Esko I. Kauppinen

Flexible high-performance carbon nanotube integrated circuits.

Carbon nanotube thin-film transistors are expected to enable the fabrication of high-performance, flexible and transparent devices using relatively simple techniques. However, as-grown nanotube networks usually contain both metallic and semiconducting nanotubes, which leads to a trade-off between charge-carrier mobility (which increases with greater metallic tube content) and on/off ratio (which decreases). Many approaches to separating metallic nanotubes from semiconducting nanotubes have been investigated, but most lead to contamination and shortening of the nanotubes, thus reducing performance. Here, we report the fabrication of high-performance thin-film transistors and integrated circuits on flexible and transparent substrates using floating-catalyst chemical vapour deposition followed by a simple gas-phase filtration and transfer process. The resulting nanotube network has a well-controlled density and a unique morphology, consisting of long (~10 µm) nanotubes connected by low-resistance Y-shaped junctions. The transistors simultaneously demonstrate a mobility of 35 cm(2) V(-1) s(-1) and an on/off ratio of 6 × 10(6). We also demonstrate flexible integrated circuits, including a 21-stage ring oscillator and master-slave delay flip-flops that are capable of sequential logic. Our fabrication procedure should prove to be scalable, for example, by using high-throughput printing techniques.

The role of metal nanoparticles in the catalytic production of single-walled carbon nanotubes?a review

Recent progress in chemical vapour deposition and aerosol synthesis of single-walled carbon nanotubes (SWCNTs) is reviewed with an emphasis on the role of metal nanoparticles in the processes. The effect of the various parameters on SWCNT formation is reported on the basis of published experiments. Evolution of the catalyst particle size distribution due to collision, sintering and evaporation of metal during SWCNT synthesis is discussed. The active catalyst has been demonstrated to be in a reduced metal form by comparison of the experimental data and calculations regarding the equilibrium concentration of carbon and oxygen in iron. Also the effect of the catalyst particle size on melting temperature and carbon solubility in metal is discussed. The stability of different carbon precursors (hydrocarbons and carbon monoxide) is considered thermodynamically. Furthermore, estimation of the maximum length of 1 and 2.5 nm diameter SWCNTs as a function of carbon solubility is conducted to determine whether carbon dissolution and precipitation are simultaneous or subsequent process steps.

A novel hybrid carbon material

Both fullerenes and single-walled carbon nanotubes (SWNTs) exhibit many advantageous properties. Despite the similarities between these two forms of carbon, there have been very few attempts to physically merge them. We have discovered a novel hybrid material that combines fullerenes and SWNTs into a single structure in which the fullerenes are covalently bonded to the outer surface of the SWNTs. These fullerene-functionalized SWNTs, which we have termed NanoBuds, were selectively synthesized in two different one-step continuous methods, during which fullerenes were formed on iron-catalyst particles together with SWNTs during CO disproportionation. The field-emission characteristics of NanoBuds suggest that they may possess advantageous properties compared with single-walled nanotubes or fullerenes alone, or in their non-bonded configurations.

On the Performance of the Berner Low Pressure Impactor

Particle collection characteristics of the compressible flow stages 1–6 of the Berner low-pressure impactor (BLPI, Hauke Aeras 25-4/0.015) have been studied. A new, real-time impactor stage efficiency measurement system has been developed. It is based on the use of two electrometers, one connected to the collection plate of the impactor, and the other to the backup filter. This method is used with singly charged, monodisperse dioctyl phthalate (DOP) particles to determine the shape of the collection efficiency curves of the BLPI. In addition, particle collection characteristics have been studied using fluorometric analysis. A new method for substrate film greasing is also introduced. Experimental cut diameters of stages 1–6, as determined with DOP particles using electrical measurement method, are 0.034, 0.066, 0.094, 0.17, 0.33, and 0.55 /un. They are clearly larger than corresponding values given by the manufacturer. The average of the square root of the Stokes number at 50% collection efficiency, based...

Aerosol-Synthesized SWCNT Networks with Tunable Conductivity and Transparency by a Dry Transfer Technique

We demonstrate an aerosol CVD process to dry deposit large-area SWCNT networks with tunable conductivity and optical transmittance on a wide range of substrates including flexible polymers. These SWCNT networks can be chemically doped to reach a sheet resistance of as low as 110 Ω/⟨ at 90% optical transmittance. A wide application potential of these networks is demonstrated by fabricating SWCNT network-based devices such as a transparent capacitive touch sensors, thin-film transistors (TFTs), and bright organic light-emitting diodes (OLEDs).

Carbon nanotube films for ultrafast broadband technology

Mode-locked sub-picosecond operation of Yb-, Er- and Tm:Hodoped fiber lasers operating at 1.05 microm, 1.56 microm and 1.99 microm, respectively, is demonstrated using the same sample carbon nanotube-based saturable absorber mirror. A mesh of single-walled carbon nanotubes was deposited on an Ag-mirror using a one-step dry-transfer contact press method to combine broadband saturable absorption and high reflectance properties. The novel fabrication method of the polymer-free absorber and device parameters determined using nonlinear reflectivity measurement are described in detail. To our knowledge the observed operation bandwidth of approximately 1 microm is the broadest reported to date for a single carbon nanotube-based saturable absorber.

Multifunctional Free-Standing Single-Walled Carbon Nanotube Films

We report a simple and rapid method to prepare multifunctional free-standing single-walled carbon nanotube (SWCNT) films with variable thicknesses ranging from a submonolayer to a few micrometers having outstanding properties for a broad range of exceptionally performing devices. We have fabricated state-of-the-art key components from the same single component multifunctional SWCNT material for several high-impact application areas: high efficiency nanoparticle filters with a figure of merit of 147 Pa(-1), transparent and conductive electrodes with a sheet resistance of 84 Ω/◻ and a transmittance of 90%, electrochemical sensors with extremely low detection limits below 100 nM, and polymer-free saturable absorbers for ultrafast femtosecond lasers. Furthermore, the films are demonstrated as the main components in gas flowmeters, gas heaters, and transparent thermoacoustic loudspeakers.

Single‐Shell Carbon‐Encapsulated Iron Nanoparticles: Synthesis and High Electrocatalytic Activity for Hydrogen Evolution Reaction

Efficient hydrogen evolution reaction (HER) through effective and inexpensive electrocatalysts is a valuable approach for clean and renewable energy systems. Here, single-shell carbon-encapsulated iron nanoparticles (SCEINs) decorated on single-walled carbon nanotubes (SWNTs) are introduced as a novel highly active and durable non-noble-metal catalyst for the HER. This catalyst exhibits catalytic properties superior to previously studied nonprecious materials and comparable to those of platinum. The SCEIN/SWNT is synthesized by a novel fast and low-cost aerosol chemical vapor deposition method in a one-step synthesis. In SCEINs the single carbon layer does not prevent desired access of the reactants to the vicinity of the iron nanoparticles but protects the active metallic core from oxidation. This finding opens new avenues for utilizing active transition metals such as iron in a wide range of applications.

Synthesis of graphene nanoribbons encapsulated in single-walled carbon nanotubes.

A novel material, graphene nanoribbons encapsulated in single-walled carbon nanotubes (GNR@SWNT), was synthesized using confined polymerization and fusion of polycyclic aromatic hydrocarbon (PAH) molecules. Formation of the GNR is possible due to confinement effects provided by the one-dimensional space inside nanotubes, which helps to align coronene or perylene molecules edge to edge to achieve dimerization and oligomerization of the molecules into long nanoribbons. Almost 100% filling of SWNT with GNR is achieved while nanoribbon length is limited only by the length of the encapsulating nanotube. The PAH fusion reaction provides a very simple and easily scalable method to synthesize GNR@SWNT in macroscopic amounts. First-principle simulations indicate that encapsulation of the GNRs is energetically favorable and that the electronic structure of the encapsulated GNRs is the same as for the free-standing ones, pointing to possible applications of the GNR@SWNT structures in photonics and nanoelectronics.

Modifying Native Nanocellulose Aerogels with Carbon Nanotubes for Mechanoresponsive Conductivity and Pressure Sensing

Mechanically excellent native cellulose nanofibers that are cleaved from plant cell walls have been modified by functionalized few-walled carbon nanotubes for hybrid nanofiber/nanotube aerogels. They show elastic mechanical behavior in combination with reversible electrical response under compression allowing responsive conductivity and pressure sensing. The concept combines wide availability of nanocellulosics and electrical functionality of carbon nanotubes synergistically.