Ultrahigh density alignment of carbon nanotube arrays by dielectrophoresis.
TL;DR: The ultrahigh density alignment of aligned single-walled carbon nanotube (SWNT) two-dimensional arrays via AC dielectrophoresis using high-quality surfactant-free and stable SWNT solutions will have important implications in fabricating high- quality devices for digital and analog electronics.
Abstract: We report ultrahigh density assembly of aligned single-walled carbon nanotube (SWNT) two-dimensional arrays via AC dielectrophoresis using high-quality surfactant-free and stable SWNT solutions. After optimization of frequency and trapping time, we can reproducibly control the linear density of the SWNT between prefabricated electrodes from 0.5 SWNT/μm to more than 30 SWNT/μm by tuning the concentration of the nanotubes in the solution. Our maximum density of 30 SWNT/μm is the highest for aligned arrays via any solution processing technique reported so far. Further increase of SWNT concentration results in a dense array with multiple layers. We discuss how the orientation and density of the nanotubes vary with concentrations and channel lengths. Electrical measurement data show that the densely packed aligned arrays have low sheet resistances. Selective removal of metallic SWNTs via controlled electrical breakdown produced field-effect transistors with high current on−off ratio. Ultrahigh density alignmen...
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TL;DR: There are a number of challenges yet to overcome to optimize the processing and performance of CNT-based flexible electronics; nonetheless, CNTs remain a highly suitable candidate for various flexible electronic applications in the near future.
Abstract: Flexible electronics offer a wide-variety of applications such as flexible circuits, flexible displays, flexible solar cells, skin-like pressure sensors, and conformable RFID tags. Carbon nanotubes (CNTs) are a promising material for flexible electronics, both as the channel material in field-effect transistors (FETs) and as transparent electrodes, due to their high intrinsic carrier mobility, conductivity, and mechanical flexibility. In this feature article, we review the recent progress of CNTs in flexible electronics by describing both the processing and the applications of CNT-based flexible devices. To employ CNTs as the channel material in FETs, single-walled carbon nanotubes (SWNTs) are used. There are generally two methods of depositing SWNTs on flexible substrates—transferring CVD-grown SWNTs or solution-depositing SWNTs. Since CVD-grown SWNTs can be highly aligned, they often outperform solution-processed SWNT films that are typically in the form of random network. However, solution-based SWNTs can be printed at a large-scale and at low-cost, rendering them more appropriate for manufacturing. In either case, the removal of metallic SWNTs in an effective and a scalable manner is critical, which must still be developed and optimized. Nevertheless, promising results demonstrating SWNT-based flexible circuits, displays, RF-devices, and biochemical sensors have been reported by various research groups, proving insight into the exciting possibilities of SWNT-based FETs. In using carbon nanotubes as transparent electrodes (TEs), two main strategies have been implemented to fabricate highly conductive, transparent, and mechanically compliant films—superaligned films of CNTs drawn from vertically grown CNT forests using the “dry-drawing” technique and the deposition or embedding of CNTs onto flexible or stretchable substrates. The main challenge for CNT based TEs is to fabricate films that are both highly conductive and transparent. These CNT based TEs have been used in stretchable and flexible pressure, strain, and chemical and biological sensors. In addition, they have also been used as the anode and cathode in flexible light emitting diodes, solar cells, and supercapacitors. In summary, there are a number of challenges yet to overcome to optimize the processing and performance of CNT-based flexible electronics; nonetheless, CNTs remain a highly suitable candidate for various flexible electronic applications in the near future.
1,036 citations
TL;DR: An extensive review of carbon nanomaterials in electronic, optoelectronic, photovoltaic, and sensing devices with a particular focus on the latest examples based on the highest purity samples is presented.
Abstract: In the last three decades, zero-dimensional, one-dimensional, and two-dimensional carbon nanomaterials (i.e., fullerenes, carbon nanotubes, and graphene, respectively) have attracted significant attention from the scientific community due to their unique electronic, optical, thermal, mechanical, and chemical properties. While early work showed that these properties could enable high performance in selected applications, issues surrounding structural inhomogeneity and imprecise assembly have impeded robust and reliable implementation of carbon nanomaterials in widespread technologies. However, with recent advances in synthesis, sorting, and assembly techniques, carbon nanomaterials are experiencing renewed interest as the basis of numerous scalable technologies. Here, we present an extensive review of carbon nanomaterials in electronic, optoelectronic, photovoltaic, and sensing devices with a particular focus on the latest examples based on the highest purity samples. Specific attention is devoted to each class of carbon nanomaterial, thereby allowing comparative analysis of the suitability of fullerenes, carbon nanotubes, and graphene for each application area. In this manner, this article will provide guidance to future application developers and also articulate the remaining research challenges confronting this field.
958 citations
TL;DR: The advantages and challenges for incorporating nanomaterials into transistors to improve performance are discussed in the context of different transistor applications, along with the breakthroughs needed to enable the next generation of technological advancement.
Abstract: For more than 50 years, silicon transistors have been continuously shrunk to meet the projections of Moore's law but are now reaching fundamental limits on speed and power use. With these limits at hand, nanomaterials offer great promise for improving transistor performance and adding new applications through the coming decades. With different transistors needed in everything from high-performance servers to thin-film display backplanes, it is important to understand the targeted application needs when considering new material options. Here the distinction between high-performance and thin-film transistors is reviewed, along with the benefits and challenges to using nanomaterials in such transistors. In particular, progress on carbon nanotubes, as well as graphene and related materials (including transition metal dichalcogenides and X-enes), outlines the advances and further research needed to enable their use in transistors for high-performance computing, thin films, or completely new technologies such as flexible and transparent devices.
471 citations
IBM1
TL;DR: This review examines the potential performance advantages of a CNT-based computing technology, outlines the remaining challenges, and describes the recent progress on these fronts.
Abstract: The slow-down in traditional silicon complementary metal-oxide–semiconductor (CMOS) scaling (Moore’s law) has created an opportunity for a disruptive innovation to bring the semiconductor industry into a postsilicon era. Due to their ultrathin body and ballistic transport, carbon nanotubes (CNTs) have the intrinsic transport and scaling properties to usher in this new era. The remaining challenges are largely materials-related and include obtaining purity levels suitable for logic technology, placement of CNTs at very tight (∼5 nm) pitch to allow for density scaling and source/drain contact scaling. This review examines the potential performance advantages of a CNT-based computing technology, outlines the remaining challenges, and describes the recent progress on these fronts. Although overcoming these issues will be challenging and will require a large, sustained effort from both industry and academia, the recent progress in the field is a cause for optimism that these materials can have an impact on fut...
270 citations
Cites methods from "Ultrahigh density alignment of carb..."
...In 2011, Shekhar et al.71 demonstrated a CNT density of 30 CNT/μm, the highest reported to that date with any solution-based method (Figure 9a c)....
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...In 2011, Shekhar et al.(71) demonstrated a CNT density of 30 CNT/μm, the highest reported to that date with any solution-based method (Figure 9a c)....
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261 citations
References
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Book•
01 Jan 1998
TL;DR: In this paper, an introductory textbook for graduate students and researchers from various fields of science who wish to learn about carbon nanotubes is presented, focusing on the basic principles behind the physical properties and giving the background necessary to understand the recent developments.
Abstract: This is an introductory textbook for graduate students and researchers from various fields of science who wish to learn about carbon nanotubes. The field is still at an early stage, and progress continues at a rapid rate. This book focuses on the basic principles behind the physical properties and gives the background necessary to understand the recent developments. Some useful computational source codes which generate coordinates for carbon nanotubes are also included in the appendix.
5,055 citations
"Ultrahigh density alignment of carb..." refers background in this paper
...S ingle-walled carbon nanotubes (SWNTs) are considered tobeapromisingbuilding block for future digital and analog electronic circuits due to their exceptional electronic properties.(1,2) Electron transport measure-...
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TL;DR: It is shown that contacting semiconducting single-walled nanotubes by palladium, a noble metal with high work function and good wetting interactions with nanotube, greatly reduces or eliminates the barriers for transport through the valence band of nanot tubes.
Abstract: A common feature of the single-walled carbon-nanotube field-effect transistors fabricated to date has been the presence of a Schottky barrier at the nanotube–metal junctions1,2,3. These energy barriers severely limit transistor conductance in the ‘ON’ state, and reduce the current delivery capability—a key determinant of device performance. Here we show that contacting semiconducting single-walled nanotubes by palladium, a noble metal with high work function and good wetting interactions with nanotubes, greatly reduces or eliminates the barriers for transport through the valence band of nanotubes. In situ modification of the electrode work function by hydrogen is carried out to shed light on the nature of the contacts. With Pd contacts, the ‘ON’ states of semiconducting nanotubes can behave like ohmically contacted ballistic metallic tubes, exhibiting room-temperature conductance near the ballistic transport limit of 4e2/h (refs 4–6), high current-carrying capability (∼25 µA per tube), and Fabry–Perot interferences5 at low temperatures. Under high voltage operation, the current saturation appears to be set by backscattering of the charge carriers by optical phonons. High-performance ballistic nanotube field-effect transistors with zero or slightly negative Schottky barriers are thus realized.
3,126 citations
"Ultrahigh density alignment of carb..." refers background in this paper
...5 kΩ).(3,4) One of the main challenges in nano-...
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IBM1
TL;DR: This work reviews the progress that has been made with carbon nanotubes and, more recently, graphene layers and nanoribbons and suggests that it could be possible to make both electronic and optoelectronic devices from the same material.
Abstract: The semiconductor industry has been able to improve the performance of electronic systems for more than four decades by making ever-smaller devices. However, this approach will soon encounter both scientific and technical limits, which is why the industry is exploring a number of alternative device technologies. Here we review the progress that has been made with carbon nanotubes and, more recently, graphene layers and nanoribbons. Field-effect transistors based on semiconductor nanotubes and graphene nanoribbons have already been demonstrated, and metallic nanotubes could be used as high-performance interconnects. Moreover, owing to the excellent optical properties of nanotubes it could be possible to make both electronic and optoelectronic devices from the same material.
2,274 citations
"Ultrahigh density alignment of carb..." refers background in this paper
...S ingle-walled carbon nanotubes (SWNTs) are considered tobeapromisingbuilding block for future digital and analog electronic circuits due to their exceptional electronic properties.(1,2) Electron transport measure-...
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TL;DR: In this article, a carbon nanotube transistors with channel lengths exceeding 300 microns have been fabricated, where the carrier transport is diffusive and the channel resistance dominates the transport.
Abstract: Semiconducting carbon nanotube transistors with channel lengths exceeding 300 microns have been fabricated. In these long transistors, carrier transport is diffusive and the channel resistance dominates the transport. Transport characteristics are used to extract the field-effect mobility (79 000 cm2/Vs) and estimate the intrinsic mobility (>100 000 cm2/Vs) at room temperature. These values exceed those for all known semiconductors, which bodes well for application of nanotubes in high-speed transistors, single- and few-electron memories, and chemical/biochemical sensors.
1,510 citations
"Ultrahigh density alignment of carb..." refers background in this paper
...5 kΩ).(3,4) One of the main challenges in nano-...
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TL;DR: Dense, perfectly aligned arrays of long, perfectly linear SWNTs are reported as an effective thin-film semiconductor suitable for integration into transistors and other classes of electronic devices, representing a route to large-scale integrated nanotube electronics.
Abstract: †Single-walled carbon nanotubes (SWNTs) have many exceptional electronic properties. Realizing the full potential of SWNTs in realistic electronic systems requires a scalable approach to device and circuit integration. We report the use of dense, perfectly aligned arrays of long, perfectly linear SWNTs as an effective thin-film semiconductor suitable for integration into transistors and other classes of electronic devices. The large number of SWNTs enable excellent device-level performance characteristics and good device-to-device uniformity, even with SWNTs that are electronically heterogeneous. Measurements on p- and n-channel transistors that involve as many as 2,100 SWNTs reveal device-level mobilities and scaled transconductances approaching 1,000 cm 2 V 21 s 21 and 3,000 S m 21 , respectively, and with current outputs of up to 1 A in devices that use interdigitated electrodes. PMOS and CMOS logic gates and mechanically flexible transistors on plastic provide examples of devices that can be formed with this approach. Collectively, these results may represent a route to large-scale integrated nanotube electronics.
1,152 citations
"Ultrahigh density alignment of carb..." refers background or methods in this paper
...to fabricate devices with massively parallel 2D arrays of SWNTs.(5-25) Such devices may be useful for radio frequency applications,(5-7,15,26) transistors,(10) plastic electronics,(10-12) display technologies,(27-29) and sensors....
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...The capacitance per unit area C is calculated by using the formula for a parallel nanotube array, C = D/[CQ -1 þ (1/2πε0ε)ln[sinh(2πtoxD)/πDr]], where ε is the dielectric constant of SiO2, tox = 250 nm is the thickness of SiO2, CQ = 4 10 F/m is the quantum capacitance, r is the radius of the nanotubes, and D is the linear density in SWNTs per μm of the array.(10) The as-assembled array shows very little gate modulation with current on-off ratio of 1....
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...aligned array to suitable substrates for device fabrication.(6,10,14) Post-growth assembly using...
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