Although single-wall carbon nanotubes (SWCNTs) exhibit various colors in suspension, directly synthesized SWCNT films usually appear black. Recently, a unique one-step method for directly fabricating green and brown films has been developed. Such remarkable progress, however, has brought up several new questions. The coloration mechanism, potentially achievable colors, and color controllability of SWCNTs are unknown. Here, a quantitative model is reported that can predict the specific colors of SWCNT films and unambiguously identify the coloration mechanism. Using this model, colors of 466 different SWCNT species are calculated, which reveals a broad spectrum of potentially achievable colors of SWCNTs. The calculated colors are in excellent agreement with existing experimental data. Furthermore, the theory predicts the existence of many brilliantly colored SWCNT films, which are experimentally expected. This study shows that SWCNTs as a form of pure carbon, can display a full spectrum of vivid colors, which is expected to complement the general understanding of carbon materials.
Direct Synthesis of Colorful Single-Walled Carbon Nanotube Thin Films
(2018-08-08) Liao, Yongping; Jiang, Hua; Wei, Nan; Laiho, Patrik; Zhang, Qiang; Khan, Sabbir A.; Kauppinen, Esko I.
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
In floating catalyst chemical vapor deposition (FC-CVD), tuning chirality distribution and obtaining narrow chirality distribution of single-walled carbon nanotubes (SWCNTs) is challenging. Herein, by introducing various amount of CO2 in FC-CVD using CO as a carbon source, we have succeeded in directly synthesizing SWCNT films with tunable chirality distribution as well as tunable colors. In particular, with 0.25 and 0.37 volume percent of CO2, the SWCNT films display green and brown colors, respectively. We ascribed various colors to suitable diameter and narrow chirality distribution of SWCNTs. Additionally, by optimizing reactor temperature, we achieved much narrower (n,m) distribution clustered around (11,9) with extremely narrow diameter range (>98% between 1.2 and 1.5 nm). We propose that CO2 may affect CO disproportionation and nucleation modes of SWCNTs, resulting in SWCNTs' various diameter ranges. Our work could provide a new route for high-yield and direct synthesis of SWCNTs with narrow chirality distribution and offer potential applications in electronics, such as touch sensors or transistors.
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.
Dual-gated mono-bilayer graphene junctions
(2021-01-21) Du, Mingde; Du, Luojun; Wei, Nan; Liu, Wei; Bai, Xueyin; Sun, Zhipei
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
A lateral junction with an atomically sharp interface is extensively studied in fundamental research and plays a key role in the development of electronics, photonics and optoelectronics. Here, we demonstrate an electrically tunable lateral junction at atomically sharp interfaces between dual-gated mono- and bilayer graphene. The transport properties of the mono–bilayer graphene interface are systematically investigated with Ids–Vds curves and transfer curves, which are measured with bias voltage Vds applied in opposite directions across the asymmetric mono–bilayer interface. Nearly 30% difference between the output Ids–Vds curves of graphene channels measured at opposite Vds directions is observed. Furthermore, the measured transfer curves confirm that the conductance difference of graphene channels greatly depends on the doping level, which is determined by dual-gating. The Vds direction dependent conductance difference indicates the existence of a gate tunable junction in the mono–bilayer graphene channel, due to different band structures of monolayer graphene with zero bandgap and bilayer graphene with a bandgap opened by dual-gating. Simulation of the Ids–Vds curves based on a new numerical model validates the gate tunable junction at the mono–bilayer graphene interface from another point of view. The dual-gated mono–bilayer graphene junction and new protocol for Ids–Vds curve simulation pave a possible way for functional applications of graphene in next-generation electronics.
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.
Immunoassays Based on Hot Electron-Induced Electrochemiluminescence at Disposable Cell Chips with Printed Electrodes
(2019-06-19) Grönroos, Päivi; Nur-E-Habiba, Nur; Salminen, Kalle; Nissinen, Marja; Tuomaala, Tomi; Miikki, Kim; Zhang, Qiang; Wei, Nan; Kauppinen, Esko; Eskola, Jarkko; Härmä, Harri; Kulmala, Sakari
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Novel hot electron-emitting working electrodes and conventional counter electrodes were created by screen printing. Thus, low-cost disposable electrode chips for bioaffinity assays were produced to replace our older expensive electrode chips manufactured by manufacturing techniques of electronics from silicon or on glass chips. The present chips were created by printing as follows: (i) silver lines provided the electronic contacts, counter electrode and the bottom of the working electrode and counter electrode, (ii) the composite layer was printed on appropriate parts of the silver layer, and (iii) finally a hydrophobic ring was added to produce the electrochemical cell boundaries. The applicability of these electrode chips in bioaffinity assays was demonstrated by an immunoassay of human C-reactive protein (i) using Tb(III) chelate label displaying long-lived hot electron-induced electrochemiluminescence (HECL) and (ii) now for the first time fluorescein isothiocyanate (FITC) was utilized as an a low-cost organic label displaying a short-lived HECL in a real-world bioaffinity assay.
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.
Rate-selected growth of ultrapure semiconducting carbon nanotube arrays
(2019-10-02) Zhu, Zhenxing; Wei, Nan; Cheng, Weijun; Shen, Boyuan; Sun, Silei; Gao, Jun; Wen, Qian; Zhang, Rufan; Xu, Jun; Wang, Yao; Wei, Fei
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Carbon nanotubes (CNTs) are promising candidates for smart electronic devices. However, it is challenging to mediate their bandgap or chirality from a vapor-liquid-solid growth process. Here, we demonstrate rate-selected semiconducting CNT arrays based on interlocking between the atomic assembly rate and bandgap of CNTs. Rate analysis confirms the Schulz-Flory distribution which leads to various decay rates as length increases in metallic and semiconducting CNTs. Quantitatively, a nearly ten-fold faster decay rate of metallic CNTs leads to a spontaneous purification of the predicted 99.9999% semiconducting CNTs at a length of 154 mm, and the longest CNT can be 650 mm through an optimized reactor. Transistors fabricated on them deliver a high current of 14 μA μm-1 with on/off ratio around 108 and mobility over 4000 cm2 V-1 s-1. Our rate-selected strategy offers more freedom to control the CNT purity in-situ and offers a robust methodology to synthesize perfectly assembled nanotubes over a long scale.
Suspended superconducting weak links from aerosol-synthesized single-walled carbon nanotubes
(2020-12) Kaikkonen, Jukka Pekka; Sebastian, Abhilash Thanniyil; Laiho, Patrik; Wei, Nan; Will, Marco; Liao, Yongping; Kauppinen, Esko I.; Hakonen, Pertti J.
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
We report a new scheme for fabrication of clean, suspended superconducting weak links from pristine single-walled carbon nanotubes (SWCNT). The SWCNTs were grown using the floating-catalyst chemical vapour deposition (FC-CVD) and directly deposited on top of prefabricated superconducting molybdenum-rhenium (MoRe) electrodes by thermophoresis at nearly ambient conditions. Transparent contacts to SWCNTs were obtained by vacuum-annealing the devices at 900 °C, which enabled proximity-induced supercurrents up to 53 nA. SWCNT weak links fabricated on MoRe/palladium bilayer sustained supercurrents up to 0.4 nA after annealing at relatively low temperature of 220 °C. The fabrication process does neither expose SWCNTs to lithographic chemicals, nor the contact electrodes to the harsh conditions of in situ CVD growth. Our scheme facilitates new experimental possibilities for hybrid superconducting devices. [Figure not available: see fulltext.]
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.
Ultra-Broadband and Electro-Optical Tunable Absorption in Double-Walled Carbon Nanotubes
(2024) Li, Diao; Ahmadi, Mohsen; Zhang, Qiang; Liu, Peng; Xu, Zhenyu; Wei, Nan; Kauppinen, Esko I.; Sun, Zhipei
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Electro-optical modulators are critical elements in the rapidly developing data communication, optical interconnects, silicon-based photonic systems and terahertz technologies. The limited optoelectronic properties and complicated material growth in traditional semiconductors hinder the rapidly surging demand for modulator performance, energy efficiency, cost, etc. The emergence of two-dimensional materials and one-dimensional carbon nanotubes in recent decades has brought new opportunities with their tremendous selection degree of freedom for exceptional optoelectronic properties. In this article, we present ultra-broadband and electro-optical tunable absorption modulators by employing double-walled carbon nanotube films in a capacitor geometry, spanning the visible to terahertz spectra. The formation of supercapacitors around the ionic gel electrolyte and carbon nanotube film interfaces accounts for the large carrier transition and optical conductivity change, which behaves a thickness dependent electroabsorption dynamics. Our findings not only broaden the understanding of low-dimensional material applications in electro-optics but also pave the way for future developments in high-performance broadband modulators.